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NFSv4                                                         S. Shepler
Internet-Draft                                                    Editor
Intended status: Standards Track                           June 20, 2006
Expires: December 22, 2006


                         NFSv4 Minor Version 1
                 draft-ietf-nfsv4-minorversion1-03.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.

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   http://www.ietf.org/shadow.html.

   This Internet-Draft will expire on December 22, 2006.

Copyright Notice

   Copyright (C) The Internet Society (2006).

Abstract

   This Internet-Draft describes the NFSv4 minor version 1 protocol
   extensions.  These most significant of these extensions are commonly
   called: Sessions, Directory Delegations, and parallel NFS or pNFS

Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this



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   document are to be interpreted as described in RFC 2119 [1].


Table of Contents

   1.  Protocol Data Types . . . . . . . . . . . . . . . . . . . . .   9
     1.1.   Basic Data Types . . . . . . . . . . . . . . . . . . . .   9
     1.2.   Structured Data Types  . . . . . . . . . . . . . . . . .  10
   2.  Filehandles . . . . . . . . . . . . . . . . . . . . . . . . .  19
     2.1.   Obtaining the First Filehandle . . . . . . . . . . . . .  19
       2.1.1.  Root Filehandle . . . . . . . . . . . . . . . . . . .  20
       2.1.2.  Public Filehandle . . . . . . . . . . . . . . . . . .  20
     2.2.   Filehandle Types . . . . . . . . . . . . . . . . . . . .  20
       2.2.1.  General Properties of a Filehandle  . . . . . . . . .  21
       2.2.2.  Persistent Filehandle . . . . . . . . . . . . . . . .  21
       2.2.3.  Volatile Filehandle . . . . . . . . . . . . . . . . .  22
     2.3.   One Method of Constructing a Volatile Filehandle . . . .  23
     2.4.   Client Recovery from Filehandle Expiration . . . . . . .  24
   3.  File Attributes . . . . . . . . . . . . . . . . . . . . . . .  25
     3.1.   Mandatory Attributes . . . . . . . . . . . . . . . . . .  26
     3.2.   Recommended Attributes . . . . . . . . . . . . . . . . .  26
     3.3.   Named Attributes . . . . . . . . . . . . . . . . . . . .  27
     3.4.   Classification of Attributes . . . . . . . . . . . . . .  27
     3.5.   Mandatory Attributes - Definitions . . . . . . . . . . .  28
     3.6.   Recommended Attributes - Definitions . . . . . . . . . .  30
     3.7.   Time Access  . . . . . . . . . . . . . . . . . . . . . .  38
     3.8.   Interpreting owner and owner_group . . . . . . . . . . .  38
     3.9.   Character Case Attributes  . . . . . . . . . . . . . . .  40
     3.10.  Quota Attributes . . . . . . . . . . . . . . . . . . . .  41
     3.11.  mounted_on_fileid  . . . . . . . . . . . . . . . . . . .  41
     3.12.  send_impl_id and recv_impl_id  . . . . . . . . . . . . .  42
     3.13.  fs_layouttype  . . . . . . . . . . . . . . . . . . . . .  43
     3.14.  layouttype . . . . . . . . . . . . . . . . . . . . . . .  43
     3.15.  layouthint . . . . . . . . . . . . . . . . . . . . . . .  43
     3.16.  Access Control Lists . . . . . . . . . . . . . . . . . .  44
       3.16.1. ACE type  . . . . . . . . . . . . . . . . . . . . . .  46
       3.16.2. ACE Access Mask . . . . . . . . . . . . . . . . . . .  47
       3.16.3. ACE flag  . . . . . . . . . . . . . . . . . . . . . .  52
       3.16.4. ACE who . . . . . . . . . . . . . . . . . . . . . . .  54
       3.16.5. Mode Attribute  . . . . . . . . . . . . . . . . . . .  55
       3.16.6. Interaction Between Mode and ACL Attributes . . . . .  56
   4.  Single-server Name Space  . . . . . . . . . . . . . . . . . .  69
     4.1.   Server Exports . . . . . . . . . . . . . . . . . . . . .  69
     4.2.   Browsing Exports . . . . . . . . . . . . . . . . . . . .  69
     4.3.   Server Pseudo Filesystem . . . . . . . . . . . . . . . .  70
     4.4.   Multiple Roots . . . . . . . . . . . . . . . . . . . . .  71
     4.5.   Filehandle Volatility  . . . . . . . . . . . . . . . . .  71
     4.6.   Exported Root  . . . . . . . . . . . . . . . . . . . . .  71



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     4.7.   Mount Point Crossing . . . . . . . . . . . . . . . . . .  71
     4.8.   Security Policy and Name Space Presentation  . . . . . .  72
   5.  File Locking and Share Reservations . . . . . . . . . . . . .  73
     5.1.   Locking  . . . . . . . . . . . . . . . . . . . . . . . .  73
       5.1.1.  Client ID . . . . . . . . . . . . . . . . . . . . . .  74
       5.1.2.  Server Release of Clientid  . . . . . . . . . . . . .  76
       5.1.3.  lock_owner and stateid Definition . . . . . . . . . .  77
       5.1.4.  Use of the stateid and Locking  . . . . . . . . . . .  79
       5.1.5.  Sequencing of Lock Requests . . . . . . . . . . . . .  81
       5.1.6.  Recovery from Replayed Requests . . . . . . . . . . .  82
       5.1.7.  Releasing lock_owner State  . . . . . . . . . . . . .  82
       5.1.8.  Use of Open Confirmation  . . . . . . . . . . . . . .  82
     5.2.   Lock Ranges  . . . . . . . . . . . . . . . . . . . . . .  84
     5.3.   Upgrading and Downgrading Locks  . . . . . . . . . . . .  84
     5.4.   Blocking Locks . . . . . . . . . . . . . . . . . . . . .  84
     5.5.   Lease Renewal  . . . . . . . . . . . . . . . . . . . . .  85
     5.6.   Crash Recovery . . . . . . . . . . . . . . . . . . . . .  86
       5.6.1.  Client Failure and Recovery . . . . . . . . . . . . .  86
       5.6.2.  Server Failure and Recovery . . . . . . . . . . . . .  87
       5.6.3.  Network Partitions and Recovery . . . . . . . . . . .  89
     5.7.   Recovery from a Lock Request Timeout or Abort  . . . . .  92
     5.8.   Server Revocation of Locks . . . . . . . . . . . . . . .  93
     5.9.   Share Reservations . . . . . . . . . . . . . . . . . . .  94
     5.10.  OPEN/CLOSE Operations  . . . . . . . . . . . . . . . . .  94
       5.10.1. Close and Retention of State Information  . . . . . .  95
     5.11.  Open Upgrade and Downgrade . . . . . . . . . . . . . . .  96
     5.12.  Short and Long Leases  . . . . . . . . . . . . . . . . .  96
     5.13.  Clocks, Propagation Delay, and Calculating Lease
            Expiration . . . . . . . . . . . . . . . . . . . . . . .  97
   6.  Client-Side Caching . . . . . . . . . . . . . . . . . . . . .  97
     6.1.   Performance Challenges for Client-Side Caching . . . . .  98
     6.2.   Delegation and Callbacks . . . . . . . . . . . . . . . .  99
       6.2.1.  Delegation Recovery . . . . . . . . . . . . . . . . . 100
     6.3.   Data Caching . . . . . . . . . . . . . . . . . . . . . . 102
       6.3.1.  Data Caching and OPENs  . . . . . . . . . . . . . . . 102
       6.3.2.  Data Caching and File Locking . . . . . . . . . . . . 103
       6.3.3.  Data Caching and Mandatory File Locking . . . . . . . 105
       6.3.4.  Data Caching and File Identity  . . . . . . . . . . . 105
     6.4.   Open Delegation  . . . . . . . . . . . . . . . . . . . . 106
       6.4.1.  Open Delegation and Data Caching  . . . . . . . . . . 109
       6.4.2.  Open Delegation and File Locks  . . . . . . . . . . . 110
       6.4.3.  Handling of CB_GETATTR  . . . . . . . . . . . . . . . 110
       6.4.4.  Recall of Open Delegation . . . . . . . . . . . . . . 113
       6.4.5.  Clients that Fail to Honor Delegation Recalls . . . . 115
       6.4.6.  Delegation Revocation . . . . . . . . . . . . . . . . 116
     6.5.   Data Caching and Revocation  . . . . . . . . . . . . . . 116
       6.5.1.  Revocation Recovery for Write Open Delegation . . . . 117
     6.6.   Attribute Caching  . . . . . . . . . . . . . . . . . . . 118



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     6.7.   Data and Metadata Caching and Memory Mapped Files  . . . 120
     6.8.   Name Caching . . . . . . . . . . . . . . . . . . . . . . 122
     6.9.   Directory Caching  . . . . . . . . . . . . . . . . . . . 123
   7.  Security Negotiation  . . . . . . . . . . . . . . . . . . . . 124
   8.  Clarification of Security Negotiation in NFSv4.1  . . . . . . 124
     8.1.   PUTFH + LOOKUP . . . . . . . . . . . . . . . . . . . . . 125
     8.2.   PUTFH + LOOKUPP  . . . . . . . . . . . . . . . . . . . . 125
     8.3.   PUTFH + SECINFO  . . . . . . . . . . . . . . . . . . . . 125
     8.4.   PUTFH + Anything Else  . . . . . . . . . . . . . . . . . 126
   9.  NFSv4.1 Sessions  . . . . . . . . . . . . . . . . . . . . . . 126
     9.1.   Sessions Background  . . . . . . . . . . . . . . . . . . 126
       9.1.1.  Introduction to Sessions  . . . . . . . . . . . . . . 126
       9.1.2.  Motivation  . . . . . . . . . . . . . . . . . . . . . 127
       9.1.3.  Problem Statement . . . . . . . . . . . . . . . . . . 128
       9.1.4.  NFSv4 Session Extension Characteristics . . . . . . . 130
     9.2.   Transport Issues . . . . . . . . . . . . . . . . . . . . 130
       9.2.1.  Session Model . . . . . . . . . . . . . . . . . . . . 130
       9.2.2.  Connection State  . . . . . . . . . . . . . . . . . . 132
       9.2.3.  NFSv4 Channels, Sessions and Connections  . . . . . . 132
       9.2.4.  Reconnection, Trunking and Failover . . . . . . . . . 134
       9.2.5.  Server Duplicate Request Cache  . . . . . . . . . . . 135
     9.3.   Session Initialization and Transfer Models . . . . . . . 136
       9.3.1.  Session Negotiation . . . . . . . . . . . . . . . . . 136
       9.3.2.  RDMA Requirements . . . . . . . . . . . . . . . . . . 138
       9.3.3.  RDMA Connection Resources . . . . . . . . . . . . . . 138
       9.3.4.  TCP and RDMA Inline Transfer Model  . . . . . . . . . 139
       9.3.5.  RDMA Direct Transfer Model  . . . . . . . . . . . . . 142
     9.4.   Connection Models  . . . . . . . . . . . . . . . . . . . 145
       9.4.1.  TCP Connection Model  . . . . . . . . . . . . . . . . 146
       9.4.2.  Negotiated RDMA Connection Model  . . . . . . . . . . 147
       9.4.3.  Automatic RDMA Connection Model . . . . . . . . . . . 148
     9.5.   Buffer Management, Transfer, Flow Control  . . . . . . . 148
     9.6.   Retry and Replay . . . . . . . . . . . . . . . . . . . . 151
     9.7.   The Back Channel . . . . . . . . . . . . . . . . . . . . 152
     9.8.   COMPOUND Sizing Issues . . . . . . . . . . . . . . . . . 153
     9.9.   Data Alignment . . . . . . . . . . . . . . . . . . . . . 153
     9.10.  NFSv4 Integration  . . . . . . . . . . . . . . . . . . . 155
       9.10.1. Minor Versioning  . . . . . . . . . . . . . . . . . . 155
       9.10.2. Slot Identifiers and Server Duplicate Request Cache . 155
       9.10.3. Resolving server callback races with sessions . . . . 159
       9.10.4. COMPOUND and CB_COMPOUND  . . . . . . . . . . . . . . 160
       9.10.5. eXternal Data Representation Efficiency . . . . . . . 161
       9.10.6. Effect of Sessions on Existing Operations . . . . . . 161
       9.10.7. Authentication Efficiencies . . . . . . . . . . . . . 162
     9.11.  Sessions Security Considerations . . . . . . . . . . . . 163
       9.11.1. Authentication  . . . . . . . . . . . . . . . . . . . 165
   10. Multi-server Name Space . . . . . . . . . . . . . . . . . . . 166
     10.1.  Location attributes  . . . . . . . . . . . . . . . . . . 166



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     10.2.  File System Presence or Absence  . . . . . . . . . . . . 166
     10.3.  Getting Attributes for an Absent File System . . . . . . 168
       10.3.1. GETATTR Within an Absent File System  . . . . . . . . 168
       10.3.2. READDIR and Absent File Systems . . . . . . . . . . . 169
     10.4.  Uses of Location Information . . . . . . . . . . . . . . 170
       10.4.1. File System Replication . . . . . . . . . . . . . . . 170
       10.4.2. File System Migration . . . . . . . . . . . . . . . . 171
       10.4.3. Referrals . . . . . . . . . . . . . . . . . . . . . . 172
     10.5.  Additional Client-side Considerations  . . . . . . . . . 172
     10.6.  Effecting File System Transitions  . . . . . . . . . . . 173
       10.6.1. Transparent File System Transitions . . . . . . . . . 174
       10.6.2. Filehandles and File System Transitions . . . . . . . 176
       10.6.3. Fileid's and File System Transitions  . . . . . . . . 176
       10.6.4. Fsid's and File System Transitions  . . . . . . . . . 177
       10.6.5. The Change Attribute and File System Transitions  . . 177
       10.6.6. Lock State and File System Transitions  . . . . . . . 178
       10.6.7. Write Verifiers and File System Transitions . . . . . 181
     10.7.  Effecting File System Referrals  . . . . . . . . . . . . 181
       10.7.1. Referral Example (LOOKUP) . . . . . . . . . . . . . . 182
       10.7.2. Referral Example (READDIR)  . . . . . . . . . . . . . 186
     10.8.  The Attribute fs_absent  . . . . . . . . . . . . . . . . 188
     10.9.  The Attribute fs_locations . . . . . . . . . . . . . . . 188
     10.10. The Attribute fs_locations_info  . . . . . . . . . . . . 190
     10.11. The Attribute fs_status  . . . . . . . . . . . . . . . . 199
   11. Directory Delegations . . . . . . . . . . . . . . . . . . . . 202
     11.1.  Introduction to Directory Delegations  . . . . . . . . . 203
     11.2.  Directory Delegation Design (in brief) . . . . . . . . . 204
     11.3.  Recommended Attributes in support of Directory
            Delegations  . . . . . . . . . . . . . . . . . . . . . . 205
     11.4.  Delegation Recall  . . . . . . . . . . . . . . . . . . . 206
     11.5.  Delegation Recovery  . . . . . . . . . . . . . . . . . . 206
   12. Introduction  . . . . . . . . . . . . . . . . . . . . . . . . 206
   13. General Definitions . . . . . . . . . . . . . . . . . . . . . 209
     13.1.  Metadata Server  . . . . . . . . . . . . . . . . . . . . 209
     13.2.  Client . . . . . . . . . . . . . . . . . . . . . . . . . 209
     13.3.  Storage Device . . . . . . . . . . . . . . . . . . . . . 209
     13.4.  Storage Protocol . . . . . . . . . . . . . . . . . . . . 209
     13.5.  Control Protocol . . . . . . . . . . . . . . . . . . . . 210
     13.6.  Metadata . . . . . . . . . . . . . . . . . . . . . . . . 210
     13.7.  Layout . . . . . . . . . . . . . . . . . . . . . . . . . 210
   14. pNFS protocol semantics . . . . . . . . . . . . . . . . . . . 211
     14.1.  Definitions  . . . . . . . . . . . . . . . . . . . . . . 211
       14.1.1. Layout Types  . . . . . . . . . . . . . . . . . . . . 211
       14.1.2. Layout Iomode . . . . . . . . . . . . . . . . . . . . 211
       14.1.3. Layout Segments . . . . . . . . . . . . . . . . . . . 212
       14.1.4. Device IDs  . . . . . . . . . . . . . . . . . . . . . 213
       14.1.5. Aggregation Schemes . . . . . . . . . . . . . . . . . 213
     14.2.  Guarantees Provided by Layouts . . . . . . . . . . . . . 214



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     14.3.  Getting a Layout . . . . . . . . . . . . . . . . . . . . 215
     14.4.  Committing a Layout  . . . . . . . . . . . . . . . . . . 216
       14.4.1. LAYOUTCOMMIT and mtime/atime/change . . . . . . . . . 216
       14.4.2. LAYOUTCOMMIT and size . . . . . . . . . . . . . . . . 217
       14.4.3. LAYOUTCOMMIT and layoutupdate . . . . . . . . . . . . 218
     14.5.  Recalling a Layout . . . . . . . . . . . . . . . . . . . 218
       14.5.1. Basic Operation . . . . . . . . . . . . . . . . . . . 218
       14.5.2. Recall Callback Robustness  . . . . . . . . . . . . . 220
       14.5.3. Recall/Return Sequencing  . . . . . . . . . . . . . . 221
     14.6.  Metadata Server Write Propagation  . . . . . . . . . . . 223
     14.7.  Crash Recovery . . . . . . . . . . . . . . . . . . . . . 223
       14.7.1. Leases  . . . . . . . . . . . . . . . . . . . . . . . 224
       14.7.2. Client Recovery . . . . . . . . . . . . . . . . . . . 225
       14.7.3. Metadata Server Recovery  . . . . . . . . . . . . . . 226
       14.7.4. Storage Device Recovery . . . . . . . . . . . . . . . 228
   15. Security Considerations . . . . . . . . . . . . . . . . . . . 229
     15.1.  File Layout Security . . . . . . . . . . . . . . . . . . 230
     15.2.  Object Layout Security . . . . . . . . . . . . . . . . . 230
     15.3.  Block/Volume Layout Security . . . . . . . . . . . . . . 232
   16. The NFSv4 File Layout Type  . . . . . . . . . . . . . . . . . 232
     16.1.  File Striping and Data Access  . . . . . . . . . . . . . 232
       16.1.1. Sparse and Dense Storage Device Data Layouts  . . . . 234
       16.1.2. Metadata and Storage Device Roles . . . . . . . . . . 236
       16.1.3. Device Multipathing . . . . . . . . . . . . . . . . . 237
       16.1.4. Operations Issued to Storage Devices  . . . . . . . . 237
       16.1.5. COMMIT through metadata server  . . . . . . . . . . . 238
     16.2.  Global Stateid Requirements  . . . . . . . . . . . . . . 238
     16.3.  The Layout Iomode  . . . . . . . . . . . . . . . . . . . 239
     16.4.  Storage Device State Propagation . . . . . . . . . . . . 239
       16.4.1. Lock State Propagation  . . . . . . . . . . . . . . . 240
       16.4.2. Open-mode Validation  . . . . . . . . . . . . . . . . 240
       16.4.3. File Attributes . . . . . . . . . . . . . . . . . . . 240
     16.5.  Storage Device Component File Size . . . . . . . . . . . 241
     16.6.  Crash Recovery Considerations  . . . . . . . . . . . . . 242
     16.7.  Security Considerations  . . . . . . . . . . . . . . . . 243
     16.8.  Alternate Approaches . . . . . . . . . . . . . . . . . . 243
   17. Layouts and Aggregation . . . . . . . . . . . . . . . . . . . 244
     17.1.  Simple Map . . . . . . . . . . . . . . . . . . . . . . . 244
     17.2.  Block Extent Map . . . . . . . . . . . . . . . . . . . . 245
     17.3.  Striped Map (RAID 0) . . . . . . . . . . . . . . . . . . 245
     17.4.  Replicated Map . . . . . . . . . . . . . . . . . . . . . 245
     17.5.  Concatenated Map . . . . . . . . . . . . . . . . . . . . 245
     17.6.  Nested Map . . . . . . . . . . . . . . . . . . . . . . . 246
   18. Minor Versioning  . . . . . . . . . . . . . . . . . . . . . . 246
   19. Internationalization  . . . . . . . . . . . . . . . . . . . . 248
     19.1.  Stringprep profile for the utf8str_cs type . . . . . . . 249
     19.2.  Stringprep profile for the utf8str_cis type  . . . . . . 251
     19.3.  Stringprep profile for the utf8str_mixed type  . . . . . 252



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     19.4.  UTF-8 Related Errors . . . . . . . . . . . . . . . . . . 254
   20. Error Definitions . . . . . . . . . . . . . . . . . . . . . . 254
   21. NFS version 4.1 Procedures  . . . . . . . . . . . . . . . . . 263
     21.1.  Procedure 0: NULL - No Operation . . . . . . . . . . . . 263
     21.2.  Procedure 1: COMPOUND - Compound Operations  . . . . . . 264
   22. NFS version 4.1 Operations  . . . . . . . . . . . . . . . . . 266
     22.1.  Operation 3: ACCESS - Check Access Rights  . . . . . . . 267
     22.2.  Operation 4: CLOSE - Close File  . . . . . . . . . . . . 269
     22.3.  Operation 5: COMMIT - Commit Cached Data . . . . . . . . 270
     22.4.  Operation 6: CREATE - Create a Non-Regular File Object . 273
     22.5.  Operation 7: DELEGPURGE - Purge Delegations Awaiting
            Recovery . . . . . . . . . . . . . . . . . . . . . . . . 276
     22.6.  Operation 8: DELEGRETURN - Return Delegation . . . . . . 277
     22.7.  Operation 9: GETATTR - Get Attributes  . . . . . . . . . 277
     22.8.  Operation 10: GETFH - Get Current Filehandle . . . . . . 279
     22.9.  Operation 11: LINK - Create Link to a File . . . . . . . 280
     22.10. Operation 12: LOCK - Create Lock . . . . . . . . . . . . 281
     22.11. Operation 13: LOCKT - Test For Lock  . . . . . . . . . . 285
     22.12. Operation 14: LOCKU - Unlock File  . . . . . . . . . . . 287
     22.13. Operation 15: LOOKUP - Lookup Filename . . . . . . . . . 288
     22.14. Operation 16: LOOKUPP - Lookup Parent Directory  . . . . 290
     22.15. Operation 17: NVERIFY - Verify Difference in
            Attributes . . . . . . . . . . . . . . . . . . . . . . . 291
     22.16. Operation 18: OPEN - Open a Regular File . . . . . . . . 292
     22.17. Operation 19: OPENATTR - Open Named Attribute
            Directory  . . . . . . . . . . . . . . . . . . . . . . . 306
     22.18. Operation 20: OPEN_CONFIRM - Confirm Open  . . . . . . . 307
     22.19. Operation 21: OPEN_DOWNGRADE - Reduce Open File Access . 309
     22.20. Operation 22: PUTFH - Set Current Filehandle . . . . . . 310
     22.21. Operation 23: PUTPUBFH - Set Public Filehandle . . . . . 311
     22.22. Operation 24: PUTROOTFH - Set Root Filehandle  . . . . . 313
     22.23. Operation 25: READ - Read from File  . . . . . . . . . . 314
     22.24. Operation 26: READDIR - Read Directory . . . . . . . . . 316
     22.25. Operation 27: READLINK - Read Symbolic Link  . . . . . . 320
     22.26. Operation 28: REMOVE - Remove Filesystem Object  . . . . 321
     22.27. Operation 29: RENAME - Rename Directory Entry  . . . . . 323
     22.28. Operation 30: RENEW - Renew a Lease  . . . . . . . . . . 325
     22.29. Operation 31: RESTOREFH - Restore Saved Filehandle . . . 326
     22.30. Operation 32: SAVEFH - Save Current Filehandle . . . . . 327
     22.31. Operation 33: SECINFO - Obtain Available Security  . . . 328
     22.32. Operation 34: SETATTR - Set Attributes . . . . . . . . . 331
     22.33. Operation 35: SETCLIENTID - Negotiate Clientid . . . . . 334
     22.34. Operation 36: SETCLIENTID_CONFIRM - Confirm Clientid . . 338
     22.35. Operation 37: VERIFY - Verify Same Attributes  . . . . . 341
     22.36. Operation 38: WRITE - Write to File  . . . . . . . . . . 342
     22.37. Operation 39: RELEASE_LOCKOWNER - Release Lockowner
            State  . . . . . . . . . . . . . . . . . . . . . . . . . 347
     22.38. Operation 10044: ILLEGAL - Illegal operation . . . . . . 348



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     22.39. SECINFO_NO_NAME - Get Security on Unnamed Object . . . . 348
     22.40. CREATECLIENTID - Instantiate Clientid  . . . . . . . . . 350
     22.41. CREATESESSION - Create New Session and Confirm
            Clientid . . . . . . . . . . . . . . . . . . . . . . . . 355
     22.42. BIND_BACKCHANNEL - Create a callback channel binding . . 360
     22.43. DESTROYSESSION - Destroy existing session  . . . . . . . 362
     22.44. SEQUENCE - Supply per-procedure sequencing and control . 363
     22.45. GET_DIR_DELEGATION - Get a directory delegation  . . . . 364
     22.46. LAYOUTGET - Get Layout Information . . . . . . . . . . . 368
     22.47. LAYOUTCOMMIT - Commit writes made using a layout . . . . 371
     22.48. LAYOUTRETURN - Release Layout Information  . . . . . . . 375
     22.49. GETDEVICEINFO - Get Device Information . . . . . . . . . 376
     22.50. GETDEVICELIST  . . . . . . . . . . . . . . . . . . . . . 377
     22.51. WANT_DELEGATION  . . . . . . . . . . . . . . . . . . . . 379
   23. NFS version 4.1 Callback Procedures . . . . . . . . . . . . . 382
     23.1.  Procedure 0: CB_NULL - No Operation  . . . . . . . . . . 382
     23.2.  Procedure 1: CB_COMPOUND - Compound Operations . . . . . 383
   24. CB_RECALLCREDIT - change flow control limits  . . . . . . . . 385
   25. CB_SEQUENCE - Supply callback channel sequencing and
       control . . . . . . . . . . . . . . . . . . . . . . . . . . . 385
   26. CB_NOTIFY - Notify directory changes  . . . . . . . . . . . . 387
   27. CB_RECALL_ANY - Keep any N delegations  . . . . . . . . . . . 390
   28. CB_SIZECHANGED  . . . . . . . . . . . . . . . . . . . . . . . 393
   29. CB_LAYOUTRECALL . . . . . . . . . . . . . . . . . . . . . . . 394
   30. CB_PUSH_DELEG . . . . . . . . . . . . . . . . . . . . . . . . 397
   31. CB_RECALLABLE_OBJ_AVAIL . . . . . . . . . . . . . . . . . . . 398
   32. References  . . . . . . . . . . . . . . . . . . . . . . . . . 398
     32.1.  Normative References . . . . . . . . . . . . . . . . . . 398
     32.2.  Informative References . . . . . . . . . . . . . . . . . 399
   Appendix A.  Acknowledgments  . . . . . . . . . . . . . . . . . . 399
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . . 400
   Intellectual Property and Copyright Statements  . . . . . . . . . 401



















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1.  Protocol Data Types

   The syntax and semantics to describe the data types of the NFS
   version 4 protocol are defined in the XDR RFC1832 [2] and RPC RFC1831
   [3] documents.  The next sections build upon the XDR data types to
   define types and structures specific to this protocol.

1.1.  Basic Data Types

                   These are the base NFSv4 data types.

   +---------------+---------------------------------------------------+
   | 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)                                           |



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   | 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 [4] for details.                          |
   | seqid4        | typedef uint32_t seqid4;                          |
   |               | 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

1.2.  Structured Data Types

1.2.1.  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



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   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 filesystem object is less than
   defined, loss of precision can occur.  An adjunct time maintenance
   protocol is recommended to reduce client and server time skew.

1.2.2.  time_how4

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

1.2.3.  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.

1.2.4.  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.

1.2.5.  fsid4

   struct fsid4 {
       uint64_t        major;
       uint64_t        minor;
   };



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1.2.6.  fs_location4

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

1.2.7.  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.

1.2.8.  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 |
   +-----------+-----------+-----------+--

1.2.9.  change_info4

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

   This structure is used with the CREATE, LINK, REMOVE, RENAME



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   operations to let the client know the value of the change attribute
   for the directory in which the target filesystem object resides.

1.2.10.  clientaddr4

   struct clientaddr4 {
       /* see struct rpcb in RFC1833 */
       string r_netid<>;    /* network id */
       string r_addr<>;     /* universal address */
   };

   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.  The r_netid and
   r_addr fields are specified in RFC1833 [9], but they are
   underspecified in RFC1833 [9] 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
   [5].  Additionally, the two alternative forms specified in Section
   2.2 of RFC1884 [5] are also acceptable.




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   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".

1.2.11.  cb_client4

   struct cb_client4 {
       unsigned int  cb_program;
       clientaddr4   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.

1.2.12.  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.

1.2.13.  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.

1.2.14.  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.









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1.2.15.  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.

1.2.16.  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.

1.2.17.  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 set of well known layout types must be
   defined.  As well, a private range of layout types is to be defined
   by this document.  This would allow custom installations to introduce
   new layout types.



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   [[Comment.1: Determine private range of layout types]]

   New layout types must be specified in RFCs approved by the IESG
   before becoming part of the pNFS specification.

   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 [10], is to be used.
   Similarly, the LAYOUT_BLOCK_VOLUME enumeration that the block/volume
   layout, as defined in [11], is to be used.

1.2.18.  pnfs_deviceid4

   typedef uint32_t pnfs_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 14.1.4 for more
   details.

1.2.19.  pnfs_netaddr4

   struct pnfs_netaddr4 {
       string  r_netid<>; /* network ID */
       string  r_addr<>;  /* universal address */
   };

   For a description of the r_netid and r_addr fields see the
   descriptions provided in the clientaddr4 structure description.

1.2.20.  pnfs_devlist_item4

   struct pnfs_devlist_item4 {
           pnfs_deviceid4          id;
           opaque                  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.



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   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 pnfs_netaddr4), which identifies a storage device by network
   IP address and port number (similar to struct clientaddr4).  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.

1.2.21.  pnfs_layout4

   struct pnfs_layout4 {
       offset4                 offset;
       length4                 length;
       pnfs_layoutiomode4      iomode;
       pnfs_layouttype4        type;
       opaque                  layout<>;
   };

   The pnfs_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 16.1 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.

   [[Comment.2: there is a discussion of moving the striping
   information, or more generally the "aggregation scheme", up to the
   generic layout level.  This creates a two-layer system where the top
   level is a switch on different data placement layouts, and the next
   level down is a switch on different data storage types.  This lets
   different layouts (e.g., striping or mirroring or redundant servers)
   to be layered over different storage devices.  This would move
   geometry information out of nfsv4_file_layouttype4 and up into a
   generic pnfs_striped_layout type that would specify a set of
   pnfs_deviceid4 and pnfs_devicetype4 to use for storage.  Instead of
   nfsv4_file_layouttype4, there would be pnfs_nfsv4_devicetype4.]]

1.2.22.  pnfs_layoutupdate4

   struct pnfs_layoutupdate4 {
       pnfs_layouttype4        type;
       opaque                  layoutupdate_data<>;
   };



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   The pnfs_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 layoutupdate_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.

1.2.23.  layouthint4

   struct pnfs_layouthint4 {
       pnfs_layouttype4      type;
       opaque                layouthint_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
   OPEN.  The NFSv4 file-based layout uses the "nfsv4_file_layouthint"
   structure as defined in Section 16.1.

1.2.24.  pnfs_layoutiomode4

   enum pnfs_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.








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1.2.25.  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.

1.2.26.  impl_ident4

   struct impl_ident4 {
       clientid4           ii_clientid;
       struct nfs_impl_id4 ii_impl_id;
   };

   This is used for exchanging implementation identification between
   client and server.


2.  Filehandles

   The filehandle in the NFS protocol is a per server unique identifier
   for a filesystem 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 filesystem
   object.

2.1.  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] and the NFS version 3 protocol [RFC1813], 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 filesystem 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



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   via firewalls.  This is one reason that the use of the public
   filehandle was introduced in [RFC2054] and [RFC2055].  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.

2.1.1.  Root Filehandle

   The first of the special filehandles is the ROOT filehandle.  The
   ROOT filehandle is the "conceptual" root of the filesystem 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".

2.1.2.  Public Filehandle

   The second special filehandle is the PUBLIC filehandle.  Unlike the
   ROOT filehandle, the PUBLIC filehandle may be bound or represent an
   arbitrary filesystem 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 filesystem 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 filesystem object.  The client may not make any
   assumptions about this binding.  The client uses the PUBLIC
   filehandle via the PUTPUBFH operation.

2.2.  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



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   implementation of a persistent filehandle infeasible.  Some server
   environments do not provide a filesystem level invariant that can be
   used to construct a persistent filehandle.  The underlying server
   filesystem may not provide the invariant or the server's filesystem
   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
   filesystem 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.

2.2.1.  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 filesystem object, the
   server SHOULD return the same filehandle for each path.  This can
   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.

2.2.2.  Persistent Filehandle

   A persistent filehandle is defined as having a fixed value for the
   lifetime of the filesystem object to which it refers.  Once the
   server creates the filehandle for a filesystem object, the server
   MUST accept the same filehandle for the object for the lifetime of



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   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 filesystem 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
   filesystem 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
   filesystem 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 filesystem in whole
   has been destroyed or the filesystem has simply been removed from the
   server's name space (i.e. unmounted in a UNIX environment).

2.2.3.  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 filesystem.  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 filesystem.  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.

   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.






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   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 file handles 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.

2.3.  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]

   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



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   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.

2.4.  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 filesystem 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 filesystem name space.

   If the expired filehandle refers to an object that has been removed
   from the filesystem, 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:

             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.







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3.  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:

        +----------+-----------+---------------------------------+
        | 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



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   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 filesystem at the server has a named attribute directory
   or not.  Therefore, operations such as SETATTR and GETATTR on the
   named attribute directory are undefined.

3.1.  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.

3.2.  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
   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.






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3.3.  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 filesystem 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 filesystem.  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.

3.4.  Classification of Attributes

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

         lease_time

   o  The per filesystem 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,



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         maxread, maxwrite, no_trunc, space_avail, space_free,
         space_total, time_delta, fs_layouttype, send_impl_id,
         recv_impl_id

   o  The per filesystem 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, layouttype, layouthint,
         layout_blksize, layout_alignment

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

3.5.  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.)                |
   | fh_expire_type  | 2  | uint32     | READ   | Server uses this to  |
   |                 |    |            |        | specify filehandle   |
   |                 |    |            |        | expiration behavior  |
   |                 |    |            |        | to the client. See   |
   |                 |    |            |        | the section          |
   |                 |    |            |        | "Filehandles" for    |
   |                 |    |            |        | additional           |
   |                 |    |            |        | description.         |







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   | 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      |
   |                 |    |            |        | filesystem 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 filesystem  |
   |                 |    |            |        | supports hard links. |
   | symlink_support | 6  | bool       | READ   | True, if the         |
   |                 |    |            |        | object's filesystem  |
   |                 |    |            |        | 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. |
   | fsid            | 8  | fsid4      | READ   | Unique filesystem    |
   |                 |    |            |        | identifier for the   |
   |                 |    |            |        | filesystem 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     |
   |                 |    |            |        | filesystem objects.  |



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   | 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).   |
   +-----------------+----+------------+--------+----------------------+

3.6.  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 |
   |                    |     |              |        | filesystem.    |
   | archive            | 14  | bool         | R/W    | True, if this  |
   |                    |     |              |        | file has been  |
   |                    |     |              |        | archived since |
   |                    |     |              |        | the time of    |
   |                    |     |              |        | last           |
   |                    |     |              |        | modification   |
   |                    |     |              |        | (deprecated in |
   |                    |     |              |        | favor of       |
   |                    |     |              |        | time_backup).  |
   | cansettime         | 15  | bool         | READ   | True, if the   |
   |                    |     |              |        | server able to |
   |                    |     |              |        | change the     |
   |                    |     |              |        | times for a    |
   |                    |     |              |        | filesystem     |
   |                    |     |              |        | object as      |
   |                    |     |              |        | specified in a |
   |                    |     |              |        | SETATTR        |
   |                    |     |              |        | operation.     |







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   | case_insensitive   | 16  | bool         | READ   | True, if       |
   |                    |     |              |        | filename       |
   |                    |     |              |        | comparisons on |
   |                    |     |              |        | this           |
   |                    |     |              |        | filesystem are |
   |                    |     |              |        | case           |
   |                    |     |              |        | insensitive.   |
   | case_preserving    | 17  | bool         | READ   | True, if       |
   |                    |     |              |        | filename case  |
   |                    |     |              |        | on this        |
   |                    |     |              |        | filesystem 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).    |
   | fileid             | 20  | uint64       | READ   | A number       |
   |                    |     |              |        | uniquely       |
   |                    |     |              |        | identifying    |
   |                    |     |              |        | the file       |
   |                    |     |              |        | within the     |
   |                    |     |              |        | filesystem.    |












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   | files_avail        | 21  | uint64       | READ   | File slots     |
   |                    |     |              |        | available to   |
   |                    |     |              |        | this user on   |
   |                    |     |              |        | the filesystem |
   |                    |     |              |        | containing     |
   |                    |     |              |        | this object -  |
   |                    |     |              |        | this should be |
   |                    |     |              |        | the smallest   |
   |                    |     |              |        | relevant       |
   |                    |     |              |        | limit.         |
   | files_free         | 22  | uint64       | READ   | Free file      |
   |                    |     |              |        | slots on the   |
   |                    |     |              |        | filesystem     |
   |                    |     |              |        | containing     |
   |                    |     |              |        | this object -  |
   |                    |     |              |        | this should be |
   |                    |     |              |        | the smallest   |
   |                    |     |              |        | relevant       |
   |                    |     |              |        | limit.         |
   | files_total        | 23  | uint64       | READ   | Total file     |
   |                    |     |              |        | slots on the   |
   |                    |     |              |        | filesystem     |
   |                    |     |              |        | containing     |
   |                    |     |              |        | this object.   |
   | fs_locations       | 24  | fs_locations | READ   | Locations      |
   |                    |     |              |        | where this     |
   |                    |     |              |        | filesystem may |
   |                    |     |              |        | be found. If   |
   |                    |     |              |        | the server     |
   |                    |     |              |        | returns        |
   |                    |     |              |        | NFS4ERR_MOVED  |
   |                    |     |              |        | as an error,   |
   |                    |     |              |        | this attribute |
   |                    |     |              |        | MUST be        |
   |                    |     |              |        | supported.     |
   | hidden             | 25  | bool         | R/W    | True, if the   |
   |                    |     |              |        | file is        |
   |                    |     |              |        | considered     |
   |                    |     |              |        | hidden with    |
   |                    |     |              |        | respect to the |
   |                    |     |              |        | Windows API?   |










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   | homogeneous        | 26  | bool         | READ   | True, if this  |
   |                    |     |              |        | object's       |
   |                    |     |              |        | filesystem is  |
   |                    |     |              |        | homogeneous,   |
   |                    |     |              |        | i.e. are per   |
   |                    |     |              |        | filesystem     |
   |                    |     |              |        | attributes the |
   |                    |     |              |        | same for all   |
   |                    |     |              |        | filesystem's   |
   |                    |     |              |        | objects.       |
   | maxfilesize        | 27  | uint64       | READ   | Maximum        |
   |                    |     |              |        | supported file |
   |                    |     |              |        | size for the   |
   |                    |     |              |        | filesystem 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.   |
   | mimetype           | 32  | utf8<>       | R/W    | MIME body      |
   |                    |     |              |        | type/subtype   |
   |                    |     |              |        | of this        |
   |                    |     |              |        | object.        |



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   | mode               | 33  | mode4        | R/W    | UNIX-style     |
   |                    |     |              |        | mode and       |
   |                    |     |              |        | permission     |
   |                    |     |              |        | bits for this  |
   |                    |     |              |        | object.        |
   | 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. |














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   | 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.        |
   | space_avail        | 42  | uint64       | READ   | Disk space in  |
   |                    |     |              |        | bytes          |
   |                    |     |              |        | available to   |
   |                    |     |              |        | this user on   |
   |                    |     |              |        | the filesystem |
   |                    |     |              |        | containing     |
   |                    |     |              |        | this object -  |
   |                    |     |              |        | this should be |
   |                    |     |              |        | the smallest   |
   |                    |     |              |        | relevant       |
   |                    |     |              |        | limit.         |
   | space_free         | 43  | uint64       | READ   | Free disk      |
   |                    |     |              |        | space in bytes |
   |                    |     |              |        | on the         |
   |                    |     |              |        | filesystem     |
   |                    |     |              |        | containing     |
   |                    |     |              |        | this object -  |
   |                    |     |              |        | this should be |
   |                    |     |              |        | the smallest   |
   |                    |     |              |        | relevant       |
   |                    |     |              |        | limit.         |
   | space_total        | 44  | uint64       | READ   | Total disk     |
   |                    |     |              |        | space in bytes |
   |                    |     |              |        | on the         |
   |                    |     |              |        | filesystem     |
   |                    |     |              |        | containing     |
   |                    |     |              |        | this object.   |
   | space_used         | 45  | uint64       | READ   | Number of      |
   |                    |     |              |        | filesystem     |
   |                    |     |              |        | bytes          |
   |                    |     |              |        | allocated to   |
   |                    |     |              |        | this object.   |





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   | 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.   |
   | 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. |







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   | time_modify_set    | 54  | settime4     | WRITE  | Set the time   |
   |                    |     |              |        | of last        |
   |                    |     |              |        | modification   |
   |                    |     |              |        | to the object. |
   |                    |     |              |        | SETATTR use    |
   |                    |     |              |        | only.          |
   | mounted_on_fileid  | 55  | uint64       | READ   | Like fileid,   |
   |                    |     |              |        | but if the     |
   |                    |     |              |        | target         |
   |                    |     |              |        | filehandle is  |
   |                    |     |              |        | the root of a  |
   |                    |     |              |        | filesystem     |
   |                    |     |              |        | return the     |
   |                    |     |              |        | fileid of the  |
   |                    |     |              |        | underlying     |
   |                    |     |              |        | directory.     |
   | send_impl_id       | TBD | impl_ident4  | WRITE  | Client         |
   |                    |     |              |        | provides       |
   |                    |     |              |        | server with    |
   |                    |     |              |        | implementation |
   |                    |     |              |        | identity via   |
   |                    |     |              |        | SETATTR.       |
   | recv_impl_id       | TBD | nfs_impl_id4 | READ   | Client obtains |
   |                    |     |              |        | server         |
   |                    |     |              |        | implementation |
   |                    |     |              |        | via GETATTR.   |
   | dir_notif_delay    | TBD | R/W          | READ   | notification   |
   |                    |     |              |        | delays on      |
   |                    |     |              |        | directory      |
   |                    |     |              |        | attributes     |
   | dirent_notif_delay | TBD | R/W          | READ   | notification   |
   |                    |     |              |        | delays on      |
   |                    |     |              |        | child          |
   |                    |     |              |        | attributes     |
   | fs_layouttype      | TBD | layouttype4  | READ   | Layout types   |
   |                    |     |              |        | available for  |
   |                    |     |              |        | the            |
   |                    |     |              |        | filesystem.    |
   | layouttype         | TBD | layouttype4  | READ   | Layout types   |
   |                    |     |              |        | available for  |
   |                    |     |              |        | the file.      |
   | layouthint         | TBD | layouthint4  | WRITE  | Client         |
   |                    |     |              |        | specified hint |
   |                    |     |              |        | for file       |
   |                    |     |              |        | layout.        |






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   | layout_blksize     | TBD | uint32_t     | READ   | Preferred      |
   |                    |     |              |        | block size for |
   |                    |     |              |        | layout related |
   |                    |     |              |        | I/O.           |
   | layout_alignment   | TBD | uint32_t     | READ   | Preferred      |
   |                    |     |              |        | alignment for  |
   |                    |     |              |        | layout related |
   |                    |     |              |        | I/O.           |
   | fs_absent          | TBD | bool         | READ   | Is current     |
   |                    |     |              |        | filesystem     |
   |                    |     |              |        | present or     |
   |                    |     |              |        | absent.        |
   | fs_locations_info  | TBD |              | READ   | Full function  |
   |                    |     |              |        | filesystem     |
   |                    |     |              |        | location.      |
   | fs_status          | TBD | fs4_status   | READ   | Generic        |
   |                    |     |              |        | filesystem     |
   |                    |     |              |        | type           |
   |                    |     |              |        | information.   |
   |                    | TBD |              | READ   | desc           |
   |                    | TBD |              | READ   | desc           |
   +--------------------+-----+--------------+--------+----------------+

3.7.  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 filesystem 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 filesystem, 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.

3.8.  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



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   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]
   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
   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.



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   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
   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.

3.9.  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] 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



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   section "Internationalization".

3.10.  Quota Attributes

   For the attributes related to filesystem quotas, the following
   definitions apply:

   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-filesystem
      or may be "choose the set with the smallest quota".

3.11.  mounted_on_fileid

   UNIX-based operating environments connect a filesystem into the
   namespace by connecting (mounting) the filesystem onto the existing
   file object (the mount point, usually a directory) of an existing
   filesystem.  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 filesystem, whereas readdir() is returning
   the fileid stat() would have returned before any filesystems were



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   mounted on the mount point.

   Unlike NFS version 3, NFS version 4 allows a client's LOOKUP request
   to cross other filesystems.  The client detects the filesystem
   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".
   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 filesystem.
   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 filesystems 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.

3.12.  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 clientid4 value along with the nfs_impl_id4.  The use of the
   clientid4 value allows the server to identify and match specific
   client interaction.  In the case of the recv_impl_id attribute, the



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   client receives the 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 implementers.  For example,
   diagnostic software may extract this information in an attempt to
   identify implementation 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
   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.

3.13.  fs_layouttype

   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.

3.14.  layouttype

   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.

3.15.  layouthint

   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.




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   [[Comment.3: it has been suggested that the HINT is a well defined
   type other than pnfs_layoutdata4, similar to pnfs_layoutupdate4.]]

3.16.  Access Control Lists

   The NFS version 4 ACL attribute is an array of access control entries
   (ACE).  Although, the client can read and write the ACL attribute,
   the NFSv4 model is the server does all access control based on the
   server's interpretation of the ACL.  If at any point the client wants
   to check access without issuing an operation that modifies or reads
   data or metadata, the client can use the OPEN and ACCESS operations
   to do so.  There are various access control entry types, as defined
   in Section 3.16.1.  The server is able to communicate which ACE types
   are supported by returning the appropriate value within the
   aclsupport attribute.  Each ACE covers one or more operations on a
   file or directory as described in Section 3.16.2.  It may also
   contain one or more flags that modify the semantics of the ACE as
   defined in Section 3.16.3.

   The NFS ACE attribute is defined as follows:

            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, each nfsace4 entry is processed
   in order by the server.  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.
   However, unlike the ALLOWED and DENIED 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.  When the ACL is fully processed, if there are bits in
   requester's mask that have not been considered whether the server
   allows or denies, the access is denied.  Even though a request is



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   denied, servers may choose to have other restrictions or
   implementation defined security policies in place.  In those cases,
   access may be decided outside of what is in the ACL.  Examples of
   such security policies or restrictions are:

   o  The owner of the file will always be able granted ACE4_WRITE_ACL
      and ACE4_READ_ACL permissions.  This would prevent the user from
      getting into the situation where they can't ever modify the ACL.

   o  The ACL may say that an entity is to be granted ACE4_WRITE_DATA
      permission, but the file system is mounted read only, therefore
      write access is denied.

   As mentioned before, this is one of the reasons that client
   implementations are not recommended to do their own access checking.

   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.

















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3.16.1.  ACE type


      Type         Description
      _____________________________________________________
      ALLOW        Explicitly grants the access defined in
                   acemask4 to the file or directory.

      DENY         Explicitly denies the access defined in
                   acemask4 to the file or directory.

      AUDIT        LOG (system dependent) any access
                   attempt to a file or directory which
                   uses any of the access methods specified
                   in acemask4.

      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.

   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:

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

   The semantics of the "type" field follow the descriptions provided
   above.

   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;

   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



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   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.

3.16.2.  ACE Access Mask

   The access_mask field contains values based on the following:

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

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

      ACE4_WRITE_DATA
          Operation(s) affected:
              WRITE
              OPEN
          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
          Discussion:
               The ability to modify a file's data, but only starting at



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               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
          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
          Discussion:
              Permission to execute a file or traverse/search a
              directory.

      ACE4_DELETE_CHILD
          Operation(s) affected:



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              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
          Discussion:
              Permission to change the times associated with a file
              or directory to an arbitrary value.  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.

      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



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          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 or
              chgrp.

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

   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;

   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 APPEND_DATA (the ability to append to a
   file) from 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
   APPEND_DATA and 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 APPEND_DATA is set but WRITE_DATA is



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   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 APPEND_DATA
   and WRITE_DATA are denied.

3.16.2.1.  ACE4_DELETE vs. ACE4_DELETE_CHILD

   There are two separate access mask bits that govern the ability to
   delete a file: ACE4_DELETE and ACE4_DELETE_CHILD.  ACE4_DELETE is
   intended to be specified by the ACL for the object to be deleted, and
   ACE4_DELETE_CHILD is intended to be specified by the ACL of the
   parent directory.

   In addition to ACE4_DELETE and ACE4_DELETE_CHILD, many systems also
   consider the "sticky bit" (MODE4_SVTX) and the appropriate "write"
   mode bit 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.
























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          if ACE4_EXECUTE is denied by the parent directory ACL:
              deny delete
          else if ACE4_EXECUTE is unspecified 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

3.16.3.  ACE flag

   The "flag" field contains values based on the following descriptions.

   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,
      only to newly created files/directories as specified by the above
      two flags.

   ACE4_NO_PROPAGATE_INHERIT_ACE
      Can be placed on a directory.  Normally when a new directory is
      created and an ACE exists on the parent directory which is marked
      ACE4_DIRECTORY_INHERIT_ACE, two ACEs are placed on the new



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      directory.  One for the directory itself and one which is an
      inheritable ACE for newly created directories.  This flag tells
      the server to not place an ACE on the newly created directory
      which is inheritable by subdirectories of the created directory.

   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, and the share reservation processing, and the OPEN
      call, it then notes if the OPEN succeeded or failed.  If the OPEN
      succeeded, and if the SUCCESS flag was set for a matching AUDIT or
      ALARM, then the appropriate AUDIT or ALARM event occurs.  If the
      OPEN failed, and if the FAILED flag was set for the matching AUDIT
      or ALARM, then the appropriate AUDIT or ALARM event occurs.
      Clearly 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
      may ignore the ACE4_IDENTIFIER_GROUP flag on ACEs with a who value
      equal to one of the special identifiers outlined in section "ACE
      who".

   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;



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   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.

3.16.4.  ACE who

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

   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@.






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3.16.4.1.  Discussion on 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.

3.16.4.2.  Discussion on OWNER@ and GROUP@

   Due to the use of the special identifiers "OWNER@" and "GROUP@" to
   indicate that an ACE applies to the the owner and owning group,
   respectively, associated with a file, the ACL cannot be used to
   determine the owner and owning group of a file.  This information
   should be indicated by the values of the owner and owner_group file
   attributes returned by the server.

3.16.5.  Mode Attribute

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

         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 the principals identified in the owner_group
   attribute.  Bits MODE4_ROTH, MODE4_WOTH, MODE4_XOTH apply to any
   principal that does not match that in the owner group, and does not
   have a group matching that of the owner_group attribute.

   The remaining bits are not defined by this protocol and MUST NOT be
   used.  The minor version mechanism must be used to define further bit
   usage.

   Note that in UNIX, if a file has the MODE4_SGID bit set and no
   MODE4_XGRP bit set, then READ and WRITE must use mandatory file
   locking.



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3.16.6.  Interaction Between Mode and ACL Attributes

   As defined, there is a certain amount of overlap between ACL and mode
   file attributes.  Even though there is overlap, ACLs don't contain
   all the information specified by a mode and modes can't possibly
   contain all the information specified by an ACL.

   For servers that support both mode and ACL, the mode's MODE4_R*,
   MODE4_W* and MODE4_X* values should be computed from the ACL and
   should be recomputed upon each SETATTR of ACL.  Similarly, upon
   SETATTR of mode, the ACL should be modified in order to allow the
   mode computed from the ACL to be the same as the mode given to
   SETATTR.  The mode computed from any given ACL should be
   deterministic.  This means that given an ACL, the same mode will
   always be computed.

   For servers that support ACL and not mode, clients may handle
   applications which set and get the mode by creating the correct ACL
   to send to the server and by computing the mode from the ACL,
   respectively.  In this case, the methods used by the server to keep
   the mode in sync with the ACL can also be used by the client.  These
   methods are explained in sections Section 3.16.6.3 Section 3.16.6.1
   and Section 3.16.6.2.

   Since the mode can't possibly represent all of the information that
   is defined by an ACL, there are some descrepencies to be aware of.
   As explained in the section "Deficiencies in a Mode Representation of
   an ACL", the mode bits computed from the ACL could potentially convey
   more restrictive permissions than what would be granted via the ACL.
   Because of this clients are not recommended to do their own access
   checks based on the mode of a file.

   Because the mode attribute includes bits (i.e.  MODE4_SUID,
   MODE4_SGID, MODE4_SVTX) that have nothing to do with ACL semantics,
   it is permitted for clients to specify both the ACL attribute and
   mode in the same SETATTR operation.  However, because there is no
   prescribed order for processing the attributes in a SETATTR, clients
   may see differing results.  For recommendations on how to achieve
   consistent behavior, see Section 3.16.6.4 for recommendations.

3.16.6.1.  Recomputing mode upon SETATTR of ACL

   Keeping the mode and ACL attributes synchronized is important, but as
   mentioned previously, the mode cannot possibly represent all of the
   information in the ACL.  Still, the mode should be modified to
   represent the access as accurately as possible.

   The general algorithm to assign a new mode attribute to an object



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   based on a new ACL being set is:

   1.  Walk through the ACEs in order, looking for ACEs with a "who"
       value of OWNER@, GROUP@, or EVERYONE@.

   2.  It is understood that ACEs with a "who" value of OWNER@ affect
       the *USR bits of the mode, GROUP@ affect *GRP bits, and EVERYONE@
       affect *USR, *GRP, and *OTH bits.

   3.  If such an ACE specifies ALLOW or DENY for ACE4_READ_DATA,
       ACE4_WRITE_DATA, or ACE4_EXECUTE, and the mode bits affected have
       not been determined yet, set them to one (if ALLOW) or zero (if
       DENY).

   4.  Upon completion, any mode bits as yet undetermined have a value
       of zero.

   This pseudocode more precisely describes the algorithm:

          /* octal constants for the mode bits */

          RUSR = 0400
          WUSR = 0200
          XUSR = 0100
          RGRP = 0040
          WGRP = 0020
          XGRP = 0010
          ROTH = 0004
          WOTH = 0002
          XOTH = 0001

         /*
          * old_mode represents the previous value
          * of the mode of the object.
          */

          mode_t mode = 0, seen = 0;
          for each ACE a {
              if a.type is ALLOW or DENY and
              ACE4_INHERIT_ONLY_ACE is not set in a.flags {
                  if a.who is OWNER@ {
                      if ((a.mask & ACE4_READ_DATA) &&
                          (! (seen & RUSR))) {
                              seen |= RUSR;
                              if a.type is ALLOW {
                                  mode |= RUSR;
                              }
                      }



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                      if ((a.mask & ACE4_WRITE_DATA) &&
                          (! (seen & WUSR))) {
                              seen |= WUSR;
                              if a.type is ALLOW {
                                  mode |= WUSR;
                              }
                      }
                      if ((a.mask & ACE4_EXECUTE) &&
                          (! (seen & XUSR))) {
                              seen |= XUSR;
                              if a.type is ALLOW {
                                  mode |= XUSR;
                              }
                      }
                  } else if a.who is GROUP@ {
                      if ((a.mask & ACE4_READ_DATA) &&
                          (! (seen & RGRP))) {
                              seen |= RGRP;
                              if a.type is ALLOW {
                                  mode |= RGRP;
                              }
                      }
                      if ((a.mask & ACE4_WRITE_DATA) &&
                          (! (seen & WGRP))) {
                              seen |= WGRP;
                              if a.type is ALLOW {
                                  mode |= WGRP;
                              }
                      }
                      if ((a.mask & ACE4_EXECUTE) &&
                          (! (seen & XGRP))) {
                              seen |= XGRP;
                              if a.type is ALLOW {
                                  mode |= XGRP;
                              }
                      }
                  } else if a.who is EVERYONE@ {
                      if (a.mask & ACE4_READ_DATA) {
                          if ! (seen & RUSR) {
                              seen |= RUSR;
                              if a.type is ALLOW {
                                  mode |= RUSR;
                              }
                          }
                          if ! (seen & RGRP) {
                              seen |= RGRP;
                              if a.type is ALLOW {
                                  mode |= RGRP;



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                              }
                          }
                          if ! (seen & ROTH) {
                              seen |= ROTH;
                              if a.type is ALLOW {
                                  mode |= ROTH;
                              }
                          }
                      }
                      if (a.mask & ACE4_WRITE_DATA) {
                          if ! (seen & WUSR) {
                              seen |= WUSR;
                              if a.type is ALLOW {
                                  mode |= WUSR;
                              }
                          }
                          if ! (seen & WGRP) {
                              seen |= WGRP;
                              if a.type is ALLOW {
                                  mode |= WGRP;
                              }
                          }
                          if ! (seen & WOTH) {
                              seen |= WOTH;
                              if a.type is ALLOW {
                                  mode |= WOTH;
                              }
                          }
                      }
                      if (a.mask & ACE4_EXECUTE) {
                          if ! (seen & XUSR) {
                              seen |= XUSR;
                              if a.type is ALLOW {
                                  mode |= XUSR;
                              }
                          }
                          if ! (seen & XGRP) {
                              seen |= XGRP;
                              if a.type is ALLOW {
                                  mode |= XGRP;
                              }
                          }
                          if ! (seen & XOTH) {
                              seen |= XOTH;
                              if a.type is ALLOW {
                                  mode |= XOTH;
                              }
                          }



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                      }
                  }
              }
          }
          return mode | (old_mode & (SUID | SGID | SVTX))

3.16.6.2.  Applying the mode given to CREATE or OPEN to an inherited ACL

   The goal of implementing ACL inheritance is for newly created objects
   to inherit the ACLs they were intended to inherit, but without
   disregarding the mode that is given with the arguments to the CREATE
   or OPEN operations.  The general algorithm is as follows:

   1.  Form an ACL on the newly created object that is the concatenation
       of all inheritable ACEs from its parent directory.  Note that
       there may be zero inheritable ACEs; thus, an object may start
       with an empty ACL.

   2.  For each ACE in the new ACL, adjust its flags if necessary, and
       possibly create two ACEs in place of one.  This is necessary to
       honor the intent of the inheritance- related flags and to
       preserve information about the original inheritable ACEs in the
       case that they will be modified by other steps.  The algorithm is
       as follows:

       A.  If the ACE4_NO_PROPAGATE_INHERIT_ACE is set, or if the object
           being created is not a directory, then clear the following
           flags:

              ACE4_NO_PROPAGATE_INHERIT_ACE

              ACE4_FILE_INHERIT_ACE

              ACE4_DIRECTORY_INHERIT_ACE

              ACE4_INHERIT_ONLY_ACE

           Continue on to the next ACE.

       B.  If the object being created is a directory and
           ACE4_FILE_INHERIT_ACE is set, but ACE4_DIRECTORY_INHERIT_ACE
           is NOT set, then we ensure that ACE4_INHERIT_ONLY_ACE is set.
           Continue on to the next ACE.  Otherwise:

       C.  If the type of the ACE is neither ALLOW nor DENY, then
           continue on to the next ACE.





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       D.  Copy the original ACE into a second, adjacent ACE.

       E.  On the first ACE, ensure that ACE4_INHERIT_ONLY_ACE is set.

       F.  On the second ACE, clear the following flags:

              ACE4_NO_PROPAGATE_INHERIT_ACE

              ACE4_FILE_INHERIT_ACE

              ACE4_DIRECTORY_INHERIT_ACE

              ACE4_INHERIT_ONLY_ACE

       G.  On the second ACE, if the type field is ALLOW, an
           implementation MAY clear the following mask bits:

              ACE4_WRITE_ACL

              ACE4_WRITE_OWNER

   3.  To ensure that the mode is honored, apply the algorithm for
       applying a mode to a file/directory with an existing ACL on the
       new object as described in Section 3.16.6.3, using the mode that
       is to be used for file creation.

3.16.6.3.  Applying a Mode to an Existing ACL

   An existing ACL can mean two things in this context.  One, that a
   file/directory already exists and it has an ACL.  Two, that a
   directory has inheritable ACEs that will make up the ACL for any new
   files or directories created therein.

   The high-level goal of the behavior when a mode is set on a file with
   an existing ACL is to take the new mode into account, without needing
   to delete a pre-existing ACL.

   When a mode is applied to an object, e.g. via SETATTR or CREATE/OPEN,
   the ACL must be modified to accommodate the mode.

   1.  The ACL is traversed, one ACE at a time.  For each ACE:

       1.  If the type of the ACE is neither ALLOW nor DENY, the ACE is
           left unchanged.  Continue to the next ACE.

       2.  If the ACE4_INHERIT_ONLY_ACE flag is set on the ACE, it is
           left unchanged.  Continue to the next ACE.




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       3.  If either or both of ACE4_FILE_INHERIT_ACE or
           ACE4_DIRECTORY_INHERIT_ACE are set:

           1.  A copy of the ACE is made, and placed in the ACL
               immediately following the current ACE.

           2.  In the first ACE, the flag ACE4_INHERIT_ONLY_ACE is set.

           3.  In the second ACE, the following flags are cleared:

                  ACE4_FILE_INHERIT_ACE

                  ACE4_DIRECTORY_INHERIT_ACE

                  ACE4_NO_PROPAGATE_INHERIT_ACE

           The algorithm continues on with the second ACE.

       4.  If the "who" field is one of the following:

              OWNER@

              GROUP@

              EVERYONE@

           then the following mask bits are cleared:

              ACE4_READ_DATA / ACE4_LIST_DIRECTORY

              ACE4_WRITE_DATA / ACE4_ADD_FILE

              ACE4_APPEND_DATA / ACE4_ADD_SUBDIRECTORY

              ACE4_EXECUTE

           At this point, we proceed to the next ACE.

       5.  Otherwise, if the "who" field did not match one of OWNER@,
           GROUP@, or EVERYONE@, the following steps SHOULD be
           performed.

           1.  If the type of the ACE is ALLOW, we check the preceding
               ACE (if any).  If it does not meet all of the following
               criteria:

               1.  The type field is DENY.




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               2.  The who field is the same as the current ACE.

               3.  The flag bit ACE4_IDENTIFIER_GROUP is the same as it
                   is in the current ACE, and no other flag bits are
                   set.

               4.  The mask bits are a subset of the mask bits of the
                   current ACE, and are also a subset of the following:

                      ACE4_READ_DATA / ACE4_LIST_DIRECTORY

                      ACE4_WRITE_DATA / ACE4_ADD_FILE

                      ACE4_APPEND_DATA / ACE4_ADD_SUBDIRECTORY

                      ACE4_EXECUTE

               then an ACE of type DENY, with a who equal to the current
               ACE, flag bits equal to (<current-ACE-flags> &
               ACE4_IDENTIFIER_GROUP), and no mask bits, is prepended.

           2.  The following modifications are made to the prepended
               ACE.  The intent is to mask the following ACE to disallow
               ACE4_READ_DATA, ACE4_WRITE_DATA, ACE4_APPEND_DATA, or
               ACE4_EXECUTE, based upon the group permissions of the new
               mode.  As a special case, if the ACE matches the current
               owner of the file, the owner bits are used, rather than
               the group bits.  This is reflected in the algorithm
               below.






















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          Let there be three bits defined:

          #define READ    04
          #define WRITE   02
          #define EXEC    01

          Let "amode" be the new mode, right-shifted three
          bits, in order to have the group permission bits
          placed in the three low order bits of amode,
          i.e. amode = mode >> 3

          If ACE4_IDENTIFIER_GROUP is not set in the flags,
          and the "who" field of the ACE matches the owner
          of the file, we shift amode three more bits, in
          order to have the owner permission bits placed in
          the three low order bits of amode:

          amode = amode >> 3

          amode is now used as follows:

          If ACE4_READ_DATA is set on the current ACE:
                     If READ is set on amode:
                         ACE4_READ_DATA is cleared on the prepended ACE
                     else:
                         ACE4_READ_DATA is set on the prepended ACE

              If ACE4_WRITE_DATA is set on the current ACE:
                     If WRITE is set on amode:
                         ACE4_WRITE_DATA is cleared on the prepended ACE
                     else:
                         ACE4_WRITE_DATA is set on the prepended ACE
              If ACE4_APPEND_DATA is set on the current ACE:
                     If WRITE is set on amode:
                         ACE4_APPEND_DATA is cleared on the
                         prepended ACE
                     else:
                         ACE4_APPEND_DATA is set on the prepended ACE

              If ACE4_EXECUTE is set on the current ACE:
                     If EXEC is set on amode:
                         ACE4_EXECUTE is cleared on the prepended ACE
                     else:
                         ACE4_EXECUTE is set on the prepended ACE

           3.  To conform with POSIX, and prevent cases where the owner
               of the file is given permissions via an explicit group,
               we implement the following step.



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                  If ACE4_IDENTIFIER_GROUP is set in the flags field of
                  the ALLOW ACE:
                      Let "mode" be the mode that we are chmoding to:
                          extramode = (mode >> 3) & 07
                          ownermode = mode >> 6
                          extramode &= ~ownermode
                      If extramode is not zero:
                          If extramode & READ:
                              Clear ACE4_READ_DATA in both the
                              prepended DENY ACE and the ALLOW ACE
                          If extramode & WRITE:
                              Clear ACE4_WRITE_DATA and ACE_APPEND_DATA
                              in both the prepended DENY ACE and the
                              ALLOW ACE
                      If extramode & EXEC:
                              Clear ACE4_EXECUTE in both the prepended
                              DENY ACE and the ALLOW ACE

   2.  If there are at least six ACEs, the final six ACEs are examined.
       If they are not equal to the following ACEs:

          A1) OWNER@:::DENY
          A2) OWNER@:ACE4_WRITE_ACL/ACE4_WRITE_OWNER/
              ACE4_WRITE_ATTRIBUTES/ACE4_WRITE_NAMED_ATTRIBUTES::ALLOW
          A3) GROUP@::ACE4_IDENTIFIER_GROUP:DENY
          A4) GROUP@::ACE4_IDENTIFIER_GROUP:ALLOW
          A5) EVERYONE@:ACE4_WRITE_ACL/ACE4_WRITE_OWNER/
              ACE4_WRITE_ATTRIBUTES/ACE4_WRITE_NAMED_ATTRIBUTES::DENY
          A6) EVERYONE@:ACE4_READ_ACL/ACE4_READ_ATTRIBUTES/
              ACE4_READ_NAMED_ATTRIBUTES/ACE4_SYNCHRONIZE::ALLOW

       Then six ACEs matching the above are appended.

   3.  The final six ACEs are adjusted according to the incoming mode.

















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          /* octal constants for the mode bits */

          RUSR = 0400
          WUSR = 0200
          XUSR = 0100
          RGRP = 0040
          WGRP = 0020
          XGRP = 0010
          ROTH = 0004
          WOTH = 0002
          XOTH = 0001

          If RUSR is set: set ACE4_READ_DATA in A2
              else: set ACE4_READ_DATA in A1
          If WUSR is set: set ACE4_WRITE_DATA and ACE4_APPEND_DATA in A2
              else: set ACE4_WRITE_DATA and ACE4_APPEND_DATA in A1
          If XUSR is set: set ACE4_EXECUTE in A2
              else: set ACE4_EXECUTE in A1
          If RGRP is set: set ACE4_READ_DATA in A4
              else: set ACE4_READ_DATA in A3
          If WGRP is set: set ACE4_WRITE_DATA and ACE4_APPEND_DATA in A4
              else: set ACE4_WRITE_DATA and ACE4_APPEND_DATA in A3
          If XGRP is set: set ACE4_EXECUTE in A4
              else: set ACE4_EXECUTE in A3
          If ROTH is set: set ACE4_READ_DATA in A6
              else: set ACE4_READ_DATA in A5
          If WOTH is set: set ACE4_WRITE_DATA and ACE4_APPEND_DATA in A6
              else: set ACE4_WRITE_DATA and ACE4_APPEND_DATA in A5
          If XOTH is set: set ACE4_EXECUTE in A6
              else: set ACE4_EXECUTE in A5

3.16.6.4.  ACL and mode in the same SETATTR

   The only reason that a mode and ACL should be set in the same SETATTR
   is if the user wants to set the SUID, SGID and SVTX bits along with
   setting the permissions by means of an ACL.  There is still no way to
   enforce which order the attributes will be set in, and it is likely
   that different orders of operations will produce different results.

3.16.6.4.1.  Client Side Recommendations

   If an application needs to enforce a certain behavior, it is
   recommended that the client implementations set mode and ACL in
   separate SETATTR requests.  This will produce consistent and expected
   results.

   If an application wants to set SUID, SGID and SVTX bits and an ACL:




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      In the first SETATTR, set the mode with SUID, SGID and SVTX bits
      as desired and all other bits with a value of 0.

      In a following SETATTR (preferably in the same COMPOUND) set the
      ACL.

3.16.6.4.2.  Server Side Recommendations

   If both mode and ACL are given to SETATTR, server implementations
   should verify that the mode and ACL don't conflict, i.e. the mode
   computed from the given ACL must be the same as the given mode,
   excluding the SUID, SGID and SVTX bits.  The algorithm for assigning
   a new mode based on the ACL can be used.  This is described in
   section Section 3.16.6.1.  If a server receives a request to set both
   mode and ACL, but the two conflict, the server should return
   NFS4ERR_INVAL.

3.16.6.5.  Inheritance and turning it off

   The inheritance of access permissions may be problematic if a user
   cannot prevent their file from inheriting unwanted permissions.  For
   example, a user, "samf", sets up a shared project directory to be
   used by everyone working on Project Foo. "lisagab" is a part of
   Project Foo, but is working on something that should not be seen by
   anyone else.  How can "lisagab" make sure that any new files that she
   creates in this shared project directory do not inherit anything that
   could compromise the security of her work?

   More relevant to the implementors of NFS version 4 clients and
   servers is the question of how to communicate the fact that user,
   "lisagab", doesn't want any permissions to be inherited to her newly
   created file or directory.

   To do this, implementors should standardize on what the behavior of
   CREATE and OPEN must be if:

   1.  just mode is given

       In this case, inheritance will take place, but the mode will be
       applied to the inherited ACL as described in Section 3.16.6.1,
       thereby modifying the ACL.

   2.  just ACL is given

       In this case, inheritance will not take place, and the ACL as
       defined in the CREATE or OPEN will be set without modification.





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   3.  both mode and ACL are given

       In this case, implementors should verify that the mode and ACL
       don't conflict, i.e. the mode computed from the given ACL must be
       the same as the given mode.  The algorithm for assigning a new
       mode based on the ACL can be used.  This is described in
       Section 3.16.6.1) If a server receives a request to set both mode
       and ACL, but the two conflict, the server should return
       NFS4ERR_INVAL.  If the mode and ACL don't conflict, inheritance
       will not take placeand both, the mode and ACL, will be set
       without modification.

   4.  neither mode nor ACL are given

       In this case, inheritance will take place and no modifications to
       the ACL will happen.  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 accesses.

3.16.6.6.  Deficiencies in a Mode Representation of an ACL

   In the presence of an ACL, there are certain cases when the
   representation of the mode is not guaranteed to be accurate.  An
   example of a situation is detailed below.

   As mentioned in Section 3.16.6, the representation of the mode is
   deterministic, but not guaranteed to be accurate.  The mode bits
   potentially convey a more restrictive permission than what will
   actually be granted via the ACL.

   Given the following ACL of two ACEs:

          GROUP@:ACE4_READ_DATA/ACE4_WRITE_DATA/ACE4_EXECUTE:
              ACE4_IDENTIFIER_GROUP:ALLOW
          EVERYONE@:ACE4_READ_DATA/ACE4_WRITE_DATA/ACE4_EXECUTE::DENY

   we would compute a mode of 0070.  However, it is possible, even
   likely, that the owner might be a member of the object's owning
   group, and thus, the owner would be granted read, write, and execute
   access to the object.  This would conflict with the mode of 0070,
   where an owner would be denied this access.

   The only way to overcome this deficiency would be to determine
   whether the object's owner is a member of the object's owning group.
   This is difficult, but worse, on a POSIX or any UNIX-like system, it
   is a process' membership in a group that is important, not a user's.
   Thus, any fixed mode intended to represent the above ACL can be
   incorrect.



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   Example: administrative databases (possibly /etc/passwd and /etc/
   group) indicate that the user "bob" is a member of the group "staff".
   An object has the ACL given above, is owned by "bob", and has an
   owning group of "staff".  User "bob" has logged into the system, and
   thus processes have been created owned by "bob" and having membership
   in group "staff".

   A mode representation of the above ACL could thus be 0770, due to
   user "bob" having membership in group "staff".  Now, the
   administrative databases are changed, such that user "bob" is no
   longer in group "staff".  User "bob" logs in to the system again, and
   thus more processes are created, this time owned by "bob" but NOT in
   group "staff".

   A mode of 0770 is inaccurate for processes not belonging to group
   "staff".  But even if the mode of the file were proactively changed
   to 0070 at the time the group database was edited, mode 0070 would be
   inaccurate for the pre-existing processes owned by user "bob" and
   having membership in group "staff".


4.  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.

4.1.  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
   the name space constitutes all the files on disks named by mapped
   disk letters.  NFS server administrators rarely make the entire
   server's filesystem 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.

4.2.  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,



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   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 filesystem.  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
   filesystem" that allows the user to browse from one mounted
   filesystem 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.

4.3.  Server Pseudo Filesystem

   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 filesystem" that provides a view of exported
   directories only.  A pseudo filesystem has a unique fsid and behaves
   like a normal, read only filesystem.

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

           /a              pseudo filesystem
           /a/b            real filesystem
           /a/b/c          pseudo filesystem
           /a/b/c/d        real filesystem

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







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4.4.  Multiple Roots

   The DOS and Windows operating environments are sometimes described as
   having "multiple roots".  Filesystems are commonly represented as
   disk letters.  MacOS represents filesystems 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.

4.5.  Filehandle Volatility

   The nature of the server's pseudo filesystem is that it is a logical
   representation of filesystem(s) available from the server.
   Therefore, the pseudo filesystem is most likely constructed
   dynamically when the server is first instantiated.  It is expected
   that the pseudo filesystem 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 filesystem, 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.

4.6.  Exported Root

   If the server's root filesystem is exported, one might conclude that
   a pseudo-filesystem is unneeded.  This not necessarily so.  Assume
   the following filesystems 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-filesystem.

4.7.  Mount Point Crossing

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

           /a/b            (filesystem 1)
           /a/b/c/d        (filesystem 2)

   The pseudo filesystem for this server may be constructed to look



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   like:

           /               (place holder/not exported)
           /a/b            (filesystem 1)
           /a/b/c/d        (filesystem 2)

   It is the server's responsibility to present the pseudo filesystem
   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 filesystem "/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 filesystem "/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.

4.8.  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 filesystem 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 filesystem, the server
   may effectively hide filesystems 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

   The /a/b/c directory is a real filesystem 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.



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5.  File Locking and Share Reservations

   Integrating locking into the NFS protocol necessarily causes it to be
   stateful.  With the inclusion of share reservations 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
   communicates its view of this state to the server as needed.  The
   client is also able to detect inconsistent state before modifying a
   file.

   To support Win32 share reservations it is necessary to 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 protocol has
   an OPEN operation that subsumes the NFS version 3 methodology of
   LOOKUP, CREATE, and ACCESS.  However, because many operations require
   a filehandle, the traditional LOOKUP is preserved to map a file name
   to filehandle without establishing state on the server.  The policy
   of granting access or modifying files is managed by the server based
   on the client's state.  These mechanisms can implement policy ranging
   from advisory only locking to full mandatory locking.

5.1.  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
   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 heavy weight
   information to the eventual stateid used for most client and server
   locking and lease interactions.




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5.1.1.  Client ID

   For each LOCK request, the client must identify itself to the server.
   This is done in such a way as to allow for correct lock
   identification and crash recovery.  A sequence of a SETCLIENTID
   operation followed by a SETCLIENTID_CONFIRM operation is required to
   establish the identification onto the server.  Establishment of
   identification by a new incarnation of the client also has the effect
   of immediately breaking any leased state that a previous incarnation
   of the client might have had on the server, as opposed to forcing the
   new client incarnation to wait for the leases to expire.  Breaking
   the lease state amounts to the server removing 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 the section "Delegation Recovery".

   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 has previously recorded 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.

   There are several considerations for how the client generates the id
   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



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      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 SETCLIENTID 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 SETCLIENTID will
      cause the server to begin the process of removing the client's
      previous leased state.

   o  The algorithm for generating the string should not assume that the
      client's network address won't change.  This includes changes
      between client incarnations and even changes while the client is
      stilling 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, will generate a
      conflicting id string.

   o  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
      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.

      *  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).



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      *  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 SETCLIENTID.

   Note that SETCLIENTID and SETCLIENTID_CONFIRM has a secondary purpose
   of establishing the information the server needs to make callbacks to
   the client for purpose of supporting delegations.  It is permitted to
   change this information via SETCLIENTID and SETCLIENTID_CONFIRM
   within the same incarnation of the client without removing the
   client's leased state.

   Once a SETCLIENTID and SETCLIENTID_CONFIRM sequence has successfully
   completed, the client uses the short hand client identifier, of type
   clientid4, instead of the longer and less compact nfs_client_id4
   structure.  This short hand 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.  When a clientid is
   presented to a server 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 SETCLIENTID operation and then
   proceed to any other necessary recovery for the server reboot case
   (See the section "Server Failure and Recovery").

   The client must also employ the SETCLIENTID operation when it
   receives a NFS4ERR_STALE_STATEID error using a stateid derived from
   its current clientid, since this also indicates a server reboot which
   has invalidated the existing clientid (see the next section
   "lock_owner and stateid Definition" for details).

   See the detailed descriptions of SETCLIENTID and SETCLIENTID_CONFIRM
   for a complete specification of the operations.

5.1.2.  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
   SETCLIENTID/SETCLIENTID_CONFIRM sequence to establish a new identity.



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   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 if the id string in a SETCLIENTID request is properly
   constructed, and if the client takes care to use the same principal
   for each successive use of SETCLIENTID, then, barring an active
   denial of service attack, NFS4ERR_CLID_INUSE should never be
   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 SETCLIENTID 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 SETCLIENTID, and confirm the new clientid if followed by
   the appropriate SETCLIENTID_CONFIRM.

5.1.3.  lock_owner and stateid Definition

   When requesting a lock, the client must present to the server the
   clientid and an identifier for the owner of the requested lock.
   These two fields are referred to as the lock_owner and the definition
   of those fields are:

   o  A clientid returned by the server as part of the client's use of
      the SETCLIENTID operation.

   o  A variable length opaque array used to uniquely define the owner
      of a lock managed by the client.

      This may be a thread id, process id, or other unique value.

   When the server grants the lock, it responds with a unique stateid.
   The stateid is used as a shorthand reference to the lock_owner, since
   the server will be maintaining the correspondence between them.

   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.
   This requirement includes those stateids generated by earlier
   instances of the server.  From this, the client can be properly
   notified of a server restart.  This notification will occur when the



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   client presents a stateid to the server from a previous
   instantiation.

   The server must be able to distinguish the following situations and
   return the error as specified:

   o  The stateid was generated by an earlier server instance (i.e.
      before a server reboot).  The error NFS4ERR_STALE_STATEID should
      be returned.

   o  The stateid was generated by the current server instance but the
      stateid no longer designates the current locking state for the
      lockowner-file pair in question (i.e. one or more locking
      operations has occurred).  The error NFS4ERR_OLD_STATEID should be
      returned.

      This error condition will only occur when the client issues a
      locking request which changes a stateid while an I/O request that
      uses that stateid is outstanding.

   o  The stateid was generated by the current server instance but the
      stateid does not designate a locking state for any active
      lockowner-file pair.  The error NFS4ERR_BAD_STATEID should be
      returned.

      This error condition will occur when there has been a logic error
      on the part of the client or server.  This should not happen.

   One mechanism that may be used to satisfy these requirements is for
   the server to,

   o  divide the "other" field of each stateid into two fields:

      *  A server verifier which uniquely designates a particular server
         instantiation.

      *  An index into a table of locking-state structures.

   o  utilize the "seqid" field of each stateid, such that seqid is
      monotonically incremented for each stateid that is associated with
      the same index into the locking-state table.

   By matching the incoming stateid and its field values with the state
   held at the server, the server is able to easily determine if a
   stateid is valid for its current instantiation and state.  If the
   stateid is not valid, the appropriate error can be supplied to the
   client.




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5.1.4.  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 lock_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 lockowner.  If
   no state is established by the client, either record lock or share
   reservation, a stateid of all bits 0 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).

   With NFS version 3, there was no notion of a stateid so there was no
   way to tell if the application process of the client sending the READ
   or WRITE operation had also acquired the appropriate record lock on
   the file.  Thus there was no way to implement mandatory locking.
   With the stateid construct, this barrier has been removed.

   Note that for UNIX environments that support mandatory file locking,
   the distinction between advisory and mandatory locking is subtle.  In



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   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
   lockowner 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
   (which can be done by attempting to acquire the conflicting lock on
   the behalf of the lockowner, 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 began the stateid
   sequence, and as modified by subsequent OPENs and OPEN_DOWNGRADEs
   within that stateid sequence.  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 stateid of all bits 1 (one) MAY allow READ operations to bypass
   locking checks at the server.  However, WRITE operations with a
   stateid with bits all 1 (one) MUST NOT bypass locking checks and are
   treated exactly the same as if a stateid of all bits 0 were used.



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   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.

5.1.5.  Sequencing of Lock Requests

   Locking is different than most NFS operations as it requires "at-
   most-one" semantics that are not provided by ONCRPC.  ONCRPC over a
   reliable transport is not sufficient because a sequence of locking
   requests may span multiple TCP connections.  In the face of
   retransmission or reordering, lock or unlock requests must have a
   well defined and consistent behavior.  To accomplish this, each lock
   request contains a sequence number that is a consecutively increasing
   integer.  Different lock_owners have different sequences.  The server
   maintains the last sequence number (L) received and the response that
   was returned.  The first request issued for any given lock_owner is
   issued with a sequence number of zero.

   Note that for requests that contain a sequence number, for each
   lock_owner, there should be no more than one outstanding request.

   If a request (r) with a previous sequence number (r < L) is received,
   it is rejected with the return of error NFS4ERR_BAD_SEQID.  Given a
   properly-functioning client, the response to (r) must have been
   received before the last request (L) was sent.  If a duplicate of
   last request (r == L) is received, the stored response is returned.
   If a request beyond the next sequence (r == L + 2) is received, it is
   rejected with the return of error NFS4ERR_BAD_SEQID.  Sequence
   history is reinitialized whenever the SETCLIENTID/SETCLIENTID_CONFIRM
   sequence changes the client verifier.

   Since the sequence number is represented with an unsigned 32-bit
   integer, the arithmetic involved with the sequence number is mod
   2^32.  For an example of modulo arithetic involving sequence numbers
   see [RFC793].

   It is critical the server maintain the last response sent to the
   client to provide a more reliable cache of duplicate non-idempotent
   requests than that of the traditional cache described in [Juszczak].
   The traditional duplicate request cache uses a least recently used
   algorithm for removing unneeded requests.  However, the last lock
   request and response on a given lock_owner must be cached as long as
   the lock state exists on the server.



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   The client MUST monotonically increment the sequence number for the
   CLOSE, LOCK, LOCKU, OPEN, OPEN_CONFIRM, and OPEN_DOWNGRADE
   operations.  This is true even in the event that the previous
   operation that used the sequence number received an error.  The only
   exception to this rule is if the previous operation received one of
   the following errors: NFS4ERR_STALE_CLIENTID, NFS4ERR_STALE_STATEID,
   NFS4ERR_BAD_STATEID, NFS4ERR_BAD_SEQID, NFS4ERR_BADXDR,
   NFS4ERR_RESOURCE, NFS4ERR_NOFILEHANDLE.

5.1.6.  Recovery from Replayed Requests

   As described above, the sequence number is per lock_owner.  As long
   as the server maintains the last sequence number received and follows
   the methods described above, there are no risks of a Byzantine router
   re-sending old requests.  The server need only maintain the
   (lock_owner, sequence number) state as long as there are open files
   or closed files with locks outstanding.

   LOCK, LOCKU, OPEN, OPEN_DOWNGRADE, and CLOSE each contain a sequence
   number and therefore the risk of the replay of these operations
   resulting in undesired effects is non-existent while the server
   maintains the lock_owner state.

5.1.7.  Releasing lock_owner State

   When a particular lock_owner no longer holds open or file locking
   state at the server, the server may choose to release the sequence
   number state associated with the lock_owner.  The server may make
   this choice based on lease expiration, for the reclamation of server
   memory, or other implementation specific details.  In any event, the
   server is able to do this safely only when the lock_owner no longer
   is being utilized by the client.  The server may choose to hold the
   lock_owner state in the event that retransmitted requests are
   received.  However, the period to hold this state is implementation
   specific.

   In the case that a LOCK, LOCKU, OPEN_DOWNGRADE, or CLOSE is
   retransmitted after the server has previously released the lock_owner
   state, the server will find that the lock_owner has no files open and
   an error will be returned to the client.  If the lock_owner does have
   a file open, the stateid will not match and again an error is
   returned to the client.

5.1.8.  Use of Open Confirmation

   In the case that an OPEN is retransmitted and the lock_owner is being
   used for the first time or the lock_owner state has been previously
   released by the server, the use of the OPEN_CONFIRM operation will



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   prevent incorrect behavior.  When the server observes the use of the
   lock_owner for the first time, it will direct the client to perform
   the OPEN_CONFIRM for the corresponding OPEN.  This sequence
   establishes the use of an lock_owner and associated sequence number.
   Since the OPEN_CONFIRM sequence connects a new open_owner on the
   server with an existing open_owner on a client, the sequence number
   may have any value.  The OPEN_CONFIRM step assures the server that
   the value received is the correct one.  See the section "OPEN_CONFIRM
   - Confirm Open" for further details.

   There are a number of situations in which the requirement to confirm
   an OPEN would pose difficulties for the client and server, in that
   they would be prevented from acting in a timely fashion on
   information received, because that information would be provisional,
   subject to deletion upon non-confirmation.  Fortunately, these are
   situations in which the server can avoid the need for confirmation
   when responding to open requests.  The two constraints are:

   o  The server must not bestow a delegation for any open which would
      require confirmation.

   o  The server MUST NOT require confirmation on a reclaim-type open
      (i.e. one specifying claim type CLAIM_PREVIOUS or
      CLAIM_DELEGATE_PREV).

   These constraints are related in that reclaim-type opens are the only
   ones in which the server may be required to send a delegation.  For
   CLAIM_NULL, sending the delegation is optional while for
   CLAIM_DELEGATE_CUR, no delegation is sent.

   Delegations being sent with an open requiring confirmation are
   troublesome because recovering from non-confirmation adds undue
   complexity to the protocol while requiring confirmation on reclaim-
   type opens poses difficulties in that the inability to resolve the
   status of the reclaim until lease expiration may make it difficult to
   have timely determination of the set of locks being reclaimed (since
   the grace period may expire).

   Requiring open confirmation on reclaim-type opens is avoidable
   because of the nature of the environments in which such opens are
   done.  For CLAIM_PREVIOUS opens, this is immediately after server
   reboot, so there should be no time for lockowners to be created,
   found to be unused, and recycled.  For CLAIM_DELEGATE_PREV opens, we
   are dealing with a client reboot situation.  A server which supports
   delegation can be sure that no lockowners for that client have been
   recycled since client initialization and thus can ensure that
   confirmation will not be required.




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5.2.  Lock Ranges

   The protocol allows a lock owner to request a lock with a byte range
   and then either upgrade 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.

5.3.  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
   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.

5.4.  Blocking Locks

   Some clients require the support of blocking locks.  The NFS version
   4 protocol must not rely on a callback mechanism and therefore is



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   unable to notify a client when a previously denied lock has been
   granted.  Clients 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.

5.5.  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.

   The following events cause implicit renewal of all of the leases for
   a given client (i.e. all those sharing a given clientid).  Each of
   these is a positive indication that the client is still active and
   that the associated state held at the server, for the client, is
   still valid.

   o  An OPEN with a valid clientid.

   o  Any operation made with a valid stateid (CLOSE, DELEGRETURN, LOCK,
      LOCKU, OPEN, OPEN_CONFIRM, OPEN_DOWNGRADE, READ, SETATTR, WRITE).
      This does not include the special stateids of all bits 0 or all
      bits 1.

      Note that if the client had restarted or rebooted, the client
      would not be making these requests without issuing the
      SETCLIENTID/SETCLIENTID_CONFIRM sequence.  The use of the
      SETCLIENTID/SETCLIENTID_CONFIRM sequence (one that changes the



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      client verifier) notifies the server to drop the locking state
      associated with the client.  SETCLIENTID/SETCLIENTID_CONFIRM never
      renews a lease.

      If the server has rebooted, the stateids (NFS4ERR_STALE_STATEID
      error) or the clientid (NFS4ERR_STALE_CLIENTID error) will not be
      valid hence preventing spurious renewals.

   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
   (i.e. a RENEW 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.

5.6.  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.

5.6.1.  Client Failure and Recovery

   In the event that a client fails, the server may recover the client's
   locks when the associated leases have expired.  Conflicting locks
   from another client may only be granted after this lease expiration.
   If the client is able to restart or reinitialize within the lease
   period the client may be forced to wait the remainder of the lease
   period before obtaining new locks.

   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 SETCLIENTID call made by the client.
   The server returns a clientid as a result of the SETCLIENTID
   operation.  The client then confirms the use of the clientid with
   SETCLIENTID_CONFIRM.  The clientid in combination with an opaque
   owner field is then used by the client to identify the lock owner for
   OPEN.  This chain of associations is then used to identify all locks
   for a particular client.



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   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.

   Note that the verifier must have the same uniqueness properties of
   the verifier for the COMMIT operation.

5.6.2.  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 the 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.  The duration of
   this recovery period is equal to the duration of the lease period.

   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 the section
   "Client ID") and re-establish the locking state as discussed below.

   The period of special handling of locking and READs and WRITEs, equal
   in duration to the lease period, is referred to as the "grace
   period".  During the grace period, clients recover locks and the
   associated state by reclaim-type locking requests (i.e.  LOCK
   requests with reclaim set to true and OPEN operations with a claim
   type of CLAIM_PREVIOUS).  During the grace 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.

   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 and the non-
   reclaim client request can be serviced.  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 an impending reclaim locking request and the READ or WRITE
   operation.  If the server is unable to offer that guarantee, the



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   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 a count of locks on a given file is available in
   stable storage, the server can track reclaimed locks for the file and
   when all reclaims have been processed, non-reclaim locking requests
   may be processed.  This way the server can ensure that non-reclaim
   locking requests will not conflict with potential reclaim requests.
   With respect to I/O requests, if the server is able to determine that
   there are no outstanding reclaim requests for a file by information
   from stable storage or another similar mechanism, the processing of
   I/O requests could proceed normally for the file.

   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.




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5.6.3.  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.  As a result, 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, all I/O submitted by
   the client with the now invalid stateids will fail with the server
   returning the error NFS4ERR_EXPIRED.  Once this error is received,
   the client will suitably notify the application that held the lock.

   As a courtesy to the client or as an optimization, the server may
   continue to hold locks on behalf of a client for which recent
   communication has extended beyond the lease period.  If the server
   receives a lock or I/O request that conflicts with one of these
   courtesy locks, the server must free the courtesy lock and grant the
   new request.

   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 has the following scenario:

   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, so server releases lock.

   4.  Client B acquires a lock that would have conflicted with that of
       Client A.

   5.  Client B releases the lock

   6.  Server reboots

   7.  Network partition between client A and server heals.

   8.  Client A issues a RENEW operation, and gets back a
       NFS4ERR_STALE_CLIENTID.

   9.  Client A reclaims its lock within the server's grace period.

   Thus, at the final step, the server has erroneously granted client



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   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 follows:

   1.   Client A acquires a lock.

   2.   Server reboots.

   3.   Client A and server experience mutual network partition, such
        that client A is unable to reclaim its lock within the grace
        period.

   4.   Server's reclaim grace period ends.  Client A has no locks
        recorded on server.

   5.   Client B acquires a lock that would have conflicted with that of
        Client A.

   6.   Client B releases the lock

   7.   Server reboots a second time

   8.   Network partition between client A and server heals.

   9.   Client A issues a RENEW operation, and gets back a
        NFS4ERR_STALE_CLIENTID.

   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
   A's lock reclaim.

   Solving the first and second edge conditions requires that the server
   either assume after it reboots that edge condition occurs, and thus
   return NFS4ERR_NO_GRACE for all reclaim attempts, or that the server
   record some information stable storage.  The amount of information
   the server records in stable storage is in inverse proportion to how
   harsh the server wants to be whenever the edge conditions occur.  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 unlocked by the
   client and the lock's lockowner advances the sequence number such
   that the lock release is not the last stateful event for the
   lockowner's sequence.  For the two aforementioned edge conditions,
   the harshest a server can be, and still support a grace period for
   reclaims, requires that the server record in stable storage



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   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 the section, Server
      Revocation of Locks) to revoke a record lock, share reservation,
      or delegation

   o  a timestamp that is updated the first time after a server boot or
      reboot the client acquires record locking, share reservation, or
      delegation state on the server.  The timestamp need not be updated
      on subsequent lock requests until the server reboots.

   The server implementation would also record in the stable storage the
   timestamps from the two most recent server reboots.

   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 record that the client had an unexpired record lock, share
   reservation, or delegation established before the server's previous
   incarnation means that the server must reject a reclaim from client A
   with the error NFS4ERR_NO_GRACE.

   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 superharsh,
       but necessary if the server does not want to 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, after a server reboot, the server determines that
       there is unrecoverable damage or corruption to the the stable
       storage, then for all clients and/or locks affected, the server



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       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 otherwords, 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 the section "Server
   Revocation of Locks".

5.7.  Recovery from a Lock Request Timeout or Abort

   In the event a lock request times out, a client may decide to not
   retry the request.  The client may also abort the request when the
   process for which it was issued is terminated (e.g. in UNIX due to a
   signal).  It is possible though that the server received the request
   and acted upon it.  This would change the state on the server without
   the client being aware of the change.  It is paramount that the
   client re-synchronize state with server before it attempts any other
   operation that takes a seqid and/or a stateid with the same
   lock_owner.  This is straightforward to do without a special re-
   synchronize operation.

   Since the server maintains the last lock request and response
   received on the lock_owner, for each lock_owner, the client should
   cache the last lock request it sent such that the lock request did
   not receive a response.  From this, the next time the client does a
   lock operation for the lock_owner, it can send the cached request, if
   there is one, and if the request was one that established state (e.g.
   a LOCK or OPEN operation), the server will return the cached result
   or if never saw the request, perform it.  The client can follow up
   with a request to remove the state (e.g. a LOCKU or CLOSE operation).
   With this approach, the sequencing and stateid information on the
   client and server for the given lock_owner will re-synchronize and in
   turn the lock state will re-synchronize.



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5.8.  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
   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 instance 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 lock revocation event is the inability to renew the lease
   before expiration.  While this is considered a rare or unusual event,
   the client must be prepared to recover.  Both the server and client
   will be able to detect the failure to renew the lease and are capable
   of recovering without data corruption.  For the server, it tracks the
   last renewal event serviced for the client and knows when the lease
   will expire.  Similarly, 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.

   The third lock revocation event can occur as a result of
   administrative intervention within the lease period.  While this is
   considered a rare event, it is possible that the server's
   administrator has decided to release or revoke a particular lock held
   by the client.  As a result of revocation, the client will receive an
   error of NFS4ERR_ADMIN_REVOKED.  In this instance the client may
   assume that only the lock_owner's locks have been lost.  The client
   notifies the lock holder appropriately.  The client may not assume
   the lease period has been renewed as a result of failed operation.

   When the client determines the lease period may have expired, the
   client must mark all locks held for the associated lease as
   "unvalidated".  This means the client has been unable to re-establish
   or confirm the appropriate lock state with the server.  As described
   in the previous section on crash recovery, there are scenarios in
   which the server may grant conflicting locks after the lease period
   has expired for a client.  When it is possible that the lease period
   has expired, the client must validate each lock currently held to
   ensure that a conflicting lock has not been granted.  The client may
   accomplish this task by issuing an I/O request, either a pending I/O



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   or a zero-length read, specifying the stateid associated with the
   lock in question.  If the response to the request is success, the
   client has validated all of the locks governed by that stateid and
   re-established the appropriate state between itself and the server.
   If the I/O request is not successful, then one or more of the locks
   associated with the stateid was revoked by the server and the client
   must notify the owner.

5.9.  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.

   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;

5.10.  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



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   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
   lock_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
   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).

5.10.1.  Close and Retention of State Information

   Since a CLOSE operation requests deallocation of a stateid, dealing
   with retransmission of the CLOSE, may pose special difficulties,
   since the state information, which normally would be used to
   determine the state of the open file being designated, might be
   deallocated, resulting in an NFS4ERR_BAD_STATEID error.

   Servers may deal with this problem in a number of ways.  To provide
   the greatest degree assurance that the protocol is being used
   properly, a server should, rather than deallocate the stateid, mark
   it as close-pending, and retain the stateid with this status, until
   later deallocation.  In this way, a retransmitted CLOSE can be
   recognized since the stateid points to state information with this
   distinctive status, so that it can be handled without error.

   When adopting this strategy, a server should retain the state
   information until the earliest of:

   o  Another validly sequenced request for the same lockowner, that is
      not a retransmission.

   o  The time that a lockowner is freed by the server due to period
      with no activity.




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   o  All locks for the client are freed as a result of a SETCLIENTID.

   Servers may avoid this complexity, at the cost of less complete
   protocol error checking, by simply responding NFS4_OK in the event of
   a CLOSE for a deallocated stateid, on the assumption that this case
   must be caused by a retransmitted close.  When adopting this
   approach, it is desirable to at least log an error when returning a
   no-error indication in this situation.  If the server maintains a
   reply-cache mechanism, it can verify the CLOSE is indeed a
   retransmission and avoid error logging in most cases.

5.11.  Open Upgrade and Downgrade

   When an OPEN is done for a file and the lockowner 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.

5.12.  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 RENEW or READ (with zero length)
   requests.  Longer leases are certainly kinder and gentler to servers



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   trying to handle very large numbers of clients.  The number of RENEW
   requests drop in proportion to the lease time.  The disadvantages of
   long leases are slower recovery after server failure (the server must
   wait for the leases to expire and the grace period to elapse before
   granting new lock requests) and increased file contention (if client
   fails to transmit an unlock request then server must wait for lease
   expiration before granting new locks).

   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.

5.13.  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.


6.  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.



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   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
   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.

6.1.  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:



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   .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
   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").

6.2.  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.



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   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
   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.

6.2.1.  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



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   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
   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.




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   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
   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.

6.3.  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.

6.3.1.  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.



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   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.

   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.

6.3.2.  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



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   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
   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 filesystem.  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.



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   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
   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.

6.3.3.  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.

6.3.4.  Data Caching and File Identity

   When clients cache data, the file data needs to be organized
   according to the filesystem 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
   filesystem 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



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   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
   two filehandles designate the same filesystem 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.

6.4.  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



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   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
   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.




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   When an open delegation is made, the response to the OPEN contains an
   open delegation structure which specifies the following:

   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



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   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
   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.

6.4.1.  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 filesystem 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



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   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
   into account available filesystem space and any applicable quotas.
   The server can recall delegations as a result of managing the
   available filesystem 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 filesystem 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.

6.4.2.  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.

6.4.3.  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.



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   Since CB_GETATTR is being used to satisfy another client's GETATTR
   request, the server only needs to know if the client holding the
   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



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   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
   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



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   processing for constructing nsc, time_modify, and time_metadata would
   use this pseudo code:

   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.

6.4.4.  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





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   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
   results in recall of an open delegation depends on the semantics of
   the server filesystem.  If that filesystem 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



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      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
      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.

6.4.5.  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.




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   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:

      *  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.

6.4.6.  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.

6.5.  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.



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   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.
   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.

6.5.1.  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 filesystem 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.



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   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 filesystem.
   Such saving may also be restricted to situations when the client has
   sufficient buffering resources to keep the cached copy available
   until it is properly stored to the target filesystem.

6.6.  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 filesystem 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.



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   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
      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



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   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.

6.7.  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



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      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
      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:



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   o  Clients and servers MAY deny memory mapping a file they know there
      are record locks for.

   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.

6.8.  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 filesystem 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.



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   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
   reported, the client should not assume that other clients have not
   changed the directory.

6.9.  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 filesystem 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



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   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.


7.  Security Negotiation

   The NFSv4.0 specification contains three oversights and ambiguities
   with respect to the SECINFO operation.

   First, it is impossible for the client to use the SECINFO operation
   to determine the correct security triple for accessing a parent
   directory.  This is because SECINFO takes as arguments the current
   file handle and a component name.  However, NFSv4.0 uses the LOOKUPP
   operation to get the parent directory of the current file handle.  If
   the client uses the wrong security when issuing the LOOKUPP, and gets
   back an NFS4ERR_WRONGSEC error, SECINFO is useless to the client.
   The client is left with guessing which security the server will
   accept.  This defeats the purpose of SECINFO, which was to provide an
   efficient method of negotiating security.

   Second, there is ambiguity as to what the server should do when it is
   passed a LOOKUP operation such that the server restricts access to
   the current file handle with one security triple, and access to the
   component with a different triple, and remote procedure call uses one
   of the two security triples.  Should the server allow the LOOKUP?

   Third, there is a problem as to what the client must do (or can do),
   whenever the server returns NFS4ERR_WRONGSEC in response to a PUTFH
   operation.  The NFSv4.0 specification says that client should issue a
   SECINFO using the parent filehandle and the component name of the
   filehandle that PUTFH was issued with.  This may not be convenient
   for the client.

   This document resolves the above three issues in the context of
   NFSv4.1.


8.  Clarification of Security Negotiation in NFSv4.1

   This section attempts to clarify NFSv4.1 security negotiation issues.
   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.





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8.1.  PUTFH + LOOKUP

   The server implementation may decide whether to impose any
   restrictions on export security administration.  There are at least
   three approaches (Sc is the flavor set of the child export, Sp that
   of the parent),

     a)  Sc <= Sp (<= for subset)

     b)  Sc ^ Sp != {} (^ for intersection, {} for the empty set)

     c)  free form

   To support b (when client chooses a flavor that is not a member of
   Sp) and c, PUTFH must NOT return NFS4ERR_WRONGSEC in case of security
   mismatch.  Instead, it should be returned from the LOOKUP that
   follows.

   Since the above guideline does not contradict a, it should be
   followed in general.

8.2.  PUTFH + LOOKUPP

   Since SECINFO only works its way down, there is no way LOOKUPP can
   return NFS4ERR_WRONGSEC without the server implementing
   SECINFO_NO_NAME.  SECINFO_NO_NAME solves this issue because via style
   "parent", it works in the opposite direction as SECINFO (component
   name is implicit in this case).

8.3.  PUTFH + SECINFO

   This case should be treated specially.

   A security sensitive client should be allowed to choose a strong
   flavor when querying a server to determine a file object's permitted
   security flavors.  The security flavor chosen by the client does not
   have to be included in the flavor list of the export.  Of course the
   server has to be configured for whatever flavor the client selects,
   otherwise the request will fail at RPC authentication.

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







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8.4.  PUTFH + Anything Else

   PUTFH must return NFS4ERR_WRONGSEC in case of security mismatch.
   This is the most straightforward approach without having to add
   NFS4ERR_WRONGSEC to every other operations.

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


9.  NFSv4.1 Sessions

9.1.  Sessions Background

9.1.1.  Introduction to Sessions

   This draft proposes extensions to NFS version 4 [RFC3530] enabling it
   to support sessions and endpoint management, and to support operation
   atop RDMA-capable RPC over transports such as iWARP.  [RDMAP, DDP]
   These extensions enable support for exactly-once semantics by NFSv4
   servers, multipathing and trunking of transport connections, and
   enhanced security.  The ability to operate over RDMA enables greatly
   enhanced performance.  Operation over existing TCP is enhanced as
   well.

   While discussed here with respect to IETF-chartered transports, the
   proposed protocol is intended to function over other standards, such
   as Infiniband.  [IB]

   The following are the major aspects of this proposal:

   o  Changes are proposed within the framework of NFSv4 minor
      versioning.  RPC, XDR, and the NFSv4 procedures and operations are
      preserved.  The proposed extension functions equally well over
      existing transports and RDMA, and interoperates transparently with
      existing implementations, both at the local programmatic interface
      and over the wire.

   o  An explicit session is introduced to NFSv4, and new operations are
      added to support it.  The session allows for enhanced trunking,
      failover and recovery, and authentication efficiency, along with
      necessary support for RDMA.  The session is implemented as
      operations within NFSv4 COMPOUND and does not impact layering or
      interoperability with existing NFSv4 implementations.  The NFSv4
      callback channel is dynamically associated and is connected by the
      client and not the server, enhancing security and operation
      through firewalls.  In fact, the callback channel will be enabled
      to share the same connection as the operations channel.



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   o  An enhanced RPC layer enables NFSv4 operation atop RDMA.  The
      session assists RDMA-mode connection, and additional facilities
      are provided for managing RDMA resources at both NFSv4 server and
      client.  Existing NFSv4 operations continue to function as before,
      though certain size limits are negotiated.  A companion draft to
      this document, "RDMA Transport for ONC RPC" [RPCRDMA] is to be
      referenced for details of RPC RDMA support.

   o  Support for exactly-once semantics ("EOS") is enabled by the new
      session facilities, by providing to the server a way to bound the
      size of the duplicate request cache for a single client, and to
      manage its persistent storage.


                                   Block Diagram

             +-----------------+-------------------------------------+
             |     NFSv4       |     NFSv4 + session extensions      |
             +-----------------+------+----------------+-------------+
             |      Operations        |   Session      |             |
             +------------------------+----------------+             |
             |                RPC/XDR                  |             |
             +-------------------------------+---------+             |
             |       Stream Transport        |    RDMA Transport     |
             +-------------------------------+-----------------------+

9.1.2.  Motivation

   NFS version 4 [RFC3530] has been granted "Proposed Standard" status.
   The NFSv4 protocol was developed along several design points,
   important among them: effective operation over wide-area networks,
   including the Internet itself; strong security integrated into the
   protocol; extensive cross-platform interoperability including
   integrated locking semantics compatible with multiple operating
   systems; and protocol extensibility.

   The NFS version 4 protocol, however, does not provide support for
   certain important transport aspects.  For example, the protocol does
   not address response caching, which is required to provide
   correctness for retried client requests across a network partition,
   nor does it provide an interoperable way to support trunking and
   multipathing of connections.  This leads to inefficiencies,
   especially where trunking and multipathing are concerned, and
   presents additional difficulties in supporting RDMA fabrics, in which
   endpoints may require dedicated or specialized resources.  Sessions
   can be employed to unify NFS-level constructs such as the clientid,
   with transport-level constructs such as transport endpoints.  Each
   transport endpoint draws on resources via its membership in a



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   session.  Resource management can be more strictly maintained,
   leading to greater server efficiency in implementing the protocol.
   The enhanced operation over a session affords an opportunity to the
   server to implement a highly reliable duplicate request cache, and
   thereby export exactly-once semantics.

   NFSv4 advances the state of high-performance local sharing, by virtue
   of its integrated security, locking, and delegation, and its
   excellent coverage of the sharing semantics of multiple operating
   systems.  It is precisely this environment where exactly-once
   semantics become a fundamental requirement.

   Additionally, efforts to standardize a set of protocols for Remote
   Direct Memory Access, RDMA, over the Internet Protocol Suite have
   made significant progress.  RDMA is a general solution to the problem
   of CPU overhead incurred due to data copies, primarily at the
   receiver.  Substantial research has addressed this and has borne out
   the efficacy of the approach.  An overview of this is the RDDP
   Problem Statement document, [RDDPPS].

   Numerous upper layer protocols achieve extremely high bandwidth and
   low overhead through the use of RDMA.  Products from a wide variety
   of vendors employ RDMA to advantage, and prototypes have demonstrated
   the effectiveness of many more.  Here, we are concerned specifically
   with NFS and NFS-style upper layer protocols; examples from Network
   Appliance [DAFS, DCK+03], Fujitsu Prime Software Technologies [FJNFS,
   FJDAFS] and Harvard University [KM02] are all relevant.

   By layering a session binding for NFS version 4 directly atop a
   standard RDMA transport, a greatly enhanced level of performance and
   transparency can be supported on a wide variety of operating system
   platforms.  These combined capabilities alter the landscape between
   local filesystems and network attached storage, enable a new level of
   performance, and lead new classes of application to take advantage of
   NFS.

9.1.3.  Problem Statement

   Two issues drive the current proposal: correctness, and performance.
   Both are instances of "raising the bar" for NFS, whereby the desire
   to use NFS in new classes applications can be accommodated by
   providing the basic features to make such use feasible.  Such
   applications include tightly coupled sharing environments such as
   cluster computing, high performance computing (HPC) and information
   processing such as databases.  These trends are explored in depth in
   [NFSPS].

   The first issue, correctness, exemplified among the attributes of



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   local filesystems, is support for exactly-once semantics.  Such
   semantics have not been reliably available with NFS.  Server-based
   duplicate request caches [CJ89] help, but do not reliably provide
   strict correctness.  For the type of application which is expected to
   make extensive use of the high-performance RDMA-enabled environment,
   the reliable provision of such semantics is a fundamental
   requirement.

   Introduction of a session to NFSv4 will address these issues.  With
   higher performance and enhanced semantics comes the problem of
   enabling advanced endpoint management, for example high-speed
   trunking, multipathing and failover.  These characteristics enable
   availability and performance.  RFC3530 presents some issues in
   permitting a single clientid to access a server over multiple
   connections.

   A second issue encountered in common by NFS implementations is the
   CPU overhead required to implement the protocol.  Primary among the
   sources of this overhead is the movement of data from NFS protocol
   messages to its eventual destination in user buffers or aligned
   kernel buffers.  The data copies consume system bus bandwidth and CPU
   time, reducing the available system capacity for applications.
   [RDDPPS] Achieving zero-copy with NFS has to date required
   sophisticated, "header cracking" hardware and/or extensive platform-
   specific virtual memory mapping tricks.

   Combined in this way, NFSv4, RDMA and the emerging high-speed network
   fabrics will enable delivery of performance which matches that of the
   fastest local filesystems, preserving the key existing local
   filesystem semantics, while enhancing them by providing network
   filesystem sharing semantics.

   RDMA implementations generally have other interesting properties,
   such as hardware assisted protocol access, and support for user space
   access to I/O. RDMA is compelling here for another reason; hardware
   offloaded networking support in itself does not avoid data copies,
   without resorting to implementing part of the NFS protocol in the
   NIC.  Support of RDMA by NFS enables the highest performance at the
   architecture level rather than by implementation; this enables
   ubiquitous and interoperable solutions.

   By providing file access performance equivalent to that of local file
   systems, NFSv4 over RDMA will enable applications running on a set of
   client machines to interact through an NFSv4 file system, just as
   applications running on a single machine might interact through a
   local file system.

   This raises the issue of whether additional protocol enhancements to



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   enable such interaction would be desirable and what such enhancements
   would be.  This is a complicated issue which the working group needs
   to address and will not be further discussed in this document.

9.1.4.  NFSv4 Session Extension Characteristics

   This draft will present a solution based upon minor versioning of
   NFSv4.  It will introduce a session to collect transport endpoints
   and resources such as reply caching, which in turn enables
   enhancements such as trunking, failover and recovery.  It will
   describe use of RDMA by employing support within an underlying RPC
   layer [RPCRDMA].  Most importantly, it will focus on making the best
   possible use of an RDMA transport.

   These extensions are proposed as elements of a new minor revision of
   NFS version 4.  In this draft, NFS version 4 will be referred to
   generically as "NFSv4", when describing properties common to all
   minor versions.  When referring specifically to properties of the
   original, minor version 0 protocol, "NFSv4.0" will be used, and
   changes proposed here for minor version 1 will be referred to as
   "NFSv4.1".

   This draft proposes only changes which are strictly upward-
   compatible with existing RPC and NFS Application Programming
   Interfaces (APIs).

9.2.  Transport Issues

   The Transport Issues section of the document explores the details of
   utilizing the various supported transports.

9.2.1.  Session Model

   The first and most evident issue in supporting diverse transports is
   how to provide for their differences.  This draft proposes
   introducing an explicit session.

   A session introduces minimal protocol requirements, and provides for
   a highly useful and convenient way to manage numerous endpoint-
   related issues.  The session is a local construct; it represents a
   named, higher-layer object to which connections can refer, and
   encapsulates properties important to each associated client.

   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.  The session in effect becomes



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   the object representing an active client on a connection or set of
   connections.

   Clients may create multiple sessions for a single clientid, and may
   wish to do so for optimization of transport resources, buffers, or
   server behavior.  A session could be created by the client to
   represent a single mount point, for separate read and write
   "channels", or for any number of other client-selected parameters.

   The session enables several things immediately.  Clients may
   disconnect and reconnect (voluntarily or not) without loss of context
   at the server.  (Of course, locks, delegations and related
   associations require special handling, and generally expire in the
   extended absence of an open connection.)  Clients may connect
   multiple transport endpoints to this common state.  The endpoints may
   have all the same attributes, for instance when trunked on multiple
   physical network links for bandwidth aggregation or path failover.
   Or, the endpoints can have specific, special purpose attributes such
   as callback channels.

   The NFSv4 specification does not provide for any form of flow
   control; instead it relies on the windowing provided by TCP to
   throttle requests.  This unfortunately does not work with RDMA, which
   in general provides no operation flow control and will terminate a
   connection in error when limits are exceeded.  Limits are therefore
   exchanged when a session is created; These limits then provide maxima
   within which each session's connections must operate, they are
   managed within these limits as described in [RPCRDMA].  The limits
   may also be modified dynamically at the server's choosing by
   manipulating certain parameters present in each NFSv4.1 request.

   The presence of a maximum request limit on the session bounds the
   requirements of the duplicate request cache.  This can be used to
   advantage by a server, which can accurately determine any storage
   needs and enable it to maintain duplicate request cache persistence
   and to provide reliable exactly-once semantics.

   Finally, given adequate connection-oriented transport security
   semantics, authentication and authorization may be cached on a per-
   session basis, enabling greater efficiency in the issuing and
   processing of requests on both client and server.  A proposal for
   transparent, server-driven implementation of this in NFSv4 has been
   made.  [CCM] The existence of the session greatly facilitates the
   implementation of this approach.  This is discussed in detail in the
   Authentication Efficiencies section later in this draft.






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9.2.2.  Connection State

   In RFC3530, the combination of a connected transport endpoint and a
   clientid forms the basis of connection state.  While has been made to
   be workable with certain limitations, there are difficulties in
   correct and robust implementation.  The NFSv4.0 protocol must provide
   a server-initiated connection for the callback channel, and must
   carefully specify the persistence of client state at the server in
   the face of transport interruptions.  The server has only the
   client's transport address binding (the IP 4-tuple) to identify the
   client RPC transaction stream and to use as a lookup tag on the
   duplicate request cache.  (A useful overview of this is in [RW96].)
   If the server listens on multiple adddresses, and the client connects
   to more than one, it must employ different clientid's on each,
   negating its ability to aggregate bandwidth and redundancy.  In
   effect, each transport connection is used as the server's
   representation of client state.  But, transport connections are
   potentially fragile and transitory.

   In this proposal, a session identifier is assigned by the server upon
   initial session negotiation on each connection.  This identifier is
   used to associate additional connections, to renegotiate after a
   reconnect, to provide an abstraction for the various session
   properties, and to address the duplicate request cache.  No
   transport-specific information is used in the duplicate request cache
   implementation of an NFSv4.1 server, nor in fact the RPC XID itself.
   The session identifier is unique within the server's scope and may be
   subject to certain server policies such as being bounded in time.

   It is envisioned that the primary transport model will be connection
   oriented.  Connection orientation brings with it certain potential
   optimizations, such as caching of per-connection properties, which
   are easily leveraged through the generality of the session.  However,
   it is possible that in future, other transport models could be
   accommodated below the session abstraction.

9.2.3.  NFSv4 Channels, Sessions and Connections

   There are at least two types of NFSv4 channels: the "operations"
   channel used for ordinary requests from client to server, and the
   "back" channel, used for callback requests from server to client.

   As mentioned above, different NFSv4 operations on these channels can
   lead to different resource needs.  For example, server callback
   operations (CB_RECALL) are specific, small messages which flow from
   server to client at arbitrary times, while data transfers such as
   read and write have very different sizes and asymmetric behaviors.
   It is sometimes impractical for the RDMA peers (NFSv4 client and



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   NFSv4 server) to post buffers for these various operations on a
   single connection.  Commingling of requests with responses at the
   client receive queue is particularly troublesome, due both to the
   need to manage both solicited and unsolicited completions, and to
   provision buffers for both purposes.  Due to the lack of any ordering
   of callback requests versus response arrivals, without any other
   mechanisms, the client would be forced to allocate all buffers sized
   to the worst case.

   The callback requests are likely to be handled by a different task
   context from that handling the responses.  Significant demultiplexing
   and thread management may be required if both are received on the
   same queue.  However, if callbacks are relatively rare (perhaps due
   to client access patterns), many of these difficulties can be
   minimized.

   Also, the client may wish to perform trunking of operations channel
   requests for performance reasons, or multipathing for availability.
   This proposal permits both, as well as many other session and
   connection possibilities, by permitting each operation to carry
   session membership information and to share session (and clientid)
   state in order to draw upon the appropriate resources.  For example,
   reads and writes may be assigned to specific, optimized connections,
   or sorted and separated by any or all of size, idempotency, etc.

   To address the problems described above, this proposal allows
   multiple sessions to share a clientid, as well as for multiple
   connections to share a session.

   Single Connection model:





















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                            NFSv4.1 Session
                               /      \
                Operations_Channel   [Back_Channel]
                                \    /
                             Connection
                                  |


        Multi-connection trunked model (2 operations channels shown):

                            NFSv4.1 Session
                               /      \
                Operations_Channels  [Back_Channel]
                    |          |               |
                Connection Connection     [Connection]
                    |          |               |


        Multi-connection split-use model (2 mounts shown):

                                     NFSv4.1 Session
                                   /                 \
                            (/home)        (/usr/local - readonly)
                            /      \                    |
             Operations_Channel  [Back_Channel]         |
                     |                 |          Operations_Channel
                 Connection       [Connection]          |
                     |                 |            Connection
                                                        |

   In this way, implementation as well as resource management may be
   optimized.  Each session will have its own response caching and
   buffering, and each connection or channel will have its own transport
   resources, as appropriate.  Clients which do not require certain
   behaviors may optimize such resources away completely, by using
   specific sessions and not even creating the additional channels and
   connections.

9.2.4.  Reconnection, Trunking and Failover

   Reconnection after failure references stored state on the server
   associated with lease recovery during the grace period.  The session
   provides a convenient handle for storing and managing information
   regarding the client's previous state on a per- connection basis,
   e.g. to be used upon reconnection.  Reconnection to a previously
   existing session, and its stored resources, are covered in the
   "Connection Models" section below.




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   One important aspect of reconnection is that of RPC library support.
   Traditionally, an Upper Layer RPC-based Protocol such as NFS leaves
   all transport knowledge to the RPC layer implementation below it.
   This allows NFS to operate over a wide variety of transports and has
   proven to be a highly successful approach.  The session, however,
   introduces an abstraction which is, in a way, "between" RPC and
   NFSv4.1.  It is important that the session abstraction not have
   ramifications within the RPC layer.

   One such issue arises within the reconnection logic of RPC.
   Previously, an explicit session binding operation, which established
   session context for each new connection, was explored.  This however
   required that the session binding also be performed during reconnect,
   which in turn required an RPC request.  This additional request
   requires new RPC semantics, both in implementation and the fact that
   a new request is inserted into the RPC stream.  Also, the binding of
   a connection to a session required the upper layer to become "aware"
   of connections, something the RPC layer abstraction architecturally
   abstracts away.  Therefore the session binding is not handled in
   connection scope but instead explicitly carried in each request.

   For Reliability Availability and Serviceability (RAS) issues such as
   bandwidth aggregation and multipathing, clients frequently seek to
   make multiple connections through multiple logical or physical
   channels.  The session is a convenient point to aggregate and manage
   these resources.

9.2.5.  Server Duplicate Request Cache

   Server duplicate request caches, while not a part of an NFS protocol,
   have become a standard, even required, part of any NFS
   implementation.  First described in [CJ89], the duplicate request
   cache was initially found to reduce work at the server by avoiding
   duplicate processing for retransmitted requests.  A second, and in
   the long run more important benefit, was improved correctness, as the
   cache avoided certain destructive non-idempotent requests from being
   reinvoked.

   However, such caches do not provide correctness guarantees; they
   cannot be managed in a reliable, persistent fashion.  The reason is
   understandable - their storage requirement is unbounded due to the
   lack of any such bound in the NFS protocol, and they are dependent on
   transport addresses for request matching.

   As proposed in this draft, the presence of maximum request count
   limits and negotiated maximum sizes allows the size and duration of
   the cache to be bounded, and coupled with a long-lived session
   identifier, enables its persistent storage on a per-session basis.



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   This provides a single unified mechanism which provides the following
   guarantees required in the NFSv4 specification, while extending them
   to all requests, rather than limiting them only to a subset of state-
   related requests:

   "It is critical the server maintain the last response sent to the
   client to provide a more reliable cache of duplicate non- idempotent
   requests than that of the traditional cache described in [CJ89]..."
   [RFC3530]

   The maximum request count limit is the count of active operations,
   which bounds the number of entries in the cache.  Constraining the
   size of operations additionally serves to limit the required storage
   to the product of the current maximum request count and the maximum
   response size.  This storage requirement enables server- side
   efficiencies.

   Session negotiation allows the server to maintain other state.  An
   NFSv4.1 client invoking the session destroy operation will cause the
   server to denegotiate (close) the session, allowing the server to
   deallocate cache entries.  Clients can potentially specify that such
   caches not be kept for appropriate types of sessions (for example,
   read-only sessions).  This can enable more efficient server operation
   resulting in improved response times, and more efficient sizing of
   buffers and response caches.

   Similarly, it is important for the client to explicitly learn whether
   the server is able to implement reliable semantics.  Knowledge of
   whether these semantics are in force is critical for a highly
   reliable client, one which must provide transactional integrity
   guarantees.  When clients request that the semantics be enabled for a
   given session, the session reply must inform the client if the mode
   is in fact enabled.  In this way the client can confidently proceed
   with operations without having to implement consistency facilities of
   its own.

9.3.  Session Initialization and Transfer Models

   Session initialization issues, and data transfer models relevant to
   both TCP and RDMA are discussed in this section.

9.3.1.  Session Negotiation

   The following parameters are exchanged between client and server at
   session creation time.  Their values allow the server to properly
   size resources allocated in order to service the client's requests,
   and to provide the server with a way to communicate limits to the
   client for proper and optimal operation.  They are exchanged prior to



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   all session-related activity, over any transport type.  Discussion of
   their use is found in their descriptions as well as throughout this
   section.

   Maximum Requests

      The client's desired maximum number of concurrent requests is
      passed, in order to allow the server to size its reply cache
      storage.  The server may modify the client's requested limit
      downward (or upward) to match its local policy and/or resources.
      Over RDMA-capable RPC transports, the per-request management of
      low-level transport message credits is handled within the RPC
      layer.  [RPCRDMA]

   Maximum Request/Response Sizes

      The maximum request and response sizes are exchanged in order to
      permit allocation of appropriately sized buffers and request cache
      entries.  The size must allow for certain protocol minima,
      allowing the receipt of maximally sized operations (e.g.  RENAME
      requests which contains two name strings).  Note the maximum
      request/response sizes cover the entire request/response message
      and not simply the data payload as traditional NFS maximum read or
      write size.  Also note the server implementation may not, in fact
      probably does not, require the reply cache entries to be sized as
      large as the maximum response.  The server may reduce the client's
      requested sizes.

   Inline Padding/Alignment

      The server can inform the client of any padding which can be used
      to deliver NFSv4 inline WRITE payloads into aligned buffers.  Such
      alignment can be used to avoid data copy operations at the server
      for both TCP and inline RDMA transfers.  For RDMA, the client
      informs the server in each operation when padding has been
      applied.  [RPCRDMA]

   Transport Attributes

      A placeholder for transport-specific attributes is provided, with
      a format to be determined.  Possible examples of information to be
      passed in this parameter include transport security attributes to
      be used on the connection, RDMA- specific attributes, legacy
      "private data" as used on existing RDMA fabrics, transport Quality
      of Service attributes, etc.  This information is to be passed to
      the peer's transport layer by local means which is currently
      outside the scope of this draft, however one attribute is provided
      in the RDMA case:



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   RDMA Read Resources

      RDMA implementations must explicitly provision resources to
      support RDMA Read requests from connected peers.  These values
      must be explicitly specified, to provide adequate resources for
      matching the peer's expected needs and the connection's delay-
      bandwidth parameters.  The client provides its chosen value to the
      server in the initial session creation, the value must be provided
      in each client RDMA endpoint.  The values are asymmetric and
      should be set to zero at the server in order to conserve RDMA
      resources, since clients do not issue RDMA Read operations in this
      proposal.  The result is communicated in the session response, to
      permit matching of values across the connection.  The value may
      not be changed in the duration of the session, although a new
      value may be requested as part of a new session.

9.3.2.  RDMA Requirements

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

   A connection oriented (reliable sequenced) RDMA transport will be
   required.  There are several reasons for this.  First, this model
   most closely reflects the general NFSv4 requirement of long-lived and
   congestion-controlled transports.  Second, to operate correctly over
   either an unreliable or unsequenced RDMA transport, or both, would
   require significant complexity in the implementation and protocol not
   appropriate for a strict minor version.  For example, retransmission
   on connected endpoints is explicitly disallowed in the current NFSv4
   draft; it would again be required with these alternate transport
   characteristics.  Third, the proposal assumes a specific RDMA
   ordering semantic, which presents the same set of ordering and
   reliability issues to the RDMA layer over such transports.

   The RDMA implementation provides for making connections to other
   RDMA-capable peers.  In the case of the current proposals before the
   RDDP working group, these RDMA connections are preceded by a
   "streaming" phase, where ordinary TCP (or NFS) traffic might flow.
   However, this is not assumed here and sizes and other parameters are
   explicitly exchanged upon a session entering RDMA mode.

9.3.3.  RDMA Connection Resources

   On transport endpoints which support automatic RDMA mode, that is,
   endpoints which are created in the RDMA-enabled state, a single,
   preposted buffer must initially be provided by both peers, and the



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   client session negotiation must be the first exchange.

   On transport endpoints supporting dynamic negotiation, a more
   sophisticated negotiation is possible, but is not discussed in the
   current draft.

   RDMA imposes several requirements on upper layer consumers.
   Registration of memory and the need to post buffers of a specific
   size and number for receive operations are a primary consideration.

   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.

   The session provides a natural way for the server to manage resource
   allocation to each client rather than to each transport connection
   itself.  This enables considerable flexibility in the administration
   of transport endpoints.

9.3.4.  TCP and RDMA Inline Transfer Model

   The basic transfer model for both TCP and RDMA is referred to as
   "inline".  For TCP, this is the only transfer model supported, since
   TCP carries both the RPC header and data together in the data stream.

   For RDMA, the RDMA Send transfer model is used for all NFS requests
   and replies, but data is optionally carried by RDMA Writes or RDMA
   Reads.  Use of Sends is required to ensure consistency of data and to
   deliver completion notifications.  The pure-Send method is typically
   used where the data payload is small, or where for whatever reason
   target memory for RDMA is not available.










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        Inline message exchange

               Client                                Server
                  :                Request              :
             Send :   ------------------------------>   : untagged
                  :                                     :  buffer
                  :               Response              :
         untagged :   <------------------------------   : Send
          buffer  :                                     :


               Client                                Server
                  :            Read request             :
             Send :   ------------------------------>   : untagged
                  :                                     :  buffer
                  :       Read response with data       :
         untagged :   <------------------------------   : Send
          buffer  :                                     :


               Client                                Server
                  :       Write request with data       :
             Send :   ------------------------------>   : untagged
                  :                                     :  buffer
                  :            Write response           :
         untagged :   <------------------------------   : Send
          buffer  :                                     :

   Responses must be sent to the client on the same connection that the
   request was sent.  It is important that the server does not assume
   any specific client implementation, in particular whether connections
   within a session share any state at the client.  This is also
   important to preserve ordering of RDMA operations, and especially
   RMDA consistency.  Additionally, it ensures that the RPC RDMA layer
   makes no requirement of the RDMA provider to open its memory
   registration handles (Steering Tags) beyond the scope of a single
   RDMA connection.  This is an important security consideration.

   Two values must be known to each peer prior to issuing Sends: the
   maximum number of sends which may be posted, and their maximum size.
   These values are referred to, respectively, as the message credits
   and the maximum message size.  While the message credits might vary
   dynamically over the duration of the session, the maximum message
   size does not.  The server must commit to preserving this number of
   duplicate request cache entires, and preparing a number of receive
   buffers equal to or greater than its currently advertised credit
   value, each of the advertised size.  These ensure that transport
   resources are allocated sufficient to receive the full advertised



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   limits.

   Note that the server must post the maximum number of session requests
   to each client operations channel.  The client is not required to
   spread its requests in any particular fashion across connections
   within a session.  If the client wishes, it may create multiple
   sessions, each with a single or small number of operations channels
   to provide the server with this resource advantage.  Or, over RDMA
   the server may employ a "shared receive queue".  The server can in
   any case protect its resources by restricting the client's request
   credits.

   While tempting to consider, it is not possible to use the TCP window
   as an RDMA operation flow control mechanism.  First, to do so would
   violate layering, requiring both senders to be aware of the existing
   TCP outbound window at all times.  Second, since requests are of
   variable size, the TCP window can hold a widely variable number of
   them, and since it cannot be reduced without actually receiving data,
   the receiver cannot limit the sender.  Third, any middlebox
   interposing on the connection would wreck any possible scheme.
   [MIDTAX] In this proposal, maximum request count limits are exchanged
   at the session level to allow correct provisioning of receive buffers
   by transports.

   When operating over TCP or other similar transport, request limits
   and sizes are still employed in NFSv4.1, but instead of being
   required for correctness, they provide the basis for efficient server
   implementation of the duplicate request cache.  The limits are chosen
   based upon the expected needs and capabilities of the client and
   server, and are in fact arbitrary.  Sizes may be specified by the
   client as zero (requesting the server's preferred or optimal value),
   and request limits may be chosen in proportion to the client's
   capabilities.  For example, a limit of 1000 allows 1000 requests to
   be in progress, which may generally be far more than adequate to keep
   local networks and servers fully utilized.

   Both client and server have independent sizes and buffering, but over
   RDMA fabrics client credits are easily managed by posting a receive
   buffer prior to sending each request.  Each such buffer may not be
   completed with the corresponding reply, since responses from NFSv4
   servers arrive in arbitrary order.  When an operations channel is
   also used for callbacks, the client must account for callback
   requests by posting additional buffers.  Note that implementation-
   specific facilities such as a shared receive queue may also allow
   optimization of these allocations.

   When a session is created, the client requests a preferred buffer
   size, and the server provides its answer.  The server posts all



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   buffers of at least this size.  The client must comply by not sending
   requests greater than this size.  It is recommended that server
   implementations do all they can to accommodate a useful range of
   possible client requests.  There is a provision in [RPCRDMA] to allow
   the sending of client requests which exceed the server's receive
   buffer size, but it requires the server to "pull" the client's
   request as a "read chunk" via RDMA Read.  This introduces at least
   one additional network roundtrip, plus other overhead such as
   registering memory for RDMA Read at the client and additional RDMA
   operations at the server, and is to be avoided.

   An issue therefore arises when considering the NFSv4 COMPOUND
   procedures.  Since an arbitrary number (total size) of operations can
   be specified in a single COMPOUND procedure, its size is effectively
   unbounded.  This cannot be supported by RDMA Sends, and therefore
   this size negotiation places a restriction on the construction and
   maximum size of both COMPOUND requests and responses.  If a COMPOUND
   results in a reply at the server that is larger than can be sent in
   an RDMA Send to the client, then the COMPOUND must terminate and the
   operation which causes the overflow will provide a TOOSMALL error
   status result.

9.3.5.  RDMA Direct Transfer Model

   Placement of data by explicitly tagged RDMA operations is referred to
   as "direct" transfer.  This method is typically used where the data
   payload is relatively large, that is, when RDMA setup has been
   performed prior to the operation, or when any overhead for setting up
   and performing the transfer is regained by avoiding the overhead of
   processing an ordinary receive.

   The client advertises RDMA buffers in this proposed model, and not
   the server.  This means the "XDR Decoding with Read Chunks" described
   in [RPCRDMA] is not employed by NFSv4.1 replies, and instead all
   results transferred via RDMA to the client employ "XDR Decoding with
   Write Chunks".  There are several reasons for this.

   First, it allows for a correct and secure mode of transfer.  The
   client may advertise specific memory buffers only during specific
   times, and may revoke access when it pleases.  The server is not
   required to expose copies of local file buffers for individual
   clients, or to lock or copy them for each client access.

   Second, client credits based on fixed-size request buffers are easily
   managed on the server, but for the server additional management of
   buffers for client RDMA Reads is not well-bounded.  For example, the
   client may not perform these RDMA Read operations in a timely
   fashion, therefore the server would have to protect itself against



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   denial-of-service on these resources.

   Third, it reduces network traffic, since buffer exposure outside the
   scope and duration of a single request/response exchange necessitates
   additional memory management exchanges.

   There are costs associated with this decision.  Primary among them is
   the need for the server to employ RDMA Read for operations such as
   large WRITE.  The RDMA Read operation is a two-way exchange at the
   RDMA layer, which incurs additional overhead relative to RDMA Write.
   Additionally, RDMA Read requires resources at the data source (the
   client in this proposal) to maintain state and to generate replies.
   These costs are overcome through use of pipelining with credits, with
   sufficient RDMA Read resources negotiated at session initiation, and
   appropriate use of RDMA for writes by the client - for example only
   for transfers above a certain size.

   A description of which NFSv4 operation results are eligible for data
   transfer via RDMA Write is in [NFSDDP].  There are only two such
   operations: READ and READLINK.  When XDR encoding these requests on
   an RDMA transport, the NFSv4.1 client must insert the appropriate
   xdr_write_list entries to indicate to the server whether the results
   should be transferred via RDMA or inline with a Send.  As described
   in [NFSDDP], a zero-length write chunk is used to indicate an inline
   result.  In this way, it is unnecessary to create new operations for
   RDMA-mode versions of READ and READLINK.

   Another tool to avoid creation of new, RDMA-mode operations is the
   Reply Chunk [RPCRDMA], which is used by RPC in RDMA mode to return
   large replies via RDMA as if they were inline.  Reply chunks are used
   for operations such as READDIR, which returns large amounts of
   information, but in many small XDR segments.  Reply chunks are
   offered by the client and the server can use them in preference to
   inline.  Reply chunks are transparent to upper layers such as NFSv4.

   In any very rare cases where another NFSv4.1 operation requires
   larger buffers than were negotiated when the session was created (for
   example extraordinarily large RENAMEs), the underlying RPC layer may
   support the use of "Message as an RDMA Read Chunk" and "RDMA Write of
   Long Replies" as described in [RPCRDMA].  No additional support is
   required in the NFSv4.1 client for this.  The client should be
   certain that its requested buffer sizes are not so small as to make
   this a frequent occurrence, however.

   All operations are initiated by a Send, and are completed with a
   Send.  This is exactly as in conventional NFSv4, but under RDMA has a
   significant purpose: RDMA operations are not complete, that is,
   guaranteed consistent, at the data sink until followed by a



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   successful Send completion (i.e. a receive).  These events provide a
   natural opportunity for the initiator (client) to enable and later
   disable RDMA access to the memory which is the target of each
   operation, in order to provide for consistent and secure operation.
   The RDMAP Send with Invalidate operation may be worth employing in
   this respect, as it relieves the client of certain overhead in this
   case.

   A "onetime" boolean advisory to each RDMA region might become a hint
   to the server that the client will use the three-tuple for only one
   NFSv4 operation.  For a transport such as iWARP, the server can
   assist the client in invalidating the three-tuple by performing a
   Send with Solicited Event and Invalidate.  The server may ignore this
   hint, in which case the client must perform a local invalidate after
   receiving the indication from the server that the NFSv4 operation is
   complete.  This may be considered in a future version of this draft
   and [NFSDDP].

   In a trusted environment, it may be desirable for the client to
   persistently enable RDMA access by the server.  Such a model is
   desirable for the highest level of efficiency and lowest overhead.






























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        RDMA message exchanges

               Client                                Server
                  :         Direct Read Request         :
             Send :   ------------------------------>   : untagged
                  :                                     :  buffer
                  :               Segment               :
          tagged  :   <------------------------------   :  RDMA Write
          buffer  :                  :                  :
                  :              [Segment]              :
          tagged  :   <------------------------------   : [RDMA Write]
          buffer  :                                     :
                  :         Direct Read Response        :
         untagged :   <------------------------------   :  Send (w/Inv.)
          buffer  :                                     :






               Client                                Server
                  :        Direct Write Request         :
             Send :   ------------------------------>   : untagged
                  :                                     :  buffer
                  :               Segment               :
          tagged  :   v------------------------------   :  RDMA Read
          buffer  :   +----------------------------->   :
                  :                  :                  :
                  :              [Segment]              :
          tagged  :   v------------------------------   : [RDMA Read]
          buffer  :   +----------------------------->   :
                  :                                     :
                  :        Direct Write Response        :
         untagged :   <------------------------------   :  Send (w/Inv.)
          buffer  :                                     :

9.4.  Connection Models

   There are three scenarios in which to discuss the connection model.
   Each will be discussed individually, after describing the common case
   encountered at initial connection establishment.

   After a successful connection, the first request proceeds, in the
   case of a new client association, to initial session creation, and
   then optionally to session callback channel binding, prior to regular
   operation.




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   Commonly, each new client "mount" will be the action which drives
   creation of a new session.  However there are any number of other
   approaches.  Clients may choose to share a single connection and
   session among all their mount points.  Or, clients may support
   trunking, where additional connections are created but all within a
   single session.  Alternatively, the client may choose to create
   multiple sessions, each tuned to the buffering and reliability needs
   of the mount point.  For example, a readonly mount can sharply reduce
   its write buffering and also makes no requirement for the server to
   support reliable duplicate request caching.

   Similarly, the client can choose among several strategies for
   clientid usage.  Sessions can share a single clientid, or create new
   clientids as the client deems appropriate.  For kernel-based clients
   which service multiple authenticated users, a single clientid shared
   across all mount points is generally the most appropriate and
   flexible approach.  For example, all the client's file operations may
   wish to share locking state and the local client kernel takes the
   responsibility for arbitrating access locally.  For clients choosing
   to support other authentication models, perhaps example userspace
   implementations, a new clientid is indicated.  Through use of session
   create options, both models are supported at the client's choice.

   Since the session is explicitly created and destroyed by the client,
   and each client is uniquely identified, the server may be
   specifically instructed to discard unneeded presistent state.  For
   this reason, it is possible that a server will retain any previous
   state indefinitely, and place its destruction under administrative
   control.  Or, a server may choose to retain state for some
   configurable period, provided that the period meets other NFSv4
   requirements such as lease reclamation time, etc.  However, since
   discarding this state at the server may affect the correctness of the
   server as seen by the client across network partitioning, such
   discarding of state should be done only in a conservative manner.

   Each client request to the server carries a new SEQUENCE operation
   within each COMPOUND, which provides the session context.  This
   session context then governs the request control, duplicate request
   caching, and other persistent parameters managed by the server for a
   session.

9.4.1.  TCP Connection Model

   The following is a schematic diagram of the NFSv4.1 protocol
   exchanges leading up to normal operation on a TCP stream.






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               Client                                Server
          TCPmode :   Create Clientid(nfs_client_id4)   : TCPmode
                  :   ------------------------------>   :
                  :                                     :
                  :     Clientid reply(clientid, ...)   :
                  :   <------------------------------   :
                  :                                     :
                  :   Create Session(clientid, size S,  :
                  :      maxreq N, STREAM, ...)         :
                  :   ------------------------------>   :
                  :                                     :
                  :   Session reply(sessionid, size S', :
                  :      maxreq N')                     :
                  :   <------------------------------   :
                  :                                     :
                  :          <normal operation>         :
                  :   ------------------------------>   :
                  :   <------------------------------   :
                  :                  :                  :

   No net additional exchange is added to the initial negotiation by
   this proposal.  In the NFSv4.1 exchange, the CREATECLIENTID replaces
   SETCLIENTID (eliding the callback "clientaddr4" addressing) and
   CREATESESSION subsumes the function of SETCLIENTID_CONFIRM, as
   described elsewhere in this document.  Callback channel binding is
   optional, as in NFSv4.0.  Note that the STREAM transport type is
   shown above, but since the transport mode remains unchanged and
   transport attributes are not necessarily exchanged, DEFAULT could
   also be passed.

9.4.2.  Negotiated RDMA Connection Model

   One possible design which has been considered is to have a
   "negotiated" RDMA connection model, supported via use of a session
   bind operation as a required first step.  However due to issues
   mentioned earlier, this proved problematic.  This section remains as
   a reminder of that fact, and it is possible such a mode can be
   supported.

   It is not considered critical that this be supported for two reasons.
   One, the session persistence provides a way for the server to
   remember important session parameters, such as sizes and maximum
   request counts.  These values can be used to restore the endpoint
   prior to making the first reply.  Two, there are currently no
   critical RDMA parameters to set in the endpoint at the server side of
   the connection.  RDMA Read resources, which are in general not
   settable after entering RDMA mode, are set only at the client - the
   originator of the connection.  Therefore as long as the RDMA provider



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   supports an automatic RDMA connection mode, no further support is
   required from the NFSv4.1 protocol for reconnection.

   Note, the client must provide at least as many RDMA Read resources to
   its local queue for the benefit of the server when reconnecting, as
   it used when negotiating the session.  If this value is no longer
   appropriate, the client should resynchronize its session state,
   destroy the existing session, and start over with the more
   appropriate values.

9.4.3.  Automatic RDMA Connection Model

   The following is a schematic diagram of the NFSv4.1 protocol
   exchanges performed on an RDMA connection.

             Client                                Server
       RDMAmode :                  :                  : RDMAmode
                :                  :                  :
       Prepost  :                  :                  : Prepost
       receive  :                  :                  : receive
                :                                     :
                :   Create Clientid(nfs_client_id4)   :
                :   ------------------------------>   :
                :                                     : Prepost
                :     Clientid reply(clientid, ...)   : receive
                :   <------------------------------   :
       Prepost  :                                     :
       receive  :   Create Session(clientid, size S,  :
                :      maxreq N, RDMA ...)            :
                :   ------------------------------>   :
                :                                     : Prepost <=N'
                :   Session reply(sessionid, size S', :     receives of
                :      maxreq N')                     :     size S'
                :   <------------------------------   :
                :                                     :
                :          <normal operation>         :
                :   ------------------------------>   :
                :   <------------------------------   :
                :                  :                  :

9.5.  Buffer Management, Transfer, Flow Control

   Inline operations in NFSv4.1 behave effectively the same as TCP
   sends.  Procedure results are passed in a single message, and its
   completion at the client signal the receiving process to inspect the
   message.

   RDMA operations are performed solely by the server in this proposal,



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   as described in the previous "RDMA Direct Model" section.  Since
   server RDMA operations do not result in a completion at the client,
   and due to ordering rules in RDMA transports, after all required RDMA
   operations are complete, a Send (Send with Solicited Event for iWARP)
   containing the procedure results is performed from server to client.
   This Send operation will result in a completion which will signal the
   client to inspect the message.

   In the case of client read-type NFSv4 operations, the server will
   have issued RDMA Writes to transfer the resulting data into client-
   advertised buffers.  The subsequent Send operation performs two
   necessary functions: finalizing any active or pending DMA at the
   client, and signaling the client to inspect the message.

   In the case of client write-type NFSv4 operations, the server will
   have issued RDMA Reads to fetch the data from the client-advertised
   buffers.  No data consistency issues arise at the client, but the
   completion of the transfer must be acknowledged, again by a Send from
   server to client.

   In either case, the client advertises buffers for direct (RDMA style)
   operations.  The client may desire certain advertisement limits, and
   may wish the server to perform remote invalidation on its behalf when
   the server has completed its RDMA.  This may be considered in a
   future version of this draft.

   In the absence of remote invalidation, the client may perform its
   own, local invalidation after the operation completes.  This
   invalidation should occur prior to any RPCSEC GSS integrity checking,
   since a validly remotely accessible buffer can possibly be modified
   by the peer.  However, after invalidation and the contents integrity
   checked, the contents are locally secure.

   Credit updates over RDMA transports are supported at the RPC layer as
   described in [RPCRDMA].  In each request, the client requests a
   desired number of credits to be made available to the connection on
   which it sends the request.  The client must not send more requests
   than the number which the server has previously advertised, or in the
   case of the first request, only one.  If the client exceeds its
   credit limit, the connection may close with a fatal RDMA error.

   The server then executes the request, and replies with an updated
   credit count accompanying its results.  Since replies are sequenced
   by their RDMA Send order, the most recent results always reflect the
   server's limit.  In this way the client will always know the maximum
   number of requests it may safely post.

   Because the client requests an arbitrary credit count in each



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   request, it is relatively easy for the client to request more, or
   fewer, credits to match its expected need.  A client that discovered
   itself frequently queuing outgoing requests due to lack of server
   credits might increase its requested credits proportionately in
   response.  Or, a client might have a simple, configurable number.
   The protocol also provides a per-operation "maxslot" exchange to
   assist in dynamic adjustment at the session level, described in a
   later section.

   Occasionally, a server may wish to reduce the total number of credits
   it offers a certain client on a connection.  This could be
   encountered if a client were found to be consuming its credits
   slowly, or not at all.  A client might notice this itself, and reduce
   its requested credits in advance, for instance requesting only the
   count of operations it currently has queued, plus a few as a base for
   starting up again.  Such mechanisms can, however, be potentially
   complicated and are implementation-defined.  The protocol does not
   require them.

   Because of the way in which RDMA fabrics function, it is not possible
   for the server (or client back channel) to cancel outstanding receive
   operations.  Therefore, effectively only one credit can be withdrawn
   per receive completion.  The server (or client back channel) would
   simply not replenish a receive operation when replying.  The server
   can still reduce the available credit advertisement in its replies to
   the target value it desires, as a hint to the client that its credit
   target is lower and it should expect it to be reduced accordingly.
   Of course, even if the server could cancel outstanding receives, it
   cannot do so, since the client may have already sent requests in
   expectation of the previous limit.

   This brings out an interesting scenario similar to the client
   reconnect discussed earlier in "Connection Models".  How does the
   server reduce the credits of an inactive client?

   One approach is for the server to simply close such a connection and
   require the client to reconnect at a new credit limit.  This is
   acceptable, if inefficient, when the connection setup time is short
   and where the server supports persistent session semantics.

   A better approach is to provide a back channel request to return the
   operations channel credits.  The server may request the client to
   return some number of credits, the client must comply by performing
   operations on the operations channel, provided of course that the
   request does not drop the client's credit count to zero (in which
   case the connection would deadlock).  If the client finds that it has
   no requests with which to consume the credits it was previously
   granted, it must send zero-length Send RDMA operations, or NULL NFSv4



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   operations in order to return the resources to the server.  If the
   client fails to comply in a timely fashion, the server can recover
   the resources by breaking the connection.

   While in principle, the back channel credits could be subject to a
   similar resource adjustment, in practice this is not an issue, since
   the back channel is used purely for control and is expected to be
   statically provisioned.

   It is important to note that in addition to maximum request counts,
   the sizes of buffers are negotiated per-session.  This permits the
   most efficient allocation of resources on both peers.  There is an
   important requirement on reconnection: the sizes posted by the server
   at reconnect must be at least as large as previously used, to allow
   recovery.  Any replies that are replayed from the server's duplicate
   request cache must be able to be received into client buffers.  In
   the case where a client has received replies to all its retried
   requests (and therefore received all its expected responses), then
   the client may disconnect and reconnect with different buffers at
   will, since no cache replay will be required.

9.6.  Retry and Replay

   NFSv4.0 forbids retransmission on active connections over reliable
   transports; this includes connected-mode RDMA.  This restriction must
   be maintained in NFSv4.1.

   If one peer were to retransmit a request (or reply), it would consume
   an additional credit on the other.  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.

   RDMA credits present a new issue to the duplicate request cache in
   NFSv4.1.  The request 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 connection, and stale values
   must not be replayed from the cache.  This implies that the request
   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.

   Finally, RDMA fabrics do not guarantee that the memory handles
   (Steering Tags) within each rdma three-tuple are valid on a scope
   outside that of a single connection.  Therefore, handles used by the



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   direct operations become invalid after connection loss.  The server
   must ensure that any RDMA operations which must be replayed from the
   request cache use the newly provided handle(s) from the most recent
   request.

9.7.  The Back Channel

   The NFSv4 callback operations present a significant resource problem
   for the RDMA enabled client.  Clearly, callbacks must be negotiated
   in the way credits are for the ordinary operations channel for
   requests flowing from client to server.  But, for callbacks to arrive
   on the same RDMA endpoint as operation replies would require
   dedicating additional resources, and specialized demultiplexing and
   event handling.  Or, callbacks may not require RDMA sevice at all
   (they do not normally carry substantial data payloads).  It is highly
   desirable to streamline this critical path via a second
   communications channel.

   The session callback channel binding facility is designed for exactly
   such a situation, by dynamically associating a new connected endpoint
   with the session, and separately negotiating sizes and counts for
   active callback channel operations.  The binding operation is
   firewall-friendly since it does not require the server to initiate
   the connection.

   This same method serves as well for ordinary TCP connection mode.  It
   is expected that all NFSv4.1 clients may make use of the session
   facility to streamline their design.

   The back channel functions exactly the same as the operations channel
   except that no RDMA operations are required to perform transfers,
   instead the sizes are required to be sufficiently large to carry all
   data inline, and of course the client and server reverse their roles
   with respect to which is in control of credit management.  The same
   rules apply for all transfers, with the server being required to flow
   control its callback requests.

   The back channel is optional.  If not bound on a given session, the
   server must not issue callback operations to the client.  This in
   turn implies that such a client must never put itself in the
   situation where the server will need to do so, lest the client lose
   its connection by force, or its operation be incorrect.  For the same
   reason, if a back channel is bound, the client is subject to
   revocation of its delegations if the back channel is lost.  Any
   connection loss should be corrected by the client as soon as
   possible.

   This can be convenient for the NFSv4.1 client; if the client expects



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   to make no use of back channel facilities such as delegations, then
   there is no need to create it.  This may save significant resources
   and complexity at the client.

   For these reasons, if the client wishes to use the back channel, that
   channel must be bound first, before using the operations channel.  In
   this way, the server will not find itself in a position where it will
   send callbacks on the operations channel when the client is not
   prepared for them.

   There is one special case, that where the back channel is bound in
   fact to the operations channel's connection.  This configuration
   would be used normally over a TCP stream connection to exactly
   implement the NFSv4.0 behavior, but over RDMA would require complex
   resource and event management at both sides of the connection.  The
   server is not required to accept such a bind request on an RDMA
   connection for this reason, though it is recommended.

9.8.  COMPOUND Sizing Issues

   Very large responses may pose duplicate request cache issues.  Since
   servers will want to bound the storage required for such a cache, the
   unlimited size of response data in COMPOUND may be troublesome.  If
   COMPOUND is used in all its generality, then the inclusion of certain
   non-idempotent operations within a single COMPOUND request may render
   the entire request non-idempotent.  (For example, a single COMPOUND
   request which read a file or symbolic link, then removed it, would be
   obliged to cache the data in order to allow identical replay).
   Therefore, many requests might include operations that return any
   amount of data.

   It is not satisfactory for the server to reject COMPOUNDs at will
   with NFS4ERR_RESOURCE when they pose such difficulties for the
   server, as this results in serious interoperability problems.
   Instead, any such limits must be explicitly exposed as attributes of
   the session, ensuring that the server can explicitly support any
   duplicate request cache needs at all times.

9.9.  Data Alignment

   A negotiated data alignment enables certain scatter/gather
   optimizations.  A facility for this is supported by [RPCRDMA].  Where
   NFS file data is the payload, specific optimizations become highly
   attractive.

   Header padding is requested by each peer at session initiation, and
   may be zero (no padding).  Padding leverages the useful property that
   RDMA receives preserve alignment of data, even when they are placed



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   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 be optimistic and simply pad all WRITEs within the RPC
   layer to the negotiated size, in the expectation that the server can
   use them efficiently.

   It is highly recommended that clients offer to pad headers to an
   appropriate size.  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 filesystem 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 perform RDMA Read to satisfy all
   but the largest client writes is obviated.  An added benefit is the
   reduction of message roundtrips 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.

   Padding is negotiated by the session creation operation, and



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   subsequently used by the RPC RDMA layer, as described in [RPCRDMA].

9.10.  NFSv4 Integration

   The following section discusses the integration of the proposed RDMA
   extensions with NFSv4.0.

9.10.1.  Minor Versioning

   Minor versioning is the existing facility to extend the NFSv4
   protocol, and this proposal takes that approach.

   Minor versioning of NFSv4 is relatively restrictive, and allows for
   tightly limited changes only.  In particular, it does not permit
   adding new "procedures" (it permits adding only new "operations").
   Interoperability concerns make it impossible to consider additional
   layering to be a minor revision.  This somewhat limits the changes
   that can be proposed when considering extensions.

   To support the duplicate request cache integrated with sessions and
   request control, it is desirable to tag each request with an
   identifier to be called a Slotid.  This identifier must be passed by
   NFSv4 when running atop any transport, including traditional TCP.
   Therefore it is not desirable to add the Slotid to a new RPC
   transport, even though such a transport is indicated for support of
   RDMA.  This draft and [RPCRDMA] do not propose such an approach.

   Instead, this proposal conforms to the requirements of NFSv4 minor
   versioning, through the use of a new operation within NFSv4 COMPOUND
   procedures as detailed below.

   If sessions are in use for a given clientid, this same clientid
   cannot be used for non-session NFSv4 operation, including NFSv4.0.
   Because the server will have allocated session-specific state to the
   active clientid, it would be an unnecessary burden on the server
   implementor to support and account for additional, non- session
   traffic, in addition to being of no benefit.  Therefore this proposal
   prohibits a single clientid from doing this.  Nevertheless, employing
   a new clientid for such traffic is supported.

9.10.2.  Slot Identifiers and Server Duplicate Request Cache

   The presence of deterministic maximum request limits on a session
   enables in-progress requests to be assigned unique values with useful
   properties.

   The RPC layer provides a transaction ID (xid), which, while required
   to be unique, is not especially convenient for tracking requests.



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   The transaction ID is only meaningful to the issuer (client), it
   cannot be interpreted at the server except to test for equality with
   previously issued requests.  Because RPC operations may be completed
   by the server in any order, many transaction IDs may be outstanding
   at any time.  The client may therefore perform a computationally
   expensive lookup operation in the process of demultiplexing each
   reply.

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

   When the client issues a new request, it selects a slotid in the
   range 0..N-1, where N is the server's current "totalrequests" limit
   granted the client on the session over which the request is to be
   issued.  The slotid must be unused by any of the requests which the
   client has already active on the session.  "Unused" here means the
   client has no outstanding request for that slotid.  Because the slot
   id is always an integer in the range 0..N-1, client implementations
   can use the slotid from a server 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
   performace-critical receive path.

   The sequenceid, which accompanies the slotid in each request, is
   important for a second, 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 greater than that
      previously seen in the slot (accounting for sequence wraparound).
      The server proceeds to execute the new request.

   o  A retransmitted request, in which the sequenceid is equal to that
      last seen in the slot.  Note that this request may be either



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      complete, or in progress.  The server performs replay processing
      in these cases.

   o  A misordered duplicate, in which the sequenceid is less than that
      previously seen in the slot.  The server must drop the incoming
      request, which may imply dropping the connection if the transport
      is reliable, as dictated by section 3.1.1 of [RFC3530].

   This last condition is possible on any connection, not just
   unreliable, unordered transports.  Delayed behavior on abandoned TCP
   connections which are not yet closed at the server, or pathological
   client implementations can cause it, among other causes.  Therefore,
   the server may wish to harden itself against certain repeated
   occurrences of this, as it would for retransmissions in [RFC3530].

   It is recommended, though not necessary for protocol correctness,
   that the client simply increment the sequenceid by one for each new
   request on each slotid.  This reduces the wraparound window to a
   minimum, and is useful for tracing and avoidance of possible
   implementation errors.

   The client may however, for implementation-specific reasons, choose a
   different algorithm.  For example it might maintain a single sequence
   space for all slots in the session - e.g. employing the RPC XID
   itself.  The sequenceid, in any case, is never interpreted by the
   server for anything but to test by comparison with previously seen
   values.

   The server may thereby use the slotid, in conjunction with the
   sessionid and sequenceid, within the SEQUENCE portion of the request
   to maintain its duplicate request cache (DRC) for the session, as
   opposed to the traditional approach of ONC RPC applications that use
   the XID along with certain transport information [RW96].

   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 server need only cache the results of a limited number
   of COMPOUND requests.  The second implication derives from the first,
   which is unlike XID-indexed DRCs, the slotid DRC by its nature cannot
   be overflowed.  Through use of the sequenceid to identify
   retransmitted requests, it is notable that the server does not need
   to actually cache the request itself, reducing the storage
   requirements of the DRC further.  These new facilities makes it
   practical to maintain all the required entries for an effective DRC.

   The slotid and sequenceid therefore take over the traditional role of
   the port number in the server DRC implementation, and the session
   replaces the IP address.  This approach is considerably more portable



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   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.

   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 a control
   operation within each NFSv4.1 COMPOUND and CB_COMPOUND procedure.
   The operation easily piggybacks within existing messages.  The
   implementation section of this document describes the specific
   proposal.

   In general, the receipt of a new sequenced request arriving on any
   valid slot is an indication that the previous DRC contents of that
   slot may be discarded.  In order to further assist the server in slot
   management, the client is required to use the lowest available slot
   when issuing a new request.  In this way, the server may be able to
   retire additional entries.

   However, in the case where the server is actively adjusting its
   granted maximum request count to the client, 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 client's session limit, because the request may have been sent
   from the client before the update was received.  Therefore, in the
   downward adjustment case, the server may have to retain a number of
   duplicate request cache entries at least as large as the old value,
   until operation sequencing rules allow it to infer that the client
   has seen its reply.

   The SEQUENCE (and CB_SEQUENCE) operation also carries a "maxslot"
   value which carries additional client slot usage information.  The
   client must always provide its highest-numbered outstanding slot
   value in the maxslot argument, and the server may reply with a new
   recognized value.  The client 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 client to yield unused
   request slots back to the server, which in turn can use the
   information to reallocate resources.  Obviously, maxslot can never be
   zero, or the session would deadlock.

   The server also provides a target maxslot value to the client, which
   is an indication to the client of the maxslot the server wishes the
   client to be using.  This permits the server to withdraw (or add)
   resources from a client that has been found to not be using them, in



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   order to more fairly share resources among a varying level of demand
   from other clients.  The client must always comply with the server's
   value updates, since they indicate newly established hard limits on
   the client's access to session resources.  However, because of
   request pipelining, the client may have active requests in flight
   reflecting prior values, therefore the server must not immediately
   require the client to comply.

   It is worthwhile to note that Sprite RPC [BW87] defined a "channel"
   which in some ways is similar to the slotid proposed here.  Sprite
   RPC used channels to implement parallel request processing and
   request/response cache retirement.

9.10.3.  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 TCP connection,
   perhaps even a different network.  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 can be used to
   alleviate 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 (duplicate request 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.

   To implement this, the CB_SEQUENCE operation which begins each server
   callback may optionally carry a related { slotid, sequenceid }
   identifier.  If the client finds this identifier to be currently
   outstanding (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 any of the session's operations channels, because it is
   possible that they will be delayed indefinitely.  However, it should
   endeavor to wait for a period of time, and if the time expires it can
   provide a more meaningful error such as NFS4ERR_DELAY.



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   [[Comment.4: 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 14.5.3
   [[Comment.5: fill in the blanks w/others, etc...]]

   Therefore, 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.  During this time, any recalls of the
   associated object should carry these identifiers, for the benefit of
   the client.  After this 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.

9.10.4.  COMPOUND and CB_COMPOUND

   Support for per-operation control can be piggybacked onto NFSv4
   COMPOUNDs with full transparency, by placing such facilities into
   their own, new operation, and placing this operation first in each
   COMPOUND under the new NFSv4 minor protocol revision.  The contents
   of the operation would then apply to the entire COMPOUND.

   Recall that the NFSv4 minor revision is contained within the COMPOUND
   header, encoded prior to the COMPOUNDed operations.  By simply
   requiring that the new operation always be contained in NFSv4 minor
   COMPOUNDs, the control protocol can piggyback perfectly with each
   request and response.

   In this way, the NFSv4 RDMA Extensions may stay in compliance with
   the minor versioning requirements specified in section 10 of
   [RFC3530].

   Referring to section 13.1 of the same document, the proposed session-
   enabled COMPOUND and CB_COMPOUND have the form:













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

      and the reply's structure is:

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

   The single control operation within each NFSv4.1 COMPOUND defines the
   context and operational session parameters which govern that COMPOUND
   request and reply.  Placing it first in the COMPOUND encoding is
   required in order to allow its processing before other operations in
   the COMPOUND.

9.10.5.  eXternal Data Representation Efficiency

   RDMA is a copy avoidance technology, and it is important to maintain
   this efficiency when decoding received messages.  Traditional XDR
   implementations frequently use generated unmarshaling code to convert
   objects to local form, incurring a data copy in the process (in
   addition to subjecting the caller to recursive calls, etc).  Often,
   such conversions are carried out even when no size or byte order
   conversion is necessary.

   It is recommended that implementations pay close attention to the
   details of memory referencing in such code.  It is far more efficient
   to inspect data in place, using native facilities to deal with word
   size and byte order conversion into registers or local variables,
   rather than formally (and blindly) performing the operation via
   fetch, reallocate and store.

   Of particular concern is the result of the READDIR operation, in
   which such encoding abounds.

9.10.6.  Effect of Sessions on Existing Operations

   The use of a session replaces the use of the SETCLIENTID and
   SETCLIENTID_CONFIRM operations, and allows certain simplification of
   the RENEW and callback addressing mechanisms in the base protocol.

   The cb_program and cb_location which are obtained by the server in
   SETCLIENTID_CONFIRM must not be used by the server, because the



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   NFSv4.1 client performs callback channel designation with
   BIND_BACKCHANNEL.  Therefore the SETCLIENTID and SETCLIENTID_CONFIRM
   operations becomes obsolete when sessions are in use, and a server
   should return an error to NFSv4.1 clients which might issue either
   operation.

   Another favorable result of the session is that the server is able to
   avoid requiring the client to perform OPEN_CONFIRM operations.  The
   existence of a reliable and effective DRC means that the server will
   be able to determine whether an OPEN request carrying a previously
   known open_owner from a client is or is not a retransmission.
   Because of this, the server no longer requires OPEN_CONFIRM to verify
   whether the client is retransmitting an open request.  This in turn
   eliminates the server's reason for requesting OPEN_CONFIRM - the
   server can simply replace any previous information on this
   open_owner.  Client OPEN operations are therefore streamlined,
   reducing overhead and latency through avoiding the additional
   OPEN_CONFIRM exchange.

   Since the session carries the client liveness indication with it
   implicitly, any request on a session associated with a given client
   will renew that client's leases.  Therefore the RENEW operation is
   made unnecessary when a session is present, as any request (including
   a SEQUENCE operation with or without additional NFSv4 operations)
   performs its function.  It is possible (though this proposal does not
   make any recommendation) that the RENEW operation could be made
   obsolete.

   An interesting issue arises however if an error occurs on such a
   SEQUENCE operation.  If the SEQUENCE operation fails, perhaps due to
   an invalid slotid or other non-renewal-based issue, the server may or
   may not have performed the RENEW.  In this case, the state of any
   renewal is undefined, and the client should make no assumption that
   it has been performed.  In practice, this should not occur but even
   if it did, it is expected the client would perform some sort of
   recovery which would result in a new, successful, SEQUENCE operation
   being run and the client assured that the renewal took place.

9.10.7.  Authentication Efficiencies

   NFSv4 requires the use of the RPCSEC_GSS ONC RPC security flavor
   [RFC2203] to provide authentication, integrity, and privacy via
   cryptography.  The server dictates to the client the use of
   RPCSEC_GSS, the service (authentication, integrity, or privacy), and
   the specific GSS-API security mechanism that each remote procedure
   call and result will use.

   If the connection's integrity is protected by an additional means



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   than RPCSEC_GSS, such as via IPsec, then the use of RPCSEC_GSS's
   integrity service is nearly redundant (See the Security
   Considerations section for more explanation of why it is "nearly" and
   not completely redundant).  Likewise, if the connection's privacy is
   protected by additional means, then the use of both RPCSEC_GSS's
   integrity and privacy services is nearly redundant.

   Connection protection schemes, such as IPsec, are more likely to be
   implemented in hardware than upper layer protocols like RPCSEC_GSS.
   Hardware-based cryptography at the IPsec layer will be more efficient
   than software-based cryptography at the RPCSEC_GSS layer.

   When transport integrity can be obtained, it is possible for server
   and client to downgrade their per-operation authentication, after an
   appropriate exchange.  This downgrade can in fact be as complete as
   to establish security mechanisms that have zero cryptographic
   overhead, effectively using the underlying integrity and privacy
   services provided by transport.

   Based on the above observations, a new GSS-API mechanism, called the
   Channel Conjunction Mechanism [CCM], is being defined.  The CCM works
   by creating a GSS-API security context using as input a cookie that
   the initiator and target have previously agreed to be a handle for
   GSS-API context created previously over another GSS-API mechanism.

   NFSv4.1 clients and servers should support CCM and they must use as
   the cookie the handle from a successful RPCSEC_GSS context creation
   over a non-CCM mechanism (such as Kerberos V5).  The value of the
   cookie will be equal to the handle field of the rpc_gss_init_res
   structure from the RPCSEC_GSS specification.

   The [CCM] Draft provides further discussion and examples.

9.11.  Sessions Security Considerations

   The NFSv4 minor version 1 retains all of existing NFSv4 security; all
   security considerations present in NFSv4.0 apply to it equally.

   Security considerations of any underlying RDMA transport are
   additionally important, all the more so due to the emerging nature of
   such transports.  Examining these issues is outside the scope of this
   draft.

   When protecting a connection with RPCSEC_GSS, all data in each
   request and response (whether transferred inline or via RDMA)
   continues to receive this protection over RDMA fabrics [RPCRDMA].
   However when performing data transfers via RDMA, RPCSEC_GSS
   protection of the data transfer portion works against the efficiency



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   which RDMA is typically employed to achieve.  This is because such
   data is normally managed solely by the RDMA fabric, and intentionally
   is not touched by software.  Therefore when employing RPCSEC_GSS
   under CCM, and where integrity protection has been "downgraded", the
   cooperation of the RDMA transport provider is critical to maintain
   any integrity and privacy otherwise in place for the session.  The
   means by which the local RPCSEC_GSS implementation is integrated with
   the RDMA data protection facilities are outside the scope of this
   draft.

   It is logical to use the same GSS context on a session's callback
   channel as that used on its operations channel(s), particularly when
   the connection is shared by both.  The client must indicate to the
   server:

   - what security flavor(s) to use in the call back.  A special
   callback flavor might be defined for this.

   - if the flavor is RPCSEC_GSS, then the client must have previously
   created an RPCSEC_GSS session with the server.  The client offers to
   the server the the opaque handle<> value from the rpc_gss_init_res
   structure, the window size of RPCSEC_GSS sequence numbers, and an
   opaque gss_cb_handle.

   This exchange can be performed as part of session and clientid
   creation, and the issue warrants careful analysis before being
   specified.

   If the NFS client wishes to maintain full control over RPCSEC_GSS
   protection, it may still perform its transfer operations using either
   the inline or RDMA transfer model, or of course employ traditional
   TCP stream operation.  In the RDMA inline case, header padding is
   recommended to optimize behavior at the server.  At the client, close
   attention should be paid to the implementation of RPCSEC_GSS
   processing to minimize memory referencing and especially copying.
   These are well-advised in any case!

   The proposed session callback channel binding improves security over
   that provided by NFSv4 for the callback channel.  The connection is
   client-initiated, 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.  The connection is set up by the client with its desired
   attributes, such as optionally securing with IPsec or similar.  The
   binding is fully authenticated before being activated.






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9.11.1.  Authentication

   Proper authentication of the principal which issues any session and
   clientid in the proposed NFSv4.1 operations exactly follows the
   similar requirement on client identifiers in NFSv4.0.  It must not be
   possible for a client to impersonate another by guessing its session
   identifiers for NFSv4.1 operations, nor to bind a callback channel to
   an existing session.  To protect against this, NFSv4.0 requires
   appropriate authentication and matching of the principal used.  This
   is discussed in Section 16, Security Considerations of [RFC3530].
   The same requirement when using a session identifier applies to
   NFSv4.1 here.

   Going beyond NFSv4.0, the presence of a session associated with any
   clientid may also be used to enhance NFSv4.1 security with respect to
   client impersonation.  In NFSv4.0, there are many operations which
   carry no clientid, including in particular those which employ a
   stateid argument.  A rogue client which wished to carry out a denial
   of service attack on another client could perform CLOSE, DELEGRETURN,
   etc operations with that client's current filehandle, sequenceid and
   stateid, after having obtained them from eavesdropping or other
   approach.  Locking and open downgrade operations could be similarly
   attacked.

   When an NFSv4.1 session is in place for any clientid, countermeasures
   are easily applied through use of authentication by the server.
   Because the sessionid is present in each request within a session,
   the server may verify that the clientid is in fact originating from a
   principal with the appropriate authenticated credentials, that the
   sessionid belongs to the clientid, and that the stateid is valid in
   these contexts.  This is in general not possible with the affected
   operations in NFSv4.0 due to the fact that the clientid is not
   present in the requests.

   In the event that authentication information is not available in the
   incoming request, for example after a reconnection when the security
   was previously downgraded using CCM, the server must require the
   client re-establish the authentication in order that the server may
   validate the other client-provided context, prior to executing any
   operation.  The sessionid, present in the newly retransmitted
   request, combined with the retransmission detection enabled by the
   NFSv4.1 duplicate request cache, are a convenient and reliable
   context for the server to use for this contingency.

   The server should take care to protect itself against denial of
   service attacks in the creation of sessions and clientids.  Clients
   who connect and create sessions, only to disconnect and never use
   them may leave significant state behind.  (The same issue applies to



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   NFSv4.0 with clients who may perform SETCLIENTID, then never perform
   SETCLIENTID_CONFIRM.)  Careful authentication coupled with resource
   checks is highly recommended.


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 filesystem 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).



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   In this case there, the file system is said to be "present" at that
   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 filesystem 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 filesystem 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 filesystem 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 filesystem happens at the start of every
   operation, operations which change the current filehandle so that it
   is within an absent filesystem 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.



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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



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   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 filesystems.  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 NFSER_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 filesystem in that case is simply
      restricted to those actually available.







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10.4.  Uses of Location Information

   The location-bearing attributes (fs_locations and fs_locations_info),
   provide, together with the possibility of absent filesystems, 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 filesystem, 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 filesystem, 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.




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   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
   filesystem 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.







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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 filesystems 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
   filesystems.  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
   filesystem that includes a referral or a relocated filesystem
   continue to see a coherent picture of that user-side filesystem
   despite the fact that it contains a number of server-side filesystems
   which may be on different servers.

   One important issue is upward navigation from the root of a server-
   side filesystem 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
   filesystem on the target server, which may not be part of the space
   that the client mounted.




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   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



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   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 filesystems 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 filesystem.

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).



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   o  Where the old and new filesystems 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 filesystems 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 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



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      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 filesystem 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 filesystem instances are
   created by a single vendor using some sort of filesystem 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 filesystem 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



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   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



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   attribute construction and handle this situation just as it would be
   handled without any filesystem 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 filesystem 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 filesystem 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



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   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



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   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 filesystem that has been transferred to another
   server.  This can occur because of the lease renewal mechanism.  The
   client renews leases for all filesystems when submitting a request to
   any one filesystem 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 filesystem 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 filesystem 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.




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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



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   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 /src/linux/2.7/latest 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 "src"

   o  LOOKUP "linux"

   o  LOOKUP "2.7"

   o  LOOKUP "latest"

   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 "src" --> NFS_OK.  The current fh is for /src and is within
      the pseudo-fs.

   o  LOOKUP "linux" --> NFS_OK.  The current fh is for /src/linux and
      is within the pseudo-fs.

   o  LOOKUP "2.7" --> NFS_OK.  The current fh is for /src/linux/2.7 and
      is within the pseudo-fs.




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   o  LOOKUP "latest" --> NFS_OK.  The current fh is for /src/linux/2.7/
      latest 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
   /src/linux/2.7 is the root of the moved filesystem and that the
   reason that the lookup of "latest" succeeded is that the filesystem
   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 /src/linux/2.7/latest 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 "src" --> NFS_OK






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   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 /src and is within pseudo-fs.

   OP06:  LOOKUP "linux" --> NFS_OK

   -  Current fh is for /src/linux 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 /src/linux and is within pseudo-fs.

   OP09:  LOOKUP "2.7" --> NFS_OK

   -  Current fh is for /src/linux/2.7 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 /src/linux/2.7 and is within pseudo-fs.

   OP12:  LOOKUP "latest" --> NFS_OK

   -  Current fh is for /src/linux/2.7/latest 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



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      that new server.

   -  In this particular case, we are pretty sure anyway that what has
      moved is /src/linux/2.7/latest rather than /src/linux/2.7 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. /src/linux/2.7
      might be a non-pseudo filesystem separate from /src/linux/2.7/
      latest), so we need to have another reliable source information on
      the boundary of the fs which is moved.  If, for example, the
      filesystem "/src/linux" had moved we would have a case of
      migration rather than referral and once the boundaries of the
      migrated filesystem 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 "/src/linux/2.7" is a filesystem 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.






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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 "src"

   o  LOOKUP "linux"

   o  LOOKUP "2.7"

   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 "src" --> NFS_OK.  The current fh is for /src and is within
      the pseudo-fs.

   o  LOOKUP "linux" --> NFS_OK.  The current fh is for /src/linux and
      is within the pseudo-fs.

   o  LOOKUP "2.7" --> NFS_OK.  The current fh is for /src/linux/2.7 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
      /src/linux/2.7 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 "src"

   o  LOOKUP "linux"




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   o  LOOKUP "2.7"

   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 "src" --> NFS_OK.  The current fh is for /src and is within
      the pseudo-fs.

   o  LOOKUP "linux" --> NFS_OK.  The current fh is for /src/linux and
      is within the pseudo-fs.

   o  LOOKUP "2.7" --> NFS_OK.  The current fh is for /src/linux/2.7 and
      is within the pseudo-fs.

   o  READDIR (rdattr_error, fsid, size, ctime, mounted_on_fileid) -->
      NFS_OK.  The attributes for "latest" 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 "src"

   o  LOOKUP "linux"

   o  LOOKUP "2.7"

   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 "src" --> NFS_OK.  The current fh is for /src and is within
      the pseudo-fs.

   o  LOOKUP "linux" --> NFS_OK.  The current fh is for /src/linux and
      is within the pseudo-fs.




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   o  LOOKUP "2.7" --> NFS_OK.  The current fh is for /src/linux/2.7 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 "latest" 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 filesystems without causing NFS4ERR_MOVED to be returned and
   it should always be available.  Servers are strongly urged to support
   this attribute on all filesystems if they support it on any
   filesystem.

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
   filesystem 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



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   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 filesystem 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 filesystem located at
   two servers (servA and servB).  At servA, the filesystem is located
   at path "/a/b/c".  At, servB the filesystem 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
   filesystem'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,



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      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.



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   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  Filesystem identity information which indicates when multiple
      replicas, from the clients point of view, correspond to the same
      target filesystem, 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.
























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             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



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   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 filesystem 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.



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   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.






























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             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:





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   o  LIGF_WRITABLE indicates that this fs target is writable, allowing
      it to be selected by clients which may need to write on this
      filesystem.  When the current filesystem instance is writable,
      then any other filesystem to which the client might switch must
      incorporate within its data any committed write made on the
      current filesystem 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 filesystem that turns out to be
      writable, turning the flag on for read-only filesystem 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
      filesystem replica.  It can only be set if LIGF_CUR_REQ is set.
      When both such bits are set it indicates that a filesystem
      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 filesystem (albeit
      absent) does not appear in the event of a referral, but only where
      a filesystem 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 filesystem 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 servers 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.




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   Attribute continuity and filesystem 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



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   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 filesystem 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 filesystem.  Where the current
      filesystem 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 filesystem 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



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      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
      filesystem at every valid_for seconds.  This is particularly
      important when filesystem 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 filesystem 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 filesystems without causing NFS4ERR_MOVED to
   be returned and it is generally expected that will be available for
   both present and absent filesystems even if only a single
   location_server entry is present, designating the current (present)
   filesystem, or two location_server entries designating the current
   (and now previous) location of an absent filesystem and its successor
   location.  Servers are strongly urged to support this attribute on
   all filesystems if they support it on any filesystem.

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.

















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             enum status4_type {
                     STATUS4_FIXED = 1,
                     STATUS4_UPDATED = 2,
                     STATUS4_INTERLOCKED = 3,
                     STATUS4_WRITABLE = 4,
                     STATUS4_ABSENT = 5
             };

             struct fs4_status {
                     status4_type    type;
                     utf8str_cs      source;
                     utf8str_cs      current;
                     int32_t         age;
                     nfstime4        version;
             };


   The type value indicates the kind of filesystem image represented.
   This is of particular importance when using the version values to
   determine appropriate succession of filesystem 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
      filesystem 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 filesystem, and then later reads data from an earlier version
      of the same filesystem.  See below for a discussion of how this
      can be done.

   o  STATUS4_WRITABLE which indicates that the filesystem is an actual
      writable one.  The client need not of course actually write to the
      filesystem, but once it does, it should not accept a transition to
      anything other than a writable instance of that same filesystem.





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   o  STATUS4_ABSENT which indicates that the information is the last
      valid for a filesystem which is no longer present.

   The opaque strings source and current provide a way of presenting
   information about the source of the filesystem 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 filesystem 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 filesystems are made in many different ways
   (e.g. simple user-level copies, filesystem- 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
   filesystem with the expectation that tools capable of creating a
   filesystem 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 filesystem
   is initially created associating with it data regarding how the
   filesystem 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.




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   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 filesystem 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 filesystem 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 filesystem 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 filesystem 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 filesystem
   in question.  Often this is most conveniently done by appending such
   a GETATTR after all other operations that reference a given
   filesystem.  When errors occur between reading filesystem 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 filesystem 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
   filesystem the client has in hand a newly-fetched current version of
   the filesystem 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 filesystem
   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 filesystem instance.


11.  Directory Delegations






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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



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   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



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   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
   absense 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



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   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.  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.


12.  Introduction

   The NFSv4 protocol [6] 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
   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



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   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 67

   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,
   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



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   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 ([12]), and FCP ([13]).  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 [14].

   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 15 on Security for
   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.



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13.  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.

13.1.  Metadata Server

   A pNFS "server" or "metadata server" is a server as defined by
   RFC3530 [6], 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.

13.2.  Client

   A pNFS "client" is a client as defined by RFC3530 [6], 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.

13.3.  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.

13.4.  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
   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



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   written to use these storage protocols.  Use of NFSv4 itself as a
   file-based storage protocol is described in Section 16.

13.5.  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.

13.6.  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.

13.7.  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
   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.







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14.  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.

14.1.  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.

14.1.1.  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 1.2.17 for its RPC definition).  The
   layout type allows for variants to handle different storage protocols
   (e.g., block/volume [11], object [10], and file [Section 16] 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 16).  Adjunct specifications are
   being drafted that precisely define other layout formats (e.g.,
   block/volume [11], and object [10] layouts) to allow interoperability
   among clients and metadata servers.

14.1.2.  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



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   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.

14.1.3.  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.

   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



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   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.

14.1.4.  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.

14.1.5.  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
   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.




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14.2.  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
   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



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   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.

14.3.  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,
   or impossible, for the server implementation to comply.







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14.4.  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 14.6 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.

14.4.1.  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
   arguments to LAYOUTCOMMIT allow the client to provide suggested
   access and modify time values to the server.  Again, depending upon



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   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.

14.4.2.  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 occured.  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
       value.




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   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.

   Since client layout holders may be unaware of changes made to the
   file's size, through LAYOUTCOMMIT or SETATTR, by other clients, an
   additional callback/notification has been added for pNFS.
   CB_SIZECHANGED is a notification that the metadata server sends to
   layout holders to notify them of a change in file size.  This is
   preferred over issuing CB_LAYOUTRECALL to each of the layout holders.

14.4.3.  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.

14.5.  Recalling a Layout

14.5.1.  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.,



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   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 29).  This callback
   can either recall a layout segment identified by a byte range, or all
   the layouts associated with a file system (FSID).  However, there is
   no single operation to return all layouts associated with an FSID;
   multiple layout segments may be returned in a single compound
   operation.  Section 14.5.3 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.



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14.5.2.  Recall Callback Robustness

   For simplicity, the discussion thus far has assumed 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 enhance information
      about what layout ranges are held by a client beyond what a client
      actually holds.  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  As well, the synchronized state assumption is not robust to minor
      errors.  A more robust design would allow for divergence between
      client and server and the ability to recover.  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 in order to avoid errors.  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 be able
      to issue the LAYOUTRETURN that the server is expecting in response
      to a recall.

   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.

   In order to ensure client/server convergence on the layout state, the
   final LAYOUTRETURN operation in a sequence of returns for a
   particular recall, SHOULD specify the entire range being recalled,



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   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.

14.5.3.  Recall/Return Sequencing

   As with other stateful operations, pNFS requires the correct
   sequencing of layout operations.  This proposal assumes that sessions
   will precede or accompany pNFS into NFSv4.x and thus, pNFS will
   require the use of sessions.  If the sessions proposal does not
   precede pNFS, then this proposal needs to be modified to provide for
   the correct sequencing of pNFS layout operations.  Also, this
   specification is reliant on the sessions protocol 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.

   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.  It MUST NOT be possible
   for a client to process the CB_LAYOUTRECALL for a layout that it has
   not received in a reply message to a LAYOUTGET.

   The callback races section (Section 9.10.3) describes the sessions
   mechanism for allowing the client to detect such situations in order
   to not process such a CB_LAYOUTRECALL.  The LAYOUTGET operation is in
   this case the dependent operation which the server should reference
   in any layout recall, if it remains active in the server's slot
   table.

14.5.3.1.  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 in the absence of a session, the client cannot
   distinguish when the callback arrives:

   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.



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   This can 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.  In the presence of a session, the server will provide
   the client with the { slotid , sequenceid } of any earlier LAYOUTGET
   which remains 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 reference, whereas in case 2
   it will not (because there is no dependent client operation).
   Therefore, the action at the client will only require waiting in the
   case that the client has not yet seen the sever's earlier reply to
   the LAYOUTGET.

   Without the session, this deadlock can be avoided 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 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.

   Now the client can wait for the LAYOUTGET response, as it will be
   received in both cases.

14.5.3.2.  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:

   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 client has two ways to avoid this result - it can issue the



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   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 a session 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.

   This leads to a more general problem; in the absence of a callback if
   a client issues concurrent overlapping LAYOUTGET and LAYOUTRETURN
   operations, it is possible for the server to process them in either
   order.  Again, a client must take the appropriate precautions in
   serializing its actions.

   [ASIDE: HighRoad forbids a client from doing this, as the per-file
   layout stateid will cause one of the two operations to be rejected
   with a stale layout stateid.  This approach is simpler and produces
   better results by comparison to allowing concurrent operations, at
   least for this sort of conflict case, because server execution of
   operations in an order not anticipated by the client may produce
   results that are not useful to the client (e.g., if a LAYOUTRETURN is
   followed by a concurrent overlapping LAYOUTGET, but executed in the
   other order, the client will not retain layout extents for the
   overlapping range).]

14.6.  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.

14.7.  Crash Recovery

   Crash recovery is complicated due to the distributed nature of the
   pNFS protocol.  In general, crash recovery for layouts is similar to



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   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.

14.7.1.  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.

14.7.1.1.  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.

14.7.1.2.  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 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



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      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,
   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 inflight I/Os, as is discussed later.

14.7.2.  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.



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14.7.3.  Metadata Server Recovery

   The server recovery case is slightly more complex.  In general, the
   recovery process again follows the standard NFSv4 recovery model: the
   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.




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   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
   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 14.7.1.

   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,



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   this is only part of the solution.  It is also necessary to deal with
   the consequences of I/Os already in flight.

   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 16.6); 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.

14.7.4.  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



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   for that storage device to become available.  That storage device may
   never be visible to the client again.

   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.


15.  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 67) 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



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   provide countermeasures.

   pNFS implementations MUST NOT remove NFSv4's access controls.  The
   combination of clients, storage devices, and the server are
   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.

   The following subsections describe security considerations
   specifically applicable to each of the three major storage device
   protocol types supported for pNFS.

   [Requiring strict equivalence to NFSv4 security mechanisms is the
   wrong approach.  Will need to lay down a set of statements that each
   protocol has to make starting with access check location/properties.]

15.1.  File Layout Security

   A NFSv4 file layout type is defined in Section 16; see Section 16.7
   for additional security considerations and details.  In summary, the
   NFSv4 file layout type requires that all I/O access checks MUST be
   performed by the storage devices, as defined by the NFSv4
   specification.  If another file layout type is being used, additional
   access checks may be required.  But in all cases, the access control
   performed by the storage devices must be at least as strict as that
   specified by the NFSv4 protocol.

15.2.  Object Layout Security

   The object storage protocol MUST implement the security aspects
   described in version 1 of the T10 OSD protocol definition [14].  The
   remainder of this section gives an overview of the security mechanism
   described in that standard.  The goal is to give the reader a basic
   understanding of the object security model.  Any discrepancies
   between this text and the actual standard are obviously to be
   resolved in favor of the OSD standard.

   The object storage protocol relies on a cryptographically secure
   capability to control accesses at the object storage devices.
   Capabilities are generated by the metadata server, returned to the
   client, and used by the client as described below to authenticate



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   their requests to the Object Storage Device (OSD).  Capabilities
   therefore achieve the required access and open mode checking.  They
   allow the file server to define and check a policy (e.g., open mode)
   and the OSD to check and enforce that policy without knowing the
   details (e.g., user IDs and ACLs).  Since capabilities are tied to
   layouts, and since they are used to enforce access control, the
   server should recall layouts and revoke capabilities when the file
   ACL or mode changes in order to signal the clients.

   Each capability is specific to a particular object, an operation on
   that object, a byte range w/in the object, and has an explicit
   expiration time.  The capabilities are signed with a secret key that
   is shared by the object storage devices (OSD) and the metadata
   managers. clients do not have device keys so they are unable to forge
   capabilities.  The the following sketch of the algorithm should help
   the reader understand the basic model.

   LAYOUTGET returns

     {CapKey = MAC<SecretKey>(CapArgs), CapArgs}

   The client uses CapKey to sign all the requests it issues for that
   object using the respective CapArgs.  In other words, the CapArgs
   appears in the request to the storage device, and that request is
   signed with the CapKey as follows:

     ReqMAC = MAC<CapKey>(Req, Nonceln)

   The following is sent to the OSD: {CapArgs, Req, Nonceln, ReqMAC}.
   The OSD uses the SecretKey it shares with the metadata server to
   compare the ReqMAC the client sent with a locally computed

     MAC<MAC<SecretKey>(CapArgs)>(Req, Nonceln)

   and if they match the OSD assumes that the capabilities came from an
   authentic metadata server and allows access to the object, as allowed
   by the CapArgs.  Therefore, if the server LAYOUTGET reply, holding
   CapKey and CapArgs, is snooped by another client, it can be used to
   generate valid OSD requests (within the CapArgs access restriction).

   To provide the required privacy requirements for the capabilities
   returned by LAYOUTGET, the GSS-API can be used, e.g. by using a
   session key known to the file server and to the client to encrypt the
   whole layout or parts of it.  Two general ways to provide privacy in
   the absence of GSS-API that are independent of NFSv4 are either an
   isolated network such as a VLAN or a secure channel provided by
   IPsec.




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15.3.  Block/Volume Layout Security

   As typically used, block/volume protocols rely on clients to enforce
   file access checks since the storage devices are generally unaware of
   the files they are storing and in particular are unaware of which
   blocks belongs to which file.  In such environments, the physical
   addresses of blocks are exported to pNFS clients via layouts.  An
   alternative method of block/volume protocol use is for the storage
   devices to export virtualized block addresses, which do reflect the
   files to which blocks belong.  These virtual block addresses are
   exported to pNFS clients via layouts.  This allows the storage device
   to make appropriate access checks, while mapping virtual block
   addresses to physical block addresses.

   In environments where access control is important and client-only
   access checks provide insufficient assurance of access control
   enforcement (e.g., there is concern about a malicious of
   malfunctioning client skipping the access checks) and where physical
   block addresses are exported to clients, the storage devices will
   generally be unable to compensate for these client deficiencies.

   In such threat environments, block/volume protocols SHOULD NOT be
   used with pNFS, unless the storage device is able to implement the
   appropriate access checks, via use of virtualized block addresses, or
   other means.  NFSv4 without pNFS or pNFS with a different type of
   storage protocol would be a more suitable means to access files in
   such environments.  Storage-device/protocol-specific methods (e.g.
   LUN masking/mapping) may be available to prevent malicious or high-
   risk clients from directly accessing storage devices.


16.  The NFSv4 File Layout Type

   This section describes the semantics and format of NFSv4 file-based
   layouts.

16.1.  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.  The structures
   used to describe the stripe layout are as follows:









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    enum stripetype4 {
           STRIPE_SPARSE = 1,
           STRIPE_DENSE = 2
    };

    struct nfsv4_file_layouthint {
            stripetype4             stripe_type;
            length4                 stripe_unit;
            uint32_t                stripe_width;
    };

    struct nfsv4_file_layout {                   /* Per data stripe */
           pnfs_deviceid4          dev_id<>;
           nfs_fh4                 fh;
    };

    struct nfsv4_file_layouttype4 {              /* Per file */
           stripetype4             stripe_type;
           bool                    commit_through_mds;
           length4                 stripe_unit;
           length4                 file_size;
           nfsv4_file_layout       dev_list<>;
    };

   The file layout specifies an ordered array of <deviceID, filehandle>
   tuples, as well as the stripe size, type of stripe layout (discussed
   a little later), and the file's current size as of LAYOUTGET time.
   The filehandle, "fh", identifies the file on a storage device
   identified by "dev_id", that holds a particular stripe of the file.
   The "dev_id" array can be used for multipathing and is discussed
   further in Section 16.1.3.  The stripe width is determined by the
   stripe unit size multiplied by the number of devices in the dev_list.
   The stripe held by <dev_id, fh> is determined by that tuples position
   within the device list, "dev_list".  For example, consider a dev_list
   consisting of the following <dev_id, fh> pairs:

   <(1,0x12), (2,0x13), (1,0x15)> and stripe_unit = 32KB

   The stripe width is 32KB * 3 devices = 96KB.  The first entry
   specifies that on device 1 in the data file with filehandle 0x12
   holds the first 32KB of data (and every 32KB stripe beginning where
   the file's offset % 96KB == 0).

   Devices may be repeated multiple times within the device list array;
   this is shown where storage device 1 holds both the first and third
   stripe of data.  Filehandles can only be repeated if a sparse stripe
   type is used.  Data is striped across the devices in the order listed
   in the device list array in increments of the stripe size.  A data



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   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 3.15.  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.

16.1.1.  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:

    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.




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   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
   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 16.5 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.







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16.1.2.  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.
   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 file handle 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



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   value not from a layout, a subsequent attempt to set the current file
   handle to a value obtained from a layout should be rejected.

16.1.3.  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 data stripe portion of the file's layout.  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
   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.]

16.1.4.  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 READ, WRITE, PUTFH, COMMIT,
   and NULL 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 14.2, 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



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   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 14.4.2).  Section 16.5, describes the
   mechanism by which the client is to handle storage device file's that
   do not reflect the metadata server's size.

16.1.5.  COMMIT through metadata server

   commit_through_mds in the file layout gives the metadata server a
   preferred way of preforming 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.

   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.

16.2.  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



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   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 16.4.
   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.]

16.3.  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
   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.

16.4.  Storage Device State Propagation

   Since the metadata server, which handles lock and open-mode state
   changes, as well as ACLs, may not be collocated 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.







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16.4.1.  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
   for I/O at all.  The stateids returned by open are sufficient and
   eliminate overhead for this kind of state propagation.

16.4.2.  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.

16.4.3.  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



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   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 14.4
   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 [6] 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.

   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.]

16.5.  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



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   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, instead, another approach as outlined below.

   First, the file's size is returned within the layout by LAYOUTGET.
   This size must reflect the latest size at the metadata server as set
   by the most recent of either the last LAYOUTCOMMIT or SETATTR;
   however, it may be more recent.  Second, if a client performs a read
   that is returned short (i.e., is fully within the file's size, but
   the storage device indicates EOF and returns partial or no data), the
   client must assume that it is a hole and substitute 0s for the data
   not read up until its known local file size.  If a client extends the
   file, it must update its local file size.  Third, if the metadata
   server receives a SETATTR of the size or a LAYOUTCOMMIT that alters
   the file's size, the metadata server must send out CB_SIZECHANGED
   messages with the new size to clients holding layouts; it need not
   send a notification to the client that performed the operation that
   resulted in the size changing).  Upon reception of the CB_SIZECHANGED
   notification, clients must update their local size for that file.  As
   well, if a new file size is returned as a result to LAYOUTCOMMIT, the
   client must update their local file size.

16.6.  Crash Recovery Considerations

   As described in Section 14.7, 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.



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   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.

16.7.  Security Considerations

   The NFSv4 file layout type MUST adhere to the security considerations
   outlined in Section 15.  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 [6].  This impacts the control
   protocol and the propagation of state from the metadata server to the
   storage devices; see Section 16.4 for more details.

16.8.  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 tieing 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



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   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
   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 16.4).


17.  Layouts and Aggregation

   This section describes several aggregation schemes in a semi-formal
   way to provide context for layout formats.  These definitions will be
   formalized in other protocols.  However, the set of understood types
   is part of this protocol in order to provide for basic
   interoperability.

   The layout descriptions include (deviceID, objectID) tuples that
   identify some storage object on some storage device.  The addressing
   formation associated with the deviceID is obtained with
   GETDEVICEINFO.  The interpretation of the objectID depends on the
   storage protocol.  The objectID could be a filehandle for an NFSv4
   storage device.  It could be a OSD object ID for an object server.
   The layout for a block device generally includes additional block map
   information to enumerate blocks or extents that are part of the
   layout.

17.1.  Simple Map

   The data is located on a single storage device.  In this case the
   file server can act as the front end for several storage devices and
   distribute files among them.  Each file is limited in its size and
   performance characteristics by a single storage device.  The simple
   map consists of (deviceID, objectID).







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17.2.  Block Extent Map

   The data is located on a LUN in the SAN.  The layout consists of an
   array of (deviceID, blockID, offset, length) tuples.  Each entry
   describes a block extent.

17.3.  Striped Map (RAID 0)

   The data is striped across storage devices.  The parameters of the
   stripe include the number of storage devices (N) and the size of each
   stripe unit (U).  A full stripe of data is N * U bytes.  The stripe
   map consists of an ordered list of (deviceID, objectID) tuples and
   the parameter value for U. The first stripe unit (the first U bytes)
   are stored on the first (deviceID, objectID), the second stripe unit
   on the second (deviceID, objectID) and so forth until the first
   complete stripe.  The data layout then wraps around so that byte
   (N*U) of the file is stored on the first (deviceID, objectID) in the
   list, but starting at offset U within that object.  The striped
   layout allows a client to read or write to the component objects in
   parallel to achieve high bandwidth.

   The striped map for a block device would be slightly different.  The
   map is an ordered list of (deviceID, blockID, blocksize), where the
   deviceID is rotated among a set of devices to achieve striping.

17.4.  Replicated Map

   The file data is replicated on N storage devices.  The map consists
   of N (deviceID, objectID) tuples.  When data is written using this
   map, it should be written to N objects in parallel.  When data is
   read, any component object can be used.

   This map type is controversial because it highlights the issues with
   error recovery.  Those issues get interesting with any scheme that
   employs redundancy.  The handling of errors (e.g., only a subset of
   replicas get updated) is outside the scope of this protocol
   extension.  Instead, it is a function of the storage protocol and the
   metadata control protocol.

17.5.  Concatenated Map

   The map consists of an ordered set of N (deviceID, objectID, size)
   tuples.  Each successive tuple describes the next segment of the
   file.







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17.6.  Nested Map

   The nested map is used to compose more complex maps out of simpler
   ones.  The map format is an ordered set of M sub-maps, each submap
   applies to a byte range within the file and has its own type such as
   the ones introduced above.  Any level of nesting is allowed in order
   to build up complex aggregation schemes.


18.  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
   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 this RFC.  The COMPOUND
   procedure will 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.




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           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.

        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.




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        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.

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

   12.  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.

   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.


19.  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 [7] allows for this type of access and follows
   the policy described in "IETF Policy on Character Sets and
   Languages", RFC2277 [8].

   [RFC-XXX-stringprep-XXX], 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.



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   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

   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 [RFC-XXX-nameprep-XXX].

19.1.  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.

19.1.1.  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
   filesystem.  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:



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   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.

19.1.2.  Character repertoire of nfs4_cs_prep

   The nfs4_cs_prep profile uses Unicode 3.2, as defined in stringprep's
   Appendix A.1

19.1.3.  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
   filesystem 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.

19.1.4.  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 filesystem (at the server).

19.1.5.  Prohibited output for nfs4_cs_prep

   The nfs4_cs_prep profile specifies prohibiting using the following
   tables from stringprep:



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      Table C.3

      Table C.4

      Table C.5

      Table C.6

      Table C.7

      Table C.8

      Table C.9

19.1.6.  Bidirectional output for nfs4_cs_prep

   The nfs4_cs_prep profile does not specify any checking of
   bidirectional strings.

19.2.  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.

19.2.1.  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.

19.2.2.  Character repertoire of nfs4_cis_prep

   The nfs4_cis_prep profile uses Unicode 3.2, as defined in
   stringprep's Appendix A.1

19.2.3.  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








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19.2.4.  Normalization used by nfs4_cis_prep

   The nfs4_cis_prep profile specifies using Unicode normalization form
   KC, as described in stringprep.

19.2.5.  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

      Table C.3

      Table C.4

      Table C.5

      Table C.6

      Table C.7

      Table C.8

      Table C.9

19.2.6.  Bidirectional output for nfs4_cis_prep

   The nfs4_cis_prep profile specifies checking bidirectional strings as
   described in stringprep's section 6.

19.3.  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.

19.3.1.  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.







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19.3.2.  Character repertoire of nfs4_mixed_prep

   The nfs4_mixed_prep profile uses Unicode 3.2, as defined in
   stringprep's Appendix A.1

19.3.3.  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:

      Table B.1

      Table B.2

19.3.4.  Normalization used by nfs4_mixed_prep

   The nfs4_mixed_prep profile specifies using Unicode normalization
   form KC, as described in stringprep.

19.3.5.  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




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19.3.6.  Bidirectional output for nfs4_mixed_prep

   The nfs4_mixed_prep profile specifies checking bidirectional strings
   as described in stringprep's section 6.

19.4.  UTF-8 Related Errors

   Where the client sends an invalid UTF-8 string, the server should
   return an NFS4ERR_INVAL (Table 5) 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 filesystem that supports Unicode characters only), the
   server should return an NFS4ERR_BADCHAR (Table 5) error.

   Where a UTF-8 string is used as a file name, and the filesystem,
   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 5).  This includes situations in which
   the server filesystem imposes a normalization constraint on name
   strings, but will also include such situations as filesystem
   prohibitions of "." and ".." as file names for certain operations,
   and other such constraints.


20.  Error Definitions

   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.

                        Protocol Error Definitions

   +------------------------------+--------+---------------------------+
   | Error                        | Number | Description               |
   +------------------------------+--------+---------------------------+
   | NFS4_OK                      | 0      | Indicates the operation   |
   |                              |        | completed successfully.   |






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   | 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.      |
   | 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            | TDB    | Layout iomode is invalid. |
   | NFS4ERR_BADLAYOUT            | TDB    | 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.     |
   | NFS4ERR_BADTYPE              | 10007  | An attempt was made to    |
   |                              |        | create an object of a     |
   |                              |        | type not supported by the |
   |                              |        | server.                   |



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   | 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           | TDB    | TDB                       |
   | NFS4ERR_BADSLOT              | TDB    | 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 SETCLIENTID operation |
   |                              |        | has found that a client   |
   |                              |        | id is already in use by   |
   |                              |        | another client.           |
   | NFS4ERR_DEADLOCK             | 10045  | The server has been able  |
   |                              |        | to determine a file       |
   |                              |        | locking deadlock          |
   |                              |        | condition for a blocking  |
   |                              |        | lock request.             |



















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   | 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 | TBD    | 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     | TBD    | TBD                       |
   | 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.        |






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   | 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).              |
   | 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       | TDB    | Layouts are temporarily   |
   |                              |        | unavailable for the file, |
   |                              |        | client should retry       |
   |                              |        | later.                    |
   | NFS4ERR_LAYOUTUNAVAILABLE    | TDB    | Layouts are not available |
   |                              |        | for the file or its       |
   |                              |        | containing file system.   |






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   | NFS4ERR_LEASE_MOVED          | 10031  | A lease being renewed is  |
   |                              |        | associated with a         |
   |                              |        | filesystem 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.          |
   | 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_MLINK                | 31     | Too many hard links.      |
   | NFS4ERR_MOVED                | 10019  | The filesystem 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        |
   |                              |        | filesystem location by    |
   |                              |        | obtaining the             |
   |                              |        | "fs_locations" attribute  |
   |                              |        | for the current           |
   |                              |        | filehandle. For further   |
   |                              |        | discussion, refer to the  |
   |                              |        | section "Multi-server     |
   |                              |        | Name Space".              |
   | NFS4ERR_NAMETOOLONG          | 63     | The filename in an        |
   |                              |        | operation was too long.   |





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   | 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).       |
   | NFS4ERR_NO_GRACE             | 10033  | A reclaim of client state |
   |                              |        | has fallen outside of the |
   |                              |        | grace period of the       |
   |                              |        | server. As a result, the  |
   |                              |        | server can not guarantee  |
   |                              |        | that conflicting state    |
   |                              |        | has not been provided to  |
   |                              |        | another client.           |
   | NFS4ERR_NOMATCHING_LAYOUT    | TBD    | Client has no matching    |
   |                              |        | layout (segment) to       |
   |                              |        | return.                   |
   | NFS4ERR_NOSPC                | 28     | No space left on device.  |
   |                              |        | The operation would have  |
   |                              |        | caused the server's       |
   |                              |        | filesystem 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.                |
   | 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.  |




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   | 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_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.  |
   | NFS4ERR_RECALLCONFLICT       | TBD    | 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.       |











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   | NFS4ERR_RESOURCE             | 10018  | For the processing of the |
   |                              |        | COMPOUND procedure, the   |
   |                              |        | server may exhaust        |
   |                              |        | available resources and   |
   |                              |        | can not continue          |
   |                              |        | processing operations     |
   |                              |        | within the COMPOUND       |
   |                              |        | procedure. This error     |
   |                              |        | will be returned from the |
   |                              |        | server in those instances |
   |                              |        | of resource exhaustion    |
   |                              |        | related to the processing |
   |                              |        | of the COMPOUND           |
   |                              |        | procedure.                |
   | NFS4ERR_RESTOREFH            | 10030  | The RESTOREFH operation   |
   |                              |        | does not have a saved     |
   |                              |        | filehandle (identified by |
   |                              |        | SAVEFH) to operate upon.  |
   | NFS4ERR_ROFS                 | 30     | Read-only filesystem. A   |
   |                              |        | modifying operation was   |
   |                              |        | attempted on a read-only  |
   |                              |        | filesystem.               |
   | 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.         |



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   | NFS4ERR_STALE_CLIENTID       | 10022  | A clientid not recognized |
   |                              |        | by the server was used in |
   |                              |        | a locking or              |
   |                              |        | SETCLIENTID_CONFIRM       |
   |                              |        | 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_UNKNOWN_LAYOUTTYPE   | TBD    | Layout type is unknown.   |
   | 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.          |
   | NFS4ERR_                     | TDB    | TDB                       |
   +------------------------------+--------+---------------------------+

                                  Table 5


21.  NFS version 4.1 Procedures

21.1.  Procedure 0: NULL - No Operation

21.1.1.  SYNOPSIS

21.1.2.  ARGUMENTS

   void;




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21.1.3.  RESULTS

   void;

21.1.4.  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.

21.1.5.  ERRORS

   None.

21.2.  Procedure 1: COMPOUND - Compound Operations

21.2.1.  SYNOPSIS

   compoundargs -> compoundres

21.2.2.  ARGUMENTS

   union nfs_argop4 switch (nfs_opnum4 argop) {
       case <OPCODE>: <argument>;
       ...
   };

   struct COMPOUND4args {
       utf8str_cs      tag;
       uint32_t        minorversion;
       nfs_argop4      argarray<>;
   };

21.2.3.  RESULTS

   union nfs_resop4 switch (nfs_opnum4 resop){
       case <OPCODE>: <result>;
       ...
   };

   struct COMPOUND4res {
       nfsstat4        status;
       utf8str_cs      tag;
       nfs_resop4      resarray<>;
   };




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21.2.4.  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.  In this case, the error
   NFS4ERR_RESOURCE will be returned for the particular operation within
   the COMPOUND procedure where the resource exhaustion occurred.  This
   assumes that all previous operations within the COMPOUND sequence
   have been evaluated successfully.  The results for all of the
   evaluated operations must be returned to the client.

   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.  The initial
   and default value for this field is 0 (zero).  This field will be
   used by future minor versions such that the client can communicate to
   the server what minor version is being requested.  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.

   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.



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   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.

21.2.5.  IMPLEMENTATION

   Since an error of any type may occur after only a portion of the
   operations have been evaluated, the client must be prepared to
   recover from any failure.  If the source of an NFS4ERR_RESOURCE error
   was a complex or lengthy set of operations, it is likely that if the
   number of operations were reduced the server would be able to
   evaluate them successfully.  Therefore, the client is responsible for
   dealing with this type of complexity in recovery.

21.2.6.  ERRORS

   All errors defined in the protocol


22.  NFS version 4.1 Operations







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22.1.  Operation 3: ACCESS - Check Access Rights

22.1.1.  SYNOPSIS

   (cfh), accessreq -> supported, accessrights

22.1.2.  ARGUMENTS

   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;
   };

22.1.3.  RESULTS

   struct ACCESS4resok {
           uint32_t        supported;
           uint32_t        access;
   };

   union ACCESS4res switch (nfsstat4 status) {
    case NFS4_OK:
            ACCESS4resok   resok4;
    default:
            void;
   };

22.1.4.  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



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   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.

22.1.5.  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
   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



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   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.

22.1.6.  ERRORS

   NFS4ERR_ACCESS NFS4ERR_BADHANDLE NFS4ERR_BADXDR NFS4ERR_DELAY
   NFS4ERR_FHEXPIRED NFS4ERR_INVAL NFS4ERR_IO NFS4ERR_MOVED
   NFS4ERR_NOFILEHANDLE NFS4ERR_RESOURCE NFS4ERR_SERVERFAULT
   NFS4ERR_STALE

22.2.  Operation 4: CLOSE - Close File

22.2.1.  SYNOPSIS

   (cfh), seqid, open_stateid -> open_stateid

22.2.2.  ARGUMENTS

   struct CLOSE4args {
           /* CURRENT_FH: object */
           seqid4          seqid
           stateid4        open_stateid;
   };





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22.2.3.  RESULTS

   union CLOSE4res switch (nfsstat4 status) {
    case NFS4_OK:
            stateid4       open_stateid;
    default:
            void;
   };

22.2.4.  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.

22.2.5.  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.

22.2.6.  ERRORS

   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_RESOURCE NFS4ERR_SERVERFAULT
   NFS4ERR_STALE NFS4ERR_STALE_STATEID

22.3.  Operation 5: COMMIT - Commit Cached Data






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22.3.1.  SYNOPSIS

   (cfh), offset, count -> verifier

22.3.2.  ARGUMENTS

   struct COMMIT4args {
           /* CURRENT_FH: file */
           offset4         offset;
           count4          count;
   };

22.3.3.  RESULTS

   struct COMMIT4resok {
           verifier4       writeverf;
   };

   union COMMIT4res switch (nfsstat4 status) {
    case NFS4_OK:
            COMMIT4resok   resok4;
    default:
            void;
   };

22.3.4.  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
   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.



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   On success, the current filehandle retains its value.

22.3.5.  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
   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



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   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.

22.3.6.  ERRORS

   NFS4ERR_ACCESS NFS4ERR_BADHANDLE NFS4ERR_BADXDR NFS4ERR_FHEXPIRED
   NFS4ERR_INVAL NFS4ERR_IO NFS4ERR_ISDIR NFS4ERR_MOVED
   NFS4ERR_NOFILEHANDLE NFS4ERR_RESOURCE NFS4ERR_ROFS
   NFS4ERR_SERVERFAULT NFS4ERR_STALE

22.4.  Operation 6: CREATE - Create a Non-Regular File Object

22.4.1.  SYNOPSIS

   (cfh), name, type, attrs -> (cfh), change_info, attrs_set

















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22.4.2.  ARGUMENTS

   union createtype4 switch (nfs_ftype4 type) {
    case NF4LNK:
            linktext4      linkdata;
    case NF4BLK:
    case NF4CHR:
            specdata4      devdata;
    case NF4SOCK:
    case NF4FIFO:
    case NF4DIR:
            void;
   };

   struct CREATE4args {
           /* CURRENT_FH: directory for creation */
           createtype4     objtype;
           component4      objname;
           fattr4          createattrs;
   };

22.4.3.  RESULTS

   struct CREATE4resok {
           change_info4    cinfo;
           bitmap4         attrset;        /* attributes set */
   };

   union CREATE4res switch (nfsstat4 status) {
    case NFS4_OK:
            CREATE4resok resok4;
    default:
            void;
   };

22.4.4.  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.

   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



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   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 filesystem 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 filesystem semantics may
   dictate other methods of derivation.  Similarly, if createattrs
   includes neither the group attribute nor a group ACE, and if the
   server's filesystem 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 filesystem 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.

22.4.5.  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.




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22.4.6.  ERRORS

   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_PERM
   NFS4ERR_RESOURCE NFS4ERR_ROFS NFS4ERR_SERVERFAULT NFS4ERR_STALE

22.5.  Operation 7: DELEGPURGE - Purge Delegations Awaiting Recovery

22.5.1.  SYNOPSIS

   clientid ->

22.5.2.  ARGUMENTS

   struct DELEGPURGE4args {
           clientid4       clientid;
   };

22.5.3.  RESULTS

   struct DELEGPURGE4res {
           nfsstat4        status;
   };

22.5.4.  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.

   The server MAY support DELEGPURGE, but if it does not, it MUST NOT



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   support CLAIM_DELEGATE_PREV.

22.5.5.  ERRORS

   NFS4ERR_BADXDR NFS4ERR_NOTSUPP NFS4ERR_LEASE_MOVED NFS4ERR_MOVED
   NFS4ERR_RESOURCE NFS4ERR_SERVERFAULT NFS4ERR_STALE_CLIENTID

22.6.  Operation 8: DELEGRETURN - Return Delegation

22.6.1.  SYNOPSIS

   (cfh), stateid ->

22.6.2.  ARGUMENTS

   struct DELEGRETURN4args {
           /* CURRENT_FH: delegated file */
           stateid4        stateid;
   };

22.6.3.  RESULTS

   struct DELEGRETURN4res {
           nfsstat4        status;
   };

22.6.4.  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.

22.6.5.  ERRORS

   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_RESOURCE NFS4ERR_SERVERFAULT NFS4ERR_STALE
   NFS4ERR_STALE_STATEID

22.7.  Operation 9: GETATTR - Get Attributes






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22.7.1.  SYNOPSIS

   (cfh), attrbits -> attrbits, attrvals

22.7.2.  ARGUMENTS

   struct GETATTR4args {
           /* CURRENT_FH: directory or file */
           bitmap4         attr_request;
   };

22.7.3.  RESULTS

   struct GETATTR4resok {
           fattr4          obj_attributes;
   };

   union GETATTR4res switch (nfsstat4 status) {
    case NFS4_OK:
            GETATTR4resok  resok4;
    default:
            void;
   };

22.7.4.  DESCRIPTION

   The GETATTR operation will obtain attributes for the filesystem
   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 3).

   On success, the current filehandle retains its value.





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22.7.5.  IMPLEMENTATION

22.7.6.  ERRORS

   NFS4ERR_ACCESS NFS4ERR_BADHANDLE NFS4ERR_BADXDR NFS4ERR_DELAY
   NFS4ERR_FHEXPIRED NFS4ERR_INVAL NFS4ERR_IO NFS4ERR_MOVED
   NFS4ERR_NOFILEHANDLE NFS4ERR_RESOURCE NFS4ERR_SERVERFAULT
   NFS4ERR_STALE

22.8.  Operation 10: GETFH - Get Current Filehandle

22.8.1.  SYNOPSIS

   (cfh) -> filehandle

22.8.2.  ARGUMENTS

   /* CURRENT_FH: */
   void;

22.8.3.  RESULTS

   struct GETFH4resok {
           nfs_fh4         object;
   };

   union GETFH4res switch (nfsstat4 status) {
    case NFS4_OK:
           GETFH4resok     resok4;
    default:
           void;
   };

22.8.4.  DESCRIPTION

   This operation returns the current filehandle value.

   On success, the current filehandle retains its value.

22.8.5.  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.






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      PUTFH (directory filehandle)

      LOOKUP (entry name)

      GETFH

22.8.6.  ERRORS

   NFS4ERR_BADHANDLE NFS4ERR_FHEXPIRED NFS4ERR_MOVED
   NFS4ERR_NOFILEHANDLE NFS4ERR_RESOURCE NFS4ERR_SERVERFAULT
   NFS4ERR_STALE

22.9.  Operation 11: LINK - Create Link to a File

22.9.1.  SYNOPSIS

   (sfh), (cfh), newname -> (cfh), change_info

22.9.2.  ARGUMENTS

   struct LINK4args {
           /* SAVED_FH: source object */
           /* CURRENT_FH: target directory */
           component4      newname;
   };

22.9.3.  RESULTS

   struct LINK4resok {
           change_info4    cinfo;
   };

   union LINK4res switch (nfsstat4 status) {
    case NFS4_OK:
            LINK4resok resok4;
    default:
            void;
   };

22.9.4.  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 filesystem
   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.



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   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.

   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.

22.9.5.  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 filesystem on the server" means that the fsid fields in the
   attributes for the objects are the same.  If they reside on different
   filesystems, 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.

22.9.6.  ERRORS

   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_RESOURCE NFS4ERR_ROFS NFS4ERR_SERVERFAULT
   NFS4ERR_STALE NFS4ERR_WRONGSEC NFS4ERR_XDEV

22.10.  Operation 12: LOCK - Create Lock

22.10.1.  SYNOPSIS

   (cfh) locktype, reclaim, offset, length, locker -> stateid










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22.10.2.  ARGUMENTS

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

   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;
   };

   enum nfs_lock_type4 {
           READ_LT         = 1,
           WRITE_LT        = 2,
           READW_LT        = 3,    /* blocking read */
           WRITEW_LT       = 4     /* blocking write */
   };

   struct LOCK4args {
           /* CURRENT_FH: file */
           nfs_lock_type4  locktype;
           bool            reclaim;
           offset4         offset;
           length4         length;
           locker4         locker;
   };















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22.10.3.  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;
   };

22.10.4.  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.

   On success, the current filehandle retains its value.



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22.10.5.  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 filesystem, 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.






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22.10.6.  ERRORS

   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_RECLAIM_BAD NFS4ERR_RECLAIM_CONFLICT NFS4ERR_RESOURCE
   NFS4ERR_SERVERFAULT NFS4ERR_STALE NFS4ERR_STALE_CLIENTID
   NFS4ERR_STALE_STATEID

22.11.  Operation 13: LOCKT - Test For Lock

22.11.1.  SYNOPSIS

   (cfh) locktype, offset, length owner -> {void, NFS4ERR_DENIED ->
   owner}

22.11.2.  ARGUMENTS

   struct LOCKT4args {
           /* CURRENT_FH: file */
           nfs_lock_type4  locktype;
           offset4         offset;
           length4         length;
           lock_owner4     owner;
   };

22.11.3.  RESULTS

   struct LOCK4denied {
           offset4         offset;
           length4         length;
           nfs_lock_type4  locktype;
           lock_owner4     owner;
   };

   union LOCKT4res switch (nfsstat4 status) {
    case NFS4ERR_DENIED:
            LOCK4denied    denied;
    case NFS4_OK:
            void;
    default:
            void;
   };




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22.11.4.  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.

22.11.5.  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.

22.11.6.  ERRORS

   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_RESOURCE
   NFS4ERR_SERVERFAULT NFS4ERR_STALE NFS4ERR_STALE_CLIENTID






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22.12.  Operation 14: LOCKU - Unlock File

22.12.1.  SYNOPSIS

   (cfh) type, seqid, stateid, offset, length -> stateid

22.12.2.  ARGUMENTS

   struct LOCKU4args {
           /* CURRENT_FH: file */
           nfs_lock_type4  locktype;
           seqid4          seqid;
           stateid4        stateid;
           offset4         offset;
           length4         length;
   };

22.12.3.  RESULTS

   union LOCKU4res switch (nfsstat4 status) {
    case   NFS4_OK:
            stateid4       stateid;
    default:
            void;
   };

22.12.4.  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.

22.12.5.  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



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   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.

22.12.6.  ERRORS

   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_RESOURCE NFS4ERR_SERVERFAULT NFS4ERR_STALE
   NFS4ERR_STALE_STATEID

22.13.  Operation 15: LOOKUP - Lookup Filename

22.13.1.  SYNOPSIS

   (cfh), component -> (cfh)

22.13.2.  ARGUMENTS

   struct LOOKUP4args {
           /* CURRENT_FH: directory */
           component4      objname;
   };

22.13.3.  RESULTS

   struct LOOKUP4res {
           /* CURRENT_FH: object */
           nfsstat4        status;
   };

22.13.4.  DESCRIPTION

   This operation LOOKUPs or finds a filesystem 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.




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   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.

22.13.5.  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

   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 filesystem.  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" filesystems
   should provide a pseudo-filesystem into which the exported
   filesystems can be integrated, so that clients can browse the
   server's name space.  The clients view of a pseudo filesystem will be
   limited to paths that lead to exported filesystems.

   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.






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22.13.6.  ERRORS

   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_RESOURCE NFS4ERR_SERVERFAULT NFS4ERR_STALE
   NFS4ERR_SYMLINK NFS4ERR_WRONGSEC

22.14.  Operation 16: LOOKUPP - Lookup Parent Directory

22.14.1.  SYNOPSIS

   (cfh) -> (cfh)

22.14.2.  ARGUMENTS

   /* CURRENT_FH: object */
   void;

22.14.3.  RESULTS

   struct LOOKUPP4res {
           /* CURRENT_FH: directory */
           nfsstat4        status;
   };

22.14.4.  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.




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22.14.5.  IMPLEMENTATION

22.14.6.  ERRORS

   NFS4ERR_ACCESS NFS4ERR_BADHANDLE NFS4ERR_FHEXPIRED NFS4ERR_IO
   NFS4ERR_MOVED NFS4ERR_NOENT NFS4ERR_NOFILEHANDLE NFS4ERR_NOTDIR
   NFS4ERR_RESOURCE NFS4ERR_SERVERFAULT NFS4ERR_STALE NFS4ERR_WRONGSEC

22.15.  Operation 17: NVERIFY - Verify Difference in Attributes

22.15.1.  SYNOPSIS

   (cfh), fattr -> -

22.15.2.  ARGUMENTS

   struct NVERIFY4args {
           /* CURRENT_FH: object */
           fattr4          obj_attributes;
   };

22.15.3.  RESULTS

   struct NVERIFY4res {
           nfsstat4        status;
   };

22.15.4.  DESCRIPTION

   This operation is used to prefix a sequence of operations to be
   performed if one or more attributes have changed on some filesystem
   object.  If all the attributes match then the error NFS4ERR_SAME must
   be returned.

   On success, the current filehandle retains its value.

22.15.5.  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



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   In the case that a recommended attribute is specified in the NVERIFY
   operation and the server does not support that attribute for the
   filesystem 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.

22.15.6.  ERRORS

   NFS4ERR_ACCESS NFS4ERR_ATTRNOTSUPP NFS4ERR_BADCHAR NFS4ERR_BADHANDLE
   NFS4ERR_BADXDR NFS4ERR_DELAY NFS4ERR_FHEXPIRED NFS4ERR_INVAL
   NFS4ERR_IO NFS4ERR_MOVED NFS4ERR_NOFILEHANDLE NFS4ERR_RESOURCE
   NFS4ERR_SAME NFS4ERR_SERVERFAULT NFS4ERR_STALE

22.16.  Operation 18: OPEN - Open a Regular File

22.16.1.  SYNOPSIS

   (cfh), seqid, share_access, share_deny, owner, openhow, claim ->
   (cfh), stateid, cinfo, rflags, open_confirm, attrset delegation

22.16.2.  ARGUMENTS

   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        = 0x1C;
   const OPEN4_SHARE_ACCESS_WANT_READ_DELEG        = 0x04;
   const OPEN4_SHARE_ACCESS_WANT_WRITE_DELEG       = 0x08;
   const OPEN4_SHARE_ACCESS_WANT_ANY_DELEG         = 0x0C;
   const OPEN4_SHARE_ACCESS_WANT_NO_DELEG          = 0x10;
   const OPEN4_SHARE_ACCESS_WANT_CANCEL            = 0x14;
   const OPEN4_SHARE_ACCESS_WANT_SIGNAL_DELEG_WHEN_RESRC_AVAIL = 0x20;
   const OPEN4_SHARE_ACCESS_WANT_PUSH_DELEG_WHEN_UNCONTENDED = 0x40;

   struct OPEN4args {
           seqid4          seqid;
           uint32_t        share_access;
           uint32_t        share_deny;



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           open_owner4     owner;
           openflag4       openhow;
           open_claim4     claim;
   };

   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;
   };

   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 */



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    case NFS_LIMIT_BLOCKS:
            nfs_modified_limit4    mod_blocks;
   } ;

   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

           /*
            * 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;



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    /*
     * 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;

    /* 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;
   /*
    * Like CLAIM_NULL. No special rights to file. Ordinary
    * OPEN of the specified file.  File is identified by
    * by file handle.
    */
    case CLAIM_FH: /* new to v4.1 */
            /* CURRENT_FH: file being opened */
            void;

   /*
    * Like CLAIM_DELEGATE_PREV. Right to file based on a
    * delegation granted to a previous boot
    * instance of the client.  File is identified by
    * by file handle.
    */
    case CLAIM_DELEG_PREV_FH: /* new to v4.1 */
            /* CURRENT_FH: file being opened */
            void;

   /*
    * Like CLAIM_DELEGATE_CUR. Right to file based on
    * a delegation granted by the server.
    * File is identified by filehandle.
    */
    case CLAIM_DELEG_CUR_FH: /* new to v4.1 */



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            /* CURRENT_FH: file being opened */
            stateid4        oc_delegate_stateid;
   };

22.16.3.  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
                                              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,
           /* not needed if v4.1 sessions are mandatory */
           WND_OPEN_CONFIRM_NEEDED = 9
   };



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   union open_none_delegation4 /* new to v4.1 */
   switch (why_no_delegation4) {
           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: /* deprecated in v4.1 */
                   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;
   };

   const OPEN4_RESULT_CONFIRM      = 0x00000002;
   const OPEN4_RESULT_LOCKTYPE_POSIX = 0x00000004;

   struct OPEN4resok {
           stateid4        stateid;        /* Stateid for open */
           change_info4    cinfo;          /* Directory Change Info */
           uint32_t        rflags;         /* Result flags */
           bitmap4         attrset;        /* attributes on 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;
   };

22.16.4.  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



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   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
   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



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   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'.

   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 four basic claim types which cover the various
   situations for an OPEN.  They are as follows:

   +---------------------+---------------------------------------------+
   | 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 file handle and the specified       |
   |                     | component name. With CLAIM_FH (new to v4.1) |
   |                     | the file is identified by just the current  |
   |                     | file handle.                                |
   | 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  |                                             |
   | CLAIM_DELEG_PREV_FH | The client is claiming a delegation for     |
   |                     | 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 file      |
   |                     | handle and and the specified component      |
   |                     | name. With CLAIM_DELEG_PREV_FH (new to      |
   |                     | v4.1), the file is identified by just the   |
   |                     | current file handle.                        |



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   | CLAIM_DELEGATE_PREV |                                             |
   | CLAIM_DELEG_PREV_FH | The client is claiming a delegation granted |
   |                     | 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
   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 indicates that the client MUST execute an
   OPEN_CONFIRM operation before using the open file.
   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
   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.



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   If the underlying filesystem 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 filesystem.

   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 filesystem.  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 acquistion of
   delegations via the following new flags for the share_access field of
   OPEN4args:

   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

   Only one of the flags named with prefix OPEN4_SHARE_ACCESS_WANT_ can
   be specified.  If none of the flags with prefix
   OPEN4_SHARE_ACCESS_WANT_ are specified, then the client is indicating
   no desire for a delegation.  The server MAY return no delegation in
   the OPEN response.

   If the server supports the new 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:



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   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 limitationa prevent the server from granting a
      delegation.

   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_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.

   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.

   If the client specifies
   OPEN4_SHARE_ACCESS_WANT_SIGNAL_DELEG_WHEN_RESRC_AVAIL, then it wishes



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   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, why_no_delegation4 to WND_RESOURCE, and
   ond_server_will_signal_avail to TRUE.  If
   ond_server_will_signal_avail is set 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,
   why_no_delegation4 to WND_CONTENTION, and ond_server_will_push_deleg
   to TRUE.  If ond_server_will_push_deleg is set 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.

22.16.5.  IMPLEMENTATION

   The OPEN operation contains support for EXCLUSIVE create.  The
   mechanism is similar to the support in NFS version 3 [RFC1813].  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 the client network address, and a unique number
   generated by the client, perhaps the RPC transaction identifier, may
   be appropriate.

   If the object does not exist, the server creates the object and
   stores the verifier in stable storage.  For filesystems 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



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   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 filesystem 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
   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.




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   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.

   "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
   same file.

22.16.6.  ERRORS

   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



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   NFS4ERR_MOVED NFS4ERR_NAMETOOLONG NFS4ERR_NOENT NFS4ERR_NOFILEHANDLE
   NFS4ERR_NOSPC NFS4ERR_NOTDIR NFS4ERR_NO_GRACE NFS4ERR_PERM
   NFS4ERR_RECLAIM_BAD NFS4ERR_RECLAIM_CONFLICT NFS4ERR_RESOURCE
   NFS4ERR_ROFS NFS4ERR_SERVERFAULT NFS4ERR_SHARE_DENIED NFS4ERR_STALE
   NFS4ERR_STALE_CLIENTID NFS4ERR_SYMLINK NFS4ERR_WRONGSEC

22.17.  Operation 19: OPENATTR - Open Named Attribute Directory

22.17.1.  SYNOPSIS

   (cfh) createdir -> (cfh)

22.17.2.  ARGUMENTS

   struct OPENATTR4args {
           /* CURRENT_FH: object */
           bool    createdir;
   };

22.17.3.  RESULTS

   struct OPENATTR4res {
           /* CURRENT_FH: named attr directory*/
           nfsstat4        status;
   };

22.17.4.  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 filesystem 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.





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22.17.5.  IMPLEMENTATION

   If the server does not support named attributes for the current
   filehandle, an error of NFS4ERR_NOTSUPP will be returned to the
   client.

22.17.6.  ERRORS

   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_RESOURCE NFS4ERR_ROFS NFS4ERR_SERVERFAULT NFS4ERR_STALE

22.18.  Operation 20: OPEN_CONFIRM - Confirm Open

22.18.1.  SYNOPSIS

   (cfh), seqid, stateid-> stateid

22.18.2.  ARGUMENTS

   struct OPEN_CONFIRM4args {
           /* CURRENT_FH: opened file */
           stateid4        open_stateid;
           seqid4          seqid;
   };

22.18.3.  RESULTS

   struct OPEN_CONFIRM4resok {
           stateid4        open_stateid;
   };

   union OPEN_CONFIRM4res switch (nfsstat4 status) {
    case NFS4_OK:
            OPEN_CONFIRM4resok     resok4;
    default:
            void;
   };

22.18.4.  DESCRIPTION

   This operation is used to confirm the sequence id usage for the first
   time that a open_owner is used by a client.  The stateid returned
   from the OPEN operation is used as the argument for this operation
   along with the next sequence id for the open_owner.  The sequence id
   passed to the OPEN_CONFIRM must be 1 (one) greater than the seqid
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   obtained.  If the server receives an unexpected sequence id with
   respect to the original open, then the server assumes that the client
   will not confirm the original OPEN and all state associated with the
   original OPEN is released by the server.

   On success, the current filehandle retains its value.

22.18.5.  IMPLEMENTATION

   A given client might generate many open_owner4 data structures for a
   given clientid.  The client will periodically either dispose of its
   open_owner4s or stop using them for indefinite periods of time.  The
   latter situation is why the NFS version 4 protocol does not have an
   explicit operation to exit an open_owner4: such an operation is of no
   use in that situation.  Instead, to avoid unbounded memory use, the
   server needs to implement a strategy for disposing of open_owner4s
   that have no current lock, open, or delegation state for any files
   and have not been used recently.  The time period used to determine
   when to dispose of open_owner4s is an implementation choice.  The
   time period should certainly be no less than the lease time plus any
   grace period the server wishes to implement beyond a lease time.  The
   OPEN_CONFIRM operation allows the server to safely dispose of unused
   open_owner4 data structures.

   In the case that a client issues an OPEN operation and the server no
   longer has a record of the open_owner4, the server needs ensure that
   this is a new OPEN and not a replay or retransmission.

   Servers must not require confirmation on OPENs that grant delegations
   or are doing reclaim operations.  See section "Use of Open
   Confirmation" for details.  The server can easily avoid this by
   noting whether it has disposed of one open_owner4 for the given
   clientid.  If the server does not support delegation, it might simply
   maintain a single bit that notes whether any open_owner4 (for any
   client) has been disposed of.

   The server must hold unconfirmed OPEN state until one of three events
   occur.  First, the client sends an OPEN_CONFIRM request with the
   appropriate sequence id and stateid within the lease period.  In this
   case, the OPEN state on the server goes to confirmed, and the
   open_owner4 on the server is fully established.

   Second, the client sends another OPEN request with a sequence id that
   is incorrect for the open_owner4 (out of sequence).  In this case,
   the server assumes the second OPEN request is valid and the first one
   is a replay.  The server cancels the OPEN state of the first OPEN
   request, establishes an unconfirmed OPEN state for the second OPEN
   request, and responds to the second OPEN request with an indication



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   that an OPEN_CONFIRM is needed.  The process then repeats itself.
   While there is a potential for a denial of service attack on the
   client, it is mitigated if the client and server require the use of a
   security flavor based on Kerberos V5, LIPKEY, or some other flavor
   that uses cryptography.

   What if the server is in the unconfirmed OPEN state for a given
   open_owner4, and it receives an operation on the open_owner4 that has
   a stateid but the operation is not OPEN, or it is OPEN_CONFIRM but
   with the wrong stateid?  Then, even if the seqid is correct, the
   server returns NFS4ERR_BAD_STATEID, because the server assumes the
   operation is a replay: if the server has no established OPEN state,
   then there is no way, for example, a LOCK operation could be valid.

   Third, neither of the two aforementioned events occur for the
   open_owner4 within the lease period.  In this case, the OPEN state is
   canceled and disposal of the open_owner4 can occur.

22.18.6.  ERRORS

   NFS4ERR_ADMIN_REVOKED NFS4ERR_BADHANDLE NFS4ERR_BAD_SEQID
   NFS4ERR_BAD_STATEID NFS4ERR_BADXDR NFS4ERR_EXPIRED NFS4ERR_FHEXPIRED
   NFS4ERR_INVAL NFS4ERR_ISDIR NFS4ERR_MOVED NFS4ERR_NOFILEHANDLE
   NFS4ERR_OLD_STATEID NFS4ERR_RESOURCE NFS4ERR_SERVERFAULT
   NFS4ERR_STALE NFS4ERR_STALE_STATEID

22.19.  Operation 21: OPEN_DOWNGRADE - Reduce Open File Access

22.19.1.  SYNOPSIS

   (cfh), stateid, seqid, access, deny -> stateid

22.19.2.  ARGUMENTS

   struct OPEN_DOWNGRADE4args {
           /* CURRENT_FH: opened file */
           stateid4        stateid;
           seqid4          seqid;
           uint32_t        share_access;
           uint32_t        share_deny;
   };










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22.19.3.  RESULTS

   struct OPEN_DOWNGRADE4resok {
           stateid4        stateid;
   };

   union OPEN_DOWNGRADE4res switch(nfsstat4 status) {
    case NFS4_OK:
           OPEN_DOWNGRADE4resok    resok4;
    default:
           void;
   };

22.19.4.  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.

   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.

22.19.5.  ERRORS

   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_RESOURCE NFS4ERR_SERVERFAULT NFS4ERR_STALE
   NFS4ERR_STALE_STATEID

22.20.  Operation 22: PUTFH - Set Current Filehandle

22.20.1.  SYNOPSIS

   filehandle -> (cfh)




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22.20.2.  ARGUMENTS

   struct PUTFH4args {
           nfs_fh4         object;
   };

22.20.3.  RESULTS

   struct PUTFH4res {
           /* CURRENT_FH: */
           nfsstat4        status;
   };

22.20.4.  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.

22.20.5.  IMPLEMENTATION

   Commonly used as the first operator in an NFS request to set the
   context for following operations.

22.20.6.  ERRORS

   NFS4ERR_BADHANDLE NFS4ERR_BADXDR NFS4ERR_FHEXPIRED NFS4ERR_MOVED
   NFS4ERR_RESOURCE NFS4ERR_SERVERFAULT NFS4ERR_STALE NFS4ERR_WRONGSEC

22.21.  Operation 23: PUTPUBFH - Set Public Filehandle

22.21.1.  SYNOPSIS

   - -> (cfh)

22.21.2.  ARGUMENT

   void;










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22.21.3.  RESULT

   struct PUTPUBFH4res {
           /* CURRENT_FH: public fh */
           nfsstat4        status;
   };

22.21.4.  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],
   [RFC2055], [RFC2224].  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.

22.21.5.  IMPLEMENTATION

   Used as the first operator in an NFS request to set the context for
   following operations.

   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] 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] 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



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   behave differently than an NFS version 4 absolute resolution.

   There is a form of security negotiation as described in [RFC2755]
   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.

22.21.6.  ERRORS

   NFS4ERR_RESOURCE NFS4ERR_SERVERFAULT NFS4ERR_WRONGSEC

22.22.  Operation 24: PUTROOTFH - Set Root Filehandle

22.22.1.  SYNOPSIS

   - -> (cfh)

22.22.2.  ARGUMENTS

   void;

22.22.3.  RESULTS

   struct PUTROOTFH4res {
           /* CURRENT_FH: root fh */
           nfsstat4        status;
   };

22.22.4.  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.

22.22.5.  IMPLEMENTATION

   Commonly used as the first operator in an NFS request to set the
   context for following operations.

22.22.6.  ERRORS

   NFS4ERR_RESOURCE NFS4ERR_SERVERFAULT NFS4ERR_WRONGSEC





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22.23.  Operation 25: READ - Read from File

22.23.1.  SYNOPSIS

   (cfh), stateid, offset, count -> eof, data

22.23.2.  ARGUMENTS

   struct READ4args {
           /* CURRENT_FH: file */
           stateid4        stateid;
           offset4         offset;
           count4          count;
   };

22.23.3.  RESULTS

   struct READ4resok {
           bool            eof;
           opaque          data<>;
   };

   union READ4res switch (nfsstat4 status) {
    case NFS4_OK:
            READ4resok     resok4;
    default:
            void;
   };

22.23.4.  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.

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   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
   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.

22.23.5.  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.





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22.23.6.  ERRORS

   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_OPENMODE NFS4ERR_RESOURCE NFS4ERR_SERVERFAULT NFS4ERR_STALE
   NFS4ERR_STALE_STATEID

22.24.  Operation 26: READDIR - Read Directory

22.24.1.  SYNOPSIS

   (cfh), cookie, cookieverf, dircount, maxcount, attr_request ->
   cookieverf { cookie, name, attrs }

22.24.2.  ARGUMENTS

   struct READDIR4args {
           /* CURRENT_FH: directory */
           nfs_cookie4     cookie;
           verifier4       cookieverf;
           count4          dircount;
           count4          maxcount;
           bitmap4         attr_request;
   };
























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22.24.3.  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;
   };

22.24.4.  DESCRIPTION

   The READDIR operation retrieves a variable number of entries from a
   filesystem 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.




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   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
   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 filesystem 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



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   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.

22.24.5.  IMPLEMENTATION

   The server's filesystem 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
   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.





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22.24.6.  ERRORS

   NFS4ERR_ACCESS NFS4ERR_BADHANDLE NFS4ERR_BAD_COOKIE NFS4ERR_BADXDR
   NFS4ERR_DELAY NFS4ERR_FHEXPIRED NFS4ERR_INVAL NFS4ERR_IO
   NFS4ERR_MOVED NFS4ERR_NOFILEHANDLE NFS4ERR_NOTDIR NFS4ERR_RESOURCE
   NFS4ERR_SERVERFAULT NFS4ERR_STALE NFS4ERR_TOOSMALL

22.25.  Operation 27: READLINK - Read Symbolic Link

22.25.1.  SYNOPSIS

   (cfh) -> linktext

22.25.2.  ARGUMENTS

   /* CURRENT_FH: symlink */
   void;

22.25.3.  RESULTS

   struct READLINK4resok {
           linktext4       link;
   };

   union READLINK4res switch (nfsstat4 status) {
    case NFS4_OK:
            READLINK4resok resok4;
    default:
            void;
   };

22.25.4.  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.

22.25.5.  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



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   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.

22.25.6.  ERRORS

   NFS4ERR_ACCESS NFS4ERR_BADHANDLE NFS4ERR_DELAY NFS4ERR_FHEXPIRED
   NFS4ERR_INVAL NFS4ERR_IO NFS4ERR_ISDIR NFS4ERR_MOVED
   NFS4ERR_NOFILEHANDLE NFS4ERR_NOTSUPP NFS4ERR_RESOURCE
   NFS4ERR_SERVERFAULT NFS4ERR_STALE

22.26.  Operation 28: REMOVE - Remove Filesystem Object

22.26.1.  SYNOPSIS

   (cfh), filename -> change_info

22.26.2.  ARGUMENTS

   struct REMOVE4args {
           /* CURRENT_FH: directory */
           component4       target;
   };

22.26.3.  RESULTS

   struct REMOVE4resok {
           change_info4    cinfo;
   }

   union REMOVE4res switch (nfsstat4 status) {
    case NFS4_OK:
            REMOVE4resok   resok4;
    default:
            void;
   }

22.26.4.  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 filesystem object, the object may be destroyed.




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   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.

22.26.5.  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.

   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




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22.26.6.  ERRORS

   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_RESOURCE NFS4ERR_ROFS NFS4ERR_SERVERFAULT NFS4ERR_STALE

22.27.  Operation 29: RENAME - Rename Directory Entry

22.27.1.  SYNOPSIS

   (sfh), oldname, (cfh), newname -> source_change_info,
   target_change_info

22.27.2.  ARGUMENTS

   struct RENAME4args {
           /* SAVED_FH: source directory */
           component4      oldname;
           /* CURRENT_FH: target directory */
           component4      newname;
   };

22.27.3.  RESULTS

   struct RENAME4resok {
           change_info4    source_cinfo;
           change_info4    target_cinfo;
   };

   union RENAME4res switch (nfsstat4 status) {
    case NFS4_OK:
            RENAME4resok   resok4;
    default:
            void;
   };

22.27.4.  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
   filesystem on the server.  On success, the current filehandle will
   continue to be the target directory.




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   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 Filesystem 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 filesystem objects, the server will
   return NFS4ERR_XDEV just as if the saved and current filehandles
   represented directories on different filesystems.

   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.

22.27.5.  IMPLEMENTATION

   The RENAME operation must be atomic to the client.  The statement
   "source and target directories must reside on the same filesystem on
   the server" means that the fsid fields in the attributes for the
   directories are the same.  If they reside on different filesystems,
   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,



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   the server will return NFS4ERR_NOTDIR.

22.27.6.  ERRORS

   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_RESOURCE
   NFS4ERR_ROFS NFS4ERR_SERVERFAULT NFS4ERR_STALE NFS4ERR_WRONGSEC
   NFS4ERR_XDEV

22.28.  Operation 30: RENEW - Renew a Lease

22.28.1.  SYNOPSIS

   clientid -> ()

22.28.2.  ARGUMENTS

   struct RENEW4args {
           clientid4       clientid;
   };

22.28.3.  RESULTS

   struct RENEW4res {
           nfsstat4        status;
   };

22.28.4.  DESCRIPTION

   The RENEW operation is used by the client to renew leases which it
   currently holds at a server.  In processing the RENEW request, the
   server renews all leases associated with the client.  The associated
   leases are determined by the clientid provided via the SETCLIENTID
   operation.

22.28.5.  IMPLEMENTATION

   When the client holds delegations, it needs to use RENEW to detect
   when the server has determined that the callback path is down.  When
   the server has made such a determination, only the RENEW operation
   will renew the lease on delegations.  If the server determines the
   callback path is down, it returns NFS4ERR_CB_PATH_DOWN.  Even though
   it returns NFS4ERR_CB_PATH_DOWN, the server MUST renew the lease on
   the record locks and share reservations that the client has
   established on the server.  If for some reason the lock and share



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   reservation lease cannot be renewed, then the server MUST return an
   error other than NFS4ERR_CB_PATH_DOWN, even if the callback path is
   also down.

   The client that issues RENEW MUST choose the principal, RPC security
   flavor, and if applicable, GSS-API mechanism and service via one of
   the following algorithms:

      The client uses the same principal, RPC security flavor -- and if
      the flavor was RPCSEC_GSS -- the same mechanism and service that
      was used when the client id was established via
      SETCLIENTID_CONFIRM.

      The client uses any principal, RPC security flavor mechanism and
      service combination that currently has an OPEN file on the server.
      I.e. the same principal had a successful OPEN operation, the file
      is still open by that principal, and the flavor, mechanism, and
      service of RENEW match that of the previous OPEN.

   The server MUST reject a RENEW that does not use one the
   aforementioned algorithms, with the error NFS4ERR_ACCESS.

22.28.6.  ERRORS

   NFS4ERR_ACCESS NFS4ERR_ADMIN_REVOKED NFS4ERR_BADXDR
   NFS4ERR_CB_PATH_DOWN NFS4ERR_EXPIRED NFS4ERR_LEASE_MOVED
   NFS4ERR_RESOURCE NFS4ERR_SERVERFAULT NFS4ERR_STALE_CLIENTID

22.29.  Operation 31: RESTOREFH - Restore Saved Filehandle

22.29.1.  SYNOPSIS

   (sfh) -> (cfh)

22.29.2.  ARGUMENTS

   /* SAVED_FH: */
   void;

22.29.3.  RESULTS

   struct RESTOREFH4res {
           /* CURRENT_FH: value of saved fh */
           nfsstat4        status;
   };






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22.29.4.  DESCRIPTION

   Set the current filehandle to the value in the saved filehandle.  If
   there is no saved filehandle then return the error NFS4ERR_RESTOREFH.

22.29.5.  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)

22.29.6.  ERRORS

   NFS4ERR_BADHANDLE NFS4ERR_FHEXPIRED NFS4ERR_MOVED NFS4ERR_RESOURCE
   NFS4ERR_RESTOREFH NFS4ERR_SERVERFAULT NFS4ERR_STALE NFS4ERR_WRONGSEC

22.30.  Operation 32: SAVEFH - Save Current Filehandle

22.30.1.  SYNOPSIS

   (cfh) -> (sfh)

22.30.2.  ARGUMENTS

   /* CURRENT_FH: */
   void;

22.30.3.  RESULTS

   struct SAVEFH4res {
           /* SAVED_FH: value of current fh */
           nfsstat4        status;
   };







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22.30.4.  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.

22.30.5.  IMPLEMENTATION

22.30.6.  ERRORS

   NFS4ERR_BADHANDLE NFS4ERR_FHEXPIRED NFS4ERR_MOVED
   NFS4ERR_NOFILEHANDLE NFS4ERR_RESOURCE NFS4ERR_SERVERFAULT
   NFS4ERR_STALE

22.31.  Operation 33: SECINFO - Obtain Available Security

22.31.1.  SYNOPSIS

   (cfh), name -> { secinfo }

22.31.2.  ARGUMENTS

   struct SECINFO4args {
           /* CURRENT_FH: directory */
           component4     name;
   };























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22.31.3.  RESULTS

   enum rpc_gss_svc_t {            /* From RFC 2203 */
           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;
   };

   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;
   };

22.31.4.  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
   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]), or RPCSEC_GSS (as defined in
   [RFC2203]).  The field flavor can also any other security flavor



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   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]), the quality of protection (as
   defined in [RFC2743]) and the service type (as defined in [RFC2203]).
   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.

22.31.5.  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:

   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.




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   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 file handled 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
   attributes, it is possible that the READDIR request's security triple
   did not match that of a directory entry.  If this is the case and the
   client has requested the rdattr_error attribute, the server will
   return the NFS4ERR_WRONGSEC error in rdattr_error for the entry.

   See the section "Security Considerations" for a discussion on the
   recommendations for security flavor used by SECINFO and
   SECINFO_NO_NAME.

22.31.6.  ERRORS

   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_RESOURCE NFS4ERR_SERVERFAULT NFS4ERR_STALE

22.32.  Operation 34: SETATTR - Set Attributes

22.32.1.  SYNOPSIS

   (cfh), stateid, attrmask, attr_vals -> attrsset

22.32.2.  ARGUMENTS

   struct SETATTR4args {
           /* CURRENT_FH: target object */
           stateid4        stateid;
           fattr4          obj_attributes;
   };




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22.32.3.  RESULTS

   struct SETATTR4res {
           nfsstat4        status;
           bitmap4         attrsset;
   };

22.32.4.  DESCRIPTION

   The SETATTR operation changes one or more of the attributes of a
   filesystem object.  The new attributes are specified with a bitmap
   and the attributes that follow the bitmap in bit order.

   The stateid argument for SETATTR is used to provide file locking
   context that is necessary for SETATTR requests that set the size
   attribute.  Since setting the size attribute modifies the file's
   data, it has the same locking requirements as a corresponding WRITE.
   Any SETATTR that sets the size attribute is incompatible with a share
   reservation that specifies DENY_WRITE.  The area between the old end-
   of-file and the new end-of-file is considered to be modified just as
   would have been the case had the area in question been specified as
   the target of WRITE, for the purpose of checking conflicts with
   record locks, for those cases in which a server is implementing
   mandatory record locking behavior.  A valid stateid should always be
   specified.  When the file size attribute is not set, the special
   stateid consisting of all bits zero should be passed.

   On either success or failure of the operation, the server will return
   the attrsset bitmask to represent what (if any) attributes were
   successfully set.  The attrsset in the response is a subset of the
   bitmap4 that is part of the obj_attributes in the argument.

   On success, the current filehandle retains its value.

22.32.5.  IMPLEMENTATION

   If the request specifies the owner attribute to be set, the server
   should allow the operation to succeed if the current owner of the
   object matches the value specified in the request.  Some servers may
   be implemented in a way as to prohibit the setting of the owner
   attribute unless the requester has privilege to do so.  If the server
   is lenient in this one case of matching owner values, the client
   implementation may be simplified in cases of creation of an object
   followed by a SETATTR.

   The file size attribute is used to request changes to the size of a
   file.  A value of 0 (zero) causes the file to be truncated, a value
   less than the current size of the file causes data from new size to



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   the end of the file to be discarded, and a size greater than the
   current size of the file causes logically zeroed data bytes to be
   added to the end of the file.  Servers are free to implement this
   using holes or actual zero data bytes.  Clients should not make any
   assumptions regarding a server's implementation of this feature,
   beyond that the bytes returned will be zeroed.  Servers must support
   extending the file size via SETATTR.

   SETATTR is not guaranteed atomic.  A failed SETATTR may partially
   change a file's attributes.

   Changing the size of a file with SETATTR indirectly changes the
   time_modify.  A client must account for this as size changes can
   result in data deletion.

   The attributes time_access_set and time_modify_set are write-only
   attributes constructed as a switched union so the client can direct
   the server in setting the time values.  If the switched union
   specifies SET_TO_CLIENT_TIME4, the client has provided an nfstime4 to
   be used for the operation.  If the switch union does not specify
   SET_TO_CLIENT_TIME4, the server is to use its current time for the
   SETATTR operation.

   If server and client times differ, programs that compare client time
   to file times can break.  A time maintenance protocol should be used
   to limit client/server time skew.

   Use of a COMPOUND containing a VERIFY operation specifying only the
   change attribute, immediately followed by a SETATTR, provides a means
   whereby a client may specify a request that emulates the
   functionality of the SETATTR guard mechanism of NFS version 3.  Since
   the function of the guard mechanism is to avoid changes to the file
   attributes based on stale information, delays between checking of the
   guard condition and the setting of the attributes have the potential
   to compromise this function, as would the corresponding delay in the
   NFS version 4 emulation.  Therefore, NFS version 4 servers should
   take care to avoid such delays, to the degree possible, when
   executing such a request.

   If the server does not support an attribute as requested by the
   client, the server should return NFS4ERR_ATTRNOTSUPP.

   A mask of the attributes actually set is returned by SETATTR in all
   cases.  That mask must not include attributes bits not requested to
   be set by the client, and must be equal to the mask of attributes
   requested to be set only if the SETATTR completes without error.





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22.32.6.  ERRORS

   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_RESOURCE NFS4ERR_ROFS
   NFS4ERR_SERVERFAULT NFS4ERR_STALE NFS4ERR_STALE_STATEID

22.33.  Operation 35: SETCLIENTID - Negotiate Clientid

22.33.1.  SYNOPSIS

   client, callback, callback_ident -> clientid, setclientid_confirm

22.33.2.  ARGUMENTS

   struct SETCLIENTID4args {
           nfs_client_id4  client;
           cb_client4      callback;
           uint32_t        callback_ident;
   };

22.33.3.  RESULTS

   struct SETCLIENTID4resok {
           clientid4       clientid;
           verifier4       setclientid_confirm;
   };

   union SETCLIENTID4res switch (nfsstat4 status) {
    case NFS4_OK:
            SETCLIENTID4resok      resok4;
    case NFS4ERR_CLID_INUSE:
            clientaddr4    client_using;
    default:
            void;
   };

22.33.4.  DESCRIPTION

   The client uses the SETCLIENTID operation to notify the server of its
   intention to use a particular client identifier, callback, and
   callback_ident for subsequent requests that entail creating lock,
   share reservation, and delegation state on the server.  Upon
   successful completion the server will return a short hand clientid



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   which, if confirmed via a separate step, will be used in subsequent
   file locking and file open requests.  Confirmation of the clientid
   must be done via the SETCLIENTID_CONFIRM operation to return the
   clientid and setclientid_confirm values, as verifiers, to the server.
   The reason why two verifiers are necessary is that it is possible to
   use SETCLIENTID and SETCLIENTID_CONFIRM to modify the callback and
   callback_ident information but not the short hand clientid.  In that
   event, the setclientid_confirm value is effectively the only
   verifier.

   The callback information provided in this operation will be used if
   the client is provided an open delegation at a future point.
   Therefore, the client must correctly reflect the program and port
   numbers for the callback program at the time SETCLIENTID is used.

   The callback_ident value is used by the server on the callback.  The
   client can use leverage the callback_ident eliminate the need for
   more than one callback RPC program number while still being able to
   determine which server is initiating the callback.

22.33.5.  IMPLEMENTATION

   To understand how to implement SETCLIENTID, make the following
   notations.  Let:

   x  be the value of the client.id subfield of the SETCLIENTID4args
      structure.

   v  be the value of the client.verifier subfield of the
      SETCLIENTID4args structure.

   c  be the value of the clientid field returned in the
      SETCLIENTID4resok structure.

   k  represent the value combination of the fields callback and
      callback_ident fields of the SETCLIENTID4args structure.

   s  be the setclientid_confirm value returned in the SETCLIENTID4resok
      structure.

   { v, x, c, k, s }  be a quintuple for a client record.  A client
      record is confirmed if there has been a SETCLIENTID_CONFIRM
      operation to confirm it.  Otherwise it is unconfirmed.  An
      unconfirmed record is established by a SETCLIENTID call.

   Since SETCLIENTID is a non-idempotent operation, let us assume that
   the server is implementing the duplicate request cache (DRC).




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   When the server gets a SETCLIENTID { v, x, k } request, it processes
   it in the following manner.

   o  It first looks up the request in the DRC.  If there is a hit, it
      returns the result cached in the DRC.  The server does NOT remove
      client state (locks, shares, delegations) nor does it modify any
      recorded callback and callback_ident information for client { x }.

      For any DRC miss, the server takes the client id string x, and
      searches for client records for x that the server may have
      recorded from previous SETCLIENTID calls.  For any confirmed
      record with the same id string x, if the recorded principal does
      not match that of SETCLIENTID call, then the server returns a
      NFS4ERR_CLID_INUSE error.

      For brevity of discussion, the remaining description of the
      processing assumes that there was a DRC miss, and that where the
      server has previously recorded a confirmed record for client x,
      the aforementioned principal check has successfully passed.

   o  The server checks if it has recorded a confirmed record for { v,
      x, c, l, s }, where l may or may not equal k.  If so, and since
      the id verifier v of the request matches that which is confirmed
      and recorded, the server treats this as a probable callback
      information update and records an unconfirmed { v, x, c, k, t }
      and leaves the confirmed { v, x, c, l, s } in place, such that t
      != s.  It does not matter if k equals l or not.  Any pre-existing
      unconfirmed { v, x, c, *, * } is removed.

      The server returns { c, t }.  It is indeed returning the old
      clientid4 value c, because the client apparently only wants to
      update callback value k to value l.  It's possible this request is
      one from the Byzantine router that has stale callback information,
      but this is not a problem.  The callback information update is
      only confirmed if followed up by a SETCLIENTID_CONFIRM { c, t }.

      The server awaits confirmation of k via SETCLIENTID_CONFIRM { c, t
      }.

      The server does NOT remove client (lock/share/delegation) state
      for x.

   o  The server has previously recorded a confirmed { u, x, c, l, s }
      record such that v != u, l may or may not equal k, and has not
      recorded any unconfirmed { *, x, *, *, * } record for x.  The
      server records an unconfirmed { v, x, d, k, t } (d != c, t != s).

      The server returns { d, t }.



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      The server awaits confirmation of { d, k } via SETCLIENTID_CONFIRM
      { d, t }.

      The server does NOT remove client (lock/share/delegation) state
      for x.

   o  The server has previously recorded a confirmed { u, x, c, l, s }
      record such that v != u, l may or may not equal k, and recorded an
      unconfirmed { w, x, d, m, t } record such that c != d, t != s, m
      may or may not equal k, m may or may not equal l, and k may or may
      not equal l.  Whether w == v or w != v makes no difference.  The
      server simply removes the unconfirmed { w, x, d, m, t } record and
      replaces it with an unconfirmed { v, x, e, k, r } record, such
      that e != d, e != c, r != t, r != s.

      The server returns { e, r }.

      The server awaits confirmation of { e, k } via SETCLIENTID_CONFIRM
      { e, r }.

      The server does NOT remove client (lock/share/delegation) state
      for x.

   o  The server has no confirmed { *, x, *, *, * } for x.  It may or
      may not have recorded an unconfirmed { u, x, c, l, s }, where l
      may or may not equal k, and u may or may not equal v.  Any
      unconfirmed record { u, x, c, l, * }, regardless whether u == v or
      l == k, is replaced with an unconfirmed record { v, x, d, k, t }
      where d != c, t != s.

      The server returns { d, t }.

      The server awaits confirmation of { d, k } via SETCLIENTID_CONFIRM
      { d, t }.  The server does NOT remove client (lock/share/
      delegation) state for x. .in -2

   The server generates the clientid and setclientid_confirm values and
   must take care to ensure that these values are extremely unlikely to
   ever be regenerated.

22.33.6.  ERRORS

   NFS4ERR_BADXDR NFS4ERR_CLID_INUSE NFS4ERR_INVAL NFS4ERR_RESOURCE
   NFS4ERR_SERVERFAULT







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22.34.  Operation 36: SETCLIENTID_CONFIRM - Confirm Clientid

22.34.1.  SYNOPSIS

   clientid, verifier -> -

22.34.2.  ARGUMENTS

   struct SETCLIENTID_CONFIRM4args {
           clientid4       clientid;
           verifier4       setclientid_confirm;
   };

22.34.3.  RESULTS

   struct SETCLIENTID_CONFIRM4res {
           nfsstat4        status;
   };

22.34.4.  DESCRIPTION

   This operation is used by the client to confirm the results from a
   previous call to SETCLIENTID.  The client provides the server
   supplied (from a SETCLIENTID response) clientid.  The server responds
   with a simple status of success or failure.

22.34.5.  IMPLEMENTATION

   The client must use the SETCLIENTID_CONFIRM operation to confirm the
   following two distinct cases:

   o  The client's use of a new shorthand client identifier (as returned
      from the server in the response to SETCLIENTID), a new callback
      value (as specified in the arguments to SETCLIENTID) and a new
      callback_ident (as specified in the arguments to SETCLIENTID)
      value.  The client's use of SETCLIENTID_CONFIRM in this case also
      confirms the removal of any of the client's previous relevant
      leased state.  Relevant leased client state includes record locks,
      share reservations, and where the server does not support the
      CLAIM_DELEGATE_PREV claim type, delegations.  If the server
      supports CLAIM_DELEGATE_PREV, then SETCLIENTID_CONFIRM MUST NOT
      remove delegations for this client; relevant leased client state
      would then just include record locks and share reservations.

   o  The client's re-use of an old, previously confirmed, shorthand
      client identifier, a new callback value, and a new callback_ident
      value.  The client's use of SETCLIENTID_CONFIRM in this case MUST
      NOT result in the removal of any previous leased state (locks,



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      share reservations, and delegations)

   We use the same notation and definitions for v, x, c, k, s, and
   unconfirmed and confirmed client records as introduced in the
   description of the SETCLIENTID operation.  The arguments to
   SETCLIENTID_CONFIRM are indicated by the notation { c, s }, where c
   is a value of type clientid4, and s is a value of type verifier4
   corresponding to the setclientid_confirm field.

   As with SETCLIENTID, SETCLIENTID_CONFIRM is a non-idempotent
   operation, and we assume that the server is implementing the
   duplicate request cache (DRC).

   When the server gets a SETCLIENTID_CONFIRM { c, s } request, it
   processes it in the following manner.

   o  It first looks up the request in the DRC.  If there is a hit, it
      returns the result cached in the DRC.  The server does not remove
      any relevant leased client state nor does it modify any recorded
      callback and callback_ident information for client { x } as
      represented by the short hand value c.

   For a DRC miss, the server checks for client records that match the
   short hand value c.  The processing cases are as follows:

   o  The server has recorded an unconfirmed { v, x, c, k, s } record
      and a confirmed { v, x, c, l, t } record, such that s != t.  If
      the principals of the records do not match that of the
      SETCLIENTID_CONFIRM, the server returns NFS4ERR_CLID_INUSE, and no
      relevant leased client state is removed and no recorded callback
      and callback_ident information for client { x } is changed.
      Otherwise, the confirmed { v, x, c, l, t } record is removed and
      the unconfirmed { v, x, c, k, s } is marked as confirmed, thereby
      modifying recorded and confirmed callback and callback_ident
      information for client { x }.

      The server does not remove any relevant leased client state.

      The server returns NFS4_OK.

   o  The server has not recorded an unconfirmed { v, x, c, *, * } and
      has recorded a confirmed { v, x, c, *, s }.  If the principals of
      the record and of SETCLIENTID_CONFIRM do not match, the server
      returns NFS4ERR_CLID_INUSE without removing any relevant leased
      client state and without changing recorded callback and
      callback_ident values for client { x }.

      If the principals match, then what has likely happened is that the



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      client never got the response from the SETCLIENTID_CONFIRM, and
      the DRC entry has been purged.  Whatever the scenario, since the
      principals match, as well as { c, s } matching a confirmed record,
      the server leaves client x's relevant leased client state intact,
      leaves its callback and callback_ident values unmodified, and
      returns NFS4_OK.

   o  The server has not recorded a confirmed { *, *, c, *, * }, and has
      recorded an unconfirmed { *, x, c, k, s }.  Even if this is a
      retry from client, nonetheless the client's first
      SETCLIENTID_CONFIRM attempt was not received by the server.  Retry
      or not, the server doesn't know, but it processes it as if were a
      first try.  If the principal of the unconfirmed { *, x, c, k, s }
      record mismatches that of the SETCLIENTID_CONFIRM request the
      server returns NFS4ERR_CLID_INUSE without removing any relevant
      leased client state.

      Otherwise, the server records a confirmed { *, x, c, k, s }.  If
      there is also a confirmed { *, x, d, *, t }, the server MUST
      remove the client x's relevant leased client state, and overwrite
      the callback state with k.  The confirmed record { *, x, d, *, t }
      is removed.

      Server returns NFS4_OK.

   o  The server has no record of a confirmed or unconfirmed { *, *, c,
      *, s }.  The server returns NFS4ERR_STALE_CLIENTID.  The server
      does not remove any relevant leased client state, nor does it
      modify any recorded callback and callback_ident information for
      any client.

   The server needs to cache unconfirmed { v, x, c, k, s } client
   records and await for some time their confirmation.  As should be
   clear from the record processing discussions for SETCLIENTID and
   SETCLIENTID_CONFIRM, there are cases where the server does not
   deterministically remove unconfirmed client records.  To avoid
   running out of resources, the server is not required to hold
   unconfirmed records indefinitely.  One strategy the server might use
   is to set a limit on how many unconfirmed client records it will
   maintain, and then when the limit would be exceeded, remove the
   oldest record.  Another strategy might be to remove an unconfirmed
   record when some amount of time has elapsed.  The choice of the
   amount of time is fairly arbitrary but it is surely no higher than
   the server's lease time period.  Consider that leases need to be
   renewed before the lease time expires via an operation from the
   client.  If the client cannot issue a SETCLIENTID_CONFIRM after a
   SETCLIENTID before a period of time equal to that of a lease expires,
   then the client is unlikely to be able maintain state on the server



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   during steady state operation.

   If the client does send a SETCLIENTID_CONFIRM for an unconfirmed
   record that the server has already deleted, the client will get
   NFS4ERR_STALE_CLIENTID back.  If so, the client should then start
   over, and send SETCLIENTID to reestablish an unconfirmed client
   record and get back an unconfirmed clientid and setclientid_confirm
   verifier.  The client should then send the SETCLIENTID_CONFIRM to
   confirm the clientid.

   SETCLIENTID_CONFIRM does not establish or renew a lease.  However, if
   SETCLIENTID_CONFIRM removes relevant leased client state, and that
   state does not include existing delegations, the server MUST allow
   the client a period of time no less than the value of lease_time
   attribute, to reclaim, (via the CLAIM_DELEGATE_PREV claim type of the
   OPEN operation) its delegations before removing unreclaimed
   delegations.

22.34.6.  ERRORS

   NFS4ERR_BADXDR NFS4ERR_CLID_INUSE NFS4ERR_DELAY NFS4ERR_RESOURCE
   NFS4ERR_SERVERFAULT NFS4ERR_STALE_CLIENTID

22.35.  Operation 37: VERIFY - Verify Same Attributes

22.35.1.  SYNOPSIS

   (cfh), fattr -> -

22.35.2.  ARGUMENTS

   struct VERIFY4args {
           /* CURRENT_FH: object */
           fattr4          obj_attributes;
   };

22.35.3.  RESULTS

   struct VERIFY4res {
           nfsstat4        status;
   };

22.35.4.  DESCRIPTION

   The VERIFY operation is used to verify that attributes have a value
   assumed by the client before proceeding with following operations in
   the compound request.  If any of the attributes do not match then the
   error NFS4ERR_NOT_SAME must be returned.  The current filehandle



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   retains its value after successful completion of the operation.

22.35.5.  IMPLEMENTATION

   One possible use of the VERIFY operation is the following compound
   sequence.  With this the client is attempting to verify that the file
   being removed will match what the client expects to be removed.  This
   sequence can help prevent the unintended deletion of a file.

         PUTFH (directory filehandle)
         LOOKUP (file name)
         VERIFY (filehandle == fh)
         PUTFH (directory filehandle)
         REMOVE (file name)

   This sequence does not prevent a second client from removing and
   creating a new file in the middle of this sequence but it does help
   avoid the unintended result.

   In the case that a recommended attribute is specified in the VERIFY
   operation and the server does not support that attribute for the
   filesystem 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.

22.35.6.  ERRORS

   NFS4ERR_ACCESS NFS4ERR_ATTRNOTSUPP NFS4ERR_BADCHAR NFS4ERR_BADHANDLE
   NFS4ERR_BADXDR NFS4ERR_DELAY NFS4ERR_FHEXPIRED NFS4ERR_INVAL
   NFS4ERR_MOVED NFS4ERR_NOFILEHANDLE NFS4ERR_NOT_SAME NFS4ERR_RESOURCE
   NFS4ERR_SERVERFAULT NFS4ERR_STALE

22.36.  Operation 38: WRITE - Write to File

22.36.1.  SYNOPSIS

   (cfh), stateid, offset, stable, data -> count, committed, writeverf











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22.36.2.  ARGUMENTS

   enum stable_how4 {
           UNSTABLE4       = 0,
           DATA_SYNC4      = 1,
           FILE_SYNC4      = 2
   };

   struct WRITE4args {
           /* CURRENT_FH: file */
           stateid4        stateid;
           offset4         offset;
           stable_how4     stable;
           opaque          data<>;
   };

22.36.3.  RESULTS

   struct WRITE4resok {
           count4          count;
           stable_how4     committed;
           verifier4       writeverf;
   };

   union WRITE4res switch (nfsstat4 status) {
    case NFS4_OK:
            WRITE4resok    resok4;
    default:
            void;
   };

22.36.4.  DESCRIPTION

   The WRITE operation is used to write data to a regular file.  The
   target file is specified by the current filehandle.  The offset
   specifies the offset where the data should be written.  An offset of
   0 (zero) specifies that the write should start at the beginning of
   the file.  The count, as encoded as part of the opaque data
   parameter, represents the number of bytes of data that are to be
   written.  If the count is 0 (zero), the WRITE will succeed and return
   a count of 0 (zero) subject to permissions checking.  The server may
   choose to write fewer bytes than requested by the client.

   Part of the write request is a specification of how the write is to
   be performed.  The client specifies with the stable parameter the
   method of how the data is to be processed by the server.  If stable
   is FILE_SYNC4, the server must commit the data written plus all
   filesystem metadata to stable storage before returning results.  This



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   corresponds to the NFS version 2 protocol semantics.  Any other
   behavior constitutes a protocol violation.  If stable is DATA_SYNC4,
   then the server must commit all of the data to stable storage and
   enough of the metadata to retrieve the data before returning.  The
   server implementor is free to implement DATA_SYNC4 in the same
   fashion as FILE_SYNC4, but with a possible performance drop.  If
   stable is UNSTABLE4, the server is free to commit any part of the
   data and the metadata to stable storage, including all or none,
   before returning a reply to the client.  There is no guarantee
   whether or when any uncommitted data will subsequently be committed
   to stable storage.  The only guarantees made by the server are that
   it will not destroy any data without changing the value of verf and
   that it will not commit the data and metadata at a level less than
   that requested by the client.

   The stateid value for a WRITE 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.

   Upon successful completion, the following results are returned.  The
   count result is the number of bytes of data written to the file.  The
   server may write fewer bytes than requested.  If so, the actual
   number of bytes written starting at location, offset, is returned.

   The server also returns an indication of the level of commitment of
   the data and metadata via committed.  If the server committed all
   data and metadata to stable storage, committed should be set to
   FILE_SYNC4.  If the level of commitment was at least as strong as
   DATA_SYNC4, then committed should be set to DATA_SYNC4.  Otherwise,
   committed must be returned as UNSTABLE4.  If stable was FILE4_SYNC,
   then committed must also be FILE_SYNC4: anything else constitutes a
   protocol violation.  If stable was DATA_SYNC4, then committed may be
   FILE_SYNC4 or DATA_SYNC4: anything else constitutes a protocol
   violation.  If stable was UNSTABLE4, then committed may be either
   FILE_SYNC4, DATA_SYNC4, or UNSTABLE4.

   The final portion of the result is the write verifier.  The write
   verifier is a cookie that the client can use to determine whether the
   server has changed instance (boot) state between a call to WRITE and
   a subsequent call to either WRITE or COMMIT.  This cookie must be
   consistent during a single instance of the NFS version 4 protocol
   service and must be unique between instances of the NFS version 4
   protocol server, where uncommitted data may be lost.

   If a client writes data to the server with the stable argument set to
   UNSTABLE4 and the reply yields a committed response of DATA_SYNC4 or



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   UNSTABLE4, the client will follow up some time in the future with a
   COMMIT operation to synchronize outstanding asynchronous data and
   metadata with the server's stable storage, barring client error.  It
   is possible that due to client crash or other error that a subsequent
   COMMIT will not be received by the server.

   For a WRITE with a stateid value of all bits 0, the server MAY allow
   the WRITE to be serviced subject to mandatory file locks or the
   current share deny modes for the file.  For a WRITE with a stateid
   value of all bits 1, the server MUST NOT allow the WRITE operation to
   bypass locking checks at the server and are treated exactly the same
   as if a stateid of all bits 0 were used.

   On success, the current filehandle retains its value.

22.36.5.  IMPLEMENTATION

   It is possible for the server to write fewer bytes of data than
   requested by the client.  In this case, the server should not return
   an error unless no data was written at all.  If the server writes
   less than the number of bytes specified, the client should issue
   another WRITE to write the remaining data.

   It is assumed that the act of writing data to a file will cause the
   time_modified of the file to be updated.  However, the time_modified
   of the file should not be changed unless the contents of the file are
   changed.  Thus, a WRITE request with count set to 0 should not cause
   the time_modified of the file to be updated.

   The definition of stable storage has been historically a point of
   contention.  The following expected properties of stable storage may
   help in resolving design issues in the implementation.  Stable
   storage is persistent storage that survives:

   1.  Repeated power failures.

   2.  Hardware failures (of any board, power supply, etc.).

   3.  Repeated software crashes, including reboot cycle.

   This definition does not address failure of the stable storage module
   itself.

   The verifier is defined to allow a client to detect different
   instances of an NFS version 4 protocol server over which cached,
   uncommitted data may be lost.  In the most likely case, the verifier
   allows the client to detect server reboots.  This information is
   required so that the client can safely determine whether the server



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   could have lost cached data.  If the server fails unexpectedly and
   the client has uncommitted data from previous WRITE requests (done
   with the stable argument set to UNSTABLE4 and in which the result
   committed was returned as UNSTABLE4 as well) it may not have flushed
   cached data to stable storage.  The burden of recovery is on the
   client and the client will need to retransmit the data to the server.

   A suggested verifier would be to use the time that the server was
   booted or the time the server was last started (if restarting the
   server without a reboot results in lost buffers).

   The committed field in the results allows the client to do more
   effective caching.  If the server is committing all WRITE requests to
   stable storage, then it should return with committed set to
   FILE_SYNC4, regardless of the value of the stable field in the
   arguments.  A server that uses an NVRAM accelerator may choose to
   implement this policy.  The client can use this to increase the
   effectiveness of the cache by discarding cached data that has already
   been committed on the server.

   Some implementations may return NFS4ERR_NOSPC instead of
   NFS4ERR_DQUOT when a user's quota is exceeded.  In the case that the
   current filehandle is a directory, the server will return
   NFS4ERR_ISDIR.  If the current filehandle is not a regular file or a
   directory, the server will return NFS4ERR_INVAL.

   If mandatory file locking is on for the file, and corresponding
   record of the data to be written file is read or write locked by an
   owner that is not associated with the stateid, the server will return
   NFS4ERR_LOCKED.  If so, the client must check if the owner
   corresponding to the stateid used with the WRITE operation has a
   conflicting read lock that overlaps with the region that was to be
   written.  If the stateid's owner has no conflicting read lock, then
   the client should try to get the appropriate write record lock via
   the LOCK operation before re-attempting the WRITE.  When the WRITE
   completes, the client should release the record lock via LOCKU.

   If the stateid's owner had a conflicting read lock, then the client
   has no choice but to return an error to the application that
   attempted the WRITE.  The reason is that since the stateid's owner
   had a read lock, the server either attempted to temporarily
   effectively upgrade this read lock to a write lock, or the server has
   no upgrade capability.  If the server attempted to upgrade the read
   lock and failed, it is pointless for the client to re-attempt the
   upgrade via the LOCK operation, because there might be another client
   also trying to upgrade.  If two clients are blocked trying upgrade
   the same lock, the clients deadlock.  If the server has no upgrade
   capability, then it is pointless to try a LOCK operation to upgrade.



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22.36.6.  ERRORS

   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_RESOURCE
   NFS4ERR_ROFS NFS4ERR_SERVERFAULT NFS4ERR_STALE NFS4ERR_STALE_STATEID

22.37.  Operation 39: RELEASE_LOCKOWNER - Release Lockowner State

22.37.1.  SYNOPSIS

   lockowner -> ()

22.37.2.  ARGUMENTS

   struct RELEASE_LOCKOWNER4args {
           lock_owner4     lock_owner;
   };

22.37.3.  RESULTS

   struct RELEASE_LOCKOWNER4res {
           nfsstat4        status;
   };

22.37.4.  DESCRIPTION

   This operation is used to notify the server that the lock_owner is no
   longer in use by the client.  This allows the server to release
   cached state related to the specified lock_owner.  If file locks,
   associated with the lock_owner, are held at the server, the error
   NFS4ERR_LOCKS_HELD will be returned and no further action will be
   taken.

22.37.5.  IMPLEMENTATION

   The client may choose to use this operation to ease the amount of
   server state that is held.  Depending on behavior of applications at
   the client, it may be important for the client to use this operation
   since the server has certain obligations with respect to holding a
   reference to a lock_owner as long as the associated file is open.
   Therefore, if the client knows for certain that the lock_owner will
   no longer be used under the context of the associated open_owner4, it
   should use RELEASE_LOCKOWNER.




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22.37.6.  ERRORS

   NFS4ERR_ADMIN_REVOKED NFS4ERR_BADXDR NFS4ERR_EXPIRED
   NFS4ERR_LEASE_MOVED NFS4ERR_LOCKS_HELD NFS4ERR_RESOURCE
   NFS4ERR_SERVERFAULT NFS4ERR_STALE_CLIENTID

22.38.  Operation 10044: ILLEGAL - Illegal operation

22.38.1.  SYNOPSIS

   -> ()

22.38.2.  ARGUMENTS

   void;

22.38.3.  RESULTS

   struct ILLEGAL4res {
       nfsstat4        status;
   };

22.38.4.  DESCRIPTION

   This operation is a placeholder for encoding a result to handle the
   case of the client sending an operation code within COMPOUND that is
   not supported.  See the COMPOUND procedure description for more
   details.

   The status field of ILLEGAL4res MUST be set to NFS4ERR_OP_ILLEGAL.

22.38.5.  IMPLEMENTATION

   A client will probably not send an operation with code OP_ILLEGAL but
   if it does, the response will be ILLEGAL4res just as it would be with
   any other invalid operation code.  Note that if the server gets an
   illegal operation code that is not OP_ILLEGAL, and if the server
   checks for legal operation codes during the XDR decode phase, then
   the ILLEGAL4res would not be returned.

22.38.6.  ERRORS

   NFS4ERR_OP_ILLEGAL

22.39.  SECINFO_NO_NAME - Get Security on Unnamed Object

   Obtain available security mechanisms with the use of the parent of an
   object or the current filehandle.



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22.39.1.  SYNOPSIS

   (cfh), secinfo_style -> { secinfo }

22.39.2.  ARGUMENT

   enum secinfo_style_4 {
       current_fh = 0,
       parent = 1
   };

   typedef secinfo_style_4 SECINFO_NO_NAME4args;

22.39.3.  RESULT

   typedef SECINFO4res SECINFO_NO_NAME4res;

22.39.4.  DESCRIPTION

   Like the SECINFO operation, SECINFO_NO_NAME is used by the client to
   obtain a list of valid RPC authentication flavors for a specific file
   object.  Unlike SECINFO, SECINFO_NO_NAME only works with objects are
   accessed by file handle.

   There are two styles of SECINFO_NO_NAME, as determined by the value
   of the secinfo_style_4 enumeration.  If "current_fh" is passed, then
   SECINFO_NO_NAME is querying for the required security for the current
   filehandle.  If "parent" is passed, then SECINFO_NO_NAME is querying
   for the required security of the current filehandles's parent.  If
   the style selected is "parent", then SECINFO should apply the same
   access methodology used for LOOKUPP when evaluating the traversal to
   the parent directory.  Therefore, if the requester does not have the
   appropriate access to LOOKUPP the parent then SECINFO_NO_NAME must
   behave the same way and return NFS4ERR_ACCESS.

   Note that if PUTFH, PUTPUBFH, or PUTROOTFH return NFS4ERR_WRONGSEC,
   this is tantamount to the server asserting that the client will have
   to guess what the required security is, because there is no way to
   query.  Therefore, the client must iterate through the security
   triples available at the client and reattempt the PUTFH, PUTROOTFH or
   PUTPUBFH operation.  In the unfortunate event none of the MANDATORY
   security triples are supported by the client and server, the client
   SHOULD try using others that support integrity.  Failing that, the
   client can try using other forms (e.g.  AUTH_SYS and AUTH_NONE), but
   because such forms lack integrity checks, this puts the client at
   risk.

   The server implementor should pay particular attention to the section



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   "Clarification of Security Negotiation in NFSv4.1" for implementation
   suggestions for avoiding NFS4ERR_WRONGSEC error returns from PUTFH,
   PUTROOTFH or PUTPUBFH.

   Everything else about SECINFO_NO_NAME is the same as SECINFO.  See
   the previous discussion on SECINFO.

22.39.5.  IMPLEMENTATION

   See the previous dicussion on SECINFO.

22.39.6.  ERRORS

   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_RESOURCE NFS4ERR_SERVERFAULT NFS4ERR_STALE

22.40.  CREATECLIENTID - Instantiate Clientid

   Create a clientid

22.40.1.  SYNOPSIS

   client -> clientid

22.40.2.  ARGUMENT

   struct CREATECLIENTID4args {
       nfs_client_id4  clientdesc;
   };

22.40.3.  RESULT

   struct CREATECLIENTID4resok {
       clientid4       clientid;
       verifier4       clientid_confirm;
   };

   union SETCLIENTID4res switch (nfsstat4 status) {
       case NFS4_OK:
           CREATECLIENTID4resok      resok4;
       case NFS4ERR_CLID_INUSE:
           void;
       default:
           void;
   };




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22.40.4.  DESCRIPTION

   The client uses the CREATECLIENTID operation to register a particular
   client identifier with the server.  The clientid returned from this
   operation will be necessary for requests that create state on the
   server and will serve as a parent object to sessions created by the
   client.  In order to verify the clientid it must first be used as an
   argument to CREATESESSION.

22.40.5.  IMPLEMENTATION

   A server's client record is a 5-tuple:

   1.  clientdesc.id:

          The long form client identifier, sent via the client.id
          subfield of the CREATECLIENTID4args structure

   2.  clientdesc.verifier:

          A client-specific value used to indicate reboots, sent via the
          clientdesc.verifier subfield of the CREATECLIENTID4args
          structure

   3.  principal:

          The RPCSEC_GSS principal sent via the RPC headers

   4.  clientid:

          The shorthand client identifier, generated by the server and
          returned via the clientid field in the CREATECLIENTID4resok
          structure

   5.  confirmed:

          A private field on the server indicating whether or not a
          client record has been confirmed.  A client record is
          confirmed if there has been a successful CREATESESSION
          operation to confirm it.  Otherwise it is unconfirmed.  An
          unconfirmed record is established by a CREATECLIENTID call.
          Any unconfirmed record that is not confirmed within a lease
          period may be removed.

   The following identifiers represent special values for the fields in
   the records.





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   id_arg:

      The value of the clientdesc.id subfield of the CREATECLIENTID4args
      structure of the current request.

   verifier_arg:

      The value of the clientdesc.verifier subfield of the
      CREATECLIENTID4args structure of the current request.

   old_verifier_arg:

      A value of the clientdesc.verifier field of a client record
      received in a previous request; this is distinct from
      verifier_arg.

   principal_arg:

      The value of the RPCSEC_GSS principal for the current request.

   old_principal_arg:

      A value of the RPCSEC_GSS principal received for a previous
      request.  This is distinct from principal_arg.

   clientid_ret:

      The value of the clientid field the server will return in the
      CREATECLIENTID4resok structure for the current request.

   old_clientid_ret:

      The value of the clientid field the server returned in the
      CREATECLIENTID4resok structure for a previous request.  This is
      distinct from clientid_ret.

   Since CREATECLIENTID is a non-idempotent operation, we must consider
   the possibility that replays may occur as a result of a client
   reboot, network partition, malfunctioning router, etc.  Replays are
   identified by the value of the client field of CREATECLIENTID4args
   and the method for dealing with them is outlined in the scenarios
   below.

   The scenarios are described in terms of what client records whose
   clientdesc.id subfield have value equal to id_arg exist in the
   server's set of client records.  Any cases in which there is more
   than one record with identical values for id_arg represent a server
   implementation error.  Operation in the potential valid cases is



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   summarized as follows.

   1.  Common case

          If no client records with clientdesc.id matching id_arg exist,
          a new shorthand client identifier clientid_ret is generated,
          and the following unconfirmed record is added to the server's
          state.

          { id_arg, verifier_arg, principal_arg, clientid_ret, FALSE }

          Subsequently, the server returns clientid_ret.

   2.  Router Replay

          If the server has the following confirmed record, then this
          request is likely the result of a replayed request due to a
          faulty router or lost connection.

          { id_arg, verifier_arg, principal_arg, clientid_ret, TRUE }

          Since the record has been confirmed, the client must have
          received the server's reply from the initial CREATECLIENTID
          request.  Since this is simply a spurious request, there is no
          modification to the server's state, and the server makes no
          reply to the client.

   3.  Client Collision

          If the server has the following confirmed record, then this
          request is likely the result of a chance collision between the
          values of the clientdesc.id subfield of CREATECLIENTID4args
          for two different clients.

          { id_arg, *, old_principal_arg, clientid_ret, TRUE }

          Since the value of the clientdesc.id subfield of each client
          record must be unique, there is no modification of the
          server's state, and NFS4ERR_CLID_INUSE is returned to indicate
          the client should retry with a different value for the
          clientdesc.id subfield of CREATECLIENTID4args.

          This scenario may also represent a malicious attempt to
          destroy a client's state on the server.  For security reasons,
          the server MUST NOT remove the client's state when there is a
          principal mismatch.





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   4.  Replay

          If the server has the following unconfirmed record then this
          request is likely the result of a client replay due to a
          network partition or some other connection failure.

          { id_arg, verifier_arg, principal_arg, clientid_ret, FALSE }

          Since the response to the CREATECLIENTID request that created
          this record may have been lost, it is not acceptable to drop
          this duplicate request.  However, rather than processing it
          normally, the existing record is left unchanged and
          clientid_ret, which was generated for the previous request, is
          returned.

   5.  Change of Principal

          If the server has the following unconfirmed record then this
          request is likely the result of a client which has for
          whatever reasons changed principals (possibly to change
          security flavor) after calling CREATECLIENTID, but before
          calling CREATESESSION.

          { id_arg, verifier_arg, old_principal_arg, clientid_ret,
          FALSE}

          Since the client has not changed, the principal field of the
          unconfirmed record is updated to principal_arg and
          clientid_ret is again returned.  There is a small possibility
          that this is merely a collision on the client field of
          CREATECLIENTID4args between unrelated clients, but since that
          is unlikely, and an unconfirmed record does not generally have
          any filesystem pertinent state, we can assume it is the same
          client without risking loss of any important state.

          After processing, the following record will exist on the
          server.

          { id_arg, verifier_arg, principal_arg, clientid_ret, FALSE}

   6.  Client Reboot

          If the server has the following confirmed client record, then
          this request is likely from a previously confirmed client
          which has rebooted.

          { id_arg, old_verifier_arg, principal_arg, clientid_ret, TRUE
          }



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          Since the previous incarnation of the same client will no
          longer be making requests, lock and share reservations should
          be released immediately rather than forcing the new
          incarnation to wait for the lease time on the previous
          incarnation to expire.  Furthermore, session state should be
          removed since if the client had maintained that information
          across reboot, this request would not have been issued.  If
          the server does not support the CLAIM_DELEGATE_PREV claim
          type, associated delegations should be purged as well;
          otherwise, delegations are retained and recovery proceeds
          according to RFC3530.  The client record is updated with the
          new verifier and its status is changed to unconfirmed.

          After processing, clientid_ret is returned to the client and
          the following record will exist on the server.

          { id_arg, verifier_arg, principal_arg, clientid_ret, FALSE }

   7.  Reboot before confirmation

          If the server has the following unconfirmed record, then this
          request is likely from a client which rebooted before sending
          a CREATESESSION request.

          { id_arg, old_verifier_arg, *, clientid_ret, FALSE }

          Since this is believed to be a request from a new incarnation
          of the original client, the server updates the value of
          clientdesc.verifier and returns the original clientid_ret.
          After processing, the following state exists on the server.

          { id_arg, verifier_arg, *, clientid_ret, FALSE }

22.40.6.  ERROR

   NFS4ERR_BADXDR NFS4ERR_CLID_INUSE NFS4ERR_INVAL NFS4ERR_RESOURCE
   NFS4ERR_SERVERFAULT

22.41.  CREATESESSION - Create New Session and Confirm Clientid

   Start up session and confirm clientid.

22.41.1.  SYNOPSIS

   clientid, session_args -> sessionid, session_args






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22.41.2.  ARGUMENT

   struct CREATESESSION4args {
       clientid4       clientid;
       bool            persist;
       count4          maxrequestsize;
       count4          maxresponsesize;
       count4          maxrequests;
       count4          headerpadsize;
       switch (bool clientid_confirm) {
       case TRUE:
           verifier4 setclientid_confirm;
       case FALSE:
           void;
       }
       switch (channelmode4 mode) {
       case DEFAULT:
           void;
       case STREAM:
           streamchannelattrs4 streamchanattrs;
       case RDMA:
           rdmachannelattrs4   rdmachanattrs;
       };
   };



























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22.41.3.  RESULT

   typedef opaque sessionid4[16];

   struct CREATESESSION4resok {
       sessionid4      sessionid;
       bool            persist;
       count4          maxrequestsize;
       count4          maxresponsesize;
       count4          maxrequests;
       count4          headerpadsize;
       switch (channelmode4 mode) {
       case DEFAULT:
           void;
       case STREAM:
           streamchannelattrs4 streamchanattrs;
       case RDMA:
           rdmachannelattrs4   rdmachanattrs;
       };
   };

   union CREATESESSION4res switch (nfsstat4 status) {
   case NFS4_OK:
       CREATESESSION4resok     resok4;
   default:
       void;
   };

22.41.4.  DESCRIPTION

   This operation is used by the client to create new session objects on
   the server.  Additionally the first session created with a new
   shorthand client identifier serves to confirm the creation of that
   client's state on the server.  The server returns the parameter
   values for the new session.

22.41.5.  IMPLEMENTATION

   To describe the implementation, the same notation for client records
   introduced in the description of CREATECLIENTID is used with the
   following addition.

   clientid_arg: The value of the clientid field of the
   CREATESESSION4args structure of the current request.

   Since CREATESESSION is a non-idempotent operation, we must consider
   the possibility that replays may occur as a result of a client
   reboot, network partition, malfunctioning router, etc.  Replays are



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   identified by the value of the clientid and sessionid fields of
   CREATESESSION4args and the method for dealing with them is outlined
   in the scenarios below.

   The processing of this operation is divided into two phases: clientid
   confirmation and session creation.  In case the state for the
   provided clientid has not been verified, it is confirmed before the
   session is created.  Otherwise the clientid confirmation phase is
   skipped and only the session creation phase occurs.  Note that since
   only confirmed clients may create sessions, the clientid confirmation
   stage does not depend upon sessionid_arg.

   CLIENTID CONFIRMATION

   The operational cases are described in terms of what client records
   whose clientid field have value equal to clientid_arg exist in the
   server's set of client records.  Any cases in which there is more
   than one record with identical values for clientid represent a server
   implementation error.  Operation in the potential valid cases is
   summarized as follows.

   1.  Common Case

          If the server has the following unconfirmed record, then this
          is the expected confirmation of an unconfirmed record.

          { *, *, principal_arg, clientid_arg, FALSE }

          The confirmed field of the record is set to TRUE and
          processing of the operation continues normally.

   2.  Stale Clientid

          If the server contains no records with clientid equal to
          clientid_arg, then most likely the client's state has been
          purged during a period of inactivity, possibly due to a loss
          of connectivity.  NFS4ERR_STALE_CLIENTID is returned, and no
          changes are made to any client records on the server.

   3.  Principal Change or Collision

          If the server has the following record, then the client has
          changed principals after the previous CREATECLIENTID request,
          or there has been a chance collision between shortand client
          identifiers.

          { *, *, old_principal_arg, clientid_arg, * }




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          Neither of these cases are permissible.  Processing stops and
          NFS4ERR_CLID_INUSE is returned to the client.  No changes are
          made to any client records on the server.

   SESSION CREATION

   To determine whether this request is a replay, the server examines
   the sessionid argument provided by the client.  If the sessionid
   matches the identifier of a previously created session, then this
   request must be interpreted as a replay.  No new state is created and
   a reply with the parameters of the existing session is returned to
   the client.  If a session corresponding to the sessionid does not
   already exist, then the request is not a replay and is processed as
   follows.

   NOTE: It is the responsibility of the client to generate appropriate
   values for sessionid.  Since the ordering of messages sent on
   different transport connections is not guaranteed, immediately
   reusing the sessionid of a previously destroyed session may yield
   unpredictable results.  Client implementations should avoid recently
   used sessionids to ensure correct behavior.

   The server examines the persist, maxrequestsize, maxresponsesize,
   maxrequests and headerpadsize arguments.  For each argument, if the
   value is acceptable to the server, it is recommended that the server
   use the provided value to create the new session.  If it is not
   acceptable, the server may use a different value, but must return the
   value used to the client.  These parameters have the following
   interpretation.

   persist:

      True if the client desires server support for "reliable"
      semantics.  For sessions in which only idempotent operations will
      be used (e.g. a read-only session), clients should set this value
      to false.  If the server does not or cannot provide "reliable"
      semantics this value must be set to false on return.

   maxrequestsize:

      The maximum size of a COMPOUND request that will be sent by the
      client including RPC headers.

   maxresponsesize:







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      The maximum size of a COMPOUND reply that the client will accept
      from the server including RPC headers.  The server must not
      increase the value of this parameter.  If a client sends a
      COMPOUND request for which the size of the reply would exceed this
      value, the server will return NFS4ERR_RESOURCE.

   maxrequests:

      The maximum number of concurrent COMPOUND requests that the client
      will issue on the session.  Subsequent COMPOUND requests will each
      be assigned a slot identifier by the client on the range 0 to
      maxrequests - 1 inclusive.  A slot id cannot be reused until the
      previous request on that slot has completed.

   headerpadsize:

      The maximum amount of padding the client is willing to apply to
      ensure that write payloads are aligned on some boundary at the
      server.  The server should reply with its preferred value, or zero
      if padding is not in use.  The server may decrease this value but
      must not increase it.

   The server creates the session by recording the parameter values used
   and if the persist parameter is true and has been accepted by the
   server, allocating space for the duplicate request cache (DRC).

   If the session state is created successfully, the server associates
   it with the session identifier provided by the client.  This
   identifier must be unique among the client's active sessions but
   there is no need for it to be globally unique.  Finally, the server
   returns the negotiated values used to create the session to the
   client.

22.41.6.  ERRORS

   NFS4ERR_BADXDR NFS4ERR_CLID_INUSE NFS4ERR_RESOURCE
   NFS4ERR_SERVERFAULT NFS4ERR_STALE_CLIENTID

22.42.  BIND_BACKCHANNEL - Create a callback channel binding

   Establish a callback channel on the connection.

22.42.1.  SYNOPSIS








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22.42.2.  ARGUMENT

   struct BIND_BACKCHANNEL4args {
       clientid4 clientid;
       uint32_t  callback_program;
       uint32_t  callback_ident;
       count4         maxrequestsize;
       count4         maxresponsesize;
       count4         maxrequests;
       switch (channelmode4 mode) {
       case DEFAULT:
           void;
       case STREAM:
           streamchannelattrs4 streamchanattrs;
       case RDMA:
           rdmachannelattrs4   rdmachanattrs;
       };
   };

22.42.3.  RESULT

   struct BIND_BACKCHANNEL4resok {
       count4         maxrequestsize;
       count4         maxresponsesize;
       count4         maxrequests;
       switch (channelmode4 mode) {
       case DEFAULT:
           void;
       case STREAM:
           streamchannelattrs4 streamchanattrs;
       case RDMA:
           rdmachannelattrs4   rdmachanattrs;
       };
   };


   union BIND_BACKCHANNEL4res switch (nfsstat4 status) {
       case NFS4_OK:
           BIND_BACKCHANNEL4resok   resok4;
       default:
           void;
   };

22.42.4.  DESCRIPTION

   The BIND_BACKCHANNEL operation serves to establish the current
   connection as a designated callback channel for the specified
   session.  Normally, only one callback channel is bound, however if



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   more than one are established, they are used at the server's
   prerogative, no affinity or preference is specified by the client.

   The arguments and results of the BIND_BACKCHANNEL call are a subset
   of the session parameters, and used identically to those values on
   the callback channel only.  However, not all session operation
   channel parameters are relevant to the callback channel, for example
   header padding (since writes of bulk data are not performed in
   callbacks).

22.42.5.  IMPLEMENTATION

   No discussion at this time.

22.42.6.  ERRORS

   TBD

22.43.  DESTROYSESSION - Destroy existing session

   Destroy existing session.

22.43.1.  SYNOPSIS

   void -> status

22.43.2.  ARGUMENT

   struct DESTROYSESSION4args {
       sessionid4     sessionid;
   };

22.43.3.  RESULT

   struct SESSION_DESTROYres {
       nfsstat status;
   };

22.43.4.  DESCRIPTION

   The SESSION_DESTROY operation closes the session and discards any
   active state such as locks, leases, and server duplicate request
   cache entries.  Any remaining connections bound to the session are
   immediately unbound and may additionally be closed by the server.

   This operation must be the final, or only operation in any request.
   Because the operation results in destruction of the session, any
   duplicate request caching for this request, as well as previously



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   completed requests, will be lost.  For this reason, it is advisable
   to not place this operation in a request with other state-modifying
   operations.  In addition, a SEQUENCE operation is not required in the
   request.

   Note that because the operation will never be replayed by the server,
   a client that retransmits the request may receive an error in
   response, even though the session may have been successfully
   destroyed.

22.43.5.  IMPLEMENTATION

   No discussion at this time.

22.43.6.  ERRORS

   TBD

22.44.  SEQUENCE - Supply per-procedure sequencing and control

   Supply per-procedure sequencing and control

22.44.1.  SYNOPSIS

   control -> control

22.44.2.  ARGUMENT

   typedef uint32_t sequenceid4;
   typedef uint32_t slotid4;

   struct SEQUENCE4args {
       sessionid4     sessionid;
       sequenceid4    sequenceid;
       slotid4        slotid;
       slotid4        maxslot;
   };














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22.44.3.  RESULT

   struct SEQUENCE4resok {
       sessionid4     sessionid;
       sequenceid4    sequenceid;
       slotid4        slotid;
       slotid4        maxslot;
       slotid4        target_maxslot;
   };

   union SEQUENCE4res switch (nfsstat4 status) {
       case NFS4_OK:
           SEQUENCE4resok resok4;
       default:
           void;
   };

22.44.4.  DESCRIPTION

   The SEQUENCE operation is used to manage operational accounting for
   the session on which the operation is sent.  The contents include the
   client and session to which this request belongs, slotid and
   sequenceid, used by the server to implement session request control
   and the duplicate reply cache semantics, and exchanged slot counts
   which are used to adjust these values.  This operation must appear
   once as the first operation in each COMPOUND sent after the channel
   is successfully bound, or a protocol error must result.

22.44.5.  IMPLEMENTATION

   No discussion at this time.

22.44.6.  ERRORS

   NFS4ERR_BADSESSION NFS4ERR_BADSLOT

22.45.  GET_DIR_DELEGATION - Get a directory delegation

   Obtain a directory delegation.

22.45.1.  SYNOPSIS

   (cfh), requested notification ->
           (cfh), cookieverf, stateid, supported notification







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22.45.2.  ARGUMENT

   /*
   * Notification types.
   */
   const DIR_NOTIFICATION_NONE                    = 0x00000000;
   const DIR_NOTIFICATION_CHANGE_CHILD_ATTRIBUTES = 0x00000001;
   const DIR_NOTIFICATION_CHANGE_DIR_ATTRIBUTES   = 0x00000002;
   const DIR_NOTIFICATION_REMOVE_ENTRY            = 0x00000004;
   const DIR_NOTIFICATION_ADD_ENTRY               = 0x00000008;
   const DIR_NOTIFICATION_RENAME_ENTRY            = 0x00000010;
   const DIR_NOTIFICATION_CHANGE_COOKIE_VERIFIER  = 0x00000020;

   typedef uint32_t dir_notification_type4;

   typedef nfstime4 attr_notice4;

   struct GET_DIR_DELEGATION4args {
       bool                        gdda_signal_deleg_avail;
       dir_notification_type4      notification_type;
       attr_notice4                child_attr_delay;
       attr_notice4                dir_attr_delay;
   };

22.45.3.  RESULT

   struct GET_DIR_DELEGATION4resok {
       verifier4                       cookieverf;
       /* Stateid for get_dir_delegation */
       stateid4                        stateid;
       /* Which notifications can the server support */
       dir_notification_type4          notification;
       bitmap4                         child_attributes;
       bitmap4                         dir_attributes;
   };

   union GET_DIR_DELEGATION4res switch (nfsstat4 status) {
       case NFS4_OK:
           /* CURRENT_FH: delegated dir */
           GET_DIR_DELEGATION4resok      resok4;
       case NFS4ERR_DIRDELEG_UNAVAIL:
           bool    gddr_will_signal_deleg_avail;
       default:
           void;
   };






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22.45.4.  DESCRIPTION

   The GET_DIR_DELEGATION operation is used by a client to request a
   directory delegation.  The directory is represented by the current
   filehandle.  The client also specifies whether it wants the server to
   notify it when the directory changes in certain ways by setting one
   or more bits in a bitmap.  The server may also choose not to grant
   the delegation.  In that case the server will return
   NFS4ERR_DIRDELEG_UNAVAIL.  If the server decides to hand out the
   delegation, it will return a cookie verifier for that directory.  If
   the cookie verifier changes when the client is holding the
   delegation, the delegation will be recalled unless the client has
   asked for notification for this event.  In that case a notification
   will be sent to the client.

   The server will also return a directory delegation stateid in
   addition to the cookie verifier as a result of the GET_DIR_DELEGATION
   operation.  This stateid will appear in callback messages related to
   the delegation, such as notifications and delegation recalls.  The
   client will use this stateid to return the delegation voluntarily or
   upon recall.  A delegation is returned by calling the DELEGRETURN
   operation.

   The server may not be able to support notifications of certain
   events.  If the client asks for such notifications, the server must
   inform the client of its inability to do so as part of the
   GET_DIR_DELEGATION reply by not setting the appropriate bits in the
   supported notifications bitmask contained in the reply.

   The GET_DIR_DELEGATION operation can be used for both normal and
   named attribute directories.  It covers all the entries in the
   directory except the ".." entry.  That means if a directory and its
   parent both hold directory delegations, any changes to the parent
   will not cause a notification to be sent for the child even though
   the child's ".." entry points to the parent.

   If client sets gdda_signal_deleg_avail to TRUE, then it is
   registering with the client a "want" for a directory delegation.  If
   the server supports and will honor the "want", the results will have
   gddr_will_signal_deleg_avail set to TRUE.  If so the client should
   expect a CB_RECALLABLE_OBJ_AVAIL operation to indicate that a
   directory delegation is available.

22.45.5.  IMPLEMENTATION

   Directory delegation provides the benefit of improving cache
   consistency of namespace information.  This is done through
   synchronous callbacks.  A server must support synchronous callbacks



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   in order to support directory delegations.  In addition to that,
   asynchronous notifications provide a way to reduce network traffic as
   well as improve client performance in certain conditions.
   Notifications would not be requested when the goal is just cache
   consitency.

   Notifications are specified in terms of potential changes to the
   directory.  A client can ask to be notified whenever an entry is
   added to a directory by setting notification_type to
   DIR_NOTIFICATION_ADD_ENTRY.  It can also ask for notifications on
   entry removal, renames, directory attribute changes and cookie
   verifier changes by setting notification_type flag appropriately.  In
   addition to that, the client can also ask for notifications upon
   attribute changes to children in the directory to keep its attribute
   cache up to date.  However any changes made to child attributes do
   not cause the delegation to be recalled.  If a client is interested
   in directory entry caching, or negative name caching, it can set the
   notification_type appropriately and the server will notify it of all
   changes that would otherwise invalidate its name cache.  The kind of
   notification a client asks for may depend on the directory size, its
   rate of change and the applications being used to access that
   directory.  However, the conditions under which a client might ask
   for a notification, is out of the scope of this specification.

   The client will set one or more bits in a bitmap (notification_type)
   to let the server know what kind of notification(s) it is interested
   in.  For attribute notifications it will set bits in another bitmap
   to indicate which attributes it wants to be notified of.  If the
   server does not support notifications for changes to a certain
   attribute, it should not set that attribute in the supported
   attribute bitmap (notification) specified in the reply.

   In addition to that, the client will also let the server know if it
   wants to get the notification as soon as the attribute change occurs
   or after a certain delay by setting a delay factor, child_attr_delay
   for attribute changes to children and dir_attr_delay for attribute
   changes to the directory.  If this delay factor is set to zero, that
   indicates to the server that the client wants to be notified of any
   attribute changes as soon as they occur.  If the delay factor is set
   to N, the server will make a best effort guarantee that attribute
   updates are not out of sync by more than that.  One value covers all
   attribute changes for the directory and another value covers all
   attribute changes for all children in the directory.  If the client
   asks for a delay factor that the server does not support or that may
   cause significant resource consumption on the server by causing the
   server to send a lot of notifications, the server should not commit
   to sending out notifications for that attribute and therefore must
   not set the approprite bit in the child_attributes and dir_attributes



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   bitmaps in the response.

   The server will let the client know about which notifications it can
   support by setting appropriate bits in a bitmap.  If it agrees to
   send attribute notifications, it will also set two attribute masks
   indicating which attributes it will send change notifications for.
   One of the masks covers changes in directory attributes and the other
   covers atttribute changes to any files in the directory.

   The client should use a security flavor that the filesystem is
   exported with.  If it uses a different flavor, the server should
   return NFS4ERR_WRONGSEC.

22.45.6.  ERRORS

   NFS4ERR_ACCESS NFS4ERR_BADHANDLE NFS4ERR_BADXDR NFS4ERR_FHEXPIRED
   NFS4ERR_INVAL NFS4ERR_MOVED NFS4ERR_NOFILEHANDLE NFS4ERR_NOTDIR
   NFS4ERR_RESOURCE NFS4ERR_SERVERFAULT NFS4ERR_STALE
   NFS4ERR_DIRDELEG_UNAVAIL NFS4ERR_WRONGSEC NFS4ERR_EIO NFS4ERR_NOTSUPP

22.46.  LAYOUTGET - Get Layout Information

22.46.1.  SYNOPSIS

   (cfh), signal_avail, layout_type, iomode, offset,
          length, minlength, maxcount -> layout example synopsis

22.46.2.  ARGUMENT

   struct LAYOUTGET4args {
       /* CURRENT_FH: file */
       bool                    loga_signal_layout_avail;

       pnfs_layouttype4        l