[Docs] [txt|pdf] [Tracker] [WG] [Email] [Diff1] [Diff2] [Nits] [IPR]

Versions: 00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 RFC 5661

NFSv4                                                         S. Shepler
Internet-Draft                                                 M. Eisler
Intended status: Standards Track                               D. Noveck
Expires: February 2, 2007                                        Editors
                                                             August 2006


                         NFSv4 Minor Version 1
                 draft-ietf-nfsv4-minorversion1-07.txt

Status of this Memo

   By submitting this Internet-Draft, each author represents that any
   applicable patent or other IPR claims of which he or she is aware
   have been or will be disclosed, and any of which he or she becomes
   aware will be disclosed, in accordance with Section 6 of BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups.  Note that
   other groups may also distribute working documents as Internet-
   Drafts.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   The list of current Internet-Drafts can be accessed at
   http://www.ietf.org/ietf/1id-abstracts.txt.

   The list of Internet-Draft Shadow Directories can be accessed at
   http://www.ietf.org/shadow.html.

   This Internet-Draft will expire on February 2, 2007.

Copyright Notice

   Copyright (C) The Internet Society (2006).

Abstract

   This Internet-Draft describes NFSv4 minor version one, including
   features retained from the base protocol and protocol extensions made
   subsequently.  The current draft includes description of the major
   extensions, Sessions, Directory Delegations, and parallel NFS (pNFS).
   This Internet-Draft is an active work item of the NFSv4 working
   group.  Active and resolved issues may be found in the issue tracker
   at: http://www.nfsv4-editor.org/cgi-bin/roundup/nfsv4.  New issues



Shepler, et al.         Expires February 2, 2007                [Page 1]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   related to this document should be raised with the NFSv4 Working
   Group nfsv4@ietf.org and logged in the issue tracker.

Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119 [1].


Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   9
     1.1.   The NFSv4.1 Protocol . . . . . . . . . . . . . . . . . .   9
     1.2.   NFS Version 4 Goals  . . . . . . . . . . . . . . . . . .   9
     1.3.   Minor Version 1 Goals  . . . . . . . . . . . . . . . . .  10
     1.4.   Inconsistencies of this Document with Section XX . . . .  10
     1.5.   Overview of NFS version 4.1 Features . . . . . . . . . .  10
       1.5.1.  RPC and Security  . . . . . . . . . . . . . . . . . .  11
       1.5.2.  Protocol Structure  . . . . . . . . . . . . . . . . .  11
       1.5.3.  File System Model . . . . . . . . . . . . . . . . . .  12
       1.5.4.  Locking Facilities  . . . . . . . . . . . . . . . . .  13
     1.6.   General Definitions  . . . . . . . . . . . . . . . . . .  14
     1.7.   Differences from NFSv4.0 . . . . . . . . . . . . . . . .  16
   2.  Core Infrastructure . . . . . . . . . . . . . . . . . . . . .  16
     2.1.   Introduction . . . . . . . . . . . . . . . . . . . . . .  16
     2.2.   RPC and XDR  . . . . . . . . . . . . . . . . . . . . . .  16
       2.2.1.  RPC-based Security  . . . . . . . . . . . . . . . . .  16
     2.3.   COMPOUND and CB_COMPOUND . . . . . . . . . . . . . . . .  20
     2.4.   Client Identifiers . . . . . . . . . . . . . . . . . . .  20
       2.4.1.  Server Release of Clientid  . . . . . . . . . . . . .  24
     2.5.   Security Service Negotiation . . . . . . . . . . . . . .  25
       2.5.1.  NFSv4 Security Tuples . . . . . . . . . . . . . . . .  25
       2.5.2.  SECINFO and SECINFO_NO_NAME . . . . . . . . . . . . .  25
       2.5.3.  Security Error  . . . . . . . . . . . . . . . . . . .  26
     2.6.   Minor Versioning . . . . . . . . . . . . . . . . . . . .  28
     2.7.   Non-RPC-based Security Services  . . . . . . . . . . . .  31
       2.7.1.  Authorization . . . . . . . . . . . . . . . . . . . .  31
       2.7.2.  Auditing  . . . . . . . . . . . . . . . . . . . . . .  31
       2.7.3.  Intrusion Detection . . . . . . . . . . . . . . . . .  31
     2.8.   Transport Layers . . . . . . . . . . . . . . . . . . . .  32
       2.8.1.  Required and Recommended Properties of Transports . .  32
       2.8.2.  Client and Server Transport Behavior  . . . . . . . .  32
       2.8.3.  Ports . . . . . . . . . . . . . . . . . . . . . . . .  34
     2.9.   Session  . . . . . . . . . . . . . . . . . . . . . . . .  34
       2.9.1.  Motivation and Overview . . . . . . . . . . . . . . .  34
       2.9.2.  NFSv4 Integration . . . . . . . . . . . . . . . . . .  35
       2.9.3.  Channels  . . . . . . . . . . . . . . . . . . . . . .  36



Shepler, et al.         Expires February 2, 2007                [Page 2]


Internet-Draft            NFSv4 Minor Version 1              August 2006


       2.9.4.  Exactly Once Semantics  . . . . . . . . . . . . . . .  38
       2.9.5.  RDMA Considerations . . . . . . . . . . . . . . . . .  46
       2.9.6.  Sessions Security . . . . . . . . . . . . . . . . . .  48
       2.9.7.  Session Mechanics - Steady State  . . . . . . . . . .  53
       2.9.8.  Session Mechanics - Recovery  . . . . . . . . . . . .  54
   3.  Protocol Data Types . . . . . . . . . . . . . . . . . . . . .  57
     3.1.   Basic Data Types . . . . . . . . . . . . . . . . . . . .  57
     3.2.   Structured Data Types  . . . . . . . . . . . . . . . . .  59
   4.  Filehandles . . . . . . . . . . . . . . . . . . . . . . . . .  68
     4.1.   Obtaining the First Filehandle . . . . . . . . . . . . .  69
       4.1.1.  Root Filehandle . . . . . . . . . . . . . . . . . . .  69
       4.1.2.  Public Filehandle . . . . . . . . . . . . . . . . . .  69
     4.2.   Filehandle Types . . . . . . . . . . . . . . . . . . . .  70
       4.2.1.  General Properties of a Filehandle  . . . . . . . . .  70
       4.2.2.  Persistent Filehandle . . . . . . . . . . . . . . . .  71
       4.2.3.  Volatile Filehandle . . . . . . . . . . . . . . . . .  71
     4.3.   One Method of Constructing a Volatile Filehandle . . . .  72
     4.4.   Client Recovery from Filehandle Expiration . . . . . . .  73
   5.  File Attributes . . . . . . . . . . . . . . . . . . . . . . .  74
     5.1.   Mandatory Attributes . . . . . . . . . . . . . . . . . .  75
     5.2.   Recommended Attributes . . . . . . . . . . . . . . . . .  75
     5.3.   Named Attributes . . . . . . . . . . . . . . . . . . . .  76
     5.4.   Classification of Attributes . . . . . . . . . . . . . .  76
     5.5.   Mandatory Attributes - Definitions . . . . . . . . . . .  77
     5.6.   Recommended Attributes - Definitions . . . . . . . . . .  79
     5.7.   Time Access  . . . . . . . . . . . . . . . . . . . . . .  87
     5.8.   Interpreting owner and owner_group . . . . . . . . . . .  87
     5.9.   Character Case Attributes  . . . . . . . . . . . . . . .  89
     5.10.  Quota Attributes . . . . . . . . . . . . . . . . . . . .  89
     5.11.  mounted_on_fileid  . . . . . . . . . . . . . . . . . . .  90
     5.12.  send_impl_id and recv_impl_id  . . . . . . . . . . . . .  91
     5.13.  fs_layout_type . . . . . . . . . . . . . . . . . . . . .  92
     5.14.  layout_type  . . . . . . . . . . . . . . . . . . . . . .  92
     5.15.  layout_hint  . . . . . . . . . . . . . . . . . . . . . .  92
     5.16.  mdsthreshold . . . . . . . . . . . . . . . . . . . . . .  92
   6.  Access Control Lists  . . . . . . . . . . . . . . . . . . . .  93
     6.1.   Goals  . . . . . . . . . . . . . . . . . . . . . . . . .  93
     6.2.   File Attributes Discussion . . . . . . . . . . . . . . .  94
       6.2.1.  ACL Attribute . . . . . . . . . . . . . . . . . . . .  94
       6.2.2.  mode Attribute  . . . . . . . . . . . . . . . . . . . 105
     6.3.   Common Methods . . . . . . . . . . . . . . . . . . . . . 106
       6.3.1.  Interpreting an ACL . . . . . . . . . . . . . . . . . 106
       6.3.2.  Computing a Mode Attribute from an ACL  . . . . . . . 107
     6.4.   Requirements . . . . . . . . . . . . . . . . . . . . . . 109
       6.4.1.  Setting the mode and/or ACL Attributes  . . . . . . . 109
       6.4.2.  Retrieving the mode and/or ACL Attributes . . . . . . 110
       6.4.3.  Creating New Objects  . . . . . . . . . . . . . . . . 111
   7.  Single-server Name Space  . . . . . . . . . . . . . . . . . . 112



Shepler, et al.         Expires February 2, 2007                [Page 3]


Internet-Draft            NFSv4 Minor Version 1              August 2006


     7.1.   Server Exports . . . . . . . . . . . . . . . . . . . . . 112
     7.2.   Browsing Exports . . . . . . . . . . . . . . . . . . . . 113
     7.3.   Server Pseudo File System  . . . . . . . . . . . . . . . 113
     7.4.   Multiple Roots . . . . . . . . . . . . . . . . . . . . . 114
     7.5.   Filehandle Volatility  . . . . . . . . . . . . . . . . . 114
     7.6.   Exported Root  . . . . . . . . . . . . . . . . . . . . . 114
     7.7.   Mount Point Crossing . . . . . . . . . . . . . . . . . . 115
     7.8.   Security Policy and Name Space Presentation  . . . . . . 115
   8.  File Locking and Share Reservations . . . . . . . . . . . . . 116
     8.1.   Locking  . . . . . . . . . . . . . . . . . . . . . . . . 116
       8.1.1.  Client and Session ID . . . . . . . . . . . . . . . . 117
       8.1.2.  State-owner and Stateid Definition  . . . . . . . . . 117
       8.1.3.  Use of the Stateid and Locking  . . . . . . . . . . . 120
     8.2.   Lock Ranges  . . . . . . . . . . . . . . . . . . . . . . 122
     8.3.   Upgrading and Downgrading Locks  . . . . . . . . . . . . 122
     8.4.   Blocking Locks . . . . . . . . . . . . . . . . . . . . . 123
     8.5.   Lease Renewal  . . . . . . . . . . . . . . . . . . . . . 124
     8.6.   Crash Recovery . . . . . . . . . . . . . . . . . . . . . 124
       8.6.1.  Client Failure and Recovery . . . . . . . . . . . . . 124
       8.6.2.  Server Failure and Recovery . . . . . . . . . . . . . 125
       8.6.3.  Network Partitions and Recovery . . . . . . . . . . . 127
     8.7.   Server Revocation of Locks . . . . . . . . . . . . . . . 131
     8.8.   Share Reservations . . . . . . . . . . . . . . . . . . . 132
     8.9.   OPEN/CLOSE Operations  . . . . . . . . . . . . . . . . . 133
     8.10.  Open Upgrade and Downgrade . . . . . . . . . . . . . . . 134
     8.11.  Short and Long Leases  . . . . . . . . . . . . . . . . . 134
     8.12.  Clocks, Propagation Delay, and Calculating Lease
            Expiration . . . . . . . . . . . . . . . . . . . . . . . 135
     8.13.  Vestigial Locking Infrastructure From V4.0 . . . . . . . 135
   9.  Client-Side Caching . . . . . . . . . . . . . . . . . . . . . 136
     9.1.   Performance Challenges for Client-Side Caching . . . . . 137
     9.2.   Delegation and Callbacks . . . . . . . . . . . . . . . . 138
       9.2.1.  Delegation Recovery . . . . . . . . . . . . . . . . . 139
     9.3.   Data Caching . . . . . . . . . . . . . . . . . . . . . . 141
       9.3.1.  Data Caching and OPENs  . . . . . . . . . . . . . . . 141
       9.3.2.  Data Caching and File Locking . . . . . . . . . . . . 142
       9.3.3.  Data Caching and Mandatory File Locking . . . . . . . 144
       9.3.4.  Data Caching and File Identity  . . . . . . . . . . . 144
     9.4.   Open Delegation  . . . . . . . . . . . . . . . . . . . . 145
       9.4.1.  Open Delegation and Data Caching  . . . . . . . . . . 148
       9.4.2.  Open Delegation and File Locks  . . . . . . . . . . . 149
       9.4.3.  Handling of CB_GETATTR  . . . . . . . . . . . . . . . 149
       9.4.4.  Recall of Open Delegation . . . . . . . . . . . . . . 152
       9.4.5.  Clients that Fail to Honor Delegation Recalls . . . . 154
       9.4.6.  Delegation Revocation . . . . . . . . . . . . . . . . 155
     9.5.   Data Caching and Revocation  . . . . . . . . . . . . . . 155
       9.5.1.  Revocation Recovery for Write Open Delegation . . . . 156
     9.6.   Attribute Caching  . . . . . . . . . . . . . . . . . . . 157



Shepler, et al.         Expires February 2, 2007                [Page 4]


Internet-Draft            NFSv4 Minor Version 1              August 2006


     9.7.   Data and Metadata Caching and Memory Mapped Files  . . . 159
     9.8.   Name Caching . . . . . . . . . . . . . . . . . . . . . . 161
     9.9.   Directory Caching  . . . . . . . . . . . . . . . . . . . 162
   10. Multi-server Name Space . . . . . . . . . . . . . . . . . . . 163
     10.1.  Location attributes  . . . . . . . . . . . . . . . . . . 163
     10.2.  File System Presence or Absence  . . . . . . . . . . . . 163
     10.3.  Getting Attributes for an Absent File System . . . . . . 165
       10.3.1. GETATTR Within an Absent File System  . . . . . . . . 165
       10.3.2. READDIR and Absent File Systems . . . . . . . . . . . 166
     10.4.  Uses of Location Information . . . . . . . . . . . . . . 167
       10.4.1. File System Replication . . . . . . . . . . . . . . . 167
       10.4.2. File System Migration . . . . . . . . . . . . . . . . 168
       10.4.3. Referrals . . . . . . . . . . . . . . . . . . . . . . 169
     10.5.  Additional Client-side Considerations  . . . . . . . . . 169
     10.6.  Effecting File System Transitions  . . . . . . . . . . . 170
       10.6.1. Transparent File System Transitions . . . . . . . . . 171
       10.6.2. Filehandles and File System Transitions . . . . . . . 173
       10.6.3. Fileid's and File System Transitions  . . . . . . . . 173
       10.6.4. Fsid's and File System Transitions  . . . . . . . . . 174
       10.6.5. The Change Attribute and File System Transitions  . . 174
       10.6.6. Lock State and File System Transitions  . . . . . . . 175
       10.6.7. Write Verifiers and File System Transitions . . . . . 178
     10.7.  Effecting File System Referrals  . . . . . . . . . . . . 178
       10.7.1. Referral Example (LOOKUP) . . . . . . . . . . . . . . 179
       10.7.2. Referral Example (READDIR)  . . . . . . . . . . . . . 183
     10.8.  The Attribute fs_absent  . . . . . . . . . . . . . . . . 185
     10.9.  The Attribute fs_locations . . . . . . . . . . . . . . . 185
     10.10. The Attribute fs_locations_info  . . . . . . . . . . . . 187
     10.11. The Attribute fs_status  . . . . . . . . . . . . . . . . 196
   11. Directory Delegations . . . . . . . . . . . . . . . . . . . . 199
     11.1.  Introduction to Directory Delegations  . . . . . . . . . 200
     11.2.  Directory Delegation Design (in brief) . . . . . . . . . 201
     11.3.  Recommended Attributes in support of Directory
            Delegations  . . . . . . . . . . . . . . . . . . . . . . 202
     11.4.  Delegation Recall  . . . . . . . . . . . . . . . . . . . 203
     11.5.  Directory Delegation Recovery  . . . . . . . . . . . . . 203
   12. Parallel NFS (pNFS) . . . . . . . . . . . . . . . . . . . . . 203
     12.1.  Introduction . . . . . . . . . . . . . . . . . . . . . . 203
     12.2.  General Definitions  . . . . . . . . . . . . . . . . . . 206
       12.2.1. Metadata Server . . . . . . . . . . . . . . . . . . . 206
       12.2.2. Client  . . . . . . . . . . . . . . . . . . . . . . . 206
       12.2.3. Storage Device  . . . . . . . . . . . . . . . . . . . 206
       12.2.4. Storage Protocol  . . . . . . . . . . . . . . . . . . 206
       12.2.5. Control Protocol  . . . . . . . . . . . . . . . . . . 207
       12.2.6. Metadata  . . . . . . . . . . . . . . . . . . . . . . 207
       12.2.7. Layout  . . . . . . . . . . . . . . . . . . . . . . . 207
     12.3.  pNFS protocol semantics  . . . . . . . . . . . . . . . . 208
       12.3.1. Definitions . . . . . . . . . . . . . . . . . . . . . 208



Shepler, et al.         Expires February 2, 2007                [Page 5]


Internet-Draft            NFSv4 Minor Version 1              August 2006


       12.3.2. Guarantees Provided by Layouts  . . . . . . . . . . . 211
       12.3.3. Getting a Layout  . . . . . . . . . . . . . . . . . . 212
       12.3.4. Committing a Layout . . . . . . . . . . . . . . . . . 213
       12.3.5. Recalling a Layout  . . . . . . . . . . . . . . . . . 215
       12.3.6. Metadata Server Write Propagation . . . . . . . . . . 221
       12.3.7. Crash Recovery  . . . . . . . . . . . . . . . . . . . 221
       12.3.8. Security Considerations . . . . . . . . . . . . . . . 227
     12.4.  The NFSv4 File Layout Type . . . . . . . . . . . . . . . 228
       12.4.1. File Striping and Data Access . . . . . . . . . . . . 228
       12.4.2. Global Stateid Requirements . . . . . . . . . . . . . 236
       12.4.3. The Layout Iomode . . . . . . . . . . . . . . . . . . 236
       12.4.4. Storage Device State Propagation  . . . . . . . . . . 237
       12.4.5. Storage Device Component File Size  . . . . . . . . . 239
       12.4.6. Crash Recovery Considerations . . . . . . . . . . . . 240
       12.4.7. Security Considerations for the File Layout Type  . . 240
       12.4.8. Alternate Approaches  . . . . . . . . . . . . . . . . 241
   13. Internationalization  . . . . . . . . . . . . . . . . . . . . 242
     13.1.  Stringprep profile for the utf8str_cs type . . . . . . . 243
     13.2.  Stringprep profile for the utf8str_cis type  . . . . . . 245
     13.3.  Stringprep profile for the utf8str_mixed type  . . . . . 246
     13.4.  UTF-8 Related Errors . . . . . . . . . . . . . . . . . . 247
   14. Error Values  . . . . . . . . . . . . . . . . . . . . . . . . 248
     14.1.  Error Definitions  . . . . . . . . . . . . . . . . . . . 248
     14.2.  Operations and their valid errors  . . . . . . . . . . . 262
     14.3.  Callback operations and their valid errors . . . . . . . 275
     14.4.  Errors and the operations that use them  . . . . . . . . 276
   15. NFS version 4.1 Procedures  . . . . . . . . . . . . . . . . . 283
     15.1.  Procedure 0: NULL - No Operation . . . . . . . . . . . . 283
     15.2.  Procedure 1: COMPOUND - Compound Operations  . . . . . . 284
   16. NFS version 4.1 Operations  . . . . . . . . . . . . . . . . . 289
     16.1.  Operation 3: ACCESS - Check Access Rights  . . . . . . . 289
     16.2.  Operation 4: CLOSE - Close File  . . . . . . . . . . . . 291
     16.3.  Operation 5: COMMIT - Commit Cached Data . . . . . . . . 293
     16.4.  Operation 6: CREATE - Create a Non-Regular File Object . 295
     16.5.  Operation 7: DELEGPURGE - Purge Delegations Awaiting
            Recovery . . . . . . . . . . . . . . . . . . . . . . . . 298
     16.6.  Operation 8: DELEGRETURN - Return Delegation . . . . . . 299
     16.7.  Operation 9: GETATTR - Get Attributes  . . . . . . . . . 299
     16.8.  Operation 10: GETFH - Get Current Filehandle . . . . . . 301
     16.9.  Operation 11: LINK - Create Link to a File . . . . . . . 302
     16.10. Operation 12: LOCK - Create Lock . . . . . . . . . . . . 303
     16.11. Operation 13: LOCKT - Test For Lock  . . . . . . . . . . 307
     16.12. Operation 14: LOCKU - Unlock File  . . . . . . . . . . . 308
     16.13. Operation 15: LOOKUP - Lookup Filename . . . . . . . . . 309
     16.14. Operation 16: LOOKUPP - Lookup Parent Directory  . . . . 311
     16.15. Operation 17: NVERIFY - Verify Difference in
            Attributes . . . . . . . . . . . . . . . . . . . . . . . 312
     16.16. Operation 18: OPEN - Open a Regular File . . . . . . . . 314



Shepler, et al.         Expires February 2, 2007                [Page 6]


Internet-Draft            NFSv4 Minor Version 1              August 2006


     16.17. Operation 19: OPENATTR - Open Named Attribute
            Directory  . . . . . . . . . . . . . . . . . . . . . . . 328
     16.18. Operation 21: OPEN_DOWNGRADE - Reduce Open File Access . 329
     16.19. Operation 22: PUTFH - Set Current Filehandle . . . . . . 330
     16.20. Operation 23: PUTPUBFH - Set Public Filehandle . . . . . 331
     16.21. Operation 24: PUTROOTFH - Set Root Filehandle  . . . . . 332
     16.22. Operation 25: READ - Read from File  . . . . . . . . . . 333
     16.23. Operation 26: READDIR - Read Directory . . . . . . . . . 335
     16.24. Operation 27: READLINK - Read Symbolic Link  . . . . . . 339
     16.25. Operation 28: REMOVE - Remove File System Object . . . . 340
     16.26. Operation 29: RENAME - Rename Directory Entry  . . . . . 342
     16.27. Operation 31: RESTOREFH - Restore Saved Filehandle . . . 344
     16.28. Operation 32: SAVEFH - Save Current Filehandle . . . . . 345
     16.29. Operation 33: SECINFO - Obtain Available Security  . . . 346
     16.30. Operation 34: SETATTR - Set Attributes . . . . . . . . . 349
     16.31. Operation 37: VERIFY - Verify Same Attributes  . . . . . 352
     16.32. Operation 38: WRITE - Write to File  . . . . . . . . . . 353
     16.33. Operation 40: BACKCHANNEL_CTL - Backchannel control  . . 357
     16.34. Operation 41: BIND_CONN_TO_SESSION . . . . . . . . . . . 359
     16.35. Operation 42: CREATE_CLIENTID - Instantiate Clientid . . 363
     16.36. Operation 43: CREATE_SESSION - Create New Session and
            Confirm Clientid . . . . . . . . . . . . . . . . . . . . 369
     16.37. Operation 44: DESTROY_SESSION - Destroy existing
            session  . . . . . . . . . . . . . . . . . . . . . . . . 379
     16.38. Operation 45: FREE_STATEID - Free stateid with no
            locks  . . . . . . . . . . . . . . . . . . . . . . . . . 380
     16.39. Operation 46: GET_DIR_DELEGATION - Get a directory
            delegation . . . . . . . . . . . . . . . . . . . . . . . 381
     16.40. Operation 47: GETDEVICEINFO - Get Device Information . . 385
     16.41. Operation 48: GETDEVICELIST  . . . . . . . . . . . . . . 386
     16.42. Operation 49: LAYOUTCOMMIT - Commit writes made using
            a layout . . . . . . . . . . . . . . . . . . . . . . . . 387
     16.43. Operation 50: LAYOUTGET - Get Layout Information . . . . 391
     16.44. Operation 51: LAYOUTRETURN - Release Layout
            Information  . . . . . . . . . . . . . . . . . . . . . . 394
     16.45. Operation 52: SECINFO_NO_NAME - Get Security on
            Unnamed Object . . . . . . . . . . . . . . . . . . . . . 396
     16.46. Operation 53: SEQUENCE - Supply per-procedure
            sequencing and control . . . . . . . . . . . . . . . . . 397
     16.47. Operation 54: SET_SSV  . . . . . . . . . . . . . . . . . 401
     16.48. Operation 55: TEST_STATEID - Test stateids for
            validity . . . . . . . . . . . . . . . . . . . . . . . . 402
     16.49. Operation 56: WANT_DELEGATION  . . . . . . . . . . . . . 403
     16.50. Operation 10044: ILLEGAL - Illegal operation . . . . . . 406
   17. NFS version 4.1 Callback Procedures . . . . . . . . . . . . . 407
     17.1.  Procedure 0: CB_NULL - No Operation  . . . . . . . . . . 407
     17.2.  Procedure 1: CB_COMPOUND - Compound Operations . . . . . 407
   18. NFS version 4.1 Callback Operations . . . . . . . . . . . . . 409



Shepler, et al.         Expires February 2, 2007                [Page 7]


Internet-Draft            NFSv4 Minor Version 1              August 2006


     18.1.  Operation 3: CB_GETATTR - Get Attributes . . . . . . . . 409
     18.2.  Operation 4: CB_RECALL - Recall an Open Delegation . . . 411
     18.3.  Operation 5: CB_LAYOUTRECALL . . . . . . . . . . . . . . 412
     18.4.  Operation 6: CB_NOTIFY - Notify directory changes  . . . 414
     18.5.  Operation 7: CB_PUSH_DELEG . . . . . . . . . . . . . . . 417
     18.6.  Operation 8: CB_RECALL_ANY - Keep any N delegations  . . 418
     18.7.  Operation 9: CB_RECALLABLE_OBJ_AVAIL . . . . . . . . . . 421
     18.8.  Operation 10: CB_RECALL_SLOT - change flow control
            limits . . . . . . . . . . . . . . . . . . . . . . . . . 422
     18.9.  Operation 11: CB_SEQUENCE - Supply callback channel
            sequencing and control . . . . . . . . . . . . . . . . . 423
     18.10. Operation 12: CB_WANTS_CANCELLED . . . . . . . . . . . . 425
     18.11. Operation 10044: CB_ILLEGAL - Illegal Callback
            Operation  . . . . . . . . . . . . . . . . . . . . . . . 426
   19. Security Considerations . . . . . . . . . . . . . . . . . . . 427
   20. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 427
     20.1.  Defining new layout types  . . . . . . . . . . . . . . . 427
   21. References  . . . . . . . . . . . . . . . . . . . . . . . . . 428
     21.1.  Normative References . . . . . . . . . . . . . . . . . . 428
     21.2.  Informative References . . . . . . . . . . . . . . . . . 429
   Appendix A.  Acknowledgments  . . . . . . . . . . . . . . . . . . 430
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . . 431
   Intellectual Property and Copyright Statements  . . . . . . . . . 432




























Shepler, et al.         Expires February 2, 2007                [Page 8]


Internet-Draft            NFSv4 Minor Version 1              August 2006


1.  Introduction

1.1.  The NFSv4.1 Protocol

   The NFSv4.1 protocol is a minor version of the NFSv4 protocol
   described in [2].  It generally follows the guidelines for minor
   versioning model laid in Section 10 of RFC 3530.  However, it
   diverges from guidelines 11 ("a client and server that supports minor
   version X must support minor versions 0 through X-1"), and 12 ("no
   features may be introduced as mandatory in a minor version").  These
   divergences are due to the introduction of the sessions model for
   managing non-idempotent operations and the RECLAIM_COMPLETE
   operation.  These two new features are infrastructural in nature and
   simplify implementation of existing and other new features.  Making
   them optional would add undue complexity to protocol definition and
   implementation.  NFSv4.1 accordingly updates the Minor Versioning
   guidelines (Section 2.6).

   NFSv4.1, as a minor version, is consistent with the overall goals for
   NFS Version 4, but extends the protocol so as to better meet those
   goals, based on experiences with NFSv4.0.  In addition, NFSv4.1 has
   adopted some additional goals, which motivate some of the major
   extensions in minor version 1.

1.2.  NFS Version 4 Goals

   The NFS version 4 protocol is a further revision of the NFS protocol
   defined already by versions 2 [17]] and 3 [18].  It retains the
   essential characteristics of previous versions: design for easy
   recovery, independent of transport protocols, operating systems and
   file systems, simplicity, and good performance.  The NFS version 4
   revision has the following goals:

   o  Improved access and good performance on the Internet.

      The protocol is designed to transit firewalls easily, perform well
      where latency is high and bandwidth is low, and scale to very
      large numbers of clients per server.

   o  Strong security with negotiation built into the protocol.

      The protocol builds on the work of the ONCRPC working group in
      supporting the RPCSEC_GSS protocol.  Additionally, the NFS version
      4 protocol provides a mechanism to allow clients and servers the
      ability to negotiate security and require clients and servers to
      support a minimal set of security schemes.





Shepler, et al.         Expires February 2, 2007                [Page 9]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   o  Good cross-platform interoperability.

      The protocol features a file system model that provides a useful,
      common set of features that does not unduly favor one file system
      or operating system over another.

   o  Designed for protocol extensions.

      The protocol is designed to accept standard extensions within a
      framework that enable and encourages backward compatibility.

1.3.  Minor Version 1 Goals

   Minor version one has the following goals, within the framework
   established by the overall version 4 goals.

   o  To correct significant structural weaknesses and oversights
      discovered in the base protocol.

   o  To add clarity and specificity to areas left unaddressed or not
      addressed in sufficient detail in the base protocol.

   o  To add specific features based on experience with the existing
      protocol and recent industry developments.

   o  To provide protocol support to take advantage of clustered server
      deployments including the ability to provide scalable parallel
      access to files distributed among multiple servers.

1.4.  Inconsistencies of this Document with Section XX

   Section XX, RPC Definition File, contains the definitions in XDR
   description language of the constructs used by the protocol.  Prior
   to this section, several of the constructs are reproduced for
   purposes of explanation.  Although every effort has been made to
   assure a correct and consistent description, the possibility of
   inconsistencies exists.  For any part of the document that is
   inconsistent with Section XX, Section XX is to be considered
   authoritative.

1.5.  Overview of NFS version 4.1 Features

   To provide a reasonable context for the reader, the major features of
   NFS version 4.1 protocol will be reviewed in brief.  This will be
   done to provide an appropriate context for both the reader who is
   familiar with the previous versions of the NFS protocol and the
   reader that is new to the NFS protocols.  For the reader new to the
   NFS protocols, there is still a set of fundamental knowledge that is



Shepler, et al.         Expires February 2, 2007               [Page 10]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   expected.  The reader should be familiar with the XDR and RPC
   protocols as described in [3] and [4].  A basic knowledge of file
   systems and distributed file systems is expected as well.

   This description of version 4.1 features will not distinguish those
   added in minor version one from those present in the base protocol
   but will treat minor version 1 as a unified whole.  See Section 1.7
   for a description of the differences between the two minor versions.

1.5.1.  RPC and Security

   As with previous versions of NFS, the External Data Representation
   (XDR) and Remote Procedure Call (RPC) mechanisms used for the NFS
   version 4.1 protocol are those defined in [3] and [4].  To meet end-
   to-end security requirements, the RPCSEC_GSS framework [5] will be
   used to extend the basic RPC security.  With the use of RPCSEC_GSS,
   various mechanisms can be provided to offer authentication,
   integrity, and privacy to the NFS version 4 protocol.  Kerberos V5
   will be used as described in [6] to provide one security framework.
   The LIPKEY and SPKM-3 GSS-API mechanisms described in [7] will be
   used to provide for the use of user password and client/server public
   key certificates by the NFS version 4 protocol.  With the use of
   RPCSEC_GSS, other mechanisms may also be specified and used for NFS
   version 4.1 security.

   To enable in-band security negotiation, the NFS version 4.1 protocol
   has operations which provide the client a method of querying the
   server about its policies regarding which security mechanisms must be
   used for access to the server's file system resources.  With this,
   the client can securely match the security mechanism that meets the
   policies specified at both the client and server.

1.5.2.  Protocol Structure

1.5.2.1.  Core Protocol

   Unlike NFS Versions 2 and 3, which used a series of ancillary
   protocols (e.g.  NLM, NSM, MOUNT), within all minor versions of NFS
   version 4 only a single RPC protocol is used to make requests of the
   server.  Facilities that had been separate protocols, such as
   locking, are now integrated within a single unified protocol.

1.5.2.2.  Parallel Access

   Minor version one supports high-performance data access to a
   clustered server implementation by enabling a separation of metadata
   access and data access, with the latter done to multiple servers in
   parallel.



Shepler, et al.         Expires February 2, 2007               [Page 11]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   Such parallel data access is controlled by recallable objects known
   as "layouts", which are integrated into the protocol locking model.
   Clients direct requests for data access to a set of data servers
   specified by the layout via a data storage protocol which may be
   NFSv4.1 or may be another protocol.

1.5.3.  File System Model

   The general file system model used for the NFS version 4.1 protocol
   is the same as previous versions.  The server file system is
   hierarchical with the regular files contained within being treated as
   opaque byte streams.  In a slight departure, file and directory names
   are encoded with UTF-8 to deal with the basics of
   internationalization.

   The NFS version 4.1 protocol does not require a separate protocol to
   provide for the initial mapping between path name and filehandle.
   All file systems exported by a server are presented as a tree so that
   all file systems are reachable from a special per-server global root
   filehandle.  This allows LOOKUP operations to be used to perform
   functions previously provided by the MOUNT protocol.  The server
   provides any necessary pseudo filesystems to bridge any gaps that
   arise due unexported gaps between exported file systems.

1.5.3.1.  Filehandles

   As in previous versions of the NFS protocol, opaque filehandles are
   used to identify individual files and directories.  Lookup-type and
   create operations are used to go from file and directory names to the
   filehandle which is then used to identify the object to subsequent
   operations.

   The NFS version 4.1 protocol provides support for both persistent
   filehandles, guaranteed to be valid for the lifetime of the file
   system object designated.  In addition it provides support to servers
   to provide filehandles with more limited validity guarantees, called
   volatile filehandles.

1.5.3.2.  File Attributes

   The NFS version 4.1 protocol has a rich and extensible attribute
   structure.  Only a small set of the defined attributes are mandatory
   and must be provided by all server implementations.  The other
   attributes are known as "recommended" attributes.

   One significant recommended file attribute is the Access Control List
   (ACL) attribute.  This attribute provides for directory and file
   access control beyond the model used in NFS Versions 2 and 3.  The



Shepler, et al.         Expires February 2, 2007               [Page 12]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   ACL definition allows for specification specific sets of permissions
   for individual users and groups.  In addition, ACL inheritance allows
   propagation of access permissions and restriction down a directory
   tree as filesystem objects are created.

   One other type of attribute is the named attribute.  A named
   attribute is an opaque byte stream that is associated with a
   directory or file and referred to by a string name.  Named attributes
   are meant to be used by client applications as a method to associate
   application specific data with a regular file or directory.

1.5.3.3.  Multi-server Namespace

   NFS Version 4.1 contains a number of features to allow implementation
   of namespaces that cross server boundaries and that allow to and
   facilitate a non-disruptive transfer of support for individual file
   systems between servers.  They are all based upon attributes that
   allow one file system to specify alternate or new locations for that
   file system.

   These attributes may be used together with the concept of absent file
   system which provide specifications for additional locations but no
   actual file system content.  This allows a number of important
   facilities:

   o  Location attributes may be used with absent file systems to
      implement referrals whereby one server may direct the client to a
      file system provided by another server.  This allows extensive
      mult-server namespaces to be constructed.

   o  Location attributes may be provided for present file systems to
      provide the locations alternate file system instances or replicas
      to be used in the event that the current file system instance
      becomes unavailable.

   o  Location attributes may be provided when a previously present file
      system becomes absent.  This allows non-disruptive migration of
      file systems to alternate servers.

1.5.4.  Locking Facilities

   As mentioned previously, NFS v4.1, is a single protocol which
   includes locking facilities.  These locking facilities include
   support for many types of locks including a number of sorts of
   recallable locks.  Recallable locks such as delegations allow the
   client to be assured that certain events will not occur so long as
   that lock is held.  When circumstances change, the lock is recalled
   via a callback via a callback request.  The assurances provided by



Shepler, et al.         Expires February 2, 2007               [Page 13]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   delegations allow more extensive caching to be done safely when
   circumstances allow it.

   o  Share reservations as established by OPEN operations.

   o  Byte-range locks.

   o  File delegations which are recallable locks that assure the holder
      that inconsistent opens and file changes cannot occur so long as
      the delegation is held.

   o  Directory delegations which are recallable delegations that assure
      the holder that inconsistent directory modifications cannot occur
      so long as the delegation is held.

   o  Layouts which are recallable objects that assure the holder that
      direct access to the file data may be performed directly by the
      client and that no change to the data's location inconsistent with
      that access may be made so long as the layout is held.

   All locks for a given client are tied together under a single client-
   wide lease.  All requests made on sessions associated with the client
   renew that lease.  When leases are not promptly renewed lock are
   subject to revocation.  In the event of server reinitialization,
   clients have the opportunity to safely reclaim their locks within a
   special grace period.

1.6.  General Definitions

   The following definitions are provided for the purpose of providing
   an appropriate context for the reader.

   Client  The "client" is the entity that accesses the NFS server's
      resources.  The client may be an application which contains the
      logic to access the NFS server directly.  The client may also be
      the traditional operating system client remote file system
      services for a set of applications.

      In the case of file locking the client is the entity that
      maintains a set of locks on behalf of one or more applications.
      This client is responsible for crash or failure recovery for those
      locks it manages.

      Note that multiple clients may share the same transport and
      multiple clients may exist on the same network node.






Shepler, et al.         Expires February 2, 2007               [Page 14]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   Clientid  A 64-bit quantity used as a unique, short-hand reference to
      a client supplied Verifier and ID.  The server is responsible for
      supplying the Clientid.

   Lease  An interval of time defined by the server for which the client
      is irrevocably granted a lock.  At the end of a lease period the
      lock may be revoked if the lease has not been extended.  The lock
      must be revoked if a conflicting lock has been granted after the
      lease interval.

      All leases granted by a server have the same fixed interval.  Note
      that the fixed interval was chosen to alleviate the expense a
      server would have in maintaining state about variable length
      leases across server failures.

   Lock  The term "lock" is used to refer any of record (byte- range)
      locks, share reservations, delegations or layouts unless
      specifically stated otherwise.

   Server  The "Server" is the entity responsible for coordinating
      client access to a set of file systems.

   Stable Storage  NFS version 4 servers must be able to recover without
      data loss from multiple power failures (including cascading power
      failures, that is, several power failures in quick succession),
      operating system failures, and hardware failure of components
      other than the storage medium itself (for example, disk,
      nonvolatile RAM).

      Some examples of stable storage that are allowable for an NFS
      server include:

      1.  Media commit of data, that is, the modified data has been
          successfully written to the disk media, for example, the disk
          platter.

      2.  An immediate reply disk drive with battery-backed on- drive
          intermediate storage or uninterruptible power system (UPS).

      3.  Server commit of data with battery-backed intermediate storage
          and recovery software.

      4.  Cache commit with uninterruptible power system (UPS) and
          recovery software.







Shepler, et al.         Expires February 2, 2007               [Page 15]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   Stateid  A 128-bit quantity returned by a server that uniquely
      defines the open and locking state provided by the server for a
      specific open or lock owner for a specific file. meaning and are
      reserved values.

   Verifier  A 64-bit quantity generated by the client that the server
      can use to determine if the client has restarted and lost all
      previous lock state.

1.7.  Differences from NFSv4.0

   The following summarizes the differences between minor version one
   and the base protocol:

   o  Implementation of the sessions model.

   o  Support for parallel access to data.

   o  Addition of the RECLAIM_COMPLETE operation to better structure the
      lock reclamation process.

   o  Support for delegations on directories and other file types in
      addition to regular files.

   o  Operations to re-obtain a delegation.

   o  Support for client and server implementation id's.


2.  Core Infrastructure

2.1.  Introduction

   NFS version 4.1 (NFSv4.1) relies on core infrastructure common to
   nearly every operation.  This core infrastructure is described in the
   remainder of this section.

2.2.  RPC and XDR

   The NFS version 4.1 (NFSv4.1) protocol is a Remote Procedure Call
   (RPC) application that uses RPC version 2 and the corresponding
   eXternal Data Representation (XDR) as defined in RFC1831 [4] and
   RFC4506 [3].

2.2.1.  RPC-based Security

   Previous NFS versions have been thought of as having a host-based
   authentication model, where the NFS server authenticates the the NFS



Shepler, et al.         Expires February 2, 2007               [Page 16]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   client, and trust the client to authenticate all users.  Actually,
   NFS has always depended on RPC for authentication.  The first form of
   RPC authentication which required a host-based authentication
   approach.  NFSv4 also depends on RPC for basic security services, and
   mandates RPC support for a user-based authentication model.  The
   user-based authentication model has user principals authenticated by
   a server, and in turn the server authenticated by user principals.
   RPC provides some basic security services which are used by NFSv4.

2.2.1.1.  RPC Security Flavors

   As described in section 7.2 "Authentication" of [4], RPC security is
   encapsulated in the RPC header, via a security or authentication
   flavor, and information specific to the specification of the security
   flavor.  Every RPC header conveys information used to identify and
   authenticate a client and server.  As discussed in Section 2.2.1.1.1,
   some security flavors provide additional security services.

   NFSv4 clients and servers MUST implement RPCSEC_GSS.  (This
   requirement to implement is not a requirement to use.)  Other
   flavors, such as AUTH_NONE, and AUTH_SYS, MAY be implemented as well.

2.2.1.1.1.  RPCSEC_GSS and Security Services

   RPCSEC_GSS ([5]) uses the functionality of GSS-API RFC2743 [8].  This
   allows for the use of various security mechanisms by the RPC layer
   without the additional implementation overhead of adding RPC security
   flavors.

2.2.1.1.1.1.  Identification, Authentication, Integrity, Privacy

   Via the GSS-API, RPCSEC_GSS can be used to identify and authenticate
   users on clients to servers, and servers to users.  It can also
   perform integrity checking on the entire RPC message, including the
   RPC header, and the arguments or results.  Finally, privacy, usually
   via encryption, is a service available with RPCSEC_GSS.  Privacy is
   performed on the arguments and results.  Note that if privacy is
   selected, integrity, authentication, and identification are enabled.
   If privacy is not selected, but integrity is selected, authentication
   and identification are enabled.  If integrity and privacy are not
   selected, but authentication is enabled, identification is enabled.
   RPCSEC_GSS does not provide identification as a separate service.

   Although GSS-API has an authentication service distinct from its
   privacy and integrity services, use GSS-API's authentication service
   is not used for RPCSEC_GSS's authentication service.  Instead, each
   RPC request and response header is integrity protected with the GSS-
   API integrity service, and this allows RPCSEC_GSS to offer per-RPC



Shepler, et al.         Expires February 2, 2007               [Page 17]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   authentication and identity.  See [5] for more information.

   NFSv4 client and servers MUST support RPCSEC_GSS's integrity and
   authentication service.  NFSv4.1 servers MUST support RPCSEC_GSS's
   privacy service.

2.2.1.1.1.2.  Security mechanisms for NFS version 4

   RPCSEC_GSS, via GSS-API, normalizes access to mechanisms that provide
   security services.  Therefore NFSv4 clients and servers MUST support
   three security mechanisms: Kerberos V5, SPKM-3, and LIPKEY.

   The use of RPCSEC_GSS requires selection of: mechanism, quality of
   protection (QOP), and service (authentication, integrity, privacy).
   For the mandated security mechanisms, NFSv4 specifies that a QOP of
   zero (0) is used, leaving it up to the mechanism or the mechanism's
   configuration to use an appropriate level of protection that QOP zero
   maps to.  Each mandated mechanism specifies minimum set of
   cryptographic algorithms for implementing integrity and privacy.
   NFSv4 clients and servers MUST be implemented on operating
   environments that comply with the mandatory cryptographic algorithms
   of each mandated mechanism.

2.2.1.1.1.2.1.  Kerberos V5

   The Kerberos V5 GSS-API mechanism as described in RFC1964 [6] (
   [[Comment.1: need new Kerberos RFC]] ) MUST be implemented with the
   RPCSEC_GSS services as specified in the following table:


      column descriptions:
      1 == number of pseudo flavor
      2 == name of pseudo flavor
      3 == mechanism's OID
      4 == RPCSEC_GSS service
      5 == NFSv4.1 clients MUST support
      6 == NFSv4.1 servers MUST support

      1      2        3                    4                     5   6
      ------------------------------------------------------------------
      390003 krb5     1.2.840.113554.1.2.2 rpc_gss_svc_none      yes yes
      390004 krb5i    1.2.840.113554.1.2.2 rpc_gss_svc_integrity yes yes
      390005 krb5p    1.2.840.113554.1.2.2 rpc_gss_svc_privacy    no yes

   Note that the number and name of the pseudo flavor is presented here
   as a mapping aid to the implementor.  Because the NFSv4 protocol
   includes a method to negotiate security and it understands the GSS-
   API mechanism, the pseudo flavor is not needed.  The pseudo flavor is



Shepler, et al.         Expires February 2, 2007               [Page 18]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   needed for the NFS version 3 since the security negotiation is done
   via the MOUNT protocol as described in [19].

2.2.1.1.1.2.2.  LIPKEY

   The LIPKEY V5 GSS-API mechanism as described in [7] MUST be
   implemented with the RPCSEC_GSS services as specified in the
   following table:


      1      2        3                    4                     5   6
      ------------------------------------------------------------------
      390006 lipkey   1.3.6.1.5.5.9        rpc_gss_svc_none      yes yes
      390007 lipkey-i 1.3.6.1.5.5.9        rpc_gss_svc_integrity yes yes
      390008 lipkey-p 1.3.6.1.5.5.9        rpc_gss_svc_privacy    no yes

2.2.1.1.1.2.3.  SPKM-3 as a security triple

   The SPKM-3 GSS-API mechanism as described in [7] MUST be implemented
   with the RPCSEC_GSS services as specified in the following table:


      1      2        3                    4                     5   6
      ------------------------------------------------------------------
      390009 spkm3    1.3.6.1.5.5.1.3      rpc_gss_svc_none      yes yes
      390010 spkm3i   1.3.6.1.5.5.1.3      rpc_gss_svc_integrity yes yes
      390011 spkm3p   1.3.6.1.5.5.1.3      rpc_gss_svc_privacy    no yes

2.2.1.1.1.3.  GSS Server Principal

   Regardless of what security mechanism under RPCSEC_GSS is being used,
   the NFS server, MUST identify itself in GSS-API via a
   GSS_C_NT_HOSTBASED_SERVICE name type.  GSS_C_NT_HOSTBASED_SERVICE
   names are of the form:

        service@hostname

   For NFS, the "service" element is

        nfs

   Implementations of security mechanisms will convert nfs@hostname to
   various different forms.  For Kerberos V5, LIPKEY, and SPKM-3, the
   following form is RECOMMENDED:

        nfs/hostname





Shepler, et al.         Expires February 2, 2007               [Page 19]


Internet-Draft            NFSv4 Minor Version 1              August 2006


2.3.  COMPOUND and CB_COMPOUND

   A significant departure from the versions of the NFS protocol before
   version 4 is the introduction of the COMPOUND procedure.  For the
   NFSv4 protocol, in all minor versions, there are exactly two RPC
   procedures, NULL and COMPOUND.  The COMPOUND procedure is defined as
   a series of individual operations and these operations perform the
   sorts of functions performed by traditional NFS procedures.

   The operations combined within a COMPOUND request are evaluated in
   order by the server, without any atomicity guarantees.  A limited set
   of facilities exist to pass results from one operation to another.
   Once an operation returns a failing result, the evaluation ends and
   the results of all evaluated operations are returned to the client.

   With the use of the COMPOUND procedure, the client is able to build
   simple or complex requests.  These COMPOUND requests allow for a
   reduction in the number of RPCs needed for logical file system
   operations.  For example, multi-component lookup requests can be
   constructed by combining multiple LOOKUP operations.  Those can be
   further combined with operations such as GETATTR, READDIR, or OPEN
   plus READ to do more complicated sets of operation without incurring
   additional latency.

   NFSv4 also contains a considerable set of callback operations in
   which the server makes an RPC directed at the client.  Callback RPC's
   have a similar structure to that of the normal server requests.  For
   the NFS version 4 protocol callbacks in all minor versions, there are
   two RPC procedures, NULL and CB_COMPOUND.  The CB_COMPOUND procedure
   is defined in analogous fashion to that of COMPOUND with its own set
   of callback operations.

   Addition of new server and callback operation within the COMPOUND and
   CB_COMPOUND request framework provide means of extending the protocol
   in subsequent minor versions.

   Except for a small number of operations needed for session creation,
   server requests and callback requests are performed within the
   context of a session.  Sessions provide a client context for every
   request and support robust replay protection for non-idempotent
   requests.

2.4.  Client Identifiers

   For each operation that obtains or depends on locking state, the
   specific client must be determinable by the server.  In NFSv4, each
   distinct client instance is represented by a clientid, which is a 64-
   bit identifier that identifies a specific client at a given time and



Shepler, et al.         Expires February 2, 2007               [Page 20]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   which is changed whenever the client or the server re-initializes.
   Clientid's are used to support lock identification and crash
   recovery.

   In NFSv4.1, the clientid associated with each operation is derived
   from the session (see Section 2.9) on which the operation is issued.
   Each session is associated with a specific clientid at session
   creation and that clientid then becomes the clientid associated with
   all requests issued using it.  Therefore, unlike NFSv4.0, no NFSv4.1
   operation is possible until a clientid is established.

   A sequence of a CREATE_CLIENTID operation followed by a
   CREATE_SESSION operation using that clientid is required to establish
   the identification on the server.  Establishment of identification by
   a new incarnation of the client also has the effect of immediately
   releasing any locking state that a previous incarnation of that same
   client might have had on the server.  Such released state would
   include all lock, share reservation, and, where the server is not
   supporting the CLAIM_DELEGATE_PREV claim type, all delegation state
   associated with same client with the same identity.  For discussion
   of delegation state recovery, see Section 9.2.1.

   Releasing such state requires that the server be able to determine
   that one client instance is the successor of another.  Where this
   cannot be done, for any of a number of reasons, the locking state
   will remain for a time subject to lease expiration (see Section 8.5)
   and the new client will need to wait for such state to be removed, if
   it makes conflicting lock requests.

   Client identification is encapsulated in the following structure:


           struct nfs_client_id4 {
            verifier4     verifier;
            opaque        id<NFS4_OPAQUE_LIMIT>;
           };

   The first field, verifier, is a client incarnation verifier that is
   used to detect client reboots.  Only if the verifier is different
   from that the server had previously recorded for the client (as
   identified by the second field of the structure, id) does the server
   start the process of canceling the client's leased state.

   The second field, id is a variable length string that uniquely
   defines the client so that subsequent instances of the same client
   bear the same id with a different verifier.

   There are several considerations for how the client generates the id



Shepler, et al.         Expires February 2, 2007               [Page 21]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   string:

   o  The string should be unique so that multiple clients do not
      present the same string.  The consequences of two clients
      presenting the same string range from one client getting an error
      to one client having its leased state abruptly and unexpectedly
      canceled.

   o  The string should be selected so the subsequent incarnations (e.g.
      reboots) of the same client cause the client to present the same
      string.  The implementor is cautioned from an approach that
      requires the string to be recorded in a local file because this
      precludes the use of the implementation in an environment where
      there is no local disk and all file access is from an NFS version
      4 server.

   o  The string should be different for each server network address
      that the client accesses, rather than common to all server network
      addresses.  The reason is that it may not be possible for the
      client to tell if same server is listening on multiple network
      addresses.  If the client issues CREATE_CLIENTID with the same id
      string to each network address of such a server, the server will
      think it is the same client, and each successive CREATE_CLIENTID
      will cause the server remove the client's previous leased state.
      Regardless, as described in Section 2.9.3.4.1, NFSv4.1 does allow
      clients to trunk traffic for a single clientid to one or more of a
      server's networking addresses.

   o  The algorithm for generating the string should not assume that the
      client's network address will not change.  This includes changes
      between client incarnations and even changes while the client is
      still running in its current incarnation.  This means that if the
      client includes just the client's and server's network address in
      the id string, there is a real risk, after the client gives up the
      network address, that another client, using a similar algorithm
      for generating the id string, would generate a conflicting id
      string.

   Given the above considerations, an example of a well generated id
   string is one that includes:

   o  The server's network address.

   o  The client's network address.

   o  For a user level NFS version 4 client, it should contain
      additional information to distinguish the client from other user
      level clients running on the same host, such as a process id or



Shepler, et al.         Expires February 2, 2007               [Page 22]


Internet-Draft            NFSv4 Minor Version 1              August 2006


      other unique sequence.

   o  Additional information that tends to be unique, such as one or
      more of:

      *  The client machine's serial number (for privacy reasons, it is
         best to perform some one way function on the serial number).

      *  A MAC address (again, a one way function should be performed).

      *  The timestamp of when the NFS version 4 software was first
         installed on the client (though this is subject to the
         previously mentioned caution about using information that is
         stored in a file, because the file might only be accessible
         over NFS version 4).

      *  A true random number.  However since this number ought to be
         the same between client incarnations, this shares the same
         problem as that of the using the timestamp of the software
         installation.

   As a security measure, the server MUST NOT cancel a client's leased
   state if the principal established the state for a given id string is
   not the same as the principal issuing the CREATE_CLIENTID.

   A server may compare an nfs_client_id4 in a CREATE_CLIENTID with an
   nfs_client_id4 established using SETCLIENTID using NFSv4 minor
   version 0, so that an NFSv4.1 client is not forced to delay until
   lease expiration for locking state established by the earlier client
   using minor version 0.

   Once a CREATE_CLIENTID has been done, and the resulting clientid
   established as associated with a session, all requests made on that
   session implicitly identify that clientid, which in turn designates
   the client specified using the long-form nfs_client_id4 structure.
   The shorthand client identifier (a clientid) is assigned by the
   server and should be chosen so that it will not conflict with a
   clientid previously assigned by the server.  This applies across
   server restarts or reboots.

   In the event of a server restart, a client will find out that its
   current clientid is no longer valid when receives a
   NFS4ERR_STALE_CLIENTID error.  The precise circumstances depend of
   the characteristics of the sessions involved, specifically whether
   the session is persistent (see Section 2.9.4.5).

   When a session is not persistent, the client will need to create a
   new session.  When the existing clientid is presented to a server as



Shepler, et al.         Expires February 2, 2007               [Page 23]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   part of creating a session and that clientid is not recognized, as
   would happen after a server reboot, the server will reject the
   request with the error NFS4ERR_STALE_CLIENTID.  When this happens,
   the client must obtain a new clientid by use of the CREATE_CLIENTID
   operation and then use that clientid as the basis of the basis of a
   new session and then proceed to any other necessary recovery for the
   server reboot case (See Section 8.6.2).

   In the case of the session being persistent, the client will re-
   establish communication using the existing session after the reboot.
   This session will be associated with a stale clientid and the client
   will receive an indication of that fact in the sr_status field
   returned by the SEQUENCE operation (see Section 2.9.2.1).  The client
   can then use the existing session to do whatever operations are
   necessary to determine the status of requests outstanding at the time
   of reboot, while avoiding issuing new requests, particularly any
   involving locking on that session.  Such requests would fail with
   NFS4ERR_STALE_CLIENTID error or an NFS4ERR_STALE_STATEID error, if
   attempted.  In any case, the client would create a new clientid using
   CREATE_CLIENTID, create a new session based on that clientid, and
   proceed to other necessary recovery for the server reboot case.

   See the detailed descriptions of CREATE_CLIENTID (Section 16.35 and
   CREATE_SESSION (Section 16.36) for a complete specification of these
   operations.

2.4.1.  Server Release of Clientid

   If the server determines that the client holds no associated state
   for its clientid, the server may choose to release the clientid.  The
   server may make this choice for an inactive client so that resources
   are not consumed by those intermittently active clients.  If the
   client contacts the server after this release, the server must ensure
   the client receives the appropriate error so that it will use the
   CREATE_CLIENTID/CREATE_SESSION sequence to establish a new identity.
   It should be clear that the server must be very hesitant to release a
   clientid since the resulting work on the client to recover from such
   an event will be the same burden as if the server had failed and
   restarted.  Typically a server would not release a clientid unless
   there had been no activity from that client for many minutes.  Note
   that "associated state" includes sessions.  As long as there are
   sessions, the server MUST not release the clientid.  See
   Section 2.9.8.1.4 for discussion on releasing inactive sessions.

   Note that if the id string in a CREATE_CLIENTID request is properly
   constructed, and if the client takes care to use the same principal
   for each successive use of CREATE_CLIENTID, then, barring an active
   denial of service attack, NFS4ERR_CLID_INUSE should never be



Shepler, et al.         Expires February 2, 2007               [Page 24]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   returned.

   However, client bugs, server bugs, or perhaps a deliberate change of
   the principal owner of the id string (such as the case of a client
   that changes security flavors, and under the new flavor, there is no
   mapping to the previous owner) will in rare cases result in
   NFS4ERR_CLID_INUSE.

   In that event, when the server gets a CREATE_CLIENTID for a client id
   that currently has no state, or it has state, but the lease has
   expired, rather than returning NFS4ERR_CLID_INUSE, the server MUST
   allow the CREATE_CLIENTID, and confirm the new clientid if followed
   by the appropriate CREATE_SESSION.

2.5.  Security Service Negotiation

   With the NFS version 4 server potentially offering multiple security
   mechanisms, the client needs a method to determine or negotiate which
   mechanism is to be used for its communication with the server.  The
   NFS server may have multiple points within its file system namespace
   that are available for use by NFS clients.  These points can be
   considered security policy boundaries, and in some NFS
   implementations are tied to NFS export points.  In turn the NFS
   server may be configured such that each of these security policy
   boundaries may have different or multiple security mechanisms in use.

   The security negotiation between client and server must be done with
   a secure channel to eliminate the possibility of a third party
   intercepting the negotiation sequence and forcing the client and
   server to choose a lower level of security than required or desired.
   See section Section 19 for further discussion.

2.5.1.  NFSv4 Security Tuples

   An NFS server can assign one or more "security tuples" to each
   security policy boundary in its namespace.  Each security tuple
   consists of a security flavor (see Section 2.2.1.1), and if the
   flavor is RPCSEC_GSS, a GSS-API mechanism OID, a GSS-API quality of
   protection, and an RPCSEC_GSS service.

2.5.2.  SECINFO and SECINFO_NO_NAME

   The SECINFO and SECINFO_NO_NAME operations allow the client to
   determine, on a per filehandle basis, what security tuple is to be
   used for server access.  In general, the client will not have to use
   either operation except during initial communication with the server
   or when the client crosses security policy boundaries at the server.
   It is possible that the server's policies change during the client's



Shepler, et al.         Expires February 2, 2007               [Page 25]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   interaction therefore forcing the client to negotiate a new security
   tuple.

2.5.3.  Security Error

   Based on the assumption that each NFS version 4 client and server
   must support a minimum set of security (i.e., LIPKEY, SPKM-3, and
   Kerberos-V5 all under RPCSEC_GSS), the NFS client will initiate file
   access to the server with one of the minimal security tuples.  During
   communication with the server, the client may receive an NFS error of
   NFS4ERR_WRONGSEC.  This error allows the server to notify the client
   that the security tuple currently being used is contravenes the
   server's security policy.  The client is then responsible for
   determining (see Section 2.5.3.1) what security tuples are available
   at the server and choose one which is appropriate for the client.

2.5.3.1.  Using NFS4ERR_WRONGSEC, SECINFO, and SECINFO_NO_NAME

   This section explains of the mechanics of NFSv4.1 security
   negotiation.  Unless noted otherwise, for any mention of PUTFH in
   this section, the reader should interpret it as applying to PUTROOTFH
   and PUTPUBFH in addition to PUTFH.

2.5.3.1.1.  PUTFH + LOOKUP (or OPEN by Name)

   This situation also applies to a put filehandle operation followed by
   an OPEN operation that specifies a component name.

   In this situation, the client is potentially crossing a security
   policy boundary, and the set of security tuples the parent directory
   supports differ from those of the child.  The server implementation
   may decide whether to impose any restrictions on security policy
   administration.  There are at least three approaches
   (sec_policy_child is the tuple set of the child export,
   sec_policy_parent is that of the parent).

     a)  sec_policy_child <= sec_policy_parent (<= for subset).  This
      means that the set of security tuples specified on the security
      policy of a child directory is always a subset of that of its
      parent directory.

     b)  sec_policy_child ^ sec_policy_parent != {} (^ for intersection,
      {} for the empty set).  This means that the security tuples
      specified on the security policy of a child directory always has a
      non empty intersection with that of the parent.






Shepler, et al.         Expires February 2, 2007               [Page 26]


Internet-Draft            NFSv4 Minor Version 1              August 2006


     c)  sec_policy_child ^ sec_policy_parent == {}.  This means that
      the set of tuples specified on the security policy of a child
      directory may not intersect with that of the parent.  In other
      words, there are no restrictions on how the system administrator
      may set.

   For a server to support approach (b) (when client chooses a flavor
   that is not a member of sec_policy_parent) and (c), PUTFH must NOT
   return NFS4ERR_WRONGSEC in case of security mismatch.  Instead, it
   should be returned from the LOOKUP (or OPEN by component name) that
   follows.

   Since the above guideline does not contradict approach (a), it should
   be followed in general.  Even if approach (a) is implemented, it is
   possible for the security tuple used to be acceptable for the target
   of LOOKUP but not for the filehandles used in PUTFH.  The PUTFH could
   really be a PUTROOTFH or PUTPUBFH, where the client does not know the
   security tuples for the root or public filehandle.  Or the security
   policy for the filehandle used by PUTFH could have changed since the
   time the filehandle was obtained.

   Therefore, an NFSv4.1 server MUST NOT return NFS4ERR_WRONGSEC in
   response to PUTFH, PUTROOTFH, or PUTPUBFH if the operation is
   immediately followed by a LOOKUP or an OPEN by component name.

2.5.3.1.2.  PUTFH + LOOKUPP

   Since SECINFO only works its way down, there is no way LOOKUPP can
   return NFS4ERR_WRONGSEC without SECINFO_NO_NAME.  SECINFO_NO_NAME
   solves this issue because via style "parent", it works in the
   opposite direction as SECINFO.  As with Section 2.5.3.1.1, PUTFH must
   not return NFS4ERR_WRONGSEC whenever it is followed by LOOKUPP.  If
   the server does not support SECINFO_NO_NAME, the client's only
   recourse is to issue the PUTFH, LOOKUPP, GETFH sequence of operations
   with every security tuple it supports.

   Regardless whether SECINFO_NO_NAME is supported, an NFSv4.1 server
   MUST NOT return NFS4ERR_WRONGSEC in response to PUTFH, PUTROOTFH, or
   PUTPUBFH if the operation is immediately followed by a LOOKUPP.

2.5.3.1.3.  PUTFH + SECINFO or PUTFH + SECINFO_NO_NAME

   A security sensitive client is allowed to choose a strong security
   tuple when querying a server to determine a file object's permitted
   security tuples.  The security tuple chosen by the client does not
   have to be included in the tuple list of the security policy of the
   either parent directory indicated in PUTFH, or the child file object
   indicated in SECINFO (or any parent directory indicated in



Shepler, et al.         Expires February 2, 2007               [Page 27]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   SECINFO_NO_NAME).  Of course the server has to be configured for
   whatever security tuple the client selects, otherwise the request
   will fail at RPC layer with an appropriate authentication error.

   In theory, there is no connection between the security flavor used by
   SECINFO or SECINFO_NO_NAME and those supported by the security
   policy.  But in practice, the client may start looking for strong
   flavors from those supported by the security policy, followed by
   those in the mandatory set.

   The NFSv4.1 server MUST NOT return NFS4ERR_WRONGSEC to PUTFH whenever
   it is immediately followed by SECINFO or SECINFO_NO_NAME.  The
   NFSv4.1 server MUST NOT return NFS4ERR_WRONGSEC from SECINFO or
   SECINFO_NO_NAME.

2.5.3.1.4.  PUTFH + PUTFH

   This is a nonsensical situation, because the first put filehandle
   operation is wasted.  The NFSv4.1 server MAY return NFS4ERR_WRONGSEC
   to the first PUTFH, or it MAY NOT.  If it does not, it then processes
   the subsequent PUTFH and any operation that follows it according to
   the rules listed in Section 2.5.3.1.

2.5.3.1.5.  PUTFH + Nothing

   This too is nonsensical because the PUTFH is wasted.  The NFSv4.1
   server MAY or MAY NOT return NFS4ERR_WRONGSEC.

2.5.3.1.6.  PUTFH + Anything Else

   "Anything Else" includes OPEN by filehandle.

   The security policy enforcement applies to the filehandle specified
   in PUTFH.  Therefore PUTFH must return NFS4ERR_WRONGSEC in case of
   security tuple on the part of the mismatch.  This avoids the
   complexity adding NFS4ERR_WRONGSEC as an allowable error to every
   other operation.

   PUTFH + SECINFO_NO_NAME (style "current_fh") is an efficient way for
   the client to recover from NFS4ERR_WRONGSEC.

   The NFSv4.1 server, MUST not return NFS4ERR_WRONGSEC to any operation
   other than LOOKUP, LOOKUPP, and OPEN (by component name).

2.6.  Minor Versioning

   To address the requirement of an NFS protocol that can evolve as the
   need arises, the NFS version 4 protocol contains the rules and



Shepler, et al.         Expires February 2, 2007               [Page 28]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   framework to allow for future minor changes or versioning.

   The base assumption with respect to minor versioning is that any
   future accepted minor version must follow the IETF process and be
   documented in a standards track RFC.  Therefore, each minor version
   number will correspond to an RFC.  Minor version zero of the NFS
   version 4 protocol is represented by [2], and minor version one is
   represented by this document [[Comment.2: change "document" to "RFC"
   when we publish]] .  The COMPOUND and CB_COMPOUND procedures support
   the encoding of the minor version being requested by the client.

   The following items represent the basic rules for the development of
   minor versions.  Note that a future minor version may decide to
   modify or add to the following rules as part of the minor version
   definition.

   1.   Procedures are not added or deleted

        To maintain the general RPC model, NFS version 4 minor versions
        will not add to or delete procedures from the NFS program.

   2.   Minor versions may add operations to the COMPOUND and
        CB_COMPOUND procedures.

        The addition of operations to the COMPOUND and CB_COMPOUND
        procedures does not affect the RPC model.

        *  Minor versions may append attributes to GETATTR4args,
           bitmap4, and GETATTR4res.

           This allows for the expansion of the attribute model to allow
           for future growth or adaptation.

        *  Minor version X must append any new attributes after the last
           documented attribute.

           Since attribute results are specified as an opaque array of
           per-attribute XDR encoded results, the complexity of adding
           new attributes in the midst of the current definitions will
           be too burdensome.

   3.   Minor versions must not modify the structure of an existing
        operation's arguments or results.

        Again the complexity of handling multiple structure definitions
        for a single operation is too burdensome.  New operations should
        be added instead of modifying existing structures for a minor
        version.



Shepler, et al.         Expires February 2, 2007               [Page 29]


Internet-Draft            NFSv4 Minor Version 1              August 2006


        This rule does not preclude the following adaptations in a minor
        version.

        *  adding bits to flag fields such as new attributes to
           GETATTR's bitmap4 data type

        *  adding bits to existing attributes like ACLs that have flag
           words

        *  extending enumerated types (including NFS4ERR_*) with new
           values

   4.   Minor versions may not modify the structure of existing
        attributes.

   5.   Minor versions may not delete operations.

        This prevents the potential reuse of a particular operation
        "slot" in a future minor version.

   6.   Minor versions may not delete attributes.

   7.   Minor versions may not delete flag bits or enumeration values.

   8.   Minor versions may declare an operation as mandatory to NOT
        implement.

        Specifying an operation as "mandatory to not implement" is
        equivalent to obsoleting an operation.  For the client, it means
        that the operation should not be sent to the server.  For the
        server, an NFS error can be returned as opposed to "dropping"
        the request as an XDR decode error.  This approach allows for
        the obsolescence of an operation while maintaining its structure
        so that a future minor version can reintroduce the operation.

        1.  Minor versions may declare attributes mandatory to NOT
            implement.

        2.  Minor versions may declare flag bits or enumeration values
            as mandatory to NOT implement.

   9.   Minor versions may downgrade features from mandatory to
        recommended, or recommended to optional.

   10.  Minor versions may upgrade features from optional to recommended
        or recommended to mandatory.





Shepler, et al.         Expires February 2, 2007               [Page 30]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   11.  A client and server that supports minor version X should support
        minor versions 0 (zero) through X-1 as well.

   12.  Except for infrastructural changes, no new features may be
        introduced as mandatory in a minor version.

        This rule allows for the introduction of new functionality and
        forces the use of implementation experience before designating a
        feature as mandatory.  On the other hand, some classes of
        features are infrastructural and have broad effects.  Allowing
        such features to not be mandatory complicates implementation of
        the minor version.

   13.  A client MUST NOT attempt to use a stateid, filehandle, or
        similar returned object from the COMPOUND procedure with minor
        version X for another COMPOUND procedure with minor version Y,
        where X != Y.

2.7.  Non-RPC-based Security Services

   As described in Section 2.2.1.1.1.1, NFSv4 relies on RPC for
   identification, authentication, integrity, and privacy.  NFSv4 itself
   provides additional security services as described in the next
   several subsections.

2.7.1.  Authorization

   Authorization to access a file object via an NFSv4 operation is
   ultimately determined by the NFSv4 server.  A client can predetermine
   its access to a file object via the OPEN (Section 16.16) and the
   ACCESS (Section 16.1) operations.

   Principals with appropriate access rights can modify the
   authorization on a file object via the SETATTR (Section 16.30)
   operation.  Four attributes that affect access rights are: mode,
   owner, owner_group, and acl.  See Section 5.

2.7.2.  Auditing

   NFSv4 provides auditing on a per file object basis, via the ACL
   attribute as described in Section 6.  It is outside the scope of this
   specification to specify audit log formats or management policies.

2.7.3.  Intrusion Detection

   NFSv4 provides alarm control on a per file object basis, via the ACL
   attribute as described in Section 6.  Alarms may serve as the basis
   for instrusion detection.  It is outside the scope of this



Shepler, et al.         Expires February 2, 2007               [Page 31]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   specification to specify heuristics for detecting intrusion via
   alarms.

2.8.  Transport Layers

2.8.1.  Required and Recommended Properties of Transports

   NFSv4 works over RDMA and non-RDMA_based transports with the
   following attributes:

   o  The transport supports reliable delivery of data, which NFSv4
      requires but neither NFSv4 nor RPC has facilities for ensuring.
      [20]

   o  The transport delivers data in the order it was sent.  Ordered
      delivery simplifies detection of transmit errors, and simplifies
      the sending of arbitrary sized requests and responses, via the
      record marking protocol [4].

   Where an NFS version 4 implementation supports operation over the IP
   network protocol, any transport used between NFS and IP MUST be among
   the IETF-approved congestion control transport protocols.  At the
   time this document was written, the only two transports that had the
   above attributes were TCP and SCTP.  To enhance the possibilities for
   interoperability, an NFS version 4 implementation MUST support
   operation over the TCP transport protocol.

   Even if NFS version 4 is used over a non-IP network protocol, it is
   RECOMMENDED that the transport support congestion control.

   Note that it is permissible for connectionless transports to be used
   under NFSv4.1, however reliable and in-order delivery of data is
   still required.  NFSv4.1 assumes that a client transport address and
   server transport address used to send data over a transport together
   constitute a connection, even if the underlying transport eschews the
   concept of a connection.

2.8.2.  Client and Server Transport Behavior

   If a connection-oriented transport (e.g.  TCP) is used the client and
   server SHOULD use long lived connections for at least three reasons:

   1.  This will prevent the weakening of the transport's congestion
       control mechanisms via short lived connections.

   2.  This will improve performance for the WAN environment by
       eliminating the need for connection setup handshakes.




Shepler, et al.         Expires February 2, 2007               [Page 32]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   3.  The NFSv4.1 callback model differs from NFSv4.0, and requires the
       client and server to maintain a client-created channel (see
       Section 2.9.3.4for the server to use.

   In order to reduce congestion, if a connection-oriented transport is
   used, and the request is not the NULL procedure,

   o  A client (or the server, if issuing a callback), MUST NOT retry a
      request unless the connection the request was issued over was
      disconnected before the reply was received.

   o  A server (or the client, if receiving a callback), MUST NOT
      silently drop a request, even if the request is a retry.  (The
      silent drop behavior of RPCSEC_GSS [5] does not apply because this
      behavior happens at the RPCSEC_GSS layer, a lower layer in the
      request processing).  Instead, the server SHOULD return an
      appropriate error (see Section 2.9.4.1) or it MAY disconnect the
      connection.

   When using RDMA transports there are other reasons not tolerating
   retries over the same connection:

   o  RDMA transports use "credits" to enforce flow control, where a
      credit is a right to a peer to transmit a message.  If one peer
      were to retransmit a request (or reply), it would consume an
      additional credit.  If the server retransmitted a reply, it would
      certainly result in an RDMA connection loss, since the client
      would typically only post a single receive buffer for each
      request.  If the client retransmitted a request, the additional
      credit consumed on the server might lead to RDMA connection
      failure unless the client accounted for it and decreased its
      available credit, leading to wasted resources.

   o  RDMA credits present a new issue to the reply cache in NFSv4.1.
      The reply cache may be used when a connection within a session is
      lost, such as after the client reconnects.  Credit information is
      a dynamic property of the RDMA connection, and stale values must
      not be replayed from the cache.  This implies that the reply cache
      contents must not be blindly used when replies are issued from it,
      and credit information appropriate to the channel must be
      refreshed by the RPC layer.

   In addition, the sender of an NFSv4.1 request is not allowed to stop
   waiting for a reply, as described in Section 2.9.4.2.







Shepler, et al.         Expires February 2, 2007               [Page 33]


Internet-Draft            NFSv4 Minor Version 1              August 2006


2.8.3.  Ports

   Historically, NFS version 2 and version 3 servers have resided on
   port 2049.  The registered port 2049 RFC3232 [21] for the NFS
   protocol should be the default configuration.  NFSv4 clients SHOULD
   NOT use the RPC binding protocols as described in RFC1833 [22].

2.9.  Session

2.9.1.  Motivation and Overview

   Previous versions and minor versions of NFS have suffered from the
   following:

   o  Lack of support for exactly once semantics (EOS).  This includes
      lack of support for EOS through server failure and recovery.

   o  Limited callback support, including no support for sending
      callbacks through firewalls, and races between responses from
      normal requests, and callbacks.

   o  Limited trunking over multiple network paths.

   o  Requiring machine credentials for fully secure operation.

   Through the introduction of a session, NFSv4.1 addresses the above
   shortfalls with practical solutions:

   o  EOS is enabled by a reply cache with a bounded size, making it
      feasible to keep on persistent storage and enable EOS through
      server failure and recovery.  One reason that previous revisions
      of NFS did not support EOS was because some EOS approaches often
      limited parallelism.  As will be explained in Section 2.9.4),
      NFSv4.1 supports both EOS and unlimited parallelism.

   o  The NFSv4.1 client provides creates transport connections and
      gives them to the server for sending callbacks, thus solving the
      firewall issue (Section 16.34).  Races between responses from
      client requests, and callbacks caused by the requests are detected
      via the session's sequencing properties which are a byproduct of
      EOS (Section 2.9.4.3).

   o  The NFSv4.1 client can add an arbitrary number of connections to
      the session, and thus provide trunking (Section 2.9.3.4.1).

   o  The NFSv4.1 session produces a session key independent of client
      and server machine credentials which can be used to compute a
      digest for protecting key session management operations



Shepler, et al.         Expires February 2, 2007               [Page 34]


Internet-Draft            NFSv4 Minor Version 1              August 2006


      Section 2.9.6.3).

   o  The NFSv4.1 client can also create secure RPCSEC_GSS contexts for
      use by the session's callback channel that do not require the
      server to authenticate to a client machine principal
      (Section 2.9.6.2).

   A session is a dynamically created, long-lived server object created
   by a client, used over time from one or more transport connections.
   Its function is to maintain the server's state relative to the
   connection(s) belonging to a client instance.  This state is entirely
   independent of the connection itself, and indeed the state exists
   whether the connection exists or not (though locks, delegations, etc.
   and generally expire in the extended absence of an open connection).
   The session in effect becomes the object representing an active
   client on a set of zero or more connections.

2.9.2.  NFSv4 Integration

   Sessions are part of NFSv4.1 and not NFSv4.0.  Normally, a major
   infrastructure change like sessions would require a new major version
   number to an RPC program like NFS.  However, because NFSv4
   encapsulates its functionality in a single procedure, COMPOUND, and
   because COMPOUND can support an arbitrary number of operations,
   sessions are almost trivially added.  COMPOUND includes a minor
   version number field, and for NFSv4.1 this minor version is set to 1.
   When the NFSv4 server processes a COMPOUND with the minor version set
   to 1, it expects a different set of operations than it does for
   NFSv4.0.  One operation it expects is the SEQUENCE operation, which
   is required for every COMPOUND that operates over an established
   session.

2.9.2.1.  SEQUENCE and CB_SEQUENCE

   In NFSv4.1, when the SEQUENCE operation is present, it is always the
   first operation in the COMPOUND procedure.  The primary purpose of
   SEQUENCE is to carry the session identifier.  The session identifier
   associates all other operations in the COMPOUND procedure with a
   particular session.  SEQUENCE also contains required information for
   maintaining EOS (see Section 2.9.4).  Session-enabled NFSv4.1
   COMPOUND requests thus have the form:










Shepler, et al.         Expires February 2, 2007               [Page 35]


Internet-Draft            NFSv4 Minor Version 1              August 2006


       +-----+--------------+-----------+------------+-----------+----
       | tag | minorversion | numops    |SEQUENCE op | op + args | ...
       |     |   (== 1)     | (limited) |  + args    |           |
       +-----+--------------+-----------+------------+-----------+----

       and the reply's structure is:

       +------------+-----+--------+-------------------------------+--//
       |last status | tag | numres |status + SEQUENCE op + results |  //
       +------------+-----+--------+-------------------------------+--//
               //-----------------------+----
               // status + op + results | ...
               //-----------------------+----

   A CB_COMPOUND procedure request and reply has a similar form, but
   instead of a SEQUENCE operation, there is a CB_SEQUENCE operation,
   and there is an additional field called "callback_ident", which is
   superfluous in NFSv4.1.  CB_SEQUENCE has the same information as
   SEQUENCE, but includes other information needed to solve callback
   races (Section 2.9.4.3).

2.9.2.2.  Clientid and Session Association

   Sessions are subordinate to the clientid (Section 2.4).  Each
   clientid can have zero or more active sessions.  A clientid, and a
   session bound to it are required to do anything useful in NFSv4.1.
   Each time a session is used, the state leased to it associated
   clientid is automatically renewed.

   State such as share reservations, locks, delegations, and layouts
   (Section 1.5.4) is tied to the clientid, not the sessions of the
   clientid.  Successive state changing operations from a given state
   owner can go over different sessions, as long each session is
   associated with the same clientid.  Callbacks can arrive over a
   different session than the session that sent the operation the
   acquired the state that the callback is for.  For example, if session
   A is used to acquire a delegation, a request to recall the delegation
   can arrive over session B.

2.9.3.  Channels

   Each session has one or two channels: the "operation" or "fore"
   channel used for ordinary requests from client to server, and the
   "back" channel, used for callback requests from server to client.
   The session allocates resources for each channel, including separate
   reply caches (see Section 2.9.4.1 These resources are for the most
   part specified at time the session is created.




Shepler, et al.         Expires February 2, 2007               [Page 36]


Internet-Draft            NFSv4 Minor Version 1              August 2006


2.9.3.1.  Operation Channel

   The operation channel carries COMPOUND requests and responses.  A
   session always has an operation channel.

2.9.3.2.  Backchannel

   The backchannel carries CB_COMPOUND requests and responses.  Whether
   there is a backchannel or not is a decision of the client; NFSv4.1
   servers MUST support backchannels.

2.9.3.3.  Session and Channel Association

   Because there are at most two channels per session, and because each
   channel has a distinct purpose, channels are not assigned
   identifiers.  The operation and backchannel are implicitly created
   and associated when the session is created.

2.9.3.4.  Connection and Channel Association

   Each channel is associated with zero or more transport connections.
   A connection can be bound to one channel or both channels of a
   session; the client and server negotiate whether a connection will
   carry traffic for one channel or both channel via the the
   CREATE_SESSION (Section 16.36) and the BIND_CONN_TO_SESSION
   (Section 16.34) operations.  When a session is created via
   CREATE_SESSION, it is automatically bound to the operation channel,
   and optionally the backchannel.  If the client does not specify
   connecting binding enforcement when the session is created, then
   additional connections are automatically bound to the operation
   channel when the are used with a SEQUENCE operation that has the
   session's sessionid.

   A connection MAY be bound to the channels of other sessions.  The
   client decides, and the NFSv4.1 server MUST allow it.  A connection
   MAY be bound to the the channels' of other sessions of other
   clientids.  Again, the client decides, and the server MUST allow it.

   It is permissible for connections of multiple types to be bound to
   the same channel.  For example a TCP and RDMA connection can be bound
   to the operation channel.  In the event an RDAM and non-RDMA
   connection are bound to the same channel, the maximum number of slots
   must be at least one more than the total number of credits.  This way
   if all RDMA credits are use, the non-RDMA connection can have at
   least one outstanding request.

   It is permissible for a connection of one type to be bound to the
   operation channel, and another type bound to the backchannel.



Shepler, et al.         Expires February 2, 2007               [Page 37]


Internet-Draft            NFSv4 Minor Version 1              August 2006


2.9.3.4.1.  Trunking

   Since multiple connections can be bound to a session's channel, these
   means that traffic between an NFSv4.1 client and server channel goes
   over all connections.  If the connections are over different network
   paths, this is trunking.  NFSv4.1 allows trunking, thus allows the
   bandwidth capacity to scale with the number of connections.

   At issue is how do NFSv4.1 clients and servers discover and verify
   multiple paths?  On the client side, each client should be aware of
   the network interfaces it has available from which to create
   connections.  However, the client cannot always be certain whether a
   server's multitide of network interfaces in fact belong to the same
   server, or even if they do, whether the server is prepared to share a
   clientid or sessionid across all its interfaces.  NFSv4.1 provides no
   discovery protocol for allowing servers to advertise multiple network
   interfaces; such a protocol is problematic because network address
   translation (NAT) may be occurring between the client and server, and
   so, unless the NAT devices are inspecting NFSv4.1 traffic, the
   network addresses the server offers to the client would be
   meaningless.  At best, short of manual configuration, an NFSv4.1
   client could use a host name to network address directory (e.g.  DNS)
   to enumerate a server's network interfaces.  This then leaves the
   problem of verification.

   NFSv4.1 provides a way for clients and servers to reliably verify if
   connections between different network paths are in fact bound to the
   same NFSv4.1 server.  The SET_SSV (Section 16.47) operation allows a
   client and server to establish a unique, shared key value (the SSV).
   When a new connection is bound to the session (via the
   BIND_CONN_TO_SESSION operation, see Section 16.34), the client must
   offer a digest that based on the SSV.  If the client mistakenly tries
   to bind a connection to a session of a wrong server, the server will
   either reject the attempt because it is not aware of the session
   identifier of the BIND_CONN_TO_SESSION arguments, or it will reject
   the attempt because the digest for the SSV does not match what the
   server expects.  Even if the server mistakenly or maliciously accept
   the connection bind attempt, the digest it computes in the response
   will not be verified by the client, the client will know it cannot
   use the connection for trunking the specified channel.

2.9.4.  Exactly Once Semantics

   Via the session, NFSv4.1 offers exactly once semantics (EOS) for
   requests sent over a channel.  EOS is supported on both the operation
   and back channels.





Shepler, et al.         Expires February 2, 2007               [Page 38]


Internet-Draft            NFSv4 Minor Version 1              August 2006


2.9.4.1.  Slot Identifiers and Reply Cache

   The RPC layer provides a transaction ID (xid), which, while required
   to be unique, is not especially convenient for tracking requests.
   The xid is only meaningful to the requester it cannot be interpreted
   at the replier except to test for equality with previously issued
   requests.  Because RPC operations may be completed by the replier in
   any order, many transaction IDs may be outstanding at any time.  The
   requester may therefore perform a computationally expensive lookup
   operation in the process of demultiplexing each reply.

   In the NFSv4.1, there is a limit to the number of active requests.
   This immediately enables a computationally efficient index for each
   request which is designated as a Slot Identifier, or slotid.

   When the requester issues a new request, it selects a slotid in the
   range 0..N-1, where N is the replier's current "totalrequests" limit
   granted to the requester on the session over which the request is to
   be issued.  The slotid must be unused by any of the requests which
   the requester has already active on the session.  "Unused" here means
   the requester has no outstanding request for that slotid.  Because
   the slot id is always an integer in the range 0..N-1, requester
   implementations can use the slotid from a replier response to
   efficiently match responses with outstanding requests, such as, for
   example, by using the slotid to index into a outstanding request
   array.  This can be used to avoid expensive hashing and lookup
   functions in the performance-critical receive path.

   The sequenceid, which accompanies the slotid in each request, is
   important for an important check at the server: it must be able to be
   determined efficiently whether a request using a certain slotid is a
   retransmit or a new, never-before-seen request.  It is not feasible
   for the client to assert that it is retransmitting to implement this,
   because for any given request the client cannot know the server has
   seen it unless the server actually replies.  Of course, if the client
   has seen the server's reply, the client would not retransmit.

   The sequenceid MUST increase monotonically for each new transmit of a
   given slotid, and MUST remain unchanged for any retransmission.  The
   server must in turn compare each newly received request's sequenceid
   with the last one previously received for that slotid, to see if the
   new request is:

   o  A new request, in which the sequenceid is one greater than that
      previously seen in the slot (accounting for sequence wraparound).
      The replier proceeds to execute the new request.





Shepler, et al.         Expires February 2, 2007               [Page 39]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   o  A retransmitted request, in which the sequenceid is equal to that
      last seen in the slot.  Note that this request may be either
      complete, or in progress.  The replier performs replay processing
      in these cases.

   o  A misordered replay, in which the sequenceid is less than
      (accounting for sequence wraparound) than that previously seen in
      the slot.  The replier MUST return NFS4ERR_SEQ_MISORDERED (as the
      result from SEQUENCE or CB_SEQUENCE).

   o  A misordered new request, in which the sequenceid is two or more
      than (accounting for sequence wraparound) than that previously
      seen in the slot.  Note that because the sequenceid must
      wraparound one it reaches 0xFFFFFFFF, a misordered new request and
      a misordered replay cannot be distinguished.  Thus, the replier
      MUST return NFS4ERR_SEQ_MISORDERED (as the result from SEQUENCE or
      CB_SEQUENCE).

   Unlike the XID, the slotid is always within a specific range; this
   has two implications.  The first implication is that for a given
   session, the replier need only cache the results of a limited number
   of COMPOUND requests.  The second implication derives from the first,
   which is unlike XID-indexed reply caches (also know as duplicate
   request caches - DRCs), the slotid-based reply cache cannot be
   overflowed.  Through use of the sequenceid to identify retransmitted
   requests, the replier does not need to actually cache the request
   itself, reducing the storage requirements of the reply cache further.
   These new facilities makes it practical to maintain all the required
   entries for an effective reply cache.

   The slotid and sequenceid therefore take over the traditional role of
   the XID and port number in the replier reply cache implementation,
   and the session replaces the IP address.  This approach is
   considerably more portable and completely robust - it is not subject
   to the frequent reassignment of ports as clients reconnect over IP
   networks.  In addition, the RPC XID is not used in the reply cache,
   enhancing robustness of the cache in the face of any rapid reuse of
   XIDs by the client.  [[Comment.3: We need to discuss the requirements
   of the client for changing the XID.]] .

   It is required to encode the slotid information into each request in
   a way that does not violate the minor versioning rules of the NFSv4.0
   specification.  This is accomplished here by encoding it in the
   SEQUENCE operation within each NFSv4.1 COMPOUND and CB_COMPOUND
   procedure.  The operation easily piggybacks within existing messages.
   [[Comment.4: Need a better term than piggyback]]

   In general, the receipt of a new sequenced request arriving on any



Shepler, et al.         Expires February 2, 2007               [Page 40]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   valid slot is an indication that the previous reply cache contents of
   that slot may be discarded.  In order to further assist the replier
   in slot management, the requester is required to use the lowest
   available slot when issuing a new request.  In this way, the replier
   may be able to retire additional entries.

   However, in the case where the replier is actively adjusting its
   granted maximum request count to the requester, it may not be able to
   use receipt of the slotid to retire cache entries.  The slotid used
   in an incoming request may not reflect the server's current idea of
   the requester's session limit, because the request may have been sent
   from the requester before the update was received.  Therefore, in the
   downward adjustment case, the replier may have to retain a number of
   reply cache entries at least as large as the old value, until
   operation sequencing rules allow it to infer that the requester has
   seen its reply.

   The SEQUENCE (and CB_SEQUENCE) operation also carries a "maxslot"
   value which carries additional client slot usage information.  The
   requester must always provide its highest-numbered outstanding slot
   value in the maxslot argument, and the replier may reply with a new
   recognized value.  The requester should in all cases provide the most
   conservative value possible, although it can be increased somewhat
   above the actual instantaneous usage to maintain some minimum or
   optimal level.  This provides a way for the requester to yield unused
   request slots back to the replier, which in turn can use the
   information to reallocate resources.  Obviously, maxslot can never be
   zero, or the session would deadlock.

   The replier also provides a target maxslot value to the requester,
   which is an indication to the requester of the maxslot the replier
   wishes the requester to be using.  This permits the server to
   withdraw (or add) resources from a requester that has been found to
   not be using them, in order to more fairly share resources among a
   varying level of demand from other requesters.  The requester must
   always comply with the replier's value updates, since they indicate
   newly established hard limits on the requester's access to session
   resources.  However, because of request pipelining, the requester may
   have active requests in flight reflecting prior values, therefore the
   replier must not immediately require the requester to comply.

2.9.4.1.1.  Errors from SEQUENCE and CB_SEQUENCE

   Any time SEQUENCE or CB_SEQUENCE return an error, the sequenceid of
   the slot MUST NOT change.  The replier MUST NOT modify the reply
   cache entry for the slot whenever an error is returned from SEQUENCE
   or CB_SEQUENCE.




Shepler, et al.         Expires February 2, 2007               [Page 41]


Internet-Draft            NFSv4 Minor Version 1              August 2006


2.9.4.1.2.  Optional Reply Caching

   On a per-request basis the requester can choose to direct the replier
   to cache the reply to all operations after the first operation
   (SEQUENCE or CB_SEQUENCE) via the sa_cachethis or csa_cachethis
   fields of the arguments to SEQUENCE or CB_SEQUENCE.  The reason it
   would not direct the replier to cache the entire reply is that the
   request is composed of all idempotent operations [20].  Caching the
   reply may offer little benefit, and if the reply is too large (see
   Section 2.9.4.4, it may not be cacheable anyway.

   Whether the requester requests the reply to be cached or not has no
   effect on the slot processing.  If the results of SEQUENCE or
   CB_SEQUENCE are NFS4_OK, then the slot's sequenceid MUST be
   incremented by one.  If a requester does not direct the replier to
   cache, the reply, the replier MUST do one of following:

   o  The replier can cache the entire original reply.  Even though
      sa_cachethis or csa_cachethis are FALSE, the replier is always
      free to cache.  It may choose this approach in order to simplify
      implementation.

   o  The replier enters into its reply cache a reply consisting of the
      original results to the SEQUENCE or CB_SEQUENCE operation,
      followed by the error NFS4ERR_RETRY_UNCACHED_REP.  Thus when the
      requester later retries the request, it will get
      NFS4ERR_RETRY_UNCACHE_REP.

2.9.4.1.3.  Multiple Connections and Sharing the Reply Cache

   Multiple connections can be bound to a session's channel, hence the
   connections share the same table of slotids.  For connections over
   non-RDMA transports like TCP, there are no particular considerations.
   Considerations for multiple RDMA connections sharing a slot table are
   discussed in Section 2.9.5.1.  [[Comment.5: Also need to discuss when
   RDMA and non-RDMA share a slot table.]]

2.9.4.2.  Retry and Replay

   A client MUST NOT retry a request, unless the connection it used to
   send the request disconnects.  The client can then reconnect and
   resend the request, or it can resend the request over a different
   connection.  In the case of the server resending over the
   backchannel, it cannot reconnect, and either resends the request over
   another connection that the client has bound to the backchannel, or
   if there is no other backchannel connection, waits for the client to
   bind a connection to the backchannel.




Shepler, et al.         Expires February 2, 2007               [Page 42]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   A client MUST wait for a reply to a request before using the slot for
   another request.  If it does not wait for a reply, then the client
   does not know what sequenceid to use for the slot on its next
   request.  For example, suppose a client sends a request with
   sequenceid 1, and does not wait for the response.  The next time it
   uses the slot, it sends the new request with sequenceid 2.  If the
   server has not seen the request with sequenceid 1, then the server is
   expecting sequenceid 2, and rejects the client's new request with
   NFS4ERR_SEQ_MISORDERED (as the result from SEQUENCE or CB_SEQUENCE).

   RDMA fabrics do not guarantee that the memory handles (Steering Tags)
   within each RDMA three-tuple are valid on a scope [[Comment.6: What
   is a three-tuple?]] outside that of a single connection.  Therefore,
   handles used by the direct operations become invalid after connection
   loss.  The server must ensure that any RDMA operations which must be
   replayed from the reply cache use the newly provided handle(s) from
   the most recent request.

2.9.4.3.  Resolving server callback races with sessions

   It is possible for server callbacks to arrive at the client before
   the reply from related forward channel operations.  For example, a
   client may have been granted a delegation to a file it has opened,
   but the reply to the OPEN (informing the client of the granting of
   the delegation) may be delayed in the network.  If a conflicting
   operation arrives at the server, it will recall the delegation using
   the callback channel, which may be on a different transport
   connection, perhaps even a different network.  In NFSv4.0, if the
   callback request arrives before the related reply, the client may
   reply to the server with an error.

   The presence of a session between client and server alleviates this
   issue.  When a session is in place, each client request is uniquely
   identified by its { slotid, sequenceid } pair.  By the rules under
   which slot entries (reply cache entries) are retired, the server has
   knowledge whether the client has "seen" each of the server's replies.
   The server can therefore provide sufficient information to the client
   to allow it to disambiguate between an erroneous or conflicting
   callback and a race condition.

   For each client operation which might result in some sort of server
   callback, the server should "remember" the { slotid, sequenceid }
   pair of the client request until the slotid retirement rules allow
   the server to determine that the client has, in fact, seen the
   server's reply.  Until the time the { slotid, sequenceid } request
   pair can be retired, any recalls of the associated object MUST carry
   an array of these referring identifiers (in the CB_SEQUENCE
   operation's arguments), for the benefit of the client.  After this



Shepler, et al.         Expires February 2, 2007               [Page 43]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   time, it is not necessary for the server to provide this information
   in related callbacks, since it is certain that a race condition can
   no longer occur.

   The CB_SEQUENCE operation which begins each server callback carries a
   list of "referring" { slotid, sequenceid } tuples.  If the client
   finds the request corresponding to the referring slotid and sequenced
   id be currently outstanding (i.e. the server's reply has not been
   seen by the client), it can determine that the callback has raced the
   reply, and act accordingly.

   The client must not simply wait forever for the expected server reply
   to arrive on any of the session's operations channels, because it is
   possible that they will be delayed indefinitely.  However, it should
   wait for a period of time, and if the time expires it can provide a
   more meaningful error such as NFS4ERR_DELAY.

   [[Comment.7: We need to consider the clients' options here, and
   describe them...  NFS4ERR_DELAY has been discussed as a legal reply
   to CB_RECALL?]]

   There are other scenarios under which callbacks may race replies,
   among them pnfs layout recalls, described in Section 12.3.5.3
   [[Comment.8: fill in the blanks w/others, etc...]]

2.9.4.4.  COMPOUND and CB_COMPOUND Construction Issues

   Very large requests and replies may pose both buffer management
   issues (especially with RDMA) and reply cache issues.  When the
   session is created, (Section 16.36) the client and server negotiate
   the maximum sized request they will send or process
   (ca_maxrequestsize), the maximum sized reply they will return or
   process (ca_maxresponsesize), and the the maximum sized reply they
   will store in the reply cache (ca_maxresponsesize_cached).

   If a request exceeds ca_maxrequestsize, the reply will have the
   status NFS4ERR_REQ_TOO_BIG.  A replier may return NFS4ERR_REQ_TOO_BIG
   as the status for first operation (SEQUENCE or CB_SEQUENCE) in the
   request, or it may chose to return it on a subsequent operation.

   If a reply exceeds ca_maxresponsesize, the reply will have the status
   NFS4ERR_REP_TOO_BIG.  A replier may return NFS4ERR_REP_TOO_BIG as the
   status for first operation (SEQUENCE or CB_SEQUENCE) in the request,
   or it may chose to return it on a subsequent operation.

   If sa_cachethis or csa_cachethis are TRUE, then the replier MUST
   cache a reply except if an error is returned by the SEQUENCE or
   CB_SEQUENCE operation (see Section 2.9.4.1.1).  If the reply exceeds



Shepler, et al.         Expires February 2, 2007               [Page 44]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   ca_maxresponsesize_cached, (and sa_cachethis or csa_cachethis are
   TRUE) then the server MUST return NFS4ERR_REP_TOO_BIG_TO_CACHE.  Even
   if NFS4ERR_REP_TOO_BIG_TO_CACHE (or any other error for that matter)
   is returned on a operation other than first operation (SEQUENCE or
   CB_SEQUENCE), then the reply MUST be cached if sa_cachethis or
   csa_cachethis are TRUE.  For example, if a COMPOUND has eleven
   operations, including SEQUENCE, the fifth operation is a RENAME, and
   the tenth operation is a READ for one million bytes, server may
   return NFS4ERR_REP_TOO_BIG_TO_CACHE on the tenth operation.  Since
   the server executed several operations, especially the non-idempotent
   RENAME, the client's request to cache the reply needs to be honored
   in order for correct operation of exactly once semantics.  If the
   client retries the request, the server will have cached a reply that
   contains results for ten of the elevent requested operations, with
   the tenth operation having a status of NFS4ERR_REP_TOO_BIG_TO_CACHE.

   A client needs to take care that when sending operations that change
   the current filehandle (except for PUTFH, PUTPUBFH, and PUTROOFFH)
   that it not exceed the maximum reply buffer before the GETFH
   operation.  Otherwise the client will have to retry the operation
   that changed the current filehandle, in order obtain the desired
   filehandle.  For the OPEN operation (see Section 16.16), retry is not
   always available as an option.  The following guidelines for the
   handling of filehandle changing operations are advised:

   o  A client SHOULD issue GETFH immediately after a current filehandle
      changing operation.  This is especially important after any
      current filehandle changing non-idempotent operation.  It is
      critical to issue GETFH immediately after OPEN.

   o  A server MAY return NFS4ERR_REP_TOO_BIG or
      NFS4ERR_REP_TOO_BIG_TO_CACHE (if sa_cachethis is TRUE) on a
      filehandle changing operation if the reply would be too large on
      the next operation.

   o  A server SHOULD return NFS4ERR_REP_TOO_BIG or
      NFS4ERR_REP_TOO_BIG_TO_CACHE (if sa_cachethis is TRUE) on a
      filehandle changing non-idempotent operation if the reply would be
      too large on the next operation, especially if the operation is
      OPEN.

   o  A server MAY return NFS4ERR_UNSAFE_COMPOUND if it looks at the
      next operation after a non-idempotent current filehandle changing
      operation, and finds it is not GETFH.  The server would do this if
      it it unable to determine in advance whether the total response
      size would exceed ca_maxresponsesize_cached or ca_maxresponsesize.





Shepler, et al.         Expires February 2, 2007               [Page 45]


Internet-Draft            NFSv4 Minor Version 1              August 2006


2.9.4.5.  Persistence

   Since the reply cache is bounded, it is practical for the server
   reply cache to persist across server reboots, and to be kept in
   stable storage (a client's reply cache for callbacks need not persist
   across client reboots unless the client intends for its session and
   other state to persist across reboots).

   o  The slot table including the sequenceid and cached reply for each
      slot.

   o  The sessionid.

   o  The clientid.

   o  The SSV (see section Section 2.9.6.3).

   The CREATE_SESSION (see Section 16.36 operation determines the
   persistence of the reply cache.

2.9.5.  RDMA Considerations

   A complete discussion of the operation of RPC-based protocols atop
   RDMA transports is in [RPCRDMA].  A discussion of the operation of
   NFSv4, including NFSv4.1 over RDMA is in [NFSDDP].  Where RDMA is
   considered, this specification assumes the use of such a layering; it
   addresses only the upper layer issues relevant to making best use of
   RPC/RDMA.

2.9.5.1.  RDMA Connection Resources

   RDMA requires its consumers to register memory and post buffers of a
   specific size and number for receive operations.

   Registration of memory can be a relatively high-overhead operation,
   since it requires pinning of buffers, assignment of attributes (e.g.
   readable/writable), and initialization of hardware translation.
   Preregistration is desirable to reduce overhead.  These registrations
   are specific to hardware interfaces and even to RDMA connection
   endpoints, therefore negotiation of their limits is desirable to
   manage resources effectively.

   Following the basic registration, these buffers must be posted by the
   RPC layer to handle receives.  These buffers remain in use by the
   RPC/NFSv4 implementation; the size and number of them must be known
   to the remote peer in order to avoid RDMA errors which would cause a
   fatal error on the RDMA connection.




Shepler, et al.         Expires February 2, 2007               [Page 46]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   NFSv4.1 manages slots as resources on a per session basis (see
   Section 2.9), while RDMA connections manage credits on a per
   connection basis.  This means that in order for a peer to send data
   over RDMA to a remote buffer, it has to have both an NFSv4.1 slot,
   and an RDMA credit.

2.9.5.2.  Flow Control

   NFSv4.0 and all previous versions do not provide for any form of flow
   control; instead they rely on the windowing provided by transports
   like TCP to throttle requests.  This does not work with RDMA, which
   provides no operation flow control and will terminate a connection in
   error when limits are exceeded.  Limits such as maximum number of
   requests outstanding are therefore negotiated when a session is
   created (see the ca_maxrequests field in Section 16.36).  These
   limits then provide the maxima each session's channels' connections
   must operate within.  RDMA connections are managed within these
   limits as described in section 3.3 of [RPCRDMA]; if there are
   multiple RDMA connections, then the maximum requests for a channel
   will be divided among the RDMA connections.  The limits may also be
   modified dynamically at the server's choosing by manipulating certain
   parameters present in each NFSv4.1 request.  In addition, the
   CB_RECALL_SLOT callback operation (see Section 18.8 can be issued by
   a server to a client to return RDMA credits to the server, thereby
   lowering the maximum number of requests a client can have outstanding
   to the server.

2.9.5.3.  Padding

   Header padding is requested by each peer at session initiation (see
   the csa_headerpadsize argument to CREATE_SESSION in Section 16.36),
   and subsequently used by the RPC RDMA layer, as described in
   [RPCRDMA].  Zero padding is permitted.

   Padding leverages the useful property that RDMA receives preserve
   alignment of data, even when they are placed into anonymous
   (untagged) buffers.  If requested, client inline writes will insert
   appropriate pad bytes within the request header to align the data
   payload on the specified boundary.  The client is encouraged to add
   sufficient padding (up to the negotiated size) so that the "data"
   field of the NFSv4.1 WRITE operation is aligned.  Most servers can
   make good use of such padding, which allows them to chain receive
   buffers in such a way that any data carried by client requests will
   be placed into appropriate buffers at the server, ready for file
   system processing.  The receiver's RPC layer encounters no overhead
   from skipping over pad bytes, and the RDMA layer's high performance
   makes the insertion and transmission of padding on the sender a
   significant optimization.  In this way, the need for servers to



Shepler, et al.         Expires February 2, 2007               [Page 47]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   perform RDMA Read to satisfy all but the largest client writes is
   obviated.  An added benefit is the reduction of message round trips
   on the network - a potentially good trade, where latency is present.

   The value to choose for padding is subject to a number of criteria.
   A primary source of variable-length data in the RPC header is the
   authentication information, the form of which is client-determined,
   possibly in response to server specification.  The contents of
   COMPOUNDs, sizes of strings such as those passed to RENAME, etc. all
   go into the determination of a maximal NFSv4 request size and
   therefore minimal buffer size.  The client must select its offered
   value carefully, so as not to overburden the server, and vice- versa.
   The payoff of an appropriate padding value is higher performance.

                    Sender gather:
        |RPC Request|Pad bytes|Length| -> |User data...|
        \------+---------------------/       \
                \                             \
                 \    Receiver scatter:        \-----------+- ...
            /-----+----------------\            \           \
            |RPC Request|Pad|Length|   ->  |FS buffer|->|FS buffer|->...

   In the above case, the server may recycle unused buffers to the next
   posted receive if unused by the actual received request, or may pass
   the now-complete buffers by reference for normal write processing.
   For a server which can make use of it, this removes any need for data
   copies of incoming data, without resorting to complicated end-to-end
   buffer advertisement and management.  This includes most kernel-based
   and integrated server designs, among many others.  The client may
   perform similar optimizations, if desired.

2.9.5.4.  Dual RDMA and Non-RDMA Transports

   Some RDMA transports (for example see [RDDP]), [[Comment.9: need
   xref]] require a "streaming" (non-RDMA) phase, where ordinary traffic
   might flow before "stepping" up to RDMA mode, commencing RDMA
   traffic.  Some RDMA transports start connections always in RDMA mode.
   NFSv4.1 allows, but does not assume, a streaming phase before RDMA
   mode.  When a connection is bound to a session, the client and server
   negotiate whether the connection is used in RDMA or non-RDMA mode
   (see Section 16.36 and Section 16.34).

2.9.6.  Sessions Security

2.9.6.1.  Session Callback Security

   The session connection binding improves security over that provided
   by NFSv4.0 for the callback channel.  The connection is client-



Shepler, et al.         Expires February 2, 2007               [Page 48]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   initiated (see Section 16.34), and subject to the same firewall and
   routing checks as the operations channel.  The connection cannot be
   hijacked by an attacker who connects to the client port prior to the
   intended server.  At the client's option (see Section 16.36 binding
   is fully authenticated before being activated (see Section 16.34).
   Traffic from the server over the callback channel is authenticated
   exactly as the client specifies (see Section 2.9.6.2).

2.9.6.2.  Backchannel RPC Security

   When the NFSv4.1 client establishes the backchannel, it informs the
   server what security flavors and principals it must use when sending
   requests over the backchannel.  If the security flavor is RPCSEC_GSS,
   the client expresses the principal in the form of an established
   RPCSEC_GSS context.  The server is free to use any flavor/principal
   combination the server offers, but MUST NOT use unoffered
   combinations.

   This way, the client does not have to provide a target GSS principal
   as it did with NFSv4.0, and the server does not have to implement an
   RPCSEC_GSS initiator as it did with NFSv4.0.  [[Comment.10: xrefs]]

   The CREATE_SESSION (Section 16.36) and BACKCHANNEL_CTL
   (Section 16.33) operations allow the client to specify flavor/
   principal combinations.

2.9.6.3.  Protection from Unauthorized State Changes

   Under some conditions, NFSv4.0 is vulnerable to a denial of service
   issue with respect to its state management.

   The attack works via an unauthorized client faking an open_owner4, an
   open_owner/lock_owner pair, or stateid, combined with a seqid.  The
   operation is sent to the NFSv4 server.  The NFSv4 server accepts the
   state information, and as long as any status code from the result of
   this operation is not NFS4ERR_STALE_CLIENTID, NFS4ERR_STALE_STATEID,
   NFS4ERR_BAD_STATEID, NFS4ERR_BAD_SEQID, NFS4ERR_BADXDR,
   NFS4ERR_RESOURCE, or NFS4ERR_NOFILEHANDLE, the sequence number is
   incremented.  When the authorized client issues an operation, it gets
   back NFS4ERR_BAD_SEQID, because its idea of the current sequence
   number is off by one.  The authorized client's recovery options are
   pretty limited, with SETCLIENTID, followed by complete reclaim of
   state, which may or may not succeed completely.  That qualifies as a
   denial of service attack.

   If the client uses RPCSEC_GSS authentication and integrity, and every
   client maps each open_owner and lock_owner one and only one
   principal, and the server enforces this binding, then the conditions



Shepler, et al.         Expires February 2, 2007               [Page 49]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   leading to vulnerability to the denial of service do not exist.  One
   should keep in mind that if AUTH_SYS is being used, far simpler
   easier denial of service and other attacks are possible.

   With NFSv4.1 sessions, the per-operation sequence number is ignored
   (see Section 8.13) therefore the NFSv4.0 denial of service
   vulnerability described above does not apply.  However as described
   to this point in the specification, an attacker could forge the
   sessionid and issue a SEQUENCE with a slot id that he expects the
   legitimate client to use next.  The legitimate client could then use
   the slotid with the same sequence number, and the server returns the
   attacker's result from the replay cache, thereby disrupting the
   legitimate client.

   If we give each NFSv4.1 user their own session, and each user uses
   RPCSEC_GSS authentication and integrity, then the denial of service
   issue is solved, at the cost of additional per session state.  The
   alternative NFSv4.1 specifies is described as follows.

   Transport connections MUST be bound to a session by the client.  The
   server MUST return an error to an operation (other than the operation
   that binds the connection to the session) that uses an unbound
   connection.  As a simplification, the transport connection used by
   CREATE_SESSION (see Section 16.36) is automatically bound to the
   session.  Additional connections are bound to a session via
   BIND_CONN_TO_SESSION (see Section 16.34).

   To prevent attackers from issuing BIND_CONN_TO_SESSION operations,
   the arguments to BIND_CONN_TO_SESSION include a digest of a shared
   secret called the secret session verifier (SSV) that only the client
   and server know.  The digest is created via a one way, collision
   resistant hash function, making it intractable for the attacker to
   forge.

   The SSV is sent to the server via SET_SSV (see Section 16.47).  To
   prevent eavesdropping, a SET_SSV for the SSV SHOULD be protected via
   RPCSEC_GSS with the privacy service.  The SSV can be changed by the
   client at any time, by any principal.  However several aspects of SSV
   changing prevent an attacker from engaging in a successful denial of
   service attack:

   o  A SET_SSV on the SSV does not replace the SSV with the argument to
      SET_SSV.  Instead, the current SSV on the server is logically
      exclusive ORed (XORed) with the argument to SET_SSV.  SET_SSV MUST
      NOT be called with an SSV value that is zero.

   o  The arguments to and results of SET_SSV include digests of the old
      and new SSV, respectively.



Shepler, et al.         Expires February 2, 2007               [Page 50]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   o  Because the initial value of the SSV is zero, therefore known, the
      client that opts for connecting binding enforcement, MUST issue at
      least one SET_SSV operation before the first BIND_CONN_TO_SESSION
      operation.  A client SHOULD issue SET_SSV as soon as a session is
      created.

   If a connection is disconnected, BIND_CONN_TO_SESSION is required to
   bind a connection to the session, even if the connection that was
   disconnected was the one CREATE_SESSION was created with.

   If a client is assigned a machine principal then the client SHOULD
   use the machine principal's RPCSEC_GSS context to privacy protect the
   SSV from eavesdropping during the SET_SSV operation.  If a machine
   principal is not being used, then the client MAY use the non-machine
   principal's RPCSEC_GSS context to privacy protect the SSV.  The
   server MUST accept either type of principal.  A client SHOULD change
   the SSV each time a new principal uses the session.

   Here are the types of attacks that can be attempted by an attacker
   named Eve, and how the connection to session binding approach
   addresses each attack:

   o  If the Eve creates a connection after the legitimate client
      establishes an SSV via privacy protection from a machine
      principal's RPCSEC_GSS session, she does not know the SSV and so
      cannot compute a digest that BIND_CONN_TO_SESSION will accept.
      Users on the legitimate client cannot be disrupted by Eve.

   o  If Eve is the first one log into the legitimate client, and the
      client does not use machine principals, then Eve can cause an SSV
      to be created via the legitimate client's NFSv4.1 implementation,
      protected by the RPCSEC_GSS context created by the legitimate
      client (which uses Eve's GSS principal and credentials).  Eve can
      then eavesdrop on the network, and because she knows her
      credentials, she can decrypt the SSV.  Eve can compute a digest
      BIND_CONN_TO_SESSION will accept, and so bind a new connection to
      the session.  Eve can change the slotid, sequence state, and/or
      the SSV state in such a way that when Bob accesses the server via
      the legitimate client, the legitimate client will be unable to use
      the session.

      The client's only recourse is to create a new session, which will
      cause any state Eve created on the legitimate client over the old
      (but hijacked) session to be lost.  This disrupts Eve, but because
      she is the attacker, this is acceptable.

      Once the legitimate client establishes an SSV over the new session
      using Bob's RPCSEC_GSS context, Eve can use the new session via



Shepler, et al.         Expires February 2, 2007               [Page 51]


Internet-Draft            NFSv4 Minor Version 1              August 2006


      the legitimate client, but she cannot disrupt Bob. Moreover,
      because the client SHOULD have modified the SSV due to Eve using
      the new session, Bob cannot get revenge on Eve by binding a rogue
      connection to the session.

      The question is how does the legitimate client detect that Eve has
      hijacked the old session?  When the client detects that a new
      principal, Bob, wants to use the session, it SHOULD have issued a
      SET_SSV.

      *  Let us suppose that from the rogue connection, Eve issued a
         SET_SSV with the same slotid and sequence that the legitimate
         client later uses.  The server will assume this is a replay,
         and return to the legitimate client the reply it sent Eve.
         However, unless Eve can correctly guess the SSV the legitimate
         client will use, the digest verification checks in the SET_SSV
         response will fail.  That is the clue to the client that the
         session has been hijacked.

      *  Alternatively, Eve issued a SET_SSV with a different slotid
         than the legitimate client uses for its SET_SSV.  Then the
         digest verification on the server fails, and the client is
         again clued that the session has been hijacked.

      *  Alternatively, Eve issued an operation other than SET_SSV, but
         with the same slotid and sequence that the legitimate client
         uses for its SET_SSV.  The server returns to the legitimate
         client the response it sent Eve. The client sees that the
         response is not at all what it expects.  The client assumes
         either session hijacking or server bug, and either way destroys
         the old session.

   o  Eve binds a rogue connection to the session as above, and then
      destroys the session.  Again, Bob goes to use the server from the
      legitimate client.  The client has a very clear indication that
      its session was hijacked, and does not even have to destroy the
      old session before creating a new session, which Eve will be
      unable to hijack because it will be protected with an SSV created
      via Bob's RPCSEC_GSS protection.

   o  If Eve creates a connection before the legitimate client
      establishes an SSV, because the initial value of the SSV is zero
      and therefore known, Eve can issue a SET_SSV that will pass the
      digest verification check.  However because the new connection has
      not been bound to the session, the SET_SSV is rejected for that
      reason.





Shepler, et al.         Expires February 2, 2007               [Page 52]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   o  The connection to session binding model does not prevent
      connection hijacking.  However, if an attacker can perform
      connection hijacking, it can issue denial of service attacks that
      are less difficult than attacks based on forging sessions.

2.9.7.  Session Mechanics - Steady State

2.9.7.1.  Obligations of the Server

   The server has the primary obligation to monitor the state of
   backchannel resources that the client has created for the server
   (RPCSEC_GSS contexts and back channel connections).  When these
   resources go away, the server takes action as specified in
   Section 2.9.8.2.

2.9.7.2.  Obligations of the Client

   The client has the following obligations in order to utilize the
   session:

   o  Keep a necessary session from going idle on the server.  A client
      that requires a session, but nonetheless is not sending operations
      risks having the session be destroyed by the server.  This is
      because sessions consume resources, and resource limitations may
      force the server to cull the least recently used session.

   o  Destroy the session when idle.  When a session has no state other
      than the session, and no outstanding requests, the client should
      consider destroying the session.

   o  Maintain GSS contexts for callback.  If the client requires the
      server to to use the RPCSEC_GSS security flavor for callbacks,
      then it needs to be sure the contexts handed to the server via
      BACKCHANNEL_CTL are unexpired.  A good practice is to keep at
      least two contexts outstanding, where the expiration time of the
      newest context at the time it was created, is N times that of the
      oldest context, where N is the number of contexts available for
      callbacks.

   o  Maintain an active connection.  The server requires a callback
      path in order to gracefully recall recallable state, or notify the
      client of certain events.

2.9.7.3.  Steps the Client Takes To Establish a Session

   The client issues CREATE_CLIENTID to establish a clientid.

   The client uses the clientid to issue a CREATE_SESSION on a



Shepler, et al.         Expires February 2, 2007               [Page 53]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   connection to the server.  The results of CREATE_SESSION indicate
   whether the server will persist the session replay cache through a
   server reboot or not, and the client notes this for future reference.

   The client SHOULD have specified connecting binding enforcement when
   the session was created.  If so, the client SHOULD issue SET_SSV in
   the first COMPOUND after the session is created.  If it is not using
   machine credentials, then each time a new principal goes to use the
   session, it SHOULD issue a SET_SSV again.

   If the client wants to use delegations, layouts, directory
   notifications, or any other state that requires a callback channel,
   then it MUST add a connection to the backchannel if CREATE_SESSION
   did not already do so.  The client creates a connection, and calls
   BIND_CONN_TO_SESSION to bind the connection to the session and the
   session's backchannel.  If CREATE_SESSION did not already do so, the
   client MUST tell the server what security is required in order for
   the client to accept callbacks.  The client does this via
   BACKCHANNEL_CTL.

   If the client wants to use additional connections for the
   backchannel, then it MUST call BIND_CONN_TO_SESSION on each
   connection it wants to use with the session.  If the client wants to
   use additional connections for the operation channel, then it MUST
   call BIND_CONN_TO_SESSION if it specified connection binding
   enforcement before using the connection.

   At this point the client has reached a steady state as far as session
   use.

2.9.8.  Session Mechanics - Recovery

2.9.8.1.  Events Requiring Client Action

   The following events require client action to recover.

2.9.8.1.1.  RPCSEC_GSS Context Loss by Callback Path

   If all RPCSEC_GSS contexts granted to by the client to the server for
   callback use have expired, the client MUST establish a new context
   via BACKCHANNEL_CTL.  The sr_status field of SEQUENCE results
   indicates when callback contexts are nearly expired, or fully expired
   (see Section 16.46.4).

2.9.8.1.2.  Connection Disconnect

   If the client loses the last connection of the session, then it MUST
   create a new connection, and if connecting binding enforcement was



Shepler, et al.         Expires February 2, 2007               [Page 54]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   specified when the session was created, bind it to the session via
   BIND_CONN_TO_SESSION.

   If there were requests outstanding at the time the of connection
   disconnect, then the client MUST retry the request, as described in
   Section 2.9.4.2.  Note that it is not necessary to retry requests
   over a connection with the same source network address or the same
   destination network address as the disconnected connection.  As long
   as the sessionid, slotid, and sequenceid in the retry match that of
   the original request, the server will recognize the request as a
   retry if it did see the request prior to disconnect.

   If the connection that was bound to the backchannel is lost, the
   client may need to reconnect, and use BIND_CONN_TO_SESSION, to give
   the connection to the backchannel.  If the connection that was lost
   was the last one bound to the backchannel, the the client MUST
   reconnect, and bind the connection to the session and backchannel.
   The server should indicate when it has no callback connection via the
   sr_status result from SEQUENCE.

2.9.8.1.3.  Backchannel GSS Context Loss

   Via the sr_status result of the SEQUENCE operation or other means,
   the client will learn if some or all of the RPCSEC_GSS contexts it
   assigned to the backchannel have been lost.  The client may need to
   use BACKCHANNEL_CTL to assign new contexts.  It MUST assign new
   contexts if there are no more contexts.

2.9.8.1.4.  Loss of Session

   The server may lose a record of the session.  Causes include:

   o  Server crash and reboot

   o  A catastrophe that causes the cache to be corrupted or lost on the
      media it was stored on.  This applies even if the server indicated
      in the CREATE_SESSION results that it would persist the cache.

   o  The server purges the session of a client that has been inactive
      for a very extended period of time.  [[Comment.11: XXX - Should we
      add a value to the CREATE_SESSION results that tells a client how
      long he can let a session stay idle before losing it?]]

   Loss of replay cache is equivalent to loss of session.  The server
   indicates loss of session to the client by returning
   NFS4ERR_BADSESSION on the next operation that uses the sessionid
   associated with the lost session.




Shepler, et al.         Expires February 2, 2007               [Page 55]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   After an event like a server reboot, the client may have lost its
   connections.  The client assumes for the moment that the session has
   not been lost.  It reconnects, and if it specified connecting binding
   enforcement when the session was created, it invokes
   BIND_CONN_TO_SESSION using the sessionid.  Otherwise, it invokes
   SEQUENCE.  If BIND_CONN_TO_SESSION or SEQUENCE returns
   NFS4ERR_BADSESSION, the client knows the session was lost.  If the
   connection survives session loss, then the next SEQUENCE operation
   the client issues over the connection will get back
   NFS4ERR_BADSESSION.  The client again knows the session was lost.

   When the client detects session loss, it must call CREATE_SESSION to
   recover.  Any non-idempotent operations that were in progress may
   have been performed on the server at the time of session loss.  The
   client has no general way to recover from this.

   Note that loss of session does not imply loss of lock, open,
   delegation, or layout state.  Nor does loss of lock, open,
   delegation, or layout state imply loss of session state.
   [[Comment.12: Add reference to lock recovery section]] .  A session
   can survive a server reboot, but lock recovery may still be needed.
   The converse is also true.

   It is possible CREATE_SESSION will fail with NFS4ERR_STALE_CLIENTID
   (for example the server reboots and does not preserve clientid
   state).  If so, the client needs to call CREATE_CLIENTID, followed by
   CREATE_SESSION.

2.9.8.1.5.  Failover

   [[Comment.13: Dave Noveck requested this section; not sure what is
   needed here if this refers to failover to a replica.  What are the
   session ramifications?]]

2.9.8.2.  Events Requiring Server Action

   The following events require server action to recover.

2.9.8.2.1.  Client Crash and Reboot

   As described in Section 16.35, a rebooted client causes the server to
   delete any sessions it had.

2.9.8.2.2.  Client Crash with No Reboot

   If a client crashes and never comes back, it will never issue
   CREATE_CLIENTID with its old clientid.  Thus the server has session
   state that will never be used again.  After an extended period of



Shepler, et al.         Expires February 2, 2007               [Page 56]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   time and if the server has resource constraints, it MAY destroy the
   old session.

2.9.8.2.3.  Extended Network Partition

   To the server, the extended network partition may be no different
   than a client crash with no reboot (see Section 2.9.8.2.2).  Unless
   the server can discern that there is a network partition, it is free
   to treat the situation as if the client has crashed for good.

2.9.8.2.4.  Backchannel Connection Loss

   If there were callback requests outstanding at the time the of a
   connection disconnect, then the server MUST retry the request, as
   described in Section 2.9.4.2.  Note that it is not necessary to retry
   requests over a connection with the same source network address or
   the same destination network address as the disconnected connection.
   As long as the sessionid, slotid, and sequenceid in the retry match
   that of the original request, the callback target will recognize the
   request as a retry if it did see the request prior to disconnect.

   If the connection lost is the last one bound to the backchannel, then
   the server MUST indicate that in the sr_status field of the next
   SEQUENCE reply.

2.9.8.2.5.  GSS Context Loss

   The server SHOULD monitor when the last RPCSEC_GSS context assigned
   to the backchannel is near expiry (i.e between one and two periods of
   lease time), and indicate so in the sr_status field of the next
   SEQUENCE reply.  The server MUST indicate when the backchannel's last
   RPCSEC_GSS context has expired in the sr_status field of the next
   SEQUENCE reply.


3.  Protocol Data Types

   The syntax and semantics to describe the data types of the NFS
   version 4 protocol are defined in the XDR RFC4506 [3] and RPC RFC1831
   [4] documents.  The next sections build upon the XDR data types to
   define types and structures specific to this protocol.

3.1.  Basic Data Types

                   These are the base NFSv4 data types.






Shepler, et al.         Expires February 2, 2007               [Page 57]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   +---------------+---------------------------------------------------+
   | Data Type     | Definition                                        |
   +---------------+---------------------------------------------------+
   | int32_t       | typedef int int32_t;                              |
   | uint32_t      | typedef unsigned int uint32_t;                    |
   | int64_t       | typedef hyper int64_t;                            |
   | uint64_t      | typedef unsigned hyper uint64_t;                  |
   | attrlist4     | typedef opaque attrlist4<>;                       |
   |               | Used for file/directory attributes                |
   | bitmap4       | typedef uint32_t bitmap4<>;                       |
   |               | Used in attribute array encoding.                 |
   | changeid4     | typedef uint64_t changeid4;                       |
   |               | Used in definition of change_info                 |
   | clientid4     | typedef uint64_t clientid4;                       |
   |               | Shorthand reference to client identification      |
   | component4    | typedef utf8str_cs component4;                    |
   |               | Represents path name components                   |
   | count4        | typedef uint32_t count4;                          |
   |               | Various count parameters (READ, WRITE, COMMIT)    |
   | length4       | typedef uint64_t length4;                         |
   |               | Describes LOCK lengths                            |
   | linktext4     | typedef utf8str_cs linktext4;                     |
   |               | Symbolic link contents                            |
   | mode4         | typedef uint32_t mode4;                           |
   |               | Mode attribute data type                          |
   | nfs_cookie4   | typedef uint64_t nfs_cookie4;                     |
   |               | Opaque cookie value for READDIR                   |
   | nfs_fh4       | typedef opaque nfs_fh4<NFS4_FHSIZE>               |
   |               | Filehandle definition; NFS4_FHSIZE is defined as  |
   |               | 128                                               |
   | nfs_ftype4    | enum nfs_ftype4;                                  |
   |               | Various defined file types                        |
   | nfsstat4      | enum nfsstat4;                                    |
   |               | Return value for operations                       |
   | offset4       | typedef uint64_t offset4;                         |
   |               | Various offset designations (READ, WRITE, LOCK,   |
   |               | COMMIT)                                           |
   | pathname4     | typedef component4 pathname4<>;                   |
   |               | Represents path name for fs_locations             |
   | qop4          | typedef uint32_t qop4;                            |
   |               | Quality of protection designation in SECINFO      |
   | sec_oid4      | typedef opaque sec_oid4<>;                        |
   |               | Security Object Identifier The sec_oid4 data type |
   |               | is not really opaque. Instead contains an ASN.1   |
   |               | OBJECT IDENTIFIER as used by GSS-API in the       |
   |               | mech_type argument to GSS_Init_sec_context. See   |
   |               | RFC2743 [8] for details.                          |
   | seqid4        | typedef uint32_t seqid4;                          |



Shepler, et al.         Expires February 2, 2007               [Page 58]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   |               | Sequence identifier used for file locking         |
   | utf8string    | typedef opaque utf8string<>;                      |
   |               | UTF-8 encoding for strings                        |
   | utf8str_cis   | typedef opaque utf8str_cis;                       |
   |               | Case-insensitive UTF-8 string                     |
   | utf8str_cs    | typedef opaque utf8str_cs;                        |
   |               | Case-sensitive UTF-8 string                       |
   | utf8str_mixed | typedef opaque utf8str_mixed;                     |
   |               | UTF-8 strings with a case sensitive prefix and a  |
   |               | case insensitive suffix.                          |
   | verifier4     | typedef opaque verifier4[NFS4_VERIFIER_SIZE];     |
   |               | Verifier used for various operations (COMMIT,     |
   |               | CREATE, OPEN, READDIR, SETCLIENTID,               |
   |               | SETCLIENTID_CONFIRM, WRITE) NFS4_VERIFIER_SIZE is |
   |               | defined as 8.                                     |
   +---------------+---------------------------------------------------+

                          End of Base Data Types

                                  Table 1

3.2.  Structured Data Types

3.2.1.  nfstime4

   struct nfstime4 {
       int64_t seconds;
       uint32_t nseconds;
   }

   The nfstime4 structure gives the number of seconds and nanoseconds
   since midnight or 0 hour January 1, 1970 Coordinated Universal Time
   (UTC).  Values greater than zero for the seconds field denote dates
   after the 0 hour January 1, 1970.  Values less than zero for the
   seconds field denote dates before the 0 hour January 1, 1970.  In
   both cases, the nseconds field is to be added to the seconds field
   for the final time representation.  For example, if the time to be
   represented is one-half second before 0 hour January 1, 1970, the
   seconds field would have a value of negative one (-1) and the
   nseconds fields would have a value of one-half second (500000000).
   Values greater than 999,999,999 for nseconds are considered invalid.

   This data type is used to pass time and date information.  A server
   converts to and from its local representation of time when processing
   time values, preserving as much accuracy as possible.  If the
   precision of timestamps stored for a file system object is less than
   defined, loss of precision can occur.  An adjunct time maintenance
   protocol is recommended to reduce client and server time skew.



Shepler, et al.         Expires February 2, 2007               [Page 59]


Internet-Draft            NFSv4 Minor Version 1              August 2006


3.2.2.  time_how4

   enum time_how4 {
       SET_TO_SERVER_TIME4 = 0,
       SET_TO_CLIENT_TIME4 = 1
   };

3.2.3.  settime4

   union settime4 switch (time_how4 set_it) {
       case SET_TO_CLIENT_TIME4:
           nfstime4       time;
       default:
           void;
   };

   The above definitions are used as the attribute definitions to set
   time values.  If set_it is SET_TO_SERVER_TIME4, then the server uses
   its local representation of time for the time value.

3.2.4.  specdata4

   struct specdata4 {
       uint32_t specdata1; /* major device number */
       uint32_t specdata2; /* minor device number */
   };

   This data type represents additional information for the device file
   types NF4CHR and NF4BLK.

3.2.5.  fsid4

   struct fsid4 {
       uint64_t        major;
       uint64_t        minor;
   };

3.2.6.  fs_location4

   struct fs_location4 {
       utf8str_cis    server<>;
       pathname4     rootpath;
   };








Shepler, et al.         Expires February 2, 2007               [Page 60]


Internet-Draft            NFSv4 Minor Version 1              August 2006


3.2.7.  fs_locations4

   struct fs_locations4 {
       pathname4     fs_root;
       fs_location4  locations<>;
   };

   The fs_location4 and fs_locations4 data types are used for the
   fs_locations recommended attribute which is used for migration and
   replication support.

3.2.8.  fattr4

   struct fattr4 {
       bitmap4       attrmask;
       attrlist4     attr_vals;
   };

   The fattr4 structure is used to represent file and directory
   attributes.

   The bitmap is a counted array of 32 bit integers used to contain bit
   values.  The position of the integer in the array that contains bit n
   can be computed from the expression (n / 32) and its bit within that
   integer is (n mod 32).


   0            1
   +-----------+-----------+-----------+--
   |  count    | 31  ..  0 | 63  .. 32 |
   +-----------+-----------+-----------+--

3.2.9.  change_info4

   struct change_info4 {
       bool          atomic;
       changeid4     before;
       changeid4     after;
   };

   This structure is used with the CREATE, LINK, REMOVE, RENAME
   operations to let the client know the value of the change attribute
   for the directory in which the target file system object resides.








Shepler, et al.         Expires February 2, 2007               [Page 61]


Internet-Draft            NFSv4 Minor Version 1              August 2006


3.2.10.  netaddr4

   struct netaddr4 {
       /* see struct rpcb in RFC1833 */
       string r_netid<>;    /* network id */
       string r_addr<>;     /* universal address */
   };

   The netaddr4 structure is used to identify TCP/IP based endpoints.
   The r_netid and r_addr fields are specified in RFC1833 [22], but they
   are underspecified in RFC1833 [22] as far as what they should look
   like for specific protocols.

   For TCP over IPv4 and for UDP over IPv4, the format of r_addr is the
   US-ASCII string:

   h1.h2.h3.h4.p1.p2

   The prefix, "h1.h2.h3.h4", is the standard textual form for
   representing an IPv4 address, which is always four octets long.
   Assuming big-endian ordering, h1, h2, h3, and h4, are respectively,
   the first through fourth octets each converted to ASCII-decimal.
   Assuming big-endian ordering, p1 and p2 are, respectively, the first
   and second octets each converted to ASCII-decimal.  For example, if a
   host, in big-endian order, has an address of 0x0A010307 and there is
   a service listening on, in big endian order, port 0x020F (decimal
   527), then complete universal address is "10.1.3.7.2.15".

   For TCP over IPv4 the value of r_netid is the string "tcp".  For UDP
   over IPv4 the value of r_netid is the string "udp".

   For TCP over IPv6 and for UDP over IPv6, the format of r_addr is the
   US-ASCII string:

   x1:x2:x3:x4:x5:x6:x7:x8.p1.p2

   The suffix "p1.p2" is the service port, and is computed the same way
   as with universal addresses for TCP and UDP over IPv4.  The prefix,
   "x1:x2:x3:x4:x5:x6:x7:x8", is the standard textual form for
   representing an IPv6 address as defined in Section 2.2 of RFC1884
   [9].  Additionally, the two alternative forms specified in Section
   2.2 of RFC1884 [9] are also acceptable.

   For TCP over IPv6 the value of r_netid is the string "tcp6".  For UDP
   over IPv6 the value of r_netid is the string "udp6".






Shepler, et al.         Expires February 2, 2007               [Page 62]


Internet-Draft            NFSv4 Minor Version 1              August 2006


3.2.11.  clientaddr4

   typedef netaddr4 clientaddr4;

   The clientaddr4 structure is used as part of the SETCLIENTID
   operation to either specify the address of the client that is using a
   clientid or as part of the callback registration.

3.2.12.  cb_client4

   struct cb_client4 {
       unsigned int  cb_program;
       netaddr4      cb_location;
   };

   This structure is used by the client to inform the server of its call
   back address; includes the program number and client address.

3.2.13.  nfs_client_id4

   struct nfs_client_id4 {
       verifier4     verifier;
       opaque        id<NFS4_OPAQUE_LIMIT>
   };

   This structure is part of the arguments to the SETCLIENTID operation.
   NFS4_OPAQUE_LIMIT is defined as 1024.

3.2.14.  open_owner4

   struct open_owner4 {
       clientid4     clientid;
       opaque        owner<NFS4_OPAQUE_LIMIT>
   };

   This structure is used to identify the owner of open state.
   NFS4_OPAQUE_LIMIT is defined as 1024.

3.2.15.  lock_owner4

   struct lock_owner4 {
       clientid4     clientid;
       opaque        owner<NFS4_OPAQUE_LIMIT>
   };

   This structure is used to identify the owner of file locking state.
   NFS4_OPAQUE_LIMIT is defined as 1024.




Shepler, et al.         Expires February 2, 2007               [Page 63]


Internet-Draft            NFSv4 Minor Version 1              August 2006


3.2.16.  open_to_lock_owner4

   struct open_to_lock_owner4 {
       seqid4          open_seqid;
       stateid4        open_stateid;
       seqid4          lock_seqid;
       lock_owner4     lock_owner;
   };

   This structure is used for the first LOCK operation done for an
   open_owner4.  It provides both the open_stateid and lock_owner such
   that the transition is made from a valid open_stateid sequence to
   that of the new lock_stateid sequence.  Using this mechanism avoids
   the confirmation of the lock_owner/lock_seqid pair since it is tied
   to established state in the form of the open_stateid/open_seqid.

3.2.17.  stateid4

   struct stateid4 {
       uint32_t        seqid;
       opaque          other[12];
   };

   This structure is used for the various state sharing mechanisms
   between the client and server.  For the client, this data structure
   is read-only.  The starting value of the seqid field is undefined.
   The server is required to increment the seqid field monotonically at
   each transition of the stateid.  This is important since the client
   will inspect the seqid in OPEN stateids to determine the order of
   OPEN processing done by the server.

3.2.18.  layouttype4

   enum layouttype4 {
       LAYOUT_NFSV4_FILES  = 1,
       LAYOUT_OSD2_OBJECTS = 2,
       LAYOUT_BLOCK_VOLUME = 3
   };

   A layout type specifies the layout being used.  The implication is
   that clients have "layout drivers" that support one or more layout
   types.  The file server advertises the layout types it supports
   through the LAYOUT_TYPES file system attribute.  A client asks for
   layouts of a particular type in LAYOUTGET, and passes those layouts
   to its layout driver.

   The layouttype4 structure is 32 bits in length.  The range
   represented by the layout type is split into two parts.  Types within



Shepler, et al.         Expires February 2, 2007               [Page 64]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   the range 0x00000000-0x7FFFFFFF are globally unique and are assigned
   according to the description in Section 20.1; they are maintained by
   IANA.  Types within the range 0x80000000-0xFFFFFFFF are site specific
   and for "private use" only.

   The LAYOUT_NFSV4_FILES enumeration specifies that the NFSv4 file
   layout type is to be used.  The LAYOUT_OSD2_OBJECTS enumeration
   specifies that the object layout, as defined in [23], is to be used.
   Similarly, the LAYOUT_BLOCK_VOLUME enumeration that the block/volume
   layout, as defined in [24], is to be used.

3.2.19.  deviceid4

   typedef uint32_t deviceid4;  /* 32-bit device ID */

   Layout information includes device IDs that specify a storage device
   through a compact handle.  Addressing and type information is
   obtained with the GETDEVICEINFO operation.  A client must not assume
   that device IDs are valid across metadata server reboots.  The device
   ID is qualified by the layout type and are unique per file system
   (FSID).  This allows different layout drivers to generate device IDs
   without the need for co-ordination.  See Section 12.3.1.4 for more
   details.

3.2.20.  devlist_item4

   struct devlist_item4 {
           deviceid4          dli_id;
           opaque             dli_device_addr<>;
   };

   An array of these values is returned by the GETDEVICELIST operation.
   They define the set of devices associated with a file system for the
   layout type specified in the GETDEVICELIST4args.

   The device address is used to set up a communication channel with the
   storage device.  Different layout types will require different types
   of structures to define how they communicate with storage devices.
   The opaque device_addr field must be interpreted based on the
   specified layout type.

   This document defines the device address for the NFSv4 file layout
   (struct netaddr4 (Section 3.2.10)), which identifies a storage device
   by network IP address and port number.  This is sufficient for the
   clients to communicate with the NFSv4 storage devices, and may be
   sufficient for other layout types as well.  Device types for object
   storage devices and block storage devices (e.g., SCSI volume labels)
   will be defined by their respective layout specifications.



Shepler, et al.         Expires February 2, 2007               [Page 65]


Internet-Draft            NFSv4 Minor Version 1              August 2006


3.2.21.  layout4

   struct layout4 {
       offset4                 lo_offset;
       length4                 lo_length;
       layoutiomode4           lo_iomode;
       layouttype4             lo_type;
       opaque                  lo_layout<>;
   };

   The layout4 structure defines a layout for a file.  The layout type
   specific data is opaque within this structure and must be
   interepreted based on the layout type.  Currently, only the NFSv4
   file layout type is defined; see Section 12.4.1 for its definition.
   Since layouts are sub-dividable, the offset and length together with
   the file's filehandle, the clientid, iomode, and layout type,
   identifies the layout.

3.2.22.  layoutupdate4

   struct layoutupdate4 {
       layouttype4             lou_type;
       opaque                  lou_data<>;
   };

   The layoutupdate4 structure is used by the client to return 'updated'
   layout information to the metadata server at LAYOUTCOMMIT time.  This
   structure provides a channel to pass layout type specific information
   back to the metadata server.  E.g., for block/volume layout types
   this could include the list of reserved blocks that were written.
   The contents of the opaque lou_data argument are determined by the
   layout type and are defined in their context.  The NFSv4 file-based
   layout does not use this structure, thus the update_data field should
   have a zero length.

3.2.23.  layouthint4

   struct layouthint4 {
       layouttype4           loh_type;
       opaque                loh_data<>;
   };

   The layouthint4 structure is used by the client to pass in a hint
   about the type of layout it would like created for a particular file.
   It is the structure specified by the FILE_LAYOUT_HINT attribute
   described below.  The metadata server may ignore the hint, or may
   selectively ignore fields within the hint.  This hint should be
   provided at create time as part of the initial attributes within



Shepler, et al.         Expires February 2, 2007               [Page 66]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   OPEN.  The NFSv4 file-based layout uses the "nfsv4_file_layouthint"
   structure as defined in Section 12.4.1.

3.2.24.  layoutiomode4

   enum layoutiomode4 {
       LAYOUTIOMODE_READ          = 1,
       LAYOUTIOMODE_RW            = 2,
       LAYOUTIOMODE_ANY           = 3
   };

   The iomode specifies whether the client intends to read or write
   (with the possibility of reading) the data represented by the layout.
   The ANY iomode MUST NOT be used for LAYOUTGET, however, it can be
   used for LAYOUTRETURN and LAYOUTRECALL.  The ANY iomode specifies
   that layouts pertaining to both READ and RW iomodes are being
   returned or recalled, respectively.  The metadata server's use of the
   iomode may depend on the layout type being used.  The storage devices
   may validate I/O accesses against the iomode and reject invalid
   accesses.

3.2.25.  nfs_impl_id4

   struct nfs_impl_id4 {
       utf8str_cis   nii_domain;
       utf8str_cs    nii_name;
       nfstime4      nii_date;
   };

   This structure is used to identify client and server implementation
   detail.  The nii_domain field is the DNS domain name that the
   implementer is associated with.  The nii_name field is the product
   name of the implementation and is completely free form.  It is
   encouraged that the nii_name be used to distinguish machine
   architecture, machine platforms, revisions, versions, and patch
   levels.  The nii_date field is the timestamp of when the software
   instance was published or built.

3.2.26.  threshold_item4

   struct threshold_item4 {
           layouttype4     thi_layout_type;
           bitmap4         thi_hintset;
           opaque          thi_hintlist<>;
   };

   This structure contains a list of hints specific to a layout type for
   helping the client determine when it should issue I/O directly



Shepler, et al.         Expires February 2, 2007               [Page 67]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   through the metadata server vs. the data servers.  The hint structure
   consists of the layout type, a bitmap describing the set of hints
   supported by the server, they may differ based on the layout type,
   and a list of hints, whose structure is determined by the hintset
   bitmap.  See the mdsthreshold attribute for more details.

   The hintset is a bitmap of the following values:

   +-------------------------+---+---------+---------------------------+
   | name                    | # | Data    | Description               |
   |                         |   | Type    |                           |
   +-------------------------+---+---------+---------------------------+
   | threshold4_read_size    | 0 | length4 | The file size below which |
   |                         |   |         | it is recommended to read |
   |                         |   |         | data through the MDS.     |
   | threshold4_write_size   | 1 | length4 | The file size below which |
   |                         |   |         | it is recommended to      |
   |                         |   |         | write data through the    |
   |                         |   |         | MDS.                      |
   | threshold4_read_iosize  | 2 | length4 | For read I/O sizes below  |
   |                         |   |         | this threshold it is      |
   |                         |   |         | recommended to read data  |
   |                         |   |         | through the MDS           |
   | threshold4_write_iosize | 3 | length4 | For write I/O sizes below |
   |                         |   |         | this threshold it is      |
   |                         |   |         | recommended to write data |
   |                         |   |         | through the MDS           |
   +-------------------------+---+---------+---------------------------+

3.2.27.  mdsthreshold4

   struct mdsthreshold4 {
           threshold_item4 mth_hints<>;
   };

   This structure holds an array of threshold_item4 structures each of
   which is valid for a particular layout type.  An array is necessary
   since a server can support multiple layout types for a single file.


4.  Filehandles

   The filehandle in the NFS protocol is a per server unique identifier
   for a file system object.  The contents of the filehandle are opaque
   to the client.  Therefore, the server is responsible for translating
   the filehandle to an internal representation of the file system
   object.




Shepler, et al.         Expires February 2, 2007               [Page 68]


Internet-Draft            NFSv4 Minor Version 1              August 2006


4.1.  Obtaining the First Filehandle

   The operations of the NFS protocol are defined in terms of one or
   more filehandles.  Therefore, the client needs a filehandle to
   initiate communication with the server.  With the NFS version 2
   protocol RFC1094 [17] and the NFS version 3 protocol RFC1813 [18],
   there exists an ancillary protocol to obtain this first filehandle.
   The MOUNT protocol, RPC program number 100005, provides the mechanism
   of translating a string based file system path name to a filehandle
   which can then be used by the NFS protocols.

   The MOUNT protocol has deficiencies in the area of security and use
   via firewalls.  This is one reason that the use of the public
   filehandle was introduced in RFC2054 [25] and RFC2055 [26].  With the
   use of the public filehandle in combination with the LOOKUP operation
   in the NFS version 2 and 3 protocols, it has been demonstrated that
   the MOUNT protocol is unnecessary for viable interaction between NFS
   client and server.

   Therefore, the NFS version 4 protocol will not use an ancillary
   protocol for translation from string based path names to a
   filehandle.  Two special filehandles will be used as starting points
   for the NFS client.

4.1.1.  Root Filehandle

   The first of the special filehandles is the ROOT filehandle.  The
   ROOT filehandle is the "conceptual" root of the file system name
   space at the NFS server.  The client uses or starts with the ROOT
   filehandle by employing the PUTROOTFH operation.  The PUTROOTFH
   operation instructs the server to set the "current" filehandle to the
   ROOT of the server's file tree.  Once this PUTROOTFH operation is
   used, the client can then traverse the entirety of the server's file
   tree with the LOOKUP operation.  A complete discussion of the server
   name space is in the section "NFS Server Name Space".

4.1.2.  Public Filehandle

   The second special filehandle is the PUBLIC filehandle.  Unlike the
   ROOT filehandle, the PUBLIC filehandle may be bound or represent an
   arbitrary file system object at the server.  The server is
   responsible for this binding.  It may be that the PUBLIC filehandle
   and the ROOT filehandle refer to the same file system object.
   However, it is up to the administrative software at the server and
   the policies of the server administrator to define the binding of the
   PUBLIC filehandle and server file system object.  The client may not
   make any assumptions about this binding.  The client uses the PUBLIC
   filehandle via the PUTPUBFH operation.



Shepler, et al.         Expires February 2, 2007               [Page 69]


Internet-Draft            NFSv4 Minor Version 1              August 2006


4.2.  Filehandle Types

   In the NFS version 2 and 3 protocols, there was one type of
   filehandle with a single set of semantics.  This type of filehandle
   is termed "persistent" in NFS Version 4.  The semantics of a
   persistent filehandle remain the same as before.  A new type of
   filehandle introduced in NFS Version 4 is the "volatile" filehandle,
   which attempts to accommodate certain server environments.

   The volatile filehandle type was introduced to address server
   functionality or implementation issues which make correct
   implementation of a persistent filehandle infeasible.  Some server
   environments do not provide a file system level invariant that can be
   used to construct a persistent filehandle.  The underlying server
   file system may not provide the invariant or the server's file system
   programming interfaces may not provide access to the needed
   invariant.  Volatile filehandles may ease the implementation of
   server functionality such as hierarchical storage management or file
   system reorganization or migration.  However, the volatile filehandle
   increases the implementation burden for the client.

   Since the client will need to handle persistent and volatile
   filehandles differently, a file attribute is defined which may be
   used by the client to determine the filehandle types being returned
   by the server.

4.2.1.  General Properties of a Filehandle

   The filehandle contains all the information the server needs to
   distinguish an individual file.  To the client, the filehandle is
   opaque.  The client stores filehandles for use in a later request and
   can compare two filehandles from the same server for equality by
   doing a byte-by-byte comparison.  However, the client MUST NOT
   otherwise interpret the contents of filehandles.  If two filehandles
   from the same server are equal, they MUST refer to the same file.
   Servers SHOULD try to maintain a one-to-one correspondence between
   filehandles and files but this is not required.  Clients MUST use
   filehandle comparisons only to improve performance, not for correct
   behavior.  All clients need to be prepared for situations in which it
   cannot be determined whether two filehandles denote the same object
   and in such cases, avoid making invalid assumptions which might cause
   incorrect behavior.  Further discussion of filehandle and attribute
   comparison in the context of data caching is presented in the section
   "Data Caching and File Identity".

   As an example, in the case that two different path names when
   traversed at the server terminate at the same file system object, the
   server SHOULD return the same filehandle for each path.  This can



Shepler, et al.         Expires February 2, 2007               [Page 70]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   occur if a hard link is used to create two file names which refer to
   the same underlying file object and associated data.  For example, if
   paths /a/b/c and /a/d/c refer to the same file, the server SHOULD
   return the same filehandle for both path names traversals.

4.2.2.  Persistent Filehandle

   A persistent filehandle is defined as having a fixed value for the
   lifetime of the file system object to which it refers.  Once the
   server creates the filehandle for a file system object, the server
   MUST accept the same filehandle for the object for the lifetime of
   the object.  If the server restarts or reboots the NFS server must
   honor the same filehandle value as it did in the server's previous
   instantiation.  Similarly, if the file system is migrated, the new
   NFS server must honor the same filehandle as the old NFS server.

   The persistent filehandle will be become stale or invalid when the
   file system object is removed.  When the server is presented with a
   persistent filehandle that refers to a deleted object, it MUST return
   an error of NFS4ERR_STALE.  A filehandle may become stale when the
   file system containing the object is no longer available.  The file
   system may become unavailable if it exists on removable media and the
   media is no longer available at the server or the file system in
   whole has been destroyed or the file system has simply been removed
   from the server's name space (i.e. unmounted in a UNIX environment).

4.2.3.  Volatile Filehandle

   A volatile filehandle does not share the same longevity
   characteristics of a persistent filehandle.  The server may determine
   that a volatile filehandle is no longer valid at many different
   points in time.  If the server can definitively determine that a
   volatile filehandle refers to an object that has been removed, the
   server should return NFS4ERR_STALE to the client (as is the case for
   persistent filehandles).  In all other cases where the server
   determines that a volatile filehandle can no longer be used, it
   should return an error of NFS4ERR_FHEXPIRED.

   The mandatory attribute "fh_expire_type" is used by the client to
   determine what type of filehandle the server is providing for a
   particular file system.  This attribute is a bitmask with the
   following values:

   FH4_PERSISTENT  The value of FH4_PERSISTENT is used to indicate a
      persistent filehandle, which is valid until the object is removed
      from the file system.  The server will not return
      NFS4ERR_FHEXPIRED for this filehandle.  FH4_PERSISTENT is defined
      as a value in which none of the bits specified below are set.



Shepler, et al.         Expires February 2, 2007               [Page 71]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   FH4_VOLATILE_ANY  The filehandle may expire at any time, except as
      specifically excluded (i.e.  FH4_NO_EXPIRE_WITH_OPEN).

   FH4_NOEXPIRE_WITH_OPEN  May only be set when FH4_VOLATILE_ANY is set.
      If this bit is set, then the meaning of FH4_VOLATILE_ANY is
      qualified to exclude any expiration of the filehandle when it is
      open.

   FH4_VOL_MIGRATION  The filehandle will expire as a result of a file
      system transition (migration or replication), in those case in
      which the continuity of filehandle use is not specified by
      _handle_ class information within the fs_locations_info attribute.
      When this bit is set, clients without access to fs_locations_info
      information should assume filehandles will expire on file system
      transitions.

   FH4_VOL_RENAME  The filehandle will expire during rename.  This
      includes a rename by the requesting client or a rename by any
      other client.  If FH4_VOL_ANY is set, FH4_VOL_RENAME is redundant.

   Servers which provide volatile filehandles that may expire while open
   (i.e. if FH4_VOL_MIGRATION or FH4_VOL_RENAME is set or if
   FH4_VOLATILE_ANY is set and FH4_NOEXPIRE_WITH_OPEN not set), should
   deny a RENAME or REMOVE that would affect an OPEN file of any of the
   components leading to the OPEN file.  In addition, the server should
   deny all RENAME or REMOVE requests during the grace period upon
   server restart.

   Servers which provide volatile filehandles that may expire while open
   require special care as regards handling of RENAMESs and REMOVEs.
   This situation can arise if FH4_VOL_MIGRATION or FH4_VOL_RENAME is
   set, if FH4_VOLATILE_ANY is set and FH4_NOEXPIRE_WITH_OPEN not set,
   or if a non-readonly file system has a transition target in a
   different _handle _ class.  In these cases, the server should deny a
   RENAME or REMOVE that would affect an OPEN file of any of the
   components leading to the OPEN file.  In addition, the server should
   deny all RENAME or REMOVE requests during the grace period, in order
   to make sure that reclaims of files where filehandles may have
   expired do not do a reclaim for the wrong file.

4.3.  One Method of Constructing a Volatile Filehandle

   A volatile filehandle, while opaque to the client could contain:

   [volatile bit = 1 | server boot time | slot | generation number]






Shepler, et al.         Expires February 2, 2007               [Page 72]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   o  slot is an index in the server volatile filehandle table

   o  generation number is the generation number for the table entry/
      slot

   When the client presents a volatile filehandle, the server makes the
   following checks, which assume that the check for the volatile bit
   has passed.  If the server boot time is less than the current server
   boot time, return NFS4ERR_FHEXPIRED.  If slot is out of range, return
   NFS4ERR_BADHANDLE.  If the generation number does not match, return
   NFS4ERR_FHEXPIRED.

   When the server reboots, the table is gone (it is volatile).

   If volatile bit is 0, then it is a persistent filehandle with a
   different structure following it.

4.4.  Client Recovery from Filehandle Expiration

   If possible, the client SHOULD recover from the receipt of an
   NFS4ERR_FHEXPIRED error.  The client must take on additional
   responsibility so that it may prepare itself to recover from the
   expiration of a volatile filehandle.  If the server returns
   persistent filehandles, the client does not need these additional
   steps.

   For volatile filehandles, most commonly the client will need to store
   the component names leading up to and including the file system
   object in question.  With these names, the client should be able to
   recover by finding a filehandle in the name space that is still
   available or by starting at the root of the server's file system name
   space.

   If the expired filehandle refers to an object that has been removed
   from the file system, obviously the client will not be able to
   recover from the expired filehandle.

   It is also possible that the expired filehandle refers to a file that
   has been renamed.  If the file was renamed by another client, again
   it is possible that the original client will not be able to recover.
   However, in the case that the client itself is renaming the file and
   the file is open, it is possible that the client may be able to
   recover.  The client can determine the new path name based on the
   processing of the rename request.  The client can then regenerate the
   new filehandle based on the new path name.  The client could also use
   the compound operation mechanism to construct a set of operations
   like:




Shepler, et al.         Expires February 2, 2007               [Page 73]


Internet-Draft            NFSv4 Minor Version 1              August 2006


             RENAME A B
             LOOKUP B
             GETFH

   Note that the COMPOUND procedure does not provide atomicity.  This
   example only reduces the overhead of recovering from an expired
   filehandle.


5.  File Attributes

   To meet the requirements of extensibility and increased
   interoperability with non-UNIX platforms, attributes must be handled
   in a flexible manner.  The NFS version 3 fattr3 structure contains a
   fixed list of attributes that not all clients and servers are able to
   support or care about.  The fattr3 structure can not be extended as
   new needs arise and it provides no way to indicate non-support.  With
   the NFS version 4 protocol, the client is able query what attributes
   the server supports and construct requests with only those supported
   attributes (or a subset thereof).

   To this end, attributes are divided into three groups: mandatory,
   recommended, and named.  Both mandatory and recommended attributes
   are supported in the NFS version 4 protocol by a specific and well-
   defined encoding and are identified by number.  They are requested by
   setting a bit in the bit vector sent in the GETATTR request; the
   server response includes a bit vector to list what attributes were
   returned in the response.  New mandatory or recommended attributes
   may be added to the NFS protocol between major revisions by
   publishing a standards-track RFC which allocates a new attribute
   number value and defines the encoding for the attribute.  See the
   section "Minor Versioning" for further discussion.

   Named attributes are accessed by the new OPENATTR operation, which
   accesses a hidden directory of attributes associated with a file
   system object.  OPENATTR takes a filehandle for the object and
   returns the filehandle for the attribute hierarchy.  The filehandle
   for the named attributes is a directory object accessible by LOOKUP
   or READDIR and contains files whose names represent the named
   attributes and whose data bytes are the value of the attribute.  For
   example:










Shepler, et al.         Expires February 2, 2007               [Page 74]


Internet-Draft            NFSv4 Minor Version 1              August 2006


        +----------+-----------+---------------------------------+
        | LOOKUP   | "foo"     | ; look up file                  |
        | GETATTR  | attrbits  |                                 |
        | OPENATTR |           | ; access foo's named attributes |
        | LOOKUP   | "x11icon" | ; look up specific attribute    |
        | READ     | 0,4096    | ; read stream of bytes          |
        +----------+-----------+---------------------------------+

   Named attributes are intended for data needed by applications rather
   than by an NFS client implementation.  NFS implementors are strongly
   encouraged to define their new attributes as recommended attributes
   by bringing them to the IETF standards-track process.

   The set of attributes which are classified as mandatory is
   deliberately small since servers must do whatever it takes to support
   them.  A server should support as many of the recommended attributes
   as possible but by their definition, the server is not required to
   support all of them.  Attributes are deemed mandatory if the data is
   both needed by a large number of clients and is not otherwise
   reasonably computable by the client when support is not provided on
   the server.

   Note that the hidden directory returned by OPENATTR is a convenience
   for protocol processing.  The client should not make any assumptions
   about the server's implementation of named attributes and whether the
   underlying file system at the server has a named attribute directory
   or not.  Therefore, operations such as SETATTR and GETATTR on the
   named attribute directory are undefined.

5.1.  Mandatory Attributes

   These MUST be supported by every NFS version 4 client and server in
   order to ensure a minimum level of interoperability.  The server must
   store and return these attributes and the client must be able to
   function with an attribute set limited to these attributes.  With
   just the mandatory attributes some client functionality may be
   impaired or limited in some ways.  A client may ask for any of these
   attributes to be returned by setting a bit in the GETATTR request and
   the server must return their value.

5.2.  Recommended Attributes

   These attributes are understood well enough to warrant support in the
   NFS version 4 protocol.  However, they may not be supported on all
   clients and servers.  A client may ask for any of these attributes to
   be returned by setting a bit in the GETATTR request but must handle
   the case where the server does not return them.  A client may ask for
   the set of attributes the server supports and should not request



Shepler, et al.         Expires February 2, 2007               [Page 75]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   attributes the server does not support.  A server should be tolerant
   of requests for unsupported attributes and simply not return them
   rather than considering the request an error.  It is expected that
   servers will support all attributes they comfortably can and only
   fail to support attributes which are difficult to support in their
   operating environments.  A server should provide attributes whenever
   they don't have to "tell lies" to the client.  For example, a file
   modification time should be either an accurate time or should not be
   supported by the server.  This will not always be comfortable to
   clients but the client is better positioned decide whether and how to
   fabricate or construct an attribute or whether to do without the
   attribute.

5.3.  Named Attributes

   These attributes are not supported by direct encoding in the NFS
   Version 4 protocol but are accessed by string names rather than
   numbers and correspond to an uninterpreted stream of bytes which are
   stored with the file system object.  The name space for these
   attributes may be accessed by using the OPENATTR operation.  The
   OPENATTR operation returns a filehandle for a virtual "attribute
   directory" and further perusal of the name space may be done using
   READDIR and LOOKUP operations on this filehandle.  Named attributes
   may then be examined or changed by normal READ and WRITE and CREATE
   operations on the filehandles returned from READDIR and LOOKUP.
   Named attributes may have attributes.

   It is recommended that servers support arbitrary named attributes.  A
   client should not depend on the ability to store any named attributes
   in the server's file system.  If a server does support named
   attributes, a client which is also able to handle them should be able
   to copy a file's data and meta-data with complete transparency from
   one location to another; this would imply that names allowed for
   regular directory entries are valid for named attribute names as
   well.

   Names of attributes will not be controlled by this document or other
   IETF standards track documents.  See the section "IANA
   Considerations" for further discussion.

5.4.  Classification of Attributes

   Each of the Mandatory and Recommended attributes can be classified in
   one of three categories: per server, per file system, or per file
   system object.  Note that it is possible that some per file system
   attributes may vary within the file system.  See the "homogeneous"
   attribute for its definition.  Note that the attributes
   time_access_set and time_modify_set are not listed in this section



Shepler, et al.         Expires February 2, 2007               [Page 76]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   because they are write-only attributes corresponding to time_access
   and time_modify, and are used in a special instance of SETATTR.

   o  The per server attributes are:

         lease_time, send_impl_id, recv_impl_id

   o  The per file system attributes are:

         supp_attr, fh_expire_type, link_support, symlink_support,
         unique_handles, aclsupport, cansettime, case_insensitive,
         case_preserving, chown_restricted, files_avail, files_free,
         files_total, fs_locations, homogeneous, maxfilesize, maxname,
         maxread, maxwrite, no_trunc, space_avail, space_free,
         space_total, time_delta, fs_layout_type

   o  The per file system object attributes are:

         type, change, size, named_attr, fsid, rdattr_error, filehandle,
         ACL, archive, fileid, hidden, maxlink, mimetype, mode,
         numlinks, owner, owner_group, rawdev, space_used, system,
         time_access, time_backup, time_create, time_metadata,
         time_modify, mounted_on_fileid, layout_type, layout_hint,
         layout_blksize, layout_alignment

   For quota_avail_hard, quota_avail_soft, and quota_used see their
   definitions below for the appropriate classification.

5.5.  Mandatory Attributes - Definitions

   +-----------------+----+------------+--------+----------------------+
   | name            | #  | Data Type  | Access | Description          |
   +-----------------+----+------------+--------+----------------------+
   | supp_attr       | 0  | bitmap     | READ   | The bit vector which |
   |                 |    |            |        | would retrieve all   |
   |                 |    |            |        | mandatory and        |
   |                 |    |            |        | recommended          |
   |                 |    |            |        | attributes that are  |
   |                 |    |            |        | supported for this   |
   |                 |    |            |        | object. The scope of |
   |                 |    |            |        | this attribute       |
   |                 |    |            |        | applies to all       |
   |                 |    |            |        | objects with a       |
   |                 |    |            |        | matching fsid.       |
   | type            | 1  | nfs4_ftype | READ   | The type of the      |
   |                 |    |            |        | object (file,        |
   |                 |    |            |        | directory, symlink,  |
   |                 |    |            |        | etc.)                |



Shepler, et al.         Expires February 2, 2007               [Page 77]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   | fh_expire_type  | 2  | uint32     | READ   | Server uses this to  |
   |                 |    |            |        | specify filehandle   |
   |                 |    |            |        | expiration behavior  |
   |                 |    |            |        | to the client. See   |
   |                 |    |            |        | the section          |
   |                 |    |            |        | "Filehandles" for    |
   |                 |    |            |        | additional           |
   |                 |    |            |        | description.         |
   | change          | 3  | uint64     | READ   | A value created by   |
   |                 |    |            |        | the server that the  |
   |                 |    |            |        | client can use to    |
   |                 |    |            |        | determine if file    |
   |                 |    |            |        | data, directory      |
   |                 |    |            |        | contents or          |
   |                 |    |            |        | attributes of the    |
   |                 |    |            |        | object have been     |
   |                 |    |            |        | modified. The server |
   |                 |    |            |        | may return the       |
   |                 |    |            |        | object's             |
   |                 |    |            |        | time_metadata        |
   |                 |    |            |        | attribute for this   |
   |                 |    |            |        | attribute's value    |
   |                 |    |            |        | but only if the file |
   |                 |    |            |        | system object can    |
   |                 |    |            |        | not be updated more  |
   |                 |    |            |        | frequently than the  |
   |                 |    |            |        | resolution of        |
   |                 |    |            |        | time_metadata.       |
   | size            | 4  | uint64     | R/W    | The size of the      |
   |                 |    |            |        | object in bytes.     |
   | link_support    | 5  | bool       | READ   | True, if the         |
   |                 |    |            |        | object's file system |
   |                 |    |            |        | supports hard links. |
   | symlink_support | 6  | bool       | READ   | True, if the         |
   |                 |    |            |        | object's file system |
   |                 |    |            |        | supports symbolic    |
   |                 |    |            |        | links.               |
   | named_attr      | 7  | bool       | READ   | True, if this object |
   |                 |    |            |        | has named            |
   |                 |    |            |        | attributes. In other |
   |                 |    |            |        | words, object has a  |
   |                 |    |            |        | non-empty named      |
   |                 |    |            |        | attribute directory. |








Shepler, et al.         Expires February 2, 2007               [Page 78]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   | fsid            | 8  | fsid4      | READ   | Unique file system   |
   |                 |    |            |        | identifier for the   |
   |                 |    |            |        | file system holding  |
   |                 |    |            |        | this object. fsid    |
   |                 |    |            |        | contains major and   |
   |                 |    |            |        | minor components     |
   |                 |    |            |        | each of which are    |
   |                 |    |            |        | uint64.              |
   | unique_handles  | 9  | bool       | READ   | True, if two         |
   |                 |    |            |        | distinct filehandles |
   |                 |    |            |        | guaranteed to refer  |
   |                 |    |            |        | to two different     |
   |                 |    |            |        | file system objects. |
   | lease_time      | 10 | nfs_lease4 | READ   | Duration of leases   |
   |                 |    |            |        | at server in         |
   |                 |    |            |        | seconds.             |
   | rdattr_error    | 11 | enum       | READ   | Error returned from  |
   |                 |    |            |        | getattr during       |
   |                 |    |            |        | readdir.             |
   | filehandle      | 19 | nfs_fh4    | READ   | The filehandle of    |
   |                 |    |            |        | this object          |
   |                 |    |            |        | (primarily for       |
   |                 |    |            |        | readdir requests).   |
   +-----------------+----+------------+--------+----------------------+

5.6.  Recommended Attributes - Definitions

   +--------------------+----+---------------+--------+----------------+
   | name               | #  | Data Type     | Access | Description    |
   +--------------------+----+---------------+--------+----------------+
   | ACL                | 12 | nfsace4<>     | R/W    | The access     |
   |                    |    |               |        | control list   |
   |                    |    |               |        | for the        |
   |                    |    |               |        | object.        |
   | aclsupport         | 13 | uint32        | READ   | Indicates what |
   |                    |    |               |        | types of ACLs  |
   |                    |    |               |        | are supported  |
   |                    |    |               |        | on the current |
   |                    |    |               |        | file system.   |
   | archive            | 14 | bool          | R/W    | True, if this  |
   |                    |    |               |        | file has been  |
   |                    |    |               |        | archived since |
   |                    |    |               |        | the time of    |
   |                    |    |               |        | last           |
   |                    |    |               |        | modification   |
   |                    |    |               |        | (deprecated in |
   |                    |    |               |        | favor of       |
   |                    |    |               |        | time_backup).  |



Shepler, et al.         Expires February 2, 2007               [Page 79]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   | cansettime         | 15 | bool          | READ   | True, if the   |
   |                    |    |               |        | server able to |
   |                    |    |               |        | change the     |
   |                    |    |               |        | times for a    |
   |                    |    |               |        | file system    |
   |                    |    |               |        | object as      |
   |                    |    |               |        | specified in a |
   |                    |    |               |        | SETATTR        |
   |                    |    |               |        | operation.     |
   | case_insensitive   | 16 | bool          | READ   | True, if       |
   |                    |    |               |        | filename       |
   |                    |    |               |        | comparisons on |
   |                    |    |               |        | this file      |
   |                    |    |               |        | system are     |
   |                    |    |               |        | case           |
   |                    |    |               |        | insensitive.   |
   | case_preserving    | 17 | bool          | READ   | True, if       |
   |                    |    |               |        | filename case  |
   |                    |    |               |        | on this file   |
   |                    |    |               |        | system are     |
   |                    |    |               |        | preserved.     |
   | chown_restricted   | 18 | bool          | READ   | If TRUE, the   |
   |                    |    |               |        | server will    |
   |                    |    |               |        | reject any     |
   |                    |    |               |        | request to     |
   |                    |    |               |        | change either  |
   |                    |    |               |        | the owner or   |
   |                    |    |               |        | the group      |
   |                    |    |               |        | associated     |
   |                    |    |               |        | with a file if |
   |                    |    |               |        | the caller is  |
   |                    |    |               |        | not a          |
   |                    |    |               |        | privileged     |
   |                    |    |               |        | user (for      |
   |                    |    |               |        | example,       |
   |                    |    |               |        | "root" in UNIX |
   |                    |    |               |        | operating      |
   |                    |    |               |        | environments   |
   |                    |    |               |        | or in Windows  |
   |                    |    |               |        | 2000 the "Take |
   |                    |    |               |        | Ownership"     |
   |                    |    |               |        | privilege).    |
   | dir_notif_delay    | 56 | nfstime4      | READ   | notification   |
   |                    |    |               |        | delays on      |
   |                    |    |               |        | directory      |
   |                    |    |               |        | attributes     |





Shepler, et al.         Expires February 2, 2007               [Page 80]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   | dirent_notif_delay | 57 | nfstime4      | READ   | notification   |
   |                    |    |               |        | delays on      |
   |                    |    |               |        | child          |
   |                    |    |               |        | attributes     |
   | fileid             | 20 | uint64        | READ   | A number       |
   |                    |    |               |        | uniquely       |
   |                    |    |               |        | identifying    |
   |                    |    |               |        | the file       |
   |                    |    |               |        | within the     |
   |                    |    |               |        | file system.   |
   | files_avail        | 21 | uint64        | READ   | File slots     |
   |                    |    |               |        | available to   |
   |                    |    |               |        | this user on   |
   |                    |    |               |        | the file       |
   |                    |    |               |        | system         |
   |                    |    |               |        | containing     |
   |                    |    |               |        | this object -  |
   |                    |    |               |        | this should be |
   |                    |    |               |        | the smallest   |
   |                    |    |               |        | relevant       |
   |                    |    |               |        | limit.         |
   | files_free         | 22 | uint64        | READ   | Free file      |
   |                    |    |               |        | slots on the   |
   |                    |    |               |        | file system    |
   |                    |    |               |        | containing     |
   |                    |    |               |        | this object -  |
   |                    |    |               |        | this should be |
   |                    |    |               |        | the smallest   |
   |                    |    |               |        | relevant       |
   |                    |    |               |        | limit.         |
   | files_total        | 23 | uint64        | READ   | Total file     |
   |                    |    |               |        | slots on the   |
   |                    |    |               |        | file system    |
   |                    |    |               |        | containing     |
   |                    |    |               |        | this object.   |
   | fs_absent          | 60 | bool          | READ   | Is current     |
   |                    |    |               |        | file system    |
   |                    |    |               |        | present or     |
   |                    |    |               |        | absent.        |
   | fs_layout_type     | 62 | layouttype4<> | READ   | Layout types   |
   |                    |    |               |        | available for  |
   |                    |    |               |        | the file       |
   |                    |    |               |        | system.        |








Shepler, et al.         Expires February 2, 2007               [Page 81]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   | fs_locations       | 24 | fs_locations  | READ   | Locations      |
   |                    |    |               |        | where this     |
   |                    |    |               |        | file system    |
   |                    |    |               |        | may be found.  |
   |                    |    |               |        | If the server  |
   |                    |    |               |        | returns        |
   |                    |    |               |        | NFS4ERR_MOVED  |
   |                    |    |               |        | as an error,   |
   |                    |    |               |        | this attribute |
   |                    |    |               |        | MUST be        |
   |                    |    |               |        | supported.     |
   | fs_locations_info  | 67 |               | READ   | Full function  |
   |                    |    |               |        | file system    |
   |                    |    |               |        | location.      |
   | fs_status          | 61 | fs4_status    | READ   | Generic file   |
   |                    |    |               |        | system type    |
   |                    |    |               |        | information.   |
   | hidden             | 25 | bool          | R/W    | True, if the   |
   |                    |    |               |        | file is        |
   |                    |    |               |        | considered     |
   |                    |    |               |        | hidden with    |
   |                    |    |               |        | respect to the |
   |                    |    |               |        | Windows API?   |
   | homogeneous        | 26 | bool          | READ   | True, if this  |
   |                    |    |               |        | object's file  |
   |                    |    |               |        | system is      |
   |                    |    |               |        | homogeneous,   |
   |                    |    |               |        | i.e. are per   |
   |                    |    |               |        | file system    |
   |                    |    |               |        | attributes the |
   |                    |    |               |        | same for all   |
   |                    |    |               |        | file system's  |
   |                    |    |               |        | objects.       |
   | layout_alignment   | 66 | uint32_t      | READ   | Preferred      |
   |                    |    |               |        | alignment for  |
   |                    |    |               |        | layout related |
   |                    |    |               |        | I/O.           |
   | layout_blksize     | 65 | uint32_t      | READ   | Preferred      |
   |                    |    |               |        | block size for |
   |                    |    |               |        | layout related |
   |                    |    |               |        | I/O.           |
   | layout_hint        | 63 | layouthint4   | WRITE  | Client         |
   |                    |    |               |        | specified hint |
   |                    |    |               |        | for file       |
   |                    |    |               |        | layout.        |
   | layout_type        | 64 | layouttype4<> | READ   | Layout types   |
   |                    |    |               |        | available for  |
   |                    |    |               |        | the file.      |



Shepler, et al.         Expires February 2, 2007               [Page 82]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   | maxfilesize        | 27 | uint64        | READ   | Maximum        |
   |                    |    |               |        | supported file |
   |                    |    |               |        | size for the   |
   |                    |    |               |        | file system of |
   |                    |    |               |        | this object.   |
   | maxlink            | 28 | uint32        | READ   | Maximum number |
   |                    |    |               |        | of links for   |
   |                    |    |               |        | this object.   |
   | maxname            | 29 | uint32        | READ   | Maximum        |
   |                    |    |               |        | filename size  |
   |                    |    |               |        | supported for  |
   |                    |    |               |        | this object.   |
   | maxread            | 30 | uint64        | READ   | Maximum read   |
   |                    |    |               |        | size supported |
   |                    |    |               |        | for this       |
   |                    |    |               |        | object.        |
   | maxwrite           | 31 | uint64        | READ   | Maximum write  |
   |                    |    |               |        | size supported |
   |                    |    |               |        | for this       |
   |                    |    |               |        | object. This   |
   |                    |    |               |        | attribute      |
   |                    |    |               |        | SHOULD be      |
   |                    |    |               |        | supported if   |
   |                    |    |               |        | the file is    |
   |                    |    |               |        | writable. Lack |
   |                    |    |               |        | of this        |
   |                    |    |               |        | attribute can  |
   |                    |    |               |        | lead to the    |
   |                    |    |               |        | client either  |
   |                    |    |               |        | wasting        |
   |                    |    |               |        | bandwidth or   |
   |                    |    |               |        | not receiving  |
   |                    |    |               |        | the best       |
   |                    |    |               |        | performance.   |
   | mdsthreshold       | 68 | mdsthreshold4 | READ   | Hint to client |
   |                    |    |               |        | as to when to  |
   |                    |    |               |        | write through  |
   |                    |    |               |        | the pnfs       |
   |                    |    |               |        | metadata       |
   |                    |    |               |        | server.        |
   | mimetype           | 32 | utf8<>        | R/W    | MIME body      |
   |                    |    |               |        | type/subtype   |
   |                    |    |               |        | of this        |
   |                    |    |               |        | object.        |







Shepler, et al.         Expires February 2, 2007               [Page 83]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   | mode               | 33 | mode4         | R/W    | UNIX-style     |
   |                    |    |               |        | mode and       |
   |                    |    |               |        | permission     |
   |                    |    |               |        | bits for this  |
   |                    |    |               |        | object.        |
   | mounted_on_fileid  | 55 | uint64        | READ   | Like fileid,   |
   |                    |    |               |        | but if the     |
   |                    |    |               |        | target         |
   |                    |    |               |        | filehandle is  |
   |                    |    |               |        | the root of a  |
   |                    |    |               |        | file system    |
   |                    |    |               |        | return the     |
   |                    |    |               |        | fileid of the  |
   |                    |    |               |        | underlying     |
   |                    |    |               |        | directory.     |
   | no_trunc           | 34 | bool          | READ   | True, if a     |
   |                    |    |               |        | name longer    |
   |                    |    |               |        | than name_max  |
   |                    |    |               |        | is used, an    |
   |                    |    |               |        | error be       |
   |                    |    |               |        | returned and   |
   |                    |    |               |        | name is not    |
   |                    |    |               |        | truncated.     |
   | numlinks           | 35 | uint32        | READ   | Number of hard |
   |                    |    |               |        | links to this  |
   |                    |    |               |        | object.        |
   | owner              | 36 | utf8<>        | R/W    | The string     |
   |                    |    |               |        | name of the    |
   |                    |    |               |        | owner of this  |
   |                    |    |               |        | object.        |
   | owner_group        | 37 | utf8<>        | R/W    | The string     |
   |                    |    |               |        | name of the    |
   |                    |    |               |        | group          |
   |                    |    |               |        | ownership of   |
   |                    |    |               |        | this object.   |
   | quota_avail_hard   | 38 | uint64        | READ   | For definition |
   |                    |    |               |        | see "Quota     |
   |                    |    |               |        | Attributes"    |
   |                    |    |               |        | section below. |
   | quota_avail_soft   | 39 | uint64        | READ   | For definition |
   |                    |    |               |        | see "Quota     |
   |                    |    |               |        | Attributes"    |
   |                    |    |               |        | section below. |
   | quota_used         | 40 | uint64        | READ   | For definition |
   |                    |    |               |        | see "Quota     |
   |                    |    |               |        | Attributes"    |
   |                    |    |               |        | section below. |




Shepler, et al.         Expires February 2, 2007               [Page 84]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   | rawdev             | 41 | specdata4     | READ   | Raw device     |
   |                    |    |               |        | identifier.    |
   |                    |    |               |        | UNIX device    |
   |                    |    |               |        | major/minor    |
   |                    |    |               |        | node           |
   |                    |    |               |        | information.   |
   |                    |    |               |        | If the value   |
   |                    |    |               |        | of type is not |
   |                    |    |               |        | NF4BLK or      |
   |                    |    |               |        | NF4CHR, the    |
   |                    |    |               |        | value return   |
   |                    |    |               |        | SHOULD NOT be  |
   |                    |    |               |        | considered     |
   |                    |    |               |        | useful.        |
   | recv_impl_id       | 59 | impl_ident4   | READ   | Client obtains |
   |                    |    |               |        | the server's   |
   |                    |    |               |        | implementation |
   |                    |    |               |        | identity via   |
   |                    |    |               |        | GETATTR.       |
   | send_impl_id       | 58 | impl_ident4   | WRITE  | Client         |
   |                    |    |               |        | provides       |
   |                    |    |               |        | server with    |
   |                    |    |               |        | its            |
   |                    |    |               |        | implementation |
   |                    |    |               |        | identity via   |
   |                    |    |               |        | SETATTR.       |
   | space_avail        | 42 | uint64        | READ   | Disk space in  |
   |                    |    |               |        | bytes          |
   |                    |    |               |        | available to   |
   |                    |    |               |        | this user on   |
   |                    |    |               |        | the file       |
   |                    |    |               |        | system         |
   |                    |    |               |        | containing     |
   |                    |    |               |        | this object -  |
   |                    |    |               |        | this should be |
   |                    |    |               |        | the smallest   |
   |                    |    |               |        | relevant       |
   |                    |    |               |        | limit.         |
   | space_free         | 43 | uint64        | READ   | Free disk      |
   |                    |    |               |        | space in bytes |
   |                    |    |               |        | on the file    |
   |                    |    |               |        | system         |
   |                    |    |               |        | containing     |
   |                    |    |               |        | this object -  |
   |                    |    |               |        | this should be |
   |                    |    |               |        | the smallest   |
   |                    |    |               |        | relevant       |
   |                    |    |               |        | limit.         |



Shepler, et al.         Expires February 2, 2007               [Page 85]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   | space_total        | 44 | uint64        | READ   | Total disk     |
   |                    |    |               |        | space in bytes |
   |                    |    |               |        | on the file    |
   |                    |    |               |        | system         |
   |                    |    |               |        | containing     |
   |                    |    |               |        | this object.   |
   | space_used         | 45 | uint64        | READ   | Number of file |
   |                    |    |               |        | system bytes   |
   |                    |    |               |        | allocated to   |
   |                    |    |               |        | this object.   |
   | system             | 46 | bool          | R/W    | True, if this  |
   |                    |    |               |        | file is a      |
   |                    |    |               |        | "system" file  |
   |                    |    |               |        | with respect   |
   |                    |    |               |        | to the Windows |
   |                    |    |               |        | API?           |
   | time_access        | 47 | nfstime4      | READ   | The time of    |
   |                    |    |               |        | last access to |
   |                    |    |               |        | the object by  |
   |                    |    |               |        | a read that    |
   |                    |    |               |        | was satisfied  |
   |                    |    |               |        | by the server. |
   | time_access_set    | 48 | settime4      | WRITE  | Set the time   |
   |                    |    |               |        | of last access |
   |                    |    |               |        | to the object. |
   |                    |    |               |        | SETATTR use    |
   |                    |    |               |        | only.          |
   | time_backup        | 49 | nfstime4      | R/W    | The time of    |
   |                    |    |               |        | last backup of |
   |                    |    |               |        | the object.    |
   | time_create        | 50 | nfstime4      | R/W    | The time of    |
   |                    |    |               |        | creation of    |
   |                    |    |               |        | the object.    |
   |                    |    |               |        | This attribute |
   |                    |    |               |        | does not have  |
   |                    |    |               |        | any relation   |
   |                    |    |               |        | to the         |
   |                    |    |               |        | traditional    |
   |                    |    |               |        | UNIX file      |
   |                    |    |               |        | attribute      |
   |                    |    |               |        | "ctime" or     |
   |                    |    |               |        | "change time". |
   | time_delta         | 51 | nfstime4      | READ   | Smallest       |
   |                    |    |               |        | useful server  |
   |                    |    |               |        | time           |
   |                    |    |               |        | granularity.   |





Shepler, et al.         Expires February 2, 2007               [Page 86]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   | time_metadata      | 52 | nfstime4      | READ   | The time of    |
   |                    |    |               |        | last meta-data |
   |                    |    |               |        | modification   |
   |                    |    |               |        | of the object. |
   | time_modify        | 53 | nfstime4      | READ   | The time of    |
   |                    |    |               |        | last           |
   |                    |    |               |        | modification   |
   |                    |    |               |        | to the object. |
   | time_modify_set    | 54 | settime4      | WRITE  | Set the time   |
   |                    |    |               |        | of last        |
   |                    |    |               |        | modification   |
   |                    |    |               |        | to the object. |
   |                    |    |               |        | SETATTR use    |
   |                    |    |               |        | only.          |
   +--------------------+----+---------------+--------+----------------+

5.7.  Time Access

   As defined above, the time_access attribute represents the time of
   last access to the object by a read that was satisfied by the server.
   The notion of what is an "access" depends on server's operating
   environment and/or the server's file system semantics.  For example,
   for servers obeying POSIX semantics, time_access would be updated
   only by the READLINK, READ, and READDIR operations and not any of the
   operations that modify the content of the object.  Of course, setting
   the corresponding time_access_set attribute is another way to modify
   the time_access attribute.

   Whenever the file object resides on a writable file system, the
   server should make best efforts to record time_access into stable
   storage.  However, to mitigate the performance effects of doing so,
   and most especially whenever the server is satisfying the read of the
   object's content from its cache, the server MAY cache access time
   updates and lazily write them to stable storage.  It is also
   acceptable to give administrators of the server the option to disable
   time_access updates.

5.8.  Interpreting owner and owner_group

   The recommended attributes "owner" and "owner_group" (and also users
   and groups within the "acl" attribute) are represented in terms of a
   UTF-8 string.  To avoid a representation that is tied to a particular
   underlying implementation at the client or server, the use of the
   UTF-8 string has been chosen.  Note that section 6.1 of RFC2624 [27]
   provides additional rationale.  It is expected that the client and
   server will have their own local representation of owner and
   owner_group that is used for local storage or presentation to the end
   user.  Therefore, it is expected that when these attributes are



Shepler, et al.         Expires February 2, 2007               [Page 87]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   transferred between the client and server that the local
   representation is translated to a syntax of the form "user@
   dns_domain".  This will allow for a client and server that do not use
   the same local representation the ability to translate to a common
   syntax that can be interpreted by both.

   Similarly, security principals may be represented in different ways
   by different security mechanisms.  Servers normally translate these
   representations into a common format, generally that used by local
   storage, to serve as a means of identifying the users corresponding
   to these security principals.  When these local identifiers are
   translated to the form of the owner attribute, associated with files
   created by such principals they identify, in a common format, the
   users associated with each corresponding set of security principals.

   The translation used to interpret owner and group strings is not
   specified as part of the protocol.  This allows various solutions to
   be employed.  For example, a local translation table may be consulted
   that maps between a numeric id to the user@dns_domain syntax.  A name
   service may also be used to accomplish the translation.  A server may
   provide a more general service, not limited by any particular
   translation (which would only translate a limited set of possible
   strings) by storing the owner and owner_group attributes in local
   storage without any translation or it may augment a translation
   method by storing the entire string for attributes for which no
   translation is available while using the local representation for
   those cases in which a translation is available.

   Servers that do not provide support for all possible values of the
   owner and owner_group attributes, should return an error
   (NFS4ERR_BADOWNER) when a string is presented that has no
   translation, as the value to be set for a SETATTR of the owner,
   owner_group, or acl attributes.  When a server does accept an owner
   or owner_group value as valid on a SETATTR (and similarly for the
   owner and group strings in an acl), it is promising to return that
   same string when a corresponding GETATTR is done.  Configuration
   changes and ill-constructed name translations (those that contain
   aliasing) may make that promise impossible to honor.  Servers should
   make appropriate efforts to avoid a situation in which these
   attributes have their values changed when no real change to ownership
   has occurred.

   The "dns_domain" portion of the owner string is meant to be a DNS
   domain name.  For example, user@ietf.org.  Servers should accept as
   valid a set of users for at least one domain.  A server may treat
   other domains as having no valid translations.  A more general
   service is provided when a server is capable of accepting users for
   multiple domains, or for all domains, subject to security



Shepler, et al.         Expires February 2, 2007               [Page 88]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   constraints.

   In the case where there is no translation available to the client or
   server, the attribute value must be constructed without the "@".
   Therefore, the absence of the @ from the owner or owner_group
   attribute signifies that no translation was available at the sender
   and that the receiver of the attribute should not use that string as
   a basis for translation into its own internal format.  Even though
   the attribute value can not be translated, it may still be useful.
   In the case of a client, the attribute string may be used for local
   display of ownership.

   To provide a greater degree of compatibility with previous versions
   of NFS (i.e. v2 and v3), which identified users and groups by 32-bit
   unsigned uid's and gid's, owner and group strings that consist of
   decimal numeric values with no leading zeros can be given a special
   interpretation by clients and servers which choose to provide such
   support.  The receiver may treat such a user or group string as
   representing the same user as would be represented by a v2/v3 uid or
   gid having the corresponding numeric value.  A server is not
   obligated to accept such a string, but may return an NFS4ERR_BADOWNER
   instead.  To avoid this mechanism being used to subvert user and
   group translation, so that a client might pass all of the owners and
   groups in numeric form, a server SHOULD return an NFS4ERR_BADOWNER
   error when there is a valid translation for the user or owner
   designated in this way.  In that case, the client must use the
   appropriate name@domain string and not the special form for
   compatibility.

   The owner string "nobody" may be used to designate an anonymous user,
   which will be associated with a file created by a security principal
   that cannot be mapped through normal means to the owner attribute.

5.9.  Character Case Attributes

   With respect to the case_insensitive and case_preserving attributes,
   each UCS-4 character (which UTF-8 encodes) has a "long descriptive
   name" RFC1345 [28] which may or may not included the word "CAPITAL"
   or "SMALL".  The presence of SMALL or CAPITAL allows an NFS server to
   implement unambiguous and efficient table driven mappings for case
   insensitive comparisons, and non-case-preserving storage.  For
   general character handling and internationalization issues, see the
   section "Internationalization".

5.10.  Quota Attributes

   For the attributes related to file system quotas, the following
   definitions apply:



Shepler, et al.         Expires February 2, 2007               [Page 89]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   quota_avail_soft  The value in bytes which represents the amount of
      additional disk space that can be allocated to this file or
      directory before the user may reasonably be warned.  It is
      understood that this space may be consumed by allocations to other
      files or directories though there is a rule as to which other
      files or directories.

   quota_avail_hard  The value in bytes which represent the amount of
      additional disk space beyond the current allocation that can be
      allocated to this file or directory before further allocations
      will be refused.  It is understood that this space may be consumed
      by allocations to other files or directories.

   quota_used  The value in bytes which represent the amount of disc
      space used by this file or directory and possibly a number of
      other similar files or directories, where the set of "similar"
      meets at least the criterion that allocating space to any file or
      directory in the set will reduce the "quota_avail_hard" of every
      other file or directory in the set.

      Note that there may be a number of distinct but overlapping sets
      of files or directories for which a quota_used value is
      maintained.  E.g. "all files with a given owner", "all files with
      a given group owner". etc.

      The server is at liberty to choose any of those sets but should do
      so in a repeatable way.  The rule may be configured per file
      system or may be "choose the set with the smallest quota".

5.11.  mounted_on_fileid

   UNIX-based operating environments connect a file system into the
   namespace by connecting (mounting) the file system onto the existing
   file object (the mount point, usually a directory) of an existing
   file system.  When the mount point's parent directory is read via an
   API like readdir(), the return results are directory entries, each
   with a component name and a fileid.  The fileid of the mount point's
   directory entry will be different from the fileid that the stat()
   system call returns.  The stat() system call is returning the fileid
   of the root of the mounted file system, whereas readdir() is
   returning the fileid stat() would have returned before any file
   systems were mounted on the mount point.

   Unlike NFS version 3, NFS version 4 allows a client's LOOKUP request
   to cross other file systems.  The client detects the file system
   crossing whenever the filehandle argument of LOOKUP has an fsid
   attribute different from that of the filehandle returned by LOOKUP.
   A UNIX-based client will consider this a "mount point crossing".



Shepler, et al.         Expires February 2, 2007               [Page 90]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   UNIX has a legacy scheme for allowing a process to determine its
   current working directory.  This relies on readdir() of a mount
   point's parent and stat() of the mount point returning fileids as
   previously described.  The mounted_on_fileid attribute corresponds to
   the fileid that readdir() would have returned as described
   previously.

   While the NFS version 4 client could simply fabricate a fileid
   corresponding to what mounted_on_fileid provides (and if the server
   does not support mounted_on_fileid, the client has no choice), there
   is a risk that the client will generate a fileid that conflicts with
   one that is already assigned to another object in the file system.
   Instead, if the server can provide the mounted_on_fileid, the
   potential for client operational problems in this area is eliminated.

   If the server detects that there is no mounted point at the target
   file object, then the value for mounted_on_fileid that it returns is
   the same as that of the fileid attribute.

   The mounted_on_fileid attribute is RECOMMENDED, so the server SHOULD
   provide it if possible, and for a UNIX-based server, this is
   straightforward.  Usually, mounted_on_fileid will be requested during
   a READDIR operation, in which case it is trivial (at least for UNIX-
   based servers) to return mounted_on_fileid since it is equal to the
   fileid of a directory entry returned by readdir().  If
   mounted_on_fileid is requested in a GETATTR operation, the server
   should obey an invariant that has it returning a value that is equal
   to the file object's entry in the object's parent directory, i.e.
   what readdir() would have returned.  Some operating environments
   allow a series of two or more file systems to be mounted onto a
   single mount point.  In this case, for the server to obey the
   aforementioned invariant, it will need to find the base mount point,
   and not the intermediate mount points.

5.12.  send_impl_id and recv_impl_id

   These recommended attributes are used to identify the client and
   server.  In the case of the send_impl_id attribute, the client sends
   its nfs_impl_id4.  In the case of the recv_impl_id attribute, the
   client receives the server's nfs_impl_id4 value.

   Access to this identification information can be most useful at both
   client and server.  Being able to identify specific implementations
   can help in planning by administrators or implementors.  For example,
   diagnostic software may extract this information in an attempt to
   identify interoperability problems, performance workload behaviors or
   general usage statistics.  Since the intent of having access to this
   information is for planning or general diagnosis only, the client and



Shepler, et al.         Expires February 2, 2007               [Page 91]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   server MUST NOT interpret this implementation identity information in
   a way that affects interoperational behavior of the implementation.
   The reason is the if clients and servers did such a thing, they might
   use fewer capabilities of the protocol than the peer can support, or
   the client and server might refuse to interoperate.

   Because it is likely some implementations will violate the protocol
   specification and interpret the identity information, implementations
   MUST allow the users of the NFSv4 client and server to set the
   contents of the sent nfs_impl_id structure to any value.

   Even though these attributes are RECOMMENDED, if the server supports
   one of them it MUST support the other.

5.13.  fs_layout_type

   This attribute applies to a file system and indicates what layout
   types are supported by the file system.  We expect this attribute to
   be queried when a client encounters a new fsid.  This attribute is
   used by the client to determine if it has applicable layout drivers.

5.14.  layout_type

   This attribute indicates the particular layout type(s) used for a
   file.  This is for informational purposes only.  The client needs to
   use the LAYOUTGET operation in order to get enough information (e.g.,
   specific device information) in order to perform I/O.

5.15.  layout_hint

   This attribute may be set on newly created files to influence the
   metadata server's choice for the file's layout.  It is suggested that
   this attribute is set as one of the initial attributes within the
   OPEN call.  The metadata server may ignore this attribute.  This
   attribute is a sub-set of the layout structure returned by LAYOUTGET.
   For example, instead of specifying particular devices, this would be
   used to suggest the stripe width of a file.  It is up to the server
   implementation to determine which fields within the layout it uses.

5.16.  mdsthreshold

   This attribute acts as a hint to the client to help it determine when
   it is more efficient to issue read and write requests to the metadata
   server vs. the dataserver.  Two types of thresholds are described:
   file size thresholds and I/O size thresholds.  If a file's size is
   smaller than the file size threshold, data accesses should be issued
   to the metadata server.  If an I/O is below the I/O size threshold,
   the I/O should be issued to the metadata server.  Each threshold can



Shepler, et al.         Expires February 2, 2007               [Page 92]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   be specified independently for read and write requests.  For either
   threshold type, a value of 0 indicates no read or write should be
   issued to the metadata server, while a value of all 1s indicates all
   reads or writes should be issued to the metadata server.

   The attribute is available on a per filehandle basis.  If the current
   filehandle refers to a non-pNFS file or directory, the metadata
   server should return an attribute that is representative of the
   filehandle's file system.  It is suggested that this attribute is
   queried as part of the OPEN operation.  Due to dynamic system
   changes, the client should not assume that the attribute will remain
   constant for any specific time period, thus it should be periodically
   refreshed.


6.  Access Control Lists

   Access Control Lists (ACLs) are a file attribute that specify fine
   grained access control.  This chapter covers the "acl", "aclsupport",
   and "mode" file attributes, and their interactions.

6.1.  Goals

   ACLs and modes represent two well established but different models
   for specifying permissions.  This chapter specifies requirements that
   attempt to meet the following goals:

   o  If a server supports the mode attribute, it should provide
      reasonable semantics to clients that only set and retrieve the
      mode attribute.

   o  If a server supports the ACL attribute, it should provide
      reasonable semantics to clients that only set and retrieve the ACL
      attribute.

   o  On servers that support the mode attribute, if the ACL attribute
      has never been set on an object, via inheritance or explicitly,
      the behavior should be traditional UNIX-like behavior.

   o  On servers that support the mode attribute, if the ACL attribute
      has been previously set on an object, either explicitly or via
      inheritance:

      *  Setting only the mode attribute should effectively control the
         traditional UNIX-like permissions of read, write, and execute
         on owner, owner_group, and other.





Shepler, et al.         Expires February 2, 2007               [Page 93]


Internet-Draft            NFSv4 Minor Version 1              August 2006


      *  Setting only the mode attribute should provide reasonable
         security.  For example, setting a mode of 000 should be enough
         to ensure that future opens for read or write by any principal
         should fail, regardless of a previously existing or inherited
         ACL.

   o  It must be possible to implement a server such that its clients
      can have POSIX compliant semantics.

   o  This minor version of NFSv4 should not introduce significantly
      different semantics relating to the mode and ACL attributes, nor
      should it render invalid any existing implementations.  Rather,
      this chapter provides clarifications based on previous
      implementations and discussions around them.

   o  If a server supports the ACL attribute, then at any time, the
      server can provide an ACL attribute when requested.  The ACL
      attribute will describe all permissions on the file object, except
      for the three high-order bits of the mode attribute (described in
      Section 6.2.2).  The ACL attribute will not conflict with the mode
      attribute, on servers that support the mode attribute.

   o  If a server supports the mode attribute, then at any time, the
      server can provide a mode attribute when requested.  The mode
      attribute will not conflict with the ACL attribute, on servers
      that support the ACL attribute.

   o  When a mode attribute is set on an object, the ACL attribute may
      need to be modified so as to not conflict with the new mode.  In
      such cases, it is desirable that the ACL keep as much information
      as possible.  This includes information about inheritance, AUDIT
      and ALARM ACEs, and permissions granted and denied that do not
      conflict with the new mode.

6.2.  File Attributes Discussion

6.2.1.  ACL Attribute

   The NFS version 4 ACL attribute is an array of access control entries
   (ACEs).  Although the client can read and write the ACL attribute,
   the server is responsible for using the ACL to perform access
   control.  The client can use the OPEN or ACCESS operations to check
   access without modifying or reading data or metadata.

   The NFS ACE attribute is defined as follows:






Shepler, et al.         Expires February 2, 2007               [Page 94]


Internet-Draft            NFSv4 Minor Version 1              August 2006


                       typedef uint32_t   acetype4;
                       typedef uint32_t   aceflag4;
                       typedef uint32_t   acemask4;

                       struct nfsace4 {
                           acetype4       type;
                           aceflag4       flag;
                           acemask4       access_mask;
                           utf8str_mixed  who;
                       };

   To determine if a request succeeds, the server processes each nfsace4
   entry in order.  Only ACEs which have a "who" that matches the
   requester are considered.  Each ACE is processed until all of the
   bits of the requester's access have been ALLOWED.  Once a bit (see
   below) has been ALLOWED by an ACCESS_ALLOWED_ACE, it is no longer
   considered in the processing of later ACEs.  If an ACCESS_DENIED_ACE
   is encountered where the requester's access still has unALLOWED bits
   in common with the "access_mask" of the ACE, the request is denied.
   When the ACL is fully processed, if there are bits in the requester's
   mask that have not been ALLOWED or DENIED, access is denied.

   Unlike the ALLOW and DENY ACE types, the ALARM and AUDIT ACE types do
   not affect a requester's access, and instead are for triggering
   events as a result of a requester's access attempt.  Therefore, all
   AUDIT and ALARM ACEs are processed until end of the ACL.

   The NFS version 4 ACL model is quite rich.  Some server platforms may
   provide access control functionality that goes beyond the UNIX-style
   mode attribute, but which is not as rich as the NFS ACL model.  So
   that users can take advantage of this more limited functionality, the
   server may indicate that it supports ACLs as long as it follows the
   guidelines for mapping between its ACL model and the NFS version 4
   ACL model.

   The situation is complicated by the fact that a server may have
   multiple modules that enforce ACLs.  For example, the enforcement for
   NFS version 4 access may be different from the enforcement for local
   access, and both may be different from the enforcement for access
   through other protocols such as SMB.  So it may be useful for a
   server to accept an ACL even if not all of its modules are able to
   support it.

   The guiding principle in all cases is that the server must not accept
   ACLs that appear to make the file more secure than it really is.






Shepler, et al.         Expires February 2, 2007               [Page 95]


Internet-Draft            NFSv4 Minor Version 1              August 2006


6.2.1.1.  ACE Type

   The constants used for the type field (acetype4) are as follows:

                     const ACE4_ACCESS_ALLOWED_ACE_TYPE = 0x00000000;
                     const ACE4_ACCESS_DENIED_ACE_TYPE  = 0x00000001;
                     const ACE4_SYSTEM_AUDIT_ACE_TYPE   = 0x00000002;
                     const ACE4_SYSTEM_ALARM_ACE_TYPE   = 0x00000003;

   +------------------------------+--------------+---------------------+
   | Value                        | Abbreviation | Description         |
   +------------------------------+--------------+---------------------+
   | ACE4_ACCESS_ALLOWED_ACE_TYPE | ALLOW        | Explicitly grants   |
   |                              |              | the access defined  |
   |                              |              | in acemask4 to the  |
   |                              |              | file or directory.  |
   | ACE4_ACCESS_DENIED_ACE_TYPE  | DENY         | Explicitly denies   |
   |                              |              | the access defined  |
   |                              |              | in acemask4 to the  |
   |                              |              | file or directory.  |
   | ACE4_SYSTEM_AUDIT_ACE_TYPE   | AUDIT        | LOG (system         |
   |                              |              | dependent) any      |
   |                              |              | access attempt to a |
   |                              |              | file or directory   |
   |                              |              | which uses any of   |
   |                              |              | the access methods  |
   |                              |              | specified in        |
   |                              |              | acemask4.           |
   | ACE4_SYSTEM_ALARM_ACE_TYPE   | ALARM        | Generate a system   |
   |                              |              | ALARM (system       |
   |                              |              | dependent) when any |
   |                              |              | access attempt is   |
   |                              |              | made to a file or   |
   |                              |              | directory for the   |
   |                              |              | access methods      |
   |                              |              | specified in        |
   |                              |              | acemask4.           |
   +------------------------------+--------------+---------------------+

    The "Abbreviation" column denotes how the types will be referred to
                   throughout the rest of this document.

6.2.1.2.  The aclsupport Attribute

   A server need not support all of the above ACE types.  The bitmask
   constants used to represent the above definitions within the
   aclsupport attribute are as follows:




Shepler, et al.         Expires February 2, 2007               [Page 96]


Internet-Draft            NFSv4 Minor Version 1              August 2006


                     const ACL4_SUPPORT_ALLOW_ACL    = 0x00000001;
                     const ACL4_SUPPORT_DENY_ACL     = 0x00000002;
                     const ACL4_SUPPORT_AUDIT_ACL    = 0x00000004;
                     const ACL4_SUPPORT_ALARM_ACL    = 0x00000008;

   Clients should not attempt to set an ACE unless the server claims
   support for that ACE type.  If the server receives a request to set
   an ACE that it cannot store, it MUST reject the request with
   NFS4ERR_ATTRNOTSUPP.  If the server receives a request to set an ACE
   that it can store but cannot enforce, the server SHOULD reject the
   request with NFS4ERR_ATTRNOTSUPP.

   Example: suppose a server can enforce NFS ACLs for NFS access but
   cannot enforce ACLs for local access.  If arbitrary processes can run
   on the server, then the server SHOULD NOT indicate ACL support.  On
   the other hand, if only trusted administrative programs run locally,
   then the server may indicate ACL support.

6.2.1.3.  ACE Access Mask

   The bitmask constants used for the access mask field are as follows:

              const ACE4_READ_DATA            = 0x00000001;
              const ACE4_LIST_DIRECTORY       = 0x00000001;
              const ACE4_WRITE_DATA           = 0x00000002;
              const ACE4_ADD_FILE             = 0x00000002;
              const ACE4_APPEND_DATA          = 0x00000004;
              const ACE4_ADD_SUBDIRECTORY     = 0x00000004;
              const ACE4_READ_NAMED_ATTRS     = 0x00000008;
              const ACE4_WRITE_NAMED_ATTRS    = 0x00000010;
              const ACE4_EXECUTE              = 0x00000020;
              const ACE4_DELETE_CHILD         = 0x00000040;
              const ACE4_READ_ATTRIBUTES      = 0x00000080;
              const ACE4_WRITE_ATTRIBUTES     = 0x00000100;
              const ACE4_DELETE               = 0x00010000;
              const ACE4_READ_ACL             = 0x00020000;
              const ACE4_WRITE_ACL            = 0x00040000;
              const ACE4_WRITE_OWNER          = 0x00080000;
              const ACE4_SYNCHRONIZE          = 0x00100000;

6.2.1.3.1.  Discussion of Mask Attributes

    ACE4_READ_DATA
       Operation(s) affected:
            READ
            OPEN
       Discussion:
            Permission to read the data of the file.



Shepler, et al.         Expires February 2, 2007               [Page 97]


Internet-Draft            NFSv4 Minor Version 1              August 2006


            Servers SHOULD allow a user the ability to read the data
            of the file when only the ACE4_EXECUTE access mask bit is
            allowed.

    ACE4_LIST_DIRECTORY
        Operation(s) affected:
            READDIR
        Discussion:
            Permission to list the contents of a directory.

    ACE4_WRITE_DATA
        Operation(s) affected:
            WRITE
            OPEN
            SETATTR of size
        Discussion:
            Permission to modify a file's data anywhere in the file's
            offset range.  This includes the ability to write to any
            arbitrary offset and as a result to grow the file.

    ACE4_ADD_FILE
        Operation(s) affected:
            CREATE
            OPEN
        Discussion:
            Permission to add a new file in a directory.  The CREATE
            operation is affected when nfs_ftype4 is NF4LNK, NF4BLK,
            NF4CHR, NF4SOCK, or NF4FIFO. (NF4DIR is not listed because
            it is covered by ACE4_ADD_SUBDIRECTORY.) OPEN is affected
            when used to create a regular file.

    ACE4_APPEND_DATA
        Operation(s) affected:
            WRITE
            OPEN
            SETATTR of size
        Discussion:
             The ability to modify a file's data, but only starting at
             EOF.  This allows for the notion of append-only files, by
             allowing ACE4_APPEND_DATA and denying ACE4_WRITE_DATA to
             the same user or group.  If a file has an ACL such as the
             one described above and a WRITE request is made for
             somewhere other than EOF, the server SHOULD return
             NFS4ERR_ACCESS.

    ACE4_ADD_SUBDIRECTORY
        Operation(s) affected:
            CREATE



Shepler, et al.         Expires February 2, 2007               [Page 98]


Internet-Draft            NFSv4 Minor Version 1              August 2006


        Discussion:
            Permission to create a subdirectory in a directory.  The
            CREATE operation is affected when nfs_ftype4 is NF4DIR.

    ACE4_READ_NAMED_ATTRS
        Operation(s) affected:
            OPENATTR
        Discussion:
            Permission to read the named attributes of a file or to
            lookup the named attributes directory.  OPENATTR is
            affected when it is not used to create a named attribute
            directory.  This is when 1.) createdir is TRUE, but a
            named attribute directory already exists, or 2.) createdir
            is FALSE.

    ACE4_WRITE_NAMED_ATTRS
        Operation(s) affected:
            OPENATTR
        Discussion:
            Permission to write the named attributes of a file or
            to create a named attribute directory.  OPENATTR is
            affected when it is used to create a named attribute
            directory.  This is when createdir is TRUE and no named
            attribute directory exists.  The ability to check whether
            or not a named attribute directory exists depends on the
            ability to look it up, therefore, users also need the
            ACE4_READ_NAMED_ATTRS permission in order to create a
            named attribute directory.

    ACE4_EXECUTE
        Operation(s) affected:
            LOOKUP
            READ
            OPEN
        Discussion:
            Permission to execute a file or traverse/search a
            directory.

            Servers SHOULD allow a user the ability to read the data
            of the file when only the ACE4_EXECUTE access mask bit is
            allowed.  This is because there is no way to execute a
            file without reading the contents.  Though a server may
            treat ACE4_EXECUTE and ACE4_READ_DATA bits identically
            when deciding to permit a READ operation, it SHOULD still
            allow the two bits to be set independently in ACLs, and
            MUST distinguish between them when replying to ACCESS
            operations.  In particular, servers SHOULD NOT silently
            turn on one of the two bits when the other is set, as



Shepler, et al.         Expires February 2, 2007               [Page 99]


Internet-Draft            NFSv4 Minor Version 1              August 2006


            that would make it impossible for the client to correctly
            enforce the distinction between read and execute
            permissions.

             As an example, following a SETATTR of the following ACL:
                     nfsuser:ACE4_EXECUTE:ALLOW

             A subsequent GETATTR of ACL for that file SHOULD return:
                     nfsuser:ACE4_EXECUTE:ALLOW
             Rather than:
                     nfsuser:ACE4_EXECUTE/ACE4_READ_DATA:ALLOW

    ACE4_DELETE_CHILD
        Operation(s) affected:
            REMOVE
        Discussion:
            Permission to delete a file or directory within a
            directory.  See section "ACE4_DELETE vs. ACE4_DELETE_CHILD"
            for information on how these two access mask bits interact.

    ACE4_READ_ATTRIBUTES
        Operation(s) affected:
            GETATTR of file system object attributes
        Discussion:
            The ability to read basic attributes (non-ACLs) of a file.
            On a UNIX system, basic attributes can be thought of as
            the stat level attributes.  Allowing this access mask bit
            would mean the entity can execute "ls -l" and stat.

    ACE4_WRITE_ATTRIBUTES
        Operation(s) affected:
            SETATTR of time_access_set, time_backup,
            time_create, time_modify_set, mimetype, hidden, system
        Discussion:
            Permission to change the times associated with a file
            or directory to an arbitrary value.  Also permission
            to change the mimetype, hidden and system attributes.
            A user having ACE4_WRITE_DATA permission, but lacking
            ACE4_WRITE_ATTRIBUTES must be allowed to implicitly set
            the times associated with a file.

    ACE4_DELETE
        Operation(s) affected:
            REMOVE
        Discussion:
            Permission to delete the file or directory.  See section
            "ACE4_DELETE vs. ACE4_DELETE_CHILD" for information on how
            these two access mask bits interact.



Shepler, et al.         Expires February 2, 2007              [Page 100]


Internet-Draft            NFSv4 Minor Version 1              August 2006


    ACE4_READ_ACL
        Operation(s) affected:
            GETATTR of acl
        Discussion:
            Permission to read the ACL.

    ACE4_WRITE_ACL
        Operation(s) affected:
            SETATTR of acl and mode
        Discussion:
            Permission to write the acl and mode attributes.

    ACE4_WRITE_OWNER
        Operation(s) affected:
            SETATTR of owner and owner_group
        Discussions:
            Permission to write the owner and owner_group attributes.
            On UNIX systems, this is the ability to execute chown().

    ACE4_SYNCHRONIZE
        Operation(s) affected:
            NONE
        Discussion:
            Permission to access file locally at the server with
            synchronized reads and writes.

   Server implementations need not provide the granularity of control
   that is implied by this list of masks.  For example, POSIX-based
   systems might not distinguish ACE4_APPEND_DATA (the ability to append
   to a file) from ACE4_WRITE_DATA (the ability to modify existing
   contents); both masks would be tied to a single "write" permission.
   When such a server returns attributes to the client, it would show
   both ACE4_APPEND_DATA and ACE4_WRITE_DATA if and only if the write
   permission is enabled.

   If a server receives a SETATTR request that it cannot accurately
   implement, it should error in the direction of more restricted
   access.  For example, suppose a server cannot distinguish overwriting
   data from appending new data, as described in the previous paragraph.
   If a client submits an ACE where ACE4_APPEND_DATA is set but
   ACE4_WRITE_DATA is not (or vice versa), the server should reject the
   request with NFS4ERR_ATTRNOTSUPP.  Nonetheless, if the ACE has type
   DENY, the server may silently turn on the other bit, so that both
   ACE4_APPEND_DATA and ACE4_WRITE_DATA are denied.







Shepler, et al.         Expires February 2, 2007              [Page 101]


Internet-Draft            NFSv4 Minor Version 1              August 2006


6.2.1.3.2.  ACE4_DELETE vs. ACE4_DELETE_CHILD

   Two access mask bits govern the ability to delete a file or directory
   object: ACE4_DELETE on the object itself, and ACE4_DELETE_CHILD on
   the object's parent directory.

   Many systems also consult the "sticky bit" (MODE4_SVTX) and write
   mode bit on the parent directory when determining whether to allow a
   file to be deleted.  The mode bit for write corresponds to
   ACE4_WRITE_DATA, which is the same physical bit as ACE4_ADD_FILE.
   Therefore, ACE4_ADD_FILE can come into play when determining
   permission to delete.

   In the algorithm below, the strategy is that ACE4_DELETE and
   ACE4_DELETE_CHILD take precedence over the sticky bit, and the sticky
   bit takes precedence over the "write" mode bits (reflected in
   ACE4_ADD_FILE).

   Server implementations SHOULD grant or deny permission to delete
   based on the following algorithm.

       if ACE4_EXECUTE is denied by the parent directory ACL:
           deny delete
       else if ACE4_DELETE is allowed by the target object ACL:
           allow delete
       else if ACE4_DELETE_CHILD is allowed by the parent
       directory ACL:
           allow delete
       else if ACE4_DELETE_CHILD is denied by the
       parent directory ACL:
           deny delete
       else if ACE4_ADD_FILE is allowed by the parent directory ACL:
           if MODE4_SVTX is set for the parent directory:
               if the principal owns the parent directory OR
                   the principal owns the target object OR
                   ACE4_WRITE_DATA is allowed by the target
                   object ACL:
                       allow delete
                   else:
                       deny delete
           else:
               allow delete
       else:
           deny delete







Shepler, et al.         Expires February 2, 2007              [Page 102]


Internet-Draft            NFSv4 Minor Version 1              August 2006


6.2.1.4.  ACE flag

   The bitmask constants used for the flag field are as follows:

              const ACE4_FILE_INHERIT_ACE             = 0x00000001;
              const ACE4_DIRECTORY_INHERIT_ACE        = 0x00000002;
              const ACE4_NO_PROPAGATE_INHERIT_ACE     = 0x00000004;
              const ACE4_INHERIT_ONLY_ACE             = 0x00000008;
              const ACE4_SUCCESSFUL_ACCESS_ACE_FLAG   = 0x00000010;
              const ACE4_FAILED_ACCESS_ACE_FLAG       = 0x00000020;
              const ACE4_IDENTIFIER_GROUP             = 0x00000040;

   A server need not support any of these flags.  If the server supports
   flags that are similar to, but not exactly the same as, these flags,
   the implementation may define a mapping between the protocol-defined
   flags and the implementation-defined flags.  Again, the guiding
   principle is that the file not appear to be more secure than it
   really is.

   For example, suppose a client tries to set an ACE with
   ACE4_FILE_INHERIT_ACE set but not ACE4_DIRECTORY_INHERIT_ACE.  If the
   server does not support any form of ACL inheritance, the server
   should reject the request with NFS4ERR_ATTRNOTSUPP.  If the server
   supports a single "inherit ACE" flag that applies to both files and
   directories, the server may reject the request (i.e., requiring the
   client to set both the file and directory inheritance flags).  The
   server may also accept the request and silently turn on the
   ACE4_DIRECTORY_INHERIT_ACE flag.

6.2.1.4.1.  Discussion of Flag Bits

   ACE4_FILE_INHERIT_ACE
      Can be placed on a directory and indicates that this ACE should be
      added to each new non-directory file created.

   ACE4_DIRECTORY_INHERIT_ACE
      Can be placed on a directory and indicates that this ACE should be
      added to each new directory created.

   ACE4_INHERIT_ONLY_ACE
      Can be placed on a directory but does not apply to the directory;
      ALLOW and DENY ACEs with this bit set do not affect access to the
      directory, and AUDIT and ALARM ACEs with this bit set do not
      trigger log or alarm events.  Such ACEs only take effect once they
      are applied (with this bit cleared) to newly created files and
      directories as specified by the above two flags.





Shepler, et al.         Expires February 2, 2007              [Page 103]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   ACE4_NO_PROPAGATE_INHERIT_ACE
      Can be placed on a directory.  This flag tells the server that
      inheritance of this ACE should stop at newly created child
      directories.

   ACE4_SUCCESSFUL_ACCESS_ACE_FLAG

   ACE4_FAILED_ACCESS_ACE_FLAG
      The ACE4_SUCCESSFUL_ACCESS_ACE_FLAG (SUCCESS) and
      ACE4_FAILED_ACCESS_ACE_FLAG (FAILED) flag bits relate only to
      ACE4_SYSTEM_AUDIT_ACE_TYPE (AUDIT) and ACE4_SYSTEM_ALARM_ACE_TYPE
      (ALARM) ACE types.  If during the processing of the file's ACL,
      the server encounters an AUDIT or ALARM ACE that matches the
      principal attempting the OPEN, the server notes that fact, and the
      presence, if any, of the SUCCESS and FAILED flags encountered in
      the AUDIT or ALARM ACE.  Once the server completes the ACL
      processing, it then notes if the operation succeeded or failed.
      If the operation succeeded, and if the SUCCESS flag was set for a
      matching AUDIT or ALARM ACE, then the appropriate AUDIT or ALARM
      event occurs.  If the operation failed, and if the FAILED flag was
      set for the matching AUDIT or ALARM ACE, then the appropriate
      AUDIT or ALARM event occurs.  Either or both of the SUCCESS or
      FAILED can be set, but if neither is set, the AUDIT or ALARM ACE
      is not useful.

      The previously described processing applies to that of the ACCESS
      operation as well, the difference being that "success" or
      "failure" does not mean whether ACCESS returns NFS4_OK or not.
      Success means whether ACCESS returns all requested and supported
      bits.  Failure means whether ACCESS failed to return a bit that
      was requested and supported.

   ACE4_IDENTIFIER_GROUP
      Indicates that the "who" refers to a GROUP as defined under UNIX
      or a GROUP ACCOUNT as defined under Windows.  Clients and servers
      must ignore the ACE4_IDENTIFIER_GROUP flag on ACEs with a who
      value equal to one of the special identifiers outlined in
      Section 6.2.1.5.

6.2.1.5.  ACE Who

   The "who" field of an ACE is an identifier that specifies the
   principal or principals to whom the ACE applies.  It may refer to a
   user or a group, with the flag bit ACE4_IDENTIFIER_GROUP specifying
   which.

   There are several special identifiers which need to be understood
   universally, rather than in the context of a particular DNS domain.



Shepler, et al.         Expires February 2, 2007              [Page 104]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   Some of these identifiers cannot be understood when an NFS client
   accesses the server, but have meaning when a local process accesses
   the file.  The ability to display and modify these permissions is
   permitted over NFS, even if none of the access methods on the server
   understands the identifiers.

   +---------------+--------------------------------------------------+
   | Who           | Description                                      |
   +---------------+--------------------------------------------------+
   | OWNER         | The owner of the file                            |
   | GROUP         | The group associated with the file.              |
   | EVERYONE      | The world, including the owner and owning group. |
   | INTERACTIVE   | Accessed from an interactive terminal.           |
   | NETWORK       | Accessed via the network.                        |
   | DIALUP        | Accessed as a dialup user to the server.         |
   | BATCH         | Accessed from a batch job.                       |
   | ANONYMOUS     | Accessed without any authentication.             |
   | AUTHENTICATED | Any authenticated user (opposite of ANONYMOUS)   |
   | SERVICE       | Access from a system service.                    |
   +---------------+--------------------------------------------------+

                                  Table 7

   To avoid conflict, these special identifiers are distinguish by an
   appended "@" and should appear in the form "xxxx@" (note: no domain
   name after the "@").  For example: ANONYMOUS@.

6.2.1.5.1.  Discussion of EVERYONE@

   It is important to note that "EVERYONE@" is not equivalent to the
   UNIX "other" entity.  This is because, by definition, UNIX "other"
   does not include the owner or owning group of a file.  "EVERYONE@"
   means literally everyone, including the owner or owning group.

6.2.2.  mode Attribute

   The NFS version 4 mode attribute is based on the UNIX mode bits.  The
   following bits are defined:













Shepler, et al.         Expires February 2, 2007              [Page 105]


Internet-Draft            NFSv4 Minor Version 1              August 2006


           const MODE4_SUID = 0x800;  /* set user id on execution */
           const MODE4_SGID = 0x400;  /* set group id on execution */
           const MODE4_SVTX = 0x200;  /* save text even after use */
           const MODE4_RUSR = 0x100;  /* read permission: owner */
           const MODE4_WUSR = 0x080;  /* write permission: owner */
           const MODE4_XUSR = 0x040;  /* execute permission: owner */
           const MODE4_RGRP = 0x020;  /* read permission: group */
           const MODE4_WGRP = 0x010;  /* write permission: group */
           const MODE4_XGRP = 0x008;  /* execute permission: group */
           const MODE4_ROTH = 0x004;  /* read permission: other */
           const MODE4_WOTH = 0x002;  /* write permission: other */
           const MODE4_XOTH = 0x001;  /* execute permission: other */

   Bits MODE4_RUSR, MODE4_WUSR, and MODE4_XUSR apply to the principal
   identified in the owner attribute.  Bits MODE4_RGRP, MODE4_WGRP, and
   MODE4_XGRP apply to principals identified in the owner_group
   attribute but who are not identified in the owner attribute.  Bits
   MODE4_ROTH, MODE4_WOTH, MODE4_XOTH apply to any principal that does
   not match that in the owner attribute, and does not have a group
   matching that of the owner_group attribute.

   The remaining bits are not defined by this protocol.  A server MUST
   NOT return bits other than those defined above in a GETATTR or
   READDIR operation, and it MUST return NFS4ERR_INVAL if bits other
   than those defined above are set in a SETATTR, CREATE, or OPEN
   operation.

6.3.  Common Methods

   The requirements in this section will be referred to in future
   sections, especially Section 6.4.

6.3.1.  Interpreting an ACL

6.3.1.1.  Server Considerations

   The server uses the algorithm described in Section 6.2.1 to determine
   whether an ACL allows access to an object.  However, the ACL may not
   be the sole determiner of access.  For example:

   o  In the case of a file system exported as read-only, the server may
      deny write permissions even though an object's ACL grants it.

   o  Server implementations MAY grant ACE4_WRITE_ACL and ACE4_READ_ACL
      permissions in order to prevent the owner from getting into the
      situation where they can't ever modify the ACL.





Shepler, et al.         Expires February 2, 2007              [Page 106]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   o  All servers will allow a user the ability to read the data of the
      file when only the execute permission is granted (i.e.  If the ACL
      denies the user the ACE4_READ_DATA access and allows the user
      ACE4_EXECUTE, the server will allow the user to read the data of
      the file).

   o  Many servers have the notion of owner-override in which the owner
      of the object is allowed to override accesses that are denied by
      the ACL.  This may be helpful, for example, to allow users
      continued access to open files on which the permissions have
      changed.

6.3.1.2.  Client Considerations

   Clients SHOULD NOT do their own access checks based on their
   interpretation the ACL, but rather use the OPEN and ACCESS operations
   to do access checks.  This allows the client to act on the results of
   having the server determine whether or not access should be granted
   based on its interpretation of the ACL.

   Clients must be aware of situations in which an object's ACL will
   define a certain access even though the server will not enforce it.
   In general, but especially in these situations, the client needs to
   do its part in the enforcement of access as defined by the ACL.  To
   do this, the client MAY issue the appropriate ACCESS operation prior
   to servicing the request of the user or application in order to
   determine whether the user or application should be granted the
   access requested.  For examples in which the ACL may define accesses
   that the server doesn't enforce see Section 6.3.1.1.

6.3.2.  Computing a Mode Attribute from an ACL

   The following method can be used to calculate the MODE4_R*, MODE4_W*
   and MODE4_X* bits of a mode attribute, based upon an ACL.

   1.  To determine MODE4_ROTH, MODE4_WOTH, and MODE4_XOTH:

       1.  If the special identifier EVERYONE@ is granted
           ACE4_READ_DATA, then the bit MODE4_ROTH SHOULD be set.
           Otherwise, MODE4_ROTH SHOULD NOT be set.

       2.  If the special identifier EVERYONE@ is granted
           ACE4_WRITE_DATA or ACE4_APPEND_DATA, then the bit MODE4_WOTH
           SHOULD be set.  Otherwise, MODE4_WOTH SHOULD NOT be set.

       3.  If the special identifier EVERYONE@ is granted ACE4_EXECUTE,
           then the bit MODE4_XOTH SHOULD be set.  Otherwise, MODE4_XOTH
           SHOULD NOT be set.



Shepler, et al.         Expires February 2, 2007              [Page 107]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   2.  To determine MODE4_RGRP, MODE4_WGRP, and MODE4_XGRP, note that
       the EVERYONE@ special identifier SHOULD be taken into account.
       In other words, when determining if the GROUP@ special identifier
       is granted a permission, ACEs with the identifier EVERYONE@
       should take effect just as ACEs with the special identifier
       GROUP@ would.

       1.  If the special identifier GROUP@ is granted ACE4_READ_DATA,
           then the bit MODE4_RGRP SHOULD be set.  Otherwise, MODE4_RGRP
           SHOULD NOT be set.

       2.  If the special identifier GROUP@ is granted ACE4_WRITE_DATA
           or ACE4_APPEND_DATA, then the bit MODE4_WGRP SHOULD be set.
           Otherwise, MODE4_WGRP SHOULD NOT be set.

       3.  If the special identifier GROUP@ is granted ACE4_EXECUTE,
           then the bit MODE4_XGRP SHOULD be set.  Otherwise, MODE4_XGRP
           SHOULD NOT be set.

   3.  To determine MODE4_RUSR, MODE4_WUSR, and MODE4_XUSR, note that
       the EVERYONE@ special identifier SHOULD be taken into account.
       In other words, when determining if the OWNER@ special identifier
       is granted a permission, ACEs with the identifier EVERYONE@
       should take effect just as ACEs with the special identifer OWNER@
       would.

       1.  If the special identifier OWNER@ is granted ACE4_READ_DATA,
           then the bit MODE4_RUSR SHOULD be set.  Otherwise, MODE4_RUSR
           SHOULD NOT be set.

       2.  If the special identifier OWNER@ is granted ACE4_WRITE_DATA
           or ACE4_APPEND_DATA, then the bit MODE4_WUSR SHOULD be set.
           Otherwise, MODE4_WUSR SHOULD NOT be set.

       3.  If the special identifier OWNER@ is granted ACE4_EXECUTE,
           then the bit MODE4_XUSR SHOULD be set.  Otherwise, MODE4_XUSR
           SHOULD NOT be set.

6.3.2.1.  Discussion

   The nine low-order mode bits (MODE4_R*, MODE4_W*, MODE4_X*)
   correspond to ACE4_READ_DATA, ACE4_WRITE_DATA/ACE4_APPEND_DATA, and
   ACE4_EXECUTE for OWNER@, GROUP@, and EVERYONE@.  On some
   implementations, mode bits may represent a superset of these
   permissions, e.g. if a specific user is granted ACE4_WRITE_DATA, then
   MODE4_WGRP will be set, even though the file's owner_group is not
   granted ACE4_WRITE_DATA.




Shepler, et al.         Expires February 2, 2007              [Page 108]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   Server implementations are discouraged from doing this, as experience
   has shown that this is confusing and annoying to end users.  The
   specifications above also discourage this practice to enforce the
   semantic that setting the mode attribute effectively specifies read,
   write, and execute for owner, group, and other.

6.4.  Requirements

   The server that supports both mode and ACL must take care to
   synchronize the MODE4_*USR, MODE4_*GRP, and MODE4_*OTH bits with the
   ACEs which have respective who fields of "OWNER@", "GROUP@", and
   "EVERYONE@" so that the client can see semantically equivalent access
   permissions exist whether the client asks for owner, owner_group and
   mode attributes, or for just the ACL.

   In this section, much is made of the methods in Section 6.3.2.  Many
   requirements refer to this section.  But note that the methods have
   behaviors specified with "SHOULD".  This is intentional, to avoid
   invalidating existing implementations that compute the mode according
   to the withdrawn POSIX ACL draft (1003.1e draft 17), rather than by
   actual permissions on owner, group, and other.

6.4.1.  Setting the mode and/or ACL Attributes

6.4.1.1.  Setting mode and not ACL

   When setting a mode attribute and not an ACL attribute, the mode
   attribute MUST be set as given.  The ACL attribute MUST be modified
   such that the mode computed via the method in Section 6.3.2 yields
   the low-order nine bits (MODE4_R*, MODE4_W*, MODE4_X*) of the newly
   set mode attribute.  The ACL SHOULD also be modified such that:

   1.  If MODE4_RGRP is not set, entities explicitly listed in the ACL
       other than OWNER@ and EVERYONE@ SHOULD NOT be granted
       ACE4_READ_DATA.

   2.  If MODE4_WGRP is not set, entities explicitly listed in the ACL
       other than OWNER@ and EVERYONE@ SHOULD NOT be granted
       ACE4_WRITE_DATA or ACE4_APPEND_DATA.

   3.  If MODE4_XGRP is not set, entities explicitly listed in the ACL
       other than OWNER@ and EVERYONE@ SHOULD NOT be granted
       ACE4_EXECUTE.

   Access mask bits other those listed above, appearing in ALLOW ACEs,
   MAY also be disabled.

   Note that ACEs with the flag ACE4_INHERIT_ONLY_ACE set do not affect



Shepler, et al.         Expires February 2, 2007              [Page 109]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   the permissions of the ACL itself, nor do ACEs of the type AUDIT and
   ALARM.  As such, it is desirable to leave these ACEs unmodified when
   modifying the ACL attribute.

   Also note that the requirement may be met by discarding the ACL, in
   favor of an ACL that represents the mode and only the mode.  This is
   permitted, but it is preferable for a server to preserve as much of
   the ACL as possible without violating the above requirements.
   Discarding the ACL makes it effectively impossible for a file created
   with a mode attribute to inherit an ACL (see Section 6.4.3).

6.4.1.2.  Setting ACL and not mode

   When setting an ACL attribute and not a mode attribute, the ACL
   attribute SHOULD be set as given.  The nine low-order bits of the
   mode attribute (MODE4_R*, MODE4_W*, MODE4_X*) MUST be modified to
   match the result of the method Section 6.3.2.  The three high-order
   bits of the mode (MODE4_SUID, MODE4_SGID, MODE4_SVTX) SHOULD remain
   unchanged.

6.4.1.3.  Setting both ACL and mode

   When setting both the mode and the ACL attribute in the same
   operation, the attributes MUST be applied in this order: mode, then
   ACL.  The mode attribute is set as given, then the ACL attribute is
   set as given, possibly changing the final mode, as described above in
   Section 6.4.1.2.

6.4.2.  Retrieving the mode and/or ACL Attributes

   This section applies only to servers that support both the mode and
   the ACL attribute.

   Some server implementations may have a concept of "objects without
   ACLs", meaning that all permissions are granted and denied according
   to the mode attribute, and that no ACL attribute is stored for that
   object.  If an ACL attribute is requested of such a server, the
   server SHOULD return an ACL that does not conflict with the mode;
   that is to say, the ACL returned SHOULD represent the nine low-order
   bits of the mode attribute (MODE4_R*, MODE4_W*, MODE4_X*) as
   described in Section 6.3.2.

   For other server implementations, the ACL attribute is always present
   for every object.  Such servers SHOULD store at least the three high-
   order bits of the mode attribute (MODE4_SUID, MODE4_SGID,
   MODE4_SVTX).  The server SHOULD return a mode attribute if one is
   requested, and the low-order nine bits of the mode (MODE4_R*,
   MODE4_W*, MODE4_X*) MUST match the result of applying the method in



Shepler, et al.         Expires February 2, 2007              [Page 110]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   Section 6.3.2 to the ACL attribute.

6.4.3.  Creating New Objects

   If a server supports the ACL attribute, it may use the ACL attribute
   on the parent directory to compute an initial ACL attribute for a
   newly created object.  This will be referred to as the inherited ACL
   within this section.  The act of adding one or more ACEs to the
   inherited ACL that are based upon ACEs in the parent directory's ACL
   will be referred to as inheriting an ACE within this section.

   Implementors should standardize on what the behavior of CREATE and
   OPEN must be depending on the presence or absence of the mode and ACL
   attributes.

   1.  If just mode is given:

       In this case, inheritance SHOULD take place, but the mode MUST be
       applied to the inherited ACL as described in Section 6.4.1.1,
       thereby modifying the ACL.

   2.  If just ACL is given:

       In this case, inheritance SHOULD NOT take place, and the ACL as
       defined in the CREATE or OPEN will be set without modification,
       and the mode modified as in Section 6.4.1.2

   3.  If both mode and ACL are given:

       In this case, inheritance SHOULD NOT take place, and both
       attributes will be set as described in Section 6.4.1.3.

   4.  If neither mode nor ACL are given:

       In the case where an object is being created without any initial
       attributes at all, e.g. an OPEN operation with an opentype4 of
       OPEN4_CREATE and a createmode4 of EXCLUSIVE4, inheritance SHOULD
       NOT take place.  Instead, the server SHOULD set permissions to
       deny all access to the newly created object.  It is expected that
       the appropriate client will set the desired attributes in a
       subsequent SETATTR operation, and the server SHOULD allow that
       operation to succeed, regardless of what permissions the object
       is created with.  For example, an empty ACL denies all
       permissions, but the server should allow the owner's SETATTR to
       succeed even though WRITE_ACL is implicitly denied.

       In other cases, inheritance SHOULD take place, and no
       modifications to the ACL will happen.  The mode attribute, if



Shepler, et al.         Expires February 2, 2007              [Page 111]


Internet-Draft            NFSv4 Minor Version 1              August 2006


       supported, MUST be as computed in Section 6.3.2, with the
       MODE4_SUID, MODE4_SGID and MODE4_SVTX bits clear.  It is worth
       noting that if no inheritable ACEs exist on the parent directory,
       the file will be created with an empty ACL, thus granting no
       access.

6.4.3.1.  The Inherited ACL

   If the object being created is not a directory, the inherited ACL
   SHOULD NOT inherit ACEs from the parent directory ACL unless the
   ACE4_FILE_INHERIT_FLAG is set.

   If the object being created is a directory, the inherited ACL should
   inherit all inheritable ACEs from the parent directory, those that
   have ACE4_FILE_INHERIT_ACE or ACE4_DIRECTORY_INHERIT_ACE flag set.
   If the inheritable ACE has ACE4_FILE_INHERIT_ACE set, but
   ACE4_DIRECTORY_INHERIT_ACE is clear, the inherited ACE on the newly
   created directory MUST have the ACE4_INHERIT_ONLY_ACE flag set to
   prevent the directory from being affected by ACEs meant for non-
   directories.

   If when a new directory is created and it inherits ACEs from its
   parent, for each inheritable ACE which affects the directory's
   permissions, a server MAY create two ACEs on the directory being
   created; one effective and one which is only inheritable (i.e. has
   ACE4_INHERIT_ONLY_ACE flag set).  This gives the user and the server,
   in the cases which it must mask certain permissions upon creation,
   the ability to modify the effective permissions without modifying the
   ACE which is to be inherited to the new directory's children.

   When a newly created object is created with attributes, and those
   attributes contain an ACL attribute and/or a mode attribute, the
   server MUST apply those attributes to the newly created object, as
   described in Section 6.4.1.


7.  Single-server Name Space

   This chapter describes the NFSv4 single-server name space.  Single-
   server namespaces may be presented directly to clients, or they may
   be used as a basis to form larger multi-server namespaces (e.g. site-
   wide or organization-wide) to be presented to clients, as described
   in Section 10.

7.1.  Server Exports

   On a UNIX server, the name space describes all the files reachable by
   pathnames under the root directory or "/".  On a Windows NT server



Shepler, et al.         Expires February 2, 2007              [Page 112]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   the name space constitutes all the files on disks named by mapped
   disk letters.  NFS server administrators rarely make the entire
   server's file system name space available to NFS clients.  More often
   portions of the name space are made available via an "export"
   feature.  In previous versions of the NFS protocol, the root
   filehandle for each export is obtained through the MOUNT protocol;
   the client sends a string that identifies the export of name space
   and the server returns the root filehandle for it.  The MOUNT
   protocol supports an EXPORTS procedure that will enumerate the
   server's exports.

7.2.  Browsing Exports

   The NFS version 4 protocol provides a root filehandle that clients
   can use to obtain filehandles for the exports of a particular server,
   via a series of LOOKUP operations within a COMPOUND, to traverse a
   path.  A common user experience is to use a graphical user interface
   (perhaps a file "Open" dialog window) to find a file via progressive
   browsing through a directory tree.  The client must be able to move
   from one export to another export via single-component, progressive
   LOOKUP operations.

   This style of browsing is not well supported by the NFS version 2 and
   3 protocols.  The client expects all LOOKUP operations to remain
   within a single server file system.  For example, the device
   attribute will not change.  This prevents a client from taking name
   space paths that span exports.

   An automounter on the client can obtain a snapshot of the server's
   name space using the EXPORTS procedure of the MOUNT protocol.  If it
   understands the server's pathname syntax, it can create an image of
   the server's name space on the client.  The parts of the name space
   that are not exported by the server are filled in with a "pseudo file
   system" that allows the user to browse from one mounted file system
   to another.  There is a drawback to this representation of the
   server's name space on the client: it is static.  If the server
   administrator adds a new export the client will be unaware of it.

7.3.  Server Pseudo File System

   NFS version 4 servers avoid this name space inconsistency by
   presenting all the exports for a given server within the framework of
   a single namespace, for that server.  An NFS version 4 client uses
   LOOKUP and READDIR operations to browse seamlessly from one export to
   another.  Portions of the server name space that are not exported are
   bridged via a "pseudo file system" that provides a view of exported
   directories only.  A pseudo file system has a unique fsid and behaves
   like a normal, read only file system.



Shepler, et al.         Expires February 2, 2007              [Page 113]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   Based on the construction of the server's name space, it is possible
   that multiple pseudo file systems may exist.  For example,

           /a              pseudo file system
           /a/b            real file system
           /a/b/c          pseudo file system
           /a/b/c/d        real file system

   Each of the pseudo file systems are considered separate entities and
   therefore will have its own unique fsid.

7.4.  Multiple Roots

   The DOS and Windows operating environments are sometimes described as
   having "multiple roots".  File Systems are commonly represented as
   disk letters.  MacOS represents file systems as top level names.  NFS
   version 4 servers for these platforms can construct a pseudo file
   system above these root names so that disk letters or volume names
   are simply directory names in the pseudo root.

7.5.  Filehandle Volatility

   The nature of the server's pseudo file system is that it is a logical
   representation of file system(s) available from the server.
   Therefore, the pseudo file system is most likely constructed
   dynamically when the server is first instantiated.  It is expected
   that the pseudo file system may not have an on disk counterpart from
   which persistent filehandles could be constructed.  Even though it is
   preferable that the server provide persistent filehandles for the
   pseudo file system, the NFS client should expect that pseudo file
   system filehandles are volatile.  This can be confirmed by checking
   the associated "fh_expire_type" attribute for those filehandles in
   question.  If the filehandles are volatile, the NFS client must be
   prepared to recover a filehandle value (e.g. with a series of LOOKUP
   operations) when receiving an error of NFS4ERR_FHEXPIRED.

7.6.  Exported Root

   If the server's root file system is exported, one might conclude that
   a pseudo-file system is unneeded.  This not necessarily so.  Assume
   the following file systems on a server:

           /       disk1  (exported)
           /a      disk2  (not exported)
           /a/b    disk3  (exported)

   Because disk2 is not exported, disk3 cannot be reached with simple
   LOOKUPs.  The server must bridge the gap with a pseudo-file system.



Shepler, et al.         Expires February 2, 2007              [Page 114]


Internet-Draft            NFSv4 Minor Version 1              August 2006


7.7.  Mount Point Crossing

   The server file system environment may be constructed in such a way
   that one file system contains a directory which is 'covered' or
   mounted upon by a second file system.  For example:

           /a/b            (file system 1)
           /a/b/c/d        (file system 2)

   The pseudo file system for this server may be constructed to look
   like:

           /               (place holder/not exported)
           /a/b            (file system 1)
           /a/b/c/d        (file system 2)

   It is the server's responsibility to present the pseudo file system
   that is complete to the client.  If the client sends a lookup request
   for the path "/a/b/c/d", the server's response is the filehandle of
   the file system "/a/b/c/d".  In previous versions of the NFS
   protocol, the server would respond with the filehandle of directory
   "/a/b/c/d" within the file system "/a/b".

   The NFS client will be able to determine if it crosses a server mount
   point by a change in the value of the "fsid" attribute.

7.8.  Security Policy and Name Space Presentation

   The application of the server's security policy needs to be carefully
   considered by the implementor.  One may choose to limit the
   viewability of portions of the pseudo file system based on the
   server's perception of the client's ability to authenticate itself
   properly.  However, with the support of multiple security mechanisms
   and the ability to negotiate the appropriate use of these mechanisms,
   the server is unable to properly determine if a client will be able
   to authenticate itself.  If, based on its policies, the server
   chooses to limit the contents of the pseudo file system, the server
   may effectively hide file systems from a client that may otherwise
   have legitimate access.

   As suggested practice, the server should apply the security policy of
   a shared resource in the server's namespace to the components of the
   resource's ancestors.  For example:

           /
           /a/b
           /a/b/c




Shepler, et al.         Expires February 2, 2007              [Page 115]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   The /a/b/c directory is a real file system and is the shared
   resource.  The security policy for /a/b/c is Kerberos with integrity.
   The server should apply the same security policy to /, /a, and /a/b.
   This allows for the extension of the protection of the server's
   namespace to the ancestors of the real shared resource.

   For the case of the use of multiple, disjoint security mechanisms in
   the server's resources, the security for a particular object in the
   server's namespace should be the union of all security mechanisms of
   all direct descendants.


8.  File Locking and Share Reservations

   Integrating locking into the NFS protocol necessarily causes it to be
   stateful.  With the inclusion of such features as share reservations,
   file and directory delegations, recallable layouts, and support for
   mandatory byte-range locking the protocol becomes substantially more
   dependent on state than the traditional combination of NFS and NLM
   [XNFS].  There are three components to making this state manageable:

   o  Clear division between client and server

   o  Ability to reliably detect inconsistency in state between client
      and server

   o  Simple and robust recovery mechanisms

   In this model, the server owns the state information.  The client
   requests changes in locks and the server responds with the changes
   made.  Non-client-initiated changes in locking state are infrequent
   and the client receives prompt notification of them and can adjust
   his view of the locking state to reflect the server's changes.

   To support Win32 share reservations it is necessary to provide
   operations which atomically OPEN or CREATE files.  Having a separate
   share/unshare operation would not allow correct implementation of the
   Win32 OpenFile API.  In order to correctly implement share semantics,
   the previous NFS protocol mechanisms used when a file is opened or
   created (LOOKUP, CREATE, ACCESS) need to be replaced.  The NFS
   version 4.1 protocol defines OPEN operation which looks up or creates
   a file and establishes locking state on the server.

8.1.  Locking

   It is assumed that manipulating a lock is rare when compared to READ
   and WRITE operations.  It is also assumed that crashes and network
   partitions are relatively rare.  Therefore it is important that the



Shepler, et al.         Expires February 2, 2007              [Page 116]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   READ and WRITE operations have a lightweight mechanism to indicate if
   they possess a held lock.  A lock request contains the heavyweight
   information required to establish a lock and uniquely define the lock
   owner.

   The following sections describe the transition from the heavyweight
   information to the eventual lightweight stateid used for most client
   and server locking interactions.

8.1.1.  Client and Session ID

   A client must establish a clientid (see Section 2.4) and then one or
   more sessionids (see Section 2.9) before performing any operations to
   open, lock, or delegate a file object.  The sessionid services as a
   shorthand referral to an NFSv4.1 client.

8.1.2.  State-owner and Stateid Definition

   When opening a file or requesting a byte-range lock, the client must
   specify an identifier which represents the owner of the requested
   lock.  This identifier is in the form of a state-owner, represented
   in the protocol by a state_owner4, a variable-length opaque array
   which, when concatenated with the current clientid uniquely defines
   the owner of lock managed by the client.  This may be a thread id,
   process id, or other unique value.

   Owners of opens and owners of byte-range locks are separate entities
   and remain separate even if the same opaque arrays are used to
   designate owners of each.  The protocol distinguishes between open-
   owners (represented by open_owner4 structures) and lock-owners
   (represented by lock_owner4 structures).

   Each open is associated with a specific open-owner while each byte-
   range lock is associated with a lock-owner and an open-owner, the
   latter being the open-owner associated with the open file under which
   the LOCK operation was done.  Delegations and layouts, on the other
   hand, are not associated with a specific owner but are associated the
   client as a whole.

   When the server grants a lock of any type (including opens, byte-
   range locks, delegations, and layouts) it responds with a unique
   stateid, that represents a set of locks (often a single lock) for the
   same file, of the same type, and sharing the same ownership
   characteristics.  Thus opens of the same file by different open-
   owners each have an identifying stateid.  Similarly, each set of
   byte-range locks on a file owned by a specific lock-owner and gotten
   via an open for a specific open-owner, has its own identifying
   stateid.  Delegations and layouts also have associated stateid's by



Shepler, et al.         Expires February 2, 2007              [Page 117]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   which they may be referenced.  The stateid is used as a shorthand
   reference to a lock or set of locks and given a stateid the client
   can determine the associated state-owner or state-owners (in the case
   of an open-owner/lock-owner pair) and the associated.  Clients,
   however, must not assume any such mapping and must not use a stateid
   returned for a given filehandle and state-owner in the context of a
   different filehandle or a different state-owner.

   The server is free to form the stateid in any manner that it chooses
   as long as it is able to recognize invalid and out-of-date stateids.
   Although the protocol XDR definition divides the stateid into into
   'seqid' and 'other' fields, for the purposes of minor version one,
   this distinction is not important and the server may use the
   available space as it chooses, with one exception.

   The exception is that stateids whose 'other' field is either all
   zeros or all ones are reserved and may not be generated by the
   server.  Clients may use the protocol-defined special stateid values
   for their defined purposes, but any use of stateid's in this reserved
   class that are not specially defined by the protocol MUST result in
   an NFS4ERR_BAD_STATED being returned.

   Clients may not compare stateids associated with different
   filehandles, so that a server might use stateids with the same bit
   pattern for all opens with a given open-owner or for all sets of
   byte-range locks associated with a given lock-owner/open-owner pair.
   However, if it does so, it must recognize and reject any use of
   stateid when the current filehandle is such that no lock for that
   filehandle by that open owner (or lock-owner/open-owner pair) exists.

   Stateid's must remain valid until either a client reboot or a sever
   reboot or until the client returns all of the locks associated with
   the stateid by means of an operation such as CLOSE or DELEGRETURN.
   If the locks are lost due to revocation the stateid remains usable
   until the client frees it by using FREE_STATEID.  Stateid's
   associated with byte-range locks are an exception.  They remain valid
   even if a LOCKU free all remaining locks, so long as the open file
   with which they are associated remains open, unless the client does a
   FREE_STATEID to caused the stateid to be freed.

   Because each operation using a stateid occurs as part of a session,
   each stateid is implicitly associated with the clientid assigned to
   that session.  Use of a stateid in the context of a session where the
   clientid is invalid should result in the error NFS4ERR_STALE_STATEID.
   Servers MUST NOT do any validation or return other errors in this
   case, even if they have sufficient information available to validate
   stateids associated with an out-of-date client.




Shepler, et al.         Expires February 2, 2007              [Page 118]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   One mechanism that may be used to satisfy the requirement that the
   server recognize invalid and out-of-date stateids is for the server
   to divide the stateid into two fields.  This division may coincide
   with the documented division into 'seqid' and 'other' fields or it
   may divide the stateid field up in any other ay it chooses.

   o  An index into a table of locking-state structures.

   o  A generation number which is incremented on each allocation of a
      table entry a particular allocation of a stateid.

   And then store in each table entry,

   o  The current generation number.

   o  The clientid with which the stateid is associated.

   o  The filehandle of the file on which the locks are taken.

   o  An indication of the type of stateid (open, byte-range lock, file
      delegation, directory delegation, layout).

   With this information, the following procedure would be used to
   validate an incoming stateid and return an appropriate error, when
   necessary:

   o  If the current session is associated with an invalid clientid,
      return NFS4ERR_STALE_STATEID.

   o  If the table index field is outside the range of the associated
      table, return NFS4ERR_BAD_STATEID.

   o  If the selected table entry is of a different generation than that
      specified in the incoming stateid, return NFS4ERR_BAD_STATEID.

   o  If the selected table entry does not match the current file
      handle, return NFS4ERR_BAD_STATEID.

   o  If the clientid in the table entry does not match the clientid
      associated with the current session, return NFS4ERR_BAD_STATEID.

   o  If the stateid type is not valid for the context in which the
      stateid appears, return NFS4ERR_BAD_STATEID.

   o  Otherwise, the stateid is valid and the table entry should contain
      any additional information about the associated set of locks, such
      as open-owner and lock-owner information, as well as information
      on the specific locks, such as open modes and byte ranges.



Shepler, et al.         Expires February 2, 2007              [Page 119]


Internet-Draft            NFSv4 Minor Version 1              August 2006


8.1.3.  Use of the Stateid and Locking

   All READ, WRITE and SETATTR operations contain a stateid.  For the
   purposes of this section, SETATTR operations which change the size
   attribute of a file are treated as if they are writing the area
   between the old and new size (i.e. the range truncated or added to
   the file by means of the SETATTR), even where SETATTR is not
   explicitly mentioned in the text.

   If the state-owner performs a READ or WRITE in a situation in which
   it has established a lock or share reservation on the server (any
   OPEN constitutes a share reservation) the stateid (previously
   returned by the server) must be used to indicate what locks,
   including both record locks and share reservations, are held by the
   state-owner.  If no state is established by the client, either record
   lock or share reservation, a special stateid of all bits 0 (including
   all fields of the stateid) is used.  Regardless whether a stateid of
   all bits 0, or a stateid returned by the server is used, if there is
   a conflicting share reservation or mandatory record lock held on the
   file, the server MUST refuse to service the READ or WRITE operation.

   Share reservations are established by OPEN operations and by their
   nature are mandatory in that when the OPEN denies READ or WRITE
   operations, that denial results in such operations being rejected
   with error NFS4ERR_LOCKED.  Record locks may be implemented by the
   server as either mandatory or advisory, or the choice of mandatory or
   advisory behavior may be determined by the server on the basis of the
   file being accessed (for example, some UNIX-based servers support a
   "mandatory lock bit" on the mode attribute such that if set, record
   locks are required on the file before I/O is possible).  When record
   locks are advisory, they only prevent the granting of conflicting
   lock requests and have no effect on READs or WRITEs.  Mandatory
   record locks, however, prevent conflicting I/O operations.  When they
   are attempted, they are rejected with NFS4ERR_LOCKED.  When the
   client gets NFS4ERR_LOCKED on a file it knows it has the proper share
   reservation for, it will need to issue a LOCK request on the region
   of the file that includes the region the I/O was to be performed on,
   with an appropriate locktype (i.e.  READ*_LT for a READ operation,
   WRITE*_LT for a WRITE operation).

   Note that for UNIX environments that support mandatory file locking,
   the distinction between advisory and mandatory locking is subtle.  In
   fact, advisory and mandatory record locks are exactly the same in so
   far as the APIs and requirements on implementation.  If the mandatory
   lock attribute is set on the file, the server checks to see if the
   lock-owner has an appropriate shared (read) or exclusive (write)
   record lock on the region it wishes to read or write to.  If there is
   no appropriate lock, the server checks if there is a conflicting lock



Shepler, et al.         Expires February 2, 2007              [Page 120]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   (which can be done by attempting to acquire the conflicting lock on
   the behalf of the lock-owner, and if successful, release the lock
   after the READ or WRITE is done), and if there is, the server returns
   NFS4ERR_LOCKED.

   For Windows environments, there are no advisory record locks, so the
   server always checks for record locks during I/O requests.

   Thus, the NFS version 4 LOCK operation does not need to distinguish
   between advisory and mandatory record locks.  It is the NFS version 4
   server's processing of the READ and WRITE operations that introduces
   the distinction.

   Every stateid other than the special stateid values noted in this
   section, whether returned by an OPEN-type operation (i.e.  OPEN,
   OPEN_DOWNGRADE), or by a LOCK-type operation (i.e.  LOCK or LOCKU),
   defines an access mode for the file (i.e.  READ, WRITE, or READ-
   WRITE) as established by the original OPEN which caused the
   allocation of the open stateid and as modified by subsequent OPENs
   and OPEN_DOWNGRADEs for the same open-owner/file pair.  Stateids
   returned by byte-range lock operations imply the access mode for the
   open stateid associated with the lock set represented by the stateid.
   Delegation stateids have an access mode based on the type of
   delegation.  When a READ, WRITE, or SETATTR which specifies the size
   attribute, is done, the operation is subject to checking against the
   access mode to verify that the operation is appropriate given the
   OPEN with which the operation is associated.

   In the case of WRITE-type operations (i.e.  WRITEs and SETATTRs which
   set size), the server must verify that the access mode allows writing
   and return an NFS4ERR_OPENMODE error if it does not.  In the case, of
   READ, the server may perform the corresponding check on the access
   mode, or it may choose to allow READ on opens for WRITE only, to
   accommodate clients whose write implementation may unavoidably do
   reads (e.g. due to buffer cache constraints).  However, even if READs
   are allowed in these circumstances, the server MUST still check for
   locks that conflict with the READ (e.g. another open specify denial
   of READs).  Note that a server which does enforce the access mode
   check on READs need not explicitly check for conflicting share
   reservations since the existence of OPEN for read access guarantees
   that no conflicting share reservation can exist.

   A special stateid of all bits 1 (one), including all fields in the
   stateid indicates a desire to bypass locking checks.  The server MAY
   allow READ operations to bypass locking checks at the server, when
   this special stateid is used.  However, WRITE operations with with
   this special stateid value MUST NOT bypass locking checks and are
   treated exactly the same as if a stateid of all bits 0 were used.



Shepler, et al.         Expires February 2, 2007              [Page 121]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   A lock may not be granted while a READ or WRITE operation using one
   of the special stateids is being performed and the range of the lock
   request conflicts with the range of the READ or WRITE operation.  For
   the purposes of this paragraph, a conflict occurs when a shared lock
   is requested and a WRITE operation is being performed, or an
   exclusive lock is requested and either a READ or a WRITE operation is
   being performed.  A SETATTR that sets size is treated similarly to a
   WRITE as discussed above.

8.2.  Lock Ranges

   The protocol allows a lock owner to request a lock with a byte range
   and then either upgrade, downgrade, or unlock a sub-range of the
   initial lock.  It is expected that this will be an uncommon type of
   request.  In any case, servers or server filesystems may not be able
   to support sub-range lock semantics.  In the event that a server
   receives a locking request that represents a sub-range of current
   locking state for the lock owner, the server is allowed to return the
   error NFS4ERR_LOCK_RANGE to signify that it does not support sub-
   range lock operations.  Therefore, the client should be prepared to
   receive this error and, if appropriate, report the error to the
   requesting application.

   The client is discouraged from combining multiple independent locking
   ranges that happen to be adjacent into a single request since the
   server may not support sub-range requests and for reasons related to
   the recovery of file locking state in the event of server failure.
   As discussed in the section "Server Failure and Recovery" below, the
   server may employ certain optimizations during recovery that work
   effectively only when the client's behavior during lock recovery is
   similar to the client's locking behavior prior to server failure.

8.3.  Upgrading and Downgrading Locks

   If a client has a write lock on a record, it can request an atomic
   downgrade of the lock to a read lock via the LOCK request, by setting
   the type to READ_LT.  If the server supports atomic downgrade, the
   request will succeed.  If not, it will return NFS4ERR_LOCK_NOTSUPP.
   The client should be prepared to receive this error, and if
   appropriate, report the error to the requesting application.

   If a client has a read lock on a record, it can request an atomic
   upgrade of the lock to a write lock via the LOCK request by setting
   the type to WRITE_LT or WRITEW_LT.  If the server does not support
   atomic upgrade, it will return NFS4ERR_LOCK_NOTSUPP.  If the upgrade
   can be achieved without an existing conflict, the request will
   succeed.  Otherwise, the server will return either NFS4ERR_DENIED or
   NFS4ERR_DEADLOCK.  The error NFS4ERR_DEADLOCK is returned if the



Shepler, et al.         Expires February 2, 2007              [Page 122]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   client issued the LOCK request with the type set to WRITEW_LT and the
   server has detected a deadlock.  The client should be prepared to
   receive such errors and if appropriate, report the error to the
   requesting application.

8.4.  Blocking Locks

   Some clients require the support of blocking locks.  NFSv4.1 does not
   provide a callback when a previously unavailable lock becomes
   available.  Clients thus have no choice but to continually poll for
   the lock.  This presents a fairness problem.  Two new lock types are
   added, READW and WRITEW, and are used to indicate to the server that
   the client is requesting a blocking lock.  The server should maintain
   an ordered list of pending blocking locks.  When the conflicting lock
   is released, the server may wait the lease period for the first
   waiting client to re-request the lock.  After the lease period
   expires the next waiting client request is allowed the lock.  Clients
   are required to poll at an interval sufficiently small that it is
   likely to acquire the lock in a timely manner.  The server is not
   required to maintain a list of pending blocked locks as it is used to
   increase fairness and not correct operation.  Because of the
   unordered nature of crash recovery, storing of lock state to stable
   storage would be required to guarantee ordered granting of blocking
   locks.

   Servers may also note the lock types and delay returning denial of
   the request to allow extra time for a conflicting lock to be
   released, allowing a successful return.  In this way, clients can
   avoid the burden of needlessly frequent polling for blocking locks.
   The server should take care in the length of delay in the event the
   client retransmits the request.

   If a server receives a blocking lock request, denies it, and then
   later receives a nonblocking request for the same lock, which is also
   denied, then it should remove the lock in question from its list of
   pending blocking locks.  Clients should use such a nonblocking
   request to indicate to the server that this is the last time they
   intend to poll for the lock, as may happen when the process
   requesting the lock is interrupted.  This is a courtesy to the
   server, to prevent it from unnecessarily waiting a lease period
   before granting other lock requests.  However, clients are not
   required to perform this courtesy, and servers must not depend on
   them doing so.  Also, clients must be prepared for the possibility
   that this final locking request will be accepted.







Shepler, et al.         Expires February 2, 2007              [Page 123]


Internet-Draft            NFSv4 Minor Version 1              August 2006


8.5.  Lease Renewal

   The purpose of a lease is to allow a server to remove stale locks
   that are held by a client that has crashed or is otherwise
   unreachable.  It is not a mechanism for cache consistency and lease
   renewals may not be denied if the lease interval has not expired.

   Since each session is associated with a specific client, any
   operation issued on that session is an indication that the associated
   client is reachable.  When a request is issued for a given session,
   execution of a SEQUENCE operation will result in all leases for the
   associated client to be implicitly renewed.  This approach allows for
   low overhead lease renewal which scales well.  In the typical case no
   extra RPC calls are required for lease renewal and in the worst case
   one RPC is required every lease period, via a COMPOUND that consists
   solely of a single SEQUENCE operation.  The number of locks held by
   the client is not a factor since all state for the client is involved
   with the lease renewal action.

   Since all operations that create a new lease also renew existing
   leases, the server must maintain a common lease expiration time for
   all valid leases for a given client.  This lease time can then be
   easily updated upon implicit lease renewal actions.

8.6.  Crash Recovery

   The important requirement in crash recovery is that both the client
   and the server know when the other has failed.  Additionally, it is
   required that a client sees a consistent view of data across server
   restarts or reboots.  All READ and WRITE operations that may have
   been queued within the client or network buffers must wait until the
   client has successfully recovered the locks protecting the READ and
   WRITE operations.

8.6.1.  Client Failure and Recovery

   In the event that a client fails, the server may release the client's
   locks when the associated leases have expired.  Conflicting locks
   from another client may only be granted after this lease expiration.
   When a client has not not failed and re-establishes his lease before
   expiration occurs, requests for conflicting locks will not be
   granted.

   To minimize client delay upon restart, lock requests are associated
   with an instance of the client by a client supplied verifier.  This
   verifier is part of the initial CREATE_CLIENTID call made by the
   client.  The server returns a clientid as a result of the
   CREATE_CLIENTID operation.  The client then confirms the use of the



Shepler, et al.         Expires February 2, 2007              [Page 124]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   clientid by establishing a session associated with that clientid.
   All locks, including opens, byte-range locks, delegations, and layout
   obtained by sessions using that clientid are associated with that
   clientid.

   Since the verifier will be changed by the client upon each
   initialization, the server can compare a new verifier to the verifier
   associated with currently held locks and determine that they do not
   match.  This signifies the client's new instantiation and subsequent
   loss of locking state.  As a result, the server is free to release
   all locks held which are associated with the old clientid which was
   derived from the old verifier.  At this point conflicting locks from
   other clients, kept waiting while the leaser had not yet expired, can
   be granted.

   Note that the verifier must have the same uniqueness properties of
   the verifier for the COMMIT operation.

8.6.2.  Server Failure and Recovery

   If the server loses locking state (usually as a result of a restart
   or reboot), it must allow clients time to discover this fact and re-
   establish the lost locking state.  The client must be able to re-
   establish the locking state without having the server deny valid
   requests because the server has granted conflicting access to another
   client.  Likewise, if there is a possibility that clients have not
   yet re-established their locking state for a file, the server must
   disallow READ and WRITE operations for that file.

   A client can determine that server failure (and thus loss of locking
   state) has occurred, when it receives one of two errors.  The
   NFS4ERR_STALE_STATEID error indicates a stateid invalidated by a
   reboot or restart.  The NFS4ERR_STALE_CLIENTID error indicates a
   clientid invalidated by reboot or restart.  When either of these are
   received, the client must establish a new clientid (See
   Section 8.1.1) and re-establish its locking state.

   Once a session is established using the new clientid, the client will
   use reclaim-type locking requests (i.e.  LOCK requests with reclaim
   set to true and OPEN operations with a claim type of CLAIM_PREVIOUS)
   to re-establish its locking state.  Once this is done, or if there is
   no such locking state to reclaim, the client does a RECLAIM_COMPLETE
   operation to indicate that it has reclaimed all of the locking state
   that it will reclaim.  Once a client does a RECLAIM_COMPLETE
   operation, it may attempt non-reclaim locking operations, although it
   may get NFS4ERR_GRACE errors on these until the period of special
   handling is over.




Shepler, et al.         Expires February 2, 2007              [Page 125]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   The period of special handling of locking and READs and WRITEs, is
   referred to as the "grace period".  During the grace period, clients
   recover locks and the associated state using reclaim-type locking
   requests.  During this period, the server must reject READ and WRITE
   operations and non-reclaim locking requests (i.e. other LOCK and OPEN
   operations) with an error of NFS4ERR_GRACE, unless it is able to
   guarantee that these may be done safely, as described below.

   The grace period may last until all clients who are known to possibly
   have had locks have done a RECLAIM_COMPLETE operation, indicating
   that they have finished reclaiming the locks they held before the
   server reboot.  The server is assumed to maintain in stable storage a
   list of clients who may have such locks.  The server may also
   terminate the grace period before all clients have done
   RECLAIM_COMPLETE.  The server SHOULD NOT terminate the grace period
   before a time equal to the lease period in order to give clients an
   opportunity to find out about the server reboot.  Some additional
   time in order to allow time to establish a new clientid and session
   and to effect lock reclaims may be added.

   If the server can reliably determine that granting a non-reclaim
   request will not conflict with reclamation of locks by other clients,
   the NFS4ERR_GRACE error does not have to be returned even within the
   grace period, although NFS4ERR_GRACE must always be returned to
   clients attempting a non-reclaim lock request before doing their own
   RECLAIM_COMPLETE.  For the server to be able to service READ and
   WRITE operations during the grace period, it must again be able to
   guarantee that no possible conflict could arise between a potential
   reclaim locking request and the READ or WRITE operation.  If the
   server is unable to offer that guarantee, the NFS4ERR_GRACE error
   must be returned to the client.

   For a server to provide simple, valid handling during the grace
   period, the easiest method is to simply reject all non-reclaim
   locking requests and READ and WRITE operations by returning the
   NFS4ERR_GRACE error.  However, a server may keep information about
   granted locks in stable storage.  With this information, the server
   could determine if a regular lock or READ or WRITE operation can be
   safely processed.

   For example, if the server maintained on stable storage summary
   information on whether mandatory locks exist, either mandatory byte-
   range locks, or share reservations specifying deny modes, many
   requests could be allowed during the grace period.  If it is known
   that no such share reservations exist, OPEN request that do not
   specify deny modes may be safely granted.  If, in addition, it is
   known that no mandatory byte-range locks exist, either through
   information stored on stable storage or simply because the server



Shepler, et al.         Expires February 2, 2007              [Page 126]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   does not support such locks, READ and WRITE requests may be safely
   processed during the grace period.

   To reiterate, for a server that allows non-reclaim lock and I/O
   requests to be processed during the grace period, it MUST determine
   that no lock subsequently reclaimed will be rejected and that no lock
   subsequently reclaimed would have prevented any I/O operation
   processed during the grace period.

   Clients should be prepared for the return of NFS4ERR_GRACE errors for
   non-reclaim lock and I/O requests.  In this case the client should
   employ a retry mechanism for the request.  A delay (on the order of
   several seconds) between retries should be used to avoid overwhelming
   the server.  Further discussion of the general issue is included in
   [Floyd].  The client must account for the server that is able to
   perform I/O and non-reclaim locking requests within the grace period
   as well as those that can not do so.

   A reclaim-type locking request outside the server's grace period can
   only succeed if the server can guarantee that no conflicting lock or
   I/O request has been granted since reboot or restart.

   A server may, upon restart, establish a new value for the lease
   period.  Therefore, clients should, once a new clientid is
   established, refetch the lease_time attribute and use it as the basis
   for lease renewal for the lease associated with that server.
   However, the server must establish, for this restart event, a grace
   period at least as long as the lease period for the previous server
   instantiation.  This allows the client state obtained during the
   previous server instance to be reliably re-established.

8.6.3.  Network Partitions and Recovery

   If the duration of a network partition is greater than the lease
   period provided by the server, the server will have not received a
   lease renewal from the client.  If this occurs, the server may free
   all locks held for the client, or it may allow the lock state to
   remain for a considerable period, subject to the constraint that if a
   request for a conflicting lock is made, locks associated with expired
   leases do not prevent such a conflicting lock from being granted but
   are revoked as necessary so as not to interfere with such conflicting
   requests.

   If the server chooses to delay freeing of lock state until there is a
   conflict, it may either free all of the clients locks once there is a
   conflict, or it may only revoke the minimum set of locks necessary to
   allow conflicting requests.  When it adopts the finer-grained
   approach, it must revoke all locks associated with a given stateid,



Shepler, et al.         Expires February 2, 2007              [Page 127]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   as long as it revokes a single such lock.

   When the server chooses to free all of a client's lock state, either
   immediately upon lease expiration, or a result of the first attempt
   to get a lock, all stateids held by the client will become invalid or
   stale.  Once the client is able to reach the server after such a
   network partition, the status returned by the SEQUENCE operation will
   indicate a loss of locking state.  In addition all I/O submitted by
   the client with the now invalid stateids will fail with the server
   returning the error NFS4ERR_EXPIRED.  Once the client learns of the
   loss of locking state, it will suitably notify the applications that
   held the invalidated locks.  The client should then take action to
   free invalidated stateid's, either by establishing a new client id
   using a new verifier or by doing a FREE_STATEID operation to release
   each of the invalidated stateid's.

   When the server adopts a finer-grained approach to revocation of
   locks when lease have expired, only a subset of stateids will
   normally become invalid during a network partition.  When the client
   is able to communicate with the server after such a network
   partition, the status returned by the SEQUENCE operation will
   indicate a partial loss of locking state.  In addition, operations,
   including I/O submitted by the client with the now invalid stateids
   will fail with the server returning the error NFS4ERR_EXPIRED.  Once
   the client learns of the loss of locking state, it will use the
   TEST_STATEID operation on all of its stateid's to determine which
   locks have been lost and them suitably notify the applications that
   held the invalidated locks.  The client can then release the
   invalidated locking state and acknowledge the revocation of the
   associated locks by doing a FREE_STATEID operation on each of the
   invalidated stateid's.

   When a network partition is combined with a server reboot, there are
   edge conditions that place requirements on the server in order to
   avoid silent data corruption following the server reboot.  Two of
   these edge conditions are known, and are discussed below.

   The first edge condition arises as a result of the scenarios such as
   the following:

   1.  Client A acquires a lock.

   2.  Client A and server experience mutual network partition, such
       that client A is unable to renew its lease.

   3.  Client A's lease expires, and the server releases lock.





Shepler, et al.         Expires February 2, 2007              [Page 128]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   4.  Client B acquires a lock that would have conflicted with that of
       Client A.

   5.  Client B releases its lock.

   6.  Server reboots.

   7.  Network partition between client A and server heals.

   8.  Client A connects to new server instance and finds out about
       server reboot.

   9.  Client A reclaims its lock within the server's grace period.

   Thus, at the final step, the server has erroneously granted client
   A's lock reclaim.  If client B modified the object the lock was
   protecting, client A will experience object corruption.

   The second known edge condition arises in situations such as the
   following:

   1.   Client A acquires one or more locks.

   2.   Server reboots.

   3.   Client A and server experience mutual network partition, such
        that client A is unable to reclaim all of its locks within the
        grace period.

   4.   Server's reclaim grace period ends.  Client A has either no
        locks or an incomplete set of locks known to the server.

   5.   Client B acquires a lock that would have conflicted with a lock
        of client A that was not reclaimed.

   6.   Client B releases the lock.

   7.   Server reboots a second time.

   8.   Network partition between client A and server heals.

   9.   Client A connects to new server instance and finds out about
        server reboot.

   10.  Client A reclaims its lock within the server's grace period.

   As with the first edge condition, the final step of the scenario of
   the second edge condition has the server erroneously granting client



Shepler, et al.         Expires February 2, 2007              [Page 129]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   A's lock reclaim.

   Solving the first and second edge conditions requires that the server
   either always assumes after it reboots that some edge condition
   occurs, and thus return NFS4ERR_NO_GRACE for all reclaim attempts, or
   that the server record some information in stable storage.  The
   amount of information the server records in stable storage is in
   inverse proportion to how harsh the server intends to be whenever
   edge conditions arise.  The server that is completely tolerant of all
   edge conditions will record in stable storage every lock that is
   acquired, removing the lock record from stable storage only when the
   lock is released.  For the two edge conditions discussed above, the
   harshest a server can be, and still support a grace period for
   reclaims, requires that the server record in stable storage
   information some minimal information.  For example, a server
   implementation could, for each client, save in stable storage a
   record containing:

   o  the client's id string

   o  a boolean that indicates if the client's lease expired or if there
      was administrative intervention (see Section 8.7) to revoke a
      record lock, share reservation, or delegation and there has been
      no acknowledgement (via FREE_STATEID) of such revocation.

   o  a boolean that indicates whether the client may have locks that it
      believes to be reclaimable in situations which the grace period
      was terminated, making the server's view of lock reclaimability
      suspect.  The server will set this for any client record in stable
      storage where the client has not done a RECLAIM_COMPLETE, before
      it grants any new (i.e. not reclaimed) lock to any client.

   Assuming the above record keeping, for the first edge condition,
   after the server reboots, the record that client A's lease expired
   means that another client could have acquired a conflicting record
   lock, share reservation, or delegation.  Hence the server must reject
   a reclaim from client A with the error NFS4ERR_NO_GRACE.

   For the second edge condition, after the server reboots for a second
   time, the indication that the client had not completed its reclaims
   at the time at which the grace period ended means that the server
   must reject a reclaim from client A with the error NFS4ERR_NO_GRACE.

   When either edge condition occurs, the client's attempt to reclaim
   locks will result in the error NFS4ERR_NO_GRACE.  When this is
   received, or after the client reboots with no lock state, the client
   will issue a RECLAIM_COMPLETE.  When the RECLAIM_COMPLETE is
   received, the server and client are again in agreement regarding



Shepler, et al.         Expires February 2, 2007              [Page 130]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   reclaimable locks and both booleans in persistent storage can be
   reset, to be set again only when there is a subsequent event that
   causes lock reclaim operations to be questionable.

   Regardless of the level and approach to record keeping, the server
   MUST implement one of the following strategies (which apply to
   reclaims of share reservations, record locks, and delegations):

   1.  Reject all reclaims with NFS4ERR_NO_GRACE.  This is extremely
       unforgiving, but necessary if the server does not record lock
       state in stable storage.

   2.  Record sufficient state in stable storage such that all known
       edge conditions involving server reboot, including the two noted
       in this section, are detected.  False positives are acceptable.
       Note that at this time, it is not known if there are other edge
       conditions.

       In the event that, after a server reboot, the server determines
       that there is unrecoverable damage or corruption to the
       information in stable storage, then for all clients and/or locks
       which may be affected, the server MUST return NFS4ERR_NO_GRACE.

   A mandate for the client's handling of the NFS4ERR_NO_GRACE error is
   outside the scope of this specification, since the strategies for
   such handling are very dependent on the client's operating
   environment.  However, one potential approach is described below.

   When the client receives NFS4ERR_NO_GRACE, it could examine the
   change attribute of the objects the client is trying to reclaim state
   for, and use that to determine whether to re-establish the state via
   normal OPEN or LOCK requests.  This is acceptable provided the
   client's operating environment allows it.  In other words, the client
   implementor is advised to document for his users the behavior.  The
   client could also inform the application that its record lock or
   share reservations (whether they were delegated or not) have been
   lost, such as via a UNIX signal, a GUI pop-up window, etc.  See the
   section, "Data Caching and Revocation" for a discussion of what the
   client should do for dealing with unreclaimed delegations on client
   state.

   For further discussion of revocation of locks see Section 8.7.

8.7.  Server Revocation of Locks

   At any point, the server can revoke locks held by a client and the
   client must be prepared for this event.  When the client detects that
   its locks have been or may have been revoked, the client is



Shepler, et al.         Expires February 2, 2007              [Page 131]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   responsible for validating the state information between itself and
   the server.  Validating locking state for the client means that it
   must verify or reclaim state for each lock currently held.

   The first occasion of lock revocation is upon server reboot or re-
   initialization.  In this instance the client will receive an error
   (NFS4ERR_STALE_STATEID or NFS4ERR_STALE_CLIENTID) and the client will
   proceed with normal crash recovery as described in the previous
   section.

   The second occasion of lock revocation is the inability to renew the
   lease before expiration, as discussed above.  While this is
   considered a rare or unusual event, the client must be prepared to
   recover.  The server is responsible for determining lease expiration,
   and deciding exactly how to deal with it, informing the client of the
   scope of the lock revocation.  The client then uses the status
   information provided by the server to synchronize his locking state
   with that of the server, in order to recover.

   The third occasion of lock revocation can occur as a result of
   revocation of locks within the lease period, either because of
   administrative intervention, or because a recallable lock (a
   delegation or layout) was not returned within the lease period after
   having been recalled.  While these are considered rare events, they
   are possible and the client must be prepared to deal with them.  When
   either of these events occur, the client finds out about the
   situation through the status returned by the SEQUENCE operation.  Any
   use of stateids associated with revoked locks will receive the error
   NFS4ERR_ADMIN_REVOKED or NFS4ERR_DELEG_REVOKED, as appropriate.

   In all situations in which a subset of locking state may have been
   revoked, which include all cases in which locking state is revoked
   within the lease period, it is up to the client to determine which
   locks have been revoked and which have not.  It does this by using
   the TEST_STATEID operation on the appropriate set of stateid's.  Once
   the set of revoked locks has been determined, the applications can be
   notified, and the invalidated stateid's can be freed and lock
   revocation acknowledged by using FREE_STATEID.

8.8.  Share Reservations

   A share reservation is a mechanism to control access to a file.  It
   is a separate and independent mechanism from record locking.  When a
   client opens a file, it issues an OPEN operation to the server
   specifying the type of access required (READ, WRITE, or BOTH) and the
   type of access to deny others (deny NONE, READ, WRITE, or BOTH).  If
   the OPEN fails the client will fail the application's open request.




Shepler, et al.         Expires February 2, 2007              [Page 132]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   Pseudo-code definition of the semantics:

           if (request.access == 0)
           return (NFS4ERR_INVAL)
           else
           if ((request.access & file_state.deny)) ||
           (request.deny & file_state.access))
           return (NFS4ERR_DENIED)

   This checking of share reservations on OPEN is done with no exception
   for an existing OPEN for the same open-owner.

   The constants used for the OPEN and OPEN_DOWNGRADE operations for the
   access and deny fields are as follows:

           const OPEN4_SHARE_ACCESS_READ   = 0x00000001;
           const OPEN4_SHARE_ACCESS_WRITE  = 0x00000002;
           const OPEN4_SHARE_ACCESS_BOTH   = 0x00000003;

           const OPEN4_SHARE_DENY_NONE     = 0x00000000;
           const OPEN4_SHARE_DENY_READ     = 0x00000001;
           const OPEN4_SHARE_DENY_WRITE    = 0x00000002;
           const OPEN4_SHARE_DENY_BOTH     = 0x00000003;

8.9.  OPEN/CLOSE Operations

   To provide correct share semantics, a client MUST use the OPEN
   operation to obtain the initial filehandle and indicate the desired
   access and what if any access to deny.  Even if the client intends to
   use a stateid of all 0's or all 1's, it must still obtain the
   filehandle for the regular file with the OPEN operation so the
   appropriate share semantics can be applied.  For clients that do not
   have a deny mode built into their open programming interfaces, deny
   equal to NONE should be used.

   The OPEN operation with the CREATE flag, also subsumes the CREATE
   operation for regular files as used in previous versions of the NFS
   protocol.  This allows a create with a share to be done atomically.

   The CLOSE operation removes all share reservations held by the open-
   owner on that file.  If record locks are held, the client SHOULD
   release all locks before issuing a CLOSE.  The server MAY free all
   outstanding locks on CLOSE but some servers may not support the CLOSE
   of a file that still has record locks held.  The server MUST return
   failure, NFS4ERR_LOCKS_HELD, if any locks would exist after the
   CLOSE.

   The LOOKUP operation will return a filehandle without establishing



Shepler, et al.         Expires February 2, 2007              [Page 133]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   any lock state on the server.  Without a valid stateid, the server
   will assume the client has the least access.  For example, a file
   opened with deny READ/WRITE cannot be accessed using a filehandle
   obtained through LOOKUP because it would not have a valid stateid
   (i.e. using a stateid of all bits 0 or all bits 1).

8.10.  Open Upgrade and Downgrade

   When an OPEN is done for a file and the open-owner for which the open
   is being done already has the file open, the result is to upgrade the
   open file status maintained on the server to include the access and
   deny bits specified by the new OPEN as well as those for the existing
   OPEN.  The result is that there is one open file, as far as the
   protocol is concerned, and it includes the union of the access and
   deny bits for all of the OPEN requests completed.  Only a single
   CLOSE will be done to reset the effects of both OPENs.  Note that the
   client, when issuing the OPEN, may not know that the same file is in
   fact being opened.  The above only applies if both OPENs result in
   the OPENed object being designated by the same filehandle.

   When the server chooses to export multiple filehandles corresponding
   to the same file object and returns different filehandles on two
   different OPENs of the same file object, the server MUST NOT "OR"
   together the access and deny bits and coalesce the two open files.
   Instead the server must maintain separate OPENs with separate
   stateids and will require separate CLOSEs to free them.

   When multiple open files on the client are merged into a single open
   file object on the server, the close of one of the open files (on the
   client) may necessitate change of the access and deny status of the
   open file on the server.  This is because the union of the access and
   deny bits for the remaining opens may be smaller (i.e. a proper
   subset) than previously.  The OPEN_DOWNGRADE operation is used to
   make the necessary change and the client should use it to update the
   server so that share reservation requests by other clients are
   handled properly.

8.11.  Short and Long Leases

   When determining the time period for the server lease, the usual
   lease tradeoffs apply.  Short leases are good for fast server
   recovery at a cost of increased operations to effect lease renewal
   (when there are no other operations during the period to effect lease
   renewal as a side-effect).  Long leases are certainly kinder and
   gentler to servers trying to handle very large numbers of clients.
   The number of extra requests to effect lock renewal drop in inverse
   proportion to the lease time.  The disadvantages of long leases
   include the possibility of slower recovery after certain failures.



Shepler, et al.         Expires February 2, 2007              [Page 134]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   After server failure, a longer grace period may be required when some
   clients do not promptly reclaim their locks and do a
   RECLAIM_COMPLETE.  In the event of client failure, it can longer
   period for leases to expire thus forcing conflicting requests to
   wait.

   Long leases are usable if the server is able to store lease state in
   non-volatile memory.  Upon recovery, the server can reconstruct the
   lease state from its non-volatile memory and continue operation with
   its clients and therefore long leases would not be an issue.

8.12.  Clocks, Propagation Delay, and Calculating Lease Expiration

   To avoid the need for synchronized clocks, lease times are granted by
   the server as a time delta.  However, there is a requirement that the
   client and server clocks do not drift excessively over the duration
   of the lock.  There is also the issue of propagation delay across the
   network which could easily be several hundred milliseconds as well as
   the possibility that requests will be lost and need to be
   retransmitted.

   To take propagation delay into account, the client should subtract it
   from lease times (e.g. if the client estimates the one-way
   propagation delay as 200 msec, then it can assume that the lease is
   already 200 msec old when it gets it).  In addition, it will take
   another 200 msec to get a response back to the server.  So the client
   must send a lock renewal or write data back to the server 400 msec
   before the lease would expire.

   The server's lease period configuration should take into account the
   network distance of the clients that will be accessing the server's
   resources.  It is expected that the lease period will take into
   account the network propagation delays and other network delay
   factors for the client population.  Since the protocol does not allow
   for an automatic method to determine an appropriate lease period, the
   server's administrator may have to tune the lease period.

8.13.  Vestigial Locking Infrastructure From V4.0

   There are a number of operations and fields within existing
   operations that no longer have a function in minor version one.  In
   one way or another, these changes are all due to the implementation
   of sessions which provides client context and replay protection as a
   base feature of the protocol, separate from locking itself.

   The following operations have become mandatory-to-not-implement.  The
   server should return NFS4ERR_NOTSUPP if these operations are found in
   an NFSv4.1 COMPOUND.



Shepler, et al.         Expires February 2, 2007              [Page 135]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   o  SETCLIENTID since its function has been replaced by
      CREATE_CLIENTID.

   o  SETCLIENTID_CONFIRM since clientid confirmation now happens by
      means of CREATE_SESSION.

   o  OPEN_CONFIRM because OPEN's no longer require confirmation to
      establish an owner-based sequence value.

   o  RELEASE_LOCKOWNER because lock-owners with no associated locks
      have any sequence-related state and so can be deleted by the
      server at will.

   o  RENEW because every SEQUENCE operation for a session causes lease
      renewal, making a separate operation useless.

   Also, there are a number of fields, present in existing operations
   related to locking that have no use in minor version one.  They were
   used in minor version zero to perform functions now provided in a
   different fashion.

   o  Sequence id's used to sequence requests for a given state-owner
      and to provide replay protection, now provided via sessions.

   o  Clientid's used to identify the client associated with a given
      request.  Client identification is now available using the
      clientid associated with the current session, without needing an
      explicit clientid field.

   Such vestigial fields in existing operations should be set by the
   client to zero.  When they are not, the server MUST return an
   NFS4ERR_INVAL error.


9.  Client-Side Caching

   Client-side caching of data, of file attributes, and of file names is
   essential to providing good performance with the NFS protocol.
   Providing distributed cache coherence is a difficult problem and
   previous versions of the NFS protocol have not attempted it.
   Instead, several NFS client implementation techniques have been used
   to reduce the problems that a lack of coherence poses for users.
   These techniques have not been clearly defined by earlier protocol
   specifications and it is often unclear what is valid or invalid
   client behavior.

   The NFS version 4 protocol uses many techniques similar to those that
   have been used in previous protocol versions.  The NFS version 4



Shepler, et al.         Expires February 2, 2007              [Page 136]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   protocol does not provide distributed cache coherence.  However, it
   defines a more limited set of caching guarantees to allow locks and
   share reservations to be used without destructive interference from
   client side caching.

   In addition, the NFS version 4 protocol introduces a delegation
   mechanism which allows many decisions normally made by the server to
   be made locally by clients.  This mechanism provides efficient
   support of the common cases where sharing is infrequent or where
   sharing is read-only.

9.1.  Performance Challenges for Client-Side Caching

   Caching techniques used in previous versions of the NFS protocol have
   been successful in providing good performance.  However, several
   scalability challenges can arise when those techniques are used with
   very large numbers of clients.  This is particularly true when
   clients are geographically distributed which classically increases
   the latency for cache revalidation requests.

   The previous versions of the NFS protocol repeat their file data
   cache validation requests at the time the file is opened.  This
   behavior can have serious performance drawbacks.  A common case is
   one in which a file is only accessed by a single client.  Therefore,
   sharing is infrequent.

   In this case, repeated reference to the server to find that no
   conflicts exist is expensive.  A better option with regards to
   performance is to allow a client that repeatedly opens a file to do
   so without reference to the server.  This is done until potentially
   conflicting operations from another client actually occur.

   A similar situation arises in connection with file locking.  Sending
   file lock and unlock requests to the server as well as the read and
   write requests necessary to make data caching consistent with the
   locking semantics (see the section "Data Caching and File Locking")
   can severely limit performance.  When locking is used to provide
   protection against infrequent conflicts, a large penalty is incurred.
   This penalty may discourage the use of file locking by applications.

   The NFS version 4 protocol provides more aggressive caching
   strategies with the following design goals:

   .IP o Compatibility with a large range of server semantics. .IP o
   Provide the same caching benefits as previous versions of the NFS
   protocol when unable to provide the more aggressive model. .IP o
   Requirements for aggressive caching are organized so that a large
   portion of the benefit can be obtained even when not all of the



Shepler, et al.         Expires February 2, 2007              [Page 137]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   requirements can be met. .LP The appropriate requirements for the
   server are discussed in later sections in which specific forms of
   caching are covered. (see the section "Open Delegation").

9.2.  Delegation and Callbacks

   Recallable delegation of server responsibilities for a file to a
   client improves performance by avoiding repeated requests to the
   server in the absence of inter-client conflict.  With the use of a
   "callback" RPC from server to client, a server recalls delegated
   responsibilities when another client engages in sharing of a
   delegated file.

   A delegation is passed from the server to the client, specifying the
   object of the delegation and the type of delegation.  There are
   different types of delegations but each type contains a stateid to be
   used to represent the delegation when performing operations that
   depend on the delegation.  This stateid is similar to those
   associated with locks and share reservations but differs in that the
   stateid for a delegation is associated with a clientid and may be
   used on behalf of all the open_owners for the given client.  A
   delegation is made to the client as a whole and not to any specific
   process or thread of control within it.

   Because callback RPCs may not work in all environments (due to
   firewalls, for example), correct protocol operation does not depend
   on them.  Preliminary testing of callback functionality by means of a
   CB_NULL procedure determines whether callbacks can be supported.  The
   CB_NULL procedure checks the continuity of the callback path.  A
   server makes a preliminary assessment of callback availability to a
   given client and avoids delegating responsibilities until it has
   determined that callbacks are supported.  Because the granting of a
   delegation is always conditional upon the absence of conflicting
   access, clients must not assume that a delegation will be granted and
   they must always be prepared for OPENs to be processed without any
   delegations being granted.

   Once granted, a delegation behaves in most ways like a lock.  There
   is an associated lease that is subject to renewal together with all
   of the other leases held by that client.

   Unlike locks, an operation by a second client to a delegated file
   will cause the server to recall a delegation through a callback.

   On recall, the client holding the delegation must flush modified
   state (such as modified data) to the server and return the
   delegation.  The conflicting request will not receive a response
   until the recall is complete.  The recall is considered complete when



Shepler, et al.         Expires February 2, 2007              [Page 138]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   the client returns the delegation or the server times out on the
   recall and revokes the delegation as a result of the timeout.
   Following the resolution of the recall, the server has the
   information necessary to grant or deny the second client's request.

   At the time the client receives a delegation recall, it may have
   substantial state that needs to be flushed to the server.  Therefore,
   the server should allow sufficient time for the delegation to be
   returned since it may involve numerous RPCs to the server.  If the
   server is able to determine that the client is diligently flushing
   state to the server as a result of the recall, the server may extend
   the usual time allowed for a recall.  However, the time allowed for
   recall completion should not be unbounded.

   An example of this is when responsibility to mediate opens on a given
   file is delegated to a client (see the section "Open Delegation").
   The server will not know what opens are in effect on the client.
   Without this knowledge the server will be unable to determine if the
   access and deny state for the file allows any particular open until
   the delegation for the file has been returned.

   A client failure or a network partition can result in failure to
   respond to a recall callback.  In this case, the server will revoke
   the delegation which in turn will render useless any modified state
   still on the client.

9.2.1.  Delegation Recovery

   There are three situations that delegation recovery must deal with:

   o  Client reboot or restart

   o  Server reboot or restart

   o  Network partition (full or callback-only)

   In the event the client reboots or restarts, the failure to renew
   leases will result in the revocation of record locks and share
   reservations.  Delegations, however, may be treated a bit
   differently.

   There will be situations in which delegations will need to be
   reestablished after a client reboots or restarts.  The reason for
   this is the client may have file data stored locally and this data
   was associated with the previously held delegations.  The client will
   need to reestablish the appropriate file state on the server.

   To allow for this type of client recovery, the server MAY extend the



Shepler, et al.         Expires February 2, 2007              [Page 139]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   period for delegation recovery beyond the typical lease expiration
   period.  This implies that requests from other clients that conflict
   with these delegations will need to wait.  Because the normal recall
   process may require significant time for the client to flush changed
   state to the server, other clients need be prepared for delays that
   occur because of a conflicting delegation.  This longer interval
   would increase the window for clients to reboot and consult stable
   storage so that the delegations can be reclaimed.  For open
   delegations, such delegations are reclaimed using OPEN with a claim
   type of CLAIM_DELEGATE_PREV.  (See the sections on "Data Caching and
   Revocation" and "Operation 18: OPEN" for discussion of open
   delegation and the details of OPEN respectively).

   A server MAY support a claim type of CLAIM_DELEGATE_PREV, but if it
   does, it MUST NOT remove delegations upon SETCLIENTID_CONFIRM, and
   instead MUST, for a period of time no less than that of the value of
   the lease_time attribute, maintain the client's delegations to allow
   time for the client to issue CLAIM_DELEGATE_PREV requests.  The
   server that supports CLAIM_DELEGATE_PREV MUST support the DELEGPURGE
   operation.

   When the server reboots or restarts, delegations are reclaimed (using
   the OPEN operation with CLAIM_PREVIOUS) in a similar fashion to
   record locks and share reservations.  However, there is a slight
   semantic difference.  In the normal case if the server decides that a
   delegation should not be granted, it performs the requested action
   (e.g.  OPEN) without granting any delegation.  For reclaim, the
   server grants the delegation but a special designation is applied so
   that the client treats the delegation as having been granted but
   recalled by the server.  Because of this, the client has the duty to
   write all modified state to the server and then return the
   delegation.  This process of handling delegation reclaim reconciles
   three principles of the NFS version 4 protocol:

   o  Upon reclaim, a client reporting resources assigned to it by an
      earlier server instance must be granted those resources.

   o  The server has unquestionable authority to determine whether
      delegations are to be granted and, once granted, whether they are
      to be continued.

   o  The use of callbacks is not to be depended upon until the client
      has proven its ability to receive them.

   When a network partition occurs, delegations are subject to freeing
   by the server when the lease renewal period expires.  This is similar
   to the behavior for locks and share reservations.  For delegations,
   however, the server may extend the period in which conflicting



Shepler, et al.         Expires February 2, 2007              [Page 140]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   requests are held off.  Eventually the occurrence of a conflicting
   request from another client will cause revocation of the delegation.
   A loss of the callback path (e.g. by later network configuration
   change) will have the same effect.  A recall request will fail and
   revocation of the delegation will result.

   A client normally finds out about revocation of a delegation when it
   uses a stateid associated with a delegation and receives the error
   NFS4ERR_EXPIRED.  It also may find out about delegation revocation
   after a client reboot when it attempts to reclaim a delegation and
   receives that same error.  Note that in the case of a revoked write
   open delegation, there are issues because data may have been modified
   by the client whose delegation is revoked and separately by other
   clients.  See the section "Revocation Recovery for Write Open
   Delegation" for a discussion of such issues.  Note also that when
   delegations are revoked, information about the revoked delegation
   will be written by the server to stable storage (as described in the
   section "Crash Recovery").  This is done to deal with the case in
   which a server reboots after revoking a delegation but before the
   client holding the revoked delegation is notified about the
   revocation.

9.3.  Data Caching

   When applications share access to a set of files, they need to be
   implemented so as to take account of the possibility of conflicting
   access by another application.  This is true whether the applications
   in question execute on different clients or reside on the same
   client.

   Share reservations and record locks are the facilities the NFS
   version 4 protocol provides to allow applications to coordinate
   access by providing mutual exclusion facilities.  The NFS version 4
   protocol's data caching must be implemented such that it does not
   invalidate the assumptions that those using these facilities depend
   upon.

9.3.1.  Data Caching and OPENs

   In order to avoid invalidating the sharing assumptions that
   applications rely on, NFS version 4 clients should not provide cached
   data to applications or modify it on behalf of an application when it
   would not be valid to obtain or modify that same data via a READ or
   WRITE operation.

   Furthermore, in the absence of open delegation (see the section "Open
   Delegation") two additional rules apply.  Note that these rules are
   obeyed in practice by many NFS version 2 and version 3 clients.



Shepler, et al.         Expires February 2, 2007              [Page 141]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   o  First, cached data present on a client must be revalidated after
      doing an OPEN.  Revalidating means that the client fetches the
      change attribute from the server, compares it with the cached
      change attribute, and if different, declares the cached data (as
      well as the cached attributes) as invalid.  This is to ensure that
      the data for the OPENed file is still correctly reflected in the
      client's cache.  This validation must be done at least when the
      client's OPEN operation includes DENY=WRITE or BOTH thus
      terminating a period in which other clients may have had the
      opportunity to open the file with WRITE access.  Clients may
      choose to do the revalidation more often (i.e. at OPENs specifying
      DENY=NONE) to parallel the NFS version 3 protocol's practice for
      the benefit of users assuming this degree of cache revalidation.

      Since the change attribute is updated for data and metadata
      modifications, some client implementors may be tempted to use the
      time_modify attribute and not change to validate cached data, so
      that metadata changes do not spuriously invalidate clean data.
      The implementor is cautioned in this approach.  The change
      attribute is guaranteed to change for each update to the file,
      whereas time_modify is guaranteed to change only at the
      granularity of the time_delta attribute.  Use by the client's data
      cache validation logic of time_modify and not change runs the risk
      of the client incorrectly marking stale data as valid.

   o  Second, modified data must be flushed to the server before closing
      a file OPENed for write.  This is complementary to the first rule.
      If the data is not flushed at CLOSE, the revalidation done after
      client OPENs as file is unable to achieve its purpose.  The other
      aspect to flushing the data before close is that the data must be
      committed to stable storage, at the server, before the CLOSE
      operation is requested by the client.  In the case of a server
      reboot or restart and a CLOSEd file, it may not be possible to
      retransmit the data to be written to the file.  Hence, this
      requirement.

9.3.2.  Data Caching and File Locking

   For those applications that choose to use file locking instead of
   share reservations to exclude inconsistent file access, there is an
   analogous set of constraints that apply to client side data caching.
   These rules are effective only if the file locking is used in a way
   that matches in an equivalent way the actual READ and WRITE
   operations executed.  This is as opposed to file locking that is
   based on pure convention.  For example, it is possible to manipulate
   a two-megabyte file by dividing the file into two one-megabyte
   regions and protecting access to the two regions by file locks on
   bytes zero and one.  A lock for write on byte zero of the file would



Shepler, et al.         Expires February 2, 2007              [Page 142]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   represent the right to do READ and WRITE operations on the first
   region.  A lock for write on byte one of the file would represent the
   right to do READ and WRITE operations on the second region.  As long
   as all applications manipulating the file obey this convention, they
   will work on a local file system.  However, they may not work with
   the NFS version 4 protocol unless clients refrain from data caching.

   The rules for data caching in the file locking environment are:

   o  First, when a client obtains a file lock for a particular region,
      the data cache corresponding to that region (if any cache data
      exists) must be revalidated.  If the change attribute indicates
      that the file may have been updated since the cached data was
      obtained, the client must flush or invalidate the cached data for
      the newly locked region.  A client might choose to invalidate all
      of non-modified cached data that it has for the file but the only
      requirement for correct operation is to invalidate all of the data
      in the newly locked region.

   o  Second, before releasing a write lock for a region, all modified
      data for that region must be flushed to the server.  The modified
      data must also be written to stable storage.

   Note that flushing data to the server and the invalidation of cached
   data must reflect the actual byte ranges locked or unlocked.
   Rounding these up or down to reflect client cache block boundaries
   will cause problems if not carefully done.  For example, writing a
   modified block when only half of that block is within an area being
   unlocked may cause invalid modification to the region outside the
   unlocked area.  This, in turn, may be part of a region locked by
   another client.  Clients can avoid this situation by synchronously
   performing portions of write operations that overlap that portion
   (initial or final) that is not a full block.  Similarly, invalidating
   a locked area which is not an integral number of full buffer blocks
   would require the client to read one or two partial blocks from the
   server if the revalidation procedure shows that the data which the
   client possesses may not be valid.

   The data that is written to the server as a prerequisite to the
   unlocking of a region must be written, at the server, to stable
   storage.  The client may accomplish this either with synchronous
   writes or by following asynchronous writes with a COMMIT operation.
   This is required because retransmission of the modified data after a
   server reboot might conflict with a lock held by another client.

   A client implementation may choose to accommodate applications which
   use record locking in non-standard ways (e.g. using a record lock as
   a global semaphore) by flushing to the server more data upon an LOCKU



Shepler, et al.         Expires February 2, 2007              [Page 143]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   than is covered by the locked range.  This may include modified data
   within files other than the one for which the unlocks are being done.
   In such cases, the client must not interfere with applications whose
   READs and WRITEs are being done only within the bounds of record
   locks which the application holds.  For example, an application locks
   a single byte of a file and proceeds to write that single byte.  A
   client that chose to handle a LOCKU by flushing all modified data to
   the server could validly write that single byte in response to an
   unrelated unlock.  However, it would not be valid to write the entire
   block in which that single written byte was located since it includes
   an area that is not locked and might be locked by another client.
   Client implementations can avoid this problem by dividing files with
   modified data into those for which all modifications are done to
   areas covered by an appropriate record lock and those for which there
   are modifications not covered by a record lock.  Any writes done for
   the former class of files must not include areas not locked and thus
   not modified on the client.

9.3.3.  Data Caching and Mandatory File Locking

   Client side data caching needs to respect mandatory file locking when
   it is in effect.  The presence of mandatory file locking for a given
   file is indicated when the client gets back NFS4ERR_LOCKED from a
   READ or WRITE on a file it has an appropriate share reservation for.
   When mandatory locking is in effect for a file, the client must check
   for an appropriate file lock for data being read or written.  If a
   lock exists for the range being read or written, the client may
   satisfy the request using the client's validated cache.  If an
   appropriate file lock is not held for the range of the read or write,
   the read or write request must not be satisfied by the client's cache
   and the request must be sent to the server for processing.  When a
   read or write request partially overlaps a locked region, the request
   should be subdivided into multiple pieces with each region (locked or
   not) treated appropriately.

9.3.4.  Data Caching and File Identity

   When clients cache data, the file data needs to be organized
   according to the file system object to which the data belongs.  For
   NFS version 3 clients, the typical practice has been to assume for
   the purpose of caching that distinct filehandles represent distinct
   file system objects.  The client then has the choice to organize and
   maintain the data cache on this basis.

   In the NFS version 4 protocol, there is now the possibility to have
   significant deviations from a "one filehandle per object" model
   because a filehandle may be constructed on the basis of the object's
   pathname.  Therefore, clients need a reliable method to determine if



Shepler, et al.         Expires February 2, 2007              [Page 144]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   two filehandles designate the same file system object.  If clients
   were simply to assume that all distinct filehandles denote distinct
   objects and proceed to do data caching on this basis, caching
   inconsistencies would arise between the distinct client side objects
   which mapped to the same server side object.

   By providing a method to differentiate filehandles, the NFS version 4
   protocol alleviates a potential functional regression in comparison
   with the NFS version 3 protocol.  Without this method, caching
   inconsistencies within the same client could occur and this has not
   been present in previous versions of the NFS protocol.  Note that it
   is possible to have such inconsistencies with applications executing
   on multiple clients but that is not the issue being addressed here.

   For the purposes of data caching, the following steps allow an NFS
   version 4 client to determine whether two distinct filehandles denote
   the same server side object:

   o  If GETATTR directed to two filehandles returns different values of
      the fsid attribute, then the filehandles represent distinct
      objects.

   o  If GETATTR for any file with an fsid that matches the fsid of the
      two filehandles in question returns a unique_handles attribute
      with a value of TRUE, then the two objects are distinct.

   o  If GETATTR directed to the two filehandles does not return the
      fileid attribute for both of the handles, then it cannot be
      determined whether the two objects are the same.  Therefore,
      operations which depend on that knowledge (e.g. client side data
      caching) cannot be done reliably.

   o  If GETATTR directed to the two filehandles returns different
      values for the fileid attribute, then they are distinct objects.

   o  Otherwise they are the same object.

9.4.  Open Delegation

   When a file is being OPENed, the server may delegate further handling
   of opens and closes for that file to the opening client.  Any such
   delegation is recallable, since the circumstances that allowed for
   the delegation are subject to change.  In particular, the server may
   receive a conflicting OPEN from another client, the server must
   recall the delegation before deciding whether the OPEN from the other
   client may be granted.  Making a delegation is up to the server and
   clients should not assume that any particular OPEN either will or
   will not result in an open delegation.  The following is a typical



Shepler, et al.         Expires February 2, 2007              [Page 145]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   set of conditions that servers might use in deciding whether OPEN
   should be delegated:

   o  The client must be able to respond to the server's callback
      requests.  The server will use the CB_NULL procedure for a test of
      callback ability.

   o  The client must have responded properly to previous recalls.

   o  There must be no current open conflicting with the requested
      delegation.

   o  There should be no current delegation that conflicts with the
      delegation being requested.

   o  The probability of future conflicting open requests should be low
      based on the recent history of the file.

   o  The existence of any server-specific semantics of OPEN/CLOSE that
      would make the required handling incompatible with the prescribed
      handling that the delegated client would apply (see below).

   There are two types of open delegations, read and write.  A read open
   delegation allows a client to handle, on its own, requests to open a
   file for reading that do not deny read access to others.  Multiple
   read open delegations may be outstanding simultaneously and do not
   conflict.  A write open delegation allows the client to handle, on
   its own, all opens.  Only one write open delegation may exist for a
   given file at a given time and it is inconsistent with any read open
   delegations.

   When a client has a read open delegation, it may not make any changes
   to the contents or attributes of the file but it is assured that no
   other client may do so.  When a client has a write open delegation,
   it may modify the file data since no other client will be accessing
   the file's data.  The client holding a write delegation may only
   affect file attributes which are intimately connected with the file
   data: size, time_modify, change.

   When a client has an open delegation, it does not send OPENs or
   CLOSEs to the server but updates the appropriate status internally.
   For a read open delegation, opens that cannot be handled locally
   (opens for write or that deny read access) must be sent to the
   server.

   When an open delegation is made, the response to the OPEN contains an
   open delegation structure which specifies the following:




Shepler, et al.         Expires February 2, 2007              [Page 146]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   o  the type of delegation (read or write)

   o  space limitation information to control flushing of data on close
      (write open delegation only, see the section "Open Delegation and
      Data Caching")

   o  an nfsace4 specifying read and write permissions

   o  a stateid to represent the delegation for READ and WRITE

   The delegation stateid is separate and distinct from the stateid for
   the OPEN proper.  The standard stateid, unlike the delegation
   stateid, is associated with a particular lock_owner and will continue
   to be valid after the delegation is recalled and the file remains
   open.

   When a request internal to the client is made to open a file and open
   delegation is in effect, it will be accepted or rejected solely on
   the basis of the following conditions.  Any requirement for other
   checks to be made by the delegate should result in open delegation
   being denied so that the checks can be made by the server itself.

   o  The access and deny bits for the request and the file as described
      in the section "Share Reservations".

   o  The read and write permissions as determined below.

   The nfsace4 passed with delegation can be used to avoid frequent
   ACCESS calls.  The permission check should be as follows:

   o  If the nfsace4 indicates that the open may be done, then it should
      be granted without reference to the server.

   o  If the nfsace4 indicates that the open may not be done, then an
      ACCESS request must be sent to the server to obtain the definitive
      answer.

   The server may return an nfsace4 that is more restrictive than the
   actual ACL of the file.  This includes an nfsace4 that specifies
   denial of all access.  Note that some common practices such as
   mapping the traditional user "root" to the user "nobody" may make it
   incorrect to return the actual ACL of the file in the delegation
   response.

   The use of delegation together with various other forms of caching
   creates the possibility that no server authentication will ever be
   performed for a given user since all of the user's requests might be
   satisfied locally.  Where the client is depending on the server for



Shepler, et al.         Expires February 2, 2007              [Page 147]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   authentication, the client should be sure authentication occurs for
   each user by use of the ACCESS operation.  This should be the case
   even if an ACCESS operation would not be required otherwise.  As
   mentioned before, the server may enforce frequent authentication by
   returning an nfsace4 denying all access with every open delegation.

9.4.1.  Open Delegation and Data Caching

   OPEN delegation allows much of the message overhead associated with
   the opening and closing files to be eliminated.  An open when an open
   delegation is in effect does not require that a validation message be
   sent to the server.  The continued endurance of the "read open
   delegation" provides a guarantee that no OPEN for write and thus no
   write has occurred.  Similarly, when closing a file opened for write
   and if write open delegation is in effect, the data written does not
   have to be flushed to the server until the open delegation is
   recalled.  The continued endurance of the open delegation provides a
   guarantee that no open and thus no read or write has been done by
   another client.

   For the purposes of open delegation, READs and WRITEs done without an
   OPEN are treated as the functional equivalents of a corresponding
   type of OPEN.  This refers to the READs and WRITEs that use the
   special stateids consisting of all zero bits or all one bits.
   Therefore, READs or WRITEs with a special stateid done by another
   client will force the server to recall a write open delegation.  A
   WRITE with a special stateid done by another client will force a
   recall of read open delegations.

   With delegations, a client is able to avoid writing data to the
   server when the CLOSE of a file is serviced.  The file close system
   call is the usual point at which the client is notified of a lack of
   stable storage for the modified file data generated by the
   application.  At the close, file data is written to the server and
   through normal accounting the server is able to determine if the
   available file system space for the data has been exceeded (i.e.
   server returns NFS4ERR_NOSPC or NFS4ERR_DQUOT).  This accounting
   includes quotas.  The introduction of delegations requires that a
   alternative method be in place for the same type of communication to
   occur between client and server.

   In the delegation response, the server provides either the limit of
   the size of the file or the number of modified blocks and associated
   block size.  The server must ensure that the client will be able to
   flush data to the server of a size equal to that provided in the
   original delegation.  The server must make this assurance for all
   outstanding delegations.  Therefore, the server must be careful in
   its management of available space for new or modified data taking



Shepler, et al.         Expires February 2, 2007              [Page 148]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   into account available file system space and any applicable quotas.
   The server can recall delegations as a result of managing the
   available file system space.  The client should abide by the server's
   state space limits for delegations.  If the client exceeds the stated
   limits for the delegation, the server's behavior is undefined.

   Based on server conditions, quotas or available file system space,
   the server may grant write open delegations with very restrictive
   space limitations.  The limitations may be defined in a way that will
   always force modified data to be flushed to the server on close.

   With respect to authentication, flushing modified data to the server
   after a CLOSE has occurred may be problematic.  For example, the user
   of the application may have logged off the client and unexpired
   authentication credentials may not be present.  In this case, the
   client may need to take special care to ensure that local unexpired
   credentials will in fact be available.  This may be accomplished by
   tracking the expiration time of credentials and flushing data well in
   advance of their expiration or by making private copies of
   credentials to assure their availability when needed.

9.4.2.  Open Delegation and File Locks

   When a client holds a write open delegation, lock operations are
   performed locally.  This includes those required for mandatory file
   locking.  This can be done since the delegation implies that there
   can be no conflicting locks.  Similarly, all of the revalidations
   that would normally be associated with obtaining locks and the
   flushing of data associated with the releasing of locks need not be
   done.

   When a client holds a read open delegation, lock operations are not
   performed locally.  All lock operations, including those requesting
   non-exclusive locks, are sent to the server for resolution.

9.4.3.  Handling of CB_GETATTR

   The server needs to employ special handling for a GETATTR where the
   target is a file that has a write open delegation in effect.  The
   reason for this is that the client holding the write delegation may
   have modified the data and the server needs to reflect this change to
   the second client that submitted the GETATTR.  Therefore, the client
   holding the write delegation needs to be interrogated.  The server
   will use the CB_GETATTR operation.  The only attributes that the
   server can reliably query via CB_GETATTR are size and change.

   Since CB_GETATTR is being used to satisfy another client's GETATTR
   request, the server only needs to know if the client holding the



Shepler, et al.         Expires February 2, 2007              [Page 149]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   delegation has a modified version of the file.  If the client's copy
   of the delegated file is not modified (data or size), the server can
   satisfy the second client's GETATTR request from the attributes
   stored locally at the server.  If the file is modified, the server
   only needs to know about this modified state.  If the server
   determines that the file is currently modified, it will respond to
   the second client's GETATTR as if the file had been modified locally
   at the server.

   Since the form of the change attribute is determined by the server
   and is opaque to the client, the client and server need to agree on a
   method of communicating the modified state of the file.  For the size
   attribute, the client will report its current view of the file size.
   For the change attribute, the handling is more involved.

   For the client, the following steps will be taken when receiving a
   write delegation:

   o  The value of the change attribute will be obtained from the server
      and cached.  Let this value be represented by c.

   o  The client will create a value greater than c that will be used
      for communicating modified data is held at the client.  Let this
      value be represented by d.

   o  When the client is queried via CB_GETATTR for the change
      attribute, it checks to see if it holds modified data.  If the
      file is modified, the value d is returned for the change attribute
      value.  If this file is not currently modified, the client returns
      the value c for the change attribute.

   For simplicity of implementation, the client MAY for each CB_GETATTR
   return the same value d.  This is true even if, between successive
   CB_GETATTR operations, the client again modifies in the file's data
   or metadata in its cache.  The client can return the same value
   because the only requirement is that the client be able to indicate
   to the server that the client holds modified data.  Therefore, the
   value of d may always be c + 1.

   While the change attribute is opaque to the client in the sense that
   it has no idea what units of time, if any, the server is counting
   change with, it is not opaque in that the client has to treat it as
   an unsigned integer, and the server has to be able to see the results
   of the client's changes to that integer.  Therefore, the server MUST
   encode the change attribute in network order when sending it to the
   client.  The client MUST decode it from network order to its native
   order when receiving it and the client MUST encode it network order
   when sending it to the server.  For this reason, change is defined as



Shepler, et al.         Expires February 2, 2007              [Page 150]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   an unsigned integer rather than an opaque array of octets.

   For the server, the following steps will be taken when providing a
   write delegation:

   o  Upon providing a write delegation, the server will cache a copy of
      the change attribute in the data structure it uses to record the
      delegation.  Let this value be represented by sc.

   o  When a second client sends a GETATTR operation on the same file to
      the server, the server obtains the change attribute from the first
      client.  Let this value be cc.

   o  If the value cc is equal to sc, the file is not modified and the
      server returns the current values for change, time_metadata, and
      time_modify (for example) to the second client.

   o  If the value cc is NOT equal to sc, the file is currently modified
      at the first client and most likely will be modified at the server
      at a future time.  The server then uses its current time to
      construct attribute values for time_metadata and time_modify.  A
      new value of sc, which we will call nsc, is computed by the
      server, such that nsc >= sc + 1.  The server then returns the
      constructed time_metadata, time_modify, and nsc values to the
      requester.  The server replaces sc in the delegation record with
      nsc.  To prevent the possibility of time_modify, time_metadata,
      and change from appearing to go backward (which would happen if
      the client holding the delegation fails to write its modified data
      to the server before the delegation is revoked or returned), the
      server SHOULD update the file's metadata record with the
      constructed attribute values.  For reasons of reasonable
      performance, committing the constructed attribute values to stable
      storage is OPTIONAL.

   As discussed earlier in this section, the client MAY return the same
   cc value on subsequent CB_GETATTR calls, even if the file was
   modified in the client's cache yet again between successive
   CB_GETATTR calls.  Therefore, the server must assume that the file
   has been modified yet again, and MUST take care to ensure that the
   new nsc it constructs and returns is greater than the previous nsc it
   returned.  An example implementation's delegation record would
   satisfy this mandate by including a boolean field (let us call it
   "modified") that is set to false when the delegation is granted, and
   an sc value set at the time of grant to the change attribute value.
   The modified field would be set to true the first time cc != sc, and
   would stay true until the delegation is returned or revoked.  The
   processing for constructing nsc, time_modify, and time_metadata would
   use this pseudo code:



Shepler, et al.         Expires February 2, 2007              [Page 151]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   if (!modified) {
       do CB_GETATTR for change and size;

       if (cc != sc)
           modified = TRUE;
   } else {
       do CB_GETATTR for size;
   }

   if (modified) {
       sc = sc + 1;
       time_modify = time_metadata = current_time;
       update sc, time_modify, time_metadata into file's metadata;
   }

   return to client (that sent GETATTR) the attributes
   it requested, but make sure size comes from what
   CB_GETATTR returned. Do not update the file's metadata
   with the client's modified size.

   In the case that the file attribute size is different than the
   server's current value, the server treats this as a modification
   regardless of the value of the change attribute retrieved via
   CB_GETATTR and responds to the second client as in the last step.

   This methodology resolves issues of clock differences between client
   and server and other scenarios where the use of CB_GETATTR break
   down.

   It should be noted that the server is under no obligation to use
   CB_GETATTR and therefore the server MAY simply recall the delegation
   to avoid its use.

9.4.4.  Recall of Open Delegation

   The following events necessitate recall of an open delegation:

   o  Potentially conflicting OPEN request (or READ/WRITE done with
      "special" stateid)

   o  SETATTR issued by another client

   o  REMOVE request for the file

   o  RENAME request for the file as either source or target of the
      RENAME

   Whether a RENAME of a directory in the path leading to the file



Shepler, et al.         Expires February 2, 2007              [Page 152]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   results in recall of an open delegation depends on the semantics of
   the server file system.  If that file system denies such RENAMEs when
   a file is open, the recall must be performed to determine whether the
   file in question is, in fact, open.

   In addition to the situations above, the server may choose to recall
   open delegations at any time if resource constraints make it
   advisable to do so.  Clients should always be prepared for the
   possibility of recall.

   When a client receives a recall for an open delegation, it needs to
   update state on the server before returning the delegation.  These
   same updates must be done whenever a client chooses to return a
   delegation voluntarily.  The following items of state need to be
   dealt with:

   o  If the file associated with the delegation is no longer open and
      no previous CLOSE operation has been sent to the server, a CLOSE
      operation must be sent to the server.

   o  If a file has other open references at the client, then OPEN
      operations must be sent to the server.  The appropriate stateids
      will be provided by the server for subsequent use by the client
      since the delegation stateid will not longer be valid.  These OPEN
      requests are done with the claim type of CLAIM_DELEGATE_CUR.  This
      will allow the presentation of the delegation stateid so that the
      client can establish the appropriate rights to perform the OPEN.
      (see the section "Operation 18: OPEN" for details.)

   o  If there are granted file locks, the corresponding LOCK operations
      need to be performed.  This applies to the write open delegation
      case only.

   o  For a write open delegation, if at the time of recall the file is
      not open for write, all modified data for the file must be flushed
      to the server.  If the delegation had not existed, the client
      would have done this data flush before the CLOSE operation.

   o  For a write open delegation when a file is still open at the time
      of recall, any modified data for the file needs to be flushed to
      the server.

   o  With the write open delegation in place, it is possible that the
      file was truncated during the duration of the delegation.  For
      example, the truncation could have occurred as a result of an OPEN
      UNCHECKED with a size attribute value of zero.  Therefore, if a
      truncation of the file has occurred and this operation has not
      been propagated to the server, the truncation must occur before



Shepler, et al.         Expires February 2, 2007              [Page 153]


Internet-Draft            NFSv4 Minor Version 1              August 2006


      any modified data is written to the server.

   In the case of write open delegation, file locking imposes some
   additional requirements.  To precisely maintain the associated
   invariant, it is required to flush any modified data in any region
   for which a write lock was released while the write delegation was in
   effect.  However, because the write open delegation implies no other
   locking by other clients, a simpler implementation is to flush all
   modified data for the file (as described just above) if any write
   lock has been released while the write open delegation was in effect.

   An implementation need not wait until delegation recall (or deciding
   to voluntarily return a delegation) to perform any of the above
   actions, if implementation considerations (e.g. resource availability
   constraints) make that desirable.  Generally, however, the fact that
   the actual open state of the file may continue to change makes it not
   worthwhile to send information about opens and closes to the server,
   except as part of delegation return.  Only in the case of closing the
   open that resulted in obtaining the delegation would clients be
   likely to do this early, since, in that case, the close once done
   will not be undone.  Regardless of the client's choices on scheduling
   these actions, all must be performed before the delegation is
   returned, including (when applicable) the close that corresponds to
   the open that resulted in the delegation.  These actions can be
   performed either in previous requests or in previous operations in
   the same COMPOUND request.

9.4.5.  Clients that Fail to Honor Delegation Recalls

   A client may fail to respond to a recall for various reasons, such as
   a failure of the callback path from server to the client.  The client
   may be unaware of a failure in the callback path.  This lack of
   awareness could result in the client finding out long after the
   failure that its delegation has been revoked, and another client has
   modified the data for which the client had a delegation.  This is
   especially a problem for the client that held a write delegation.

   The server also has a dilemma in that the client that fails to
   respond to the recall might also be sending other NFS requests,
   including those that renew the lease before the lease expires.
   Without returning an error for those lease renewing operations, the
   server leads the client to believe that the delegation it has is in
   force.

   This difficulty is solved by the following rules:

   o  When the callback path is down, the server MUST NOT revoke the
      delegation if one of the following occurs:



Shepler, et al.         Expires February 2, 2007              [Page 154]


Internet-Draft            NFSv4 Minor Version 1              August 2006


      *  The client has issued a RENEW operation and the server has
         returned an NFS4ERR_CB_PATH_DOWN error.  The server MUST renew
         the lease for any record locks and share reservations the
         client has that the server has known about (as opposed to those
         locks and share reservations the client has established but not
         yet sent to the server, due to the delegation).  The server
         SHOULD give the client a reasonable time to return its
         delegations to the server before revoking the client's
         delegations.

      *  The client has not issued a RENEW operation for some period of
         time after the server attempted to recall the delegation.  This
         period of time MUST NOT be less than the value of the
         lease_time attribute.

   o  When the client holds a delegation, it can not rely on operations,
      except for RENEW, that take a stateid, to renew delegation leases
      across callback path failures.  The client that wants to keep
      delegations in force across callback path failures must use RENEW
      to do so.

9.4.6.  Delegation Revocation

   At the point a delegation is revoked, if there are associated opens
   on the client, the applications holding these opens need to be
   notified.  This notification usually occurs by returning errors for
   READ/WRITE operations or when a close is attempted for the open file.

   If no opens exist for the file at the point the delegation is
   revoked, then notification of the revocation is unnecessary.
   However, if there is modified data present at the client for the
   file, the user of the application should be notified.  Unfortunately,
   it may not be possible to notify the user since active applications
   may not be present at the client.  See the section "Revocation
   Recovery for Write Open Delegation" for additional details.

9.5.  Data Caching and Revocation

   When locks and delegations are revoked, the assumptions upon which
   successful caching depend are no longer guaranteed.  For any locks or
   share reservations that have been revoked, the corresponding owner
   needs to be notified.  This notification includes applications with a
   file open that has a corresponding delegation which has been revoked.
   Cached data associated with the revocation must be removed from the
   client.  In the case of modified data existing in the client's cache,
   that data must be removed from the client without it being written to
   the server.  As mentioned, the assumptions made by the client are no
   longer valid at the point when a lock or delegation has been revoked.



Shepler, et al.         Expires February 2, 2007              [Page 155]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   For example, another client may have been granted a conflicting lock
   after the revocation of the lock at the first client.  Therefore, the
   data within the lock range may have been modified by the other
   client.  Obviously, the first client is unable to guarantee to the
   application what has occurred to the file in the case of revocation.

   Notification to a lock owner will in many cases consist of simply
   returning an error on the next and all subsequent READs/WRITEs to the
   open file or on the close.  Where the methods available to a client
   make such notification impossible because errors for certain
   operations may not be returned, more drastic action such as signals
   or process termination may be appropriate.  The justification for
   this is that an invariant for which an application depends on may be
   violated.  Depending on how errors are typically treated for the
   client operating environment, further levels of notification
   including logging, console messages, and GUI pop-ups may be
   appropriate.

9.5.1.  Revocation Recovery for Write Open Delegation

   Revocation recovery for a write open delegation poses the special
   issue of modified data in the client cache while the file is not
   open.  In this situation, any client which does not flush modified
   data to the server on each close must ensure that the user receives
   appropriate notification of the failure as a result of the
   revocation.  Since such situations may require human action to
   correct problems, notification schemes in which the appropriate user
   or administrator is notified may be necessary.  Logging and console
   messages are typical examples.

   If there is modified data on the client, it must not be flushed
   normally to the server.  A client may attempt to provide a copy of
   the file data as modified during the delegation under a different
   name in the file system name space to ease recovery.  Note that when
   the client can determine that the file has not been modified by any
   other client, or when the client has a complete cached copy of file
   in question, such a saved copy of the client's view of the file may
   be of particular value for recovery.  In other case, recovery using a
   copy of the file based partially on the client's cached data and
   partially on the server copy as modified by other clients, will be
   anything but straightforward, so clients may avoid saving file
   contents in these situations or mark the results specially to warn
   users of possible problems.

   Saving of such modified data in delegation revocation situations may
   be limited to files of a certain size or might be used only when
   sufficient disk space is available within the target file system.
   Such saving may also be restricted to situations when the client has



Shepler, et al.         Expires February 2, 2007              [Page 156]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   sufficient buffering resources to keep the cached copy available
   until it is properly stored to the target file system.

9.6.  Attribute Caching

   The attributes discussed in this section do not include named
   attributes.  Individual named attributes are analogous to files and
   caching of the data for these needs to be handled just as data
   caching is for ordinary files.  Similarly, LOOKUP results from an
   OPENATTR directory are to be cached on the same basis as any other
   pathnames and similarly for directory contents.

   Clients may cache file attributes obtained from the server and use
   them to avoid subsequent GETATTR requests.  Such caching is write
   through in that modification to file attributes is always done by
   means of requests to the server and should not be done locally and
   cached.  The exception to this are modifications to attributes that
   are intimately connected with data caching.  Therefore, extending a
   file by writing data to the local data cache is reflected immediately
   in the size as seen on the client without this change being
   immediately reflected on the server.  Normally such changes are not
   propagated directly to the server but when the modified data is
   flushed to the server, analogous attribute changes are made on the
   server.  When open delegation is in effect, the modified attributes
   may be returned to the server in the response to a CB_RECALL call.

   The result of local caching of attributes is that the attribute
   caches maintained on individual clients will not be coherent.
   Changes made in one order on the server may be seen in a different
   order on one client and in a third order on a different client.

   The typical file system application programming interfaces do not
   provide means to atomically modify or interrogate attributes for
   multiple files at the same time.  The following rules provide an
   environment where the potential incoherences mentioned above can be
   reasonably managed.  These rules are derived from the practice of
   previous NFS protocols.

   o  All attributes for a given file (per-fsid attributes excepted) are
      cached as a unit at the client so that no non-serializability can
      arise within the context of a single file.

   o  An upper time boundary is maintained on how long a client cache
      entry can be kept without being refreshed from the server.

   o  When operations are performed that change attributes at the
      server, the updated attribute set is requested as part of the
      containing RPC.  This includes directory operations that update



Shepler, et al.         Expires February 2, 2007              [Page 157]


Internet-Draft            NFSv4 Minor Version 1              August 2006


      attributes indirectly.  This is accomplished by following the
      modifying operation with a GETATTR operation and then using the
      results of the GETATTR to update the client's cached attributes.

   Note that if the full set of attributes to be cached is requested by
   READDIR, the results can be cached by the client on the same basis as
   attributes obtained via GETATTR.

   A client may validate its cached version of attributes for a file by
   fetching just both the change and time_access attributes and assuming
   that if the change attribute has the same value as it did when the
   attributes were cached, then no attributes other than time_access
   have changed.  The reason why time_access is also fetched is because
   many servers operate in environments where the operation that updates
   change does not update time_access.  For example, POSIX file
   semantics do not update access time when a file is modified by the
   write system call.  Therefore, the client that wants a current
   time_access value should fetch it with change during the attribute
   cache validation processing and update its cached time_access.

   The client may maintain a cache of modified attributes for those
   attributes intimately connected with data of modified regular files
   (size, time_modify, and change).  Other than those three attributes,
   the client MUST NOT maintain a cache of modified attributes.
   Instead, attribute changes are immediately sent to the server.

   In some operating environments, the equivalent to time_access is
   expected to be implicitly updated by each read of the content of the
   file object.  If an NFS client is caching the content of a file
   object, whether it is a regular file, directory, or symbolic link,
   the client SHOULD NOT update the time_access attribute (via SETATTR
   or a small READ or READDIR request) on the server with each read that
   is satisfied from cache.  The reason is that this can defeat the
   performance benefits of caching content, especially since an explicit
   SETATTR of time_access may alter the change attribute on the server.
   If the change attribute changes, clients that are caching the content
   will think the content has changed, and will re-read unmodified data
   from the server.  Nor is the client encouraged to maintain a modified
   version of time_access in its cache, since this would mean that the
   client will either eventually have to write the access time to the
   server with bad performance effects, or it would never update the
   server's time_access, thereby resulting in a situation where an
   application that caches access time between a close and open of the
   same file observes the access time oscillating between the past and
   present.  The time_access attribute always means the time of last
   access to a file by a read that was satisfied by the server.  This
   way clients will tend to see only time_access changes that go forward
   in time.



Shepler, et al.         Expires February 2, 2007              [Page 158]


Internet-Draft            NFSv4 Minor Version 1              August 2006


9.7.  Data and Metadata Caching and Memory Mapped Files

   Some operating environments include the capability for an application
   to map a file's content into the application's address space.  Each
   time the application accesses a memory location that corresponds to a
   block that has not been loaded into the address space, a page fault
   occurs and the file is read (or if the block does not exist in the
   file, the block is allocated and then instantiated in the
   application's address space).

   As long as each memory mapped access to the file requires a page
   fault, the relevant attributes of the file that are used to detect
   access and modification (time_access, time_metadata, time_modify, and
   change) will be updated.  However, in many operating environments,
   when page faults are not required these attributes will not be
   updated on reads or updates to the file via memory access (regardless
   whether the file is local file or is being access remotely).  A
   client or server MAY fail to update attributes of a file that is
   being accessed via memory mapped I/O. This has several implications:

   o  If there is an application on the server that has memory mapped a
      file that a client is also accessing, the client may not be able
      to get a consistent value of the change attribute to determine
      whether its cache is stale or not.  A server that knows that the
      file is memory mapped could always pessimistically return updated
      values for change so as to force the application to always get the
      most up to date data and metadata for the file.  However, due to
      the negative performance implications of this, such behavior is
      OPTIONAL.

   o  If the memory mapped file is not being modified on the server, and
      instead is just being read by an application via the memory mapped
      interface, the client will not see an updated time_access
      attribute.  However, in many operating environments, neither will
      any process running on the server.  Thus NFS clients are at no
      disadvantage with respect to local processes.

   o  If there is another client that is memory mapping the file, and if
      that client is holding a write delegation, the same set of issues
      as discussed in the previous two bullet items apply.  So, when a
      server does a CB_GETATTR to a file that the client has modified in
      its cache, the response from CB_GETATTR will not necessarily be
      accurate.  As discussed earlier, the client's obligation is to
      report that the file has been modified since the delegation was
      granted, not whether it has been modified again between successive
      CB_GETATTR calls, and the server MUST assume that any file the
      client has modified in cache has been modified again between
      successive CB_GETATTR calls.  Depending on the nature of the



Shepler, et al.         Expires February 2, 2007              [Page 159]


Internet-Draft            NFSv4 Minor Version 1              August 2006


      client's memory management system, this weak obligation may not be
      possible.  A client MAY return stale information in CB_GETATTR
      whenever the file is memory mapped.

   o  The mixture of memory mapping and file locking on the same file is
      problematic.  Consider the following scenario, where a page size
      on each client is 8192 bytes.

      *  Client A memory maps first page (8192 bytes) of file X

      *  Client B memory maps first page (8192 bytes) of file X

      *  Client A write locks first 4096 bytes

      *  Client B write locks second 4096 bytes

      *  Client A, via a STORE instruction modifies part of its locked
         region.

      *  Simultaneous to client A, client B issues a STORE on part of
         its locked region.

   Here the challenge is for each client to resynchronize to get a
   correct view of the first page.  In many operating environments, the
   virtual memory management systems on each client only know a page is
   modified, not that a subset of the page corresponding to the
   respective lock regions has been modified.  So it is not possible for
   each client to do the right thing, which is to only write to the
   server that portion of the page that is locked.  For example, if
   client A simply writes out the page, and then client B writes out the
   page, client A's data is lost.

   Moreover, if mandatory locking is enabled on the file, then we have a
   different problem.  When clients A and B issue the STORE
   instructions, the resulting page faults require a record lock on the
   entire page.  Each client then tries to extend their locked range to
   the entire page, which results in a deadlock.  Communicating the
   NFS4ERR_DEADLOCK error to a STORE instruction is difficult at best.

   If a client is locking the entire memory mapped file, there is no
   problem with advisory or mandatory record locking, at least until the
   client unlocks a region in the middle of the file.

   Given the above issues the following are permitted:

   o  Clients and servers MAY deny memory mapping a file they know there
      are record locks for.




Shepler, et al.         Expires February 2, 2007              [Page 160]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   o  Clients and servers MAY deny a record lock on a file they know is
      memory mapped.

   o  A client MAY deny memory mapping a file that it knows requires
      mandatory locking for I/O. If mandatory locking is enabled after
      the file is opened and mapped, the client MAY deny the application
      further access to its mapped file.

9.8.  Name Caching

   The results of LOOKUP and READDIR operations may be cached to avoid
   the cost of subsequent LOOKUP operations.  Just as in the case of
   attribute caching, inconsistencies may arise among the various client
   caches.  To mitigate the effects of these inconsistencies and given
   the context of typical file system APIs, an upper time boundary is
   maintained on how long a client name cache entry can be kept without
   verifying that the entry has not been made invalid by a directory
   change operation performed by another client. .LP When a client is
   not making changes to a directory for which there exist name cache
   entries, the client needs to periodically fetch attributes for that
   directory to ensure that it is not being modified.  After determining
   that no modification has occurred, the expiration time for the
   associated name cache entries may be updated to be the current time
   plus the name cache staleness bound.

   When a client is making changes to a given directory, it needs to
   determine whether there have been changes made to the directory by
   other clients.  It does this by using the change attribute as
   reported before and after the directory operation in the associated
   change_info4 value returned for the operation.  The server is able to
   communicate to the client whether the change_info4 data is provided
   atomically with respect to the directory operation.  If the change
   values are provided atomically, the client is then able to compare
   the pre-operation change value with the change value in the client's
   name cache.  If the comparison indicates that the directory was
   updated by another client, the name cache associated with the
   modified directory is purged from the client.  If the comparison
   indicates no modification, the name cache can be updated on the
   client to reflect the directory operation and the associated timeout
   extended.  The post-operation change value needs to be saved as the
   basis for future change_info4 comparisons.

   As demonstrated by the scenario above, name caching requires that the
   client revalidate name cache data by inspecting the change attribute
   of a directory at the point when the name cache item was cached.
   This requires that the server update the change attribute for
   directories when the contents of the corresponding directory is
   modified.  For a client to use the change_info4 information



Shepler, et al.         Expires February 2, 2007              [Page 161]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   appropriately and correctly, the server must report the pre and post
   operation change attribute values atomically.  When the server is
   unable to report the before and after values atomically with respect
   to the directory operation, the server must indicate that fact in the
   change_info4 return value.  When the information is not atomically
   reported, the client should not assume that other clients have not
   changed the directory.

9.9.  Directory Caching

   The results of READDIR operations may be used to avoid subsequent
   READDIR operations.  Just as in the cases of attribute and name
   caching, inconsistencies may arise among the various client caches.
   To mitigate the effects of these inconsistencies, and given the
   context of typical file system APIs, the following rules should be
   followed:

   o  Cached READDIR information for a directory which is not obtained
      in a single READDIR operation must always be a consistent snapshot
      of directory contents.  This is determined by using a GETATTR
      before the first READDIR and after the last of READDIR that
      contributes to the cache.

   o  An upper time boundary is maintained to indicate the length of
      time a directory cache entry is considered valid before the client
      must revalidate the cached information.

   The revalidation technique parallels that discussed in the case of
   name caching.  When the client is not changing the directory in
   question, checking the change attribute of the directory with GETATTR
   is adequate.  The lifetime of the cache entry can be extended at
   these checkpoints.  When a client is modifying the directory, the
   client needs to use the change_info4 data to determine whether there
   are other clients modifying the directory.  If it is determined that
   no other client modifications are occurring, the client may update
   its directory cache to reflect its own changes.

   As demonstrated previously, directory caching requires that the
   client revalidate directory cache data by inspecting the change
   attribute of a directory at the point when the directory was cached.
   This requires that the server update the change attribute for
   directories when the contents of the corresponding directory is
   modified.  For a client to use the change_info4 information
   appropriately and correctly, the server must report the pre and post
   operation change attribute values atomically.  When the server is
   unable to report the before and after values atomically with respect
   to the directory operation, the server must indicate that fact in the
   change_info4 return value.  When the information is not atomically



Shepler, et al.         Expires February 2, 2007              [Page 162]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   reported, the client should not assume that other clients have not
   changed the directory.


10.  Multi-server Name Space

   NFSv4.1 supports attributes that allow a namespace to extend beyond
   the boundaries of a single server.  Use of such multi-server
   namespaces is optional, and for many purposes, single-server
   namespace are perfectly acceptable.  Use of multi-server namespaces
   can provide many advantages, however, by separating a file system's
   logical position in a name space from the (possibly changing)
   logistical and administrative considerations that result in
   particular file systems being located on particular servers.

10.1.  Location attributes

   NFSv4 contains recommended attributes that allow file systems on one
   server to be associated with one or more instances of that file
   system on other servers.  These attributes specify such file systems
   by specifying a server name (either a DNS name or an IP address)
   together with the path of that file system within that server's
   single-server name space.

   The fs_locations_info recommended attribute allows specification of
   one more file systems locations where the data corresponding to a
   given file system may be found.  This attributes provides to the
   client, in addition to information about file system locations,
   extensive information about the various file system choices (e.g.
   priority for use, writability, currency, etc.) as well as information
   to help the client efficiently effect as seamless a transition as
   possible among multiple file system instances, when and if that
   should be necessary.

   The fs_locations recommended attribute is inherited from NFSv4.0 and
   only allows specification of the file system locations where the data
   corresponding to a given file system may be found.  Servers should
   make this attribute available whenever fs_locations_info is
   supported, but client use of fs_locations_info is to be preferred.

10.2.  File System Presence or Absence

   A given location in an NFSv4 namespace (typically but not necessarily
   a multi-server namespace) can have a number of file system locations
   associated with it (via the fs_locations or fs_locations_info
   attribute).  There may also be an actual current file system at that
   location, accessible via normal namespace operations (e.g.  LOOKUP).
   In this case there, the file system is said to be "present" at that



Shepler, et al.         Expires February 2, 2007              [Page 163]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   position in the namespace and clients will typically use it,
   reserving use of additional locations specified via the location-
   related attributes to situations in which the principal location is
   no longer available.

   When there is no actual file system at the namespace location in
   question, the file system is said to be "absent".  An absent file
   system contains no files or directories other than the root and any
   reference to it, except to access a small set of attributes useful in
   determining alternate locations, will result in an error,
   NFS4ERR_MOVED.  Note that if the server ever returns NFS4ERR_MOVED
   (i.e. file systems may be absent), it MUST support the fs_locations
   attribute and SHOULD support the fs_locations_info and fs_absent
   attributes.

   While the error name suggests that we have a case of a file system
   which once was present, and has only become absent later, this is
   only one possibility.  A position in the namespace may be permanently
   absent with the file system(s) designated by the location attributes
   the only realization.  The name NFS4ERR_MOVED reflects an earlier,
   more limited conception of its function, but this error will be
   returned whenever the referenced file system is absent, whether it
   has moved or not.

   Except in the case of GETATTR-type operations (to be discussed
   later), when the current filehandle at the start of an operation is
   within an absent file system, that operation is not performed and the
   error NFS4ERR_MOVED returned, to indicate that the file system is
   absent on the current server.

   Because a GETFH cannot succeed, if the current filehandle is within
   an absent file system, filehandles within an absent file system
   cannot be transferred to the client.  When a client does have
   filehandles within an absent file system, it is the result of
   obtaining them when the file system was present, and having the file
   system become absent subsequently.

   It should be noted that because the check for the current filehandle
   being within an absent file system happens at the start of every
   operation, operations which change the current filehandle so that it
   is within an absent file system will not result in an error.  This
   allows such combinations as PUTFH-GETATTR and LOOKUP-GETATTR to be
   used to get attribute information, particularly location attribute
   information, as discussed below.

   The recommended file system attribute fs_absent can used to
   interrogate the present/absent status of a given file system.




Shepler, et al.         Expires February 2, 2007              [Page 164]


Internet-Draft            NFSv4 Minor Version 1              August 2006


10.3.  Getting Attributes for an Absent File System

   When a file system is absent, most attributes are not available, but
   it is necessary to allow the client access to the small set of
   attributes that are available, and most particularly those that give
   information about the correct current locations for this file system,
   fs_locations and fs_locations_info.

10.3.1.  GETATTR Within an Absent File System

   As mentioned above, an exception is made for GETATTR in that
   attributes may be obtained for a filehandle within an absent file
   system.  This exception only applies if the attribute mask contains
   at least one attribute bit that indicates the client is interested in
   a result regarding an absent file system: fs_locations,
   fs_locations_info, or fs_absent.  If none of these attributes is
   requested, GETATTR will result in an NFS4ERR_MOVED error.

   When a GETATTR is done on an absent file system, the set of supported
   attributes is very limited.  Many attributes, including those that
   are normally mandatory will not be available on an absent file
   system.  In addition to the attributes mentioned above (fs_locations,
   fs_locations_info, fs_absent), the following attributes SHOULD be
   available on absent file systems, in the case of recommended
   attributes at least to the same degree that they are available on
   present file systems.

   change:  This attribute is useful for absent file systems and can be
      helpful in summarizing to the client when any of the location-
      related attributes changes.

   fsid:  This attribute should be provided so that the client can
      determine file system boundaries, including, in particular, the
      boundary between present and absent file systems.

   mounted_on_fileid:  For objects at the top of an absent file system
      this attribute needs to be available.  Since the fileid is one
      which is within the present parent file system, there should be no
      need to reference the absent file system to provide this
      information.

   Other attributes SHOULD NOT be made available for absent file
   systems, even when it is possible to provide them.  The server should
   not assume that more information is always better and should avoid
   gratuitously providing additional information.

   When a GETATTR operation includes a bit mask for one of the
   attributes fs_locations, fs_locations_info, or absent, but where the



Shepler, et al.         Expires February 2, 2007              [Page 165]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   bit mask includes attributes which are not supported, GETATTR will
   not return an error, but will return the mask of the actual
   attributes supported with the results.

   Handling of VERIFY/NVERIFY is similar to GETATTR in that if the
   attribute mask does not include fs_locations, fs_locations_info, or
   absent, the error NFS4ERR_MOVED will result.  It differs in that any
   appearance in the attribute mask of an attribute not supported for an
   absent file system (and note that this will include some normally
   mandatory attributes), will also cause an NFS4ERR_MOVED result.

10.3.2.  READDIR and Absent File Systems

   A READDIR performed when the current filehandle is within an absent
   file system will result in an NFS4ERR_MOVED error, since, unlike the
   case of GETATTR, no such exception is made for READDIR.

   Attributes for an absent file system may be fetched via a READDIR for
   a directory in a present file system, when that directory contains
   the root directories of one or more absent file systems.  In this
   case, the handling is as follows:

   o  If the attribute set requested includes one of the attributes
      fs_locations, fs_locations_info, or absent, then fetching of
      attributes proceeds normally and no NFS4ERR_MOVED indication is
      returned, even when the rdattr_error attribute is requested.

   o  If the attribute set requested does not include one of the
      attributes fs_locations, fs_locations_info, or fs_absent, then if
      the rdattr_error attribute is requested, each directory entry for
      the root of an absent file system, will report NFS4ERR_MOVED as
      the value of the rdattr_error attribute.

   o  If the attribute set requested does not include any of the
      attributes fs_locations, fs_locations_info, fs_absent, or
      rdattr_error then the occurrence of the root of an absent file
      system within the directory will result in the READDIR failing
      with an NFSERR_MOVED error.

   o  The unavailability of an attribute because of a file system's
      absence, even one that is ordinarily mandatory, does not result in
      any error indication.  The set of attributes returned for the root
      directory of the absent file system in that case is simply
      restricted to those actually available.







Shepler, et al.         Expires February 2, 2007              [Page 166]


Internet-Draft            NFSv4 Minor Version 1              August 2006


10.4.  Uses of Location Information

   The location-bearing attributes (fs_locations and fs_locations_info),
   provide, together with the possibility of absent file systems, a
   number of important facilities in providing reliable, manageable, and
   scalable data access.

   When a file system is present, these attribute can provide
   alternative locations, to be used to access the same data, in the
   event that server failures, communications problems, or other
   difficulties, make continued access to the current file system
   impossible or otherwise impractical.  Provision of such alternate
   locations is referred to as "replication" although there are cases in
   which replicated sets of data are not in fact present, and the
   replicas are instead different paths to the same data.

   When a file system is present and becomes absent, clients can be
   given the opportunity to have continued access to their data, at an
   alternate location.  In this case, a continued attempt to use the
   data in the now-absent file system will result in an NFSERR_MOVED
   error and at that point the successor locations (typically only one
   but multiple choices are possible) can be fetched and used to
   continue access.  Transfer of the file system contents to the new
   location is referred to as "migration", but it should be kept in mind
   that there are cases in which this term can be used, like
   "replication" when there is no actual data migration per se.

   Where a file system was not previously present, specification of file
   system location provides a means by which file systems located on one
   server can be associated with a name space defined by another server,
   thus allowing a general multi-server namespace facility.  Designation
   of such a location, in place of an absent file system, is called
   "referral".

10.4.1.  File System Replication

   The fs_locations and fs_locations_info attributes provide alternative
   locations, to be used to access data in place of the current file
   system.  On first access to a file system, the client should obtain
   the value of the set alternate locations by interrogating the
   fs_locations or fs_locations_info attribute, with the latter being
   preferred.

   In the event that server failures, communications problems, or other
   difficulties, make continued access to the current file system
   impossible or otherwise impractical, the client can use the alternate
   locations as a way to get continued access to his data.




Shepler, et al.         Expires February 2, 2007              [Page 167]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   The alternate locations may be physical replicas of the (typically
   read-only) file system data, or they may reflect alternate paths to
   the same server or provide for the use of various form of server
   clustering in which multiple servers provide alternate ways of
   accessing the same physical file system.  How these different modes
   of file system transition are represented within the fs_locations and
   fs_locations_info attributes and how the client deals with file
   system transition issues will be discussed in detail below.

10.4.2.  File System Migration

   When a file system is present and becomes absent, clients can be
   given the opportunity to have continued access to their data, at an
   alternate location, as specified by the fs_locations or
   fs_locations_info attribute.  Typically, a client will be accessing
   the file system in question, get a an NFS4ERR_MOVED error, and then
   use the fs_locations or fs_locations_info attribute to determine the
   new location of the data.  When fs_locations_info is used, additional
   information will be available which will define the nature of the
   client's handling of the transition to a new server.

   Such migration can be helpful in providing load balancing or general
   resource reallocation.  The protocol does not specify how the file
   system will be moved between servers.  It is anticipated that a
   number of different server-to-server transfer mechanisms might be
   used with the choice left to the server implementor.  The NFSv4.1
   protocol specifies the method used to communicate the migration event
   between client and server.

   The new location may be an alternate communication path to the same
   server, or, in the case of various forms of server clustering,
   another server providing access to the same physical file system.
   The client's responsibilities in dealing with this transition depend
   on the specific nature of the new access path and how and whether
   data was in fact migrated.  These issues will be discussed in detail
   below.

   Although a single successor location is typical, multiple locations
   may be provided, together with information that allows priority among
   the choices to be indicated, via information in the fs_locations_info
   attribute.  Where suitable clustering mechanisms make it possible to
   provide multiple identical file systems or paths to them, this allows
   the client the opportunity to deal with any resource or
   communications issues that might limit data availability.







Shepler, et al.         Expires February 2, 2007              [Page 168]


Internet-Draft            NFSv4 Minor Version 1              August 2006


10.4.3.  Referrals

   Referrals provide a way of placing a file system in a location
   essentially without respect to its physical location on a given
   server.  This allows a single server of a set of servers to present a
   multi-server namespace that encompasses file systems located on
   multiple servers.  Some likely uses of this include establishment of
   site-wide or organization-wide namespaces, or even knitting such
   together into a truly global namespace.

   Referrals occur when a client determines, upon first referencing a
   position in the current namespace, that it is part of a new file
   system and that that file system is absent.  When this occurs,
   typically by receiving the error NFS4ERR_MOVED, the actual location
   or locations of the file system can be determined by fetching the
   fs_locations or fs_locations_info attribute.

   Use of multi-server namespaces is enabled by NFSv4 but is not
   required.  The use of multi-server namespaces and their scope will
   depend on the application used, and system administration
   preferences.

   Multi-server namespaces can be established by a single server
   providing a large set of referrals to all of the included file
   systems.  Alternatively, a single multi-server namespace may be
   administratively segmented with separate referral file systems (on
   separate servers) for each separately-administered section of the
   name space.  Any segment or the top-level referral file system may
   use replicated referral file systems for higher availability.

10.5.  Additional Client-side Considerations

   When clients make use of servers that implement referrals and
   migration, care should be taken so that a user who mounts a given
   file system that includes a referral or a relocated file system
   continue to see a coherent picture of that user-side file system
   despite the fact that it contains a number of server-side file
   systems which may be on different servers.

   One important issue is upward navigation from the root of a server-
   side file system to its parent (specified as ".." in UNIX).  The
   client needs to determine when it hits an fsid root going up the
   filetree.  When at such a point, and needs to ascend to the parent,
   it must do so locally instead of sending a LOOKUPP call to the
   server.  The LOOKUPP would normally return the ancestor of the target
   file system on the target server, which may not be part of the space
   that the client mounted.




Shepler, et al.         Expires February 2, 2007              [Page 169]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   Another issue concerns refresh of referral locations.  When referrals
   are used extensively, they may change as server configurations
   change.  It is expected that clients will cache information related
   to traversing referrals so that future client side requests are
   resolved locally without server communication.  This is usually
   rooted in client-side name lookup caching.  Clients should
   periodically purge this data for referral points in order to detect
   changes in location information.  When the change attribute changes
   for directories that hold referral entries or for the referral
   entries themselves, clients should consider any associated cached
   referral information to be out of date.

10.6.  Effecting File System Transitions

   Transitions between file system instances, whether due to switching
   between replicas upon server unavailability, or in response to a
   server-initiated migration event are best dealt with together.  Even
   though the prototypical use cases of replication and migration
   contain distinctive sets of features, when all possibilities for
   these operations are considered, the underlying unity of these
   operations, from the client's point of view is clear, even though for
   the server pragmatic considerations will normally force different
   implementation strategies for planned and unplanned transitions.

   A number of methods are possible for servers to replicate data and to
   track client state in order to allow clients to transition between
   file system instances with a minimum of disruption.  Such methods
   vary between those that use inter-server clustering techniques to
   limit the changes seen by the client, to those that are less
   aggressive, use more standard methods of replicating data, and impose
   a greater burden on the client to adapt to the transition.

   The NFSv4.1 protocol does not impose choices on clients and servers
   with regard to that spectrum of transition methods.  In fact, there
   are many valid choices, depending on client and application
   requirements and their interaction with server implementation
   choices.  The NFSv4.1 protocol does define the specific choices that
   can be made, how these choices are communicated to the client and how
   the client is to deal with any discontinuities.

   In the sections below references will be made to various possible
   server implementation choices as a way of illustrating the transition
   scenarios that clients may deal with.  The intent here is not to
   define or limit server implementations but rather to illustrate the
   range of issues that clients may face.

   In the discussion below, references will be made to a file system
   having a particular property or of two file systems (typically the



Shepler, et al.         Expires February 2, 2007              [Page 170]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   source and destination) belonging to a common class of any of several
   types.  Two file systems that belong to such a class share some
   important aspect of file system behavior that clients may depend upon
   when present, to easily effect a seamless transition between file
   system instances.  Conversely, where the file systems do not belong
   to such a common class, the client has to deal with various sorts of
   implementation discontinuities which may cause performance or other
   issues in effecting a transition.

   Where the fs_locations_info attribute is available, such file system
   classification data will be made directly available to the client.
   See Section 10.10 for details.  When only fs_locations is available,
   default assumptions with regard to such classifications have to be
   inferred.  See Section 10.9 for details.

   In cases in which one server is expected to accept opaque values from
   the client that originated from another server, it is a wise
   implementation practice for the servers to encode the "opaque" values
   in network byte order.  If this is done, servers acting as replicas
   or immigrating file systems will be able to parse values like
   stateids, directory cookies, filehandles, etc. even if their native
   byte order is different from that of other servers cooperating in the
   replication and migration of the file system.

10.6.1.  Transparent File System Transitions

   Discussion of transition possibilities will start at the most
   transparent end of the spectrum of possibilities.  When there are
   multiple paths to a single server, and there are network problems
   that force another path to be used, or when a path is to be put out
   of service, a replication or migration event may occur without any
   real replication or migration.  Nevertheless, such events fit within
   the same general framework in that there is a transition between file
   system locations, communicated just as other, less transparent
   transitions are communicated.

   There are cases of transparent transitions that may happen
   independent of location information, in that a specific host name,
   may map to several IP addresses, allowing session trunking to provide
   alternate paths.  In other cases, however multiple addresses may have
   separate location entries for specific file systems to preferentially
   direct traffic for those specific file systems to certain server
   addresses, subject to planned or unplanned, corresponding to a
   nominal replication or migrations event.

   The specific details of the transition depend on file system
   equivalence class information (as provided by the fs_locations_info
   and fs_locations attributes).



Shepler, et al.         Expires February 2, 2007              [Page 171]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   o  Where the old and new file systems belong to the same _endpoint_
      class, the transition consists of creating a new connection which
      is associated with the existing session to the old server
      endpoint.  Where a connection cannot be associated with the
      existing session, the target server must be able to recognize the
      sessionid as invalid and force creation on a new session or a new
      client id.

   o  Where the old and new file systems do not belong to the same
      _endpoint_ classes, but to the same _server_ class, the transition
      consists of creating a new session, associated with the existing
      clientid.  Where the clientid is stale, the target server must be
      able to recognize the clientid as no longer valid and force
      creation of a new clientid.

   In either of the above cases, the file system may be shown as
   belonging to the same _sharing_ class, class allowing the alternate
   session or connection to be established in advance and used either to
   accelerate the file system transition when necessary (avoiding
   connection latency), or to provide higher performance by actively
   using multiple paths simultaneously.

   When two file systems belong to the same _endpoint_ class, or
   _sharing_ class, many transition issues are eliminated, and any
   information indicating otherwise is ignored as erroneous.

   In all such transparent transition cases, the following apply:

   o  File handles stay the same if persistent and if volatile are only
      subject to expiration, if they would be in the absence of file
      system transition.

   o  Fileid values do not change across the transition.

   o  The file system will have the same fsid in both the old and new
      the old and new locations.

   o  Change attribute values are consistent across the transition and
      do not have to be refetched.  When change attributes indicate that
      a cached object is still valid, it can remain cached.

   o  Session, client, and state identifier retain their validity across
      the transition, except where their staleness is recognized and
      reported by the new server.  Except where such staleness requires
      it, no lock reclamation is needed.

   o  Write verifiers are presumed to retain their validity and can be
      presented to COMMIT, with the expectation that if COMMIT on the



Shepler, et al.         Expires February 2, 2007              [Page 172]


Internet-Draft            NFSv4 Minor Version 1              August 2006


      new server accept them as valid, then that server has all of the
      data unstably written to the original server and has committed it
      to stable storage as requested.

10.6.2.  Filehandles and File System Transitions

   There are a number of ways in which filehandles can be handled across
   a file system transition.  These can be divided into two broad
   classes depending upon whether the two file systems across which the
   transition happens share sufficient state to effect some sort of
   continuity of file system handling.

   When there is no such co-operation in filehandle assignment, the two
   file systems are reported as being in different _handle_ classes.  In
   this case, all filehandles are assumed to expire as part of the file
   system transition.  Note that this behavior does not depend on
   fh_expire_type attribute and supersedes the specification of
   FH4_VOL_MIGRATION bit, which only affects behavior when
   fs_locations_info is not available.

   When there is co-operation in filehandle assignment, the two file
   systems are reported as being in the same _handle_ classes.  In this
   case, persistent filehandle remain valid after the file system
   transition, while volatile filehandles (excluding those while are
   only volatile due to the FH4_VOL_MIGRATION bit) are subject to
   expiration on the target server.

10.6.3.  Fileid's and File System Transitions

   In NFSv4.0, the issue of continuity of fileid's in the event of a
   file system transition was not addressed.  The general expectation
   had been that in situations in which the two file system instances
   are created by a single vendor using some sort of file system image
   copy, fileid's will be consistent across the transition while in the
   analogous multi-vendor transitions they will not.  This poses
   difficulties, especially for the client without special knowledge of
   the of the transition mechanisms adopted by the server.

   It is important to note that while clients themselves may have no
   trouble with a fileid changing as a result of a file system
   transition event, applications do typically have access to the fileid
   (e.g. via stat), and the result of this is that an application may
   work perfectly well if there is no file system instance transition or
   if any such transition is among instances created by a single vendor,
   yet be unable to deal with the situation in which a multi-vendor
   transition occurs, at the wrong time.

   Providing the same fileid's in a multi-vendor (multiple server



Shepler, et al.         Expires February 2, 2007              [Page 173]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   vendors) environment has generally been held to be quite difficult.
   While there is work to be done, it needs to be pointed out that this
   difficulty is partly self-imposed.  Servers have typically identified
   fileid with inode number, i.e. with a quantity used to find the file
   in question.  This identification poses special difficulties for
   migration of an fs between vendors where assigning the same index to
   a given file may not be possible.  Note here that a fileid does not
   require that it be useful to find the file in question, only that it
   is unique within the given fs.  Servers prepared to accept a fileid
   as a single piece of metadata and store it apart from the value used
   to index the file information can relatively easily maintain a fileid
   value across a migration event, allowing a truly transparent
   migration event.

   In any case, where servers can provide continuity of fileids, they
   should and the client should be able to find out that such continuity
   is available, and take appropriate action.  Information about the
   continuity (or lack thereof) of fileid's across a file system is
   represented by specifying whether the file systems in question are of
   the same _fileid_ class.

10.6.4.  Fsid's and File System Transitions

   Since fsid's are only unique within a per-server basis, it is to be
   expected that they will change during a file system transition.
   Clients should not make the fsid's received from the server visible
   to application since they may not be globally unique, and because
   they may change during a file system transition event.  Applications
   are best served if they are isolated from such transitions to the
   extent possible.

10.6.5.  The Change Attribute and File System Transitions

   Since the change attribute is defined as a server-specific one,
   change attributes fetched from one server are normally presumed to be
   invalid on another server.  Such a presumption is troublesome since
   it would invalidate all cached change attributes, requiring
   refetching.  Even more disruptive, the absence of any assured
   continuity for the change attribute means that even if the same value
   is gotten on refetch no conclusions can drawn as to whether the
   object in question has changed.  The identical change attribute could
   be merely an artifact, of a modified file with a different change
   attribute construction algorithm, with that new algorithm just
   happening to result in an identical change value.

   When the two file systems have consistent change attribute formats,
   and this fact is communicated to the client by reporting as in the
   same _change_ class, the client may assume a continuity of change



Shepler, et al.         Expires February 2, 2007              [Page 174]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   attribute construction and handle this situation just as it would be
   handled without any file system transition.

10.6.6.  Lock State and File System Transitions

   In a file system transition, the two file systems may have co-
   operated in state management.  When this is the case, and the two
   file systems belong to the same _state_ class, the two file systems
   will have compatible state environments.  In the case of migration,
   the servers involved in the migration of a file system SHOULD
   transfer all server state from the original to the new server.  When
   this done, it must be done in a way that is transparent to the
   client.  With replication, such a degree of common state is typically
   not the case.  Clients, however should use the information provided
   by the fs_locations_info attribute to determine whether such sharing
   is in effect when this is available, and only if that attribute is
   not available depend on these defaults.

   This state transfer will reduce disruption to the client when a file
   system transition If the servers are successful in transferring all
   state, the client will continue to use stateids assigned by the
   original server.  Therefore the new server must recognize these
   stateids as valid.  This holds true for the clientid as well.  Since
   responsibility for an entire file system is transferred is with such
   an event, there is no possibility that conflicts will arise on the
   new server as a result of the transfer of locks.

   As part of the transfer of information between servers, leases would
   be transferred as well.  The leases being transferred to the new
   server will typically have a different expiration time from those for
   the same client, previously on the old server.  To maintain the
   property that all leases on a given server for a given client expire
   at the same time, the server should advance the expiration time to
   the later of the leases being transferred or the leases already
   present.  This allows the client to maintain lease renewal of both
   classes without special effort.

   When the two servers belong to the same _state_ class, it does not
   necessarily mean that when dealing with the transition, the client
   will not have to reclaim state.  However it does mean that the client
   may proceed using his current clientid and stateid's just as if there
   had been no file system transition event and only reclaim state when
   an NFS4ERR_STALE_CLIENTID or NFS4ERR_STALE_STATEID error is received.

   File systems co-operating in state management may actually share
   state or simply divide the id space so as to recognize (and reject as
   stale) each others state and clients id's.  Servers which do share
   state may not do under all conditions or all times.  The requirement



Shepler, et al.         Expires February 2, 2007              [Page 175]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   for the server is that if it cannot be sure in accepting an id that
   it reflects the locks the client was given, it must treat all
   associated state as stale and report it as such to the client.

   When two file systems belong to different _state_ classes, the client
   must establish a new state on the destination, and reclaim if
   possible.  In this case, old stateids and clientid's should not be
   presented to the new server since there is no assurance that they
   will not conflict with id's valid on that server.

   In either case, when actual locks are not known to be maintained, the
   destination server may establish a grace period specific to the given
   file system, with non-reclaim locks being rejected for that file
   system, even though normal locks are being granted for other file
   systems.  Clients should not infer the absence of a grace period for
   file systems being transitioned to a server from responses to
   requests for other file systems.

   In the case of lock reclamation for a given file system after a file
   system transition, edge conditions can arise similar to those for
   reclaim after server reboot (although in the case of the planned
   state transfer associated with migration, these can be avoided by
   securely recording lock state as part of state migration.  Where the
   destination server cannot guarantee that locks will not be
   incorrectly granted, the destination server should not establish a
   file-system-specific grace period.

   In place of a file-system-specific version of RECLAIM_COMPLETE,
   servers may assume that an attempt to obtain a new lock, other than
   be reclaim, indicate the end of the client's attempt to reclaim locks
   for that file system.  [NOTE: The alternative would be to adapt
   RECLAIM_COMPLETE to this task].

   Information about client identity that may be propagated between
   servers in the form of nfs_client_id4 and associated verifiers, under
   the assumption that the client presents the same values to all the
   servers with which it deals.  [NOTE: This contradicts what is
   currently said about SETCLIENTID, and interacts with the issue of
   what sessions should do about this.]

   Servers are encouraged to provide facilities to allow locks to be
   reclaimed on the new server after a file system transition.  Often,
   however, in cases in which the two file systems are not of the same
   _state _ class, such facilities may not be available and client
   should be prepared to re-obtain locks, even though it is possible
   that the client may have his LOCK or OPEN request denied due to a
   conflicting lock.  In some environments, such as the transition
   between read-only file systems, such denial of locks should not pose



Shepler, et al.         Expires February 2, 2007              [Page 176]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   large difficulties in practice.  When an attempt to re-establish a
   lock on a new server is denied, the client should treat the situation
   as if his original lock had been revoked.  In all cases in which the
   lock is granted, the client cannot assume that no conflicting could
   have been granted in the interim.  Where change attribute continuity
   is present, the client may check the change attribute to check for
   unwanted file modifications.  Where even this is not available, and
   the file system is not read-only a client may reasonably treat all
   pending locks as having been revoked.

10.6.6.1.  Leases and File System Transitions

   In the case of lease renewal, the client may not be submitting
   requests for a file system that has been transferred to another
   server.  This can occur because of the lease renewal mechanism.  The
   client renews leases for all file systems when submitting a request
   to any one file system at the server.

   In order for the client to schedule renewal of leases that may have
   been relocated to the new server, the client must find out about
   lease relocation before those leases expire.  To accomplish this, all
   operations which renew leases for a client (i.e.  OPEN, CLOSE, READ,
   WRITE, RENEW, LOCK, LOCKT, LOCKU), will return the error
   NFS4ERR_LEASE_MOVED if responsibility for any of the leases to be
   renewed has been transferred to a new server.  This condition will
   continue until the client receives an NFS4ERR_MOVED error and the
   server receives the subsequent GETATTR for the fs_locations or
   fs_locations_info attribute for an access to each file system for
   which a lease has been moved to a new server.

   [ISSUE: There is a conflict between this and the idea in the sessions
   text that we can have every op in the session implicitly renew the
   lease.  This needs to be dealt with.  D. Noveck will create an issue
   in the issue tracker.]

   When a client receives an NFS4ERR_LEASE_MOVED error, it should
   perform an operation on each file system associated with the server
   in question.  When the client receives an NFS4ERR_MOVED error, the
   client can follow the normal process to obtain the new server
   information (through the fs_locations and fs_locations_info
   attributes) and perform renewal of those leases on the new server,
   unless information in fs_locations_info attribute shows that no state
   could have been transferred.  If the server has not had state
   transferred to it transparently, the client will receive either
   NFS4ERR_STALE_CLIENTID or NFS4ERR_STALE_STATEID from the new server,
   as described above, and the client can then recover state information
   as it does in the event of server failure.




Shepler, et al.         Expires February 2, 2007              [Page 177]


Internet-Draft            NFSv4 Minor Version 1              August 2006


10.6.6.2.  Transitions and the Lease_time Attribute

   In order that the client may appropriately manage its leases in the
   case of a file system transition, the destination server must
   establish proper values for the lease_time attribute.

   When state is transferred transparently, that state should include
   the correct value of the lease_time attribute.  The lease_time
   attribute on the destination server must never be less than that on
   the source since this would result in premature expiration of leases
   granted by the source server.  Upon transitions in which state is
   transferred transparently, the client is under no obligation to re-
   fetch the lease_time attribute and may continue to use the value
   previously fetched (on the source server).

   If state has not been transferred transparently, either because the
   file systems are show as being in different state classes or because
   the client sees a real or simulated server reboot), the client should
   fetch the value of lease_time on the new (i.e. destination) server,
   and use it for subsequent locking requests.  However the server must
   respect a grace period at least as long as the lease_time on the
   source server, in order to ensure that clients have ample time to
   reclaim their lock before potentially conflicting non-reclaimed locks
   are granted.

10.6.7.  Write Verifiers and File System Transitions

   In a file system transition, the two file systems may be clustered in
   the handling of unstably written data.  When this is the case, and
   the two file systems belong to the same _verifier_ class, valid
   verifiers from one system may be recognized by the other and
   superfluous writes avoided.  There is no requirement that all valid
   verifiers be recognized, but it cannot be the case that a verifier is
   recognized as valid when it is not.  [NOTE: We need to resolve the
   issue of proper verifier scope].

   When two file systems belong to different _verifier_ classes, the
   client must assume that all unstable writes in existence at the time
   file system transition, have been lost since there is no way the old
   verifier can recognized as valid (or not) on the target server.

10.7.  Effecting File System Referrals

   Referrals are effected when an absent file system is encountered, and
   one or more alternate locations are made available by the
   fs_locations or fs_locations_info attributes.  The client will
   typically get an NFS4ERR_MOVED error, fetch the appropriate location
   information and proceed to access the file system on different



Shepler, et al.         Expires February 2, 2007              [Page 178]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   server, even though it retains its logical position within the
   original namespace.

   The examples given in the sections below are somewhat artificial in
   that an actual client will not typically do a multi-component lookup,
   but will have cached information regarding the upper levels of the
   name hierarchy.  However, these example are chosen to make the
   required behavior clear and easy to put within the scope of a small
   number of requests, without getting unduly into details of how
   specific clients might choose to cache things.

10.7.1.  Referral Example (LOOKUP)

   Let us suppose that the following COMPOUND is issued in an
   environment in which /this/is/the/path is absent from the target
   server.  This may be for a number of reasons.  It may be the case
   that the file system has moved, or, it may be the case that the
   target server is functioning mainly, or solely, to refer clients to
   the servers on which various file systems are located.

   o  PUTROOTFH

   o  LOOKUP "this"

   o  LOOKUP "is"

   o  LOOKUP "the"

   o  LOOKUP "path"

   o  GETFH

   o  GETATTR fsid,fileid,size,ctime

   Under the given circumstances, the following will be the result.

   o  PUTROOTFH --> NFS_OK.  The current fh is now the root of the
      pseudo-fs.

   o  LOOKUP "this" --> NFS_OK.  The current fh is for /this and is
      within the pseudo-fs.

   o  LOOKUP "is" --> NFS_OK.  The current fh is for /this/is and is
      within the pseudo-fs.

   o  LOOKUP "the" --> NFS_OK.  The current fh is for /this/is/the and
      is within the pseudo-fs.




Shepler, et al.         Expires February 2, 2007              [Page 179]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   o  LOOKUP "path" --> NFS_OK.  The current fh is for /this/is/the/path
      and is within a new, absent fs, but ... the client will never see
      the value of that fh.

   o  GETFH --> NFS4ERR_MOVED.  Fails because current fh is in an absent
      fs at the start of the operation and the spec makes no exception
      for GETFH.

   o  GETATTR fsid,fileid,size,ctime.  Not executed because the failure
      of the GETFH stops processing of the COMPOUND.

   Given the failure of the GETFH, the client has the job of determining
   the root of the absent file system and where to find that file
   system, i.e. the server and path relative to that server's root fh.
   Note here that in this example, the client did not obtain filehandles
   and attribute information (e.g. fsid) for the intermediate
   directories, so that he would not be sure where the absent file
   system starts.  It could be the case, for example, that /this/is/the
   is the root of the moved file system and that the reason that the
   lookup of "path" succeeded is that the file system was not absent on
   that op but was moved between the last LOOKUP and the GETFH (since
   COMPOUND is not atomic).  Even if we had the fsid's for all of the
   intermediate directories, we could have no way of knowing that /this/
   is/the/path was the root of a new fs, since we don't yet have its
   fsid.

   In order to get the necessary information, let us re-issue the chain
   of lookup's with GETFH's and GETATTR's to at least get the fsid's so
   we can be sure where the appropriate fs boundaries are.  The client
   could choose to get fs_locations_info at the same time but in most
   cases the client will have a good guess as to where fs boundaries are
   (because of where NFS4ERR_MOVED was gotten and where not) making
   fetching of fs_locations_info unnecessary.

   OP01:  PUTROOTFH --> NFS_OK

   -  Current fh is root of pseudo-fs.

   OP02:  GETATTR(fsid) --> NFS_OK

   -  Just for completeness.  Normally, clients will know the fsid of
      the pseudo-fs as soon as they establish communication with a
      server.

   OP03:  LOOKUP "this" --> NFS_OK






Shepler, et al.         Expires February 2, 2007              [Page 180]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   OP04:  GETATTR(fsid) --> NFS_OK

   -  Get current fsid to see where fs boundaries are.  The fsid will be
      that for the pseudo-fs in this example, so no boundary.

   OP05:  GETFH --> NFS_OK

   -  Current fh is for /this and is within pseudo-fs.

   OP06:  LOOKUP "is" --> NFS_OK

   -  Current fh is for /this/is and is within pseudo-fs.

   OP07:  GETATTR(fsid) --> NFS_OK

   -  Get current fsid to see where fs boundaries are.  The fsid will be
      that for the pseudo-fs in this example, so no boundary.

   OP08:  GETFH --> NFS_OK

   -  Current fh is for /this/is and is within pseudo-fs.

   OP09:  LOOKUP "the" --> NFS_OK

   -  Current fh is for /this/is/the and is within pseudo-fs.

   OP10:  GETATTR(fsid) --> NFS_OK

   -  Get current fsid to see where fs boundaries are.  The fsid will be
      that for the pseudo-fs in this example, so no boundary.

   OP11:  GETFH --> NFS_OK

   -  Current fh is for /this/is/the and is within pseudo-fs.

   OP12:  LOOKUP "path" --> NFS_OK

   -  Current fh is for /this/is/the/path and is within a new, absent
      fs, but ...

   -  The client will never see the value of that fh

   OP13:  GETATTR(fsid, fs_locations_info) --> NFS_OK

   -  We are getting the fsid to know where the fs boundaries are.  Note
      that the fsid we are given will not necessarily be preserved at
      the new location.  That fsid might be different and in fact the
      fsid we have for this fs might a valid fsid of a different fs on



Shepler, et al.         Expires February 2, 2007              [Page 181]


Internet-Draft            NFSv4 Minor Version 1              August 2006


      that new server.

   -  In this particular case, we are pretty sure anyway that what has
      moved is /this/is/the/path rather than /this/is/the since we have
      the fsid of the latter and it is that of the pseudo-fs, which
      presumably cannot move.  However, in other examples, we might not
      have this kind of information to rely on (e.g. /this/is/the might
      be a non-pseudo file system separate from /this/is/the/path), so
      we need to have another reliable source information on the
      boundary of the fs which is moved.  If, for example, the file
      system "/this/is" had moved we would have a case of migration
      rather than referral and once the boundaries of the migrated file
      system was clear we could fetch fs_locations_info.

   -  We are fetching fs_locations_info because the fact that we got an
      NFS4ERR_MOVED at this point means that it most likely that this is
      a referral and we need the destination.  Even if it is the case
      that "/this/is/the" is a file system which has migrated, we will
      still need the location information for that file system.

   OP14:  GETFH --> NFS4ERR_MOVED

   -  Fails because current fh is in an absent fs at the start of the
      operation and the spec makes no exception for GETFH.  Note that
      this has the happy consequence that we don't have to worry about
      the volatility or lack thereof of the fh.  If the root of the fs
      on the new location is a persistent fh, then we can assume that
      this fh, which we never saw is a persistent fh, which, if we could
      see it, would exactly match the new fh.  At least, there is no
      evidence to disprove that.  On the other hand, if we find a
      volatile root at the new location, then the filehandle which we
      never saw must have been volatile or at least nobody can prove
      otherwise.

   Given the above, the client knows where the root of the absent file
   system is, by noting where the change of fsid occurred.  The
   fs_locations_info attribute also gives the client the actual location
   of the absent file system, so that the referral can proceed.  The
   server gives the client the bare minimum of information about the
   absent file system so that there will be very little scope for
   problems of conflict between information sent by the referring server
   and information of the file system's home.  No filehandles and very
   few attributes are present on the referring server and the client can
   treat those it receives as basically transient information with the
   function of enabling the referral.






Shepler, et al.         Expires February 2, 2007              [Page 182]


Internet-Draft            NFSv4 Minor Version 1              August 2006


10.7.2.  Referral Example (READDIR)

   Another context in which a client may encounter referrals is when it
   does a READDIR on directory in which some of the sub-directories are
   the roots of absent file systems.

   Suppose such a directory is read as follows:

   o  PUTROOTFH

   o  LOOKUP "this"

   o  LOOKUP "is"

   o  LOOKUP "the"

   o  READDIR (fsid, size, ctime, mounted_on_fileid)

   In this case, because rdattr_error is not requested,
   fs_locations_info is not requested, and some of attributes cannot be
   provided the result will be an NFS4ERR_MOVED error on the READDIR,
   with the detailed results as follows:

   o  PUTROOTFH --> NFS_OK.  The current fh is at the root of the
      pseudo-fs.

   o  LOOKUP "this" --> NFS_OK.  The current fh is for /this and is
      within the pseudo-fs.

   o  LOOKUP "is" --> NFS_OK.  The current fh is for /this/is and is
      within the pseudo-fs.

   o  LOOKUP "the" --> NFS_OK.  The current fh is for /this/is/the and
      is within the pseudo-fs.

   o  READDIR (fsid, size, ctime, mounted_on_fileid) --> NFS4ERR_MOVED.
      Note that the same error would have been returned if /this/is/the
      had migrated, when in fact it is because the directory contains
      the root of an absent fs.

   So now suppose that we reissue with rdattr_error:

   o  PUTROOTFH

   o  LOOKUP "this"

   o  LOOKUP "is"




Shepler, et al.         Expires February 2, 2007              [Page 183]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   o  LOOKUP "the"

   o  READDIR (rdattr_error, fsid, size, ctime, mounted_on_fileid)

   The results will be:

   o  PUTROOTFH --> NFS_OK.  The current fh is at the root of the
      pseudo-fs.

   o  LOOKUP "this" --> NFS_OK.  The current fh is for /this and is
      within the pseudo-fs.

   o  LOOKUP "is" --> NFS_OK.  The current fh is for /this/is and is
      within the pseudo-fs.

   o  LOOKUP "the" --> NFS_OK.  The current fh is for /this/is/the and
      is within the pseudo-fs.

   o  READDIR (rdattr_error, fsid, size, ctime, mounted_on_fileid) -->
      NFS_OK.  The attributes for "path" will only contain rdattr_error
      with the value will be NFS4ERR_MOVED, together with an fsid value
      and an a value for mounted_on_fileid.

   So suppose we do another READDIR to get fs_locations_info, although
   we could have used a GETATTR directly, as in the previous section.

   o  PUTROOTFH

   o  LOOKUP "this"

   o  LOOKUP "is"

   o  LOOKUP "the"

   o  READDIR (rdattr_error, fs_locations_info, mounted_on_fileid, fsid,
      size, ctime)

   The results would be:

   o  PUTROOTFH --> NFS_OK.  The current fh is at the root of the
      pseudo-fs.

   o  LOOKUP "this" --> NFS_OK.  The current fh is for /this and is
      within the pseudo-fs.

   o  LOOKUP "is" --> NFS_OK.  The current fh is for /this/is and is
      within the pseudo-fs.




Shepler, et al.         Expires February 2, 2007              [Page 184]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   o  LOOKUP "the" --> NFS_OK.  The current fh is for /this/is/the and
      is within the pseudo-fs.

   o  READDIR (rdattr_error, fs_locations_info, mounted_on_fileid, fsid,
      size, ctime) --> NFS_OK.  The attributes will be as shown below.

   The attributes for "path" will only contain

   o  rdattr_error (value: NFS4ERR_MOVED)

   o  fs_locations_info )

   o  mounted_on_fileid (value: unique fileid within referring fs)

   o  fsid (value: unique value within referring server)

   The attribute entry for "latest" will not contain size or ctime.

10.8.  The Attribute fs_absent

   In order to provide the client information about whether the current
   file system is present or absent, the fs_absent attribute may be
   interrogated.

   As noted above, this attribute, when supported, may be requested of
   absent file systems without causing NFS4ERR_MOVED to be returned and
   it should always be available.  Servers are strongly urged to support
   this attribute on all file systems if they support it on any file
   system.

10.9.  The Attribute fs_locations

   The fs_locations attribute is structured in the following way:

           struct fs_location {
               utf8str_cis     server<>;
               pathname4       rootpath;
           };

           struct fs_locations {
               pathname4       fs_root;
               fs_location     locations<>;
           };

   The fs_location struct is used to represent the location of a file
   system by providing a server name and the path to the root of the
   file system within that server's namespace.  When a set of servers
   have corresponding file systems at the same path within their



Shepler, et al.         Expires February 2, 2007              [Page 185]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   namespaces, an array of server names may be provided.  An entry in
   the server array is an UTF8 string and represents one of a
   traditional DNS host name, IPv4 address, or IPv6 address.  It is not
   a requirement that all servers that share the same rootpath be listed
   in one fs_location struct.  The array of server names is provided for
   convenience.  Servers that share the same rootpath may also be listed
   in separate fs_location entries in the fs_locations attribute.

   The fs_locations struct and attribute contains an array of such
   locations.  Since the name space of each server may be constructed
   differently, the "fs_root" field is provided.  The path represented
   by fs_root represents the location of the file system in the current
   server's name space, i.e. that of the server from which the
   fs_locations attribute was obtained.  The fs_root path is meant to
   aid the client by clearly referencing the root of the file system
   whose locations are being reported, no matter what object within the
   current file system, the current filehandle designates.

   As an example, suppose there is a replicated file system located at
   two servers (servA and servB).  At servA, the file system is located
   at path "/a/b/c".  At, servB the file system is located at path
   "/x/y/z".  If the client were to obtain the fs_locations value for
   the directory at "/a/b/c/d", it might not necessarily know that the
   file system's root is located in servA's name space at "/a/b/c".
   When the client switches to servB, it will need to determine that the
   directory it first referenced at servA is now represented by the path
   "/x/y/z/d" on servB.  To facilitate this, the fs_locations attribute
   provided by servA would have a fs_root value of "/a/b/c" and two
   entries in fs_locations.  One entry in fs_locations will be for
   itself (servA) and the other will be for servB with a path of
   "/x/y/z".  With this information, the client is able to substitute
   "/x/y/z" for the "/a/b/c" at the beginning of its access path and
   construct "/x/y/z/d" to use for the new server.

   Since fs_locations attribute lacks information defining various
   attributes of the various file system choices presented, it should
   only be interrogated and used when fs_locations_info is not
   available.  When fs_locations is used, information about the specific
   locations should be assumed based on the following rules.

   The following rules are general and apply irrespective of the
   context.

   o  When a DNS server name maps to multiple IP addresses, they should
      be considered identical, i.e. of the same _endpoint_ class.

   o  Except in the case of servers sharing an _endpoint_ class, all
      listed servers should be considered as of the same _handle_ class,



Shepler, et al.         Expires February 2, 2007              [Page 186]


Internet-Draft            NFSv4 Minor Version 1              August 2006


      if and only if, the current fh_expire_type attribute does not
      include the FH4_VOL_MIGRATION bit.  Note that in the case of
      referral, filehandle issues do not apply since there can be no
      filehandles known within the current file system nor is there any
      access to the fh_expire_type attribute on the referring (absent)
      file system.

   o  Except in the case of servers sharing an _endpoint_ class, all
      listed servers should be considered as of the same _fileid_ class,
      if and only if, the fh_expire_type attribute indicates persistent
      filehandles and does not include the FH4_VOL_MIGRATION bit.  Note
      that in the case of referral, fileid issues do not apply since
      there can be no fileids known within the referring (absent) file
      system nor is there any access to the fh_expire_type attribute.

   o  Except in the case of servers sharing an _endpoint_ class, all
      listed servers should be considered as of different _change_
      classes.

   For other class assignments, handling depends of file system
   transitions depends on the reasons for the transition:

   o  When the transition is due to migration, the target should be
      treated as being of the same _state_ and _verifier_ class as the
      source.

   o  When the transition is due to failover to another replica, the
      target should be treated as being of a different _state_ and
      _verifier_ class from the source.

   The specific choices reflect typical implementation patterns for
   failover and controlled migration respectively.  Since other choices
   are possible and useful, this information is better obtained by using
   fs_locations_info.

   See the section "Security Considerations" for a discussion on the
   recommendations for the security flavor to be used by any GETATTR
   operation that requests the "fs_locations" attribute.

10.10.  The Attribute fs_locations_info

   The fs_locations_info attribute is intended as a more functional
   replacement for fs_locations which will continue to exist and be
   supported.  Clients can use it get a more complete set of information
   about alternative file system locations.  When the server does not
   support fs_locations_info, fs_locations can be used to get a subset
   of the information.  A server which supports fs_locations_info MUST
   support fs_locations as well.



Shepler, et al.         Expires February 2, 2007              [Page 187]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   There are several sorts of additional information present in
   fs_locations_info, that aren't available in fs_locations:

   o  Attribute continuity information to allow a client to select a
      location which meets the transparency requirements of the
      applications accessing the data and to take advantage of
      optimizations that server guarantees as to attribute continuity
      may provide (e.g. change attribute).

   o  File System identity information which indicates when multiple
      replicas, from the clients point of view, correspond to the same
      target file system, allowing them to be used interchangeably,
      without disruption, as multiple paths to the same thing.

   o  Information which will bear on the suitability of various
      replicas, depending on the use that the client intends.  For
      example, many applications need an absolutely up-to-date copy
      (e.g. those that write), while others may only need access to the
      most up-to-date copy reasonably available.

   o  Server-derived preference information for replicas, which can be
      used to implement load-balancing while giving the client the
      entire fs list to be used in case the primary fails.

   The fs_locations_info attribute consists of a root pathname (just
   like fs_locations), together with an array of location4_item
   structures.
























Shepler, et al.         Expires February 2, 2007              [Page 188]


Internet-Draft            NFSv4 Minor Version 1              August 2006


             struct locations4_server {
                     int32_t         currency;
                     uint32_t        info<>;
                     utf8str_cis     server;
             };

             const LIBX_GFLAGS     = 0;
             const LIBX_TFLAGS     = 1;

             const LIBX_CLSHARE    = 2;
             const LIBX_CLSERVER   = 3;
             const LIBX_CLENDPOINT = 4;
             const LIBX_CLHANDLE   = 5;
             const LIBX_CLFILEID   = 6;
             const LIBX_CLVERIFIER = 7;
             const LIBX_CLSTATE    = 8;

             const LIBX_READRANK   = 9;
             const LIBX_WRITERANK  = 10;
             const LIBX_READORDER  = 11;
             const LIBX_WRITEORDER = 12;

             const LIGF_WRITABLE   = 0x01;
             const LIGF_CUR_REQ    = 0x02;
             const LIGF_ABSENT     = 0x04;
             const LIGF_GOING      = 0x08;

             const LITF_RDMA       = 0x01;

             struct locations4_item {
                     locations4_server entries<>;
                     pathname4       rootpath;
             };

             struct locations4_info {
                     pathname4       fs_root;
                     locations4_item items<>;
             };


   The fs_locations_info attribute is structured similarly to the
   fs_locations attribute.  A top-level structure (fs_locations4 or
   locations4_info) contains the entire attribute including the root
   pathname of the fs and an array of lower-level structures that define
   replicas that share a common root path on their respective servers.
   Those lower-level structures in turn (fs_locations4 or
   location4_item) contain a specific pathname and information on one or
   more individual server replicas.  For that last lowest-level



Shepler, et al.         Expires February 2, 2007              [Page 189]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   information, fs_locations has a server name in the form of
   utf8str_cis, while fs_locations_info has a location4_server structure
   that contains per-server-replica information in addition to the
   server name.

   The location4_server structure consists of the following items:

   o  An indication of file system up-to-date-ness (currency) in terms
      of approximate seconds before the present.  A negative value
      indicates that the server is unable to give any reasonably useful
      value here.  A zero indicates that file system is the actual
      writable data or a reliably coherent and fully up-to-date copy.
      Positive values indicate how out- of-date this copy can normally
      be before it is considered for update.  Such a value is not a
      guarantee that such updates will always be performed on the
      required schedule but instead serve as a hint about how far behind
      the most up-to-date copy of the data, this copy would normally be
      expected to be.

   o  A counted array of 32-but words containing various sorts of data,
      about the particular file system instance.  This data includes
      general flags, transport capability flags, file system equivalence
      class information, and selection priority information.  The
      encoding will be discussed below.

   o  The server string.  For the case of the replica currently being
      accessed (via GETATTR), a null string may be used to indicate the
      current address being used for the RPC call.

   Data within the info array, is in the form of 8-bit data items even
   though that array is, from XDR's point of view an array of 32-bit
   integers.  This definition was chosen because:

   o  The kinds of data in the info array, representing, flags, file
      system classes and priorities among set of file systems
      representing the same data are such that eight bits provides a
      quite acceptable range of values.  Even where there might be more
      than 256 such file system instances, having more than 256 distinct
      classes or priorities is unlikely.

   o  XDR does not have any means to declare an 8-bit data type, other
      than an ASCII string, and using 32-bit data types would lead to
      significant space inefficiency.

   o  Explicit definition of the various specific data items within XDR
      would limit expandability in that any extension within a
      subsequent minor version would require yet another attribute,
      leading to specification and implementation clumsiness.



Shepler, et al.         Expires February 2, 2007              [Page 190]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   o  Such explicit definitions would also make it impossible to propose
      standards-track extensions apart from a full minor version.

   Each 8-bit successive field within this array is designated by a
   constant byte-index as defined above.  More significant bit fields
   within a single word have successive indices with a transition to the
   next word following the most significant 8-bit field in each word.

   The set of info data is subject to expansion in a future minor
   version, or in a standard-track RFC, within the context of a single
   minor version.  The server SHOULD NOT send and the client MUST not
   use indices within the info array that are not defined in standards-
   track RFC's.

   The following fragment of c++ code (with Doxygen-style comments)
   illustrates how data items within the info array can be found using a
   byte-index such as specified by the constants beginning with "LIBX_".
   The associated InfoArray object is assume to be initialized with
   "Length" containing the XDR-specified length in terms of 32-bit words
   and "Data" containing the array of words encoded by the "info<>"
   specification.






























Shepler, et al.         Expires February 2, 2007              [Page 191]


Internet-Draft            NFSv4 Minor Version 1              August 2006


             class InfoArray {
               private:
                 uint32_t    Length;
                 uint32_t    Data[];

               public:
                 uint8_t     GetValue(int byteIndex);
             };

             /// @brief Get the value of a locations4_server info value
             ///
             /// This method obtains the specific info value given a
             /// byte index defined in the NFSv4.1 spec or another
             /// later standards-track document.
             ///
             /// @param[in] byteIndex The byte index identifying the
             ///                      item requested.
             /// @returns The value of the requested item.

             uint8_t InfoArray::GetItem(int byteIndex) {

                 int         wordIndex = byteIndex/4;
                 int         byteWithinWord = byteIndex % 4;

                 if (wordIndex >= Length) {
                     return (0);
                 }

                 uint32_t    ourWord = Data[wordIndex];
                 return ((ourWord >> (byteWithinWord*8)) & 0xff);
             }

   The info array contains within it:

   o  Two 8-bit flag fields, one devoted to general file-system
      characteristics and a second reserved for transport-related
      capabilities.

   o  Seven 8-bit class values which define various file system
      equivalence classes as explained below.

   o  Four 8-bit priority values which govern file system selection as
      explained below.

   The general file system characteristics flag (at byte index
   LIBX_GFLAGS) has the following bits defined within it:





Shepler, et al.         Expires February 2, 2007              [Page 192]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   o  LIGF_WRITABLE indicates that this fs target is writable, allowing
      it to be selected by clients which may need to write on this file
      system.  When the current file system instance is writable, then
      any other file system to which the client might switch must
      incorporate within its data any committed write made on the
      current file system instance.  See the section on verifier class,
      for issues related to uncommitted writes.  While there is no harm
      in not setting this flag for a file system that turns out to be
      writable, turning the flag on for read-only file system can cause
      problems for clients who select a migration or replication target
      based on it and then find themselves unable to write.

   o  LIGF_CUR_REQ indicates that this replica is the one on which the
      request is being made.  Only a single server entry may have this
      flag set and in the case of a referral, no entry will have it.

   o  LIGF_ABSENT indicates that this entry corresponds an absent file
      system replica.  It can only be set if LIGF_CUR_REQ is set.  When
      both such bits are set it indicates that a file system instance is
      not usable but that the information in the entry can be used to
      determine the sorts of continuity available when switching from
      this replica to other possible replicas.  Since this bit can only
      be true if LIGF_CUR_REQ is true, the value could be determined
      using the fs_absent attribute but the information is also made
      available here for the convenience of the client.  An entry with
      this bit, since it represents a true file system (albeit absent)
      does not appear in the event of a referral, but only where a file
      system has been accessed at this location and subsequently been
      migrated.

   o  LIGF_GOING indicates that a replica, while still available, should
      not be used further.  The client, if using it, should make an
      orderly transfer to another file system instance as expeditiously
      as possible.  It is expected that file systems going out of
      service will be announced as LIGF_GOING some time before the
      actual loss of service and that the valid_for value will be
      sufficiently small to allow clients to detect and act on scheduled
      events while large enough that the cost of the requests to fetch
      the fs_locations_info values will not be excessive.  Values on the
      order of ten minutes seem reasonable.

   The transport-flag field (at byte index LIBX_TFLAGS) contains the
   following bits related to the transport capabilities of the specific
   file system.

   o  LITF_RDMA indicates that this file system provides NFSv4.1 file
      system access using an RDMA-capable transport.




Shepler, et al.         Expires February 2, 2007              [Page 193]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   Attribute continuity and file system identity information are
   expressed by defining equivalence relations on the sets of file
   systems presented to the client.  Each such relation is expressed as
   a set of file system equivalence classes.  For each relation, a file
   system has an 8-bit class number.  Two file systems belong to the
   same class if both have identical non-zero class numbers.  Zero is
   treated as non-matching.  Most often, the relevant question for the
   client will be whether a given replica is identical-with/
   continuous-to the current one in a given respect but the information
   should be available also as to whether two other replicas match in
   that respect as well.

   The following fields specify the file system's class numbers for the
   equivalence relations used in determining the nature of file system
   transitions.  See Section 10.6 for details about how this information
   is to be used.

   o  The field with byte-index LIBX_CLSHARE defines the sharing class
      for the file system.

   o  The field with byte-index LIBX_CLSERVER defines the server class
      for the file system.

   o  The field with byte-index LIBX_CLENDPOINT defines the endpoint
      class for the file system.

   o  The field with byte-index LIBX_CLHANDLE defines the handle class
      for the file system.

   o  The field with byte-index LIBX_CLFILEID defines the fileid class
      for the file system.

   o  The field with byte-index LIBX_CLVERIFIER defines the verifier
      class for the file system.

   o  The field with byte-index LIBX_CLSTATE defines the state class for
      the file system.

   Server-specified preference information is also provided via 8-bit
   values within the info array.  The values provide a rank and an order
   (see below) to be used with separate values specifiable for the cases
   of read-only and writable file systems.  These values are compared
   for different file systems to establish the server-specified
   preference, with lower values indicating "more preferred".

   Rank is used to express a strict server-imposed ordering on clients,
   with lower values indicating "more preferred."  Clients should
   attempt to use all replicas with a given rank before they use one



Shepler, et al.         Expires February 2, 2007              [Page 194]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   with a higher rank.  Only if all of those file systems are
   unavailable should the client proceed to those of a higher rank.

   Within a rank, the order value is used to specify the server's
   preference to guide the client's selection when the client's own
   preferences are not controlling, with lower values of order
   indicating "more preferred."  If replicas are approximately equal in
   all respects, clients should defer to the order specified by the
   server.  When clients look at server latency as part of their
   selection, they are free to use this criterion but it is suggested
   that when latency differences are not significant, the server-
   specified order should guide selection.

   o  The field at byte index LIBX_READRANK gives the rank value to be
      used for read-only access.

   o  The field at byte index LIBX_READOREDER gives the order value to
      be used for read-only access.

   o  The field at byte index LIBX_WRITERANK gives the rank value to be
      used for writable access.

   o  The field at byte index LIBX_WRITEOREDER gives the order value to
      be used for writable access.

   Depending on the potential need for write access by a given client,
   one of the pairs of rank and order values is used.  The read rank and
   order should only be used if the client knows that only reading will
   ever be done or if it is prepared to switch to a different replica in
   the event that any write access capability is required in the future.

   The locations4_info structure, encoding the fs_locations_info
   attribute contains the following:

   o  The fs_root field which contains the pathname of the root of the
      current file system on the current server, just as it does the
      fs_locations4 structure.

   o  An array of locations4_item structures, which contain information
      about replicas of the current file system.  Where the current file
      system is actually present, or has been present, i.e. this is not
      a referral situation, one of the locations4_item structure will
      contain a locations4_server for the current server.  This
      structure will have LIGF_ABSENT set if the current file system is
      absent, i.e. normal access to it will return NFS4ERR_MOVED.

   o  The valid_for field specifies a time for which it is reasonable
      for a client to use the fs_locations_info attribute without



Shepler, et al.         Expires February 2, 2007              [Page 195]


Internet-Draft            NFSv4 Minor Version 1              August 2006


      refetch.  The valid_for value does not provide a guarantee of
      validity since servers can unexpectedly go out of service or
      become inaccessible for any number of reasons.  Clients are well-
      advised to refetch this information for actively accessed file
      system at every valid_for seconds.  This is particularly important
      when file system replicas may go out of service in a controlled
      way using the LIGF_GOING flag to communicate an ongoing change.
      The server should set valid_for to a value which allows well-
      behaved clients to notice the LIF_GOING flag and make an orderly
      switch before the loss of service becomes effective.  If this
      value is zero, then no refetch interval is appropriate and the
      client need not refetch this data on any particular schedule.  In
      the event of a transition to a new file system instance, a new
      value of the fs_locations_info attribute will be fetched at the
      destination and it is to be expected that this may have a
      different valid_for value, which the client should then use, in
      the same fashion as the previous value.

   As noted above, the fs_locations_info attribute, when supported, may
   be requested of absent file systems without causing NFS4ERR_MOVED to
   be returned and it is generally expected that will be available for
   both present and absent file systems even if only a single
   location_server entry is present, designating the current (present)
   file system, or two location_server entries designating the current
   (and now previous) location of an absent file system and its
   successor location.  Servers are strongly urged to support this
   attribute on all file systems if they support it on any file system.

10.11.  The Attribute fs_status

   In an environment in which multiple copies of the same basic set of
   data are available, information regarding the particular source of
   such data and the relationships among different copies, can be very
   helpful in providing consistent data to applications.

















Shepler, et al.         Expires February 2, 2007              [Page 196]


Internet-Draft            NFSv4 Minor Version 1              August 2006


             enum fs4_status_type {
                     STATUS4_FIXED = 1,
                     STATUS4_UPDATED = 2,
                     STATUS4_VERSIONED = 3,
                     STATUS4_WRITABLE = 4,
                     STATUS4_ABSENT = 5
             };

             struct fs4_status {
                     fs4_status_type fsstat_type;
                     utf8str_cs      fsstat_source;
                     utf8str_cs      fsstat_current;
                     int32_t         fsstat_age;
                     nfstime4        fsstat_version;
             };


   The type value indicates the kind of file system image represented.
   This is of particular importance when using the version values to
   determine appropriate succession of file system images.  Five types
   are distinguished:

   o  STATUS4_FIXED which indicates a read-only image in the sense that
      it will never change.  The possibility is allowed that as a result
      of migration or switch to a different image, changed data can be
      accessed but within the confines of this instance, no change is
      allowed.  The client can use this fact to aggressively cache.

   o  STATUS4_UPDATED which indicates an image that cannot be updated by
      the user writing to it but may be changed exogenously, typically
      because it is a periodically updated copy of another writable file
      system somewhere else.

   o  STATUS4_VERSIONED which indicates that the image, like the
      STATUS4_UPDATED case, is updated exogenously, but it provides a
      guarantee that the server will carefully update the associated
      version value so that the client, may if it chooses, protect
      itself from a situation in which it reads data from one version of
      the file system, and then later reads data from an earlier version
      of the same file system.  See below for a discussion of how this
      can be done.

   o  STATUS4_WRITABLE which indicates that the file system is an actual
      writable one.  The client need not of course actually write to the
      file system, but once it does, it should not accept a transition
      to anything other than a writable instance of that same file
      system.




Shepler, et al.         Expires February 2, 2007              [Page 197]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   o  STATUS4_ABSENT which indicates that the information is the last
      valid for a file system which is no longer present.

   The opaque strings source and current provide a way of presenting
   information about the source of the file system image being present.
   It is not intended that client do anything with this information
   other than make it available to administrative tools.  It is intended
   that this information be helpful when researching possible problems
   with a file system image that might arise when it is unclear if the
   correct image is being accessed and if not, how that image came to be
   made.  This kind of debugging information will be helpful, if, as
   seems likely, copies of file systems are made in many different ways
   (e.g. simple user-level copies, file system- level point-in-time
   copies, cloning of the underlying storage), under a variety of
   administrative arrangements.  In such environments, determining how a
   given set of data was constructed can be very helpful in resolving
   problems.

   The opaque string 'source' is used to indicate the source of a given
   file system with the expectation that tools capable of creating a
   file system image propagate this information, when that is possible.
   It is understood that this may not always be possible since a user-
   level copy may be thought of as creating a new data set and the tools
   used may have no mechanism to propagate this data.  When a file
   system is initially created associating with it data regarding how
   the file system was created, where it was created, by whom, etc. can
   be put in this attribute in a human- readable string form so that it
   will be available when propagated to subsequent copies of this data.

   The opaque string 'current' should provide whatever information is
   available about the source of the current copy.  Such information as
   the tool creating it, any relevant parameters to that tool, the time
   at which the copy was done, the user making the change, the server on
   which the change was made etc.  All information should be in a human-
   readable string form.

   The age provides an indication of how out-of-date the file system
   currently is with respect to its ultimate data source (in case of
   cascading data updates).  This complements the currency field of
   locations4_server (See Section 10.10) in the following way: the
   information in locations4_server.currency gives a bound for how out
   of date the data in a file system might typically get, while the age
   gives a bound on how out of date that data actually is.  Negative
   values imply no information is available.  A zero means that this
   data is known to be current.  A positive value means that this data
   is known to be no older than that number of seconds with respect to
   the ultimate data source.




Shepler, et al.         Expires February 2, 2007              [Page 198]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   The version field provides a version identification, in the form of a
   time value, such that successive versions always have later time
   values.  When the file system type is anything other than
   STATUS4_VERSIONED, the server may provide such a value but there is
   no guarantee as to its validity and clients will not use it except to
   provide additional information to add to 'source' and 'current'.

   When the type is STATUS4_VERSIONED, servers should provide a value of
   version which progresses monotonically whenever any new version of
   the data is established.  This allows the client, if reliable image
   progression is important to it, to fetch this attribute as part of
   each COMPOUND where data or metadata from the file system is used.

   When it is important to the client to make sure that only valid
   successor images are accepted, it must make sure that it does not
   read data or metadata from the file system without updating its sense
   of the current state of the image, to avoid the possibility that the
   fs_status which the client holds will be one for an earlier image,
   and so accept a new file system instance which is later than that but
   still earlier than updated data read by the client.

   In order to do this reliably, it must do a GETATTR of fs_status that
   follows any interrogation of data or metadata within the file system
   in question.  Often this is most conveniently done by appending such
   a GETATTR after all other operations that reference a given file
   system.  When errors occur between reading file system data and
   performing such a GETATTR, care must be exercised to make sure that
   the data in question is not used before obtaining the proper
   fs_status value.  In this connection, when an OPEN is done within
   such a versioned file system and the associated GETATTR of fs_status
   is not successfully completed, the open file in question must not be
   accessed until that fs_status is fetched.

   The procedure above will ensure that before using any data from the
   file system the client has in hand a newly-fetched current version of
   the file system image.  Multiple values for multiple requests in
   flight can be resolved by assembling them into the required partial
   order (and the elements should form a total order within it) and
   using the last.  The client may then, when switching among file
   system instances, decline to use an instance which is not of type
   STATUS4_VERSIONED or whose version field is earlier than the last one
   obtained from the predecessor file system instance.


11.  Directory Delegations






Shepler, et al.         Expires February 2, 2007              [Page 199]


Internet-Draft            NFSv4 Minor Version 1              August 2006


11.1.  Introduction to Directory Delegations

   The major addition to NFS version 4 in the area of caching is the
   ability of the server to delegate certain responsibilities to the
   client.  When the server grants a delegation for a file to a client,
   the client receives certain semantics with respect to the sharing of
   that file with other clients.  At OPEN, the server may provide the
   client either a read or write delegation for the file.  If the client
   is granted a read delegation, it is assured that no other client has
   the ability to write to the file for the duration of the delegation.
   If the client is granted a write delegation, the client is assured
   that no other client has read or write access to the file.  This
   reduces network traffic and server load by allowing the client to
   perform certain operations on local file data and can also provide
   stronger consistency for the local data.

   Directory caching for the NFS version 4 protocol is similar to
   previous versions.  Clients typically cache directory information for
   a duration determined by the client.  At the end of a predefined
   timeout, the client will query the server to see if the directory has
   been updated.  By caching attributes, clients reduce the number of
   GETATTR calls made to the server to validate attributes.
   Furthermore, frequently accessed files and directories, such as the
   current working directory, have their attributes cached on the client
   so that some NFS operations can be performed without having to make
   an RPC call.  By caching name and inode information about most
   recently looked up entries in DNLC (Directory Name Lookup Cache),
   clients do not need to send LOOKUP calls to the server every time
   these files are accessed.

   This caching approach works reasonably well at reducing network
   traffic in many environments.  However, it does not address
   environments where there are numerous queries for files that do not
   exist.  In these cases of "misses", the client must make RPC calls to
   the server in order to provide reasonable application semantics and
   promptly detect the creation of new directory entries.  Examples of
   high miss activity are compilation in software development
   environments.  The current behavior of NFS limits its potential
   scalability and wide-area sharing effectiveness in these types of
   environments.  Other distributed stateful filesystem architectures
   such as AFS and DFS have proven that adding state around directory
   contents can greatly reduce network traffic in high miss
   environments.

   Delegation of directory contents is proposed as an extension for
   NFSv4.  Such an extension would provide similar traffic reduction
   benefits as with file delegations.  By allowing clients to cache
   directory contents (in a read-only fashion) while being notified of



Shepler, et al.         Expires February 2, 2007              [Page 200]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   changes, the client can avoid making frequent requests to interrogate
   the contents of slowly-changing directories, reducing network traffic
   and improving client performance.

   These extensions allow improved namespace cache consistency to be
   achieved through delegations and synchronous recalls alone without
   asking for notifications.  In addition, if time-based consistency is
   sufficient, asynchronous notifications can provide performance
   benefits for the client, and possibly the server, under some common
   operating conditions such as slowly-changing and/or very large
   directories.

11.2.  Directory Delegation Design (in brief)

   A new operation GET_DIR_DELEGATION is used by the client to ask for a
   directory delegation.  The delegation covers directory attributes and
   all entries in the directory.  If either of these change the
   delegation will be recalled synchronously.  The operation causing the
   recall will have to wait before the recall is complete.  Any changes
   to directory entry attributes will not cause the delegation to be
   recalled.

   In addition to asking for delegations, a client can also ask for
   notifications for certain events.  These events include changes to
   directory attributes and/or its contents.  If a client asks for
   notification for a certain event, the server will notify the client
   when that event occurs.  This will not result in the delegation being
   recalled for that client.  The notifications are asynchronous and
   provide a way of avoiding recalls in situations where a directory is
   changing enough that the pure recall model may not be effective while
   trying to allow the client to get substantial benefit.  In the
   absence of notifications, once the delegation is recalled the client
   has to refresh its directory cache which might not be very efficient
   for very large directories.

   The delegation is read only and the client may not make changes to
   the directory other than by performing NFSv4 operations that modify
   the directory or the associated file attributes so that the server
   has knowledge of these changes.  In order to keep the client
   namespace in sync with the server, the server will notify the client
   holding the delegation of the changes made as a result.  This is to
   avoid any subsequent GETATTR or READDIR calls to the server.  If a
   client holding the delegation makes any changes to the directory, the
   delegation will not be recalled.

   Delegations can be recalled by the server at any time.  Normally, the
   server will recall the delegation when the directory changes in a way
   that is not covered by the notification, or when the directory



Shepler, et al.         Expires February 2, 2007              [Page 201]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   changes and notifications have not been requested.

   Also if the server notices that handing out a delegation for a
   directory is causing too many notifications to be sent out, it may
   decide not to hand out a delegation for that directory or recall
   existing delegations.  If another client removes the directory for
   which a delegation has been granted, the server will recall the
   delegation.

   Both the notification and recall operations need a callback path to
   exist between the client and server.  If the callback path does not
   exist, then delegation can not be granted.  Note that with the
   session extensions [talpey] that should not be an issue.  In the
   absence of sessions, the server will have to establish a callback
   path to the client to send callbacks.

11.3.  Recommended Attributes in support of Directory Delegations

   dir_notif_delay -  notification delays on directory attributes

   dir_entry_notif_delay -  notification delays on child attributes

   These attributes allow the client and server to negotiate the
   frequency of notifications sent due to changes in attributes.  These
   attributes are returned as part of a GETATTR call on the directory.
   The dir_notif_delay value covers all attribute changes to the
   directory and the dir_entry_notif_delay covers all attribute changes
   to any child in the directory.

   These attributes are per directory.  The client needs to get these
   values by doing a GETATTR on the directory for which it wants
   notifications.  However these attributes are only required when the
   client is interested in getting attribute notifications.  For all
   other types of notifications and delegation requests without
   notifications, these attributes are not required.

   When the client calls the GET_DIR_DELEGATION operation and asks for
   attribute change notifications, it should request notification delays
   that are no less than the values in the server-provided attributes.
   If the client requests smaller delays, the server should not commit
   to sending notifications for that change event.

   A value of zero for these attributes means the server will send the
   notification as soon as the change occurs.  It is not recommended to
   set this value to zero since that can put a lot of burden on the
   server.nfstime4 values that compute to negative values are illegal.

   By granting a request for notifications, the server commits to



Shepler, et al.         Expires February 2, 2007              [Page 202]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   delaying notifications to that client by no more than the
   notification delay which the client requested.

11.4.  Delegation Recall

   The server will recall the directory delegation by sending a callback
   to the client.  It will use the same callback procedure as used for
   recalling file delegations.  The server will recall the delegation
   when the directory changes in a way that is not covered by the
   notification.  However the server will not recall the delegation if
   attributes of an entry within the directory change.  Also if the
   server notices that handing out a delegation for a directory is
   causing too many notifications to be sent out, it may decide not to
   hand out a delegation for that directory.  If another client tries to
   remove the directory for which a delegation has been granted, the
   server will recall the delegation.

   The server will recall the delegation by sending a CB_RECALL callback
   to the client.  If the recall is done because of a directory changing
   event, the request making that change will need to wait while the
   client returns the delegation.

11.5.  Directory Delegation Recovery

   Crash recovery has two main goals, avoiding the necessity of breaking
   application guarantees with respect to locked files and delivery of
   updates cached at the client.  Neither of these applies to
   directories protected by read delegations and notifications.  Thus,
   the client is required to establish a new delegation on a server or
   client reboot.  [[Comment.14: we have special reclaim types allow
   clients to recovery delegations through client reboot.  Do we really
   want CREATE_CLIENTID/CREATE_SESSION to destroy directory delegation
   state?]]


12.  Parallel NFS (pNFS)

12.1.  Introduction

   The NFSv4.0 protocol [2] specifies the interaction between a client
   that accesses files and a server that provides access to files and is
   responsible for coordinating access by multiple clients.  As
   described in the pNFS problem statement, this requires that all
   access to a set of files exported by a single NFSv4 server be
   performed by that server; at high data rates the server may become a
   bottleneck.

   The parallel NFS (pNFS) extensions to NFSv4 allow data accesses to



Shepler, et al.         Expires February 2, 2007              [Page 203]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   bypass this bottleneck by permitting direct client access to the
   storage devices containing the file data.  When file data for a
   single NFSv4 server is stored on multiple and/or higher throughput
   storage devices (by comparison to the server's throughput
   capability), the result can be significantly better file access
   performance.  The relationship among multiple clients, a single
   server, and multiple storage devices for pNFS (server and clients
   have access to all storage devices) is shown in this diagram:

       +-----------+
       |+-----------+                                 +-----------+
       ||+-----------+                                |           |
       |||           |        NFSv4 + pNFS            |           |
       +||  Clients  |<------------------------------>|   Server  |
        +|           |                                |           |
         +-----------+                                |           |
              |||                                     +-----------+
              |||                                           |
              |||                                           |
              ||| Storage        +-----------+              |
              ||| Protocol       |+-----------+             |
              ||+----------------||+-----------+  Control|
              |+-----------------|||           |    Protocol|
              +------------------+||  Storage  |------------+
                                  +|  Devices  |
                                   +-----------+

                                 Figure 60

   In this structure, the responsibility for coordination of file access
   by multiple clients is shared among the server, clients, and storage
   devices.  This is in contrast to NFSv4 without pNFS extensions, in
   which this is primarily the server's responsibility, some of which
   can be delegated to clients under strictly specified conditions.

   The pNFS extension to NFSv4 takes the form of new operations that
   manage data location information called a "layout".  The layout is
   managed in a similar fashion as NFSv4 data delegations (e.g., they
   are recallable and revocable).  However, they are distinct
   abstractions and are manipulated with new operations.  When a client
   holds a layout, it has rights to access the data directly using the
   location information in the layout.

   There are new attributes that describe general layout
   characteristics.  However, much of the required information cannot be
   managed solely within the attribute framework, because it will need
   to have a strictly limited term of validity, subject to invalidation
   by the server.  This requires the use of new operations to obtain,



Shepler, et al.         Expires February 2, 2007              [Page 204]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   return, recall, and modify layouts, in addition to new attributes.

   This document specifies both the NFSv4 extensions required to
   distribute file access coordination between the server and its
   clients and a NFSv4 file storage protocol that may be used to access
   data stored on NFSv4 storage devices.

   Storage protocols used to access a variety of other storage devices
   are deliberately not specified here.  These might include:

   o  Block/volume protocols such as iSCSI ([29]), and FCP ([30]).  The
      block/volume protocol support can be independent of the addressing
      structure of the block/volume protocol used, allowing more than
      one protocol to access the same file data and enabling
      extensibility to other block/volume protocols.

   o  Object protocols such as OSD over iSCSI or Fibre Channel [31].

   o  Other storage protocols, including PVFS and other file systems
      that are in use in HPC environments.

   pNFS is designed to accommodate these protocols and be extensible to
   new classes of storage protocols that may be of interest.

   The distribution of file access coordination between the server and
   its clients increases the level of responsibility placed on clients.
   Clients are already responsible for ensuring that suitable access
   checks are made to cached data and that attributes are suitably
   propagated to the server.  Generally, a misbehaving client that hosts
   only a single-user can only impact files accessible to that single
   user.  Misbehavior by a client hosting multiple users may impact
   files accessible to all of its users.  NFSv4 delegations increase the
   level of client responsibility as a client that carries out actions
   requiring a delegation without obtaining that delegation will cause
   its user(s) to see unexpected and/or incorrect behavior.

   Some uses of pNFS extend the responsibility of clients beyond
   delegations.  In some configurations, the storage devices cannot
   perform fine-grained access checks to ensure that clients are only
   performing accesses within the bounds permitted to them by the pNFS
   operations with the server (e.g., the checks may only be possible at
   file system granularity rather than file granularity).  In situations
   where this added responsibility placed on clients creates
   unacceptable security risks, pNFS configurations in which storage
   devices cannot perform fine-grained access checks SHOULD NOT be used.
   All pNFS server implementations MUST support NFSv4 access to any file
   accessible via pNFS in order to provide an interoperable means of
   file access in such situations.  See Section 12.3.8 on Security for



Shepler, et al.         Expires February 2, 2007              [Page 205]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   further discussion.

   Finally, there are issues about how layouts interact with the
   existing NFSv4 abstractions of data delegations and byte range
   locking.  These issues, and others, are also discussed here.

12.2.  General Definitions

   This protocol extension partitions the NFSv4 file system protocol
   into two parts, the control path and the data path.  The control path
   is implemented by the extended (p)NFSv4 server.  When the file system
   being exported by (p)NFSv4 uses storage devices that are visible to
   clients over the network, the data path may be implemented by direct
   communication between the extended (p)NFSv4 file system client and
   the storage devices.  This leads to a few new terms used to describe
   the protocol extension and some clarifications of existing terms.

12.2.1.  Metadata Server

   A pNFS "server" or "metadata server" is a server as defined by
   RFC3530 RFC3530 [2], which additionally provides support of the pNFS
   minor extension.  When using the pNFS NFSv4 minor extension, the
   metadata server may hold only the metadata associated with a file,
   while the data can be stored on the storage devices.  However,
   similar to NFSv4, data may also be written through the metadata
   server.  Note: directory data is always accessed through the metadata
   server.

12.2.2.  Client

   A pNFS "client" is a client as defined by RFC3530 [2], with the
   addition of supporting the pNFS minor extension server protocol and
   with the addition of supporting at least one storage protocol for
   performing I/O directly to storage devices.

12.2.3.  Storage Device

   This is a device, or server, that controls the file's data, but
   leaves other metadata management up to the metadata server.  A
   storage device could be another NFS server, or an Object Storage
   Device (OSD) or a block device accessed over a SAN (e.g., either
   FiberChannel or iSCSI SAN).  The goal of this extension is to allow
   direct communication between clients and storage devices.

12.2.4.  Storage Protocol

   This is the protocol between the pNFS client and the storage device
   used to access the file data.  Three following types have been



Shepler, et al.         Expires February 2, 2007              [Page 206]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   described: file protocols (e.g., NFSv4), object protocols (e.g.,
   OSD), and block/volume protocols (e.g., based on SCSI-block
   commands).  These protocols are in turn realizable over a variety of
   transport stacks.  We anticipate there will be variations on these
   storage protocols, including new protocols that are unknown at this
   time or experimental in nature.  The details of the storage protocols
   will be described in other documents so that pNFS clients can be
   written to use these storage protocols.  Use of NFSv4 itself as a
   file-based storage protocol is described in Section 12.4.

12.2.5.  Control Protocol

   This is a protocol used by the exported file system between the
   server and storage devices.  Specification of such protocols is
   outside the scope of this draft.  Such control protocols would be
   used to control such activities as the allocation and deallocation of
   storage and the management of state required by the storage devices
   to perform client access control.  The control protocol should not be
   confused with protocols used to manage LUNs in a SAN and other
   sysadmin kinds of tasks.

   While the pNFS protocol allows for any control protocol, in practice
   the control protocol is closely related to the storage protocol.  For
   example, if the storage devices are NFS servers, then the protocol
   between the pNFS metadata server and the storage devices is likely to
   involve NFS operations.  Similarly, when object storage devices are
   used, the pNFS metadata server will likely use iSCSI/OSD commands to
   manipulate storage.

   However, this document does not mandate any particular control
   protocol.  Instead, it just describes the requirements on the control
   protocol for maintaining attributes like modify time, the change
   attribute, and the end-of-file position.

12.2.6.  Metadata

   This is information about a file, like its name, owner, where it
   stored, and so forth.  The information is managed by the exported
   file system server (metadata server).  Metadata also includes lower-
   level information like block addresses and indirect block pointers.
   Depending the storage protocol, block-level metadata may or may not
   be managed by the metadata server, but is instead managed by Object
   Storage Devices or other servers acting as a storage device.

12.2.7.  Layout

   A layout defines how a file's data is organized on one or more
   storage devices.  There are many possible layout types.  They vary in



Shepler, et al.         Expires February 2, 2007              [Page 207]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   the storage protocol used to access the data, and in the aggregation
   scheme that lays out the file data on the underlying storage devices.
   Layouts are described in more detail below.

12.3.  pNFS protocol semantics

   This section describes the semantics of the pNFS protocol extension
   to NFSv4; this is the protocol between the client and the metadata
   server.

12.3.1.  Definitions

   This sub-section defines a number of terms necessary for describing
   layouts and their semantics.  In addition, it more precisely defines
   how layouts are identified and how they can be composed of smaller
   granularity layout segments.

12.3.1.1.  Layout Types

   A layout describes the mapping of a file's data to the storage
   devices that hold the data.  A layout is said to belong to a specific
   "layout type" (see Section 3.2.18 for its RPC definition).  The
   layout type allows for variants to handle different storage protocols
   (e.g., block/volume [24], object [23], and file [Section 12.4] layout
   types).  A metadata server, along with its control protocol, must
   support at least one layout type.  A private sub-range of the layout
   type name space is also defined.  Values from the private layout type
   range can be used for internal testing or experimentation.

   As an example, a file layout type could be an array of tuples (e.g.,
   deviceID, file_handle), along with a definition of how the data is
   stored across the devices (e.g., striping).  A block/volume layout
   might be an array of tuples that store <deviceID, block_number, block
   count> along with information about block size and the file offset of
   the first block.  An object layout might be an array of tuples
   <deviceID, objectID> and an additional structure (i.e., the
   aggregation map) that defines how the logical byte sequence of the
   file data is serialized into the different objects.  Note, the actual
   layouts are more complex than these simple expository examples.

   This document defines a NFSv4 file layout type using a stripe-based
   aggregation scheme (see Section 12.4).  Adjunct specifications are
   being drafted that precisely define other layout formats (e.g.,
   block/volume [24], and object [23] layouts) to allow interoperability
   among clients and metadata servers.






Shepler, et al.         Expires February 2, 2007              [Page 208]


Internet-Draft            NFSv4 Minor Version 1              August 2006


12.3.1.2.  Layout Iomode

   The iomode indicates to the metadata server the client's intent to
   perform either READs (only) or a mixture of I/O possibly containing
   WRITEs as well as READs (i.e., READ/WRITE).  For certain layout
   types, it is useful for a client to specify this intent at LAYOUTGET
   time.  E.g., for block/volume based protocols, block allocation could
   occur when a READ/WRITE iomode is specified.  A special
   LAYOUTIOMODE_ANY iomode is defined and can only be used for
   LAYOUTRETURN and LAYOUTRECALL, not for LAYOUTGET.  It specifies that
   layouts pertaining to both READ and RW iomodes are being returned or
   recalled, respectively.

   A storage device may validate I/O with regards to the iomode; this is
   dependent upon storage device implementation.  Thus, if the client's
   layout iomode differs from the I/O being performed the storage device
   may reject the client's I/O with an error indicating a new layout
   with the correct I/O mode should be fetched.  E.g., if a client gets
   a layout with a READ iomode and performs a WRITE to a storage device,
   the storage device is allowed to reject that WRITE.

   The iomode does not conflict with OPEN share modes or lock requests;
   open mode checks and lock enforcement are always enforced, and are
   logically separate from the pNFS layout level.  As well, open modes
   and locks are the preferred method for restricting user access to
   data files.  E.g., an OPEN of read, deny-write does not conflict with
   a LAYOUTGET containing an iomode of READ/WRITE performed by another
   client.  Applications that depend on writing into the same file
   concurrently may use byte range locking to serialize their accesses.

12.3.1.3.  Layout Segments

   Until this point, layouts have been defined in a fairly vague manner.
   A layout is more precisely identified by the following tuple:
   <ClientID, FH, layout type>; the FH refers to the FH of the file on
   the metadata server.  Note, layouts describe a file, not a byte-range
   of a file.

   Since a layout that describes an entire file may be very large, there
   is a desire to manage layouts in smaller chunks that correspond to
   byte-ranges of the file.  For example, the entire layout need not be
   returned, recalled, or committed.  These chunks are called "layout
   segments" and are further identified by the byte-range they
   represent.  Layout operations require the identification of the
   layout segment (i.e., clientID, FH, layout type, and byte-range), as
   well as the iomode.  This structure allows clients and metadata
   servers to aggregate the results of layout operations into a singly
   maintained layout.



Shepler, et al.         Expires February 2, 2007              [Page 209]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   It is important to define when layout segments overlap and/or
   conflict with each other.  For a layout segment to overlap another
   layout segment both segments must be of the same layout type,
   correspond to the same filehandle, and have the same iomode; in
   addition, the byte-ranges of the segments must overlap.  Layout
   segments conflict, when they overlap and differ in the content of the
   layout (i.e., the storage device/file mapping parameters differ).
   Note, differing iomodes do not lead to conflicting layouts.  It is
   permissible for layout segments with different iomodes, pertaining to
   the same byte range, to be held by the same client.

12.3.1.4.  Device IDs

   The "deviceID" is a short name for a storage device.  In practice, a
   significant amount of information may be required to fully identify a
   storage device.  Instead of embedding all that information in a
   layout, a level of indirection is used.  Layouts embed device IDs,
   and a new operation (GETDEVICEINFO) is used to retrieve the complete
   identity information about the storage device according to its layout
   type.  For example, the identity of a file server or object server
   could be an IP address and port.  The identity of a block device
   could be a volume label.  Due to multipath connectivity in a SAN
   environment, agreement on a volume label is considered the reliable
   way to locate a particular storage device.

   The device ID is qualified by the layout type and unique per file
   system (FSID).  This allows different layout drivers to generate
   device IDs without the need for co-ordination.  In addition to
   GETDEVICEINFO, another operation, GETDEVICELIST, has been added to
   allow clients to fetch the mappings of multiple storage devices
   attached to a metadata server.

   Clients cannot expect the mapping between device ID and storage
   device address to persist across server reboots, hence a client MUST
   fetch new mappings on startup or upon detection of a metadata server
   reboot unless it can revalidate its existing mappings.  Not all
   layout types support such revalidation, and the means of doing so is
   layout specific.  If data are reorganized from a storage device with
   a given device ID to a different storage device (i.e., if the mapping
   between storage device and data changes), the layout describing the
   data MUST be recalled rather than assigning the new storage device to
   the old device ID.

12.3.1.5.  Aggregation Schemes

   Aggregation schemes can describe layouts like simple one-to-one
   mapping, concatenation, and striping.  A general aggregation scheme
   allows nested maps so that more complex layouts can be compactly



Shepler, et al.         Expires February 2, 2007              [Page 210]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   described.  The canonical aggregation type for this extension is
   striping, which allows a client to access storage devices in
   parallel.  Even a one-to-one mapping is useful for a file server that
   wishes to distribute its load among a set of other file servers.

12.3.2.  Guarantees Provided by Layouts

   Layouts delegate to the client the ability to access data out of
   band.  The layout guarantees the holder that the layout will be
   recalled when the state encapsulated by the layout becomes invalid
   (e.g., through some operation that directly or indirectly modifies
   the layout) or, possibly, when a conflicting layout is requested, as
   determined by the layout's iomode.  When a layout is recalled, and
   then returned by the client, the client retains the ability to access
   file data with normal NFSv4 I/O operations through the metadata
   server.  Only the right to do I/O out-of-band is affected.

   Holding a layout does not guarantee that a user of the layout has the
   rights to access the data represented by the layout.  All user access
   rights MUST be obtained through the appropriate open, lock, and
   access operations (i.e., those that would be used in the absence of
   pNFS).  However, if a valid layout for a file is not held by the
   client, the storage device should reject all I/Os to that file's byte
   range that originate from that client.  In summary, layouts and
   ordinary file access controls are independent.  The act of modifying
   a file for which a layout is held, does not necessarily conflict with
   the holding of the layout that describes the file being modified.
   However, with certain layout types (e.g., block/volume layouts), the
   layout's iomode must agree with the type of I/O being performed.

   Depending upon the layout type and storage protocol in use, storage
   device access permissions may be granted by LAYOUTGET and may be
   encoded within the type specific layout.  If access permissions are
   encoded within the layout, the metadata server must recall the layout
   when those permissions become invalid for any reason; for example
   when a file becomes unwritable or inaccessible to a client.  Note,
   clients are still required to perform the appropriate access
   operations as described above (e.g., open and lock ops).  The degree
   to which it is possible for the client to circumvent these access
   operations must be clearly addressed by the individual layout type
   documents, as well as the consequences of doing so.  In addition,
   these documents must be clear about the requirements and non-
   requirements for the checking performed by the server.

   If the pNFS metadata server supports mandatory byte range locks then
   byte range locks must behave as specified by the NFSv4 protocol, as
   observed by users of files.  If a storage device is unable to
   restrict access by a pNFS client who does not hold a required



Shepler, et al.         Expires February 2, 2007              [Page 211]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   mandatory byte range lock then the metadata server must not grant
   layouts to a client, for that storage device, that permits any access
   that conflicts with a mandatory byte range lock held by another
   client.  In this scenario, it is also necessary for the metadata
   server to ensure that byte range locks are not granted to a client if
   any other client holds a conflicting layout; in this case all
   conflicting layouts must be recalled and returned before the lock
   request can be granted.  This requires the pNFS server to understand
   the capabilities of its storage devices.

12.3.3.  Getting a Layout

   A client obtains a layout through a new operation, LAYOUTGET.  The
   metadata server will give out layouts of a particular type (e.g.,
   block/volume, object, or file) and aggregation as requested by the
   client.  The client selects an appropriate layout type which the
   server supports and the client is prepared to use.  The layout
   returned to the client may not line up exactly with the requested
   byte range.  A field within the LAYOUTGET request, "minlength",
   specifies the minimum overlap that MUST exist between the requested
   layout and the layout returned by the metadata server.  The
   "minlength" field should specify a size of at least one.  A metadata
   server may give-out multiple overlapping, non-conflicting layout
   segments to the same client in response to a LAYOUTGET.

   There is no implied ordering between getting a layout and performing
   a file OPEN.  For example, a layout may first be retrieved by placing
   a LAYOUTGET operation in the same compound as the initial file OPEN.
   Once the layout has been retrieved, it can be held across multiple
   OPEN and CLOSE sequences.

   The storage protocol used by the client to access the data on the
   storage device is determined by the layout's type.  The client needs
   to select a "layout driver" that understands how to interpret and use
   that layout.  The API used by the client to talk to its drivers is
   outside the scope of the pNFS extension.  The storage protocol
   between the client's layout driver and the actual storage is covered
   by other protocols specifications such as iSCSI (block storage), OSD
   (object storage) or NFS (file storage).

   Although, the metadata server is in control of the layout for a file,
   the pNFS client can provide hints to the server when a file is opened
   or created about preferred layout type and aggregation scheme.  The
   pNFS extension introduces a LAYOUT_HINT attribute that the client can
   set at creation time to provide a hint to the server for new files.
   It is suggested that this attribute be set as one of the initial
   attributes to OPEN when creating a new file.  Setting this attribute
   separately, after the file has been created could make it difficult,



Shepler, et al.         Expires February 2, 2007              [Page 212]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   or impossible, for the server implementation to comply.

12.3.4.  Committing a Layout

   Due to the nature of the protocol, the file attributes, and data
   location mapping (e.g., which offsets store data vs. store holes)
   that exist on the metadata storage device may become inconsistent in
   relation to the data stored on the storage devices; e.g., when WRITEs
   occur before a layout has been committed (e.g., between a LAYOUTGET
   and a LAYOUTCOMMIT).  Thus, it is necessary to occasionally re-sync
   this state and make it visible to other clients through the metadata
   server.

   The LAYOUTCOMMIT operation is responsible for committing a modified
   layout segment to the metadata server.  Note: the data should be
   written and committed to the appropriate storage devices before the
   LAYOUTCOMMIT occurs.  Note, if the data is being written
   asynchronously through the metadata server a COMMIT to the metadata
   server is required to sync the data and make it visible on the
   storage devices (see Section 12.3.6 for more details).  The scope of
   this operation depends on the storage protocol in use.  For block/
   volume-based layouts, it may require updating the block list that
   comprises the file and committing this layout to stable storage.
   While, for file-layouts it requires some synchronization of
   attributes between the metadata and storage devices (i.e., mainly the
   size attribute; EOF).  It is important to note that the level of
   synchronization is from the point of view of the client who issued
   the LAYOUTCOMMIT.  The updated state on the metadata server need only
   reflect the state as of the client's last operation previous to the
   LAYOUTCOMMIT, it need not reflect a globally synchronized state
   (e.g., other clients may be performing, or may have performed I/O
   since the client's last operation and the LAYOUTCOMMIT).

   The control protocol is free to synchronize the attributes before it
   receives a LAYOUTCOMMIT, however upon successful completion of a
   LAYOUTCOMMIT, state that exists on the metadata server that describes
   the file MUST be in sync with the state existing on the storage
   devices that comprise that file as of the issuing client's last
   operation.  Thus, a client that queries the size of a file between a
   WRITE to a storage device and the LAYOUTCOMMIT may observe a size
   that does not reflects the actual data written.

12.3.4.1.  LAYOUTCOMMIT and mtime/atime/change

   The change attribute and the modify/access times may be updated, by
   the server, at LAYOUTCOMMIT time; since for some layout types, the
   change attribute and atime/mtime can not be updated by the
   appropriate I/O operation performed at a storage device.  The



Shepler, et al.         Expires February 2, 2007              [Page 213]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   arguments to LAYOUTCOMMIT allow the client to provide suggested
   access and modify time values to the server.  Again, depending upon
   the layout type, these client provided values may or may not be used.
   The server should sanity check the client provided values before they
   are used.  For example, the server should ensure that time does not
   flow backwards.  According to the NFSv4 specification, The client
   always has the option to set these attributes through an explicit
   SETATTR operation.

   As mentioned, for some layout protocols the change attribute and
   mtime/atime may be updated at or after the time the I/O occurred
   (e.g., if the storage device is able to communicate these attributes
   to the metadata server).  If, upon receiving a LAYOUTCOMMIT, the
   server implementation is able to determine that the file did not
   change since the last time the change attribute was updated (e.g., no
   WRITEs or over-writes occurred), the implementation need not update
   the change attribute; file-based protocols may have enough state to
   make this determination or may update the change attribute upon each
   file modification.  This also applies for mtime and atime; if the
   server implementation is able to determine that the file has not been
   modified since the last mtime update, the server need not update
   mtime at LAYOUTCOMMIT time.  Once LAYOUTCOMMIT completes, the new
   change attribute and mtime/atime should be visible if that file was
   modified since the latest previous LAYOUTCOMMIT or LAYOUTGET.

12.3.4.2.  LAYOUTCOMMIT and size

   The file's size may be updated at LAYOUTCOMMIT time as well.  The
   LAYOUTCOMMIT operation contains an argument ("last_write_offset")
   that indicates the highest byte offset written but not yet committed
   via LAYOUTCOMMIT.  Note: this argument is switched on a boolean value
   indicating whether or not a previous write occurred.  If the switch
   is false, no "last_write_offset" is given; a "last_write_offset"
   specifying an offset of 0 means byte 0 was the highest last byte
   written.

   The metadata server may do one of the following:

   1.  It may update the file's size based on the last write offset.
       However, to the extent possible, the metadata server should
       sanity check any value to which the file's size is going to be
       set.  E.g., it must not truncate the file based on the client
       presenting a smaller last write offset than the file's current
       size.

   2.  If it has sufficient other knowledge of file size (e.g., by
       querying the storage devices through the control protocol), it
       may ignore the client provided argument and use the query-derived



Shepler, et al.         Expires February 2, 2007              [Page 214]


Internet-Draft            NFSv4 Minor Version 1              August 2006


       value.

   3.  It may use the last write offset as a hint, subject to correction
       when other information is available as above.

   The method chosen to update the file's size will depend on the
   storage device's and/or the control protocol's implementation.  For
   example, if the storage devices are block devices with no knowledge
   of file size, the metadata server must rely on the client to set the
   size appropriately.  A new size flag and length are also returned in
   the results of a LAYOUTCOMMIT.  This union indicates whether a new
   size was set, and to what length it was set.  If a new size is set as
   a result of LAYOUTCOMMIT, then the metadata server must reply with
   the new size.  As well, if the size is updated, the metadata server
   in conjunction with the control protocol SHOULD ensure that the new
   size is reflected by the storage devices immediately upon return of
   the LAYOUTCOMMIT operation; e.g., a READ up to the new file size
   should succeed on the storage devices (assuming no intervening
   truncations).  Again, if the client wants to explicitly zero-extend
   or truncate a file, SETATTR must be used; it need not be used when
   simply writing past EOF.

12.3.4.3.  LAYOUTCOMMIT and layoutupdate

   The LAYOUTCOMMIT operation contains a "layoutupdate" argument.  This
   argument is a layout type specific structure.  The structure can be
   used to pass arbitrary layout type specific information from the
   client to the metadata server at LAYOUTCOMMIT time.  For example, if
   using a block/volume layout, the client can indicate to the metadata
   server which reserved or allocated blocks it used and which it did
   not.  The "layoutupdate" structure need not be the same structure as
   the layout returned by LAYOUTGET.  The structure is defined by the
   layout type and is opaque to LAYOUTCOMMIT.

12.3.5.  Recalling a Layout

12.3.5.1.  Basic Operation

   Since a layout protects a client's access to a file via a direct
   client-storage-device path, a layout need only be recalled when it is
   semantically unable to serve this function.  Typically, this occurs
   when the layout no longer encapsulates the true location of the file
   over the byte range it represents.  Any operation or action (e.g.,
   server driven restriping or load balancing) that changes the layout
   will result in a recall of the layout.  A layout is recalled by the
   CB_LAYOUTRECALL callback operation (see Section 18.3).  This callback
   can either recall a layout segment identified by a byte range, all
   the layouts associated with a filesystem (FSID), or all layouts.



Shepler, et al.         Expires February 2, 2007              [Page 215]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   Recalling all layouts or all the layouts associated with a filesystem
   also invalidates the client's device cache for the affected
   filesystems.  Multiple layout segments may be returned in a single
   compound operation.  Section 12.3.5.3 discusses sequencing issues
   surrounding the getting, returning, and recalling of layouts.

   The iomode is also specified when recalling a layout or layout
   segment.  Generally, the iomode in the recall request must match the
   layout, or segment, being returned; e.g., a recall with an iomode of
   RW should cause the client to only return RW layout segments (not R
   segments).  However, a special LAYOUTIOMODE_ANY enumeration is
   defined to enable recalling a layout of any type (i.e., the client
   must return both read-only and read/write layouts).

   A REMOVE operation may cause the metadata server to recall the layout
   to prevent the client from accessing a non-existent file and to
   reclaim state stored on the client.  Since a REMOVE may be delayed
   until the last close of the file has occurred, the recall may also be
   delayed until this time.  As well, once the file has been removed,
   after the last reference, the client SHOULD no longer be able to
   perform I/O using the layout (e.g., with file-based layouts an error
   such as ESTALE could be returned).

   Although, the pNFS extension does not alter the caching capabilities
   of clients, or their semantics, it recognizes that some clients may
   perform more aggressive write-behind caching to optimize the benefits
   provided by pNFS.  However, write-behind caching may impact the
   latency in returning a layout in response to a CB_LAYOUTRECALL; just
   as caching impacts DELEGRETURN with regards to data delegations.
   Client implementations should limit the amount of dirty data they
   have outstanding at any one time.  Server implementations may fence
   clients from performing direct I/O to the storage devices if they
   perceive that the client is taking too long to return a layout once
   recalled.  A server may be able to monitor client progress by
   watching client I/Os or by observing LAYOUTRETURNs of sub-portions of
   the recalled layout.  The server can also limit the amount of dirty
   data to be flushed to storage devices by limiting the byte ranges
   covered in the layouts it gives out.

   Once a layout has been returned, the client MUST NOT issue I/Os to
   the storage devices for the file, byte range, and iomode represented
   by the returned layout.  If a client does issue an I/O to a storage
   device for which it does not hold a layout, the storage device SHOULD
   reject the I/O.







Shepler, et al.         Expires February 2, 2007              [Page 216]


Internet-Draft            NFSv4 Minor Version 1              August 2006


12.3.5.2.  Recall Callback Robustness

   It has been assumed thus far that pNFS client state for a file
   exactly matches the pNFS server state for that file and client
   regarding layout ranges and permissions.  This assumption leads to
   the implicit assumption that any callback results in a LAYOUTRETURN
   or set of LAYOUTRETURNs that exactly match the range in the callback,
   since both client and server agree about the state being maintained.
   However, it can be useful if this assumption does not always hold.
   For example:

   o  It may be useful for clients to be able to discard layout
      information without calling LAYOUTRETURN.  If conflicts that
      require callbacks are very rare, and a server can use a multi-file
      callback to recover per-client resources (e.g., via a FSID recall,
      or a multi-file recall within a single compound), the result may
      be significantly less client-server pNFS traffic.

   o  It may be similarly useful for servers to maintain information
      about what ranges are held by a client on a coarse-grained basis,
      leading to the server's layout ranges being beyond those actually
      held by the client.  In the extreme, a server could manage
      conflicts on a per-file basis, only issuing whole-file callbacks
      even though clients may request and be granted sub-file ranges.

   o  In order to avoid errors, it is vital that a client not assign
      itself layout permissions beyond what the server has granted and
      that the server not forget layout permissions that have been
      granted.  On the other hand, if a server believes that a client
      holds a layout segment that the client does not know about, it's
      useful for the client to cleanly indicate completion of the
      requested recall either by issuing a LAYOUTRETURN for the entire
      requested range or by returning an NFS4ERR_NOMATCHING_LAYOUT error
      to the layout recall callback.

   Thus, in light of the above, it is useful for a server to be able to
   issue callbacks for layout ranges it has not granted to a client, and
   for a client to return ranges it does not hold.  A pNFS client must
   always return layout segments that comprise the full range specified
   by the recall.  Note, the full recalled layout range need not be
   returned as part of a single operation, but may be returned in
   segments.  This allows the client to stage the flushing of dirty
   data, layout commits, and returns.  Also, it indicates to the
   metadata server that the client is making progress.

   It is possible that write requests may be presented to a data server
   no longer allowed to perform them.  This behavior is limited by
   requiring that a client MUST wait for completion of all writes



Shepler, et al.         Expires February 2, 2007              [Page 217]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   covered by a layout range before returning a layout that covers that
   range.  Since, the server has no control as to when the client will
   return the layout, the server may, at some time, decide to
   unilaterally revoke the client's access provided by the layout in
   question.  Upon doing so the server must deal with the possibility of
   lingering writes, outstanding writes still in flight to data servers
   identified by the revoked layout.  Each layout-specification MUST
   define whether unilateral layout revocation by the metadata server is
   supported, and if so, the specification must also outline how
   lingering writes are to be dealt with; e.g., data servers identified
   by the revoked layout in question could be fenced off from the
   appropriate client.  If unilateral revocation is not supported, there
   MUST be no possibility that the client has outstanding write requests
   when a layout is returned.

   In order to ensure client/server convergence on the layout state, the
   final LAYOUTRETURN operation in a sequence of returns for a
   particular recall, MUST specify the entire range being recalled,
   echoing the recalled layout type, iomode, recall/return type (FILE,
   FSID, or ALL), and byte range; even if layout segments pertaining to
   partial ranges were previously returned.  In addition, if the client
   holds no layout segment that overlaps the range being recalled, the
   client should return the NFS4ERR_NOMATCHING_LAYOUT error code.  This
   allows the server to update its view of the client's layout state.

12.3.5.3.  Serialization of Layout Operations

   As with other stateful operations, pNFS requires the correct
   sequencing of layout operations. pNFS relies on the sessions feature
   of NFSv4.1 to provide the correct sequencing between regular
   operations and callbacks.  It is the server's responsibility to avoid
   inconsistencies regarding the layouts it hands out and the client's
   responsibility to properly serialize its layout requests and layout
   returns.

12.3.5.3.1.  Get/Return Serialization

   The protocol allows the client to send concurrent LAYOUTGET and
   LAYOUTRETURN operations to the server.  However, the protocol does
   not provide any means for the server to process the requests in the
   same order in which they were created, nor it provides a way for the
   client to determine the order in which parallel outstanding
   operations were processed by the server.  Thus, when a layout segment
   retrieved by an outstanding LAYOUTGET operation intersects with a
   layout segment returned by an outstanding LAYOUTRETURN the order in
   which the two conflicting operations are processed determines the
   final state of the overlapping segment.  To disambiguate between the
   two cases the client MUST serialize LAYOUTGET operations and



Shepler, et al.         Expires February 2, 2007              [Page 218]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   voluntary LAYOUTRETURN operations for the same file.

   It is permissible for the client to send in parallel multiple
   LAYOUTGET operations for the same file or multiple LAYOUTRETURN
   operations for the same file; but never a mix of both.  It is also
   permissible for the client to combine LAYOUTRETURN and LAYOUTGET
   operations for the same file in the same COMPOUND request as the
   server must process these in order.  If a client does issue such
   requests, it must not have more than one outstanding for the same
   file at the same time and must not have other LAYOUTGET or
   LAYOUTRETURN operations outstanding at the same time for that same
   file.

12.3.5.3.2.  Recall/Return Sequencing

   One critical issue with operation sequencing concerns callbacks.  The
   protocol must defend against races between the reply to a LAYOUTGET
   operation and a subsequent CB_LAYOUTRECALL.  A client MUST NOT
   process a CB_LAYOUTRECALL that identifies an outstanding LAYOUTGET
   operation to which the client has not yet received a reply.
   Conflicting LAYOUTGET operations are identified in the CB_SEQUENCE
   preceding the CB_LAYOUTRECALL.

   The callback races section (Section 2.9.4.3) describes the sessions
   mechanism for allowing the client to detect such situations in order
   to not process such a CB_LAYOUTRECALL.  The server MUST reference all
   conflicting LAYOUTGET operations in the CB_SEQUENCE that precedes the
   CB_LAYOUTRECALL.  A zero length array of referenced operations is
   used by the server to tell the client that the server does not know
   of any LAYOUTGET operations that conflict with the recall.

12.3.5.3.2.1.  Client Side Considerations

   Consider a pNFS client that has issued a LAYOUTGET and then receives
   an overlapping recall callback for the same file.  There are two
   possibilities, which the client would be unable to distinguish
   without additional information provided by the sessions
   implementation.

   1.  The server processed the LAYOUTGET before issuing the recall, so
       the LAYOUTGET response is in flight, and must be waited for
       because it may be carrying layout info that will need to be
       returned to deal with the recall callback.

   2.  The server issued the callback before receiving the LAYOUTGET.
       The server will not respond to the LAYOUTGET until the recall
       callback is processed.




Shepler, et al.         Expires February 2, 2007              [Page 219]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   This could cause deadlock, as the client must wait for the LAYOUTGET
   response before processing the recall in the first case, but that
   response will not arrive until after the recall is processed in the
   second case.  Via the CB_SEQUENCE operation, the server provides the
   client with the { slotid , sequenceid } of any earlier LAYOUTGET
   operations which remain unconfirmed at the server by the session slot
   usage rules.  This allows the client to disambiguate between the two
   cases, in case 1, the server will provide the operation reference(s),
   whereas in case 2 it will not (because there are no dependent client
   operations).  Therefore, the action at the client will only require
   waiting in the case that the client has not yet seen the server's
   earlier responses to the LAYOUTGET operation(s).

   The following requirements apply to avoid this deadlock: by adhering
   to the following requirements:

   o  A LAYOUTGET MUST be rejected with an error (i.e.,
      NFS4ERR_RECALLCONFLICT) if there's an overlapping outstanding
      recall callback to the same client.

   o  When processing a recall, the client MUST wait for a response to
      all conflicting outstanding LAYOUTGETs that are referenced in the
      CB_SEQUENCE for the recall before performing any RETURN that could
      be affected by any such response.

   o  The client SHOULD wait for responses to all operations required to
      complete a recall before sending any LAYOUTGETs that would
      conflict with the recall because the server is likely to return
      errors for them.

   o  Before sending a new LAYOUTGET for a range covered by a layout
      recall, the client SHOULD wait for responses to any outstanding
      LAYOUTGET that overlaps any portion of the new LAYOUTGET's range .
      This is because it is possible (although unlikely) that the prior
      operation may have arrived at the server after the recall
      completed and hence will succeed.

   o  The recall process can be considered as done by the client when
      the final LAYOUTRETURN operation for the recalled range is issued.

12.3.5.3.2.2.  Server Side Considerations

   Consider a related situation from the pNFS server's point of view.
   The server has issued a recall callback and receives an overlapping
   LAYOUTGET for the same file before the LAYOUTRETURN(s) that respond
   to the recall callback.  Again, there are two cases:





Shepler, et al.         Expires February 2, 2007              [Page 220]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   1.  The client issued the LAYOUTGET before processing the recall
       callback.

   2.  The client issued the LAYOUTGET after processing the recall
       callback, but it arrived before the LAYOUTRETURN that completed
       that processing.

   The simplest approach is to always reject the overlapping LAYOUTGET;
   the pNFS server MUST do this.  The client has two ways to avoid this
   result - it can issue the LAYOUTGET as a subsequent element of a
   COMPOUND containing the LAYOUTRETURN that completes the recall
   callback, or it can wait for the response to that LAYOUTRETURN.

   There is little the session sequence logic can do to disambiguate
   between these two cases, because both operations are independent of
   one another.  They are simply asynchronous events which crossed.  The
   situation can even occur if the session is configured to use a single
   connection for both operations and callbacks.

12.3.6.  Metadata Server Write Propagation

   Asynchronous writes written through the metadata server may be
   propagated lazily to the storage devices.  For data written
   asynchronously through the metadata server, a client performing a
   read at the appropriate storage device is not guaranteed to see the
   newly written data until a COMMIT occurs at the metadata server.
   While the write is pending, reads to the storage device can give out
   either the old data, the new data, or a mixture thereof.  After
   either a synchronous write completes, or a COMMIT is received (for
   asynchronously written data), the metadata server must ensure that
   storage devices give out the new data and that the data has been
   written to stable storage.  If the server implements its storage in
   any way such that it cannot obey these constraints, then it must
   recall the layouts to prevent reads being done that cannot be handled
   correctly.

12.3.7.  Crash Recovery

   Crash recovery is complicated due to the distributed nature of the
   pNFS protocol.  In general, crash recovery for layouts is similar to
   crash recovery for delegations in the base NFSv4 protocol.  However,
   the client's ability to perform I/O without contacting the metadata
   server introduces subtleties that must be handled correctly if file
   system corruption is to be avoided.







Shepler, et al.         Expires February 2, 2007              [Page 221]


Internet-Draft            NFSv4 Minor Version 1              August 2006


12.3.7.1.  Leases

   The layout lease period plays a critical role in crash recovery.
   Depending on the capabilities of the storage protocol, it is crucial
   that the client is able to maintain an accurate layout lease timer to
   ensure that I/Os are not issued to storage devices after expiration
   of the layout lease period.  In order for the client to do so, it
   must know which operations renew a lease.

12.3.7.1.1.  Lease Renewal

   The current NFSv4 specification allows for implicit lease renewals to
   occur upon receiving an I/O. However, due to the distributed pNFS
   architecture, implicit lease renewals are limited to operations
   performed at the metadata server; this includes I/O performed through
   the metadata server.  So, a client must not assume that READ and
   WRITE I/O to storage devices implicitly renew lease state.

   If sessions are required for pNFS, as has been suggested, then the
   SEQUENCE operation is to be used to explicitly renew leases.  It is
   proposed that the SEQUENCE operation be extended to return all the
   specific information that RENEW does, but not as an error as RENEW
   returns it.  Since, when using session, beginning each compound with
   the SEQUENCE op allows renews to be performed without an additional
   operation and without an additional request.  Again, the client must
   not rely on any operation to the storage devices to renew a lease.
   Using the SEQUENCE operation for renewals, simplifies the client's
   perception of lease renewal.

12.3.7.1.2.  Client Lease Timer

   Depending on the storage protocol and layout type in use, it may be
   crucial that the client not issue I/Os to storage devices if the
   corresponding layout's lease has expired.  Doing so may lead to file
   system corruption if the layout has been given out and used by
   another client.  In order to prevent this, the client must maintain
   an accurate lease timer for all layouts held.  RFC3530 [2] has the
   following to say regarding the maintenance of a client lease timer:

      ...the client must track operations which will renew the lease
      period.  Using the time that each such request was sent and the
      time that the corresponding reply was received, the client should
      bound the time that the corresponding renewal could have occurred
      on the server and thus determine if it is possible that a lease
      period expiration could have occurred.

   To be conservative, the client should start its lease timer based on
   the time that the it issued the operation to the metadata server,



Shepler, et al.         Expires February 2, 2007              [Page 222]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   rather than based on the time of the response.

   It is also necessary to take propagation delay into account when
   requesting a renewal of the lease:

      ...the client should subtract it from lease times (e.g., if the
      client estimates the one-way propagation delay as 200 msec, then
      it can assume that the lease is already 200 msec old when it gets
      it).  In addition, it will take another 200 msec to get a response
      back to the server.  So the client must send a lock renewal or
      write data back to the server 400 msec before the lease would
      expire.

   Thus, the client must be aware of the one-way propagation delay and
   should issue renewals well in advance of lease expiration.  Clients,
   to the extent possible, should try not to issue I/Os that may extend
   past the lease expiration time period.  However, since this is not
   always possible, the storage protocol must be able to protect against
   the effects of in-flight I/Os, as is discussed later.

12.3.7.2.  Client Recovery

   Client recovery for layouts works in much the same way as NFSv4
   client recovery works for other lock/delegation state.  When an NFSv4
   client reboots, it will lose all information about the layouts that
   it previously owned.  There are two methods by which the server can
   reclaim these resources and allow otherwise conflicting layouts to be
   provided to other clients.

   The first is through the expiry of the client's lease.  If the client
   recovery time is longer than the lease period, the client's lease
   will expire and the server will know that state may be released. for
   layouts the server may release the state immediately upon lease
   expiry or it may allow the layout to persist awaiting possible lease
   revival, as long as there are no conflicting requests.

   On the other hand, the client may recover in less time than it takes
   for the lease period to expire.  In such a case, the client will
   contact the server through the standard SETCLIENTID protocol.  The
   server will find that the client's id matches the id of the previous
   client invocation, but that the verifier is different.  The server
   uses this as a signal to release all the state associated with the
   client's previous invocation.

12.3.7.3.  Metadata Server Recovery

   The server recovery case is slightly more complex.  In general, the
   recovery process again follows the standard NFSv4 recovery model: the



Shepler, et al.         Expires February 2, 2007              [Page 223]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   client will discover that the metadata server has rebooted when it
   receives an unexpected STALE_STATEID or STALE_CLIENTID reply from the
   server; it will then proceed to try to reclaim its previous
   delegations during the server's recovery grace period.  However,
   layouts have a slightly different mechanism for reclaim.  The problem
   is that a client which uses LAYOUTGET to reclaim a layout might not
   get the same layout it had previously.  The range might be different
   or it might get the same range but the content of the layout might be
   different.  For example, if using a block/volume-based layout, the
   blocks provisionally assigned by the layout might be different, in
   which case the client will have to write the corresponding blocks
   again.

   Instead of reclaiming a layout with LAYOUTGET, a client can attempt
   to commit data written before the file server crash by setting a
   reclaim bit on the LAYOUTCOMMIT operation.  This should only be done
   for data that the client has already written using a layout obtained
   before the server restart.  For data still dirty in the client
   memory, the client should get a new layout segment after the server's
   grace period has elapsed.  Alternatively, the client can write that
   data through the metadata server using the standard NFSv4 WRITE.  In
   the case that the client has written dirty data to a provisionally
   allocated region of the layout, but was unable to commit the layout
   changes for this data before the server rebooted, the client may be
   unable to reliably re-read the data from the data storage devices in
   order to write it again via the metadata server.  In this case the
   client needs to inform the metadata server that the layout has
   changed, before the server has completed its recovery grace period
   and starts allowing updates to the file-system.  For this purpose,
   the LAYOUTCOMMIT operation contains a "reclaim" field.  During the
   metadata server's recovery grace period (and only during the recovery
   grace period) the client may send a LAYOUTCOMMIT request with the
   "reclaim" field set to "true".  This indicates that the client is
   attempting to commit changes to the file layout that occurred prior
   to the reboot of the metadata server.  The "layout update" field of
   the request must contain the portion of the layout that the client
   held prior to the metadata server reboot which covers the outstanding
   writes.  The metadata server is free to apply consistency checks on
   the layout update provided by the client, and reject the request if
   the checks fail.  If the checks do not fail, then the server MUST
   commit the changes to the file layout contained in the "layoutupdate"
   field of the LAYOUTCOMMIT request, ensuring that the clients
   outstanding writes are not lost.

   During the recovery grace period the metadata server should apply the
   standard approach to handling WRITE and LAYOUTGET requests.  That is,
   if the server can reliably determine that servicing such a request
   will not conflict with an impending LAYOUTCOMMIT reclaim request, it



Shepler, et al.         Expires February 2, 2007              [Page 224]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   may choose to service the request.  If the server is unable to offer
   this guarantee, it MUST reject the request with status NFS4ERR_GRACE.

   For a metadata server to provide simple, valid handling during the
   grace period with respect to pNFS layouts, the easiest method is to
   simply reject all non-reclaim pNFS requests and WRITE operations by
   returning the NFS4ERR_GRACE error.  However, depending on the storage
   protocol and server implementation, the server may be able to
   determine that a particular request is safe.  For example, a server
   may save provisional allocation mappings for each file to stable
   storage, and use this information during the recovery grace period to
   determine that a WRITE request is safe.  Under such circumstances,
   the WRITE request MAY be serviced.  To re-iterate, for a server to
   allow non-reclaim pNFS requests and WRITE operations to be serviced
   during the recovery grace period, it MUST determine that the request
   will not conflict with any subsequent LAYOUTCOMMIT with reclaim
   request.

   There is an important safety concern associated with layouts that
   does not come into play in the standard NFSv4 case.  If a standard
   NFSv4 client makes use of a stale delegation, while reading, the
   consequence could be to deliver stale data to an application.  If
   writing, using a stale delegation or a stale state stateid for an
   open or lock would result in the rejection of the client's write with
   the appropriate stale stateid error.

   However, the pNFS layout enables the client to directly access the
   file system storage; if this access is not properly managed by the
   NFSv4 server the client can potentially corrupt the file system data
   or metadata.  Thus, it is vitally important that the client discover
   that the metadata server has rebooted, and that the client stops
   using stale layouts before the metadata server gives them away to
   other clients.  To ensure this, the client must be implemented so
   that layouts are never used to access the storage after the client's
   lease timer has expired.  It is crucial that clients have precise
   knowledge of the lease periods of their layouts.  For specific
   details on lease renewal and client lease timers, see
   Section 12.3.7.1.

   The prohibition on using stale layouts applies to all layout related
   accesses, especially the flushing of dirty data to the storage
   devices.  If the client's lease timer expires because the client
   could not contact the server for any reason, the client MUST
   immediately stop using the layout until the server can be contacted
   and the layout can be officially recovered or reclaimed.  However,
   this is only part of the solution.  It is also necessary to deal with
   the consequences of I/Os already in flight.




Shepler, et al.         Expires February 2, 2007              [Page 225]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   The issue of the effects of I/Os started before lease expiration and
   possibly continuing through lease expiration is the responsibility of
   the data storage protocol and as such is layout type specific.  There
   are two approaches the data storage protocol can take.  The protocol
   may adopt a global solution which prevents all I/Os from being
   executed after the lease expiration and thus is safe against a client
   who issues I/Os after lease expiration.  This is the preferred
   solution and the solution used by NFSv4 file based layouts (see
   Section 12.4.6); as well, the object storage device protocol allows
   storage to fence clients after lease expiration.  Alternatively, the
   storage protocol may rely on proper client operation and only deal
   with the effects of lingering I/Os.  These solutions may impact the
   client layout-driver, the metadata server layout-driver, and the
   control protocol.

12.3.7.4.  Storage Device Recovery

   Storage device crash recovery is mostly dependent upon the layout
   type in use.  However, there are a few general techniques a client
   can use if it discovers a storage device has crashed while holding
   asynchronously written, non-committed, data.  First and foremost, it
   is important to realize that the client is the only one who has the
   information necessary to recover asynchronously written data; since,
   it holds the dirty data and most probably nobody else does.  Second,
   the best solution is for the client to err on the side or caution and
   attempt to re-write the dirty data through another path.

   The client, rather than hold the asynchronously written data
   indefinitely, is encouraged to, and can make sure that the data is
   written by using other paths to that data.  The client may write the
   data to the metadata server, either synchronously or asynchronously
   with a subsequent COMMIT.  Once it does this, there is no need to
   wait for the original storage device.  In the event that the data
   range to be committed is transferred to a different storage device,
   as indicated in a new layout, the client may write to that storage
   device.  Once the data has been committed at that storage device,
   either through a synchronous write or through a commit to that
   storage device (e.g., through the NFSv4 COMMIT operation for the
   NFSv4 file layout), the client should consider the transfer of
   responsibility for the data to the new server as strong evidence that
   this is the intended and most effective method for the client to get
   the data written.  In either case, once the write is on stable
   storage (through either the storage device or metadata server), there
   is no need to continue either attempting to commit or attempting to
   synchronously write the data to the original storage device or wait
   for that storage device to become available.  That storage device may
   never be visible to the client again.




Shepler, et al.         Expires February 2, 2007              [Page 226]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   This approach does have a "lingering write" problem, similar to
   regular NFSv4.  Suppose a WRITE is issued to a storage device for
   which no response is received.  The client breaks the connection,
   trying to re-establish a new one, and gets a recall of the layout.
   The client issues the I/O for the dirty data through an alternative
   path, for example, through the metadata server and it succeeds.  The
   client then goes on to perform additional writes that all succeed.
   If at some time later, the original write to the storage device
   succeeds, data inconsistency could result.  The same problem can
   occur in regular NFSv4.  For example, a WRITE is held in a switch for
   some period of time while other writes are issued and replied to, if
   the original WRITE finally succeeds, the same issues can occur.
   However, this is solved by sessions in NFSv4.x.

12.3.8.  Security Considerations

   The pNFS extension partitions the NFSv4 file system protocol into two
   parts, the control path and the data path (i.e., storage protocol).
   The control path contains all the new operations described by this
   extension; all existing NFSv4 security mechanisms and features apply
   to the control path.  The combination of components in a pNFS system
   (see Figure 60) is required to preserve the security properties of
   NFSv4 with respect to an entity accessing data via a client,
   including security countermeasures to defend against threats that
   NFSv4 provides defenses for in environments where these threats are
   considered significant.

   In some cases, the security countermeasures for connections to
   storage devices may take the form of physical isolation or a
   recommendation not to use pNFS in an environment.  For example, it is
   currently infeasible to provide confidentiality protection for some
   storage device access protocols to protect against eavesdropping; in
   environments where eavesdropping on such protocols is of sufficient
   concern to require countermeasures, physical isolation of the
   communication channel (e.g., via direct connection from client(s) to
   storage device(s)) and/or a decision to forego use of pNFS (e.g., and
   fall back to NFSv4) may be appropriate courses of action.

   In full generality where communication with storage devices is
   subject to the same threats as client-server communication, the
   protocols used for that communication need to provide security
   mechanisms comparable to those available via RPSEC_GSS for NFSv4.
   Many situations in which pNFS is likely to be used will not be
   subject to the overall threat profile for which NFSv4 is required to
   provide countermeasures.

   pNFS implementations MUST NOT remove NFSv4's access controls.  The
   combination of clients, storage devices, and the server are



Shepler, et al.         Expires February 2, 2007              [Page 227]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   responsible for ensuring that all client to storage device file data
   access respects NFSv4 ACLs and file open modes.  This entails
   performing both of these checks on every access in the client, the
   storage device, or both.  If a pNFS configuration performs these
   checks only in the client, the risk of a misbehaving client obtaining
   unauthorized access is an important consideration in determining when
   it is appropriate to use such a pNFS configuration.  Such
   configurations SHOULD NOT be used when client- only access checks do
   not provide sufficient assurance that NFSv4 access control is being
   applied correctly.

12.4.  The NFSv4 File Layout Type

   This section describes the semantics and format of NFSv4 file-based
   layouts.

12.4.1.  File Striping and Data Access

   The file layout type describes a method for striping data across
   multiple devices.  The data for each stripe unit is stored within an
   NFSv4 file located on a particular storage device.

   Before discussing the file layout, it is necessary to describe the
   file layout device type; the structures are as follows:

   typedef netaddr4 nfsv4_file_layout_simple_device4;

   enum file_layout_device_type {
           FILE_SIMPLE  = 1,
           FILE_COMPLEX = 2
   };

   union nfsv4_file_layout_device4
       switch (file_layout_device_type fld_type) {
           case FILE_SIMPLE:
                   nfsv4_file_layout_simple_device4 nfld_dev_list<>;
           case FILE_COMPLEX:
                   deviceid4 dev_list<>;
           default:
                   void;
   };

   The "nfsv4_file_layout_device4" structure is a union composed of a
   SIMPLE or a COMPLEX device type.  A Simple device is composed of an
   array of nfsv4_file_layout_simple_device4 structures.  All devices
   identified by a Simple device must be 'equivalent' and are used for
   device multipathing; see Section 12.4.1.3 for more details on
   equivalent devices.  Simple devices always refer to actual physical



Shepler, et al.         Expires February 2, 2007              [Page 228]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   devices.  On the other hand, a Complex device is a virtual device
   that is constructed of multiple Simple devices.  Each device within
   the Complex device list is identified by its device ID.  A Complex
   device MUST NOT reference other Complex devices; only Simple devices
   are to be referenced.  This enables multiple physical devices to be
   identified through a single device ID and provides a space efficient
   mechanism by which to identify multiple devices within a layout.
   Complex devices can be thought of as a table of devices.  Complex and
   Simple devices share the same device ID space and should be cached
   similarly by the client.

   The structures used to describe the stripe layout are as follows:

   enum stripetype4 {
           STRIPE_SPARSE = 1,
           STRIPE_DENSE = 2
   };

   struct nfsv4_file_layouthint4 {
           stripetype4     nflh_stripe_type;
           length4         nflh_stripe_unit;
           uint32_t        nflh_stripe_width;
   };

   struct nfsv4_file_layout4 {
           deviceid4       nfl_dev_id;
           uint32_t        nfl_dev_index;
           nfs_fh4         nfl_fh;
   };

   struct nfsv4_file_layouttype4 {
           stripetype4             nflt_stripe_type;
           bool                    nflt_commit_through_mds;
           length4                 nflt_stripe_unit;
           length4                 nflt_file_size;
           uint32_t                nflt_stripe_devs<>;
           nfsv4_file_layout4      nflt_dev_list<>;
   };

   At a high level, the file layout specifies an ordered array of
   <deviceID, filehandle> tuples, as well as the stripe size, type of
   stripe layout (discussed later), and the file's current size as of
   LAYOUTGET time.

   The "dev_list" array within the nfsv4_file_layouttype4 contains a
   list of nfsv4_file_layout structures ("dev_list").  Each of these
   structures describes one or more physical devices that contribute to
   a stripe of the file.  The "stripe_devs" array contains a list of



Shepler, et al.         Expires February 2, 2007              [Page 229]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   indices into the "dev_list" array; an index of zero specifies the
   first "dev_list" entry.  Each successive index selects a "dev_list"
   entry whose filehandle and device id are to be used next in sequence
   for that stripe.  This allows an arbitrary sequencing through the
   possible devices to be encoded compactly.  When the "stripe_devs"
   array is of zero length, the elements of the "dev_list" array are
   simply used in order, so that the portion of the stripe held by the
   corresponding entry is determined by its position within the device
   list.

   Each "dev_list" entry (the nfsv4_file_layout structure) contains a
   filehandle, device ID, and device index.  The filehandle, "fh",
   identifies the file on the storage device identified.  The device ID
   ("dev_id") may refer to either a Simple or a Complex device; see the
   description of the nfsv4_file_layout_device4 for details.  When a
   Complex device is referenced by the "dev_id", the "dev_index" field
   specifies the starting index within the device's "dev_list".  If the
   "dev_id" references a Simple device, the "dev_index" has no meaning
   and should be zero.  The "dev_index" plays a critical role in the
   flattening of a Complex device.

   The client is expected to construct a 'flat' list of devices over
   which the file is striped.  A flat device list can be constructed by
   concatenating each device encountered while traversing "stripe_devs"
   (or "dev_list" in the case of a zero sized "stripe_devs" array),
   while expanding out each Complex device.  The flat device list must
   contain only Simple devices.  The client must expand the Complex
   device's device list by starting at the device indexed by
   "dev_index", ending with the device prior to "dev_index".  All
   devices in the device list must be consumed; this may require
   wrapping around the end of the array if "dev_index" is non-zero.  The
   stripe width is determined by the stripe unit size multiplied by the
   number of device entries within the flattened stripe.

   Consider the following example:

   Given a set of devices as follows:

   1->{simple}; 2->{complex, dev_list=<3,4>}; 3->{simple}; 4->{simple}

   Device ID 1,3,4 and 5 are Simple devices.  Device ID 2 is a Complex
   device constructed of Simple devices 3 and 4.

   Within the nfsv4_file_layouttype4, imagine a "dev_list" constructed
   of <device ID, device index, FH> tuples:

   dev_list = [<1, 0, 0x12>, <2, 0, 0x13>, <3, 0, 0x14>, <4, 0, 0x15>]




Shepler, et al.         Expires February 2, 2007              [Page 230]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   And a "stripe_devs" array containing the following indices:

   stripe_devs = [2, 3, 0, 1]

   Using the stripe_devs as indices into the dev_list, we get the
   following ordered list of nfsv4_file_layouts:

   [<3, 0, 0x14>, <4, 0, 0x15>, <1, 0, 0x12>, <2, 0, 0x13>]

   Continuing to flatten the Complex devices gives us the following list
   of 5 simple <device ID, FH> tuples.  Note device 2 is a Complex
   device that gets replaced with devices 3 and 4:

   [<3, 0x14>, <4, 0x15>, <1, 0x12>, <3, 0x13>, <4, 0x13>]

   The flattened device list specifies the order over which the devices
   must be striped.  It also specifies the filehandle to be used for
   each stripe unit.  Data must be written in increments of the stripe
   unit size.  Devices may be repeated multiple times within the
   flattened device list.  However, if a dense stripe type is used
   (described later), the same filehandle MUST NOT be used on the same
   device for different stripe units of the same file.

   A data file stored on a storage device MUST map to a single file as
   defined by the metadata server; i.e., data from two files as viewed
   by the metadata server MUST NOT be stored within the same data file
   on any storage device.

   The "stripe_type" field specifies how the data is laid out within the
   data file on a storage device.  It allows for two different data
   layouts: sparse and dense or packed.  The stripe type determines the
   calculation that must be made to map the client visible file offset
   to the offset within the data file located on the storage device.

   The layout hint structure is described in more detail in Section
   4.15.  It is used, by the client, as by the FILE_LAYOUT_HINT
   attribute to specify the type of layout to be used for a newly
   created file.

12.4.1.1.  Sparse and Dense Storage Device Data Layouts

   The stripe_type field allows for two storage device data file
   representations.  Example sparse and dense storage device data
   layouts are illustrated below:







Shepler, et al.         Expires February 2, 2007              [Page 231]


Internet-Draft            NFSv4 Minor Version 1              August 2006


    Sparse file-layout (stripe_unit = 4KB)
    ------------------

    Is represented by the following file layout on the storage devices:

        Offset  ID:0    ID:1   ID:2
        0       +--+    +--+   +--+                 +--+  indicates a
                |//|    |  |   |  |                 |//|  stripe that
        4KB     +--+    +--+   +--+                 +--+  contains data
                |  |    |//|   |  |
        8KB     +--+    +--+   +--+
                |  |    |  |   |//|
        12KB    +--+    +--+   +--+
                |//|    |  |   |  |
        16KB    +--+    +--+   +--+
                |  |    |//|   |  |
                +--+    +--+   +--+

   The sparse file-layout has holes for the byte ranges not exported by
   that storage device.  This allows clients to access data using the
   real offset into the file, regardless of the storage device's
   position within the stripe.  However, if a client writes to one of
   the holes (e.g., offset 4-12KB on device 1), then an error MUST be
   returned by the storage device.  This requires that the storage
   device have knowledge of the layout for each file.

   When using a sparse layout, the offset into the storage device data
   file is the same as the offset into the main file.

    Dense/packed file-layout (stripe_unit = 4KB)
    ------------------------

    Is represented by the following file layout on the storage devices:

        Offset  ID:0    ID:1   ID:2
        0       +--+    +--+   +--+
                |//|    |//|   |//|
        4KB     +--+    +--+   +--+
                |//|    |//|   |//|
        8KB     +--+    +--+   +--+
                |//|    |//|   |//|
        12KB    +--+    +--+   +--+
                |//|    |//|   |//|
        16KB    +--+    +--+   +--+
                |//|    |//|   |//|
                +--+    +--+   +--+

   The dense or packed file-layout does not leave holes on the storage



Shepler, et al.         Expires February 2, 2007              [Page 232]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   devices.  Each stripe unit is spread across the storage devices.  As
   such, the storage devices need not know the file's layout since the
   client is allowed to write to any offset.

   The calculation to determine the byte offset within the data file for
   dense storage device layouts is:

     stripe_width = stripe_unit * N; where N = |dev_list|
     dev_offset = floor(file_offset / stripe_width) * stripe_unit +
                  file_offset % stripe_unit

   Regardless of the storage device data file layout, the calculation to
   determine the index into the device array is the same:

     dev_idx = floor(file_offset / stripe_unit) mod N

   Section 12.4.5 describe the semantics for dealing with reads to holes
   within the striped file.  This is of particular concern, since each
   individual component stripe file (i.e., the component of the striped
   file that lives on a particular storage device) may be of different
   length.  Thus, clients may experience 'short' reads when reading off
   the end of one of these component files.

12.4.1.2.  Metadata and Storage Device Roles

   In many cases, the metadata server and the storage device will be
   separate pieces of physical hardware.  The specification text is
   written as if that were always case.  However, it can be the case
   that the same physical hardware is used to implement both a metadata
   and storage device and in this case, the specification text's
   references to these two entities are to be understood as referring to
   the same physical hardware implementing two distinct roles and it is
   important that it be clearly understood on behalf of which role the
   hardware is executing at any given time.

   Two sub-cases can be distinguished.  In the first sub-case, the same
   physical hardware is used to implement both a metadata and data
   server in which each role is addressed through a distinct network
   interface (e.g., IP addresses for the metadata server and storage
   device are distinct).  As long as the storage device address is
   obtained from the layout and is distinct from the metadata server's
   address, using the device ID therein to obtain the appropriate
   storage device address, it is always clear, for any given request, to
   what role it is directed, based on the destination IP address.

   However, it may also be the case that even though the metadata server
   and storage device are distinct from one client's point of view, the
   roles may be reversed according to another client's point of view.



Shepler, et al.         Expires February 2, 2007              [Page 233]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   For example, in the cluster file system model a metadata server to
   one client, may be a storage device to another client.  Thus, it is
   safer to always mark the filehandle so that operations addressed to
   storage devices can be distinguished.

   The second sub-case is where both the metadata and storage device
   have the same network address.  This requires us to make the
   distinction as to which role each request is directed, on a another
   basis.  Since the network address is the same, the request is
   understood as being directed at one or the other, based on the
   filehandle of the first current filehandle value for the request.  If
   the first current filehandle is one derived from a layout (i.e., it
   is specified within the layout) (and it is recommended that these be
   distinguishable), then the request is to be considered as executed by
   a storage device.  Otherwise, the operation is to be understood as
   executed by the metadata server.

   If a current filehandle is set that is inconsistent with the role to
   which it is directed, then the error NFS4ERR_BADHANDLE should result.
   For example, if a request is directed at the storage device, because
   the first current handle is from a layout, any attempt to set the
   current filehandle to be a value not from a layout should be
   rejected.  Similarly, if the first current file handle was for a
   value not from a layout, a subsequent attempt to set the current
   filehandle to a value obtained from a layout should be rejected.

12.4.1.3.  Device Multipathing

   The NFSv4 file layout supports multipathing to 'equivalent' devices.
   Device-level multipathing is primarily of use in the case of a data
   server failure --- it allows the client to switch to another storage
   device that is exporting the same data stripe, without having to
   contact the metadata server for a new layout.

   To support device multipathing, an array of device IDs is encoded
   within the SIMPLE case of the nfsv4_file_layout_device4 union.  This
   array represents an ordered list of devices where the first element
   has the highest priority.  Each device in the list MUST be
   'equivalent' to every other device in the list and each device must
   be attempted in the order specified.

   Equivalent devices MUST export the same system image (e.g., the
   stateids and filehandles that they use are the same) and must provide
   the same consistency guarantees.  Two equivalent storage devices must
   also have sufficient connections to the storage, such that writing to
   one storage device is equivalent to writing to another, this also
   applies to reading.  Also, if multiple copies of the same data exist,
   reading from one must provide access to all existing copies.  As



Shepler, et al.         Expires February 2, 2007              [Page 234]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   such, it is unlikely that multipathing will provide additional
   benefit in the case of an I/O error.

   [NOTE: the error cases in which a client is expected to attempt an
   equivalent storage device should be specified.]

12.4.1.4.  Operations Issued to Storage Devices

   Clients MUST use the filehandle described within the layout when
   accessing data on the storage devices.  When using the layout's
   filehandle, the client MUST only issue BIND_BACKCHANNEL,
   BIND_CONN_TO_SESSION, CREATE_SESSION, COMMIT, DESTROY_SESSION, NULL,
   READ, WRITE, PUTFH, SECINFO_NO_NAME, SET_SSV, and SEQUENCE operations
   to the storage device associated with that filehandle.  If a client
   issues an operation other than those specified above, using the
   filehandle and storage device listed in the client's layout, that
   storage device SHOULD return an error to the client.  The client MUST
   follow the instruction implied by the layout (i.e., which filehandles
   to use on which devices).  As described in Section 12.3.2, a client
   MUST NOT issue I/Os to storage devices for which it does not hold a
   valid layout.  The storage devices may reject such requests.

   GETATTR and SETATTR MUST be directed to the metadata server.  In the
   case of a SETATTR of the size attribute, the control protocol is
   responsible for propagating size updates/truncations to the storage
   devices.  In the case of extending WRITEs to the storage devices, the
   new size must be visible on the metadata server once a LAYOUTCOMMIT
   has completed (see Section 12.3.4.2).  Section 12.4.5, describes the
   mechanism by which the client is to handle storage device file's that
   do not reflect the metadata server's size.

12.4.1.5.  COMMIT through metadata server

   commit_through_mds in the file layout gives the metadata server a
   preferred way of performing COMMIT.  If this flag is true, the client
   SHOULD send COMMIT to the metadata server instead of sending it to
   the same data server to which the associated WRITEs were sent.  In
   order to maintain the current NFSv4 commit and recovery model, all
   the data servers MUST return a common verifier for all WRITEs in a
   given file layout.  The value of the write verifier MUST be changed
   at the metadata server or any data server that is referenced in the
   layout, whenever there is a server event that can possibly lead to
   loss of uncommitted data.  The scope of the verifier can be for a
   file or for the entire pNFS server.  It might be more difficult for
   the server to maintain the verifier at the file level but the benefit
   is that only events that impact a given file will require recovery
   action.




Shepler, et al.         Expires February 2, 2007              [Page 235]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   The single COMMIT to the metadata server will return a verifier and
   the client should compare it to all the verifiers from the WRITEs and
   fail the COMMIT if there is any mismatched verifiers.  If COMMIT to
   the MDS fails, the client should reissue WRITEs for all the dirty
   data in the file.  The client should treat dirty data with mismatched
   verifier as WRITE failure and try to recover by reissuing the WRITEs
   to the original DS or using other path to that data if the layout has
   not been recalled.  Other option the client has is getting a new
   layout or just rewrite the data through the metadata server.  If the
   flag commit_through_mds is false the client should not send COMMIT to
   the metadata server.  Although it is valid to send COMMIT to the
   metadata server it should be used only to commit data that was
   written through the metadata server.  See also section 14.7.4
   "Storage Device Recover" for recovery options.

12.4.2.  Global Stateid Requirements

   Note, there are no stateids returned embedded within the layout.  The
   client MUST use the stateid representing open or lock state as
   returned by an earlier metadata operation (e.g., OPEN, LOCK), or a
   special stateid to perform I/O on the storage devices, as in regular
   NFSv4.  Special stateid usage for I/O is subject to the NFSv4
   protocol specification.  The stateid used for I/O MUST have the same
   effect and be subject to the same validation on storage device as it
   would if the I/O was being performed on the metadata server itself in
   the absence of pNFS.  This has the implication that stateids are
   globally valid on both the metadata and storage devices.  This
   requires the metadata server to propagate changes in lock and open
   state to the storage devices, so that the storage devices can
   validate I/O accesses.  This is discussed further in Section 12.4.4.
   Depending on when stateids are propagated, the existence of a valid
   stateid on the storage device may act as proof of a valid layout.

   [NOTE: a number of proposals have been made that have the possibility
   of limiting the amount of validation performed by the storage device,
   if any of these proposals are accepted or obtain consensus, the
   global stateid requirement can be revisited.]

12.4.3.  The Layout Iomode

   The layout iomode need not used by the metadata server when servicing
   NFSv4 file-based layouts, although in some circumstances it may be
   useful to use.  For example, if the server implementation supports
   reading from read-only replicas or mirrors, it would be useful for
   the server to return a layout enabling the client to do so.  As such,
   the client should set the iomode based on its intent to read or write
   the data.  The client may default to an iomode of READ/WRITE
   (LAYOUTIOMODE_RW).  The iomode need not be checked by the storage



Shepler, et al.         Expires February 2, 2007              [Page 236]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   devices when clients perform I/O. However, the storage devices SHOULD
   still validate that the client holds a valid layout and return an
   error if the client does not.

12.4.4.  Storage Device State Propagation

   Since the metadata server, which handles lock and open-mode state
   changes, as well as ACLs, may not be co-located with the storage
   devices where I/O access are validated, as such, the server
   implementation MUST take care of propagating changes of this state to
   the storage devices.  Once the propagation to the storage devices is
   complete, the full effect of those changes must be in effect at the
   storage devices.  However, some state changes need not be propagated
   immediately, although all changes SHOULD be propagated promptly.
   These state propagations have an impact on the design of the control
   protocol, even though the control protocol is outside of the scope of
   this specification.  Immediate propagation refers to the synchronous
   propagation of state from the metadata server to the storage
   device(s); the propagation must be complete before returning to the
   client.

12.4.4.1.  Lock State Propagation

   Mandatory locks MUST be made effective at the storage devices before
   the request that establishes them returns to the caller.  Thus,
   mandatory lock state MUST be synchronously propagated to the storage
   devices.  On the other hand, since advisory lock state is not used
   for checking I/O accesses at the storage devices, there is no
   semantic reason for propagating advisory lock state to the storage
   devices.  However, since all lock, unlock, open downgrades and
   upgrades affect the sequence ID stored within the stateid, the
   stateid changes which may cause difficulty if this state is not
   propagated.  Thus, when a client uses a stateid on a storage device
   for I/O with a newer sequence number than the one the storage device
   has, the storage device should query the metadata server and get any
   pending updates to that stateid.  This allows stateid sequence number
   changes to be propagated lazily, on-demand.

   [NOTE: With the reliance on the sessions protocol, there is no real
   need for sequence ID portion of the stateid to be validated on I/O
   accesses.  It is proposed that the seq.  ID checking is obsoleted.]

   Since updates to advisory locks neither confer nor remove privileges,
   these changes need not be propagated immediately, and may not need to
   be propagated promptly.  The updates to advisory locks need only be
   propagated when the storage device needs to resolve a question about
   a stateid.  In fact, if byte-range locking is not mandatory (i.e., is
   advisory) the clients are advised not to use the lock-based stateids



Shepler, et al.         Expires February 2, 2007              [Page 237]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   for I/O at all.  The stateids returned by open are sufficient and
   eliminate overhead for this kind of state propagation.

12.4.4.2.  Open-mode Validation

   Open-mode validation MUST be performed against the open mode(s) held
   by the storage devices.  However, the server implementation may not
   always require the immediate propagation of changes.  Reduction in
   access because of CLOSEs or DOWNGRADEs do not have to be propagated
   immediately, but SHOULD be propagated promptly; whereas changes due
   to revocation MUST be propagated immediately.  On the other hand,
   changes that expand access (e.g., new OPEN's and upgrades) don't have
   to be propagated immediately but the storage device SHOULD NOT reject
   a request because of mode issues without making sure that the upgrade
   is not in flight.

12.4.4.3.  File Attributes

   Since the SETATTR operation has the ability to modify state that is
   visible on both the metadata and storage devices (e.g., the size),
   care must be taken to ensure that the resultant state across the set
   of storage devices is consistent; especially when truncating or
   growing the file.

   As described earlier, the LAYOUTCOMMIT operation is used to ensure
   that the metadata is synced with changes made to the storage devices.
   For the file-based protocol, it is necessary to re-sync state such as
   the size attribute, and the setting of mtime/atime.  See
   Section 12.3.4 for a full description of the semantics regarding
   LAYOUTCOMMIT and attribute synchronization.  It should be noted, that
   by using a file-based layout type, it is possible to synchronize this
   state before LAYOUTCOMMIT occurs.  For example, the control protocol
   can be used to query the attributes present on the storage devices.

   Any changes to file attributes that control authorization or access
   as reflected by ACCESS calls or READs and WRITEs on the metadata
   server, MUST be propagated to the storage devices for enforcement on
   READ and WRITE I/O calls.  If the changes made on the metadata server
   result in more restrictive access permissions for any user, those
   changes MUST be propagated to the storage devices synchronously.

   Recall that the NFSv4 protocol RFC3530 [2] specifies that:

      ...since the NFS version 4 protocol does not impose any
      requirement that READs and WRITEs issued for an open file have the
      same credentials as the OPEN itself, the server still must do
      appropriate access checking on the READs and WRITEs themselves.




Shepler, et al.         Expires February 2, 2007              [Page 238]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   This also includes changes to ACLs.  The propagation of access right
   changes due to changes in ACLs may be asynchronous only if the server
   implementation is able to determine that the updated ACL is not more
   restrictive for any user specified in the old ACL.  Due to the
   relative infrequency of ACL updates, it is suggested that all changes
   be propagated synchronously.

   [NOTE: it has been suggested that the NFSv4 specification is in error
   with regard to allowing principles other than those used for OPEN to
   be used for file I/O. If changes within a minor version alter the
   behavior of NFSv4 with regard to OPEN principals and stateids some
   access control checking at the storage device can be made less
   expensive. pNFS should be altered to take full advantage of these
   changes.]

12.4.5.  Storage Device Component File Size

   A potential problem exists when a component data file on a particular
   storage device is grown past EOF; the problem exists for both dense
   and sparse layouts.  Imagine the following scenario: a client creates
   a new file (size == 0) and writes to byte 128KB; the client then
   seeks to the beginning of the file and reads byte 100.  The client
   should receive 0s back as a result of the read.  However, if the read
   falls on a different storage device to the client's original write,
   the storage device servicing the READ may still believe that the
   file's size is at 0 and return no data with the EOF flag set.  The
   storage device can only return 0s if it knows that the file's size
   has been extended.  This would require the immediate propagation of
   the file's size to all storage devices, which is potentially very
   costly.  Therefore, the client that has initiated the extension of
   the file's size MUST be prepared to deal with these EOF conditions;
   the EOF'd or short reads will be treated as a hole in the file and
   the NFS client will substitute 0s for the data when the offset is
   less than the client's view of the file size.

   The NFS protocol only provides close to open file data cache
   semantics; meaning that when the file is closed all modified data is
   written to the NFS server.  When a subsequent open of the file is
   done, the change time is inspected for a difference from a cached
   value for the change time.  For the case above, this means that a
   LAYOUTCOMMIT will be done at close (along with the data writes) and
   will update the file's size and change time.  Access from another
   client after that point will result in the appropriate size being
   returned.







Shepler, et al.         Expires February 2, 2007              [Page 239]


Internet-Draft            NFSv4 Minor Version 1              August 2006


12.4.6.  Crash Recovery Considerations

   As described in Section 12.3.7, the layout type specific storage
   protocol is responsible for handling the effects of I/Os started
   before lease expiration, extending through lease expiration.  The
   NFSv4 file layout type prevents all I/Os from being executed after
   lease expiration, without relying on a precise client lease timer and
   without requiring storage devices to maintain lease timers.

   It works as follows.  In the presence of sessions, each compound
   begins with a SEQUENCE operation that contains the "clientID".  On
   the storage device, the clientID can be used to validate that the
   client has a valid layout for the I/O being performed, if it does
   not, the I/O is rejected.  Before the metadata server takes any
   action to invalidate a layout given out by a previous instance, it
   must make sure that all layouts from that previous instance are
   invalidated at the storage devices.  Note: it is sufficient to
   invalidate the stateids associated with the layout only if special
   stateids are not being used for I/O at the storage devices, otherwise
   the layout itself must be invalidated.

   This means that a metadata server may not restripe a file until it
   has contacted all of the storage devices to invalidate the layouts
   from the previous instance nor may it give out locks that conflict
   with locks embodied by the stateids associated with any layout from
   the previous instance without either doing a specific invalidation
   (as it would have to do anyway) or doing a global storage device
   invalidation.

12.4.7.  Security Considerations for the File Layout Type

   The NFSv4 file layout type MUST adhere to the security considerations
   outlined in Section 12.3.8.  More specifically, storage devices must
   make all of the required access checks on each READ or WRITE I/O as
   determined by the NFSv4 protocol RFC3530 [2].  If the metadata server
   would deny an operation on a given file due its ACL, mode attribute,
   open mode, open deny mode, mandatory lock state, or any other
   attributes and state, the data server MUST also deny the operation.
   This impacts the control protocol and the propagation of state from
   the metadata server to the storage devices; see Section 12.4.4 for
   more details.

   The methods for authentication, integrity, and privacy for file
   layout-based data servers are the same as that used for metadata
   servers.  Metadata and data servers use ONC RPC security flavors to
   authenticate, and SECINFO and SECINFO_NO_NAME to negotiate the
   security mechanism and services to be used.




Shepler, et al.         Expires February 2, 2007              [Page 240]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   For a given file object, a metadata server MAY require different
   security parameters (secinfo4 value) than the data server.  For a
   given file object with multiple data servers, the secinfo4 value
   SHOULD be the same across all data servers.

   If an NFSv4.1 implementation supports parallel NFS and supports file
   layouts, then the implementation MUST support the SECINFO_NO_NAME
   operation, on both the metadata and data servers.

12.4.8.  Alternate Approaches

   Two alternate approaches exist for file-based layouts and the method
   used by clients to obtain stateids used for I/O. Both approaches
   embed stateids within the layout.

   However, before examining these approaches it is important to
   understand the distinction between clients and owners.  Delegations
   belong to clients, while locks (e.g., record and share reservations)
   are held by owners which in turn belong to a specific client.  As
   such, delegations can only protect against inter-client conflicts,
   not intra-client conflicts.  Layouts are held by clients and SHOULD
   NOT be associated with state held by owners.  Therefore, if stateids
   used for data access are embedded within a layout, these stateids can
   only act as delegation stateids, protecting against inter-client
   conflicts; stateids pertaining to an owner can not be embedded within
   the layout.  This has the implication that the client MUST arbitrate
   among all intra-client conflicts (e.g., arbitrating among lock
   requests by different processes) before issuing pNFS operations.
   Using the stateids stored within the layout, storage devices can only
   arbitrate between clients (not owners).

   The first alternate approach is to do away with global stateids,
   stateids returned by OPEN/LOCK that are valid on the metadata server
   and storage devices, and use only stateids embedded within the
   layout.  This approach has the drawback that the stateids used for
   I/O access can not be validated against per owner state, since they
   are only associated with the client holding the layout.  It breaks
   the semantics of tying a stateid used for I/O to an open instance.
   This has the implication that clients must delegate per owner lock
   and open requests internally, rather than push the work onto the
   storage devices.  The storage devices can still arbitrate and enforce
   inter-client lock and open state.

   The second approach is a hybrid approach.  This approach allows for
   stateids to be embedded with the layout, but also allows for the
   possibility of global stateids.  If the stateid embedded within the
   layout is a special stateid of all zeros, then the stateid referring
   to the last successful OPEN/LOCK should be used.  This approach is



Shepler, et al.         Expires February 2, 2007              [Page 241]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   recommended if it is decided that using NFSv4 as a control protocol
   is required.

   This proposal suggests the global stateid approach due to the cleaner
   semantics it provides regarding the relationship between stateids
   used for I/O and their corresponding open instance or lock state.
   However, it does have a profound impact on the control protocol's
   implementation and the state propagation that is required (as
   described in Section 12.4.4).


13.  Internationalization

   The primary issue in which NFS version 4 needs to deal with
   internationalization, or I18N, is with respect to file names and
   other strings as used within the protocol.  The choice of string
   representation must allow reasonable name/string access to clients
   which use various languages.  The UTF-8 encoding of the UCS as
   defined by ISO10646 [10] allows for this type of access and follows
   the policy described in "IETF Policy on Character Sets and
   Languages", RFC2277 [11].

   RFC3454 [12], otherwise know as "stringprep", documents a framework
   for using Unicode/UTF-8 in networking protocols, so as "to increase
   the likelihood that string input and string comparison work in ways
   that make sense for typical users throughout the world."  A protocol
   must define a profile of stringprep "in order to fully specify the
   processing options."  The remainder of this Internationalization
   section defines the NFS version 4 stringprep profiles.  Much of
   terminology used for the remainder of this section comes from
   stringprep.

   There are three UTF-8 string types defined for NFS version 4:
   utf8str_cs, utf8str_cis, and utf8str_mixed.  Separate profiles are
   defined for each.  Each profile defines the following, as required by
   stringprep:

   o  The intended applicability of the profile

   o  The character repertoire that is the input and output to
      stringprep (which is Unicode 3.2 for referenced version of
      stringprep)

   o  The mapping tables from stringprep used (as described in section 3
      of stringprep)

   o  Any additional mapping tables specific to the profile




Shepler, et al.         Expires February 2, 2007              [Page 242]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   o  The Unicode normalization used, if any (as described in section 4
      of stringprep)

   o  The tables from stringprep listing of characters that are
      prohibited as output (as described in section 5 of stringprep)

   o  The bidirectional string testing used, if any (as described in
      section 6 of stringprep)

   o  Any additional characters that are prohibited as output specific
      to the profile

   Stringprep discusses Unicode characters, whereas NFS version 4
   renders UTF-8 characters.  Since there is a one to one mapping from
   UTF-8 to Unicode, where ever the remainder of this document refers to
   to Unicode, the reader should assume UTF-8.

   Much of the text for the profiles comes from RFC3491 [13].

13.1.  Stringprep profile for the utf8str_cs type

   Every use of the utf8str_cs type definition in the NFS version 4
   protocol specification follows the profile named nfs4_cs_prep.

13.1.1.  Intended applicability of the nfs4_cs_prep profile

   The utf8str_cs type is a case sensitive string of UTF-8 characters.
   Its primary use in NFS Version 4 is for naming components and
   pathnames.  Components and pathnames are stored on the server's file
   system.  Two valid distinct UTF-8 strings might be the same after
   processing via the utf8str_cs profile.  If the strings are two names
   inside a directory, the NFS version 4 server will need to either:

   o  disallow the creation of a second name if it's post processed form
      collides with that of an existing name, or

   o  allow the creation of the second name, but arrange so that after
      post processing, the second name is different than the post
      processed form of the first name.

13.1.2.  Character repertoire of nfs4_cs_prep

   The nfs4_cs_prep profile uses Unicode 3.2, as defined in stringprep's
   Appendix A.1







Shepler, et al.         Expires February 2, 2007              [Page 243]


Internet-Draft            NFSv4 Minor Version 1              August 2006


13.1.3.  Mapping used by nfs4_cs_prep

   The nfs4_cs_prep profile specifies mapping using the following tables
   from stringprep:

      Table B.1

   Table B.2 is normally not part of the nfs4_cs_prep profile as it is
   primarily for dealing with case-insensitive comparisons.  However, if
   the NFS version 4 file server supports the case_insensitive file
   system attribute, and if case_insensitive is true, the NFS version 4
   server MUST use Table B.2 (in addition to Table B1) when processing
   utf8str_cs strings, and the NFS version 4 client MUST assume Table
   B.2 (in addition to Table B.1) are being used.

   If the case_preserving attribute is present and set to false, then
   the NFS version 4 server MUST use table B.2 to map case when
   processing utf8str_cs strings.  Whether the server maps from lower to
   upper case or the upper to lower case is an implementation
   dependency.

13.1.4.  Normalization used by nfs4_cs_prep

   The nfs4_cs_prep profile does not specify a normalization form.  A
   later revision of this specification may specify a particular
   normalization form.  Therefore, the server and client can expect that
   they may receive unnormalized characters within protocol requests and
   responses.  If the operating environment requires normalization, then
   the implementation must normalize utf8str_cs strings within the
   protocol before presenting the information to an application (at the
   client) or local file system (at the server).

13.1.5.  Prohibited output for nfs4_cs_prep

   The nfs4_cs_prep profile specifies prohibiting using the following
   tables from stringprep:

      Table C.3

      Table C.4

      Table C.5

      Table C.6

      Table C.7





Shepler, et al.         Expires February 2, 2007              [Page 244]


Internet-Draft            NFSv4 Minor Version 1              August 2006


      Table C.8

      Table C.9

13.1.6.  Bidirectional output for nfs4_cs_prep

   The nfs4_cs_prep profile does not specify any checking of
   bidirectional strings.

13.2.  Stringprep profile for the utf8str_cis type

   Every use of the utf8str_cis type definition in the NFS version 4
   protocol specification follows the profile named nfs4_cis_prep.

13.2.1.  Intended applicability of the nfs4_cis_prep profile

   The utf8str_cis type is a case insensitive string of UTF-8
   characters.  Its primary use in NFS Version 4 is for naming NFS
   servers.

13.2.2.  Character repertoire of nfs4_cis_prep

   The nfs4_cis_prep profile uses Unicode 3.2, as defined in
   stringprep's Appendix A.1

13.2.3.  Mapping used by nfs4_cis_prep

   The nfs4_cis_prep profile specifies mapping using the following
   tables from stringprep:

      Table B.1

      Table B.2

13.2.4.  Normalization used by nfs4_cis_prep

   The nfs4_cis_prep profile specifies using Unicode normalization form
   KC, as described in stringprep.

13.2.5.  Prohibited output for nfs4_cis_prep

   The nfs4_cis_prep profile specifies prohibiting using the following
   tables from stringprep:

      Table C.1.2

      Table C.2.2




Shepler, et al.         Expires February 2, 2007              [Page 245]


Internet-Draft            NFSv4 Minor Version 1              August 2006


      Table C.3

      Table C.4

      Table C.5

      Table C.6

      Table C.7

      Table C.8

      Table C.9

13.2.6.  Bidirectional output for nfs4_cis_prep

   The nfs4_cis_prep profile specifies checking bidirectional strings as
   described in stringprep's section 6.

13.3.  Stringprep profile for the utf8str_mixed type

   Every use of the utf8str_mixed type definition in the NFS version 4
   protocol specification follows the profile named nfs4_mixed_prep.

13.3.1.  Intended applicability of the nfs4_mixed_prep profile

   The utf8str_mixed type is a string of UTF-8 characters, with a prefix
   that is case sensitive, a separator equal to '@', and a suffix that
   is fully qualified domain name.  Its primary use in NFS Version 4 is
   for naming principals identified in an Access Control Entry.

13.3.2.  Character repertoire of nfs4_mixed_prep

   The nfs4_mixed_prep profile uses Unicode 3.2, as defined in
   stringprep's Appendix A.1

13.3.3.  Mapping used by nfs4_cis_prep

   For the prefix and the separator of a utf8str_mixed string, the
   nfs4_mixed_prep profile specifies mapping using the following table
   from stringprep:

      Table B.1

   For the suffix of a utf8str_mixed string, the nfs4_mixed_prep profile
   specifies mapping using the following tables from stringprep:





Shepler, et al.         Expires February 2, 2007              [Page 246]


Internet-Draft            NFSv4 Minor Version 1              August 2006


      Table B.1

      Table B.2

13.3.4.  Normalization used by nfs4_mixed_prep

   The nfs4_mixed_prep profile specifies using Unicode normalization
   form KC, as described in stringprep.

13.3.5.  Prohibited output for nfs4_mixed_prep

   The nfs4_mixed_prep profile specifies prohibiting using the following
   tables from stringprep:

      Table C.1.2

      Table C.2.2

      Table C.3

      Table C.4

      Table C.5

      Table C.6

      Table C.7

      Table C.8

      Table C.9

13.3.6.  Bidirectional output for nfs4_mixed_prep

   The nfs4_mixed_prep profile specifies checking bidirectional strings
   as described in stringprep's section 6.

13.4.  UTF-8 Related Errors

   Where the client sends an invalid UTF-8 string, the server should
   return an NFS4ERR_INVAL (Table 8) error.  This includes cases in
   which inappropriate prefixes are detected and where the count
   includes trailing bytes that do not constitute a full UCS character.

   Where the client supplied string is valid UTF-8 but contains
   characters that are not supported by the server as a value for that
   string (e.g. names containing characters that have more than two
   octets on a file system that supports Unicode characters only), the



Shepler, et al.         Expires February 2, 2007              [Page 247]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   server should return an NFS4ERR_BADCHAR (Table 8) error.

   Where a UTF-8 string is used as a file name, and the file system,
   while supporting all of the characters within the name, does not
   allow that particular name to be used, the server should return the
   error NFS4ERR_BADNAME (Table 8).  This includes situations in which
   the server file system imposes a normalization constraint on name
   strings, but will also include such situations as file system
   prohibitions of "." and ".." as file names for certain operations,
   and other such constraints.


14.  Error Values

   NFS error numbers are assigned to failed operations within a compound
   request.  A compound request contains a number of NFS operations that
   have their results encoded in sequence in a compound reply.  The
   results of successful operations will consist of an NFS4_OK status
   followed by the encoded results of the operation.  If an NFS
   operation fails, an error status will be entered in the reply and the
   compound request will be terminated.

14.1.  Error Definitions

                        Protocol Error Definitions

   +-----------------------------------+--------+----------------------+
   | Error                             | Number | Description          |
   +-----------------------------------+--------+----------------------+
   | NFS4_OK                           | 0      | Indicates the        |
   |                                   |        | operation completed  |
   |                                   |        | successfully.        |
   | NFS4ERR_ACCESS                    | 13     | Permission denied.   |
   |                                   |        | The caller does not  |
   |                                   |        | have the correct     |
   |                                   |        | permission to        |
   |                                   |        | perform the          |
   |                                   |        | requested operation. |
   |                                   |        | Contrast this with   |
   |                                   |        | NFS4ERR_PERM, which  |
   |                                   |        | restricts itself to  |
   |                                   |        | owner or privileged  |
   |                                   |        | user permission      |
   |                                   |        | failures.            |







Shepler, et al.         Expires February 2, 2007              [Page 248]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   | NFS4ERR_ATTRNOTSUPP               | 10032  | An attribute         |
   |                                   |        | specified is not     |
   |                                   |        | supported by the     |
   |                                   |        | server. Does not     |
   |                                   |        | apply to the GETATTR |
   |                                   |        | operation.           |
   | NFS4ERR_ADMIN_REVOKED             | 10047  | Due to administrator |
   |                                   |        | intervention, the    |
   |                                   |        | lockowner's record   |
   |                                   |        | locks, share         |
   |                                   |        | reservations, and    |
   |                                   |        | delegations have     |
   |                                   |        | been revoked by the  |
   |                                   |        | server.              |
   | NFS4ERR_BADCHAR                   | 10040  | A UTF-8 string       |
   |                                   |        | contains a character |
   |                                   |        | which is not         |
   |                                   |        | supported by the     |
   |                                   |        | server in the        |
   |                                   |        | context in which it  |
   |                                   |        | being used.          |
   | NFS4ERR_BAD_COOKIE                | 10003  | READDIR cookie is    |
   |                                   |        | stale.               |
   | NFS4ERR_BADHANDLE                 | 10001  | Illegal NFS          |
   |                                   |        | filehandle. The      |
   |                                   |        | filehandle failed    |
   |                                   |        | internal consistency |
   |                                   |        | checks.              |
   | NFS4ERR_BADIOMODE                 | 10049  | Layout iomode is     |
   |                                   |        | invalid.             |
   | NFS4ERR_BADLAYOUT                 | 10050  | Layout specified is  |
   |                                   |        | invalid.             |
   | NFS4ERR_BADNAME                   | 10041  | A name string in a   |
   |                                   |        | request consists of  |
   |                                   |        | valid UTF-8          |
   |                                   |        | characters supported |
   |                                   |        | by the server but    |
   |                                   |        | the name is not      |
   |                                   |        | supported by the     |
   |                                   |        | server as a valid    |
   |                                   |        | name for current     |
   |                                   |        | operation.           |
   | NFS4ERR_BADOWNER                  | 10039  | An owner,            |
   |                                   |        | owner_group, or ACL  |
   |                                   |        | attribute value can  |
   |                                   |        | not be translated to |
   |                                   |        | local                |
   |                                   |        | representation.      |



Shepler, et al.         Expires February 2, 2007              [Page 249]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   | NFS4ERR_BAD_SESSION_DIGEST        | 10051  | The digest used in a |
   |                                   |        | SET_SSV or           |
   |                                   |        | BIND_CONN_TO_SESSION |
   |                                   |        | request is not       |
   |                                   |        | valid.               |
   | NFS4ERR_BADTYPE                   | 10007  | An attempt was made  |
   |                                   |        | to create an object  |
   |                                   |        | of a type not        |
   |                                   |        | supported by the     |
   |                                   |        | server.              |
   | NFS4ERR_BAD_RANGE                 | 10042  | The range for a      |
   |                                   |        | LOCK, LOCKT, or      |
   |                                   |        | LOCKU operation is   |
   |                                   |        | not appropriate to   |
   |                                   |        | the allowable range  |
   |                                   |        | of offsets for the   |
   |                                   |        | server.              |
   | NFS4ERR_BAD_SEQID                 | 10026  | The sequence number  |
   |                                   |        | in a locking request |
   |                                   |        | is neither the next  |
   |                                   |        | expected number or   |
   |                                   |        | the last number      |
   |                                   |        | processed.           |
   | NFS4ERR_BADSESSION                | 10052  | TDB                  |
   | NFS4ERR_BADSLOT                   | 10053  | TDB                  |
   | NFS4ERR_BAD_STATEID               | 10025  | A stateid generated  |
   |                                   |        | by the current       |
   |                                   |        | server instance, but |
   |                                   |        | which does not       |
   |                                   |        | designate any        |
   |                                   |        | locking state        |
   |                                   |        | (either current or   |
   |                                   |        | superseded) for a    |
   |                                   |        | current              |
   |                                   |        | lockowner-file pair, |
   |                                   |        | was used.            |
   | NFS4ERR_BADXDR                    | 10036  | The server           |
   |                                   |        | encountered an XDR   |
   |                                   |        | decoding error while |
   |                                   |        | processing an        |
   |                                   |        | operation.           |
   | NFS4ERR_CLID_INUSE                | 10017  | The CREATE_CLIENTID  |
   |                                   |        | operation has found  |
   |                                   |        | that a client id is  |
   |                                   |        | already in use by    |
   |                                   |        | another client.      |





Shepler, et al.         Expires February 2, 2007              [Page 250]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   | NFS4ERR_COMPLETE_ALREADY          | 10054  | A RECLAIM_COMPLETE   |
   |                                   |        | operation was done   |
   |                                   |        | by a client which    |
   |                                   |        | had already          |
   |                                   |        | performed one.       |
   | NFS4ERR_CONN_NOT_BOUND_TO_SESSION | 10055  | The connection is    |
   |                                   |        | not bound to the     |
   |                                   |        | specified session.   |
   | NFS4ERR_CONN_BINDING_NOT_ENFORCED | 10073  | Client is trying use |
   |                                   |        | enforced connection  |
   |                                   |        | binding, but it      |
   |                                   |        | disabled enforcement |
   |                                   |        | when the session was |
   |                                   |        | created.             |
   | NFS4ERR_DEADLOCK                  | 10045  | The server has been  |
   |                                   |        | able to determine a  |
   |                                   |        | file locking         |
   |                                   |        | deadlock condition   |
   |                                   |        | for a blocking lock  |
   |                                   |        | request.             |































Shepler, et al.         Expires February 2, 2007              [Page 251]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   | NFS4ERR_DELAY                     | 10008  | The server initiated |
   |                                   |        | the request, but was |
   |                                   |        | not able to complete |
   |                                   |        | it in a timely       |
   |                                   |        | fashion. The client  |
   |                                   |        | should wait and then |
   |                                   |        | try the request with |
   |                                   |        | a new RPC            |
   |                                   |        | transaction ID. For  |
   |                                   |        | example, this error  |
   |                                   |        | should be returned   |
   |                                   |        | from a server that   |
   |                                   |        | supports             |
   |                                   |        | hierarchical storage |
   |                                   |        | and receives a       |
   |                                   |        | request to process a |
   |                                   |        | file that has been   |
   |                                   |        | migrated. In this    |
   |                                   |        | case, the server     |
   |                                   |        | should start the     |
   |                                   |        | immigration process  |
   |                                   |        | and respond to       |
   |                                   |        | client with this     |
   |                                   |        | error. This error    |
   |                                   |        | may also occur when  |
   |                                   |        | a necessary          |
   |                                   |        | delegation recall    |
   |                                   |        | makes processing a   |
   |                                   |        | request in a timely  |
   |                                   |        | fashion impossible.  |
   | NFS4ERR_DELEG_ALREADY_WANTED      | 10056  | The client has       |
   |                                   |        | already registered   |
   |                                   |        | that it wants a      |
   |                                   |        | delegation.          |
   | NFS4ERR_DENIED                    | 10010  | An attempt to lock a |
   |                                   |        | file is denied.      |
   |                                   |        | Since this may be a  |
   |                                   |        | temporary condition, |
   |                                   |        | the client is        |
   |                                   |        | encouraged to retry  |
   |                                   |        | the lock request     |
   |                                   |        | until the lock is    |
   |                                   |        | accepted.            |
   | NFS4ERR_DIRDELEG_UNAVAIL          | 10057  | TBD                  |







Shepler, et al.         Expires February 2, 2007              [Page 252]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   | NFS4ERR_DQUOT                     | 69     | Resource (quota)     |
   |                                   |        | hard limit exceeded. |
   |                                   |        | The user's resource  |
   |                                   |        | limit on the server  |
   |                                   |        | has been exceeded.   |
   | NFS4ERR_EXIST                     | 17     | File exists. The     |
   |                                   |        | file specified       |
   |                                   |        | already exists.      |
   | NFS4ERR_EXPIRED                   | 10011  | A lease has expired  |
   |                                   |        | that is being used   |
   |                                   |        | in the current       |
   |                                   |        | operation.           |
   | NFS4ERR_FBIG                      | 27     | File too large. The  |
   |                                   |        | operation would have |
   |                                   |        | caused a file to     |
   |                                   |        | grow beyond the      |
   |                                   |        | server's limit.      |
   | NFS4ERR_FHEXPIRED                 | 10014  | The filehandle       |
   |                                   |        | provided is volatile |
   |                                   |        | and has expired at   |
   |                                   |        | the server.          |
   | NFS4ERR_FILE_OPEN                 | 10046  | The operation can    |
   |                                   |        | not be successfully  |
   |                                   |        | processed because a  |
   |                                   |        | file involved in the |
   |                                   |        | operation is         |
   |                                   |        | currently open.      |
   | NFS4ERR_GRACE                     | 10013  | The server is in its |
   |                                   |        | recovery or grace    |
   |                                   |        | period which should  |
   |                                   |        | match the lease      |
   |                                   |        | period of the        |
   |                                   |        | server.              |
   | NFS4ERR_INVAL                     | 22     | Invalid argument or  |
   |                                   |        | unsupported argument |
   |                                   |        | for an operation.    |
   |                                   |        | Two examples are     |
   |                                   |        | attempting a         |
   |                                   |        | READLINK on an       |
   |                                   |        | object other than a  |
   |                                   |        | symbolic link or     |
   |                                   |        | specifying a value   |
   |                                   |        | for an enum field    |
   |                                   |        | that is not defined  |
   |                                   |        | in the protocol      |
   |                                   |        | (e.g. nfs_ftype4).   |





Shepler, et al.         Expires February 2, 2007              [Page 253]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   | NFS4ERR_IO                        | 5      | I/O error. A hard    |
   |                                   |        | error (for example,  |
   |                                   |        | a disk error)        |
   |                                   |        | occurred while       |
   |                                   |        | processing the       |
   |                                   |        | requested operation. |
   | NFS4ERR_ISDIR                     | 21     | Is a directory. The  |
   |                                   |        | caller specified a   |
   |                                   |        | directory in a       |
   |                                   |        | non-directory        |
   |                                   |        | operation.           |
   | NFS4ERR_LAYOUTTRYLATER            | 10058  | Layouts are          |
   |                                   |        | temporarily          |
   |                                   |        | unavailable for the  |
   |                                   |        | file, client should  |
   |                                   |        | retry later.         |
   | NFS4ERR_LAYOUTUNAVAILABLE         | 10059  | Layouts are not      |
   |                                   |        | available for the    |
   |                                   |        | file or its          |
   |                                   |        | containing file      |
   |                                   |        | system.              |
   | NFS4ERR_LEASE_MOVED               | 10031  | A lease being        |
   |                                   |        | renewed is           |
   |                                   |        | associated with a    |
   |                                   |        | file system that has |
   |                                   |        | been migrated to a   |
   |                                   |        | new server.          |
   | NFS4ERR_LOCKED                    | 10012  | A read or write      |
   |                                   |        | operation was        |
   |                                   |        | attempted on a       |
   |                                   |        | locked file.         |
   | NFS4ERR_LOCK_NOTSUPP              | 10043  | Server does not      |
   |                                   |        | support atomic       |
   |                                   |        | upgrade or downgrade |
   |                                   |        | of locks.            |
   | NFS4ERR_LOCK_RANGE                | 10028  | A lock request is    |
   |                                   |        | operating on a       |
   |                                   |        | sub-range of a       |
   |                                   |        | current lock for the |
   |                                   |        | lock owner and the   |
   |                                   |        | server does not      |
   |                                   |        | support this type of |
   |                                   |        | request.             |
   | NFS4ERR_LOCKS_HELD                | 10037  | A CLOSE was          |
   |                                   |        | attempted and file   |
   |                                   |        | locks would exist    |
   |                                   |        | after the CLOSE.     |




Shepler, et al.         Expires February 2, 2007              [Page 254]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   | NFS4ERR_MINOR_VERS_MISMATCH       | 10021  | The server has       |
   |                                   |        | received a request   |
   |                                   |        | that specifies an    |
   |                                   |        | unsupported minor    |
   |                                   |        | version. The server  |
   |                                   |        | must return a        |
   |                                   |        | COMPOUND4res with a  |
   |                                   |        | zero length          |
   |                                   |        | operations result    |
   |                                   |        | array.               |
   | NFS4ERR_SEQ_MISORDERED            | 10063  | The requester sent a |
   |                                   |        | SEQUENCE or          |
   |                                   |        | CB_SEQUENCE          |
   |                                   |        | operation with an    |
   |                                   |        | invalid sequenceid.  |
   | NFS4ERR_SEQUENCE_POS              | 10064  | The requester sent a |
   |                                   |        | COMPOUND or          |
   |                                   |        | CB_COMPOUND with a   |
   |                                   |        | SEQUENCE or          |
   |                                   |        | CB_SEQUENCE          |
   |                                   |        | operation that was   |
   |                                   |        | not the first        |
   |                                   |        | operation.           |
   | NFS4ERR_MLINK                     | 31     | Too many hard links. |
   | NFS4ERR_MOVED                     | 10019  | The file system      |
   |                                   |        | which contains the   |
   |                                   |        | current filehandle   |
   |                                   |        | object is not        |
   |                                   |        | present at the       |
   |                                   |        | server. It may have  |
   |                                   |        | been relocated,      |
   |                                   |        | migrated to another  |
   |                                   |        | server or may have   |
   |                                   |        | never been present.  |
   |                                   |        | The client may       |
   |                                   |        | obtain the new file  |
   |                                   |        | system location by   |
   |                                   |        | obtaining the        |
   |                                   |        | "fs_locations"       |
   |                                   |        | attribute for the    |
   |                                   |        | current filehandle.  |
   |                                   |        | For further          |
   |                                   |        | discussion, refer to |
   |                                   |        | the section          |
   |                                   |        | "Multi-server Name   |
   |                                   |        | Space".              |





Shepler, et al.         Expires February 2, 2007              [Page 255]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   | NFS4ERR_NAMETOOLONG               | 63     | The filename in an   |
   |                                   |        | operation was too    |
   |                                   |        | long.                |
   | NFS4ERR_NOENT                     | 2      | No such file or      |
   |                                   |        | directory. The file  |
   |                                   |        | or directory name    |
   |                                   |        | specified does not   |
   |                                   |        | exist.               |
   | NFS4ERR_NOFILEHANDLE              | 10020  | The logical current  |
   |                                   |        | filehandle value     |
   |                                   |        | (or, in the case of  |
   |                                   |        | RESTOREFH, the saved |
   |                                   |        | filehandle value)    |
   |                                   |        | has not been set     |
   |                                   |        | properly. This may   |
   |                                   |        | be a result of a     |
   |                                   |        | malformed COMPOUND   |
   |                                   |        | operation (i.e. no   |
   |                                   |        | PUTFH or PUTROOTFH   |
   |                                   |        | before an operation  |
   |                                   |        | that requires the    |
   |                                   |        | current filehandle   |
   |                                   |        | be set).             |




























Shepler, et al.         Expires February 2, 2007              [Page 256]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   | NFS4ERR_NO_GRACE                  | 10033  | A reclaim of client  |
   |                                   |        | state was attempted  |
   |                                   |        | in circumstances in  |
   |                                   |        | which the server     |
   |                                   |        | cannot guarantee     |
   |                                   |        | that conflicting     |
   |                                   |        | state has not been   |
   |                                   |        | provided to another  |
   |                                   |        | client. This can     |
   |                                   |        | occur because the    |
   |                                   |        | reclaim has been     |
   |                                   |        | done outside of the  |
   |                                   |        | grace period of the  |
   |                                   |        | server, after the    |
   |                                   |        | client has done a    |
   |                                   |        | RECLAIM_COMPLETE     |
   |                                   |        | operation, or        |
   |                                   |        | because previous     |
   |                                   |        | operations have      |
   |                                   |        | created a situation  |
   |                                   |        | in which the server  |
   |                                   |        | is not able to       |
   |                                   |        | determine that a     |
   |                                   |        | reclaim-interfering  |
   |                                   |        | edge condition does  |
   |                                   |        | not exist.           |
   | NFS4ERR_NOMATCHING_LAYOUT         | 10060  | Client has no        |
   |                                   |        | matching layout      |
   |                                   |        | (segment) to return. |
   | NFS4ERR_NOSPC                     | 28     | No space left on     |
   |                                   |        | device. The          |
   |                                   |        | operation would have |
   |                                   |        | caused the server's  |
   |                                   |        | file system to       |
   |                                   |        | exceed its limit.    |
   | NFS4ERR_NOTDIR                    | 20     | Not a directory. The |
   |                                   |        | caller specified a   |
   |                                   |        | non-directory in a   |
   |                                   |        | directory operation. |
   | NFS4ERR_NOTEMPTY                  | 66     | An attempt was made  |
   |                                   |        | to remove a          |
   |                                   |        | directory that was   |
   |                                   |        | not empty.           |
   | NFS4ERR_NOTSUPP                   | 10004  | Operation is not     |
   |                                   |        | supported.           |






Shepler, et al.         Expires February 2, 2007              [Page 257]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   | NFS4ERR_NOT_SAME                  | 10027  | This error is        |
   |                                   |        | returned by the      |
   |                                   |        | VERIFY operation to  |
   |                                   |        | signify that the     |
   |                                   |        | attributes compared  |
   |                                   |        | were not the same as |
   |                                   |        | provided in the      |
   |                                   |        | client's request.    |
   | NFS4ERR_NXIO                      | 6      | I/O error. No such   |
   |                                   |        | device or address.   |
   | NFS4ERR_OLD_STATEID               | 10024  | A stateid which      |
   |                                   |        | designates the       |
   |                                   |        | locking state for a  |
   |                                   |        | lockowner-file at an |
   |                                   |        | earlier time was     |
   |                                   |        | used.                |
   | NFS4ERR_OPENMODE                  | 10038  | The client attempted |
   |                                   |        | a READ, WRITE, LOCK  |
   |                                   |        | or SETATTR operation |
   |                                   |        | not sanctioned by    |
   |                                   |        | the stateid passed   |
   |                                   |        | (e.g. writing to a   |
   |                                   |        | file opened only for |
   |                                   |        | read).               |
   | NFS4ERR_OP_ILLEGAL                | 10044  | An illegal operation |
   |                                   |        | value has been       |
   |                                   |        | specified in the     |
   |                                   |        | argop field of a     |
   |                                   |        | COMPOUND or          |
   |                                   |        | CB_COMPOUND          |
   |                                   |        | procedure.           |
   | NFS4ERR_OP_NOT_IN_SESSION         | 10070  | The COMPOUND or      |
   |                                   |        | CB_COMPOUND contains |
   |                                   |        | an operation that    |
   |                                   |        | requires a SEQUENCE  |
   |                                   |        | or CB_SEQUENCE       |
   |                                   |        | operation to precede |
   |                                   |        | it in order to       |
   |                                   |        | establish a session. |
   | NFS4ERR_PERM                      | 1      | Not owner. The       |
   |                                   |        | operation was not    |
   |                                   |        | allowed because the  |
   |                                   |        | caller is either not |
   |                                   |        | a privileged user    |
   |                                   |        | (root) or not the    |
   |                                   |        | owner of the target  |
   |                                   |        | of the operation.    |




Shepler, et al.         Expires February 2, 2007              [Page 258]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   | NFS4ERR_RECALLCONFLICT            | 10061  | Layout is            |
   |                                   |        | unavailable due to a |
   |                                   |        | conflicting          |
   |                                   |        | LAYOUTRECALL that is |
   |                                   |        | in progress.         |
   | NFS4ERR_RECLAIM_BAD               | 10034  | The reclaim provided |
   |                                   |        | by the client does   |
   |                                   |        | not match any of the |
   |                                   |        | server's state       |
   |                                   |        | consistency checks   |
   |                                   |        | and is bad.          |
   | NFS4ERR_RECLAIM_CONFLICT          | 10035  | The reclaim provided |
   |                                   |        | by the client has    |
   |                                   |        | encountered a        |
   |                                   |        | conflict and can not |
   |                                   |        | be provided.         |
   |                                   |        | Potentially          |
   |                                   |        | indicates a          |
   |                                   |        | misbehaving client.  |
   | NFS4ERR_REP_TOO_BIG               | 10066  | The reply to a       |
   |                                   |        | COMPOUND or          |
   |                                   |        | CB_COMPOUND would    |
   |                                   |        | exceed the channel's |
   |                                   |        | negotiated maximum   |
   |                                   |        | response size.       |
   | NFS4ERR_REP_TOO_BIG_TO_CACHE      | 10067  | The reply to a       |
   |                                   |        | COMPOUND or          |
   |                                   |        | CB_COMPOUND would    |
   |                                   |        | exceed the channel's |
   |                                   |        | negotiated maximum   |
   |                                   |        | size for replies     |
   |                                   |        | cached in the reply  |
   |                                   |        | cache.               |
   | NFS4ERR_REQ_TOO_BIG               | 10065  | The COMPOUND or      |
   |                                   |        | CB_COMPOUND request  |
   |                                   |        | exceeds the          |
   |                                   |        | channel's negotiated |
   |                                   |        | maximum size for     |
   |                                   |        | requests.            |
   | NFS4ERR_RESTOREFH                 | 10030  | The RESTOREFH        |
   |                                   |        | operation does not   |
   |                                   |        | have a saved         |
   |                                   |        | filehandle           |
   |                                   |        | (identified by       |
   |                                   |        | SAVEFH) to operate   |
   |                                   |        | upon.                |





Shepler, et al.         Expires February 2, 2007              [Page 259]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   | NFS4ERR_RETRY_UNCACHED_REP        | 10068  | The requester has    |
   |                                   |        | attempted a retry of |
   |                                   |        | COMPOUND or          |
   |                                   |        | CB_COMPOUND which it |
   |                                   |        | previously requested |
   |                                   |        | not be placed in the |
   |                                   |        | reply cache.         |
   | NFS4ERR_ROFS                      | 30     | Read-only file       |
   |                                   |        | system. A modifying  |
   |                                   |        | operation was        |
   |                                   |        | attempted on a       |
   |                                   |        | read-only file       |
   |                                   |        | system.              |
   | NFS4ERR_SAME                      | 10009  | This error is        |
   |                                   |        | returned by the      |
   |                                   |        | NVERIFY operation to |
   |                                   |        | signify that the     |
   |                                   |        | attributes compared  |
   |                                   |        | were the same as     |
   |                                   |        | provided in the      |
   |                                   |        | client's request.    |
   | NFS4ERR_SERVERFAULT               | 10006  | An error occurred on |
   |                                   |        | the server which     |
   |                                   |        | does not map to any  |
   |                                   |        | of the legal NFS     |
   |                                   |        | version 4 protocol   |
   |                                   |        | error values. The    |
   |                                   |        | client should        |
   |                                   |        | translate this into  |
   |                                   |        | an appropriate       |
   |                                   |        | error. UNIX clients  |
   |                                   |        | may choose to        |
   |                                   |        | translate this to    |
   |                                   |        | EIO.                 |
   | NFS4ERR_SHARE_DENIED              | 10015  | An attempt to OPEN a |
   |                                   |        | file with a share    |
   |                                   |        | reservation has      |
   |                                   |        | failed because of a  |
   |                                   |        | share conflict.      |
   | NFS4ERR_STALE                     | 70     | Invalid filehandle.  |
   |                                   |        | The filehandle given |
   |                                   |        | in the arguments was |
   |                                   |        | invalid. The file    |
   |                                   |        | referred to by that  |
   |                                   |        | filehandle no longer |
   |                                   |        | exists or access to  |
   |                                   |        | it has been revoked. |




Shepler, et al.         Expires February 2, 2007              [Page 260]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   | NFS4ERR_STALE_CLIENTID            | 10022  | A clientid not       |
   |                                   |        | recognized by the    |
   |                                   |        | server was used in a |
   |                                   |        | locking or           |
   |                                   |        | CREATE_SESSION       |
   |                                   |        | request.             |
   | NFS4ERR_STALE_STATEID             | 10023  | A stateid generated  |
   |                                   |        | by an earlier server |
   |                                   |        | instance was used.   |
   | NFS4ERR_SYMLINK                   | 10029  | The current          |
   |                                   |        | filehandle provided  |
   |                                   |        | for a LOOKUP is not  |
   |                                   |        | a directory but a    |
   |                                   |        | symbolic link. Also  |
   |                                   |        | used if the final    |
   |                                   |        | component of the     |
   |                                   |        | OPEN path is a       |
   |                                   |        | symbolic link.       |
   | NFS4ERR_TOOSMALL                  | 10005  | The encoded response |
   |                                   |        | to a READDIR request |
   |                                   |        | exceeds the size     |
   |                                   |        | limit set by the     |
   |                                   |        | initial request.     |
   | NFS4ERR_TOO_MANY_OPS              | 10070  | The COMPOUND or      |
   |                                   |        | CB_COMPOUND request  |
   |                                   |        | has too many         |
   |                                   |        | operations.          |
   | NFS4ERR_UNKNOWN_LAYOUTTYPE        | 10062  | Layout type is       |
   |                                   |        | unknown.             |
   | NFS4ERR_UNSAFE_COMPOUND           | 10069  | The client has sent  |
   |                                   |        | a COMPOUND request   |
   |                                   |        | with an usafe mix of |
   |                                   |        | operations.          |
   | NFS4ERR_WRONGSEC                  | 10016  | The security         |
   |                                   |        | mechanism being used |
   |                                   |        | by the client for    |
   |                                   |        | the operation does   |
   |                                   |        | not match the        |
   |                                   |        | server's security    |
   |                                   |        | policy. The client   |
   |                                   |        | should change the    |
   |                                   |        | security mechanism   |
   |                                   |        | being used and retry |
   |                                   |        | the operation.       |
   | NFS4ERR_XDEV                      | 18     | Attempt to do an     |
   |                                   |        | operation between    |
   |                                   |        | different fsids.     |
   +-----------------------------------+--------+----------------------+



Shepler, et al.         Expires February 2, 2007              [Page 261]


Internet-Draft            NFSv4 Minor Version 1              August 2006


                                  Table 8

14.2.  Operations and their valid errors

        Mappings of valid error returns for each protocol operation

   +----------------------+--------------------------------------------+
   | Operation            | Errors                                     |
   +----------------------+--------------------------------------------+
   | ACCESS               | NFS4ERR_ACCESS, NFS4ERR_BADHANDLE,         |
   |                      | NFS4ERR_BADXDR, NFS4ERR_DELAY,             |
   |                      | NFS4ERR_FHEXPIRED, NFS4ERR_INVAL,          |
   |                      | NFS4ERR_IO, NFS4ERR_MOVED,                 |
   |                      | NFS4ERR_NOFILEHANDLE,                      |
   |                      | NFS4ERR_OP_NOT_IN_SESSION,                 |
   |                      | NFS4ERR_REQ_TOO_BIG, NFS4ERR_TOO_MANY_OPS, |
   |                      | NFS4ERR_REP_TOO_BIG,                       |
   |                      | NFS4ERR_REP_TOO_BIG_TO_CACHE,              |
   |                      | NFS4ERR_UNSAFE_COMPOUND,                   |
   |                      | NFS4ERR_SERVERFAULT, NFS4ERR_STALE         |
   | BIND_CONN_TO_SESSION | NFS4ERR_BAD_SESSION_DIGEST,                |
   |                      | NFS4ERR_CONN_BINDING_NOT_ENFORCED          |
   | CLOSE                | NFS4ERR_ADMIN_REVOKED, NFS4ERR_BADHANDLE,  |
   |                      | NFS4ERR_BAD_SEQID, NFS4ERR_BAD_STATEID,    |
   |                      | NFS4ERR_BADXDR, NFS4ERR_DELAY,             |
   |                      | NFS4ERR_EXPIRED, NFS4ERR_FHEXPIRED,        |
   |                      | NFS4ERR_INVAL, NFS4ERR_ISDIR,              |
   |                      | NFS4ERR_LEASE_MOVED, NFS4ERR_LOCKS_HELD,   |
   |                      | NFS4ERR_MOVED, NFS4ERR_NOFILEHANDLE,       |
   |                      | NFS4ERR_OLD_STATEID,                       |
   |                      | NFS4ERR_OP_NOT_IN_SESSION,                 |
   |                      | NFS4ERR_REQ_TOO_BIG, NFS4ERR_TOO_MANY_OPS, |
   |                      | NFS4ERR_REP_TOO_BIG,                       |
   |                      | NFS4ERR_REP_TOO_BIG_TO_CACHE,              |
   |                      | NFS4ERR_UNSAFE_COMPOUND,                   |
   |                      | NFS4ERR_SERVERFAULT, NFS4ERR_STALE,        |
   |                      | NFS4ERR_STALE_STATEID                      |
   | COMMIT               | NFS4ERR_ACCESS, NFS4ERR_BADHANDLE,         |
   |                      | NFS4ERR_BADXDR, NFS4ERR_FHEXPIRED,         |
   |                      | NFS4ERR_INVAL, NFS4ERR_IO, NFS4ERR_ISDIR,  |
   |                      | NFS4ERR_MOVED, NFS4ERR_NOFILEHANDLE,       |
   |                      | NFS4ERR_OP_NOT_IN_SESSION,                 |
   |                      | NFS4ERR_REQ_TOO_BIG, NFS4ERR_TOO_MANY_OPS, |
   |                      | NFS4ERR_REP_TOO_BIG,                       |
   |                      | NFS4ERR_REP_TOO_BIG_TO_CACHE,              |
   |                      | NFS4ERR_UNSAFE_COMPOUND, NFS4ERR_ROFS,     |
   |                      | NFS4ERR_SERVERFAULT, NFS4ERR_STALE         |




Shepler, et al.         Expires February 2, 2007              [Page 262]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   | CREATE               | NFS4ERR_ACCESS, NFS4ERR_ATTRNOTSUPP,       |
   |                      | NFS4ERR_BADCHAR, NFS4ERR_BADHANDLE,        |
   |                      | NFS4ERR_BADNAME, NFS4ERR_BADOWNER,         |
   |                      | NFS4ERR_BADTYPE, NFS4ERR_BADXDR,           |
   |                      | NFS4ERR_DELAY, NFS4ERR_DQUOT,              |
   |                      | NFS4ERR_EXIST, NFS4ERR_FHEXPIRED,          |
   |                      | NFS4ERR_INVAL, NFS4ERR_IO, NFS4ERR_MOVED,  |
   |                      | NFS4ERR_NAMETOOLONG, NFS4ERR_NOFILEHANDLE, |
   |                      | NFS4ERR_NOSPC, NFS4ERR_NOTDIR,             |
   |                      | NFS4ERR_OP_NOT_IN_SESSION, NFS4ERR_PERM,   |
   |                      | NFS4ERR_REQ_TOO_BIG, NFS4ERR_TOO_MANY_OPS, |
   |                      | NFS4ERR_REP_TOO_BIG,                       |
   |                      | NFS4ERR_REP_TOO_BIG_TO_CACHE,              |
   |                      | NFS4ERR_UNSAFE_COMPOUND, NFS4ERR_ROFS,     |
   |                      | NFS4ERR_SERVERFAULT, NFS4ERR_STALE         |
   | CREATE_CLIENTID      |                                            |
   | CREATE_SESSION       | NFS4ERR_BADXDR, NFS4ERR_CLID_INUSE,        |
   |                      | NFS4ERR_SERVERFAULT,                       |
   |                      | NFS4ERR_STALE_CLIENTID                     |
   | DELEGPURGE           | NFS4ERR_BADXDR, NFS4ERR_NOTSUPP,           |
   |                      | NFS4ERR_LEASE_MOVED, NFS4ERR_MOVED,        |
   |                      | NFS4ERR_OP_NOT_IN_SESSION,                 |
   |                      | NFS4ERR_REQ_TOO_BIG, NFS4ERR_TOO_MANY_OPS, |
   |                      | NFS4ERR_REP_TOO_BIG,                       |
   |                      | NFS4ERR_REP_TOO_BIG_TO_CACHE,              |
   |                      | NFS4ERR_UNSAFE_COMPOUND,                   |
   |                      | NFS4ERR_SERVERFAULT,                       |
   |                      | NFS4ERR_STALE_CLIENTID                     |
   | DELEGRETURN          | NFS4ERR_ADMIN_REVOKED,                     |
   |                      | NFS4ERR_BAD_STATEID, NFS4ERR_BADXDR,       |
   |                      | NFS4ERR_EXPIRED, NFS4ERR_INVAL,            |
   |                      | NFS4ERR_LEASE_MOVED, NFS4ERR_MOVED,        |
   |                      | NFS4ERR_NOFILEHANDLE, NFS4ERR_NOTSUPP,     |
   |                      | NFS4ERR_OLD_STATEID,                       |
   |                      | NFS4ERR_OP_NOT_IN_SESSION,                 |
   |                      | NFS4ERR_REQ_TOO_BIG, NFS4ERR_TOO_MANY_OPS, |
   |                      | NFS4ERR_REP_TOO_BIG,                       |
   |                      | NFS4ERR_REP_TOO_BIG_TO_CACHE,              |
   |                      | NFS4ERR_UNSAFE_COMPOUND,                   |
   |                      | NFS4ERR_SERVERFAULT, NFS4ERR_STALE,        |
   |                      | NFS4ERR_STALE_STATEID                      |
   | DESTROY_SESSION      |                                            |









Shepler, et al.         Expires February 2, 2007              [Page 263]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   | GET_DIR_DELEGATION   | NFS4ERR_ACCESS, NFS4ERR_BADHANDLE,         |
   |                      | NFS4ERR_BADXDR, NFS4ERR_FHEXPIRED,         |
   |                      | NFS4ERR_INVAL, NFS4ERR_MOVED,              |
   |                      | NFS4ERR_NOFILEHANDLE, NFS4ERR_NOTDIR,      |
   |                      | NFS4ERR_OP_NOT_IN_SESSION,                 |
   |                      | NFS4ERR_REQ_TOO_BIG, NFS4ERR_TOO_MANY_OPS, |
   |                      | NFS4ERR_REP_TOO_BIG,                       |
   |                      | NFS4ERR_REP_TOO_BIG_TO_CACHE,              |
   |                      | NFS4ERR_UNSAFE_COMPOUND,                   |
   |                      | NFS4ERR_SERVERFAULT, NFS4ERR_STALE,        |
   |                      | NFS4ERR_DIRDELEG_UNAVAIL,                  |
   |                      | NFS4ERR_WRONGSEC, NFS4ERR_EIO,             |
   |                      | NFS4ERR_NOTSUPP                            |
   | GETATTR              | NFS4ERR_ACCESS, NFS4ERR_BADHANDLE,         |
   |                      | NFS4ERR_BADXDR, NFS4ERR_DELAY,             |
   |                      | NFS4ERR_FHEXPIRED, NFS4ERR_INVAL,          |
   |                      | NFS4ERR_IO, NFS4ERR_MOVED,                 |
   |                      | NFS4ERR_NOFILEHANDLE,                      |
   |                      | NFS4ERR_OP_NOT_IN_SESSION,                 |
   |                      | NFS4ERR_REQ_TOO_BIG, NFS4ERR_TOO_MANY_OPS, |
   |                      | NFS4ERR_REP_TOO_BIG,                       |
   |                      | NFS4ERR_REP_TOO_BIG_TO_CACHE,              |
   |                      | NFS4ERR_UNSAFE_COMPOUND,                   |
   |                      | NFS4ERR_SERVERFAULT, NFS4ERR_STALE         |
   | GETDEVICEINFO        | NFS4ERR_FHEXPIRED, NFS4ERR_INVAL,          |
   |                      | NFS4ERR_TOOSMALL,                          |
   |                      | NFS4ERR_UNKNOWN_LAYOUTTYPE                 |
   | GETDEVICELIST        | NFS4ERR_BAD_COOKIE, NFS4ERR_FHEXPIRED,     |
   |                      | NFS4ERR_INVAL, NFS4ERR_TOOSMALL,           |
   |                      | NFS4ERR_UNKNOWN_LAYOUTTYPE                 |
   | GETFH                | NFS4ERR_BADHANDLE, NFS4ERR_FHEXPIRED,      |
   |                      | NFS4ERR_MOVED, NFS4ERR_NOFILEHANDLE,       |
   |                      | NFS4ERR_OP_NOT_IN_SESSION,                 |
   |                      | NFS4ERR_REQ_TOO_BIG, NFS4ERR_TOO_MANY_OPS, |
   |                      | NFS4ERR_REP_TOO_BIG,                       |
   |                      | NFS4ERR_REP_TOO_BIG_TO_CACHE,              |
   |                      | NFS4ERR_UNSAFE_COMPOUND,                   |
   |                      | NFS4ERR_SERVERFAULT, NFS4ERR_STALE         |
   | ILLEGAL              | NFS4ERR_OP_ILLEGAL                         |
   | LAYOUTCOMMIT         | NFS4ERR_BADLAYOUT, NFS4ERR_BADIOMODE,      |
   |                      | NFS4ERR_FHEXPIRED, NFS4ERR_INVAL,          |
   |                      | NFS4ERR_NOFILEHANDLE, NFS4ERR_NO_GRACE,    |
   |                      | NFS4ERR_RECLAIM_BAD, NFS4ERR_STALE,        |
   |                      | NFS4ERR_STALE_CLIENTID,                    |
   |                      | NFS4ERR_UNKNOWN_LAYOUTTYPE                 |






Shepler, et al.         Expires February 2, 2007              [Page 264]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   | LAYOUTGET            | NFS4ERR_BADLAYOUT, NFS4ERR_BADIOMODE,      |
   |                      | NFS4ERR_FHEXPIRED, NFS4ERR_INVAL,          |
   |                      | NFS4ERR_LAYOUTUNAVAILABLE,                 |
   |                      | NFS4ERR_LAYOUTTRYLATER, NFS4ERR_LOCKED,    |
   |                      | NFS4ERR_NOFILEHANDLE, NFS4ERR_NOTSUPP,     |
   |                      | NFS4ERR_RECALLCONFLICT, NFS4ERR_STALE,     |
   |                      | NFS4ERR_STALE_CLIENTID, NFS4ERR_TOOSMALL,  |
   |                      | NFS4ERR_UNKNOWN_LAYOUTTYPE                 |
   | LAYOUTRETURN         | NFS4ERR_BADLAYOUT, NFS4ERR_BADIOMODE,      |
   |                      | NFS4ERR_FHEXPIRED, NFS4ERR_INVAL,          |
   |                      | NFS4ERR_NOFILEHANDLE, NFS4ERR_NO_GRACE,    |
   |                      | NFS4ERR_STALE, NFS4ERR_STALE_CLIENTID,     |
   |                      | NFS4ERR_UNKNOWN_LAYOUTTYPE                 |
   | LINK                 | NFS4ERR_ACCESS, NFS4ERR_BADCHAR,           |
   |                      | NFS4ERR_BADHANDLE, NFS4ERR_BADNAME,        |
   |                      | NFS4ERR_BADXDR, NFS4ERR_DELAY,             |
   |                      | NFS4ERR_DQUOT, NFS4ERR_EXIST,              |
   |                      | NFS4ERR_FHEXPIRED, NFS4ERR_FILE_OPEN,      |
   |                      | NFS4ERR_INVAL, NFS4ERR_IO, NFS4ERR_ISDIR,  |
   |                      | NFS4ERR_MLINK, NFS4ERR_MOVED,              |
   |                      | NFS4ERR_NAMETOOLONG, NFS4ERR_NOENT,        |
   |                      | NFS4ERR_NOFILEHANDLE, NFS4ERR_NOSPC,       |
   |                      | NFS4ERR_NOTDIR, NFS4ERR_NOTSUPP,           |
   |                      | NFS4ERR_OP_NOT_IN_SESSION,                 |
   |                      | NFS4ERR_REQ_TOO_BIG, NFS4ERR_TOO_MANY_OPS, |
   |                      | NFS4ERR_REP_TOO_BIG,                       |
   |                      | NFS4ERR_REP_TOO_BIG_TO_CACHE,              |
   |                      | NFS4ERR_UNSAFE_COMPOUND, NFS4ERR_ROFS,     |
   |                      | NFS4ERR_SERVERFAULT, NFS4ERR_STALE,        |
   |                      | NFS4ERR_WRONGSEC, NFS4ERR_XDEV             |





















Shepler, et al.         Expires February 2, 2007              [Page 265]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   | LOCK                 | NFS4ERR_ACCESS, NFS4ERR_ADMIN_REVOKED,     |
   |                      | NFS4ERR_BADHANDLE, NFS4ERR_BAD_RANGE,      |
   |                      | NFS4ERR_BAD_SEQID, NFS4ERR_BAD_STATEID,    |
   |                      | NFS4ERR_BADXDR, NFS4ERR_DEADLOCK,          |
   |                      | NFS4ERR_DELAY, NFS4ERR_DENIED,             |
   |                      | NFS4ERR_EXPIRED, NFS4ERR_FHEXPIRED,        |
   |                      | NFS4ERR_GRACE, NFS4ERR_INVAL,              |
   |                      | NFS4ERR_ISDIR, NFS4ERR_LEASE_MOVED,        |
   |                      | NFS4ERR_LOCK_NOTSUPP, NFS4ERR_LOCK_RANGE,  |
   |                      | NFS4ERR_MOVED, NFS4ERR_NOFILEHANDLE,       |
   |                      | NFS4ERR_NO_GRACE, NFS4ERR_OLD_STATEID,     |
   |                      | NFS4ERR_OPENMODE,                          |
   |                      | NFS4ERR_OP_NOT_IN_SESSION,                 |
   |                      | NFS4ERR_RECLAIM_BAD,                       |
   |                      | NFS4ERR_RECLAIM_CONFLICT,                  |
   |                      | NFS4ERR_REQ_TOO_BIG, NFS4ERR_TOO_MANY_OPS, |
   |                      | NFS4ERR_REP_TOO_BIG,                       |
   |                      | NFS4ERR_REP_TOO_BIG_TO_CACHE,              |
   |                      | NFS4ERR_UNSAFE_COMPOUND,                   |
   |                      | NFS4ERR_SERVERFAULT, NFS4ERR_STALE,        |
   |                      | NFS4ERR_STALE_CLIENTID,                    |
   |                      | NFS4ERR_STALE_STATEID                      |
   | LOCKT                | NFS4ERR_ACCESS, NFS4ERR_BADHANDLE,         |
   |                      | NFS4ERR_BAD_RANGE, NFS4ERR_BADXDR,         |
   |                      | NFS4ERR_DELAY, NFS4ERR_DENIED,             |
   |                      | NFS4ERR_FHEXPIRED, NFS4ERR_GRACE,          |
   |                      | NFS4ERR_INVAL, NFS4ERR_ISDIR,              |
   |                      | NFS4ERR_LEASE_MOVED, NFS4ERR_LOCK_RANGE,   |
   |                      | NFS4ERR_MOVED, NFS4ERR_NOFILEHANDLE,       |
   |                      | NFS4ERR_OP_NOT_IN_SESSION,                 |
   |                      | NFS4ERR_REQ_TOO_BIG, NFS4ERR_TOO_MANY_OPS, |
   |                      | NFS4ERR_REP_TOO_BIG,                       |
   |                      | NFS4ERR_REP_TOO_BIG_TO_CACHE,              |
   |                      | NFS4ERR_UNSAFE_COMPOUND,                   |
   |                      | NFS4ERR_SERVERFAULT, NFS4ERR_STALE,        |
   |                      | NFS4ERR_STALE_CLIENTID                     |















Shepler, et al.         Expires February 2, 2007              [Page 266]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   | LOCKU                | NFS4ERR_ACCESS, NFS4ERR_ADMIN_REVOKED,     |
   |                      | NFS4ERR_BADHANDLE, NFS4ERR_BAD_RANGE,      |
   |                      | NFS4ERR_BAD_SEQID, NFS4ERR_BAD_STATEID,    |
   |                      | NFS4ERR_BADXDR, NFS4ERR_EXPIRED,           |
   |                      | NFS4ERR_FHEXPIRED, NFS4ERR_GRACE,          |
   |                      | NFS4ERR_INVAL, NFS4ERR_ISDIR,              |
   |                      | NFS4ERR_LEASE_MOVED, NFS4ERR_LOCK_RANGE,   |
   |                      | NFS4ERR_MOVED, NFS4ERR_NOFILEHANDLE,       |
   |                      | NFS4ERR_OLD_STATEID,                       |
   |                      | NFS4ERR_OP_NOT_IN_SESSION,                 |
   |                      | NFS4ERR_REQ_TOO_BIG, NFS4ERR_TOO_MANY_OPS, |
   |                      | NFS4ERR_REP_TOO_BIG,                       |
   |                      | NFS4ERR_REP_TOO_BIG_TO_CACHE,              |
   |                      | NFS4ERR_UNSAFE_COMPOUND,                   |
   |                      | NFS4ERR_SERVERFAULT, NFS4ERR_STALE,        |
   |                      | NFS4ERR_STALE_STATEID                      |
   | LOOKUP               | NFS4ERR_ACCESS, NFS4ERR_BADCHAR,           |
   |                      | NFS4ERR_BADHANDLE, NFS4ERR_BADNAME,        |
   |                      | NFS4ERR_BADXDR, NFS4ERR_FHEXPIRED,         |
   |                      | NFS4ERR_INVAL, NFS4ERR_IO, NFS4ERR_MOVED,  |
   |                      | NFS4ERR_NAMETOOLONG, NFS4ERR_NOENT,        |
   |                      | NFS4ERR_NOFILEHANDLE, NFS4ERR_NOTDIR,      |
   |                      | NFS4ERR_OP_NOT_IN_SESSION,                 |
   |                      | NFS4ERR_REQ_TOO_BIG, NFS4ERR_TOO_MANY_OPS, |
   |                      | NFS4ERR_REP_TOO_BIG,                       |
   |                      | NFS4ERR_REP_TOO_BIG_TO_CACHE,              |
   |                      | NFS4ERR_UNSAFE_COMPOUND,                   |
   |                      | NFS4ERR_SERVERFAULT, NFS4ERR_STALE,        |
   |                      | NFS4ERR_SYMLINK, NFS4ERR_WRONGSEC          |
   | LOOKUPP              | NFS4ERR_ACCESS, NFS4ERR_BADHANDLE,         |
   |                      | NFS4ERR_FHEXPIRED, NFS4ERR_IO,             |
   |                      | NFS4ERR_MOVED, NFS4ERR_NOENT,              |
   |                      | NFS4ERR_NOFILEHANDLE, NFS4ERR_NOTDIR,      |
   |                      | NFS4ERR_OP_NOT_IN_SESSION,                 |
   |                      | NFS4ERR_REQ_TOO_BIG, NFS4ERR_TOO_MANY_OPS, |
   |                      | NFS4ERR_REP_TOO_BIG,                       |
   |                      | NFS4ERR_REP_TOO_BIG_TO_CACHE,              |
   |                      | NFS4ERR_UNSAFE_COMPOUND,                   |
   |                      | NFS4ERR_SERVERFAULT, NFS4ERR_STALE,        |
   |                      | NFS4ERR_WRONGSEC                           |











Shepler, et al.         Expires February 2, 2007              [Page 267]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   | NVERIFY              | NFS4ERR_ACCESS, NFS4ERR_ATTRNOTSUPP,       |
   |                      | NFS4ERR_BADCHAR, NFS4ERR_BADHANDLE,        |
   |                      | NFS4ERR_BADXDR, NFS4ERR_DELAY,             |
   |                      | NFS4ERR_FHEXPIRED, NFS4ERR_INVAL,          |
   |                      | NFS4ERR_IO, NFS4ERR_MOVED,                 |
   |                      | NFS4ERR_NOFILEHANDLE,                      |
   |                      | NFS4ERR_OP_NOT_IN_SESSION,                 |
   |                      | NFS4ERR_REQ_TOO_BIG, NFS4ERR_TOO_MANY_OPS, |
   |                      | NFS4ERR_REP_TOO_BIG,                       |
   |                      | NFS4ERR_REP_TOO_BIG_TO_CACHE,              |
   |                      | NFS4ERR_UNSAFE_COMPOUND, NFS4ERR_SAME,     |
   |                      | NFS4ERR_SERVERFAULT, NFS4ERR_STALE         |
   | OPEN                 | NFS4ERR_ACCESS, NFS4ERR_ADMIN_REVOKED,     |
   |                      | NFS4ERR_ATTRNOTSUPP, NFS4ERR_BADCHAR,      |
   |                      | NFS4ERR_BADHANDLE, NFS4ERR_BADNAME,        |
   |                      | NFS4ERR_BADOWNER, NFS4ERR_BAD_SEQID,       |
   |                      | NFS4ERR_BADXDR, NFS4ERR_DELAY,             |
   |                      | NFS4ERR_DQUOT, NFS4ERR_EXIST,              |
   |                      | NFS4ERR_EXPIRED, NFS4ERR_FHEXPIRED,        |
   |                      | NFS4ERR_GRACE, NFS4ERR_IO, NFS4ERR_INVAL,  |
   |                      | NFS4ERR_ISDIR, NFS4ERR_LEASE_MOVED,        |
   |                      | NFS4ERR_MOVED, NFS4ERR_NAMETOOLONG,        |
   |                      | NFS4ERR_NOENT, NFS4ERR_NOFILEHANDLE,       |
   |                      | NFS4ERR_NOSPC, NFS4ERR_NOTDIR,             |
   |                      | NFS4ERR_NO_GRACE, NFS4ERR_PERM,            |
   |                      | NFS4ERR_RECLAIM_BAD,                       |
   |                      | NFS4ERR_RECLAIM_CONFLICT,                  |
   |                      | NFS4ERR_OP_NOT_IN_SESSION,                 |
   |                      | NFS4ERR_REQ_TOO_BIG, NFS4ERR_TOO_MANY_OPS, |
   |                      | NFS4ERR_REP_TOO_BIG,                       |
   |                      | NFS4ERR_REP_TOO_BIG_TO_CACHE,              |
   |                      | NFS4ERR_UNSAFE_COMPOUND, NFS4ERR_ROFS,     |
   |                      | NFS4ERR_SERVERFAULT, NFS4ERR_SHARE_DENIED, |
   |                      | NFS4ERR_STALE, NFS4ERR_STALE_CLIENTID,     |
   |                      | NFS4ERR_SYMLINK, NFS4ERR_WRONGSEC          |
   | OPEN_DOWNGRADE       | NFS4ERR_ADMIN_REVOKED, NFS4ERR_BADHANDLE,  |
   |                      | NFS4ERR_BAD_SEQID, NFS4ERR_BAD_STATEID,    |
   |                      | NFS4ERR_BADXDR, NFS4ERR_EXPIRED,           |
   |                      | NFS4ERR_FHEXPIRED, NFS4ERR_INVAL,          |
   |                      | NFS4ERR_MOVED, NFS4ERR_NOFILEHANDLE,       |
   |                      | NFS4ERR_OLD_STATEID,                       |
   |                      | NFS4ERR_OP_NOT_IN_SESSION,                 |
   |                      | NFS4ERR_REQ_TOO_BIG, NFS4ERR_TOO_MANY_OPS, |
   |                      | NFS4ERR_REP_TOO_BIG,                       |
   |                      | NFS4ERR_REP_TOO_BIG_TO_CACHE,              |
   |                      | NFS4ERR_UNSAFE_COMPOUND,                   |
   |                      | NFS4ERR_SERVERFAULT, NFS4ERR_STALE,        |
   |                      | NFS4ERR_STALE_STATEID                      |



Shepler, et al.         Expires February 2, 2007              [Page 268]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   | OPENATTR             | NFS4ERR_ACCESS, NFS4ERR_BADHANDLE,         |
   |                      | NFS4ERR_BADXDR, NFS4ERR_DELAY,             |
   |                      | NFS4ERR_DQUOT, NFS4ERR_FHEXPIRED,          |
   |                      | NFS4ERR_IO, NFS4ERR_MOVED, NFS4ERR_NOENT,  |
   |                      | NFS4ERR_NOFILEHANDLE, NFS4ERR_NOSPC,       |
   |                      | NFS4ERR_NOTSUPP,                           |
   |                      | NFS4ERR_OP_NOT_IN_SESSION,                 |
   |                      | NFS4ERR_REQ_TOO_BIG, NFS4ERR_TOO_MANY_OPS, |
   |                      | NFS4ERR_REP_TOO_BIG,                       |
   |                      | NFS4ERR_REP_TOO_BIG_TO_CACHE,              |
   |                      | NFS4ERR_UNSAFE_COMPOUND, NFS4ERR_ROFS,     |
   |                      | NFS4ERR_SERVERFAULT, NFS4ERR_STALE         |
   | PUTFH                | NFS4ERR_BADHANDLE, NFS4ERR_BADXDR,         |
   |                      | NFS4ERR_FHEXPIRED, NFS4ERR_MOVED,          |
   |                      | NFS4ERR_OP_NOT_IN_SESSION,                 |
   |                      | NFS4ERR_REQ_TOO_BIG, NFS4ERR_TOO_MANY_OPS, |
   |                      | NFS4ERR_REP_TOO_BIG,                       |
   |                      | NFS4ERR_REP_TOO_BIG_TO_CACHE,              |
   |                      | NFS4ERR_UNSAFE_COMPOUND,                   |
   |                      | NFS4ERR_SERVERFAULT, NFS4ERR_STALE,        |
   |                      | NFS4ERR_WRONGSEC                           |
   | PUTPUBFH             | NFS4ERR_OP_NOT_IN_SESSION,                 |
   |                      | NFS4ERR_REQ_TOO_BIG, NFS4ERR_TOO_MANY_OPS, |
   |                      | NFS4ERR_REP_TOO_BIG,                       |
   |                      | NFS4ERR_REP_TOO_BIG_TO_CACHE,              |
   |                      | NFS4ERR_UNSAFE_COMPOUND,                   |
   |                      | NFS4ERR_SERVERFAULT, NFS4ERR_WRONGSEC      |
   | PUTROOTFH            | NFS4ERR_OP_NOT_IN_SESSION,                 |
   |                      | NFS4ERR_REQ_TOO_BIG, NFS4ERR_TOO_MANY_OPS, |
   |                      | NFS4ERR_REP_TOO_BIG,                       |
   |                      | NFS4ERR_REP_TOO_BIG_TO_CACHE,              |
   |                      | NFS4ERR_UNSAFE_COMPOUND,                   |
   |                      | NFS4ERR_SERVERFAULT, NFS4ERR_WRONGSEC      |


















Shepler, et al.         Expires February 2, 2007              [Page 269]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   | READ                 | NFS4ERR_ACCESS, NFS4ERR_ADMIN_REVOKED,     |
   |                      | NFS4ERR_BADHANDLE, NFS4ERR_BAD_STATEID,    |
   |                      | NFS4ERR_BADXDR, NFS4ERR_DELAY,             |
   |                      | NFS4ERR_EXPIRED, NFS4ERR_FHEXPIRED,        |
   |                      | NFS4ERR_GRACE, NFS4ERR_IO, NFS4ERR_INVAL,  |
   |                      | NFS4ERR_ISDIR, NFS4ERR_LEASE_MOVED,        |
   |                      | NFS4ERR_LOCKED, NFS4ERR_MOVED,             |
   |                      | NFS4ERR_NOFILEHANDLE, NFS4ERR_NXIO,        |
   |                      | NFS4ERR_OLD_STATEID,                       |
   |                      | NFS4ERR_OP_NOT_IN_SESSION,                 |
   |                      | NFS4ERR_OPENMODE, NFS4ERR_REQ_TOO_BIG,     |
   |                      | NFS4ERR_TOO_MANY_OPS, NFS4ERR_REP_TOO_BIG, |
   |                      | NFS4ERR_REP_TOO_BIG_TO_CACHE,              |
   |                      | NFS4ERR_UNSAFE_COMPOUND,                   |
   |                      | NFS4ERR_SERVERFAULT, NFS4ERR_STALE,        |
   |                      | NFS4ERR_STALE_STATEID                      |
   | READDIR              | NFS4ERR_ACCESS, NFS4ERR_BADHANDLE,         |
   |                      | NFS4ERR_BAD_COOKIE, NFS4ERR_BADXDR,        |
   |                      | NFS4ERR_DELAY, NFS4ERR_FHEXPIRED,          |
   |                      | NFS4ERR_INVAL, NFS4ERR_IO, NFS4ERR_MOVED,  |
   |                      | NFS4ERR_NOFILEHANDLE, NFS4ERR_NOTDIR,      |
   |                      | NFS4ERR_NOT_SAME,                          |
   |                      | NFS4ERR_OP_NOT_IN_SESSION,                 |
   |                      | NFS4ERR_REQ_TOO_BIG, NFS4ERR_TOO_MANY_OPS, |
   |                      | NFS4ERR_REP_TOO_BIG,                       |
   |                      | NFS4ERR_REP_TOO_BIG_TO_CACHE,              |
   |                      | NFS4ERR_UNSAFE_COMPOUND,                   |
   |                      | NFS4ERR_SERVERFAULT, NFS4ERR_STALE,        |
   |                      | NFS4ERR_TOOSMALL                           |
   | READLINK             | NFS4ERR_ACCESS, NFS4ERR_BADHANDLE,         |
   |                      | NFS4ERR_DELAY, NFS4ERR_FHEXPIRED,          |
   |                      | NFS4ERR_INVAL, NFS4ERR_IO, NFS4ERR_ISDIR,  |
   |                      | NFS4ERR_MOVED, NFS4ERR_NOFILEHANDLE,       |
   |                      | NFS4ERR_NOTSUPP,                           |
   |                      | NFS4ERR_OP_NOT_IN_SESSION,                 |
   |                      | NFS4ERR_REQ_TOO_BIG, NFS4ERR_TOO_MANY_OPS, |
   |                      | NFS4ERR_REP_TOO_BIG,                       |
   |                      | NFS4ERR_REP_TOO_BIG_TO_CACHE,              |
   |                      | NFS4ERR_UNSAFE_COMPOUND,                   |
   |                      | NFS4ERR_SERVERFAULT, NFS4ERR_STALE         |
   | RECLAIM_COMPLETE     | NFS4ERR_COMPLETE_ALREADY                   |










Shepler, et al.         Expires February 2, 2007              [Page 270]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   | RELEASE_LOCKOWNER    | NFS4ERR_ADMIN_REVOKED, NFS4ERR_BADXDR,     |
   |                      | NFS4ERR_EXPIRED, NFS4ERR_LEASE_MOVED,      |
   |                      | NFS4ERR_LOCKS_HELD,                        |
   |                      | NFS4ERR_OP_NOT_IN_SESSION,                 |
   |                      | NFS4ERR_REQ_TOO_BIG, NFS4ERR_TOO_MANY_OPS, |
   |                      | NFS4ERR_REP_TOO_BIG,                       |
   |                      | NFS4ERR_REP_TOO_BIG_TO_CACHE,              |
   |                      | NFS4ERR_UNSAFE_COMPOUND,                   |
   |                      | NFS4ERR_SERVERFAULT,                       |
   |                      | NFS4ERR_STALE_CLIENTID                     |
   | REMOVE               | NFS4ERR_ACCESS, NFS4ERR_BADCHAR,           |
   |                      | NFS4ERR_BADHANDLE, NFS4ERR_BADNAME,        |
   |                      | NFS4ERR_BADXDR, NFS4ERR_DELAY,             |
   |                      | NFS4ERR_FHEXPIRED, NFS4ERR_FILE_OPEN,      |
   |                      | NFS4ERR_INVAL, NFS4ERR_IO, NFS4ERR_MOVED,  |
   |                      | NFS4ERR_NAMETOOLONG, NFS4ERR_NOENT,        |
   |                      | NFS4ERR_NOFILEHANDLE, NFS4ERR_NOTDIR,      |
   |                      | NFS4ERR_NOTEMPTY,                          |
   |                      | NFS4ERR_OP_NOT_IN_SESSION,                 |
   |                      | NFS4ERR_REQ_TOO_BIG, NFS4ERR_TOO_MANY_OPS, |
   |                      | NFS4ERR_REP_TOO_BIG,                       |
   |                      | NFS4ERR_REP_TOO_BIG_TO_CACHE,              |
   |                      | NFS4ERR_UNSAFE_COMPOUND, NFS4ERR_ROFS,     |
   |                      | NFS4ERR_SERVERFAULT, NFS4ERR_STALE         |
   | RENAME               | NFS4ERR_ACCESS, NFS4ERR_BADCHAR,           |
   |                      | NFS4ERR_BADHANDLE, NFS4ERR_BADNAME,        |
   |                      | NFS4ERR_BADXDR, NFS4ERR_DELAY,             |
   |                      | NFS4ERR_DQUOT, NFS4ERR_EXIST,              |
   |                      | NFS4ERR_FHEXPIRED, NFS4ERR_FILE_OPEN,      |
   |                      | NFS4ERR_INVAL, NFS4ERR_IO, NFS4ERR_MOVED,  |
   |                      | NFS4ERR_NAMETOOLONG, NFS4ERR_NOENT,        |
   |                      | NFS4ERR_NOFILEHANDLE, NFS4ERR_NOSPC,       |
   |                      | NFS4ERR_NOTDIR, NFS4ERR_NOTEMPTY,          |
   |                      | NFS4ERR_OP_NOT_IN_SESSION,                 |
   |                      | NFS4ERR_REQ_TOO_BIG, NFS4ERR_TOO_MANY_OPS, |
   |                      | NFS4ERR_REP_TOO_BIG,                       |
   |                      | NFS4ERR_REP_TOO_BIG_TO_CACHE,              |
   |                      | NFS4ERR_UNSAFE_COMPOUND, NFS4ERR_ROFS,     |
   |                      | NFS4ERR_SERVERFAULT, NFS4ERR_STALE,        |
   |                      | NFS4ERR_WRONGSEC, NFS4ERR_XDEV             |
   | RESTOREFH            | NFS4ERR_BADHANDLE, NFS4ERR_FHEXPIRED,      |
   |                      | NFS4ERR_MOVED, NFS4ERR_OP_NOT_IN_SESSION,  |
   |                      | NFS4ERR_REQ_TOO_BIG, NFS4ERR_TOO_MANY_OPS, |
   |                      | NFS4ERR_REP_TOO_BIG,                       |
   |                      | NFS4ERR_REP_TOO_BIG_TO_CACHE,              |
   |                      | NFS4ERR_UNSAFE_COMPOUND,                   |
   |                      | NFS4ERR_RESTOREFH, NFS4ERR_SERVERFAULT,    |
   |                      | NFS4ERR_STALE, NFS4ERR_WRONGSEC            |



Shepler, et al.         Expires February 2, 2007              [Page 271]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   | SAVEFH               | NFS4ERR_BADHANDLE, NFS4ERR_FHEXPIRED,      |
   |                      | NFS4ERR_MOVED, NFS4ERR_NOFILEHANDLE,       |
   |                      | NFS4ERR_OP_NOT_IN_SESSION,                 |
   |                      | NFS4ERR_REQ_TOO_BIG, NFS4ERR_TOO_MANY_OPS, |
   |                      | NFS4ERR_REP_TOO_BIG,                       |
   |                      | NFS4ERR_REP_TOO_BIG_TO_CACHE,              |
   |                      | NFS4ERR_UNSAFE_COMPOUND,                   |
   |                      | NFS4ERR_SERVERFAULT, NFS4ERR_STALE         |
   | SECINFO              | NFS4ERR_ACCESS, NFS4ERR_BADCHAR,           |
   |                      | NFS4ERR_BADHANDLE, NFS4ERR_BADNAME,        |
   |                      | NFS4ERR_BADXDR, NFS4ERR_FHEXPIRED,         |
   |                      | NFS4ERR_INVAL, NFS4ERR_MOVED,              |
   |                      | NFS4ERR_NAMETOOLONG, NFS4ERR_NOENT,        |
   |                      | NFS4ERR_NOFILEHANDLE, NFS4ERR_NOTDIR,      |
   |                      | NFS4ERR_OP_NOT_IN_SESSION,                 |
   |                      | NFS4ERR_REQ_TOO_BIG, NFS4ERR_TOO_MANY_OPS, |
   |                      | NFS4ERR_REP_TOO_BIG,                       |
   |                      | NFS4ERR_REP_TOO_BIG_TO_CACHE,              |
   |                      | NFS4ERR_UNSAFE_COMPOUND,                   |
   |                      | NFS4ERR_SERVERFAULT, NFS4ERR_STALE         |
   | SECINFO_NO_NAME      | NFS4ERR_ACCESS, NFS4ERR_BADCHAR,           |
   |                      | NFS4ERR_BADHANDLE, NFS4ERR_BADNAME,        |
   |                      | NFS4ERR_BADXDR, NFS4ERR_FHEXPIRED,         |
   |                      | NFS4ERR_INVAL, NFS4ERR_MOVED,              |
   |                      | NFS4ERR_NAMETOOLONG, NFS4ERR_NOENT,        |
   |                      | NFS4ERR_NOFILEHANDLE, NFS4ERR_NOTDIR,      |
   |                      | NFS4ERR_OP_NOT_IN_SESSION,                 |
   |                      | NFS4ERR_REQ_TOO_BIG, NFS4ERR_TOO_MANY_OPS, |
   |                      | NFS4ERR_REP_TOO_BIG,                       |
   |                      | NFS4ERR_REP_TOO_BIG_TO_CACHE,              |
   |                      | NFS4ERR_UNSAFE_COMPOUND,                   |
   |                      | NFS4ERR_SERVERFAULT, NFS4ERR_STALE         |
   | SEQUENCE             | NFS4ERR_BADSESSION, NFS4ERR_BADSLOT,       |
   |                      | NFS4ERR_CONN_NOT_BOUND_TO_SESSION,         |
   |                      | NFS4ERR_SEQ_MISORDERED,                    |
   |                      | NFS4ERR_SEQUENCE_POS, NFS4ERR_REQ_TOO_BIG, |
   |                      | NFS4ERR_TOO_MANY_OPS, NFS4ERR_REP_TOO_BIG, |
   |                      | NFS4ERR_REP_TOO_BIG_TO_CACHE               |
   | SET_SSV              | NFS4ERR_BAD_SESSION_DIGEST,                |
   |                      | NFS4ERR_CONN_BINDING_NOT_ENFORCED          |











Shepler, et al.         Expires February 2, 2007              [Page 272]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   | SETATTR              | NFS4ERR_ACCESS, NFS4ERR_ADMIN_REVOKED,     |
   |                      | NFS4ERR_ATTRNOTSUPP, NFS4ERR_BADCHAR,      |
   |                      | NFS4ERR_BADHANDLE, NFS4ERR_BADOWNER,       |
   |                      | NFS4ERR_BAD_STATEID, NFS4ERR_BADXDR,       |
   |                      | NFS4ERR_DELAY, NFS4ERR_DQUOT,              |
   |                      | NFS4ERR_EXPIRED, NFS4ERR_FBIG,             |
   |                      | NFS4ERR_FHEXPIRED, NFS4ERR_GRACE,          |
   |                      | NFS4ERR_INVAL, NFS4ERR_IO, NFS4ERR_ISDIR,  |
   |                      | NFS4ERR_LOCKED, NFS4ERR_MOVED,             |
   |                      | NFS4ERR_NOFILEHANDLE, NFS4ERR_NOSPC,       |
   |                      | NFS4ERR_OLD_STATEID, NFS4ERR_OPENMODE,     |
   |                      | NFS4ERR_PERM, NFS4ERR_OP_NOT_IN_SESSION,   |
   |                      | NFS4ERR_REQ_TOO_BIG, NFS4ERR_TOO_MANY_OPS, |
   |                      | NFS4ERR_REP_TOO_BIG,                       |
   |                      | NFS4ERR_REP_TOO_BIG_TO_CACHE,              |
   |                      | NFS4ERR_UNSAFE_COMPOUND, NFS4ERR_ROFS,     |
   |                      | NFS4ERR_SERVERFAULT, NFS4ERR_STALE,        |
   |                      | NFS4ERR_STALE_STATEID                      |
   | CREATE_CLIENTID      | NFS4ERR_BADXDR, NFS4ERR_CLID_INUSE,        |
   |                      | NFS4ERR_INVAL, NFS4ERR_SERVERFAULT         |
   | CREATE_SESSION       | NFS4ERR_BADXDR, NFS4ERR_CLID_INUSE,        |
   |                      | NFS4ERR_DELAY, NFS4ERR_SERVERFAULT,        |
   |                      | NFS4ERR_STALE_CLIENTID                     |
   | VERIFY               | NFS4ERR_ACCESS, NFS4ERR_ATTRNOTSUPP,       |
   |                      | NFS4ERR_BADCHAR, NFS4ERR_BADHANDLE,        |
   |                      | NFS4ERR_BADXDR, NFS4ERR_DELAY,             |
   |                      | NFS4ERR_FHEXPIRED, NFS4ERR_INVAL,          |
   |                      | NFS4ERR_MOVED, NFS4ERR_NOFILEHANDLE,       |
   |                      | NFS4ERR_NOT_SAME,                          |
   |                      | NFS4ERR_OP_NOT_IN_SESSION,                 |
   |                      | NFS4ERR_REQ_TOO_BIG, NFS4ERR_TOO_MANY_OPS, |
   |                      | NFS4ERR_REP_TOO_BIG,                       |
   |                      | NFS4ERR_REP_TOO_BIG_TO_CACHE,              |
   |                      | NFS4ERR_UNSAFE_COMPOUND,                   |
   |                      | NFS4ERR_SERVERFAULT, NFS4ERR_STALE         |
   | WANT_DELEGATION      |                                            |















Shepler, et al.         Expires February 2, 2007              [Page 273]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   | WRITE                | NFS4ERR_ACCESS, NFS4ERR_ADMIN_REVOKED,     |
   |                      | NFS4ERR_BADHANDLE, NFS4ERR_BAD_STATEID,    |
   |                      | NFS4ERR_BADXDR, NFS4ERR_DELAY,             |
   |                      | NFS4ERR_DQUOT, NFS4ERR_EXPIRED,            |
   |                      | NFS4ERR_FBIG, NFS4ERR_FHEXPIRED,           |
   |                      | NFS4ERR_GRACE, NFS4ERR_INVAL, NFS4ERR_IO,  |
   |                      | NFS4ERR_ISDIR, NFS4ERR_LEASE_MOVED,        |
   |                      | NFS4ERR_LOCKED, NFS4ERR_MOVED,             |
   |                      | NFS4ERR_NOFILEHANDLE, NFS4ERR_NOSPC,       |
   |                      | NFS4ERR_NXIO, NFS4ERR_OLD_STATEID,         |
   |                      | NFS4ERR_OPENMODE,                          |
   |                      | NFS4ERR_OP_NOT_IN_SESSION,                 |
   |                      | NFS4ERR_REQ_TOO_BIG, NFS4ERR_TOO_MANY_OPS, |
   |                      | NFS4ERR_REP_TOO_BIG,                       |
   |                      | NFS4ERR_REP_TOO_BIG_TO_CACHE,              |
   |                      | NFS4ERR_UNSAFE_COMPOUND, NFS4ERR_ROFS,     |
   |                      | NFS4ERR_SERVERFAULT, NFS4ERR_STALE,        |
   |                      | NFS4ERR_STALE_STATEID                      |
   +----------------------+--------------------------------------------+

                                  Table 9






























Shepler, et al.         Expires February 2, 2007              [Page 274]


Internet-Draft            NFSv4 Minor Version 1              August 2006


14.3.  Callback operations and their valid errors

   Mappings of valid error returns for each protocol callback operation

   +-------------------------+-----------------------------------------+
   | Callback Operation      | Errors                                  |
   +-------------------------+-----------------------------------------+
   | CB_GETATTR              | NFS4ERR_BADHANDLE NFS4ERR_BADXDR        |
   |                         | NFS4ERR_OP_NOT_IN_SESSION,              |
   |                         | NFS4ERR_REQ_TOO_BIG,                    |
   |                         | NFS4ERR_TOO_MANY_OPS,                   |
   |                         | NFS4ERR_REP_TOO_BIG,                    |
   |                         | NFS4ERR_REP_TOO_BIG_TO_CACHE,           |
   |                         | NFS4ERR_UNSAFE_COMPOUND,                |
   |                         | NFS4ERR_SERVERFAULT                     |
   | CB_ILLEGAL              | NFS4ERR_OP_ILLEGAL                      |
   | CB_LAYOUTRECALL         | NFS4ERR_NOMATCHING_LAYOUT               |
   | CB_NOTIFY               | NFS4ERR_BAD_STATEID NFS4ERR_INVAL       |
   |                         | NFS4ERR_BADXDR NFS4ERR_SERVERFAULT      |
   | CB_PUSH_DELEG           |                                         |
   | CB_RECALL               | NFS4ERR_BADHANDLE NFS4ERR_BAD_STATEID   |
   |                         | NFS4ERR_BADXDR                          |
   |                         | NFS4ERR_OP_NOT_IN_SESSION,              |
   |                         | NFS4ERR_REQ_TOO_BIG,                    |
   |                         | NFS4ERR_TOO_MANY_OPS,                   |
   |                         | NFS4ERR_REP_TOO_BIG,                    |
   |                         | NFS4ERR_REP_TOO_BIG_TO_CACHE,           |
   |                         | NFS4ERR_SERVERFAULT                     |
   | CB_RECALL_ANY           | NFS4ERR_OP_NOT_IN_SESSION,              |
   |                         | NFS4ERR_REQ_TOO_BIG,                    |
   |                         | NFS4ERR_TOO_MANY_OPS,                   |
   |                         | NFS4ERR_REP_TOO_BIG,                    |
   |                         | NFS4ERR_REP_TOO_BIG_TO_CACHE,           |
   |                         | NFS4ERR_INVAL                           |
   | CB_RECALLABLE_OBJ_AVAIL |                                         |
   | CB_RECALL_CREDIT        |                                         |
   | CB_SEQUENCE             | NFS4ERR_BADSESSION, NFS4ERR_BADSLOT,    |
   |                         | NFS4ERR_CONN_NOT_BOUND_TO_SESSION,      |
   |                         | NFS4ERR_SEQ_MISORDERED,                 |
   |                         | NFS4ERR_SEQUENCE_POS,                   |
   |                         | NFS4ERR_REQ_TOO_BIG,                    |
   |                         | NFS4ERR_TOO_MANY_OPS,                   |
   |                         | NFS4ERR_REP_TOO_BIG,                    |
   |                         | NFS4ERR_REP_TOO_BIG_TO_CACHE            |
   +-------------------------+-----------------------------------------+

                                 Table 10




Shepler, et al.         Expires February 2, 2007              [Page 275]


Internet-Draft            NFSv4 Minor Version 1              August 2006


14.4.  Errors and the operations that use them

   +-----------------------------------+-------------------------------+
   | Error                             | Operations                    |
   +-----------------------------------+-------------------------------+
   | NFS4ERR_ACCESS                    | ACCESS, COMMIT, CREATE,       |
   |                                   | GETATTR, GET_DIR_DELEGATION,  |
   |                                   | LINK, LOCK, LOCKT, LOCKU,     |
   |                                   | LOOKUP, LOOKUPP, NVERIFY,     |
   |                                   | OPEN, OPENATTR, READ,         |
   |                                   | READDIR, READLINK, REMOVE,    |
   |                                   | RENAME, SECINFO,              |
   |                                   | SECINFO_NO_NAME, SETATTR,     |
   |                                   | VERIFY, WRITE                 |
   | NFS4ERR_ADMIN_REVOKED             | CLOSE, DELEGRETURN, LOCK,     |
   |                                   | LOCKU, OPEN, OPEN_DOWNGRADE,  |
   |                                   | READ, RELEASE_LOCKOWNER,      |
   |                                   | SETATTR, WRITE                |
   | NFS4ERR_ATTRNOTSUPP               | CREATE, NVERIFY, OPEN,        |
   |                                   | SETATTR, VERIFY               |
   | NFS4ERR_BADCHAR                   | CREATE, LINK, LOOKUP,         |
   |                                   | NVERIFY, OPEN, REMOVE,        |
   |                                   | RENAME, SECINFO,              |
   |                                   | SECINFO_NO_NAME, SETATTR,     |
   |                                   | VERIFY                        |
   | NFS4ERR_BADHANDLE                 | ACCESS, CB_GETATTR,           |
   |                                   | CB_RECALL, CLOSE, COMMIT,     |
   |                                   | CREATE, GETATTR, GETFH,       |
   |                                   | GET_DIR_DELEGATION, LINK,     |
   |                                   | LOCK, LOCKT, LOCKU, LOOKUP,   |
   |                                   | LOOKUPP, NVERIFY, OPEN,       |
   |                                   | OPENATTR, OPEN_DOWNGRADE,     |
   |                                   | PUTFH, READ, READDIR,         |
   |                                   | READLINK, REMOVE, RENAME,     |
   |                                   | RESTOREFH, SAVEFH, SECINFO,   |
   |                                   | SECINFO_NO_NAME, SETATTR,     |
   |                                   | VERIFY, WRITE                 |
   | NFS4ERR_BADIOMODE                 | LAYOUTCOMMIT, LAYOUTGET,      |
   |                                   | LAYOUTRETURN                  |
   | NFS4ERR_BADLAYOUT                 | LAYOUTCOMMIT, LAYOUTGET,      |
   |                                   | LAYOUTRETURN                  |
   | NFS4ERR_BADNAME                   | CREATE, LINK, LOOKUP, OPEN,   |
   |                                   | REMOVE, RENAME, SECINFO,      |
   |                                   | SECINFO_NO_NAME               |
   | NFS4ERR_BADOWNER                  | CREATE, OPEN, SETATTR         |
   | NFS4ERR_BADSESSION                | CB_SEQUENCE, SEQUENCE         |
   | NFS4ERR_BADSLOT                   | CB_SEQUENCE, SEQUENCE         |
   | NFS4ERR_BADTYPE                   | CREATE                        |



Shepler, et al.         Expires February 2, 2007              [Page 276]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   | NFS4ERR_BADXDR                    | ACCESS, CB_GETATTR,           |
   |                                   | CB_NOTIFY, CB_RECALL, CLOSE,  |
   |                                   | COMMIT, CREATE,               |
   |                                   | CREATE_CLIENTID,              |
   |                                   | CREATE_SESSION, DELEGPURGE,   |
   |                                   | DELEGRETURN, GETATTR,         |
   |                                   | GET_DIR_DELEGATION, LINK,     |
   |                                   | LOCK, LOCKT, LOCKU, LOOKUP,   |
   |                                   | NVERIFY, OPEN, OPENATTR,      |
   |                                   | OPEN_DOWNGRADE, PUTFH, READ,  |
   |                                   | READDIR, RELEASE_LOCKOWNER,   |
   |                                   | REMOVE, RENAME, SECINFO,      |
   |                                   | SECINFO_NO_NAME, SETATTR,     |
   |                                   | VERIFY, WRITE                 |
   | NFS4ERR_BAD_COOKIE                | GETDEVICELIST, READDIR        |
   | NFS4ERR_BAD_RANGE                 | LOCK, LOCKT, LOCKU            |
   | NFS4ERR_BAD_SEQID                 | CLOSE, LOCK, LOCKU, OPEN,     |
   |                                   | OPEN_DOWNGRADE                |
   | NFS4ERR_BAD_SESSION_DIGEST        | BIND_CONN_TO_SESSION, SET_SSV |
   | NFS4ERR_BAD_STATEID               | CB_NOTIFY, CB_RECALL, CLOSE,  |
   |                                   | DELEGRETURN, LOCK, LOCKU,     |
   |                                   | OPEN_DOWNGRADE, READ,         |
   |                                   | SETATTR, WRITE                |
   | NFS4ERR_CLID_INUSE                | CREATE_CLIENTID,              |
   |                                   | CREATE_SESSION                |
   | NFS4ERR_COMPLETE_ALREADY          | RECLAIM_COMPLETE              |
   | NFS4ERR_CONN_BINDING_NOT_ENFORCED | BIND_CONN_TO_SESSION, SET_SSV |
   | NFS4ERR_CONN_NOT_BOUND_TO_SESSION | CB_SEQUENCE, SEQUENCE         |
   | NFS4ERR_DEADLOCK                  | LOCK                          |
   | NFS4ERR_DELAY                     | ACCESS, CLOSE, CREATE,        |
   |                                   | CREATE_SESSION, GETATTR,      |
   |                                   | LINK, LOCK, LOCKT, NVERIFY,   |
   |                                   | OPEN, OPENATTR, READ,         |
   |                                   | READDIR, READLINK, REMOVE,    |
   |                                   | RENAME, SETATTR, VERIFY,      |
   |                                   | WRITE                         |
   | NFS4ERR_DENIED                    | LOCK, LOCKT                   |
   | NFS4ERR_DIRDELEG_UNAVAIL          | GET_DIR_DELEGATION            |
   | NFS4ERR_DQUOT                     | CREATE, LINK, OPEN, OPENATTR, |
   |                                   | RENAME, SETATTR, WRITE        |
   | NFS4ERR_EIO                       | GET_DIR_DELEGATION            |
   | NFS4ERR_EXIST                     | CREATE, LINK, OPEN, RENAME    |
   | NFS4ERR_EXPIRED                   | CLOSE, DELEGRETURN, LOCK,     |
   |                                   | LOCKU, OPEN, OPEN_DOWNGRADE,  |
   |                                   | READ, RELEASE_LOCKOWNER,      |
   |                                   | SETATTR, WRITE                |
   | NFS4ERR_FBIG                      | SETATTR, WRITE                |




Shepler, et al.         Expires February 2, 2007              [Page 277]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   | NFS4ERR_FHEXPIRED                 | ACCESS, CLOSE, COMMIT,        |
   |                                   | CREATE, GETATTR,              |
   |                                   | GETDEVICEINFO, GETDEVICELIST, |
   |                                   | GETFH, GET_DIR_DELEGATION,    |
   |                                   | LAYOUTCOMMIT, LAYOUTGET,      |
   |                                   | LAYOUTRETURN, LINK, LOCK,     |
   |                                   | LOCKT, LOCKU, LOOKUP,         |
   |                                   | LOOKUPP, NVERIFY, OPEN,       |
   |                                   | OPENATTR, OPEN_DOWNGRADE,     |
   |                                   | PUTFH, READ, READDIR,         |
   |                                   | READLINK, REMOVE, RENAME,     |
   |                                   | RESTOREFH, SAVEFH, SECINFO,   |
   |                                   | SECINFO_NO_NAME, SETATTR,     |
   |                                   | VERIFY, WRITE                 |
   | NFS4ERR_FILE_OPEN                 | LINK, REMOVE, RENAME          |
   | NFS4ERR_GRACE                     | LOCK, LOCKT, LOCKU, OPEN,     |
   |                                   | READ, SETATTR, WRITE          |
   | NFS4ERR_INVAL                     | ACCESS, CB_NOTIFY,            |
   |                                   | CB_RECALL_ANY, CLOSE, COMMIT, |
   |                                   | CREATE, CREATE_CLIENTID,      |
   |                                   | DELEGRETURN, GETATTR,         |
   |                                   | GETDEVICEINFO, GETDEVICELIST, |
   |                                   | GET_DIR_DELEGATION,           |
   |                                   | LAYOUTCOMMIT, LAYOUTGET,      |
   |                                   | LAYOUTRETURN, LINK, LOCK,     |
   |                                   | LOCKT, LOCKU, LOOKUP,         |
   |                                   | NVERIFY, OPEN,                |
   |                                   | OPEN_DOWNGRADE, READ,         |
   |                                   | READDIR, READLINK, REMOVE,    |
   |                                   | RENAME, SECINFO,              |
   |                                   | SECINFO_NO_NAME, SETATTR,     |
   |                                   | VERIFY, WRITE                 |
   | NFS4ERR_IO                        | ACCESS, COMMIT, CREATE,       |
   |                                   | GETATTR, LINK, LOOKUP,        |
   |                                   | LOOKUPP, NVERIFY, OPEN,       |
   |                                   | OPENATTR, READ, READDIR,      |
   |                                   | READLINK, REMOVE, RENAME,     |
   |                                   | SETATTR, WRITE                |
   | NFS4ERR_ISDIR                     | CLOSE, COMMIT, LINK, LOCK,    |
   |                                   | LOCKT, LOCKU, OPEN, READ,     |
   |                                   | READLINK, SETATTR, WRITE      |
   | NFS4ERR_LAYOUTTRYLATER            | LAYOUTGET                     |
   | NFS4ERR_LAYOUTUNAVAILABLE         | LAYOUTGET                     |
   | NFS4ERR_LEASE_MOVED               | CLOSE, DELEGPURGE,            |
   |                                   | DELEGRETURN, LOCK, LOCKT,     |
   |                                   | LOCKU, OPEN, READ,            |
   |                                   | RELEASE_LOCKOWNER, WRITE      |




Shepler, et al.         Expires February 2, 2007              [Page 278]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   | NFS4ERR_LOCKED                    | LAYOUTGET, READ, SETATTR,     |
   |                                   | WRITE                         |
   | NFS4ERR_LOCKS_HELD                | CLOSE, RELEASE_LOCKOWNER      |
   | NFS4ERR_LOCK_NOTSUPP              | LOCK                          |
   | NFS4ERR_LOCK_RANGE                | LOCK, LOCKT, LOCKU            |
   | NFS4ERR_MLINK                     | LINK                          |
   | NFS4ERR_MOVED                     | ACCESS, CLOSE, COMMIT,        |
   |                                   | CREATE, DELEGPURGE,           |
   |                                   | DELEGRETURN, GETATTR, GETFH,  |
   |                                   | GET_DIR_DELEGATION, LINK,     |
   |                                   | LOCK, LOCKT, LOCKU, LOOKUP,   |
   |                                   | LOOKUPP, NVERIFY, OPEN,       |
   |                                   | OPENATTR, OPEN_DOWNGRADE,     |
   |                                   | PUTFH, READ, READDIR,         |
   |                                   | READLINK, REMOVE, RENAME,     |
   |                                   | RESTOREFH, SAVEFH, SECINFO,   |
   |                                   | SECINFO_NO_NAME, SETATTR,     |
   |                                   | VERIFY, WRITE                 |
   | NFS4ERR_NAMETOOLONG               | CREATE, LINK, LOOKUP, OPEN,   |
   |                                   | REMOVE, RENAME, SECINFO,      |
   |                                   | SECINFO_NO_NAME               |
   | NFS4ERR_NOENT                     | LINK, LOOKUP, LOOKUPP, OPEN,  |
   |                                   | OPENATTR, REMOVE, RENAME,     |
   |                                   | SECINFO, SECINFO_NO_NAME      |
   | NFS4ERR_NOFILEHANDLE              | ACCESS, CLOSE, COMMIT,        |
   |                                   | CREATE, DELEGRETURN, GETATTR, |
   |                                   | GETFH, GET_DIR_DELEGATION,    |
   |                                   | LAYOUTCOMMIT, LAYOUTGET,      |
   |                                   | LAYOUTRETURN, LINK, LOCK,     |
   |                                   | LOCKT, LOCKU, LOOKUP,         |
   |                                   | LOOKUPP, NVERIFY, OPEN,       |
   |                                   | OPENATTR, OPEN_DOWNGRADE,     |
   |                                   | READ, READDIR, READLINK,      |
   |                                   | REMOVE, RENAME, SAVEFH,       |
   |                                   | SECINFO, SECINFO_NO_NAME,     |
   |                                   | SETATTR, VERIFY, WRITE        |
   | NFS4ERR_NOMATCHING_LAYOUT         | CB_LAYOUTRECALL               |
   | NFS4ERR_NOSPC                     | CREATE, LINK, OPEN, OPENATTR, |
   |                                   | RENAME, SETATTR, WRITE        |
   | NFS4ERR_NOTDIR                    | CREATE, GET_DIR_DELEGATION,   |
   |                                   | LINK, LOOKUP, LOOKUPP, OPEN,  |
   |                                   | READDIR, REMOVE, RENAME,      |
   |                                   | SECINFO, SECINFO_NO_NAME      |
   | NFS4ERR_NOTEMPTY                  | REMOVE, RENAME                |
   | NFS4ERR_NOTSUPP                   | DELEGPURGE, DELEGRETURN,      |
   |                                   | GET_DIR_DELEGATION,           |
   |                                   | LAYOUTGET, LINK, OPENATTR,    |
   |                                   | READLINK                      |



Shepler, et al.         Expires February 2, 2007              [Page 279]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   | NFS4ERR_NOT_SAME                  | READDIR, VERIFY               |
   | NFS4ERR_NO_GRACE                  | LAYOUTCOMMIT, LAYOUTRETURN,   |
   |                                   | LOCK, OPEN                    |
   | NFS4ERR_NXIO                      | READ, WRITE                   |
   | NFS4ERR_OLD_STATEID               | CLOSE, DELEGRETURN, LOCK,     |
   |                                   | LOCKU, OPEN_DOWNGRADE, READ,  |
   |                                   | SETATTR, WRITE                |
   | NFS4ERR_OPENMODE                  | LOCK, READ, SETATTR, WRITE    |
   | NFS4ERR_OP_ILLEGAL                | CB_ILLEGAL, ILLEGAL           |
   | NFS4ERR_OP_NOT_IN_SESSION         | ACCESS, CB_GETATTR,           |
   |                                   | CB_RECALL, CB_RECALL_ANY,     |
   |                                   | CLOSE, COMMIT, CREATE,        |
   |                                   | DELEGPURGE, DELEGRETURN,      |
   |                                   | GETATTR, GETFH,               |
   |                                   | GET_DIR_DELEGATION, LINK,     |
   |                                   | LOCK, LOCKT, LOCKU, LOOKUP,   |
   |                                   | LOOKUPP, NVERIFY, OPEN,       |
   |                                   | OPENATTR, OPEN_DOWNGRADE,     |
   |                                   | PUTFH, PUTPUBFH, PUTROOTFH,   |
   |                                   | READ, READDIR, READLINK,      |
   |                                   | RELEASE_LOCKOWNER, REMOVE,    |
   |                                   | RENAME, RESTOREFH, SAVEFH,    |
   |                                   | SECINFO, SECINFO_NO_NAME,     |
   |                                   | SETATTR, VERIFY, WRITE        |
   | NFS4ERR_PERM                      | CREATE, OPEN, SETATTR         |
   | NFS4ERR_RECALLCONFLICT            | LAYOUTGET                     |
   | NFS4ERR_RECLAIM_BAD               | LAYOUTCOMMIT, LOCK, OPEN      |
   | NFS4ERR_RECLAIM_CONFLICT          | LOCK, OPEN                    |
   | NFS4ERR_REP_TOO_BIG               | ACCESS, CB_GETATTR,           |
   |                                   | CB_RECALL, CB_RECALL_ANY,     |
   |                                   | CB_SEQUENCE, CLOSE, COMMIT,   |
   |                                   | CREATE, DELEGPURGE,           |
   |                                   | DELEGRETURN, GETATTR, GETFH,  |
   |                                   | GET_DIR_DELEGATION, LINK,     |
   |                                   | LOCK, LOCKT, LOCKU, LOOKUP,   |
   |                                   | LOOKUPP, NVERIFY, OPEN,       |
   |                                   | OPENATTR, OPEN_DOWNGRADE,     |
   |                                   | PUTFH, PUTPUBFH, PUTROOTFH,   |
   |                                   | READ, READDIR, READLINK,      |
   |                                   | RELEASE_LOCKOWNER, REMOVE,    |
   |                                   | RENAME, RESTOREFH, SAVEFH,    |
   |                                   | SECINFO, SECINFO_NO_NAME,     |
   |                                   | SEQUENCE, SETATTR, VERIFY,    |
   |                                   | WRITE                         |







Shepler, et al.         Expires February 2, 2007              [Page 280]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   | NFS4ERR_REP_TOO_BIG_TO_CACHE      | ACCESS, CB_GETATTR,           |
   |                                   | CB_RECALL, CB_RECALL_ANY,     |
   |                                   | CB_SEQUENCE, CLOSE, COMMIT,   |
   |                                   | CREATE, DELEGPURGE,           |
   |                                   | DELEGRETURN, GETATTR, GETFH,  |
   |                                   | GET_DIR_DELEGATION, LINK,     |
   |                                   | LOCK, LOCKT, LOCKU, LOOKUP,   |
   |                                   | LOOKUPP, NVERIFY, OPEN,       |
   |                                   | OPENATTR, OPEN_DOWNGRADE,     |
   |                                   | PUTFH, PUTPUBFH, PUTROOTFH,   |
   |                                   | READ, READDIR, READLINK,      |
   |                                   | RELEASE_LOCKOWNER, REMOVE,    |
   |                                   | RENAME, RESTOREFH, SAVEFH,    |
   |                                   | SECINFO, SECINFO_NO_NAME,     |
   |                                   | SEQUENCE, SETATTR, VERIFY,    |
   |                                   | WRITE                         |
   | NFS4ERR_REQ_TOO_BIG               | ACCESS, CB_GETATTR,           |
   |                                   | CB_RECALL, CB_RECALL_ANY,     |
   |                                   | CB_SEQUENCE, CLOSE, COMMIT,   |
   |                                   | CREATE, DELEGPURGE,           |
   |                                   | DELEGRETURN, GETATTR, GETFH,  |
   |                                   | GET_DIR_DELEGATION, LINK,     |
   |                                   | LOCK, LOCKT, LOCKU, LOOKUP,   |
   |                                   | LOOKUPP, NVERIFY, OPEN,       |
   |                                   | OPENATTR, OPEN_DOWNGRADE,     |
   |                                   | PUTFH, PUTPUBFH, PUTROOTFH,   |
   |                                   | READ, READDIR, READLINK,      |
   |                                   | RELEASE_LOCKOWNER, REMOVE,    |
   |                                   | RENAME, RESTOREFH, SAVEFH,    |
   |                                   | SECINFO, SECINFO_NO_NAME,     |
   |                                   | SEQUENCE, SETATTR, VERIFY,    |
   |                                   | WRITE                         |
   | NFS4ERR_RESTOREFH                 | RESTOREFH                     |
   | NFS4ERR_ROFS                      | COMMIT, CREATE, LINK, OPEN,   |
   |                                   | OPENATTR, REMOVE, RENAME,     |
   |                                   | SETATTR, WRITE                |
   | NFS4ERR_SAME                      | NVERIFY                       |
   | NFS4ERR_SEQUENCE_POS              | CB_SEQUENCE, SEQUENCE         |
   | NFS4ERR_SEQ_MISORDERED            | CB_SEQUENCE, SEQUENCE         |












Shepler, et al.         Expires February 2, 2007              [Page 281]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   | NFS4ERR_SERVERFAULT               | ACCESS, CB_GETATTR,           |
   |                                   | CB_NOTIFY, CB_RECALL, CLOSE,  |
   |                                   | COMMIT, CREATE,               |
   |                                   | CREATE_CLIENTID,              |
   |                                   | CREATE_SESSION, DELEGPURGE,   |
   |                                   | DELEGRETURN, GETATTR, GETFH,  |
   |                                   | GET_DIR_DELEGATION, LINK,     |
   |                                   | LOCK, LOCKT, LOCKU, LOOKUP,   |
   |                                   | LOOKUPP, NVERIFY, OPEN,       |
   |                                   | OPENATTR, OPEN_DOWNGRADE,     |
   |                                   | PUTFH, PUTPUBFH, PUTROOTFH,   |
   |                                   | READ, READDIR, READLINK,      |
   |                                   | RELEASE_LOCKOWNER, REMOVE,    |
   |                                   | RENAME, RESTOREFH, SAVEFH,    |
   |                                   | SECINFO, SECINFO_NO_NAME,     |
   |                                   | SETATTR, VERIFY, WRITE        |
   | NFS4ERR_SHARE_DENIED              | OPEN                          |
   | NFS4ERR_STALE                     | ACCESS, CLOSE, COMMIT,        |
   |                                   | CREATE, DELEGRETURN, GETATTR, |
   |                                   | GETFH, GET_DIR_DELEGATION,    |
   |                                   | LAYOUTCOMMIT, LAYOUTGET,      |
   |                                   | LAYOUTRETURN, LINK, LOCK,     |
   |                                   | LOCKT, LOCKU, LOOKUP,         |
   |                                   | LOOKUPP, NVERIFY, OPEN,       |
   |                                   | OPENATTR, OPEN_DOWNGRADE,     |
   |                                   | PUTFH, READ, READDIR,         |
   |                                   | READLINK, REMOVE, RENAME,     |
   |                                   | RESTOREFH, SAVEFH, SECINFO,   |
   |                                   | SECINFO_NO_NAME, SETATTR,     |
   |                                   | VERIFY, WRITE                 |
   | NFS4ERR_STALE_CLIENTID            | CREATE_SESSION, DELEGPURGE,   |
   |                                   | LAYOUTCOMMIT, LAYOUTGET,      |
   |                                   | LAYOUTRETURN, LOCK, LOCKT,    |
   |                                   | OPEN, RELEASE_LOCKOWNER       |
   | NFS4ERR_STALE_STATEID             | CLOSE, DELEGRETURN, LOCK,     |
   |                                   | LOCKU, OPEN_DOWNGRADE, READ,  |
   |                                   | SETATTR, WRITE                |
   | NFS4ERR_SYMLINK                   | LOOKUP, OPEN                  |
   | NFS4ERR_TOOSMALL                  | GETDEVICEINFO, GETDEVICELIST, |
   |                                   | LAYOUTGET, READDIR            |











Shepler, et al.         Expires February 2, 2007              [Page 282]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   | NFS4ERR_TOO_MANY_OPS              | ACCESS, CB_GETATTR,           |
   |                                   | CB_RECALL, CB_RECALL_ANY,     |
   |                                   | CB_SEQUENCE, CLOSE, COMMIT,   |
   |                                   | CREATE, DELEGPURGE,           |
   |                                   | DELEGRETURN, GETATTR, GETFH,  |
   |                                   | GET_DIR_DELEGATION, LINK,     |
   |                                   | LOCK, LOCKT, LOCKU, LOOKUP,   |
   |                                   | LOOKUPP, NVERIFY, OPEN,       |
   |                                   | OPENATTR, OPEN_DOWNGRADE,     |
   |                                   | PUTFH, PUTPUBFH, PUTROOTFH,   |
   |                                   | READ, READDIR, READLINK,      |
   |                                   | RELEASE_LOCKOWNER, REMOVE,    |
   |                                   | RENAME, RESTOREFH, SAVEFH,    |
   |                                   | SECINFO, SECINFO_NO_NAME,     |
   |                                   | SEQUENCE, SETATTR, VERIFY,    |
   |                                   | WRITE                         |
   | NFS4ERR_UNKNOWN_LAYOUTTYPE        | GETDEVICEINFO, GETDEVICELIST, |
   |                                   | LAYOUTCOMMIT, LAYOUTGET,      |
   |                                   | LAYOUTRETURN                  |
   | NFS4ERR_UNSAFE_COMPOUND           | ACCESS, CB_GETATTR, CLOSE,    |
   |                                   | COMMIT, CREATE, DELEGPURGE,   |
   |                                   | DELEGRETURN, GETATTR, GETFH,  |
   |                                   | GET_DIR_DELEGATION, LINK,     |
   |                                   | LOCK, LOCKT, LOCKU, LOOKUP,   |
   |                                   | LOOKUPP, NVERIFY, OPEN,       |
   |                                   | OPENATTR, OPEN_DOWNGRADE,     |
   |                                   | PUTFH, PUTPUBFH, PUTROOTFH,   |
   |                                   | READ, READDIR, READLINK,      |
   |                                   | RELEASE_LOCKOWNER, REMOVE,    |
   |                                   | RENAME, RESTOREFH, SAVEFH,    |
   |                                   | SECINFO, SECINFO_NO_NAME,     |
   |                                   | SETATTR, VERIFY, WRITE        |
   | NFS4ERR_WRONGSEC                  | GET_DIR_DELEGATION, LINK,     |
   |                                   | LOOKUP, LOOKUPP, OPEN, PUTFH, |
   |                                   | PUTPUBFH, PUTROOTFH, RENAME,  |
   |                                   | RESTOREFH                     |
   | NFS4ERR_XDEV                      | LINK, RENAME                  |
   +-----------------------------------+-------------------------------+

                                 Table 11


15.  NFS version 4.1 Procedures

15.1.  Procedure 0: NULL - No Operation






Shepler, et al.         Expires February 2, 2007              [Page 283]


Internet-Draft            NFSv4 Minor Version 1              August 2006


15.1.1.  SYNOPSIS

15.1.2.  ARGUMENTS

   void;

15.1.3.  RESULTS

   void;

15.1.4.  DESCRIPTION

   Standard NULL procedure.  Void argument, void response.  This
   procedure has no functionality associated with it.  Because of this
   it is sometimes used to measure the overhead of processing a service
   request.  Therefore, the server should ensure that no unnecessary
   work is done in servicing this procedure.

15.1.5.  ERRORS

   None.

15.2.  Procedure 1: COMPOUND - Compound Operations

15.2.1.  SYNOPSIS

   compoundargs -> compoundres

15.2.2.  ARGUMENTS

   union nfs_argop4 switch (nfs_opnum4 argop) {
       case <OPCODE>: <argument>;
       ...
   };

   struct COMPOUND4args {
       utf8str_cs      tag;
       uint32_t        minorversion;
       nfs_argop4      argarray<>;
   };











Shepler, et al.         Expires February 2, 2007              [Page 284]


Internet-Draft            NFSv4 Minor Version 1              August 2006


15.2.3.  RESULTS

   union nfs_resop4 switch (nfs_opnum4 resop){
       case <OPCODE>: <result>;
       ...
   };

   struct COMPOUND4res {
       nfsstat4        status;
       utf8str_cs      tag;
       nfs_resop4      resarray<>;
   };

15.2.4.  DESCRIPTION

   The COMPOUND procedure is used to combine one or more of the NFS
   operations into a single RPC request.  The main NFS RPC program has
   two main procedures: NULL and COMPOUND.  All other operations use the
   COMPOUND procedure as a wrapper.

   The COMPOUND procedure is used to combine individual operations into
   a single RPC request.  The server interprets each of the operations
   in turn.  If an operation is executed by the server and the status of
   that operation is NFS4_OK, then the next operation in the COMPOUND
   procedure is executed.  The server continues this process until there
   are no more operations to be executed or one of the operations has a
   status value other than NFS4_OK.

   In the processing of the COMPOUND procedure, the server may find that
   it does not have the available resources to execute any or all of the
   operations within the COMPOUND sequence.  See Section 2.9.4.4 for a
   more detailed discussion.

   The server will generally choose between two methods of decoding the
   client's request.  The first would be the traditional one pass XDR
   decode.  If there is an XDR decoding error in this case, the RPC XDR
   decode error would be returned.  The second method would be to make
   an initial pass to decode the basic COMPOUND request and then to XDR
   decode the individual operations; the most interesting is the decode
   of attributes.  In this case, the server may encounter an XDR decode
   error during the second pass.  In this case, the server would return
   the error NFS4ERR_BADXDR to signify the decode error.

   The COMPOUND arguments contain a "minorversion" field.  For NFSv4.1,
   the value for this field is 1.  If the server receives a COMPOUND
   procedure with a minorversion field value that it does not support,
   the server MUST return an error of NFS4ERR_MINOR_VERS_MISMATCH and a
   zero length resultdata array.



Shepler, et al.         Expires February 2, 2007              [Page 285]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   Contained within the COMPOUND results is a "status" field.  If the
   results array length is non-zero, this status must be equivalent to
   the status of the last operation that was executed within the
   COMPOUND procedure.  Therefore, if an operation incurred an error
   then the "status" value will be the same error value as is being
   returned for the operation that failed.

   Note that operations, 0 (zero) and 1 (one) are not defined for the
   COMPOUND procedure.  Operation 2 is not defined but reserved for
   future definition and use with minor versioning.  If the server
   receives a operation array that contains operation 2 and the
   minorversion field has a value of 0 (zero), an error of
   NFS4ERR_OP_ILLEGAL, as described in the next paragraph, is returned
   to the client.  If an operation array contains an operation 2 and the
   minorversion field is non-zero and the server does not support the
   minor version, the server returns an error of
   NFS4ERR_MINOR_VERS_MISMATCH.  Therefore, the
   NFS4ERR_MINOR_VERS_MISMATCH error takes precedence over all other
   errors.

   It is possible that the server receives a request that contains an
   operation that is less than the first legal operation (OP_ACCESS) or
   greater than the last legal operation (OP_RELEASE_LOCKOWNER).  In
   this case, the server's response will encode the opcode OP_ILLEGAL
   rather than the illegal opcode of the request.  The status field in
   the ILLEGAL return results will set to NFS4ERR_OP_ILLEGAL.  The
   COMPOUND procedure's return results will also be NFS4ERR_OP_ILLEGAL.

   The definition of the "tag" in the request is left to the
   implementor.  It may be used to summarize the content of the compound
   request for the benefit of packet sniffers and engineers debugging
   implementations.  However, the value of "tag" in the response SHOULD
   be the same value as provided in the request.  This applies to the
   tag field of the CB_COMPOUND procedure as well.

15.2.4.1.  Current File Handle and Stateid

   The COMPOUND procedure offers a simple environment for the execution
   of the operations specified by the clinet.  The first two relate to
   the file handle while the second two relate to the current stateid.

15.2.4.1.1.  Current File Handle

   The current and saved file handle are used throughout the protocol.
   Most operations implicitly use the current file handle as a argument
   and many set the current file handle as part of the results.  The
   combination of client specified sequences of operations and current
   and saved file handle arguments and results allows for greater



Shepler, et al.         Expires February 2, 2007              [Page 286]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   protocol flexibility.  The best or easiest example of current file
   handle usage is a sequence like the following:


         PUTFH fh1              {fh1}
         LOOKUP "compA"         {fh2}
         GETATTR                {fh2}
         LOOKUP "compB"         {fh3}
         GETATTR                {fh3}
         LOOKUP "compC"         {fh4}
         GETATTR                {fh4}
         GETFH

                                 Figure 71

   In this example, the PUTFH operation explicitly sets the current file
   handle value while the result of each LOOKUP operation sets the
   current file handle value to the resultant file system object.  Also,
   the client is able to insert GETATTR operations using the current
   file handle as an argument.

   Along with the current file handle, there is a saved file handle.
   While the current file handle is set as the result of operations like
   LOOKUP, the saved file handle must be set directly with the use of
   the SAVEFH operation.  The SAVEFH operations copies the current file
   handle value to the saved value.  The saved file handle value is used
   in combination with the current file handle value for the LINK and
   RENAME operations.  The RESTOREFH operation will copy the saved file
   handle value to the current file handle value; as a result, the saved
   file handle value may be used a sort of "scratch" area for the
   client's series of operations.

15.2.4.1.2.  Current Stateid

   With NFSv4.1, additions of a current stateid and a saved stateid have
   been made to the COMPOUND processing environment; this allows for the
   passing of stateids between operations.  There are no changes to the
   syntax of the protocol, only changes to the semantics of a few
   operations.

   A "current stateid" is the stateid that is associated with the
   current file handle.  The current stateid may only be changed by an
   operation that modifies the current file handle or returns a stateid.
   If an operation returns a stateid it MUST set the current stateid to
   the returned value.  If an operation sets the current file handle but
   does not return a stateid, the current stateid MUST be set to the
   all-zeros special stateid.  As an example, PUTFH will change the
   current server state from {ocfh, osid} to {cfh, 0} while LOCK will



Shepler, et al.         Expires February 2, 2007              [Page 287]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   change the current state from {cfh, osid} to {cfh, nsid}.  The SAVEFH
   and RESTOREFH operations will save and restore both the file handle
   and the stateid as a set.

   Any operation which takes as an argument a stateid that is not the
   special all-zeros stateid MUST set the current stateid to the all-
   zeros value before evaluating the operation.  If the argument is the
   special all-zeros stateid, the operation is evaluated using the
   current stateid.

   The following example is the common case of a simple READ operation
   with a supplied stateid showing that the PUTFH initializes the
   current stateid to zero.  The subsequent READ with stateid sid1
   replaces the current stateid before evaluating the operation.

       PUTFH fh1                        - -> {fh1, 0}
       READ sid1,0,1024       {fh1, sid1} -> {fh1, sid1}

                                 Figure 72

   This next example performs an OPEN with the client provided stateid
   sid1 and as a result generates stateid sid2.  The next operation
   specifies the READ with the special all-zero stateid but the current
   stateid set by the previous operation is actually used when the
   operation is evaluated, allowing correct interaction with any
   existing, potentially conflicting, locks.

       PUTFH fh1                        - -> {fh1, 0}
       OPEN R,sid1,"compA"    {fh1, sid1} -> {fh2, sid2}
       READ 0,0,1024          {fh2, sid2} -> {fh2, sid2}
       CLOSE 0                {fh2, sid2} -> {fh2, sid3}

                                 Figure 73

   The final example is similar to the second in how it passes the
   stateid sid2 generated by the LOCK operation to the next READ
   operation.  This allows the client to explicitly surround a single
   I/O operation with a lock and its appropriate stateid to guarantee
   correctness with other client locks.

       PUTFH fh1                        - -> {fh1, 0}
       LOCK W,0,1024,sid1     {fh1, sid1} -> {fh1, sid2}
       READ 0,0,1024          {fh1, sid2} -> {fh1, sid2}
       LOCKU W,0,1024,0       {fh1, sid2} -> {fh1, sid3}

                                 Figure 74





Shepler, et al.         Expires February 2, 2007              [Page 288]


Internet-Draft            NFSv4 Minor Version 1              August 2006


15.2.5.  IMPLEMENTATION

15.2.6.  ERRORS

   All errors defined in the protocol


16.  NFS version 4.1 Operations

16.1.  Operation 3: ACCESS - Check Access Rights

16.1.1.  SYNOPSIS

   (cfh), accessreq -> supported, accessrights

16.1.2.  ARGUMENTS


   /*
    * ACCESS: Check access permission
    */
   const ACCESS4_READ      = 0x00000001;
   const ACCESS4_LOOKUP    = 0x00000002;
   const ACCESS4_MODIFY    = 0x00000004;
   const ACCESS4_EXTEND    = 0x00000008;
   const ACCESS4_DELETE    = 0x00000010;
   const ACCESS4_EXECUTE   = 0x00000020;

   struct ACCESS4args {
           /* CURRENT_FH: object */
           uint32_t        access;
   };


16.1.3.  RESULTS

   struct ACCESS4resok {
           uint32_t        supported;
           uint32_t        access;
   };

   union ACCESS4res switch (nfsstat4 status) {
    case NFS4_OK:
            ACCESS4resok   resok4;
    default:
            void;
   };




Shepler, et al.         Expires February 2, 2007              [Page 289]


Internet-Draft            NFSv4 Minor Version 1              August 2006


16.1.4.  DESCRIPTION

   ACCESS determines the access rights that a user, as identified by the
   credentials in the RPC request, has with respect to the file system
   object specified by the current filehandle.  The client encodes the
   set of access rights that are to be checked in the bit mask "access".
   The server checks the permissions encoded in the bit mask.  If a
   status of NFS4_OK is returned, two bit masks are included in the
   response.  The first, "supported", represents the access rights for
   which the server can verify reliably.  The second, "access",
   represents the access rights available to the user for the filehandle
   provided.  On success, the current filehandle retains its value.

   Note that the supported field will contain only as many values as was
   originally sent in the arguments.  For example, if the client sends
   an ACCESS operation with only the ACCESS4_READ value set and the
   server supports this value, the server will return only ACCESS4_READ
   even if it could have reliably checked other values.

   The results of this operation are necessarily advisory in nature.  A
   return status of NFS4_OK and the appropriate bit set in the bit mask
   does not imply that such access will be allowed to the file system
   object in the future.  This is because access rights can be revoked
   by the server at any time.

   The following access permissions may be requested:

   ACCESS4_READ  Read data from file or read a directory.

   ACCESS4_LOOKUP  Look up a name in a directory (no meaning for non-
      directory objects).

   ACCESS4_MODIFY  Rewrite existing file data or modify existing
      directory entries.

   ACCESS4_EXTEND  Write new data or add directory entries.

   ACCESS4_DELETE  Delete an existing directory entry.

   ACCESS4_EXECUTE  Execute file (no meaning for a directory).

   On success, the current filehandle retains its value.

16.1.5.  IMPLEMENTATION

   In general, it is not sufficient for the client to attempt to deduce
   access permissions by inspecting the uid, gid, and mode fields in the
   file attributes or by attempting to interpret the contents of the ACL



Shepler, et al.         Expires February 2, 2007              [Page 290]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   attribute.  This is because the server may perform uid or gid mapping
   or enforce additional access control restrictions.  It is also
   possible that the server may not be in the same ID space as the
   client.  In these cases (and perhaps others), the client can not
   reliably perform an access check with only current file attributes.

   In the NFS version 2 protocol, the only reliable way to determine
   whether an operation was allowed was to try it and see if it
   succeeded or failed.  Using the ACCESS operation in the NFS version 4
   protocol, the client can ask the server to indicate whether or not
   one or more classes of operations are permitted.  The ACCESS
   operation is provided to allow clients to check before doing a series
   of operations which will result in an access failure.  The OPEN
   operation provides a point where the server can verify access to the
   file object and method to return that information to the client.  The
   ACCESS operation is still useful for directory operations or for use
   in the case the UNIX API "access" is used on the client.

   The information returned by the server in response to an ACCESS call
   is not permanent.  It was correct at the exact time that the server
   performed the checks, but not necessarily afterwards.  The server can
   revoke access permission at any time.

   The client should use the effective credentials of the user to build
   the authentication information in the ACCESS request used to
   determine access rights.  It is the effective user and group
   credentials that are used in subsequent read and write operations.

   Many implementations do not directly support the ACCESS4_DELETE
   permission.  Operating systems like UNIX will ignore the
   ACCESS4_DELETE bit if set on an access request on a non-directory
   object.  In these systems, delete permission on a file is determined
   by the access permissions on the directory in which the file resides,
   instead of being determined by the permissions of the file itself.
   Therefore, the mask returned enumerating which access rights can be
   determined will have the ACCESS4_DELETE value set to 0.  This
   indicates to the client that the server was unable to check that
   particular access right.  The ACCESS4_DELETE bit in the access mask
   returned will then be ignored by the client.

16.2.  Operation 4: CLOSE - Close File

16.2.1.  SYNOPSIS

   (cfh), seqid, open_stateid -> open_stateid






Shepler, et al.         Expires February 2, 2007              [Page 291]


Internet-Draft            NFSv4 Minor Version 1              August 2006


16.2.2.  ARGUMENTS

   /*
    * CLOSE: Close a file and release share reservations
    */
   struct CLOSE4args {
           /* CURRENT_FH: object */
           seqid4          seqid;
           stateid4        open_stateid;
   };


16.2.3.  RESULTS

   union CLOSE4res switch (nfsstat4 status) {
    case NFS4_OK:
            stateid4       open_stateid;
    default:
            void;
   };


16.2.4.  DESCRIPTION

   The CLOSE operation releases share reservations for the regular or
   named attribute file as specified by the current filehandle.  The
   share reservations and other state information released at the server
   as a result of this CLOSE is only associated with the supplied
   stateid.  The sequence id provides for the correct ordering.  State
   associated with other OPENs is not affected.

   If record locks are held, the client SHOULD release all locks before
   issuing a CLOSE.  The server MAY free all outstanding locks on CLOSE
   but some servers may not support the CLOSE of a file that still has
   record locks held.  The server MUST return failure if any locks would
   exist after the CLOSE.

   On success, the current filehandle retains its value.

16.2.5.  IMPLEMENTATION

   Even though CLOSE returns a stateid, this stateid is not useful to
   the client and should be treated as deprecated.  CLOSE "shuts down"
   the state associated with all OPENs for the file by a single
   open_owner.  As noted above, CLOSE will either release all file
   locking state or return an error.  Therefore, the stateid returned by
   CLOSE is not useful for operations that follow.




Shepler, et al.         Expires February 2, 2007              [Page 292]


Internet-Draft            NFSv4 Minor Version 1              August 2006


16.3.  Operation 5: COMMIT - Commit Cached Data

16.3.1.  SYNOPSIS

   (cfh), offset, count -> verifier

16.3.2.  ARGUMENTS

   /*
    * COMMIT: Commit cached data on server to stable storage
    */
   struct COMMIT4args {
           /* CURRENT_FH: file */
           offset4         offset;
           count4          count;
   };


16.3.3.  RESULTS

   struct COMMIT4resok {
           verifier4       writeverf;
   };


   union COMMIT4res switch (nfsstat4 status) {
    case NFS4_OK:
            COMMIT4resok   resok4;
    default:
            void;
   };


16.3.4.  DESCRIPTION

   The COMMIT operation forces or flushes data to stable storage for the
   file specified by the current filehandle.  The flushed data is that
   which was previously written with a WRITE operation which had the
   stable field set to UNSTABLE4.

   The offset specifies the position within the file where the flush is
   to begin.  An offset value of 0 (zero) means to flush data starting
   at the beginning of the file.  The count specifies the number of
   bytes of data to flush.  If count is 0 (zero), a flush from offset to
   the end of the file is done.

   The server returns a write verifier upon successful completion of the
   COMMIT.  The write verifier is used by the client to determine if the



Shepler, et al.         Expires February 2, 2007              [Page 293]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   server has restarted or rebooted between the initial WRITE(s) and the
   COMMIT.  The client does this by comparing the write verifier
   returned from the initial writes and the verifier returned by the
   COMMIT operation.  The server must vary the value of the write
   verifier at each server event or instantiation that may lead to a
   loss of uncommitted data.  Most commonly this occurs when the server
   is rebooted; however, other events at the server may result in
   uncommitted data loss as well.

   On success, the current filehandle retains its value.

16.3.5.  IMPLEMENTATION

   The COMMIT operation is similar in operation and semantics to the
   POSIX fsync(2) system call that synchronizes a file's state with the
   disk (file data and metadata is flushed to disk or stable storage).
   COMMIT performs the same operation for a client, flushing any
   unsynchronized data and metadata on the server to the server's disk
   or stable storage for the specified file.  Like fsync(2), it may be
   that there is some modified data or no modified data to synchronize.
   The data may have been synchronized by the server's normal periodic
   buffer synchronization activity.  COMMIT should return NFS4_OK,
   unless there has been an unexpected error.

   COMMIT differs from fsync(2) in that it is possible for the client to
   flush a range of the file (most likely triggered by a buffer-
   reclamation scheme on the client before file has been completely
   written).

   The server implementation of COMMIT is reasonably simple.  If the
   server receives a full file COMMIT request, that is starting at
   offset 0 and count 0, it should do the equivalent of fsync()'ing the
   file.  Otherwise, it should arrange to have the cached data in the
   range specified by offset and count to be flushed to stable storage.
   In both cases, any metadata associated with the file must be flushed
   to stable storage before returning.  It is not an error for there to
   be nothing to flush on the server.  This means that the data and
   metadata that needed to be flushed have already been flushed or lost
   during the last server failure.

   The client implementation of COMMIT is a little more complex.  There
   are two reasons for wanting to commit a client buffer to stable
   storage.  The first is that the client wants to reuse a buffer.  In
   this case, the offset and count of the buffer are sent to the server
   in the COMMIT request.  The server then flushes any cached data based
   on the offset and count, and flushes any metadata associated with the
   file.  It then returns the status of the flush and the write
   verifier.  The other reason for the client to generate a COMMIT is



Shepler, et al.         Expires February 2, 2007              [Page 294]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   for a full file flush, such as may be done at close.  In this case,
   the client would gather all of the buffers for this file that contain
   uncommitted data, do the COMMIT operation with an offset of 0 and
   count of 0, and then free all of those buffers.  Any other dirty
   buffers would be sent to the server in the normal fashion.

   After a buffer is written by the client with the stable parameter set
   to UNSTABLE4, the buffer must be considered as modified by the client
   until the buffer has either been flushed via a COMMIT operation or
   written via a WRITE operation with stable parameter set to FILE_SYNC4
   or DATA_SYNC4.  This is done to prevent the buffer from being freed
   and reused before the data can be flushed to stable storage on the
   server.

   When a response is returned from either a WRITE or a COMMIT operation
   and it contains a write verifier that is different than previously
   returned by the server, the client will need to retransmit all of the
   buffers containing uncommitted cached data to the server.  How this
   is to be done is up to the implementor.  If there is only one buffer
   of interest, then it should probably be sent back over in a WRITE
   request with the appropriate stable parameter.  If there is more than
   one buffer, it might be worthwhile retransmitting all of the buffers
   in WRITE requests with the stable parameter set to UNSTABLE4 and then
   retransmitting the COMMIT operation to flush all of the data on the
   server to stable storage.  The timing of these retransmissions is
   left to the implementor.

   The above description applies to page-cache-based systems as well as
   buffer-cache-based systems.  In those systems, the virtual memory
   system will need to be modified instead of the buffer cache.

16.4.  Operation 6: CREATE - Create a Non-Regular File Object

16.4.1.  SYNOPSIS

   (cfh), name, type, attrs -> (cfh), change_info, attrs_set















Shepler, et al.         Expires February 2, 2007              [Page 295]


Internet-Draft            NFSv4 Minor Version 1              August 2006


16.4.2.  ARGUMENTS

   /*
    * CREATE: Create a non-regular file
    */
   union createtype4 switch (nfs_ftype4 type) {
    case NF4LNK:
            linktext4      linkdata;
    case NF4BLK:
    case NF4CHR:
            specdata4      devdata;
    case NF4SOCK:
    case NF4FIFO:
    case NF4DIR:
            void;
    default:
            void;          /* server should return NFS4ERR_BADTYPE */
   };

   struct CREATE4args {
           /* CURRENT_FH: directory for creation */
           createtype4     objtype;
           component4      objname;
           fattr4          createattrs;
   };


16.4.3.  RESULTS

   struct CREATE4resok {
           change_info4    cinfo;
           bitmap4         attrset;        /* attributes set */
   };

   union CREATE4res switch (nfsstat4 status) {
    case NFS4_OK:
            CREATE4resok resok4;
    default:
            void;
   };


16.4.4.  DESCRIPTION

   The CREATE operation creates a non-regular file object in a directory
   with a given name.  The OPEN operation MUST be used to create a
   regular file.




Shepler, et al.         Expires February 2, 2007              [Page 296]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   The objname specifies the name for the new object.  The objtype
   determines the type of object to be created: directory, symlink, etc.

   If an object of the same name already exists in the directory, the
   server will return the error NFS4ERR_EXIST.

   For the directory where the new file object was created, the server
   returns change_info4 information in cinfo.  With the atomic field of
   the change_info4 struct, the server will indicate if the before and
   after change attributes were obtained atomically with respect to the
   file object creation.

   If the objname has a length of 0 (zero), or if objname does not obey
   the UTF-8 definition, the error NFS4ERR_INVAL will be returned.

   The current filehandle is replaced by that of the new object.

   The createattrs specifies the initial set of attributes for the
   object.  The set of attributes may include any writable attribute
   valid for the object type.  When the operation is successful, the
   server will return to the client an attribute mask signifying which
   attributes were successfully set for the object.

   If createattrs includes neither the owner attribute nor an ACL with
   an ACE for the owner, and if the server's file system both supports
   and requires an owner attribute (or an owner ACE) then the server
   MUST derive the owner (or the owner ACE).  This would typically be
   from the principal indicated in the RPC credentials of the call, but
   the server's operating environment or file system semantics may
   dictate other methods of derivation.  Similarly, if createattrs
   includes neither the group attribute nor a group ACE, and if the
   server's file system both supports and requires the notion of a group
   attribute (or group ACE), the server MUST derive the group attribute
   (or the corresponding owner ACE) for the file.  This could be from
   the RPC call's credentials, such as the group principal if the
   credentials include it (such as with AUTH_SYS), from the group
   identifier associated with the principal in the credentials (for
   e.g., POSIX systems have a passwd database that has the group
   identifier for every user identifier), inherited from directory the
   object is created in, or whatever else the server's operating
   environment or file system semantics dictate.  This applies to the
   OPEN operation too.

   Conversely, it is possible the client will specify in createattrs an
   owner attribute or group attribute or ACL that the principal
   indicated the RPC call's credentials does not have permissions to
   create files for.  The error to be returned in this instance is
   NFS4ERR_PERM.  This applies to the OPEN operation too.



Shepler, et al.         Expires February 2, 2007              [Page 297]


Internet-Draft            NFSv4 Minor Version 1              August 2006


16.4.5.  IMPLEMENTATION

   If the client desires to set attribute values after the create, a
   SETATTR operation can be added to the COMPOUND request so that the
   appropriate attributes will be set.

16.5.  Operation 7: DELEGPURGE - Purge Delegations Awaiting Recovery

16.5.1.  SYNOPSIS

   clientid ->

16.5.2.  ARGUMENTS

   /*
    * DELEGPURGE: Purge Delegations Awaiting Recovery
    */
   struct DELEGPURGE4args {
           clientid4       clientid;
   };


16.5.3.  RESULTS

   struct DELEGPURGE4res {
           nfsstat4        status;
   };


16.5.4.  DESCRIPTION

   Purges all of the delegations awaiting recovery for a given client.
   This is useful for clients which do not commit delegation information
   to stable storage to indicate that conflicting requests need not be
   delayed by the server awaiting recovery of delegation information.

   This operation should be used by clients that record delegation
   information on stable storage on the client.  In this case,
   DELEGPURGE should be issued immediately after doing delegation
   recovery on all delegations known to the client.  Doing so will
   notify the server that no additional delegations for the client will
   be recovered allowing it to free resources, and avoid delaying other
   clients who make requests that conflict with the unrecovered
   delegations.  The set of delegations known to the server and the
   client may be different.  The reason for this is that a client may
   fail after making a request which resulted in delegation but before
   it received the results and committed them to the client's stable
   storage.



Shepler, et al.         Expires February 2, 2007              [Page 298]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   The server MAY support DELEGPURGE, but if it does not, it MUST NOT
   support CLAIM_DELEGATE_PREV.

16.6.  Operation 8: DELEGRETURN - Return Delegation

16.6.1.  SYNOPSIS

   (cfh), stateid ->

16.6.2.  ARGUMENTS

   /*
    * DELEGRETURN: Return a delegation
    */
   struct DELEGRETURN4args {
           /* CURRENT_FH: delegated file */
           stateid4        deleg_stateid;
   };


16.6.3.  RESULTS

   struct DELEGRETURN4res {
           nfsstat4        status;
   };


16.6.4.  DESCRIPTION

   Returns the delegation represented by the current filehandle and
   stateid.

   Delegations may be returned when recalled or voluntarily (i.e. before
   the server has recalled them).  In either case the client must
   properly propagate state changed under the context of the delegation
   to the server before returning the delegation.

16.7.  Operation 9: GETATTR - Get Attributes

16.7.1.  SYNOPSIS

   (cfh), attrbits -> attrbits, attrvals









Shepler, et al.         Expires February 2, 2007              [Page 299]


Internet-Draft            NFSv4 Minor Version 1              August 2006


16.7.2.  ARGUMENTS

   /*
    * GETATTR: Get file attributes
    */
   struct GETATTR4args {
           /* CURRENT_FH: directory or file */
           bitmap4         attr_request;
   };


16.7.3.  RESULTS

   struct GETATTR4resok {
           fattr4          obj_attributes;
   };

   union GETATTR4res switch (nfsstat4 status) {
    case NFS4_OK:
            GETATTR4resok  resok4;
    default:
            void;
   };


16.7.4.  DESCRIPTION

   The GETATTR operation will obtain attributes for the file system
   object specified by the current filehandle.  The client sets a bit in
   the bitmap argument for each attribute value that it would like the
   server to return.  The server returns an attribute bitmap that
   indicates the attribute values for which it was able to return,
   followed by the attribute values ordered lowest attribute number
   first.

   The server must return a value for each attribute that the client
   requests if the attribute is supported by the server.  If the server
   does not support an attribute or cannot approximate a useful value
   then it must not return the attribute value and must not set the
   attribute bit in the result bitmap.  The server must return an error
   if it supports an attribute but cannot obtain its value.  In that
   case no attribute values will be returned.

   All servers must support the mandatory attributes as specified in
   File Attributes (Section 5).

   On success, the current filehandle retains its value.




Shepler, et al.         Expires February 2, 2007              [Page 300]


Internet-Draft            NFSv4 Minor Version 1              August 2006


16.7.5.  IMPLEMENTATION

16.8.  Operation 10: GETFH - Get Current Filehandle

16.8.1.  SYNOPSIS

   (cfh) -> filehandle

16.8.2.  ARGUMENTS

   /* CURRENT_FH: */
   void;

16.8.3.  RESULTS

   /*
    * GETFH: Get current filehandle
    */
   struct GETFH4resok {
           nfs_fh4         object;
   };

   union GETFH4res switch (nfsstat4 status) {
    case NFS4_OK:
           GETFH4resok     resok4;
    default:
           void;
   };


16.8.4.  DESCRIPTION

   This operation returns the current filehandle value.

   On success, the current filehandle retains its value.

16.8.5.  IMPLEMENTATION

   Operations that change the current filehandle like LOOKUP or CREATE
   do not automatically return the new filehandle as a result.  For
   instance, if a client needs to lookup a directory entry and obtain
   its filehandle then the following request is needed.

      PUTFH (directory filehandle)

      LOOKUP (entry name)





Shepler, et al.         Expires February 2, 2007              [Page 301]


Internet-Draft            NFSv4 Minor Version 1              August 2006


      GETFH

16.9.  Operation 11: LINK - Create Link to a File

16.9.1.  SYNOPSIS

   (sfh), (cfh), newname -> (cfh), change_info

16.9.2.  ARGUMENTS

   /*
    * LINK: Create link to an object
    */
   struct LINK4args {
           /* SAVED_FH: source object */
           /* CURRENT_FH: target directory */
           component4      newname;
   };


16.9.3.  RESULTS

   struct LINK4resok {
           change_info4    cinfo;
   };

   union LINK4res switch (nfsstat4 status) {
    case NFS4_OK:
            LINK4resok resok4;
    default:
            void;
   };


16.9.4.  DESCRIPTION

   The LINK operation creates an additional newname for the file
   represented by the saved filehandle, as set by the SAVEFH operation,
   in the directory represented by the current filehandle.  The existing
   file and the target directory must reside within the same file system
   on the server.  On success, the current filehandle will continue to
   be the target directory.  If an object exists in the target directory
   with the same name as newname, the server must return NFS4ERR_EXIST.

   For the target directory, the server returns change_info4 information
   in cinfo.  With the atomic field of the change_info4 struct, the
   server will indicate if the before and after change attributes were
   obtained atomically with respect to the link creation.



Shepler, et al.         Expires February 2, 2007              [Page 302]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   If the newname has a length of 0 (zero), or if newname does not obey
   the UTF-8 definition, the error NFS4ERR_INVAL will be returned.

16.9.5.  IMPLEMENTATION

   Changes to any property of the "hard" linked files are reflected in
   all of the linked files.  When a link is made to a file, the
   attributes for the file should have a value for numlinks that is one
   greater than the value before the LINK operation.

   The statement "file and the target directory must reside within the
   same file system on the server" means that the fsid fields in the
   attributes for the objects are the same.  If they reside on different
   file systems, the error, NFS4ERR_XDEV, is returned.  On some servers,
   the filenames, "." and "..", are illegal as newname.

   In the case that newname is already linked to the file represented by
   the saved filehandle, the server will return NFS4ERR_EXIST.

   Note that symbolic links are created with the CREATE operation.

16.10.  Operation 12: LOCK - Create Lock

16.10.1.  SYNOPSIS

   (cfh) locktype, reclaim, offset, length, locker -> stateid

























Shepler, et al.         Expires February 2, 2007              [Page 303]


Internet-Draft            NFSv4 Minor Version 1              August 2006


16.10.2.  ARGUMENTS

   /*
    * For LOCK, transition from open_owner to new lock_owner
    */
   struct open_to_lock_owner4 {
           seqid4          open_seqid;
           stateid4        open_stateid;
           seqid4          lock_seqid;
           lock_owner4     lock_owner;
   };

   /*
    * For LOCK, existing lock_owner continues to request file locks
    */
   struct exist_lock_owner4 {
           stateid4        lock_stateid;
           seqid4          lock_seqid;
   };

   union locker4 switch (bool new_lock_owner) {
    case TRUE:
           open_to_lock_owner4     open_owner;
    case FALSE:
           exist_lock_owner4       lock_owner;
   };

   /*
    * LOCK/LOCKT/LOCKU: Record lock management
    */
   struct LOCK4args {
           /* CURRENT_FH: file */
           nfs_lock_type4  locktype;
           bool            reclaim;
           offset4         offset;
           length4         length;
           locker4         locker;
   };













Shepler, et al.         Expires February 2, 2007              [Page 304]


Internet-Draft            NFSv4 Minor Version 1              August 2006


16.10.3.  RESULTS

   struct LOCK4denied {
           offset4         offset;
           length4         length;
           nfs_lock_type4  locktype;
           lock_owner4     owner;
   };

   struct LOCK4resok {
           stateid4        lock_stateid;
   };

   union LOCK4res switch (nfsstat4 status) {
    case NFS4_OK:
            LOCK4resok     resok4;
    case NFS4ERR_DENIED:
            LOCK4denied    denied;
    default:
            void;
   };


16.10.4.  DESCRIPTION

   The LOCK operation requests a record lock for the byte range
   specified by the offset and length parameters.  The lock type is also
   specified to be one of the nfs_lock_type4s.  If this is a reclaim
   request, the reclaim parameter will be TRUE;

   Bytes in a file may be locked even if those bytes are not currently
   allocated to the file.  To lock the file from a specific offset
   through the end-of-file (no matter how long the file actually is) use
   a length field with all bits set to 1 (one).  If the length is zero,
   or if a length which is not all bits set to one is specified, and
   length when added to the offset exceeds the maximum 64-bit unsigned
   integer value, the error NFS4ERR_INVAL will result.

   Some servers may only support locking for byte offsets that fit
   within 32 bits.  If the client specifies a range that includes a byte
   beyond the last byte offset of the 32-bit range, but does not include
   the last byte offset of the 32-bit and all of the byte offsets beyond
   it, up to the end of the valid 64-bit range, such a 32-bit server
   MUST return the error NFS4ERR_BAD_RANGE.

   In the case that the lock is denied, the owner, offset, and length of
   a conflicting lock are returned.




Shepler, et al.         Expires February 2, 2007              [Page 305]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   On success, the current filehandle retains its value.

16.10.5.  IMPLEMENTATION

   If the server is unable to determine the exact offset and length of
   the conflicting lock, the same offset and length that were provided
   in the arguments should be returned in the denied results.  The File
   Locking section contains a full description of this and the other
   file locking operations.

   LOCK operations are subject to permission checks and to checks
   against the access type of the associated file.  However, the
   specific right and modes required for various type of locks, reflect
   the semantics of the server-exported file system, and are not
   specified by the protocol.  For example, Windows 2000 allows a write
   lock of a file open for READ, while a POSIX-compliant system does
   not.

   When the client makes a lock request that corresponds to a range that
   the lockowner has locked already (with the same or different lock
   type), or to a sub-region of such a range, or to a region which
   includes multiple locks already granted to that lockowner, in whole
   or in part, and the server does not support such locking operations
   (i.e. does not support POSIX locking semantics), the server will
   return the error NFS4ERR_LOCK_RANGE.  In that case, the client may
   return an error, or it may emulate the required operations, using
   only LOCK for ranges that do not include any bytes already locked by
   that lock_owner and LOCKU of locks held by that lock_owner
   (specifying an exactly-matching range and type).  Similarly, when the
   client makes a lock request that amounts to upgrading (changing from
   a read lock to a write lock) or downgrading (changing from write lock
   to a read lock) an existing record lock, and the server does not
   support such a lock, the server will return NFS4ERR_LOCK_NOTSUPP.
   Such operations may not perfectly reflect the required semantics in
   the face of conflicting lock requests from other clients.

   The locker argument specifies the lock_owner that is associated with
   the LOCK request.  The locker4 structure is a switched union that
   indicates whether the lock_owner is known to the server or if the
   lock_owner is new to the server.  In the case that the lock_owner is
   known to the server and has an established lock_seqid, the argument
   is just the lock_owner and lock_seqid.  In the case that the
   lock_owner is not known to the server, the argument contains not only
   the lock_owner and lock_seqid but also the open_stateid and
   open_seqid.  The new lock_owner case covers the very first lock done
   by the lock_owner and offers a method to use the established state of
   the open_stateid to transition to the use of the lock_owner.




Shepler, et al.         Expires February 2, 2007              [Page 306]


Internet-Draft            NFSv4 Minor Version 1              August 2006


16.11.  Operation 13: LOCKT - Test For Lock

16.11.1.  SYNOPSIS

   (cfh) locktype, offset, length owner -> {void, NFS4ERR_DENIED ->
   owner}

16.11.2.  ARGUMENTS

   struct LOCKT4args {
           /* CURRENT_FH: file */
           nfs_lock_type4  locktype;
           offset4         offset;
           length4         length;
           lock_owner4     owner;
   };


16.11.3.  RESULTS

   union LOCKT4res switch (nfsstat4 status) {
    case NFS4ERR_DENIED:
            LOCK4denied    denied;
    case NFS4_OK:
            void;
    default:
            void;
   };

16.11.4.  DESCRIPTION

   The LOCKT operation tests the lock as specified in the arguments.  If
   a conflicting lock exists, the owner, offset, length, and type of the
   conflicting lock are returned; if no lock is held, nothing other than
   NFS4_OK is returned.  Lock types READ_LT and READW_LT are processed
   in the same way in that a conflicting lock test is done without
   regard to blocking or non-blocking.  The same is true for WRITE_LT
   and WRITEW_LT.

   The ranges are specified as for LOCK.  The NFS4ERR_INVAL and
   NFS4ERR_BAD_RANGE errors are returned under the same circumstances as
   for LOCK.

   On success, the current filehandle retains its value.







Shepler, et al.         Expires February 2, 2007              [Page 307]


Internet-Draft            NFSv4 Minor Version 1              August 2006


16.11.5.  IMPLEMENTATION

   If the server is unable to determine the exact offset and length of
   the conflicting lock, the same offset and length that were provided
   in the arguments should be returned in the denied results.  The File
   Locking section contains further discussion of the file locking
   mechanisms.

   LOCKT uses a lock_owner4 rather a stateid4, as is used in LOCK to
   identify the owner.  This is because the client does not have to open
   the file to test for the existence of a lock, so a stateid may not be
   available.

   The test for conflicting locks should exclude locks for the current
   lockowner.  Note that since such locks are not examined the possible
   existence of overlapping ranges may not affect the results of LOCKT.
   If the server does examine locks that match the lockowner for the
   purpose of range checking, NFS4ERR_LOCK_RANGE may be returned..  In
   the event that it returns NFS4_OK, clients may do a LOCK and receive
   NFS4ERR_LOCK_RANGE on the LOCK request because of the flexibility
   provided to the server.

16.12.  Operation 14: LOCKU - Unlock File

16.12.1.  SYNOPSIS

   (cfh) type, seqid, stateid, offset, length -> stateid

16.12.2.  ARGUMENTS

   struct LOCKU4args {
           /* CURRENT_FH: file */
           nfs_lock_type4  locktype;
           seqid4          seqid;
           stateid4        lock_stateid;
           offset4         offset;
           length4         length;
   };













Shepler, et al.         Expires February 2, 2007              [Page 308]


Internet-Draft            NFSv4 Minor Version 1              August 2006


16.12.3.  RESULTS

   union LOCKU4res switch (nfsstat4 status) {
    case   NFS4_OK:
            stateid4       lock_stateid;
    default:
            void;
   };


16.12.4.  DESCRIPTION

   The LOCKU operation unlocks the record lock specified by the
   parameters.  The client may set the locktype field to any value that
   is legal for the nfs_lock_type4 enumerated type, and the server MUST
   accept any legal value for locktype.  Any legal value for locktype
   has no effect on the success or failure of the LOCKU operation.

   The ranges are specified as for LOCK.  The NFS4ERR_INVAL and
   NFS4ERR_BAD_RANGE errors are returned under the same circumstances as
   for LOCK.

   On success, the current filehandle retains its value.

16.12.5.  IMPLEMENTATION

   If the area to be unlocked does not correspond exactly to a lock
   actually held by the lockowner the server may return the error
   NFS4ERR_LOCK_RANGE.  This includes the case in which the area is not
   locked, where the area is a sub-range of the area locked, where it
   overlaps the area locked without matching exactly or the area
   specified includes multiple locks held by the lockowner.  In all of
   these cases, allowed by POSIX locking semantics, a client receiving
   this error, should if it desires support for such operations,
   simulate the operation using LOCKU on ranges corresponding to locks
   it actually holds, possibly followed by LOCK requests for the sub-
   ranges not being unlocked.

16.13.  Operation 15: LOOKUP - Lookup Filename

16.13.1.  SYNOPSIS

   (cfh), component -> (cfh)








Shepler, et al.         Expires February 2, 2007              [Page 309]


Internet-Draft            NFSv4 Minor Version 1              August 2006


16.13.2.  ARGUMENTS

   /*
    * LOOKUP: Lookup filename
    */
   struct LOOKUP4args {
           /* CURRENT_FH: directory */
           component4      objname;
   };


16.13.3.  RESULTS

   struct LOOKUP4res {
           /* CURRENT_FH: object */
           nfsstat4        status;
   };


16.13.4.  DESCRIPTION

   This operation LOOKUPs or finds a file system object using the
   directory specified by the current filehandle.  LOOKUP evaluates the
   component and if the object exists the current filehandle is replaced
   with the component's filehandle.

   If the component cannot be evaluated either because it does not exist
   or because the client does not have permission to evaluate the
   component, then an error will be returned and the current filehandle
   will be unchanged.

   If the component is a zero length string or if any component does not
   obey the UTF-8 definition, the error NFS4ERR_INVAL will be returned.

16.13.5.  IMPLEMENTATION

   If the client wants to achieve the effect of a multi-component
   lookup, it may construct a COMPOUND request such as (and obtain each
   filehandle):

         PUTFH  (directory filehandle)
         LOOKUP "pub"
         GETFH
         LOOKUP "foo"
         GETFH
         LOOKUP "bar"
         GETFH




Shepler, et al.         Expires February 2, 2007              [Page 310]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   NFS version 4 servers depart from the semantics of previous NFS
   versions in allowing LOOKUP requests to cross mountpoints on the
   server.  The client can detect a mountpoint crossing by comparing the
   fsid attribute of the directory with the fsid attribute of the
   directory looked up.  If the fsids are different then the new
   directory is a server mountpoint.  UNIX clients that detect a
   mountpoint crossing will need to mount the server's file system.
   This needs to be done to maintain the file object identity checking
   mechanisms common to UNIX clients.

   Servers that limit NFS access to "shares" or "exported" file systems
   should provide a pseudo file system into which the exported file
   systems can be integrated, so that clients can browse the server's
   name space.  The clients view of a pseudo file system will be limited
   to paths that lead to exported file systems.

   Note: previous versions of the protocol assigned special semantics to
   the names "." and "..".  NFS version 4 assigns no special semantics
   to these names.  The LOOKUPP operator must be used to lookup a parent
   directory.

   Note that this operation does not follow symbolic links.  The client
   is responsible for all parsing of filenames including filenames that
   are modified by symbolic links encountered during the lookup process.

   If the current filehandle supplied is not a directory but a symbolic
   link, the error NFS4ERR_SYMLINK is returned as the error.  For all
   other non-directory file types, the error NFS4ERR_NOTDIR is returned.

16.14.  Operation 16: LOOKUPP - Lookup Parent Directory

16.14.1.  SYNOPSIS

   (cfh) -> (cfh)

16.14.2.  ARGUMENTS

   /* CURRENT_FH: object */
   void;












Shepler, et al.         Expires February 2, 2007              [Page 311]


Internet-Draft            NFSv4 Minor Version 1              August 2006


16.14.3.  RESULTS

   /*
    * LOOKUPP: Lookup parent directory
    */
   struct LOOKUPP4res {
           /* CURRENT_FH: directory */
           nfsstat4        status;
   };


16.14.4.  DESCRIPTION

   The current filehandle is assumed to refer to a regular directory or
   a named attribute directory.  LOOKUPP assigns the filehandle for its
   parent directory to be the current filehandle.  If there is no parent
   directory an NFS4ERR_NOENT error must be returned.  Therefore,
   NFS4ERR_NOENT will be returned by the server when the current
   filehandle is at the root or top of the server's file tree.

   As for LOOKUP, LOOKUPP will also cross mountpoints.

   If the current filehandle is not a directory or named attribute
   directory, the error NFS4ERR_NOTDIR is returned.

   If the requester's security flavor does not match that configured for
   the parent directory, then the server SHOULD return NFS4ERR_WRONGSEC
   (a future minor revision of NFSv4 may upgrade this to MUST) in the
   LOOKUPP response.  However, if the server does so, it MUST support
   the new SECINFO_NO_NAME operation, so that the client can gracefully
   determine the correct security flavor.  See the discussion of the
   SECINFO_NO_NAME operation for a description.

16.14.5.  IMPLEMENTATION

16.15.  Operation 17: NVERIFY - Verify Difference in Attributes

16.15.1.  SYNOPSIS

   (cfh), fattr -> -











Shepler, et al.         Expires February 2, 2007              [Page 312]


Internet-Draft            NFSv4 Minor Version 1              August 2006


16.15.2.  ARGUMENTS

   /*
    * NVERIFY: Verify attributes different
    */
   struct NVERIFY4args {
           /* CURRENT_FH: object */
           fattr4          obj_attributes;
   };


16.15.3.  RESULTS

   struct NVERIFY4res {
           nfsstat4        status;
   };


16.15.4.  DESCRIPTION

   This operation is used to prefix a sequence of operations to be
   performed if one or more attributes have changed on some file system
   object.  If all the attributes match then the error NFS4ERR_SAME must
   be returned.

   On success, the current filehandle retains its value.

16.15.5.  IMPLEMENTATION

   This operation is useful as a cache validation operator.  If the
   object to which the attributes belong has changed then the following
   operations may obtain new data associated with that object.  For
   instance, to check if a file has been changed and obtain new data if
   it has:

         PUTFH  (public)
         LOOKUP "foobar"
         NVERIFY attrbits attrs
         READ 0 32767

   In the case that a recommended attribute is specified in the NVERIFY
   operation and the server does not support that attribute for the file
   system object, the error NFS4ERR_ATTRNOTSUPP is returned to the
   client.

   When the attribute rdattr_error or any write-only attribute (e.g.
   time_modify_set) is specified, the error NFS4ERR_INVAL is returned to
   the client.



Shepler, et al.         Expires February 2, 2007              [Page 313]


Internet-Draft            NFSv4 Minor Version 1              August 2006


16.16.  Operation 18: OPEN - Open a Regular File

16.16.1.  SYNOPSIS

   (cfh), seqid, share_access, share_deny, owner, openhow, claim ->
   (cfh), stateid, cinfo, rflags, open_confirm, attrset delegation

16.16.2.  ARGUMENTS

  /*
   * Various definitions for OPEN
   */
  enum createmode4 {
          UNCHECKED4      = 0,
          GUARDED4        = 1,
          EXCLUSIVE4      = 2
  };

  union createhow4 switch (createmode4 mode) {
   case UNCHECKED4:
   case GUARDED4:
           fattr4         createattrs;
   case EXCLUSIVE4:
           verifier4      createverf;
  };

  enum opentype4 {
          OPEN4_NOCREATE  = 0,
          OPEN4_CREATE    = 1
  };

  union openflag4 switch (opentype4 opentype) {
   case OPEN4_CREATE:
           createhow4     how;
   default:
           void;
  };

  /* Next definitions used for OPEN delegation */
  enum limit_by4 {
          NFS_LIMIT_SIZE          = 1,
          NFS_LIMIT_BLOCKS        = 2
          /* others as needed */
  };

  struct nfs_modified_limit4 {
          uint32_t        num_blocks;
          uint32_t        bytes_per_block;



Shepler, et al.         Expires February 2, 2007              [Page 314]


Internet-Draft            NFSv4 Minor Version 1              August 2006


  };

  union nfs_space_limit4 switch (limit_by4 limitby) {
   /* limit specified as file size */
   case NFS_LIMIT_SIZE:
           uint64_t               filesize;
   /* limit specified by number of blocks */
   case NFS_LIMIT_BLOCKS:
           nfs_modified_limit4    mod_blocks;
  } ;

  /*
   * Share Access and Deny constants for open argument
   */
  const OPEN4_SHARE_ACCESS_READ   = 0x00000001;
  const OPEN4_SHARE_ACCESS_WRITE  = 0x00000002;
  const OPEN4_SHARE_ACCESS_BOTH   = 0x00000003;

  const OPEN4_SHARE_DENY_NONE     = 0x00000000;
  const OPEN4_SHARE_DENY_READ     = 0x00000001;
  const OPEN4_SHARE_DENY_WRITE    = 0x00000002;
  const OPEN4_SHARE_DENY_BOTH     = 0x00000003;

  /* new flags for share_access field of OPEN4args */
  const OPEN4_SHARE_ACCESS_WANT_DELEG_MASK        = 0xFF00;
  const OPEN4_SHARE_ACCESS_WANT_NO_PREFERENCE     = 0x0000;
  const OPEN4_SHARE_ACCESS_WANT_READ_DELEG        = 0x0100;
  const OPEN4_SHARE_ACCESS_WANT_WRITE_DELEG       = 0x0200;
  const OPEN4_SHARE_ACCESS_WANT_ANY_DELEG         = 0x0300;
  const OPEN4_SHARE_ACCESS_WANT_NO_DELEG          = 0x0400;
  const OPEN4_SHARE_ACCESS_WANT_CANCEL            = 0x0500;

  const OPEN4_SHARE_ACCESS_WANT_SIGNAL_DELEG_WHEN_RESRC_AVAIL = 0x10000;
  const OPEN4_SHARE_ACCESS_WANT_PUSH_DELEG_WHEN_UNCONTENDED = 0x20000;

  enum open_delegation_type4 {
          OPEN_DELEGATE_NONE      = 0,
          OPEN_DELEGATE_READ      = 1,
          OPEN_DELEGATE_WRITE     = 2,
          OPEN_DELEGATE_NONE_EXT  = 3 /* new to v4.1 */
  };

  enum open_claim_type4 {
          CLAIM_NULL              = 0,
          CLAIM_PREVIOUS          = 1,
          CLAIM_DELEGATE_CUR      = 2,
          CLAIM_DELEGATE_PREV     = 3,




Shepler, et al.         Expires February 2, 2007              [Page 315]


Internet-Draft            NFSv4 Minor Version 1              August 2006


          /*
           * Like CLAIM_NULL, but object identified
           * by the current filehandle.
           */
          CLAIM_FH                = 4, /* new to v4.1 */

          /*
           * Like CLAIM_DELEGATE_CUR, but object identified
           * by current filehandle.
           */
          CLAIM_DELEG_CUR_FH      = 5, /* new to v4.1 */

          /*
           * Like CLAIM_DELEGATE_PREV, but object identified
           * by current filehandle.
           */
          CLAIM_DELEG_PREV_FH     = 6 /* new to v4.1 */
  };

  struct open_claim_delegate_cur4 {
          stateid4        delegate_stateid;
          component4      file;
  };

  union open_claim4 switch (open_claim_type4 claim) {
   /*
    * No special rights to file. Ordinary OPEN of the specified file.
    */
   case CLAIM_NULL:
          /* CURRENT_FH: directory */
          component4      file;

   /*
    * Right to the file established by an open previous to server
    * reboot.  File identified by filehandle obtained at that time
    * rather than by name.
    */
   case CLAIM_PREVIOUS:
          /* CURRENT_FH: file being reclaimed */
          open_delegation_type4   delegate_type;

   /*
    * Right to file based on a delegation granted by the server.
    * File is specified by name.
    */
   case CLAIM_DELEGATE_CUR:
          /* CURRENT_FH: directory */
          open_claim_delegate_cur4        delegate_cur_info;



Shepler, et al.         Expires February 2, 2007              [Page 316]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   /* Right to file based on a delegation granted to a previous boot
    * instance of the client.  File is specified by name.
    */
   case CLAIM_DELEGATE_PREV:
           /* CURRENT_FH: directory */
          component4      file_delegate_prev;
  };

  /*
   * OPEN: Open a file, potentially receiving an open delegation
   */
  struct OPEN4args {
          seqid4          seqid;
          uint32_t        share_access;
          uint32_t        share_deny;
          open_owner4     owner;
          openflag4       openhow;
          open_claim4     claim;
  };


16.16.3.  RESULTS

   struct open_read_delegation4 {
           stateid4        stateid;        /* Stateid for delegation*/
           bool            recall;         /* Pre-recalled flag for
                                              delegations obtained
                                              by reclaim
                                              (CLAIM_PREVIOUS) */
           nfsace4         permissions;    /* Defines users who don't
                                              need an ACCESS call to
                                              open for read */
   };

   struct open_write_delegation4 {
           stateid4        stateid;        /* Stateid for delegation */
           bool            recall;         /* Pre-recalled flag for
                                              delegations obtained
                                              by reclaim
                                              (CLAIM_PREVIOUS) */
           nfs_space_limit4 space_limit;   /* Defines condition that
                                              the client must check to
                                              determine whether the
                                              file needs to be flushed
                                              to the server on close.
                                              */
           nfsace4         permissions;    /* Defines users who don't
                                              need an ACCESS call as



Shepler, et al.         Expires February 2, 2007              [Page 317]


Internet-Draft            NFSv4 Minor Version 1              August 2006


                                              part of a delegated
                                              open. */
   };


   enum why_no_delegation4 { /* new to v4.1 */
           WND_NOT_WANTED          = 0,
           WND_CONTENTION          = 1,
           WND_RESOURCE            = 2,
           WND_NOT_SUPP_FTYPE      = 3,
           WND_WRITE_DELEG_NOT_SUPP_FTYPE = 4,
           WND_NOT_SUPP_UPGRADE    = 5,
           WND_NOT_SUPP_DOWNGRADE  = 6,
           WND_CANCELED            = 7,
           WND_IS_DIR              = 8
   };

   union open_none_delegation4 /* new to v4.1 */
   switch (why_no_delegation4 ond_why) {
           case WND_CONTENTION:
                   bool ond_server_will_push_deleg;
           case WND_RESOURCE:
                   bool ond_server_will_signal_avail;
           default:
                   void;
   };

   union open_delegation4
   switch (open_delegation_type4 delegation_type) {
           case OPEN_DELEGATE_NONE:
                   void;
           case OPEN_DELEGATE_READ:
                   open_read_delegation4 read;
           case OPEN_DELEGATE_WRITE:
                   open_write_delegation4 write;
           case OPEN_DELEGATE_NONE_EXT: /* new to v4.1 */
                   open_none_delegation4 od_whynone;
   };

   /*
    * Result flags
    */
   /* Client must confirm open */
   const OPEN4_RESULT_CONFIRM      = 0x00000002;
   /* Type of file locking behavior at the server */
   const OPEN4_RESULT_LOCKTYPE_POSIX = 0x00000004;

   struct OPEN4resok {



Shepler, et al.         Expires February 2, 2007              [Page 318]


Internet-Draft            NFSv4 Minor Version 1              August 2006


           stateid4        stateid;        /* Stateid for open */
           change_info4    cinfo;          /* Directory Change Info */
           uint32_t        rflags;         /* Result flags */
           bitmap4         attrset;        /* attribute set for create*/
           open_delegation4 delegation;    /* Info on any open
                                              delegation */
   };

   union OPEN4res switch (nfsstat4 status) {
    case NFS4_OK:
           /* CURRENT_FH: opened file */
           OPEN4resok      resok4;
    default:
           void;
   };


16.16.4.  DESCRIPTION

   The OPEN operation creates and/or opens a regular file in a directory
   with the provided name.  If the file does not exist at the server and
   creation is desired, specification of the method of creation is
   provided by the openhow parameter.  The client has the choice of
   three creation methods: UNCHECKED, GUARDED, or EXCLUSIVE.

   If the current filehandle is a named attribute directory, OPEN will
   then create or open a named attribute file.  Note that exclusive
   create of a named attribute is not supported.  If the createmode is
   EXCLUSIVE4 and the current filehandle is a named attribute directory,
   the server will return EINVAL.

   UNCHECKED means that the file should be created if a file of that
   name does not exist and encountering an existing regular file of that
   name is not an error.  For this type of create, createattrs specifies
   the initial set of attributes for the file.  The set of attributes
   may include any writable attribute valid for regular files.  When an
   UNCHECKED create encounters an existing file, the attributes
   specified by createattrs are not used, except that when an size of
   zero is specified, the existing file is truncated.  If GUARDED is
   specified, the server checks for the presence of a duplicate object
   by name before performing the create.  If a duplicate exists, an
   error of NFS4ERR_EXIST is returned as the status.  If the object does
   not exist, the request is performed as described for UNCHECKED.  For
   each of these cases (UNCHECKED and GUARDED) where the operation is
   successful, the server will return to the client an attribute mask
   signifying which attributes were successfully set for the object.

   EXCLUSIVE specifies that the server is to follow exclusive creation



Shepler, et al.         Expires February 2, 2007              [Page 319]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   semantics, using the verifier to ensure exclusive creation of the
   target.  The server should check for the presence of a duplicate
   object by name.  If the object does not exist, the server creates the
   object and stores the verifier with the object.  If the object does
   exist and the stored verifier matches the client provided verifier,
   the server uses the existing object as the newly created object.  If
   the stored verifier does not match, then an error of NFS4ERR_EXIST is
   returned.  No attributes may be provided in this case, since the
   server may use an attribute of the target object to store the
   verifier.  If the server uses an attribute to store the exclusive
   create verifier, it will signify which attribute by setting the
   appropriate bit in the attribute mask that is returned in the
   results.

   For the target directory, the server returns change_info4 information
   in cinfo.  With the atomic field of the change_info4 struct, the
   server will indicate if the before and after change attributes were
   obtained atomically with respect to the link creation.

   Upon successful creation, the current filehandle is replaced by that
   of the new object.

   The OPEN operation provides for Windows share reservation capability
   with the use of the share_access and share_deny fields of the OPEN
   arguments.  The client specifies at OPEN the required share_access
   and share_deny modes.  For clients that do not directly support
   SHAREs (i.e.  UNIX), the expected deny value is DENY_NONE.  In the
   case that there is a existing SHARE reservation that conflicts with
   the OPEN request, the server returns the error NFS4ERR_SHARE_DENIED.
   For a complete SHARE request, the client must provide values for the
   owner and seqid fields for the OPEN argument.  For additional
   discussion of SHARE semantics see the section on 'Share
   Reservations'.  [[Comment.15: Add an xref to the Share Reservations
   section]]

   In the case that the client is recovering state from a server
   failure, the claim field of the OPEN argument is used to signify that
   the request is meant to reclaim state previously held.

   The "claim" field of the OPEN argument is used to specify the file to
   be opened and the state information which the client claims to
   possess.  There are seven claim types as follows:









Shepler, et al.         Expires February 2, 2007              [Page 320]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   +---------------------+---------------------------------------------+
   | open type           | description                                 |
   +---------------------+---------------------------------------------+
   | CLAIM_NULL CLAIM_FH | For the client, this is a new OPEN request  |
   |                     | and there is no previous state associate    |
   |                     | with the file for the client. With          |
   |                     | CLAIM_NULL the file is identified by the    |
   |                     | current filehandle and the specified        |
   |                     | component name. With CLAIM_FH (new to v4.1) |
   |                     | the file is identified by just the current  |
   |                     | filehandle.                                 |
   | CLAIM_PREVIOUS      | The client is claiming basic OPEN state for |
   |                     | a file that was held previous to a server   |
   |                     | reboot. Generally used when a server is     |
   |                     | returning persistent filehandles; the       |
   |                     | client may not have the file name to        |
   |                     | reclaim the OPEN.                           |
   | CLAIM_DELEGATE_CUR  | The client is claiming a delegation for     |
   | CLAIM_DELEG_PREV_FH | OPEN as granted by the server. Generally    |
   |                     | this is done as part of recalling a         |
   |                     | delegation. With CLAIM_DELEGATE_CUR, the    |
   |                     | file is identified by the current           |
   |                     | filehandle and and the specified component  |
   |                     | name. With CLAIM_DELEG_PREV_FH (new to      |
   |                     | v4.1), the file is identified by just the   |
   |                     | current filehandle.                         |
   | CLAIM_DELEGATE_PREV | The client is claiming a delegation granted |
   | CLAIM_DELEG_PREV_FH | to a previous client instance; used after   |
   |                     | the client reboots. The server MAY support  |
   |                     | CLAIM_DELEGATE_PREV or CLAIM_DELEG_PREV_FH. |
   |                     | If it does support either open type,        |
   |                     | SETCLIENTID_CONFIRM MUST NOT remove the     |
   |                     | client's delegation state, and the server   |
   |                     | MUST support the DELEGPURGE operation.      |
   +---------------------+---------------------------------------------+

   For OPEN requests whose claim type is other than CLAIM_PREVIOUS (i.e.
   requests other than those devoted to reclaiming opens after a server
   reboot) that reach the server during its grace or lease expiration
   period, the server returns an error of NFS4ERR_GRACE.

   For any OPEN request, the server may return an open delegation, which
   allows further opens and closes to be handled locally on the client
   as described in the section Open Delegation.  Note that delegation is
   up to the server to decide.  The client should never assume that
   delegation will or will not be granted in a particular instance.  It
   should always be prepared for either case.  A partial exception is
   the reclaim (CLAIM_PREVIOUS) case, in which a delegation type is



Shepler, et al.         Expires February 2, 2007              [Page 321]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   claimed.  In this case, delegation will always be granted, although
   the server may specify an immediate recall in the delegation
   structure.

   The rflags returned by a successful OPEN allow the server to return
   information governing how the open file is to be handled.
   OPEN4_RESULT_CONFIRM is deprecated and MUST not be returned by an
   NFSv4.1 server.  OPEN4_RESULT_LOCKTYPE_POSIX indicates the server's
   file locking behavior supports the complete set of Posix locking
   techniques.  From this the client can choose to manage file locking
   state in a way to handle a mis-match of file locking management.

   If the component is of zero length, NFS4ERR_INVAL will be returned.
   The component is also subject to the normal UTF-8, character support,
   and name checks.  See the section "UTF-8 Related Errors" for further
   [[Comment.16: add an xref to the UTD-8 section]]. discussion.

   When an OPEN is done and the specified lockowner already has the
   resulting filehandle open, the result is to "OR" together the new
   share and deny status together with the existing status.  In this
   case, only a single CLOSE need be done, even though multiple OPENs
   were completed.  When such an OPEN is done, checking of share
   reservations for the new OPEN proceeds normally, with no exception
   for the existing OPEN held by the same lockowner.

   If the underlying file system at the server is only accessible in a
   read-only mode and the OPEN request has specified ACCESS_WRITE or
   ACCESS_BOTH, the server will return NFS4ERR_ROFS to indicate a read-
   only file system.

   As with the CREATE operation, the server MUST derive the owner, owner
   ACE, group, or group ACE if any of the four attributes are required
   and supported by the server's file system.  For an OPEN with the
   EXCLUSIVE4 createmode, the server has no choice, since such OPEN
   calls do not include the createattrs field.  Conversely, if
   createattrs is specified, and includes owner or group (or
   corresponding ACEs) that the principal in the RPC call's credentials
   does not have authorization to create files for, then the server may
   return NFS4ERR_PERM.

   In the case of a OPEN which specifies a size of zero (e.g.
   truncation) and the file has named attributes, the named attributes
   are left as is.  They are not removed.

   NFSv4.1 gives more precise control to clients over acquisition of
   delegations via the following new flags for the share_access field of
   OPEN4args:




Shepler, et al.         Expires February 2, 2007              [Page 322]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   OPEN4_SHARE_ACCESS_WANT_READ_DELEG

   OPEN4_SHARE_ACCESS_WANT_WRITE_DELEG

   OPEN4_SHARE_ACCESS_WANT_ANY_DELEG

   OPEN4_SHARE_ACCESS_WANT_NO_DELEG

   OPEN4_SHARE_ACCESS_WANT_CANCEL

   OPEN4_SHARE_ACCESS_WANT_SIGNAL_DELEG_WHEN_RESRC_AVAIL

   OPEN4_SHARE_ACCESS_WANT_PUSH_DELEG_WHEN_UNCONTENDED

   If (share_access & OPEN4_SHARE_ACCESS_WANT_DELEG_MASK) is not zero,
   then the client will have specified one and only one of:

   OPEN4_SHARE_ACCESS_WANT_READ_DELEG

   OPEN4_SHARE_ACCESS_WANT_WRITE_DELEG

   OPEN4_SHARE_ACCESS_WANT_ANY_DELEG

   OPEN4_SHARE_ACCESS_WANT_NO_DELEG

   OPEN4_SHARE_ACCESS_WANT_CANCEL

   Otherwise the client is indicating no desire for a delegation and the
   server MAY or MAY not return a delegation in the OPEN response.

   If the server supports the new _WANT_ flags and the client issues one
   or more of the new flags, then in the event the server does not
   return a delegation, it MUST return a delegation type of
   OPEN_DELEGATE_NONE_EXT. od_whynone indicates why no delegation was
   returned and will be one of:

   WND_NOT_WANTED  The client specified
      OPEN4_SHARE_ACCESS_WANT_NO_DELEG.

   WND_CONTENTION  There is a conflicting delegation or open on the
      file.

   WND_RESOURCE  Resource limitations prevent the server from granting a
      delegation.







Shepler, et al.         Expires February 2, 2007              [Page 323]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   WND_NOT_SUPP_FTYPE  The server does not support delegations on this
      file type.

   WND_WRITE_DELEG_NOT_SUPP_FTYPE  The server does not support write
      delegations on this file type.

   WND_NOT_SUPP_UPGRADE  The server does not support atomic upgrade of a
      read delegation to a write delegation.

   WND_NOT_SUPP_DOWNGRADE  The server does not support atomic downgrade
      of a write delegation to a read delegation.

   WND_CANCELED  The client specified OPEN4_SHARE_ACCESS_WANT_CANCEL and
      now any "want" for this file object is cancelled.

   WND_IS_DIR  The specified file object is a directory, and the
      operation is OPEN or WANT_DELEGATION which do not support
      delegations on directories.

   OPEN4_SHARE_ACCESS_WANT_READ_DELEG,
   OPEN_SHARE_ACCESS_WANT_WRITE_DELEG, or
   OPEN_SHARE_ACCESS_WANT_ANY_DELEG mean, respectively, the client wants
   a read, write, or any delegation regardless which of
   OPEN4_SHARE_ACCESS_READ, OPEN4_SHARE_ACCESS_WRITE, or
   OPEN4_SHARE_ACCESS_BOTH is set.  If the client has a read delegation
   on a file, and requests a write delegation, then the client is
   requesting atomic upgrade of its read delegation to a write
   delegation.  If the client has a write delegation on a file, and
   requests a read delegation, then the client is requesting atomic
   downgrade to a read delegation.  A server MAY support atomic upgrade
   or downgrade.  If it does, then the returned delegation_type of
   OPEN_DELEGATE_READ or OPEN_DELEGATE_WRITE that is different than the
   delegation type the client currently has, indicates successful
   upgrade or downgrade.  If it does not support atomic delegation
   upgrade or downgrade, then od_whynone will be WND_NOT_SUPP_UPGRADE or
   WND_NOT_SUPP_DOWNGRADE.

   OPEN4_SHARE_ACCESS_WANT_NO_DELEG means the client wants no
   delegation.

   OPEN4_SHARE_ACCESS_WANT_CANCEL means the client wants no delegation
   and wants to cancel any previously registered "want" for a
   delegation.

   The client may set one or both of
   OPEN4_SHARE_ACCESS_WANT_SIGNAL_DELEG_WHEN_RESRC_AVAIL and
   OPEN4_SHARE_ACCESS_WANT_PUSH_DELEG_WHEN_UNCONTENDED.  However, they
   will have no effect unless one of following are set:



Shepler, et al.         Expires February 2, 2007              [Page 324]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   o  OPEN4_SHARE_ACCESS_WANT_READ_DELEG

   o  OPEN4_SHARE_ACCESS_WANT_WRITE_DELEG

   o  OPEN4_SHARE_ACCESS_WANT_ANY_DELEG

   If the client specifies
   OPEN4_SHARE_ACCESS_WANT_SIGNAL_DELEG_WHEN_RESRC_AVAIL, then it wishes
   to register a "want" for a delegation, in the event the OPEN results
   do not include a delegation.  If so and the server denies the
   delegation due to insufficient resources, the server MAY later inform
   the client, via the CB_RECALLABLE_OBJ_AVAIL operation, that the
   resource limitation condition has eased.  The server will tell the
   client that it intends to send a future CB_RECALLABLE_OBJ_AVAIL
   operation by setting delegation_type in the results to
   OPEN_DELEGATE_NONE_EXT, ond_why to WND_RESOURCE, and
   ond_server_will_signal_avail set to TRUE.  If
   ond_server_will_signal_avail is set to TRUE, the server MUST later
   send a CB_RECALLABLE_OBJ_AVAIL operation.

   If the client specifies
   OPEN4_SHARE_ACCESS_WANT_SIGNAL_DELEG_WHEN_UNCONTENDED, then it wishes
   to register a "want" for a delegation, in the event the OPEN results
   do not include a delegation.  If so and the server denies the
   delegation due to insufficient resources, the server MAY later inform
   the client, via the CB_PUSH_DELEG operation operation, that the
   resource limitation condition has eased.  The server will tell the
   client that it intends to send a future CB_PUSH_DELEG operation by
   setting delegation_type in the results to OPEN_DELEGATE_NONE_EXT,
   ond_why to WND_CONTENTION, and ond_server_will_push_deleg to TRUE.
   If ond_server_will_push_deleg is TRUE, the server MUST later send a
   CB_RECALLABLE_OBJ_AVAIL operation.

   If the client has previously registered a want for a delegation on a
   file, and then sends a request to register a want for a delegation on
   the same file, the server MUST return a new error:
   NFS4ERR_DELEG_ALREADY_WANTED.  If the client wishes to register a
   different type of delegation want for the same file, it MUST cancel
   the existing delegation WANT.

16.16.5.  IMPLEMENTATION

   The OPEN operation contains support for EXCLUSIVE create.  The
   mechanism is similar to the support in NFS version 3 [18].  As in NFS
   version 3, this mechanism provides reliable exclusive creation.
   Exclusive create is invoked when the how parameter is EXCLUSIVE.  In
   this case, the client provides a verifier that can reasonably be
   expected to be unique.  A combination of a client identifier, perhaps



Shepler, et al.         Expires February 2, 2007              [Page 325]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   the client network address, and a unique number generated by the
   client, perhaps the RPC transaction identifier, may be appropriate.
   [[Comment.17: Isn't this mechanism redundant if the server supports a
   stable session replay cache?]]

   If the object does not exist, the server creates the object and
   stores the verifier in stable storage.  For file systems that do not
   provide a mechanism for the storage of arbitrary file attributes, the
   server may use one or more elements of the object meta-data to store
   the verifier.  The verifier must be stored in stable storage to
   prevent erroneous failure on retransmission of the request.  It is
   assumed that an exclusive create is being performed because exclusive
   semantics are critical to the application.  Because of the expected
   usage, exclusive CREATE does not rely solely on the normally volatile
   duplicate request cache for storage of the verifier.  The duplicate
   request cache in volatile storage does not survive a crash and may
   actually flush on a long network partition, opening failure windows.
   In the UNIX local file system environment, the expected storage
   location for the verifier on creation is the meta-data (time stamps)
   of the object.  For this reason, an exclusive object create may not
   include initial attributes because the server would have nowhere to
   store the verifier.

   If the server can not support these exclusive create semantics,
   possibly because of the requirement to commit the verifier to stable
   storage, it should fail the OPEN request with the error,
   NFS4ERR_NOTSUPP.

   During an exclusive CREATE request, if the object already exists, the
   server reconstructs the object's verifier and compares it with the
   verifier in the request.  If they match, the server treats the
   request as a success.  The request is presumed to be a duplicate of
   an earlier, successful request for which the reply was lost and that
   the server duplicate request cache mechanism did not detect.  If the
   verifiers do not match, the request is rejected with the status,
   NFS4ERR_EXIST.

   Once the client has performed a successful exclusive create, it must
   issue a SETATTR to set the correct object attributes.  Until it does
   so, it should not rely upon any of the object attributes, since the
   server implementation may need to overload object meta-data to store
   the verifier.  The subsequent SETATTR must not occur in the same
   COMPOUND request as the OPEN.  This separation will guarantee that
   the exclusive create mechanism will continue to function properly in
   the face of retransmission of the request.

   Use of the GUARDED attribute does not provide exactly-once semantics.
   In particular, if a reply is lost and the server does not detect the



Shepler, et al.         Expires February 2, 2007              [Page 326]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   retransmission of the request, the operation can fail with
   NFS4ERR_EXIST, even though the create was performed successfully.
   The client would use this behavior in the case that the application
   has not requested an exclusive create but has asked to have the file
   truncated when the file is opened.  In the case of the client timing
   out and retransmitting the create request, the client can use GUARDED
   to prevent against a sequence like: create, write, create
   (retransmitted) from occurring.

   For SHARE reservations, the client must specify a value for
   share_access that is one of READ, WRITE, or BOTH.  For share_deny,
   the client must specify one of NONE, READ, WRITE, or BOTH.  If the
   client fails to do this, the server must return NFS4ERR_INVAL.

   Based on the share_access value (READ, WRITE, or BOTH) the client
   should check that the requester has the proper access rights to
   perform the specified operation.  This would generally be the results
   of applying the ACL access rules to the file for the current
   requester.  However, just as with the ACCESS operation, the client
   should not attempt to second-guess the server's decisions, as access
   rights may change and may be subject to server administrative
   controls outside the ACL framework.  If the requester is not
   authorized to READ or WRITE (depending on the share_access value),
   the server must return NFS4ERR_ACCESS.  Note that since the NFS
   version 4 protocol does not impose any requirement that READs and
   WRITEs issued for an open file have the same credentials as the OPEN
   itself, the server still must do appropriate access checking on the
   READs and WRITEs themselves.

   If the component provided to OPEN is a symbolic link, the error
   NFS4ERR_SYMLINK will be returned to the client.  If the current
   filehandle is not a directory, the error NFS4ERR_NOTDIR will be
   returned.

16.16.5.1.  WARNING TO CLIENT IMPLEMENTORS

   OPEN resembles LOOKUP in that it generates a filehandle for the
   client to use.  Unlike LOOKUP though, OPEN creates server state on
   the filehandle.  In normal circumstances, the client can only release
   this state with a CLOSE operation.  CLOSE uses the current filehandle
   to determine which file to close.  Therefore the client MUST follow
   every OPEN operation with a GETFH operation in the same COMPOUND
   procedure.  This will supply the client with the filehandle such that
   CLOSE can be used appropriately.

   Simply waiting for the lease on the file to expire is insufficient
   because the server may maintain the state indefinitely as long as
   another client does not attempt to make a conflicting access to the



Shepler, et al.         Expires February 2, 2007              [Page 327]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   same file.

16.17.  Operation 19: OPENATTR - Open Named Attribute Directory

16.17.1.  SYNOPSIS

   (cfh) createdir -> (cfh)

16.17.2.  ARGUMENTS

   /*
    * OPENATTR: open named attributes directory
    */
   struct OPENATTR4args {
           /* CURRENT_FH: object */
           bool    createdir;
   };


16.17.3.  RESULTS

   struct OPENATTR4res {
           /* CURRENT_FH: named attr directory */
           nfsstat4        status;
   };


16.17.4.  DESCRIPTION

   The OPENATTR operation is used to obtain the filehandle of the named
   attribute directory associated with the current filehandle.  The
   result of the OPENATTR will be a filehandle to an object of type
   NF4ATTRDIR.  From this filehandle, READDIR and LOOKUP operations can
   be used to obtain filehandles for the various named attributes
   associated with the original file system object.  Filehandles
   returned within the named attribute directory will have a type of
   NF4NAMEDATTR.

   The createdir argument allows the client to signify if a named
   attribute directory should be created as a result of the OPENATTR
   operation.  Some clients may use the OPENATTR operation with a value
   of FALSE for createdir to determine if any named attributes exist for
   the object.  If none exist, then NFS4ERR_NOENT will be returned.  If
   createdir has a value of TRUE and no named attribute directory
   exists, one is created.  The creation of a named attribute directory
   assumes that the server has implemented named attribute support in
   this fashion and is not required to do so by this definition.




Shepler, et al.         Expires February 2, 2007              [Page 328]


Internet-Draft            NFSv4 Minor Version 1              August 2006


16.17.5.  IMPLEMENTATION

   If the server does not support named attributes for the current
   filehandle, an error of NFS4ERR_NOTSUPP will be returned to the
   client.

16.18.  Operation 21: OPEN_DOWNGRADE - Reduce Open File Access

16.18.1.  SYNOPSIS

   (cfh), stateid, seqid, access, deny -> stateid

16.18.2.  ARGUMENTS

   /*
    * OPEN_DOWNGRADE: downgrade the access/deny for a file
    */
   struct OPEN_DOWNGRADE4args {
           /* CURRENT_FH: opened file */
           stateid4        open_stateid;
           seqid4          seqid;
           uint32_t        share_access;
           uint32_t        share_deny;
   };


16.18.3.  RESULTS

   struct OPEN_DOWNGRADE4resok {
           stateid4        open_stateid;
   };

   union OPEN_DOWNGRADE4res switch(nfsstat4 status) {
    case NFS4_OK:
           OPEN_DOWNGRADE4resok    resok4;
    default:
            void;
   };


16.18.4.  DESCRIPTION

   This operation is used to adjust the share_access and share_deny bits
   for a given open.  This is necessary when a given lockowner opens the
   same file multiple times with different share_access and share_deny
   flags.  In this situation, a close of one of the opens may change the
   appropriate share_access and share_deny flags to remove bits
   associated with opens no longer in effect.



Shepler, et al.         Expires February 2, 2007              [Page 329]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   The share_access and share_deny bits specified in this operation
   replace the current ones for the specified open file.  The
   share_access and share_deny bits specified must be exactly equal to
   the union of the share_access and share_deny bits specified for some
   subset of the OPENs in effect for current openowner on the current
   file.  If that constraint is not respected, the error NFS4ERR_INVAL
   should be returned.  Since share_access and share_deny bits are
   subsets of those already granted, it is not possible for this request
   to be denied because of conflicting share reservations.

   On success, the current filehandle retains its value.

16.19.  Operation 22: PUTFH - Set Current Filehandle

16.19.1.  SYNOPSIS

   filehandle -> (cfh)

16.19.2.  ARGUMENTS

   /*
    * PUTFH: Set current filehandle
    */
   struct PUTFH4args {
           nfs_fh4         object;
   };


16.19.3.  RESULTS

   struct PUTFH4res {
           /* CURRENT_FH: */
           nfsstat4        status;
   };


16.19.4.  DESCRIPTION

   Replaces the current filehandle with the filehandle provided as an
   argument.

   If the security mechanism used by the requester does not meet the
   requirements of the filehandle provided to this operation, the server
   MUST return NFS4ERR_WRONGSEC.







Shepler, et al.         Expires February 2, 2007              [Page 330]


Internet-Draft            NFSv4 Minor Version 1              August 2006


16.19.5.  IMPLEMENTATION

   Commonly used as the first operator in an NFS request to set the
   context for following operations.

16.20.  Operation 23: PUTPUBFH - Set Public Filehandle

16.20.1.  SYNOPSIS

   - -> (cfh)

16.20.2.  ARGUMENT

   void;

16.20.3.  RESULT

   /*
    * PUTPUBFH: Set public filehandle
    */
   struct PUTPUBFH4res {
           /* CURRENT_FH: public fh */
           nfsstat4        status;
   };


16.20.4.  DESCRIPTION

   Replaces the current filehandle with the filehandle that represents
   the public filehandle of the server's name space.  This filehandle
   may be different from the "root" filehandle which may be associated
   with some other directory on the server.

   The public filehandle represents the concepts embodied in RFC2054
   [25], RFC2055 [26], RFC2224 [32].  The intent for NFS version 4 is
   that the public filehandle (represented by the PUTPUBFH operation) be
   used as a method of providing WebNFS server compatibility with NFS
   versions 2 and 3.

   The public filehandle and the root filehandle (represented by the
   PUTROOTFH operation) should be equivalent.  If the public and root
   filehandles are not equivalent, then the public filehandle MUST be a
   descendant of the root filehandle.

16.20.5.  IMPLEMENTATION

   Used as the first operator in an NFS request to set the context for
   following operations.



Shepler, et al.         Expires February 2, 2007              [Page 331]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   With the NFS version 2 and 3 public filehandle, the client is able to
   specify whether the path name provided in the LOOKUP should be
   evaluated as either an absolute path relative to the server's root or
   relative to the public filehandle.  RFC2224 [32] contains further
   discussion of the functionality.  With NFS version 4, that type of
   specification is not directly available in the LOOKUP operation.  The
   reason for this is because the component separators needed to specify
   absolute vs. relative are not allowed in NFS version 4.  Therefore,
   the client is responsible for constructing its request such that the
   use of either PUTROOTFH or PUTPUBFH are used to signify absolute or
   relative evaluation of an NFS URL respectively.

   Note that there are warnings mentioned in RFC2224 [32] with respect
   to the use of absolute evaluation and the restrictions the server may
   place on that evaluation with respect to how much of its namespace
   has been made available.  These same warnings apply to NFS version 4.
   It is likely, therefore that because of server implementation
   details, an NFS version 3 absolute public filehandle lookup may
   behave differently than an NFS version 4 absolute resolution.

   There is a form of security negotiation as described in RFC2755 [33]
   that uses the public filehandle a method of employing SNEGO.  This
   method is not available with NFS version 4 as filehandles are not
   overloaded with special meaning and therefore do not provide the same
   framework as NFS versions 2 and 3.  Clients should therefore use the
   security negotiation mechanisms described in this RFC.

16.20.6.  ERRORS

16.21.  Operation 24: PUTROOTFH - Set Root Filehandle

16.21.1.  SYNOPSIS

   - -> (cfh)

16.21.2.  ARGUMENTS

   void;













Shepler, et al.         Expires February 2, 2007              [Page 332]


Internet-Draft            NFSv4 Minor Version 1              August 2006


16.21.3.  RESULTS

   /*
    * PUTROOTFH: Set root filehandle
    */
   struct PUTROOTFH4res {
           /* CURRENT_FH: root fh */
           nfsstat4        status;
   };


16.21.4.  DESCRIPTION

   Replaces the current filehandle with the filehandle that represents
   the root of the server's name space.  From this filehandle a LOOKUP
   operation can locate any other filehandle on the server.  This
   filehandle may be different from the "public" filehandle which may be
   associated with some other directory on the server.

16.21.5.  IMPLEMENTATION

   Commonly used as the first operator in an NFS request to set the
   context for following operations.

16.22.  Operation 25: READ - Read from File

16.22.1.  SYNOPSIS

   (cfh), stateid, offset, count -> eof, data

16.22.2.  ARGUMENTS

   /*
    * READ: Read from file
    */
   struct READ4args {
           /* CURRENT_FH: file */
           stateid4        stateid;
           offset4         offset;
           count4          count;
   };










Shepler, et al.         Expires February 2, 2007              [Page 333]


Internet-Draft            NFSv4 Minor Version 1              August 2006


16.22.3.  RESULTS

   struct READ4resok {
           bool            eof;
           opaque          data<>;
   };

   union READ4res switch (nfsstat4 status) {
    case NFS4_OK:
            READ4resok     resok4;
    default:
            void;
   };


16.22.4.  DESCRIPTION

   The READ operation reads data from the regular file identified by the
   current filehandle.

   The client provides an offset of where the READ is to start and a
   count of how many bytes are to be read.  An offset of 0 (zero) means
   to read data starting at the beginning of the file.  If offset is
   greater than or equal to the size of the file, the status, NFS4_OK,
   is returned with a data length set to 0 (zero) and eof is set to
   TRUE.  The READ is subject to access permissions checking.

   If the client specifies a count value of 0 (zero), the READ succeeds
   and returns 0 (zero) bytes of data again subject to access
   permissions checking.  The server may choose to return fewer bytes
   than specified by the client.  The client needs to check for this
   condition and handle the condition appropriately.

   The stateid value for a READ request represents a value returned from
   a previous record lock or share reservation request.  The stateid is
   used by the server to verify that the associated share reservation
   and any record locks are still valid and to update lease timeouts for
   the client.

   If the read ended at the end-of-file (formally, in a correctly formed
   READ request, if offset + count is equal to the size of the file), or
   the read request extends beyond the size of the file (if offset +
   count is greater than the size of the file), eof is returned as TRUE;
   otherwise it is FALSE.  A successful READ of an empty file will
   always return eof as TRUE.

   If the current filehandle is not a regular file, an error will be
   returned to the client.  In the case the current filehandle



Shepler, et al.         Expires February 2, 2007              [Page 334]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   represents a directory, NFS4ERR_ISDIR is return; otherwise,
   NFS4ERR_INVAL is returned.

   For a READ with a stateid value of all bits 0, the server MAY allow
   the READ to be serviced subject to mandatory file locks or the
   current share deny modes for the file.  For a READ with a stateid
   value of all bits 1, the server MAY allow READ operations to bypass
   locking checks at the server.

   On success, the current filehandle retains its value.

16.22.5.  IMPLEMENTATION

   It is possible for the server to return fewer than count bytes of
   data.  If the server returns less than the count requested and eof is
   set to FALSE, the client should issue another READ to get the
   remaining data.  A server may return less data than requested under
   several circumstances.  The file may have been truncated by another
   client or perhaps on the server itself, changing the file size from
   what the requesting client believes to be the case.  This would
   reduce the actual amount of data available to the client.  It is
   possible that the server may back off the transfer size and reduce
   the read request return.  Server resource exhaustion may also occur
   necessitating a smaller read return.

   If mandatory file locking is on for the file, and if the region
   corresponding to the data to be read from file is write locked by an
   owner not associated the stateid, the server will return the
   NFS4ERR_LOCKED error.  The client should try to get the appropriate
   read record lock via the LOCK operation before re-attempting the
   READ.  When the READ completes, the client should release the record
   lock via LOCKU.

16.23.  Operation 26: READDIR - Read Directory

16.23.1.  SYNOPSIS

   (cfh), cookie, cookieverf, dircount, maxcount, attr_request ->
   cookieverf { cookie, name, attrs }












Shepler, et al.         Expires February 2, 2007              [Page 335]


Internet-Draft            NFSv4 Minor Version 1              August 2006


16.23.2.  ARGUMENTS

   /*
    * READDIR: Read directory
    */
   struct READDIR4args {
           /* CURRENT_FH: directory */
           nfs_cookie4     cookie;
           verifier4       cookieverf;
           count4          dircount;
           count4          maxcount;
           bitmap4         attr_request;
   };


16.23.3.  RESULTS

   struct entry4 {
           nfs_cookie4     cookie;
           component4      name;
           fattr4          attrs;
           entry4          *nextentry;
   };

   struct dirlist4 {
           entry4          *entries;
           bool            eof;
   };

   struct READDIR4resok {
           verifier4       cookieverf;
           dirlist4        reply;
   };


   union READDIR4res switch (nfsstat4 status) {
    case NFS4_OK:
            READDIR4resok  resok4;
    default:
            void;
   };










Shepler, et al.         Expires February 2, 2007              [Page 336]


Internet-Draft            NFSv4 Minor Version 1              August 2006


16.23.4.  DESCRIPTION

   The READDIR operation retrieves a variable number of entries from a
   file system directory and returns client requested attributes for
   each entry along with information to allow the client to request
   additional directory entries in a subsequent READDIR.

   The arguments contain a cookie value that represents where the
   READDIR should start within the directory.  A value of 0 (zero) for
   the cookie is used to start reading at the beginning of the
   directory.  For subsequent READDIR requests, the client specifies a
   cookie value that is provided by the server on a previous READDIR
   request.

   The cookieverf value should be set to 0 (zero) when the cookie value
   is 0 (zero) (first directory read).  On subsequent requests, it
   should be a cookieverf as returned by the server.  The cookieverf
   must match that returned by the READDIR in which the cookie was
   acquired.  If the server determines that the cookieverf is no longer
   valid for the directory, the error NFS4ERR_NOT_SAME must be returned.

   The dircount portion of the argument is a hint of the maximum number
   of bytes of directory information that should be returned.  This
   value represents the length of the names of the directory entries and
   the cookie value for these entries.  This length represents the XDR
   encoding of the data (names and cookies) and not the length in the
   native format of the server.

   The maxcount value of the argument is the maximum number of bytes for
   the result.  This maximum size represents all of the data being
   returned within the READDIR4resok structure and includes the XDR
   overhead.  The server may return less data.  If the server is unable
   to return a single directory entry within the maxcount limit, the
   error NFS4ERR_TOOSMALL will be returned to the client.

   Finally, attr_request represents the list of attributes to be
   returned for each directory entry supplied by the server.

   On successful return, the server's response will provide a list of
   directory entries.  Each of these entries contains the name of the
   directory entry, a cookie value for that entry, and the associated
   attributes as requested.  The "eof" flag has a value of TRUE if there
   are no more entries in the directory.

   The cookie value is only meaningful to the server and is used as a
   "bookmark" for the directory entry.  As mentioned, this cookie is
   used by the client for subsequent READDIR operations so that it may
   continue reading a directory.  The cookie is similar in concept to a



Shepler, et al.         Expires February 2, 2007              [Page 337]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   READ offset but should not be interpreted as such by the client.
   Ideally, the cookie value should not change if the directory is
   modified since the client may be caching these values.

   In some cases, the server may encounter an error while obtaining the
   attributes for a directory entry.  Instead of returning an error for
   the entire READDIR operation, the server can instead return the
   attribute 'fattr4_rdattr_error'.  With this, the server is able to
   communicate the failure to the client and not fail the entire
   operation in the instance of what might be a transient failure.
   Obviously, the client must request the fattr4_rdattr_error attribute
   for this method to work properly.  If the client does not request the
   attribute, the server has no choice but to return failure for the
   entire READDIR operation.

   For some file system environments, the directory entries "." and ".."
   have special meaning and in other environments, they may not.  If the
   server supports these special entries within a directory, they should
   not be returned to the client as part of the READDIR response.  To
   enable some client environments, the cookie values of 0, 1, and 2 are
   to be considered reserved.  Note that the UNIX client will use these
   values when combining the server's response and local representations
   to enable a fully formed UNIX directory presentation to the
   application.

   For READDIR arguments, cookie values of 1 and 2 should not be used
   and for READDIR results cookie values of 0, 1, and 2 should not be
   returned.

   On success, the current filehandle retains its value.

16.23.5.  IMPLEMENTATION

   The server's file system directory representations can differ
   greatly.  A client's programming interfaces may also be bound to the
   local operating environment in a way that does not translate well
   into the NFS protocol.  Therefore the use of the dircount and
   maxcount fields are provided to allow the client the ability to
   provide guidelines to the server.  If the client is aggressive about
   attribute collection during a READDIR, the server has an idea of how
   to limit the encoded response.  The dircount field provides a hint on
   the number of entries based solely on the names of the directory
   entries.  Since it is a hint, it may be possible that a dircount
   value is zero.  In this case, the server is free to ignore the
   dircount value and return directory information based on the
   specified maxcount value.

   The cookieverf may be used by the server to help manage cookie values



Shepler, et al.         Expires February 2, 2007              [Page 338]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   that may become stale.  It should be a rare occurrence that a server
   is unable to continue properly reading a directory with the provided
   cookie/cookieverf pair.  The server should make every effort to avoid
   this condition since the application at the client may not be able to
   properly handle this type of failure.

   The use of the cookieverf will also protect the client from using
   READDIR cookie values that may be stale.  For example, if the file
   system has been migrated, the server may or may not be able to use
   the same cookie values to service READDIR as the previous server
   used.  With the client providing the cookieverf, the server is able
   to provide the appropriate response to the client.  This prevents the
   case where the server may accept a cookie value but the underlying
   directory has changed and the response is invalid from the client's
   context of its previous READDIR.

   Since some servers will not be returning "." and ".." entries as has
   been done with previous versions of the NFS protocol, the client that
   requires these entries be present in READDIR responses must fabricate
   them.

16.24.  Operation 27: READLINK - Read Symbolic Link

16.24.1.  SYNOPSIS

   (cfh) -> linktext

16.24.2.  ARGUMENTS

   /* CURRENT_FH: symlink */
   void;

16.24.3.  RESULTS

   /*
    * READLINK: Read symbolic link
    */
   struct READLINK4resok {
           linktext4       link;
   };

   union READLINK4res switch (nfsstat4 status) {
    case NFS4_OK:
            READLINK4resok resok4;
    default:
            void;
   };




Shepler, et al.         Expires February 2, 2007              [Page 339]


Internet-Draft            NFSv4 Minor Version 1              August 2006


16.24.4.  DESCRIPTION

   READLINK reads the data associated with a symbolic link.  The data is
   a UTF-8 string that is opaque to the server.  That is, whether
   created by an NFS client or created locally on the server, the data
   in a symbolic link is not interpreted when created, but is simply
   stored.

   On success, the current filehandle retains its value.

16.24.5.  IMPLEMENTATION

   A symbolic link is nominally a pointer to another file.  The data is
   not necessarily interpreted by the server, just stored in the file.
   It is possible for a client implementation to store a path name that
   is not meaningful to the server operating system in a symbolic link.
   A READLINK operation returns the data to the client for
   interpretation.  If different implementations want to share access to
   symbolic links, then they must agree on the interpretation of the
   data in the symbolic link.

   The READLINK operation is only allowed on objects of type NF4LNK.
   The server should return the error, NFS4ERR_INVAL, if the object is
   not of type, NF4LNK.

16.25.  Operation 28: REMOVE - Remove File System Object

16.25.1.  SYNOPSIS

   (cfh), filename -> change_info

16.25.2.  ARGUMENTS

   /*
    * REMOVE: Remove filesystem object
    */
   struct REMOVE4args {
           /* CURRENT_FH: directory */
           component4      target;
   };











Shepler, et al.         Expires February 2, 2007              [Page 340]


Internet-Draft            NFSv4 Minor Version 1              August 2006


16.25.3.  RESULTS

   struct REMOVE4resok {
           change_info4    cinfo;
   };

   union REMOVE4res switch (nfsstat4 status) {
    case NFS4_OK:
            REMOVE4resok   resok4;
    default:
            void;
   };


16.25.4.  DESCRIPTION

   The REMOVE operation removes (deletes) a directory entry named by
   filename from the directory corresponding to the current filehandle.
   If the entry in the directory was the last reference to the
   corresponding file system object, the object may be destroyed.

   For the directory where the filename was removed, the server returns
   change_info4 information in cinfo.  With the atomic field of the
   change_info4 struct, the server will indicate if the before and after
   change attributes were obtained atomically with respect to the
   removal.

   If the target has a length of 0 (zero), or if target does not obey
   the UTF-8 definition, the error NFS4ERR_INVAL will be returned.

   On success, the current filehandle retains its value.

16.25.5.  IMPLEMENTATION

   NFS versions 2 and 3 required a different operator RMDIR for
   directory removal and REMOVE for non-directory removal.  This allowed
   clients to skip checking the file type when being passed a non-
   directory delete system call (e.g. unlink() in POSIX) to remove a
   directory, as well as the converse (e.g. a rmdir() on a non-
   directory) because they knew the server would check the file type.
   NFS version 4 REMOVE can be used to delete any directory entry
   independent of its file type.  The implementor of an NFS version 4
   client's entry points from the unlink() and rmdir() system calls
   should first check the file type against the types the system call is
   allowed to remove before issuing a REMOVE.  Alternatively, the
   implementor can produce a COMPOUND call that includes a LOOKUP/VERIFY
   sequence to verify the file type before a REMOVE operation in the
   same COMPOUND call.



Shepler, et al.         Expires February 2, 2007              [Page 341]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   The concept of last reference is server specific.  However, if the
   numlinks field in the previous attributes of the object had the value
   1, the client should not rely on referring to the object via a
   filehandle.  Likewise, the client should not rely on the resources
   (disk space, directory entry, and so on) formerly associated with the
   object becoming immediately available.  Thus, if a client needs to be
   able to continue to access a file after using REMOVE to remove it,
   the client should take steps to make sure that the file will still be
   accessible.  The usual mechanism used is to RENAME the file from its
   old name to a new hidden name.

   If the server finds that the file is still open when the REMOVE
   arrives: .in 7 .IP o The server SHOULD NOT delete the file's
   directory entry if the file was opened with OPEN4_SHARE_DENY_WRITE or
   OPEN4_SHARE_DENY_BOTH. .IP o If the file was not opened with
   OPEN4_SHARE_DENY_WRITE or OPEN4_SHARE_DENY_BOTH, the server SHOULD
   delete the file's directory entry.  However, until last CLOSE of the
   file, the server MAY continue to allow access to the file via its
   filehandle. .in 5

16.26.  Operation 29: RENAME - Rename Directory Entry

16.26.1.  SYNOPSIS

   (sfh), oldname, (cfh), newname -> source_change_info,
   target_change_info

16.26.2.  ARGUMENTS

   /*
    * RENAME: Rename directory entry
    */
   struct RENAME4args {
           /* SAVED_FH: source directory */
           component4      oldname;
           /* CURRENT_FH: target directory */
           component4      newname;
   };













Shepler, et al.         Expires February 2, 2007              [Page 342]


Internet-Draft            NFSv4 Minor Version 1              August 2006


16.26.3.  RESULTS

   struct RENAME4resok {
           change_info4    source_cinfo;
           change_info4    target_cinfo;
   };

   union RENAME4res switch (nfsstat4 status) {
    case NFS4_OK:
           RENAME4resok    resok4;
    default:
           void;
   };


16.26.4.  DESCRIPTION

   The RENAME operation renames the object identified by oldname in the
   source directory corresponding to the saved filehandle, as set by the
   SAVEFH operation, to newname in the target directory corresponding to
   the current filehandle.  The operation is required to be atomic to
   the client.  Source and target directories must reside on the same
   file system on the server.  On success, the current filehandle will
   continue to be the target directory.

   If the target directory already contains an entry with the name,
   newname, the source object must be compatible with the target: either
   both are non-directories or both are directories and the target must
   be empty.  If compatible, the existing target is removed before the
   rename occurs (See the IMPLEMENTATION subsection of the section
   "Operation 28: REMOVE - Remove File System Object" for client and
   server actions whenever a target is removed).  If they are not
   compatible or if the target is a directory but not empty, the server
   will return the error, NFS4ERR_EXIST.

   If oldname and newname both refer to the same file (they might be
   hard links of each other), then RENAME should perform no action and
   return success.

   For both directories involved in the RENAME, the server returns
   change_info4 information.  With the atomic field of the change_info4
   struct, the server will indicate if the before and after change
   attributes were obtained atomically with respect to the rename.

   If the oldname refers to a named attribute and the saved and current
   filehandles refer to different file system objects, the server will
   return NFS4ERR_XDEV just as if the saved and current filehandles
   represented directories on different file systems.



Shepler, et al.         Expires February 2, 2007              [Page 343]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   If the oldname or newname has a length of 0 (zero), or if oldname or
   newname does not obey the UTF-8 definition, the error NFS4ERR_INVAL
   will be returned.

16.26.5.  IMPLEMENTATION

   The RENAME operation must be atomic to the client.  The statement
   "source and target directories must reside on the same file system on
   the server" means that the fsid fields in the attributes for the
   directories are the same.  If they reside on different file systems,
   the error, NFS4ERR_XDEV, is returned.

   Based on the value of the fh_expire_type attribute for the object,
   the filehandle may or may not expire on a RENAME.  However, server
   implementors are strongly encouraged to attempt to keep filehandles
   from expiring in this fashion.

   On some servers, the file names "." and ".." are illegal as either
   oldname or newname, and will result in the error NFS4ERR_BADNAME.  In
   addition, on many servers the case of oldname or newname being an
   alias for the source directory will be checked for.  Such servers
   will return the error NFS4ERR_INVAL in these cases.

   If either of the source or target filehandles are not directories,
   the server will return NFS4ERR_NOTDIR.

16.27.  Operation 31: RESTOREFH - Restore Saved Filehandle

16.27.1.  SYNOPSIS

   (sfh) -> (cfh)

16.27.2.  ARGUMENTS

   /* SAVED_FH: */
   void;

16.27.3.  RESULTS

   /*
    * RESTOREFH: Restore saved filehandle
    */

   struct RESTOREFH4res {
           /* CURRENT_FH: value of saved fh */
           nfsstat4        status;
   };




Shepler, et al.         Expires February 2, 2007              [Page 344]


Internet-Draft            NFSv4 Minor Version 1              August 2006


16.27.4.  DESCRIPTION

   Set the current filehandle to the value in the saved filehandle.  If
   there is no saved filehandle then return the error NFS4ERR_RESTOREFH.

16.27.5.  IMPLEMENTATION

   Operations like OPEN and LOOKUP use the current filehandle to
   represent a directory and replace it with a new filehandle.  Assuming
   the previous filehandle was saved with a SAVEFH operator, the
   previous filehandle can be restored as the current filehandle.  This
   is commonly used to obtain post-operation attributes for the
   directory, e.g.

         PUTFH (directory filehandle)
         SAVEFH
         GETATTR attrbits     (pre-op dir attrs)
         CREATE optbits "foo" attrs
         GETATTR attrbits     (file attributes)
         RESTOREFH
         GETATTR attrbits     (post-op dir attrs)

16.27.6.  ERRORS

16.28.  Operation 32: SAVEFH - Save Current Filehandle

16.28.1.  SYNOPSIS

   (cfh) -> (sfh)

16.28.2.  ARGUMENTS

   /* CURRENT_FH: */
   void;

16.28.3.  RESULTS

   /*
    * SAVEFH: Save current filehandle
    */
   struct SAVEFH4res {
           /* SAVED_FH: value of current fh */
           nfsstat4        status;
   };







Shepler, et al.         Expires February 2, 2007              [Page 345]


Internet-Draft            NFSv4 Minor Version 1              August 2006


16.28.4.  DESCRIPTION

   Save the current filehandle.  If a previous filehandle was saved then
   it is no longer accessible.  The saved filehandle can be restored as
   the current filehandle with the RESTOREFH operator.

   On success, the current filehandle retains its value.

16.28.5.  IMPLEMENTATION

16.29.  Operation 33: SECINFO - Obtain Available Security

16.29.1.  SYNOPSIS

   (cfh), name -> { secinfo }

16.29.2.  ARGUMENTS

   /*
    * SECINFO: Obtain Available Security Mechanisms
    */
   struct SECINFO4args {
           /* CURRENT_FH: directory */
           component4      name;
   };


























Shepler, et al.         Expires February 2, 2007              [Page 346]


Internet-Draft            NFSv4 Minor Version 1              August 2006


16.29.3.  RESULTS

   /*
    * From RFC 2203
    */
   enum rpc_gss_svc_t {
           RPC_GSS_SVC_NONE        = 1,
           RPC_GSS_SVC_INTEGRITY   = 2,
           RPC_GSS_SVC_PRIVACY     = 3
   };

   struct rpcsec_gss_info {
           sec_oid4        oid;
           qop4            qop;
           rpc_gss_svc_t   service;
   };

   /* RPCSEC_GSS has a value of '6' - See RFC 2203 */
   union secinfo4 switch (uint32_t flavor) {
    case RPCSEC_GSS:
            rpcsec_gss_info        flavor_info;
    default:
            void;
   };

   typedef secinfo4 SECINFO4resok<>;

   union SECINFO4res switch (nfsstat4 status) {
    case NFS4_OK:
            SECINFO4resok resok4;
    default:
            void;
   };


16.29.4.  DESCRIPTION

   The SECINFO operation is used by the client to obtain a list of valid
   RPC authentication flavors for a specific directory filehandle, file
   name pair.  SECINFO should apply the same access methodology used for
   LOOKUP when evaluating the name.  Therefore, if the requester does
   not have the appropriate access to LOOKUP the name then SECINFO must
   behave the same way and return NFS4ERR_ACCESS.

   The result will contain an array which represents the security
   mechanisms available, with an order corresponding to the server's
   preferences, the most preferred being first in the array.  The client
   is free to pick whatever security mechanism it both desires and



Shepler, et al.         Expires February 2, 2007              [Page 347]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   supports, or to pick in the server's preference order the first one
   it supports.  The array entries are represented by the secinfo4
   structure.  The field 'flavor' will contain a value of AUTH_NONE,
   AUTH_SYS (as defined in RFC1831 [4]), or RPCSEC_GSS (as defined in
   RFC2203 [5]).  The field flavor can also any other security flavor
   registered with IANA.

   For the flavors AUTH_NONE and AUTH_SYS, no additional security
   information is returned.  The same is true of many (if not most)
   other security flavors, including AUTH_DH.  For a return value of
   RPCSEC_GSS, a security triple is returned that contains the mechanism
   object id (as defined in RFC2743 [8]), the quality of protection (as
   defined in RFC2743 [8]) and the service type (as defined in RFC2203
   [5]).  It is possible for SECINFO to return multiple entries with
   flavor equal to RPCSEC_GSS with different security triple values.

   On success, the current filehandle retains its value.

   If the name has a length of 0 (zero), or if name does not obey the
   UTF-8 definition, the error NFS4ERR_INVAL will be returned.

16.29.5.  IMPLEMENTATION

   The SECINFO operation is expected to be used by the NFS client when
   the error value of NFS4ERR_WRONGSEC is returned from another NFS
   operation.  This signifies to the client that the server's security
   policy is different from what the client is currently using.  At this
   point, the client is expected to obtain a list of possible security
   flavors and choose what best suits its policies.

   As mentioned, the server's security policies will determine when a
   client request receives NFS4ERR_WRONGSEC.  The operations which may
   receive this error are: LINK, LOOKUP, LOOKUPP, OPEN, PUTFH, PUTPUBFH,
   PUTROOTFH, RESTOREFH, RENAME, and indirectly READDIR.  LINK and
   RENAME will only receive this error if the security used for the
   operation is inappropriate for saved filehandle.  With the exception
   of READDIR, these operations represent the point at which the client
   can instantiate a filehandle into the "current filehandle" at the
   server.  The filehandle is either provided by the client (PUTFH,
   PUTPUBFH, PUTROOTFH) or generated as a result of a name to filehandle
   translation (LOOKUP and OPEN).  RESTOREFH is different because the
   filehandle is a result of a previous SAVEFH.  Even though the
   filehandle, for RESTOREFH, might have previously passed the server's
   inspection for a security match, the server will check it again on
   RESTOREFH to ensure that the security policy has not changed.

   If the client wants to resolve an error return of NFS4ERR_WRONGSEC,
   the following will occur:



Shepler, et al.         Expires February 2, 2007              [Page 348]


Internet-Draft            NFSv4 Minor Version 1              August 2006


   o  For LOOKUP and OPEN, the client will use SECINFO with the same
      current filehandle and name as provided in the original LOOKUP or
      OPEN to enumerate the available security triples.

   o  For LINK, PUTFH, PUTROOTFH, PUTPUBFH, RENAME, and RESTOREFH, the
      client will use SECINFO_NO_NAME { style = current_fh }.  The
      client will prefix the SECINFO_NO_NAME operation with the
      appropriate PUTFH, PUTPUBFH, or PUTROOTFH operation that provides
      the filehandle originally provided by the PUTFH, PUTPUBFH,
      PUTROOTFH, or RESTOREFH, or for the failed LINK or RENAME, the
      SAVEFH.

   o  NOTE: In NFSv4.0, the client was required to use SECINFO, and had
      to reconstruct the parent of the original file handle, and the
      component name of the original filehandle.

   o  For LOOKUPP, the client will use SECINFO_NO_NAME { style = parent
      } and provide the filehandle with equals the filehandle originally
      provided to LOOKUPP.

   The READDIR operation will not directly return the NFS4ERR_WRONGSEC
   error.  However, if the READDIR request included a request for
   attrib