NFSv4                                                         S. Shepler
Internet-Draft                                                 M. Eisler
Intended status: Standards Track                               D. Noveck
Expires: February 26, 2, 2007                                        Editors
                                                             August 25, 2006

                         NFSv4 Minor Version 1
                 draft-ietf-nfsv4-minorversion1-06.txt
                 draft-ietf-nfsv4-minorversion1-07.txt

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Copyright Notice

   Copyright (C) The Internet Society (2006).

Abstract

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

Requirements Language

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

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .  10   9
     1.1.   The NFSv4.1 Protocol . . . . . . . . . . . . . . . . . .  10   9
     1.2.   NFS Version 4 Goals  . . . . . . . . . . . . . . . . . .  10   9
     1.3.   Minor Version 1 Goals  . . . . . . . . . . . . . . . . .  11  10
     1.4.   Inconsistencies of this Document with Section XX . . . .  11  10
     1.5.   Overview of NFS version 4.1 Features . . . . . . . . . .  11  10
       1.5.1.  RPC and Security  . . . . . . . . . . . . . . . . . .  12  11
       1.5.2.  Protocol Structure  . . . . . . . . . . . . . . . . .  12  11
       1.5.3.  File System Model . . . . . . . . . . . . . . . . . .  14  12
       1.5.4.  Locking Facilities  . . . . . . . . . . . . . . . . .  15  13
     1.6.   General Definitions  . . . . . . . . . . . . . . . . . .  16  14
     1.7.   Differences from NFSv4.0 . . . . . . . . . . . . . . . .  18  16
   2.  Core Infrastructure . . . . . . . . . . . . . . . . . . . . .  18  16
     2.1.   Introduction . . . . . . . . . . . . . . . . . . . . . .  18  16
     2.2.   RPC and XDR  . . . . . . . . . . . . . . . . . . . . . .  18  16
       2.2.1.  RPC-based Security  . . . . . . . . . . . . . . . . .  18  16
     2.3.   Non-RPC-based Security Services   COMPOUND and CB_COMPOUND . . . . . . . . . . . .  19
       2.3.1.  Authorization . . . .  20
     2.4.   Client Identifiers . . . . . . . . . . . . . . . .  19
       2.3.2.  Auditing . . .  20
       2.4.1.  Server Release of Clientid  . . . . . . . . . . . . .  24
     2.5.   Security Service Negotiation . . . . . .  19
       2.3.3.  Intrusion Detection . . . . . . . .  25
       2.5.1.  NFSv4 Security Tuples . . . . . . . . .  19
     2.4.   Transport Layers . . . . . . .  25
       2.5.2.  SECINFO and SECINFO_NO_NAME . . . . . . . . . . . . .  19
       2.4.1.  Ports  25
       2.5.3.  Security Error  . . . . . . . . . . . . . . . . . . .  26
     2.6.   Minor Versioning . . . . . .  19
       2.4.2.  Stream Transports . . . . . . . . . . . . . .  28
     2.7.   Non-RPC-based Security Services  . . . .  19
       2.4.3.  RDMA Transports . . . . . . . .  31
       2.7.1.  Authorization . . . . . . . . . . .  19
     2.5.   Session . . . . . . . . .  31
       2.7.2.  Auditing  . . . . . . . . . . . . . . .  19
       2.5.1.  Motivation and Overview . . . . . . .  31
       2.7.3.  Intrusion Detection . . . . . . . .  19
       2.5.2.  NFSv4 Integration . . . . . . . . .  31
     2.8.   Transport Layers . . . . . . . . .  19
       2.5.3.  Channels . . . . . . . . . . .  32
       2.8.1.  Required and Recommended Properties of Transports . .  32
       2.8.2.  Client and Server Transport Behavior  . . . . . . . .  32
       2.8.3.  Ports .  19
       2.5.4.  Exactly Once Semantics . . . . . . . . . . . . . . .  20
     2.6.   Channel Management . . . . . . . .  34
     2.9.   Session  . . . . . . . . . . .  20
       2.6.1.  Buffer Management . . . . . . . . . . . . .  34
       2.9.1.  Motivation and Overview . . . . .  20
       2.6.2.  Data Transfer . . . . . . . . . .  34
       2.9.2.  NFSv4 Integration . . . . . . . . . .  20
       2.6.3.  Flow Control . . . . . . . .  35
       2.9.3.  Channels  . . . . . . . . . . . .  20
       2.6.4.  COMPOUND Sizing Issues . . . . . . . . . .  36
       2.9.4.  Exactly Once Semantics  . . . . .  20
       2.6.5.  Data Alignment . . . . . . . . . .  38
       2.9.5.  RDMA Considerations . . . . . . . . .  20
     2.7.   Sessions Security . . . . . . . .  46
       2.9.6.  Sessions Security . . . . . . . . . . .  20
       2.7.1.  Denial of Service via Unauthorized State Changes . .  20
     2.8. . . . . .  48
       2.9.7.  Session Mechanics - Steady State  . . . . . . . . . . . .  20
       2.8.1.  Obligations of the Server .  53
       2.9.8.  Session Mechanics - Recovery  . . . . . . . . . . . .  54
   3.  Protocol Data Types .  20
       2.8.2.  Obligations of the Client . . . . . . . . . . . . . .  20
       2.8.3.  Steps the Client Takes To Establish a Session . . . .  20
       2.8.4.  Session Mechanics - Recovery . .  57
     3.1.   Basic Data Types . . . . . . . . . .  20
   3.  RPC and Security Flavor . . . . . . . . . .  57
     3.2.   Structured Data Types  . . . . . . . . .  21
     3.1.   Ports and Transports . . . . . . . .  59
   4.  Filehandles . . . . . . . . . .  21
       3.1.1.  Client Retransmission Behavior . . . . . . . . . . .  22
     3.2.   Security Flavors . . . .  68
     4.1.   Obtaining the First Filehandle . . . . . . . . . . . . .  69
       4.1.1.  Root Filehandle . . .  23
       3.2.1.  Security mechanisms for NFS version 4 . . . . . . . .  23
     3.3.   Security Negotiation . . . . . . . .  69
       4.1.2.  Public Filehandle . . . . . . . . . .  24
       3.3.1.  SECINFO and SECINFO_NO_NAME . . . . . . . .  69
     4.2.   Filehandle Types . . . . .  25
       3.3.2.  Security Error . . . . . . . . . . . . . . .  70
       4.2.1.  General Properties of a Filehandle  . . . .  25
       3.3.3.  Callback RPC Authentication . . . . .  70
       4.2.2.  Persistent Filehandle . . . . . . . .  25
       3.3.4.  GSS Server Principal . . . . . . . .  71
       4.2.3.  Volatile Filehandle . . . . . . . .  26
   4.  Security Negotiation . . . . . . . . .  71
     4.3.   One Method of Constructing a Volatile Filehandle . . . .  72
     4.4.   Client Recovery from Filehandle Expiration . . . . . . .  26  73
   5.  Clarification of Security Negotiation in NFSv4.1  . .  File Attributes . . . .  27
     5.1.   PUTFH + LOOKUP . . . . . . . . . . . . . . . . . . .  74
     5.1.   Mandatory Attributes . .  27
     5.2.   PUTFH + LOOKUPP . . . . . . . . . . . . . . . .  75
     5.2.   Recommended Attributes . . . .  27
     5.3.   PUTFH + SECINFO . . . . . . . . . . . . .  75
     5.3.   Named Attributes . . . . . . .  27
     5.4.   PUTFH + Anything Else . . . . . . . . . . . . .  76
     5.4.   Classification of Attributes . . . .  28
   6.  NFSv4.1 Sessions . . . . . . . . . .  76
     5.5.   Mandatory Attributes - Definitions . . . . . . . . . . .  77
     5.6.   Recommended Attributes - Definitions .  28
     6.1.   Sessions Background . . . . . . . . .  79
     5.7.   Time Access  . . . . . . . . .  28
       6.1.1.  Introduction to Sessions . . . . . . . . . . . . .  87
     5.8.   Interpreting owner and owner_group .  28
       6.1.2.  Session Model . . . . . . . . . .  87
     5.9.   Character Case Attributes  . . . . . . . . . .  29
       6.1.3.  Connection State . . . . .  89
     5.10.  Quota Attributes . . . . . . . . . . . . .  30
       6.1.4.  NFSv4 Channels, Sessions and Connections . . . . . .  31
       6.1.5.  Reconnection, Trunking and Failover .  89
     5.11.  mounted_on_fileid  . . . . . . . .  33
       6.1.6.  Server Duplicate Request Cache . . . . . . . . . . .  33
     6.2.   Session Initialization  90
     5.12.  send_impl_id and Transfer Models recv_impl_id  . . . . . . .  35
       6.2.1.  Session Negotiation . . . . . .  91
     5.13.  fs_layout_type . . . . . . . . . . .  35
       6.2.2.  RDMA Requirements . . . . . . . . . .  92
     5.14.  layout_type  . . . . . . . .  36
       6.2.3.  RDMA Connection Resources . . . . . . . . . . . . . .  37
       6.2.4.  TCP and RDMA Inline Transfer Model  92
     5.15.  layout_hint  . . . . . . . . .  37
       6.2.5.  RDMA Direct Transfer Model . . . . . . . . . . . . .  40
     6.3.   Connection Models  92
     5.16.  mdsthreshold . . . . . . . . . . . . . . . . . . .  43
       6.3.1.  TCP Connection Model . . .  92
   6.  Access Control Lists  . . . . . . . . . . . . .  44
       6.3.2.  Negotiated RDMA Connection Model . . . . . . .  93
     6.1.   Goals  . . .  45
       6.3.3.  Automatic RDMA Connection Model . . . . . . . . . . .  46
     6.4.   Buffer Management, Transfer, Flow Control . . . . . . .  46
     6.5.   Retry and Replay . . . .  93
     6.2.   File Attributes Discussion . . . . . . . . . . . . . . .  94
       6.2.1.  ACL Attribute .  49
     6.6.   The Back Channel . . . . . . . . . . . . . . . . . . .  94
       6.2.2.  mode Attribute  .  50
     6.7.   COMPOUND Sizing Issues . . . . . . . . . . . . . . . . .  51
     6.8.   Data Alignment . 105
     6.3.   Common Methods . . . . . . . . . . . . . . . . . . . .  51
     6.9.   NFSv4 Integration . 106
       6.3.1.  Interpreting an ACL . . . . . . . . . . . . . . . . . 106
       6.3.2.  Computing a Mode Attribute from an ACL  .  53
       6.9.1.  Minor Versioning . . . . . . 107
     6.4.   Requirements . . . . . . . . . . . .  53
       6.9.2.  Slot Identifiers and Server Duplicate Request Cache .  53
       6.9.3.  Resolving server callback races with sessions . . . .  56
       6.9.4.  COMPOUND and CB_COMPOUND . . . . . 109
       6.4.1.  Setting the mode and/or ACL Attributes  . . . . . . . 109
       6.4.2.  Retrieving the mode and/or ACL Attributes . .  57
     6.10.  Sessions Security Considerations . . . . 110
       6.4.3.  Creating New Objects  . . . . . . . .  59
       6.10.1. Denial of Service via Unauthorized State Changes . .  59
     6.11.  Session Mechanics - Steady State . . . . . . 111
   7.  Single-server Name Space  . . . . . .  63
       6.11.1. Obligations of the Server . . . . . . . . . . . . 112
     7.1.   Server Exports . .  63
       6.11.2. Obligations of the Client . . . . . . . . . . . . . .  63
       6.11.3. Steps the Client Takes To Establish a Session . . . .  64
     6.12.  Session Mechanics - Recovery . 112
     7.2.   Browsing Exports . . . . . . . . . . . . .  64
       6.12.1. Events Requiring Client Action . . . . . . . 113
     7.3.   Server Pseudo File System  . . . .  64
       6.12.2. Events Requiring Server Action . . . . . . . . . . .  66
   7.  Minor Versioning 113
     7.4.   Multiple Roots . . . . . . . . . . . . . . . . . . . . . 114
     7.5.   Filehandle Volatility  .  66
   8.  Protocol Data Types . . . . . . . . . . . . . . . . 114
     7.6.   Exported Root  . . . . .  69
     8.1.   Basic Data Types . . . . . . . . . . . . . . . . 114
     7.7.   Mount Point Crossing . . . .  69
     8.2.   Structured Data Types . . . . . . . . . . . . . . 115
     7.8.   Security Policy and Name Space Presentation  . . .  70
   9.  Filehandles . . . 115
   8.  File Locking and Share Reservations . . . . . . . . . . . . . 116
     8.1.   Locking  . . . . . . . . .  80
     9.1.   Obtaining the First Filehandle . . . . . . . . . . . . .  80
       9.1.1.  Root Filehandle . . 116
       8.1.1.  Client and Session ID . . . . . . . . . . . . . . . . 117
       8.1.2.  State-owner and Stateid Definition  .  80
       9.1.2.  Public Filehandle . . . . . . . . 117
       8.1.3.  Use of the Stateid and Locking  . . . . . . . . . .  80
     9.2.   Filehandle Types . 120
     8.2.   Lock Ranges  . . . . . . . . . . . . . . . . . . .  81
       9.2.1.  General Properties of a Filehandle . . . 122
     8.3.   Upgrading and Downgrading Locks  . . . . . .  81
       9.2.2.  Persistent Filehandle . . . . . . 122
     8.4.   Blocking Locks . . . . . . . . . .  82
       9.2.3.  Volatile Filehandle . . . . . . . . . . . 123
     8.5.   Lease Renewal  . . . . . .  82
     9.3.   One Method of Constructing a Volatile Filehandle . . . .  84
     9.4.   Client Recovery from Filehandle Expiration . . . . . . .  84
   10. File Attributes . . . . 124
     8.6.   Crash Recovery . . . . . . . . . . . . . . . . . . . .  85
     10.1.  Mandatory Attributes . 124
       8.6.1.  Client Failure and Recovery . . . . . . . . . . . . . 124
       8.6.2.  Server Failure and Recovery . . . .  86
     10.2.  Recommended Attributes . . . . . . . . . 125
       8.6.3.  Network Partitions and Recovery . . . . . . . .  86
     10.3.  Named Attributes . . . 127
     8.7.   Server Revocation of Locks . . . . . . . . . . . . . . . 131
     8.8.   Share Reservations . .  87
     10.4.  Classification of Attributes . . . . . . . . . . . . . .  87
     10.5.  Mandatory Attributes - Definitions . . . 132
     8.9.   OPEN/CLOSE Operations  . . . . . . . .  89
     10.6.  Recommended Attributes - Definitions . . . . . . . . . 133
     8.10.  Open Upgrade and Downgrade .  90
     10.7.  Time Access . . . . . . . . . . . . . . 134
     8.11.  Short and Long Leases  . . . . . . . .  99
     10.8.  Interpreting owner and owner_group . . . . . . . . . 134
     8.12.  Clocks, Propagation Delay, and Calculating Lease
            Expiration . .  99
     10.9.  Character Case Attributes . . . . . . . . . . . . . . . 101
     10.10. Quota Attributes . . . . . . 135
     8.13.  Vestigial Locking Infrastructure From V4.0 . . . . . . . 135
   9.  Client-Side Caching . . . . . . . 101
     10.11. mounted_on_fileid . . . . . . . . . . . . . . 136
     9.1.   Performance Challenges for Client-Side Caching . . . . . 102
     10.12. send_impl_id 137
     9.2.   Delegation and recv_impl_id  . Callbacks . . . . . . . . . . . . 103
     10.13. fs_layout_type . . . . 138
       9.2.1.  Delegation Recovery . . . . . . . . . . . . . . . . . 104
     10.14. layout_type 139
     9.3.   Data Caching . . . . . . . . . . . . . . . . . . . . . . 104
     10.15. layout_hint 141
       9.3.1.  Data Caching and OPENs  . . . . . . . . . . . . . . . 141
       9.3.2.  Data Caching and File Locking . . . . . . . 104
     10.16. mdsthreshold . . . . . 142
       9.3.3.  Data Caching and Mandatory File Locking . . . . . . . 144
       9.3.4.  Data Caching and File Identity  . . . . . . . . . . 104
   11. Access Control Lists . 144
     9.4.   Open Delegation  . . . . . . . . . . . . . . . . . . . 105
     11.1.  Goals . 145
       9.4.1.  Open Delegation and Data Caching  . . . . . . . . . . 148
       9.4.2.  Open Delegation and File Locks  . . . . . . . . . . . 149
       9.4.3.  Handling of CB_GETATTR  . . . 105
     11.2.  File Attributes Discussion . . . . . . . . . . . . 149
       9.4.4.  Recall of Open Delegation . . . 106
       11.2.1. ACL Attribute . . . . . . . . . . . 152
       9.4.5.  Clients that Fail to Honor Delegation Recalls . . . . 154
       9.4.6.  Delegation Revocation . . . . . 106
       11.2.2. mode Attribute . . . . . . . . . . . 155
     9.5.   Data Caching and Revocation  . . . . . . . . 117
     11.3.  Common Methods . . . . . . 155
       9.5.1.  Revocation Recovery for Write Open Delegation . . . . 156
     9.6.   Attribute Caching  . . . . . . . . . . . 118
       11.3.1. Interpreting an ACL . . . . . . . . 157
     9.7.   Data and Metadata Caching and Memory Mapped Files  . . . 159
     9.8.   Name Caching . . . . . . 118
       11.3.2. Computing a Mode Attribute from an ACL . . . . . . . 119
     11.4.  Requirements . . . . . . . . . 161
     9.9.   Directory Caching  . . . . . . . . . . . . . 120
       11.4.1. Setting the mode and/or ACL Attributes . . . . . . 162
   10. Multi-server Name Space . 121
       11.4.2. Retrieving the mode and/or ACL Attributes . . . . . . 122
       11.4.3. Creating New Objects . . . . . . . . . . . . 163
     10.1.  Location attributes  . . . . 122
   12. Single-server Name Space . . . . . . . . . . . . . . . . . . 124
     12.1.  Server Exports 163
     10.2.  File System Presence or Absence  . . . . . . . . . . . . 163
     10.3.  Getting Attributes for an Absent File System . . . . . . 165
       10.3.1. GETATTR Within an Absent File System  . . . 124
     12.2.  Browsing Exports . . . . . 165
       10.3.2. READDIR and Absent File Systems . . . . . . . . . . . 166
     10.4.  Uses of Location Information . . . . 125
     12.3.  Server Pseudo File System . . . . . . . . . . 167
       10.4.1. File System Replication . . . . . 125
     12.4.  Multiple Roots . . . . . . . . . . 167
       10.4.2. File System Migration . . . . . . . . . . . 126
     12.5.  Filehandle Volatility . . . . . 168
       10.4.3. Referrals . . . . . . . . . . . . 126
     12.6.  Exported Root . . . . . . . . . . 169
     10.5.  Additional Client-side Considerations  . . . . . . . . . 169
     10.6.  Effecting File System Transitions  . . 126
     12.7.  Mount Point Crossing . . . . . . . . . 170
       10.6.1. Transparent File System Transitions . . . . . . . . . 126
     12.8.  Security Policy 171
       10.6.2. Filehandles and Name Space Presentation  . . . . . . 127
   13. File Locking and Share Reservations System Transitions . . . . . . . 173
       10.6.3. Fileid's and File System Transitions  . . . . . . 128
     13.1.  Locking . . 173
       10.6.4. Fsid's and File System Transitions  . . . . . . . . . 174
       10.6.5. The Change Attribute and File System Transitions  . . 174
       10.6.6. Lock State and File System Transitions  . . . . . . . 175
       10.6.7. Write Verifiers and File System Transitions . . . . 128
       13.1.1. Client ID . 178
     10.7.  Effecting File System Referrals  . . . . . . . . . . . . 178
       10.7.1. Referral Example (LOOKUP) . . . . . . . . . 129
       13.1.2. Server Release of Clientid . . . . . 179
       10.7.2. Referral Example (READDIR)  . . . . . . . . 132
       13.1.3. State-owner and Stateid Definition . . . . . 183
     10.8.  The Attribute fs_absent  . . . . 133
       13.1.4. Use of the Stateid and Locking . . . . . . . . . . . 136
     13.2.  Lock Ranges . 185
     10.9.  The Attribute fs_locations . . . . . . . . . . . . . . . 185
     10.10. The Attribute fs_locations_info  . . . . . . 138
     13.3.  Upgrading and Downgrading Locks . . . . . . 187
     10.11. The Attribute fs_status  . . . . . . 138
     13.4.  Blocking Locks . . . . . . . . . . 196
   11. Directory Delegations . . . . . . . . . . . 139
     13.5.  Lease Renewal . . . . . . . . . 199
     11.1.  Introduction to Directory Delegations  . . . . . . . . . 200
     11.2.  Directory Delegation Design (in brief) . . . 140
     13.6.  Crash Recovery . . . . . . 201
     11.3.  Recommended Attributes in support of Directory
            Delegations  . . . . . . . . . . . . . . . 140
       13.6.1. Client Failure and Recovery . . . . . . . 202
     11.4.  Delegation Recall  . . . . . . 140
       13.6.2. Server Failure and Recovery . . . . . . . . . . . . . 141
       13.6.3. Network Partitions and 203
     11.5.  Directory Delegation Recovery  . . . . . . . . . . . 143
     13.7.  Server Revocation of Locks . . 203
   12. Parallel NFS (pNFS) . . . . . . . . . . . . . 147
     13.8.  Share Reservations . . . . . . . . 203
     12.1.  Introduction . . . . . . . . . . . 148
     13.9.  OPEN/CLOSE Operations . . . . . . . . . . . 203
     12.2.  General Definitions  . . . . . . 149
     13.10. Open Upgrade and Downgrade . . . . . . . . . . . . 206
       12.2.1. Metadata Server . . . 150
     13.11. Short and Long Leases . . . . . . . . . . . . . . . . 206
       12.2.2. Client  . 150
     13.12. Clocks, Propagation Delay, and Calculating Lease
            Expiration . . . . . . . . . . . . . . . . . . . . . . 206
       12.2.3. Storage Device  . 151
     13.13. Vestigial Locking Infrastructure From V4.0 . . . . . . . 151
   14. Client-Side Caching . . . . . . . . . . . 206
       12.2.4. Storage Protocol  . . . . . . . . . . 152
     14.1.  Performance Challenges for Client-Side Caching . . . . . 153
     14.2.  Delegation and Callbacks . . . 206
       12.2.5. Control Protocol  . . . . . . . . . . . . . 154
       14.2.1. Delegation Recovery . . . . . 207
       12.2.6. Metadata  . . . . . . . . . . . . 155
     14.3.  Data Caching . . . . . . . . . . 207
       12.2.7. Layout  . . . . . . . . . . . . 157
       14.3.1. Data Caching and OPENs . . . . . . . . . . . 207
     12.3.  pNFS protocol semantics  . . . . 157
       14.3.2. Data Caching and File Locking . . . . . . . . . . . . 158
       14.3.3. Data Caching and Mandatory File Locking 208
       12.3.1. Definitions . . . . . . . 160
       14.3.4. Data Caching and File Identity . . . . . . . . . . . 160
     14.4.  Open Delegation . . . 208
       12.3.2. Guarantees Provided by Layouts  . . . . . . . . . . . 211
       12.3.3. Getting a Layout  . . . . . . 161
       14.4.1. Open Delegation and Data Caching . . . . . . . . . . 164
       14.4.2. Open Delegation and File Locks . . 212
       12.3.4. Committing a Layout . . . . . . . . . 165
       14.4.3. Handling of CB_GETATTR . . . . . . . . 213
       12.3.5. Recalling a Layout  . . . . . . . 165
       14.4.4. Recall of Open Delegation . . . . . . . . . . 215
       12.3.6. Metadata Server Write Propagation . . . . 168
       14.4.5. Clients that Fail to Honor Delegation Recalls . . . . 170
       14.4.6. Delegation Revocation . . 221
       12.3.7. Crash Recovery  . . . . . . . . . . . . . . 171
     14.5.  Data Caching and Revocation . . . . . 221
       12.3.8. Security Considerations . . . . . . . . . 171
       14.5.1. Revocation Recovery for Write Open Delegation . . . . 172
     14.6.  Attribute Caching . . 227
     12.4.  The NFSv4 File Layout Type . . . . . . . . . . . . . . . 228
       12.4.1. File Striping and Data Access . . 173
     14.7.  Data and Metadata Caching and Memory Mapped Files . . . 175
     14.8.  Name Caching . . . . . . . 228
       12.4.2. Global Stateid Requirements . . . . . . . . . . . . . 236
       12.4.3. The Layout Iomode . . 177
     14.9.  Directory Caching . . . . . . . . . . . . . . . . 236
       12.4.4. Storage Device State Propagation  . . . 178
   15. Multi-server Name Space . . . . . . . 237
       12.4.5. Storage Device Component File Size  . . . . . . . . . 239
       12.4.6. Crash Recovery Considerations . . . 179
     15.1.  Location attributes . . . . . . . . . 240
       12.4.7. Security Considerations for the File Layout Type  . . 240
       12.4.8. Alternate Approaches  . . . . . . . 179
     15.2.  File System Presence or Absence . . . . . . . . . 241
   13. Internationalization  . . . 179
     15.3.  Getting Attributes for an Absent File System . . . . . . 181
       15.3.1. GETATTR Within an Absent File System . . . . . . . . 181
       15.3.2. READDIR and Absent File Systems . . . 242
     13.1.  Stringprep profile for the utf8str_cs type . . . . . . . 243
     13.2.  Stringprep profile for the utf8str_cis type  . 182
     15.4.  Uses of Location Information . . . . . 245
     13.3.  Stringprep profile for the utf8str_mixed type  . . . . . 246
     13.4.  UTF-8 Related Errors . . . . 183
       15.4.1. File System Replication . . . . . . . . . . . . . . 247
   14. Error Values  . 183
       15.4.2. File System Migration . . . . . . . . . . . . . . . . 184
       15.4.3. Referrals . . . . . . . 248
     14.1.  Error Definitions  . . . . . . . . . . . . . . . 185
     15.5.  Additional Client-side Considerations . . . . 248
     14.2.  Operations and their valid errors  . . . . . 185
     15.6.  Effecting File System Transitions . . . . . . 262
     14.3.  Callback operations and their valid errors . . . . . 186
       15.6.1. Transparent File System Transitions . . 275
     14.4.  Errors and the operations that use them  . . . . . . . 187
       15.6.2. Filehandles and File System Transitions . 276
   15. NFS version 4.1 Procedures  . . . . . . 189
       15.6.3. Fileid's and File System Transitions . . . . . . . . 189
       15.6.4. Fsid's and File System Transitions . . . 283
     15.1.  Procedure 0: NULL - No Operation . . . . . . 190
       15.6.5. The Change Attribute and File System Transitions . . 190
       15.6.6. Lock State and File System Transitions . . . . 283
     15.2.  Procedure 1: COMPOUND - Compound Operations  . . . 191
       15.6.7. Write Verifiers and File System Transitions . . . 284
   16. NFS version 4.1 Operations  . . . 194
     15.7.  Effecting File System Referrals . . . . . . . . . . . . 194
       15.7.1. Referral Example (LOOKUP) . . 289
     16.1.  Operation 3: ACCESS - Check Access Rights  . . . . . . . 289
     16.2.  Operation 4: CLOSE - Close File  . . . . . 195
       15.7.2. Referral Example (READDIR) . . . . . . . 291
     16.3.  Operation 5: COMMIT - Commit Cached Data . . . . . . 199
     15.8.  The Attribute fs_absent . . 293
     16.4.  Operation 6: CREATE - Create a Non-Regular File Object . 295
     16.5.  Operation 7: DELEGPURGE - Purge Delegations Awaiting
            Recovery . . . . . . . . . . . . . 201
     15.9.  The Attribute fs_locations . . . . . . . . . . . 298
     16.6.  Operation 8: DELEGRETURN - Return Delegation . . . . 201
     15.10. The Attribute fs_locations_info . . 299
     16.7.  Operation 9: GETATTR - Get Attributes  . . . . . . . . . 299
     16.8.  Operation 10: GETFH - Get Current Filehandle . 203
     15.11. The Attribute fs_status . . . . . 301
     16.9.  Operation 11: LINK - Create Link to a File . . . . . . . 302
     16.10. Operation 12: LOCK - Create Lock . . . . 212
   16. Directory Delegations . . . . . . . . 303
     16.11. Operation 13: LOCKT - Test For Lock  . . . . . . . . . . 307
     16.12. Operation 14: LOCKU - Unlock File  . . 215
     16.1.  Introduction to Directory Delegations . . . . . . . . . 216
     16.2.  Directory Delegation Design (in brief) 308
     16.13. Operation 15: LOOKUP - Lookup Filename . . . . . . . . . 217
     16.3.  Recommended Attributes in support of 309
     16.14. Operation 16: LOOKUPP - Lookup Parent Directory
            Delegations  . . . . 311
     16.15. Operation 17: NVERIFY - Verify Difference in
            Attributes . . . . . . . . . . . . . . . . . . 218
     16.4.  Delegation Recall . . . . . 312
     16.16. Operation 18: OPEN - Open a Regular File . . . . . . . . 314
     16.17. Operation 19: OPENATTR - Open Named Attribute
            Directory  . . . . . . 219
     16.5.  Directory Delegation Recovery . . . . . . . . . . . . . 219
   17. Parallel NFS (pNFS) . . . . 328
     16.18. Operation 21: OPEN_DOWNGRADE - Reduce Open File Access . 329
     16.19. Operation 22: PUTFH - Set Current Filehandle . . . . . . 330
     16.20. Operation 23: PUTPUBFH - Set Public Filehandle . . . . . 331
     16.21. Operation 24: PUTROOTFH - Set Root Filehandle  . . . . . 219
     17.1.  Introduction 332
     16.22. Operation 25: READ - Read from File  . . . . . . . . . . 333
     16.23. Operation 26: READDIR - Read Directory . . . . . . . . . 335
     16.24. Operation 27: READLINK - Read Symbolic Link  . . . 219
     17.2.  General Definitions . . . 339
     16.25. Operation 28: REMOVE - Remove File System Object . . . . 340
     16.26. Operation 29: RENAME - Rename Directory Entry  . . . . . 342
     16.27. Operation 31: RESTOREFH - Restore Saved Filehandle . . . 344
     16.28. Operation 32: SAVEFH - Save Current Filehandle . . . 222
       17.2.1. Metadata Server . . 345
     16.29. Operation 33: SECINFO - Obtain Available Security  . . . 346
     16.30. Operation 34: SETATTR - Set Attributes . . . . . . . . . 349
     16.31. Operation 37: VERIFY - Verify Same Attributes  . . . . . 222
       17.2.2. Client 352
     16.32. Operation 38: WRITE - Write to File  . . . . . . . . . . 353
     16.33. Operation 40: BACKCHANNEL_CTL - Backchannel control  . . 357
     16.34. Operation 41: BIND_CONN_TO_SESSION . . . . . . . . . . . 222
       17.2.3. Storage Device 359
     16.35. Operation 42: CREATE_CLIENTID - Instantiate Clientid . . 363
     16.36. Operation 43: CREATE_SESSION - Create New Session and
            Confirm Clientid . . . . . . . . . . . . . . . . . 222
       17.2.4. Storage Protocol . . . 369
     16.37. Operation 44: DESTROY_SESSION - Destroy existing
            session  . . . . . . . . . . . . . . . 222
       17.2.5. Control Protocol . . . . . . . . . . . . . . . . . . 223
       17.2.6. Metadata  . . . . . . . . . . . . . . . . . . . . . . 223
       17.2.7. Layout  . . . . . . . 379
     16.38. Operation 45: FREE_STATEID - Free stateid with no
            locks  . . . . . . . . . . . . . . . . 223
     17.3.  pNFS protocol semantics . . . . . . . . . 380
     16.39. Operation 46: GET_DIR_DELEGATION - Get a directory
            delegation . . . . . . . 224
       17.3.1. Definitions . . . . . . . . . . . . . . . . 381
     16.40. Operation 47: GETDEVICEINFO - Get Device Information . . 385
     16.41. Operation 48: GETDEVICELIST  . . . 224
       17.3.2. Guarantees Provided by Layouts . . . . . . . . . . . 227
       17.3.3. Getting 386
     16.42. Operation 49: LAYOUTCOMMIT - Commit writes made using
            a Layout  . . . . . . . . . . . layout . . . . . . . 228
       17.3.4. Committing a Layout . . . . . . . . . . . . . . . . . 229
       17.3.5. Recalling a 387
     16.43. Operation 50: LAYOUTGET - Get Layout Information . . . . 391
     16.44. Operation 51: LAYOUTRETURN - Release Layout
            Information  . . . . . . . . . . . . . 231
       17.3.6. Metadata Server Write Propagation . . . . . . . . . . 237
       17.3.7. Crash Recovery  . . . . . . . . . . . . . . . . . . . 237
       17.3.8. 394
     16.45. Operation 52: SECINFO_NO_NAME - Get Security Considerations . . . . . . . . . on
            Unnamed Object . . . . . . 243
     17.4.  The NFSv4 File Layout Type . . . . . . . . . . . . . . . 244
       17.4.1. File Striping 396
     16.46. Operation 53: SEQUENCE - Supply per-procedure
            sequencing and Data Access . . . . . . . . . . . . 244
       17.4.2. Global Stateid Requirements . . . . . . . . . . . . . 252
       17.4.3. The Layout Iomode . . . . . . . . . . . . . . . . . . 252
       17.4.4. Storage Device State Propagation  . . . . . . . . . . 253
       17.4.5. Storage Device Component File Size  . . . . . . . . . 255
       17.4.6. Crash Recovery Considerations . . . . . . . . . . . . 256
       17.4.7. Security Considerations for the File Layout Type  . . 256
       17.4.8. Alternate Approaches  . . . . . . . . . . . . . . . control . 257
   18. Internationalization . . . . . . . . . . . . . . . . 397
     16.47. Operation 54: SET_SSV  . . . . 258
     18.1.  Stringprep profile for the utf8str_cs type . . . . . . . 259
     18.2.  Stringprep profile for the utf8str_cis type . . . . . . 261
     18.3.  Stringprep profile 401
     16.48. Operation 55: TEST_STATEID - Test stateids for the utf8str_mixed type  . . . . . 262
     18.4.  UTF-8 Related Errors . . . . . . . . . . . . . . . . . . 263
   19. Error Values  . . . . . . . . . . . . . . . . . . . . . . . . 264
     19.1.  Error Definitions  . .
            validity . . . . . . . . . . . . . . . . . 264
     19.2.  Operations and their valid errors . . . . . . . 402
     16.49. Operation 56: WANT_DELEGATION  . . . . 276
     19.3.  Callback operations and their valid errors . . . . . . . 284
     19.4.  Errors and the operations that use them . . 403
     16.50. Operation 10044: ILLEGAL - Illegal operation . . . . . . 284
   20. 406
   17. NFS version 4.1 Callback Procedures . . . . . . . . . . . . . . . . . 290
     20.1. 407
     17.1.  Procedure 0: NULL CB_NULL - No Operation  . . . . . . . . . . . . 290
     20.2. 407
     17.2.  Procedure 1: COMPOUND CB_COMPOUND - Compound Operations . . . . . . 291
   21. 407
   18. NFS version 4.1 Callback Operations . . . . . . . . . . . . . . . . . 295
     21.1. 409
     18.1.  Operation 3: ACCESS CB_GETATTR - Check Access Rights Get Attributes . . . . . . . 296
     21.2. . 409
     18.2.  Operation 4: CLOSE CB_RECALL - Close File  . . . Recall an Open Delegation . . . 411
     18.3.  Operation 5: CB_LAYOUTRECALL . . . . . . 298
     21.3.  Operation 5: COMMIT - Commit Cached Data . . . . . . . . 299
     21.4. 412
     18.4.  Operation 6: CREATE - Create a Non-Regular File Object . 302
     21.5.  Operation 7: DELEGPURGE CB_NOTIFY - Purge Delegations Awaiting
            Recovery . . . . . . Notify directory changes  . . . 414
     18.5.  Operation 7: CB_PUSH_DELEG . . . . . . . . . . . . . . . 304
     21.6. 417
     18.6.  Operation 8: DELEGRETURN CB_RECALL_ANY - Return Delegation . . . . Keep any N delegations  . . 305
     21.7. 418
     18.7.  Operation 9: GETATTR - Get Attributes  . . . . . CB_RECALLABLE_OBJ_AVAIL . . . . 306
     21.8.  Operation 10: GETFH - Get Current Filehandle . . . . . . 307
     21.9. 421
     18.8.  Operation 11: LINK 10: CB_RECALL_SLOT - Create Link to a File . . . . change flow control
            limits . . . 308
     21.10. Operation 12: LOCK - Create Lock . . . . . . . . . . . . 309
     21.11. Operation 13: LOCKT - Test For Lock . . . . . . . . . . 313
     21.12. 422
     18.9.  Operation 14: LOCKU 11: CB_SEQUENCE - Unlock File  . . . . . . . Supply callback channel
            sequencing and control . . . . 314
     21.13. Operation 15: LOOKUP - Lookup Filename . . . . . . . . . 315
     21.14. Operation 16: LOOKUPP - Lookup Parent Directory . . . . 317
     21.15. 423
     18.10. Operation 17: NVERIFY - Verify Difference in
            Attributes . . . . . . . . . . . 12: CB_WANTS_CANCELLED . . . . . . . . . . . . 318
     21.16. 425
     18.11. Operation 18: OPEN 10044: CB_ILLEGAL - Open a Regular File . . . . . . . . 319
     21.17. Illegal Callback
            Operation 19: OPENATTR - Open Named Attribute
            Directory  . .  . . . . . . . . . . . . . . . . . . . . . 333
     21.18. Operation 21: OPEN_DOWNGRADE - Reduce Open File Access . 334
     21.19. Operation 22: PUTFH - Set Current Filehandle . . . . 426
   19. Security Considerations . . 335
     21.20. Operation 23: PUTPUBFH - Set Public Filehandle . . . . . 336
     21.21. Operation 24: PUTROOTFH - Set Root Filehandle . . . . . 338
     21.22. Operation 25: READ - Read from File . . . . . . . 427
   20. IANA Considerations . . . 338
     21.23. Operation 26: READDIR - Read Directory . . . . . . . . . 340
     21.24. Operation 27: READLINK - Read Symbolic Link . . . . . . 344
     21.25. Operation 28: REMOVE - Remove File System Object . . . 427
     20.1.  Defining new layout types  . 345
     21.26. Operation 29: RENAME - Rename Directory Entry . . . . . 347
     21.27. Operation 31: RESTOREFH - Restore Saved Filehandle . . . 348
     21.28. Operation 32: SAVEFH - Save Current Filehandle . . . . . 349
     21.29. Operation 33: SECINFO - Obtain Available Security . 427
   21. References  . . 350
     21.30. Operation 34: SETATTR - Set Attributes . . . . . . . . . 353
     21.31. Operation 37: VERIFY - Verify Same Attributes . . . . . 355
     21.32. Operation 38: WRITE - Write to File . . . . . . . . . 428
     21.1.  Normative References . 357
     21.33. Operation 40: BACKCHANNEL_CTL - Backchannel control . . 361
     21.34. Operation 41: BIND_CONN_TO_SESSION . . . . . . . . . . . 361
     21.35. Operation 42: CREATE_CLIENTID - Instantiate Clientid . . 365
     21.36. Operation 43: CREATE_SESSION - Create New Session and
            Confirm Clientid . . 428
     21.2.  Informative References . . . . . . . . . . . . . . . . . 429
   Appendix A.  Acknowledgments  . 371
     21.37. Operation 44: DESTROY_SESSION - Destroy existing
            session . . . . . . . . . . . . . . . . . 430
   Authors' Addresses  . . . . . . . 379
     21.38. Operation 45: FREE_STATEID - Free stateid with no
            locks . . . . . . . . . . . . . . . . 431
   Intellectual Property and Copyright Statements  . . . . . . . . . 380
     21.39. Operation 46: GET_DIR_DELEGATION - Get 432

1.  Introduction

1.1.  The NFSv4.1 Protocol

   The NFSv4.1 protocol is a directory
            delegation . . . . . . . . . . . . . . . . . . . . . . . 381
     21.40. Operation 47: GETDEVICEINFO - Get Device Information . . 385
     21.41. Operation 48: GETDEVICELIST  . . . . . . . . . . . . . . 386
     21.42. Operation 49: LAYOUTCOMMIT - Commit writes made using
            a layout . . . . . . . . . . . . . . . . . . . . . . . . 387
     21.43. Operation 50: LAYOUTGET - Get Layout Information . . . . 391
     21.44. Operation 51: LAYOUTRETURN - Release Layout
            Information  . . . . . . . . . . . . . . . . . . . . . . 394
     21.45. Operation 52: SECINFO_NO_NAME - Get Security on
            Unnamed Object . . . . . . . . . . . . . . . . . . . . . 396
     21.46. Operation 53: SEQUENCE - Supply per-procedure
            sequencing and control . . . . . . . . . . . . . . . . . 398
     21.47. Operation 54: SET_SSV  . . . . . . . . . . . . . . . . . 401
     21.48. Operation 55: TEST_STATEID - Test stateids for
            validity . . . . . . . . . . . . . . . . . . . . . . . . 402
     21.49. Operation 56: WANT_DELEGATION  . . . . . . . . . . . . . 404
     21.50. Operation 10044: ILLEGAL - Illegal operation . . . . . . 407
   22. NFS version 4.1 Callback Procedures . . . . . . . . . . . . . 407
     22.1.  Procedure 0: CB_NULL - No Operation  . . . . . . . . . . 408
     22.2.  Procedure 1: CB_COMPOUND - Compound Operations . . . . . 408
   23. NFS version 4.1 Callback Operations . . . . . . . . . . . . . 410
     23.1.  Operation 3: CB_GETATTR - Get Attributes . . . . . . . . 410
     23.2.  Operation 4: CB_RECALL - Recall an Open Delegation . . . 411
     23.3.  Operation 5: CB_LAYOUTRECALL . . . . . . . . . . . . . . 412
     23.4.  Operation 6: CB_NOTIFY - Notify directory changes  . . . 415
     23.5.  Operation 7: CB_PUSH_DELEG . . . . . . . . . . . . . . . 418
     23.6.  Operation 8: CB_RECALL_ANY - Keep any N delegations  . . 419
     23.7.  Operation 9: CB_RECALLABLE_OBJ_AVAIL . . . . . . . . . . 422
     23.8.  Operation 10: CB_RECALL_CREDIT - change flow control
            limits . . . . . . . . . . . . . . . . . . . . . . . . . 423
     23.9.  Operation 11: CB_SEQUENCE - Supply callback channel
            sequencing and control . . . . . . . . . . . . . . . . . 423
     23.10. Operation 12: CB_WANTS_CANCELLED . . . . . . . . . . . . 425
     23.11. Operation 10044: CB_ILLEGAL - Illegal Callback
            Operation  . . . . . . . . . . . . . . . . . . . . . . . 426
   24. Security Considerations . . . . . . . . . . . . . . . . . . . 426
   25. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 427
     25.1.  Defining new layout types  . . . . . . . . . . . . . . . 427
   26. References  . . . . . . . . . . . . . . . . . . . . . . . . . 427
     26.1.  Normative References . . . . . . . . . . . . . . . . . . 427
     26.2.  Informative References . . . . . . . . . . . . . . . . . 429
   Appendix A.  ACL Algorithm Examples . . . . . . . . . . . . . . . 430
     A.1.   Recomputing mode upon SETATTR of ACL . . . . . . . . . . 430
     A.2.   Computing the Inherited ACL  . . . . . . . . . . . . . . 433
       A.2.1.  Discussion  . . . . . . . . . . . . . . . . . . . . . 434
     A.3.   Applying a Mode to an Existing ACL . . . . . . . . . . . 435
   Appendix B.  Acknowledgments  . . . . . . . . . . . . . . . . . . 439
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . . 440
   Intellectual Property and Copyright Statements  . . . . . . . . . 441

1.  Introduction

1.1.  The NFSv4.1 Protocol

   The NFSv4.1 protocol is a minor version of the NFSv4 protocol
   described in [2].  It generally follows the guidelines for minor
   versioning model laid in Section 10 of RFC 3530.  However, it
   diverges from guidelines 11 ("a client and server that supports minor
   version X must support minor versions 0 through X-1"), and 12 ("no
   features may be introduced as mandatory in minor version of the NFSv4 protocol
   described in [2].  It generally follows the guidelines for minor
   versioning model laid in Section 10 of RFC 3530.  However, it
   diverges from guidelines 11 ("a client and server that supports minor
   version X must support minor versions 0 through X-1"), and 12 ("no
   features may be introduced as mandatory in a minor version").  These
   divergences are due to the introduction of the sessions model for
   managing non-idempotent operations and the RECLAIM_COMPLETE
   operation.  These two new features are infrastructural in nature and
   simplify implementation of existing and other new features.  Making
   them optional would add undue complexity to protocol definition and
   implementation.  NFSv4.1 accordingly updates the Minor Versioning
   guidelines (Section 7). 2.6).

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

1.2.  NFS Version 4 Goals

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

   o  Improved access and good performance on the Internet.

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

   o  Strong security with negotiation built into the protocol.

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

   o  Good cross-platform interoperability.

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

   o  Designed for protocol extensions.

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

1.3.  Minor Version 1 Goals

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

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

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

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

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

1.4.  Inconsistencies of this Document with Section XX

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

1.5.  Overview of NFS version 4.1 Features

   To provide a reasonable context for the reader, the major features of
   NFS version 4.1 protocol will be reviewed in brief.  This will be
   done to provide an appropriate context for both the reader who is
   familiar with the previous versions of the NFS protocol and the
   reader that is new to the NFS protocols.  For the reader new to the
   NFS protocols, there is still a set of fundamental knowledge that is
   expected.  The reader should be familiar with the XDR and RPC
   protocols as described in [3] and [4].  A basic knowledge of file
   systems and distributed file systems is expected as well.

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

1.5.1.  RPC and Security

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

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

1.5.2.  Protocol Structure

1.5.2.1.  Core Protocol

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

   A significant departure from the versions

1.5.2.2.  Parallel Access

   Minor version one supports high-performance data access to a
   clustered server implementation by enabling a separation of metadata
   access and data access, with the NFS protocol before
   version 4 latter done to multiple servers in
   parallel.

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

1.5.3.  File System Model

   The general file system model used for the NFS version 4 protocol, in all minor versions, there are two RPC
   procedures, NULL and COMPOUND. 4.1 protocol
   is the same as previous versions.  The COMPOUND procedure server file system is defined
   hierarchical with the regular files contained within being treated as
   opaque byte streams.  In a series of individual operations slight departure, file and these operations perform directory names
   are encoded with UTF-8 to deal with the
   sorts basics of functions performed by traditional NFS procedures.
   internationalization.

   The operations combined within NFS version 4.1 protocol does not require a COMPOUND request are evaluated in
   order by the server, without any atomicity guarantees.  A limited set
   of facilities exist to pass results from one operation to another.
   Once an operation returns a failing result, the evaluation ends and
   the results of all evaluated operations are returned to the client.

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

   NFS Version 4.1 also contains a a considerable set of callback
   operations in which the server makes an RPC directed at the client.
   Callback RPC's have a similar structure to that of the normal server
   requests.  For the NFS version 4 protocol callbacks in all minor
   versions, there are two RPC procedures, NULL and CB_COMPOUND.  The
   CB_COMPOUND procedure is defined in analogous fashion to that of
   COMPOUND with its own set of callback operations.

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

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

1.5.2.2.  Parallel Access

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

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

1.5.3.  File System Model

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

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

1.5.3.1.  Filehandles

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

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

1.5.3.2.  File Attributes

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

   One significant recommended file attribute is the Access Control List
   (ACL) attribute.  This attribute provides for directory and file
   access control beyond the model used in NFS Versions 2 and 3.  The
   ACL definition allows for specification specific sets of permissions
   for individual users and groups.  In addition, ACL inheritance allows
   propagation of access permissions and restriction down a directory
   tree as fileystsme filesystem objects are created.

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

1.5.3.3.  Multi-server Namespace

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

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

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

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

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

1.5.4.  Locking Facilities

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

   o  Share reservations as established by OPEN operations.

   o  Byte-range locks.

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

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

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

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

1.6.  General Definitions

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

1.7.  Differences from NFSv4.0

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

   o  Implementation of the sessions model.

   o  Support for parallel access to data.

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

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

   o  Operations to re-obtain a delegation.

   o  Support for client and server implementation id's.

2.  Core Infrastructure

2.1.  Introduction

2.2.  RPC and XDR

2.2.1.  RPC-based Security

2.2.1.1.  RPC Security Flavors

2.2.1.1.1.  RPCSEC_GSS and Security Services

2.2.1.1.1.1.  Authentication, Integrity, Privacy

2.2.1.1.1.2.  GSS Server Principal

2.2.1.2.  NFSv4 Security Tuples

2.2.1.2.1.  Security Service Negotiation

2.2.1.2.1.1.  SECINFO and SECINFO_NO_NAME

2.2.1.2.1.2.  Security Error

2.2.1.2.1.3.  PUTFH + LOOKUP

2.2.1.2.1.4.  PUTFH + LOOKUPP

2.2.1.2.1.5.  PUTFH + SECINFO

2.2.1.2.1.6.  PUTFH + Anything Else

2.3.  Non-RPC-based Security Services

2.3.1.  Authorization

2.3.2.  Auditing

2.3.3.  Intrusion Detection

2.4.  Transport Layers

2.4.1.  Ports

2.4.2.  Stream Transports

2.4.3.  RDMA Transports

2.4.3.1.  RDMA Requirements

2.4.3.2.  RDMA Connection Resources

2.5.  Session

2.5.1.  Motivation and Overview

2.5.2.  NFSv4 Integration

2.5.2.1.  COMPOUND and CB_COMPOUND

2.5.2.2.  SEQUENCE and CB_SEQUENCE

2.5.2.3.  Clientid and Session Association

2.5.3.  Channels

2.5.3.1.  Operation Channel

2.5.3.2.  Back Channel

2.5.3.2.1.  Back Channel RPC Security

2.5.3.3.  Session and Channel Association

2.5.3.4.  Connection and Channel Association

2.5.3.4.1.  Trunking

2.5.4.  Exactly Once Semantics

2.5.4.1.  Slot Identifiers and Server Duplicate Request Cache

2.5.4.2.  Retry and Replay

2.5.4.3.  Resolving server callback races with sessions

2.6.  Channel Management

2.6.1.  Buffer Management

2.6.2.  Data Transfer

2.6.2.1.  Inline Data Transfer (Stream and RDMA)

2.6.2.2.  Direct Data Transfer (RDMA)

2.6.3.  Flow Control

2.6.4.  COMPOUND Sizing Issues

2.6.5.  Data Alignment

2.7.  Sessions Security

2.7.1.  Denial of Service via Unauthorized State Changes

2.8.  Session Mechanics - Steady State

2.8.1.  Obligations of

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

2.8.2.  Obligations
   remainder of the Client

2.8.3.  Steps the Client Takes To Establish a Session

2.8.4.  Session Mechanics - Recovery

2.8.4.1.  Reconnection

2.8.4.2.  Failover

2.8.4.3.  Events Requiring Client Action

2.8.4.4.  Events Requiring Server Action

3. this section.

2.2.  RPC and Security Flavor XDR

   The NFS version 4.1 (NFSv4.1) protocol is a Remote Procedure Call
   (RPC) application that uses RPC version 2 and the corresponding
   eXternal Data Representation (XDR) as defined in RFC1831 [4] and
   RFC4506 [3].
   The RPCSEC_GSS security flavor as defined in RFC2203 [5] MUST be used
   as the mechanism to deliver stronger security for the NFS version 4
   protocol.

3.1.  Ports and Transports

   Historically,

2.2.1.  RPC-based Security

   Previous NFS version 2 and version 3 servers versions have resided on
   port 2049.  The registered port 2049 RFC3232 [19] for the NFS
   protocol should be the default configuration.  NFSv4 clients SHOULD
   NOT use the RPC binding protocols been thought of as described in RFC1833 [20].

   Where an NFS version 4 implementation supports operation over the IP
   network protocol, having a host-based
   authentication model, where the supported transports between NFS and IP MUST
   have the following two attributes:

   1.  The transport must support reliable delivery of data in the order
       it was sent.

   2.  The transport must be among the IETF-approved congestion control
       transport protocols.

   At the time this document was written, the only two transports that
   had server authenticates the above attributes were TCP and SCTP.  To enhance the
   possibilities for interoperability, an NFS version 4 implementation
   MUST support operation over the TCP transport protocol.

   If TCP is used as the transport,
   client, and trust the client and server SHOULD use
   persistent connections to authenticate all users.  Actually,
   NFS has always depended on RPC for at least two reasons:

   1.  This will prevent the weakening authentication.  The first form of TCP's congestion control via
       short lived connections and will improve performance
   RPC authentication which required a host-based authentication
   approach.  NFSv4 also depends on RPC for the WAN
       environment by eliminating the need basic security services, and
   mandates RPC support for SYN handshakes.

   2. a user-based authentication model.  The NFSv4.1 callback
   user-based authentication model has changed from NFSv4.0, and requires
       the client and server to maintain user principals authenticated by
   a client-created channel for server, and in turn the server to use. authenticated by user principals.
   RPC provides some basic security services which are used by NFSv4.

2.2.1.1.  RPC Security Flavors

   As noted described in the Security Considerations section, the authentication
   model for NFS version 4 has moved from machine-based to principal-
   based.  However, this modification section 7.2 "Authentication" of [4], RPC security is
   encapsulated in the authentication model does
   not imply RPC header, via a technical requirement security or authentication
   flavor, and information specific to move the transport connection
   management model from whole machine-based specification of the security
   flavor.  Every RPC header conveys information used to one based on a per user
   model.  In particular, NFS over TCP client implementations have
   traditionally multiplexed traffic for multiple users over identify and
   authenticate a common
   TCP connection between an NFS client and server.  This has been true,
   regardless whether the NFS client is using AUTH_SYS, AUTH_DH,
   RPCSEC_GSS or any other flavor.  Similarly, NFS over TCP server
   implementations have assumed such a model and thus scale the
   implementation of TCP connection management  As discussed in proportion to the
   number of expected client machines.  NFS version 4.1 will not modify
   this connection management model.  NFS version 4.1 clients that
   violate this assumption can expect scaling issues on the server and
   hence reduced service.

   Note that for various timers, the client and server should avoid
   inadvertent synchronization of those timers.  For further discussion
   of the general issue refer to [Floyd].

3.1.1.  Client Retransmission Behavior

   When processing a request received over a reliable transport such as
   TCP, the NFS version 4.1 server MUST NOT silently drop the request,
   except if the transport connection has been broken.  Given such a
   contract between NFS version 4.1 Section 2.2.1.1.1,
   some security flavors provide additional security services.

   NFSv4 clients and servers, clients servers MUST
   NOT retry a request unless one or both of the following are true:

   o  The transport connection has been broken

   o  The procedure being retried is the NULL procedure

   Since reliable transports, such as TCP, do not always synchronously
   inform a peer when the other peer has broken the connection (for
   example, when an NFS server reboots), the NFS version 4.1 client may
   want to actively "probe" the connection implement RPCSEC_GSS.  (This
   requirement to see if has been broken.
   Use of the NULL procedure implement is one recommended way to do so.  So, when
   a client experiences a remote procedure call timeout (of some
   arbitrary implementation specific amount), rather than retrying the
   remote procedure call, it could instead issue a NULL procedure call
   to the server.  If the server has died, the transport connection
   break will eventually be indicated to the NFS version 4.1 client.
   The client can then reconnect, and then retry the original request.
   If the NULL procedure call gets a response, the connection has not
   broken.  The client can decide to wait longer for the original
   request's response, or it can break the transport connection and
   reconnect before re-sending the original request.

   For callbacks from the server a requirement to the client, the same rules apply,
   but the server doing the callback becomes the client, and the client
   receiving the callback becomes the server.

3.2.  Security Flavors

   Traditional RPC implementations have included use.)  Other
   flavors, such as AUTH_NONE, AUTH_SYS,
   AUTH_DH, and AUTH_KRB4 AUTH_SYS, MAY be implemented as security flavors.  With RFC2203 [5] an
   additional security flavor of well.

2.2.1.1.1.  RPCSEC_GSS has been introduced which and Security Services

   RPCSEC_GSS ([5]) uses the functionality of GSS-API RFC2743 [8].  This
   allows for the use of various security mechanisms by the RPC layer
   without the additional implementation overhead of adding RPC security
   flavors.
   For NFS version 4,

2.2.1.1.1.1.  Identification, Authentication, Integrity, Privacy

   Via the GSS-API, RPCSEC_GSS security flavor MUST can be implemented used to enable identify and authenticate
   users on clients to servers, and servers to users.  It can also
   perform integrity checking on the mandatory security mechanism.  Other flavors, such as,
   AUTH_NONE, AUTH_SYS, entire RPC message, including the
   RPC header, and AUTH_DH MAY be implemented the arguments or results.  Finally, privacy, usually
   via encryption, is a service available with RPCSEC_GSS.  Privacy is
   performed on the arguments and results.  Note that if privacy is
   selected, integrity, authentication, and identification are enabled.
   If privacy is not selected, but integrity is selected, authentication
   and identification are enabled.  If integrity and privacy are not
   selected, but authentication is enabled, identification is enabled.
   RPCSEC_GSS does not provide identification as well.

3.2.1. a separate service.

   Although GSS-API has an authentication service distinct from its
   privacy and integrity services, use GSS-API's authentication service
   is not used for RPCSEC_GSS's authentication service.  Instead, each
   RPC request and response header is integrity protected with the GSS-
   API integrity service, and this allows RPCSEC_GSS to offer per-RPC
   authentication and identity.  See [5] for more information.

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

2.2.1.1.1.2.  Security mechanisms for NFS version 4

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

   The use of RPCSEC_GSS requires selection of: mechanism, quality of
   protection,
   protection (QOP), and service (authentication, integrity, privacy).  The
   remainder
   For the mandated security mechanisms, NFSv4 specifies that a QOP of this document will refer
   zero (0) is used, leaving it up to these three parameters of the RPCSEC_GSS security as mechanism or the security triple.

3.2.1.1. mechanism's
   configuration to use an appropriate level of protection that QOP zero
   maps to.  Each mandated mechanism specifies minimum set of
   cryptographic algorithms for implementing integrity and privacy.
   NFSv4 clients and servers MUST be implemented on operating
   environments that comply with the mandatory cryptographic algorithms
   of each mandated mechanism.

2.2.1.1.1.2.1.  Kerberos V5

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

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

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

   Note that the number and name of the pseudo flavor is presented here
   as a mapping aid to the implementor.  Because this NFS the NFSv4 protocol
   includes a method to negotiate security and it understands the GSS-API GSS-
   API mechanism, the pseudo flavor is not needed.  The pseudo flavor is
   needed for the NFS version 3 since the security negotiation is done
   via the MOUNT
   protocol.

   For a discussion of NFS' use of RPCSEC_GSS and Kerberos V5, please
   see RFC2623 [21].

3.2.1.2.  LIPKEY protocol as a security triple described in [19].

2.2.1.1.1.2.2.  LIPKEY

   The LIPKEY V5 GSS-API mechanism as described in RFC2847 [7] MUST be
   implemented and provide the following security triples.  The
   definition of the columns matches with the previous subsection "Kerberos
   V5 RPCSEC_GSS services as security triple" specified in the
   following table:

      1      2        3                    4
    --------------------------------------------------------------------                     5   6
      ------------------------------------------------------------------
      390006 lipkey   1.3.6.1.5.5.9        rpc_gss_svc_none      yes yes
      390007 lipkey-i 1.3.6.1.5.5.9        rpc_gss_svc_integrity yes yes
      390008 lipkey-p 1.3.6.1.5.5.9        rpc_gss_svc_privacy

3.2.1.3.    no yes

2.2.1.1.1.2.3.  SPKM-3 as a security triple

   The SPKM-3 GSS-API mechanism as described in RFC2847 [7] MUST be implemented and provide the following security triples.  The
   definition of the columns matches
   with the previous subsection "Kerberos
   V5 RPCSEC_GSS services as security triple". specified in the following table:

      1      2        3                    4                     5
    --------------------------------------------------------------------   6
      ------------------------------------------------------------------
      390009 spkm3    1.3.6.1.5.5.1.3      rpc_gss_svc_none      yes yes
      390010 spkm3i   1.3.6.1.5.5.1.3      rpc_gss_svc_integrity yes yes
      390011 spkm3p   1.3.6.1.5.5.1.3      rpc_gss_svc_privacy

3.3.  Security Negotiation

   With the NFS version 4 server potentially offering multiple    no yes

2.2.1.1.1.3.  GSS Server Principal

   Regardless of what security
   mechanisms, the client needs a method to determine or negotiate which mechanism under RPCSEC_GSS is to be used for its communication with being used,
   the server.  The NFS server may have multiple points within its file system server, MUST identify itself in GSS-API via a
   GSS_C_NT_HOSTBASED_SERVICE name space
   that type.  GSS_C_NT_HOSTBASED_SERVICE
   names are available for use by NFS clients.  In turn of the NFS server
   may be configured such that each form:

        service@hostname

   For NFS, the "service" element is

        nfs

   Implementations of these entry points may have
   different or multiple security mechanisms in use.

   The security negotiation between client and server must be done with
   a secure channel will convert nfs@hostname to eliminate
   various different forms.  For Kerberos V5, LIPKEY, and SPKM-3, the possibility
   following form is RECOMMENDED:

        nfs/hostname

2.3.  COMPOUND and CB_COMPOUND

   A significant departure from the versions of a third party
   intercepting the negotiation sequence and forcing NFS protocol before
   version 4 is the client and
   server to choose a lower level introduction of security than required or desired.
   See the section "Security Considerations" for further discussion.

3.3.1.  SECINFO COMPOUND procedure.  For the
   NFSv4 protocol, in all minor versions, there are exactly two RPC
   procedures, NULL and SECINFO_NO_NAME COMPOUND.  The SECINFO COMPOUND procedure is defined as
   a series of individual operations and SECINFO_NO_NAME these operations allow perform the client to
   determine, on
   sorts of functions performed by traditional NFS procedures.

   The operations combined within a per filehandle basis, what security triple is to be
   used for server access.  In general, COMPOUND request are evaluated in
   order by the client will not have server, without any atomicity guarantees.  A limited set
   of facilities exist to use
   either pass results from one operation except during initial communication with to another.
   Once an operation returns a failing result, the server
   or when evaluation ends and
   the client crosses policy boundaries at results of all evaluated operations are returned to the server.  It is
   possible that client.

   With the server's policies change during use of the client's
   interaction therefore forcing COMPOUND procedure, the client is able to negotiate build
   simple or complex requests.  These COMPOUND requests allow for a new security
   triple.

3.3.2.  Security Error

   Based on
   reduction in the assumption that each NFS version 4 client and server
   must support number of RPCs needed for logical file system
   operations.  For example, multi-component lookup requests can be
   constructed by combining multiple LOOKUP operations.  Those can be
   further combined with operations such as GETATTR, READDIR, or OPEN
   plus READ to do more complicated sets of operation without incurring
   additional latency.

   NFSv4 also contains a minimum considerable set of security (i.e., LIPKEY, SPKM-3, and
   Kerberos-V5 all under RPCSEC_GSS), the NFS client will start its
   communication with callback operations in
   which the server with one of the minimal security
   triples.  During communication with the server, the client may
   receive makes an NFS error of NFS4ERR_WRONGSEC.  This error allows RPC directed at the
   server client.  Callback RPC's
   have a similar structure to notify the client that of the security triple currently being
   used is not appropriate for access to normal server requests.  For
   the server's file system
   resources. NFS version 4 protocol callbacks in all minor versions, there are
   two RPC procedures, NULL and CB_COMPOUND.  The client CB_COMPOUND procedure
   is then responsible for determining what
   security triples are available at the defined in analogous fashion to that of COMPOUND with its own set
   of callback operations.

   Addition of new server and choose one which is
   appropriate for the client.  See the section for the "SECINFO" callback operation for further discussion of how the client will respond to within the NFS4ERR_WRONGSEC error COMPOUND and use SECINFO.

3.3.3.  Callback RPC Authentication

   Callback authentication has changed in NFSv4.1 from NFSv4.0.

   NFSv4.0 required
   CB_COMPOUND request framework provide means of extending the NFS server to create protocol
   in subsequent minor versions.

   Except for a security context small number of operations needed for
   RPCSEC_GSS, AUTH_DH, and AUTH_KERB4, session creation,
   server requests and any other security flavor
   that had a security context.  It also required that principal issuing
   the callback be the same as the principal that accepted requests are performed within the callback
   parameters (via SETCLIENTID),
   context of a session.  Sessions provide a client context for every
   request and support robust replay protection for non-idempotent
   requests.

2.4.  Client Identifiers

   For each operation that obtains or depends on locking state, the
   specific client principal accepting
   the callback must be determinable by the same as that which issued the SETCLIENTID.  This
   required the NFS server.  In NFSv4, each
   distinct client to have an assigned machine credential.
   NFSv4.1 does not require a machine credential.  Instead, NFSv4.1
   allows an RPCSEC_GSS security context initiated instance is represented by the a clientid, which is a 64-
   bit identifier that identifies a specific client at a given time and
   eswtablished on both
   which is changed whenever the client and server to be used on callback
   RPCs sent by or the server re-initializes.
   Clientid's are used to support lock identification and crash
   recovery.

   In NFSv4.1, the client.  The BIND_BACKCHANNEL clientid associated with each operation is used establish RPCSEC_GSS contexts (if derived
   from the client so
   desires) session (see Section 2.9) on which the server.  No support for AUTH_DH, or AUTH_KERB4 operation is
   specified.

3.3.4.  GSS Server Principal

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

   service@hostname

   For NFS, the "service" element is

   nfs

   Implementations of security mechanisms will convert nfs@hostname to
   various different forms.  For Kerberos V5, LIPKEY, specific clientid at session
   creation and SPKM-3, that clientid then becomes the
   following form is RECOMMENDED:

   nfs/hostname

4.  Security Negotiation

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

   First, it is impossible for the client to use the SECINFO
   all requests issued using it.  Therefore, unlike NFSv4.0, no NFSv4.1
   operation
   to determine the correct security triple for accessing is possible until a parent
   directory.  This clientid is because SECINFO takes as arguments the current
   file handle and established.

   A sequence of a component name.  However, NFSv4.0 uses the LOOKUPP CREATE_CLIENTID operation followed by a
   CREATE_SESSION operation using that clientid is required to get establish
   the parent directory identification on the server.  Establishment of identification by
   a new incarnation of the current filehandle.  If client also has the effect of immediately
   releasing any locking state that a previous incarnation of that same
   client uses might have had on the wrong security when issuing server.  Such released state would
   include all lock, share reservation, and, where the LOOKUPP, and gets
   back an NFS4ERR_WRONGSEC error, SECINFO server is useless to not
   supporting the client.
   The CLAIM_DELEGATE_PREV claim type, all delegation state
   associated with same client is left with guessing which security the server will
   accept.  This defeats the purpose of SECINFO, which was to provide an
   efficient method same identity.  For discussion
   of negotiating security.

   Second, there is ambiguity as to what the server should do when it is
   passed a LOOKUP operation delegation state recovery, see Section 9.2.1.

   Releasing such state requires that the server restricts access be able to
   the current file handle with determine
   that one security triple, and access to client instance is the
   component with successor of another.  Where this
   cannot be done, for any of a different triple, and remote procedure call uses one number of reasons, the two security triples.  Should the server allow the LOOKUP?

   Third, there is locking state
   will remain for a problem as time subject to what lease expiration (see Section 8.5)
   and the new client must do (or can do),
   whenever the server returns NFS4ERR_WRONGSEC in response will need to a PUTFH
   operation. wait for such state to be removed, if
   it makes conflicting lock requests.

   Client identification is encapsulated in the following structure:

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

   The NFSv4.0 specification says first field, verifier, is a client incarnation verifier that is
   used to detect client should issue a
   SECINFO using the parent filehandle and the component name of reboots.  Only if the
   filehandle verifier is different
   from that PUTFH was issued with.  This may not be convenient the server had previously recorded for the client.

   This document resolves client (as
   identified by the above three issues in second field of the context structure, id) does the server
   start the process of
   NFSv4.1.

5.  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, canceling the
   reader should interpret it as applying to PUTROOTFH and PUTPUBFH in
   addition to PUTFH.

5.1.  PUTFH + LOOKUP client's leased state.

   The server implementation may decide whether to impose any
   restrictions on export security administration.  There are at least
   three approaches (Sc second field, id is a variable length string that uniquely
   defines the flavor set of the child export, Sp client so that subsequent instances of the parent),

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

     b)  Sc ^ Sp != {} (^ for intersection, {} same client
   bear the same id with a different verifier.

   There are several considerations for how the empty set)

     c)  free form

   To support b (when client chooses a flavor generates the id
   string:

   o  The string should be unique so that is multiple clients do not a member
      present the same string.  The consequences of
   Sp) two clients
      presenting the same string range from one client getting an error
      to one client having its leased state abruptly and c, PUTFH must NOT return NFS4ERR_WRONGSEC in case of security
   mismatch.  Instead, it unexpectedly
      canceled.

   o  The string should be returned from selected so the LOOKUP 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
   follows.

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

5.2.  PUTFH + LOOKUPP

   Since SECINFO only works its way down, a local file because this
      precludes the use of the implementation in an environment where
      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 local disk and all file access is implicit in this case).

5.3.  PUTFH + SECINFO

   This case from an NFS version
      4 server.

   o  The string should be treated specially.

   A security sensitive different for each server network address
      that the client should be allowed accesses, rather than common to choose a strong
   flavor when querying a all server to determine a file object's permitted
   security flavors. network
      addresses.  The security flavor chosen by reason is that it may not be possible for the
      client does not
   have to be included in tell if same server is listening on multiple network
      addresses.  If the flavor list client issues CREATE_CLIENTID with the same id
      string to each network address of such a server, the export.  Of course server will
      think it is the same client, and each successive CREATE_CLIENTID
      will cause the server has remove the client's previous leased state.
      Regardless, as described in Section 2.9.3.4.1, NFSv4.1 does allow
      clients to be configured trunk traffic for whatever flavor a single clientid to one or more of a
      server's networking addresses.

   o  The algorithm for generating the client selects,
   otherwise string should not assume that the request
      client's network address will fail at RPC authentication.

   In theory, there is no connection not change.  This includes changes
      between the security flavor used by
   SECINFO client incarnations and those supported by even changes while the export.  But client is
      still running in practice, its current incarnation.  This means that if the
      client may start looking for strong flavors from those supported by
   the export, followed by those in includes just the mandatory set.

5.4.  PUTFH + Anything Else

   PUTFH must return NFS4ERR_WRONGSEC client's and server's network address 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") id string, there is needed for a real risk, after the client
   to recover from NFS4ERR_WRONGSEC.

6.  NFSv4.1 Sessions

6.1.  Sessions Background

6.1.1.  Introduction to Sessions

   [[Comment.1: Noveck: Anyway, I think that trying to hack at gives up the
   existing text is basically hopeless.  I think you have to figure out
   what
      network address, that another client, using a new chapter (on sessions or basic protocol structure) should
   say and then write it, pulling in text from the existing chapter when
   appropriate.  Apart from similar algorithm
      for generating the issues you have found, that document was
   written with id string, would generate a whole different purpose in mind.  It discusses conflicting id
      string.

   Given the
   seesions "feature" and justifies it and talks about intergating it
   into v4.0, etc.  Instead, it is not above considerations, an example of a feature but well generated id
   string is one that includes:

   o  The server's network address.

   o  The client's network address.

   o  For a basic
   underpinning of v4.1 and we just explain what client and server need
   to do, and some why but user level NFS version 4 client, it is why this works not why we have made
   these design choices vs. others we might have made.  It's a totally
   different story and I don't think you can get there incrementally.]]
   NFSv4.1 adds extensions which allow NFSv4 should contain
      additional information to support sessions and
   endpoint management, and 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 support operation atop RDMA-capable RPC
   over transports be unique, 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. one or
      more of:

      *  The
   ability to operate over RDMA enables greatly enhanced performance.
   Operation over existing TCP client machine's serial number (for privacy reasons, it is enhanced as well.

   While discussed here with respect
         best to IETF-chartered transports, perform some one way function on the
   intent is NFSv4.1 will serial number).

      *  A MAC address (again, a one way function over other standards, such as
   Infiniband.  [IB] should be performed).

      *  The following are the major aspects timestamp of when the session feature:

   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 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 NFS version 4 software was first
         installed on the client and not the server,
      enhancing security and operation through firewalls.  [[Comment.2:
      XXX (though this is subject to the following true:]]In fact,
         previously mentioned caution about using information that is
         stored in a file, because the callback channel will file might only be
      enabled accessible
         over NFS version 4).

      *  A true random number.  However since this number ought to share be
         the same connection between client incarnations, this shares the same
         problem as that of the operations channel.

   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 specification, "RDMA Transport for ONC RPC" [RPCRDMA] is to
      be referenced for details using the timestamp of RPC RDMA support.

   o  Support for exactly-once semantics ("EOS") is enabled by the new
      session facilities, by providing to software
         installation.

   As a security measure, the server MUST NOT cancel a way to bound client's leased
   state if the
      size of principal established the duplicate request cache state for a single client, and to
      manage its persistent storage.

                                   Block Diagram

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

6.1.2.  Session Model

   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 given id string is to maintain
   not the server's state relative to same as the
   connection(s) belonging to a client instance.  This state is entirely
   independent of principal issuing the connection itself.  The session CREATE_CLIENTID.

   A server may compare an nfs_client_id4 in effect becomes
   the object representing a CREATE_CLIENTID with an active
   nfs_client_id4 established using SETCLIENTID using NFSv4 minor
   version 0, so that an NFSv4.1 client on a connection or set of
   connections.

   Clients may create multiple sessions for a single clientid, and may
   wish is not forced to do so delay until
   lease expiration for optimization of transport resources, buffers, or
   server behavior.  A session could be created locking state established by the earlier client to
   represent
   using minor version 0.

   Once 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, CREATE_CLIENTID has been done, 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 resulting clientid
   established as callback channels.

   The NFSv4.0 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 associated 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, all requests made on that
   session is created; These limits then provide maxima
   within implicitly identify that clientid, 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 turn designates
   the session bounds client specified using the
   requirements of long-form nfs_client_id4 structure.
   The shorthand client identifier (a clientid) is assigned by the duplicate request cache.  This can
   server and should be used chosen so that it will not conflict with a
   clientid previously assigned by the server.  This applies across
   server accurately determine any storage needs, enable it to maintain
   duplicate request cache persistence, and to provide reliable exactly-
   once semantics.

6.1.3.  Connection State restarts or reboots.

   In NFSv4.0, the combination event of a connected transport endpoint and server restart, a client will find out that its
   current clientid forms the basis of connection state.  While this has been
   made to be workable with certain limitations, there are difficulties
   in correct and robust implementation.  The NFSv4.0 protocol must
   provide is no longer valid when receives a server-initiated connection for the callback channel, and
   must carefully specify the persistence
   NFS4ERR_STALE_CLIENTID error.  The precise circumstances depend of client state at the server
   in
   the face characteristics of transport interruptions.  The server has only the
   client's transport address binding (the IP 4-tuple) to identify sessions involved, specifically whether
   the session is persistent (see Section 2.9.4.5).

   When a session is not persistent, the client RPC transaction stream and will need to use as create a lookup tag on
   new session.  When the
   duplicate request cache.  (A useful overview existing clientid is presented to a server as
   part of this creating a session and that clientid is in [RW96].)
   If not recognized, as
   would happen after a server reboot, the server listens on multiple addresses, and will reject the
   request with the error NFS4ERR_STALE_CLIENTID.  When this happens,
   the client connects
   to more than one, it must employ different clientid's on each,
   negating its ability to aggregate bandwidth obtain a new clientid by use of the CREATE_CLIENTID
   operation and redundancy.  In
   effect, each transport connection is used then use that clientid as the server's
   representation basis of client state.  But, transport connections are
   potentially fragile and transitory.

   In this specification, 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 basis of a
   reconnect, to provide an abstraction for the various
   new session
   properties, and then proceed to address any other necessary recovery for the duplicate request cache.  No
   transport-specific information is used in
   server reboot case (See Section 8.6.2).

   In the duplicate request cache
   implementation case of an NFSv4.1 server, nor in fact the RPC XID itself.
   The session identifier is unique within being persistent, the server's scope and may client will re-
   establish communication using the existing session after the reboot.
   This session will be
   subject to certain server policies such as being bounded in time.

6.1.4.  NFSv4 Channels, Sessions associated with a stale clientid and Connections

   There are two types of NFSv4 channels: the "operations" or "fore"
   channel used for ordinary requests from client to server, and
   will receive an indication of that fact in the
   "back" channel, used for callback requests from server to client.

   Different NFSv4 operations on these channels sr_status field
   returned by the SEQUENCE operation (see Section 2.9.2.1).  The client
   can lead then use the existing session to different
   resource needs.  For example, server callback do whatever operations (CB_RECALL) are specific, small messages which flow from server
   necessary 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 determine the RDMA peers (NFSv4 client and NFSv4 server) to
   post buffers for these various operations on a single connection.
   Commingling status of requests with responses outstanding 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 time
   of reboot, while avoiding issuing new requests, particularly any ordering of callback
   involving locking on that session.  Such requests
   versus response arrivals, without would fail with
   NFS4ERR_STALE_CLIENTID error or an NFS4ERR_STALE_STATEID error, if
   attempted.  In any other mechanisms, case, the client would be forced to allocate all buffers sized to the worst case.

   The callback requests are likely to be handled by create a different task
   context from that handling the responses.  Significant demultiplexing
   and thread management may be required if both are received new clientid using
   CREATE_CLIENTID, create a new session based on the
   same connection.  The client that clientid, and server have full control as
   proceed to
   whether a connection will service one channel or both channels.

   [[Comment.3: I think trunking remains an open issue has there is no
   way yet other necessary recovery for clients to determine whether two different server network
   addresses refer to the same server]].  Also, server reboot case.

   See the client may wish to
   perform trunking detailed descriptions of operations channel requests for performance
   reasons, or multipathing CREATE_CLIENTID (Section 16.35 and
   CREATE_SESSION (Section 16.36) for availability.  This a complete specification
   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) of these
   operations.

2.4.1.  Server Release of Clientid

   If the server determines that the client holds no associated state in
   order to draw upon
   for its clientid, the appropriate resources.  For example, reads and
   writes server may be assigned choose to specific, optimized connections, or sorted
   and separated by any or all of size, idempotency, etc.

   To address release the problems described above, clientid.  The
   server may make this specification allows
   multiple sessions to share a clientid, as well as choice for multiple
   connections to share a session.

   Single Connection model:

                            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 an inactive client so that resources away completely, by using
   specific sessions and
   are not even creating consumed by those intermittently active clients.  If the additional channels and
   connections.

6.1.5.  Reconnection, Trunking and Failover

   Reconnection
   client contacts the server after failure references stored state on this release, the server
   associated with lease recovery during must ensure
   the grace period.  The session
   provides a convenient handle for storing and managing information
   regarding client receives the client's previous state on a per- connection basis,
   e.g. to be used upon reconnection.  Reconnection appropriate error so that it will use the
   CREATE_CLIENTID/CREATE_SESSION sequence to establish a previously
   existing session, and its stored resources, are covered in
   Section 6.3.

   One important aspect of reconnection is new identity.
   It should be clear 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 server must be very hesitant to operate over release a wide variety of transports and has
   proven
   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 highly successful approach.  The session, however,
   introduces an abstraction which is, in server would not release a way, "between" RPC and
   NFSv4.1.  It is important clientid unless
   there had been no activity from that client for many minutes.  Note
   that "associated state" includes sessions.  As long as there are
   sessions, the session abstraction server MUST not have
   ramifications within the RPC layer.

   One such issue arises within release the reconnection logic of RPC.
   Previously, an explicit session binding operation, which established
   session context clientid.  See
   Section 2.9.8.1.4 for each new connection, was explored.  This however
   required discussion on releasing inactive sessions.

   Note that if the session binding also be performed during reconnect,
   which in turn required an RPC request.  This additional request
   requires new RPC semantics, both id string in implementation and the fact that a new CREATE_CLIENTID request is inserted into properly
   constructed, and if the RPC stream.  Also, client takes care to use the binding same principal
   for each successive use of CREATE_CLIENTID, then, barring an active
   denial of service attack, NFS4ERR_CLID_INUSE should never be
   returned.

   However, client bugs, server bugs, or perhaps a connection to a session required the upper layer to become "aware" deliberate change of connections, something
   the RPC layer abstraction architecturally
   abstracts away.  Therefore principal owner of the session binding is not handled in
   connection scope but instead explicitly carried in each request.

   For Reliability Availability and Serviceability (RAS) issues such id string (such as
   bandwidth aggregation the case of a client
   that changes security flavors, and multipathing, clients frequently seek to
   make multiple connections through multiple logical or physical
   channels.  The session under the new flavor, there is a convenient point no
   mapping to aggregate and manage
   these resources.

6.1.6.  Server Duplicate Request Cache

   RPC-based the previous owner) will in rare cases result in
   NFS4ERR_CLID_INUSE.

   In that event, when the server duplicate request caches, while not gets a part of an NFS
   protocol, have become CREATE_CLIENTID for a de-facto requirement of any NFS
   implementation.  First described in [CJ89], client id
   that currently has no state, or it has state, but the duplicate request
   cache was initially found to reduce work at lease has
   expired, rather than returning NFS4ERR_CLID_INUSE, the server by avoiding
   duplicate processing for retransmitted requests.  A second, MUST
   allow the CREATE_CLIENTID, and in confirm the long run more important benefit, was improved correctness, as new clientid if followed
   by the
   cache avoided certain destructive non-idempotent requests from being
   reinvoked.

   However, RPC-based caches do not provide correctness guarantees; they
   cannot be managed in appropriate CREATE_SESSION.

2.5.  Security Service Negotiation

   With the NFS version 4 server potentially offering multiple security
   mechanisms, the client needs a reliable, persistent fashion.  The reason is
   understandable - their storage requirement method to determine or negotiate which
   mechanism is unbounded due to be used for its communication with the
   lack of any such bound in the server.  The
   NFS protocol, and they server may have multiple points within its file system namespace
   that are dependent on
   transport addresses available for request matching.

   The session model, the presence of maximum request count limits and
   negotiated maximum sizes allows the size use by NFS clients.  These points can be
   considered security policy boundaries, and duration of the cache in some NFS
   implementations are tied to NFS export points.  In turn the NFS
   server may be bounded, configured such that each of these security policy
   boundaries may have different or multiple security mechanisms in use.

   The security negotiation between client and coupled server must be done with
   a long-lived session identifier, enables
   its persistent storage on a per-session basis.

   This provides secure channel to eliminate the possibility of a single unified mechanism which provides third party
   intercepting 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 negotiation sequence and forcing the client and
   server to provide choose a more reliable cache lower level of duplicate non- idempotent
   requests security than that of the traditional cache described required or desired.
   See section Section 19 for further discussion.

2.5.1.  NFSv4 Security Tuples

   An NFS server can assign one or more "security tuples" to each
   security policy boundary in [CJ89]..."
   RFC3530 [2]

   The maximum request count limit is the count of active operations,
   which bounds the number its namespace.  Each security tuple
   consists of entries in the cache.  Constraining a security flavor (see Section 2.2.1.1), and if the
   size
   flavor is RPCSEC_GSS, a GSS-API mechanism OID, a GSS-API quality of
   protection, and an RPCSEC_GSS service.

2.5.2.  SECINFO and SECINFO_NO_NAME

   The SECINFO and SECINFO_NO_NAME operations additionally serves to limit allow the required storage client to
   determine, on a per filehandle basis, what security tuple is to be
   used for server access.  In general, the product of the current maximum request count and the maximum
   response size.  This storage requirement enables server- side
   efficiencies.

   Session negotiation allows client will not have to use
   either operation except during initial communication with the server to maintain other state.  An
   NFSv4.1
   or when the client invoking crosses security policy boundaries at the session destroy operation will cause server.
   It is possible that the
   server to close server's policies change during the session, allowing client's
   interaction therefore forcing the server client to deallocate cache
   entries.  Clients can potentially specify negotiate a new security
   tuple.

2.5.3.  Security Error

   Based on the assumption 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, each NFS version 4 client and more efficient sizing server
   must support a minimum set of buffers security (i.e., LIPKEY, SPKM-3, and
   response caches.

   Similarly, it is important for
   Kerberos-V5 all under RPCSEC_GSS), the NFS client will initiate file
   access 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, with one which must provide transactional integrity
   guarantees.  When clients request that of the semantics be enabled for a
   given session, minimal security tuples.  During
   communication with the session reply must inform server, the client if may receive an NFS error of
   NFS4ERR_WRONGSEC.  This error allows the mode server to notify the client
   that the security tuple currently being used is in fact enabled.  In this way contravenes the
   server's security policy.  The client can confidently proceed
   with operations without having to implement consistency facilities of
   its own.

6.2.  Session Initialization and Transfer Models

   Session initialization issues, is then responsible for
   determining (see Section 2.5.3.1) what security tuples are available
   at the server and data transfer models relevant to
   both TCP choose one which is appropriate for the client.

2.5.3.1.  Using NFS4ERR_WRONGSEC, SECINFO, and RDMA are discussed SECINFO_NO_NAME

   This section explains of the mechanics of NFSv4.1 security
   negotiation.  Unless noted otherwise, for any mention of PUTFH in
   this section.

6.2.1.  Session Negotiation

   The following parameters are exchanged between client and server at
   session creation time.  Their values allow section, the server reader should interpret it as applying to properly
   size resources allocated PUTROOTFH
   and PUTPUBFH in order addition to service the client's requests,
   and PUTFH.

2.5.3.1.1.  PUTFH + LOOKUP (or OPEN by Name)

   This situation also applies to provide the server with a way to communicate limits to put filehandle operation followed by
   an OPEN operation that specifies a component name.

   In this situation, the client for proper is potentially crossing a security
   policy boundary, and optimal operation.  They are exchanged prior to
   all session-related activity, over any transport type.  Discussion the set of
   their use is found in their descriptions as well as throughout this
   section.

   Maximum Requests

      The client's desired maximum number security tuples the parent directory
   supports differ from those of concurrent requests is
      passed, in order to allow the server to size its reply cache
      storage. child.  The server implementation
   may modify the client's requested limit
      downward (or upward) decide whether to match its local impose any restrictions on security policy and/or resources.
      Over RDMA-capable RPC transports,
   administration.  There are at least three approaches
   (sec_policy_child is the per-request management tuple set of
      low-level transport message credits the child export,
   sec_policy_parent is handled within that of the RPC
      layer.  [RPCRDMA]

   Maximum Request/Response Sizes

      The maximum request and response sizes are exchanged in order to
      permit allocation parent).

     a)  sec_policy_child <= sec_policy_parent (<= for subset).  This
      means that the set of appropriately sized buffers and request cache
      entries.  The size must allow security tuples specified on the security
      policy of a child directory is always a subset of that of its
      parent directory.

     b)  sec_policy_child ^ sec_policy_parent != {} (^ for intersection,
      {} for certain protocol minima,
      allowing the receipt empty set).  This means that the security tuples
      specified on the security policy of a child directory always has a
      non empty intersection with that of maximally sized operations (e.g.  RENAME
      requests which contains two name strings).  Note the maximum
      request/response sizes cover parent.

     c)  sec_policy_child ^ sec_policy_parent == {}.  This means that
      the entire request/response message
      and set of tuples specified on the security policy of a child
      directory may not simply intersect with that of the data payload as traditional NFS maximum read or
      write size.  Also note parent.  In other
      words, there are no restrictions on how the server implementation system administrator
      may not, set.

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

   Since the above guideline does not, require not contradict approach (a), it should
   be followed in general.  Even if approach (a) is implemented, it is
   possible for the reply cache entries security tuple used to be sized as
      large as acceptable for the maximum response.  The server may reduce target
   of LOOKUP but not for the client's
      requested sizes.

   Inline Padding/Alignment filehandles used in PUTFH.  The server can inform PUTFH could
   really be a PUTROOTFH or PUTPUBFH, where 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 does not know the server
   security tuples for both TCP and inline RDMA transfers.  For RDMA, the client
      informs root or public filehandle.  Or the security
   policy for the filehandle used by PUTFH could have changed since the
   time the filehandle was obtained.

   Therefore, an NFSv4.1 server MUST NOT return NFS4ERR_WRONGSEC in each
   response to PUTFH, PUTROOTFH, or PUTPUBFH if the operation when padding has been
      applied.  [RPCRDMA]
   Transport Attributes

      A placeholder for transport-specific attributes is provided, with
   immediately followed by 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 LOOKUP or an OPEN by local means which component name.

2.5.3.1.2.  PUTFH + LOOKUPP

   Since SECINFO only works its way down, there is currently
      outside the scope of no way LOOKUPP can
   return NFS4ERR_WRONGSEC without SECINFO_NO_NAME.  SECINFO_NO_NAME
   solves this draft, however one attribute is provided issue because via style "parent", it works in the RDMA case:

   RDMA Read Resources

      RDMA implementations must explicitly provision resources to
      support RDMA Read requests from connected peers.  These values
   opposite direction as SECINFO.  As with Section 2.5.3.1.1, PUTFH must be explicitly specified, to provide adequate resources for
      matching
   not return NFS4ERR_WRONGSEC whenever it is followed by LOOKUPP.  If
   the peer's expected needs and server does not support SECINFO_NO_NAME, the connection's delay-
      bandwidth parameters.  The client provides its chosen value client's only
   recourse is to issue the PUTFH, LOOKUPP, GETFH sequence of operations
   with every security tuple it supports.

   Regardless whether SECINFO_NO_NAME is supported, an NFSv4.1 server
   MUST NOT return NFS4ERR_WRONGSEC in response to PUTFH, PUTROOTFH, or
   PUTPUBFH if the initial session creation, the value must be provided
      in each operation is immediately followed by a LOOKUPP.

2.5.3.1.3.  PUTFH + SECINFO or PUTFH + SECINFO_NO_NAME

   A security sensitive client RDMA endpoint.  The values are asymmetric and
      should be set is allowed to zero at the choose a strong security
   tuple when querying a server in order to conserve RDMA
      resources, since clients do not issue RDMA Read operations in this
      specification. determine a file object's permitted
   security tuples.  The result is communicated in the session
      response, to permit matching of values across security tuple chosen by the connection.  The
      value may client does not
   have to be changed included in the duration tuple list of the session, although
      a new value may be requested as part of a new session.

6.2.2.  RDMA Requirements

   A complete discussion security policy of the operation of RPC-based protocols atop
   RDMA transports is
   either parent directory indicated in [RPCRDMA].  Where RDMA is considered, this
   specification assumes PUTFH, or the use of such a layering; it addresses only child file object
   indicated in SECINFO (or any parent directory indicated in
   SECINFO_NO_NAME).  Of course the upper layer issues relevant server has to making best use of RPC/RDMA.

   A connection oriented (reliable sequenced) RDMA transport will be
   required.  There are several reasons configured for this.  First, this model
   most closely reflects
   whatever security tuple the general NFSv4 requirement of long-lived and
   congestion-controlled transports.  Second, to operate correctly over
   either client selects, otherwise the request
   will fail at RPC layer with an unreliable or unsequenced RDMA transport, appropriate authentication error.

   In theory, there is no connection between the security flavor used by
   SECINFO or both, would
   require significant complexity SECINFO_NO_NAME and those supported by the security
   policy.  But in practice, the implementation and protocol not
   appropriate client may start looking for a strict minor version.  For example, retransmission
   on connected endpoints is explicitly disallowed strong
   flavors from those supported by the security policy, followed by
   those in the current NFSv4
   draft; mandatory set.

   The NFSv4.1 server MUST NOT return NFS4ERR_WRONGSEC to PUTFH whenever
   it would again be required with these alternate transport
   characteristics.  Third, this specification assumes is immediately followed by SECINFO or SECINFO_NO_NAME.  The
   NFSv4.1 server MUST NOT return NFS4ERR_WRONGSEC from SECINFO or
   SECINFO_NO_NAME.

2.5.3.1.4.  PUTFH + PUTFH

   This is a specific RDMA
   ordering semantic, which presents nonsensical situation, because the same set of ordering first put filehandle
   operation is wasted.  The NFSv4.1 server MAY return NFS4ERR_WRONGSEC
   to the first PUTFH, or it MAY NOT.  If it does not, it then processes
   the subsequent PUTFH and
   reliability issues any operation that follows it according to
   the RDMA layer over such transports. rules listed in Section 2.5.3.1.

2.5.3.1.5.  PUTFH + Nothing

   This too is nonsensical because the PUTFH is wasted.  The RDMA implementation provides for making connections NFSv4.1
   server MAY or MAY NOT return NFS4ERR_WRONGSEC.

2.5.3.1.6.  PUTFH + Anything Else

   "Anything Else" includes OPEN by filehandle.

   The security policy enforcement applies to other
   RDMA-capable peers.  In the filehandle specified
   in PUTFH.  Therefore PUTFH must return NFS4ERR_WRONGSEC in case of
   security tuple on the part of the current proposals before mismatch.  This avoids the
   RDDP working group, these RDMA connections are preceded by a
   "streaming" phase, where ordinary TCP (or NFS) traffic might flow.
   However, this
   complexity adding NFS4ERR_WRONGSEC as an allowable error to every
   other operation.

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

   The NFSv4.1 server, MUST not assumed here and sizes and return NFS4ERR_WRONGSEC to any operation
   other parameters are
   explicitly exchanged upon a session entering RDMA mode.

6.2.3.  RDMA Connection Resources

   On transport endpoints which support automatic RDMA mode, than LOOKUP, LOOKUPP, and OPEN (by component name).

2.6.  Minor Versioning

   To address the requirement of an NFS protocol that is,
   endpoints which are created in can evolve as the RDMA-enabled state, a single,
   preposted buffer must initially be provided by both peers, and
   need arises, the
   client session negotiation 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 be follow the first exchange.

   On transport endpoints supporting dynamic negotiation, IETF process and be
   documented in a more
   sophisticated negotiation standards track RFC.  Therefore, each minor version
   number will correspond to an RFC.  Minor version zero of the NFS
   version 4 protocol is possible, but represented by [2], and minor version one is not discussed in the
   current draft.

   RDMA imposes several requirements on upper layer consumers.
   Registration of memory
   represented by this document [[Comment.2: change "document" to "RFC"
   when we publish]] .  The COMPOUND and CB_COMPOUND procedures support
   the need to post buffers encoding of a specific
   size and number the minor version being requested by the client.

   The following items represent the basic rules for receive operations are a primary consideration.

   Registration the development of memory can be
   minor versions.  Note that 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 future minor version may decide to hardware interfaces and even
   modify or add to RDMA connection
   endpoints, therefore negotiation the following rules as part of their limits is desirable to
   manage resources effectively.

   Following the basic registration, these buffers must be posted by minor version
   definition.

   1.   Procedures are not added or deleted

        To maintain the general RPC layer model, NFS version 4 minor versions
        will not add to handle receives.  These buffers remain in use by or delete procedures from the
   RPC/NFSv4 implementation; NFS program.

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

        The addition of them must be known operations 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 COMPOUND and CB_COMPOUND
        procedures does not affect the server to manage resource
   allocation to each client rather than RPC model.

        *  Minor versions may append attributes to each transport connection
   itself. GETATTR4args,
           bitmap4, and GETATTR4res.

           This enables considerable flexibility in allows for the administration expansion of transport endpoints.

6.2.4.  TCP and RDMA Inline Transfer Model

   The basic transfer the attribute model for both TCP and RDMA is referred to as
   "inline".  For TCP, this is allow
           for future growth or adaptation.

        *  Minor version X must append any new attributes after the only transfer model supported, since
   TCP carries both last
           documented attribute.

           Since attribute results are specified as an opaque array of
           per-attribute XDR encoded results, the RPC header and data together complexity of adding
           new attributes in the data stream.

   For RDMA, midst of the RDMA Send transfer model is used for all NFS requests
   and replies, but data is optionally carried by RDMA Writes current definitions will
           be too burdensome.

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

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

        This rule does not available.

        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 preclude the following adaptations in a minor
        version.

        *  adding bits to flag fields such as new attributes to
           GETATTR's bitmap4 data       :
             Send :   ------------------------------>   : untagged
                  :                                     :  buffer
                  :            Write response           :
         untagged :   <------------------------------   : Send
          buffer  :                                     :

   Responses must be sent type

        *  adding bits to the client on the same connection that the
   request was sent.  It is important existing attributes like ACLs that have flag
           words

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

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

   5.   Minor versions may not assume
   any specific client implementation, in delete operations.

        This prevents the potential reuse of a particular whether connections
   within operation
        "slot" in a session share any state at the client.  This 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 also
   important
        equivalent to preserve ordering of RDMA operations, and especially
   RMDA consistency.  Additionally, obsoleting an operation.  For the client, it ensures means
        that the RPC RDMA layer
   makes no requirement of operation should not be sent to the RDMA provider server.  For the
        server, an NFS error can be returned as opposed to open its memory
   registration handles (Steering Tags) beyond "dropping"
        the scope of a single
   RDMA connection. request as an XDR decode error.  This is approach allows for
        the obsolescence of an important security consideration.

   Two operation while maintaining its structure
        so that a future minor version can reintroduce the operation.

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

        2.  Minor versions may declare flag bits or enumeration values must be known
            as mandatory to each peer prior NOT implement.

   9.   Minor versions may downgrade features from mandatory to issuing Sends: the
   maximum number of sends which
        recommended, or recommended to optional.

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

   11.  A client and their maximum size.
   These values are referred to, respectively, server that supports minor version X should support
        minor versions 0 (zero) through X-1 as well.

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

        This rule allows for the message credits introduction of new functionality and
        forces the maximum message size.  While the message credits might vary
   dynamically over the duration use of implementation experience before designating a
        feature as mandatory.  On the session, the maximum message
   size does not.  The server must commit to preserving this number other hand, some classes of
   duplicate request cache entires,
        features are infrastructural and preparing a number of receive
   buffers equal have broad effects.  Allowing
        such features to or greater than its currently advertised credit
   value, each not be mandatory complicates implementation of
        the advertised size.  These ensure that transport
   resources are allocated sufficient to receive the full advertised
   limits.

   Note that the server must post the maximum number of session requests
   to each client operations channel.  The minor version.

   13.  A client is not required MUST NOT attempt to
   spread its requests in any particular fashion across connections
   within a session.  If the client wishes, it may create multiple
   sessions, each with use a single stateid, filehandle, or small number of operations channels
   to provide
        similar returned object from the server COMPOUND procedure with this resource advantage.  Or, over RDMA
   the server may employ a "shared receive queue".  The server can minor
        version X for another COMPOUND procedure with minor version Y,
        where X != Y.

2.7.  Non-RPC-based Security Services

   As described in Section 2.2.1.1.1.1, NFSv4 relies on RPC for
   identification, authentication, integrity, and privacy.  NFSv4 itself
   provides additional security services as described in
   any case protect its resources by restricting the client's request
   credits.

   While tempting to consider, it is not possible next
   several subsections.

2.7.1.  Authorization

   Authorization to use the TCP window
   as access a file object via an RDMA NFSv4 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, is
   ultimately determined by the TCP window NFSv4 server.  A client can hold predetermine
   its access to a widely variable number of
   them, file object via the OPEN (Section 16.16) and since it cannot be reduced without actually receiving data, the receiver cannot limit
   ACCESS (Section 16.1) operations.

   Principals with appropriate access rights can modify the sender.  Third, any middlebox
   interposing
   authorization on a file object via the connection would wreck any possible scheme.
   [MIDTAX] In this specification, 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 SETATTR (Section 16.30)
   operation.  Four attributes that affect access rights are: mode,
   owner, owner_group, and sizes are still employed acl.  See Section 5.

2.7.2.  Auditing

   NFSv4 provides auditing on a per file object basis, via the ACL
   attribute as described in NFSv4.1, but instead of being
   required for correctness, they provide Section 6.  It is outside the basis for efficient server
   implementation of the duplicate request cache.  The limits are chosen
   based upon the expected needs and capabilities scope of this
   specification to specify audit log formats or management policies.

2.7.3.  Intrusion Detection

   NFSv4 provides alarm control on a per file object basis, via the client and
   server, and are ACL
   attribute as described in fact arbitrary.  Sizes Section 6.  Alarms may be specified by the
   client serve as zero (requesting the server's preferred or optimal value),
   and request limits may be chosen in proportion to basis
   for instrusion detection.  It is outside the client's
   capabilities.  For example, a limit scope of 1000 allows 1000 requests to
   be in progress, which may generally be far more than adequate this
   specification to keep
   local networks and servers fully utilized.

   Both client and server have independent sizes specify heuristics for detecting intrusion via
   alarms.

2.8.  Transport Layers

2.8.1.  Required and buffering, but Recommended Properties of Transports

   NFSv4 works 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 and non-RDMA_based transports with the corresponding reply, since responses from
   following attributes:

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

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

   Where an operations channel is
   also NFS version 4 implementation supports operation over the IP
   network protocol, any transport used for callbacks, between NFS and IP MUST be among
   the client must account for callback
   requests by posting additional buffers.  Note IETF-approved congestion control transport protocols.  At the
   time this document was written, the only two transports that implementation-
   specific facilities such as a shared receive queue may also allow
   optimization of these allocations.

   When had the
   above attributes were TCP and SCTP.  To enhance the possibilities for
   interoperability, an NFS version 4 implementation MUST support
   operation over the TCP transport protocol.

   Even if NFS version 4 is used over a session non-IP network protocol, it is created,
   RECOMMENDED that the client requests a preferred buffer
   size, transport support congestion control.

   Note that it is permissible for connectionless transports to be used
   under NFSv4.1, however reliable and the server provides its answer.  The server posts all
   buffers in-order delivery of at least this size.  The client must comply by not sending
   requests greater than this size.  It data is recommended
   still required.  NFSv4.1 assumes that a client transport address and
   server
   implementations do all they can transport address used to accommodate send data over a useful range of
   possible client requests.  There is transport together
   constitute a provision in [RPCRDMA] to allow connection, even if the sending of client requests which exceed underlying transport eschews the server's receive
   buffer size, but it requires
   concept of a connection.

2.8.2.  Client and Server Transport Behavior

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

   1.  This will prevent the client's
   request as a "read chunk" weakening of the transport's congestion
       control mechanisms via RDMA Read. short lived connections.

   2.  This introduces at least
   one additional network roundtrip, plus other overhead such as
   registering memory will improve performance for RDMA Read at the client WAN environment by
       eliminating the need for connection setup handshakes.

   3.  The NFSv4.1 callback model differs from NFSv4.0, and additional RDMA
   operations at requires the server,
       client and is server to be avoided.

   An issue therefore arises when considering maintain a client-created channel (see
       Section 2.9.3.4for the NFSv4 COMPOUND
   procedures.  Since an arbitrary number (total size) of operations can
   be specified in server to use.

   In order to reduce congestion, if a single COMPOUND procedure, its size connection-oriented transport is effectively
   unbounded.  This cannot be supported by RDMA Sends,
   used, and therefore
   this size negotiation places a restriction on the construction and
   maximum size of both COMPOUND requests and responses.  If request is not the NULL procedure,

   o  A client (or the server, if issuing a COMPOUND
   results in callback), MUST NOT retry a reply at the server that is larger than can be sent in
   an RDMA Send to
      request unless the client, then connection the COMPOUND must terminate and request was issued over was
      disconnected before the
   operation which causes reply was received.

   o  A server (or the overflow will provide client, if receiving a TOOSMALL error
   status result.

6.2.5.  RDMA Direct Transfer Model

   Placement of data by explicitly tagged RDMA operations is referred to
   as "direct" transfer.  This method is typically used where callback), MUST NOT
      silently drop a request, even if the data
   payload request is relatively large, that is, when RDMA setup has been
   performed prior to a retry.  (The
      silent drop behavior of RPCSEC_GSS [5] does not apply because this
      behavior happens at the operation, or when any overhead for setting up
   and performing RPCSEC_GSS layer, a lower layer in the transfer is regained by avoiding
      request processing).  Instead, the overhead of
   processing server SHOULD return an ordinary receive.

   The client advertises
      appropriate error (see Section 2.9.4.1) or it MAY disconnect the
      connection.

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

   o  RDMA transports use "credits" to the client employ "XDR Decoding with Write Chunks".  There
   are several reasons for this.

   First, it allows for enforce flow control, where 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
      credit is not
   required a right to expose copies of local file buffers for individual
   clients, or a peer to lock or copy them for each client access.

   Second, client credits based on fixed-size transmit a message.  If one peer
      were to retransmit a request buffers are easily
   managed on the server, but for (or reply), it would consume an
      additional credit.  If the server additional management of
   buffers for client retransmitted a reply, it would
      certainly result in an RDMA Reads is not well-bounded.  For example, connection loss, since the client may not perform these RDMA Read operations in a timely
   fashion, therefore the server
      would have to protect itself against
   denial-of-service on these resources.

   Third, it reduces network traffic, since typically only post a single receive buffer exposure outside for each
      request.  If the
   scope and duration of client retransmitted a single request/response exchange necessitates
   additional memory management exchanges.

   There are costs associated with this decision.  Primary among them is request, the need for additional
      credit consumed on the server might lead to employ RDMA Read connection
      failure unless the client accounted for operations such as
   large WRITE.  The it and decreased its
      available credit, leading to wasted resources.

   o  RDMA Read operation is credits present a two-way exchange at the
   RDMA layer, which incurs additional overhead relative new issue to RDMA Write.
   Additionally, RDMA Read requires resources at the data source (the
   client reply cache in this specification) to maintain state and to generate
   replies.  These costs are overcome through use of pipelining with
   credits, with sufficient RDMA Read resources negotiated at NFSv4.1.
      The reply cache may be used when a connection within a session
   initiation, and appropriate use of RDMA for writes by is
      lost, such as after the client -
   for example only for transfers above reconnects.  Credit information is
      a certain size.

   A description dynamic property of which NFSv4 operation results are eligible for data
   transfer via the RDMA Write is in [NFSDDP].  There are only two such
   operations: READ connection, and READLINK.  When XDR encoding these requests on
   an RDMA transport, the NFSv4.1 client stale values must insert the appropriate
   xdr_write_list entries to indicate to
      not be replayed from the server whether cache.  This implies that the results
   should reply cache
      contents must not be transferred via RDMA or inline with a Send.  As described
   in [NFSDDP], a zero-length write chunk is blindly used to indicate an inline
   result.  In this way, it is unnecessary to create new operations for
   RDMA-mode versions of READ when replies are issued from it,
      and READLINK.

   Another tool credit information appropriate to avoid creation of new, RDMA-mode operations is the
   Reply Chunk [RPCRDMA], which is used channel must be
      refreshed by the RPC in RDMA mode layer.

   In addition, the sender of an NFSv4.1 request is not allowed to return
   large replies via RDMA as if they were inline.  Reply chunks are used stop
   waiting for operations such a reply, as READDIR, which returns large amounts of
   information, but described in many small XDR segments.  Reply chunks are
   offered by the client Section 2.9.4.2.

2.8.3.  Ports

   Historically, NFS version 2 and version 3 servers have resided on
   port 2049.  The registered port 2049 RFC3232 [21] for the 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 NFS
   protocol should be the session was created (for
   example extraordinarily large RENAMEs), default configuration.  NFSv4 clients SHOULD
   NOT use the underlying RPC layer may
   support the use of "Message as an RDMA Read Chunk" and "RDMA Write of
   Long Replies" binding protocols as described in [RPCRDMA].  No additional support is
   required in RFC1833 [22].

2.9.  Session

2.9.1.  Motivation and Overview

   Previous versions and minor versions of NFS have suffered from the NFSv4.1 client
   following:

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

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

   o  Limited trunking over multiple network paths.

   o  Requiring machine credentials for fully secure operation.

   Through the introduction of a
   significant purpose: RDMA operations are not complete, that is,
   guaranteed consistent, at session, NFSv4.1 addresses the data sink until followed above
   shortfalls with practical solutions:

   o  EOS is enabled by a
   successful Send completion (i.e. a receive).  These events provide reply cache with a
   natural opportunity for the initiator (client) bounded size, making it
      feasible to keep on persistent storage and enable EOS through
      server failure and later
   disable RDMA access to the memory which is the target recovery.  One reason that previous revisions
      of each
   operation, NFS did not support EOS was because some EOS approaches often
      limited parallelism.  As will be explained in order to provide for consistent Section 2.9.4),
      NFSv4.1 supports both EOS and secure operation. unlimited parallelism.

   o  The RDMAP Send with Invalidate operation may be worth employing in
   this respect, as it relieves the NFSv4.1 client of certain overhead in this
   case.

   A "onetime" boolean advisory to each RDMA region might become a hint provides creates transport connections and
      gives them to the server that for sending callbacks, thus solving the
      firewall issue (Section 16.34).  Races between responses from
      client will use the three-tuple for only one
   NFSv4 operation.  For a transport such as iWARP, requests, and callbacks caused by the server can
   assist requests are detected
      via the session's sequencing properties which are a byproduct of
      EOS (Section 2.9.4.3).

   o  The NFSv4.1 client in invalidating can add an arbitrary number of connections to
      the three-tuple by performing a
   Send with Solicited Event session, and Invalidate. thus provide trunking (Section 2.9.3.4.1).

   o  The NFSv4.1 session produces a session key independent of client
      and server may ignore this
   hint, in machine credentials which case the client must perform can be used to compute a local invalidate after
   receiving the indication from
      digest for protecting key session management operations
      Section 2.9.6.3).

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

   A session is
   complete.  This may be considered in a future version of this draft
   and [NFSDDP].

   In dynamically created, long-lived server object created
   by a trusted environment, it may be desirable for client, used over time from one or more transport connections.
   Its function is to maintain the client server's state relative to
   persistently enable RDMA access by the server.  Such
   connection(s) belonging to a model client instance.  This state is
   desirable for the highest level entirely
   independent of efficiency and lowest overhead.

        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  :                                     :

6.3.  Connection Models

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

   After a successful connection, state exists
   whether the first request proceeds, connection exists or not (though locks, delegations, etc.
   and generally expire in the
   case extended absence of a new client association, to initial session creation, and
   then optionally to an open connection).
   The session callback channel binding, prior to regular
   operation.

   Commonly, each new client "mount" will be in effect becomes the action which drives
   creation object representing an active
   client on a set of zero or more connections.

2.9.2.  NFSv4 Integration

   Sessions are part of NFSv4.1 and not NFSv4.0.  Normally, a major
   infrastructure change like sessions would require a new session.  However there are any major version
   number of other
   approaches.  Clients may choose to share an RPC program like NFS.  However, because NFSv4
   encapsulates its functionality in a single connection procedure, COMPOUND, and
   session among all their mount points.  Or, clients may
   because COMPOUND can 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 an arbitrary number of the mount point.  For example, operations,
   sessions are almost trivially added.  COMPOUND includes a readonly mount can sharply reduce
   its write buffering minor
   version number field, and also makes no requirement for NFSv4.1 this minor version is set to 1.
   When the NFSv4 server to
   support reliable duplicate request caching.

   Similarly, the client can choose among several strategies for
   clientid usage.  Sessions can share processes a single clientid, or create new
   clientids as COMPOUND with the client deems appropriate.  For kernel-based clients
   which service multiple authenticated users, minor version set
   to 1, it expects a single clientid shared
   across all mount points different set of operations than it does for
   NFSv4.0.  One operation it expects is generally the most appropriate SEQUENCE operation, which
   is required for every COMPOUND that operates over an established
   session.

2.9.2.1.  SEQUENCE and
   flexible approach.  For example, all CB_SEQUENCE

   In NFSv4.1, when the client's file operations may
   wish to share locking state and SEQUENCE operation is present, it is always the local client kernel takes
   first operation in the
   responsibility for arbitrating access locally.  For clients choosing COMPOUND procedure.  The primary purpose of
   SEQUENCE is to support carry the session identifier.  The session identifier
   associates all other authentication models, perhaps example userspace
   implementations, operations in the COMPOUND procedure with a new clientid is indicated.  Through use of session
   create options, both models are supported at
   particular session.  SEQUENCE also contains required information for
   maintaining EOS (see Section 2.9.4).  Session-enabled NFSv4.1
   COMPOUND requests thus have the client's choice.

   Since form:

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

       and the session reply's structure is:

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

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

2.9.2.2.  Clientid and each client is uniquely identified, Session Association

   Sessions are subordinate to the server may be
   specifically instructed clientid (Section 2.4).  Each
   clientid can have zero or more active sessions.  A clientid, and a
   session bound to discard unneeded persistent state.  For
   this reason, it is possible that are required to do anything useful in NFSv4.1.
   Each time a server will retain any previous session is used, the state indefinitely, and place its destruction under administrative
   control.  Or, a server may choose leased to retain state for some
   configurable period, provided that the period meets other NFSv4
   requirements it associated
   clientid is automatically renewed.

   State such as lease reclamation time, etc.  However, since
   discarding this state at share reservations, locks, delegations, and layouts
   (Section 1.5.4) is tied to the server may affect clientid, not the correctness sessions of the
   server
   clientid.  Successive state changing operations from a given state
   owner can go over different sessions, as seen by long each session is
   associated with the same clientid.  Callbacks can arrive over a
   different session than the session that sent the operation the
   acquired the client across network partitioning, such
   discarding of state should be done only in that the callback is for.  For example, if session
   A is used to acquire a delegation, a conservative manner.

   Each client request to recall the server carries a new SEQUENCE operation
   within each COMPOUND, which provides the delegation
   can arrive over session context.  This B.

2.9.3.  Channels

   Each session context then governs has one or two channels: the request control, duplicate request
   caching, "operation" or "fore"
   channel used for ordinary requests from client to server, and other persistent parameters managed by the
   "back" channel, used for callback requests from server to client.
   The session allocates resources for a
   session.

6.3.1.  TCP Connection Model each channel, including separate
   reply caches (see Section 2.9.4.1 These resources are for the most
   part specified at time the session is created.

2.9.3.1.  Operation Channel

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

2.9.3.2.  Backchannel

   The backchannel carries CB_COMPOUND requests and responses.  Whether
   there is a backchannel or not is a schematic diagram decision of the client; NFSv4.1 protocol
   exchanges leading up to normal operation on a TCP stream.

               Client                                Server
          TCPmode :   Create Clientid(nfs_client_id4)   : TCPmode
                  :   ------------------------------>   :
                  :                                     :
                  :     Clientid reply(clientid, ...)   :
                  :   <------------------------------   :
                  :                                     :
                  :   Create Session(clientid, size S,  :
                  :      maxreq N, STREAM, ...)         :
                  :   ------------------------------>   :
                  :                                     :
                  :
   servers MUST support backchannels.

2.9.3.3.  Session reply(sessionid, size S', :
                  :      maxreq N')                     :
                  :   <------------------------------   :
                  :                                     :
                  :          <normal operation>         :
                  :   ------------------------------>   :
                  :   <------------------------------   :
                  :                  :                  :

   No net additional exchange and Channel Association

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

2.9.3.4.  Connection and Channel Association

   Each channel is associated with zero or more transport connections.
   A connection can be bound to one channel or both channels of a
   session; the initial negotiation.  In
   the NFSv4.1 exchange, client and server negotiate whether a connection will
   carry traffic for one channel or both channel via the CREATE_CLIENTID replaces SETCLIENTID
   (eliding the callback "clientaddr4" addressing) and
   CREATE_SESSION
   subsumes (Section 16.36) and the function of SETCLIENTID_CONFIRM, as described elsewhere
   in this specification.  Callback channel binding BIND_CONN_TO_SESSION
   (Section 16.34) operations.  When a session is optional, as in
   NFSv4.0.  Note that the STREAM transport type created via
   CREATE_SESSION, it is shown above, but
   since automatically bound to the transport mode remains unchanged operation channel,
   and transport attributes
   are optionally the backchannel.  If the client does not necessarily exchanged, DEFAULT could also be passed.

6.3.2.  Negotiated RDMA Connection Model

   One possible design which has been considered specify
   connecting binding enforcement when the session is created, then
   additional connections are automatically bound to have a
   "negotiated" RDMA connection model, supported via use of a session
   bind the operation as
   channel when the are used with a required first step.  However due SEQUENCE operation that has the
   session's sessionid.

   A connection MAY be bound to issues
   mentioned earlier, this proved problematic.  This section remains as
   a reminder the channels of that fact, other sessions.  The
   client decides, and it is possible such a mode can the NFSv4.1 server MUST allow it.  A connection
   MAY be
   supported. bound to the the channels' of other sessions of other
   clientids.  Again, the client decides, and the server MUST allow it.

   It is not considered critical that this be supported permissible for two reasons.
   One, connections of multiple types to be bound to
   the session persistence provides same channel.  For example a way for the server to
   remember important session parameters, such as sizes TCP and maximum
   request counts.  These values RDMA connection can be used bound
   to restore the endpoint
   prior to making operation channel.  In the first reply.  Two, there event an RDAM and non-RDMA
   connection are currently no
   critical RDMA parameters bound to set in the endpoint at same channel, the server side maximum number of slots
   must be at least one more than the connection.  RDMA Read resources, which are in general not
   settable after entering total number of credits.  This way
   if all RDMA mode, credits are set only at the client - use, the
   originator non-RDMA connection can have at
   least one outstanding request.

   It is permissible for a connection of one type to be bound to the connection.  Therefore as long as
   operation channel, and another type bound to the RDMA provider
   supports backchannel.

2.9.3.4.1.  Trunking

   Since multiple connections can be bound to a session's channel, these
   means that traffic between an automatic RDMA connection mode, no further support is
   required from NFSv4.1 client and server channel goes
   over all connections.  If the connections are over different network
   paths, this is trunking.  NFSv4.1 protocol for reconnection.

   Note, allows trunking, thus allows the client must provide at least as many RDMA Read resources
   bandwidth capacity to
   its local queue for scale with the benefit number of the server when reconnecting, as
   it used when negotiating the session.  If this value connections.

   At issue is no longer
   appropriate, how do NFSv4.1 clients and servers discover and verify
   multiple paths?  On the client side, each client should resynchronize its session state,
   destroy be aware of
   the existing session, and start over with network interfaces it has available from which to create
   connections.  However, the more
   appropriate values.

6.3.3.  Automatic RDMA Connection Model

   The following is client cannot always be certain whether 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
   server's multitide of
                :      maxreq N')                     :     size S'
                :   <------------------------------   :
                :                                     :
                :          <normal operation>         :
                :   ------------------------------>   :
                :   <------------------------------   :
                :                  :                  :

6.4.  Buffer Management, Transfer, Flow Control

   Inline operations network interfaces in NFSv4.1 behave effectively fact belong to the same as TCP
   sends.  Procedure results are passed in
   server, or even if they do, whether the server is prepared to share a single message, and
   clientid or sessionid across all its
   completion at interfaces.  NFSv4.1 provides no
   discovery protocol for allowing servers to advertise multiple network
   interfaces; such a protocol is problematic because network address
   translation (NAT) may be occurring between the client signal the receiving process to inspect and server, and
   so, unless the
   message.

   RDMA operations NAT devices are performed solely by inspecting NFSv4.1 traffic, the
   network addresses the server in NFSv4.1, as
   described in Section 6.2.5 RDMA Direct Transfer Model.  Since server
   RDMA operations do not result in a completion at offers to the client, and due client would be
   meaningless.  At best, short of manual configuration, an NFSv4.1
   client could use a host name to ordering rules in RDMA transports, after all required RDMA
   operations are complete, network address directory (e.g.  DNS)
   to enumerate a Send (Send with Solicited Event for iWARP)
   containing server's network interfaces.  This then leaves the procedure results is performed from server
   problem of verification.

   NFSv4.1 provides a way for clients and servers to client.
   This Send operation will result reliably verify if
   connections between different network paths are in a completion which will signal the
   client fact bound to inspect the message.

   In the case of
   same NFSv4.1 server.  The SET_SSV (Section 16.47) operation allows a
   client read-type NFSv4 operations, the and server will
   have issued RDMA Writes to transfer establish a unique, shared key value (the SSV).
   When a new connection is bound to the resulting data into client-
   advertised buffers.  The subsequent Send operation performs two
   necessary functions: finalizing any active or pending DMA at session (via the
   client, and signaling
   BIND_CONN_TO_SESSION operation, see Section 16.34), the client to inspect must
   offer a digest that based on the message.

   In SSV.  If the case of client write-type NFSv4 operations, mistakenly tries
   to bind a connection to a session of a wrong server, the server will
   have issued RDMA Reads to fetch the data from the client-advertised
   buffers.  No data consistency issues arise at
   either reject the client, but attempt because it is not aware of the
   completion session
   identifier of the transfer must be acknowledged, again by a Send from
   server to client.

   In either case, BIND_CONN_TO_SESSION arguments, or it will reject
   the client advertises buffers attempt because the digest for direct (RDMA style)
   operations.  The client may desire certain advertisement limits, and
   may wish the SSV does not match what the
   server to perform remote invalidation on its behalf when expects.  Even if the server has completed its RDMA.  This may be considered in a
   future version of this draft.

   In mistakenly or maliciously accept
   the absence of remote invalidation, connection bind attempt, the client may perform its
   own, local invalidation after digest it computes in the operation completes.  This
   invalidation should occur prior to any RPCSEC GSS integrity checking,
   since a validly remotely accessible buffer can possibly response
   will not be modified verified by the peer.  However, after invalidation and client, the contents integrity
   checked, client will know it cannot
   use the contents are locally secure.

   Credit updates connection for trunking the specified channel.

2.9.4.  Exactly Once Semantics

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

2.9.4.1.  Slot Identifiers and Reply Cache

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

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

   When the requester issues a new request, it selects a slotid in the
   range 0..N-1, where N is the replier's current "totalrequests" limit
   granted to the connection requester on the session over which it sends the request. request is to
   be issued.  The client slotid must not send more requests
   than be unused by any of the number requests which
   the server requester has previously advertised, or in already active on the
   case of session.  "Unused" here means
   the first request, only one.  If requester has no outstanding request for that slotid.  Because
   the client exceeds its
   credit limit, slot id is always an integer in the connection may close with a fatal RDMA error.

   The server then executes range 0..N-1, requester
   implementations can use the request, and replies slotid from a replier response to
   efficiently match responses with an updated
   credit count accompanying its results.  Since replies are sequenced outstanding requests, such as, for
   example, by their RDMA Send order, the most recent results always reflect the
   server's limit.  In this way using the client will always know slotid to index into a outstanding request
   array.  This can be used to avoid expensive hashing and lookup
   functions in the maximum
   number of requests it may safely post.

   Because performance-critical receive path.

   The sequenceid, which accompanies the client requests an arbitrary credit count slotid in each request, it is relatively easy
   important for an important check at the client server: it must be able to be
   determined efficiently whether a request more, using a certain slotid is a
   retransmit or
   fewer, credits to match its expected need.  A a new, never-before-seen request.  It is not feasible
   for the client to assert that discovered
   itself frequently queuing outgoing requests due it is retransmitting to lack of server
   credits might increase its requested credits proportionately in
   response.  Or, a implement this,
   because for any given request the client might have a simple, configurable number. 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 protocol also provides sequenceid MUST increase monotonically for each new transmit of a per-operation "maxslot" exchange
   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
   assist see if the
   new request is:

   o  A new request, in dynamic adjustment at which the session level, described sequenceid is one greater than that
      previously seen in a
   later section.

   Occasionally, a server may wish the slot (accounting for sequence wraparound).
      The replier proceeds to reduce execute the total number of credits
   it offers a certain client on a connection.  This could be
   encountered if a client were found 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 consuming its credits
   slowly, either
      complete, or not at all. in progress.  The replier performs replay processing
      in these cases.

   o  A client might notice this itself, and reduce
   its requested credits misordered replay, in advance, for instance requesting only which the
   count of operations it currently has queued, plus a few as a base sequenceid is less than
      (accounting for
   starting up again.  Such mechanisms can, however, be potentially
   complicated and are implementation-defined. sequence wraparound) than that previously seen in
      the slot.  The protocol does not
   require them.

   Because of replier MUST return NFS4ERR_SEQ_MISORDERED (as the way
      result from SEQUENCE or CB_SEQUENCE).

   o  A misordered new request, in which RDMA fabrics function, it the sequenceid is not possible two or more
      than (accounting for sequence wraparound) than that previously
      seen in the server (or client back channel) to cancel outstanding receive
   operations.  Therefore, effectively only slot.  Note that because the sequenceid must
      wraparound one credit can it reaches 0xFFFFFFFF, a misordered new request and
      a misordered replay cannot be withdrawn
   per receive completion.  The server (or client back channel) would
   simply not replenish distinguished.  Thus, the replier
      MUST return NFS4ERR_SEQ_MISORDERED (as the result from SEQUENCE or
      CB_SEQUENCE).

   Unlike the XID, the slotid is always within a receive operation when replying. specific range; this
   has two implications.  The server
   can still reduce first implication is that for a given
   session, the available credit advertisement in its replies to replier need only cache the target value it desires, as results of a hint to limited number
   of COMPOUND requests.  The second implication derives from the client that its credit
   target first,
   which is lower and it should expect it to be reduced accordingly.
   Of course, even if unlike XID-indexed reply caches (also know as duplicate
   request caches - DRCs), the server could cancel outstanding receives, it slotid-based reply cache cannot do so, since the client may have already sent requests in
   expectation be
   overflowed.  Through use of the previous limit.

   This brings out an interesting scenario similar sequenceid to that of client
   reconnect discussed in Section 6.3.  How identify retransmitted
   requests, the replier does not need to actually cache the server reduce request
   itself, reducing the
   credits storage requirements of an inactive client?

   One approach is for the server reply cache further.
   These new facilities makes it practical to simply close such a connection maintain all the required
   entries for an effective reply cache.

   The slotid and
   require sequenceid therefore take over the client to reconnect at a new credit limit.  This is
   acceptable, if inefficient, when traditional role of
   the connection setup time is short XID and port number in the replier reply cache implementation,
   and where the server supports persistent session semantics.

   A better replaces the IP address.  This approach is
   considerably more portable and completely robust - it is not subject
   to provide a back channel request to return the
   operations channel credits.  The server may request the client to
   return some number frequent reassignment of credits, ports as clients reconnect over IP
   networks.  In addition, the client must comply by performing
   operations on RPC XID is not used in the operations channel, provided reply cache,
   enhancing robustness of course that the
   request does not drop cache in the client's credit count face of any rapid reuse of
   XIDs by the client.  [[Comment.3: We need to zero (in which
   case discuss the connection would deadlock).  If requirements
   of 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
   operations in order to return for changing the resources XID.]] .

   It is required to encode the server.  If the
   client fails to comply slotid information into each request in
   a timely fashion, way that does not violate the server can recover minor versioning rules of the resources NFSv4.0
   specification.  This is accomplished here by breaking the connection.

   While encoding it in principle, the back channel credits could be subject to
   SEQUENCE operation within each NFSv4.1 COMPOUND and CB_COMPOUND
   procedure.  The operation easily piggybacks within existing messages.
   [[Comment.4: Need a
   similar resource adjustment, in practice this better term than piggyback]]

   In general, the receipt of a new sequenced request arriving on any
   valid slot is not an issue, since indication that the back channel is used purely for control and previous reply cache contents of
   that slot may be discarded.  In order to further assist the replier
   in slot management, the requester is expected required to use the lowest
   available slot when issuing a new request.  In this way, the replier
   may be
   statically provisioned.

   It is important able to note that retire additional entries.

   However, in addition to the case where the replier is actively adjusting its
   granted maximum request counts, count to the sizes requester, it may not be able to
   use receipt of buffers are negotiated per-session.  This permits the
   most efficient allocation of resources on both peers.  There is slotid to retire cache entries.  The slotid used
   in an
   important requirement on reconnection: incoming request may not reflect the sizes posted by server's current idea of
   the server
   at reconnect must be requester's session limit, because the request may have been sent
   from the requester before the update was received.  Therefore, in the
   downward adjustment case, the replier may have to retain a number of
   reply cache entries at least as large as previously used, to allow
   recovery.  Any replies that are replayed from the server's duplicate
   request cache must be able old value, until
   operation sequencing rules allow it to be received into client buffers.  In infer that the case where a client requester has received replies to all
   seen its retried
   requests reply.

   The SEQUENCE (and therefore received all its expected responses), then
   the CB_SEQUENCE) operation also carries a "maxslot"
   value which carries additional client may disconnect and reconnect with different buffers at
   will, since no cache replay will be required.

6.5.  Retry and Replay

   NFSv4.0 forbids retransmission on active connections over reliable
   transports; this includes connected-mode RDMA.  This restriction slot usage information.  The
   requester must
   be maintained always provide its highest-numbered outstanding slot
   value in NFSv4.1.

   If one peer were the maxslot argument, and the replier may reply with a new
   recognized value.  The requester should in all cases provide the most
   conservative value possible, although it can be increased somewhat
   above the actual instantaneous usage to retransmit maintain some minimum or
   optimal level.  This provides a way for the requester to yield unused
   request (or reply), it slots back to the replier, which in turn can use the
   information to reallocate resources.  Obviously, maxslot can never be
   zero, or the session would consume deadlock.

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

2.9.4.1.1.  Errors from SEQUENCE and CB_SEQUENCE

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

2.9.4.1.2.  Optional Reply Caching

   On a request, per-request basis the additional
   credit consumed on requester can choose to direct the server might lead replier
   to RDMA connection failure
   unless cache the client accounted for reply to all operations after the first operation
   (SEQUENCE or CB_SEQUENCE) via the sa_cachethis or csa_cachethis
   fields of the arguments to SEQUENCE or CB_SEQUENCE.  The reason it
   would not direct the replier to cache the entire reply is that the
   request is composed of all idempotent operations [20].  Caching the
   reply may offer little benefit, and decreased its available
   credit, leading if the reply is too large (see
   Section 2.9.4.4, it may not be cacheable anyway.

   Whether the requester requests the reply to wasted resources.

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

   o  The replier can cache the entire original reply.  Even though
      sa_cachethis or csa_cachethis are FALSE, the replier is always
      free to cache.  It may choose this approach in
   NFSv4.1. order to simplify
      implementation.

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

2.9.4.1.3.  Multiple Connections and Sharing the Reply Cache

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

2.9.4.2.  Retry and Replay

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

   A client MUST wait for a reply to a request before using the slot for
   another request.  If it does not wait for a reply, then the client
   does not know what sequenceid to use for the slot on its next
   request.  For example, suppose a client sends a request with
   sequenceid 1, and stale values
   must does not be replayed from wait for the cache.  This implies that response.  The next time it
   uses the slot, it sends the new request
   cache contents must with sequenceid 2.  If the
   server has not be blindly used when replies are issued from
   it, seen the request with sequenceid 1, then the server is
   expecting sequenceid 2, and credit information appropriate to rejects the channel must be
   refreshed by client's new request with
   NFS4ERR_SEQ_MISORDERED (as the RPC layer.

   Finally, result from SEQUENCE or CB_SEQUENCE).

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

6.6.  The Back Channel

   The NFSv4

2.9.4.3.  Resolving server callback operations present a significant resource problem races with sessions

   It is possible for the RDMA enabled client.  Clearly, server callbacks must be negotiated
   in to arrive at the way credits are for client before
   the ordinary operations channel for
   requests flowing reply from related forward channel operations.  For example, a
   client may have been granted a delegation to server.  But, for callbacks a file it has opened,
   but the reply to arrive
   on the same RDMA endpoint as operation replies would require
   dedicating additional resources, and specialized demultiplexing and
   event handling.  Or, callbacks OPEN (informing the client of the granting of
   the delegation) 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 be delayed in the session, and separately negotiating sizes and counts for
   active callback channel operations.  The binding network.  If a conflicting
   operation is
   firewall-friendly since arrives at the server, it does not require will recall the server to initiate delegation using
   the connection.

   This same method serves as well for ordinary TCP connection mode.  It
   is expected that all NFSv4.1 clients callback channel, which may make use of be on a different transport
   connection, perhaps even a different network.  In NFSv4.0, if the session
   facility to streamline their design.

   The back channel functions exactly
   callback request arrives before the same as related reply, the operations channel
   except that no RDMA operations are required client may
   reply to perform transfers,
   instead the sizes are required to be sufficiently large to carry all
   data inline, and server with an error.

   The presence of course the a session between client and server reverse their roles
   with respect to which alleviates this
   issue.  When a session is in control of credit management.  The same place, each client request is uniquely
   identified by its { slotid, sequenceid } pair.  By the rules apply for all transfers, with under
   which slot entries (reply cache entries) are retired, the server being required to flow
   control its callback requests.

   The back channel is optional.  If not bound on a given session, has
   knowledge whether the client has "seen" each of the server's replies.
   The server must not issue callback operations can therefore provide sufficient information to the client.  This in
   turn implies that such client
   to allow it to disambiguate between an erroneous or conflicting
   callback and a race condition.

   For each client must never put itself operation which might result in the
   situation where some sort of server
   callback, the server will need to do so, lest should "remember" the { slotid, sequenceid }
   pair of the client lose
   its connection by force, or its operation be incorrect.  For request until the same
   reason, if a back channel is bound, slotid retirement rules allow
   the client is subject server to
   revocation of its delegations if the back channel is lost.  Any
   connection loss should be corrected by determine that the client as soon as
   possible.

   This has, in fact, seen the
   server's reply.  Until the time the { slotid, sequenceid } request
   pair can be convenient retired, any recalls of the associated object MUST carry
   an array of these referring identifiers (in the CB_SEQUENCE
   operation's arguments), for the NFSv4.1 client; if benefit of the client expects client.  After this
   time, it is not necessary for the server to make no use of back channel facilities such as delegations, then
   there provide this information
   in related callbacks, since it is certain that a race condition can
   no need to create it.  This may save significant resources
   and complexity at the client.

   For these reasons, if longer occur.

   The CB_SEQUENCE operation which begins each server callback carries a
   list of "referring" { slotid, sequenceid } tuples.  If the client wishes
   finds the request corresponding to use the back channel, that
   channel must referring slotid and sequenced
   id be bound first, before using the operations channel.  In
   this way, currently outstanding (i.e. the server will server's reply has not find itself in a position where been
   seen by the client), it will
   send callbacks on can determine that the operations channel when callback has raced the
   reply, and act accordingly.

   The client is must not
   prepared simply wait forever for them.

   [[Comment.4: [XXX - do we want to support this?]]]  There is one
   special case, that where the back channel is bound in fact expected server reply
   to arrive on any of the session's operations channel's connection.  This configuration would channels, because it is
   possible that they will be used
   normally over delayed indefinitely.  However, it should
   wait for a TCP stream connection to exactly implement the
   NFSv4.0 behavior, but over RDMA would require complex resource and
   event management at both sides period of time, and if the connection.  The server is not
   required to accept time expires it can provide a
   more meaningful error such as NFS4ERR_DELAY.

   [[Comment.7: We need to consider the clients' options here, and
   describe them...  NFS4ERR_DELAY has been discussed as a bind request on an RDMA connection for this
   reason, though it is recommended.

6.7. legal reply
   to CB_RECALL?]]

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

2.9.4.4.  COMPOUND Sizing and CB_COMPOUND Construction Issues

   Very large responses requests and replies may pose duplicate request both buffer management
   issues (especially with RDMA) and reply cache issues.  Since
   servers  When the
   session is created, (Section 16.36) the client and server negotiate
   the maximum sized request they will want to bound send or process
   (ca_maxrequestsize), the storage required for such a cache, maximum sized reply they will return or
   process (ca_maxresponsesize), and the
   unlimited size of response data in COMPOUND may be troublesome.  If
   COMPOUND is used the maximum sized reply they
   will store in all its generality, then the inclusion of certain
   non-idempotent operations within reply cache (ca_maxresponsesize_cached).

   If a single COMPOUND request exceeds ca_maxrequestsize, the reply will have the
   status NFS4ERR_REQ_TOO_BIG.  A replier may render return NFS4ERR_REQ_TOO_BIG
   as the entire request non-idempotent.  (For example, a single COMPOUND
   request which read a file status for first operation (SEQUENCE or symbolic link, then removed it, would be
   obliged to cache the data CB_SEQUENCE) in order the
   request, or it may chose to allow identical replay).
   Therefore, many requests might include operations that return any
   amount of data.

   It is not satisfactory for it on a subsequent operation.

   If a reply exceeds ca_maxresponsesize, the server to reject COMPOUNDs at reply will
   with NFS4ERR_RESOURCE when they pose such difficulties for have the
   server, status
   NFS4ERR_REP_TOO_BIG.  A replier may return NFS4ERR_REP_TOO_BIG as this results the
   status for first operation (SEQUENCE or CB_SEQUENCE) in serious interoperability problems.
   Instead, any such limits must be explicitly exposed as attributes of the session, ensuring that request,
   or it may chose to return it on a subsequent operation.

   If sa_cachethis or csa_cachethis are TRUE, then the server can explicitly support any
   duplicate request replier MUST
   cache needs at all times.

6.8.  Data Alignment

   A negotiated data alignment enables certain scatter/gather
   optimizations.  A facility for this a reply except if an error is supported returned by [RPCRDMA].  Where
   NFS file data the SEQUENCE or
   CB_SEQUENCE operation (see Section 2.9.4.1.1).  If the reply exceeds
   ca_maxresponsesize_cached, (and sa_cachethis or csa_cachethis are
   TRUE) then the server MUST return NFS4ERR_REP_TOO_BIG_TO_CACHE.  Even
   if NFS4ERR_REP_TOO_BIG_TO_CACHE (or any other error for that matter)
   is returned on a operation other than first operation (SEQUENCE or
   CB_SEQUENCE), then the payload, specific optimizations become highly
   attractive.

   Header padding reply MUST be cached if sa_cachethis or
   csa_cachethis are TRUE.  For example, if a COMPOUND has eleven
   operations, including SEQUENCE, the fifth operation is requested by each peer at session initiation, a RENAME, and
   the tenth operation is a READ for one million bytes, server may be zero (no padding).  Padding leverages
   return NFS4ERR_REP_TOO_BIG_TO_CACHE on the useful property that
   RDMA receives preserve alignment of data, even when they are placed
   into anonymous (untagged) buffers.  If requested, client inline
   writes will insert appropriate pad bytes within tenth operation.  Since
   the request header to
   align server executed several operations, especially the data payload on non-idempotent
   RENAME, the specified boundary.  The client is
   encouraged client's request to be optimistic and simply pad all WRITEs within cache the RPC
   layer reply needs to the negotiated size, be honored
   in order for correct operation of exactly once semantics.  If the expectation that
   client retries the request, 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 will have cached a way reply that any
   data carried
   contains results for ten of the elevent requested operations, with
   the tenth operation having a status of NFS4ERR_REP_TOO_BIG_TO_CACHE.

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

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

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

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

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

2.9.4.5.  Persistence

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

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

   o  The sessionid.

   o  The clientid.

   o  The SSV (see section Section 2.9.6.3).

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

2.9.5.  RDMA Considerations

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

2.9.5.1.  RDMA Connection Resources

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

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

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

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

2.9.5.2.  Flow Control

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

2.9.5.3.  Padding

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

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

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

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

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

   Padding is negotiated by the session creation operation,

2.9.5.4.  Dual RDMA and
   subsequently used by the RPC Non-RDMA Transports

   Some RDMA layer, as described transports (for example see [RDDP]), [[Comment.9: need
   xref]] require a "streaming" (non-RDMA) phase, where ordinary traffic
   might flow before "stepping" up to RDMA mode, commencing RDMA
   traffic.  Some RDMA transports start connections always in [RPCRDMA].

6.9.  NFSv4 Integration

   The following section discusses the integration of the session
   infrastructure into RDMA mode.
   NFSv4.1

6.9.1.  Minor Versioning

   Minor versioning of NFSv4 is relatively restrictive, and allows for
   tightly limited changes only.  In particular, it allows, but does not permit
   adding new "procedures" (it permits adding only new "operations").
   Interoperability concerns make it impossible to consider additional
   layering assume, a streaming phase before RDMA
   mode.  When a connection is bound to be a minor revision.  This somewhat limits session, the changes
   that can be introduced when considering extensions.

   To support client and server
   negotiate whether the duplicate request cache integrated with sessions connection is used in RDMA or non-RDMA mode
   (see Section 16.36 and
   request control, it Section 16.34).

2.9.6.  Sessions Security

2.9.6.1.  Session Callback Security

   The session connection binding improves security over that provided
   by NFSv4.0 for the callback channel.  The connection is desirable client-
   initiated (see Section 16.34), and subject to tag each request with an
   identifier to be called a Slotid.  This identifier must the same firewall and
   routing checks as the operations channel.  The connection cannot be passed
   hijacked by
   NFSv4.1 when running atop any transport, including traditional TCP.
   Therefore it is not desirable an attacker who connects to add the Slotid client port prior to a new RPC
   transport, even though such a transport the
   intended server.  At the client's option (see Section 16.36 binding
   is indicated for support of
   RDMA.  This specification and [RPCRDMA] do not specify such an
   approach.

   Instead, this specification conforms to fully authenticated before being activated (see Section 16.34).
   Traffic from the requirements of NFSv4
   minor versioning, through server over the use of a new operation within NFSv4
   COMPOUND procedures callback channel is authenticated
   exactly as detailed below. the client specifies (see Section 2.9.6.2).

2.9.6.2.  Backchannel RPC Security

   When the NFSv4.1 client establishes the backchannel, it informs the
   server what security flavors and principals it must use when sending
   requests over the backchannel.  If sessions are the security flavor is RPCSEC_GSS,
   the client expresses the principal in the form of an established
   RPCSEC_GSS context.  The server is free to use for a given clientid, this same clientid
   cannot be used for non-session NFSv4 operation, including NFSv4.0.
   Because any flavor/principal
   combination the server will offers, but MUST NOT use unoffered
   combinations.

   This way, the client does not have allocated session-specific state to the
   active clientid, provide a target GSS principal
   as it would be an unnecessary burden on did with NFSv4.0, and the server
   implementor does not have to support implement an
   RPCSEC_GSS initiator as it did with NFSv4.0.  [[Comment.10: xrefs]]

   The CREATE_SESSION (Section 16.36) and account for additional, non- session
   traffic, in addition BACKCHANNEL_CTL
   (Section 16.33) operations allow the client to being of no benefit.  Therefore this
   specification prohibits a single clientid specify flavor/
   principal combinations.

2.9.6.3.  Protection from doing this.
   Nevertheless, employing a new clientid for such traffic Unauthorized State Changes

   Under some conditions, NFSv4.0 is supported.

6.9.2.  Slot Identifiers and Server Duplicate Request Cache

   The presence of deterministic maximum request limits on a session
   enables in-progress requests vulnerable to be assigned unique values a denial of service
   issue with useful
   properties. respect to its state management.

   The RPC layer provides attack works via an unauthorized client faking an open_owner4, an
   open_owner/lock_owner pair, or stateid, combined with a transaction ID (xid), which, while required
   to be unique, is not especially convenient for tracking requests. seqid.  The transaction ID
   operation is only meaningful sent to the issuer (client), it
   cannot be interpreted at the NFSv4 server.  The NFSv4 server except to test for equality with
   previously issued requests.  Because RPC operations may be completed
   by accepts the server in any order, many transaction IDs may be outstanding
   at
   state information, and as long as any time.  The client may therefore perform a computationally
   expensive lookup operation in status code from the process result of demultiplexing each
   reply.

   In the specification, there
   this operation is a limit to not NFS4ERR_STALE_CLIENTID, NFS4ERR_STALE_STATEID,
   NFS4ERR_BAD_STATEID, NFS4ERR_BAD_SEQID, NFS4ERR_BADXDR,
   NFS4ERR_RESOURCE, or NFS4ERR_NOFILEHANDLE, the sequence number of active
   requests.  This immediately enables a convenient, computationally
   efficient index for each request which is designated as a Slot
   Identifier, or slotid.
   incremented.  When the authorized client issues a new request, an operation, it selects a slotid in the
   range 0..N-1, where N is gets
   back NFS4ERR_BAD_SEQID, because its idea of the server's current "totalrequests" limit
   granted the client on the session over which the request sequence
   number is to be
   issued. off by one.  The slotid must be unused authorized client's recovery options are
   pretty limited, with SETCLIENTID, followed by any complete reclaim of the requests
   state, which may or may not succeed completely.  That qualifies as a
   denial of service attack.

   If the client has already active on uses RPCSEC_GSS authentication and integrity, and every
   client maps each open_owner and lock_owner one and only one
   principal, and the session.  "Unused" here means server enforces this binding, then the
   client has no outstanding request for conditions
   leading to vulnerability to the denial of service do not exist.  One
   should keep in mind that slotid.  Because if AUTH_SYS is being used, far simpler
   easier denial of service and other attacks are possible.

   With NFSv4.1 sessions, the slot
   id per-operation sequence number is always an integer ignored
   (see Section 8.13) therefore the NFSv4.0 denial of service
   vulnerability described above does not apply.  However as described
   to this point in the range 0..N-1, specification, an attacker could forge the
   sessionid and issue a SEQUENCE with a slot id that he expects the
   legitimate client implementations
   can to use next.  The legitimate client could then 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 same sequence number, and lookup functions in the
   performance-critical receive path.

   The sequenceid, which accompanies server returns the slotid in
   attacker's result from the replay cache, thereby disrupting the
   legitimate client.

   If we give each request, NFSv4.1 user their own session, and each user uses
   RPCSEC_GSS authentication and integrity, then the denial of service
   issue is
   important for a second, important check solved, at the server: it must cost of additional per session state.  The
   alternative NFSv4.1 specifies is described as follows.

   Transport connections MUST be
   able bound 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 session by the client to assert that it is retransmitting client.  The
   server MUST return an error to
   implement this, because for any given request an operation (other than the client cannot know operation
   that binds the server has seen it unless connection to the server actually replies.  Of
   course, if session) that uses an unbound
   connection.  As a simplification, the client has seen transport connection used by
   CREATE_SESSION (see Section 16.36) is automatically bound to the server's reply,
   session.  Additional connections are bound to a session via
   BIND_CONN_TO_SESSION (see Section 16.34).

   To prevent attackers from issuing BIND_CONN_TO_SESSION operations,
   the client would
   not retransmit!

   The sequenceid must increase monotonically for each new transmit arguments to BIND_CONN_TO_SESSION include a digest of a
   given slotid, and must remain unchanged for any retransmission.  The
   server must in turn compare each newly received request's sequenceid
   with shared
   secret called the last one previously received for secret session verifier (SSV) that slotid, to see if the
   new request is:

   o  A new request, in which only the sequenceid client
   and server know.  The digest is created via a one greater than that
      previously seen in the slot (accounting way, collision
   resistant hash function, making it intractable for sequence wraparound).
      The server proceeds to execute the new request.

   o  A retransmitted request, in which the sequenceid attacker to
   forge.

   The SSV is equal sent to that
      last seen in the slot.  Note that this request may be either
      complete, or in progress.  The server performs replay processing via SET_SSV (see Section 16.47).  To
   prevent eavesdropping, a SET_SSV for the SSV SHOULD be protected via
   RPCSEC_GSS with the privacy service.  The SSV can be changed by the
   client at any time, by any principal.  However several aspects of SSV
   changing prevent an attacker from engaging in these cases. a successful denial of
   service attack:

   o  A misordered duplicate, in which SET_SSV on the sequenceid is less than
      (acounting for sequence wraparound) than that previously seen in SSV does not replace the SSV with the argument to
      SET_SSV.  Instead, the current SSV on the slot.  The server is logically
      exclusive ORed (XORed) with the argument to SET_SSV.  SET_SSV MUST return NFS4ERR_SEQ_MISORDERED.
      NOT be called with an SSV value that is zero.

   o  A misordered  The arguments to and results of SET_SSV include digests of the old
      and new request, in which SSV, respectively.

   o  Because the sequenceid initial value of the SSV is two or more
      than (acounting for sequence wraparound) than that previously seen
      in zero, therefore known, the slot.  Note
      client that because the sequenceid must wraparound opts for connecting binding enforcement, MUST issue at
      least one
      it reaches 0xFFFFFFFF, SET_SSV operation before the first BIND_CONN_TO_SESSION
      operation.  A client SHOULD issue SET_SSV as soon as a misordered new request and session is
      created.

   If a misordered
      duplicate cannot be distinguished.  Thus, connection is disconnected, BIND_CONN_TO_SESSION is required to
   bind a connection to the server MUST return
      NFS4ERR_SEQ_MISORDERED.

   Unlike session, even if the XID, connection that was
   disconnected was the slotid is always within one CREATE_SESSION was created with.

   If a specific range; this
   has two implications.  The first implication client is that for assigned a given
   session, machine principal then the server need only cache client SHOULD
   use the results of a limited number
   of COMPOUND requests.  The second implication derives machine principal's RPCSEC_GSS context to privacy protect the
   SSV from eavesdropping during the first,
   which SET_SSV operation.  If a machine
   principal is unlike XID-indexed DRCs, not being used, then the slotid DRC by its nature cannot
   be overflowed.  Through client MAY use of the sequenceid non-machine
   principal's RPCSEC_GSS context to identify
   retransmitted requests, it is notable that privacy protect the SSV.  The
   server does not need
   to actually cache the request itself, reducing the storage
   requirements MUST accept either type of principal.  A client SHOULD change
   the DRC further.  These SSV each time a new facilities makes it
   practical to maintain all principal uses the required entries for an effective DRC.

   The slotid and sequenceid therefore take over session.

   Here are the traditional role types of
   the XID and port number in the server DRC implementation, attacks that can be attempted by an attacker
   named Eve, and how the connection to session replaces the IP address.  This binding approach is considerably more
   portable and completely robust - it is not subject to
   addresses each attack:

   o  If the frequent
   reassignment of ports as clients reconnect over IP networks.  In
   addition, Eve creates a connection after the RPC XID is legitimate client
      establishes an SSV via privacy protection from a machine
      principal's RPCSEC_GSS session, she does not used in the reply cache, enhancing
   robustness of know the cache in SSV and so
      cannot compute a digest that BIND_CONN_TO_SESSION will accept.
      Users on the face of any rapid reuse of XIDs legitimate client cannot be disrupted by Eve.

   o  If Eve is the
   client.  [[Comment.5: We need to discuss first one log into the requirements of legitimate client, and the
      client for changing the XID.]].

   It is required to encode the slotid information into each request in
   a way that does not violate use machine principals, then Eve can cause an SSV
      to be created via the minor versioning rules of legitimate client's NFSv4.1 implementation,
      protected by the NFSv4.0
   specification.  This is accomplished here RPCSEC_GSS context created by encoding it in a control
   operation (SEQUENCE) within each NFSv4.1 COMPOUND the legitimate
      client (which uses Eve's GSS principal and CB_COMPOUND
   procedure.  The operation easily piggybacks within existing messages.

   In general, credentials).  Eve can
      then eavesdrop on the receipt of network, and because she knows her
      credentials, she can decrypt the SSV.  Eve can compute a digest
      BIND_CONN_TO_SESSION will accept, and so bind a new sequenced request arriving on any
   valid slot is an indication that the previous DRC contents of that
   slot may be discarded.  In order connection to further assist the server in slot
   management,
      the client is required to use session.  Eve can change the lowest available slot
   when issuing a new request.  In this way, slotid, sequence state, and/or
      the server may be able to
   retire additional entries.

   However, SSV state in the case where such a way that when Bob accesses the server is actively adjusting its
   granted maximum request count to via
      the legitimate client, it may not the legitimate client will be able unable to use receipt of
      the slotid to retire cache entries. session.

      The slotid used
   in an incoming request may not reflect client's only recourse is to create a new session, which will
      cause any state Eve created on the server's current idea of legitimate client over the client's old
      (but hijacked) session limit, to be lost.  This disrupts Eve, but because
      she is the request may have been sent
   from attacker, this is acceptable.

      Once the legitimate client before establishes an SSV over the update was received.  Therefore, in new session
      using Bob's RPCSEC_GSS context, Eve can use the
   downward adjustment case, new session via
      the server may legitimate client, but she cannot disrupt Bob. Moreover,
      because the client SHOULD have modified the SSV due to retain Eve using
      the new session, Bob cannot get revenge on Eve by binding a number of
   duplicate request cache entries at least as large as rogue
      connection to the session.

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

      *  Let us suppose that from the client
   has seen its reply.

   The SEQUENCE (and CB_SEQUENCE) operation also carries rogue connection, Eve issued a "maxslot"
   value which carries additional client slot usage information.  The
   client must always provide its highest-numbered outstanding slot
   value in
         SET_SSV with the maxslot argument, same slotid and sequence that the legitimate
         client later uses.  The server may reply with will assume this is a new
   recognized value.  The replay,
         and return to the legitimate client should in all cases provide the most
   conservative value possible, although reply it sent Eve.
         However, unless Eve can be increased somewhat
   above correctly guess the actual instantaneous usage to maintain some minimum or
   optimal level.  This provides a way for SSV the legitimate
         client to yield unused
   request slots back to will use, the server, which digest verification checks in turn can use the
   information SET_SSV
         response will fail.  That is the clue to reallocate resources.  Obviously, maxslot can never be
   zero, or the client that the
         session would deadlock.

   The server also provides has been hijacked.

      *  Alternatively, Eve issued a target maxslot value to the client, which
   is an indication to SET_SSV with a different slotid
         than the legitimate client of uses for its SET_SSV.  Then the maxslot
         digest verification on the server wishes the
   client to be using.  This permits fails, and the server to withdraw (or add)
   resources from a client is
         again clued that the session has been found to not be using them, in
   order to more fairly share resources among a varying level of demand
   from hijacked.

      *  Alternatively, Eve issued an operation other clients.  The client must always comply than SET_SSV, but
         with the server's
   value updates, since they indicate newly established hard limits on same slotid and sequence that the client's access legitimate client
         uses for its SET_SSV.  The server returns to session resources.  However, because of
   request pipelining, the legitimate
         client may have active requests in flight
   reflecting prior values, therefore the server must not immediately
   require the response it sent Eve. The client to comply.

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

6.9.3.  Resolving server callback races with sessions

   It is possible for server callbacks to arrive not at the all what it expects.  The client before assumes
         either session hijacking or server bug, and either way destroys
         the reply from related forward channel operations.  For example, a
   client may have been granted old session.

   o  Eve binds a delegation rogue connection to a file it has opened,
   but the reply session as above, and then
      destroys the session.  Again, Bob goes to use the OPEN (informing server from the
      legitimate client.  The client of the granting of
   the delegation) may be delayed in the network.  If has a conflicting
   operation arrives at very clear indication that
      its session was hijacked, and does not even have to destroy the server,
      old session before creating a new session, which Eve will be
      unable to hijack because it will recall the delegation using
   the callback channel, which may be on a different transport
   connection, perhaps even protected with an SSV created
      via Bob's RPCSEC_GSS protection.

   o  If Eve creates a different network.  In NFSv4.0, if the
   callback request arrives connection before the related reply, the legitimate client may
   reply to the server with
      establishes an error.

   The presence SSV, because the initial value of a session between client the SSV is zero
      and server alleviates this
   issue.  When therefore known, Eve can issue a session is in place, each client request is uniquely
   identified by its { slotid, sequenceid } pair.  By SET_SSV that will pass the rules under
   which slot entries (duplicate request cache entries) are retired,
      digest verification check.  However because the
   server new connection has knowledge whether
      not been bound to the client has "seen" each of session, the
   server's replies. SET_SSV is rejected for that
      reason.

   o  The server can therefore provide sufficient
   information to the client to allow it connection to disambiguate between session binding model does not prevent
      connection hijacking.  However, if an
   erroneous or conflicting callback and a race condition.

   For each client operation which might result in some sort attacker can perform
      connection hijacking, it can issue denial of service attacks that
      are less difficult than attacks based on forging sessions.

2.9.7.  Session Mechanics - Steady State

2.9.7.1.  Obligations of server
   callback, the Server

   The server should "remember" has the { slotid, sequenceid }
   pair primary obligation to monitor the state of
   backchannel resources that the client request until has created for the slotid retirement rules allow server
   (RPCSEC_GSS contexts and back channel connections).  When these
   resources go away, the server to determine that takes action as specified in
   Section 2.9.8.2.

2.9.7.2.  Obligations of the Client

   The client has, has the following obligations in fact, seen order to utilize the
   server's reply.  Until
   session:

   o  Keep a necessary session from going idle on the time server.  A client
      that requires a session, but nonetheless is not sending operations
      risks having the { slotid, sequencedid } request
   pair can session be retired, any recalls of the associated object MUST carry
   an array of these referring identifiers (in the CB_SEQUENCE
   operation's arguments), for the benefit of destroyed by the client.  After this
   time, it server.  This is not necessary for
      because sessions consume resources, and resource limitations may
      force the server to provide this information
   in related callbacks, since it is certain that a race condition can
   no longer occur.

   The CB_SEQUENCE operation which begins each server callback carries a
   list of "referring" { slotid, sequenceid } tuples.  If cull the client
   finds least recently used session.

   o  Destroy the request corresponding to session when idle.  When a session has no state other
      than the referring slotid session, and sequenced
   id be currently no outstanding (i.e. the server's reply has not been
   seen by requests, the client), it can determine that client should
      consider destroying the callback has raced session.

   o  Maintain GSS contexts for callback.  If the
   reply, and act accordingly.

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

   [[Comment.6: XXX ...  We need needs to consider be sure the clients' options here,
   and describe them...  NFS4ERR_DELAY has been discussed as a legal
   reply contexts handed to CB_RECALL?]]

   There are other scenarios under which callbacks may race replies,
   among them pnfs layout recalls, described in Section 17.3.5.3
   [[Comment.7: XXX fill in the blanks w/others, etc...]]

6.9.4.  COMPOUND and CB_COMPOUND

   [[Comment.8: Noveck: This is about the twelfth time we say that this
   is minor version.  The diagram makes sense if you server via
      BACKCHANNEL_CTL are explaining
   which should be done somewhere, but this is supposedly explaining
   sessions.]]

   Support for per-operation control unexpired.  A good practice is added to NFSv4 COMPOUNDs by
   placing such facilities into their own, new operation, and placing
   this operation first in each COMPOUND under keep at
      least two contexts outstanding, where the new NFSv4 minor
   protocol revision.  The contents expiration time of the operation would then apply to
      newest context at the entire COMPOUND.

   Recall time it was created, is N times that of the NFSv4 minor version number
      oldest context, where N is contained within the
   COMPOUND header, encoded prior to the COMPOUNDed operations.  By
   simply requiring that the new operation always be contained number of contexts available for
      callbacks.

   o  Maintain an active connection.  The server requires a callback
      path in NFSv4
   minor COMPOUNDs, order to gracefully recall recallable state, or notify the control protocol can piggyback perfectly with
   each request and response.

   In this way,
      client of certain events.

2.9.7.3.  Steps the NFSv4 Client Takes To Establish a Session Extensions may stay in compliance with

   The client issues CREATE_CLIENTID to establish a clientid.

   The client uses the minor versioning requirements specified in section 10 of RFC3530
   [2].

   Referring clientid to section 13.1 issue a CREATE_SESSION on a
   connection to the server.  The results of RFC3530 [2], CREATE_SESSION indicate
   whether the specified session-
   enabled COMPOUND and CB_COMPOUND have server will persist the form:

      +-----+--------------+-----------+------------+-----------+----
      | tag | minorversion | numops    | control op | op + args | ...
      |     |   (== 1)     | (limited) |  + args    |           |
      +-----+--------------+-----------+------------+-----------+---- session replay cache through a
   server reboot or not, and the reply's structure is:

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

   [[Comment.9: The artwork above doesn't mention callback_ident that is
   used for CB_COMPOUND.  We need to mention that client notes this for NFSv4.1,
   callback_ident is superfluous]] future reference.

   The single control operation,
   SEQUENCE, within each NFSv4.1 COMPOUND defines client SHOULD have specified connecting binding enforcement when
   the context and
   operational session parameters which govern that COMPOUND request and
   reply.  Placing it first was created.  If so, the client SHOULD issue SET_SSV in
   the first COMPOUND encoding after the session is required in
   order created.  If it is not using
   machine credentials, then each time a new principal goes to allow its processing before other operations in use the
   COMPOUND.

6.10.  Sessions Security Considerations

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

   Security considerations of any underlying RDMA transport are
   additionally important, all SHOULD issue a SET_SSV again.

   If the more so due client wants to the emerging nature of
   such transports.  Examining these issues is outside the scope of this
   specification.

   When protecting use delegations, layouts, directory
   notifications, or any other state that requires a callback channel,
   then it MUST add 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 backchannel if CREATE_SESSION
   did not already do so.  The client creates a connection, and calls
   BIND_CONN_TO_SESSION to bind the efficiency
   which RDMA is typically employed connection to achieve.  This is because such
   data is normally managed solely by the RDMA fabric, session and intentionally
   is the
   session's backchannel.  If CREATE_SESSION did not touched by software.  The means by which already do so, the local RPCSEC_GSS
   implementation is integrated with
   client MUST tell the RDMA data protection facilities
   are outside server what security is required in order for
   the scope of client to accept callbacks.  The client does this specification. via
   BACKCHANNEL_CTL.

   If the NFS client wishes wants to maintain full control over RPCSEC_GSS
   protection, use additional connections for the
   backchannel, then it may still perform its transfer operations using either MUST call BIND_CONN_TO_SESSION on each
   connection it wants to use with the inline or RDMA transfer model, or of course employ traditional
   TCP stream operation.  In session.  If the RDMA inline case, header padding is
   recommended client wants to optimize behavior at
   use additional connections for the server. operation channel, then it MUST
   call BIND_CONN_TO_SESSION if it specified connection binding
   enforcement before using the connection.

   At this point the client, close
   attention should be paid client has reached a steady state as far as session
   use.

2.9.8.  Session Mechanics - Recovery

2.9.8.1.  Events Requiring Client Action

   The following events require client action to the implementation of recover.

2.9.8.1.1.  RPCSEC_GSS
   processing Context Loss by Callback Path

   If all RPCSEC_GSS contexts granted to minimize memory referencing and especially copying.

   The session callback channel binding improves security over that
   provided by NFSv4 for the client to the server for
   callback channel. use have expired, the client MUST establish a new context
   via BACKCHANNEL_CTL.  The sr_status field of SEQUENCE results
   indicates when callback contexts are nearly expired, or fully expired
   (see Section 16.46.4).

2.9.8.1.2.  Connection Disconnect

   If the client loses the last connection is
   client-initiated, and subject to of the same firewall session, then it MUST
   create a new connection, and routing checks
   as if connecting binding enforcement was
   specified when the operations channel.  The connection cannot be hijacked by an
   attacker who connects session was created, bind it to the client port prior to session via
   BIND_CONN_TO_SESSION.

   If there were requests outstanding at the intended
   server.  The time the of connection is set up by
   disconnect, then the client with its desired
   attributes, such MUST retry the request, as optionally securing with IPsec or similar.  The
   binding is fully authenticated before being activated.

6.10.1.  Denial of Service via Unauthorized State Changes

   Under some conditions, NFSv4.0 described in
   Section 2.9.4.2.  Note that it is vulnerable not necessary to retry requests
   over a denial of service
   issue with respect to its state management.

   The attack works via an unauthorized client faking an open_owner4, an
   open_owner/lock_owner pair, or stateid, combined connection with a seqid.  The
   operation is sent to the NFSv4 server.  The NFSv4 server accepts same source network address or the
   state information, and same
   destination network address as the disconnected connection.  As long
   as any status code from the result sessionid, slotid, and sequenceid in the retry match that of
   this operation is not NFS4ERR_STALE_CLIENTID, NFS4ERR_STALE_STATEID,
   NFS4ERR_BAD_STATEID, NFS4ERR_BAD_SEQID, NFS4ERR_BADXDR,
   NFS4ERR_RESOURCE, or NFS4ERR_NOFILEHANDLE,
   the sequence number is
   incremented.  When original request, the authorized client issues an operation, it gets
   back NFS4ERR_BAD_SEQID, because its idea of server will recognize the current sequence
   number is off by one.  The authorized client's recovery options are
   pretty limited, with SETCLIENTID, followed by complete reclaim of
   state, which may or may not succeed completely.  That qualifies request as a
   denial of service attack.
   retry if it did see the request prior to disconnect.

   If the connection that was bound to the backchannel is lost, the
   client uses RPCSEC_GSS authentication and integrity, and every
   client maps each open_owner and lock_owner one may need to reconnect, and only use BIND_CONN_TO_SESSION, to give
   the connection to the backchannel.  If the connection that was lost
   was the last one
   principal, bound to the backchannel, the the client MUST
   reconnect, and bind the connection to the session and backchannel.
   The server enforces this binding, then should indicate when it has no callback connection via the conditions
   leading to vulnerability to
   sr_status result from SEQUENCE.

2.9.8.1.3.  Backchannel GSS Context Loss

   Via the denial sr_status result of service do not exist.  One
   should keep in mind that the SEQUENCE operation or other means,
   the client will learn if AUTH_SYS is being used, far simpler
   easier denial some or all of service and other attacks are possible.

   With NFSv4.1 sessions, the per-operation sequence number is ignored
   (see Section 13.13) therefore RPCSEC_GSS contexts it
   assigned to the NFSv4.0 denial backchannel have been lost.  The client may need to
   use BACKCHANNEL_CTL to assign new contexts.  It MUST assign new
   contexts if there are no more contexts.

2.9.8.1.4.  Loss of service
   vulnerability described above does not apply.  However as described Session

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

   o  Server crash and reboot

   o  A catastrophe that causes the cache to this point be corrupted or lost on the
      media it was stored on.  This applies even if the server indicated
      in the specification, an attacker could forge CREATE_SESSION results that it would persist the
   sessionid and issue a SEQUENCE with cache.

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

   Loss of replay cache is equivalent to use next. loss of session.  The legitimate server
   indicates loss of session to the client could then use by returning
   NFS4ERR_BADSESSION on the slotid next operation that uses the sessionid
   associated with the same sequence number, lost session.

   After an event like a server reboot, the client may have lost its
   connections.  The client assumes for the moment that the session has
   not been lost.  It reconnects, and if it specified connecting binding
   enforcement when the server returns session was created, it invokes
   BIND_CONN_TO_SESSION using the
   attacker's result from sessionid.  Otherwise, it invokes
   SEQUENCE.  If BIND_CONN_TO_SESSION or SEQUENCE returns
   NFS4ERR_BADSESSION, the replay cache, thereby disrupting client knows the
   legitimate client. session was lost.  If we give each NFSv4.1 user their own session, and each user uses
   RPCSEC_GSS authentication and integrity, the
   connection survives session loss, then the denial of service
   issue is solved, next SEQUENCE operation
   the client issues over the connection will get back
   NFS4ERR_BADSESSION.  The client again knows the session was lost.

   When the client detects session loss, it must call CREATE_SESSION to
   recover.  Any non-idempotent operations that were in progress may
   have been performed on the server at the cost time of additional per session state. loss.  The
   alternative NFSv4.1 specifies is described as follows.

   Transport connections MUST be bound
   client has no general way to recover from this.

   Note that loss of session does not imply loss of lock, open,
   delegation, or layout state.  Nor does loss of lock, open,
   delegation, or layout state imply loss of session state.
   [[Comment.12: Add reference to a lock recovery section]] .  A session by the client.
   The
   can survive a server MUST return an error to an operation (other than reboot, but lock recovery may still be needed.
   The converse is also true.

   It is possible CREATE_SESSION will fail with NFS4ERR_STALE_CLIENTID
   (for example the
   operation that binds server reboots and does not preserve clientid
   state).  If so, the connection client needs to the session) that uses an
   unbound connection.  As a simplification, the transport connection
   used call CREATE_CLIENTID, followed by CREATE_SESSION
   CREATE_SESSION.

2.9.8.1.5.  Failover

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

2.9.8.2.  Events Requiring Server Action

   The following events require server action to recover.

2.9.8.2.1.  Client Crash and Reboot

   As described in Section 16.35, a new operation,
   BIND_CONN_TO_SESSION.

   To prevent attackers from issuing BIND_CONN_TO_SESSION operations, rebooted client causes the arguments server to BIND_CONN_TO_SESSION include a digest of
   delete any sessions it had.

2.9.8.2.2.  Client Crash with No Reboot

   If a shared
   secret called client crashes and never comes back, it will never issue
   CREATE_CLIENTID with its old clientid.  Thus the secret server has session verifier (SSV)
   state that only the client will never be used again.  After an extended period of
   time and if the server know.  The digest is created via a one way, collision
   resistance hash function, making has resource constraints, it intractable for the attacker to
   forge.

   The SSV is sent to MAY destroy the server via SET_SSV.
   old session.

2.9.8.2.3.  Extended Network Partition

   To prevent eavesdropping,
   a SET_SSV for the SSV can server, the extended network partition may be protected via RPCSEC_GSS no different
   than a client crash with no reboot (see Section 2.9.8.2.2).  Unless
   the
   privacy service.  The SSV server can be changed by the client at any time,
   by any principal.  However several aspects of SSV changing prevent an
   attacker from engaging in discern that there is a successful denial of service attack:

   1.  A SET_SSV on network partition, it is free
   to treat the SSV does not replace situation as if the SSV with client has crashed for good.

2.9.8.2.4.  Backchannel Connection Loss

   If there were callback requests outstanding at the argument
       to SET_SVV.  Instead, time the current SSV on of a
   connection disconnect, then the server is logically
       exclusive ORed (XORed) with the argument to SET_SSV.  SET_SSV MUST NOT be called with an SSV value retry the request, as
   described in Section 2.9.4.2.  Note that it is zero.

   2.  The arguments not necessary to and results of SET_SSV include digests of retry
   requests over a connection with the
       old same source network address or
   the same destination network address as the disconnected connection.
   As long as the sessionid, slotid, and new SSV, respectively.

   3.  Because sequenceid in the initial value retry match
   that of the SSV is zero, therefore known, original request, the client MUST issue at least one SET_SSV operation before callback target will recognize the
       first BIND_CONN_TO_SESSION operation.  A client SHOULD issue
       SET_SSV as soon
   request as a session is created. retry if it did see the request prior to disconnect.

   If a the connection lost is disconnected, BIND_CONN_TO_SESSION is required to
   bind a connection the last one bound to the session, even if backchannel, then
   the connection server MUST indicate that was
   disconnected was in the one CREATE_SESSION was created with.

   If a client is assigned a machine principal then sr_status field of the client next
   SEQUENCE reply.

2.9.8.2.5.  GSS Context Loss

   The server SHOULD
   use monitor when the machine principal's last RPCSEC_GSS context assigned
   to privacy protect the
   SSV from eavesdropping during the SET_SSV operation.  If a machine
   principal backchannel is not being used, then the client MAY use near expiry (i.e between one and two periods of
   lease time), and indicate so in the non-machine
   principal's RPCSEC_GSS context to privacy protect sr_status field of the SSV. next
   SEQUENCE reply.  The server MUST accept either type of principal.  A client SHOULD change indicate when the SSV each time a new principal uses the session.

   Here are backchannel's last
   RPCSEC_GSS context has expired in the types sr_status field of attacks that can be attempted an attacker named
   Eve, and how the connection next
   SEQUENCE reply.

3.  Protocol Data Types

   The syntax and semantics to session binding approach addresses
   each attack:

   o  If describe the Eve creates a connection after data types of the legitimate client
      establishes an SSV via privacy protection from a machine
      principal's RPCSEC_GSS session, she does not know NFS
   version 4 protocol are defined in the SSV XDR RFC4506 [3] and so
      cannot compute a digest that BIND_CONN_TO_SESSION will accept.
      Users on the legitimate client cannot be disrupted by Eve.

   o  If Eve first logs into RPC RFC1831
   [4] documents.  The next sections build upon the legitimate client, XDR data types to
   define types and structures specific to this protocol.

3.1.  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 does identification      |
   | component4    | typedef utf8str_cs component4;                    |
   |               | Represents path name components                   |
   | count4        | typedef uint32_t count4;                          |
   |               | Various count parameters (READ, WRITE, COMMIT)    |
   | length4       | typedef uint64_t length4;                         |
   |               | Describes LOCK lengths                            |
   | linktext4     | typedef utf8str_cs linktext4;                     |
   |               | Symbolic link contents                            |
   | mode4         | typedef uint32_t mode4;                           |
   |               | Mode attribute data type                          |
   | nfs_cookie4   | typedef uint64_t nfs_cookie4;                     |
   |               | Opaque cookie value for READDIR                   |
   | nfs_fh4       | typedef opaque nfs_fh4<NFS4_FHSIZE>               |
   |               | Filehandle definition; NFS4_FHSIZE is defined as  |
   |               | 128                                               |
   | nfs_ftype4    | enum nfs_ftype4;                                  |
   |               | Various defined file types                        |
   | nfsstat4      | enum nfsstat4;                                    |
   |               | Return value for operations                       |
   | offset4       | typedef uint64_t offset4;                         |
   |               | Various offset designations (READ, WRITE, LOCK,   |
   |               | COMMIT)                                           |
   | pathname4     | typedef component4 pathname4<>;                   |
   |               | Represents path name for fs_locations             |
   | qop4          | typedef uint32_t qop4;                            |
   |               | Quality of protection designation in SECINFO      |
   | sec_oid4      | typedef opaque sec_oid4<>;                        |
   |               | Security Object Identifier The sec_oid4 data type |
   |               | is not use machine principals, then Eve can cause really opaque. Instead contains an SSV to be
      created via the legitimate client's NFSv4.1 implementation,
      protected by the RPCSEC_GSS context created ASN.1   |
   |               | OBJECT IDENTIFIER as used by GSS-API in the legitimate
      client (which uses Eve's GSS principal and credentials).  Eve can
      eavesdrop on the network, and because she knows her credentials,
      she can decrypt the SSV.  Eve can compute       |
   |               | mech_type argument to GSS_Init_sec_context. See   |
   |               | RFC2743 [8] 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 digest
      BIND_CONN_TO_SESSION will accept, case sensitive prefix and so bind a new connection to  |
   |               | case insensitive suffix.                          |
   | verifier4     | typedef opaque verifier4[NFS4_VERIFIER_SIZE];     |
   |               | Verifier used for various operations (COMMIT,     |
   |               | CREATE, OPEN, READDIR, SETCLIENTID,               |
   |               | SETCLIENTID_CONFIRM, WRITE) NFS4_VERIFIER_SIZE is |
   |               | defined as 8.                                     |
   +---------------+---------------------------------------------------+

                          End of Base Data Types

                                  Table 1

3.2.  Structured Data Types

3.2.1.  nfstime4

   struct nfstime4 {
       int64_t seconds;
       uint32_t nseconds;
   }

   The nfstime4 structure gives the session.  Eve can change number of seconds and nanoseconds
   since midnight or 0 hour January 1, 1970 Coordinated Universal Time
   (UTC).  Values greater than zero for the slotid, sequence state, and/or seconds field denote dates
   after the SSV state in such a way that when Bob accesses 0 hour January 1, 1970.  Values less than zero for the server via
   seconds field denote dates before the legitimate client, 0 hour January 1, 1970.  In
   both cases, the legitimate client will nseconds field is to be unable added to use the session.  The client's only recourse is to create a new
      session, which will cause any state Eve created on seconds field
   for the legitimate
      client over final time representation.  For example, if the old (but hijacked) session time to be lost.  This
      disrupts Eve, but because she is the attacker, this
   represented is acceptable.
      Once the legitimate client establishes an SSV over the new session
      using Bob's RPCSEC_GSS context, Eve can use the new session via
      the legitimate client, but she cannot disrupt Bob. Moreover,
      because one-half second before 0 hour January 1, 1970, the client SHOULD
   seconds field would have modified the SSV due to Eve using
      the new session, Bob cannot get revenge on Eve by binding a rogue
      connection to the session.  The question is how does the
      legitimate client detect that Eve has hijacked the old session?
      When the client detects that a new principal, Bob, wants to use value of negative one (-1) and the session, it SHOULD
   nseconds fields would have issued a SET_SSV.

      *  Let us suppose that 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 rogue connection, Eve issued
   precision of timestamps stored for a
         SET_SSV with the same slotid and sequence that the legitimate
         client later uses.  The server will assume this file system object is a replay,
         and return less than
   defined, loss of precision can occur.  An adjunct time maintenance
   protocol is recommended to the legitimate reduce client and server time skew.

3.2.2.  time_how4

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

3.2.3.  settime4

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

   The above definitions are used as the reply it sent Eve.
         However, unless Eve can correctly guess the SSV the legitimate
         client will use, the digest verification checks in the SET_SSV
         response will fail.  That is the clue attribute definitions to set
   time values.  If set_it is SET_TO_SERVER_TIME4, then the client that the
         session has been hijacked.

      *  Alternatively, Eve issued a SET_SSV with a different slotid
         than the legitimate client server uses for
   its SET_SSV.  Then local representation of time for the
         digest verification on time value.

3.2.4.  specdata4

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

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

3.2.5.  fsid4

   struct fsid4 {
       uint64_t        major;
       uint64_t        minor;
   };

3.2.6.  fs_location4

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

3.2.7.  fs_locations4

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

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

3.2.8.  fattr4

   struct fattr4 {
       bitmap4       attrmask;
       attrlist4     attr_vals;
   };

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

   The bitmap is a counted array of 32 bit integers used to contain bit
   values.  The position of the session has been hijacked.

      *  Alternatively, Eve issued an operation other than SET_SSV, but
         with integer in the same slotid and sequence array that contains bit n
   can be computed from the legitimate client
         uses for expression (n / 32) and its SET_SSV.  The server returns bit within that
   integer is (n mod 32).

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

3.2.9.  change_info4

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

   This structure is used with the CREATE, LINK, REMOVE, RENAME
   operations to let the legitimate client know the response it sent Eve. The client sees that value of the
         response change attribute
   for the directory in which the target file system object resides.

3.2.10.  netaddr4

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

   The netaddr4 structure is not at all what it expects. used to identify TCP/IP based endpoints.
   The client assumes
         either session hijacking or server bug, r_netid and either way destroys
         the old session.

   o  Eve binds a rogue connection to the session r_addr fields are specified in RFC1833 [22], but they
   are underspecified in RFC1833 [22] as above, far as what they should look
   like for specific protocols.

   For TCP over IPv4 and then
      destroys the session.  Again, Bob goes to use for UDP over IPv4, the server from format of r_addr is the
      legitimate client.
   US-ASCII string:

   h1.h2.h3.h4.p1.p2

   The client has a very clear indication that
      its session was hijacked, 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 does not even have h4, are respectively,
   the first through fourth octets each converted to destroy ASCII-decimal.
   Assuming big-endian ordering, p1 and p2 are, respectively, the
      old session before creating a new session, which Eve will be
      unable first
   and second octets each converted to hijack because it will be protected with an SSV created
      via Bob's RPCSEC_GSS protection.

   o  If Eve creates ASCII-decimal.  For example, if a connection before the legitimate client
      establishes
   host, in big-endian order, has an SSV, because 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 initial value of r_netid is the SSV string "tcp".  For UDP
   over IPv4 the value of r_netid is zero
      and therefore known, Eve can issue a SET_SSV that will pass the
      digest verification check.  However because string "udp".

   For TCP over IPv6 and for UDP over IPv6, the new connection has
      not been bound to format of r_addr is the session,
   US-ASCII string:

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

   The suffix "p1.p2" is the SET_SSV service port, and is rejected computed the same way
   as with universal addresses for that
      reason.

   o TCP and UDP over IPv4.  The connection to session binding model does not prevent
      connection hijacking.  However, if prefix,
   "x1:x2:x3:x4:x5:x6:x7:x8", is the standard textual form for
   representing an attacker can perform
      connection hijacking, it can issue denial IPv6 address as defined in Section 2.2 of service attacks that RFC1884
   [9].  Additionally, the two alternative forms specified in Section
   2.2 of RFC1884 [9] are less difficult than attacks based on forging sessions.

6.11.  Session Mechanics - Steady State

6.11.1.  Obligations also acceptable.

   For TCP over IPv6 the value of r_netid is the Server

   [[Comment.10: XXX - TBD]]

6.11.2.  Obligations string "tcp6".  For UDP
   over IPv6 the value of r_netid is the Client string "udp6".

3.2.11.  clientaddr4

   typedef netaddr4 clientaddr4;

   The client has clientaddr4 structure is used as part of the following obligations in order SETCLIENTID
   operation to utilize either specify the
   session:

   o  Keep a necessary session from going idle on address of the server.  A client that requires a session, but nonetheless is not sending operations
      risks having the session be destroyed by using a
   clientid or as part of the server. callback registration.

3.2.12.  cb_client4

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

   This structure is
      because sessions consume resources, and resource limitations may
      force the server to cull the least recently used session.

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

   o  Maintain GSS contexts for callback.  If by the client requires to inform the server to to use of its call
   back address; includes the RPCSEC_GSS security flavor for callbacks,
      then it needs to be sure program number and client address.

3.2.13.  nfs_client_id4

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

   This structure is part of the contexts handed arguments to the server via
      BACKCHANNEL_CTL are unexpired.  A good practice SETCLIENTID operation.
   NFS4_OPAQUE_LIMIT is defined as 1024.

3.2.14.  open_owner4

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

   This structure is used to keep at
      least two contexts outstanding, where identify the expiration time owner of the
      newest context at the time it was created, open state.
   NFS4_OPAQUE_LIMIT is N times that of the
      oldest context, where N defined as 1024.

3.2.15.  lock_owner4

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

   This structure is used to identify the number owner of contexts available for
      callbacks.

   o  Maintain file locking state.
   NFS4_OPAQUE_LIMIT is defined as 1024.

3.2.16.  open_to_lock_owner4

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

   This structure is used for the first LOCK operation done for an active connection.  The server requires a callback
      path in order to gracefully recall recallable state, or notify
   open_owner4.  It provides both the
      client of certain events.

6.11.3.  Steps open_stateid and lock_owner such
   that the Client Takes To Establish transition is made from a Session

   The client issues CREATE_CLIENTID valid open_stateid sequence to establish a clientid.

   The client uses
   that of the clientid to issue a CREATE_SESSION on a
   connection 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 server.  The results form of CREATE_SESSION indicate
   whether the server will persist open_stateid/open_seqid.

3.2.17.  stateid4

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

   This structure is used for the session replay cache through a
   server reboot or not, and various state sharing mechanisms
   between the client notes and server.  For the client, this for future reference. data structure
   is read-only.  The client SHOULD issue SET_SSV in first COMPOUND after starting value of the session seqid field is created.  If it undefined.
   The server is not using machine credentials, then each time a
   new principal goes required to use increment the session, it SHOULD issue a SET_SSV
   again.

   If seqid field monotonically at
   each transition of the stateid.  This is important since the client wants
   will inspect the seqid in OPEN stateids to use delegations, layouts, directory
   notifications, or any other state determine the order of
   OPEN processing done by the server.

3.2.18.  layouttype4

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

   A layout type specifies the layout being used.  The implication is
   that requires a call back channel,
   then clients have "layout drivers" that support one or more layout
   types.  The file server advertises the layout types it must add connection to supports
   through the backchannel if CREATE_SESSION did
   not already do so.  The LAYOUT_TYPES file system attribute.  A client creates asks for
   layouts of a connection, particular type in LAYOUTGET, and calls
   BIND_CONN_TO_SESSION passes those layouts
   to bind its layout driver.

   The layouttype4 structure is 32 bits in length.  The range
   represented by the connection to layout type is split into two parts.  Types within
   the session range 0x00000000-0x7FFFFFFF are globally unique and are assigned
   according to the
   session's backchannel.  If CREATE_SESSION did not already do so, the
   client MUST tell the server what security is required description in order Section 20.1; they are maintained by
   IANA.  Types within the range 0x80000000-0xFFFFFFFF are site specific
   and for "private use" only.

   The LAYOUT_NFSV4_FILES enumeration specifies that the client NFSv4 file
   layout type is to accept callbacks. be used.  The client does this via
   BACKCHANNEL_CTL.

   If LAYOUT_OSD2_OBJECTS enumeration
   specifies that the client wants object layout, as defined in [23], is to use additional connections for be used.
   Similarly, the operations
   and back channels, then it MUST call BIND_CONN_TO_SESSION on each
   connection it wants LAYOUT_BLOCK_VOLUME enumeration that the block/volume
   layout, as defined in [24], is to use be used.

3.2.19.  deviceid4

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

   Layout information includes device IDs that specify a storage device
   through a compact handle.  Addressing and type information is
   obtained with the session.

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

6.12.  Session Mechanics - Recovery

   This section discussions session related events must not assume
   that require
   recovery.

6.12.1.  Events Requiring Client Action device IDs are valid across metadata server reboots.  The following events require client action to recover.

6.12.1.1.  RPCSEC_GSS Context Loss device
   ID is qualified by Callback Path

   If all RPCSEC_GSS contexts granted the layout type and are unique per file system
   (FSID).  This allows different layout drivers to generate device IDs
   without the need for co-ordination.  See Section 12.3.1.4 for more
   details.

3.2.20.  devlist_item4

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

   An array of these values is returned by the client to GETDEVICELIST operation.
   They define the server set of devices associated with a file system for
   callback use have expired, the client MUST establish
   layout type specified in the GETDEVICELIST4args.

   The device address is used to set up a new context
   via BIND_CONN_TO_SESSION. communication channel with the
   storage device.  Different layout types will require different types
   of structures to define how they communicate with storage devices.
   The sr_status opaque device_addr field of SEQUENCE results
   indicates when callback contexts are nearly expired, or fully expired
   (see Section 21.46.4).

6.12.1.2.  Connection Disconnect

   If must be interpreted based on the client loses
   specified layout type.

   This document defines the last connection of device address for the session, then it MUST
   create NFSv4 file layout
   (struct netaddr4 (Section 3.2.10)), which identifies a new connection, storage device
   by network IP address and bind it port number.  This is sufficient for the
   clients to communicate with the session via
   BIND_CONN_TO_SESSION.

6.12.1.3.  Loss of Session

   The server NFSv4 storage devices, and may lose 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.

3.2.21.  layout4

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

   The layout4 structure defines a record of the session.  Causes include:

   o  Server crash layout for a file.  The layout type
   specific data is opaque within this structure and reboot

   o  A catastrophe that causes the cache to must be corrupted or lost
   interepreted based on the
      media it was stored on.  This applies even if layout type.  Currently, only the server indicated
      in NFSv4
   file layout type is defined; see Section 12.4.1 for its definition.
   Since layouts are sub-dividable, the CREATE_SESSION results that it would persist offset and length together with
   the cache.

   o file's filehandle, the clientid, iomode, and layout type,
   identifies the layout.

3.2.22.  layoutupdate4

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

   The server purges layoutupdate4 structure is used by the session of a client that has been inactive
      for a very extended period of time.  [[Comment.11: XXX - Should we
      add a value to return 'updated'
   layout information to the CREATE_SESSION results that tells a client how
      long he can let metadata server at LAYOUTCOMMIT time.  This
   structure provides a session stay idle before losing it?]].

   Loss of replay cache is equivalent channel to loss pass layout type specific information
   back to the metadata server.  E.g., for block/volume layout types
   this could include the list of session. reserved blocks that were written.
   The server
   indicates loss contents of session to the client opaque lou_data argument are determined by returning
   NFS4ERR_BADSESSION on the next operation that uses the sessionid
   associated with the lost session.

   After an event like a server reboot,
   layout type and are defined in their context.  The NFSv4 file-based
   layout does not use this structure, thus the client may update_data field should
   have lost its
   connections. a zero length.

3.2.23.  layouthint4

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

   The client assumes for layouthint4 structure is used by the moment that client to pass in a hint
   about the session has
   not been lost. type of layout it would like created for a particular file.
   It reconnects, and invokes BIND_CONN_TO_SESSION using
   the sessionid.  If BIND_CONN_TO_SESSION returns NFS4ERR_BADSESSION,
   the client knows is the session was lost.  If structure specified by the connection survives
   session loss, then FILE_LAYOUT_HINT attribute
   described below.  The metadata server may ignore the next SEQUENCE operation hint, or may
   selectively ignore fields within the client issues over hint.  This hint should be
   provided at create time as part of the connection will get back NFS4ERR_BADSESSION. initial attributes within
   OPEN.  The client again
   knows NFSv4 file-based layout uses the session was lost.

   When "nfsv4_file_layouthint"
   structure as defined in Section 12.4.1.

3.2.24.  layoutiomode4

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

   The iomode specifies whether the client detects session loss, it must call CREATE_SESSION intends to
   recover.  Any non-idempotent operations that were in progress may
   have been performed on the server at read or write
   (with the time possibility of session loss. reading) the data represented by the layout.
   The
   client has no general way to recover from this.

   Note ANY iomode MUST NOT be used for LAYOUTGET, however, it can be
   used for LAYOUTRETURN and LAYOUTRECALL.  The ANY iomode specifies
   that loss of session does not imply loss of lock, open,
   delegation, layouts pertaining to both READ and RW iomodes are being
   returned or layout state.  Nor does loss recalled, respectively.  The metadata server's use of lock, open,
   delegation, or the
   iomode may depend on the layout state imply loss of session state.[[Comment.12:
   Add reference type being used.  The storage devices
   may validate I/O accesses against the iomode and reject invalid
   accesses.

3.2.25.  nfs_impl_id4

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

   This structure is used to lock recovery section]].  A session can survive a identify client and server reboot, but lock recovery may still be needed. implementation
   detail.  The converse nii_domain field is also true.

   It the DNS domain name that the
   implementer is associated with.  The nii_name field is possible CREATE_SESSION will fail with NFS4ERR_STALE_CLIENTID
   (for example the server reboots product
   name of the implementation and does not preserve clientid
   state).  If so, is completely free form.  It is
   encouraged that the client needs to call CREATE_CLIENTID, followed by
   CREATE_SESSION.

6.12.2.  Events Requiring Server Action

   The following events require server action nii_name be used to recover.

6.12.2.1.  Client Crash distinguish machine
   architecture, machine platforms, revisions, versions, and Reboot

   As described in Section 21.35, a rebooted client causes patch
   levels.  The nii_date field is the server timestamp of when the software
   instance was published or built.

3.2.26.  threshold_item4

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

   This structure contains a list of hints specific to
   delete any sessions it had.

6.12.2.2.  Client Crash with No Reboot

   If a layout type for
   helping the client crashes and never comes back, determine when it will never should issue
   CREATE_CLIENTID with its old clientid.  Thus I/O directly
   through the metadata server has session
   state that will never be used again.  After an extended period vs. the data servers.  The hint structure
   consists of
   time and if the server has resource constraints, it MAY destroy layout type, a bitmap describing the
   old session.

6.12.2.2.1.  Extended Network Parition

   To set of hints
   supported by the server, the extended network partition they may be no different
   than a client crash with no reboot (see Section 6.12.2.2 Client Crash
   with No Reboot).  Unless differ based on the server can discern that there is layout type,
   and a
   network partition, it list of hints, whose structure is free to treat determined by the situation as if hintset
   bitmap.  See the client
   has crashed mdsthreshold attribute for good.

7.  Minor Versioning

   To address the requirement more details.

   The hintset is a bitmap of an NFS protocol that can evolve as the
   need arises, the NFS version 4 protocol contains the rules and
   framework following values:

   +-------------------------+---+---------+---------------------------+
   | name                    | # | Data    | Description               |
   |                         |   | Type    |                           |
   +-------------------------+---+---------+---------------------------+
   | threshold4_read_size    | 0 | length4 | The file size below which |
   |                         |   |         | it is recommended to allow for future minor changes or versioning. read |
   |                         |   |         | data through the MDS.     |
   | threshold4_write_size   | 1 | length4 | The base assumption with respect file size below which |
   |                         |   |         | it is recommended to minor versioning      |
   |                         |   |         | write data through the    |
   |                         |   |         | MDS.                      |
   | threshold4_read_iosize  | 2 | length4 | For read I/O sizes below  |
   |                         |   |         | this threshold it is that any
   future accepted minor version must follow      |
   |                         |   |         | recommended to read data  |
   |                         |   |         | through the IETF process and be
   documented in a standards track RFC.  Therefore, each minor version
   number will correspond MDS           |
   | threshold4_write_iosize | 3 | length4 | For write I/O sizes below |
   |                         |   |         | this threshold it is      |
   |                         |   |         | recommended to write data |
   |                         |   |         | through the MDS           |
   +-------------------------+---+---------+---------------------------+

3.2.27.  mdsthreshold4

   struct mdsthreshold4 {
           threshold_item4 mth_hints<>;
   };

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

4.  Filehandles

   The filehandle in the NFS
   version 4 protocol is represented by this RFC. a per server unique identifier
   for a file system object.  The COMPOUND
   procedure will support the encoding contents of the minor version being
   requested by filehandle are opaque
   to the client.

   The following items represent  Therefore, the basic rules server is responsible for translating
   the development of
   minor versions.  Note that a future minor version may decide to
   modify or add filehandle to an internal representation of the following rules as part file system
   object.

4.1.  Obtaining the First Filehandle

   The operations of the minor version
   definition.

   1.   Procedures NFS protocol are not added defined in terms of one or deleted

        To maintain
   more filehandles.  Therefore, 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 client needs a filehandle to
   initiate communication with the COMPOUND server.  With the NFS version 2
   protocol RFC1094 [17] and
        CB_COMPOUND procedures. the NFS version 3 protocol RFC1813 [18],
   there exists an ancillary protocol to obtain this first filehandle.
   The addition MOUNT protocol, RPC program number 100005, provides the mechanism
   of operations translating a string based file system path name to a filehandle
   which can then be used by the COMPOUND and CB_COMPOUND
        procedures does not affect NFS protocols.

   The MOUNT protocol has deficiencies in the RPC model.

        *  Minor versions may append attributes to GETATTR4args,
           bitmap4, area of security and GETATTR4res. use
   via firewalls.  This allows for is one reason that the expansion use of the attribute model to allow
           for future growth or adaptation.

        *  Minor version X must append any new attributes after public
   filehandle was introduced in RFC2054 [25] and RFC2055 [26].  With the last
           documented attribute.

           Since attribute results are specified as an opaque array
   use of
           per-attribute XDR encoded results, the complexity of adding
           new attributes public filehandle in combination with the midst of LOOKUP operation
   in the current definitions 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
           be too burdensome.

   3.   Minor versions must not modify 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 structure NFS client.

4.1.1.  Root Filehandle

   The first of an existing
        operation's arguments the special filehandles is the ROOT filehandle.  The
   ROOT filehandle is the "conceptual" root of the file system name
   space at the NFS server.  The client uses or results.

        Again starts with the complexity ROOT
   filehandle by employing the PUTROOTFH operation.  The PUTROOTFH
   operation instructs the server to set the "current" filehandle to the
   ROOT of handling multiple structure definitions
        for a single the server's file tree.  Once this PUTROOTFH operation is too burdensome.  New operations should
        be added instead
   used, the client can then traverse the entirety 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_*) server's file
   tree with new
           values

   4.   Minor versions may not modify the structure LOOKUP operation.  A complete discussion of existing
        attributes.

   5.   Minor versions may not delete operations.

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

   6.   Minor versions may not delete attributes.

   7.   Minor versions the section "NFS Server Name Space".

4.1.2.  Public Filehandle

   The second special filehandle is the PUBLIC filehandle.  Unlike the
   ROOT filehandle, the PUBLIC filehandle may not delete flag bits be bound or enumeration values.

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

        Specifying represent an operation as "mandatory to not implement"
   arbitrary file system object at the server.  The server is
        equivalent
   responsible for this binding.  It may be that the PUBLIC filehandle
   and the ROOT filehandle refer to obsoleting an operation.  For the client, same file system object.
   However, it means
        that is up to the operation should not be sent administrative software at the server and
   the policies of the server administrator to define the server.  For binding of the
   PUBLIC filehandle and server file system object.  The client may not
   make any assumptions about this binding.  The client uses the PUBLIC
   filehandle via the PUTPUBFH operation.

4.2.  Filehandle Types

   In the
        server, an NFS error can be returned as opposed to "dropping" 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 request same as an XDR decode error.  This approach allows for before.  A new type of
   filehandle introduced in NFS Version 4 is the obsolescence "volatile" filehandle,
   which attempts to accommodate certain server environments.

   The volatile filehandle type was introduced to address server
   functionality or implementation issues which make correct
   implementation of an operation while maintaining its structure
        so that a future minor version persistent filehandle infeasible.  Some server
   environments do not provide a file system level invariant that can reintroduce the operation.

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

        2.  Minor versions construct a persistent filehandle.  The underlying server
   file system may declare flag bits not provide the invariant or enumeration values
            as mandatory to NOT implement.

   9.   Minor versions the server's file system
   programming interfaces may downgrade features from mandatory to
        recommended, or recommended not provide access to optional.

   10.  Minor versions the needed
   invariant.  Volatile filehandles may upgrade features from optional to recommended ease the implementation of
   server functionality such as hierarchical storage management or recommended to mandatory.

   11.  A file
   system reorganization or migration.  However, the volatile filehandle
   increases the implementation burden for the client.

   Since the client will need to handle persistent and server that support minor version X must support
        minor versions 0 (zero) through X-1 as well.

   12.  No new features volatile
   filehandles differently, a file attribute is defined which may be introduced as mandatory in a minor
        version.

        This rule allows for
   used by the introduction of new functionality and
        forces client to determine the use filehandle types being returned
   by the server.

4.2.1.  General Properties of implementation experience before designating a
        feature as mandatory.

   13.  A client MUST NOT attempt 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 stateid, filehandle, or
        similar returned object later request and
   can compare two filehandles from the COMPOUND procedure with minor
        version X same server for another COMPOUND procedure with minor version Y,
        where X != Y.

8.  Protocol Data Types

   The syntax and semantics to describe equality by
   doing a byte-by-byte comparison.  However, the data types client MUST NOT
   otherwise interpret the contents of filehandles.  If two filehandles
   from the NFS
   version 4 protocol same server are defined in the XDR RFC4506 [3] and RPC RFC1831
   [4] documents.  The next sections build upon the XDR data types equal, they MUST refer to
   define types and structures specific the same file.
   Servers SHOULD try to this protocol.

8.1.  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 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 file/directory attributes                |
   | bitmap4       | typedef uint32_t bitmap4<>;                       |
   |               | Used correct
   behavior.  All clients need to be prepared for situations in attribute array encoding.                 |
   | changeid4     | typedef uint64_t changeid4;                       |
   |               | Used which it
   cannot be determined whether two filehandles denote the same object
   and in definition such cases, avoid making invalid assumptions which might cause
   incorrect behavior.  Further discussion 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 filehandle and attribute data type                          |
   | nfs_cookie4   | typedef uint64_t nfs_cookie4;                     |
   |               | Opaque cookie value for READDIR                   |
   | nfs_fh4       | typedef opaque nfs_fh4<NFS4_FHSIZE>               |
   |               | Filehandle definition; NFS4_FHSIZE is defined as  |
   |               | 128                                               |
   | nfs_ftype4    | enum nfs_ftype4;                                  |
   |               | Various defined file types                        |
   | nfsstat4      | enum nfsstat4;                                    |
   |               | Return value for operations                       |
   | offset4       | typedef uint64_t offset4;                         |
   |               | Various offset designations (READ, WRITE, LOCK,   |
   |               | COMMIT)                                           |
   | pathname4     | typedef component4 pathname4<>;                   |
   |               | Represents path name for fs_locations             |
   | qop4          | typedef uint32_t qop4;                            |
   |               | Quality of protection designation
   comparison in SECINFO      |
   | sec_oid4      | typedef opaque sec_oid4<>;                        |
   |               | Security Object Identifier The sec_oid4 the context of data type |
   |               | caching is not really opaque. Instead contains presented in the section
   "Data Caching and File Identity".

   As an ASN.1   |
   |               | OBJECT IDENTIFIER as used by GSS-API example, in the       |
   |               | mech_type argument to GSS_Init_sec_context. See   |
   |               | RFC2743 [8] for details.                          |
   | seqid4        | typedef uint32_t seqid4;                          |
   |               | Sequence identifier used for case that two different path names when
   traversed at the server terminate at the same file locking         |
   | utf8string    | typedef opaque utf8string<>;                      |
   |               | UTF-8 encoding system object, the
   server SHOULD return the same filehandle 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 each path.  This can
   occur if a  |
   |               | case insensitive suffix.                          |
   | verifier4     | typedef opaque verifier4[NFS4_VERIFIER_SIZE];     |
   |               | Verifier 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 various operations (COMMIT,     |
   |               | CREATE, OPEN, READDIR, SETCLIENTID,               |
   |               | SETCLIENTID_CONFIRM, WRITE) NFS4_VERIFIER_SIZE both path names traversals.

4.2.2.  Persistent Filehandle

   A persistent filehandle is |
   |               | defined as 8.                                     |
   +---------------+---------------------------------------------------+

                          End of Base Data Types

                                  Table 1

8.2.  Structured Data Types

8.2.1.  nfstime4

   struct nfstime4 {
       int64_t seconds;
       uint32_t nseconds;
   }

   The nfstime4 structure gives having a fixed value for the number
   lifetime of seconds and nanoseconds
   since midnight or 0 hour January 1, 1970 Coordinated Universal Time
   (UTC).  Values greater than zero the file system object to which it refers.  Once the
   server creates the filehandle for a file system object, the seconds field denote dates
   after server
   MUST accept the 0 hour January 1, 1970.  Values less than zero same filehandle for the
   seconds field denote dates before object for the 0 hour January 1, 1970.  In
   both cases, lifetime of
   the nseconds field is to be added to object.  If the seconds field
   for server restarts or reboots the final time representation.  For example, NFS server must
   honor the same filehandle value as it did in the server's previous
   instantiation.  Similarly, if the time to be
   represented file system is one-half second before 0 hour January 1, 1970, migrated, the
   seconds field would have a value of negative one (-1) and new
   NFS server must honor 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 same filehandle as the old NFS server.

   The persistent filehandle will be become stale or invalid when the
   file system object is used to pass time and date information.  A removed.  When the server
   converts is presented with a
   persistent filehandle that refers to and from its local representation a deleted object, it MUST return
   an error of time NFS4ERR_STALE.  A filehandle may become stale when processing
   time values, preserving as much accuracy as possible.  If the
   precision of timestamps stored for a
   file system containing the object is less than
   defined, loss of precision can occur.  An adjunct time maintenance
   protocol is recommended to reduce client and server time skew.

8.2.2.  time_how4

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

8.2.3.  settime4

   union settime4 switch (time_how4 set_it) {
       case SET_TO_CLIENT_TIME4:
           nfstime4       time;
       default:
           void;
   }; no longer available.  The above definitions are used as file
   system may become unavailable if it exists on removable media and the attribute definitions to set
   time values.  If set_it
   media is SET_TO_SERVER_TIME4, then no longer available at the server uses
   its local representation of time for or the time value.

8.2.4.  specdata4

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

   This data type represents additional information for file system in
   whole has been destroyed or the device file
   types NF4CHR and NF4BLK.

8.2.5.  fsid4

   struct fsid4 {
       uint64_t        major;
       uint64_t        minor;
   };

8.2.6.  fs_location4

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

8.2.7.  fs_locations4

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

   The fs_location4 and fs_locations4 data types are used for system has simply been removed
   from the
   fs_locations recommended attribute which is used for migration and
   replication support.

8.2.8.  fattr4

   struct fattr4 {
       bitmap4       attrmask;
       attrlist4     attr_vals;
   };

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

   The bitmap is server's name space (i.e. unmounted in a counted array UNIX environment).

4.2.3.  Volatile Filehandle

   A volatile filehandle does not share the same longevity
   characteristics of 32 bit integers used to contain bit
   values. a persistent filehandle.  The position of the integer server may determine
   that a volatile filehandle is no longer valid at many different
   points in time.  If the array that contains bit n server can be computed from the expression (n / 32) and its bit within definitively determine that
   integer is (n mod 32).

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

8.2.9.  change_info4

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

   This structure is used with a
   volatile filehandle refers to an object that has been removed, the CREATE, LINK, REMOVE, RENAME
   operations
   server should return NFS4ERR_STALE to let the client know the value of (as is the change attribute case for
   persistent filehandles).  In all other cases where the directory in which the target file system object resides.

8.2.10.  netaddr4

   struct netaddr4 {
       /* see struct rpcb in RFC1833 */
       string r_netid<>;    /* network id */
       string r_addr<>;     /* universal address */
   }; server
   determines that a volatile filehandle can no longer be used, it
   should return an error of NFS4ERR_FHEXPIRED.

   The netaddr4 structure mandatory attribute "fh_expire_type" is used by the client to identify TCP/IP based endpoints.
   The r_netid and r_addr fields are specified in RFC1833 [20], but they
   are underspecified in RFC1833 [20] as far as
   determine what they should look
   like for specific protocols.

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

   h1.h2.h3.h4.p1.p2

   The prefix, "h1.h2.h3.h4", server is the standard textual form providing 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
   particular file system.  This attribute 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 bitmask with the
   following values:

   FH4_PERSISTENT  The value of r_netid FH4_PERSISTENT is the string "tcp".  For UDP
   over IPv4 the value of r_netid used to indicate a
      persistent filehandle, which is valid until the string "udp".

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

   x1:x2:x3:x4:x5:x6:x7:x8.p1.p2 file system.  The suffix "p1.p2" is the service port, and is computed the same way
   as with universal addresses server will not return
      NFS4ERR_FHEXPIRED for TCP and UDP over IPv4.  The prefix,
   "x1:x2:x3:x4:x5:x6:x7:x8", this filehandle.  FH4_PERSISTENT is the standard textual form for
   representing an IPv6 address as defined
      as a value in Section 2.2 which none of RFC1884
   [9].  Additionally, the two alternative forms bits specified in Section
   2.2 of RFC1884 [9] below are also acceptable.

   For TCP over IPv6 the value of r_netid 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 string "tcp6".  For UDP
   over IPv6 the value meaning of r_netid FH4_VOLATILE_ANY is
      qualified to exclude any expiration of the string "udp6".

8.2.11.  clientaddr4

   typedef netaddr4 clientaddr4;

   The clientaddr4 structure filehandle when it is used
      open.

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

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

   Servers which provide volatile filehandles that may expire while open
   (i.e. if FH4_VOL_MIGRATION or FH4_VOL_RENAME is using set or if
   FH4_VOLATILE_ANY is set and FH4_NOEXPIRE_WITH_OPEN not set), should
   deny a
   clientid RENAME or as part REMOVE that would affect an OPEN file of any of the callback registration.

8.2.12.  cb_client4

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

   This structure is used by the client
   components leading to inform the OPEN file.  In addition, the server of its call
   back address; includes should
   deny all RENAME or REMOVE requests during the program number grace period upon
   server restart.

   Servers which provide volatile filehandles that may expire while open
   require special care as regards handling of RENAMESs and client address.

8.2.13.  nfs_client_id4

   struct nfs_client_id4 {
       verifier4     verifier;
       opaque        id<NFS4_OPAQUE_LIMIT>
   }; REMOVEs.
   This structure situation can arise if FH4_VOL_MIGRATION or FH4_VOL_RENAME is part
   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 arguments
   components leading to the SETCLIENTID operation.
   NFS4_OPAQUE_LIMIT is defined as 1024.

8.2.14.  open_owner4

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

   This structure is used OPEN file.  In addition, the server should
   deny all RENAME or REMOVE requests during the grace period, in order
   to identify make sure that reclaims of files where filehandles may have
   expired do not do a reclaim for the owner wrong file.

4.3.  One Method of open state.
   NFS4_OPAQUE_LIMIT is defined as 1024.

8.2.15.  lock_owner4

   struct lock_owner4 {
       clientid4     clientid; Constructing a Volatile Filehandle

   A volatile filehandle, while opaque        owner<NFS4_OPAQUE_LIMIT>
   };

   This structure is used to identify the owner of file locking state.
   NFS4_OPAQUE_LIMIT client could contain:

   [volatile bit = 1 | server boot time | slot | generation number]
   o  slot is defined as 1024.

8.2.16.  open_to_lock_owner4

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

   This structure an index in the server volatile filehandle table

   o  generation number is used for the first LOCK operation done generation number for an
   open_owner4.  It provides both the open_stateid and lock_owner such
   that table entry/
      slot

   When the transition is made from client presents a valid open_stateid sequence to volatile filehandle, the server makes the
   following checks, which assume that of the new lock_stateid sequence.  Using this mechanism avoids check for the confirmation of volatile bit
   has passed.  If the lock_owner/lock_seqid pair since it server boot time is tied
   to established state in less than the form current server
   boot time, return NFS4ERR_FHEXPIRED.  If slot is out of range, return
   NFS4ERR_BADHANDLE.  If the open_stateid/open_seqid.

8.2.17.  stateid4

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

   This structure is used for generation number does not match, return
   NFS4ERR_FHEXPIRED.

   When the various state sharing mechanisms
   between server reboots, the table is gone (it is volatile).

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

4.4.  Client Recovery from Filehandle Expiration

   If possible, the client and server.  For SHOULD recover from the client, this data structure
   is read-only.  The starting value receipt of the seqid field is undefined. an
   NFS4ERR_FHEXPIRED error.  The server is required client must take on additional
   responsibility so that it may prepare itself to increment recover from the seqid field monotonically at
   each transition
   expiration of a volatile filehandle.  If the stateid.  This is important since server returns
   persistent filehandles, the client does not need these additional
   steps.

   For volatile filehandles, most commonly the client will inspect need to store
   the seqid in OPEN stateids component names leading up to determine and including the order of
   OPEN processing done by file system
   object in question.  With these names, the server.

8.2.18.  layouttype4

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

   A layout type specifies client should be able to
   recover by finding a filehandle in the layout being used.  The implication is
   that clients have "layout drivers" name space that support one is still
   available or more layout
   types.  The file server advertises by starting at the layout types it supports
   through root of the LAYOUT_TYPES server's file system attribute.  A client asks for
   layouts of a particular type in LAYOUTGET, and passes those layouts name
   space.

   If the expired filehandle refers to its layout driver.

   The layouttype4 structure is 32 bits in length.  The range
   represented by an object that has been removed
   from the layout type is split into two parts.  Types within file system, obviously the range 0x00000000-0x7FFFFFFF are globally unique and are assigned
   according client will not be able to
   recover from the description in Section 25.1; they are maintained by
   IANA.  Types within expired filehandle.

   It is also possible that the range 0x80000000-0xFFFFFFFF are site specific
   and for "private use" only.

   The LAYOUT_NFSV4_FILES enumeration specifies expired filehandle refers to a file that
   has been renamed.  If the NFSv4 file
   layout type was renamed by another client, again
   it is to be used.  The LAYOUT_OSD2_OBJECTS enumeration
   specifies possible that the object layout, as defined in [22], is to original client will not be used.
   Similarly, able to recover.
   However, in the LAYOUT_BLOCK_VOLUME enumeration case that the block/volume
   layout, as defined in [23], client itself is to be used.

8.2.19.  deviceid4

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

   Layout information includes device IDs that specify a storage device
   through a compact handle.  Addressing renaming the file and type information
   the file is
   obtained with open, it is possible that the GETDEVICEINFO operation.  A client must not assume
   that device IDs are valid across metadata server reboots. may be able to
   recover.  The device
   ID is qualified by client can determine the layout type and are unique per file system
   (FSID).  This allows different layout drivers to generate device IDs
   without new path name based on the need for co-ordination.  See Section 17.3.1.4 for more
   details.

8.2.20.  devlist_item4

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

   An array
   processing of these values is returned by the GETDEVICELIST operation.
   They define the set of devices associated with a file system for rename request.  The client can then regenerate the
   layout type specified in
   new filehandle based on the GETDEVICELIST4args. new path name.  The device address is used client could also use
   the compound operation mechanism to set up construct a communication channel with the
   storage device.  Different layout types will require different types set of structures to define how they communicate with storage devices.
   The opaque device_addr field must be interpreted based on operations
   like:

             RENAME A B
             LOOKUP B
             GETFH

   Note that the
   specified layout type. COMPOUND procedure does not provide atomicity.  This document defines
   example only reduces the device address for overhead of recovering from an expired
   filehandle.

5.  File Attributes

   To meet the NFSv4 file layout
   (struct netaddr4 (Section 8.2.10)), which identifies a storage device
   by network IP address requirements of extensibility and port number.  This is sufficient for the
   clients to communicate increased
   interoperability 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 non-UNIX platforms, attributes must be defined by their respective layout specifications.

8.2.21.  layout4

   struct layout4 {
       offset4                 lo_offset;
       length4                 lo_length;
       layoutiomode4           lo_iomode;
       layouttype4             lo_type;
       opaque                  lo_layout<>;
   }; handled
   in a flexible manner.  The layout4 NFS version 3 fattr3 structure defines a layout for contains a file.
   fixed list of attributes that not all clients and servers are able to
   support or care about.  The layout type
   specific data is opaque within this fattr3 structure and must can not be
   interepreted based on extended as
   new needs arise and it provides no way to indicate non-support.  With
   the layout type.  Currently, only NFS version 4 protocol, the NFSv4
   file layout type client is defined; see Section 17.4.1 for its definition.
   Since layouts are sub-dividable, able query what attributes
   the offset server supports and length together construct requests with
   the file's filehandle, the clientid, iomode, only those supported
   attributes (or a subset thereof).

   To this end, attributes are divided into three groups: mandatory,
   recommended, and layout type,
   identifies named.  Both mandatory and recommended attributes
   are supported in the layout.

8.2.22.  layoutupdate4

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

   The layoutupdate4 structure is used 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 client to return 'updated'
   layout information to bit vector sent in the GETATTR request; the metadata
   server at LAYOUTCOMMIT time.  This
   structure provides response includes a channel to pass layout type specific information
   back bit vector to the metadata server.  E.g., for block/volume layout types
   this could include the list of reserved blocks that what attributes were written.
   The contents of
   returned in the opaque lou_data argument are determined by response.  New mandatory or recommended attributes
   may be added to 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.

8.2.23.  layouthint4

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

   The layouthint4 structure is used NFS protocol between major revisions by the client to pass in
   publishing a hint
   about the type of layout it would like created for standards-track RFC which allocates a particular file.
   It is the structure specified by the FILE_LAYOUT_HINT new 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 17.4.1.

8.2.24.  layoutiomode4

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

   The iomode specifies whether the client intends to read or write
   (with
   number value and defines the possibility of reading) encoding for the data represented by attribute.  See the layout.
   The ANY iomode MUST NOT be used for LAYOUTGET, however, it can be
   used
   section "Minor Versioning" for LAYOUTRETURN and LAYOUTRECALL.  The ANY iomode specifies
   that layouts pertaining to both READ and RW iomodes further discussion.

   Named attributes are being
   returned or recalled, respectively.  The metadata server's use of the
   iomode may depend on accessed by the layout type being used.  The storage devices
   may validate I/O new OPENATTR operation, which
   accesses against the iomode and reject invalid
   accesses.

8.2.25.  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.

8.2.26.  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.

8.2.27.  threshold_item4

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

   This structure contains a list hidden directory of hints specific to attributes associated with a layout type file
   system object.  OPENATTR takes a filehandle for
   helping the client determine when it should issue I/O directly
   through object and
   returns the metadata server vs. filehandle for the data servers. attribute hierarchy.  The hint structure
   consists of filehandle
   for the layout type, named attributes is a bitmap describing the set of hints
   supported directory object accessible by the server, they may differ based on the layout type, LOOKUP
   or READDIR and a list of hints, contains files whose structure is determined by names represent the hintset
   bitmap.  See named
   attributes and whose data bytes are the mdsthreshold attribute for more details.

   The hintset is a bitmap value of the following values:

   +-------------------------+---+---------+---------------------------+ attribute.  For
   example:

        +----------+-----------+---------------------------------+
        | name LOOKUP   | # "foo"     | Data ; look up file                  | Description
        | GETATTR  | attrbits  |                                 | Type
        | OPENATTR |
   +-------------------------+---+---------+---------------------------+           | threshold4_read_size ; access foo's named attributes | 0
        | length4 LOOKUP   | The file size below which "x11icon" | ; look up specific attribute    |
        | READ     | 0,4096    | it is recommended to ; read stream of bytes          |
   |                         |   |         |
        +----------+-----------+---------------------------------+

   Named attributes are intended for data through 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 MDS.     |
   | threshold4_write_size   | 1 | length4 | IETF standards-track process.

   The file size below set of attributes which |
   |                         |   |         | it are classified as mandatory is recommended to      |
   |                         |   |         | write data through the    |
   |                         |   |         | MDS.                      |
   | threshold4_read_iosize  | 2 | length4 | For read I/O sizes below  |
   |                         |   |         | this threshold
   deliberately small since servers must do whatever it is      |
   |                         |   |         | recommended takes to read data  |
   |                         |   |         | through support
   them.  A server should support as many of the MDS           |
   | threshold4_write_iosize | 3 | length4 | For write I/O sizes below |
   |                         |   |         | this threshold it is      |
   |                         |   |         | recommended to write data |
   |                         |   |         | through attributes
   as possible but by their definition, the MDS           |
   +-------------------------+---+---------+---------------------------+

8.2.28.  mdsthreshold4

   struct mdsthreshold4 {
           threshold_item4 mth_hints<>;
   };

   This structure holds an array of threshold_item4 structures each of
   which is valid for a particular layout type.  An array is necessary
   since a server can is not required to
   support multiple layout types for a single file.

9.  Filehandles

   The filehandle in all of them.  Attributes are deemed mandatory if the NFS protocol data is
   both needed by a per server unique identifier
   for a file system object.  The contents large number of clients and is not otherwise
   reasonably computable by the filehandle are opaque
   to client when support is not provided on
   the client.  Therefore, server.

   Note that the server hidden directory returned by OPENATTR is responsible a convenience
   for translating protocol processing.  The client should not make any assumptions
   about the filehandle to an internal representation server's implementation of named attributes and whether the
   underlying file system
   object.

9.1.  Obtaining at the First Filehandle

   The server has a named attribute directory
   or not.  Therefore, operations of such as SETATTR and GETATTR on the NFS protocol
   named attribute directory are defined undefined.

5.1.  Mandatory Attributes

   These MUST be supported by every NFS version 4 client and server in terms
   order to ensure a minimum level of one or
   more filehandles.  Therefore, interoperability.  The server must
   store and return these attributes and the client needs a filehandle must be able to
   initiate communication
   function with the server.  With the NFS version 2
   protocol RFC1094 [17] and the NFS version 3 protocol RFC1813 [18],
   there exists an ancillary protocol attribute set limited to obtain this first filehandle.
   The MOUNT protocol, RPC program number 100005, provides these attributes.  With
   just the mechanism mandatory attributes some client functionality may be
   impaired or limited in some ways.  A client may ask for any of translating a string based file system path name these
   attributes to a filehandle
   which can then be used returned by the NFS protocols.

   The MOUNT protocol has deficiencies setting a bit in the area of security GETATTR request and use
   via firewalls.  This is one reason that the use of
   the public
   filehandle was introduced server must return their value.

5.2.  Recommended Attributes

   These attributes are understood well enough to warrant support in RFC2054 [24] and RFC2055 [25].  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 protocol.  However, they may not use an ancillary
   protocol for translation from string based path names to a
   filehandle.  Two special filehandles will be used as starting points supported on all
   clients and servers.  A client may ask for the NFS client.

9.1.1.  Root Filehandle

   The first of the special filehandles is the ROOT filehandle.  The
   ROOT filehandle is the "conceptual" root any of the file system name
   space at the NFS server.  The client uses or starts with the ROOT
   filehandle by employing the PUTROOTFH operation.  The PUTROOTFH
   operation instructs the server to set the "current" filehandle these attributes to
   be returned by setting a bit in the
   ROOT of GETATTR request but must handle
   the server's file tree.  Once this PUTROOTFH operation is
   used, case where the server does not return them.  A client can then traverse may ask for
   the entirety set of attributes the server's file
   tree with server supports and should not request
   attributes the LOOKUP operation. server does not support.  A complete discussion server should be tolerant
   of requests for unsupported attributes and simply not return them
   rather than considering the server
   name space 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 section "NFS Server Name Space".

9.1.2.  Public Filehandle

   The second special filehandle is the PUBLIC filehandle.  Unlike the
   ROOT filehandle, the PUBLIC filehandle may client.  For example, a file
   modification time should be bound or represent either an
   arbitrary file system object at accurate time or should not be
   supported by the server.  The server is
   responsible for this binding.  It may  This will not always be that the PUBLIC filehandle
   and the ROOT filehandle refer comfortable to
   clients but the same file system object.
   However, it client is up better positioned decide whether and how to
   fabricate or construct an attribute or whether to do without the administrative software at
   attribute.

5.3.  Named Attributes

   These attributes are not supported by direct encoding in the server NFS
   Version 4 protocol but are accessed by string names rather than
   numbers and
   the policies of the server administrator correspond to define the binding an uninterpreted stream of bytes which are
   stored with the
   PUBLIC filehandle and server file system object.  The client name space for these
   attributes may not
   make any assumptions about this binding.  The client uses the PUBLIC
   filehandle via be accessed by using the PUTPUBFH OPENATTR operation.

9.2.  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
   OPENATTR operation returns a
   persistent filehandle remain the same as before.  A new type for a virtual "attribute
   directory" and further perusal of
   filehandle introduced in NFS Version 4 is the "volatile" filehandle,
   which attempts to accommodate certain server environments.

   The volatile filehandle type was introduced to address server
   functionality or implementation issues which make correct
   implementation of a persistent filehandle infeasible.  Some server
   environments do not provide a file system level invariant that can name space may be
   used to construct a persistent done using
   READDIR and LOOKUP operations on this filehandle.  The underlying server
   file system  Named attributes
   may not provide the invariant then be examined or changed by normal READ and WRITE and CREATE
   operations on the server's file system
   programming interfaces may not provide access to the needed
   invariant.  Volatile filehandles may ease the implementation of
   server functionality such as hierarchical storage management or file
   system reorganization or migration.  However, the volatile filehandle
   increases the implementation burden for the client.

   Since the client will need to handle persistent returned from READDIR and volatile
   filehandles differently, a file attribute is defined which LOOKUP.
   Named attributes may be
   used by the have attributes.

   It is recommended that servers support arbitrary named attributes.  A
   client to determine the filehandle types being returned
   by the server.

9.2.1.  General Properties of a Filehandle

   The filehandle contains all the information should not depend on the server needs ability to
   distinguish an individual file.  To the client, the filehandle is
   opaque.  The client stores filehandles for use store any named attributes
   in a later request and
   can compare two filehandles from the same server's file system.  If a server for equality by
   doing does support named
   attributes, 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 which is also able to the same file.
   Servers SHOULD try handle them should be able
   to maintain copy a one-to-one correspondence between
   filehandles file's data and files but this is not required.  Clients MUST use
   filehandle comparisons only meta-data with complete transparency from
   one location to improve performance, not another; this would imply that names allowed for correct
   behavior.  All clients need to be prepared
   regular directory entries are valid for situations in which it
   cannot named attribute names as
   well.

   Names of attributes will not be determined whether two filehandles denote controlled by this document or other
   IETF standards track documents.  See the same object
   and in such cases, avoid making invalid assumptions which might cause
   incorrect behavior.  Further discussion section "IANA
   Considerations" for further discussion.

5.4.  Classification of filehandle and attribute
   comparison in the context Attributes

   Each of data caching is presented in the section
   "Data Caching Mandatory and File Identity".

   As an example, Recommended attributes can be classified in the case that two different path names when
   traversed at the server terminate at the same
   one of three categories: per server, per file system, or per file
   system object, the
   server SHOULD return the same filehandle for each path.  This can
   occur if a hard link object.  Note that it is used to create two possible that some per file names which refer to system
   attributes may vary within 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 system.  See the same filehandle for both path names traversals.

9.2.2.  Persistent Filehandle

   A persistent filehandle is defined as having a fixed value "homogeneous"
   attribute for its definition.  Note that the
   lifetime of the file system object attributes
   time_access_set and time_modify_set are not listed in this section
   because they are write-only attributes corresponding to which it refers.  Once the
   server creates the filehandle for time_access
   and time_modify, and are used in a file system object, the server
   MUST accept the same filehandle for the object for the lifetime special instance of
   the object.  If the server restarts or reboots the NFS server must
   honor the same filehandle value as it did in the server's previous
   instantiation.  Similarly, if the file system is migrated, the new
   NFS server must honor the same filehandle as the old NFS server. SETATTR.

   o  The persistent filehandle will be become stale or invalid when the
   file system object is removed.  When the per 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 attributes are:

         lease_time, send_impl_id, recv_impl_id

   o  The per file system containing the object is no longer available. attributes are:

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

   o  The per file system may become unavailable if it exists on removable media object attributes are:

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

   For quota_avail_hard, quota_avail_soft, and quota_used see their
   definitions below for the
   media is no longer available at the server or the file system in
   whole has been destroyed or the file system has simply been removed
   from the server's appropriate classification.

5.5.  Mandatory Attributes - Definitions

   +-----------------+----+------------+--------+----------------------+
   | name space (i.e. unmounted in a UNIX environment).

9.2.3.  Volatile Filehandle

   A volatile filehandle does not share the same longevity
   characteristics of a persistent filehandle.            | #  | Data Type  | Access | Description          |
   +-----------------+----+------------+--------+----------------------+
   | supp_attr       | 0  | bitmap     | READ   | The server may determine 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 volatile filehandle is no longer valid at many different
   points in time.  If       |
   |                 |    |            |        | matching fsid.       |
   | type            | 1  | nfs4_ftype | READ   | The type of the server can definitively determine that a
   volatile filehandle refers to an      |
   |                 |    |            |        | object that has been removed, the
   server should return NFS4ERR_STALE (file,        |
   |                 |    |            |        | directory, symlink,  |
   |                 |    |            |        | etc.)                |
   | fh_expire_type  | 2  | uint32     | READ   | Server uses this to  |
   |                 |    |            |        | specify filehandle   |
   |                 |    |            |        | expiration behavior  |
   |                 |    |            |        | to the client (as is client. See   |
   |                 |    |            |        | the case section          |
   |                 |    |            |        | "Filehandles" for
   persistent filehandles).  In all other cases where    |
   |                 |    |            |        | additional           |
   |                 |    |            |        | description.         |
   | change          | 3  | uint64     | READ   | A value created by   |
   |                 |    |            |        | 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 can use to    |
   |                 |    |            |        | determine what type of filehandle the server is providing for a
   particular if file system.  This attribute is a bitmask with the
   following values:

   FH4_PERSISTENT  The value    |
   |                 |    |            |        | data, directory      |
   |                 |    |            |        | contents or          |
   |                 |    |            |        | attributes of FH4_PERSISTENT is used to indicate a
      persistent filehandle, which is valid until the    |
   |                 |    |            |        | object is removed
      from the file system. have been     |
   |                 |    |            |        | modified. The server will not |
   |                 |    |            |        | may return
      NFS4ERR_FHEXPIRED the       |
   |                 |    |            |        | object's             |
   |                 |    |            |        | time_metadata        |
   |                 |    |            |        | attribute for this filehandle.  FH4_PERSISTENT is defined
      as a   |
   |                 |    |            |        | attribute's 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    |
   |                 |    |            |        | but only if the file |
   |                 |    |            |        | system object can    |
   |                 |    |            |        | not be set when FH4_VOLATILE_ANY is set.
      If this bit is set, then updated more  |
   |                 |    |            |        | frequently than the meaning of FH4_VOLATILE_ANY is
      qualified to exclude any expiration  |
   |                 |    |            |        | resolution of the filehandle when it is
      open.

   FH4_VOL_MIGRATION        |
   |                 |    |            |        | time_metadata.       |
   | size            | 4  | uint64     | R/W    | The filehandle will expire as a result size 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      |
   |                 |    |            |        | object in bytes.     |
   | link_support    | 5  | bool       | READ   | True, if the fs_locations_info attribute.
      When this bit is set, clients without access to fs_locations_info
      information should assume filehandles will expire on         |
   |                 |    |            |        | object's 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 |
   |                 |    |            |        | supports hard links. |
   | symlink_support | 6  | bool       | READ   | True, 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         |
   |                 |    |            |        | object's file system |
   |                 |    |            |        | supports symbolic    |
   |                 |    |            |        | links.               |
   | named_attr      | 7  | bool       | READ   | True, if this object |
   |                 |    |            |        | 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. named            |
   |                 |    |            |        | attributes. 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.

9.3.  One Method of Constructing a Volatile Filehandle

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

   [volatile bit = 1 other | 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
   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.

9.4.  Client Recovery from Filehandle Expiration

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

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

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

   It is also possible that the expired filehandle refers to a file that has been renamed.  If the file was renamed by another client, again
   it is possible that the original client will not be able to recover.

   However, in the case that the client itself is renaming the file and
   the file is open, it is possible that the client may be able to
   recover.  The client can determine the new path name based on the
   processing of the rename request.  The client can then regenerate the
   new filehandle based on the new path name.  The client could also use
   the compound operation mechanism to construct a set of operations
   like:

             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.

10.  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  |
   |                 |    |            |        | non-empty named      |
   |                 |    |            |        | attribute
   number value and defines the encoding for the attribute.  See the
   section "Minor Versioning" directory. |
   | fsid            | 8  | fsid4      | READ   | Unique file system   |
   |                 |    |            |        | identifier for further discussion.

   Named attributes are accessed by the new OPENATTR operation, which
   accesses a hidden directory of attributes associated with a   |
   |                 |    |            |        | file system holding  |
   |                 |    |            |        | this 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 fsid    |
   |                 |    |            |        | contains files whose names represent the named
   attributes major and whose data bytes are the value of the attribute.  For
   example:

        +----------+-----------+---------------------------------+   | LOOKUP
   | "foo"                 | ; look up file    |            | GETATTR        | attrbits minor components     |
   |                 | OPENATTR    |            | ; access foo's named attributes        | each of which are    | LOOKUP
   | "x11icon"                 | ; look up specific attribute    |            |        | uint64.              |
   | unique_handles  | 9  | bool       | READ   | 0,4096 True, if two         | ; 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                 |    |            |        | distinct filehandles |
   |                 |    |            |        | guaranteed to define their new attributes as recommended attributes
   by bringing them to the IETF standards-track process.

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

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

10.1.  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.

10.2.  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.

10.3.  Named Attributes

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

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

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

10.4.  Classification of Attributes

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

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

   o  The per file system object attributes are:

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

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

10.5.  Mandatory Attributes - Definitions

   +-----------------+----+------------+--------+----------------------+ two different     | name
   | #                 | Data Type    | Access            | Description        |
   +-----------------+----+------------+--------+----------------------+ file system objects. | supp_attr
   | 0 lease_time      | bitmap 10 | nfs_lease4 | READ   | The bit vector which Duration of leases   |
   |                 |    |            |        | would retrieve all at server in         |
   |                 |    |            |        | mandatory and seconds.             |
   | rdattr_error    | 11 | enum       | READ   | recommended Error returned from  |
   |                 |    |            |        | attributes that are getattr during       |
   |                 |    |            |        | supported for this readdir.             |
   | filehandle      | 19 | nfs_fh4    | READ   | object. The scope filehandle of    |
   |                 |    |            |        | this attribute object          |
   |                 |    |            |        | applies to all (primarily for       |
   |                 |    |            |        | objects with a readdir requests).   |
   +-----------------+----+------------+--------+----------------------+

5.6.  Recommended Attributes - Definitions

   +--------------------+----+---------------+--------+----------------+
   | name               | #  | Data Type     | Access | matching fsid. Description    |
   +--------------------+----+---------------+--------+----------------+
   | type ACL                | 1 12 | nfs4_ftype nfsace4<>     | READ R/W    | The type of the access     |
   |                    |    |               |        | object (file, control list   |
   |                    |    |               |        | directory, symlink, for the        |
   |                    |    |               |        | etc.) object.        |
   | fh_expire_type aclsupport         | 2 13 | uint32        | READ   | Server uses this to Indicates what |
   |                    |    |               |        | specify filehandle types of ACLs  |
   |                    |    |               |        | expiration behavior are supported  |
   |                    |    |               |        | to on the client. See current |
   |                    |    |               |        | the section file system.   |
   | archive            | 14 | bool          | R/W    | "Filehandles" for True, if this  |
   |                    |    |               |        | additional file has been  |
   |                    |    |               |        | description. archived since |
   | change                    | 3    | uint64               | READ        | A value created by the time of    |
   |                    |    |               |        | the server that the last           |
   |                    |    |               |        | client can use to modification   |
   |                    |    |               |        | determine if file (deprecated in |
   |                    |    |               |        | data, directory      |
   |                 |    |            |        | contents or          |
   |                 |    |            |        | attributes of the    |
   |                 |    |            |        | object have been     |
   |                 |    |            |        | modified. The server |
   |                 |    |            |        | may return the       |
   |                 |    |            |        | object's             |
   |                 |    |            |        | time_metadata        |
   |                 |    |            |        | attribute for this   |
   |                 |    |            |        | attribute's value    |
   |                 |    |            |        | but only if the file |
   |                 |    |            |        | system object can    |
   |                 |    |            |        | not be updated more  |
   |                 |    |            |        | frequently than the  |
   |                 |    |            |        | resolution of        |
   |                 |    |            |        | time_metadata.       |
   | size            | 4  | uint64     | R/W    | The size of the      |
   |                 |    |            |        | object in bytes.     |
   | link_support    | 5  | bool       | READ   | True, if the         |
   |                 |    |            |        | object's file system |
   |                 |    |            |        | supports hard links. |
   | symlink_support | 6  | bool       | READ   | True, if the         |
   |                 |    |            |        | object's file system |
   |                 |    |            |        | supports symbolic    |
   |                 |    |            |        | links.               |
   | named_attr      | 7  | bool       | READ   | True, if this object |
   |                 |    |            |        | has named            |
   |                 |    |            |        | attributes. In other |
   |                 |    |            |        | words, object has a  |
   |                 |    |            |        | non-empty named      |
   |                 |    |            |        | attribute directory. |
   | fsid            | 8  | fsid4      | READ   | Unique file system   |
   |                 |    |            |        | identifier for the   |
   |                 |    |            |        | file system holding  |
   |                 |    |            |        | this object. fsid    |
   |                 |    |            |        | contains major and   |
   |                 |    |            |        | minor components     |
   |                 |    |            |        | each of which are    |
   |                 |    |            |        | uint64.              |
   | unique_handles  | 9  | bool       | READ   | True, if two         |
   |                 |    |            |        | distinct filehandles |
   |                 |    |            |        | guaranteed to refer  |
   |                 |    |            |        | to two different     |
   |                 |    |            |        | file system objects. |
   | lease_time      | 10 | nfs_lease4 | READ   | Duration of leases   |
   |                 |    |            |        | at server in         |
   |                 |    |            |        | seconds.             |
   | rdattr_error    | 11 | enum       | READ   | Error returned from  |
   |                 |    |            |        | getattr during       |
   |                 |    |            |        | readdir.             |
   | filehandle      | 19 | nfs_fh4    | READ   | The filehandle of    |
   |                 |    |            |        | this object          |
   |                 |    |            |        | (primarily for       |
   |                 |    |            |        | readdir requests).   |
   +-----------------+----+------------+--------+----------------------+

10.6.  Recommended Attributes - Definitions
   +--------------------+----+---------------+--------+----------------+
   | name               | #  | Data Type     | Access | Description    |
   +--------------------+----+---------------+--------+----------------+
   | ACL                | 12 | nfsace4<>     | R/W    | The access     |
   |                    |    |               |        | control list   |
   |                    |    |               |        | for the        |
   |                    |    |               |        | object.        |
   | aclsupport         | 13 | uint32        | READ   | Indicates what |
   |                    |    |               |        | types of ACLs  |
   |                    |    |               |        | are supported  |
   |                    |    |               |        | on the current |
   |                    |    |               |        | file system.   |
   | archive            | 14 | bool          | R/W    | True, if this  |
   |                    |    |               |        | file has been  |
   |                    |    |               |        | archived since |
   |                    |    |               |        | the time of    |
   |                    |    |               |        | last           |
   |                    |    |               |        | modification   |
   |                    |    |               |        | (deprecated in |
   |                    |    |               |        | favor of favor of       |
   |                    |    |               |        | time_backup).  |
   | cansettime         | 15 | bool          | READ   | True, if the   |
   |                    |    |               |        | server able to |
   |                    |    |               |        | change the     |
   |                    |    |               |        | times for a    |
   |                    |    |               |        | file system    |
   |                    |    |               |        | object as      |
   |                    |    |               |        | specified in a |
   |                    |    |               |        | SETATTR        |
   |                    |    |               |        | operation.     |
   | case_insensitive   | 16 | bool          | READ   | True, if       |
   |                    |    |               |        | filename       |
   |                    |    |               |        | comparisons on |
   |                    |    |               |        | this file      |
   |                    |    |               |        | system are     |
   |                    |    |               |        | case           |
   |                    |    |               |        | insensitive.   |
   | case_preserving    | 17 | bool          | READ   | True, if       |
   |                    |    |               |        | filename case  |
   |                    |    |               |        | on this file   |
   |                    |    |               |        | system are     |
   |                    |    |               |        | preserved.     |
   | chown_restricted   | 18 | bool          | READ   | If TRUE, the   |
   |                    |    |               |        | server will    |
   |                    |    |               |        | reject any     |
   |                    |    |               |        | request to     |
   |                    |    |               |        | change either  |
   |                    |    |               |        | the owner or   |
   |                    |    |               |        | the group      |
   |                    |    |               |        | associated     |
   |                    |    |               |        | with a file if |
   |                    |    |               |        | the caller is  |
   |                    |    |               |        | not a          |
   |                    |    |               |        | privileged     |
   |                    |    |               |        | user (for      |
   |                    |    |               |        | example,       |
   |                    |    |               |        | "root" in UNIX |
   |                    |    |               |        | operating      |
   |                    |    |               |        | environments   |
   |                    |    |               |        | or in Windows  |
   |                    |    |               |        | 2000 the "Take |
   |                    |    |               |        | Ownership"     |
   |                    |    |               |        | privilege).    |
   | dir_notif_delay    | 56 | nfstime4      | READ   | notification   |
   |                    |    |               |        | delays on      |
   |                    |    |               |        | directory      |
   |                    |    |               |        | attributes     |
   | dirent_notif_delay | 57 | nfstime4      | READ   | notification   |
   |                    |    |               |        | delays on      |
   |                    |    |               |        | child          |
   |                    |    |               |        | attributes     |
   | fileid             | 20 | uint64        | READ   | A number       |
   |                    |    |               |        | uniquely       |
   |                    |    |               |        | identifying    |
   |                    |    |               |        | the file       |
   |                    |    |               |        | within the     |
   |                    |    |               |        | file system.   |
   | files_avail        | 21 | uint64        | READ   | File slots     |
   |                    |    |               |        | available to   |
   |                    |    |               |        | this user on   |
   |                    |    |               |        | the file       |
   |                    |    |               |        | system         |
   |                    |    |               |        | containing     |
   |                    |    |               |        | this object -  |
   |                    |    |               |        | this should be |
   |                    |    |               |        | the smallest   |
   |                    |    |               |        | relevant       |
   |                    |    |               |        | limit.         |
   | files_free         | 22 | uint64        | READ   | Free file      |
   |                    |    |               |        | slots on the   |
   |                    |    |               |        | file system    |
   |                    |    |               |        | containing     |
   |                    |    |               |        | this object -  |
   |                    |    |               |        | this should be |
   |                    |    |               |        | the smallest   |
   |                    |    |               |        | relevant       |
   |                    |    |               |        | limit.         |
   | files_total        | 23 | uint64        | READ   | Total file     |
   |                    |    |               |        | slots on the   |
   |                    |    |               |        | file system    |
   |                    |    |               |        | containing     |
   |                    |    |               |        | this object.   |
   | fs_absent          | 60 | bool          | READ   | Is current     |
   |                    |    |               |        | file system    |
   |                    |    |               |        | present or     |
   |                    |    |               |        | absent.        |
   | fs_layout_type     | 62 | layouttype4 layouttype4<> | READ   | Layout types   |
   |                    |    |               |        | available for  |
   |                    |    |               |        | the file       |
   |                    |    |               |        | system.        |
   | fs_locations       | 24 | fs_locations  | READ   | Locations      |
   |                    |    |               |        | where this     |
   |                    |    |               |        | file system    |
   |                    |    |               |        | may be found.  |
   |                    |    |               |        | If the server  |
   |                    |    |               |        | returns        |
   |                    |    |               |        | NFS4ERR_MOVED  |
   |                    |    |               |        | as an error,   |
   |                    |    |               |        | this attribute |
   |                    |    |               |        | MUST be        |
   |                    |    |               |        | supported.     |
   | fs_locations_info  | 67 |               | READ   | Full function  |
   |                    |    |               |        | file system    |
   |                    |    |               |        | location.      |
   | fs_status          | 61 | fs4_status    | READ   | Generic file   |
   |                    |    |               |        | system type    |
   |                    |    |               |        | information.   |
   | hidden             | 25 | bool          | R/W    | True, if the   |
   |                    |    |               |        | file is        |
   |                    |    |               |        | considered     |
   |                    |    |               |        | hidden with    |
   |                    |    |               |        | respect to the |
   |                    |    |               |        | Windows API?   |
   | homogeneous        | 26 | bool          | READ   | True, if this  |
   |                    |    |               |        | object's file  |
   |                    |    |               |        | system is      |
   |                    |    |               |        | homogeneous,   |
   |                    |    |               |        | i.e. are per   |
   |                    |    |               |        | file system    |
   |                    |    |               |        | attributes the |
   |                    |    |               |        | same for all   |
   |                    |    |               |        | file system's  |
   |                    |    |               |        | objects.       |
   | layout_alignment   | 66 | uint32_t      | READ   | Preferred      |
   |                    |    |               |        | alignment for  |
   |                    |    |               |        | layout related |
   |                    |    |               |        | I/O.           |
   | layout_blksize     | 65 | uint32_t      | READ   | Preferred      |
   |                    |    |               |        | block size for |
   |                    |    |               |        | layout related |
   |                    |    |               |        | I/O.           |
   | layout_hint        | 63 | layouthint4   | WRITE  | Client         |
   |                    |    |               |        | specified hint |
   |                    |    |               |        | for file       |
   |                    |    |               |        | layout.        |
   | layout_type        | 64 | layouttype4 layouttype4<> | READ   | Layout types   |
   |                    |    |               |        | available for  |
   |                    |    |               |        | the file.      |
   | maxfilesize        | 27 | uint64        | READ   | Maximum        |
   |                    |    |               |        | supported file |
   |                    |    |               |        | size for the   |
   |                    |    |               |        | file system of |
   |                    |    |               |        | this object.   |
   | maxlink            | 28 | uint32        | READ   | Maximum number |
   |                    |    |               |        | of links for   |
   |                    |    |               |        | this object.   |
   | maxname            | 29 | uint32        | READ   | Maximum        |
   |                    |    |               |        | filename size  |
   |                    |    |               |        | supported for  |
   |                    |    |               |        | this object.   |
   | maxread            | 30 | uint64        | READ   | Maximum read   |
   |                    |    |               |        | size supported |
   |                    |    |               |        | for this       |
   |                    |    |               |        | object.        |
   | maxwrite           | 31 | uint64        | READ   | Maximum write  |
   |                    |    |               |        | size supported |
   |                    |    |               |        | for this       |
   |                    |    |               |        | object. This   |
   |                    |    |               |        | attribute      |
   |                    |    |               |        | SHOULD be      |
   |                    |    |               |        | supported if   |
   |                    |    |               |        | the file is    |
   |                    |    |               |        | writable. Lack |
   |                    |    |               |        | of this        |
   |                    |    |               |        | attribute can  |
   |                    |    |               |        | lead to the    |
   |                    |    |               |        | client either  |
   |                    |    |               |        | wasting        |
   |                    |    |               |        | bandwidth or   |
   |                    |    |               |        | not receiving  |
   |                    |    |               |        | the best       |
   |                    |    |               |        | performance.   |
   | mdsthreshold       | 68 | mdsthreshold4 | READ   | Hint to client |
   |                    |    |               |        | as to when to  |
   |                    |    |               |        | write through  |
   |                    |    |               |        | the pnfs       |
   |                    |    |               |        | metadata       |
   |                    |    |               |        | server.        |
   | mimetype           | 32 | utf8<>        | R/W    | MIME body      |
   |                    |    |               |        | type/subtype   |
   |                    |    |               |        | of this        |
   |                    |    |               |        | object.        |
   | mode               | 33 | mode4         | R/W    | UNIX-style     |
   |                    |    |               |        | mode and       |
   |                    |    |               |        | permission     |
   |                    |    |               |        | bits for this  |
   |                    |    |               |        | object.        |
   | mounted_on_fileid  | 55 | uint64        | READ   | Like fileid,   |
   |                    |    |               |        | but if the     |
   |                    |    |               |        | target         |
   |                    |    |               |        | filehandle is  |
   |                    |    |               |        | the root of a  |
   |                    |    |               |        | file system    |
   |                    |    |               |        | return the     |
   |                    |    |               |        | fileid of the  |
   |                    |    |               |        | underlying     |
   |                    |    |               |        | directory.     |
   | no_trunc           | 34 | bool          | READ   | True, if a     |
   |                    |    |               |        | name longer    |
   |                    |    |               |        | than name_max  |
   |                    |    |               |        | is used, an    |
   |                    |    |               |        | error be       |
   |                    |    |               |        | returned and   |
   |                    |    |               |        | name is not    |
   |                    |    |               |        | truncated.     |
   | numlinks           | 35 | uint32        | READ   | Number of hard |
   |                    |    |               |        | links to this  |
   |                    |    |               |        | object.        |
   | owner              | 36 | utf8<>        | R/W    | The string     |
   |                    |    |               |        | name of the    |
   |                    |    |               |        | owner of this  |
   |                    |    |               |        | object.        |
   | owner_group        | 37 | utf8<>        | R/W    | The string     |
   |                    |    |               |        | name of the    |
   |                    |    |               |        | group          |
   |                    |    |               |        | ownership of   |
   |                    |    |               |        | this object.   |
   | quota_avail_hard   | 38 | uint64        | READ   | For definition |
   |                    |    |               |        | see "Quota     |
   |                    |    |               |        | Attributes"    |
   |                    |    |               |        | section below. |
   | quota_avail_soft   | 39 | uint64        | READ   | For definition |
   |                    |    |               |        | see "Quota     |
   |                    |    |               |        | Attributes"    |
   |                    |    |               |        | section below. |
   | quota_used         | 40 | uint64        | READ   | For definition |
   |                    |    |               |        | see "Quota     |
   |                    |    |               |        | Attributes"    |
   |                    |    |               |        | section below. |
   | rawdev             | 41 | specdata4     | READ   | Raw device     |
   |                    |    |               |        | identifier.    |
   |                    |    |               |        | UNIX device    |
   |                    |    |               |        | major/minor    |
   |                    |    |               |        | node           |
   |                    |    |               |        | information.   |
   |                    |    |               |        | If the value   |
   |                    |    |               |        | of type is not |
   |                    |    |               |        | NF4BLK or      |
   |                    |    |               |        | NF4CHR, the    |
   |                    |    |               |        | value return   |
   |                    |    |               |        | SHOULD NOT be  |
   |                    |    |               |        | considered     |
   |                    |    |               |        | useful.        |
   | recv_impl_id       | 59 | nfs_impl_id4 impl_ident4   | READ   | Client obtains |
   |                    |    |               |        | server the server's   |
   |                    |    |               |        | implementation |
   |                    |    |               |        | identity via   |
   |                    |    |               |        | GETATTR.       |
   | send_impl_id       | 58 | impl_ident4   | WRITE  | Client         |
   |                    |    |               |        | provides       |
   |                    |    |               |        | server with    |
   |                    |    |               |        | its            |
   |                    |    |               |        | implementation |
   |                    |    |               |        | identity via   |
   |                    |    |               |        | SETATTR.       |
   | space_avail        | 42 | uint64        | READ   | Disk space in  |
   |                    |    |               |        | bytes          |
   |                    |    |               |        | available to   |
   |                    |    |               |        | this user on   |
   |                    |    |               |        | the file       |
   |                    |    |               |        | system         |
   |                    |    |               |        | containing     |
   |                    |    |               |        | this object -  |
   |                    |    |               |        | this should be |
   |                    |    |               |        | the smallest   |
   |                    |    |               |        | relevant       |
   |                    |    |               |        | limit.         |
   | space_free         | 43 | uint64        | READ   | Free disk      |
   |                    |    |               |        | space in bytes |
   |                    |    |               |        | on the file    |
   |                    |    |               |        | system         |
   |                    |    |               |        | containing     |
   |                    |    |               |        | this object -  |
   |                    |    |               |        | this should be |
   |                    |    |               |        | the smallest   |
   |                    |    |               |        | relevant       |
   |                    |    |               |        | limit.         |
   | space_total        | 44 | uint64        | READ   | Total disk     |
   |                    |    |               |        | space in bytes |
   |                    |    |               |        | on the file    |
   |                    |    |               |        | system         |
   |                    |    |               |        | containing     |
   |                    |    |               |        | this object.   |
   | space_used         | 45 | uint64        | READ   | Number of file |
   |                    |    |               |        | system bytes   |
   |                    |    |               |        | allocated to   |
   |                    |    |               |        | this object.   |
   | system             | 46 | bool          | R/W    | True, if this  |
   |                    |    |               |        | file is a      |
   |                    |    |               |        | "system" file  |
   |                    |    |               |        | with respect   |
   |                    |    |               |        | to the Windows |
   |                    |    |               |        | API?           |
   | time_access        | 47 | nfstime4      | READ   | The time of    |
   |                    |    |               |        | last access to |
   |                    |    |               |        | the object by  |
   |                    |    |               |        | a read that    |
   |                    |    |               |        | was satisfied  |
   |                    |    |               |        | by the server. |
   | time_access_set    | 48 | settime4      | WRITE  | Set the time   |
   |                    |    |               |        | of last access |
   |                    |    |               |        | to the object. |
   |                    |    |               |        | SETATTR use    |
   |                    |    |               |        | only.          |
   | time_backup        | 49 | nfstime4      | R/W    | The time of    |
   |                    |    |               |        | last backup of |
   |                    |    |               |        | the object.    |
   | time_create        | 50 | nfstime4      | R/W    | The time of    |
   |                    |    |               |        | creation of    |
   |                    |    |               |        | the object.    |
   |                    |    |               |        | This attribute |
   |                    |    |               |        | does not have  |
   |                    |    |               |        | any relation   |
   |                    |    |               |        | to the         |
   |                    |    |               |        | traditional    |
   |                    |    |               |        | UNIX file      |
   |                    |    |               |        | attribute      |
   |                    |    |               |        | "ctime" or     |
   |                    |    |               |        | "change time". |
   | time_delta         | 51 | nfstime4      | READ   | Smallest       |
   |                    |    |               |        | useful server  |
   |                    |    |               |        | time           |
   |                    |    |               |        | granularity.   |
   | time_metadata      | 52 | nfstime4      | READ   | The time of    |
   |                    |    |               |        | last meta-data |
   |                    |    |               |        | modification   |
   |                    |    |               |        | of the object. |
   | time_modify        | 53 | nfstime4      | READ   | The time of    |
   |                    |    |               |        | last           |
   |                    |    |               |        | modification   |
   |                    |    |               |        | to the object. |
   | time_modify_set    | 54 | settime4      | WRITE  | Set the time   |
   |                    |    |               |        | of last        |
   |                    |    |               |        | modification   |
   |                    |    |               |        | to the object. |
   |                    |    |               |        | SETATTR use    |
   |                    |    |               |        | only.          |
   +--------------------+----+---------------+--------+----------------+

10.7.  Time Access

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

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

10.8.  Interpreting owner and owner_group

   The recommended attributes "owner" and "owner_group" (and also users
   and groups within the "acl" attribute) are represented in terms of a
   UTF-8 string.  To avoid a representation that is tied to a particular
   underlying implementation at the client or server, the use of the
   UTF-8 string has been chosen.  Note that section 6.1 of RFC2624 [26]
   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.

   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.

10.9.  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 [27] which may or may not included the word "CAPITAL"
   or "SMALL".  The presence of SMALL or CAPITAL allows an NFS server to
   implement unambiguous and efficient table driven mappings for case
   insensitive comparisons, and non-case-preserving storage.  For
   general character handling and internationalization issues, see the
   section "Internationalization".

10.10.  Quota Attributes

   For the attributes related to file system 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 file
      system or may be "choose the set with the smallest quota".

10.11.  mounted_on_fileid

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

   Unlike NFS version 3, NFS version 4 allows a client's LOOKUP request
   to cross other file systems.  The client detects the file system
   crossing whenever the filehandle argument of LOOKUP has an fsid
   attribute different from that of the filehandle returned by LOOKUP.
   A UNIX-based client will consider this a "mount point crossing".
   UNIX has a legacy scheme for allowing a process to determine its
   current working directory.  This relies on readdir() of a mount
   point's parent and stat() of the mount point returning fileids as
   previously described.  The mounted_on_fileid attribute corresponds to
   the fileid that readdir() would have returned as described
   previously.

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

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

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

10.12.  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
   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.

10.13.  fs_layout_type

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

10.14.  layout_type

   This attribute indicates the particular layout type(s) used for a
   file.  This is for informational purposes only.  The client needs to
   use this object -  |
   |                    |    |               |        | this should be |
   |                    |    |               |        | the LAYOUTGET operation in order to get enough information (e.g.,
   specific device information) smallest   |
   |                    |    |               |        | relevant       |
   |                    |    |               |        | limit.         |
   | space_total        | 44 | uint64        | READ   | Total disk     |
   |                    |    |               |        | space in order to perform I/O.

10.15.  layout_hint

   This attribute may be set bytes |
   |                    |    |               |        | on newly created files to influence the
   metadata server's choice for the file's layout.  It is suggested that file    |
   |                    |    |               |        | system         |
   |                    |    |               |        | containing     |
   |                    |    |               |        | this attribute is set as one object.   |
   | space_used         | 45 | uint64        | READ   | Number of the initial attributes within the
   OPEN call.  The metadata server may ignore file |
   |                    |    |               |        | system bytes   |
   |                    |    |               |        | allocated to   |
   |                    |    |               |        | this attribute.  This
   attribute object.   |
   | system             | 46 | bool          | R/W    | True, if this  |
   |                    |    |               |        | file is a sub-set of the layout structure returned by LAYOUTGET.
   For example, instead of specifying particular devices, this would be
   used      |
   |                    |    |               |        | "system" file  |
   |                    |    |               |        | with respect   |
   |                    |    |               |        | to suggest the stripe width Windows |
   |                    |    |               |        | API?           |
   | time_access        | 47 | nfstime4      | READ   | The time of a file.  It is up to the server
   implementation    |
   |                    |    |               |        | last access to determine which fields within |
   |                    |    |               |        | the layout it uses.

10.16.  mdsthreshold

   This attribute acts as object by  |
   |                    |    |               |        | a hint to the client to help it determine when
   it is more efficient to issue read and write requests to the metadata
   server vs. the dataserver.  Two types of thresholds are described:
   file size thresholds and I/O size thresholds.  If a file's size is
   smaller than the file size threshold, data accesses should be issued
   to that    |
   |                    |    |               |        | was satisfied  |
   |                    |    |               |        | by the metadata server.  If an I/O is below the I/O size threshold,
   the I/O should be issued to |
   | time_access_set    | 48 | settime4      | WRITE  | Set the metadata server.  Each threshold can
   be specified independently for read and write requests.  For either
   threshold type, a value time   |
   |                    |    |               |        | of 0 indicates no read or write should be
   issued last access |
   |                    |    |               |        | to the metadata server, while a value object. |
   |                    |    |               |        | SETATTR use    |
   |                    |    |               |        | only.          |
   | time_backup        | 49 | nfstime4      | R/W    | The time of all 1s indicates all
   reads or writes should be issued to    |
   |                    |    |               |        | last backup of |
   |                    |    |               |        | the metadata server. object.    |
   | time_create        | 50 | nfstime4      | R/W    | The attribute is available on a per filehandle basis.  If time of    |
   |                    |    |               |        | creation of    |
   |                    |    |               |        | the current
   filehandle refers object.    |
   |                    |    |               |        | This attribute |
   |                    |    |               |        | does not have  |
   |                    |    |               |        | any relation   |
   |                    |    |               |        | to a non-pNFS the         |
   |                    |    |               |        | traditional    |
   |                    |    |               |        | UNIX file      |
   |                    |    |               |        | attribute      |
   |                    |    |               |        | "ctime" or directory, the metadata     |
   |                    |    |               |        | "change time". |
   | time_delta         | 51 | nfstime4      | READ   | Smallest       |
   |                    |    |               |        | useful server should return an attribute that is representative  |
   |                    |    |               |        | time           |
   |                    |    |               |        | granularity.   |
   | time_metadata      | 52 | nfstime4      | READ   | The time of the
   filehandle's file system.  It is suggested that this attribute is
   queried as part    |
   |                    |    |               |        | last meta-data |
   |                    |    |               |        | modification   |
   |                    |    |               |        | of the OPEN operation.  Due object. |
   | time_modify        | 53 | nfstime4      | READ   | The time of    |
   |                    |    |               |        | last           |
   |                    |    |               |        | modification   |
   |                    |    |               |        | to dynamic system
   changes, the client should not assume that object. |
   | time_modify_set    | 54 | settime4      | WRITE  | Set the attribute will remain
   constant for any specific time period, thus it should be periodically
   refreshed.

11.  Access Control Lists

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

11.1.  Goals

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

   o  If a server supports the mode attribute, it should provide
      reasonable semantics to clients that only set and retrieve object. |
   |                    |    |               |        | SETATTR use    |
   |                    |    |               |        | only.          |
   +--------------------+----+---------------+--------+----------------+

5.7.  Time Access

   As defined above, the
      mode attribute.

   o  If a server supports time_access attribute represents the ACL attribute, it should provide
      reasonable semantics time of
   last access to clients that only set and retrieve the ACL
      attribute.

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

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

      *  Setting only the mode attribute should effectively control was satisfied by the
         traditional UNIX-like permissions server.
   The notion of read, write, and execute what is an "access" depends on owner, owner_group, and other.

      *  Setting only server's operating
   environment and/or the mode attribute should provide reasonable
         security. server's file system semantics.  For example, setting a mode of 000 should be enough
         to ensure that future opens
   for read or write servers obeying POSIX semantics, time_access would be updated
   only by the READLINK, READ, and READDIR operations and not any principal
         should fail, regardless of a previously existing or inherited
         ACL.

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

   o  This minor version modify the content of NFSv4 should not introduce significantly
      different semantics relating the object.  Of course, setting
   the corresponding time_access_set attribute is another way to modify
   the mode and ACL attributes, nor
      should it render invalid any existing conformant implementations.

      Rather, this chapter provides clarifications based time_access attribute.

   Whenever the file object resides on previous
      implementations and discussions around them.

   o  If a writable file system, the
   server supports should make best efforts to record time_access into stable
   storage.  However, to mitigate the ACL attribute, then at any time, performance effects of doing so,
   and most especially whenever the server can provide an ACL attribute when requested.  The ACL
      attribute will describe all permissions on is satisfying the file object, except
      for read of the three high-order bits
   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 mode attribute (described in
      Section 11.2.2). server the option to disable
   time_access updates.

5.8.  Interpreting owner and owner_group

   The ACL attribute will not conflict with recommended attributes "owner" and "owner_group" (and also users
   and groups within the
      mode attribute, on servers "acl" attribute) are represented in terms of a
   UTF-8 string.  To avoid a representation that support the mode attribute.

   o  If is tied to a server supports the mode attribute, then particular
   underlying implementation at any time, the
      server can provide a mode attribute when requested.  The mode
      attribute will not conflict with client or server, the ACL attribute, on servers
      that support use of the ACL attribute.

   o  When a mode attribute
   UTF-8 string has been chosen.  Note that section 6.1 of RFC2624 [27]
   provides additional rationale.  It is set on an object, expected that the ACL attribute may
      need to be modified so as client and
   server will have their own local representation of owner and
   owner_group that is used for local storage or presentation to not conflict with the new mode.  In
      such cases, end
   user.  Therefore, it is desirable expected that when these attributes are
   transferred between the ACL keep as much information
      as possible.  This includes information about inheritance, AUDIT
      and ALARM ACEs, and permissions granted client and denied server that do not
      conflict with the new mode.

11.2.  File Attributes Discussion

11.2.1.  ACL Attribute

   The NFS version 4 ACL attribute local
   representation is an array translated to a syntax of access control entries
   (ACEs).  Although the form "user@
   dns_domain".  This will allow for a client can read and write the ACL attribute,
   the server is responsible for using the ACL to perform access
   control.  The client can that do not use
   the OPEN or ACCESS operations same local representation the ability to translate to check
   access without modifying or reading data or metadata.

   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, the server processes each nfsace4
   entry common
   syntax that can be interpreted by both.

   Similarly, security principals may be represented in order.  Only ACEs which have different ways
   by different security mechanisms.  Servers normally translate these
   representations into a "who" common format, generally that matches used by local
   storage, to serve as a means of identifying the
   requester users corresponding
   to these security principals.  When these local identifiers are considered.  Each ACE is processed until all of
   translated to the
   bits form of the requester's access have been ALLOWED.  Once a bit (see
   below) has been ALLOWED owner attribute, associated with files
   created by an ACCESS_ALLOWED_ACE, it is no longer
   considered such principals they identify, in a common format, the processing
   users associated with each corresponding set of later ACEs.  If an ACCESS_DENIED_ACE security principals.

   The translation used to interpret owner and group strings is encountered where not
   specified as part of the requester's access still has unALLOWED bits
   in common with 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 "access_mask" 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 ACE, owner and owner_group attributes in local
   storage without any translation or it may augment a translation
   method by storing the request entire string for attributes for which no
   translation is denied.
   When available while using the ACL is fully processed, if there are bits local representation for
   those cases in the requester's
   mask which a translation is available.

   Servers that have do not been ALLOWED or DENIED, access is denied.

   Unlike the ALLOW and DENY ACE types, provide support for all possible values of the ALARM
   owner and AUDIT ACE types do
   not affect owner_group attributes, should return an error
   (NFS4ERR_BADOWNER) when a requester's access, and instead are for triggering
   events string is presented that has no
   translation, as the value to be set for a result SETATTR of the owner,
   owner_group, or acl attributes.  When a requester's access attempt.  Therefore, all
   AUDIT server does accept an owner
   or owner_group value as valid on a SETATTR (and similarly for the
   owner and ALARM ACEs are processed until end group strings in an acl), it is promising to return that
   same string when a corresponding GETATTR is done.  Configuration
   changes and ill-constructed name translations (those that contain
   aliasing) may make that promise impossible to honor.  Servers should
   make appropriate efforts to avoid a situation in which these
   attributes have their values changed when no real change to ownership
   has occurred.

   The "dns_domain" portion of the ACL.

   The NFS version 4 ACL model owner string is quite rich.  Some 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 platforms may
   provide access control functionality that goes beyond 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 UNIX-style
   mode attribute, but which case where there is not as rich as no translation available to the NFS ACL model.  So
   that users can take advantage client or
   server, the attribute value must be constructed without the "@".
   Therefore, the absence of this more limited functionality, the
   server may indicate @ from the owner or owner_group
   attribute signifies that it supports ACLs as long as it follows no translation was available at the
   guidelines for mapping between its ACL model sender
   and that the NFS version 4
   ACL model.

   The situation is complicated by receiver of the fact attribute should not use that string as
   a server may have
   multiple modules that enforce ACLs.  For example, the enforcement basis for
   NFS version 4 access may be different from translation into its own internal format.  Even though
   the enforcement for local
   access, and both attribute value can not be translated, it may still be different from useful.
   In the enforcement for access
   through other protocols such as SMB.  So it case of a client, the attribute string may be useful used for local
   display of ownership.

   To provide a
   server to accept an ACL even if not all greater degree of its modules are able to
   support it.

   The guiding principle in all cases is that the server must not accept
   ACLs 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 appear consist of
   decimal numeric values with no leading zeros can be given a special
   interpretation by clients and servers which choose to make the file more secure than it really is.

11.2.1.1.  ACE Type provide such
   support.  The constants used for the type field (acetype4) are receiver may treat such a user or group string as follows:

                     const ACE4_ACCESS_ALLOWED_ACE_TYPE = 0x00000000;
                     const ACE4_ACCESS_DENIED_ACE_TYPE  = 0x00000001;
                     const ACE4_SYSTEM_AUDIT_ACE_TYPE   = 0x00000002;
                     const ACE4_SYSTEM_ALARM_ACE_TYPE   = 0x00000003;
   +------------------------------+--------------+---------------------+
   | Value                        | Abbreviation | Description         |
   +------------------------------+--------------+---------------------+
   | ACE4_ACCESS_ALLOWED_ACE_TYPE | ALLOW        | Explicitly grants   |
   |                              |              | the access defined  |
   |                              |              | in acemask4 to
   representing the  |
   |                              |              | file same user as would be represented by a v2/v3 uid or directory.  |
   | ACE4_ACCESS_DENIED_ACE_TYPE  | DENY         | Explicitly denies   |
   |                              |              |
   gid having the access defined  |
   |                              |              | in acemask4 corresponding numeric value.  A server is not
   obligated to the  |
   |                              |              | file or directory.  |
   | ACE4_SYSTEM_AUDIT_ACE_TYPE   | AUDIT        | LOG (system         |
   |                              |              | dependent) any      |
   |                              |              | access attempt 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 |
   |                              |              | file or directory   |
   |                              |              | which uses any client might pass all of   |
   |                              |              | the access methods  |
   |                              |              | specified owners and
   groups in        |
   |                              |              | acemask4.           |
   | ACE4_SYSTEM_ALARM_ACE_TYPE   | ALARM        | Generate numeric form, a system   |
   |                              |              | ALARM (system       |
   |                              |              | dependent) server SHOULD return an NFS4ERR_BADOWNER
   error when any |
   |                              |              | access attempt there is   |
   |                              |              | made to a file or   |
   |                              |              | directory valid translation for the   |
   |                              |              | access methods      |
   |                              |              | specified user or owner
   designated in        |
   |                              |              | acemask4.           |
   +------------------------------+--------------+---------------------+

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

11.2.1.2.  The aclsupport Attribute

   A server need not support all of the above ACE types.  The bitmask
   constants used to represent way.  In that case, the above definitions within client must use 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;

   Clients should
   appropriate name@domain string and not attempt to set an ACE unless the server claims
   support special form for that ACE type.  If the server receives a request
   compatibility.

   The owner string "nobody" may be used to set designate an ACE that it cannot store, it MUST reject the request anonymous user,
   which will be associated with
   NFS4ERR_ATTRNOTSUPP.  If the server receives a request to set an ACE file created by a security principal
   that it can store but cannot enforce, be mapped through normal means to the server SHOULD reject owner attribute.

5.9.  Character Case Attributes

   With respect to the
   request with NFS4ERR_ATTRNOTSUPP.

   Example: suppose case_insensitive and case_preserving attributes,
   each UCS-4 character (which UTF-8 encodes) has a server can enforce NFS ACLs for NFS access but
   cannot enforce ACLs for local access.  If arbitrary processes can run
   on the server, then the server SHOULD NOT indicate ACL support.  On
   the other hand, if only trusted administrative programs run locally,
   then the server "long descriptive
   name" RFC1345 [28] which may indicate ACL support.

11.2.1.3.  ACE Access Mask

   The bitmask constants used for or may not included 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;

11.2.1.3.1.  Discussion word "CAPITAL"
   or "SMALL".  The presence of Mask Attributes

    ACE4_READ_DATA
       Operation(s) affected:
            READ
            OPEN
       Discussion:
            Permission SMALL or CAPITAL allows an NFS server to read the data of
   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 file.

            Servers SHOULD allow a user
   section "Internationalization".

5.10.  Quota Attributes

   For the ability attributes related to read the data
            of the file when only system quotas, the ACE4_EXECUTE access mask bit is
            allowed.

    ACE4_LIST_DIRECTORY
        Operation(s) affected:
            READDIR
        Discussion:

            Permission to list following
   definitions apply:

   quota_avail_soft  The value in bytes which represents the contents of a directory.

    ACE4_WRITE_DATA
        Operation(s) affected:
            WRITE
            OPEN
            SETATTR amount of size
        Discussion:
            Permission
      additional disk space that can be allocated to modify a file's data anywhere in the file's
            offset range.  This includes this file or
      directory before the ability to write user may reasonably be warned.  It is
      understood that this space may be consumed by allocations to any
            arbitrary offset and as other
      files or directories though there is a result rule as to grow which other
      files or directories.

   quota_avail_hard  The value in bytes which represent the file.

    ACE4_ADD_FILE
        Operation(s) affected:
            CREATE
            OPEN
        Discussion:
            Permission amount of
      additional disk space beyond the current allocation that can be
      allocated to add a new this 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 directory before further allocations
      will be refused.  It is covered understood that this space may be consumed
      by ACE4_ADD_SUBDIRECTORY.) OPEN is affected
            when used allocations to create a regular file.

    ACE4_APPEND_DATA
        Operation(s) affected:
            WRITE
            OPEN
            SETATTR of size
        Discussion: other files or directories.

   quota_used  The ability to modify a file's data, but only starting at
             EOF.  This allows for value in bytes which represent the notion amount of append-only files, disc
      space used by
             allowing ACE4_APPEND_DATA and denying ACE4_WRITE_DATA to
             the same user or group.  If a this file has an ACL such as the
             one described above or directory and possibly a WRITE request is made for
             somewhere number of
      other than EOF, similar files or directories, where the server SHOULD return
             NFS4ERR_ACCESS.

    ACE4_ADD_SUBDIRECTORY
        Operation(s) affected:
            CREATE
        Discussion:
            Permission set of "similar"
      meets at least the criterion that allocating space to create a subdirectory any file or
      directory 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 set will reduce the "quota_avail_hard" of a every
      other file or to
            lookup directory in the named attributes directory.  OPENATTR is
            affected when it is not used to create set.

      Note that there may be a named attribute
            directory.  This is when 1.) createdir is TRUE, number of distinct 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 overlapping sets
      of a file files or
            to create directories for which a named attribute directory.  OPENATTR quota_used value is
            affected when it
      maintained.  E.g. "all files with a given owner", "all files with
      a given group owner". etc.

      The server is used at liberty to create choose any of those sets but should do
      so in a named attribute
            directory.  This is when createdir is TRUE and no named
            attribute directory exists. repeatable way.  The ability to check whether rule may be configured per file
      system or not a named attribute directory exists depends on may be "choose the
            ability to look it up, therefore, users also need set with the
            ACE4_READ_NAMED_ATTRS permission in order to create a
            named attribute directory.

    ACE4_EXECUTE
        Operation(s) affected:
            LOOKUP
            READ
            OPEN
        Discussion:
            Permission to execute smallest quota".

5.11.  mounted_on_fileid

   UNIX-based operating environments connect a file or traverse/search a
            directory.

            Servers SHOULD allow a user the ability to read system into the data
            of
   namespace by connecting (mounting) the file when only system onto the ACE4_EXECUTE access mask bit is
            allowed.  This is because there is no way to execute existing
   file object (the mount point, usually a directory) of an existing
   file without reading system.  When the contents.  Though mount point's parent directory is read via an
   API like readdir(), the return results are directory entries, each
   with a server may
            treat ACE4_EXECUTE component name and ACE4_READ_DATA bits identically
            when deciding to permit a READ operation, it SHOULD still
            allow fileid.  The fileid of the two bits to mount point's
   directory entry will be set independently in ACLs, and
            MUST distinguish between them when replying to ACCESS
            operations.  In particular, servers SHOULD NOT silently
            turn on one different from the fileid that the stat()
   system call returns.  The stat() system call is returning the fileid
   of the two bits when root of the other mounted file system, whereas readdir() is set, as
            that
   returning the fileid stat() would make it impossible for have returned before any file
   systems were mounted on the client mount point.

   Unlike NFS version 3, NFS version 4 allows a client's LOOKUP request
   to correctly
            enforce cross other file systems.  The client detects the distinction between read and execute
            permissions.

             As file system
   crossing whenever the filehandle argument of LOOKUP has an example, following a SETATTR fsid
   attribute different from that of the following ACL:
                     nfsuser:ACE4_EXECUTE:ALLOW filehandle returned by LOOKUP.
   A subsequent GETATTR of ACL for that file SHOULD return:

                     nfsuser:ACE4_EXECUTE:ALLOW
             Rather than:
                     nfsuser:ACE4_EXECUTE/ACE4_READ_DATA:ALLOW

    ACE4_DELETE_CHILD
        Operation(s) affected:
            REMOVE
        Discussion:
            Permission to delete UNIX-based client will consider this a file or directory within "mount point crossing".

   UNIX has a
            directory.  See section "ACE4_DELETE vs. ACE4_DELETE_CHILD" legacy scheme 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 allowing a process to read basic attributes (non-ACLs) determine its
   current working directory.  This relies on readdir() of a file.
            On a UNIX system, basic attributes can be thought mount
   point's parent and stat() of the mount point returning fileids as
   previously described.  The mounted_on_fileid attribute corresponds to
   the stat level attributes.  Allowing this access mask bit fileid that readdir() would mean have returned as described
   previously.

   While the entity can execute "ls -l" and stat.

    ACE4_WRITE_ATTRIBUTES
        Operation(s) affected:
            SETATTR of time_access_set, time_backup,
            time_create, time_modify_set, mimetype, hidden, system
        Discussion:
            Permission NFS version 4 client could simply fabricate a fileid
   corresponding to change what mounted_on_fileid provides (and if the times associated with server
   does not support mounted_on_fileid, the client has no choice), there
   is a file
            or directory to an arbitrary value.  Also permission risk that the client will generate a fileid that conflicts with
   one that is already assigned to change another object in the mimetype, hidden file system.
   Instead, if the server can provide the mounted_on_fileid, the
   potential for client operational problems in this area is eliminated.

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

   The mounted_on_fileid attribute is RECOMMENDED, so the server SHOULD
   provide it if possible, and system attributes.
            A user having ACE4_WRITE_DATA permission, but lacking
            ACE4_WRITE_ATTRIBUTES must for a UNIX-based server, this is
   straightforward.  Usually, mounted_on_fileid will be allowed 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 implicitly set the times associated with
   fileid of a file.

    ACE4_DELETE
        Operation(s) affected:
            REMOVE
        Discussion:
            Permission 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 delete 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 directory.  See section
            "ACE4_DELETE vs. ACE4_DELETE_CHILD" more file systems to be mounted onto a
   single mount point.  In this case, for information on how
            these two access mask bits interact.

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

    ACE4_WRITE_ACL
        Operation(s) affected:
            SETATTR of acl and mode
        Discussion:
            Permission
   aforementioned invariant, it will need to write find the acl base mount point,
   and mode attributes.

    ACE4_WRITE_OWNER
        Operation(s) affected:
            SETATTR of owner not the intermediate mount points.

5.12.  send_impl_id and owner_group
        Discussions:
            Permission recv_impl_id

   These recommended attributes are used to write identify the owner client and owner_group attributes.
            On UNIX systems, this is
   server.  In the ability to execute chown().

    ACE4_SYNCHRONIZE
        Operation(s) affected:
            NONE
        Discussion:
            Permission case of the send_impl_id attribute, the client sends
   its nfs_impl_id4.  In the case of the recv_impl_id attribute, the
   client receives the server's nfs_impl_id4 value.

   Access to access file locally this identification information can be most useful at the server with
            synchronized reads both
   client and writes.

   Server server.  Being able to identify specific implementations need not provide the granularity of control
   that is implied
   can help in planning by this list of masks. administrators or implementors.  For example, POSIX-based
   systems might not distinguish ACE4_APPEND_DATA (the ability to append
   to a file) from ACE4_WRITE_DATA (the ability
   diagnostic software may extract this information in an attempt to modify existing
   contents); both masks would be tied
   identify interoperability problems, performance workload behaviors or
   general usage statistics.  Since the intent of having access to this
   information is for planning or general diagnosis only, the client and
   server MUST NOT interpret this implementation identity information in
   a single "write" permission.
   When 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 returns attributes might refuse to the client, interoperate.

   Because it would show
   both ACE4_APPEND_DATA and ACE4_WRITE_DATA if is likely some implementations will violate the protocol
   specification and only if interpret the write
   permission is enabled.

   If a server receives a SETATTR request that it cannot accurately
   implement, it should error in identity information, implementations
   MUST allow the direction users 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 NFSv4 client submits an ACE where ACE4_APPEND_DATA is and server to set but
   ACE4_WRITE_DATA is not (or vice versa), the server should reject
   contents of the
   request with NFS4ERR_ATTRNOTSUPP.  Nonetheless, sent nfs_impl_id structure to any value.

   Even though these attributes are RECOMMENDED, if the ACE has type
   DENY, the server may silently turn on the other bit, so that both
   ACE4_APPEND_DATA and ACE4_WRITE_DATA are denied.

11.2.1.3.2.  ACE4_DELETE vs. ACE4_DELETE_CHILD

   Two access mask bits govern supports
   one of them it MUST support the ability other.

5.13.  fs_layout_type

   This attribute applies to delete a file or directory
   object: ACE4_DELETE on the object itself, and ACE4_DELETE_CHILD on
   the object's parent directory.

   Many systems also consult the "sticky bit" (MODE4_SVTX) system and write
   mode bit on indicates what layout
   types are supported by the parent directory when determining whether to allow a file system.  We expect this attribute to
   be deleted.  The mode bit for write corresponds to
   ACE4_WRITE_DATA, which queried when a client encounters a new fsid.  This attribute is
   used by the same physical bit as ACE4_ADD_FILE.

   Therefore, ACE4_ADD_FILE can come into play when determining
   permission client to delete.

   In the algorithm below, determine if it has applicable layout drivers.

5.14.  layout_type

   This attribute indicates the strategy particular layout type(s) used for a
   file.  This is that ACE4_DELETE and
   ACE4_DELETE_CHILD take precedence over the sticky bit, and the sticky
   bit takes precedence over for informational purposes only.  The client needs to
   use the "write" mode bits (reflected LAYOUTGET operation in
   ACE4_ADD_FILE).

   Server implementations SHOULD grant or deny permission order to delete
   based get enough information (e.g.,
   specific device information) in order to perform I/O.

5.15.  layout_hint

   This attribute may be set on newly created files to influence the following algorithm.

       if ACE4_EXECUTE is denied by
   metadata server's choice for the parent directory ACL:
           deny delete
       else if ACE4_DELETE file's layout.  It is allowed by the target object ACL:
           allow delete
       else if ACE4_DELETE_CHILD suggested that
   this attribute is allowed by set as one of the parent
       directory ACL:
           allow delete
       else if ACE4_DELETE_CHILD is denied by initial attributes within the
       parent directory ACL:
           deny delete
       else if ACE4_ADD_FILE
   OPEN call.  The metadata server may ignore this attribute.  This
   attribute is allowed a sub-set of the layout structure returned by LAYOUTGET.
   For example, instead of specifying particular devices, this would be
   used to suggest the parent directory ACL:
           if MODE4_SVTX stripe width of a file.  It is set for up to the parent directory:
               if server
   implementation to determine which fields within the principal owns layout it uses.

5.16.  mdsthreshold

   This attribute acts as a hint to the parent directory OR client to help it determine when
   it is more efficient to issue read and write requests to the principal owns metadata
   server vs. the target object OR
                   ACE4_WRITE_DATA dataserver.  Two types of thresholds are described:
   file size thresholds and I/O size thresholds.  If a file's size is allowed by
   smaller than the target
                   object ACL:
                       allow delete
                   else:
                       deny delete
           else:
               allow delete
       else:
           deny delete

11.2.1.4.  ACE flag

   The bitmask constants used file size threshold, data accesses should be issued
   to the metadata server.  If an I/O is below the I/O size threshold,
   the I/O should be issued to the metadata server.  Each threshold can
   be specified independently for read and write requests.  For either
   threshold type, a value of 0 indicates no read or write should be
   issued to the flag field are as follows:

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

   A server need not support any metadata server, while a value of these flags. all 1s indicates all
   reads or writes should be issued to the metadata server.

   The attribute is available on a per filehandle basis.  If the current
   filehandle refers to a non-pNFS file or directory, the metadata
   server supports
   flags should return an attribute that are similar to, but not exactly the same as, these flags,
   the implementation may define a mapping between is representative of the protocol-defined
   flags and
   filehandle's file system.  It is suggested that this attribute is
   queried as part of the implementation-defined flags.  Again, OPEN operation.  Due to dynamic system
   changes, the guiding
   principle is client should not assume that the file not appear to be more secure than attribute will remain
   constant for any specific time period, thus it
   really is.

   For example, suppose should be periodically
   refreshed.

6.  Access Control Lists

   Access Control Lists (ACLs) are a client tries to set an ACE with
   ACE4_FILE_INHERIT_ACE set file attribute that specify fine
   grained access control.  This chapter covers the "acl", "aclsupport",
   and "mode" file attributes, and their interactions.

6.1.  Goals

   ACLs and modes represent two well established but not ACE4_DIRECTORY_INHERIT_ACE.  If different models
   for specifying permissions.  This chapter specifies requirements that
   attempt to meet the following goals:

   o  If a server does not support any form of ACL inheritance, supports the server mode attribute, it should reject provide
      reasonable semantics to clients that only set and retrieve the request with NFS4ERR_ATTRNOTSUPP.
      mode attribute.

   o  If the a server supports a single "inherit ACE" flag that applies the ACL attribute, it should provide
      reasonable semantics to both files clients that only set and
   directories, retrieve the server may reject ACL
      attribute.

   o  On servers that support the request (i.e., requiring mode attribute, if the
   client to ACL attribute
      has never been set both the file and directory on an object, via inheritance flags).  The
   server may also accept or explicitly,
      the request and silently turn behavior should be traditional UNIX-like behavior.

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

      *  Setting only the
   ACE4_DIRECTORY_INHERIT_ACE flag.

11.2.1.4.1.  Discussion mode attribute should effectively control the
         traditional UNIX-like permissions of Flag Bits

   ACE4_FILE_INHERIT_ACE
      Can be placed read, write, and execute
         on a directory owner, owner_group, and indicates that this ACE other.

      *  Setting only the mode attribute should provide reasonable
         security.  For example, setting a mode of 000 should be
      added enough
         to each new non-directory file created.

   ACE4_DIRECTORY_INHERIT_ACE
      Can be placed on a directory and indicates ensure that this ACE future opens for read or write by any principal
         should fail, regardless of a previously existing or inherited
         ACL.

   o  It must be
      added possible to each new directory created.

   ACE4_INHERIT_ONLY_ACE
      Can be placed on implement a directory but does server such that its clients
      can have POSIX compliant semantics.

   o  This minor version of NFSv4 should not apply introduce significantly
      different semantics relating to the directory;
      ALLOW mode and DENY ACEs with ACL attributes, nor
      should it render invalid any existing implementations.  Rather,
      this bit set do not affect access to the
      directory, and AUDIT chapter provides clarifications based on previous
      implementations and ALARM ACEs with this bit set do discussions around them.

   o  If a server supports the ACL attribute, then at any time, the
      server can provide an ACL attribute when requested.  The ACL
      attribute will describe all permissions on the file object, except
      for the three high-order bits of the mode attribute (described in
      Section 6.2.2).  The ACL attribute will not
      trigger log or alarm events.  Such ACEs only take effect once they
      are applied (with this bit cleared) to newly created files and
      directories as specified by conflict with the above two flags.

   ACE4_NO_PROPAGATE_INHERIT_ACE
      Can be placed mode
      attribute, on a directory.  This flag tells servers that support the mode attribute.

   o  If a server that
      inheritance of this ACE should stop supports the mode attribute, then at newly created child
      directories.

   ACE4_SUCCESSFUL_ACCESS_ACE_FLAG

   ACE4_FAILED_ACCESS_ACE_FLAG any time, the
      server can provide a mode attribute when requested.  The ACE4_SUCCESSFUL_ACCESS_ACE_FLAG (SUCCESS) and
      ACE4_FAILED_ACCESS_ACE_FLAG (FAILED) flag bits relate only mode
      attribute will not conflict with the ACL attribute, on servers
      that support the ACL attribute.

   o  When a mode attribute is set on an object, the ACL attribute may
      need to
      ACE4_SYSTEM_AUDIT_ACE_TYPE (AUDIT) be modified so as to not conflict with the new mode.  In
      such cases, it is desirable that the ACL keep as much information
      as possible.  This includes information about inheritance, AUDIT
      and ACE4_SYSTEM_ALARM_ACE_TYPE
      (ALARM) ACE types.  If during ALARM ACEs, and permissions granted and denied that do not
      conflict with the processing new mode.

6.2.  File Attributes Discussion

6.2.1.  ACL Attribute

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

   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, the server processes each nfsace4
   entry in order.  Only ACEs which have a "who" that matches the
      principal attempting
   requester are considered.  Each ACE is processed until all of the OPEN,
   bits of the server notes that fact, and 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
      presence, if any, processing of the SUCCESS and FAILED flags later ACEs.  If an ACCESS_DENIED_ACE
   is encountered where the requester's access still has unALLOWED bits
   in common with the AUDIT or ALARM ACE.  Once "access_mask" of the server completes ACE, the request is denied.
   When the ACL
      processing, it then notes is fully processed, if there are bits in the operation succeeded requester's
   mask that have not been ALLOWED or failed.
      If DENIED, access is denied.

   Unlike the operation succeeded, ALLOW and if DENY ACE types, the SUCCESS flag was set for a
      matching AUDIT or ALARM ACE, then the appropriate and AUDIT or ALARM
      event occurs.  If the operation failed, ACE types do
   not affect a requester's access, and if the FAILED flag was
      set instead are for the matching AUDIT or ALARM ACE, then the appropriate triggering
   events as a result of a requester's access attempt.  Therefore, all
   AUDIT or and ALARM event occurs.  Either or both ACEs are processed until end of the SUCCESS or
      FAILED can be set, but if neither ACL.

   The NFS version 4 ACL model is set, quite rich.  Some server platforms may
   provide access control functionality that goes beyond the AUDIT or ALARM ACE UNIX-style
   mode attribute, but which is not useful.

      The previously described processing applies to that of the ACCESS
      operation as well, rich as 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 NFS ACL model.  So
   that users can take advantage of this more limited functionality, the "who" refers to a GROUP
   server may indicate that it supports ACLs as defined under UNIX
      or a GROUP ACCOUNT long as defined under Windows.  Clients and servers
      must ignore it follows the ACE4_IDENTIFIER_GROUP flag on ACEs with a who
      value equal to one of
   guidelines for mapping between its ACL model and the special identifiers outlined in
      Section 11.2.1.5.

11.2.1.5.  ACE Who NFS version 4
   ACL model.

   The "who" field of an ACE situation is an identifier that specifies the
   principal or principals to whom complicated by the ACE applies.  It may refer to a
   user or fact that a group, with server may have
   multiple modules that enforce ACLs.  For example, the flag bit ACE4_IDENTIFIER_GROUP specifying
   which.

   There are several special identifiers which need to enforcement for
   NFS version 4 access may be understood
   universally, rather than in different from the context of a particular DNS domain.
   Some of these identifiers cannot enforcement for local
   access, and both may be understood when an NFS client
   accesses different from the server, but have meaning when enforcement for access
   through other protocols such as SMB.  So it may be useful for a local process accesses
   the file.  The ability
   server to display and modify these permissions is
   permitted over NFS, accept an ACL even if none not all of the access methods on its modules are able to
   support it.

   The guiding principle in all cases is that the server
   understands must not accept
   ACLs that appear to make the identifiers.

   +---------------+--------------------------------------------------+ file more secure than it really is.

6.2.1.1.  ACE Type

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

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

   +------------------------------+--------------+---------------------+
   | Who Value                        | Abbreviation | Description         |
   +---------------+--------------------------------------------------+
   +------------------------------+--------------+---------------------+
   | OWNER ACE4_ACCESS_ALLOWED_ACE_TYPE | ALLOW        | Explicitly grants   | The owner of the file
   |                              | GROUP              | The group associated with the file. access defined  |
   | EVERYONE                              | The world, including              | in acemask4 to the owner and owning group.  |
   | INTERACTIVE                              | Accessed from an interactive terminal.              | file or directory.  |
   | ACE4_ACCESS_DENIED_ACE_TYPE  | DENY         | Explicitly denies   |
   |                              | NETWORK              | Accessed via the network. access defined  |
   | DIALUP                              | Accessed as a dialup user              | in acemask4 to the server.  |
   | BATCH                              | Accessed from a batch job.              | file or directory.  |
   | ANONYMOUS ACE4_SYSTEM_AUDIT_ACE_TYPE   | Accessed without AUDIT        | LOG (system         |
   |                              |              | dependent) any authentication.      |
   | AUTHENTICATED                              | Any authenticated user (opposite              | access attempt to a |
   |                              |              | file or directory   |
   |                              |              | which uses any of ANONYMOUS)   |
   | SERVICE                              | Access from              | the access methods  |
   |                              |              | specified in        |
   |                              |              | acemask4.           |
   | ACE4_SYSTEM_ALARM_ACE_TYPE   | ALARM        | Generate a system service.   |
   +---------------+--------------------------------------------------+

                                  Table 7

   To avoid conflict, these special identifiers are distinguish by an
   appended "@" and should appear
   |                              |              | ALARM (system       |
   |                              |              | dependent) when any |
   |                              |              | access attempt is   |
   |                              |              | made to a file or   |
   |                              |              | directory for the   |
   |                              |              | access methods      |
   |                              |              | specified in        |
   |                              |              | acemask4.           |
   +------------------------------+--------------+---------------------+

    The "Abbreviation" column denotes how the form "xxxx@" (note: no domain
   name after types will be referred to
                   throughout the "@").  For example: ANONYMOUS@.

11.2.1.5.1.  Discussion rest of EVERYONE@

   It is important to note that "EVERYONE@" is this document.

6.2.1.2.  The aclsupport Attribute

   A server need not equivalent support all of the above ACE types.  The bitmask
   constants used to represent the
   UNIX "other" entity.  This is because, by definition, UNIX "other"
   does 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;

   Clients should not include attempt to set an ACE unless the owner or owning group of server claims
   support for that ACE type.  If the server receives a file.  "EVERYONE@"
   means literally everyone, including request to set
   an ACE that it cannot store, it MUST reject the owner or owning group.

11.2.2.  mode Attribute

   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 version 4 mode attribute is based ACLs for NFS access but
   cannot enforce ACLs for local access.  If arbitrary processes can run
   on the UNIX mode bits. server, then the server SHOULD NOT indicate ACL support.  On
   the other hand, if only trusted administrative programs run locally,
   then the server may indicate ACL support.

6.2.1.3.  ACE Access Mask

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

              const MODE4_SUID ACE4_READ_DATA            = 0x800;  /* set user id on execution */ 0x00000001;
              const MODE4_SGID ACE4_LIST_DIRECTORY       = 0x400;  /* set group id on execution */ 0x00000001;
              const MODE4_SVTX ACE4_WRITE_DATA           = 0x200;  /* save text even after use */ 0x00000002;
              const MODE4_RUSR ACE4_ADD_FILE             = 0x100;  /* read permission: owner */ 0x00000002;
              const MODE4_WUSR ACE4_APPEND_DATA          = 0x080;  /* write permission: owner */ 0x00000004;
              const MODE4_XUSR ACE4_ADD_SUBDIRECTORY     = 0x040;  /* execute permission: owner */ 0x00000004;
              const MODE4_RGRP ACE4_READ_NAMED_ATTRS     = 0x020;  /* read permission: group */ 0x00000008;
              const MODE4_WGRP ACE4_WRITE_NAMED_ATTRS    = 0x010;  /* write permission: group */ 0x00000010;
              const MODE4_XGRP ACE4_EXECUTE              = 0x008;  /* execute permission: group */ 0x00000020;
              const MODE4_ROTH ACE4_DELETE_CHILD         = 0x004;  /* read permission: other */ 0x00000040;
              const MODE4_WOTH ACE4_READ_ATTRIBUTES      = 0x002;  /* write permission: other */ 0x00000080;
              const MODE4_XOTH ACE4_WRITE_ATTRIBUTES     = 0x001;  /* execute permission: other */

   Bits MODE4_RUSR, MODE4_WUSR, 0x00000100;
              const ACE4_DELETE               = 0x00010000;
              const ACE4_READ_ACL             = 0x00020000;
              const ACE4_WRITE_ACL            = 0x00040000;
              const ACE4_WRITE_OWNER          = 0x00080000;
              const ACE4_SYNCHRONIZE          = 0x00100000;

6.2.1.3.1.  Discussion of Mask Attributes

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

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

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

    ACE4_WRITE_DATA
        Operation(s) affected:
            WRITE
            OPEN
            SETATTR of size
        Discussion:
            Permission to modify a file's data anywhere in the file's
            offset range.  This includes the ability to write to any
            arbitrary offset and MODE4_XUSR apply as a result to grow the file.

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

    ACE4_APPEND_DATA
        Operation(s) affected:
            WRITE
            OPEN
            SETATTR of size
        Discussion:
             The ability to modify a file's data, but only starting at
             EOF.  This allows for the principal
   identified in the owner attribute.  Bits MODE4_RGRP, MODE4_WGRP, notion of append-only files, by
             allowing ACE4_APPEND_DATA and
   MODE4_XGRP apply denying ACE4_WRITE_DATA to principals identified in the owner_group
   attribute but who are not identified in
             the owner attribute.  Bits
   MODE4_ROTH, MODE4_WOTH, MODE4_XOTH apply to any principal that does
   not match that in same user or group.  If a file has an ACL such as the owner attribute,
             one described above and does not have a group
   matching that of WRITE request is made for
             somewhere other than EOF, the owner_group attribute.

   The remaining bits are not defined by this protocol.  A server MUST
   NOT SHOULD return bits other than those defined above in
             NFS4ERR_ACCESS.

    ACE4_ADD_SUBDIRECTORY
        Operation(s) affected:
            CREATE
        Discussion:
            Permission to create a GETATTR or
   READDIR operation, and it MUST return NFS4ERR_INVAL if bits other
   than those defined above are set subdirectory in a SETATTR, CREATE, or OPEN
   operation.

11.3.  Common Methods directory.  The requirements in this section will be referred
            CREATE operation is affected when nfs_ftype4 is NF4DIR.

    ACE4_READ_NAMED_ATTRS
        Operation(s) affected:
            OPENATTR
        Discussion:
            Permission to in future
   sections, especially Section 11.4.

11.3.1.  Interpreting an ACL

11.3.1.1.  Server Considerations

   The server uses read the algorithm described in Section 11.2.1 to
   determine whether an ACL allows access named attributes of a file or to an object.  However,
            lookup the
   ACL may named attributes directory.  OPENATTR is
            affected when it is not be the sole determiner of access.  For example:

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

   o  Server implementations MAY grant ACE4_WRITE_ACL 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 ACE4_READ_ACL
      permissions in order no named
            attribute directory exists.  The ability to prevent the owner from getting into check whether
            or not a named attribute directory exists depends on the
      situation where they can't ever modify
            ability to look it up, therefore, users also need the ACL.

   o  All servers will
            ACE4_READ_NAMED_ATTRS permission in order to create a
            named attribute directory.

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

            Servers SHOULD allow a user the ability to read the data
            of the file when only the execute permission is granted (i.e.  If the ACL
      denies the user the ACE4_READ_DATA ACE4_EXECUTE access and allows the user
      ACE4_EXECUTE, mask bit is
            allowed.  This is because there is no way to execute a
            file without reading the contents.  Though a server will may
            treat ACE4_EXECUTE and ACE4_READ_DATA bits identically
            when deciding to permit a READ operation, it SHOULD still
            allow the user two bits to read the data of
      the file).

   o  Many be set independently in ACLs, and
            MUST distinguish between them when replying to ACCESS
            operations.  In particular, servers have the notion SHOULD NOT silently
            turn on one of owner-override in which the owner
      of two bits when the object other is allowed to override accesses set, as
            that are denied by
      the ACL.  This may be helpful, would make it impossible for the client to correctly
            enforce the distinction between read and execute
            permissions.

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

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

    ACE4_DELETE_CHILD
        Operation(s) affected:
            REMOVE
        Discussion:
            Permission to allow users
      continued 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 open files on which read basic attributes (non-ACLs) of a file.
            On a UNIX system, basic attributes can be thought of as
            the permissions have
      changed.

11.3.1.2.  Client Considerations

   Clients SHOULD NOT do their own stat level attributes.  Allowing this access checks based on their
   interpretation the ACL, but rather use mask bit
            would mean the OPEN entity can execute "ls -l" and ACCESS operations stat.

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

    ACE4_DELETE
        Operation(s) affected:
            REMOVE
        Discussion:
            Permission to delete the file or not access should be granted
   based directory.  See section
            "ACE4_DELETE vs. ACE4_DELETE_CHILD" for information on its interpretation how
            these two access mask bits interact.

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

   Clients must be aware

    ACE4_WRITE_ACL
        Operation(s) affected:
            SETATTR of situations in which an object's ACL will
   define a certain acl and mode
        Discussion:
            Permission to write the acl and mode attributes.

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

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

   Server implementations need not enforce it.
   In general, but especially in these situations, the client needs to
   do its part in provide the enforcement granularity of access as defined control
   that is implied by the ACL.  To
   do this, the client MAY issue the appropriate ACCESS operation prior this list of masks.  For example, POSIX-based
   systems might not distinguish ACE4_APPEND_DATA (the ability to servicing append
   to a file) from ACE4_WRITE_DATA (the ability to modify existing
   contents); both masks would be tied to a single "write" permission.
   When such a server returns attributes to the client, it would show
   both ACE4_APPEND_DATA and ACE4_WRITE_DATA if and only if the write
   permission is enabled.

   If a server receives a SETATTR request of that it cannot accurately
   implement, it should error in the user or application direction of more restricted
   access.  For example, suppose a server cannot distinguish overwriting
   data from appending new data, as described in order to
   determine whether the user or application previous paragraph.
   If a client submits an ACE where ACE4_APPEND_DATA is set but
   ACE4_WRITE_DATA is not (or vice versa), the server should be granted reject the
   access requested.  For examples in which
   request with NFS4ERR_ATTRNOTSUPP.  Nonetheless, if the ACL may define accesses
   that ACE has type
   DENY, the server doesn't enforce see Section 11.3.1.1.

11.3.2.  Computing a Mode Attribute from an ACL

   The following method can be used to calculate may silently turn on the MODE4_R*, MODE4_W* other bit, so that both
   ACE4_APPEND_DATA and MODE4_X* ACE4_WRITE_DATA are denied.

6.2.1.3.2.  ACE4_DELETE vs. ACE4_DELETE_CHILD

   Two access mask bits of govern the ability to delete a mode attribute, based upon an ACL.

   1.  To determine MODE4_ROTH, MODE4_WOTH, file or directory
   object: ACE4_DELETE on the object itself, and MODE4_XOTH:

       1.  If ACE4_DELETE_CHILD on
   the special identifier EVERYONE@ is granted
           ACE4_READ_DATA, then object's parent directory.

   Many systems also consult the "sticky bit" (MODE4_SVTX) and write
   mode bit MODE4_ROTH SHOULD be set.
           Otherwise, MODE4_ROTH SHOULD NOT be set.

       2.  If the special identifier EVERYONE@ is granted
           ACE4_WRITE_DATA or ACE4_APPEND_DATA, then on the bit MODE4_WOTH
           SHOULD be set.  Otherwise, MODE4_WOTH SHOULD NOT parent directory when determining whether to allow a
   file to be set.

       3.  If the special identifier EVERYONE@ deleted.  The mode bit for write corresponds to
   ACE4_WRITE_DATA, which is granted ACE4_EXECUTE,
           then the same physical bit MODE4_XOTH SHOULD be set.  Otherwise, MODE4_XOTH
           SHOULD NOT be set.

   2.  To determine MODE4_RGRP, MODE4_WGRP, and MODE4_XGRP, note that
       the EVERYONE@ special identifier SHOULD be taken as ACE4_ADD_FILE.
   Therefore, ACE4_ADD_FILE can come into account.
       In other words, play when determining if
   permission to delete.

   In the GROUP@ special identifier
       is granted a permission, ACEs with algorithm below, the identifier EVERYONE@
       should strategy is that ACE4_DELETE and
   ACE4_DELETE_CHILD take effect just as ACEs with the special identifier
       GROUP@ would.

       1.  If precedence over the special identifier GROUP@ is granted ACE4_READ_DATA,
           then sticky bit, and the sticky
   bit MODE4_RGRP SHOULD be set.  Otherwise, MODE4_RGRP takes precedence over the "write" mode bits (reflected in
   ACE4_ADD_FILE).

   Server implementations SHOULD NOT be set.

       2.  If grant or deny permission to delete
   based on the special identifier GROUP@ following algorithm.

       if ACE4_EXECUTE is granted ACE4_WRITE_DATA
           or ACE4_APPEND_DATA, then denied by the bit MODE4_WGRP SHOULD be set.
           Otherwise, MODE4_WGRP SHOULD NOT be set.

       3.  If parent directory ACL:
           deny delete
       else if ACE4_DELETE is allowed by the special identifier GROUP@ target object ACL:
           allow delete
       else if ACE4_DELETE_CHILD is granted ACE4_EXECUTE,
           then allowed by the bit MODE4_XGRP SHOULD be set.  Otherwise, MODE4_XGRP
           SHOULD NOT be set.

   3.  To determine MODE4_RUSR, MODE4_WUSR, and MODE4_XUSR, note that parent
       directory ACL:
           allow delete
       else if ACE4_DELETE_CHILD is denied by the EVERYONE@ special identifier SHOULD be taken into account.
       In other words, when determining
       parent directory ACL:
           deny delete
       else if ACE4_ADD_FILE is allowed by the OWNER@ special identifier parent directory ACL:
           if MODE4_SVTX is granted a permission, ACEs with set for the identifier EVERYONE@
       should take effect just as ACEs with parent directory:
               if the special identifer OWNER@
       would.

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

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

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

11.3.2.1.  Discussion target
                   object ACL:
                       allow delete
                   else:
                       deny delete
           else:
               allow delete
       else:
           deny delete

6.2.1.4.  ACE flag

   The nine low-order mode bits (MODE4_R*, MODE4_W*, MODE4_X*)
   correspond to ACE4_READ_DATA, ACE4_WRITE_DATA/ACE4_APPEND_DATA, and
   ACE4_EXECUTE bitmask constants used for OWNER@, GROUP@, and EVERYONE@.  On some
   implementations, mode bits may represent a superset the flag field are as follows:

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

   A server need not support any of these
   permissions, e.g. if flags.  If the server supports
   flags that are similar to, but not exactly the same as, these flags,
   the implementation may define a specific user is granted ACE4_WRITE_DATA, then
   MODE4_WGRP will be set, even though mapping between the file's owner_group protocol-defined
   flags and the implementation-defined flags.  Again, the guiding
   principle is not
   granted ACE4_WRITE_DATA.

   Server implementations are discouraged from doing this, as experience
   has shown that this is confusing and annoying the file not appear to end users.  The
   specifications above also discourage this practice be more secure than it
   really is.

   For example, suppose a client tries to enforce set an ACE with
   ACE4_FILE_INHERIT_ACE set but not ACE4_DIRECTORY_INHERIT_ACE.  If the
   semantic that setting
   server does not support any form of ACL inheritance, the server
   should reject the request with NFS4ERR_ATTRNOTSUPP.  If the mode attribute effectively specifies read,
   write, and execute for owner, group, and other.

11.4.  Requirements

   The server that
   supports a single "inherit ACE" flag that applies to both mode files and ACL must take care to
   synchronize
   directories, the MODE4_*USR, MODE4_*GRP, and MODE4_*OTH bits with server may reject the
   ACEs which have respective who fields of "OWNER@", "GROUP@", and
   "EVERYONE@" so that request (i.e., requiring the
   client can see semantically equivalent access
   permissions exist whether to set both the client asks for owner, owner_group file and
   mode attributes, or for just directory inheritance flags).  The
   server may also accept the ACL.

   In this section, much is made of request and silently turn on the methods in Section 11.3.2.  Many
   requirements refer to this section.  But note
   ACE4_DIRECTORY_INHERIT_ACE flag.

6.2.1.4.1.  Discussion of Flag Bits

   ACE4_FILE_INHERIT_ACE
      Can be placed on a directory and indicates that the methods have
   behaviors specified with "SHOULD".  This is intentional, this ACE should be
      added to avoid
   invalidating existing implementations each new non-directory file created.

   ACE4_DIRECTORY_INHERIT_ACE
      Can be placed on a directory and indicates that compute the mode according this ACE should be
      added to the withdrawn POSIX ACL draft (1003.1e draft 17), rather than by
   actual permissions each new directory created.

   ACE4_INHERIT_ONLY_ACE
      Can be placed on owner, group, a directory but does not apply to the directory;
      ALLOW and other.

11.4.1.  Setting DENY ACEs with this bit set do not affect access to the mode and/or ACL Attributes

11.4.1.1.  Setting mode
      directory, and AUDIT and ALARM ACEs with this bit set do not ACL

   When setting
      trigger log or alarm events.  Such ACEs only take effect once they
      are applied (with this bit cleared) to newly created files and
      directories as specified by the above two flags.

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

   ACE4_SUCCESSFUL_ACCESS_ACE_FLAG

   ACE4_FAILED_ACCESS_ACE_FLAG
      The ACE4_SUCCESSFUL_ACCESS_ACE_FLAG (SUCCESS) and not an ACL attribute,
      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 mode
   attribute MUST be set as given.  The ACL attribute MUST be modified
   such processing of the file's ACL,
      the server encounters an AUDIT or ALARM ACE that matches the mode computed via
      principal attempting the method in Section 11.3.2 yields OPEN, the low-order nine bits (MODE4_R*, MODE4_W*, MODE4_X*) server notes that fact, and the
      presence, if any, of the newly
   set mode attribute.  The ACL SHOULD also be modified such that:

   1.  If MODE4_RGRP is not set, entities explicitly listed SUCCESS and FAILED flags encountered in
      the AUDIT or ALARM ACE.  Once the server completes the ACL
       other than OWNER@ and EVERYONE@ SHOULD NOT be granted
       ACE4_READ_DATA.

   2.
      processing, it then notes if the operation succeeded or failed.
      If MODE4_WGRP is not set, entities explicitly listed in the ACL
       other than OWNER@ operation succeeded, and EVERYONE@ SHOULD NOT be granted
       ACE4_WRITE_DATA if the SUCCESS flag was set for a
      matching AUDIT or ACE4_APPEND_DATA.

   3. ALARM ACE, then the appropriate AUDIT or ALARM
      event occurs.  If MODE4_XGRP is not set, entities explicitly listed in the ACL
       other than OWNER@ operation failed, and EVERYONE@ SHOULD NOT be granted
       ACE4_EXECUTE.

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

   Note that ACEs with if the FAILED flag ACE4_INHERIT_ONLY_ACE was
      set do not affect for the permissions of matching AUDIT or ALARM ACE, then the ACL itself, nor do ACEs appropriate
      AUDIT or ALARM event occurs.  Either or both of the type SUCCESS or
      FAILED can be set, but if neither is set, the AUDIT and
   ALARM.  As such, it or ALARM ACE
      is desirable not useful.

      The previously described processing applies to leave these ACEs unmodified when
   modifying the ACL attribute.

   Also note that of the requirement may be met by discarding ACCESS
      operation as well, the ACL, in
   favor of an ACL difference being that represents the mode "success" or
      "failure" does not mean whether ACCESS returns NFS4_OK or not.
      Success means whether ACCESS returns all requested and only the mode.  This is
   permitted, but it is preferable for supported
      bits.  Failure means whether ACCESS failed to return a server bit that
      was requested and supported.

   ACE4_IDENTIFIER_GROUP
      Indicates that the "who" refers to preserve a GROUP as much of
   the ACL defined under UNIX
      or a GROUP ACCOUNT as possible without violating the above requirements.
   Discarding defined under Windows.  Clients and servers
      must ignore the ACL makes it effectively impossible for a file created ACE4_IDENTIFIER_GROUP flag on ACEs with a mode attribute who
      value equal to inherit an ACL (see one of the special identifiers outlined in
      Section 11.4.3).

11.4.1.2.  Setting ACL and not mode

   When setting 6.2.1.5.

6.2.1.5.  ACE Who

   The "who" field of an ACL attribute and not ACE is an identifier that specifies the
   principal or principals to whom the ACE applies.  It may refer to a mode attribute,
   user or a group, with the ACL
   attribute SHOULD flag bit ACE4_IDENTIFIER_GROUP specifying
   which.

   There are several special identifiers which need to be set as given.  The nine low-order bits of understood
   universally, rather than in the
   mode attribute (MODE4_R*, MODE4_W*, MODE4_X*) MUST context of a particular DNS domain.

   Some of these identifiers cannot be modified to
   match understood when an NFS client
   accesses the result of server, but have meaning when a local process accesses
   the method Section 11.3.2. file.  The three high-order
   bits ability to display and modify these permissions is
   permitted over NFS, even if none of the mode (MODE4_SUID, MODE4_SGID, MODE4_SVTX) SHOULD remain
   unchanged.

11.4.1.3.  Setting both ACL and mode

   When setting both access methods on the mode and server
   understands the ACL attribute in identifiers.

   +---------------+--------------------------------------------------+
   | Who           | Description                                      |
   +---------------+--------------------------------------------------+
   | OWNER         | The owner of the same
   operation, file                            |
   | GROUP         | The group associated with the attributes MUST be applied in this order: mode, then
   ACL. file.              |
   | EVERYONE      | The mode attribute is set as given, then world, including the ACL attribute is
   set as given, possibly changing owner and owning group. |
   | INTERACTIVE   | Accessed from an interactive terminal.           |
   | NETWORK       | Accessed via the final mode, network.                        |
   | DIALUP        | Accessed as described above in
   Section 11.4.1.2.

11.4.2.  Retrieving the mode and/or ACL Attributes

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

   Some server implementations may have server.         |
   | BATCH         | Accessed from a concept of "objects batch job.                       |
   | ANONYMOUS     | Accessed without
   ACLs", meaning that all permissions any authentication.             |
   | AUTHENTICATED | Any authenticated user (opposite of ANONYMOUS)   |
   | SERVICE       | Access from a system service.                    |
   +---------------+--------------------------------------------------+

                                  Table 7

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

6.2.1.5.1.  Discussion of EVERYONE@

   It is stored for important to note that
   object.  If an ACL attribute "EVERYONE@" is requested of such a server, the
   server SHOULD return an ACL that does not conflict with the mode;
   that is equivalent to say, the ACL returned SHOULD represent the nine low-order
   bits of the mode attribute (MODE4_R*, MODE4_W*, MODE4_X*) as
   described in Section 11.3.2.

   For other server implementations, the ACL attribute
   UNIX "other" entity.  This is always present
   for every object.  Such servers SHOULD store at least because, by definition, UNIX "other"
   does not include the three high-
   order bits owner or owning group of a file.  "EVERYONE@"
   means literally everyone, including the owner or owning group.

6.2.2.  mode attribute (MODE4_SUID, MODE4_SGID,
   MODE4_SVTX). Attribute

   The server SHOULD return a NFS version 4 mode attribute if one is
   requested, and the low-order nine bits of based on the UNIX mode (MODE4_R*,
   MODE4_W*, MODE4_X*) MUST match the result of applying the method in
   Section 11.3.2 to the ACL attribute.

11.4.3.  Creating New Objects

   If a server supports the ACL attribute, it may use the ACL attribute bits.  The
   following bits are defined:

           const MODE4_SUID = 0x800;  /* set user id on the parent directory to compute an initial ACL attribute for a
   newly created object.  This will be referred 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 as the inherited ACL
   within this section.  The act of adding one or more ACEs principal
   identified in the owner attribute.  Bits MODE4_RGRP, MODE4_WGRP, and
   MODE4_XGRP apply to principals identified in the
   inherited ACL that owner_group
   attribute but who are based upon ACEs not identified in the parent directory's ACL
   will be referred owner attribute.  Bits
   MODE4_ROTH, MODE4_WOTH, MODE4_XOTH apply to as inheriting an ACE within this section.

   Implementors should standardize on what any principal that does
   not match that in the behavior of CREATE owner attribute, and
   OPEN must be depending on the presence or absence does not have a group
   matching that of the mode and ACL
   attributes.

   1.  If just mode is given:

       In owner_group attribute.

   The remaining bits are not defined by this case, inheritance SHOULD take place, but the mode protocol.  A server MUST be
       applied to the inherited ACL as described in Section 11.4.1.1,
       thereby modifying the ACL.

   2.  If just ACL is given:

       In this case, inheritance SHOULD
   NOT take place, return bits other than those defined above in a GETATTR or
   READDIR operation, and the ACL as it MUST return NFS4ERR_INVAL if bits other
   than those defined above are set in the CREATE a SETATTR, CREATE, or OPEN will be set without modification,
       and the mode modified as
   operation.

6.3.  Common Methods

   The requirements in Section 11.4.1.2

   3.  If both mode and ACL are given:

       In this case, inheritance SHOULD NOT take place, and both
       attributes section will be set as described referred to in future
   sections, especially Section 11.4.1.3.

   4.  If neither mode nor ACL are given:

       In the case where an object is being created without any initial
       attributes at all, e.g. an OPEN operation with 6.4.

6.3.1.  Interpreting an opentype4 of
       OPEN4_CREATE and a createmode4 of EXCLUSIVE4, inheritance SHOULD
       NOT take place.  Instead, the ACL

6.3.1.1.  Server Considerations

   The server SHOULD set permissions uses the algorithm described in Section 6.2.1 to
       deny all determine
   whether an ACL allows access to the newly created an object.  It is expected that
       the appropriate client will set  However, the desired attributes in a
       subsequent SETATTR operation, and ACL may not
   be the server SHOULD allow that
       operation to succeed, regardless sole determiner of what permissions the object
       is created with. access.  For example, an empty ACL denies all
       permissions, but example:

   o  In the server should allow case of a file system exported as read-only, the owner's SETATTR to
       succeed server may
      deny write permissions even though WRITE_ACL is implicitly denied.

       In other cases, inheritance SHOULD take place, and no
       modifications to the an object's ACL will happen.  The mode attribute, if
       supported, MUST be as computed grants it.

   o  Server implementations MAY grant ACE4_WRITE_ACL and ACE4_READ_ACL
      permissions in Section 11.3.2, with order to prevent the
       MODE4_SUID, MODE4_SGID and MODE4_SVTX bits clear.  It is worth
       noting that if no inheritable ACEs exist on owner from getting into the parent directory,
      situation where they can't ever modify the file ACL.

   o  All servers will be created with an empty ACL, thus granting no
       access.

11.4.3.1.  The Inherited ACL

   If the object being created is not allow a directory, user the inherited ACL
   SHOULD NOT inherit ACEs from ability to read the parent directory ACL unless data of the
   ACE4_FILE_INHERIT_FLAG is set.

   If
      file when only the object being created execute permission is a directory, granted (i.e.  If the inherited ACL should
   inherit all inheritable ACEs from
      denies the parent directory, those that
   have ACE4_FILE_INHERIT_ACE or ACE4_DIRECTORY_INHERIT_ACE flag set.
   If user the inheritable ACE has ACE4_FILE_INHERIT_ACE set, but
   ACE4_DIRECTORY_INHERIT_ACE is clear, ACE4_READ_DATA access and allows the inherited ACE on user
      ACE4_EXECUTE, the newly
   created directory MUST have server will allow the ACE4_INHERIT_ONLY_ACE flag set user to
   prevent the directory from being affected by ACEs meant for non-
   directories.

   If when a new directory is created and it inherits ACEs from its
   parent, for each inheritable ACE which affects the directory's
   permissions, a server MAY create two ACEs on read the directory being
   created; one effective and one which is only inheritable (i.e. has
   ACE4_INHERIT_ONLY_ACE flag set).  This gives data of
      the user and file).

   o  Many servers have the server, notion of owner-override in the cases which it must mask certain permissions upon creation,
   the ability to modify the effective permissions without modifying the
   ACE which is to be inherited to owner
      of the new directory's children.

   When a newly created object is created with attributes, and those
   attributes contain an ACL attribute and/or a mode attribute, the
   server MUST apply those attributes allowed to override accesses that are denied by
      the newly created object, as
   described in Section 11.4.1.

12.  Single-server Name Space ACL.  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) helpful, for example, to be presented allow users
      continued access to clients, as described
   in Section 15.

12.1.  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 open files on disks named by mapped
   disk letters.  NFS server administrators rarely make the entire
   server's file system name space available to NFS clients.  More often
   portions of the name space are made available via an "export"
   feature.  In previous versions of which the NFS protocol, permissions have
      changed.

6.3.1.2.  Client Considerations

   Clients SHOULD NOT do their own access checks based on their
   interpretation the root
   filehandle for each export is obtained through ACL, but rather use the MOUNT protocol; OPEN and ACCESS operations
   to do access checks.  This allows the client sends a string that identifies to act on the export results of name space
   and
   having the server returns determine whether or not access should be granted
   based on its interpretation of the root filehandle for it.  The MOUNT
   protocol supports ACL.

   Clients must be aware of situations in which an EXPORTS procedure that object's ACL will enumerate the
   server's exports.

12.2.  Browsing Exports

   The NFS version 4 protocol provides
   define a root filehandle that clients
   can use certain access even though the server will not enforce it.
   In general, but especially in these situations, the client needs to obtain filehandles for
   do its part in the exports of a particular server,
   via a series enforcement of LOOKUP operations within a COMPOUND, access as defined by the ACL.  To
   do this, the client MAY issue the appropriate ACCESS operation prior
   to traverse a
   path.  A common servicing the request of the user experience is or application in order to use a graphical
   determine whether the user interface
   (perhaps a file "Open" dialog window) to find a file via progressive
   browsing through or application should be granted the
   access requested.  For examples in which the ACL may define accesses
   that the server doesn't enforce see Section 6.3.1.1.

6.3.2.  Computing a directory tree. Mode Attribute from an ACL

   The client must following method can be able to move
   from one export used to another export via single-component, progressive
   LOOKUP operations.

   This style of browsing is not well supported by calculate the NFS version 2 MODE4_R*, MODE4_W*
   and
   3 protocols.  The client expects all LOOKUP operations to remain
   within MODE4_X* bits of a single server file system.  For example, mode attribute, based upon an ACL.

   1.  To determine MODE4_ROTH, MODE4_WOTH, and MODE4_XOTH:

       1.  If the device
   attribute will not change.  This prevents a client from taking name
   space paths special identifier EVERYONE@ is granted
           ACE4_READ_DATA, then the bit MODE4_ROTH SHOULD be set.
           Otherwise, MODE4_ROTH SHOULD NOT be set.

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

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

   2.  To determine MODE4_RGRP, MODE4_WGRP, and MODE4_XGRP, note that span exports.

   An automounter on
       the client can obtain EVERYONE@ special identifier SHOULD be taken into account.
       In other words, when determining if the GROUP@ special identifier
       is granted a snapshot of permission, ACEs with the server's
   name space using identifier EVERYONE@
       should take effect just as ACEs with the EXPORTS procedure of special identifier
       GROUP@ would.

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

       2.  If it
   understands the server's pathname syntax, it can create an image of special identifier GROUP@ is granted ACE4_WRITE_DATA
           or ACE4_APPEND_DATA, then the server's name space on bit MODE4_WGRP SHOULD be set.
           Otherwise, MODE4_WGRP SHOULD NOT be set.

       3.  If the client.  The parts of special identifier GROUP@ is granted ACE4_EXECUTE,
           then the name space bit MODE4_XGRP SHOULD be set.  Otherwise, MODE4_XGRP
           SHOULD NOT be set.

   3.  To determine MODE4_RUSR, MODE4_WUSR, and MODE4_XUSR, note that are not exported by
       the server are filled in with a "pseudo file
   system" that allows EVERYONE@ special identifier SHOULD be taken into account.
       In other words, when determining if the user to browse from one mounted file system
   to another.  There OWNER@ special identifier
       is granted a drawback to this representation of permission, ACEs with the
   server's name space on identifier EVERYONE@
       should take effect just as ACEs with the client: it special identifer OWNER@
       would.

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

       2.  If the server
   administrator adds a new export special identifier OWNER@ is granted ACE4_WRITE_DATA
           or ACE4_APPEND_DATA, then the client will bit MODE4_WUSR SHOULD be unaware of it.

12.3.  Server Pseudo File System

   NFS version 4 servers avoid this name space inconsistency by
   presenting all set.
           Otherwise, MODE4_WUSR SHOULD NOT be set.

       3.  If the exports for a given server within special identifier OWNER@ is granted ACE4_EXECUTE,
           then the framework of
   a single namespace, bit MODE4_XUSR SHOULD be set.  Otherwise, MODE4_XUSR
           SHOULD NOT be set.

6.3.2.1.  Discussion

   The nine low-order mode bits (MODE4_R*, MODE4_W*, MODE4_X*)
   correspond to ACE4_READ_DATA, ACE4_WRITE_DATA/ACE4_APPEND_DATA, and
   ACE4_EXECUTE for that server.  An NFS version 4 client uses
   LOOKUP OWNER@, GROUP@, and READDIR operations to browse seamlessly from one export to
   another.  Portions EVERYONE@.  On some
   implementations, mode bits may represent a superset of these
   permissions, e.g. if a specific user is granted ACE4_WRITE_DATA, then
   MODE4_WGRP will be set, even though the server name space that are file's owner_group is not exported
   granted ACE4_WRITE_DATA.

   Server implementations are
   bridged via a "pseudo file system" that provides a view of exported
   directories only.  A pseudo file system discouraged from doing this, as experience
   has a unique fsid shown that this is confusing and behaves
   like a normal, read only file system.

   Based on annoying to end users.  The
   specifications above also discourage this practice to enforce the construction of
   semantic that setting the server's name space, it is possible mode attribute effectively specifies read,
   write, and execute for owner, group, and other.

6.4.  Requirements

   The server that multiple pseudo file systems may exist.  For example,

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

   Each of supports both mode and ACL must take care to
   synchronize the pseudo file systems are considered separate entities MODE4_*USR, MODE4_*GRP, and
   therefore will MODE4_*OTH bits with the
   ACEs which have its own unique fsid.

12.4.  Multiple Roots

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

12.5.  Filehandle Volatility

   The nature of the server's pseudo file system is that it is a logical
   representation of file system(s) available from client can see semantically equivalent access
   permissions exist whether the server.
   Therefore, client asks for owner, owner_group and
   mode attributes, or for just the pseudo file system ACL.

   In this section, much is most likely constructed
   dynamically when made of the server is first instantiated.  It is expected methods in Section 6.3.2.  Many
   requirements refer to this section.  But note that the pseudo file system may not methods have an on disk counterpart from
   which persistent filehandles could be constructed.  Even though it
   behaviors specified with "SHOULD".  This is
   preferable intentional, to avoid
   invalidating existing implementations that compute the server provide persistent filehandles for mode according
   to the
   pseudo file system, withdrawn POSIX ACL draft (1003.1e draft 17), rather than by
   actual permissions on owner, group, and other.

6.4.1.  Setting the NFS client should expect that pseudo file
   system filehandles are volatile.  This can mode and/or ACL Attributes

6.4.1.1.  Setting mode and not ACL

   When setting a mode attribute and not an ACL attribute, the mode
   attribute MUST be confirmed by checking set as given.  The ACL attribute MUST be modified
   such that the mode computed via the associated "fh_expire_type" attribute for those filehandles method in
   question.  If Section 6.3.2 yields
   the filehandles are volatile, low-order nine bits (MODE4_R*, MODE4_W*, MODE4_X*) of the NFS client must newly
   set mode attribute.  The ACL SHOULD also be
   prepared to recover a filehandle value (e.g. with a series of LOOKUP
   operations) when receiving an error of NFS4ERR_FHEXPIRED.

12.6.  Exported Root modified such that:

   1.  If the server's root file system is exported, one might conclude that
   a pseudo-file system MODE4_RGRP is unneeded.  This not necessarily so.  Assume set, entities explicitly listed in the following file systems on a server:

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

   Because disk2 ACL
       other than OWNER@ and EVERYONE@ SHOULD NOT be granted
       ACE4_READ_DATA.

   2.  If MODE4_WGRP is not exported, disk3 cannot be reached with simple
   LOOKUPs.  The server must bridge set, entities explicitly listed in the gap with a pseudo-file system.

12.7.  Mount Point Crossing

   The server file system environment may ACL
       other than OWNER@ and EVERYONE@ SHOULD NOT be constructed in such a way
   that one file system contains a directory which is 'covered' granted
       ACE4_WRITE_DATA or
   mounted upon by a second file system.  For example:

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

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

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

   It ACE4_APPEND_DATA.

   3.  If MODE4_XGRP is not set, entities explicitly listed in the server's responsibility to present the pseudo file system ACL
       other than OWNER@ and EVERYONE@ SHOULD NOT be granted
       ACE4_EXECUTE.

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

   Note that is complete to ACEs with the client.  If flag ACE4_INHERIT_ONLY_ACE set do not affect
   the client sends a lookup request
   for permissions of the path "/a/b/c/d", ACL itself, nor do ACEs of the server's response type AUDIT and
   ALARM.  As such, it is desirable to leave these ACEs unmodified when
   modifying the filehandle of ACL attribute.

   Also note that the file system "/a/b/c/d".  In previous versions requirement may be met by discarding the ACL, in
   favor of an ACL that represents the NFS
   protocol, mode and only the mode.  This is
   permitted, but it is preferable for a server would respond with the filehandle to preserve as much of directory
   "/a/b/c/d" within
   the file system "/a/b".

   The NFS client will be able to determine if ACL as possible without violating the above requirements.
   Discarding the ACL makes it crosses effectively impossible for a server mount
   point by file created
   with a change in the value of the "fsid" attribute.

12.8.  Security Policy mode attribute to inherit an ACL (see Section 6.4.3).

6.4.1.2.  Setting ACL and Name Space Presentation not mode

   When setting an ACL attribute and not a mode attribute, the ACL
   attribute SHOULD be set as given.  The application nine low-order bits of the server's security policy needs to
   mode attribute (MODE4_R*, MODE4_W*, MODE4_X*) MUST be carefully
   considered by the implementor.  One may choose modified to limit
   match the
   viewability of portions result of the pseudo file system based on the
   server's perception method Section 6.3.2.  The three high-order
   bits of the client's ability to authenticate itself
   properly.  However, with mode (MODE4_SUID, MODE4_SGID, MODE4_SVTX) SHOULD remain
   unchanged.

6.4.1.3.  Setting both ACL and mode

   When setting both the support of multiple security mechanisms mode and the ability to negotiate ACL attribute in the appropriate use of these mechanisms, same
   operation, the server is unable to properly determine if a client will attributes MUST be able
   to authenticate itself.  If, based on its policies, applied in this order: mode, then
   ACL.  The mode attribute is set as given, then the server
   chooses to limit ACL attribute is
   set as given, possibly changing the contents of final mode, as described above in
   Section 6.4.1.2.

6.4.2.  Retrieving the pseudo file system, mode and/or ACL Attributes

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

   Some server implementations may effectively hide file systems from have a client concept of "objects without
   ACLs", meaning that may otherwise
   have legitimate access.

   As suggested practice, the server should apply all permissions are granted and denied according
   to the security policy mode attribute, and that no ACL attribute is stored for that
   object.  If an ACL attribute is requested of such a shared resource in server, the server's namespace
   server SHOULD return an ACL that does not conflict with the mode;
   that is to say, the components ACL returned SHOULD represent the nine low-order
   bits of the
   resource's ancestors. mode attribute (MODE4_R*, MODE4_W*, MODE4_X*) as
   described in Section 6.3.2.

   For example:

           /
           /a/b
           /a/b/c

   The /a/b/c directory is a real file system and is the shared
   resource.  The security policy for /a/b/c is Kerberos with integrity.
   The other server should apply implementations, the same security policy to /, /a, and /a/b.
   This allows ACL attribute is always present
   for every object.  Such servers SHOULD store at least the extension three high-
   order bits of the protection mode attribute (MODE4_SUID, MODE4_SGID,
   MODE4_SVTX).  The server SHOULD return a mode attribute if one is
   requested, and the low-order nine bits of the server's
   namespace to mode (MODE4_R*,
   MODE4_W*, MODE4_X*) MUST match the ancestors result of applying the real shared resource.

   For method in
   Section 6.3.2 to the case of ACL attribute.

6.4.3.  Creating New Objects

   If a server supports the ACL attribute, it may use of multiple, disjoint security mechanisms in the server's resources, ACL attribute
   on the security parent directory to compute an initial ACL attribute for a particular object in the
   server's namespace should
   newly created object.  This will be referred to as the union of all security mechanisms inherited ACL
   within this section.  The act of
   all direct descendants.

13.  File Locking and Share Reservations

   Integrating locking into the NFS protocol necessarily causes it adding one or more ACEs to the
   inherited ACL that are based upon ACEs in the parent directory's ACL
   will be
   stateful.  With referred to as inheriting an ACE within this section.

   Implementors should standardize on what the inclusion behavior of such features as share reservations,
   file and directory delegations, recallable layouts, CREATE and support for
   mandatory byte-range locking the protocol becomes substantially more
   dependent
   OPEN must be depending on state than the traditional combination presence or absence of NFS the mode and NLM
   [XNFS].  There are three components to making ACL
   attributes.

   1.  If just mode is given:

       In this state manageable:

   o  Clear division between client and server

   o  Ability case, inheritance SHOULD take place, but the mode MUST be
       applied to reliably detect inconsistency the inherited ACL as described in state between client
      and server

   o  Simple and robust recovery mechanisms Section 6.4.1.1,
       thereby modifying the ACL.

   2.  If just ACL is given:

       In this model, the server owns case, inheritance SHOULD NOT take place, and the state information.  The client
   requests changes ACL as
       defined in locks and the server responds with CREATE or OPEN will be set without modification,
       and the changes
   made.  Non-client-initiated changes mode modified as in locking state Section 6.4.1.2

   3.  If both mode and ACL are infrequent given:

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

   4.  If neither mode nor ACL are given:

       In the client receives prompt notification case where an object is being created without any initial
       attributes at all, e.g. an OPEN operation with an opentype4 of them
       OPEN4_CREATE and can adjust
   his view a createmode4 of EXCLUSIVE4, inheritance SHOULD
       NOT take place.  Instead, the locking state server SHOULD set permissions to
       deny all access to reflect the server's changes.

   To support Win32 share reservations it newly created object.  It is necessary to provide
   operations which atomically OPEN or CREATE files.  Having expected that
       the appropriate client will set the desired attributes in a separate
   share/unshare operation would not allow correct implementation of
       subsequent SETATTR operation, and the
   Win32 OpenFile API.  In order server SHOULD allow that
       operation to correctly implement share semantics, succeed, regardless of what permissions the previous NFS protocol mechanisms used when a file object
       is opened or created (LOOKUP, CREATE, ACCESS) need to be replaced.  The NFS
   version 4.1 protocol defines OPEN operation which looks up or creates
   a file and establishes locking state on with.  For example, an empty ACL denies all
       permissions, but the server.

13.1.  Locking

   It is assumed that manipulating a lock server should allow the owner's SETATTR to
       succeed even though WRITE_ACL is rare when compared implicitly denied.

       In other cases, inheritance SHOULD take place, and no
       modifications to READ the ACL will happen.  The mode attribute, if
       supported, MUST be as computed in Section 6.3.2, with the
       MODE4_SUID, MODE4_SGID and WRITE operations. MODE4_SVTX bits clear.  It is also assumed that crashes and network
   partitions are relatively rare.  Therefore it is important worth
       noting that the
   READ and WRITE operations have a lightweight mechanism to indicate if
   they possess a held lock.  A lock request contains no inheritable ACEs exist on the heavyweight
   information required to establish a lock and uniquely define parent directory,
       the lock
   owner. file will be created with an empty ACL, thus granting no
       access.

6.4.3.1.  The following sections describe Inherited ACL

   If the transition object being created is not a directory, the inherited ACL
   SHOULD NOT inherit ACEs from the heavyweight
   information to parent directory ACL unless the eventual lightwieght stateid used for most client
   and server locking interactions.

13.1.1.  Client ID

   For each operation
   ACE4_FILE_INHERIT_FLAG is set.

   If the object being created is a directory, the inherited ACL should
   inherit all inheritable ACEs from the parent directory, those that obtains
   have ACE4_FILE_INHERIT_ACE or depends ACE4_DIRECTORY_INHERIT_ACE flag set.
   If the inheritable ACE has ACE4_FILE_INHERIT_ACE set, but
   ACE4_DIRECTORY_INHERIT_ACE is clear, the inherited ACE on locking state, the
   specific client must be determinable by newly
   created directory MUST have the server.  In NFSv4, each
   distinct client instance is represented ACE4_INHERIT_ONLY_ACE flag set to
   prevent the directory from being affected by ACEs meant for non-
   directories.

   If when a clientid, which new directory is created and it inherits ACEs from its
   parent, for each inheritable ACE which affects the directory's
   permissions, a 64-
   bit identifier that identifies a specific client at a given time server MAY create two ACEs on the directory being
   created; one effective and one which is changed whenever the client or only inheritable (i.e. has
   ACE4_INHERIT_ONLY_ACE flag set).  This gives the server re-initializes.
   Clientid's are used to support lock identification user and crash
   recovery.

   In NFSv4.1, the clientid associated with each operation is derived
   from server,
   in the session on cases which it must mask certain permissions upon creation,
   the operation ability to modify the effective permissions without modifying the
   ACE which is issued.  Each session to be inherited to the new directory's children.

   When a newly created object is
   associated created with a specific clientid at session creation attributes, and that
   clientid then becomes the clientid associated with all requests
   issued using it.

   A sequence of those
   attributes contain an ACL attribute and/or a CREATE_CLIENTID operation followed by mode attribute, the
   server MUST apply those attributes to the newly created object, as
   described in Section 6.4.1.

7.  Single-server Name Space

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

7.1.  Server Exports

   On a UNIX server, the identification on name space describes all the server.  Establishment of identification files reachable by
   pathnames under the root directory or "/".  On a new incarnation of Windows NT server
   the client also has name space constitutes all the effect files on disks named by mapped
   disk letters.  NFS server administrators rarely make the entire
   server's file system name space available to NFS clients.  More often
   portions of immediately
   releasing any locking state that a the name space are made available via an "export"
   feature.  In previous incarnation versions of that same
   client might have had on the server.  Such released state would
   include all lock, share reservation, and, where NFS protocol, the server root
   filehandle for each export is not
   supporting obtained through the MOUNT protocol;
   the CLAIM_DELEGATE_PREV claim type, all delegation state
   associated with same client with sends a string that identifies the same identity.  For discussion export of delegation state recovery, see the section "Delegation Recovery".

   Releasing such state requires that name space
   and the server be able to determine returns the root filehandle for it.  The MOUNT
   protocol supports an EXPORTS procedure that one client instance is will enumerate the successor of another.  Where this
   cannot be done,
   server's exports.

7.2.  Browsing Exports

   The NFS version 4 protocol provides a root filehandle that clients
   can use to obtain filehandles for any the exports of a number particular server,
   via a series of reasons, the locking state
   will remain for LOOKUP operations within a time subject COMPOUND, to lease expiration (see Section 13.5)
   and the new client will need traverse a
   path.  A common user experience is to wait for such state 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 removed, if
   it makes conflicting lock requests.

   Client identification able to move
   from one export to another export via single-component, progressive
   LOOKUP operations.

   This style of browsing is encapsulated in not well supported by the following structure:

               struct nfs_client_id4 {
               verifier4     verifier;
               opaque        id<NFS4_OPAQUE_LIMIT>;
               }; NFS version 2 and
   3 protocols.  The first field, verifier, is a client incarnation verifier that is
   used expects all LOOKUP operations to detect client reboots.  Only if remain
   within a single server file system.  For example, the verifier is different device
   attribute will not change.  This prevents a client from taking name
   space paths that the server had previously recorded for span exports.

   An automounter on the client (as
   identified by the second field can obtain a snapshot of the structure, id) does the server
   start server's
   name space using the process EXPORTS procedure of canceling the client's leased state.

   The second field, id is a variable length string that uniquely
   defines MOUNT protocol.  If it
   understands the client so that subsequent instances server's pathname syntax, it can create an image of
   the same client
   bear the same id with a different verifier.

   There are several considerations for how the client generates server's name space on the id
   string:

   o client.  The string should be unique so parts of the name space
   that multiple clients do are not
      present exported by the same string.  The consequences of two clients
      presenting server are filled in with a "pseudo file
   system" that allows the same string range user to browse from one client getting an error mounted file system
   to one 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 having its leased state abruptly and unexpectedly
      canceled.

   o  The string should will be selected so the subsequent incarnations (e.g.
      reboots) unaware of it.

7.3.  Server Pseudo File System

   NFS version 4 servers avoid this name space inconsistency by
   presenting all the same client cause 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 present the same
      string.  The implementor is cautioned browse seamlessly from an approach that
      requires the string one export to be recorded in
   another.  Portions of the server name space that are not exported are
   bridged via a local "pseudo file because this
      precludes system" that provides a view of exported
   directories only.  A pseudo file system has a unique fsid and behaves
   like a normal, read only file system.

   Based on the use construction of the implementation in an environment where
      there server's name space, it is no local disk possible
   that multiple pseudo file systems may exist.  For example,

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

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

7.4.  Multiple Roots

   The DOS and Windows operating environments are sometimes described as
   having "multiple roots".  File Systems are commonly represented as
   disk letters.  MacOS represents file access is from an systems as top level names.  NFS
   version 4 server.

   o  The string should be different servers for each server network address 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 client accesses, rather than common to all server network
      addresses. pseudo root.

7.5.  Filehandle Volatility

   The reason nature of the server's pseudo file system is that it may not be possible for the
      client to tell if same server is listening on multiple network
      addresses.  If a logical
   representation of file system(s) available from the client issues CREATE_CLIENTID with server.
   Therefore, the same id
      string to each network address of such a server, pseudo file system is most likely constructed
   dynamically when the server will
      think it is first instantiated.  It is expected
   that the same client, and each successive CREATE_CLIENTID
      will cause pseudo file system may not have an on disk counterpart from
   which persistent filehandles could be constructed.  Even though it is
   preferable that the server remove the client's previous leased state.

   o  The algorithm provide persistent filehandles 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
   pseudo file system, the NFS client is
      still running in its current incarnation.  This means should expect that if the
      client includes just pseudo file
   system filehandles are volatile.  This can be confirmed by checking
   the client's and server's network address associated "fh_expire_type" attribute for those filehandles in
   question.  If the id string, there is a real risk, after filehandles are volatile, the NFS client gives up the
      network address, that another client, using must be
   prepared to recover a similar algorithm
      for generating the id string, would generate filehandle value (e.g. with a conflicting id
      string.

   Given the above considerations, series of LOOKUP
   operations) when receiving an example error of a well generated id
   string NFS4ERR_FHEXPIRED.

7.6.  Exported Root

   If the server's root file system is exported, one might conclude 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 pseudo-file system is unneeded.  This not necessarily so.  Assume
   the client from other user
      level clients running following file systems on the same host, such as a process id or
      other unique sequence.

   o  Additional information that tends to server:

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

   Because disk2 is not exported, disk3 cannot be unique, such as one or
      more of:

      * reached with simple
   LOOKUPs.  The client machine's serial number (for privacy reasons, it is
         best to perform some one way function on server must bridge the serial number).

      *  A MAC address.

      * gap with a pseudo-file system.

7.7.  Mount Point Crossing

   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 server file system environment may be constructed in such a way
   that one file system contains a directory which is
         stored in 'covered' or
   mounted upon by a file, because the second file might only be accessible
         over NFS version 4).

      *  A true random number.  However since system.  For example:

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

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

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

   It is the same between client incarnations, this shares the same
         problem as that of the using server's responsibility to present the timestamp of pseudo file system
   that is complete to the software
         installation.

   As a security measure, client.  If the server MUST NOT cancel client sends a client's leased
   state if lookup request
   for the principal established path "/a/b/c/d", the state for a given id string server's response is
   not the same as filehandle of
   the principal issuing file system "/a/b/c/d".  In previous versions of the NFS
   protocol, the CREATE_CLIENTID.

   A server may compare an nfs_client_id4 in a CREATE_CLIENTID would respond with an
   nfs_client_id4 established using SETCLIENTID using NFSv4 minor
   version 0, so that an NFSv4.1 client is not forced to delay until
   lease expiration for locking state established by the earlier filehandle of directory
   "/a/b/c/d" within the file system "/a/b".

   The NFS client
   using minor version 0.

   Once will be able to determine if it crosses a CREATE_CLIENTID has been done, and the resulting clientid
   established as associated with server mount
   point by a session, all requests made on that
   session implicitly identify that clientid, which change in turn designates the client specified using value of the long-form nfs_client_id4 structure. "fsid" attribute.

7.8.  Security Policy and Name Space Presentation

   The shorthand client identifier (a clientid) is assigned by application of the
   server and should server's security policy needs to be chosen so that it will not conflict with a
   clientid previously assigned carefully
   considered by the server.  This applies across
   server restarts or reboots.

   In implementor.  One may choose to limit the event
   viewability of a server restart, a client will find out that its
   current clientid is no longer valid when receives a
   NFS4ERR_STALE_CLIENTID error.  The precise circumstances depend portions of the characteristics pseudo file system based on the
   server's perception of the sessions involved, specifically whether client's ability to authenticate itself
   properly.  However, with the session is persistent.

   When a session is not persistent, support of multiple security mechanisms
   and the client will need ability to create a
   new session.  When negotiate the existing clientid appropriate use of these mechanisms,
   the server is presented unable to properly determine if a client will be able
   to authenticate itself.  If, based on its policies, the server as
   part
   chooses to limit the contents of creating the pseudo file system, the server
   may effectively hide file systems from a session and client that clientid is not recognized, as
   would happen after a server reboot, may otherwise
   have legitimate access.

   As suggested practice, the server will reject the
   request with the error NFS4ERR_STALE_CLIENTID.  When this happens, should apply the client must obtain a new clientid by use security policy of
   a shared resource in the CREATE_CLIENTID
   operation and then use that clientid as server's namespace to the basis components of the basis of
   resource's ancestors.  For example:

           /
           /a/b
           /a/b/c
   The /a/b/c directory is a
   new session real file system and then proceed is the shared
   resource.  The security policy for /a/b/c is Kerberos with integrity.
   The server should apply the same security policy to any other necessary recovery /, /a, and /a/b.
   This allows for the
   server reboot case (See Section 13.6.2).

   In extension of the case protection of the session being persistent, server's
   namespace to the client will re-
   establish communication using ancestors of the existing session after real shared resource.

   For the reboot.
   This session will be associated with a stale clientid and case of the client
   will receive an indication use of that fact multiple, disjoint security mechanisms in
   the status field returned
   by server's resources, the SEQUENCE operation.  The client, can then use security for a particular object in the existing
   session to do whatever operations are necessary to determine
   server's namespace should be the
   status union of requests outstanding at the time all security mechanisms of reboot, while avoiding
   issuing new requests, particularly any involving
   all direct descendants.

8.  File Locking and Share Reservations

   Integrating locking on that
   session.  Such requests would fail with NFS4ERR_STALE_CLIENTID error
   or an NFS4ERR_STALE_STATEID error, if attempted.  In any case, into the
   client would create a new clientid using CREATE_CLIENTID, create a
   new session based on that clientid, and proceed NFS protocol necessarily causes it to other necessary
   recovery for the server reboot case.

   See be
   stateful.  With the detailed descriptions inclusion of CREATE_CLIENTID such features as share reservations,
   file and CREATE_SESSION directory delegations, recallable layouts, and support for a complete specification of these operations.

13.1.2.  Server Release of Clientid

   If the server determines that
   mandatory byte-range locking the client holds no associated protocol becomes substantially more
   dependent on state
   for its clientid, than the server may choose traditional combination of NFS and NLM
   [XNFS].  There are three components to release the clientid.  The
   server may make making this choice for an inactive state manageable:

   o  Clear division between client so that resources
   are not consumed by those intermittently active clients.  If the and server

   o  Ability to reliably detect inconsistency in state between client contacts the
      and server after

   o  Simple and robust recovery mechanisms

   In this release, model, the server must ensure owns the state information.  The client receives the appropriate error so that it will use the
   CREATE_CLIENTID/CREATE_SESSION sequence to establish a new identity.
   It should be clear that
   requests changes in locks and the server must be very hesitant to release a
   clientid since responds with the resulting work on changes
   made.  Non-client-initiated changes in locking state are infrequent
   and the client to recover from such
   an event will be receives prompt notification of them and can adjust
   his view of the same burden as if locking state to reflect the server had failed and
   restarted.  Typically server's changes.

   To support Win32 share reservations it is necessary to provide
   operations which atomically OPEN or CREATE files.  Having a server separate
   share/unshare operation would not release a clientid unless
   there had been no activity from that client for many minutes.

   Note that if allow correct implementation of the id string in
   Win32 OpenFile API.  In order to correctly implement share semantics,
   the previous NFS protocol mechanisms used when a CREATE_CLIENTID request file is properly
   constructed, and if the client takes care opened or
   created (LOOKUP, CREATE, ACCESS) need to use the same principal
   for each successive use of CREATE_CLIENTID, then, barring an active
   denial of service attack, NFS4ERR_CLID_INUSE should never be
   returned.

   However, client bugs, server bugs, replaced.  The NFS
   version 4.1 protocol defines OPEN operation which looks up or perhaps creates
   a deliberate change of file and establishes locking state on the principal owner of server.

8.1.  Locking

   It is assumed that manipulating a lock is rare when compared to READ
   and WRITE operations.  It is also assumed that crashes and network
   partitions are relatively rare.  Therefore it is important that the id string (such as
   READ and WRITE operations have a lightweight mechanism to indicate if
   they possess a held lock.  A lock request contains the case of heavyweight
   information required to establish a client
   that changes security flavors, lock and under uniquely define the new flavor, there is no
   mapping to lock
   owner.

   The following sections describe the previous owner) will in rare cases result in
   NFS4ERR_CLID_INUSE.

   In that event, when transition from the server gets a CREATE_CLIENTID heavyweight
   information to the eventual lightweight stateid used for a most client id
   that currently has no state, or it has state, but the lease has
   expired, rather than returning NFS4ERR_CLID_INUSE, the
   and server MUST
   allow the CREATE_CLIENTID, locking interactions.

8.1.1.  Client and confirm the new Session ID

   A client must establish a clientid if followed
   by the appropriate CRREATESESSION.

13.1.3. (see Section 2.4) and then one or
   more sessionids (see Section 2.9) before performing any operations to
   open, lock, or delegate a file object.  The sessionid services as a
   shorthand referral to an NFSv4.1 client.

8.1.2.  State-owner and Stateid Definition

   When opening a file or requesting a byte-range lock, the client must
   specify an identifier which represents the owner of the requested
   lock.  This identifier is in the form of a state-owner, represented
   in the protocol by a state_owner4, a variable-length opaque array
   which, when concatenated with the current clientid uniquely defines
   the owner of lock managed by the client.  This may be a thread id,
   process id, or other unique value.

   Owners of opens and owners of byte-range locks are separate entities
   and remain separate even if the same opaque arrays are used to
   designate owners of each.  The protocol distinguishes between open-
   owners (represented by open_owner4 structures) and lock-owners
   (represented by lock_owner4 structures).

   Each open is associated with a specific open-owner while each byte-
   range lock is associated with a lock-owner and an open-owner, the
   latter being the open-owner associated with the open file under which
   the LOCK operation was done.  Delegations and layouts, on the other
   hand, are not associated with a specific owner but are associated the
   client as a whole.

   When the server grants a lock of any type (including opens, byte-
   range locks, delegations, and layouts) it responds with a unique
   stateid, that represents a set of locks (often a single lock) for the
   same file, of the same type, and sharing the same ownership
   characteristics.  Thus opens of the same file by different open-
   owners each have an identifying stateid.  Similarly, each set of
   byte-range locks on a file owned by a specific lock-owner and gotten
   via an open for a specific open-owner, has its own identifying
   stateid.  Delegations and layouts also have associated stateid's by
   which they may be referenced.  The stateid is used as a shorthand
   reference to a lock or set of locks and given a stateid the client
   can determine the associated state-owner or state-owners (in the case
   of an open-owner/lock-owner pair) and the associated.  Clients,
   however, must not assume any such mapping and must not use a stateid
   returned for a given filehandle and state-owner in the context of a
   different filehandle or a different state-owner.

   The server is free to form the stateid in any manner that it chooses
   as long as it is able to recognize invalid and out-of-date stateids.
   Although the protocol XDR definition divides the stateid into into
   'seqid' and 'other' fields, for the purposes of minor version one,
   this distinction is not important and the server may use the
   available space as it chooses, with one exception.

   The exception is that stateids whose 'other' field is either all
   zeros or all ones are reserved and may not be generated by the
   server.  Clients may use the protocol-defined special stateid values
   for their defined purposes, but any use of stateid's in this reserved
   class that are not specially defined by the protocol MUST result in
   an NFS4ERR_BAD_STATED being returned.

   Clients may not compare stateids associated with different
   filehandles, so that a server might use stateids with the same bit
   pattern for all opens with a given open-owner or for all sets of
   byte-range locks associated with a given lock-owner/open-owner pair.
   However, if it does so, it must recognize and reject any use of
   stateid when the current filehandle is such that no lock for that
   filehandle by that open owner (or lock-owner/open-owner pair) exists.

   Stateid's must remain valid until either a client reboot or a sever
   reobot
   reboot or until the client returns all of the locks associated with
   the stateid by means of an operation such as CLOSE or DELEGRETURN.
   If the locks are lost due to revocation the sateid stateid remains usable
   until the client frees it by using FREE_STATEID.  Stateid's
   associated with byte-range locks are an exception.  They remain valid
   even if a LOCKU free all remaining locks, so long as the opefile open file
   with which they are associated remains open, unless the client does a
   FREE_STATEID to caused the stateid to be freed.

   Because each operation using a stateid occurs as part of a session,
   each stateid is implicitly associated with the clientid assigned to
   that session.  Use of a stateid in the context of a session where the
   clientid is invalid should result in the error NFS4ERR_STALE_STATEID.
   Servers MUST NOT do any validation or return other errors in this
   case, even if they have sufficient information available to validate
   stateids associated with an out-of-date client.

   One mechanism that may be used to satisfy the requirement that the
   server recognize invalid and out-of-date stateids is for the server
   to divide the stateid into two fields.  This division may coincide
   with the documented division into 'seqid' and 'other' fields or it
   may divide the stateid field up in any other ay it chooses.

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

   o  A generation number which is incremented on each allocation of a
      table entry a particular allocation of a stateid.

   And then store in each table entry,

   o  The current generation number.

   o  The clientid with which the stateid is associated.

   o  The filehandle of the file on which the locks are taken.

   o  An indication of the type of stateid (open, byte-range lock, file
      delegation, directory delegation, layout).

   With this information, the following procedure would be used to
   validate an incoming stateid and return an appropriate error, when
   necessary:

   o  If the current session is associated with an invalid clientid,
      return NFS4ERR_STALE_STATEID.

   o  If the table index field is outside the range of the associated
      table, return NFS4ERR_BAD_STATEID.

   o  If the selected table entry is of a different generation than that
      specified in the incoming stateid, return NFS4ERR_BAD_STATEID.

   o  If the selected table entry does not match the current file
      handle, return NFS4ERR_BAD_STATEID.

   o  If the clientid in the table entry does not match the clientid
      associated with the current session, return NFS4ERR_BAD_STATEID.

   o  If the stateid type is not valid for the context in which the
      stateid appears, return NFS4ERR_BAD_STATEID.

   o  Otherwise, the stateid is valid and the table entry should contain
      any additional information about the associated set of locks, such
      as open-owner and lock-owner information, as well as information
      on the specific locks, such as open modes and byte ranges.

13.1.4.

8.1.3.  Use of the Stateid and Locking

   All READ, WRITE and SETATTR operations contain a stateid.  For the
   purposes of this section, SETATTR operations which change the size
   attribute of a file are treated as if they are writing the area
   between the old and new size (i.e. the range truncated or added to
   the file by means of the SETATTR), even where SETATTR is not
   explicitly mentioned in the text.

   If the state-owner performs a READ or WRITE in a situation in which
   it has established a lock or share reservation on the server (any
   OPEN constitutes a share reservation) the stateid (previously
   returned by the server) must be used to indicate what locks,
   including both record locks and share reservations, are held by the
   state-owner.  If no state is established by the client, either record
   lock or share reservation, a special stateid of all bits 0 (including
   all fields of the stateid) is used.  Regardless whether a stateid of
   all bits 0, or a stateid returned by the server is used, if there is
   a conflicting share reservation or mandatory record lock held on the
   file, the server MUST refuse to service the READ or WRITE operation.

   Share reservations are established by OPEN operations and by their
   nature are mandatory in that when the OPEN denies READ or WRITE
   operations, that denial results in such operations being rejected
   with error NFS4ERR_LOCKED.  Record locks may be implemented by the
   server as either mandatory or advisory, or the choice of mandatory or
   advisory behavior may be determined by the server on the basis of the
   file being accessed (for example, some UNIX-based servers support a
   "mandatory lock bit" on the mode attribute such that if set, record
   locks are required on the file before I/O is possible).  When record
   locks are advisory, they only prevent the granting of conflicting
   lock requests and have no effect on READs or WRITEs.  Mandatory
   record locks, however, prevent conflicting I/O operations.  When they
   are attempted, they are rejected with NFS4ERR_LOCKED.  When the
   client gets NFS4ERR_LOCKED on a file it knows it has the proper share
   reservation for, it will need to issue a LOCK request on the region
   of the file that includes the region the I/O was to be performed on,
   with an appropriate locktype (i.e.  READ*_LT for a READ operation,
   WRITE*_LT for a WRITE operation).

   Note that for UNIX environments that support mandatory file locking,
   the distinction between advisory and mandatory locking is subtle.  In
   fact, advisory and mandatory record locks are exactly the same in so
   far as the APIs and requirements on implementation.  If the mandatory
   lock attribute is set on the file, the server checks to see if the
   lock-owner has an appropriate shared (read) or exclusive (write)
   record lock on the region it wishes to read or write to.  If there is
   no appropriate lock, the server checks if there is a conflicting lock
   (which can be done by attempting to acquire the conflicting lock on
   the behalf of the lock-owner, and if successful, release the lock
   after the READ or WRITE is done), and if there is, the server returns
   NFS4ERR_LOCKED.

   For Windows environments, there are no advisory record locks, so the
   server always checks for record locks during I/O requests.

   Thus, the NFS version 4 LOCK operation does not need to distinguish
   between advisory and mandatory record locks.  It is the NFS version 4
   server's processing of the READ and WRITE operations that introduces
   the distinction.

   Every stateid other than the special stateid values noted in this
   section, whether returned by an OPEN-type operation (i.e.  OPEN,
   OPEN_DOWNGRADE), or by a LOCK-type operation (i.e.  LOCK or LOCKU),
   defines an access mode for the file (i.e.  READ, WRITE, or READ-
   WRITE) as established by the original OPEN which caused the
   allocation of the open stateid and as modified by subsequent OPENs
   and OPEN_DOWNGRADEs for the same open-owner/file pair.  Stateids
   returned by byte-range lock operations imply the access mode for the
   open stateid associated with the lock set represented by the stateid.
   Delegation stateids have an access mode based on the type of
   delegation.  When a READ, WRITE, or SETATTR which specifies the size
   attribute, is done, the operation is subject to checking against the
   access mode to verify that the operation is appropriate given the
   OPEN with which the operation is associated.

   In the case of WRITE-type operations (i.e.  WRITEs and SETATTRs which
   set size), the server must verify that the access mode allows writing
   and return an NFS4ERR_OPENMODE error if it does not.  In the case, of
   READ, the server may perform the corresponding check on the access
   mode, or it may choose to allow READ on opens for WRITE only, to
   accommodate clients whose write implementation may unavoidably do
   reads (e.g. due to buffer cache constraints).  However, even if READs
   are allowed in these circumstances, the server MUST still check for
   locks that conflict with the READ (e.g. another open specify denial
   of READs).  Note that a server which does enforce the access mode
   check on READs need not explicitly check for conflicting share
   reservations since the existence of OPEN for read access guarantees
   that no conflicting share reservation can exist.

   A special stateid of all bits 1 (one), including all fields in the
   stateid indicates a desire to bypass locking checks.  The server MAY
   allow READ operations to bypass locking checks at the server, when
   this special stateid is used.  However, WRITE operations with with
   this special stateid value MUST NOT bypass locking checks and are
   treated exactly the same as if a stateid of all bits 0 were used.

   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.

13.2.

8.2.  Lock Ranges

   The protocol allows a lock owner to request a lock with a byte range
   and then either upgrade, downgrade, or unlock a sub-range of the
   initial lock.  It is expected that this will be an uncommon type of
   request.  In any case, servers or server filesystems may not be able
   to support sub-range lock semantics.  In the event that a server
   receives a locking request that represents a sub-range of current
   locking state for the lock owner, the server is allowed to return the
   error NFS4ERR_LOCK_RANGE to signify that it does not support sub-
   range lock operations.  Therefore, the client should be prepared to
   receive this error and, if appropriate, report the error to the
   requesting application.

   The client is discouraged from combining multiple independent locking
   ranges that happen to be adjacent into a single request since the
   server may not support sub-range requests and for reasons related to
   the recovery of file locking state in the event of server failure.
   As discussed in the section "Server Failure and Recovery" below, the
   server may employ certain optimizations during recovery that work
   effectively only when the client's behavior during lock recovery is
   similar to the client's locking behavior prior to server failure.

13.3.

8.3.  Upgrading and Downgrading Locks

   If a client has a write lock on a record, it can request an atomic
   downgrade of the lock to a read lock via the LOCK request, by setting
   the type to READ_LT.  If the server supports atomic downgrade, the
   request will succeed.  If not, it will return NFS4ERR_LOCK_NOTSUPP.
   The client should be prepared to receive this error, and if
   appropriate, report the error to the requesting application.

   If a client has a read lock on a record, it can request an atomic
   upgrade of the lock to a write lock via the LOCK request by setting
   the type to WRITE_LT or WRITEW_LT.  If the server does not support
   atomic upgrade, it will return NFS4ERR_LOCK_NOTSUPP.  If the upgrade
   can be achieved without an existing conflict, the request will
   succeed.  Otherwise, the server will return either NFS4ERR_DENIED or
   NFS4ERR_DEADLOCK.  The error NFS4ERR_DEADLOCK is returned if the
   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.

13.4.

8.4.  Blocking Locks

   Some clients require the support of blocking locks.  NFSv4.1 does not
   provide a callback when a previously unavailable lock becomes
   available.  Clients thus have no choice but to continually poll for
   the lock.  This presents a fairness problem.  Two new lock types are
   added, READW and WRITEW, and are used to indicate to the server that
   the client is requesting a blocking lock.  The server should maintain
   an ordered list of pending blocking locks.  When the conflicting lock
   is released, the server may wait the lease period for the first
   waiting client to re-request the lock.  After the lease period
   expires the next waiting client request is allowed the lock.  Clients
   are required to poll at an interval sufficiently small that it is
   likely to acquire the lock in a timely manner.  The server is not
   required to maintain a list of pending blocked locks as it is used to
   increase fairness and not correct operation.  Because of the
   unordered nature of crash recovery, storing of lock state to stable
   storage would be required to guarantee ordered granting of blocking
   locks.

   Servers may also note the lock types and delay returning denial of
   the request to allow extra time for a conflicting lock to be
   released, allowing a successful return.  In this way, clients can
   avoid the burden of needlessly frequent polling for blocking locks.
   The server should take care in the length of delay in the event the
   client retransmits the request.

   If a server receives a blocking lock request, denies it, and then
   later receives a nonblocking request for the same lock, which is also
   denied, then it should remove the lock in question from its list of
   pending blocking locks.  Clients should use such a nonblocking
   request to indicate to the server that this is the last time they
   intend to poll for the lock, as may happen when the process
   requesting the lock is interrupted.  This is a courtesy to the
   server, to prevent it from unnecessarily waiting a lease period
   before granting other lock requests.  However, clients are not
   required to perform this courtesy, and servers must not depend on
   them doing so.  Also, clients must be prepared for the possibility
   that this final locking request will be accepted.

13.5.

8.5.  Lease Renewal

   The purpose of a lease is to allow a server to remove stale locks
   that are held by a client that has crashed or is otherwise
   unreachable.  It is not a mechanism for cache consistency and lease
   renewals may not be denied if the lease interval has not expired.

   Since each session is associated with a specific client, any
   operation issued on that session is an indication that the associated
   client is reachable.  When a request is issued for a given session,
   execution of a SEQUENCE operation will result in all leases for the
   associated client to be implicitly renewed.  This approach allows for
   low overhead lease renewal which scales well.  In the typical case no
   extra RPC calls are required for lease renewal and in the worst case
   one RPC is required every lease period, via a COMPOUND that consists
   solely of a single SEQUENCE operation.  The number of locks held by
   the client is not a factor since all state for the client is involved
   with the lease renewal action.

   Since all operations that create a new lease also renew existing
   leases, the server must maintain a common lease expiration time for
   all valid leases for a given client.  This lease time can then be
   easily updated upon implicit lease renewal actions.

13.6.

8.6.  Crash Recovery

   The important requirement in crash recovery is that both the client
   and the server know when the other has failed.  Additionally, it is
   required that a client sees a consistent view of data across server
   restarts or reboots.  All READ and WRITE operations that may have
   been queued within the client or network buffers must wait until the
   client has successfully recovered the locks protecting the READ and
   WRITE operations.

13.6.1.

8.6.1.  Client Failure and Recovery

   In the event that a client fails, the server may release the client's
   locks when the associated leases have expired.  Conflicting locks
   from another client may only be granted after this lease expiration.
   When a client has not not failed and re-establishes his lease before
   expiration occurs, requests for conflicting locks will not be
   granted.

   To minimize client delay upon restart, lock requests are associated
   with an instance of the client by a client supplied verifier.  This
   verifier is part of the initial CREATE_CLIENTID call made by the
   client.  The server returns a clientid as a result of the
   CREATE_CLIENTID operation.  The client then confirms the use of the
   clientid by establishing a session associated with that clientid.
   All locks, including opens, byte-range locks, delegations, and layout
   obtained by sessions using that clientid are associated with that
   clientid.

   Since the verifier will be changed by the client upon each
   initialization, the server can compare a new verifier to the verifier
   associated with currently held locks and determine that they do not
   match.  This signifies the client's new instantiation and subsequent
   loss of locking state.  As a result, the server is free to release
   all locks held which are associated with the old clientid which was
   derived from the old verifier.  At this point conflicting locks from
   other clients, kept waiting while the leaser had not yet expired, can
   be granted.

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

13.6.2.

8.6.2.  Server Failure and Recovery

   If the server loses locking state (usually as a result of a restart
   or reboot), it must allow clients time to discover this fact and re-
   establish the lost locking state.  The client must be able to re-
   establish the locking state without having the server deny valid
   requests because the server has granted conflicting access to another
   client.  Likewise, if there is a possibility that clients have not
   yet re-established their locking state for a file, the server must
   disallow READ and WRITE operations for that file.

   A client can determine that server failure (and thus loss of locking
   state) has occurred, when it receives one of two errors.  The
   NFS4ERR_STALE_STATEID error indicates a stateid invalidated by a
   reboot or restart.  The NFS4ERR_STALE_CLIENTID error indicates a
   clientid invalidated by reboot or restart.  When either of these are
   received, the client must establish a new clientid (See
   Section 13.1.1) 8.1.1) and re-establish its locking state.

   Once a session is established using the new clientid, the client will
   use reclaim-type locking requests (i.e.  LOCK requests with reclaim
   set to true and OPEN operations with a claim type of CLAIM_PREVIOUS)
   to re-establish its locking state.  Once this is done, or if there is
   no such locking state to reclaim, the client does a RECLAIM_COMPLETE
   operation to indicate that it has reclaimed all of the locking state
   that it will reclaim.  Once a client does a RECLAIM_COMPLETE
   operation, it may attempt non-reclaim locking operations, although it
   may get NFS4ERR_GRACE errors on these until the period of special
   handling is over.

   The period of special handling of locking and READs and WRITEs, is
   referred to as the "grace period".  During the grace period, clients
   recover locks and the associated state using reclaim-type locking
   requests.  During this period, the server must reject READ and WRITE
   operations and non-reclaim locking requests (i.e. other LOCK and OPEN
   operations) with an error of NFS4ERR_GRACE, unless it is able to
   guarantee that these may be done safely, as described below.

   The grace period may last until all clients who are known to possibly
   have had locks have done a RECLAIM_COMPLETE operation, indicating
   that they have finished reclaiming the locks they held before the
   server reboot.  The server is assumed to maintain in stable storage a
   list of clients who may have such locks.  The server may also
   terminate the grace period before all clients have done
   RECLAIM_COMPLETE.  The server SHOULD NOT terminate the grace period
   before a time equal to the lease period in order to give clients an
   opportunity to find out about the server reboot.  Some additional
   time in order to allow time to establish a new clientid and session
   and to effect lock reclaims may be added.

   If the server can reliably determine that granting a non-reclaim
   request will not conflict with reclamation of locks by other clients,
   the NFS4ERR_GRACE error does not have to be returned even within the
   grace period, although NFS4ERR_GRACE must always be returned to
   clients attempting a non-reclaim lock request before doing their own
   RECLAIM_COMPLETE.  For the server to be able to service READ and
   WRITE operations during the grace period, it must again be able to
   guarantee that no possible conflict could arise between a potential
   reclaim locking request and the READ or WRITE operation.  If the
   server is unable to offer that guarantee, the NFS4ERR_GRACE error
   must be returned to the client.

   For a server to provide simple, valid handling during the grace
   period, the easiest method is to simply reject all non-reclaim
   locking requests and READ and WRITE operations by returning the
   NFS4ERR_GRACE error.  However, a server may keep information about
   granted locks in stable storage.  With this information, the server
   could determine if a regular lock or READ or WRITE operation can be
   safely processed.

   For example, if the server maintained on stable storage summary
   information on whether mandatory locks exist, either mandatory byte-
   range locks, or share reservations specifying deny modes, many
   requests could be allowed during the grace period.  If it is known
   that no such share reservations exist, OPEN request that do not
   specify deny modes may be safely granted.  If, in addition, it is
   known that no mandatory byte-range locks exist, either through
   information stored on stable storage or simply because the server
   does not support such locks, READ and WRITE requests may be safely
   processed during the grace period.

   To reiterate, for a server that allows non-reclaim lock and I/O
   requests to be processed during the grace period, it MUST determine
   that no lock subsequently reclaimed will be rejected and that no lock
   subsequently reclaimed would have prevented any I/O operation
   processed during the grace period.

   Clients should be prepared for the return of NFS4ERR_GRACE errors for
   non-reclaim lock and I/O requests.  In this case the client should
   employ a retry mechanism for the request.  A delay (on the order of
   several seconds) between retries should be used to avoid overwhelming
   the server.  Further discussion of the general issue is included in
   [Floyd].  The client must account for the server that is able to
   perform I/O and non-reclaim locking requests within the grace period
   as well as those that can not do so.

   A reclaim-type locking request outside the server's grace period can
   only succeed if the server can guarantee that no conflicting lock or
   I/O request has been granted since reboot or restart.

   A server may, upon restart, establish a new value for the lease
   period.  Therefore, clients should, once a new clientid is
   established, refetch the lease_time attribute and use it as the basis
   for lease renewal for the lease associated with that server.
   However, the server must establish, for this restart event, a grace
   period at least as long as the lease period for the previous server
   instantiation.  This allows the client state obtained during the
   previous server instance to be reliably re-established.

13.6.3.

8.6.3.  Network Partitions and Recovery

   If the duration of a network partition is greater than the lease
   period provided by the server, the server will have not received a
   lease renewal from the client.  If this occurs, the server may free
   all locks held for the client, or it may allow the lock state to
   remain for a considerable period, subject to the constraint that if a
   request for a conflicting lock is made, locks associated with expired
   leases do not prevent such a conflicting lock from being granted but
   are revoked as necessary so as not to interfere with such conflicting
   requests.

   If the server chooses to delay freeing of lock state until there is a
   conflict, it may either free all of the clients locks once there is a
   conflict, or it may only revoke the minimum set of locks necessary to
   allow conflicting requests.  When it adopts the finer-grained
   approach, it must revoke all locks associated with a given stateid,
   as long as it revokes a single such lock.

   When the server chooses to free all of a client's lock state, either
   immediately upon lease expiration, or a result of the first attempt
   to get a lock, all stateids held by the client will become invalid or
   stale.  Once the client is able to reach the server after such a
   network partition, the status returned by the SEQUENCE operation will
   indicate a loss of locking state.  In addition all I/O submitted by
   the client with the now invalid stateids will fail with the server
   returning the error NFS4ERR_EXPIRED.  Once the client learns of the
   loss of locking state, it will suitably notify the applications that
   held the invalidated locks.  The client should then take action to
   free invalidated stateid's, either by establishing a new client id
   using a new verifier or by doing a FREE_STATEID operation to release
   each of the invalidated stateid's.

   When the server adopts a finer-grained approach to revocation of
   locks when lease have expired, only a subset of stateids will
   normally become invalid during a network partition.  When the client
   is able to communicate with the server after such a network
   partition, the status returned by the SEQUENCE operation will
   indicate a partial loss of locking state.  In addition, operations,
   including I/O submitted by the client with the now invalid stateids
   will fail with the server returning the error NFS4ERR_EXPIRED.  Once
   the client learns of the loss of locking state, it will use the
   TEST_STATEID operation on all of its stateid's to determine which
   locks have been lost and them suitably notify the applications that
   held the invalidated locks.  The client can then release the
   invalidated locking state and acknowledge the revocation of the
   associated locks by doing a FREE_STATEID operation on each of the
   invalidated stateid's.

   When a network partition is combined with a server reboot, there are
   edge conditions that place requirements on the server in order to
   avoid silent data corruption following the server reboot.  Two of
   these edge conditions are known, and are discussed below.

   The first edge condition arises as a result of the scenarios such as
   the follwing: following:

   1.  Client A acquires a lock.

   2.  Client A and server experience mutual network partition, such
       that client A is unable to renew its lease.

   3.  Client A's lease expires, and the server releases lock.

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

   5.  Client B releases its lock.

   6.  Server reboots.

   7.  Network partition between client A and server heals.

   8.  Client A connects to new server instance and finds out about
       server reboot.

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

   Thus, at the final step, the server has erroneously granted client
   A's lock reclaim.  If client B modified the object the lock was
   protecting, client A will experience object corruption.

   The second known edge condition arises in situations such as the
   following:

   1.   Client A acquires one or more locks.

   2.   Server reboots.

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

   4.   Server's reclaim grace period ends.  Client A has either no
        locks or an incomplete set of locks known to the server.

   5.   Client B acquires a lock that would have conflicted with a lock
        of client A that was not reclaimed.

   6.   Client B releases the lock.

   7.   Server reboots a second time.

   8.   Network partition between client A and server heals.

   9.   Client A connects to new server instance and finds out about
        server reboot.

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

   As with the first edge condition, the final step of the scenario of
   the second edge condition has the server erroneously granting client
   A's lock reclaim.

   Solving the first and second edge conditions requires that the server
   either always assumes after it reboots that some edge condition
   occurs, and thus return NFS4ERR_NO_GRACE for all reclaim attempts, or
   that the server record some information in stable storage.  The
   amount of information the server records in stable storage is in
   inverse proportion to how harsh the server intends to be whenever
   edge conditions arise.  The server that is completely tolerant of all
   edge conditions will record in stable storage every lock that is
   acquired, removing the lock record from stable storage only when the
   lock is released.  For the two edge conditions discussed above, the
   harshest a server can be, and still support a grace period for
   reclaims, requires that the server record in stable storage
   information some minimal information.  For example, a server
   implementation could, for each client, save in stable storage a
   record containing:

   o  the client's id string

   o  a boolean that indicates if the client's lease expired or if there
      was administrative intervention (see Section 13.7) 8.7) to revoke a
      record lock, share reservation, or delegation and there has been
      no acknowledgement (via FREE_STATEID) of such revocation.

   o  a boolean that indicates whether the client may have locks that it
      believes to be reclaimable in situations which the grace period
      was terminated, making the server's view of lock reclaimability
      suspect.  The server will set this for any client record in stable
      storage where the client has not done a RECLAIM_COMPLETE, before
      it grants any new (i.e. not reclaimed) lock to any client.

   Assuming the above record keeping, for the first edge condition,
   after the server reboots, the record that client A's lease expired
   means that another client could have acquired a conflicting record
   lock, share reservation, or delegation.  Hence the server must reject
   a reclaim from client A with the error NFS4ERR_NO_GRACE.

   For the second edge condition, after the server reboots for a second
   time, the indication that the client had not completed its reclaims
   at the time at which the grace period ended means that the server
   must reject a reclaim from client A with the error NFS4ERR_NO_GRACE.

   When either edge condition occurs, the client's attempt to reclaim
   locks will result in the error NFS4ERR_NO_GRACE.  When this is
   received, or after the client reboots with no lock state, the client
   will issue a RECLAIM_COMPLETE.  When the RECLAIM_COMPLETE is
   received, the server and client are again in agreement regarding
   reclaimable locks and both booleans in persistent storage can be
   reset, to be set again only when there is a subsequent event that
   causes lock reclaim operations to be questionable.

   Regardless of the level and approach to record keeping, the server
   MUST implement one of the following strategies (which apply to
   reclaims of share reservations, record locks, and delegations):

   1.  Reject all reclaims with NFS4ERR_NO_GRACE.  This is extremely
       unforgiving, but necessary if the server does not record lock
       state in stable storage.

   2.  Record sufficient state in stable storage such that all known
       edge conditions involving server reboot, including the two noted
       in this section, are detected.  False positives are acceptable.
       Note that at this time, it is not known if there are other edge
       conditions.

       In the event that, after a server reboot, the server determines
       that there is unrecoverable damage or corruption to the
       information in stable storage, then for all clients and/or locks
       which may be affected, the server MUST return NFS4ERR_NO_GRACE.

   A mandate for the client's handling of the NFS4ERR_NO_GRACE error is
   outside the scope of this specification, since the strategies for
   such handling are very dependent on the client's operating
   environment.  However, one potential approach is described below.

   When the client receives NFS4ERR_NO_GRACE, it could examine the
   change attribute of the objects the client is trying to reclaim state
   for, and use that to determine whether to re-establish the state via
   normal OPEN or LOCK requests.  This is acceptable provided the
   client's operating environment allows it.  In other words, the client
   implementor is advised to document for his users the behavior.  The
   client could also inform the application that its record lock or
   share reservations (whether they were delegated or not) have been
   lost, such as via a UNIX signal, a GUI pop-up window, etc.  See the
   section, "Data Caching and Revocation" for a discussion of what the
   client should do for dealing with unreclaimed delegations on client
   state.

   For further discussion of revocation of locks see Section 13.7.

13.7. 8.7.

8.7.  Server Revocation of Locks

   At any point, the server can revoke locks held by a client and the
   client must be prepared for this event.  When the client detects that
   its locks have been or may have been revoked, the client is
   responsible for validating the state information between itself and
   the server.  Validating locking state for the client means that it
   must verify or reclaim state for each lock currently held.

   The first occasion of lock revocation is upon server reboot or re-
   initialization.  In this instance the client will receive an error
   (NFS4ERR_STALE_STATEID or NFS4ERR_STALE_CLIENTID) and the client will
   proceed with normal crash recovery as described in the previous
   section.

   The second occasion of lock revocation is the inability to renew the
   lease before expiration, as discussed above.  While this is
   considered a rare or unusual event, the client must be prepared to
   recover.  The server is responsible for determining lease expiration,
   and deciding exactly how to deal with it, informing the client of the
   scope of the lock revocation.  The client then uses the status
   information provided by the server to synchronize his locking state
   with that of the server, in order to recover.

   The third occasion of lock revocation can occur as a result of
   revocation of locks within the lease period, either because of
   administrative intervention, or because a recallable lock (a
   delegation or layout) was not returned within the lease period after
   having been recalled.  While these are considered rare events, they
   are possible and the client must be prepared to deal with them.  When
   either of these events occur, the client finds out about the
   situation through the status returned by the SEQUENCE operation.  Any
   use of stateids associated with revoked locks will receive the error
   NFS4ERR_ADMIN_REVOKED or NFS4ERR_DELEG_REVOKED, as appropriate.

   In all situations in which a subset of locking state may have been
   revoked, which include all cases in which locking state is revoked
   within the lease period, it is up to the client to determine which
   locks have been revoked and which have not.  It does this by using
   the TEST_STATEID operation on the appropriate set of stateid's.  Once
   the set of revoked locks has been determined, the applications can be
   notified, and the invalidated stateid's can be freed and lock
   revocation acknowledged by using FREE_STATEID.

13.8.

8.8.  Share Reservations

   A share reservation is a mechanism to control access to a file.  It
   is a separate and independent mechanism from record locking.  When a
   client opens a file, it issues an OPEN operation to the server
   specifying the type of access required (READ, WRITE, or BOTH) and the
   type of access to deny others (deny NONE, READ, WRITE, or BOTH).  If
   the OPEN fails the client will fail the application's open request.

   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;

13.9.

8.9.  OPEN/CLOSE Operations

   To provide correct share semantics, a client MUST use the OPEN
   operation to obtain the initial filehandle and indicate the desired
   access and what if any access to deny.  Even if the client intends to
   use a stateid of all 0's or all 1's, it must still obtain the
   filehandle for the regular file with the OPEN operation so the
   appropriate share semantics can be applied.  For clients that do not
   have a deny mode built into their open programming interfaces, deny
   equal to NONE should be used.

   The OPEN operation with the CREATE flag, also subsumes the CREATE
   operation for regular files as used in previous versions of the NFS
   protocol.  This allows a create with a share to be done atomically.

   The CLOSE operation removes all share reservations held by the open-
   owner on that file.  If record locks are held, the client SHOULD
   release all locks before issuing a CLOSE.  The server MAY free all
   outstanding locks on CLOSE but some servers may not support the CLOSE
   of a file that still has record locks held.  The server MUST return
   failure, NFS4ERR_LOCKS_HELD, if any locks would exist after the
   CLOSE.

   The LOOKUP operation will return a filehandle without establishing
   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).

13.10.

8.10.  Open Upgrade and Downgrade

   When an OPEN is done for a file and the open-owner for which the open
   is being done already has the file open, the result is to upgrade the
   open file status maintained on the server to include the access and
   deny bits specified by the new OPEN as well as those for the existing
   OPEN.  The result is that there is one open file, as far as the
   protocol is concerned, and it includes the union of the access and
   deny bits for all of the OPEN requests completed.  Only a single
   CLOSE will be done to reset the effects of both OPENs.  Note that the
   client, when issuing the OPEN, may not know that the same file is in
   fact being opened.  The above only applies if both OPENs result in
   the OPENed object being designated by the same filehandle.

   When the server chooses to export multiple filehandles corresponding
   to the same file object and returns different filehandles on two
   different OPENs of the same file object, the server MUST NOT "OR"
   together the access and deny bits and coalesce the two open files.
   Instead the server must maintain separate OPENs with separate
   stateids and will require separate CLOSEs to free them.

   When multiple open files on the client are merged into a single open
   file object on the server, the close of one of the open files (on the
   client) may necessitate change of the access and deny status of the
   open file on the server.  This is because the union of the access and
   deny bits for the remaining opens may be smaller (i.e. a proper
   subset) than previously.  The OPEN_DOWNGRADE operation is used to
   make the necessary change and the client should use it to update the
   server so that share reservation requests by other clients are
   handled properly.

13.11.

8.11.  Short and Long Leases

   When determining the time period for the server lease, the usual
   lease tradeoffs apply.  Short leases are good for fast server
   recovery at a cost of increased operations to effect lease renewal
   (when there are no other operations during the period to effect lease
   renewal as a side-effect).  Long leases are certainly kinder and
   gentler to servers trying to handle very large numbers of clients.
   The number of extra requests to effect lock renewal drop in inverse
   proportion to the lease time.  The disadvantages of long leases
   include the possibility of slower recovery after certain failures.

   After server failure, a longer grace period may be required when some
   clients do not promptly reclaim their locks and do a
   RECLAIM_COMPLETE.  In the event of client failure, it can longer
   period for leases to expire thus forcing conflicting requests to
   wait.

   Long leases are usable if the server is able to store lease state in
   non-volatile memory.  Upon recovery, the server can reconstruct the
   lease state from its non-volatile memory and continue operation with
   its clients and therefore long leases would not be an issue.

13.12.

8.12.  Clocks, Propagation Delay, and Calculating Lease Expiration

   To avoid the need for synchronized clocks, lease times are granted by
   the server as a time delta.  However, there is a requirement that the
   client and server clocks do not drift excessively over the duration
   of the lock.  There is also the issue of propagation delay across the
   network which could easily be several hundred milliseconds as well as
   the possibility that requests will be lost and need to be
   retransmitted.

   To take propagation delay into account, the client should subtract it
   from lease times (e.g. if the client estimates the one-way
   propagation delay as 200 msec, then it can assume that the lease is
   already 200 msec old when it gets it).  In addition, it will take
   another 200 msec to get a response back to the server.  So the client
   must send a lock renewal or write data back to the server 400 msec
   before the lease would expire.

   The server's lease period configuration should take into account the
   network distance of the clients that will be accessing the server's
   resources.  It is expected that the lease period will take into
   account the network propagation delays and other network delay
   factors for the client population.  Since the protocol does not allow
   for an automatic method to determine an appropriate lease period, the
   server's administrator may have to tune the lease period.

13.13.

8.13.  Vestigial Locking Infrastructure From V4.0

   There are a number of operations and fields within existing
   operations that no longer have a function in minor version one.  In
   one way or another, these changes are all due to the implementation
   of sessions which provides client context and replay protection as a
   base feature of the protocol, separate from locking itself.

   The following operations have become mandatory-to-not-implement.  The
   server should return NFS4ERR_NOTSUPP if these operations are found in
   an NFSv4.1 COMPOUND.

   o  SETCLIENTID since its function has been replaced by
      CREATE_CLIENTID.

   o  SETCLIENTID_CONFIRM since clientid confirmation now happens by
      means of CREATE_SESSION.

   o  OPEN_CONFIRM because OPEN's no longer require confirmation to
      establish an owner-based sequence value.

   o  RELEASE_LOCKOWNER because lock-owners with no associated locks
      have any sequence-related state and so can be deleted by the
      server at will.

   o  RENEW because every SEQUENCE operation for a session causes lease
      renewal, making a separate operation useless.

   Also, there are a number of fields, present in existing operations
   related to locking that have no use in minor version one.  They were
   used in minor version zero to perform functions now provided in a
   different fashion.

   o  Sequence id's used to sequence requests for a given state-owner
      and to provide replay protection, now provided via sessions.

   o  Clientid's used to identify the client associated with a given
      request.  Client identification is now available using the
      clientid associated with the current session, without needing an
      explicit clientid field.

   Such vestigial fields in existing operations should be set by the
   client to zero.  When they are not, the server MUST return an
   NFS4ERR_INVAL error.

14.

9.  Client-Side Caching

   Client-side caching of data, of file attributes, and of file names is
   essential to providing good performance with the NFS protocol.
   Providing distributed cache coherence is a difficult problem and
   previous versions of the NFS protocol have not attempted it.
   Instead, several NFS client implementation techniques have been used
   to reduce the problems that a lack of coherence poses for users.
   These techniques have not been clearly defined by earlier protocol
   specifications and it is often unclear what is valid or invalid
   client behavior.

   The NFS version 4 protocol uses many techniques similar to those that
   have been used in previous protocol versions.  The NFS version 4
   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.

14.1.

9.1.  Performance Challenges for Client-Side Caching

   Caching techniques used in previous versions of the NFS protocol have
   been successful in providing good performance.  However, several
   scalability challenges can arise when those techniques are used with
   very large numbers of clients.  This is particularly true when
   clients are geographically distributed which classically increases
   the latency for cache revalidation requests.

   The previous versions of the NFS protocol repeat their file data
   cache validation requests at the time the file is opened.  This
   behavior can have serious performance drawbacks.  A common case is
   one in which a file is only accessed by a single client.  Therefore,
   sharing is infrequent.

   In this case, repeated reference to the server to find that no
   conflicts exist is expensive.  A better option with regards to
   performance is to allow a client that repeatedly opens a file to do
   so without reference to the server.  This is done until potentially
   conflicting operations from another client actually occur.

   A similar situation arises in connection with file locking.  Sending
   file lock and unlock requests to the server as well as the read and
   write requests necessary to make data caching consistent with the
   locking semantics (see the section "Data Caching and File Locking")
   can severely limit performance.  When locking is used to provide
   protection against infrequent conflicts, a large penalty is incurred.
   This penalty may discourage the use of file locking by applications.

   The NFS version 4 protocol provides more aggressive caching
   strategies with the following design goals:

   .IP o Compatibility with a large range of server semantics. .IP o
   Provide the same caching benefits as previous versions of the NFS
   protocol when unable to provide the more aggressive model. .IP o
   Requirements for aggressive caching are organized so that a large
   portion of the benefit can be obtained even when not all of the
   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").

14.2.

9.2.  Delegation and Callbacks

   Recallable delegation of server responsibilities for a file to a
   client improves performance by avoiding repeated requests to the
   server in the absence of inter-client conflict.  With the use of a
   "callback" RPC from server to client, a server recalls delegated
   responsibilities when another client engages in sharing of a
   delegated file.

   A delegation is passed from the server to the client, specifying the
   object of the delegation and the type of delegation.  There are
   different types of delegations but each type contains a stateid to be
   used to represent the delegation when performing operations that
   depend on the delegation.  This stateid is similar to those
   associated with locks and share reservations but differs in that the
   stateid for a delegation is associated with a clientid and may be
   used on behalf of all the open_owners for the given client.  A
   delegation is made to the client as a whole and not to any specific
   process or thread of control within it.

   Because callback RPCs may not work in all environments (due to
   firewalls, for example), correct protocol operation does not depend
   on them.  Preliminary testing of callback functionality by means of a
   CB_NULL procedure determines whether callbacks can be supported.  The
   CB_NULL procedure checks the continuity of the callback path.  A
   server makes a preliminary assessment of callback availability to a
   given client and avoids delegating responsibilities until it has
   determined that callbacks are supported.  Because the granting of a
   delegation is always conditional upon the absence of conflicting
   access, clients must not assume that a delegation will be granted and
   they must always be prepared for OPENs to be processed without any
   delegations being granted.

   Once granted, a delegation behaves in most ways like a lock.  There
   is an associated lease that is subject to renewal together with all
   of the other leases held by that client.

   Unlike locks, an operation by a second client to a delegated file
   will cause the server to recall a delegation through a callback.

   On recall, the client holding the delegation must flush modified
   state (such as modified data) to the server and return the
   delegation.  The conflicting request will not receive a response
   until the recall is complete.  The recall is considered complete when
   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.

14.2.1.

9.2.1.  Delegation Recovery

   There are three situations that delegation recovery must deal with:

   o  Client reboot or restart

   o  Server reboot or restart

   o  Network partition (full or callback-only)

   In the event the client reboots or restarts, the failure to renew
   leases will result in the revocation of record locks and share
   reservations.  Delegations, however, may be treated a bit
   differently.

   There will be situations in which delegations will need to be
   reestablished after a client reboots or restarts.  The reason for
   this is the client may have file data stored locally and this data
   was associated with the previously held delegations.  The client will
   need to reestablish the appropriate file state on the server.

   To allow for this type of client recovery, the server MAY extend the
   period for delegation recovery beyond the typical lease expiration
   period.  This implies that requests from other clients that conflict
   with these delegations will need to wait.  Because the normal recall
   process may require significant time for the client to flush changed
   state to the server, other clients need be prepared for delays that
   occur because of a conflicting delegation.  This longer interval
   would increase the window for clients to reboot and consult stable
   storage so that the delegations can be reclaimed.  For open
   delegations, such delegations are reclaimed using OPEN with a claim
   type of CLAIM_DELEGATE_PREV.  (See the sections on "Data Caching and
   Revocation" and "Operation 18: OPEN" for discussion of open
   delegation and the details of OPEN respectively).

   A server MAY support a claim type of CLAIM_DELEGATE_PREV, but if it
   does, it MUST NOT remove delegations upon SETCLIENTID_CONFIRM, and
   instead MUST, for a period of time no less than that of the value of
   the lease_time attribute, maintain the client's delegations to allow
   time for the client to issue CLAIM_DELEGATE_PREV requests.  The
   server that supports CLAIM_DELEGATE_PREV MUST support the DELEGPURGE
   operation.

   When the server reboots or restarts, delegations are reclaimed (using
   the OPEN operation with CLAIM_PREVIOUS) in a similar fashion to
   record locks and share reservations.  However, there is a slight
   semantic difference.  In the normal case if the server decides that a
   delegation should not be granted, it performs the requested action
   (e.g.  OPEN) without granting any delegation.  For reclaim, the
   server grants the delegation but a special designation is applied so
   that the client treats the delegation as having been granted but
   recalled by the server.  Because of this, the client has the duty to
   write all modified state to the server and then return the
   delegation.  This process of handling delegation reclaim reconciles
   three principles of the NFS version 4 protocol:

   o  Upon reclaim, a client reporting resources assigned to it by an
      earlier server instance must be granted those resources.

   o  The server has unquestionable authority to determine whether
      delegations are to be granted and, once granted, whether they are
      to be continued.

   o  The use of callbacks is not to be depended upon until the client
      has proven its ability to receive them.

   When a network partition occurs, delegations are subject to freeing
   by the server when the lease renewal period expires.  This is similar
   to the behavior for locks and share reservations.  For delegations,
   however, the server may extend the period in which conflicting
   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.

14.3.

9.3.  Data Caching

   When applications share access to a set of files, they need to be
   implemented so as to take account of the possibility of conflicting
   access by another application.  This is true whether the applications
   in question execute on different clients or reside on the same
   client.

   Share reservations and record locks are the facilities the NFS
   version 4 protocol provides to allow applications to coordinate
   access by providing mutual exclusion facilities.  The NFS version 4
   protocol's data caching must be implemented such that it does not
   invalidate the assumptions that those using these facilities depend
   upon.

14.3.1.

9.3.1.  Data Caching and OPENs

   In order to avoid invalidating the sharing assumptions that
   applications rely on, NFS version 4 clients should not provide cached
   data to applications or modify it on behalf of an application when it
   would not be valid to obtain or modify that same data via a READ or
   WRITE operation.

   Furthermore, in the absence of open delegation (see the section "Open
   Delegation") two additional rules apply.  Note that these rules are
   obeyed in practice by many NFS version 2 and version 3 clients.

   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.

14.3.2.

9.3.2.  Data Caching and File Locking

   For those applications that choose to use file locking instead of
   share reservations to exclude inconsistent file access, there is an
   analogous set of constraints that apply to client side data caching.
   These rules are effective only if the file locking is used in a way
   that matches in an equivalent way the actual READ and WRITE
   operations executed.  This is as opposed to file locking that is
   based on pure convention.  For example, it is possible to manipulate
   a two-megabyte file by dividing the file into two one-megabyte
   regions and protecting access to the two regions by file locks on
   bytes zero and one.  A lock for write on byte zero of the file would
   represent the right to do READ and WRITE operations on the first
   region.  A lock for write on byte one of the file would represent the
   right to do READ and WRITE operations on the second region.  As long
   as all applications manipulating the file obey this convention, they
   will work on a local file system.  However, they may not work with
   the NFS version 4 protocol unless clients refrain from data caching.

   The rules for data caching in the file locking environment are:

   o  First, when a client obtains a file lock for a particular region,
      the data cache corresponding to that region (if any cache data
      exists) must be revalidated.  If the change attribute indicates
      that the file may have been updated since the cached data was
      obtained, the client must flush or invalidate the cached data for
      the newly locked region.  A client might choose to invalidate all
      of non-modified cached data that it has for the file but the only
      requirement for correct operation is to invalidate all of the data
      in the newly locked region.

   o  Second, before releasing a write lock for a region, all modified
      data for that region must be flushed to the server.  The modified
      data must also be written to stable storage.

   Note that flushing data to the server and the invalidation of cached
   data must reflect the actual byte ranges locked or unlocked.
   Rounding these up or down to reflect client cache block boundaries
   will cause problems if not carefully done.  For example, writing a
   modified block when only half of that block is within an area being
   unlocked may cause invalid modification to the region outside the
   unlocked area.  This, in turn, may be part of a region locked by
   another client.  Clients can avoid this situation by synchronously
   performing portions of write operations that overlap that portion
   (initial or final) that is not a full block.  Similarly, invalidating
   a locked area which is not an integral number of full buffer blocks
   would require the client to read one or two partial blocks from the
   server if the revalidation procedure shows that the data which the
   client possesses may not be valid.

   The data that is written to the server as a prerequisite to the
   unlocking of a region must be written, at the server, to stable
   storage.  The client may accomplish this either with synchronous
   writes or by following asynchronous writes with a COMMIT operation.
   This is required because retransmission of the modified data after a
   server reboot might conflict with a lock held by another client.

   A client implementation may choose to accommodate applications which
   use record locking in non-standard ways (e.g. using a record lock as
   a global semaphore) by flushing to the server more data upon an LOCKU
   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.

14.3.3.

9.3.3.  Data Caching and Mandatory File Locking

   Client side data caching needs to respect mandatory file locking when
   it is in effect.  The presence of mandatory file locking for a given
   file is indicated when the client gets back NFS4ERR_LOCKED from a
   READ or WRITE on a file it has an appropriate share reservation for.
   When mandatory locking is in effect for a file, the client must check
   for an appropriate file lock for data being read or written.  If a
   lock exists for the range being read or written, the client may
   satisfy the request using the client's validated cache.  If an
   appropriate file lock is not held for the range of the read or write,
   the read or write request must not be satisfied by the client's cache
   and the request must be sent to the server for processing.  When a
   read or write request partially overlaps a locked region, the request
   should be subdivided into multiple pieces with each region (locked or
   not) treated appropriately.

14.3.4.

9.3.4.  Data Caching and File Identity

   When clients cache data, the file data needs to be organized
   according to the file system object to which the data belongs.  For
   NFS version 3 clients, the typical practice has been to assume for
   the purpose of caching that distinct filehandles represent distinct
   file system objects.  The client then has the choice to organize and
   maintain the data cache on this basis.

   In the NFS version 4 protocol, there is now the possibility to have
   significant deviations from a "one filehandle per object" model
   because a filehandle may be constructed on the basis of the object's
   pathname.  Therefore, clients need a reliable method to determine if
   two filehandles designate the same file system object.  If clients
   were simply to assume that all distinct filehandles denote distinct
   objects and proceed to do data caching on this basis, caching
   inconsistencies would arise between the distinct client side objects
   which mapped to the same server side object.

   By providing a method to differentiate filehandles, the NFS version 4
   protocol alleviates a potential functional regression in comparison
   with the NFS version 3 protocol.  Without this method, caching
   inconsistencies within the same client could occur and this has not
   been present in previous versions of the NFS protocol.  Note that it
   is possible to have such inconsistencies with applications executing
   on multiple clients but that is not the issue being addressed here.

   For the purposes of data caching, the following steps allow an NFS
   version 4 client to determine whether two distinct filehandles denote
   the same server side object:

   o  If GETATTR directed to two filehandles returns different values of
      the fsid attribute, then the filehandles represent distinct
      objects.

   o  If GETATTR for any file with an fsid that matches the fsid of the
      two filehandles in question returns a unique_handles attribute
      with a value of TRUE, then the two objects are distinct.

   o  If GETATTR directed to the two filehandles does not return the
      fileid attribute for both of the handles, then it cannot be
      determined whether the two objects are the same.  Therefore,
      operations which depend on that knowledge (e.g. client side data
      caching) cannot be done reliably.

   o  If GETATTR directed to the two filehandles returns different
      values for the fileid attribute, then they are distinct objects.

   o  Otherwise they are the same object.

14.4.

9.4.  Open Delegation

   When a file is being OPENed, the server may delegate further handling
   of opens and closes for that file to the opening client.  Any such
   delegation is recallable, since the circumstances that allowed for
   the delegation are subject to change.  In particular, the server may
   receive a conflicting OPEN from another client, the server must
   recall the delegation before deciding whether the OPEN from the other
   client may be granted.  Making a delegation is up to the server and
   clients should not assume that any particular OPEN either will or
   will not result in an open delegation.  The following is a typical
   set of conditions that servers might use in deciding whether OPEN
   should be delegated:

   o  The client must be able to respond to the server's callback
      requests.  The server will use the CB_NULL procedure for a test of
      callback ability.

   o  The client must have responded properly to previous recalls.

   o  There must be no current open conflicting with the requested
      delegation.

   o  There should be no current delegation that conflicts with the
      delegation being requested.

   o  The probability of future conflicting open requests should be low
      based on the recent history of the file.

   o  The existence of any server-specific semantics of OPEN/CLOSE that
      would make the required handling incompatible with the prescribed
      handling that the delegated client would apply (see below).

   There are two types of open delegations, read and write.  A read open
   delegation allows a client to handle, on its own, requests to open a
   file for reading that do not deny read access to others.  Multiple
   read open delegations may be outstanding simultaneously and do not
   conflict.  A write open delegation allows the client to handle, on
   its own, all opens.  Only one write open delegation may exist for a
   given file at a given time and it is inconsistent with any read open
   delegations.

   When a client has a read open delegation, it may not make any changes
   to the contents or attributes of the file but it is assured that no
   other client may do so.  When a client has a write open delegation,
   it may modify the file data since no other client will be accessing
   the file's data.  The client holding a write delegation may only
   affect file attributes which are intimately connected with the file
   data: size, time_modify, change.

   When a client has an open delegation, it does not send OPENs or
   CLOSEs to the server but updates the appropriate status internally.
   For a read open delegation, opens that cannot be handled locally
   (opens for write or that deny read access) must be sent to the
   server.

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

   o  the type of delegation (read or write)

   o  space limitation information to control flushing of data on close
      (write open delegation only, see the section "Open Delegation and
      Data Caching")

   o  an nfsace4 specifying read and write permissions

   o  a stateid to represent the delegation for READ and WRITE

   The delegation stateid is separate and distinct from the stateid for
   the OPEN proper.  The standard stateid, unlike the delegation
   stateid, is associated with a particular lock_owner and will continue
   to be valid after the delegation is recalled and the file remains
   open.

   When a request internal to the client is made to open a file and open
   delegation is in effect, it will be accepted or rejected solely on
   the basis of the following conditions.  Any requirement for other
   checks to be made by the delegate should result in open delegation
   being denied so that the checks can be made by the server itself.

   o  The access and deny bits for the request and the file as described
      in the section "Share Reservations".

   o  The read and write permissions as determined below.

   The nfsace4 passed with delegation can be used to avoid frequent
   ACCESS calls.  The permission check should be as follows:

   o  If the nfsace4 indicates that the open may be done, then it should
      be granted without reference to the server.

   o  If the nfsace4 indicates that the open may not be done, then an
      ACCESS request must be sent to the server to obtain the definitive
      answer.

   The server may return an nfsace4 that is more restrictive than the
   actual ACL of the file.  This includes an nfsace4 that specifies
   denial of all access.  Note that some common practices such as
   mapping the traditional user "root" to the user "nobody" may make it
   incorrect to return the actual ACL of the file in the delegation
   response.

   The use of delegation together with various other forms of caching
   creates the possibility that no server authentication will ever be
   performed for a given user since all of the user's requests might be
   satisfied locally.  Where the client is depending on the server for
   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.

14.4.1.

9.4.1.  Open Delegation and Data Caching

   OPEN delegation allows much of the message overhead associated with
   the opening and closing files to be eliminated.  An open when an open
   delegation is in effect does not require that a validation message be
   sent to the server.  The continued endurance of the "read open
   delegation" provides a guarantee that no OPEN for write and thus no
   write has occurred.  Similarly, when closing a file opened for write
   and if write open delegation is in effect, the data written does not
   have to be flushed to the server until the open delegation is
   recalled.  The continued endurance of the open delegation provides a
   guarantee that no open and thus no read or write has been done by
   another client.

   For the purposes of open delegation, READs and WRITEs done without an
   OPEN are treated as the functional equivalents of a corresponding
   type of OPEN.  This refers to the READs and WRITEs that use the
   special stateids consisting of all zero bits or all one bits.
   Therefore, READs or WRITEs with a special stateid done by another
   client will force the server to recall a write open delegation.  A
   WRITE with a special stateid done by another client will force a
   recall of read open delegations.

   With delegations, a client is able to avoid writing data to the
   server when the CLOSE of a file is serviced.  The file close system
   call is the usual point at which the client is notified of a lack of
   stable storage for the modified file data generated by the
   application.  At the close, file data is written to the server and
   through normal accounting the server is able to determine if the
   available file system space for the data has been exceeded (i.e.
   server returns NFS4ERR_NOSPC or NFS4ERR_DQUOT).  This accounting
   includes quotas.  The introduction of delegations requires that a
   alternative method be in place for the same type of communication to
   occur between client and server.

   In the delegation response, the server provides either the limit of
   the size of the file or the number of modified blocks and associated
   block size.  The server must ensure that the client will be able to
   flush data to the server of a size equal to that provided in the
   original delegation.  The server must make this assurance for all
   outstanding delegations.  Therefore, the server must be careful in
   its management of available space for new or modified data taking
   into account available file system space and any applicable quotas.
   The server can recall delegations as a result of managing the
   available file system space.  The client should abide by the server's
   state space limits for delegations.  If the client exceeds the stated
   limits for the delegation, the server's behavior is undefined.

   Based on server conditions, quotas or available file system space,
   the server may grant write open delegations with very restrictive
   space limitations.  The limitations may be defined in a way that will
   always force modified data to be flushed to the server on close.

   With respect to authentication, flushing modified data to the server
   after a CLOSE has occurred may be problematic.  For example, the user
   of the application may have logged off the client and unexpired
   authentication credentials may not be present.  In this case, the
   client may need to take special care to ensure that local unexpired
   credentials will in fact be available.  This may be accomplished by
   tracking the expiration time of credentials and flushing data well in
   advance of their expiration or by making private copies of
   credentials to assure their availability when needed.

14.4.2.

9.4.2.  Open Delegation and File Locks

   When a client holds a write open delegation, lock operations are
   performed locally.  This includes those required for mandatory file
   locking.  This can be done since the delegation implies that there
   can be no conflicting locks.  Similarly, all of the revalidations
   that would normally be associated with obtaining locks and the
   flushing of data associated with the releasing of locks need not be
   done.

   When a client holds a read open delegation, lock operations are not
   performed locally.  All lock operations, including those requesting
   non-exclusive locks, are sent to the server for resolution.

14.4.3.

9.4.3.  Handling of CB_GETATTR

   The server needs to employ special handling for a GETATTR where the
   target is a file that has a write open delegation in effect.  The
   reason for this is that the client holding the write delegation may
   have modified the data and the server needs to reflect this change to
   the second client that submitted the GETATTR.  Therefore, the client
   holding the write delegation needs to be interrogated.  The server
   will use the CB_GETATTR operation.  The only attributes that the
   server can reliably query via CB_GETATTR are size and change.

   Since CB_GETATTR is being used to satisfy another client's GETATTR
   request, the server only needs to know if the client holding the
   delegation has a modified version of the file.  If the client's copy
   of the delegated file is not modified (data or size), the server can
   satisfy the second client's GETATTR request from the attributes
   stored locally at the server.  If the file is modified, the server
   only needs to know about this modified state.  If the server
   determines that the file is currently modified, it will respond to
   the second client's GETATTR as if the file had been modified locally
   at the server.

   Since the form of the change attribute is determined by the server
   and is opaque to the client, the client and server need to agree on a
   method of communicating the modified state of the file.  For the size
   attribute, the client will report its current view of the file size.
   For the change attribute, the handling is more involved.

   For the client, the following steps will be taken when receiving a
   write delegation:

   o  The value of the change attribute will be obtained from the server
      and cached.  Let this value be represented by c.

   o  The client will create a value greater than c that will be used
      for communicating modified data is held at the client.  Let this
      value be represented by d.

   o  When the client is queried via CB_GETATTR for the change
      attribute, it checks to see if it holds modified data.  If the
      file is modified, the value d is returned for the change attribute
      value.  If this file is not currently modified, the client returns
      the value c for the change attribute.

   For simplicity of implementation, the client MAY for each CB_GETATTR
   return the same value d.  This is true even if, between successive
   CB_GETATTR operations, the client again modifies in the file's data
   or metadata in its cache.  The client can return the same value
   because the only requirement is that the client be able to indicate
   to the server that the client holds modified data.  Therefore, the
   value of d may always be c + 1.

   While the change attribute is opaque to the client in the sense that
   it has no idea what units of time, if any, the server is counting
   change with, it is not opaque in that the client has to treat it as
   an unsigned integer, and the server has to be able to see the results
   of the client's changes to that integer.  Therefore, the server MUST
   encode the change attribute in network order when sending it to the
   client.  The client MUST decode it from network order to its native
   order when receiving it and the client MUST encode it network order
   when sending it to the server.  For this reason, change is defined as
   an unsigned integer rather than an opaque array of octets.

   For the server, the following steps will be taken when providing a
   write delegation:

   o  Upon providing a write delegation, the server will cache a copy of
      the change attribute in the data structure it uses to record the
      delegation.  Let this value be represented by sc.

   o  When a second client sends a GETATTR operation on the same file to
      the server, the server obtains the change attribute from the first
      client.  Let this value be cc.

   o  If the value cc is equal to sc, the file is not modified and the
      server returns the current values for change, time_metadata, and
      time_modify (for example) to the second client.

   o  If the value cc is NOT equal to sc, the file is currently modified
      at the first client and most likely will be modified at the server
      at a future time.  The server then uses its current time to
      construct attribute values for time_metadata and time_modify.  A
      new value of sc, which we will call nsc, is computed by the
      server, such that nsc >= sc + 1.  The server then returns the
      constructed time_metadata, time_modify, and nsc values to the
      requester.  The server replaces sc in the delegation record with
      nsc.  To prevent the possibility of time_modify, time_metadata,
      and change from appearing to go backward (which would happen if
      the client holding the delegation fails to write its modified data
      to the server before the delegation is revoked or returned), the
      server SHOULD update the file's metadata record with the
      constructed attribute values.  For reasons of reasonable
      performance, committing the constructed attribute values to stable
      storage is OPTIONAL.

   As discussed earlier in this section, the client MAY return the same
   cc value on subsequent CB_GETATTR calls, even if the file was
   modified in the client's cache yet again between successive
   CB_GETATTR calls.  Therefore, the server must assume that the file
   has been modified yet again, and MUST take care to ensure that the
   new nsc it constructs and returns is greater than the previous nsc it
   returned.  An example implementation's delegation record would
   satisfy this mandate by including a boolean field (let us call it
   "modified") that is set to false when the delegation is granted, and
   an sc value set at the time of grant to the change attribute value.
   The modified field would be set to true the first time cc != sc, and
   would stay true until the delegation is returned or revoked.  The
   processing for constructing nsc, time_modify, and time_metadata would
   use this pseudo code:

   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.

14.4.4.

9.4.4.  Recall of Open Delegation

   The following events necessitate recall of an open delegation:

   o  Potentially conflicting OPEN request (or READ/WRITE done with
      "special" stateid)

   o  SETATTR issued by another client

   o  REMOVE request for the file

   o  RENAME request for the file as either source or target of the
      RENAME

   Whether a RENAME of a directory in the path leading to the file
   results in recall of an open delegation depends on the semantics of
   the server file system.  If that file system denies such RENAMEs when
   a file is open, the recall must be performed to determine whether the
   file in question is, in fact, open.

   In addition to the situations above, the server may choose to recall
   open delegations at any time if resource constraints make it
   advisable to do so.  Clients should always be prepared for the
   possibility of recall.

   When a client receives a recall for an open delegation, it needs to
   update state on the server before returning the delegation.  These
   same updates must be done whenever a client chooses to return a
   delegation voluntarily.  The following items of state need to be
   dealt with:

   o  If the file associated with the delegation is no longer open and
      no previous CLOSE operation has been sent to the server, a CLOSE
      operation must be sent to the server.

   o  If a file has other open references at the client, then OPEN
      operations must be sent to the server.  The appropriate stateids
      will be provided by the server for subsequent use by the client
      since the delegation stateid will not longer be valid.  These OPEN
      requests are done with the claim type of CLAIM_DELEGATE_CUR.  This
      will allow the presentation of the delegation stateid so that the
      client can establish the appropriate rights to perform the OPEN.
      (see the section "Operation 18: OPEN" for details.)

   o  If there are granted file locks, the corresponding LOCK operations
      need to be performed.  This applies to the write open delegation
      case only.

   o  For a write open delegation, if at the time of recall the file is
      not open for write, all modified data for the file must be flushed
      to the server.  If the delegation had not existed, the client
      would have done this data flush before the CLOSE operation.

   o  For a write open delegation when a file is still open at the time
      of recall, any modified data for the file needs to be flushed to
      the server.

   o  With the write open delegation in place, it is possible that the
      file was truncated during the duration of the delegation.  For
      example, the truncation could have occurred as a result of an OPEN
      UNCHECKED with a size attribute value of zero.  Therefore, if a
      truncation of the file has occurred and this operation has not
      been propagated to the server, the truncation must occur before
      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.

14.4.5.

9.4.5.  Clients that Fail to Honor Delegation Recalls

   A client may fail to respond to a recall for various reasons, such as
   a failure of the callback path from server to the client.  The client
   may be unaware of a failure in the callback path.  This lack of
   awareness could result in the client finding out long after the
   failure that its delegation has been revoked, and another client has
   modified the data for which the client had a delegation.  This is
   especially a problem for the client that held a write delegation.

   The server also has a dilemma in that the client that fails to
   respond to the recall might also be sending other NFS requests,
   including those that renew the lease before the lease expires.
   Without returning an error for those lease renewing operations, the
   server leads the client to believe that the delegation it has is in
   force.

   This difficulty is solved by the following rules:

   o  When the callback path is down, the server MUST NOT revoke the
      delegation if one of the following occurs:

      *  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.

14.4.6.

9.4.6.  Delegation Revocation

   At the point a delegation is revoked, if there are associated opens
   on the client, the applications holding these opens need to be
   notified.  This notification usually occurs by returning errors for
   READ/WRITE operations or when a close is attempted for the open file.

   If no opens exist for the file at the point the delegation is
   revoked, then notification of the revocation is unnecessary.
   However, if there is modified data present at the client for the
   file, the user of the application should be notified.  Unfortunately,
   it may not be possible to notify the user since active applications
   may not be present at the client.  See the section "Revocation
   Recovery for Write Open Delegation" for additional details.

14.5.

9.5.  Data Caching and Revocation

   When locks and delegations are revoked, the assumptions upon which
   successful caching depend are no longer guaranteed.  For any locks or
   share reservations that have been revoked, the corresponding owner
   needs to be notified.  This notification includes applications with a
   file open that has a corresponding delegation which has been revoked.
   Cached data associated with the revocation must be removed from the
   client.  In the case of modified data existing in the client's cache,
   that data must be removed from the client without it being written to
   the server.  As mentioned, the assumptions made by the client are no
   longer valid at the point when a lock or delegation has been revoked.

   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.

14.5.1.

9.5.1.  Revocation Recovery for Write Open Delegation

   Revocation recovery for a write open delegation poses the special
   issue of modified data in the client cache while the file is not
   open.  In this situation, any client which does not flush modified
   data to the server on each close must ensure that the user receives
   appropriate notification of the failure as a result of the
   revocation.  Since such situations may require human action to
   correct problems, notification schemes in which the appropriate user
   or administrator is notified may be necessary.  Logging and console
   messages are typical examples.

   If there is modified data on the client, it must not be flushed
   normally to the server.  A client may attempt to provide a copy of
   the file data as modified during the delegation under a different
   name in the file system name space to ease recovery.  Note that when
   the client can determine that the file has not been modified by any
   other client, or when the client has a complete cached copy of file
   in question, such a saved copy of the client's view of the file may
   be of particular value for recovery.  In other case, recovery using a
   copy of the file based partially on the client's cached data and
   partially on the server copy as modified by other clients, will be
   anything but straightforward, so clients may avoid saving file
   contents in these situations or mark the results specially to warn
   users of possible problems.

   Saving of such modified data in delegation revocation situations may
   be limited to files of a certain size or might be used only when
   sufficient disk space is available within the target file system.
   Such saving may also be restricted to situations when the client has
   sufficient buffering resources to keep the cached copy available
   until it is properly stored to the target file system.

14.6.

9.6.  Attribute Caching

   The attributes discussed in this section do not include named
   attributes.  Individual named attributes are analogous to files and
   caching of the data for these needs to be handled just as data
   caching is for ordinary files.  Similarly, LOOKUP results from an
   OPENATTR directory are to be cached on the same basis as any other
   pathnames and similarly for directory contents.

   Clients may cache file attributes obtained from the server and use
   them to avoid subsequent GETATTR requests.  Such caching is write
   through in that modification to file attributes is always done by
   means of requests to the server and should not be done locally and
   cached.  The exception to this are modifications to attributes that
   are intimately connected with data caching.  Therefore, extending a
   file by writing data to the local data cache is reflected immediately
   in the size as seen on the client without this change being
   immediately reflected on the server.  Normally such changes are not
   propagated directly to the server but when the modified data is
   flushed to the server, analogous attribute changes are made on the
   server.  When open delegation is in effect, the modified attributes
   may be returned to the server in the response to a CB_RECALL call.

   The result of local caching of attributes is that the attribute
   caches maintained on individual clients will not be coherent.
   Changes made in one order on the server may be seen in a different
   order on one client and in a third order on a different client.

   The typical file system application programming interfaces do not
   provide means to atomically modify or interrogate attributes for
   multiple files at the same time.  The following rules provide an
   environment where the potential incoherences mentioned above can be
   reasonably managed.  These rules are derived from the practice of
   previous NFS protocols.

   o  All attributes for a given file (per-fsid attributes excepted) are
      cached as a unit at the client so that no non-serializability can
      arise within the context of a single file.

   o  An upper time boundary is maintained on how long a client cache
      entry can be kept without being refreshed from the server.

   o  When operations are performed that change attributes at the
      server, the updated attribute set is requested as part of the
      containing RPC.  This includes directory operations that update
      attributes indirectly.  This is accomplished by following the
      modifying operation with a GETATTR operation and then using the
      results of the GETATTR to update the client's cached attributes.

   Note that if the full set of attributes to be cached is requested by
   READDIR, the results can be cached by the client on the same basis as
   attributes obtained via GETATTR.

   A client may validate its cached version of attributes for a file by
   fetching just both the change and time_access attributes and assuming
   that if the change attribute has the same value as it did when the
   attributes were cached, then no attributes other than time_access
   have changed.  The reason why time_access is also fetched is because
   many servers operate in environments where the operation that updates
   change does not update time_access.  For example, POSIX file
   semantics do not update access time when a file is modified by the
   write system call.  Therefore, the client that wants a current
   time_access value should fetch it with change during the attribute
   cache validation processing and update its cached time_access.

   The client may maintain a cache of modified attributes for those
   attributes intimately connected with data of modified regular files
   (size, time_modify, and change).  Other than those three attributes,
   the client MUST NOT maintain a cache of modified attributes.
   Instead, attribute changes are immediately sent to the server.

   In some operating environments, the equivalent to time_access is
   expected to be implicitly updated by each read of the content of the
   file object.  If an NFS client is caching the content of a file
   object, whether it is a regular file, directory, or symbolic link,
   the client SHOULD NOT update the time_access attribute (via SETATTR
   or a small READ or READDIR request) on the server with each read that
   is satisfied from cache.  The reason is that this can defeat the
   performance benefits of caching content, especially since an explicit
   SETATTR of time_access may alter the change attribute on the server.
   If the change attribute changes, clients that are caching the content
   will think the content has changed, and will re-read unmodified data
   from the server.  Nor is the client encouraged to maintain a modified
   version of time_access in its cache, since this would mean that the
   client will either eventually have to write the access time to the
   server with bad performance effects, or it would never update the
   server's time_access, thereby resulting in a situation where an
   application that caches access time between a close and open of the
   same file observes the access time oscillating between the past and
   present.  The time_access attribute always means the time of last
   access to a file by a read that was satisfied by the server.  This
   way clients will tend to see only time_access changes that go forward
   in time.

14.7.

9.7.  Data and Metadata Caching and Memory Mapped Files

   Some operating environments include the capability for an application
   to map a file's content into the application's address space.  Each
   time the application accesses a memory location that corresponds to a
   block that has not been loaded into the address space, a page fault
   occurs and the file is read (or if the block does not exist in the
   file, the block is allocated and then instantiated in the
   application's address space).

   As long as each memory mapped access to the file requires a page
   fault, the relevant attributes of the file that are used to detect
   access and modification (time_access, time_metadata, time_modify, and
   change) will be updated.  However, in many operating environments,
   when page faults are not required these attributes will not be
   updated on reads or updates to the file via memory access (regardless
   whether the file is local file or is being access remotely).  A
   client or server MAY fail to update attributes of a file that is
   being accessed via memory mapped I/O. This has several implications:

   o  If there is an application on the server that has memory mapped a
      file that a client is also accessing, the client may not be able
      to get a consistent value of the change attribute to determine
      whether its cache is stale or not.  A server that knows that the
      file is memory mapped could always pessimistically return updated
      values for change so as to force the application to always get the
      most up to date data and metadata for the file.  However, due to
      the negative performance implications of this, such behavior is
      OPTIONAL.

   o  If the memory mapped file is not being modified on the server, and
      instead is just being read by an application via the memory mapped
      interface, the client will not see an updated time_access
      attribute.  However, in many operating environments, neither will
      any process running on the server.  Thus NFS clients are at no
      disadvantage with respect to local processes.

   o  If there is another client that is memory mapping the file, and if
      that client is holding a write delegation, the same set of issues
      as discussed in the previous two bullet items apply.  So, when a
      server does a CB_GETATTR to a file that the client has modified in
      its cache, the response from CB_GETATTR will not necessarily be
      accurate.  As discussed earlier, the client's obligation is to
      report that the file has been modified since the delegation was
      granted, not whether it has been modified again between successive
      CB_GETATTR calls, and the server MUST assume that any file the
      client has modified in cache has been modified again between
      successive CB_GETATTR calls.  Depending on the nature of the
      client's memory management system, this weak obligation may not be
      possible.  A client MAY return stale information in CB_GETATTR
      whenever the file is memory mapped.

   o  The mixture of memory mapping and file locking on the same file is
      problematic.  Consider the following scenario, where a page size
      on each client is 8192 bytes.

      *  Client A memory maps first page (8192 bytes) of file X

      *  Client B memory maps first page (8192 bytes) of file X

      *  Client A write locks first 4096 bytes

      *  Client B write locks second 4096 bytes

      *  Client A, via a STORE instruction modifies part of its locked
         region.

      *  Simultaneous to client A, client B issues a STORE on part of
         its locked region.

   Here the challenge is for each client to resynchronize to get a
   correct view of the first page.  In many operating environments, the
   virtual memory management systems on each client only know a page is
   modified, not that a subset of the page corresponding to the
   respective lock regions has been modified.  So it is not possible for
   each client to do the right thing, which is to only write to the
   server that portion of the page that is locked.  For example, if
   client A simply writes out the page, and then client B writes out the
   page, client A's data is lost.

   Moreover, if mandatory locking is enabled on the file, then we have a
   different problem.  When clients A and B issue the STORE
   instructions, the resulting page faults require a record lock on the
   entire page.  Each client then tries to extend their locked range to
   the entire page, which results in a deadlock.  Communicating the
   NFS4ERR_DEADLOCK error to a STORE instruction is difficult at best.

   If a client is locking the entire memory mapped file, there is no
   problem with advisory or mandatory record locking, at least until the
   client unlocks a region in the middle of the file.

   Given the above issues the following are permitted:

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

   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.

14.8.

9.8.  Name Caching

   The results of LOOKUP and READDIR operations may be cached to avoid
   the cost of subsequent LOOKUP operations.  Just as in the case of
   attribute caching, inconsistencies may arise among the various client
   caches.  To mitigate the effects of these inconsistencies and given
   the context of typical file system APIs, an upper time boundary is
   maintained on how long a client name cache entry can be kept without
   verifying that the entry has not been made invalid by a directory
   change operation performed by another client. .LP When a client is
   not making changes to a directory for which there exist name cache
   entries, the client needs to periodically fetch attributes for that
   directory to ensure that it is not being modified.  After determining
   that no modification has occurred, the expiration time for the
   associated name cache entries may be updated to be the current time
   plus the name cache staleness bound.

   When a client is making changes to a given directory, it needs to
   determine whether there have been changes made to the directory by
   other clients.  It does this by using the change attribute as
   reported before and after the directory operation in the associated
   change_info4 value returned for the operation.  The server is able to
   communicate to the client whether the change_info4 data is provided
   atomically with respect to the directory operation.  If the change
   values are provided atomically, the client is then able to compare
   the pre-operation change value with the change value in the client's
   name cache.  If the comparison indicates that the directory was
   updated by another client, the name cache associated with the
   modified directory is purged from the client.  If the comparison
   indicates no modification, the name cache can be updated on the
   client to reflect the directory operation and the associated timeout
   extended.  The post-operation change value needs to be saved as the
   basis for future change_info4 comparisons.

   As demonstrated by the scenario above, name caching requires that the
   client revalidate name cache data by inspecting the change attribute
   of a directory at the point when the name cache item was cached.
   This requires that the server update the change attribute for
   directories when the contents of the corresponding directory is
   modified.  For a client to use the change_info4 information
   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.

14.9.

9.9.  Directory Caching

   The results of READDIR operations may be used to avoid subsequent
   READDIR operations.  Just as in the cases of attribute and name
   caching, inconsistencies may arise among the various client caches.
   To mitigate the effects of these inconsistencies, and given the
   context of typical file system APIs, the following rules should be
   followed:

   o  Cached READDIR information for a directory which is not obtained
      in a single READDIR operation must always be a consistent snapshot
      of directory contents.  This is determined by using a GETATTR
      before the first READDIR and after the last of READDIR that
      contributes to the cache.

   o  An upper time boundary is maintained to indicate the length of
      time a directory cache entry is considered valid before the client
      must revalidate the cached information.

   The revalidation technique parallels that discussed in the case of
   name caching.  When the client is not changing the directory in
   question, checking the change attribute of the directory with GETATTR
   is adequate.  The lifetime of the cache entry can be extended at
   these checkpoints.  When a client is modifying the directory, the
   client needs to use the change_info4 data to determine whether there
   are other clients modifying the directory.  If it is determined that
   no other client modifications are occurring, the client may update
   its directory cache to reflect its own changes.

   As demonstrated previously, directory caching requires that the
   client revalidate directory cache data by inspecting the change
   attribute of a directory at the point when the directory was cached.
   This requires that the server update the change attribute for
   directories when the contents of the corresponding directory is
   modified.  For a client to use the change_info4 information
   appropriately and correctly, the server must report the pre and post
   operation change attribute values atomically.  When the server is
   unable to report the before and after values atomically with respect
   to the directory operation, the server must indicate that fact in the
   change_info4 return value.  When the information is not atomically
   reported, the client should not assume that other clients have not
   changed the directory.

15.

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.

15.1.

10.1.  Location attributes

   NFSv4 contains recommended attributes that allow file systems on one
   server to be associated with one or more instances of that file
   system on other servers.  These attributes specify such file systems
   by specifying a server name (either a DNS name or an IP address)
   together with the path of that file system within that server's
   single-server name space.

   The fs_locations_info recommended attribute allows specification of
   one more file systems locations where the data corresponding to a
   given file system may be found.  This attributes provides to the
   client, in addition to information about file system locations,
   extensive information about the various file system choices (e.g.
   priority for use, writability, currency, etc.) as well as information
   to help the client efficiently effect as seamless a transition as
   possible among multiple file system instances, when and if that
   should be necessary.

   The fs_locations recommended attribute is inherited from NFSv4.0 and
   only allows specification of the file system locations where the data
   corresponding to a given file system may be found.  Servers should
   make this attribute available whenever fs_locations_info is
   supported, but client use of fs_locations_info is to be preferred.

15.2.

10.2.  File System Presence or Absence

   A given location in an NFSv4 namespace (typically but not necessarily
   a multi-server namespace) can have a number of file system locations
   associated with it (via the fs_locations or fs_locations_info
   attribute).  There may also be an actual current file system at that
   location, accessible via normal namespace operations (e.g.  LOOKUP).
   In this case there, the file system is said to be "present" at that
   position in the namespace and clients will typically use it,
   reserving use of additional locations specified via the location-
   related attributes to situations in which the principal location is
   no longer available.

   When there is no actual file system at the namespace location in
   question, the file system is said to be "absent".  An absent file
   system contains no files or directories other than the root and any
   reference to it, except to access a small set of attributes useful in
   determining alternate locations, will result in an error,
   NFS4ERR_MOVED.  Note that if the server ever returns NFS4ERR_MOVED
   (i.e. file systems may be absent), it MUST support the fs_locations
   attribute and SHOULD support the fs_locations_info and fs_absent
   attributes.

   While the error name suggests that we have a case of a file system
   which once was present, and has only become absent later, this is
   only one possibility.  A position in the namespace may be permanently
   absent with the file system(s) designated by the location attributes
   the only realization.  The name NFS4ERR_MOVED reflects an earlier,
   more limited conception of its function, but this error will be
   returned whenever the referenced file system is absent, whether it
   has moved or not.

   Except in the case of GETATTR-type operations (to be discussed
   later), when the current filehandle at the start of an operation is
   within an absent file system, that operation is not performed and the
   error NFS4ERR_MOVED returned, to indicate that the file system is
   absent on the current server.

   Because a GETFH cannot succeed, if the current filehandle is within
   an absent file system, filehandles within an absent file system
   cannot be transferred to the client.  When a client does have
   filehandles within an absent file system, it is the result of
   obtaining them when the file system was present, and having the file
   system become absent subsequently.

   It should be noted that because the check for the current filehandle
   being within an absent file system happens at the start of every
   operation, operations which change the current filehandle so that it
   is within an absent file system will not result in an error.  This
   allows such combinations as PUTFH-GETATTR and LOOKUP-GETATTR to be
   used to get attribute information, particularly location attribute
   information, as discussed below.

   The recommended file system attribute fs_absent can used to
   interrogate the present/absent status of a given file system.

15.3.

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.

15.3.1.

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
   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.

15.3.2.

10.3.2.  READDIR and Absent File Systems

   A READDIR performed when the current filehandle is within an absent
   file system will result in an NFS4ERR_MOVED error, since, unlike the
   case of GETATTR, no such exception is made for READDIR.

   Attributes for an absent file system may be fetched via a READDIR for
   a directory in a present file system, when that directory contains
   the root directories of one or more absent file systems.  In this
   case, the handling is as follows:

   o  If the attribute set requested includes one of the attributes
      fs_locations, fs_locations_info, or absent, then fetching of
      attributes proceeds normally and no NFS4ERR_MOVED indication is
      returned, even when the rdattr_error attribute is requested.

   o  If the attribute set requested does not include one of the
      attributes fs_locations, fs_locations_info, or fs_absent, then if
      the rdattr_error attribute is requested, each directory entry for
      the root of an absent file system, will report NFS4ERR_MOVED as
      the value of the rdattr_error attribute.

   o  If the attribute set requested does not include any of the
      attributes fs_locations, fs_locations_info, fs_absent, or
      rdattr_error then the occurrence of the root of an absent file
      system within the directory will result in the READDIR failing
      with an NFSER_MOVED NFSERR_MOVED error.

   o  The unavailability of an attribute because of a file system's
      absence, even one that is ordinarily mandatory, does not result in
      any error indication.  The set of attributes returned for the root
      directory of the absent file system in that case is simply
      restricted to those actually available.

15.4.

10.4.  Uses of Location Information

   The location-bearing attributes (fs_locations and fs_locations_info),
   provide, together with the possibility of absent file systems, a
   number of important facilities in providing reliable, manageable, and
   scalable data access.

   When a file system is present, these attribute can provide
   alternative locations, to be used to access the same data, in the
   event that server failures, communications problems, or other
   difficulties, make continued access to the current file system
   impossible or otherwise impractical.  Provision of such alternate
   locations is referred to as "replication" although there are cases in
   which replicated sets of data are not in fact present, and the
   replicas are instead different paths to the same data.

   When a file system is present and becomes absent, clients can be
   given the opportunity to have continued access to their data, at an
   alternate location.  In this case, a continued attempt to use the
   data in the now-absent file system will result in an NFSERR_MOVED
   error and at that point the successor locations (typically only one
   but multiple choices are possible) can be fetched and used to
   continue access.  Transfer of the file system contents to the new
   location is referred to as "migration", but it should be kept in mind
   that there are cases in which this term can be used, like
   "replication" when there is no actual data migration per se.

   Where a file system was not previously present, specification of file
   system location provides a means by which file systems located on one
   server can be associated with a name space defined by another server,
   thus allowing a general multi-server namespace facility.  Designation
   of such a location, in place of an absent file system, is called
   "referral".

15.4.1.

10.4.1.  File System Replication

   The fs_locations and fs_locations_info attributes provide alternative
   locations, to be used to access data in place of the current file
   system.  On first access to a file system, the client should obtain
   the value of the set alternate locations by interrogating the
   fs_locations or fs_locations_info attribute, with the latter being
   preferred.

   In the event that server failures, communications problems, or other
   difficulties, make continued access to the current file system
   impossible or otherwise impractical, the client can use the alternate
   locations as a way to get continued access to his data.

   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.

15.4.2.

10.4.2.  File System Migration

   When a file system is present and becomes absent, clients can be
   given the opportunity to have continued access to their data, at an
   alternate location, as specified by the fs_locations or
   fs_locations_info attribute.  Typically, a client will be accessing
   the file system in question, get a an NFS4ERR_MOVED error, and then
   use the fs_locations or fs_locations_info attribute to determine the
   new location of the data.  When fs_locations_info is used, additional
   information will be available which will define the nature of the
   client's handling of the transition to a new server.

   Such migration can be helpful in providing load balancing or general
   resource reallocation.  The protocol does not specify how the file
   system will be moved between servers.  It is anticipated that a
   number of different server-to-server transfer mechanisms might be
   used with the choice left to the server implementor.  The NFSv4.1
   protocol specifies the method used to communicate the migration event
   between client and server.

   The new location may be an alternate communication path to the same
   server, or, in the case of various forms of server clustering,
   another server providing access to the same physical file system.
   The client's responsibilities in dealing with this transition depend
   on the specific nature of the new access path and how and whether
   data was in fact migrated.  These issues will be discussed in detail
   below.

   Although a single successor location is typical, multiple locations
   may be provided, together with information that allows priority among
   the choices to be indicated, via information in the fs_locations_info
   attribute.  Where suitable clustering mechanisms make it possible to
   provide multiple identical file systems or paths to them, this allows
   the client the opportunity to deal with any resource or
   communications issues that might limit data availability.

15.4.3.

10.4.3.  Referrals

   Referrals provide a way of placing a file system in a location
   essentially without respect to its physical location on a given
   server.  This allows a single server of a set of servers to present a
   multi-server namespace that encompasses file systems located on
   multiple servers.  Some likely uses of this include establishment of
   site-wide or organization-wide namespaces, or even knitting such
   together into a truly global namespace.

   Referrals occur when a client determines, upon first referencing a
   position in the current namespace, that it is part of a new file
   system and that that file system is absent.  When this occurs,
   typically by receiving the error NFS4ERR_MOVED, the actual location
   or locations of the file system can be determined by fetching the
   fs_locations or fs_locations_info attribute.

   Use of multi-server namespaces is enabled by NFSv4 but is not
   required.  The use of multi-server namespaces and their scope will
   depend on the application used, and system administration
   preferences.

   Multi-server namespaces can be established by a single server
   providing a large set of referrals to all of the included file
   systems.  Alternatively, a single multi-server namespace may be
   administratively segmented with separate referral file systems (on
   separate servers) for each separately-administered section of the
   name space.  Any segment or the top-level referral file system may
   use replicated referral file systems for higher availability.

15.5.

10.5.  Additional Client-side Considerations

   When clients make use of servers that implement referrals and
   migration, care should be taken so that a user who mounts a given
   file system that includes a referral or a relocated file system
   continue to see a coherent picture of that user-side file system
   despite the fact that it contains a number of server-side file
   systems which may be on different servers.

   One important issue is upward navigation from the root of a server-
   side file system to its parent (specified as ".." in UNIX).  The
   client needs to determine when it hits an fsid root going up the
   filetree.  When at such a point, and needs to ascend to the parent,
   it must do so locally instead of sending a LOOKUPP call to the
   server.  The LOOKUPP would normally return the ancestor of the target
   file system on the target server, which may not be part of the space
   that the client mounted.

   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.

15.6.

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
   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 15.10 10.10 for details.  When only fs_locations is available,
   default assumptions with regard to such classifications have to be
   inferred.  See Section 15.9 10.9 for details.

   In cases in which one server is expected to accept opaque values from
   the client that originated from another server, it is a wise
   implementation practice for the servers to encode the "opaque" values
   in network byte order.  If this is done, servers acting as replicas
   or immigrating file systems will be able to parse values like
   stateids, directory cookies, filehandles, etc. even if their native
   byte order is different from that of other servers cooperating in the
   replication and migration of the file system.

15.6.1.

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).

   o  Where the old and new file systems belong to the same _endpoint_
      class, the transition consists of creating a new connection which
      is associated with the existing session to the old server
      endpoint.  Where a connection cannot be associated with the
      existing session, the target server must be able to recognize the
      sessionid as invalid and force creation on a new session or a new
      client id.

   o  Where the old and new file systems do not belong to the same
      _endpoint_ classes, but to the same _server_ class, the transition
      consists of creating a new session, associated with the existing
      clientid.  Where the clientid is stale, the target server must be
      able to recognize the clientid as no longer valid and force
      creation of a new clientid.

   In either of the above cases, the file system may be shown as
   belonging to the same _sharing_ class, class allowing the alternate
   session or connection to be established in advance and used either to
   accelerate the file system transition when necessary (avoiding
   connection latency), or to provide higher performance by actively
   using multiple paths simultaneously.

   When two file systems belong to the same _endpoint_ class, or
   _sharing_ class, many transition issues are eliminated, and any
   information indicating otherwise is ignored as erroneous.

   In all such transparent transition cases, the following apply:

   o  File handles stay the same if persistent and if volatile are only
      subject to expiration, if they would be in the absence of file
      system transition.

   o  Fileid values do not change across the transition.

   o  The file system will have the same fsid in both the old and new
      the old and new locations.

   o  Change attribute values are consistent across the transition and
      do not have to be refetched.  When change attributes indicate that
      a cached object is still valid, it can remain cached.

   o  Session, client, and state identifier retain their validity across
      the transition, except where their staleness is recognized and
      reported by the new server.  Except where such staleness requires
      it, no lock reclamation is needed.

   o  Write verifiers are presumed to retain their validity and can be
      presented to COMMIT, with the expectation that if COMMIT on the
      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.

15.6.2.

10.6.2.  Filehandles and File System Transitions

   There are a number of ways in which filehandles can be handled across
   a file system transition.  These can be divided into two broad
   classes depending upon whether the two file systems across which the
   transition happens share sufficient state to effect some sort of
   continuity of file system handling.

   When there is no such co-operation in filehandle assignment, the two
   file systems are reported as being in different _handle_ classes.  In
   this case, all filehandles are assumed to expire as part of the file
   system transition.  Note that this behavior does not depend on
   fh_expire_type attribute and supersedes the specification of
   FH4_VOL_MIGRATION bit, which only affects behavior when
   fs_locations_info is not available.

   When there is co-operation in filehandle assignment, the two file
   systems are reported as being in the same _handle_ classes.  In this
   case, persistent filehandle remain valid after the file system
   transition, while volatile filehandles (excluding those while are
   only volatile due to the FH4_VOL_MIGRATION bit) are subject to
   expiration on the target server.

15.6.3.

10.6.3.  Fileid's and File System Transitions

   In NFSv4.0, the issue of continuity of fileid's in the event of a
   file system transition was not addressed.  The general expectation
   had been that in situations in which the two file system instances
   are created by a single vendor using some sort of file system image
   copy, fileid's will be consistent across the transition while in the
   analogous multi-vendor transitions they will not.  This poses
   difficulties, especially for the client without special knowledge of
   the of the transition mechanisms adopted by the server.

   It is important to note that while clients themselves may have no
   trouble with a fileid changing as a result of a file system
   transition event, applications do typically have access to the fileid
   (e.g. via stat), and the result of this is that an application may
   work perfectly well if there is no file system instance transition or
   if any such transition is among instances created by a single vendor,
   yet be unable to deal with the situation in which a multi-vendor
   transition occurs, at the wrong time.

   Providing the same fileid's in a multi-vendor (multiple server
   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.

15.6.4.

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.

15.6.5.

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
   attribute construction and handle this situation just as it would be
   handled without any file system transition.

15.6.6.

10.6.6.  Lock State and File System Transitions

   In a file system transition, the two file systems may have co-
   operated in state management.  When this is the case, and the two
   file systems belong to the same _state_ class, the two file systems
   will have compatible state environments.  In the case of migration,
   the servers involved in the migration of a file system SHOULD
   transfer all server state from the original to the new server.  When
   this done, it must be done in a way that is transparent to the
   client.  With replication, such a degree of common state is typically
   not the case.  Clients, however should use the information provided
   by the fs_locations_info attribute to determine whether such sharing
   is in effect when this is available, and only if that attribute is
   not available depend on these defaults.

   This state transfer will reduce disruption to the client when a file
   system transition If the servers are successful in transferring all
   state, the client will continue to use stateids assigned by the
   original server.  Therefore the new server must recognize these
   stateids as valid.  This holds true for the clientid as well.  Since
   responsibility for an entire file system is transferred is with such
   an event, there is no possibility that conflicts will arise on the
   new server as a result of the transfer of locks.

   As part of the transfer of information between servers, leases would
   be transferred as well.  The leases being transferred to the new
   server will typically have a different expiration time from those for
   the same client, previously on the old server.  To maintain the
   property that all leases on a given server for a given client expire
   at the same time, the server should advance the expiration time to
   the later of the leases being transferred or the leases already
   present.  This allows the client to maintain lease renewal of both
   classes without special effort.

   When the two servers belong to the same _state_ class, it does not
   necessarily mean that when dealing with the transition, the client
   will not have to reclaim state.  However it does mean that the client
   may proceed using his current clientid and stateid's just as if there
   had been no file system transition event and only reclaim state when
   an NFS4ERR_STALE_CLIENTID or NFS4ERR_STALE_STATEID error is received.

   File systems co-operating in state management may actually share
   state or simply divide the id space so as to recognize (and reject as
   stale) each others state and clients id's.  Servers which do share
   state may not do under all conditions or all times.  The requirement
   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
   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.

15.6.6.1.

10.6.6.1.  Leases and File System Transitions

   In the case of lease renewal, the client may not be submitting
   requests for a file system that has been transferred to another
   server.  This can occur because of the lease renewal mechanism.  The
   client renews leases for all file systems when submitting a request
   to any one file system at the server.

   In order for the client to schedule renewal of leases that may have
   been relocated to the new server, the client must find out about
   lease relocation before those leases expire.  To accomplish this, all
   operations which renew leases for a client (i.e.  OPEN, CLOSE, READ,
   WRITE, RENEW, LOCK, LOCKT, LOCKU), will return the error
   NFS4ERR_LEASE_MOVED if responsibility for any of the leases to be
   renewed has been transferred to a new server.  This condition will
   continue until the client receives an NFS4ERR_MOVED error and the
   server receives the subsequent GETATTR for the fs_locations or
   fs_locations_info attribute for an access to each file system for
   which a lease has been moved to a new server.

   [ISSUE: There is a conflict between this and the idea in the sessions
   text that we can have every op in the session implicitly renew the
   lease.  This needs to be dealt with.  D. Noveck will create an issue
   in the issue tracker.]

   When a client receives an NFS4ERR_LEASE_MOVED error, it should
   perform an operation on each file system associated with the server
   in question.  When the client receives an NFS4ERR_MOVED error, the
   client can follow the normal process to obtain the new server
   information (through the fs_locations and fs_locations_info
   attributes) and perform renewal of those leases on the new server,
   unless information in fs_locations_info attribute shows that no state
   could have been transferred.  If the server has not had state
   transferred to it transparently, the client will receive either
   NFS4ERR_STALE_CLIENTID or NFS4ERR_STALE_STATEID from the new server,
   as described above, and the client can then recover state information
   as it does in the event of server failure.

15.6.6.2.

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.

15.6.7.

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.

15.7.

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
   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.

15.7.1.

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 /this/is/the/path is absent from the target
   server.  This may be for a number of reasons.  It may be the case
   that the file system has moved, or, it may be the case that the
   target server is functioning mainly, or solely, to refer clients to
   the servers on which various file systems are located.

   o  PUTROOTFH

   o  LOOKUP "src" "this"

   o  LOOKUP "linux" "is"

   o  LOOKUP "2.7" "the"

   o  LOOKUP "latest" "path"

   o  GETFH

   o  GETATTR fsid,fileid,size,ctime

   Under the given circumstances, the following will be the result.

   o  PUTROOTFH --> NFS_OK.  The current fh is now the root of the
      pseudo-fs.

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

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

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

   o  LOOKUP "latest" "path" --> NFS_OK.  The current fh is for /src/linux/2.7/
      latest /this/is/the/path
      and is within a new, absent fs, but ... the client will never see
      the value of that fh.

   o  GETFH --> NFS4ERR_MOVED.  Fails because current fh is in an absent
      fs at the start of the operation and the spec makes no exception
      for GETFH.

   o  GETATTR fsid,fileid,size,ctime.  Not executed because the failure
      of the GETFH stops processing of the COMPOUND.

   Given the failure of the GETFH, the client has the job of determining
   the root of the absent file system and where to find that file
   system, i.e. the server and path relative to that server's root fh.
   Note here that in this example, the client did not obtain filehandles
   and attribute information (e.g. fsid) for the intermediate
   directories, so that he would not be sure where the absent file
   system starts.  It could be the case, for example, that
   /src/linux/2.7 /this/is/the
   is the root of the moved file system and that the reason that the
   lookup of "latest" "path" succeeded is that the file system was not absent on
   that op but was moved between the last LOOKUP and the GETFH (since
   COMPOUND is not atomic).  Even if we had the fsid's for all of the
   intermediate directories, we could have no way of knowing that /src/linux/2.7/latest /this/
   is/the/path was the root of a new fs, since we don't yet have its
   fsid.

   In order to get the necessary information, let us re-issue the chain
   of lookup's with GETFH's and GETATTR's to at least get the fsid's so
   we can be sure where the appropriate fs boundaries are.  The client
   could choose to get fs_locations_info at the same time but in most
   cases the client will have a good guess as to where fs boundaries are
   (because of where NFS4ERR_MOVED was gotten and where not) making
   fetching of fs_locations_info unnecessary.

   OP01:  PUTROOTFH --> NFS_OK

   -  Current fh is root of pseudo-fs.

   OP02:  GETATTR(fsid) --> NFS_OK

   -  Just for completeness.  Normally, clients will know the fsid of
      the pseudo-fs as soon as they establish communication with a
      server.

   OP03:  LOOKUP "src" "this" --> NFS_OK
   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 /this and is within pseudo-fs.

   OP06:  LOOKUP "linux" "is" --> NFS_OK

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

   OP07:  GETATTR(fsid) --> NFS_OK

   -  Get current fsid to see where fs boundaries are.  The fsid will be
      that for the pseudo-fs in this example, so no boundary.

   OP08:  GETFH --> NFS_OK

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

   OP09:  LOOKUP "2.7" "the" --> NFS_OK

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

   OP10:  GETATTR(fsid) --> NFS_OK

   -  Get current fsid to see where fs boundaries are.  The fsid will be
      that for the pseudo-fs in this example, so no boundary.

   OP11:  GETFH --> NFS_OK

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

   OP12:  LOOKUP "latest" "path" --> NFS_OK

   -  Current fh is for /src/linux/2.7/latest /this/is/the/path and is within a new, absent
      fs, but ...

   -  The client will never see the value of that fh

   OP13:  GETATTR(fsid, fs_locations_info) --> NFS_OK

   -  We are getting the fsid to know where the fs boundaries are.  Note
      that the fsid we are given will not necessarily be preserved at
      the new location.  That fsid might be different and in fact the
      fsid we have for this fs might a valid fsid of a different fs on
      that new server.

   -  In this particular case, we are pretty sure anyway that what has
      moved is /src/linux/2.7/latest /this/is/the/path rather than /src/linux/2.7 /this/is/the since we have
      the fsid of the latter and it is that of the pseudo-fs, which
      presumably cannot move.  However, in other examples, we might not
      have this kind of information to rely on (e.g. /src/linux/2.7 /this/is/the might
      be a non-pseudo file system separate from /src/linux/2.7/
      latest), /this/is/the/path), so
      we need to have another reliable source information on the
      boundary of the fs which is moved.  If, for example, the file
      system "/src/linux" "/this/is" had moved we would have a case of migration
      rather than referral and once the boundaries of the migrated file
      system was clear we could fetch fs_locations_info.

   -  We are fetching fs_locations_info because the fact that we got an
      NFS4ERR_MOVED at this point means that it most likely that this is
      a referral and we need the destination.  Even if it is the case
      that "/src/linux/2.7" "/this/is/the" is a file system which has migrated, we will
      still need the location information for that file system.

   OP14:  GETFH --> NFS4ERR_MOVED

   -  Fails because current fh is in an absent fs at the start of the
      operation and the spec makes no exception for GETFH.  Note that
      this has the happy consequence that we don't have to worry about
      the volatility or lack thereof of the fh.  If the root of the fs
      on the new location is a persistent fh, then we can assume that
      this fh, which we never saw is a persistent fh, which, if we could
      see it, would exactly match the new fh.  At least, there is no
      evidence to disprove that.  On the other hand, if we find a
      volatile root at the new location, then the filehandle which we
      never saw must have been volatile or at least nobody can prove
      otherwise.

   Given the above, the client knows where the root of the absent file
   system is, by noting where the change of fsid occurred.  The
   fs_locations_info attribute also gives the client the actual location
   of the absent file system, so that the referral can proceed.  The
   server gives the client the bare minimum of information about the
   absent file system so that there will be very little scope for
   problems of conflict between information sent by the referring server
   and information of the file system's home.  No filehandles and very
   few attributes are present on the referring server and the client can
   treat those it receives as basically transient information with the
   function of enabling the referral.

15.7.2.

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" "this"

   o  LOOKUP "linux" "is"

   o  LOOKUP "2.7" "the"

   o  READDIR (fsid, size, ctime, mounted_on_fileid)

   In this case, because rdattr_error is not requested,
   fs_locations_info is not requested, and some of attributes cannot be
   provided the result will be an NFS4ERR_MOVED error on the READDIR,
   with the detailed results as follows:

   o  PUTROOTFH --> NFS_OK.  The current fh is at the root of the
      pseudo-fs.

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

   o  LOOKUP