NFSv4                                                          T. Haynes
Internet-Draft                                                    Editor                                                 D. Noveck
Intended status: Standards Track                          March 05, 2010                                 Editors
Expires: September 6, January 8, 2011                                   July 07, 2010

                         NFS Version 4 Protocol
                   draft-ietf-nfsv4-rfc3530bis-03.txt
                   draft-ietf-nfsv4-rfc3530bis-04.txt

Abstract

   The Network File System (NFS) version 4 is a distributed filesystem
   protocol which owes heritage to NFS protocol version 2, RFC 1094, and
   version 3, RFC 1813.  Unlike earlier versions, the NFS version 4
   protocol supports traditional file access while integrating support
   for file locking and the mount protocol.  In addition, support for
   strong security (and its negotiation), compound operations, client
   caching, and internationalization have been added.  Of course,
   attention has been applied to making NFS version 4 operate well in an
   Internet environment.

   This document document, together with the companion XDR description document,
   replaces RFC 3530 as the definition of the NFS version 4 protocol.

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].

Status of this Memo

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   7   8
     1.1.   Changes since RFC 3530 . . . . . . . . . . . . . . . . .   7   8
     1.2.   Changes since RFC 3010 . . . . . . . . . . . . . . . . .   7   8
     1.3.   NFS Version 4 Goals  . . . . . . . . . . . . . . . . . .   8  10
     1.4.   Inconsistencies of this Document with Section 18 the companion
            document NFS Version 4 Protocol  . . . .   9 . . . . . . . .  10
     1.5.   Overview of NFS version 4 Features . . . . . . . . . . .   9  11
       1.5.1.   RPC and Security . . . . . . . . . . . . . . . . . .   9  11
       1.5.2.   Procedure and Operation Structure  . . . . . . . . . .  10  11
       1.5.3.   Filesystem Model . . . . . . . . . . . . . . . . . .  10  12
       1.5.4.   OPEN and CLOSE . . . . . . . . . . . . . . . . . . .  12  14
       1.5.5.   File locking Locking . . . . . . . . . . . . . . . . . . . .  12  14
       1.5.6.   Client Caching and Delegation  . . . . . . . . . . . .  13  14
     1.6.   General Definitions  . . . . . . . . . . . . . . . . . .  13  15
   2.  Protocol Data Types . . . . . . . . . . . . . . . . . . . . .  15  17
     2.1.   Basic Data Types . . . . . . . . . . . . . . . . . . . .  15  17
     2.2.   Structured Data Types  . . . . . . . . . . . . . . . . .  17  18
   3.  RPC and Security Flavor . . . . . . . . . . . . . . . . . . .  22  24
     3.1.   Ports and Transports . . . . . . . . . . . . . . . . . .  22  24
       3.1.1.   Client Retransmission Behavior . . . . . . . . . . .  23  25
     3.2.   Security Flavors . . . . . . . . . . . . . . . . . . . .  23  25
       3.2.1.   Security mechanisms for NFS version 4  . . . . . . . .  24  26
     3.3.   Security Negotiation . . . . . . . . . . . . . . . . . .  26  28
       3.3.1.   SECINFO  . . . . . . . . . . . . . . . . . . . . . . .  26  28
       3.3.2.   Security Error . . . . . . . . . . . . . . . . . . .  27  28
       3.3.3.   Callback RPC Authentication  . . . . . . . . . . . . .  27  29
   4.  Filehandles . . . . . . . . . . . . . . . . . . . . . . . . .  29  31
     4.1.   Obtaining the First Filehandle . . . . . . . . . . . . .  29  31
       4.1.1.   Root Filehandle  . . . . . . . . . . . . . . . . . . .  29  31
       4.1.2.   Public Filehandle  . . . . . . . . . . . . . . . . . .  30  31
     4.2.   Filehandle Types . . . . . . . . . . . . . . . . . . . .  30  32
       4.2.1.   General Properties of a Filehandle . . . . . . . . .  30  32
       4.2.2.   Persistent Filehandle  . . . . . . . . . . . . . . . .  31  33
       4.2.3.   Volatile Filehandle  . . . . . . . . . . . . . . . . .  31  33
       4.2.4.   One Method of Constructing a Volatile Filehandle . .  33  35
     4.3.   Client Recovery from Filehandle Expiration . . . . . . .  33  35
   5.  File Attributes . . . . . . . . . . . . . . . . . . . . . . .  34  36
     5.1.   Mandatory   REQUIRED Attributes  . . . . . . . . . . . . . . . . . .  35  37
     5.2.   Recommended   RECOMMENDED Attributes . . . . . . . . . . . . . . . . .  35  37
     5.3.   Named Attributes . . . . . . . . . . . . . . . . . . . .  36  38
     5.4.   Classification of Attributes . . . . . . . . . . . . . .  36  39
     5.5.   Mandatory   Set-Only and Get-Only Attributes - Definitions . . . . . . . . . . .  37 .  40
     5.6.   Recommended   REQUIRED Attributes - Definitions . List and Definition References . .  40
     5.7.   RECOMMENDED Attributes - List and Definition
            References . . . . . . .  39
     5.7.   Time Access . . . . . . . . . . . . . . . .  41
     5.8.   Attribute Definitions  . . . . . .  45
     5.8.   Interpreting owner and owner_group . . . . . . . . . . .  46
     5.9.   Character Case  42
       5.8.1.   Definitions of REQUIRED Attributes . . . . . . . . .  42
       5.8.2.   Definitions of Uncategorized RECOMMENDED
                Attributes . . . . . .  48
     5.10.  Quota Attributes . . . . . . . . . . . . . . . .  44
     5.9.   Interpreting owner and owner_group . . . .  48
     5.11.  Access Control Lists . . . . . . .  50
     5.10.  Character Case Attributes  . . . . . . . . . . .  49
       5.11.1. ACE type . . . .  52
   6.  Access Control Attributes . . . . . . . . . . . . . . . . . .  50
       5.11.2. ACE Access Mask  53
     6.1.   Goals  . . . . . . . . . . . . . . . . . . .  51
       5.11.3. ACE flag . . . . . .  53
     6.2.   File Attributes Discussion . . . . . . . . . . . . . . .  54
       6.2.1.   Attribute 12: acl  .  53
       5.11.4. ACE who . . . . . . . . . . . . . . . .  54
       6.2.2.   Attribute 33: mode . . . . . . .  55
       5.11.5. Mode Attribute . . . . . . . . . .  68
     6.3.   Common Methods . . . . . . . . .  56
       5.11.6. Mode and ACL Attribute . . . . . . . . . . . .  68
       6.3.1.   Interpreting an ACL  . . .  57
       5.11.7. mounted_on_fileid . . . . . . . . . . . . .  68
       6.3.2.   Computing a Mode Attribute from an ACL . . . . .  57
   6.  Filesystem Migration and Replication . .  69
     6.4.   Requirements . . . . . . . . . .  58
     6.1.   Replication . . . . . . . . . . . .  70
       6.4.1.   Setting the mode and/or ACL Attributes . . . . . . .  71
       6.4.2.   Retrieving the mode and/or ACL Attributes  . . .  59
     6.2.   Migration . .  72
       6.4.3.   Creating New Objects . . . . . . . . . . . . . . . .  72
   7.  Multi-Server Namespace  . . . . .  59
     6.3.   Interpretation of the fs_locations Attribute . . . . . .  60
     6.4.   Filehandle Recovery for Migration or Replication . . . .  61
   7.  NFS Server Name Space . . . .  74
     7.1.   Location Attributes  . . . . . . . . . . . . . . . .  61
     7.1.   Server Exports . .  74
     7.2.   File System Presence or Absence  . . . . . . . . . . . .  75
     7.3.   Getting Attributes for an Absent File System . . . . . .  76
       7.3.1.   GETATTR Within an Absent File System .  61
     7.2.   Browsing Exports . . . . . . .  76
       7.3.2.   READDIR and Absent File Systems  . . . . . . . . . .  77
     7.4.   Uses of Location Information . . .  62
     7.3.   Server Pseudo Filesystem . . . . . . . . . . .  78
       7.4.1.   File System Replication  . . . . .  62
     7.4.   Multiple Roots . . . . . . . . .  78
       7.4.2.   File System Migration  . . . . . . . . . . . .  63
     7.5.   Filehandle Volatility . . .  79
       7.4.3.   Referrals  . . . . . . . . . . . . . .  63
     7.6.   Exported Root . . . . . . .  80
     7.5.   Location Entries and Server Identity . . . . . . . . . .  80
     7.6.   Additional Client-side Considerations  . . . .  63
     7.7.   Mount Point Crossing . . . . .  81
     7.7.   Effecting File System Transitions  . . . . . . . . . . .  82
       7.7.1.   File System Transitions and Simultaneous Access  . .  63
     7.8.   Security Policy  83
       7.7.2.   Filehandles and Name Space Presentation File System Transitions  . . . . . .  64
   8.  File Locking  83
       7.7.3.   Fileids and Share Reservations File System Transitions  . . . . . . . .  84
       7.7.4.   Fsids and File System Transitions  . . . . .  65
     8.1.   Locking . . . .  85
       7.7.5.   The Change Attribute and File System Transitions . .  85
       7.7.6.   Lock State and File System Transitions . . . . . . .  86
       7.7.7.   Write Verifiers and File System Transitions  . . . .  88
       7.7.8.   Readdir Cookies and Verifiers and File System
                Transitions  . . . . . . .  65
       8.1.1.  Client ID . . . . . . . . . . . . .  88
       7.7.9.   File System Data and File System Transitions . . . .  88
     7.8.   Effecting File System Referrals  . . . . .  66
       8.1.2.  Server Release of Clientid . . . . . . .  90
       7.8.1.   Referral Example (LOOKUP)  . . . . . .  69
       8.1.3.  lock_owner and stateid Definition . . . . . . .  90
       7.8.2.   Referral Example (READDIR) . . .  69
       8.1.4.  Use of the stateid and Locking . . . . . . . . . .  94
     7.9.   The Attribute fs_locations .  71
       8.1.5.  Sequencing of Lock Requests . . . . . . . . . . . . .  73
       8.1.6.  Recovery from Replayed Requests .  97
       7.9.1.   Inferring Transition Modes . . . . . . . . . .  74
       8.1.7.  Releasing lock_owner State . . .  98
   8.  NFS Server Name Space . . . . . . . . . .  74
       8.1.8.  Use of Open Confirmation . . . . . . . . . .  99
     8.1.   Server Exports . . . .  75
     8.2.   Lock Ranges . . . . . . . . . . . . . . . . . 100
     8.2.   Browsing Exports . . . . .  76
     8.3.   Upgrading and Downgrading Locks . . . . . . . . . . . .  76
     8.4.   Blocking Locks . . . 100
     8.3.   Server Pseudo Filesystem . . . . . . . . . . . . . . . . 100
     8.4.   Multiple Roots . .  77
     8.5. . . . . . . . . . . . . . . . . . . . 101
     8.5.   Filehandle Volatility  . . . . . . . . . . . . . . . . . 101
     8.6.   Exported Root  . . . . . . . . . . . . . . . . . . . . . 101
     8.7.   Mount Point Crossing . . . . . . . . . . . . . . . . . . 102
     8.8.   Security Policy and Name Space Presentation  . . . . . . 102
   9.  File Locking and Share Reservations . . . . . . . . . . . . . 103
     9.1.   Locking  . . . . . . . . . . . . . . . . . . . . . . . . 104
       9.1.1.   Client ID  . . . . . . . . . . . . . . . . . . . . . 104
       9.1.2.   Server Release of Clientid . . . . . . . . . . . . . 107
       9.1.3.   lock_owner and stateid Definition  . . . . . . . . . 107
       9.1.4.   Use of the stateid and Locking . . . . . . . . . . . 109
       9.1.5.   Sequencing of Lock Requests  . . . . . . . . . . . . 111
       9.1.6.   Recovery from Replayed Requests  . . . . . . . . . . 112
       9.1.7.   Releasing lock_owner State . . . . . . . . . . . . . 112
       9.1.8.   Use of Open Confirmation . . . . . . . . . . . . . . 113
     9.2.   Lock Ranges  . . . . . . . . . . . . . . . . . . . . . . 114
     9.3.   Upgrading and Downgrading Locks  . . . . . . . . . . . . 114
     9.4.   Blocking Locks . . . . . . . . . . . . . . . . . . . . . 115
     9.5.   Lease Renewal  . . . . . . . . . . . . . . . . . . . . .  77
     8.6. 115
     9.6.   Crash Recovery . . . . . . . . . . . . . . . . . . . . .  78
       8.6.1. 116
       9.6.1.   Client Failure and Recovery  . . . . . . . . . . . . .  78
       8.6.2. 117
       9.6.2.   Server Failure and Recovery  . . . . . . . . . . . . .  79
       8.6.3. 117
       9.6.3.   Network Partitions and Recovery  . . . . . . . . . . .  81
     8.7. 119
     9.7.   Recovery from a Lock Request Timeout or Abort  . . . . .  84
     8.8. 122
     9.8.   Server Revocation of Locks . . . . . . . . . . . . . . .  85
     8.9. 123
     9.9.   Share Reservations . . . . . . . . . . . . . . . . . . .  86
     8.10. 124
     9.10.  OPEN/CLOSE Operations  . . . . . . . . . . . . . . . . .  87
       8.10.1. 125
       9.10.1.  Close and Retention of State Information . . . . . .  87
     8.11. 125
     9.11.  Open Upgrade and Downgrade . . . . . . . . . . . . . . .  88
     8.12. 126
     9.12.  Short and Long Leases  . . . . . . . . . . . . . . . . .  89
     8.13. 127
     9.13.  Clocks, Propagation Delay, and Calculating Lease
            Expiration . . . . . . . . . . . . . . . . . . . . . . .  89
     8.14. 127
     9.14.  Migration, Replication and State . . . . . . . . . . . .  90
       8.14.1. 128
       9.14.1.  Migration and State  . . . . . . . . . . . . . . . . .  90
       8.14.2. 128
       9.14.2.  Replication and State  . . . . . . . . . . . . . . . .  91
       8.14.3. 129
       9.14.3.  Notification of Migrated Lease . . . . . . . . . . .  91
       8.14.4. 129
       9.14.4.  Migration and the Lease_time Attribute . . . . . . .  92
   9. 130
   10. Client-Side Caching . . . . . . . . . . . . . . . . . . . . .  93
     9.1. 131
     10.1.  Performance Challenges for Client-Side Caching . . . . .  93
     9.2. 131
     10.2.  Delegation and Callbacks . . . . . . . . . . . . . . . .  94
       9.2.1. 132
       10.2.1.  Delegation Recovery  . . . . . . . . . . . . . . . . .  95
     9.3. 133
     10.3.  Data Caching . . . . . . . . . . . . . . . . . . . . . .  97
       9.3.1. 135
       10.3.1.  Data Caching and OPENs . . . . . . . . . . . . . . .  98
       9.3.2. 136
       10.3.2.  Data Caching and File Locking  . . . . . . . . . . . .  99
       9.3.3. 137
       10.3.3.  Data Caching and Mandatory File Locking  . . . . . . . 100
       9.3.4. 138
       10.3.4.  Data Caching and File Identity . . . . . . . . . . . 101
     9.4. 139
     10.4.  Open Delegation  . . . . . . . . . . . . . . . . . . . . 102
       9.4.1. 140
       10.4.1.  Open Delegation and Data Caching . . . . . . . . . . 104
       9.4.2. 142
       10.4.2.  Open Delegation and File Locks . . . . . . . . . . . 105
       9.4.3. 143
       10.4.3.  Handling of CB_GETATTR . . . . . . . . . . . . . . . 106
       9.4.4. 144
       10.4.4.  Recall of Open Delegation  . . . . . . . . . . . . . . 109
       9.4.5. 147
       10.4.5.  Clients that Fail to Honor Delegation Recalls  . . . . 111
       9.4.6. 149
       10.4.6.  Delegation Revocation  . . . . . . . . . . . . . . . . 111
     9.5. 149
     10.5.  Data Caching and Revocation  . . . . . . . . . . . . . . 112
       9.5.1. 150
       10.5.1.  Revocation Recovery for Write Open Delegation  . . . . 112
     9.6. 150
     10.6.  Attribute Caching  . . . . . . . . . . . . . . . . . . . 113
     9.7. 151
     10.7.  Data and Metadata Caching and Memory Mapped Files  . . . 115
     9.8. 153
     10.8.  Name Caching . . . . . . . . . . . . . . . . . . . . . . 117
     9.9. 155
     10.9.  Directory Caching  . . . . . . . . . . . . . . . . . . . 118
   10. 156
   11. Minor Versioning  . . . . . . . . . . . . . . . . . . . . . . 119
   11. 157
   12. Internationalization  . . . . . . . . . . . . . . . . . . . . 122
     11.1.  Stringprep profile for the utf8str_cs type 160
     12.1.  Use of UTF-8 . . . . . . . 123
       11.1.1. Intended applicability of the nfs4_cs_prep profile . 123
       11.1.2. Character repertoire of nfs4_cs_prep . . . . . . . . 123
       11.1.3. Mapping used by nfs4_cs_prep . . . . . . 161
       12.1.1.  Relation to Stringprep . . . . . . 123
       11.1.4. Normalization used by nfs4_cs_prep . . . . . . . . . 124
       11.1.5. Prohibited output for nfs4_cs_prep 161
       12.1.2.  Normalization, Equivalence, and Confusability  . . . 162
     12.2.  String Type Overview . . . . . . 124
       11.1.6. Bidirectional output for nfs4_cs_prep . . . . . . . . 124
     11.2.  Stringprep profile for the utf8str_cis type . . . . 164
       12.2.1.  Overall String Class Divisions . . 124
       11.2.1. Intended applicability of the nfs4_cis_prep profile . 125
       11.2.2. Character repertoire of nfs4_cis_prep . . . . . . . . 125
       11.2.3. Mapping used 164
       12.2.2.  Divisions by nfs4_cis_prep . . . Typedef Parent types  . . . . . . . . . 125
       11.2.4. Normalization used by nfs4_cis_prep 165
       12.2.3.  Individual Types and Their Handling  . . . . . . . . 166
     12.3.  Errors Related to Strings  . 125
       11.2.5. Prohibited output for nfs4_cis_prep . . . . . . . . . 125
       11.2.6. Bidirectional output for nfs4_cis_prep . . . . . 167
     12.4.  Types with Pre-processing to Resolve Mixture Issues  . . 126
     11.3.  Stringprep profile for the utf8str_mixed type 168
       12.4.1.  Processing of Principal Strings  . . . . . 126
       11.3.1. Intended applicability . . . . . 168
       12.4.2.  Processing of the nfs4_mixed_prep
               profile Server Id Strings  . . . . . . . . . . 168
     12.5.  String Types without Internationalization Processing . . 169
     12.6.  Types with Processing Defined by Other Internet Areas  . 169
     12.7.  String Types with NFS-specific Processing  . . . . . . . 170
       12.7.1.  Handling of File Came Components . . . 126
       11.3.2. Character repertoire . . . . . . . 171
       12.7.2.  Processing of nfs4_mixed_prep Link Text  . . . . . . . 126
       11.3.3. Mapping used by nfs4_cis_prep . . . . . . . 178
       12.7.3.  Processing of Principal Prefixes . . . . . 126
       11.3.4. Normalization used by nfs4_mixed_prep . . . . . 179
   13. Error Values  . . . 126
       11.3.5. Prohibited output for nfs4_mixed_prep . . . . . . . . 126
       11.3.6. Bidirectional output for nfs4_mixed_prep . . . . . . 127
     11.4.  UTF-8 Related . . . . . . . 179
     13.1.  Error Definitions  . . . . . . . . . . . . . . . . . . . 180
       13.1.1.  General Errors . . . . . . . . . . . . . . . . . . 127
   12. Error Definitions . 181
       13.1.2.  Filehandle Errors  . . . . . . . . . . . . . . . . . 183
       13.1.3.  Compound Structure Errors  . . . . 128
   13. . . . . . . . . . 184
       13.1.4.  File System Errors . . . . . . . . . . . . . . . . . 185
       13.1.5.  State Management Errors  . . . . . . . . . . . . . . 187
       13.1.6.  Security Errors  . . . . . . . . . . . . . . . . . . 188
       13.1.7.  Name Errors  . . . . . . . . . . . . . . . . . . . . 188
       13.1.8.  Locking Errors . . . . . . . . . . . . . . . . . . . 189
       13.1.9.  Reclaim Errors . . . . . . . . . . . . . . . . . . . 190
       13.1.10. Client Management Errors . . . . . . . . . . . . . . 191
       13.1.11. Attribute Handling Errors  . . . . . . . . . . . . . 191
     13.2.  Operations and their valid errors  . . . . . . . . . . . 192
     13.3.  Callback operations and their valid errors . . . . . . . 199
     13.4.  Errors and the operations that use them  . . . . . . . . 199
   14. NFS version 4 Requests  . . . . . . . . . . . . . . . . . . . 133
     13.1. 204
     14.1.  Compound Procedure . . . . . . . . . . . . . . . . . . . 133
     13.2. 204
     14.2.  Evaluation of a Compound Request . . . . . . . . . . . . 134
     13.3. 205
     14.3.  Synchronous Modifying Operations . . . . . . . . . . . . 135
     13.4. 206
     14.4.  Operation Values . . . . . . . . . . . . . . . . . . . . 135
   14. 206
   15. NFS version 4 Procedures  . . . . . . . . . . . . . . . . . . 135
     14.1. 206
     15.1.  Procedure 0: NULL - No Operation . . . . . . . . . . . . 135
     14.2. 206
     15.2.  Procedure 1: COMPOUND - Compound Operations  . . . . . . 136
     14.3. 207
     15.3.  Operation 3: ACCESS - Check Access Rights  . . . . . . . 139
     14.4. 209
     15.4.  Operation 4: CLOSE - Close File  . . . . . . . . . . . . 142
     14.5. 212
     15.5.  Operation 5: COMMIT - Commit Cached Data . . . . . . . . 143
     14.6. 213
     15.6.  Operation 6: CREATE - Create a Non-Regular File Object . 146
     14.7. 216
     15.7.  Operation 7: DELEGPURGE - Purge Delegations Awaiting
            Recovery . . . . . . . . . . . . . . . . . . . . . . . . 149
     14.8. 218
     15.8.  Operation 8: DELEGRETURN - Return Delegation . . . . . . 150
     14.9. 219
     15.9.  Operation 9: GETATTR - Get Attributes  . . . . . . . . . 151
     14.10. 220
     15.10. Operation 10: GETFH - Get Current Filehandle . . . . . . 153
     14.11. 221
     15.11. Operation 11: LINK - Create Link to a File . . . . . . . 154
     14.12. 222
     15.12. Operation 12: LOCK - Create Lock . . . . . . . . . . . . 156
     14.13. 224
     15.13. Operation 13: LOCKT - Test For Lock  . . . . . . . . . . 160
     14.14. 228
     15.14. Operation 14: LOCKU - Unlock File  . . . . . . . . . . . 162
     14.15. 229
     15.15. Operation 15: LOOKUP - Lookup Filename . . . . . . . . . 164
     14.16. 230
     15.16. Operation 16: LOOKUPP - Lookup Parent Directory  . . . . 166
     14.17. 232
     15.17. Operation 17: NVERIFY - Verify Difference in
            Attributes . . . . . . . . . . . . . . . . . . . . . . . 167
     14.18. 233
     15.18. Operation 18: OPEN - Open a Regular File . . . . . . . . 169
     14.19. 234
     15.19. Operation 19: OPENATTR - Open Named Attribute
            Directory  . . . . . . . . . . . . . . . . . . . . . . . 179
     14.20. 243
     15.20. Operation 20: OPEN_CONFIRM - Confirm Open  . . . . . . . 181
     14.21. 244
     15.21. Operation 21: OPEN_DOWNGRADE - Reduce Open File Access . 184
     14.22. 246
     15.22. Operation 22: PUTFH - Set Current Filehandle . . . . . . 185
     14.23. 248
     15.23. Operation 23: PUTPUBFH - Set Public Filehandle . . . . . 186
     14.24. 248
     15.24. Operation 24: PUTROOTFH - Set Root Filehandle  . . . . . 188
     14.25. 250
     15.25. Operation 25: READ - Read from File  . . . . . . . . . . 188
     14.26. 250
     15.26. Operation 26: READDIR - Read Directory . . . . . . . . . 191
     14.27. 252
     15.27. Operation 27: READLINK - Read Symbolic Link  . . . . . . 195
     14.28. 256
     15.28. Operation 28: REMOVE - Remove Filesystem Object  . . . . 196
     14.29. 257
     15.29. Operation 29: RENAME - Rename Directory Entry  . . . . . 199
     14.30. 259
     15.30. Operation 30: RENEW - Renew a Lease  . . . . . . . . . . 202
     14.31. 261
     15.31. Operation 31: RESTOREFH - Restore Saved Filehandle . . . 204
     14.32. 262
     15.32. Operation 32: SAVEFH - Save Current Filehandle . . . . . 205
     14.33. 263
     15.33. Operation 33: SECINFO - Obtain Available Security  . . . 206
     14.34. 263
     15.34. Operation 34: SETATTR - Set Attributes . . . . . . . . . 210
     14.35. 266
     15.35. Operation 35: SETCLIENTID - Negotiate Clientid . . . . . 213
     14.36. 269
     15.36. Operation 36: SETCLIENTID_CONFIRM - Confirm Clientid . . 216
     14.37. 272
     15.37. Operation 37: VERIFY - Verify Same Attributes  . . . . . 220
     14.38. 276
     15.38. Operation 38: WRITE - Write to File  . . . . . . . . . . 222
     14.39. 277
     15.39. Operation 39: RELEASE_LOCKOWNER - Release Lockowner
            State  . . . . . . . . . . . . . . . . . . . . . . . . . 226
     14.40. 281

     15.40. Operation 10044: ILLEGAL - Illegal operation . . . . . . 228
   15. 282
   16. NFS version 4 Callback Procedures . . . . . . . . . . . . . . 228
     15.1. 283
     16.1.  Procedure 0: CB_NULL - No Operation  . . . . . . . . . . 229
     15.2. 283
     16.2.  Procedure 1: CB_COMPOUND - Compound Operations . . . . . 229
       15.2.7. 284
       16.2.6.  Operation 3: CB_GETATTR - Get Attributes . . . . . . 231
       15.2.8. 285
       16.2.7.  Operation 4: CB_RECALL - Recall an Open Delegation . 232
       15.2.9. 286
       16.2.8.  Operation 10044: CB_ILLEGAL - Illegal Callback
                Operation  . . . . . . . . . . . . . . . . . . . . . . 234
   16. 287
   17. Security Considerations . . . . . . . . . . . . . . . . . . . 234
   17. 288
   18. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 236
     17.1. 290
     18.1.  Named Attribute Definition . . . . . . . . . . . . . . . 236
     17.2. 290
     18.2.  ONC RPC Network Identifiers (netids) . . . . . . . . . . 236
   18. 290
   19. References  . . . . . . . . . . . . . . . . . . . . . . . . . 238
     18.1. 291
     19.1.  Normative References . . . . . . . . . . . . . . . . . . 238
     18.2. 291
     19.2.  Informative References . . . . . . . . . . . . . . . . . 238 292
   Appendix A.  Acknowledgments  . . . . . . . . . . . . . . . . . . 240 294
   Appendix B.  RFC Editor Notes . . . . . . . . . . . . . . . . . . 240
   Author's Address  . 294
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . . 240 294

1.  Introduction

1.1.  Changes since RFC 3530

   This document, together with the companion XDR description document
   [2], obsoletes RFC 3530 [10] [11] as the authoritative document describing NFSv4, without introducing
   NFSv4.  It does not introduce any over-the-wire protocol
   changes. changes, in
   the sense that previously valid requests requests remain valid.
   However, some requests previously defined as invalid, although not
   generally rejected, are now explicitly allowed, in that
   internationalization handling has been generalized and liberalized.
   The main changes from RFC 3530 are:

   o  The RPC XDR definition has been moved to a companion document [2]

   o  Updates for the latest IETF intellectual property statements

   o  LIPKEY SPKM/3 has been moved from being mandatory to optional

   o  Some clarification on  There is a client re-establishing callback
      information to the restructured and more complete explanation of multi-
      server namespace features.  In particular, this explanation
      explicitly describes handling of inter-server referrals, even
      where neither migration nor replication is involved.

   o  More liberal handling of internationalization for file names and
      user and group names, with the elimination of restrictions imposed
      by stringprep, with the recognition that rules for the forms of
      these name are the province of the receiving entity.

   o  Updating handling of domain names to reflect IDNA.

   o  Restructuring of string types to more appropriately reflect the
      reality of required string processing.

   o  LIPKEY SPKM/3 has been moved from being mandatory to optional

   o  Some clarification on a client re-establishing callback
      information to the new server if state has been migrated

1.2.  Changes since RFC 3010

   This definition of the NFS version 4 protocol replaces or obsoletes
   the definition present in [11]. [12].  While portions of the two documents
   have remained the same, there have been substantive changes in
   others.  The changes made between [11] [12] and this document represent
   implementation experience and further review of the protocol.  While
   some modifications were made for ease of implementation or
   clarification, most updates represent errors or situations where the
   [11]
   [12] definition were untenable.

   The following list is not all inclusive of all changes but presents
   some of the most notable changes or additions made:

   o  The state model has added an open_owner4 identifier.  This was
      done to accommodate Posix based clients and the model they use for
      file locking.  For Posix clients, an open_owner4 would correspond
      to a file descriptor potentially shared amongst a set of processes
      and the lock_owner4 identifier would correspond to a process that
      is locking a file.

   o  Clarifications and error conditions were added for the handling of
      the owner and group attributes.  Since these attributes are string
      based (as opposed to the numeric uid/gid of previous versions of
      NFS), translations may not be available and hence the changes
      made.

   o  Clarifications for the ACL and mode attributes to address
      evaluation and partial support.

   o  For identifiers that are defined as XDR opaque, limits were set on
      their size.

   o  Added the mounted_on_filed attribute to allow Posix clients to
      correctly construct local mounts.

   o  Modified the SETCLIENTID/SETCLIENTID_CONFIRM operations to deal
      correctly with confirmation details along with adding the ability
      to specify new client callback information.  Also added
      clarification of the callback information itself.

   o  Added a new operation LOCKOWNER_RELEASE to enable notifying the
      server that a lock_owner4 will no longer be used by the client.

   o  RENEW operation changes to identify the client correctly and allow
      for additional error returns.

   o  Verify error return possibilities for all operations.

   o  Remove use of the pathname4 data type from LOOKUP and OPEN in
      favor of having the client construct a sequence of LOOKUP
      operations to achieive the same effect.

   o  Clarification of the internationalization issues and adoption of
      the new stringprep profile framework.

1.3.  NFS Version 4 Goals

   The NFS version 4 protocol is a further revision of the NFS protocol
   defined already by versions 2 [12] [13] and 3 [13]. [14].  It retains the
   essential characteristics of previous versions: design for easy
   recovery, independent of transport protocols, operating systems and
   filesystems, 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 filesystem model that provides a useful,
      common set of features that does not unduly favor one filesystem
      or operating system over another.

   o  Designed for protocol extensions.

      The protocol is designed to accept standard extensions that do not
      compromise backward compatibility.

1.4.  Inconsistencies of this Document with Section 18

   Section 18, RPC Definition File, the companion document NFS
      Version 4 Protocol

   [2], NFS Version 4 Protocol, contains the definitions in XDR
   description language of the constructs used by the protocol.  Prior
   to Section 18,  Inside
   this document, several of the constructs are reproduced for purposes
   of explanation.  The reader is warned of the possibility of errors in
   the reproduced constructs outside of Section 18. [2].  For any part of the
   document that is inconsistent with Section 18, Section 18 [2], [2] is to be considered
   authoritative.

1.5.  Overview of NFS version 4 Features

   To provide a reasonable context for the reader, the major features of
   NFS version 4 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 fundamental knowledge that is expected.  The reader
   should be familiar with the XDR and RPC protocols as described in [3]
   and [14]. [15].  A basic knowledge of filesystems and distributed
   filesystems is expected as well.

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 protocol are those defined in [3] and [14]. [15].  To meet end to
   end security requirements, the RPCSEC_GSS framework [4] 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 [15] [16] to provide one security framework.
   The LIPKEY GSS-API mechanism described in [5] will be used to provide
   for the use of user password and server public key by the NFS version
   4 protocol.  With the use of RPCSEC_GSS, other mechanisms may also be
   specified and used for NFS version 4 security.

   To enable in-band security negotiation, the NFS version 4 protocol
   has added a new operation which provides the client a method of
   querying the server about its policies regarding which security
   mechanisms must be used for access to the server's filesystem
   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.  Procedure and Operation Structure

   A significant departure from the previous versions of the NFS
   protocol is the introduction of the COMPOUND procedure.  For the NFS
   version 4 protocol, there are two RPC procedures, NULL and COMPOUND.
   The COMPOUND procedure is defined in terms of operations and these
   operations correspond more closely to the traditional NFS procedures.

   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 filesystem
   operations.  For example, without previous contact with a server a
   client will be able to read data from a file in one request by
   combining LOOKUP, OPEN, and READ operations in a single COMPOUND RPC.
   With previous versions of the NFS protocol, this type of single
   request was not possible.

   The model used for COMPOUND is very simple.  There is no logical OR
   or ANDing of operations.  The operations combined within a COMPOUND
   request are evaluated in order by the server.  Once an operation
   returns a failing result, the evaluation ends and the results of all
   evaluated operations are returned to the client.

   The NFS version 4 protocol continues to have the client refer to a
   file or directory at the server by a "filehandle".  The COMPOUND
   procedure has a method of passing a filehandle from one operation to
   another within the sequence of operations.  There is a concept of a
   "current filehandle" and "saved filehandle".  Most operations use the
   "current filehandle" as the filesystem object to operate upon.  The
   "saved filehandle" is used as temporary filehandle storage within a
   COMPOUND procedure as well as an additional operand for certain
   operations.

1.5.3.  Filesystem Model

   The general filesystem model used for the NFS version 4 protocol is
   the same as previous versions.  The server filesystem 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 protocol does not require a separate protocol to
   provide for the initial mapping between path name and filehandle.
   Instead of using the older MOUNT protocol for this mapping, the
   server provides a ROOT filehandle that represents the logical root or
   top of the filesystem tree provided by the server.  The server
   provides multiple filesystems by gluing them together with pseudo
   filesystems.  These pseudo filesystems provide for potential gaps in
   the path names between real filesystems.

1.5.3.1.  Filehandle Types

   In previous versions of the NFS protocol, the filehandle provided by
   the server was guaranteed to be valid or persistent for the lifetime
   of the filesystem object to which it referred.  For some server
   implementations, this persistence requirement has been difficult to
   meet.  For the NFS version 4 protocol, this requirement has been
   relaxed by introducing another type of filehandle, volatile.  With
   persistent and volatile filehandle types, the server implementation
   can match the abilities of the filesystem at the server along with
   the operating environment.  The client will have knowledge of the
   type of filehandle being provided by the server and can be prepared
   to deal with the semantics of each.

1.5.3.2.  Attribute Types

   The NFS version 4 protocol introduces three classes of filesystem or
   file attributes.  Like the additional filehandle type, the
   classification of file attributes has been done to ease server
   implementations along with extending the overall functionality of the
   NFS protocol.  This attribute model is structured to be extensible
   such that new attributes can be introduced in minor revisions of the
   protocol without requiring significant rework.

   The three classifications are: mandatory, recommended and named
   attributes.  This is a significant departure from the previous
   attribute model used in the NFS protocol.  Previously, the attributes
   for the filesystem and file objects were a fixed set of mainly UNIX
   attributes.  If the server or client did not support a particular
   attribute, it would have to simulate the attribute the best it could.

   Mandatory attributes are the minimal set of file or filesystem
   attributes that must be provided by the server and must be properly
   represented by the server.  Recommended attributes represent
   different filesystem types and operating environments.  The
   recommended attributes will allow for better interoperability and the
   inclusion of more operating environments.  The mandatory and
   recommended attribute sets are traditional file or filesystem
   attributes.  The third 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.

   One significant addition to the recommended set of file attributes is
   the Access Control List (ACL) attribute.  This attribute provides for
   directory and file access control beyond the model used in previous
   versions of the NFS protocol.  The ACL definition allows for
   specification of user and group level access control.

1.5.3.3.  Filesystem Replication and Migration

   With the use of a special file attribute, the ability to migrate or
   replicate inform the
   client of filesystem locations on another server filesystems is enabled within the protocol. enabled.  The
   filesystem locations attribute provides a method for the client to
   probe the server about the location of a filesystem.  In the event
   that a fileystems is not present on server the client will receive an
   error when attempting to operate on the filesystem and it can then
   query as to the correct filesystem location.  Thus is allowed
   construction of multi-server namespaces..

   These features also allow file system replication and migration.  In
   the event of a migration of a filesystem, the client will receive an
   error when operating on the filesystem and it can then query as location
   attribute to determine the new file system location.  Similar steps
   are used for replication, the client is able to query the server for
   the multiple available locations of a particular filesystem.  From
   this information, the client can use its own policies to access the
   appropriate filesystem location.

1.5.4.  OPEN and CLOSE

   The NFS version 4 protocol introduces OPEN and CLOSE operations.  The
   OPEN operation provides a single point where file lookup, creation,
   and share semantics can be combined.  The CLOSE operation also
   provides for the release of state accumulated by OPEN.

1.5.5.  File locking Locking

   With the NFS version 4 protocol, the support for byte range file
   locking is part of the NFS protocol.  The file locking support is
   structured so that an RPC callback mechanism is not required.  This
   is a departure from the previous versions of the NFS file locking
   protocol, Network Lock Manager (NLM).  The state associated with file
   locks is maintained at the server under a lease-based model.  The
   server defines a single lease period for all state held by a NFS
   client.  If the client does not renew its lease within the defined
   period, all state associated with the client's lease may be released
   by the server.  The client may renew its lease with use of the RENEW
   operation or implicitly by use of other operations (primarily READ).

1.5.6.  Client Caching and Delegation

   The file, attribute, and directory caching for the NFS version 4
   protocol is similar to previous versions.  Attributes and directory
   information are cached for a duration determined by the client.  At
   the end of a predefined timeout, the client will query the server to
   see if the related filesystem object has been updated.

   For file data, the client checks its cache validity when the file is
   opened.  A query is sent to the server to determine if the file has
   been changed.  Based on this information, the client determines if
   the data cache for the file should kept or released.  Also, when the
   file is closed, any modified data is written to the server.

   If an application wants to serialize access to file data, file
   locking of the file data ranges in question should be used.

   The major addition to NFS version 4 in the area of caching is the
   ability of the server to delegate certain responsibilities to the
   client.  When the server grants a delegation for a file to a client,
   the client is guaranteed certain semantics with respect to the
   sharing of that file with other clients.  At OPEN, the server may
   provide the client either a read or write delegation for the file.
   If the client is granted a read delegation, it is assured that no
   other client has the ability to write to the file for the duration of
   the delegation.  If the client is granted a write delegation, the
   client is assured that no other client has read or write access to
   the file.

   Delegations can be recalled by the server.  If another client
   requests access to the file in such a way that the access conflicts
   with the granted delegation, the server is able to notify the initial
   client and recall the delegation.  This requires that a callback path
   exist between the server and client.  If this callback path does not
   exist, then delegations can not be granted.  The essence of a
   delegation is that it allows the client to locally service operations
   such as OPEN, CLOSE, LOCK, LOCKU, READ, WRITE without immediate
   interaction with the server.

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 filesystem 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 to both record (byte-range)
      locks as well as share reservations unless specifically stated
      otherwise.

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

   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.

      Stateids composed of all bits 0 or all bits 1 have special 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.

2.  Protocol Data Types

   The syntax and semantics to describe the data types of the NFS
   version 4 protocol are defined in the XDR [14] [15] and RPC [3] documents.
   The next sections build upon the XDR data types to define types and
   structures specific to this protocol.

2.1.  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 the definition of change_info4.          |
   | clientid4      | typedef uint64_t clientid4;                      |
   |                | Shorthand reference to client identification.    |
   | count4         | typedef uint32_t count4;                         |
   |                | Various count parameters (READ, WRITE, COMMIT).  |
   | length4        | typedef uint64_t length4;                        |
   |                | Describes LOCK lengths.                          |
   | 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.                           |
   | 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).                                         |
   | qop4           | typedef uint32_t qop4;                           |
   |                | Quality of protection designation in SECINFO.    |
   | sec_oid4       | typedef opaque sec_oid4<>;                       |
   |                | Security Object Identifier.  The sec_oid4 data   |
   |                | type is not really opaque.  Instead it contains an  |
   |                | an ASN.1 OBJECT IDENTIFIER as used by GSS-API in the |
   |                | the mech_type argument to GSS_Init_sec_context. See  |
   |                | See [6] for details.                             |
   | seqid4         | typedef uint32_t seqid4;                         |
   |                | Sequence identifier used for file locking.       |
   | utf8string     | typedef opaque utf8string<>;                     |
   |                | UTF-8 encoding for strings.                      |
   | utf8str_cis utf8_should    | typedef utf8string utf8str_cis; utf8_should;                  |
   |                | Case-insensitive UTF-8 string. String expected to be UTF8 but no validation     |
   | utf8str_cs utf8val_should | typedef utf8string utf8str_cs; utf8val_should;               |
   |                | Case-sensitive UTF-8 string. String SHOULD be sent UTF8 and SHOULD be         |
   | utf8str_mixed                | validated                                        |
   | utf8val_must   | typedef utf8string utf8str_mixed; utf8val_must;                 |
   |                | UTF-8 strings with a case sensitive prefix String MUST be sent UTF8 and a MUST be validated   |
   | ascii_must     | typedef utf8string ascii_must;                   | case insensitive suffix.
   |                | String MUST be sent as ASCII and thus is         |
   |                | automatically UTF8                               |
   | comptag4       | typedef utf8_should comptag4;                    |
   |                | Tag should be UTF8 but is not checked            |
   | component4     | typedef utf8str_cs utf8val_should component4;               |
   |                | Represents path name components.                 |
   | linktext4      | typedef utf8str_cs utf8val_should linktext4;                |
   |                | Symbolic link contents.                          |
   | pathname4      | typedef component4 pathname4<>;                  |
   |                | Represents path name for fs_locations.           |
   | nfs_lockid4    | typedef uint64_t nfs_lockid4;                    |
   | verifier4      | typedef opaque verifier4[NFS4_VERIFIER_SIZE];    |
   |                | Verifier used for various operations (COMMIT,    |
   |                | CREATE, EXCHANGE_ID, OPEN, READDIR, WRITE)       |
   |                | NFS4_VERIFIER_SIZE is defined as 8.              |
   +---------------+---------------------------------------------------+
   +----------------+--------------------------------------------------+

                          End of Base Data Types

                                  Table 1

2.2.  Structured Data Types
2.2.1.  nfstime4

   struct nfstime4 {
           int64_t         seconds;
           uint32_t        nseconds;
   };

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

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

2.2.2.  time_how4

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

2.2.3.  settime4

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

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

2.2.4.  specdata4

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

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

2.2.5.  fsid4

   struct fsid4 {
           uint64_t        major;
           uint64_t        minor;
   };

   This type is the filesystem identifier that is used as a mandatory
   attribute.

2.2.6.  fs_location4

   struct fs_location4 {
           utf8str_cis
           utf8val_must    server<>;
           pathname4       rootpath;
   };

2.2.7.  fs_locations4

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

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

2.2.8.  fattr4

   struct fattr4 {
           bitmap4         attrmask;
           attrlist4       attr_vals;
   };

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

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

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

2.2.9.  change_info4

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

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

2.2.10.  clientaddr4

   struct clientaddr4 {
           /* see struct rpcb in RFC 1833 */
           string r_netid<>;    /* network id */
           string r_addr<>;     /* universal address */
   };

   The clientaddr4 structure is used as part of the SETCLIENTID
   operation to either specify the address of the client that is using a
   clientid or as part of the callback registration.  The r_netid and
   r_addr fields are specified in [16], [17], but they are underspecified in
   [16]
   [17] as far as what they should look like for specific protocols.

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

   h1.h2.h3.h4.p1.p2

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

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

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

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

   The suffix "p1.p2" is the service port, and is computed the same way
   as with universal addresses for TCP and UDP over IPv4.  The prefix,
   "x1:x2:x3:x4:x5:x6:x7:x8", is the standard textual form for
   representing an IPv6 address as defined in Section 2.2 of [17]. [18].
   Additionally, the two alternative forms specified in Section 2.2 of
   [17]
   [18] are also acceptable.

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

2.2.11.  cb_client4

   struct cb_client4 {
           unsigned int    cb_program;
           clientaddr4     cb_location;
   };

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

2.2.12.  nfs_client_id4

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

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

2.2.13.  open_owner4

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

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

2.2.14.  lock_owner4

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

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

2.2.15.  open_to_lock_owner4

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

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

2.2.16.  stateid4

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

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

3.  RPC and Security Flavor

   The NFS version 4 protocol is a Remote Procedure Call (RPC)
   application that uses RPC version 2 and the corresponding eXternal
   Data Representation (XDR) as defined in [3] and [14]. [15].  The RPCSEC_GSS
   security flavor as defined in [4] MUST be used as the mechanism to
   deliver stronger security for the NFS version 4 protocol.

3.1.  Ports and Transports

   Historically, NFS version 2 and version 3 servers have resided on
   port 2049.  The registered port 2049 [18] [19] for the NFS protocol should
   be the default configuration.  Using the registered port for NFS
   services means the NFS client will not need to use the RPC binding
   protocols as described in [16]; [17]; this will allow NFS to transit
   firewalls.

   Where an NFS version 4 implementation supports operation over the IP
   network protocol, the supported transports between NFS and IP MUST be
   among the IETF-approved congestion control transport protocols, which
   include TCP and SCTP.  To enhance the possibilities for
   interoperability, an NFS version 4 implementation MUST support
   operation over the TCP transport protocol, at least until such time
   as a standards track RFC revises this requirement to use a different
   IETF-approved congestion control transport protocol.

   If TCP is used as the transport, the client and server SHOULD use
   persistent connections.  This will prevent the weakening of TCP's
   congestion control via short lived connections and will improve
   performance for the WAN environment by eliminating the need for SYN
   handshakes.

   As noted in the Security Considerations section, Section 17, the authentication model for NFS version 4
   has moved from machine-based to principal- based.  However, this
   modification of the authentication model does not imply a technical
   requirement to move the TCP connection management model from whole
   machine-based to one based on a per user model.  In particular, NFS
   over TCP client implementations have traditionally multiplexed
   traffic for multiple users over 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 in proportion to the number of expected client machines.

   It is intended that NFS version 4 will not modify this connection
   management model.  NFS version 4 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 [19]. [20].

3.1.1.  Client Retransmission Behavior

   When processing a request received over a reliable transport such as
   TCP, the NFS version 4 server MUST NOT silently drop the request,
   except if the transport connection has been broken.  Given such a
   contract between NFS version 4 clients and servers, clients 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 client may
   want to actively "probe" the connection to see if has been broken.
   Use of the NULL procedure 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 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 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 AUTH_NONE, AUTH_SYS,
   AUTH_DH, and AUTH_KRB4 as security flavors.  With [4] an additional
   security flavor of RPCSEC_GSS has been introduced which uses the
   functionality of GSS-API [6].  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, the RPCSEC_GSS security flavor MUST be used to enable the
   mandatory security mechanism.  Other flavors, such as, AUTH_NONE,
   AUTH_SYS, and AUTH_DH MAY be implemented as well.

3.2.1.  Security mechanisms for NFS version 4

   The use of RPCSEC_GSS requires selection of: mechanism, quality of
   protection, and service (authentication, integrity, privacy).  The
   remainder of this document will refer to these three parameters of
   the RPCSEC_GSS security as the security triple.

3.2.1.1.  Kerberos V5 as a security triple

   The Kerberos V5 GSS-API mechanism as described in [15] [16] MUST be
   implemented and provide the following security triples.

   column descriptions:

   1 == number of pseudo flavor
   2 == name of pseudo flavor
   3 == mechanism's OID
   4 == mechanism's algorithm(s)
   5 == RPCSEC_GSS service

   1      2     3                    4             5
   --------------------------------------------------------------------
   390003 krb5  1.2.840.113554.1.2.2 DES MAC MD5   rpc_gss_svc_none
   390004 krb5i 1.2.840.113554.1.2.2 DES MAC MD5   rpc_gss_svc_integrity
   390005 krb5p 1.2.840.113554.1.2.2 DES MAC MD5   rpc_gss_svc_privacy
                                     for integrity,
                                     and 56 bit DES
                                     for privacy.

   Note that the pseudo flavor is presented here as a mapping aid to the
   implementor.  Because this NFS protocol includes a method to
   negotiate security and it understands the GSS-API mechanism, the
   pseudo flavor is not needed.  The pseudo flavor is needed for 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 [20]. [21].

   Users and implementors are warned that 56 bit DES is no longer
   considered state of the art in terms of resistance to brute force
   attacks.  Once a revision to [15] [16] is available that adds support for
   AES, implementors are urged to incorporate AES into their NFSv4 over
   Kerberos V5 protocol stacks, and users are similarly urged to migrate
   to the use of AES.

3.2.1.2.  LIPKEY as a security triple

   The LIPKEY GSS-API mechanism as described in [5] MAY be implemented
   and provide the following security triples.  The definition of the
   columns matches the previous subsection "Kerberos V5 as security
   triple". those in Section 3.2.1.1.

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

   The mechanism algorithm is listed as "negotiated".  This is because
   LIPKEY is layered on SPKM-3 and in SPKM-3 [5] the confidentiality and
   integrity algorithms are negotiated.  Since SPKM-3 specifies HMAC-MD5
   for integrity as MANDATORY, 128 bit cast5CBC for confidentiality for
   privacy as MANDATORY, and further specifies that HMAC-MD5 and
   cast5CBC MUST be listed first before weaker algorithms, specifying
   "negotiated" in column 4 does not impair interoperability.  In the
   event an SPKM-3 peer does not support the mandatory algorithms, the
   other peer is free to accept or reject the GSS-API context creation.

   Because SPKM-3 negotiates the algorithms, subsequent calls to
   LIPKEY's GSS_Wrap() and GSS_GetMIC() by RPCSEC_GSS will use a quality
   of protection value of 0 (zero).  See section 5.2 of [21] [22] for an
   explanation.

   LIPKEY uses SPKM-3 to create a secure channel in which to pass a user
   name and password from the client to the server.  Once the user name
   and password have been accepted by the server, calls to the LIPKEY
   context are redirected to the SPKM-3 context.  See [5] for more
   details.

3.2.1.3.  SPKM-3 as a security triple

   The SPKM-3 GSS-API mechanism as described in [5] MAY be implemented
   and provide the following security triples.  The definition of the
   columns matches the previous subsection "Kerberos V5 as security
   triple". those in Section 3.2.1.1.

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

   For a discussion as to why the mechanism algorithm is listed as
   "negotiated", see Section 3.2.1.2 "LIPKEY as a security triple." 3.2.1.2.

   Because SPKM-3 negotiates the algorithms, subsequent calls to SPKM-
   3's GSS_Wrap() and GSS_GetMIC() by RPCSEC_GSS will use a quality of
   protection value of 0 (zero).  See section 5.2 of [21] [22] for an
   explanation.

   Even though LIPKEY is layered over SPKM-3, SPKM-3 is specified as a
   mandatory set of triples to handle the situations where the initiator
   (the client) is anonymous or where the initiator has its own
   certificate.  If the initiator is anonymous, there will not be a user
   name and password to send to the target (the server).  If the
   initiator has its own certificate, then using passwords is
   superfluous.

3.3.  Security Negotiation

   With the NFS version 4 server potentially offering multiple security
   mechanisms, the client needs a method to determine or negotiate which
   mechanism is to be used for its communication with the server.  The
   NFS server may have multiple points within its filesystem name space
   that are available for use by NFS clients.  In turn the NFS server
   may be configured such that each 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 to eliminate the possibility of a third party
   intercepting the negotiation sequence and forcing the client and
   server to choose a lower level of security than required or desired.
   See Section 16 "Security Considerations" 17 for further discussion.

3.3.1.  SECINFO

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

3.3.2.  Security Error

   Based on the assumption that each NFS version 4 client and server
   must support a minimum set of security (i.e., LIPKEY, SPKM-3, and
   Kerberos-V5 all under RPCSEC_GSS), the NFS client will start its
   communication with the server with one of the minimal security
   triples.  During communication with the server, the client may
   receive an NFS error of NFS4ERR_WRONGSEC.  This error allows the
   server to notify the client that the security triple currently being
   used is not appropriate for access to the server's filesystem
   resources.  The client is then responsible for determining what
   security triples are available at the server and choose one which is
   appropriate for the client.  See Section 14.33 for the "SECINFO"
   operation 15.33 for further discussion
   of how the client will respond to the NFS4ERR_WRONGSEC error and use
   SECINFO.

3.3.3.  Callback RPC Authentication

   Except as noted elsewhere in this section, the callback RPC
   (described later) MUST mutually authenticate the NFS server to the
   principal that acquired the clientid (also described later), using
   the security flavor the original SETCLIENTID operation used.

   For AUTH_NONE, there are no principals, so this is a non-issue.

   AUTH_SYS has no notions of mutual authentication or a server
   principal, so the callback from the server simply uses the AUTH_SYS
   credential that the user used when he set up the delegation.

   For AUTH_DH, one commonly used convention is that the server uses the
   credential corresponding to this AUTH_DH principal:

   unix.host@domain

   where host and domain are variables corresponding to the name of
   server host and directory services domain in which it lives such as a
   Network Information System domain or a DNS domain.

   Because LIPKEY is layered over SPKM-3, it is permissible for the
   server to use SPKM-3 and not LIPKEY for the callback even if the
   client used LIPKEY for SETCLIENTID.

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

   service@hostname

   For NFS, the "service" element is

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

   nfs/hostname

   For Kerberos V5, nfs/hostname would be a server principal in the
   Kerberos Key Distribution Center database.  This is the same
   principal the client acquired a GSS-API context for when it issued
   the SETCLIENTID operation, therefore, the realm name for the server
   principal must be the same for the callback as it was for the
   SETCLIENTID.

   For LIPKEY, this would be the username passed to the target (the NFS
   version 4 client that receives the callback).

   It should be noted that LIPKEY may not work for callbacks, since the
   LIPKEY client uses a user id/password.  If the NFS client receiving
   the callback can authenticate the NFS server's user name/password
   pair, and if the user that the NFS server is authenticating to has a
   public key certificate, then it works.

   In situations where the NFS client uses LIPKEY and uses a per-host
   principal for the SETCLIENTID operation, instead of using LIPKEY for
   SETCLIENTID, it is RECOMMENDED that SPKM-3 with mutual authentication
   be used.  This effectively means that the client will use a
   certificate to authenticate and identify the initiator to the target
   on the NFS server.  Using SPKM-3 and not LIPKEY has the following
   advantages:

   o  When the server does a callback, it must authenticate to the
      principal used in the SETCLIENTID.  Even if LIPKEY is used,
      because LIPKEY is layered over SPKM-3, the NFS client will need to
      have a certificate that corresponds to the principal used in the
      SETCLIENTID operation.  From an administrative perspective, having
      a user name, password, and certificate for both the client and
      server is redundant.

   o  LIPKEY was intended to minimize additional infrastructure
      requirements beyond a certificate for the target, and the
      expectation is that existing password infrastructure can be
      leveraged for the initiator.  In some environments, a per-host
      password does not exist yet.  If certificates are used for any
      per-host principals, then additional password infrastructure is
      not needed.

   o  In cases when a host is both an NFS client and server, it can
      share the same per-host certificate.

4.  Filehandles

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

4.1.  Obtaining the First Filehandle

   The operations of the NFS protocol are defined in terms of one or
   more filehandles.  Therefore, the client needs a filehandle to
   initiate communication with the server.  With the NFS version 2
   protocol [12] [13] and the NFS version 3 protocol [13], [14], there exists an
   ancillary protocol to obtain this first filehandle.  The MOUNT
   protocol, RPC program number 100005, provides the mechanism of
   translating a string based filesystem path name to a filehandle which
   can then be used by the NFS protocols.

   The MOUNT protocol has deficiencies in the area of security and use
   via firewalls.  This is one reason that the use of the public
   filehandle was introduced in [22] [23] and [23]. [24].  With the use of the
   public filehandle in combination with the LOOKUP operation in the NFS
   version 2 and 3 protocols, it has been demonstrated that the MOUNT
   protocol is unnecessary for viable interaction between NFS client and
   server.

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

4.1.1.  Root Filehandle

   The first of the special filehandles is the ROOT filehandle.  The
   ROOT filehandle is the "conceptual" root of the filesystem name space
   at the NFS server.  The client uses or starts with the ROOT
   filehandle by employing the PUTROOTFH operation.  The PUTROOTFH
   operation instructs the server to set the "current" filehandle to the
   ROOT of the server's file tree.  Once this PUTROOTFH operation is
   used, the client can then traverse the entirety of the server's file
   tree with the LOOKUP operation.  A complete discussion of the server
   name space is in the section "NFS Server Name Space". Section 8.

4.1.2.  Public Filehandle

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

4.2.  Filehandle Types

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

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

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

4.2.1.  General Properties of a Filehandle

   The filehandle contains all the information the server needs to
   distinguish an individual file.  To the client, the filehandle is
   opaque.  The client stores filehandles for use in a later request and
   can compare two filehandles from the same server for equality by
   doing a byte-by-byte comparison.  However, the client MUST NOT
   otherwise interpret the contents of filehandles.  If two filehandles
   from the same server are equal, they MUST refer to the same file.
   Servers SHOULD try to maintain a one-to-one correspondence between
   filehandles and files but this is not required.  Clients MUST use
   filehandle comparisons only to improve performance, not for correct
   behavior.  All clients need to be prepared for situations in which it
   cannot be determined whether two filehandles denote the same object
   and in such cases, avoid making invalid assumptions which might cause
   incorrect behavior.  Further discussion of filehandle and attribute
   comparison in the context of data caching is presented in the section
   "Data Caching and File Identity".
   Section 10.3.4.

   As an example, in the case that two different path names when
   traversed at the server terminate at the same filesystem object, the
   server SHOULD return the same filehandle for each path.  This can
   occur if a hard link is used to create two file names which refer to
   the same underlying file object and associated data.  For example, if
   paths /a/b/c and /a/d/c refer to the same file, the server SHOULD
   return the same filehandle for both path names traversals.

4.2.2.  Persistent Filehandle

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

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

4.2.3.  Volatile Filehandle

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

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

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

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

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

   FH4_VOL_MIGRATION  The filehandle will expire as a result of
      migration.  If FH4_VOL_ANY is set, FH4_VOL_MIGRATION is redundant.

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

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

   Note that the bits FH4_VOL_MIGRATION and FH4_VOL_RENAME allow the
   client to determine that expiration has occurred whenever a specific
   event occurs, without an explicit filehandle expiration error from
   the server.  FH4_VOL_ANY does not provide this form of information.
   In situations where the server will expire many, but not all
   filehandles upon migration (e.g., all but those that are open),
   FH4_VOLATILE_ANY (in this case with FH4_NOEXPIRE_WITH_OPEN) is a
   better choice since the client may not assume that all filehandles
   will expire when migration occurs, and it is likely that additional
   expirations will occur (as a result of file CLOSE) that are separated
   in time from the migration event itself.

4.2.4.  One Method of Constructing a Volatile Filehandle

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

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

   o  slot is an index in the server volatile filehandle table

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

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

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

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

4.3.  Client Recovery from Filehandle Expiration

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

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

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

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

   RENAME A B
   LOOKUP B
   GETFH

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

5.  File Attributes

   To meet the requirements of extensibility and increased
   interoperability with non-UNIX platforms, attributes must be handled
   in a flexible manner.  The NFS version 3 NFSv3 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 NFSv4.0 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, REQUIRED,
   RECOMMENDED, and named.  Both mandatory REQUIRED and recommended RECOMMENDED attributes are
   supported in the NFS version 4 NFSv4.0 protocol by a specific and well-
   defined 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 REQUIRED or recommended RECOMMENDED attributes may be added
   to the NFS NFSv4 protocol between major revisions as part of a new minor version by publishing a
   standards-track RFC which allocates a new attribute number value and
   defines the encoding for the attribute.  See Section 10 "Minor Versioning" 11 for further
   discussion.

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

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

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

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

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

5.1.  Mandatory  REQUIRED Attributes

   These MUST be supported by every NFS version 4 NFSv4.0 client and server in order
   to ensure a minimum level of interoperability.  The server must MUST store
   and return these attributes and the client must MUST be able to function
   with an attribute set limited to these attributes.  With just the mandatory
   REQUIRED attributes some client functionality may be impaired or
   limited in some ways.  A client may ask for any of these attributes
   to be returned by setting a bit in the GETATTR request and the server
   must return their value.

5.2.  Recommended  RECOMMENDED Attributes

   These attributes are understood well enough to warrant support in the
   NFS version 4
   NFSv4.0 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 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.

5.3.  Named Attributes

   These attributes are not supported by direct encoding in the NFS
   Version 4 NFSv4
   protocol but are accessed by string names rather than numbers and
   correspond to an uninterpreted stream of bytes which are stored with
   the filesystem 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 "named attribute directory" and
   further perusal and modification of the name space may be done using
   operations that work on more typical directories.  In particular,
   READDIR may be used to get a list of such named attributes and LOOKUP operations on this filehandle.  Named
   and OPEN may select a particular attribute.  Creation of a new named
   attribute may be the result of an OPEN specifying file creation.

   Once an OPEN is done, named attributes may then be examined or and changed by
   normal READ and WRITE and CREATE operations on using the filehandles returned from READDIR and LOOKUP. stateids
   returned by OPEN.

   Named attributes may have and the named attribute directory may have their own
   (non-named) attributes.  Each of objects must have all of the
   REQUIRED attributes and may have additional RECOMMENDED attributes.
   However, the set of attributes for named attributes and the named
   attribute directory need not be as large as, and typically will not
   be as large as that for other objects in that file system.

   Named attributes and the named attribute directory may be the target
   of delegations (in the case of the named attribute directory these
   will be directory delegations).  However, since granting of
   delegations or not is within the server's discretion, a server need
   not support delegations on named attributes or the named attribute
   directory.

   It is recommended RECOMMENDED that servers support arbitrary named attributes.  A
   client should not depend on the ability to store any named attributes
   in the server's filesystem. 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 metadata 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.

   In NFSv4.0, the structure of named attribute directories is
   restricted in a number of ways, in order to prevent the development
   of non-interoperable implementations in which some servers support a
   fully general hierarchical directory structure for named attributes
   while others support a limited set, but fully adequate to the
   feature's goals.  In such an environment, clients or applications
   might come to depend on non-portable extensions.  The restrictions
   are:

   o  CREATE is not allowed in a named attribute directory.  Thus, such
      objects as symbolic links and special files are not allowed to be
      named attributes.  Further, directories may not be created in a
      named attribute directory so no hierarchical structure of named
      attributes for a single object is allowed.

   o  If OPENATTR is done on a named attribute directory or on a named
      attribute, the server MUST return NFS4ERR_WRONG_TYPE.

   o  Doing a RENAME of a named attribute to a different named attribute
      directory or to an ordinary (i.e. non-named-attribute) directory
      is not allowed.

   o  Creating hard links between named attribute directories or between
      named attribute directories and ordinary directories is not
      allowed.

   Names of attributes will not be controlled by this document or other
   IETF standards track documents.  See Section 17 "IANA Considerations" 18 for further
   discussion.

5.4.  Classification of Attributes

   Each of the Mandatory REQUIRED and Recommended RECOMMENDED attributes can be classified in
   one of three categories: per server, per filesystem, file system, or per
   filesystem file
   system object.  Note that it is possible that some per filesystem file system
   attributes may vary within the filesystem. 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 to time_access
   and time_modify, and are used in a special instance of SETATTR.

   o  The per server attribute is:

         lease_time

   o  The per filesystem file system attributes are:

      supp_attr,

         supported_attrs, 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 time_delta,

   o  The per filesystem file system object attributes are:

         type, change, size, named_attr, fsid, rdattr_error, filehandle,
      ACL,
         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

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

5.5.  Mandatory  Set-Only and Get-Only Attributes

   Some REQUIRED and RECOMMENDED attributes are set-only, i.e. they can
   be set via SETATTR but not retrieved via GETATTR.  Similarly, some
   REQUIRED and RECOMMENDED attributes are get-only, i.e. they can be
   retrieved GETATTR but not set via SETATTR.  If a client attempts to
   set a get-only attribute or get a set-only attributes, the server
   MUST return NFS4ERR_INVAL.

5.6.  REQUIRED Attributes - Definitions

   +-----------------+----+------------+--------+----------------------+ List and Definition References

   The list of REQUIRED attributes appears in Table 2.  The meaning of
   the columns of the table are:

   o  Name: the name of attribute

   o  Id: the number assigned to the attribute.  In the event of
      conflicts between the assigned number and [2], the latter is
      authoritative.

   o  Data Type: The XDR data type of the attribute.

   o  Acc: Access allowed to the attribute.  R means read-only (GETATTR
      may retrieve, SETATTR may not set).  W means write-only (SETATTR
      may set, GETATTR may not retrieve).  R W means read/write (GETATTR
      may retrieve, SETATTR may set).

   o  Defined in: the section of this specification that describes the
      attribute.

      +-----------------+----+------------+-----+------------------+
      | Name            | Id | Data Type  | Access Acc | Description Defined in:      |
   +-----------------+----+------------+--------+----------------------+
      +-----------------+----+------------+-----+------------------+
      | supp_attr supported_attrs | 0  | bitmap bitmap4    | READ R   | The bit vector which Section 5.8.1.1  |
      | type            | 1  | nfs_ftype4 | R   | would retrieve all Section 5.8.1.2  |
      | fh_expire_type  | 2  | uint32_t   | R   | mandatory and Section 5.8.1.3  |
      | change          | 3  | uint64_t   | R   | recommended Section 5.8.1.4  |
      | size            | 4  | uint64_t   | R W | attributes that are Section 5.8.1.5  |
      | link_support    | 5  | bool       | R   | supported for this Section 5.8.1.6  |
      | symlink_support | 6  | bool       | R   | object. The scope of Section 5.8.1.7  |
      | named_attr      | 7  | bool       | R   | this attribute Section 5.8.1.8  |
      | fsid            | 8  | fsid4      | R   | applies to all Section 5.8.1.9  |
      | unique_handles  | 9  | bool       | R   | objects with a       |
   |                 |    |            |        | matching fsid.       |
   | type            | 1  | nfs4_ftype | READ   | The type of the      |
   |                 |    |            |        | object (file,        |
   |                 |    |            |        | directory, symlink,  |
   |                 |    | Section 5.8.1.10 |
      | etc.) lease_time      | 10 | fh_expire_type nfs_lease4 | 2 R   | uint32 Section 5.8.1.11 | READ
      | Server uses this to rdattr_error    | 11 | enum       | R   | Section 5.8.1.12 |
      | specify filehandle      | 19 | nfs_fh4    | R   | Section 5.8.1.13 |        | expiration behavior  |
   |                 |    |            |        | to
      +-----------------+----+------------+-----+------------------+

                                  Table 2

5.7.  RECOMMENDED Attributes - List and Definition References

   The RECOMMENDED attributes are defined in Table 3.  The meanings of
   the client. See   |
   |                 |    |            |        | column headers are the same as Table 2; see Section 4            |
   |                 |    |            |        | "Filehandles" 5.6 for the
   meanings.

    +-------------------+----+--------------+-----+------------------+
    | Name              | Id | Data Type    | Acc | Defined in:      | additional
    +-------------------+----+--------------+-----+------------------+
    | acl               | 12 | nfsace4<>    | R W | Section 6.2.1    | description.
    | aclsupport        | change 13 | 3 uint32_t     | uint64 R   | READ Section 6.2.1.2  | A value created by
    | archive           | 14 | bool         | R W | Section 5.8.2.1  | the server that the
    | cansettime        | 15 | bool         | R   | Section 5.8.2.2  | client can use to
    | case_insensitive  | 16 | bool         | R   | Section 5.8.2.3  | determine if file
    | case_preserving   | 17 | bool         | R   | Section 5.8.2.4  | data, directory
    | chown_restricted  | 18 | bool         | R   | Section 5.8.2.5  | contents or
    | fileid            | 20 | uint64_t     | R   | Section 5.8.2.6  | attributes of the
    | files_avail       | 21 | uint64_t     | R   | Section 5.8.2.7  | object have been
    | files_free        | 22 | uint64_t     | R   | Section 5.8.2.8  | modified. The server
    | files_total       | 23 | uint64_t     | R   | Section 5.8.2.9  | may return the
    | fs_locations      | 24 | fs_locations | R   | Section 5.8.2.10 | object's
    | hidden            | 25 | bool         | R W | Section 5.8.2.11 | time_metadata
    | homogeneous       | 26 | bool         | R   | Section 5.8.2.12 | attribute for this
    | maxfilesize       | 27 | uint64_t     | R   | Section 5.8.2.13 | attribute's value
    | maxlink           | 28 | uint32_t     | R   | Section 5.8.2.14 | but only if the
    | maxname           | 29 | uint32_t     | R   | Section 5.8.2.15 | filesystem object
    | maxread           | 30 | uint64_t     | R   | Section 5.8.2.16 | can not be updated
    | maxwrite          | 31 | uint64_t     | R   | Section 5.8.2.17 | more frequently than
    | mimetype          | 32 | utf8<>       | R W | Section 5.8.2.18 | the resolution of
    | mode              | 33 | mode4        | R W | Section 6.2.2    | time_metadata.
    | mounted_on_fileid | size 55 | 4 uint64_t     | uint64 R   | R/W Section 5.8.2.19 | The size of the
    | no_trunc          | 34 | bool         | R   | Section 5.8.2.20 | object in bytes.
    | numlinks          | link_support 35 | 5 uint32_t     | bool R   | READ Section 5.8.2.21 | True, if the
    | owner             | 36 | utf8<>       | R W | Section 5.8.2.22 | object's filesystem
    | owner_group       | 37 | utf8<>       | R W | Section 5.8.2.23 | supports hard links.
    | quota_avail_hard  | symlink_support 38 | 6 uint64_t     | bool R   | READ Section 5.8.2.24 | True, if the
    | quota_avail_soft  | 39 | uint64_t     | R   | Section 5.8.2.25 | object's filesystem
    | quota_used        | 40 | uint64_t     | R   | Section 5.8.2.26 | supports symbolic
    | rawdev            | 41 | specdata4    | R   | Section 5.8.2.27 | links.
    | space_avail       | named_attr 42 | 7 uint64_t     | bool R   | READ Section 5.8.2.28 | True, if this object
    | space_free        | 43 | uint64_t     | R   | Section 5.8.2.29 | has named
    | space_total       | 44 | uint64_t     | R   | Section 5.8.2.30 | attributes. In other
    | space_used        | 45 | uint64_t     | R   | Section 5.8.2.31 | words, object has a
    | system            | 46 | bool         | R W | Section 5.8.2.32 | non-empty named
    | time_access       | 47 | nfstime4     | R   | Section 5.8.2.33 | attribute directory.
    | time_access_set   | fsid 48 | 8 settime4     | fsid4   W | READ Section 5.8.2.34 | Unique filesystem
    | time_backup       | 49 | nfstime4     | R W | Section 5.8.2.35 | identifier for the
    | time_create       | 50 | nfstime4     | R W | Section 5.8.2.36 | filesystem holding
    | time_delta        | 51 | nfstime4     | R   | Section 5.8.2.37 | this object. fsid
    | time_metadata     | 52 | nfstime4     | R   | Section 5.8.2.38 | contains major and
    | time_modify       | 53 | nfstime4     | R   | Section 5.8.2.39 | minor components
    | time_modify_set   | 54 | settime4     |   W | Section 5.8.2.40 | each
    +-------------------+----+--------------+-----+------------------+

                                  Table 3

5.8.  Attribute Definitions

5.8.1.  Definitions of REQUIRED Attributes

5.8.1.1.  Attribute 0: supported_attrs

   The bit vector which would retrieve all REQUIRED and RECOMMENDED
   attributes that are    |
   |                 |    |            |        | uint64.              |
   | unique_handles  | 9  | bool       | READ   | True, if two         |
   |                 |    |            |        | distinct filehandles |
   |                 |    |            |        | guaranteed to refer  |
   |                 |    |            |        | supported for this object.  The scope of this
   attribute applies to two different     |
   |                 |    |            |        | filesystem objects.  |
   | all objects with a matching fsid.

5.8.1.2.  Attribute 1: type

   Designates the type of an object in terms of one of a number of
   special constants:

   o  NF4REG designates a regular file.

   o  NF4DIR designates a directory.

   o  NF4BLK designates a block device special file.

   o  NF4CHR designates a character device special file.

   o  NF4LNK designates a symbolic link.

   o  NF4SOCK designates a named socket special file.

   o  NF4FIFO designates a fifo special file.

   o  NF4ATTRDIR designates a named attribute directory.

   o  NF4NAMEDATTR designates a named attribute.

   Within the explanatory text and operation descriptions, the following
   phrases will be used with the meanings given below:

   o  The phrase "is a directory" means that the object is of type
      NF4DIR or of type NF4ATTRDIR.

   o  The phrase "is a special file" means that the object is of one of
      the types NF4BLK, NF4CHR, NF4SOCK, or NF4FIFO.

   o  The phrase "is an ordinary file" means that the object is of type
      NF4REG or of type NF4NAMEDATTR.

5.8.1.3.  Attribute 2: fh_expire_type

   Server uses this to specify filehandle expiration behavior to the
   client.  See Section 4 for additional description.

5.8.1.4.  Attribute 3: change

   A value created by the server that the client can use to determine if
   file data, directory contents or attributes of the object have been
   modified.  The server may return the object's time_metadata attribute
   for this attribute's value but only if the file system object can not
   be updated more frequently than the resolution of time_metadata.

5.8.1.5.  Attribute 4: size

   The size of the object in bytes.

5.8.1.6.  Attribute 5: link_support

   True, if the object's file system supports hard links.

5.8.1.7.  Attribute 6: symlink_support

   True, if the object's file system supports symbolic links.

5.8.1.8.  Attribute 7: named_attr

   True, if this object has named attributes.  In other words, object
   has a non-empty named attribute directory.

5.8.1.9.  Attribute 8: fsid

   Unique file system identifier for the file system holding this
   object. fsid contains major and minor components each of which are of
   data type uint64_t.

5.8.1.10.  Attribute 9: unique_handles

   True, if two distinct filehandles guaranteed to refer to two
   different file system objects.

5.8.1.11.  Attribute 10: lease_time      | 10 | nfs_lease4 | READ   |

   Duration of leases   |
   |                 |    |            |        | at server in         |
   |                 |    |            |        | seconds.             |
   |

5.8.1.12.  Attribute 11: rdattr_error    | 11 | enum       | READ   |

   Error returned from  |
   |                 |    |            |        | getattr an attempt to retrieve attributes during       |
   |                 |    |            |        | readdir.             |
   | a
   READDIR operation.

5.8.1.13.  Attribute 19: filehandle      | 19 | nfs_fh4    | READ   |

   The filehandle of    |
   |                 |    |            |        | this object          |
   |                 |    |            |        | (primarily for       |
   |                 |    |            |        | readdir READDIR requests).   |
   +-----------------+----+------------+--------+----------------------+

                                  Table 2

5.6.  Recommended Attributes -

5.8.2.  Definitions

   +-------------------+----+--------------+--------+------------------+
   | Name              | Id | Data Type    | Access | Description      |
   +-------------------+----+--------------+--------+------------------+
   | ACL               | 12 | nfsace4<>    | R/W    | of Uncategorized RECOMMENDED Attributes

   The access       |
   |                   |    |              |        | control list for |
   |                   |    |              |        | the object.      |
   | aclsupport        | 13 | uint32       | READ   | Indicates what   |
   |                   |    |              |        | types definitions of most of ACLs    |
   |                   |    |              |        | are supported on |
   |                   |    |              |        | the current      |
   |                   |    |              |        | filesystem.      |
   | RECOMMENDED attributes follow.
   Collections that share a common category are defined in other
   sections.

5.8.2.1.  Attribute 14: archive           | 14 | bool         | R/W    |

   True, if this    |
   |                   |    |              |        | file has been    |
   |                   |    |              |        | archived since   |
   |                   |    |              |        | the time of last |
   |                   |    |              |        |
   modification     |
   |                   |    |              |        | (deprecated in   |
   |                   |    |              |        | favor of         |
   |                   |    |              |        | time_backup).    |
   |

5.8.2.2.  Attribute 15: cansettime        | 15 | bool         | READ   |

   True, if the     |
   |                   |    |              |        | server is able   |
   |                   |    |              |        | to change the    |
   |                   |    |              |        | times for a      |
   |                   |    |              |        | filesystem       |
   |                   |    |              |        | file system object
   as        |
   |                   |    |              |        | specified in a   |
   |                   |    |              |        | SETATTR          |
   |                   |    |              |        | operation.       |
   |

5.8.2.3.  Attribute 16: case_insensitive  | 16 | bool         | READ   |

   True, if         |
   |                   |    |              |        | filename         |
   |                   |    |              |        | file name comparisons on   |
   |                   |    |              |        | this filesystem  |
   |                   |    |              |        | file system are case         |
   |                   |    |              |        |
   insensitive.     |
   |

5.8.2.4.  Attribute 17: case_preserving   | 17 | bool         | READ   |

   True, if         |
   |                   |    |              |        | filename file name case on |
   |                   |    |              |        | this filesystem  |
   |                   |    |              |        | are file system is preserved.   |
   |

5.8.2.5.  Attribute 18: 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).      |
   |

5.8.2.6.  Attribute 20: fileid            | 20 | uint64       | READ   |

   A number         |
   |                   |    |              |        | uniquely         |
   |                   |    |              |        | identifying the  |
   |                   |    |              |        | file within the  |
   |                   |    |              |        | filesystem.      |
   | file system.

5.8.2.7.  Attribute 21: files_avail       | 21 | uint64       | READ   |

   File slots       |
   |                   |    |              |        | available to     |
   |                   |    |              |        | this user on the |
   |                   |    |              |        | filesystem       |
   |                   |    |              |        | file system containing this  |
   |                   |    |              |        |
   object - this    |
   |                   |    |              |        | should be the    |
   |                   |    |              |        | smallest         |
   |                   |    |              |        | relevant limit.  |
   |

5.8.2.8.  Attribute 22: files_free        | 22 | uint64       | READ   |

   Free file slots  |
   |                   |    |              |        | on the           |
   |                   |    |              |        | filesystem       |
   |                   |    |              |        | file system containing this  |
   |                   |    |              |        | object - this    |
   |                   |    |              |        |
   should be the    |
   |                   |    |              |        | smallest         |
   |                   |    |              |        | relevant limit.  |
   |

5.8.2.9.  Attribute 23: files_total       | 23 | uint64       | READ   |

   Total file slots |
   |                   |    |              |        | on the           |
   |                   |    |              |        | filesystem       |
   |                   |    |              |        | file system containing this  |
   |                   |    |              |        | object.          |
   | fs_locations      | 24 |

5.8.2.10.  Attribute 24: fs_locations | READ   |

   Locations where  |
   |                   |    |              |        | this filesystem  |
   |                   |    |              |        | file system may be found.  If |
   |                   |    |              |        | the server       |
   |                   |    |              |        | returns          |
   |                   |    |              |        |
   NFS4ERR_MOVED as |
   |                   |    |              |        | an error, this   |
   |                   |    |              |        | attribute MUST   |
   |                   |    |              |        | be supported.    |
   |

5.8.2.11.  Attribute 25: hidden            | 25 | bool         | R/W    |

   True, if the     |
   |                   |    |              |        | file is          |
   |                   |    |              |        | considered       |
   |                   |    |              |        | hidden with      |
   |                   |    |              |        | respect to the   |
   |                   |    |              |        | Windows
   API.     |
   |

5.8.2.12.  Attribute 26: homogeneous       | 26 | bool         | READ   |

   True, if this    |
   |                   |    |              |        | object's         |
   |                   |    |              |        | filesystem file system is    |
   |                   |    |              |        | homogeneous,     |
   |                   |    |              |        | i.e., i.e. are per    |
   |                   |    |              |        | filesystem       |
   |                   |    |              |        | file
   system attributes the   |
   |                   |    |              |        | same for all     |
   |                   |    |              |        | filesystem's     |
   |                   |    |              |        | objects?         |
   | file system's objects.

5.8.2.13.  Attribute 27: maxfilesize       | 27 | uint64       | READ   |

   Maximum          |
   |                   |    |              |        | supported file   |
   |                   |    |              |        | size for the     |
   |                   |    |              |        | filesystem file system of    |
   |                   |    |              |        | this object.     |
   |

5.8.2.14.  Attribute 28: maxlink           | 28 | uint32       | READ   |

   Maximum number   |
   |                   |    |              |        | of links for     |
   |                   |    |              |        | this object.     |
   |

5.8.2.15.  Attribute 29: maxname           | 29 | uint32       | READ   |

   Maximum filename |
   |                   |    |              |        | file name size supported   |
   |                   |    |              |        | for this object. |
   |

5.8.2.16.  Attribute 30: maxread           | 30 | uint64       | READ   |

   Maximum read     |
   |                   |    |              |        | size supported   |
   |                   |    |              |        | for this object. |
   |

5.8.2.17.  Attribute 31: 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.     |
   |

5.8.2.18.  Attribute 32: 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.          |
   | no_trunc          | 34 | bool         | READ   | True,

5.8.2.19.  Attribute 55: mounted_on_fileid

   Like fileid, but if a name  |
   |                   |    |              |        | longer than      |
   |                   |    |              |        | name_max is      |
   |                   |    |              |        | used, an error   |
   |                   |    |              |        | be returned and  |
   |                   |    |              |        | name the target filehandle is not      |
   |                   |    |              |        | truncated.       |
   | numlinks          | 35 | uint32       | READ   | Number the root of hard   |
   |                   |    |              |        | links to a file
   system, this    |
   |                   |    |              |        | object.          |
   | owner             | 36 | utf8<>       | R/W    | The string name  |
   |                   |    |              |        | attribute represents the fileid of the owner underlying
   directory.

   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  |
   |                   |    |              |        | this object.     |
   | owner_group       | 37 | utf8<>       | R/W    | The string 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 group     |
   |                   |    |              |        | ownership 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     |
   |                   |    |              |        | this object.     |
   | quota_avail_hard  | 38 | uint64       | READ   | For definition   |
   |                   |    |              |        | see Section 5.10 |
   |                   |    |              |        | "Quota           |
   |                   |    |              |        | Attributes"      |
   |                   |    |              |        | below.           |
   | quota_avail_soft  | 39 | uint64       | READ   | For definition   |
   |                   |    |              |        | see Section 5.10 |
   |                   |    |              |        | "Quota           |
   |                   |    |              |        | Attributes"      |
   |                   |    |              |        | below.           |
   | quota_used        | 40 | uint64       | READ   | For definition   |
   |                   |    |              |        | see Section 5.10 |
   |                   |    |              |        | "Quota           |
   |                   |    |              |        | Attributes"      |
   |                   |    |              |        | below.           |
   | rawdev            | 41 | specdata4    | READ   | Raw device       |
   |                   |    |              |        | identifier. UNIX |
   |                   |    |              |        | device           |
   |                   |    |              |        | major/minor node |
   |                   |    |              |        | information. If  |
   |                   |    |              |        | the value root of     |
   |                   |    |              |        | type the mounted file system, whereas readdir() is not      |
   |                   |    |              |        | NF4BLK or        |
   |                   |    |              |        | NF4CHR,
   returning the      |
   |                   |    |              |        | value return     |
   |                   |    |              |        | SHOULD NOT be    |
   |                   |    |              |        | considered       |
   |                   |    |              |        | useful.          |
   | space_avail       | 42 | uint64       | READ   | Disk space in    |
   |                   |    |              |        | bytes available  |
   |                   |    |              |        | fileid stat() would have returned before any file
   systems were mounted on the mount point.

   Unlike NFSv3, NFSv4.0 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 user 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 filesystem   |
   |                   |    |              |        | containing this  |
   |                   |    |              |        | object - this    |
   |                   |    |              |        | should be mount point returning fileids as previously described.
   The mounted_on_fileid attribute corresponds to the    |
   |                   |    |              |        | smallest         |
   |                   |    |              |        | relevant limit.  |
   | space_free        | 43 | uint64       | READ   | Free disk space  |
   |                   |    |              |        | in bytes on fileid that
   readdir() would have returned as described previously.

   While the  |
   |                   |    |              |        | filesystem       |
   |                   |    |              |        | containing this  |
   |                   |    |              |        | object - this    |
   |                   |    |              |        | should be NFSv4.0 client could simply fabricate a fileid
   corresponding to what mounted_on_fileid provides (and if the    |
   |                   |    |              |        | smallest         |
   |                   |    |              |        | relevant limit.  |
   | space_total       | 44 | uint64       | READ   | Total disk space |
   |                   |    |              |        | 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 bytes on the  |
   |                   |    |              |        | filesystem       |
   |                   |    |              |        | containing file system.
   Instead, if the server can provide the mounted_on_fileid, the
   potential for client operational problems in this  |
   |                   |    |              |        | object.          |
   | space_used        | 45 | uint64       | READ   | Number 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        |
   |                   |    |              |        | filesystem bytes |
   |                   |    |              |        | allocated to     |
   |                   |    |              |        | this object.     |
   | system            | 46 | bool         | R/W    | True, 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    |
   |                   |    |              |        | file is
   straightforward.  Usually, mounted_on_fileid will be requested during
   a        |
   |                   |    |              |        | "system" file    |
   |                   |    |              |        | with respect READDIR operation, in which case it is trivial (at least for UNIX-
   based servers) to  |
   |                   |    |              |        | the Windows API. |
   | time_access       | 47 | nfstime4     | READ   | The time of last |
   |                   |    |              |        | access return mounted_on_fileid since it is equal to the    |
   |                   |    |              |        | object
   fileid of a directory entry returned by readdir().  If
   mounted_on_fileid is requested in a read |
   |                   |    |              |        | GETATTR operation, the server
   should obey an invariant that was         |
   |                   |    |              |        | satisfied by has it returning a value that is equal
   to the |
   |                   |    |              |        | server.          |
   | time_access_set   | 48 | settime4     | WRITE  | Set file object's entry in the time object's parent directory, i.e.
   what readdir() would have returned.  Some operating environments
   allow a series of  |
   |                   |    |              |        | last access two or more file systems to   |
   |                   |    |              |        | the object.      |
   |                   |    |              |        | SETATTR use      |
   |                   |    |              |        | only.            |
   | time_backup       | 49 | nfstime4     | R/W    | The time of last |
   |                   |    |              |        | backup of be mounted onto a
   single mount point.  In this case, for the    |
   |                   |    |              |        | object.          |
   | time_create       | 50 | nfstime4     | R/W    | The time of      |
   |                   |    |              |        | creation of server to obey the  |
   |                   |    |              |        | object. This     |
   |                   |    |              |        | attribute does   |
   |                   |    |              |        | not have any     |
   |                   |    |              |        | relation
   aforementioned invariant, it will need to find the  |
   |                   |    |              |        | traditional UNIX |
   |                   |    |              |        | file base mount point,
   and not the intermediate mount points.

5.8.2.20.  Attribute 34: no_trunc

   If this 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 is TRUE, then if the client uses a file name longer
   than name_max, an error will be returned instead of  |
   |                   |    |              |        | the object.      |
   | time_modify       | 53 | nfstime4     | READ   | The time name being
   truncated.

5.8.2.21.  Attribute 35: numlinks

   Number of last |
   |                   |    |              |        | modification hard links to  |
   |                   |    |              |        | the this object.      |
   | time_modify_set   | 54 | settime4     | WRITE  | Set the time

5.8.2.22.  Attribute 36: owner

   The string name of  |
   |                   |    |              |        | last             |
   |                   |    |              |        | modification to  |
   |                   |    |              |        | the owner of this object.      |
   |                   |    |              |        | SETATTR use      |
   |                   |    |              |        | only.            |
   | mounted_on_fileid | 55 | uint64       | READ   | Like fileid, but |
   |                   |    |              |        | if the target    |
   |                   |    |              |        | filehandle is    |
   |                   |    |              |        | the root

5.8.2.23.  Attribute 37: owner_group

   The string name of a    |
   |                   |    |              |        | filesystem       |
   |                   |    |              |        | return the       |
   |                   |    |              |        | fileid group ownership of the    |
   |                   |    |              |        | underlying       |
   |                   |    |              |        | directory.       |
   +-------------------+----+--------------+--------+------------------+

                                  Table 3

5.7.  Time Access

   As defined above, the time_access attribute this object.

5.8.2.24.  Attribute 38: quota_avail_hard

   The value in bytes which represents the time amount of
   last access to additional disk
   space beyond the object by a read current allocation that was satisfied by the server.
   The notion of what can be allocated to this
   file or directory before further allocations will be refused.  It is an "access" depends on server's operating
   environment and/or the server's filesystem semantics.  For example,
   for servers obeying POSIX semantics, time_access would
   understood that this space may be updated
   only consumed by the READLINK, READ, and READDIR operations allocations to other
   files or directories.

5.8.2.25.  Attribute 39: 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.

5.8.2.26.  Attribute 40: quota_used

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

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

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

5.8.2.27.  Attribute 41: rawdev

   Raw device identifier; the UNIX device major/minor node information.
   If the value of type is not NF4BLK or NF4CHR, the value returned
   SHOULD NOT be considered useful.

5.8.2.28.  Attribute 42: space_avail

   Disk space in bytes available to this user on the file system
   containing this object - this should be the smallest relevant limit.

5.8.2.29.  Attribute 43: space_free

   Free disk space in bytes on the file system containing this object -
   this should be the smallest relevant limit.

5.8.2.30.  Attribute 44: space_total

   Total disk space in bytes on the file system containing this object.

5.8.2.31.  Attribute 45: space_used

   Number of file system bytes allocated to this object.

5.8.2.32.  Attribute 46: system

   This attribute is TRUE if this file is a "system" file with respect
   to the Windows operating environment.

5.8.2.33.  Attribute 47: time_access

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

5.8.

5.8.2.34.  Attribute 48: time_access_set

   Set the time of last access to the object.  SETATTR use only.

5.8.2.35.  Attribute 49: time_backup

   The time of last backup of the object.

5.8.2.36.  Attribute 50: time_create

   The time of creation of the object.  This attribute does not have any
   relation to the traditional UNIX file attribute "ctime" or "change
   time".

5.8.2.37.  Attribute 51: time_delta

   Smallest useful server time granularity.

5.8.2.38.  Attribute 52: time_metadata

   The time of last metadata modification of the object.

5.8.2.39.  Attribute 53: time_modify

   The time of last modification to the object.

5.8.2.40.  Attribute 54: time_modify_set

   Set the time of last modification to the object.  SETATTR use only.

5.9.  Interpreting owner and owner_group

   The recommended 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 [24] RFC2624 [25]
   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". "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 identifier 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 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 needs to try to return that
   same string for which see below) when a corresponding GETATTR is
   done.  For some internationalization-related exceptions where this is
   not possible, see below.  Configuration changes and ill-constructed name translations (those that contain
   aliasing) may make that (including changes
   from the mapping of the string to the local representation) 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.

   As mentioned above, it is desirable that a server when accepting a
   string of the form user@domain or group@domain in an attribute,
   return this same string when that corresponding attribute is fetched.
   Internationalization issues (for a general discussion of which see
   Section 12) make this impossible and the client needs to take note of
   the following situations:

   o  The string representing the domain may be converted to equivalent
      U-label, if presented using a form other a a U-label.  See
      Section 12.6 for details.

   o  The user or group may be returned in a different form, due to
      normalization issues, although it will always be a canonically
      equivalent string.  See See Section 12.7.3 for details.

   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), NFSv3, which
   identified users and groups by 32-bit unsigned uid's user identifiers and gid's,
   group identifiers, 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 an NFSv3 uid or
   gid having the corresponding numeric value.  A server is not
   obligated to accept such a string, but may return an NFS4ERR_BADOWNER
   instead.  To avoid this mechanism being used to subvert user and
   group translation, so that a client might pass all of the owners and
   groups in numeric form, a server SHOULD return an NFS4ERR_BADOWNER
   error when there is a valid translation for the user or owner
   designated in this way.  In that case, the client must use the
   appropriate name@domain string and not the special form for
   compatibility.

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

5.9.

5.10.  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" [25] RFC1345 [26] which may or may not included include 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. storage, although
   there are variations that occur additional characters with a name
   including "SMALL" or "CAPITAL" are added in a subsequent version of
   Unicode.

   For general character handling and internationalization issues, see
   Section 1 "Internationalization".

5.10.  Quota Attributes 12.  For details regarding case mapping, see the section
   Case-based Mapping Used for Component4 Strings.

6.  Access Control Attributes

   Access Control Lists (ACLs) are file attributes related to filesystem quotas, the following
   definitions apply:

   quota_avail_soft  The value in bytes which represents the amount of
      additional disk space that can be allocated to this file or
      directory before specify fine
   grained access control.  This chapter covers the user may reasonably be warned.  It is
      understood "acl", "aclsupport",
   "mode", file attributes, and their interactions.  Note that this space file
   attributes may be consumed by allocations to other
      files or directories though there is a rule as apply to which other
      files or directories.

   quota_avail_hard  The value in bytes which any file system object.

6.1.  Goals

   ACLs and modes represent two well established models for specifying
   permissions.  This chapter specifies requirements that attempt to
   meet the amount of
      additional disk space beyond following goals:

   o  If a server supports the current allocation that can be
      allocated mode attribute, it should provide
      reasonable semantics to this file or directory before further allocations
      will be refused.  It is understood clients 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 only set and possibly retrieve the
      mode attribute.

   o  If a number of
      other similar files or directories, where server supports ACL attributes, it should provide reasonable
      semantics to clients that only set and retrieve those attributes.

   o  On servers that support the mode attribute, if ACL attributes have
      never been set of "similar"
      meets at least on an object, via inheritance or explicitly, the criterion
      behavior should be traditional UNIX-like behavior.

   o  On servers that allocating space to any file or
      directory in support the mode attribute, if the ACL attributes
      have been previously set will reduce on an object, either explicitly or via
      inheritance:

      *  Setting only the "quota_avail_hard" mode attribute should effectively control the
         traditional UNIX-like permissions of every
      other file or directory in read, write, and execute
         on owner, owner_group, and other.

      *  Setting only the set.

      Note that there may be mode attribute should provide reasonable
         security.  For example, setting a number of distinct but overlapping sets mode of files or directories 000 should be enough
         to ensure that future opens 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 read or write by any principal
         fail, regardless of those sets but should do
      so in a repeatable way.  The rule may be configured per-filesystem previously existing or inherited ACL.

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

5.11.  Access Control Lists new mode.

6.2.  File Attributes Discussion

6.2.1.  Attribute 12: acl

   The NFS version 4 NFSv4.0 ACL attribute is contains an array of access control entries
   (ACE).  Although,
   (ACEs) that are associated with the file system object.  Although the
   client can read and write the ACL acl attribute, the NFSv4 model is the server does all access control based on the
   server's interpretation of the ACL.  If at any point is
   responsible for using the client wants ACL to check perform access without issuing an operation that modifies or reads
   data or metadata, the control.  The client
   can use the OPEN and or ACCESS operations to do so.  There are various check access control entry types, as defined
   in the Section "ACE type".  The server is able to communicate which
   ACE types are supported by returning the appropriate value within the
   aclsupport attribute.  Each ACE covers one or more operations on a
   file without
   modifying or directory as described in the Section "ACE Access Mask".  It
   may also contain one reading data or more flags that modify the semantics of the
   ACE as defined in the Section "ACE flag". metadata.

   The NFS ACE attribute structure 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
           utf8_must       who;
   };

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

   Unlike the ALLOW and DENIED DENY ACE types, the ALARM and AUDIT ACE types do
   not affect a requester's access, and instead are for triggering
   events as a result of a requester's access attempt.  Therefore, all AUDIT
   and ALARM ACEs are processed until end of the
   ACL.  When the ACL is fully processed, if there are bits in
   requester's mask that have not been considered whether the server
   allows or denies the access is undefined.  If there is a mode
   attribute on the file, then this cannot happen, since the mode's
   MODE4_*OTH bits will map to EVERYONE@ ACEs that unambiguously specify
   the requester's access. only after processing ALLOW and DENY
   ACEs.

   The NFS version 4 NFSv4.0 ACL model is quite rich.  Some server platforms may
   provide access control functionality that goes beyond the UNIX-style
   mode attribute, but which is not as rich as the NFS ACL model.  So
   that users can take advantage of this more limited functionality, the
   server may indicate that it supports ACLs as long as it follows support the
   guidelines for acl attributes by mapping between its ACL
   model and the NFS version 4 NFSv4.0 ACL model.

   The situation  Servers must ensure that the ACL
   they actually store or enforce is complicated by at least as strict as the fact NFSv4 ACL
   that a server may have
   multiple modules was set.  It is tempting to accomplish this by rejecting any ACL
   that enforce ACLs.  For example, falls outside the enforcement for
   NFS version 4 access may small set that can be different from represented accurately.
   However, such an approach can render ACLs unusable without special
   client-side knowledge of the enforcement for local
   access, and both may be different from server's mapping, which defeats the enforcement for access
   through other protocols such as SMB.  So it may be useful for
   purpose of having a
   server to common NFSv4 ACL protocol.  Therefore servers
   should accept an every ACL even if not all of its modules are able to
   support it.

   The guiding principle in all cases is that they can without compromising security.
   To help accomplish this, servers may make a special exception, in the
   case of unsupported permission bits, to the rule that bits not
   ALLOWED or DENIED by an ACL must be denied.  For example, a UNIX-
   style server might choose to silently allow read attribute
   permissions even though an ACL does not explicitly allow those
   permissions.  (An ACL that explicitly denies permission to read
   attributes should still be rejected.)

   The situation is complicated by the fact that a server may have
   multiple modules that enforce ACLs.  For example, the enforcement for
   NFSv4.0 access may be different from, but not weaker than, the
   enforcement for local access, and both may be different from the
   enforcement for access through other protocols such as SMB.  So it
   may be useful for a server to accept an ACL even if not all of its
   modules are able to support it.

   The guiding principle with regard to NFSv4 access is that the server
   must not accept ACLs that appear to make access to the file more secure
   restrictive than it really is.

5.11.1.

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;
   All four but types are permitted in the acl attribute.

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

                                  Table 4
   +------------------------------+--------------+---------------------+

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

6.2.1.2.  Attribute 13: aclsupport

   A server need not support all of the above ACE types.  This attribute
   indicates which ACE types are supported for the current file system.
   The bitmask constants used to represent the above definitions within
   the aclsupport attribute are as follows:

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

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

   The constants used for

   Servers which support either the ALLOW or DENY ACE 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; SHOULD
   support both ALLOW and DENY ACE types.

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

   Example: suppose a server can enforce NFS ACLs

   Support 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 any of the server may indicate ACL support.

5.11.2. attributes is optional (albeit,
   RECOMMENDED).

6.2.1.3.  ACE Access Mask

   The access_mask field contains values based on the following:

   +-------------------+-----------------------------------------------+
   | Access            | Description                                   |
   +-------------------+-----------------------------------------------+
   | READ_DATA         | Permission to read the data of the file       |
   | LIST_DIRECTORY    | Permission to list the contents of a          |
   |                   | directory                                     |
   | WRITE_DATA        | Permission to modify the file's data          |
   | ADD_FILE          | Permission to add a new file to a directory   |
   | APPEND_DATA       | Permission to append data to a file           |
   | ADD_SUBDIRECTORY  | Permission to create a subdirectory to a      |
   |                   | directory                                     |
   | READ_NAMED_ATTRS  | Permission to read the named attributes of a  |
   |                   | file                                          |
   | WRITE_NAMED_ATTRS | Permission to write the named attributes of a |
   |                   | file                                          |
   | EXECUTE           | Permission to execute a file                  |
   | DELETE_CHILD      | Permission to delete a file or directory      |
   |                   | within a directory                            |
   | READ_ATTRIBUTES   | The ability to read basic attributes          |
   |                   | (non-acls) of a file                          |
   | WRITE_ATTRIBUTES  | Permission to change basic attributes         |
   |                   | (non-acls) of a file                          |
   | DELETE            | Permission to Delete the file                 |
   | READ_ACL          | Permission to Read the ACL                    |
   | WRITE_ACL         | Permission to Write the ACL                   |
   | WRITE_OWNER       | Permission to change the owner                |
   | SYNCHRONIZE       | Permission to access file locally at the      |
   |                   | server with synchronous reads and writes      |
   +-------------------+-----------------------------------------------+

                                  Table 5

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

   const ACE4_READ_DATA            = 0x00000001;
   const ACE4_LIST_DIRECTORY       = 0x00000001;
   const ACE4_WRITE_DATA           = 0x00000002;
   const ACE4_ADD_FILE             = 0x00000002;
   const ACE4_APPEND_DATA          = 0x00000004;
   const ACE4_ADD_SUBDIRECTORY     = 0x00000004;
   const ACE4_READ_NAMED_ATTRS     = 0x00000008;
   const ACE4_WRITE_NAMED_ATTRS    = 0x00000010;
   const ACE4_EXECUTE              = 0x00000020;
   const ACE4_DELETE_CHILD         = 0x00000040;
   const ACE4_READ_ATTRIBUTES      = 0x00000080;
   const ACE4_WRITE_ATTRIBUTES     = 0x00000100;

   const ACE4_DELETE               = 0x00010000;
   const ACE4_READ_ACL             = 0x00020000;
   const ACE4_WRITE_ACL            = 0x00040000;
   const ACE4_WRITE_OWNER          = 0x00080000;
   const ACE4_SYNCHRONIZE          = 0x00100000;

   Server implementations need not provide the granularity of control

   Note that is implied by this list of masks.  For some masks have coincident values, for example, POSIX-based
   systems might not distinguish APPEND_DATA (the ability to append
   ACE4_READ_DATA and ACE4_LIST_DIRECTORY.  The mask entries
   ACE4_LIST_DIRECTORY, ACE4_ADD_FILE, and ACE4_ADD_SUBDIRECTORY are
   intended to a
   file) from WRITE_DATA (the ability be used with directory objects, while ACE4_READ_DATA,
   ACE4_WRITE_DATA, and ACE4_APPEND_DATA are intended to modify existing contents); both
   masks would be tied used with
   non-directory objects.

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 single "write" permission.  When such a
   server returns attributes user the ability to read the client, it would show both
   APPEND_DATA and WRITE_DATA if and data of the
         file when only if the write permission ACE4_EXECUTE access mask bit is
   enabled.

   If a server receives 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 request that it cannot accurately
   implement, it should error in the direction of more restricted
   access.  For example, suppose size

      Discussion:

         Permission to modify a file's data.

   ACE4_ADD_FILE

      Operation(s) affected:

         CREATE
         LINK

         OPEN

         RENAME

      Discussion:

         Permission to add a server cannot distinguish overwriting
   data from appending new data, as described file in the previous paragraph.
   If a client submits an ACE where APPEND_DATA directory.  The CREATE
         operation is set but WRITE_DATA affected when nfs_ftype4 is NF4LNK, NF4BLK,
         NF4CHR, NF4SOCK, or NF4FIFO.  (NF4DIR is not (or vice versa), the server should reject the request with
   NFS4ERR_ATTRNOTSUPP.  Nonetheless, if the ACE has type DENY, the
   server may silently turn on the other bit, so that both APPEND_DATA
   and WRITE_DATA are denied.

5.11.3.  ACE flag

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

   ACE4_FILE_INHERIT_ACE  Can be placed on a directory and indicates
      that this ACE should be added listed because it
         is covered by ACE4_ADD_SUBDIRECTORY.)  OPEN is affected when
         used to each new non-directory file
      created.

   ACE4_DIRECTORY_INHERIT_ACE  Can be placed on create a directory regular file.  LINK and
      indicates that this ACE should be added RENAME are always
         affected.

   ACE4_APPEND_DATA

      Operation(s) affected:

         WRITE

         OPEN

         SETATTR of size

      Discussion:

         The ability to each new directory
      created.

   ACE4_INHERIT_ONLY_ACE  Can be placed on modify a directory file's data, but does not
      apply to the directory, only to newly created files/directories as
      specified starting at EOF.
         This allows for the notion of append-only files, by allowing
         ACE4_APPEND_DATA and denying ACE4_WRITE_DATA to the above two flags.

   ACE4_NO_PROPAGATE_INHERIT_ACE  Can be placed on a directory.
      Normally when same user
         or group.  If a new directory is created and file has an ACE exists on ACL such as the
      parent directory which one described above
         and a WRITE request is marked ACL4_DIRECTORY_INHERIT_ACE, two
      ACEs are placed on made for somewhere other than EOF, the new
         server SHOULD return NFS4ERR_ACCESS.

   ACE4_ADD_SUBDIRECTORY

      Operation(s) affected:

         CREATE

         RENAME

      Discussion:

         Permission to create a subdirectory in a directory.  One for the directory
      itself and one which  The CREATE
         operation is an inheritable ACE for newly created
      directories.  This flag tells affected when nfs_ftype4 is NF4DIR.  The RENAME
         operation is always affected.

   ACE4_READ_NAMED_ATTRS

      Operation(s) affected:

         OPENATTR

      Discussion:

         Permission to read the server named attributes of a file or to not place an ACE on lookup
         the newly created named attributes directory.  OPENATTR is affected when it
         is not used to create a named attribute directory.  This is
         when 1.) createdir is TRUE, but a named attribute directory which
         already exists, or 2.) createdir is inheritable by subdirectories
      of FALSE.

   ACE4_WRITE_NAMED_ATTRS

      Operation(s) affected:

         OPENATTR

      Discussion:

         Permission to write the created named attributes of a file or to create
         a named attribute directory.

   ACE4_SUCCESSFUL_ACCESS_ACE_FLAG

   ACL4_FAILED_ACCESS_ACE_FLAG  The ACE4_SUCCESSFUL_ACCESS_ACE_FLAG
      (SUCCESS) and ACE4_FAILED_ACCESS_ACE_FLAG (FAILED) flag bits
      relate only  OPENATTR is affected when it is
         used to ACE4_SYSTEM_AUDIT_ACE_TYPE (AUDIT) create a named attribute directory.  This is when
         createdir is TRUE and
      ACE4_SYSTEM_ALARM_ACE_TYPE (ALARM) ACE types.  If during the
      processing of the file's ACL, the server encounters an AUDIT no named attribute directory exists.  The
         ability to check whether or
      ALARM ACE that matches not a named attribute directory
         exists depends on the principal attempting ability to look it up, therefore, users
         also need the OPEN, ACE4_READ_NAMED_ATTRS permission in order to
         create a named attribute directory.

   ACE4_EXECUTE

      Operation(s) affected:

         READ

         OPEN

         REMOVE

         RENAME
         LINK

         CREATE

      Discussion:

         Permission to execute a file.

         Servers SHOULD allow a user the
      server notes that fact, and ability to read the presence, if any, data of the SUCCESS
      and FAILED flags encountered in
         file when only the AUDIT or ALARM ACE.  Once ACE4_EXECUTE access mask bit is allowed.
         This is because there is no way to execute a file without
         reading the contents.  Though a server completes the ACL processing, may treat ACE4_EXECUTE
         and ACE4_READ_DATA bits identically when deciding to permit a
         READ operation, it SHOULD still allow the share reservation
      processing, two bits to be set
         independently in ACLs, and MUST distinguish between them when
         replying to ACCESS operations.  In particular, servers SHOULD
         NOT silently turn on one of the OPEN call, two bits when the other is set,
         as that would make it then notes if impossible for the OPEN succeeded
      or failed.  If client to correctly
         enforce the OPEN succeeded, distinction between read and if execute permissions.

         As an example, following a SETATTR of the SUCCESS flag was set 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_EXECUTE

      Operation(s) affected:

         LOOKUP

      Discussion:

         Permission to traverse/search a matching AUDIT or ALARM, then the appropriate AUDIT directory.

   ACE4_DELETE_CHILD

      Operation(s) affected:

         REMOVE

         RENAME

      Discussion:

         Permission to delete a file or ALARM
      event occurs.  If the OPEN failed, and if the FAILED flag was set directory within a directory.
         See Section 6.2.1.3.2 for the matching AUDIT or ALARM, then the appropriate AUDIT or
      ALARM event occurs.  Clearly either or both information on ACE4_DELETE and
         ACE4_DELETE_CHILD interact.

   ACE4_READ_ATTRIBUTES

      Operation(s) affected:

         GETATTR of file system object attributes

         VERIFY

         NVERIFY

         READDIR

      Discussion:

         The ability to read basic attributes (non-ACLs) of a file.  On
         a UNIX system, basic attributes can be thought of as the SUCCESS or
      FAILED stat
         level attributes.  Allowing this access mask bit would mean the
         entity can execute "ls -l" and stat.  If a READDIR operation
         requests attributes, this mask must be set, but if neither is set, allowed for the AUDIT or ALARM ACE
      is not useful.

      The previously described processing applies READDIR
         to that succeed.

   ACE4_WRITE_ATTRIBUTES

      Operation(s) affected:

         SETATTR of the ACCESS
      operation as well.  The difference being that "success" time_access_set, time_backup,

         time_create, time_modify_set, mimetype, hidden, system

      Discussion:

         Permission to change the times associated with a file or
      "failure" does
         directory to an arbitrary value.  Also permission to change the
         mimetype, hidden and system attributes.  A user having
         ACE4_WRITE_DATA or ACE4_WRITE_ATTRIBUTES will be allowed to set
         the times associated with a file to the current server time.

   ACE4_DELETE

      Operation(s) affected:

         REMOVE

      Discussion:

         Permission to delete the file or directory.  See
         Section 6.2.1.3.2 for information on ACE4_DELETE and
         ACE4_DELETE_CHILD interact.

   ACE4_READ_ACL

      Operation(s) affected:

         GETATTR of acl

         NVERIFY

         VERIFY

      Discussion:

         Permission to read the ACL.

   ACE4_WRITE_ACL

      Operation(s) affected:

         SETATTR of acl and mode

      Discussion:

         Permission to write the acl and mode attributes.

   ACE4_WRITE_OWNER

      Operation(s) affected:

         SETATTR of owner and owner_group

      Discussion:

         Permission to write the owner and owner_group attributes.  On
         UNIX systems, this is the ability to execute chown() and
         chgrp().

   ACE4_SYNCHRONIZE

      Operation(s) affected:

         NONE

      Discussion:

         Permission to access file locally at the server with
         synchronized reads and writes.

   Server implementations need not mean whether ACCESS provide the granularity of control
   that is implied by this list of masks.  For example, POSIX-based
   systems might not distinguish ACE4_APPEND_DATA (the ability to append
   to a file) from ACE4_WRITE_DATA (the ability to modify existing
   contents); both masks would be tied to a single "write" permission.
   When such a server returns NFS4_OK attributes to the client, it would show
   both ACE4_APPEND_DATA and ACE4_WRITE_DATA if and only if the write
   permission is enabled.

   If a server receives a SETATTR request that it cannot accurately
   implement, it should err in the direction of more restricted access,
   except in the previously discussed cases of execute and read.  For
   example, suppose a server cannot distinguish overwriting data from
   appending new data, as described in the previous paragraph.  If a
   client submits an ALLOW ACE where ACE4_APPEND_DATA is set but
   ACE4_WRITE_DATA is not (or vice versa), the server should either turn
   off ACE4_APPEND_DATA or not.
      Success means whether ACCESS returns all requested reject the request with NFS4ERR_ATTRNOTSUPP.

6.2.1.3.2.  ACE4_DELETE vs. ACE4_DELETE_CHILD

   Two access mask bits govern the ability to delete a directory entry:
   ACE4_DELETE on the object itself (the "target"), and supported
      bits.  Failure means whether ACCESS failed
   ACE4_DELETE_CHILD on the containing directory (the "parent").

   Many systems also take the "sticky bit" (MODE4_SVTX) on a directory
   to allow unlink only to return a bit user that
      was requested and supported.

   ACE4_IDENTIFIER_GROUP  Indicates owns either the target or the
   parent; on some such systems the decision also depends on whether the
   target is writable.

   Servers SHOULD allow unlink if either ACE4_DELETE is permitted on the
   target, or ACE4_DELETE_CHILD is permitted on the parent.  (Note that
   this is true even if the "who" refers parent or target explicitly denies one of
   these permissions.)

   If the ACLs in question neither explicitly ALLOW nor DENY either of
   the above, and if MODE4_SVTX is not set on the parent, then the
   server SHOULD allow the removal if and only if ACE4_ADD_FILE is
   permitted.  In the case where MODE4_SVTX is set, the server may also
   require the remover to a GROUP as
      defined under UNIX. own either the parent or the target, or may
   require the target to be writable.

   This allows servers to support something close to traditional UNIX-
   like semantics, with ACE4_ADD_FILE taking the place of the write bit.

6.2.1.4.  ACE flag

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

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

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

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

5.11.4.

6.2.1.4.1.  Discussion of Flag Bits

   ACE4_FILE_INHERIT_ACE
      Any non-directory file in any sub-directory will get this ACE
      inherited.

   ACE4_DIRECTORY_INHERIT_ACE
      Can be placed on a directory and indicates that this ACE should be
      added to each new directory created.
      If this flag is set in an ACE in an ACL attribute to be set on a
      non-directory file system object, the operation attempting to set
      the ACL SHOULD fail with NFS4ERR_ATTRNOTSUPP.

   ACE4_INHERIT_ONLY_ACE
      Can be placed on a directory but does not apply to the directory;
      ALLOW and DENY ACEs with this bit set do not affect access to the
      directory, and AUDIT and ALARM ACEs with this bit set do not
      trigger log or alarm events.  Such ACEs only take effect once they
      are applied (with this bit cleared) to newly created files and
      directories as specified by the above two flags.
      If this flag is present on an ACE, but neither
      ACE4_DIRECTORY_INHERIT_ACE nor ACE4_FILE_INHERIT_ACE is present,
      then an operation attempting to set such an attribute SHOULD fail
      with NFS4ERR_ATTRNOTSUPP.

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

   ACE4_SUCCESSFUL_ACCESS_ACE_FLAG

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

      The previously described processing applies to ACCESS operations
      even when they return NFS4_OK.  For the purposes of AUDIT and
      ALARM, we consider an ACCESS operation to be a "failure" if it
      fails to return a bit that was requested and supported.

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

6.2.1.5.  ACE Who

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

   There are several special identifiers ("who") which need to be understood
   universally, rather than in the context of a particular DNS domain.
   Some of these identifiers cannot be understood when an NFS client
   accesses the server, but have meaning when a local process accesses
   the file.  The ability to display and modify these permissions is
   permitted over NFS, even if none of the access methods on the server
   understands the identifiers.

   +-----------------+------------------------------------------------+

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

                                  Table 6 4

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

5.11.5.  Mode Attribute

   The NFS version 4 mode attribute is based ACE4_IDENTIFIER_GROUP flag MUST be ignored on entries with these
   special identifiers.  When encoding entries with these special
   identifiers, the UNIX mode bits.  The
   following bits are defined:

   const MODE4_SUID = 0x800;  /* ACE4_IDENTIFIER_GROUP flag SHOULD be set user to zero.

6.2.1.5.1.  Discussion of EVERYONE@

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

6.2.2.  Attribute 33: mode

   The NFSv4.0 mode attribute is based on the UNIX mode bits.  The
   following bits are defined:

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

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

   The remaining bits

   Bits within the mode other than those specified above are not defined
   by this protocol and protocol.  A server MUST NOT be
   used. return bits other than those
   defined above in a GETATTR or READDIR operation, and it MUST return
   NFS4ERR_INVAL if bits other than those defined above are set in a
   SETATTR, CREATE, OPEN, VERIFY or NVERIFY operation.

6.3.  Common Methods

   The minor version mechanism must requirements in this section will be used referred to define further bit
   usage.

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

5.11.6.  Mode and future
   sections, especially Section 6.4.

6.3.1.  Interpreting an ACL Attribute

6.3.1.1.  Server Considerations

   The server that supports both mode and uses the algorithm described in Section 6.2.1 to determine
   whether an ACL must take care allows access to
   synchronize an object.  However, the MODE4_*USR, MODE4_*GRP, and MODE4_*OTH bits with ACL may not
   be the
   ACEs which have respective who fields sole determiner of "OWNER@", "GROUP@", and
   "EVERYONE@" so that the client can see semantically equivalent access
   permissions exist whether the client asks for owner, owner_group and
   mode attributes, or for just the ACL.

   Because access.  For example:

   o  In the mode attribute includes bits (e.g., MODE4_SVTX) that have
   nothing to do with ACL semantics, it is permitted for clients to
   specify both case of a file system exported as read-only, the server may
      deny write permissions even though an object's ACL attribute grants it.

   o  Server implementations MAY grant ACE4_WRITE_ACL and mode ACE4_READ_ACL
      permissions to prevent a situation from arising in the same SETATTR
   operation.  However, because which there is
      no prescribed order for
   processing the attributes in a SETATTR, the client must ensure that
   ACL attribute, if specified without mode, would produce the desired
   mode bits, and conversely, the mode attribute if specified without
   ACL, would produce valid way to ever modify the desired "OWNER@", "GROUP@", and "EVERYONE@"
   ACEs.

5.11.7.  mounted_on_fileid

   UNIX-based operating environments connect ACL.

   o  All servers will allow a filesystem into user the
   namespace by connecting (mounting) ability to read the filesystem onto data of the existing
      file object (the mount point, usually a directory) of an existing
   filesystem.  When when only the mount point's parent directory execute permission is read via an
   API like readdir(), granted (i.e.  If the return results are directory entries, each
   with a component name ACL
      denies the user the ACE4_READ_DATA access and a fileid.  The fileid of allows the mount point's
   directory entry user
      ACE4_EXECUTE, the server will be different from allow the fileid that user to read the stat()
   system call returns.  The stat() system call is returning data of
      the fileid file).

   o  Many servers have the notion of owner-override in which the root owner
      of the mounted filesystem, whereas readdir() object is returning
   the fileid stat() would have returned before any filesystems were
   mounted on allowed to override accesses that are denied by
      the mount point.

   Unlike NFS version 3, NFS version 4 allows a client's LOOKUP request ACL.  This may be helpful, for example, to cross other filesystems.  The client detects allow users
      continued access to open files on which the filesystem
   crossing whenever permissions have
      changed.

   o  Many servers have the filehandle argument notion of LOOKUP a "superuser" that has privileges
      beyond an fsid
   attribute different from ordinary user.  The superuser may be able to read or
      write data or metadata in ways that of the filehandle returned would not be permitted 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 the
      ACL.

6.3.1.2.  Client Considerations

   Clients SHOULD NOT do their own access checks based on readdir() of a mount
   point's parent and stat() of their
   interpretation the mount point returning fileids as
   previously described.  The mounted_on_fileid attribute corresponds to ACL, but rather use the fileid that readdir() would have returned as described
   previously.

   While OPEN and ACCESS operations
   to do access checks.  This allows the NFS version 4 client could simply fabricate a fileid
   corresponding to what mounted_on_fileid provides (and if act on the results of
   having the server
   does determine whether or not support mounted_on_fileid, the client has no choice), there
   is a risk that access should be granted
   based on its interpretation of the client ACL.

   Clients must be aware of situations in which an object's ACL will generate
   define a fileid that conflicts with
   one that is already assigned to another object in the filesystem.
   Instead, if certain access even though the server can provide the mounted_on_fileid, will not enforce it.
   In general, but especially in these situations, the
   potential for client operational problems needs to
   do its part in this area is eliminated.

   If the server detects that there is no mounted point at enforcement of access as defined by the target
   file object, then ACL.  To
   do this, the value for mounted_on_fileid that it returns is client MAY send the same as that appropriate ACCESS operation prior
   to servicing the request of the fileid attribute.

   The mounted_on_fileid attribute is RECOMMENDED, so user or application in order to
   determine whether the server SHOULD
   provide it if possible, and for a UNIX-based server, this is
   straightforward.  Usually, mounted_on_fileid will user or application should be requested during
   a READDIR operation, granted the
   access requested.  For examples 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, ACL may define accesses
   that the server
   should obey an invariant that has it returning doesn't enforce see Section 6.3.1.1.

6.3.2.  Computing a value that is equal Mode Attribute from an ACL

   The following method can be used to calculate the file object's entry in the object's parent directory, i.e.,
   what readdir() would have returned.  Some operating environments
   allow a series MODE4_R*, MODE4_W*
   and MODE4_X* bits of two or more filesystems to be mounted onto a single
   mount point.  In this case, mode attribute, based upon an ACL.

   First, for each of the server to obey the aforementioned
   invariant, it will need to find the base mount point, special identifiers OWNER@, GROUP@, and not
   EVERYONE@, evaluate the
   intermediate mount points.

6.  Filesystem Migration ACL in order, considering only ALLOW and Replication

   With DENY
   ACEs for the use of the recommended attribute "fs_locations", identifier EVERYONE@ and for the NFS
   version 4 server has a method identifier under
   consideration.  The result of providing filesystem migration or
   replication services.  For the purposes of migration and replication,
   a filesystem evaluation will be defined as all files an NFSv4 ACL
   mask showing exactly which bits are permitted to that share a given fsid
   (both major identifier.

   Then translate the calculated mask for OWNER@, GROUP@, and minor values are EVERYONE@
   into mode bits for, respectively, the same).

   The fs_locations attribute provides a list of filesystem locations.
   These locations are specified by providing user, group, and other, as
   follows:

   1.  Set the server name (either
   DNS domain read bit (MODE4_RUSR, MODE4_RGRP, or IP address) MODE4_ROTH) if and
       only if ACE4_READ_DATA is set in the path name representing the root of corresponding mask.

   2.  Set the filesystem.  Depending on write bit (MODE4_WUSR, MODE4_WGRP, or MODE4_WOTH) if and
       only if ACE4_WRITE_DATA and ACE4_APPEND_DATA are both set in the type of service being provided,
       corresponding mask.

   3.  Set the
   list will provide a new location execute bit (MODE4_XUSR, MODE4_XGRP, or a MODE4_XOTH), if
       and only if ACE4_EXECUTE is set of alternate locations for in the filesystem.  The client will use this information corresponding mask.

6.3.2.1.  Discussion

   Some server implementations also add bits permitted to redirect its
   requests named users
   and groups to the new server.

6.1.  Replication

   It is expected group bits (MODE4_RGRP, MODE4_WGRP, and
   MODE4_XGRP).

   Implementations are discouraged from doing this, because it has been
   found to cause confusion for users who see members of a file's group
   denied access that filesystem replication will be used in the case mode bits appear to allow.  (The presence of read-only data.  Typically, the filesystem will
   DENY ACEs may also lead to such behavior, but DENY ACEs are expected
   to be replicated on
   two or more servers. rarely used.)

   The fs_locations attribute will provide the
   list of these locations to the client.  On first access of same user confusion seen when fetching the
   filesystem, mode also results if
   setting the client should obtain mode does not effectively control permissions for the value
   owner, group, and other users; this motivates some of the fs_locations
   attribute.  If, in the future,
   requirements that follow.

6.4.  Requirements

   The server that supports both mode and ACL must take care to
   synchronize the client finds MODE4_*USR, MODE4_*GRP, and MODE4_*OTH bits with the server
   unresponsive,
   ACEs which have respective who fields of "OWNER@", "GROUP@", and
   "EVERYONE@" so that the client may attempt to use another server specified
   by fs_locations.

   If applicable, can see semantically equivalent access
   permissions exist whether the client must take the appropriate steps to recover
   valid filehandles from asks for owner, owner_group and
   mode attributes, or for just the new server.  This ACL.

   In this section, much is described in more
   detail in made of the following sections.

6.2.  Migration

   Filesystem migration is used to move a filesystem from one server methods in Section 6.3.2.  Many
   requirements refer to
   another.  Migration is typically used for a filesystem this section.  But note that is
   writable and has a single copy.  The expected use of migration is for
   load balancing or general resource reallocation.  The protocol does
   not specify how the filesystem will be moved between servers. methods have
   behaviors specified with "SHOULD".  This
   server-to-server transfer mechanism is left intentional, to avoid
   invalidating existing implementations that compute the server
   implementor.  However, the method used mode according
   to communicate the migration
   event between client withdrawn POSIX ACL draft (1003.1e draft 17), rather than by
   actual permissions on owner, group, and server is specified here.

   Once the servers participating in the migration have completed other.

6.4.1.  Setting the
   move of mode and/or ACL Attributes

6.4.1.1.  Setting mode and not ACL

   When any of the filesystem, nine low-order mode bits are subject to change,
   either because the error NFS4ERR_MOVED will be returned for
   subsequent requests received by mode attribute was set or because the original server.  The
   NFS4ERR_MOVED error is returned for all operations except PUTFH
   mode_set_masked attribute was set and
   GETATTR.  Upon receiving the NFS4ERR_MOVED error, mask included one or more
   bits from the client will
   obtain nine low-order mode bits, and no ACL attribute is
   explicitly set, the acl attribute must be modified in accordance with
   the updated value of those bits.  This must happen even if the fs_locations attribute.  The client will then
   use the contents value
   of the attribute low-order bits is the same after the mode is set as before.

   Note that any AUDIT or ALARM ACEs are unaffected by changes to redirect its requests the
   mode.

   In cases in which the permissions bits are subject to change, the
   specified server.  To facilitate acl
   attribute MUST be modified such that the use mode computed via the method
   in Section 6.3.2 yields the low-order nine bits (MODE4_R*, MODE4_W*,
   MODE4_X*) of GETATTR, operations such the mode attribute as PUTFH must modified by the attribute change.
   The ACL attributes SHOULD also be accepted by modified such that:

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

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

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

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

   Note that if the server returns NFS4ERR_MOVED, ACEs with the server MUST support flag ACE4_INHERIT_ONLY_ACE set do not affect
   the fs_locations attribute.

   If permissions of the client requests more attributes than just fs_locations, ACL itself, nor do ACEs of the
   server may return fs_locations only.  This type AUDIT and
   ALARM.  As such, it is desirable to be expected since leave these ACEs unmodified when
   modifying the server has migrated ACL attributes.

   Also note that the filesystem and requirement may not have a method of
   obtaining additional attribute data.

   The server implementor needs to be careful met by discarding the acl in developing a migration
   solution.  The server must consider all
   favor of an ACL that represents the state information
   clients may have outstanding at mode and only the server. mode.  This includes is
   permitted, but it is not
   limited to locking/share state, delegation state, and asynchronous
   file writes which are represented by WRITE and COMMIT verifiers.  The preferable for a server should strive to minimize the impact on its clients during and
   after the migration process.

6.3.  Interpretation preserve as much of
   the fs_locations Attribute

   The fs_location attribute is structured in ACL as possible without violating the following way:

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

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

   The fs_location struct is used to represent above requirements.
   Discarding the location of ACL makes it effectively impossible for a
   filesystem by providing file created
   with a server name and the path mode attribute to inherit an ACL (see Section 6.4.3).

6.4.1.2.  Setting ACL and not mode

   When setting the root of acl and not setting the
   filesystem.  For a multi-homed server mode or a set of servers that use mode_set_masked
   attributes, the same rootpath, an array permission bits of server names may the mode need to be provided.  An
   entry in derived from
   the server array is an UTF8 string and represents one of a
   traditional DNS host name, IPv4 address, or IPv6 address.  It is not
   a requirement that all servers that share ACL.  In this case, the same rootpath ACL attribute SHOULD be listed
   in one fs_location struct. set as given.
   The array nine low-order bits of server names is provided for
   convenience.  Servers that share the same rootpath may also mode attribute (MODE4_R*, MODE4_W*,
   MODE4_X*) MUST be listed
   in separate fs_location entries in modified to match the fs_locations attribute.

   The fs_locations struct and attribute then contains an array result of
   locations.  Since the name space method
   Section 6.3.2.  The three high-order bits of each server may be constructed
   differently, the "fs_root" field is provided.  The path represented
   by fs_root represents mode (MODE4_SUID,
   MODE4_SGID, MODE4_SVTX) SHOULD remain unchanged.

6.4.1.3.  Setting both ACL and mode

   When setting both the location mode (includes use of either the filesystem mode attribute
   or the mode_set_masked attribute) and the acl attribute in the server's
   name space.  Therefore, same
   operation, the fs_root path attributes MUST be applied in this order: mode (or
   mode_set_masked), then ACL.  The mode-related attribute is only associated with the
   server from which set as
   given, then the fs_locations ACL attribute was obtained.  The
   fs_root path is meant to aid set as given, possibly changing the client
   final mode, as described above in locating the filesystem at Section 6.4.1.2.

6.4.2.  Retrieving the various mode and/or ACL Attributes

   This section applies only to servers listed.

   As an example, there is that support both the mode and
   ACL attributes.

   Some server implementations may have a replicated filesystem located at two
   servers (servA concept of "objects without
   ACLs", meaning that all permissions are granted and servB).  At servA denied according
   to the filesystem mode attribute, and that no ACL attribute is located at
   path "/a/b/c".  At servB the filesystem stored for that
   object.  If an ACL attribute is located at path "/x/y/z".
   In this example the client accesses the filesystem first at servA
   with a multi-component lookup path requested of "/a/b/c/d".  Since the client
   used such a multi-component lookup to obtain server, the filehandle at "/a/b/c/d",
   it is unaware
   server SHOULD return an ACL that does not conflict with the filesystem's root mode;
   that is located in servA's name
   space at "/a/b/c".  When the client switches to servB, it will need to determine that say, the directory it first referenced at servA is now
   represented by ACL returned SHOULD represent the path "/x/y/z/d" on servB.  To facilitate this, nine low-order
   bits of the
   fs_locations mode attribute provided by servA would have a fs_root value
   of "/a/b/c" and two entries in fs_location.  One entry (MODE4_R*, MODE4_W*, MODE4_X*) as
   described in fs_location
   will be for itself (servA) and the Section 6.3.2.

   For other will be for servB with a
   path of "/x/y/z".  With this information, server implementations, the client ACL attribute is able to
   substitute "/x/y/z" always present
   for the "/a/b/c" every object.  Such servers SHOULD store at least the beginning three high-
   order bits of its access
   path the mode attribute (MODE4_SUID, MODE4_SGID,
   MODE4_SVTX).  The server SHOULD return a mode attribute if one is
   requested, and construct "/x/y/z/d" to use for the new server.

   See low-order nine bits of the mode (MODE4_R*,
   MODE4_W*, MODE4_X*) MUST match the result of applying the method in
   Section 16 "Security Considerations" for 6.3.2 to the ACL attribute.

6.4.3.  Creating New Objects

   If a discussion on server supports any ACL attributes, it may use the
   recommendations for ACL
   attributes on the security flavor parent directory to compute an initial ACL
   attribute for a newly created object.  This will be used by any GETATTR
   operation that requests referred to as
   the "fs_locations" attribute.

6.4.  Filehandle Recovery for Migration or Replication

   Filehandles for filesystems that are replicated inherited ACL within this section.  The act of adding one or migrated generally
   have more
   ACEs to the same semantics as for filesystems inherited ACL that are not replicated or
   migrated.  For example, if a filesystem has persistent filehandles
   and it is migrated to another server, the filehandle values for based upon ACEs in the
   filesystem parent
   directory's ACL will be valid at the new server.

   For volatile filehandles, the servers involved likely do not have a
   mechanism referred to transfer filehandle format and content between
   themselves.  Therefore, a server may have difficulty in determining
   if a volatile filehandle from as inheriting an old server ACE within this
   section.

   Implementors should return an error of
   NFS4ERR_FHEXPIRED.  Therefore, the client is informed, with standardize on what the use behavior of CREATE and
   OPEN must be depending on the fh_expire_type attribute, whether volatile filehandles will
   expire at the migration presence or replication event. absence of the mode and ACL
   attributes.

   1.  If just the bit
   FH4_VOL_MIGRATION mode is set given in the fh_expire_type attribute, call:

       In this case, inheritance SHOULD take place, but the client
   must treat mode MUST be
       applied to the volatile filehandle inherited ACL as if the server had returned described in Section 6.4.1.1,
       thereby modifying the
   NFS4ERR_FHEXPIRED error.  At ACL.

   2.  If just the migration or replication event ACL is given in the presence of call:

       In this case, inheritance SHOULD NOT take place, and the FH4_VOL_MIGRATION bit, ACL as
       defined in the client CREATE or OPEN will not
   present be set without modification,
       and the original or old volatile filehandle to mode modified as in Section 6.4.1.2

   3.  If both mode and ACL are given in the new server.
   The client call:

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

   4.  If neither mode nor ACL are given in the new server by
   recovering its filehandles using call:

       In the saved file names.

7.  NFS Server Name Space

7.1.  Server Exports

   On case where an object is being created without any initial
       attributes at all, e.g. an OPEN operation with an opentype4 of
       OPEN4_CREATE and a UNIX server createmode4 of EXCLUSIVE4, inheritance SHOULD
       NOT take place.  Instead, the name space describes server SHOULD set permissions to
       deny all access to the files reachable by
   pathnames under newly created object.  It is expected that
       the root directory or "/".  On a Windows NT server appropriate client will set the name space constitutes all desired attributes in a
       subsequent SETATTR operation, and the files on disks named by mapped
   disk letters.  NFS server administrators rarely make the entire
   server's filesystem name space available SHOULD allow that
       operation to NFS clients.  More often
   portions succeed, regardless of what permissions the name space are made available via object
       is created with.  For example, an "export"
   feature.  In previous versions of empty ACL denies all
       permissions, but the NFS protocol, server should allow the root
   filehandle for each export owner's SETATTR to
       succeed even though WRITE_ACL is obtained through the MOUNT protocol; implicitly denied.

       In other cases, inheritance SHOULD take place, and no
       modifications to the client sends a string that identifies ACL will happen.  The mode attribute, if
       supported, MUST be as computed in Section 6.3.2, with the export of name space
       MODE4_SUID, MODE4_SGID and MODE4_SVTX bits clear.  If no
       inheritable ACEs exist on the server returns parent directory, the root filehandle rules for it.
       creating acl attributes are implementation defined.

6.4.3.1.  The MOUNT
   protocol supports an EXPORTS procedure that will enumerate Inherited ACL

   If the
   server's exports.

7.2.  Browsing Exports

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

   This style of browsing object being created is not well supported by the NFS version 2 and
   3 protocols.  The client expects all LOOKUP operations to remain
   within a single server filesystem.  For example, directory, the device attribute
   will not change.  This prevents a client inherited ACL
   SHOULD NOT inherit ACEs from taking name space paths
   that span exports.

   An automounter on the client can obtain a snapshot of parent directory ACL unless the server's
   name space using
   ACE4_FILE_INHERIT_FLAG is set.

   If the EXPORTS procedure of object being created is a directory, the MOUNT protocol. inherited ACL should
   inherit all inheritable ACEs from the parent directory, those that
   have ACE4_FILE_INHERIT_ACE or ACE4_DIRECTORY_INHERIT_ACE flag set.
   If it
   understands the server's pathname syntax, it can create an image of inheritable ACE has ACE4_FILE_INHERIT_ACE set, but
   ACE4_DIRECTORY_INHERIT_ACE is clear, the server's name space inherited ACE on the client.  The parts of newly
   created directory MUST have the name space
   that are not exported ACE4_INHERIT_ONLY_ACE flag set to
   prevent the directory from being affected by ACEs meant for non-
   directories.

   When a new directory is created, the server are filled in MAY split any inherited
   ACE which is both inheritable and effective (in other words, which
   has neither ACE4_INHERIT_ONLY_ACE nor ACE4_NO_PROPAGATE_INHERIT_ACE
   set), into two ACEs, one with a "pseudo
   filesystem" that allows the user to browse from no inheritance flags, and one mounted
   filesystem to another.  There is a drawback with
   ACE4_INHERIT_ONLY_ACE set.  This makes it simpler to this representation of modify the server's name space
   effective permissions on the client: it is static.  If the server
   administrator adds a new export directory without modifying the client will ACE
   which is to be unaware of it.

7.3.  Server Pseudo Filesystem

   NFS version 4 servers avoid this name space inconsistency by
   presenting all inherited to the exports within new directory's children.

7.  Multi-Server Namespace

   NFSv4 supports attributes that allow a namespace to extend beyond the framework
   boundaries of a single server
   name space.  An NFS version 4 client uses LOOKUP server.  It is RECOMMENDED that clients and READDIR
   operations to browse seamlessly from one export to another.  Portions
   servers support construction of the server name space that are not exported such multi-server namespaces.  Use of
   such multi-server namespaces is OPTIONAL however, and for many
   purposes, single-server namespace are bridged via a
   "pseudo filesystem" that provides a view perfectly acceptable.  Use of exported directories
   only.  A pseudo filesystem has
   multi-server namespaces can provide many advantages, however, by
   separating a unique fsid and behaves like file system's logical position in a
   normal, read only filesystem.

   Based on namespace from the construction
   (possibly changing) logistical and administrative considerations that
   result in particular file systems being located on particular
   servers.

7.1.  Location Attributes

   NFSv4 contains RECOMMENDED attributes that allow file systems on one
   server to be associated with one or more instances of the server's name space, it is possible that multiple pseudo filesystems may exist.  For example,

   /a         pseudo filesystem
   /a/b       real filesystem
   /a/b/c     pseudo filesystem
   /a/b/c/d   real filesystem
   Each of the pseudo filesystems are considered separate entities and
   therefore will have file
   system on other servers.  These attributes specify such file system
   instances by specifying a unique fsid.

7.4.  Multiple Roots

   The DOS and Windows operating environments are sometimes described as
   having "multiple roots".  Filesystems are commonly represented server address target (either as
   disk letters.  MacOS represents filesystems a DNS name
   representing one or more IP addresses or as top level names.  NFS
   version 4 servers for these platforms can construct a pseudo literal IP address)
   together with the path of that file system above these root names so that disk letters or volume names
   are simply directory names in within the pseudo root.

7.5.  Filehandle Volatility associated
   single-server namespace.

   The nature fs_locations RECOMMENDED attribute allows specification of the server's pseudo filesystem is that it is
   file system locations where the data corresponding to a logical
   representation given file
   system may be found.

7.2.  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 filesystem(s) available from file system instance
   locations associated with it via the server.
   Therefore, fs_locations attribute.  There
   may also be an actual current file system at that location,
   accessible via normal namespace operations (e.g.  LOOKUP).  In this
   case, the pseudo filesystem file system is most likely constructed
   dynamically when said to be "present" at that position in the server
   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 first instantiated.  It no longer available.

   When there is expected
   that no actual file system at the pseudo filesystem may not have an on disk counterpart from
   which persistent filehandles could be constructed.  Even though it namespace location in
   question, the file system is
   preferable said to be "absent".  An absent file
   system contains no files or directories other than the root.  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 provide persistent filehandles for ever returns the
   pseudo filesystem, error
   NFS4ERR_MOVED, it MUST support the NFS client should expect fs_locations attribute.

   While the error name suggests that pseudo we have a case of a file system filehandles are volatile.  This can be confirmed by checking
   the associated "fh_expire_type" attribute for those filehandles
   which once was present, and has only become absent later, this is
   only one possibility.  A position in
   question.  If the filehandles are volatile, the NFS client must namespace may be
   prepared to recover a filehandle value (e.g., permanently
   absent with a multi-component
   LOOKUP) when receiving the set of file system(s) designated by the location
   attributes being 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 NFS4ERR_FHEXPIRED.

7.6.  Exported Root

   If GETATTR-type operations (to be discussed
   later), when the server's root filesystem current filehandle at the start of an operation is exported, one might conclude
   within an absent file system, that
   a pseudo-filesystem operation is not needed.  This would be wrong.  Assume performed and the
   following filesystems
   error NFS4ERR_MOVED returned, to indicate that the file system is
   absent on a server:

   /       disk1  (exported)
   /a      disk2  (not exported)
   /a/b    disk3  (exported) the current server.

   Because disk2 is not exported, disk3 a GETFH cannot be reached with simple
   LOOKUPs.  The server must bridge succeed if the gap with a pseudo-filesystem.

7.7.  Mount Point Crossing

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

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

   The pseudo filesystem for this server may within an
   absent file system, filehandles within an absent file system cannot
   be constructed to look
   like:

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

   It is the server's responsibility to present the pseudo filesystem
   that is complete transferred to the client.  If the client sends  When a lookup request
   for the path "/a/b/c/d", the server's response client does have filehandles
   within an absent file system, it is the filehandle result of obtaining them when
   the filesystem "/a/b/c/d".  In previous versions of file system was present, and having the NFS protocol, file system become absent
   subsequently.

   It should be noted that because the server would respond with check for the current filehandle of directory "/a/b/c/d"
   being within an absent file system happens at the filesystem "/a/b".

   The NFS client will be able to determine if it crosses a server mount
   point by a change in the value start of every
   operation, operations that change the "fsid" attribute.

7.8.  Security Policy 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 Name Space Presentation

   The application of the server's security policy needs LOOKUP-GETATTR to be carefully
   considered by the implementor.  One may choose
   used to limit the
   viewability of portions of the pseudo filesystem based on the
   server's perception of get attribute information, particularly location attribute
   information, as discussed below.

7.3.  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's ability client access to authenticate itself
   properly.  However, with the support small set of multiple security mechanisms
   attributes that are available, and most particularly that which gives
   information about the ability to negotiate correct current locations for this file system,
   fs_locations.

7.3.1.  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 appropriate use of these mechanisms, attribute mask contains
   at least the server fs_locations attribute bit, which indicates the client
   is unable to properly determine if interested in a client result regarding an absent file system.  If it is
   not requested, GETATTR will be able
   to authenticate itself.  If, based result in an NFS4ERR_MOVED error.

   When a GETATTR is done on its policies, the server
   chooses to limit an absent file system, the contents set of the pseudo filesystem, the server
   may effectively hide filesystems from a client supported
   attributes is very limited.  Many attributes, including those that may otherwise
   have legitimate access.

   As suggested practice,
   are normally REQUIRED, will not be available on an absent file
   system.  In addition to the server should apply fs_locations attribute, the security policy of
   a shared resource following
   attributes SHOULD be available on absent file systems, in the server's namespace case of
   RECOMMENDED attributes at least to the components of same degree that they are
   available on present file systems.

   fsid:  This attribute should be provided so that the
   resource's ancestors.  For example:

   /
   /a/b
   /a/b/c

   The /a/b/c directory is a real filesystem and is the shared resource.
   The security policy for /a/b/c is Kerberos with integrity.  The
   server should apply client can
      determine file system boundaries, including, in particular, the same security policy to /, /a,
      boundary between present and /a/b. absent file systems.  This allows for the extension of the protection of value must
      be different from any other fsid on the server's
   namespace current server and need
      have no particular relationship to the ancestors of the real shared resource.

   For the case of the use of multiple, disjoint security mechanisms in
   the server's resources, the security for a fsids on any particular object in
      destination to which the
   server's namespace should client might be directed.

   mounted_on_fileid:  For objects at the union of all security mechanisms top of
   all direct descendants.

8.  File Locking and Share Reservations

   Integrating locking into the NFS protocol necessarily causes it an absent file system
      this attribute needs to be
   stateful.  With the inclusion of share reservations available.  Since the protocol
   becomes substantially more dependent on state than fileid is one
      which is within the traditional
   combination of NFS and NLM [26].  There are three components present parent file system, there should be no
      need to
   making this state manageable:

   o  Clear division between client and server

   o  Ability reference the absent file system to reliably detect inconsistency in state between client
      and server

   o  Simple and robust recovery mechanisms

   In provide this model, the server owns the state
      information.  The client
   communicates its view of this state to the server as needed.  The
   client is also able to detect inconsistent state before modifying a
   file.

   To support Win32 share reservations

   Other attributes SHOULD NOT be made available for absent file
   systems, even when it is necessary possible to atomically
   OPEN or CREATE files.  Having provide them.  The server should
   not assume that more information is always better and should avoid
   gratuitously providing additional information.

   When a separate share/unshare GETATTR operation
   would includes a bit mask for the attribute
   fs_locations, but where the bit mask includes attributes which are
   not allow correct implementation supported, GETATTR will not return an error, but will return the
   mask of the Win32 OpenFile API.  In
   order to correctly implement share semantics, actual attributes supported with the previous NFS
   protocol mechanisms used when a file results.

   Handling of VERIFY/NVERIFY is opened or created (LOOKUP,
   CREATE, ACCESS) need similar to be replaced.  The NFS version 4 protocol has
   an OPEN operation GETATTR in that subsumes if the NFS version 3 methodology
   attribute mask does not include fs_locations the error NFS4ERR_MOVED
   will result.  It differs in that any appearance in the attribute mask
   of
   LOOKUP, CREATE, an attribute not supported for an absent file system (and note
   that this will include some normally REQUIRED attributes), will also
   cause an NFS4ERR_MOVED result.

7.3.2.  READDIR and ACCESS.  However, because many operations require
   a filehandle, Absent File Systems

   A READDIR performed when the traditional LOOKUP current filehandle is preserved to map a within an absent
   file name
   to filehandle without establishing state on system will result in an NFS4ERR_MOVED error, since, unlike the server.  The policy
   case of granting access or modifying files GETATTR, no such exception is managed by 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 server based
   on root directories of one or more absent file systems.  In this
   case, the client's state.  These mechanisms can implement policy ranging
   from advisory only locking to full mandatory locking.

8.1.  Locking

   It is assumed that manipulating a lock handling is rare when compared to READ as follows:

   o  If the attribute set requested includes fs_locations, then
      fetching of attributes proceeds normally and WRITE operations.  It no NFS4ERR_MOVED
      indication is also assumed that crashes and network
   partitions are relatively rare.  Therefore it returned, even when the rdattr_error attribute is important that
      requested.

   o  If the
   READ and WRITE operations have a lightweight mechanism to indicate attribute set requested does not include fs_locations, then
      if
   they possess a held lock.  A lock request contains the heavyweight
   information required to establish a lock and uniquely define the lock
   owner.

   The following sections describe the transition from rdattr_error attribute is requested, each directory entry
      for the heavy weight
   information to root of an absent file system, will report NFS4ERR_MOVED
      as the eventual stateid used for most client and server
   locking and lease interactions.

8.1.1.  Client ID

   For each LOCK request, value of the client must identify itself to rdattr_error attribute.

   o  If the server.

   This is done in such a way as to allow for correct lock
   identification and crash recovery.  A sequence attribute set requested does not include either of a SETCLIENTID
   operation followed by a SETCLIENTID_CONFIRM operation is required to
   establish the identification onto
      attributes fs_locations or rdattr_error then the server.  Establishment occurrence of
   identification by a new incarnation the
      root of an absent file system within the client also has directory will result in
      the effect READDIR failing with an NFS4ERR_MOVED error.

   o  The unavailability of an attribute because of immediately breaking any leased state that a previous incarnation file system's
      absence, even one that is ordinarily REQUIRED, does not result in
      any error indication.  The set of the client might have had on the server, as opposed to forcing the
   new client incarnation to wait attributes returned for the leases to expire.  Breaking
   the lease state amounts to the server removing all lock, share
   reservation, and, where root
      directory of the server absent file system in that case is not supporting the
   CLAIM_DELEGATE_PREV claim type, all delegation state associated with
   same client simply
      restricted to those actually available.

7.4.  Uses of Location Information

   The location-bearing attribute of fs_locations provides, together
   with the same identity.  For discussion possibility of delegation
   state recovery, see Section 9.2.1 "Delegation Recovery".

   Client identification is encapsulated absent file systems, a number of important
   facilities in the following structure:

   struct SETCLIENTID4args {
           nfs_client_id4  client;
           cb_client4      callback;
           uint32_t        callback_ident;
   };

   The first field, verifier is providing reliable, manageable, and scalable data
   access.

   When a client incarnation verifier that file system is present, these attributes can provide
   alternative locations, to be used to detect client reboots.  Only if access the verifier is different
   from that which same data, in the
   event of server has previously recorded failures, communications problems, or other
   difficulties that make continued access to the client (as
   identified by current file system
   impossible or otherwise impractical.  Under some circumstances
   multiple alternative locations may be used simultaneously to provide
   higher performance access to the second field file system in question.  Provision
   of the structure, id) does the server
   start the process such alternate locations is referred to as "replication" although
   there are cases in which replicated sets of canceling data are not in fact
   present, and the client's leased state.

   The second field, id is a variable length string that uniquely
   defines the client.

   There replicas are several considerations for how the client generates the id
   string:

   o  The string should be unique so that multiple clients do not
      present instead different paths to the same string.  The consequences of two
   data.

   When a file system is present and becomes absent, clients
      presenting can be
   given the same string range from one client getting opportunity to have continued access to their data, at an error
   alternate location.  In this case, a continued attempt to one client having its leased state abruptly use the
   data in the now-absent file system will result in an NFS4ERR_MOVED
   error and unexpectedly
      canceled.

   o  The string should be selected so at that point the subsequent incarnations
      (e.g., reboots) successor locations (typically only one
   but multiple choices are possible) can be fetched and used to
   continue access.  Transfer of the same client cause the client file system contents to present the
      same string.  The implementor new
   location is cautioned against an approach
      that requires the string referred to as "migration", but it should be recorded 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 local file because
      this precludes the use system was not previously present, specification of the implementation file
   system location provides a means by which file systems located on one
   server can be associated with a namespace defined by another server,
   thus allowing a general multi-server namespace facility.  A
   designation of such a location, in place of an environment
      where there is no local disk and all absent file access system, is from an NFS
      version 4 server.

   o  The string should be different for each server network address
      that the
   called a "referral".

   Because client accesses, rather than common to all server network
      addresses.  The reason support for location-related attributes is that it OPTIONAL, a
   server may (but is not be possible required to) take action to hide migration and
   referral events from such clients, by acting as a proxy, for the
      client example.

7.4.1.  File System Replication

   The fs_locations attribute provides alternative locations, to be used
   to access data in place of or in addition to tell if the same server is listening on multiple network
      addresses.  If current file system
   instance.  On first access to a file system, the client issues SETCLIENTID with should obtain
   the same id
      string to each network address value of such a server, the server will
      think it is set of alternate locations by interrogating the same client, and each successive SETCLIENTID will
      cause
   fs_locations attribute.

   In the event that server failures, communications problems, or other
   difficulties make continued access to begin the process of removing current file system
   impossible or otherwise impractical, the client's
      previous leased state.

   o  The algorithm for generating client can use the string should not assume that alternate
   locations as a way to get continued access to its data.  Multiple
   locations may be used simultaneously, to provide higher performance
   through the
      client's network address won't change.  This includes changes exploitation of multiple paths between client incarnations and even changes while the client is
      stilling running in its current incarnation.  This means that if target
   file system.

   The alternate locations may be physical replicas of the client includes just (typically
   read-only) file system data, or they may reflect alternate paths to
   the client's and server's network address
      in same server or provide for the id string, there is a real risk, after the client gives up
      the network address, that another client, using a similar
      algorithm for generating use of various forms of server
   clustering in which multiple servers provide alternate ways of
   accessing the id string, will generate same physical file system.

   Multiple server addresses, whether they are derived from a
      conflicting id string.

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

   o  The server's network address.

   o  The client's network address.

   o  For DNS name representing a user level NFS version 4 client, it should contain
      additional information to distinguish the client set of IP addresses, or from other user
      level clients running on
   multiple entries each with its own server address may correspond to
   the same host, such as actual server.

7.4.2.  File System Migration

   When a process id or
      other unique sequence.

   o  Additional information that tends to file system is present and becomes absent, clients can be unique, such
   given the opportunity to have continued access to their data, at an
   alternate location, as one or
      more of:

      *  The specified by the fs_locations attribute.
   Typically, a client machine's serial number (for privacy reasons, it is
         best will be accessing the file system in question,
   get an NFS4ERR_MOVED error, and then use the fs_locations attribute
   to perform some one way function on determine the serial number).

      *  A MAC address.

      *  The timestamp new location of when the NFS version 4 software was first
         installed on data.

   Such migration can be helpful in providing load balancing or general
   resource reallocation.  The protocol does not specify how the client (though this file
   system will be moved between servers.  It is subject to the
         previously mentioned caution about using information anticipated that is
         stored in a file, because the file
   number of different server-to-server transfer mechanisms might only be accessible
         over NFS version 4).

      *  A true random number.  However since this number ought
   used with the choice left to be the same server implementer.  The NFSv4
   protocol specifies the method used to communicate the migration event
   between client incarnations, this shares and server.

   The new location may be an alternate communication path to the same
         problem as that of the using
   server, or, in the timestamp case of various forms of the software
         installation.

   As a security measure, the server MUST NOT cancel a client's leased
   state if clustering,
   another server providing access to the principal established same physical file system.

   When an alternate location is designated as the state target for a given id string is
   not migration,
   it must designate the same as the principal issuing data.  Where file systems are writable, a
   change made on the SETCLIENTID.

   Note that SETCLIENTID and SETCLIENTID_CONFIRM has original file system must be visible on all
   migration targets.  Where a secondary purpose file system is not writable but
   represents a read-only copy (possibly periodically updated) of establishing the information the server needs to make callbacks a
   writable file system, similar requirements apply to the client for purpose propagation
   of supporting delegations.  It is permitted to updates.  Any change this information via SETCLIENTID and SETCLIENTID_CONFIRM
   within the same incarnation of visible in the original file system must
   already be effected on all migration targets, to avoid any
   possibility, that a client without removing in effecting a transition to the
   client's leased migration
   target will see any reversion in file system state.

   Once

7.4.3.  Referrals

   Referrals provide a SETCLIENTID and SETCLIENTID_CONFIRM sequence has successfully
   completed, the client uses the shorthand client identifier, of type
   clientid4, instead way of the longer and less compact nfs_client_id4
   structure.  This shorthand client identifier (a clientid) is assigned
   by the server and should be chosen so that it will not conflict with placing a clientid previously assigned by file system in a location within
   the namespace essentially without respect to its physical location on
   a given server.  This applies across allows a single server restarts or reboots.  When a clientid is presented set of servers to
   present a server
   and multi-server namespace that clientid is not recognized, as would happen after 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 server
   reboot, the server will reject truly global namespace.

   Referrals occur when a client determines, upon first referencing a
   position in the request with current namespace, that it is part of a new file
   system and that the error
   NFS4ERR_STALE_CLIENTID. file system is absent.  When this happens, the client must obtain a
   new clientid occurs,
   typically by use receiving the error NFS4ERR_MOVED, the actual location
   or locations of the SETCLIENTID operation and then proceed to
   any other necessary recovery for file system can be determined by fetching the server reboot case (See
   Section 8.6.2 "Server Failure and Recovery").
   fs_locations attribute.

   The client must also employ the SETCLIENTID operation when it
   receives a NFS4ERR_STALE_STATEID error using a stateid derived from
   its current clientid, since this also indicates locations-related attribute may designate a server reboot which
   has invalidated single file system
   location or multiple file system locations, to be selected based on
   the existing clientid (see Section 8.1.3 "lock_owner
   and stateid Definition" for details).

   See needs of the detailed descriptions client.

   Use of SETCLIENTID multi-server namespaces is enabled by NFSv4 but is not
   required.  The use of multi-server namespaces and SETCLIENTID_CONFIRM
   for their scope will
   depend on the applications used, and system administration
   preferences.

   Multi-server namespaces can be established by a complete specification single server
   providing a large set of the operations.

8.1.2.  Server Release referrals to all of Clientid

   If the server determines that the client holds no associated state included file
   systems.  Alternatively, a single multi-server namespace may be
   administratively segmented with separate referral file systems (on
   separate servers) for its clientid, each separately-administered portion of the server may choose to release
   namespace.  Any segment or the clientid.  The
   server top-level referral file system may make this choice use
   replicated referral file systems for an inactive client so that resources higher availability.

   Generally, multi-server namespaces are not consumed by those intermittently active clients.  If the
   client contacts the server after this release, the server must ensure
   the client receives for the appropriate error so most part uniform, in
   that it will use the
   SETCLIENTID/SETCLIENTID_CONFIRM sequence same data made available to establish one client at a new identity.
   It should be clear that given location
   in the server must be very hesitant namespace is made available to release all clients at that location.

7.5.  Location Entries and Server Identity

   As mentioned above, a
   clientid since the resulting work on single location entry may have a server address
   target in the client to recover from such
   an event will be form of a DNS name which may represent multiple IP
   addresses, while multiple location entries may have their own server
   address targets, that reference the same burden as if server.

   When multiple addresses for the same server had failed and
   restarted.  Typically exist, the client may
   assume that for each file system in the namespace of a given server would not release a clientid unless
   network address, there had been no activity from that client for many minutes.

   Note that if the id string in a SETCLIENTID request is properly
   constructed, and if the client takes care to use the same principal exist file systems at corresponding namespace
   locations for each successive use of SETCLIENTID, then, barring an active
   denial of service attack, NFS4ERR_CLID_INUSE should never be
   returned.

   However, client bugs, the other server bugs, or perhaps a deliberate change of network addresses.  It may do
   this even in the principal owner absence of the id string (such explicit listing in fs_locations.  Such
   corresponding file system locations can be used as alternate
   locations, just as those explicitly specified via the case of fs_locations
   attribute.

   If a single location entry designates multiple server IP addresses,
   the client cannot assume that changes security flavors, and under the new flavor, there is no
   mapping these addresses are multiple paths to
   the previous owner) will in rare cases result in
   NFS4ERR_CLID_INUSE. same server.  In that event, when most case they will be, but the server gets a SETCLIENTID for a client id MUST
   verify that currently has no state, or it has state, but the lease has
   expired, rather than returning NFS4ERR_CLID_INUSE, the before acting on that assumption.  When two server MUST
   allow the SETCLIENTID, and confirm the new clientid if followed
   addresses are designated by
   the appropriate SETCLIENTID_CONFIRM.

8.1.3.  lock_owner and stateid Definition

   When requesting a lock, the client must present single location entry and they
   correspond to the server the
   clientid different servers, this normally indicates some sort of
   misconfiguration, and an identifier for so the owner client should avoid use such location
   entries when alternatives are available.  When they are not, clients
   should pick one of the requested lock.
   These two fields IP addresses and use it, without using others that
   are referred not directed to as the lock_owner same server.

7.6.  Additional Client-side Considerations

   When clients make use of servers that implement referrals,
   replication, and the definition migration, care should be taken so that a user who
   mounts a given file system that includes a referral or a relocated
   file system continues to see a coherent picture of those fields are:

   o  A clientid returned by that user-side
   file system despite the server as part 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 client's use root of
      the SETCLIENTID operation.

   o  A variable length opaque array used a server-
   side file system to uniquely define its parent (specified as ".." in UNIX), in the owner
   case in which it transitions to that file system as a result of
   referral, migration, or a lock managed by the client.

      This may be transition as a thread id, process id, or other unique value. result of replication.
   When the server grants the lock, it responds with a unique stateid.
   The stateid client is used as at such a shorthand reference point, and it needs to ascend to the lock_owner, since
   parent, it must go back to the server will be maintaining parent as seen within the correspondence between them.

   The server is free multi-server
   namespace rather issuing a LOOKUPP call to form the stateid server, which would
   result in any manner the parent within that it chooses
   as long as it is able server's single-server namespace.
   In order to recognize invalid and out-of-date stateids.
   This requirement includes those stateids generated by earlier
   instances of the server.  From do this, the client can be properly
   notified needs to remember the filehandles
   that represent such file system roots, and use these instead of
   issuing a server restart. LOOKUPP to the current server.  This notification will occur when allow the client presents a stateid
   to the server from a previous
   instantiation.

   The server must be able present to distinguish the following situations applications a consistent namespace, where upward
   navigation and
   return the error downward navigation are consistent.

   Another issue concerns refresh of referral locations.  When referrals
   are used extensively, they may change as specified:

   o  The stateid was generated by an earlier server instance (i.e.,
      before a 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 reboot).  The error NFS4ERR_STALE_STATEID communication.  This is usually
   rooted in client-side name lookup caching.  Clients should
      be returned.

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

      This error condition will only occur when order to detect
   changes in location information.  When the client issues a
      locking request which change_policy attribute
   changes a stateid while an I/O request that
      uses for directories that stateid is outstanding.

   o  The stateid was generated by the current server instance but the
      stateid does not designate a locking state hold referral entries or for any active
      lockowner-file pair.  The error NFS4ERR_BAD_STATEID the
   referral entries themselves, clients should consider any associated
   cached referral information to be
      returned.

      This error condition will occur when there has been a logic error
      on the part out of the client date.

7.7.  Effecting File System Transitions

   Transitions between file system instances, whether due to switching
   between replicas upon server unavailability, or server.  This should not happen.

   One mechanism that may be used in response to satisfy these requirements
   server-initiated migration events are best dealt with together.  This
   is so even though for the server to,

   o  divide server, pragmatic considerations will
   normally force different implementation strategies for planned and
   unplanned transitions.  Even though the "other" field prototypical use cases of each stateid into two fields:

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

      *  An index into a table
   replication and migration contain distinctive sets of locking-state structures.

   o  utilize features, when
   all possibilities for these operations are considered, there is an
   underlying unity of these operations, from the "seqid" field client's point of each stateid, such
   view, that seqid is
      monotonically incremented makes treating them together desirable.

   A number of methods are possible for each stateid that is associated 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 same index into the locking-state table.

   By matching changes seen by the incoming stateid client, to those that are less
   aggressive, use more standard methods of replicating data, and its field values with the state
   held at impose
   a greater burden on the server, client to adapt to the server is able transition.

   The NFSv4 protocol does not impose choices on clients and servers
   with regard to easily determine if that spectrum of transition methods.  The NFSv4.0
   protocol does not provide the servers a
   stateid is valid for its current instantiation and state.  If means of communicating the
   stateid
   transiation methods.  In the NFSv4.1 protocol [27], an additional
   attribute "fs_locations_info" is not valid, presented, which will define the appropriate error
   specific choices that can be supplied made, how these choices are communicated
   to the
   client.

8.1.4.  Use of the stateid and Locking

   All READ, WRITE client and SETATTR operations contain a stateid.  For how the
   purposes of this section, SETATTR operations which change client is to deal with any discontinuities.

   In the size
   attribute of a file are treated sections below, references will be made to various possible
   server issues as if they are writing the area
   between the old and new size (i.e., a way of illustrating the range truncated transition scenarios that
   clients may deal with.  The intent here is not to define or added limit
   server implementations but rather to illustrate the file by means range of issues
   that clients may face.  Again, as the SETATTR), even where SETATTR is NFSv4.0 protocol does not
   explicitly mentioned in have
   an explict means of communicating these issues to the text.

   If client, the lock_owner performs a READ or WRITE in a situation
   intent is to document the problems that can be faced in which it
   has established a lock or share reservation on the multi-
   server (any OPEN
   constitutes a share reservation) the stateid (previously returned by name space and allow the server) must be used client to indicate what locks, including both
   record locks and share reservations, are held by use the lockowner.  If
   no state is established by inferred
   transitions available via fs_locations and other attributes (see
   Section 7.9.1).

   In the client, either record lock discussion below, references will be made to a file system
   having a particular property or share
   reservation, of two file systems (typically the
   source and destination) belonging to a stateid common class of all bits 0 is used.  Regardless whether any of several
   types.  Two file systems that belong to such a
   stateid class share some
   important aspect of all bits 0, or file system behavior that clients may depend upon
   when present, to easily effect a stateid returned by seamless transition between file
   system instances.  Conversely, where the server is used,
   if there is file systems do not belong
   to such a conflicting share reservation or mandatory record lock
   held on the file, common class, the server MUST refuse client has 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 deal with various sorts of
   implementation discontinuities which may cause performance or WRITE
   operations, that denial results other
   issues in such operations being rejected effecting a transition.

   While fs_locations is available, default assumptions with error NFS4ERR_LOCKED.  Record locks may regard to
   such classifications have to be implemented by the inferred (see Section 7.9.1 for
   details).

   In cases in which one server as either mandatory or advisory, or the choice of mandatory or
   advisory behavior may be determined by is expected to accept opaque values from
   the server on client that originated from another server, the basis of servers SHOULD
   encode the "opaque" values in big endian byte order.  If this is
   done, servers acting as replicas or immigrating file being accessed (for example, some UNIX-based 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 support a
   "mandatory lock bit" on cooperating in the mode attribute such that if set, record
   locks are required on replication and migration of the file before I/O is possible).
   system.

7.7.1.  File System Transitions and Simultaneous Access

   When record
   locks are advisory, they only prevent the granting a single file system may be accessed at multiple locations,
   whether this is because 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 an indication of file system identity as
   reported by the fs_locations attribute, the client gets NFS4ERR_LOCKED will, depending on a file it knows it has the proper share
   reservation for, it will need
   specific circumstances as discussed below, either:

   o  The client accesses multiple instances simultaneously, as
      representing alternate paths to issue a LOCK request on the region same data and metadata.

   o  The client accesses one instance (or set of the file that includes the region the I/O was instances) and then
      transitions to be performed on,
   with an appropriate locktype (i.e., READ*_LT for a READ operation,
   WRITE*_LT for a WRITE operation).

   With NFS version 3, there was no notion alternative instance (or set of instances) as a stateid so there was no
   way to tell if the application process
      result of the client sending the READ network issues, server unresponsiveness, or WRITE operation had also acquired server-
      directed migration.

7.7.2.  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 appropriate record lock on two file systems across which the file.  Thus
   transition happens share sufficient state to effect some sort of
   continuity of file system handling.

   When there was is no way to implement mandatory locking.
   With such co-operation in filehandle assignment, the stateid construct, this barrier has been removed.

   Note that for UNIX environments that support mandatory two
   file locking,
   the distinction between advisory and mandatory locking is subtle.  In
   fact, advisory and mandatory record locks systems are exactly the same reported as being in so
   far different _handle_ classes.  In
   this case, all filehandles are assumed to expire as part of the APIs file
   system transition.  Note that this behavior does not depend on
   fh_expire_type attribute and requirements depends on implementation.  If the mandatory
   lock attribute specification of the
   FH4_VOL_MIGRATION bit.

   When there is set on co-operation in filehandle assignment, the file, two file
   systems are reported as being in the server checks same _handle_ classes.  In this
   case, persistent filehandles remain valid after the file system
   transition, while volatile filehandles (excluding those that are only
   volatile due to see if the
   lockowner has an appropriate shared (read) or exclusive (write)
   record lock FH4_VOL_MIGRATION bit) are subject to expiration
   on the region it wishes to read or write to.  If there is
   no appropriate lock, target server.

7.7.3.  Fileids and File System Transitions

   The issue of continuity of fileids in the server checks if there is event of a conflicting lock
   (which can file system
   transition needs to be done addressed.  The general expectation had been
   that in situations in which the two file system instances are created
   by attempting to acquire a single vendor using some sort of file system image copy, fileids
   will be consistent across the conflicting lock on transition while in the behalf of analogous
   multi-vendor transitions they will not.  This poses difficulties,
   especially for the lockowner, and if successful, release client without special knowledge of the lock
   after transition
   mechanisms adopted by the READ or WRITE server.  Note that although fileid is done), not a
   REQUIRED attribute, many servers support fileids 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. many clients
   provide API's that depend on fileids.

   It is the NFS version 4
   server's processing 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 READ fileid
   (e.g. via stat), and WRITE operations that introduces the distinction.

   Every stateid other than the special stateid values noted in result of 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 is that an access mode for the application may
   work perfectly well if there is no file (i.e., READ, WRITE, system instance transition or READ-
   WRITE) as established
   if any such transition is among instances created by a single vendor,
   yet be unable to deal with the original OPEN situation in which began the stateid
   sequence, and as modified by subsequent OPENs and OPEN_DOWNGRADEs
   within that stateid sequence.  When a READ, WRITE, or SETATTR which
   specifies multi-vendor
   transition occurs, at the size attribute, wrong time.

   Providing the same fileids in a multi-vendor (multiple server
   vendors) environment has generally been held to be quite difficult.
   While there is work to be done, the operation it needs to be pointed out that this
   difficulty is subject partly self-imposed.  Servers have typically identified
   fileid with inode number, i.e. with a quantity used to
   checking against find the access mode file
   in question.  This identification poses special difficulties for
   migration of a file system between vendors where assigning the same
   index to verify a given file may not be possible.  Note here that the operation a fileid
   is
   appropriate given the OPEN with which not required to be useful to find the operation file in question, only that
   it is associated.

   In unique within the case given file system.  Servers prepared to
   accept a fileid as a single piece of WRITE-type operations (i.e., WRITEs metadata and SETATTRs which
   set size), store it apart from
   the server must verify that value used to index the access mode allows writing
   and return an NFS4ERR_OPENMODE error if it does not. file information can relatively easily
   maintain a fileid value across a migration event, allowing a truly
   transparent migration event.

   In the any case, where servers can provide continuity of
   READ, the server may perform the corresponding check on fileids, they
   should, and 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 client should be able to buffer cache constraints).  However, even if
   READs are allowed in these circumstances, the server MUST still check
   for locks find out that conflict with such
   continuity is available and take appropriate action.  Information
   about the READ (e.g., another open specify
   denial continuity (or lack thereof) of READs).  Note that fileids across a server which does enforce the access
   mode check on READs need not explicitly check for conflicting share
   reservations since file
   system transition is represented by specifying whether the existence file
   systems in question are of OPEN for read access guarantees the same _fileid_ class.

   Note that when consistent fileids do not exist across a transition
   (either because there is no conflicting share reservation can exist.

   A stateid of all bits 1 (one) MAY allow READ operations to bypass
   locking checks at the server.  However, WRITE operations with a
   stateid with bits all 1 (one) MUST NOT bypass locking checks and are
   treated exactly the same as if a stateid continuity of all bits 0 were used.

   A lock may fileids or because fileid
   is not be granted while a READ or WRITE operation using supported attribute on 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 instances involved), and there
   are no reliable filehandles across a WRITE operation transition event (either because
   there is being performed, no filehandle continuity or an
   exclusive lock because the filehandles are
   volatile), the client is requested and either a READ or in a WRITE operation is
   being performed.  A SETATTR position where it cannot verify that sets size
   files it was accessing before the transition are the same objects.
   It is treated similarly forced to a
   WRITE as discussed above.

8.1.5.  Sequencing of Lock Requests

   Locking is different than most NFS operations as it requires "at-
   most-one" semantics assume that no object has been renamed, and, unless
   there are not provided by ONCRPC.  ONCRPC over a
   reliable transport guarantees that provide this (e.g. the file system is not sufficient because a sequence of locking
   requests read-
   only), problems for applications may span multiple TCP connections.  In the face occur.  Therefore, use of
   retransmission or reordering, lock or unlock requests must have a
   well defined such
   configurations should be limited to situations where the problems
   that this may cause can be tolerated.

7.7.4.  Fsids and consistent behavior.  To accomplish this, each lock
   request contains File System Transitions

   Since fsids are generally only unique within a sequence number that per-server basis, it
   is likely that they will change during a consecutively increasing
   integer.  Different lock_owners have different sequences.  The server
   maintains file system transition.
   Clients should not make the last sequence number (L) fsids received from the server visible to
   applications 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 response that
   was returned. extent
   possible.

7.7.5.  The first request issued for any given lock_owner Change Attribute and File System Transitions

   Since the change attribute is
   issued with a sequence number of zero.

   Note that for requests that contain defined as a sequence number, for each
   lock_owner, there should be no more than server-specific one,
   change attributes fetched from one outstanding request.

   If a request (r) with server are normally presumed to be
   invalid on another server.  Such a previous sequence number (r < L) presumption is received, troublesome since
   it is rejected with would invalidate all cached change attributes, requiring
   refetching.  Even more disruptive, the return absence of error NFS4ERR_BAD_SEQID.  Given a
   properly-functioning client, any assured
   continuity for the response to (r) must have been
   received before change attribute means that even if the last request (L) was sent.  If a duplicate of
   last request (r == L) same value
   is received, retrieved on refetch no conclusions can drawn as to whether the stored response is returned.
   If
   object in question has changed.  The identical change attribute could
   be merely an artifact of a request beyond the next sequence (r == L + 2) is received, it is
   rejected with the return of error NFS4ERR_BAD_SEQID.  Sequence
   history is reinitialized whenever the SETCLIENTID/SETCLIENTID_CONFIRM
   sequence changes the client verifier.

   Since the sequence number is represented modified file with an unsigned 32-bit
   integer, the arithmetic involved a different change
   attribute construction algorithm, with the sequence number is mod
   2^32.  For that new algorithm just
   happening to result in an example of modulo arithmetic involving sequence numbers
   see [27].

   It is critical identical change value.

   When the server maintain two file systems have consistent change attribute formats,
   and we say that they are in the last response sent to same _change_ class, the client to provide may
   assume a more reliable cache of duplicate non-idempotent
   requests than that continuity of the traditional cache described in [28].  The
   traditional duplicate request cache uses a least recently used
   algorithm for removing unneeded requests.  However, the last lock
   request change attribute construction and response on a given lock_owner must be cached as long handle this
   situation just as it would be handled without any file system
   transition.

7.7.6.  Lock State and File System Transitions

   In a file system transition, the lock state exists on the server.

   The client MUST monotonically increment the sequence number for needs to handle cases in
   which the
   CLOSE, LOCK, LOCKU, OPEN, OPEN_CONFIRM, two servers have cooperated in state management and OPEN_DOWNGRADE
   operations.  This is true even in
   which they have not.  Cooperation by two servers in state management
   requires coordination of client IDs.  Before the event that the previous
   operation that used the sequence number received an error.  The only
   exception client attempts to this rule is if the previous operation received
   use a client ID associated with one server in a request to the server
   of the following errors: NFS4ERR_STALE_CLIENTID, NFS4ERR_STALE_STATEID,
   NFS4ERR_BAD_STATEID, NFS4ERR_BAD_SEQID, NFS4ERR_BADXDR,
   NFS4ERR_RESOURCE, NFS4ERR_NOFILEHANDLE.

8.1.6.  Recovery from Replayed Requests

   As described above, other file system, it must eliminate the sequence number is per lock_owner.  As long
   as possibility that two
   non-cooperating servers have assigned the server maintains same client ID by accident.

   In the last sequence number received and follows case of migration, the methods described above, there are no risks servers involved in the migration of a Byzantine router
   re-sending old requests.  The
   file system SHOULD transfer all server need only maintain the
   (lock_owner, sequence number) state as long as there are open files
   or closed files with locks outstanding.

   LOCK, LOCKU, OPEN, OPEN_DOWNGRADE, and CLOSE each contain a sequence
   number and therefore from the risk of original to the replay of these operations
   resulting
   new server.  When this is done, it must be done in undesired effects a way that is non-existent while
   transparent to the server
   maintains client.  With replication, such a degree of common
   state is typically not the lock_owner state.

8.1.7.  Releasing lock_owner State

   When case.

   This state transfer will reduce disruption to the client when a particular lock_owner no longer holds open or file locking
   state at
   system transition occurs.  If the server, servers are successful in
   transferring all state, the server may choose client can attempt to release the sequence
   number state establish sessions
   associated with the lock_owner.  The server may make
   this choice based on lease expiration, client ID used for the reclamation of server
   memory, or other implementation specific details.  In any event, source file system
   instance.  If the server is able to do this safely only when the lock_owner no longer
   is being utilized by accepts that as a valid client ID, then the client.  The server
   client may choose to hold use the
   lock_owner state in existing stateids associated with that client ID
   for the event old file system instance in connection with that retransmitted requests are
   received.  However, same client
   ID in connection with the period to hold this transitioned file system instance.

   File systems co-operating in state management may actually share
   state is implementation
   specific.

   In the case that a LOCK, LOCKU, OPEN_DOWNGRADE, or CLOSE is
   retransmitted after the server has previously released simply divide the lock_owner
   state, identifier space so as to recognize (and
   reject as stale) each other's stateids and client IDs.  Servers which
   do share state may not do so under all conditions or at all times.
   The requirement for the server will find is that if it cannot be sure in
   accepting a client ID that it reflects the lock_owner has no files open locks the client was
   given, it must treat all associated state as stale and
   an error will be returned report it as
   such to the client.  If

   The client must establish a new client ID on the lock_owner destination, if it
   does not have
   a file open, one already, and reclaim locks if possible.  In this
   case, old stateids and client IDs should not be presented to the stateid new
   server since there is no assurance that they will not match and again an error is
   returned conflict with
   IDs valid on that server.

   When actual locks are not known to be maintained, the client.

8.1.8.  Use of Open Confirmation

   In destination
   server may establish a grace period specific to the case given file
   system, with non-reclaim locks being rejected for that an OPEN is retransmitted and file system,
   even though normal locks are being granted for other file systems.
   Clients should not infer the lock_owner is absence of a grace period for file
   systems being
   used transitioned to a server from responses to requests for
   other file systems.

   In the first time or 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 restart (although in the lock_owner case of the planned
   state has been previously
   released transfer associated with migration, these can be avoided by the server, the use
   securely recording lock state as part of state migration).  Unless
   the OPEN_CONFIRM operation destination server can guarantee that locks will
   prevent incorrect behavior.  When not be
   incorrectly granted, the destination server observes the use of the
   lock_owner should not allow lock
   reclaims and avoid establishing a grace period.  (See Section 9.14
   for the first time, it will direct the further details.)

   Information about client to perform
   the OPEN_CONFIRM for the corresponding OPEN.  This sequence
   establishes identity may be propagated between servers
   in the use form of an lock_owner client_owner4 and associated sequence number.
   Since verifiers, under the OPEN_CONFIRM sequence connects a new open_owner on
   assumption that the
   server client presents the same values to all the
   servers with an existing open_owner which it deals.

   Servers are encouraged to provide facilities to allow locks to be
   reclaimed on the new server after a client, file system transition.  Often
   such facilities may not be available and client should be prepared to
   re-obtain locks, even though it is possible that the sequence number client may have any value.
   its LOCK or OPEN request denied due to a conflicting lock.

   The OPEN_CONFIRM step assures consequences of having no facilities available to reclaim locks
   on the sew server that
   the value received is will depend on the correct one.  See Section 14.20
   "OPEN_CONFIRM - Confirm Open" for further details.

   There are a number type of situations in which environment.  In some
   environments, such as the requirement to confirm
   an OPEN would transition between read-only file systems,
   such denial of locks should not pose large difficulties for in practice.
   When an attempt to re-establish a lock on a new server is denied, the
   client and server, in should treat the situation as if its original lock had been
   revoked.  Note that
   they would be prevented from acting when the lock is granted, the client cannot
   assume that no conflicting lock 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 timely fashion on
   information received, because client may reasonably treat all pending locks as
   having been revoked.

7.7.6.1.  Transitions and the Lease_time Attribute

   In order that information would be provisional,
   subject to deletion upon non-confirmation.  Fortunately, these are
   situations the client may appropriately manage its leases in which the server can avoid
   case of a file system transition, the need for confirmation
   when responding to open requests.  The two constraints are:

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

   o 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 NOT require confirmation must never be less than that on a reclaim-type open
      (i.e., one specifying claim type CLAIM_PREVIOUS or
      CLAIM_DELEGATE_PREV).

   These constraints are related
   the source since this would result in that reclaim-type opens are premature expiration of leases
   granted by the only
   ones source server.  Upon transitions in which state is
   transferred transparently, the server client is under no obligation to re-
   fetch the lease_time attribute and may be required continue to send a delegation.  For
   CLAIM_NULL, sending use the delegation is optional while for
   CLAIM_DELEGATE_CUR, no delegation is sent.

   Delegations being sent with an open requiring confirmation are
   troublesome value
   previously fetched (on the source server).

   If state has not been transferred transparently because recovering from non-confirmation adds undue
   complexity the client ID
   is rejected when presented to the protocol while requiring confirmation on reclaim-
   type opens poses difficulties in that new server, the inability to resolve client should fetch
   the
   status value of lease_time on the reclaim until lease expiration may make new (i.e. destination) server, and use
   it difficult to
   have timely determination of the set of locks being reclaimed (since for subsequent locking requests.  However the server must respect
   a grace period may expire).

   Requiring open confirmation on reclaim-type opens is avoidable
   because of at least as long as the nature of lease_time on the environments source
   server, in which such opens order to ensure that clients have ample time to reclaim
   their lock before potentially conflicting non-reclaimed locks are
   done.  For CLAIM_PREVIOUS opens,
   granted.

7.7.7.  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 immediately after server
   reboot, so there should be no time for lockowners the case, and
   the two file systems belong to the same _write-verifier_ class, write
   verifiers returned from one system may be created,
   found compared to be unused, and recycled.  For CLAIM_DELEGATE_PREV opens, we
   are dealing with a client reboot situation.  A server which supports
   delegation can be sure that no lockowners for that client have been
   recycled since client initialization those returned
   by the other and thus can ensure that
   confirmation will not be required.

8.2.  Lock Ranges

   The protocol allows a lock owner superfluous writes avoided.

   When two file systems belong to request a lock with a byte range
   and then either upgrade or unlock a sub-range of the initial lock.
   It is expected that this will be an uncommon type of request.  In different _write-verifier_ classes,
   any
   case, servers or server filesystems may verifier generated by one must 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 compared to return one provided by
   the error
   NFS4ERR_LOCK_RANGE to signify that other.  Instead, 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 treated as not equal even when the requesting
   application.

   The client is discouraged from combining multiple independent locking
   ranges that happen to be adjacent into
   values are identical.

7.7.8.  Readdir Cookies and Verifiers and File System Transitions

   In a single request since file system transition, the
   server two file systems may not support sub-range requests be consistent
   in their handling of READDIR cookies and for reasons related to verifiers.  When this is the recovery of file locking state in
   case, and the event of server failure.
   As discussed in two file systems belong to the section "Server Failure same _readdir_ class,
   READDIR cookies and Recovery" below, verifiers from one system may be recognized by
   the other and READDIR operations started on one server may employ certain optimizations during recovery that work
   effectively only when be validly
   continued on the client's behavior during lock recovery is
   similar to other, simply by presenting the client's locking behavior prior to server failure.

8.3.  Upgrading cookie and Downgrading Locks

   If a client has verifier
   returned by a write lock READDIR operation done on a record, it can request an atomic
   downgrade of the lock first file system to a read lock via the LOCK request,
   second.

   When two file systems belong to different _readdir_ classes, any
   READDIR cookie and verifier generated by setting one is not valid on the type
   second, and must not be presented to READ_LT.  If the that server supports atomic downgrade, by the
   request will succeed.  If not, it will return NFS4ERR_LOCK_NOTSUPP. client.  The
   client should be prepared to receive this error, and act as if
   appropriate, report the error to the requesting application.

   If a client has a read lock on verifier was rejected.

7.7.9.  File System Data and File System Transitions

   When multiple replicas exist and are used simultaneously or in
   succession by a record, it can request an atomic
   upgrade of client, applications using them will normally expect
   that they contain data the lock to a write lock via same data or data which is consistent with
   the LOCK request normal sorts of changes that are made by setting other clients updating
   the type to WRITE_LT or WRITEW_LT.  If data of the server does not support
   atomic upgrade, it will return NFS4ERR_LOCK_NOTSUPP.  If file system. (with metadata being the upgrade
   can be achieved without an existing conflict, same to the request will
   succeed.  Otherwise,
   degree inferred by the server will return either NFS4ERR_DENIED or
   NFS4ERR_DEADLOCK.  The error NFS4ERR_DEADLOCK is returned if the
   client issued fs_locations attribute).  However, when
   multiple file systems are presented as replicas of one another, the LOCK request with
   precise relationship between the type set to WRITEW_LT data of one and the
   server has detected data of another
   is not, as a deadlock.  The client should be prepared to
   receive such errors and if appropriate, report general matter, specified by the error NFSv4 protocol.  It is
   quite possible to present as replicas file systems where the
   requesting application.

8.4.  Blocking Locks

   Some clients require the support data of blocking locks.  The NFS version
   4 protocol must not rely on a callback mechanism and therefore
   those file systems is
   unable to notify a client when a previously denied lock has been
   granted.  Clients sufficiently different that some applications
   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 problems dealing with the server transition between replicas.  The
   namespace will typically be constructed so that applications can
   choose an appropriate level of support, so that in one position in
   the client is requesting namespace a blocking lock. varied set of replicas will be listed while in
   another only those that are up-to-date may be considered replicas.
   The server should maintain
   an ordered list protocol does define three special cases of pending blocking locks.  When the conflicting lock
   is released, relationship
   among replicas to be specified by the server may wait the lease period for the first
   waiting client and relied upon by
   clients:

   o  When multiple server addresses correspond to re-request the lock.  After the lease period
   expires same actual
      server, the next waiting client request is allowed may depend on the lock.  Clients
   are required to poll at an interval sufficiently small fact that it is
   likely to acquire the lock in a timely manner.  The server is not
   required changes to maintain a list of pending blocked data,
      metadata, or 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 made on one file system are immediately
      reflected on others.

   o  When multiple replicas exist and delay returning denial of are used simultaneously by a
      client, they must designate the request to allow extra time for same data.  Where file systems are
      writable, a conflicting lock to change made on one instance must be
   released, allowing a successful return.  In this way, clients can
   avoid visible on all
      instances, immediately upon the burden earlier of needlessly frequent polling for blocking locks.
   The server should take care in the length return of delay in the event the
   client retransmits
      modifying requester or the request.

8.5.  Lease Renewal

   The purpose visibility of that change on any of the
      associated replicas.  This allows a lease is client to allow a server use these replicas
      simultaneously without any special adaptation to remove stale locks the fact that
      there are held by a client that has crashed multiple replicas.  In this case, locks, whether shared
      or is otherwise
   unreachable.  It is not a mechanism for cache consistency byte-range, and lease
   renewals may not delegations obtained one replica are
      immediately reflected on all replicas, even though these locks
      will be denied if the lease interval has not expired.

   The following events cause implicit renewal of all of the leases for
   a given client (i.e., all those sharing managed under a given clientid).  Each set of
   these is a positive indication that the client IDs.

   o  When one replica is still active and
   that the associated state held at the server, for designated as the client, is
   still valid.

   o  An OPEN with a valid clientid.

   o  Any operation made with a valid stateid (CLOSE, DELEGPURGE,
      DELEGRETURN, LOCK, LOCKU, OPEN, OPEN_CONFIRM, OPEN_DOWNGRADE,
      READ, RENEW, SETATTR, WRITE).  This does not include successor instance to
      another existing instance after return NFS4ERR_MOVED (i.e. the special
      stateids
      case of all bits 0 or all bits 1.

      Note that if the client had restarted or rebooted, migration), the client
      would not be making these requests without issuing the
      SETCLIENTID/SETCLIENTID_CONFIRM sequence.  The use of may depend on the
      SETCLIENTID/SETCLIENTID_CONFIRM sequence (one fact that all
      changes securely made to data (uncommitted writes are dealt with
      in Section 7.7.7) on the
      client verifier) notifies the server original instance are made to drop the locking state
      associated
      successor image.

   o  Where a file system is not writable but represents a read-only
      copy (possibly periodically updated) of a writable file system,
      clients have similar requirements with regard to the client.  SETCLIENTID/SETCLIENTID_CONFIRM never
      renews propagation
      of updates.  They may need a lease.

      If the server has rebooted, guarantee that any change visible on
      the stateids (NFS4ERR_STALE_STATEID
      error) or original file system instance must be immediately visible on
      any replica before the clientid (NFS4ERR_STALE_CLIENTID error) client transitions access to that replica,
      in order to avoid any possibility that a client, in effecting a
      transition to a replica, will see any reversion in file system
      state.  Since these file systems are presumed not to be
      valid hence preventing spurious renewals.

   This approach allows suitable
      for low overhead lease renewal which scales
   well.  In the typical case simultaneous use, there is no extra RPC calls are required for lease
   renewal specification of how locking is
      handled and in it generally will be the worst case one RPC is required every lease period
   (i.e., a RENEW operation).  The number of that locks held by the client obtained one
      file system will be separate from those on others.  Since these
      are going to be read-only file systems, this is not a factor since all state expected to
      pose an issue for clients or applications.

7.8.  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 attribute.  The client is involved with will typically get an
   NFS4ERR_MOVED error, fetch the
   lease renewal action.

   Since all operations that create a new lease also renew existing
   leases, appropriate location information and
   proceed to access the server must maintain a common lease expiration time for
   all valid leases for file system on a given client.  This lease time can then be
   easily updated upon implicit lease renewal actions.

8.6.  Crash Recovery

   The important requirement different server, even though
   it retains its logical position within the original namespace.
   Referrals differ from migration events in crash recovery is that both they happen only when
   the client
   and has not previously referenced the server know file system in question
   (so there is nothing to transition).  Referrals can only come into
   effect when the other has failed.  Additionally, it an absent file system is
   required encountered at its root.

   The examples given in the sections below are somewhat artificial in
   that a an actual client sees will not typically do a consistent view of data across server
   restarts or reboots.  All READ and WRITE operations that may multi-component lookup,
   but will have
   been queued within the client or network buffers must wait until cached information regarding the
   client has successfully recovered upper levels of the locks protecting
   name hierarchy.  However, these example are chosen to make the READ and
   WRITE operations.

8.6.1.  Client Failure
   required behavior clear and Recovery

   In easy to put within the event that scope of a client fails, small
   number of requests, without getting unduly into details of how
   specific clients might choose to cache things.

7.8.1.  Referral Example (LOOKUP)

   Let us suppose that the server following COMPOUND is sent in an environment
   in which /this/is/the/path is absent from the target server.  This
   may recover be for a number of reasons.  It may be the client's
   locks when case that the associated leases have expired.  Conflicting locks
   from another client file
   system has moved, or, it may only be granted after this lease expiration.
   If the client case that the target server is able to restart
   functioning mainly, or reinitialize within solely, to refer clients to the lease
   period servers on
   which various file systems are located.

   o  PUTROOTFH

   o  LOOKUP "this"

   o  LOOKUP "is"

   o  LOOKUP "the"

   o  LOOKUP "path"
   o  GETFH

   o  GETATTR fsid,fileid,size,time_modify

   Under the client may given circumstances, the following will be forced to wait the remainder of result.

   o  PUTROOTFH --> NFS_OK.  The current fh is now the lease
   period before obtaining new locks.

   To minimize client delay upon restart, lock requests are associated
   with an instance root of the client by a client supplied verifier.  This
   verifier
      pseudo-fs.

   o  LOOKUP "this" --> NFS_OK.  The current fh is part of for /this and is
      within the initial SETCLIENTID call made by pseudo-fs.

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

   o  LOOKUP "the" --> NFS_OK.  The server returns a clientid as a result of current fh is for /this/is/the and
      is within the SETCLIENTID
   operation. pseudo-fs.

   o  LOOKUP "path" --> NFS_OK.  The current fh is for /this/is/the/path
      and is within a new, absent file system, but ... the client then confirms will
      never see the use value of the clientid with
   SETCLIENTID_CONFIRM.  The clientid that fh.

   o  GETFH --> NFS4ERR_MOVED.  Fails because current fh is in combination with an opaque
   owner field is then used by absent
      file system at the client to identify start of the lock owner operation and the spec makes no
      exception for
   OPEN.  This chain GETFH.

   o  GETATTR fsid,fileid,size,time_modify.  Not executed because the
      failure of associations is then used to identify all locks
   for a particular client.

   Since the verifier will be changed by GETFH stops processing of the COMPOUND.

   Given the failure of the GETFH, the client upon each
   initialization, has the job of determining
   the root of the absent file system and where to find that file
   system, i.e. the server can compare a new verifier and path relative to that server's root fh.
   Note here that in this example, the verifier
   associated with currently held locks client did not obtain filehandles
   and determine attribute information (e.g. fsid) for the intermediate
   directories, so that they do it would not
   match.  This signifies be sure where the client's new instantiation and subsequent
   loss of locking state.  As a result, absent file
   system starts.  It could be the server case, for example, that /this/is/the
   is free to release
   all locks held which are associated with the old clientid which was
   derived from root of the old verifier.

   Note moved file system and that the verifier must have reason that the same uniqueness properties
   lookup of "path" succeeded is that the verifier for the COMMIT operation.

8.6.2.  Server Failure file system was not absent on
   that operation but was moved between the last LOOKUP and Recovery

   If the server loses locking state (usually as a result GETFH
   (since COMPOUND is not atomic).  Even if we had the fsids for all of
   the intermediate directories, we could have no way of knowing that
   /this/is/the/path was the root of a restart
   or reboot), it must allow clients time new file system, since we don't
   yet have its fsid.

   In order to discover this fact get the necessary information, let us re-send the chain
   of LOOKUPs with GETFHs and re-
   establish GETATTRs to at least get the lost locking state. fsids so we
   can be sure where the appropriate file system boundaries are.  The
   client must be able could choose to re-
   establish the locking state without having the server deny valid
   requests because get fs_locations at the server has granted conflicting access to another
   client.  Likewise, if there is same time but in most
   cases the possibility that clients client will have not
   yet re-established their locking state for a file, the server must
   disallow READ good guess as to where file system
   boundaries are (because of where and WRITE operations for that file.  The duration where not NFS4ERR_MOVED was
   received) making fetching of
   this recovery period fs_locations unnecessary.

   OP01:  PUTROOTFH --> NFS_OK

   -  Current fh is equal to the duration root of pseudo-fs.

   OP02:  GETATTR(fsid) --> NFS_OK

   -  Just for completeness.  Normally, clients will know the lease period.

   A client can determine that server failure (and thus loss of locking
   state) has occurred, when it receives one of two errors.  The
   NFS4ERR_STALE_STATEID error indicates a stateid invalidated by a
   reboot or restart.  The NFS4ERR_STALE_CLIENTID error indicates a
   clientid invalidated by reboot or restart.  When either fsid of these are
   received,
      the client must pseudo-fs as soon as they establish communication with a new clientid (See Section 8.1.1
   "Client ID") and re-establish the locking state as discussed below.
      server.

   OP03:  LOOKUP "this" --> NFS_OK

   OP04:  GETATTR(fsid) --> NFS_OK

   -  Get current fsid to see where file system boundaries are.  The period of special handling of locking
      fsid will be that for the pseudo-fs in this example, so no
      boundary.

   OP05:  GETFH --> NFS_OK

   -  Current fh is for /this and READs is within pseudo-fs.

   OP06:  LOOKUP "is" --> NFS_OK

   -  Current fh is for /this/is and WRITEs, equal
   in duration is within pseudo-fs.

   OP07:  GETATTR(fsid) --> NFS_OK

   -  Get current fsid to see where file system boundaries are.  The
      fsid will be that for the lease period, pseudo-fs in this example, so no
      boundary.

   OP08:  GETFH --> NFS_OK

   -  Current fh is referred for /this/is and is within pseudo-fs.

   OP09:  LOOKUP "the" --> NFS_OK

   -  Current fh is for /this/is/the and is within pseudo-fs.

   OP10:  GETATTR(fsid) --> NFS_OK
   -  Get current fsid to as the "grace
   period".  During see where file system boundaries are.  The
      fsid will be that for the grace period, clients recover locks pseudo-fs in this example, so no
      boundary.

   OP11:  GETFH --> NFS_OK

   -  Current fh is for /this/is/the and the
   associated state by reclaim-type locking requests (i.e., LOCK
   requests with reclaim set to true is within pseudo-fs.

   OP12:  LOOKUP "path" --> NFS_OK

   -  Current fh is for /this/is/the/path and OPEN operations with is within a claim
   type new, absent
      file system, but ...

   -  The client will never see the value of CLAIM_PREVIOUS).  During that fh

   OP13:  GETATTR(fsid, fs_locations) --> NFS_OK

   -  We are getting the grace period, fsid to know where the server must
   reject READ and WRITE operations and non-reclaim locking requests
   (i.e., other LOCK and OPEN operations) with an error of
   NFS4ERR_GRACE.

   If file system boundaries
      are.  In this operation the server can reliably determine that granting a non-reclaim
   request fsid will not conflict with reclamation be different than that of locks by other clients,
   the NFS4ERR_GRACE error does not have to be returned and
      the non-
   reclaim client request can be serviced.  For parent directory (which in turn was retrieved in OP10).  Note
      that the server to fsid we are given will not necessarily be able to
   service READ and WRITE operations during preserved at
      the grace period, it must
   again new location.  That fsid might be able to guarantee that no possible conflict could arise
   between an impending reclaim locking request different and in fact the READ or WRITE
   operation.  If the server is unable to offer that guarantee, the
   NFS4ERR_GRACE error must
      fsid we have for this file system might be returned to the client.

   For a server to provide simple, valid handling during fsid of a
      different file system on that new server.

   -  In this particular case, we are pretty sure anyway that what has
      moved is /this/is/the/path rather than /this/is/the since we have
      the grace
   period, fsid of the easiest method is to simply reject all non-reclaim
   locking requests and READ latter and WRITE operations by returning it is that of the
   NFS4ERR_GRACE error. pseudo-fs, which
      presumably cannot move.  However, a server may keep information about
   granted locks in stable storage.  With other examples, we might not
      have this information, the server
   could determine if a regular lock or READ or WRITE operation can be
   safely processed.

   For example, if a count kind of locks information to rely on (e.g. /this/is/the might
      be a given file is available in
   stable storage, the server can track reclaimed locks for the non-pseudo file and
   when all reclaims system separate from /this/is/the/path), so
      we need to have been processed, non-reclaim locking requests
   may be processed.  This way another reliable source information on the server can ensure that non-reclaim
   locking requests will not conflict with potential reclaim requests.
   With respect to I/O requests, if
      boundary of the server file system which is able to determine that
   there are no outstanding reclaim requests moved.  If, for a example, the
      file by information
   from stable storage or another similar mechanism, system "/this/is" had moved we would have a case of migration
      rather than referral and once the processing boundaries of
   I/O requests the migrated file
      system was clear we could proceed normally for fetch fs_locations.

   -  We are fetching fs_locations because the file.

   To reiterate, for a server fact that allows non-reclaim lock we got an
      NFS4ERR_MOVED at this point means that it most likely that this is
      a referral and I/O
   requests to be processed during we need the grace period, destination.  Even if it MUST determine is the case
      that no lock subsequently reclaimed "/this/is/the" is a file system which has migrated, we will be rejected and that no lock
   subsequently reclaimed would have prevented any I/O operation
   processed during
      still need the grace period.

   Clients should be prepared location information for that file system.

   OP14:  GETFH --> NFS4ERR_MOVED
   -  Fails because current fh is in an absent file system at the return start
      of NFS4ERR_GRACE errors for
   non-reclaim lock the operation and I/O requests.  In the spec makes no exception for GETFH.  Note
      that this case means the server will never send the client should
   employ a retry mechanism for filehandle
      from within an absent file system.

   Given the request.  A delay (on above, the order of
   several seconds) between retries should be used to avoid overwhelming client knows where the server.  Further discussion root of the general issue absent file
   system is included in
   [19].  The client must account for the server that is able to perform
   I/O (/this/is/the/path), by noting where the change of fsid
   occurred (between "the" and non-reclaim locking requests within "path").  The fs_locations attribute also
   gives the grace period as well
   as those that can not do so.

   A reclaim-type locking request outside client the server's grace period can
   only succeed if actual location of the server can guarantee absent file system, so
   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 referral can proceed.  The server gives the lease_time attribute and use it as client the basis
   for lease renewal for bare
   minimum of information about the lease associated with absent file system so that server.
   However, the server must establish, for this restart event, a grace
   period at least as long as the lease period there
   will be very little scope for problems of conflict between
   information sent by the previous server
   instantiation.  This allows the client state obtained during the
   previous referring server instance to be reliably re-established.

8.6.3.  Network Partitions and Recovery

   If the duration information of a network partition is greater than the lease
   period provided by the server, file
   system's home.  No filehandles and very few attributes are present on
   the referring server will have not received a
   lease renewal from and the client.  If this occurs, client can treat those it receives as
   basically transient information with the server may free
   all locks held for function of enabling the client.  As
   referral.

7.8.2.  Referral Example (READDIR)

   Another context in which a result, all stateids held by the
   client will become invalid or stale.  Once the client may encounter referrals is able to
   reach the server after such when it
   does a network partition, all I/O submitted by
   the client with the now invalid stateids will fail with READDIR on directory in which some of the server
   returning sub-directories are
   the error NFS4ERR_EXPIRED.  Once roots of absent file systems.

   Suppose such a directory is read as follows:

   o  PUTROOTFH

   o  LOOKUP "this"

   o  LOOKUP "is"

   o  LOOKUP "the"

   o  READDIR (fsid, size, time_modify, mounted_on_fileid)

   In this error case, because rdattr_error is received, not requested, fs_locations is
   not requested, and some of attributes cannot be provided, the client result
   will suitably notify the application that held the lock.

   As a courtesy to the client or as be an optimization, the server may
   continue to hold locks NFS4ERR_MOVED error on behalf of a client for which recent
   communication has extended beyond the lease period.  If the server
   receives a lock or I/O request that conflicts READDIR, with one the detailed
   results as follows:

   o  PUTROOTFH --> NFS_OK.  The current fh is at the root of these
   courtesy locks, the server must free
      pseudo-fs.

   o  LOOKUP "this" --> NFS_OK.  The current fh is for /this and is
      within the courtesy lock pseudo-fs.

   o  LOOKUP "is" --> NFS_OK.  The current fh is for /this/is and grant is
      within the
   new request.

   When a network partition pseudo-fs.

   o  LOOKUP "the" --> NFS_OK.  The current fh is combined with a server reboot, there are
   edge conditions for /this/is/the and
      is within the pseudo-fs.

   o  READDIR (fsid, size, time_modify, mounted_on_fileid) -->
      NFS4ERR_MOVED.  Note that place requirements on the server same error would have been returned
      if /this/is/the had migrated, when in order to
   avoid silent data corruption following fact it is because the server reboot.  Two of
   these edge conditions are known, and are discussed below.

   The first edge condition has
      directory contains the following scenario:

   1.  Client A acquires a lock.

   2.  Client A and server experience mutual network partition, such
       that client A is unable to renew its lease.

   3.  Client A's lease expires, so server releases lock.

   4.  Client B acquires a lock root of an absent file system.

   So now suppose that would have conflicted we re-send with that rdattr_error:

   o  PUTROOTFH

   o  LOOKUP "this"

   o  LOOKUP "is"

   o  LOOKUP "the"

   o  READDIR (rdattr_error, fsid, size, time_modify, mounted_on_fileid)

   The results will be:

   o  PUTROOTFH --> NFS_OK.  The current fh is at the root of
       Client A.

   5.  Client B releases the lock

   6.  Server reboots

   7.  Network partition between client A and server heals.

   8.  Client A issues a RENEW operation,
      pseudo-fs.

   o  LOOKUP "this" --> NFS_OK.  The current fh is for /this and gets back a
       NFS4ERR_STALE_CLIENTID.

   9.  Client A reclaims its lock is
      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. pseudo-fs.

   o  LOOKUP "is" --> NFS_OK.  The second known edge condition follows:

   1.   Client A acquires a lock.

   2.   Server reboots.

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

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

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

   6.   Client B releases the lock.

   7.   Server reboots a second time.

   8.   Network partition between client A and server heals.

   9.   Client A issues a RENEW operation, pseudo-fs.

   o  LOOKUP "the" --> NFS_OK.  The current fh is for /this/is/the and gets back a
        NFS4ERR_STALE_CLIENTID.

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

   As pseudo-fs.

   o  READDIR (rdattr_error, fsid, size, time_modify, mounted_on_fileid)
      --> NFS_OK.  The attributes for directory entry 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 component
      named "path" will only contain rdattr_error with the server
   either assume after it reboots that edge condition occurs, value
      NFS4ERR_MOVED, together with an fsid value and thus
   return NFS4ERR_NO_GRACE a value for all reclaim attempts, or that the server
   record some information stable storage.  The amount of information
   the server records
      mounted_on_fileid.

   So suppose we do another READDIR to get fs_locations (although we
   could have used a GETATTR directly, as in stable storage Section 7.8.1).

   o  PUTROOTFH

   o  LOOKUP "this"

   o  LOOKUP "is"

   o  LOOKUP "the"

   o  READDIR (rdattr_error, fs_locations, mounted_on_fileid, fsid,
      size, time_modify)

   The results would be:

   o  PUTROOTFH --> NFS_OK.  The current fh is in inverse proportion to how
   harsh at the server wants to be whenever root of the edge conditions occur.
      pseudo-fs.

   o  LOOKUP "this" --> NFS_OK.  The
   server that current fh is completely tolerant of all edge conditions will record
   in stable storage every lock that for /this and is acquired, removing the lock
   record from stable storage only when
      within the lock pseudo-fs.

   o  LOOKUP "is" --> NFS_OK.  The current fh is unlocked by the
   client for /this/is and the lock's lockowner advances the sequence number such
   that the lock release is not
      within the last stateful event pseudo-fs.

   o  LOOKUP "the" --> NFS_OK.  The current fh is for /this/is/the and
      is within the
   lockowner's sequence.  For pseudo-fs.

   o  READDIR (rdattr_error, fs_locations, mounted_on_fileid, fsid,
      size, time_modify) --> NFS_OK.  The attributes will be as shown
      below.

   The attributes for the two aforementioned edge conditions, directory entry with the harshest component named
   "path" will only contain

   o  rdattr_error (value: NFS_OK)

   o  fs_locations

   o  mounted_on_fileid (value: unique fileid within referring file
      system)

   o  fsid (value: unique value within referring server)

   The attributes for entry "path" will not contain size or time_modify
   because these attributes are not available within an absent file
   system.

7.9.  The Attribute fs_locations

   The fs_locations attribute is structured in the following way:

   struct fs_location4 {
           utf8val_must    server<>;
           pathname4       rootpath;
   };

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

   The fs_location4 data type is used to represent the location of a
   file system by providing a server can be, name and still support a grace period for
   reclaims, requires the path to the root of
   the file system within that server's namespace.  When a set of
   servers have corresponding file systems at the same path within their
   namespaces, an array of server record names may be provided.  An entry in stable storage
   information some minimal information.  For example, a
   the server
   implementation could, for each client, save in stable storage array is a
   record containing:

   o  the client's id UTF-8 string

   o  a boolean that indicates if the client's lease expired or if there
      was administrative intervention (see the section, Server
      Revocation and represents one of Locks) to revoke a record lock, share reservation,
   traditional DNS host name, IPv4 address, or delegation

   o  a timestamp that is updated the first time after a server boot IPv6 address, or
      reboot an zero-
   length string.  A zero-length string SHOULD be used to indicate the client acquires record locking, share reservation, or
      delegation state on
   current address being used for the server.  The timestamp need RPC call.  It is not be updated
      on subsequent lock requests until a requirement
   that all servers that share the server reboots. same rootpath be listed in one
   fs_location4 instance.  The array of server implementation would names is provided for
   convenience.  Servers that share the same rootpath may also record be listed
   in separate fs_location4 entries in the stable storage the
   timestamps from fs_locations attribute.

   The fs_locations4 data type and fs_locations attribute contain an
   array of such locations.  Since the two most recent namespace of each server reboots.

   Assuming may be
   constructed differently, the above record keeping, for "fs_root" field is provided.  The path
   represented by fs_root represents the first edge condition,
   after location of the server reboots, file system in
   the record that client A's lease expired
   means current server's namespace, i.e. that another client could have acquired a conflicting record
   lock, share reservation, or delegation.  Hence of the server must reject
   a reclaim from which
   the fs_locations attribute was obtained.  The fs_root path is meant
   to aid the client A with by clearly referencing the error NFS4ERR_NO_GRACE.

   For root of the second edge condition, after file system
   whose locations are being reported, no matter what object within the server reboots for a second
   time,
   current file system the record that current filehandle designates.  The fs_root
   is simply the pathname the client had an unexpired record lock, share
   reservation, or delegation established before used to reach the server's previous
   incarnation means that object on the server must reject a reclaim from client A
   with
   current server, the error NFS4ERR_NO_GRACE.

   Regardless of object being that the level fs_locations attribute
   applies to.

   When the fs_locations attribute is interrogated and approach to record keeping, there are no
   alternate file system locations, the server
   MUST implement one SHOULD return a zero-
   length array of the following strategies (which apply to
   reclaims of share reservations, record locks, and delegations):

   1.  Reject all reclaims fs_location4 structures, together with NFS4ERR_NO_GRACE.  This a valid
   fs_root.

   As an example, suppose there is superharsh,
       but necessary if a replicated file system located at
   two servers (servA and servB).  At servA, the server does not want file system is located
   at path "/a/b/c".  At, servB the file system is located at path
   "/x/y/z".  If the client were to record lock state in
       stable storage.

   2.  Record sufficient state in stable storage such that all known
       edge conditions involving server reboot, including obtain the two noted
       in this section, are detected.  False positives are acceptable.
       Note that fs_locations value for
   the directory at this time, "/a/b/c/d", it is might not known if there are other edge
       conditions.  In necessarily know that the event, after a server reboot,
   file system's root is located in servA's namespace at "/a/b/c".  When
   the server
       determines client switches to servB, it will need to determine that there the
   directory it first referenced at servA is unrecoverable damage or corruption to now represented by the path
   "/x/y/z/d" on servB.  To facilitate this, the stable storage, then fs_locations attribute
   provided by servA would have a fs_root value of "/a/b/c" and two
   entries in fs_locations.  One entry in fs_locations will be for all clients and/or locks
       affected,
   itself (servA) and the server MUST return NFS4ERR_NO_GRACE.

   A mandate other will be for the client's handling servB with a path of
   "/x/y/z".  With this information, the NFS4ERR_NO_GRACE error client is
   outside able to substitute
   "/x/y/z" for the scope of this specification, since "/a/b/c" at the strategies beginning of its access path and
   construct "/x/y/z/d" to use for
   such handling are very dependent on the client's operating
   environment.  However, one potential approach new server.

   Note that: there is described below.

   When the client receives NFS4ERR_NO_GRACE, it could examine no requirement that the
   change attribute number of components in
   each rootpath be the objects the client same; there is trying to reclaim state
   for, and use that to determine whether to re-establish no relation between the state via
   normal OPEN number of
   components in rootpath or LOCK requests.  This is acceptable provided fs_root; and the
   client's operating environment allows it.  In otherwords, none of the client
   implementor is advised components in
   each rootpath and fs_root have to document for his users be the behavior.  The
   client could also inform same.  In the application that its record lock or
   share reservations (whether they were delegated or not) above example,
   we could have been
   lost, such as via had a UNIX signal, third element in the locations array, with server
   equal to "servC", and rootpath equal to "/I/II", and a GUI pop-up window, etc.  See
   Section 9.5, "Data Caching fourth element
   in locations with server equal to "servD", and Revocation" for rootpath equal to
   "/aleph/beth/gimel/daleth/he".

   The relationship between fs_root to a discussion of what rootpath is that the client should do
   replaces the pathname indicated in fs_root for dealing with unreclaimed delegations on
   client state. the current server for
   the substitute indicated in rootpath for the new server.

   For further discussion of revocation of locks see Section 8.8 "Server
   Revocation of Locks".

8.7.  Recovery from an example for a Lock Request Timeout referred or Abort

   In the event a lock request times out, migrated file system, suppose there
   is a client may decide to not
   retry file system located at serv1.  At serv1, the request. file system is
   located at "/az/buky/vedi/glagoli".  The client may also abort the request when finds that object at
   "glagoli" has migrated (or is a referral).  The client gets the
   process for
   fs_locations attribute, which it was issued is terminated (e.g., contains an fs_root of "/az/buky/vedi/
   glagoli", and one element in UNIX due to a
   signal).  It is possible though that the locations array, with server received the request equal
   to "serv2", and acted upon it.  This would change rootpath equal to "/izhitsa/fita".  The client
   replaces "/az/buky/vedi/glagoli" with "/izhitsa/fita", and uses the state
   latter pathname on "serv2".

   Thus, the server without MUST return an fs_root that is equal to the path the
   client being aware of used to reach the change.  It is paramount that object the fs_locations attribute applies
   to.  Otherwise the client re-synchronize state with server before it attempts any other
   operation that takes a seqid and/or a stateid with cannot determine the same
   lock_owner.  This is straightforward new path to do without a special re-
   synchronize operation.

   Since use on the server maintains
   new server.

7.9.1.  Inferring Transition Modes

   When fs_locations is used, information about the last lock request and response
   received specific locations
   should be assumed based on the lock_owner, for each lock_owner, following rules.

   The following rules are general and apply irrespective of the client
   context.

   o  All listed file system instances should
   cache be considered as of the last lock request it sent such that
      same _handle_ class, if and only if, the lock request did current fh_expire_type
      attribute does not receive a response.  From this, the next time include the client does a
   lock operation for FH4_VOL_MIGRATION bit.  Note that
      in the lock_owner, it case of referral, filehandle issues do not apply since
      there can send be no filehandles known within the cached request, if
   there current file system
      nor is one, and if there any access to the request was one that established state
   (e.g., a LOCK or OPEN operation), fh_expire_type attribute on the server will return
      referring (absent) file system.

   o  All listed file system instances should be considered as of the cached
   result or
      same _fileid_ class, if never saw the request, perform it.  The client can
   follow up with a request to remove the state (e.g., a LOCKU or CLOSE
   operation).  With this approach, the sequencing and stateid
   information on only if, the client fh_expire_type attribute
      indicates persistent filehandles and server for does not include the given lock_owner will
   re-synchronize and
      FH4_VOL_MIGRATION bit.  Note that in turn the lock state will re-synchronize.

8.8.  Server Revocation case of Locks

   At any point, the server referral, fileid
      issues do not apply since there 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, no fileids known within the client
      referring (absent) file system nor is
   responsible for validating there any access to the state information between itself and
      fh_expire_type attribute.

   o  All file system instances servers should be considered as of
      different _change_ classes.

   For other class assignments, handling of file system transitions
   depends on the server.  Validating locking state reasons for the client means transition:

   o  When the transition is due to migration, that it
   must verify or reclaim state for each lock currently held.

   The first instance of lock revocation is upon server reboot or re-
   initialization.  In this instance the client will receive was
      directed to new file system after receiving an error
   (NFS4ERR_STALE_STATEID or NFS4ERR_STALE_CLIENTID) and NFS4ERR_MOVED
      error, the client will
   proceed with normal crash recovery target should be treated as described in being of the previous
   section.

   The second lock revocation event is same _write-
      verifier_ class as the inability to renew source.

   o  When the lease
   before expiration.  While this transition is considered a rare or unusual event, due to failover to another replica, that
      is, the client must selected another replica without receiving and
      NFS4ERR_MOVED error, the target should be prepared to recover.  Both treated as being of a
      different _write-verifier_ class from the server source.

   The specific choices reflect typical implementation patterns for
   failover and client
   will be able to detect controlled migration respectively.

   See Section 17 for a discussion on the failure recommendations for the
   security flavor to renew be used by any GETATTR operation that requests the lease and are capable
   of recovering without data corruption.  For
   "fs_locations" attribute.

8.  NFS Server Name Space
8.1.  Server Exports

   On a UNIX server the server, it tracks name space describes all the
   last renewal event serviced for files reachable by
   pathnames under the client and knows when root directory or "/".  On a Windows NT server
   the lease
   will expire.  Similarly, name space constitutes all the client must track operations which will
   renew files on disks named by mapped
   disk letters.  NFS server administrators rarely make the lease period.  Using entire
   server's filesystem name space available to NFS clients.  More often
   portions of the time that each such request was
   sent and name space are made available via an "export"
   feature.  In previous versions of the time that NFS protocol, the corresponding reply was received, root
   filehandle for each export is obtained through the
   client should bound MOUNT protocol;
   the time client sends a string that identifies the corresponding renewal could
   have occurred on export of name space
   and the server and thus determine if it is possible returns the root filehandle for it.  The MOUNT
   protocol supports an EXPORTS procedure that
   a lease period expiration could have occurred. will enumerate the
   server's exports.

8.2.  Browsing Exports

   The third lock revocation event NFS version 4 protocol provides a root filehandle that clients
   can occur as use to obtain filehandles for these exports via a result of
   administrative intervention within the lease period.  While this multi-component
   LOOKUP.  A common user experience is
   considered to use a rare event, it is possible that the server's
   administrator has decided graphical user
   interface (perhaps a file "Open" dialog window) to release or revoke find a particular lock held
   by the client.  As file via
   progressive browsing through a result directory tree.  The client must be
   able to move from one export to another export via single-component,
   progressive LOOKUP operations.

   This style of revocation, browsing is not well supported by the NFS version 2 and
   3 protocols.  The client will receive an
   error of NFS4ERR_ADMIN_REVOKED.  In this instance expects all LOOKUP operations to remain
   within a single server filesystem.  For example, the device attribute
   will not change.  This prevents a client may
   assume from taking name space paths
   that only span exports.

   An automounter on the lock_owner's locks have been lost.  The client
   notifies can obtain a snapshot of the lock holder appropriately.  The client may not assume server's
   name space using the lease period has been renewed as a result EXPORTS procedure of a failed operation.

   When the client determines MOUNT protocol.  If it
   understands the lease period may have expired, server's pathname syntax, it can create an image of
   the
   client must mark all locks held for server's name space on the associated lease as
   "unvalidated".  This means client.  The parts of the client has been unable to re-establish
   or confirm name space
   that are not exported by the appropriate lock state server are filled in with a "pseudo
   filesystem" that allows the server.  As described
   in user to browse from one mounted
   filesystem to another.  There is a drawback to this representation of
   the previous section server's name space on crash recovery, there are scenarios in
   which the server may grant conflicting locks after the lease period
   has expired for a client.  When client: it is possible that static.  If the lease period
   has expired, server
   administrator adds a new export the client must validate each lock currently held will be unaware of it.

8.3.  Server Pseudo Filesystem

   NFS version 4 servers avoid this name space inconsistency by
   presenting all the exports within the framework of a single server
   name space.  An NFS version 4 client uses LOOKUP and READDIR
   operations to
   ensure browse seamlessly from one export to another.  Portions
   of the server name space that are not exported are bridged via a
   "pseudo filesystem" that provides a conflicting lock view of exported directories
   only.  A pseudo filesystem has not been granted.  The client may
   accomplish this task by issuing an I/O request, either a pending I/O
   or unique fsid and behaves like a zero-length read, specifying the stateid associated with the
   lock in question.  If
   normal, read only filesystem.

   Based on the response to construction of the request server's name space, it is success, the
   client has validated all possible
   that multiple pseudo filesystems may exist.  For example,

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

   Each of the locks governed by that stateid pseudo filesystems are considered separate entities and
   re-established the appropriate state between itself
   therefore will have a unique fsid.

8.4.  Multiple Roots

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

   If pseudo root.

8.5.  Filehandle Volatility

   The nature of the I/O request server's pseudo filesystem is not successful, then one or more that it is a logical
   representation of filesystem(s) available from the locks
   associated with server.
   Therefore, the stateid was revoked by pseudo filesystem is most likely constructed
   dynamically when the server and the client
   must notify the owner.

8.9.  Share Reservations

   A share reservation is a mechanism to control access to a file. first instantiated.  It is a separate and independent mechanism expected
   that the pseudo filesystem may not have an on disk counterpart from record locking.  When a
   client opens a file,
   which persistent filehandles could be constructed.  Even though it issues an OPEN operation to is
   preferable that the server
   specifying provide persistent filehandles for the type of access required (READ, WRITE, or BOTH) and
   pseudo filesystem, the
   type of access to deny others (deny NONE, READ, WRITE, or BOTH). NFS client should expect that pseudo file
   system filehandles are volatile.  This can be confirmed by checking
   the associated "fh_expire_type" attribute for those filehandles in
   question.  If the OPEN fails filehandles are volatile, the NFS client will fail the application's open request.

   Pseudo-code definition must be
   prepared to recover a filehandle value (e.g., with a multi-component
   LOOKUP) when receiving an error of NFS4ERR_FHEXPIRED.

8.6.  Exported Root

   If the semantics:

   if (request.access == 0)
           return (NFS4ERR_INVAL)
   else if ((request.access & file_state.deny)) ||
       (request.deny & file_state.access))
           return (NFS4ERR_DENIED) server's root filesystem is exported, one might conclude that
   a pseudo-filesystem is not needed.  This checking of share reservations would be wrong.  Assume the
   following filesystems on OPEN a server:

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

   Because disk2 is done not exported, disk3 cannot be reached with no exception
   for an existing OPEN for the same open_owner. simple
   LOOKUPs.  The constants used for the OPEN and OPEN_DOWNGRADE operations for server must bridge the
   access and deny fields are as follows:

   const OPEN4_SHARE_ACCESS_READ   = 0x00000001;
   const OPEN4_SHARE_ACCESS_WRITE  = 0x00000002;
   const OPEN4_SHARE_ACCESS_BOTH   = 0x00000003;

   const OPEN4_SHARE_DENY_NONE     = 0x00000000;
   const OPEN4_SHARE_DENY_READ     = 0x00000001;
   const OPEN4_SHARE_DENY_WRITE    = 0x00000002;
   const OPEN4_SHARE_DENY_BOTH     = 0x00000003;

8.10.  OPEN/CLOSE Operations

   To provide correct share semantics, gap with a client MUST use the OPEN
   operation pseudo-filesystem.

8.7.  Mount Point Crossing

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

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

   The pseudo filesystem for this server may be constructed to obtain look
   like:

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

   It is the initial filehandle and indicate server's responsibility to present the desired
   access and what if any access pseudo filesystem
   that is complete to deny.  Even if the client.  If the client intends to
   use sends a stateid of all 0's or all 1's, it must still obtain the
   filehandle lookup request
   for the regular file with the OPEN operation so path "/a/b/c/d", 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 server's response is the CREATE flag, also subsumes filehandle of
   the CREATE
   operation for regular files as used in filesystem "/a/b/c/d".  In previous versions of the NFS
   protocol.  This allows a create with a share to be done atomically.

   The CLOSE operation removes all share reservations held by the
   lock_owner on that file.  If record locks are held, the client SHOULD
   release all locks before issuing a CLOSE.  The server MAY free all
   outstanding locks on CLOSE but some servers may not support protocol,
   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 respond with 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 of directory "/a/b/c/d"
   within the filesystem "/a/b".

   The NFS client has the least access.  For example, a file
   opened with deny READ/WRITE cannot will be accessed using a filehandle
   obtained through LOOKUP because able to determine if it would not have crosses a valid stateid
   (i.e., using server mount
   point by a stateid change in the value of all bits 0 or all bits 1).

8.10.1.  Close the "fsid" attribute.

8.8.  Security Policy and Retention Name Space Presentation

   The application of State Information

   Since a CLOSE operation requests deallocation of a stateid, dealing
   with retransmission of the CLOSE, may pose special difficulties,
   since the state information, which normally would server's security policy needs to be used carefully
   considered by the implementor.  One may choose to
   determine limit the state
   viewability of the open file being designated, might be
   deallocated, resulting in an NFS4ERR_BAD_STATEID error.

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

   When adopting this strategy, a server should retain the state
   information until support of multiple security mechanisms
   and the earliest of:

   o  Another validly sequenced request for ability to negotiate the same lockowner, that appropriate use of these mechanisms,
   the server is
      not a retransmission.

   o  The time that unable to properly determine if a lockowner is freed by client will be able
   to authenticate itself.  If, based on its policies, the server due
   chooses to period
      with no activity.

   o  All locks for limit the client are freed as a result contents of the pseudo filesystem, the server
   may effectively hide filesystems from a SETCLIENTID.

   Servers client that may avoid this complexity, at otherwise
   have legitimate access.

   As suggested practice, the cost of less complete
   protocol error checking, by simply responding NFS4_OK in server should apply the event security policy of
   a CLOSE for a deallocated stateid, on shared resource in the assumption that this case
   must be caused by a retransmitted close.  When adopting this
   approach, it is desirable server's namespace to at least log an error when returning a
   no-error indication in this situation.  If the server maintains a
   reply-cache mechanism, it can verify components of the CLOSE
   resource's ancestors.  For example:

   /
   /a/b
   /a/b/c

   The /a/b/c directory is indeed a
   retransmission and avoid error logging in most cases.

8.11.  Open Upgrade real filesystem and Downgrade

   When an OPEN is done the shared resource.
   The security policy for a file and /a/b/c is Kerberos with integrity.  The
   server should apply the lockowner same security policy to /, /a, and /a/b.
   This allows for which the open
   is being done already has extension of the file open, protection of the result is server's
   namespace to upgrade the
   open file status maintained on ancestors of the server to include real shared resource.

   For the access and
   deny bits specified by case of the new OPEN as well as those for use of multiple, disjoint security mechanisms in
   the existing
   OPEN.  The result is that there is one open file, as far as server's resources, the
   protocol is concerned, and it includes security for a particular object in the
   server's namespace should be the union of the access and
   deny bits for all security mechanisms of
   all direct descendants.

9.  File Locking and Share Reservations

   Integrating locking into the OPEN requests completed.  Only a single
   CLOSE will be done NFS protocol necessarily causes it to reset be
   stateful.  With the effects inclusion of both OPENs.  Note that share reservations the
   client, when issuing the OPEN, may not know that protocol
   becomes substantially more dependent on state than the same file is in
   fact being opened.  The above only applies if both OPENs result traditional
   combination of NFS and NLM [28].  There are three components to
   making this state manageable:

   o  Clear division between client and server

   o  Ability to reliably detect inconsistency in state between client
      and server

   o  Simple and robust recovery mechanisms

   In this model, the OPENed object being designated by server owns the same filehandle.

   When state information.  The client
   communicates its view of this state to the server chooses as needed.  The
   client is also able to export multiple filehandles corresponding detect inconsistent state before modifying a
   file.

   To support Win32 share reservations it is necessary to atomically
   OPEN or CREATE files.  Having a separate share/unshare operation
   would not allow correct implementation of the Win32 OpenFile API.  In
   order to correctly implement share semantics, the same previous NFS
   protocol mechanisms used when a file object and returns different filehandles on two
   different OPENs is opened or created (LOOKUP,
   CREATE, ACCESS) need to be replaced.  The NFS version 4 protocol has
   an OPEN operation that subsumes the NFS version 3 methodology of
   LOOKUP, CREATE, and ACCESS.  However, because many operations require
   a filehandle, the same traditional LOOKUP is preserved to map a file object, name
   to filehandle without establishing state on the server.  The policy
   of granting access or modifying files is managed by the server MUST NOT "OR"
   together based
   on the access client's state.  These mechanisms can implement policy ranging
   from advisory only locking to full mandatory locking.

9.1.  Locking

   It is assumed that manipulating a lock is rare when compared to READ
   and deny bits WRITE operations.  It is also assumed that crashes and coalesce the two open files.
   Instead network
   partitions are relatively rare.  Therefore it is important that the server must maintain separate OPENs with separate
   stateids
   READ and will require separate CLOSEs WRITE operations have a lightweight mechanism to free them.

   When multiple open files on the client are merged into indicate if
   they possess a single open
   file object on held lock.  A lock request contains the server, heavyweight
   information required to establish a lock and uniquely define the close of one of lock
   owner.

   The following sections describe the open files (on transition from the
   client) may necessitate change of heavy weight
   information to the access eventual stateid used for most client and deny status of server
   locking and lease interactions.

9.1.1.  Client ID

   For each LOCK request, the
   open file on client must identify itself to the server.

   This is because the union of the access and
   deny bits done in such a way as to allow for the remaining opens may be smaller (i.e., correct lock
   identification and crash recovery.  A sequence of a proper
   subset) than previously.  The OPEN_DOWNGRADE SETCLIENTID
   operation followed by a SETCLIENTID_CONFIRM operation is used required to
   make
   establish the necessary change and identification onto the server.  Establishment of
   identification by a new incarnation of the client should use it to update also has the
   server so effect
   of immediately breaking any leased state that share reservation requests by other clients are
   handled properly.

8.12.  Short and Long Leases

   When determining the time period for a previous incarnation
   of the server lease, the usual
   lease tradeoffs apply.  Short leases are good for fast server
   recovery at a cost of increased RENEW or READ (with zero length)
   requests.  Longer leases are certainly kinder and gentler to servers
   trying to handle very large numbers of clients.  The number of RENEW
   requests drop in proportion to the lease time.  The disadvantages of
   long leases are slower recovery after server failure (the server must
   wait for client might have had on the leases server, as opposed to expire and forcing the grace period to elapse before
   granting
   new lock requests) and increased file contention (if client
   fails incarnation to transmit an unlock request then server must wait for lease
   expiration before granting new locks).

   Long leases are usable if the server is able leases to store expire.  Breaking
   the lease state in
   non-volatile memory.  Upon recovery, amounts to the server can reconstruct removing all lock, share
   reservation, and, where the
   lease server is not supporting the
   CLAIM_DELEGATE_PREV claim type, all delegation state from its non-volatile memory and continue operation associated with
   same client with
   its clients and therefore long leases would not be an issue.

8.13.  Clocks, Propagation Delay, and Calculating Lease Expiration

   To avoid the need for synchronized clocks, lease times are granted by same identity.  For discussion of delegation
   state recovery, see Section 10.2.1.

   Client identification is encapsulated in the server as a time delta.  However, there following structure:

   struct SETCLIENTID4args {
           nfs_client_id4  client;
           cb_client4      callback;
           uint32_t        callback_ident;
   };

   The first field, verifier is a requirement client incarnation verifier that the is
   used to detect client and server clocks do not drift excessively over the duration
   of reboots.  Only if the lock.  There verifier is also the issue of propagation delay across the
   network different
   from that 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, server has previously recorded the client should subtract it
   from lease times (e.g., if (as
   identified by the client estimates second field of the one-way
   propagation delay as 200 msec, then it can assume that structure, id) does the lease server
   start the process of canceling the client's leased state.

   The second field, id is
   already 200 msec old when it gets it).  In addition, it will take
   another 200 msec to get a response back to variable length string that uniquely
   defines the server.  So client.

   There are several considerations for how the client
   must send a lock renewal or write data back to the server 400 msec
   before generates the lease would expire. id
   string:

   o  The server's lease period configuration string should take into account be unique so that multiple clients do not
      present the
   network distance same string.  The consequences of the two clients that will be accessing
      presenting the server's
   resources.  It is expected that same string range from one client getting an error
      to one client having its leased state abruptly and unexpectedly
      canceled.

   o  The string should be selected so the lease period will take into
   account subsequent incarnations
      (e.g., reboots) of the network propagation delays and other network delay
   factors for same client cause the client population.  Since to present the protocol does not allow
   for
      same string.  The implementor is cautioned against an automatic method approach
      that requires the string to determine an appropriate lease period, be recorded in a local file because
      this precludes the
   server's administrator may have to tune use of the lease period.

8.14.  Migration, Replication implementation in an environment
      where there is no local disk and State

   When responsibility for handling a given all file system access is transferred
   to a new from an NFS
      version 4 server.

   o  The string should be different for each server (migration) or network address
      that the client chooses accesses, rather than common to use an alternate all server (e.g., in response network
      addresses.  The reason is that it may not be possible for the
      client to tell if the same server unresponsiveness) in is listening on multiple network
      addresses.  If the context
   of file system replication, client issues SETCLIENTID with the appropriate handling same id
      string to each network address of state shared
   between such a server, the client and server (i.e., locks, leases, stateids, and
   clientids) will
      think it is as described below.  The handling differs between
   migration and replication.  For related discussion of file server
   state and recover of such see the sections under "File Locking same client, and
   Share Reservations".

   If server replica or a each successive SETCLIENTID will
      cause the server immigrating a filesystem agrees to, or
   is expected to, accept opaque values from to begin the client that originated
   from another server, then it is a wise implementation practice process of removing the client's
      previous leased state.

   o  The algorithm for generating the servers to encode string should not assume that the "opaque" values in
      client's network byte order. address won't change.  This way, servers acting as replicas or immigrating filesystems will
   be able to parse values like stateids, directory cookies,
   filehandles, etc. includes changes
      between client incarnations and even if their native byte order changes while the client is different from
   other servers cooperating
      stilling running in its current incarnation.  This means that if
      the replication and migration of client includes just the
   filesystem.

8.14.1.  Migration client's and State

   In the case of migration, the servers involved server's network address
      in the migration of id string, there is a
   filesystem SHOULD transfer all server state from real risk, after the original to client gives up
      the
   new server.  This must be done in a way network address, that is transparent to the
   client.  This state transfer will ease the client's transition when another client, using a
   filesystem migration occurs.  If the servers are successful in
   transferring all state, similar
      algorithm for generating the client id string, will continue to use stateids
   assigned by the original server.  Therefore the new server must
   recognize these stateids as valid.  This holds true for generate a
      conflicting id string.

   Given the clientid
   as well.  Since responsibility for above considerations, an entire filesystem is
   transferred with example of a migration event, there well generated id
   string is no possibility one that
   conflicts will arise includes:

   o  The server's network address.

   o  The client's network address.

   o  For a user level NFS version 4 client, it should contain
      additional information to distinguish the client from other user
      level clients running on the new server same host, such as a result of the transfer of
   locks.

   As part of the transfer of process id or
      other unique sequence.

   o  Additional information between servers, leases would that tends to be transferred unique, such as well. one or
      more of:

      *  The leases being transferred client machine's serial number (for privacy reasons, it is
         best to perform some one way function on the new
   server will typically have a different expiration time from those for serial number).

      *  A MAC address.

      *  The timestamp of when the same client, previously NFS version 4 software was first
         installed on the old server.  To maintain client (though this is subject to the
   property
         previously mentioned caution about using information that all leases on a given server for is
         stored in a given client expire
   at file, because the file might only be accessible
         over NFS version 4).

      *  A true random number.  However since this number ought to be
         the same time, between client incarnations, this shares the server should advance same
         problem as that of the expiration time to using the later timestamp of the leases being transferred or software
         installation.

   As a security measure, the leases already
   present.  This allows server MUST NOT cancel a client's leased
   state if the client to maintain lease renewal of both
   classes without special effort.

   The servers may choose not to transfer principal established the state information upon
   migration.  However, this choice for a given id string is discouraged.  In this case, when
   not the client presents state information from same as the original server (e.g.
   in a RENEW op or principal issuing the SETCLIENTID.

   Note that SETCLIENTID and SETCLIENTID_CONFIRM has a READ op secondary purpose
   of zero length), the client must be
   prepared to receive either NFS4ERR_STALE_CLIENTID or
   NFS4ERR_STALE_STATEID from establishing the new server.  The client should then
   recover its state information as it normally would in response to a
   server failure.  The new the server must take care needs to make callbacks to allow for
   the
   recovery client for purpose of state supporting delegations.  It is permitted to
   change this information as it would in via SETCLIENTID and SETCLIENTID_CONFIRM
   within the event same incarnation of server
   restart.

   A the client SHOULD re-establish new callback information with without removing the new
   server as soon as possible, according to sequences described in
   sections Section 14.35
   client's leased state.

   Once a SETCLIENTID and Section 14.36.  This ensures that server
   operations are not blocked by SETCLIENTID_CONFIRM sequence has successfully
   completed, the inability to recall delegations.

8.14.2.  Replication and State

   Since client switch-over in uses the case shorthand client identifier, of replication is not under
   server control, the handling type
   clientid4, instead of state the longer and less compact nfs_client_id4
   structure.  This shorthand client identifier (a clientid) is different.  In this case,
   leases, stateids assigned
   by the server and clientids do should be chosen so that it will not have validity across conflict with
   a
   transition from one server to another.  The client must re-establish
   its locks on clientid previously assigned by the new server.  This can be compared applies across
   server restarts or reboots.  When a clientid is presented to the re-
   establishment of locks by means of reclaim-type requests after a server reboot.  The difference is
   and that clientid is not recognized, as would happen after a server
   reboot, the server has no provision to
   distinguish requests reclaiming locks from those obtaining new locks
   or to defer will reject the request with the error
   NFS4ERR_STALE_CLIENTID.  When this happens, the latter.  Thus, a client re-establishing must obtain a lock on the
   new server (by means clientid by use of a LOCK or OPEN request), may have the
   requests denied due SETCLIENTID operation and then proceed to a conflicting lock.  Since replication is
   intended
   any other necessary recovery for read-only use of filesystems, such denial of locks
   should not pose large difficulties in practice.  When an attempt to
   re-establish the server reboot case (See
   Section 9.6.2).

   The client must also employ the SETCLIENTID operation when it
   receives a lock on NFS4ERR_STALE_STATEID error using a stateid derived from
   its current clientid, since this also indicates a new server is denied, reboot which
   has invalidated the client should
   treat existing clientid (see Section 9.1.3 for
   details).

   See the situation as if his original lock had been revoked.

8.14.3.  Notification detailed descriptions of SETCLIENTID and SETCLIENTID_CONFIRM
   for a complete specification of Migrated Lease

   In the case operations.

9.1.2.  Server Release of lease renewal, Clientid

   If the client may not be submitting
   requests for a filesystem server determines that has been migrated to another server.
   This can occur because of the implicit lease renewal mechanism.  The client renews leases for all filesystems when submitting a request to
   any one filesystem at the server.

   In order holds no associated state
   for its clientid, the client to schedule renewal of leases that server may have
   been relocated choose to release the new server, the clientid.  The
   server may make this choice for an inactive client must find out about
   lease relocation before so that resources
   are not consumed by those leases expire.  To accomplish this, all
   operations which implicitly renew leases for a intermittently active clients.  If the
   client (i.e., OPEN,
   CLOSE, READ, WRITE, RENEW, LOCK, LOCKT, LOCKU), will return contacts the error
   NFS4ERR_LEASE_MOVED if responsibility for any of server after this release, the leases to be
   renewed has been transferred to a new server.  This condition will
   continue until server must ensure
   the client receives an NFS4ERR_MOVED error and the
   server receives appropriate error so that it will use the subsequent GETATTR(fs_locations) for an access to
   each filesystem for which a lease has been moved
   SETCLIENTID/SETCLIENTID_CONFIRM sequence to establish a new server.

   When a client receives an NFS4ERR_LEASE_MOVED error, it identity.
   It should
   perform an operation on each filesystem associated with be clear that the server in
   question.  When must be very hesitant to release a
   clientid since the client receives an NFS4ERR_MOVED error, resulting work on the client can follow the normal process to obtain recover from such
   an event will be the new server
   information (through same burden as if the fs_locations attribute) server had failed and perform renewal
   of those leases on the new server.  If the
   restarted.  Typically a server has would not release a clientid unless
   there had state
   transferred to it transparently, the client will receive either
   NFS4ERR_STALE_CLIENTID or NFS4ERR_STALE_STATEID been no activity from that client for many minutes.

   Note that if the new server,
   as described above, id string in a SETCLIENTID request is properly
   constructed, and if the client can then recover state information
   as it does in takes care to use the event same principal
   for each successive use of SETCLIENTID, then, barring an active
   denial of service attack, NFS4ERR_CLID_INUSE should never be
   returned.

   However, client bugs, server failure.

8.14.4.  Migration and bugs, or perhaps a deliberate change of
   the Lease_time Attribute

   In order that principal owner of the client may appropriately manage its leases in id string (such as the case of migration, the destination server must establish proper
   values for a client
   that changes security flavors, and under the lease_time attribute.

   When state new flavor, there 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 no
   mapping to the source since this would result previous owner) will in premature expiration of leases
   granted by the source server.  Upon migration rare cases result in which state is
   transferred transparently,
   NFS4ERR_CLID_INUSE.

   In that event, when the server gets a SETCLIENTID for a client is under id
   that currently has no obligation to re-
   fetch the lease_time attribute and may continue to use the value
   previously fetched (on state, or it has state, but the source server).

   If state lease has not been transferred transparently (i.e.,
   expired, rather than returning NFS4ERR_CLID_INUSE, the client
   sees a real or simulated server reboot), the client should fetch MUST
   allow the
   value of lease_time on SETCLIENTID, and confirm the new (i.e., destination) server, and use it
   for subsequent locking requests.  However clientid if followed by
   the server must respect appropriate SETCLIENTID_CONFIRM.

9.1.3.  lock_owner and stateid Definition

   When requesting a
   grace period at least as long as the lease_time on lock, the source server,
   in order to ensure that clients have ample time client must present to reclaim their
   locks before potentially conflicting non-reclaimed locks are granted.
   The means by which the new server obtains the value
   clientid and an identifier for the owner of lease_time on the old server is left requested lock.
   These two fields are referred to as the server implementations.  It is not
   specified by lock_owner and the NFS version 4 protocol.

9.  Client-Side Caching

   Client-side caching of data, definition
   of file attributes, and those fields are:

   o  A clientid returned by the server as part of file names is
   essential to providing good performance with the NFS protocol.
   Providing distributed cache coherence is a difficult problem and
   previous versions client's use of
      the NFS protocol have not attempted it.
   Instead, several NFS client implementation techniques have been SETCLIENTID operation.

   o  A variable length opaque array used to reduce uniquely define the problems that a lack owner
      of coherence poses for users.
   These techniques have not been clearly defined a lock managed by earlier protocol
   specifications and it is often unclear what is valid the client.

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

   When the server grants the lock, it responds with a unique stateid.
   The NFS version 4 protocol uses many techniques similar to those that
   have been stateid is used in previous protocol versions.  The NFS version 4
   protocol does not provide distributed cache coherence.  However, it
   defines as a more limited set of caching guarantees to allow locks and
   share reservations shorthand reference 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 lock_owner, since
   the server to will be made locally by clients.  This mechanism provides efficient
   support of maintaining the common cases where sharing is infrequent or where
   sharing correspondence between them.

   The server is read-only.

9.1.  Performance Challenges for Client-Side Caching

   Caching techniques used free to form the stateid in previous versions any manner that it chooses
   as long as it is able to recognize invalid and out-of-date stateids.
   This requirement includes those stateids generated by earlier
   instances of the NFS protocol have
   been successful in providing good performance.  However, several
   scalability challenges server.  From this, the client can arise when those techniques are used with
   very large numbers be properly
   notified of clients. a server restart.  This is particularly true notification will occur 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
   client presents a single client.  Therefore,
   sharing is infrequent.

   In this case, repeated reference stateid 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 from a file to do
   so without reference previous
   instantiation.

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

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

   o  The stateid was generated by the read and
   write requests necessary to make data caching consistent with current server instance but the
      stateid no longer designates the current locking semantics (see Section 9.3.2 "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 state for the use of file
      lockowner-file pair in question (i.e., one or more locking by applications.
      operations has occurred).  The NFS version 4 protocol provides more aggressive caching
   strategies with error NFS4ERR_OLD_STATEID should be
      returned.

      This error condition will only occur when the following design goals:

   o  Compatibility with client issues a large range of server semantics.
      locking request which changes a stateid while an I/O request that
      uses that stateid is outstanding.

   o  Provide the same caching benefits as previous versions of  The stateid was generated by the NFS
      protocol when unable to provide current server instance but the more aggressive model.

   o  Requirements for aggressive caching are organized so that
      stateid does not designate a large
      portion of the benefit can locking state for any active
      lockowner-file pair.  The error NFS4ERR_BAD_STATEID should be obtained even
      returned.

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

   One mechanism that may be met.

   The appropriate used to satisfy these requirements is for
   the server are discussed in later
   sections in which specific forms of caching are covered. (see
   Section 9.4 "Open Delegation").

9.2.  Delegation and Callbacks

   Recallable delegation to,
   o  divide the "other" field of each stateid into two fields:

      *  A server responsibilities for a file to verifier which uniquely designates a
   client improves performance by avoiding repeated requests to the particular server in the absence
         instantiation.

      *  An index into a table of inter-client conflict.  With locking-state structures.

   o  utilize the use "seqid" field 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 each stateid, such that seqid is passed from the server to
      monotonically incremented for each stateid that is associated with
      the client, specifying same index into the
   object of locking-state table.

   By matching the delegation incoming stateid and its field values with the type of delegation.  There are
   different types of delegations but each type contains a stateid to be
   used to represent state
   held at the delegation when performing operations that
   depend on server, the delegation.  This stateid server is similar able to those
   associated with locks easily determine if a
   stateid is valid for its current instantiation and share reservations but differs in that state.  If the
   stateid for a delegation is associated with a clientid and may not valid, the appropriate error can be
   used on behalf supplied to the
   client.

9.1.4.  Use of all the open_owners for stateid and Locking

   All READ, WRITE and SETATTR operations contain a stateid.  For the given client.  A
   delegation is made to
   purposes of this section, SETATTR operations which change the client as size
   attribute of a whole file are treated as if they are writing the area
   between the old and not to any specific
   process new size (i.e., the range truncated or thread of control within it.

   Because callback RPCs may not work in all environments (due added to
   firewalls, for example), correct protocol operation does not depend
   on them.  Preliminary testing of callback functionality
   the file by means of a
   CB_NULL procedure determines whether callbacks can be supported.  The
   CB_NULL procedure checks the continuity of SETATTR), even where SETATTR is not
   explicitly mentioned in the callback path.  A
   server makes text.

   If the lock_owner performs a preliminary assessment of callback availability to READ or WRITE in a
   given client and avoids delegating responsibilities until situation in which it
   has
   determined that callbacks are supported.  Because the granting of established a
   delegation is always conditional upon lock or share reservation on the absence of conflicting
   access, clients must not assume that server (any OPEN
   constitutes a delegation will be granted and
   they share reservation) the stateid (previously returned by
   the server) 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 used to renewal together with all
   of the other leases indicate what locks, including both
   record locks and share reservations, are held by that client.

   Unlike locks, an operation the lockowner.  If
   no state is established by a second client to a delegated file
   will cause the server to recall client, either record lock or share
   reservation, a delegation through stateid of all bits 0 is used.  Regardless whether 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
   stateid of all bits 0, or a response
   until stateid returned by the recall server is complete.  The recall used,
   if there is considered complete when
   the client returns the delegation a conflicting share reservation or the server times out mandatory record lock
   held on the
   recall and revokes the delegation as a result of the timeout.
   Following the resolution of the recall, file, the server has the
   information necessary MUST refuse to grant or deny the second client's request.

   At service the time READ or WRITE
   operation.

   Share reservations are established by OPEN operations and by their
   nature are mandatory in that when the client receives a delegation recall, it may have
   substantial state OPEN denies READ or WRITE
   operations, that needs to denial results in such operations being rejected
   with error NFS4ERR_LOCKED.  Record locks may be flushed to the server.  Therefore, implemented by the
   server should allow sufficient time for as either mandatory or advisory, or the delegation to be
   returned since it choice of mandatory or
   advisory behavior may involve numerous RPCs to the server.  If be determined by the server is able to determine that the client is diligently flushing
   state to on the server as a result basis of the recall, the server may extend
   the usual time allowed for
   file being accessed (for example, some UNIX-based servers support a recall.  However,
   "mandatory lock bit" on the time allowed for
   recall completion should not be unbounded.

   An example of this is when responsibility to mediate opens mode attribute such that if set, record
   locks are required on a given the file before I/O is delegated to a client (see Section 9.4 "Open Delegation").
   The server will not know what opens possible).  When record
   locks are in 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.
   Without this knowledge
   client gets NFS4ERR_LOCKED on a file it knows it has the server proper share
   reservation for, it will be unable need to determine if issue a LOCK request on the
   access and deny state for region
   of the file allows any particular open until that includes the delegation for region the file has been returned.

   A client failure or a network partition can result in failure to
   respond I/O was to be performed on,
   with an appropriate locktype (i.e., READ*_LT for a recall callback.  In this case, READ operation,
   WRITE*_LT for a WRITE operation).

   With NFS version 3, there was no notion of a stateid so there was no
   way to tell if the server will revoke application process of the delegation which in turn will render useless any modified state
   still on client sending the client.

9.2.1.  Delegation Recovery

   There are three situations that delegation recovery must deal with:

   o  Client reboot or restart

   o  Server reboot or restart

   o  Network partition (full READ
   or callback-only)

   In the event WRITE operation had also acquired the client reboots or restarts, appropriate record lock on
   the failure file.  Thus there was no way to renew
   leases will result in implement mandatory locking.
   With the revocation of stateid construct, this barrier has been removed.

   Note that for UNIX environments that support mandatory file locking,
   the distinction between advisory and mandatory locking is subtle.  In
   fact, advisory and mandatory record locks and share
   reservations.  Delegations, however, may be treated a bit
   differently.

   There will be situations are exactly the same in which delegations will need to be
   reestablished after a client reboots or restarts.  The reason for
   this is so
   far as the client may have file data stored locally APIs and this data
   was associated with requirements on implementation.  If the previously held delegations.  The client will
   need mandatory
   lock attribute is set on the file, the server checks to reestablish see if the
   lockowner has an appropriate file state shared (read) or exclusive (write)
   record lock on the server.

   To allow for this type of client recovery, region it wishes to read or write to.  If there is
   no appropriate lock, the server MAY extend checks if there is a conflicting lock
   (which can be done by attempting to acquire the
   period for delegation recovery beyond conflicting lock on
   the typical lease expiration
   period.  This implies that requests from other clients that conflict
   with these delegations will need to wait.  Because behalf of the normal recall
   process may require significant time lockowner, and if successful, release the lock
   after the READ or WRITE is done), and if there is, the server returns
   NFS4ERR_LOCKED.

   For Windows environments, there are no advisory record locks, so the
   server always checks for record locks during I/O requests.

   Thus, the client to flush changed
   state NFS version 4 LOCK operation does not need to distinguish
   between advisory and mandatory record locks.  It is the server, other clients need be prepared for delays that
   occur because NFS version 4
   server's processing of a conflicting delegation.  This longer interval
   would increase the window for clients to reboot READ and consult stable
   storage so WRITE operations that introduces
   the delegations can be reclaimed.  For open
   delegations, such delegations are reclaimed using OPEN with 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 claim
   type of CLAIM_DELEGATE_PREV.  (See Section 9.5 "Data Caching and
   Revocation" and Section 14.18 "Operation 18: OPEN" LOCK-type operation (i.e., LOCK or LOCKU),
   defines an access mode for discussion of
   open delegation and the details of file (i.e., READ, WRITE, or READ-
   WRITE) as established by the original 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, which began the stateid
   sequence, and
   instead MUST, for a period of time no less than as modified by subsequent OPENs and OPEN_DOWNGRADEs
   within that of the value of stateid sequence.  When a READ, WRITE, or SETATTR which
   specifies the lease_time size attribute, maintain is done, the client's delegations operation is subject to allow
   time for
   checking against the client access mode to issue CLAIM_DELEGATE_PREV requests.  The
   server verify that supports CLAIM_DELEGATE_PREV MUST support the DELEGPURGE
   operation.

   When the server reboots or restarts, delegations are reclaimed (using operation is
   appropriate given the OPEN operation with CLAIM_PREVIOUS) in a similar fashion to
   record locks and share reservations.  However, there which the operation is a slight
   semantic difference. associated.

   In the normal case if of WRITE-type operations (i.e., WRITEs and SETATTRs which
   set size), the server decides must verify that a
   delegation should not be granted, the access mode allows writing
   and return an NFS4ERR_OPENMODE error if it performs does not.  In the requested action
   (e.g., OPEN) without granting any delegation.  For reclaim, case, of
   READ, 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, may perform the client has corresponding check on the duty access
   mode, or it may choose to
   write all modified state allow READ on opens for WRITE only, 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
   accommodate clients whose write implementation may unavoidably do
   reads (e.g., due to receive them.

   When a network partition occurs, delegations buffer cache constraints).  However, even if
   READs are subject to freeing
   by allowed in these circumstances, the server when the lease renewal period expires.  This is similar
   to the behavior MUST still check
   for locks and share reservations.  For delegations,
   however, that conflict with the READ (e.g., another open specify
   denial of READs).  Note that a server may extend the period in which does enforce the access
   mode check on READs need not explicitly check for conflicting
   requests are held off.  Eventually share
   reservations since the occurrence existence of a OPEN for read access guarantees
   that no conflicting
   request from another client will cause revocation of the delegation. share reservation can exist.

   A loss stateid of all bits 1 (one) MAY allow READ operations to bypass
   locking checks at the callback path (e.g., by later network configuration
   change) will have server.  However, WRITE operations with a
   stateid with bits all 1 (one) MUST NOT bypass locking checks and are
   treated exactly the same effect. as if a stateid of all bits 0 were used.

   A recall request will fail lock may not be granted while a READ or WRITE operation using one
   of the special stateids is being performed and
   revocation the range of the delegation will result.

   A client normally finds out about revocation lock
   request conflicts with the range of the READ or WRITE operation.  For
   the purposes of this paragraph, a delegation conflict occurs when it
   uses a stateid associated with shared lock
   is requested and a delegation WRITE operation is being performed, or an
   exclusive lock is requested and receives the error
   NFS4ERR_EXPIRED.  It also may find out about delegation revocation
   after either a client reboot when it attempts to reclaim READ or a delegation and
   receives that same error.  Note WRITE operation is
   being performed.  A SETATTR that in the case of a revoked write
   open delegation, there are issues because data may have been modified
   by the client whose delegation sets size is revoked and separately by other
   clients.  See Section 9.5.1 "Revocation Recovery for Write Open
   Delegation" for treated similarly to a discussion
   WRITE as discussed above.

9.1.5.  Sequencing of such issues.  Note also Lock Requests

   Locking is different than most NFS operations as it requires "at-
   most-one" semantics that when
   delegations are revoked, information about the revoked delegation
   will be written not provided by the server to stable storage (as described in
   Section 8.6 "Crash Recovery").  This is done to deal with the case in
   which a server reboots after revoking ONCRPC.  ONCRPC over a delegation but before the
   client holding the revoked delegation
   reliable transport is notified about the
   revocation.

9.3.  Data Caching

   When applications share access to not sufficient because a set of files, they need to be
   implemented so as to take account sequence of locking
   requests may span multiple TCP connections.  In the possibility face of conflicting
   access by another application.  This
   retransmission or reordering, lock or unlock requests must have a
   well defined and consistent behavior.  To accomplish this, each lock
   request contains a sequence number that is true whether the applications
   in question execute on a consecutively increasing
   integer.  Different lock_owners have different clients or reside on sequences.  The server
   maintains the same
   client.

   Share reservations last sequence number (L) received 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 response that it does not
   invalidate the assumptions
   was returned.  The first request issued for any given lock_owner is
   issued with a sequence number of zero.

   Note that those using these facilities depend
   upon.

9.3.1.  Data Caching and OPENs

   In order to avoid invalidating the sharing assumptions for requests that
   applications rely on, NFS version 4 clients contain a sequence number, for each
   lock_owner, there 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 no more than one outstanding request.

   If a READ or
   WRITE operation.

   Furthermore, in request (r) with a previous sequence number (r < L) is received,
   it is rejected with the absence return of open delegation (see Section 9.4 "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 error NFS4ERR_BAD_SEQID.  Given a client
   properly-functioning client, the response to (r) must be revalidated after
      doing an OPEN.  Revalidating means that have been
   received before the client fetches last request (L) was sent.  If a duplicate of
   last request (r == L) is received, the
      change attribute from stored response is returned.
   If a request beyond the server, compares next sequence (r == L + 2) is received, it is
   rejected with the cached
      change attribute, and if different, declares return of error NFS4ERR_BAD_SEQID.  Sequence
   history is reinitialized whenever the cached data (as
      well as SETCLIENTID/SETCLIENTID_CONFIRM
   sequence changes the cached attributes) as invalid.  This client verifier.

   Since the sequence number is to ensure that represented with an unsigned 32-bit
   integer, the data for arithmetic involved with the OPENed file sequence number is still correctly reflected in the
      client's cache.  This validation must be done at least when mod
   2^32.  For an example of modulo arithmetic involving sequence numbers
   see [29].

   It is critical the
      client's OPEN operation includes DENY=WRITE or BOTH thus
      terminating a period in which other clients may have had server maintain the
      opportunity last response sent to open the file with WRITE access.  Clients may
      choose
   client to do the revalidation provide a more often (i.e., at OPENs
      specifying DENY=NONE) to parallel the NFS version 3 protocol's
      practice for the benefit reliable cache of users assuming this degree duplicate non-idempotent
   requests than that of cache
      revalidation.  Since the change attribute is updated traditional cache described in [30].  The
   traditional duplicate request cache uses a least recently used
   algorithm for data removing unneeded requests.  However, the last lock
   request and
      metadata modifications, some client implementors may response on a given lock_owner must 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. as long as
   the lock state exists on the server.

   The implementor client MUST monotonically increment the sequence number for the
   CLOSE, LOCK, LOCKU, OPEN, OPEN_CONFIRM, and OPEN_DOWNGRADE
   operations.  This is cautioned true even in this approach. the event that the previous
   operation that used the sequence number received an error.  The change
      attribute is guaranteed to change for each update only
   exception to the file,
      whereas time_modify this rule is guaranteed to change only at if the
      granularity previous operation received one of
   the time_delta attribute.  Use by following errors: NFS4ERR_STALE_CLIENTID, NFS4ERR_STALE_STATEID,
   NFS4ERR_BAD_STATEID, NFS4ERR_BAD_SEQID, NFS4ERR_BADXDR,
   NFS4ERR_RESOURCE, NFS4ERR_NOFILEHANDLE.

9.1.6.  Recovery from Replayed Requests

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

   LOCK, LOCKU, OPEN, OPEN_DOWNGRADE, and not change runs CLOSE each contain a sequence
   number and therefore the risk of the client incorrectly marking stale data as valid.

   o  Second, modified data must be flushed to replay of these operations
   resulting in undesired effects is non-existent while the server before closing
   maintains the lock_owner state.

9.1.7.  Releasing lock_owner State

   When a particular lock_owner no longer holds open or file OPENed for write.  This is complementary to the first rule.
      If the data is not flushed locking
   state at CLOSE, the revalidation done after
      client OPENs as file is unable server, the server may choose to achieve its purpose. release the sequence
   number state associated with the lock_owner.  The server may make
   this choice based on lease expiration, for the reclamation of server
   memory, or other
      aspect to flushing implementation specific details.  In any event, the data before close
   server is that the data must be
      committed able to stable storage, at the server, before do this safely only when the CLOSE
      operation lock_owner no longer
   is requested being utilized by the client.  The server may choose to hold the
   lock_owner state in the event that retransmitted requests are
   received.  However, the period to hold this state is implementation
   specific.

   In the case of that a server
      reboot LOCK, LOCKU, OPEN_DOWNGRADE, or restart CLOSE is
   retransmitted after the server has previously released the lock_owner
   state, the server will find that the lock_owner has no files open and a CLOSEd file, it may not
   an error will be possible returned to
      retransmit the data to be written to client.  If the file.  Hence, this
      requirement.

9.3.2.  Data Caching and File Locking

   For those applications that choose to use file locking instead of
   share reservations to exclude inconsistent lock_owner does have
   a file access, there is open, the stateid will not match and again an
   analogous set error is
   returned to the client.

9.1.8.  Use of constraints Open Confirmation

   In the case that apply to client side data caching.
   These rules are effective only if an OPEN is retransmitted and the file locking lock_owner is being
   used in a way
   that matches in an equivalent way for 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 first time or the lock_owner state has been previously
   released by dividing the file into two one-megabyte
   regions and protecting access to server, the two regions by file locks on
   bytes zero and one.  A lock for write on byte zero use of the file would
   represent OPEN_CONFIRM operation will
   prevent incorrect behavior.  When the right to do READ and WRITE operations on server observes the first
   region.  A lock for write on byte one use of the file would represent
   lock_owner for the
   right first time, it will direct the client to do READ and WRITE operations on perform
   the second region.  As long
   as all applications manipulating OPEN_CONFIRM for the file obey this convention, they
   will work on a local filesystem.  However, they may not work with corresponding OPEN.  This sequence
   establishes the
   NFS version 4 protocol unless clients refrain from data caching.

   The rules for data caching in use of an lock_owner and associated sequence number.
   Since the file locking environment are:

   o  First, when a client obtains OPEN_CONFIRM sequence connects a file lock for new open_owner on the
   server with an existing open_owner on a particular region, client, the data cache corresponding to that region (if sequence number
   may have any cached data
      exists) must be revalidated.  If value.  The OPEN_CONFIRM step assures the change attribute indicates server that
   the file may have been updated since the cached data was
      obtained, value received is the client must flush or invalidate correct one. (see Section 15.20 for further
   details.)

   There are a number of situations in which the cached data requirement to confirm
   an OPEN would pose difficulties for the newly locked region.  A client might choose to invalidate all
      of non-modified cached data and server, in that it has for
   they would be prevented from acting in a timely fashion on
   information received, because that information would be provisional,
   subject to deletion upon non-confirmation.  Fortunately, these are
   situations in which the file but server can avoid the only
      requirement need for correct operation is confirmation
   when responding to invalidate all of the data
      in the newly locked region. open requests.  The two constraints are:

   o  Second, before releasing  The server must not bestow a write lock delegation for any open which would
      require confirmation.

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

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

   Delegations being sent with an open requiring confirmation are
   troublesome because recovering from non-confirmation adds undue
   complexity to stable storage.

   Note the protocol while requiring confirmation on reclaim-
   type opens poses difficulties in that flushing data to the server and inability to resolve the invalidation
   status of cached
   data must reflect the actual byte ranges locked or unlocked.
   Rounding these up or down reclaim until lease expiration may make it difficult to reflect client cache block boundaries
   will cause problems if not carefully done.  For example, writing a
   modified block when only half
   have timely determination of that block is within an area the set of locks being
   unlocked reclaimed (since
   the grace period may cause invalid modification to expire).

   Requiring open confirmation on reclaim-type opens is avoidable
   because of the region outside nature of the
   unlocked area.  This, environments in turn, may which such opens are
   done.  For CLAIM_PREVIOUS opens, this is immediately after server
   reboot, so there should be part of no time for lockowners to be created,
   found to be unused, and recycled.  For CLAIM_DELEGATE_PREV opens, we
   are dealing with a region locked by
   another client.  Clients client reboot situation.  A server which supports
   delegation can avoid this situation by synchronously
   performing portions of write operations be sure that overlap no lockowners for that portion
   (initial or final) client have been
   recycled since client initialization and thus can ensure that is
   confirmation will not be required.

9.2.  Lock Ranges

   The protocol allows a full block.  Similarly, invalidating lock owner to request a locked area which lock with a byte range
   and then either upgrade or unlock a sub-range of the initial lock.
   It is not expected that this will be an integral number uncommon type of full buffer blocks
   would require the client to read one request.  In any
   case, servers or two partial blocks from the server if the revalidation procedure shows that the data which the
   client possesses filesystems may not be valid.

   The data that is written able to support sub-
   range lock semantics.  In the event that a server as receives a prerequisite locking
   request that represents a sub-range of current locking state for the
   lock owner, the server is allowed to return the
   unlocking of a region must error
   NFS4ERR_LOCK_RANGE to signify that it does not support sub-range lock
   operations.  Therefore, the client should be written, at prepared to receive this
   error and, if appropriate, report the server, error to stable
   storage. the requesting
   application.

   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 discouraged from combining multiple independent locking
   ranges that happen to be adjacent into a single request since the
   server reboot might conflict with a lock held by another client.

   A client implementation may choose not support sub-range requests and for reasons related to accommodate applications which
   use record
   the recovery of file locking state in non-standard ways (e.g., using a record lock as
   a global semaphore) by flushing to the event of 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 failure.
   As discussed in the unlocks are being done.
   In such cases, Section 9.6.2 below, the client must not interfere with applications whose
   READs and WRITEs are being done server may employ
   certain optimizations during recovery that work effectively only within when
   the bounds of record
   locks which client's behavior during lock recovery is similar to the application holds.  For example, an application locks client's
   locking behavior prior to server failure.

9.3.  Upgrading and Downgrading Locks

   If a single byte of client has a file and proceeds to write that single byte.  A
   client that chose to handle lock on 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 record, 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 request an appropriate record atomic
   downgrade of the lock and those for which there
   are modifications not covered by to a record lock.  Any writes done for read lock via the former class of files must not include areas not locked and thus
   not modified on LOCK request, by setting
   the client.

9.3.3.  Data Caching and Mandatory File Locking

   Client side data caching needs type to respect mandatory file locking when READ_LT.  If the server supports atomic downgrade, the
   request will succeed.  If not, it is in effect. will return NFS4ERR_LOCK_NOTSUPP.
   The presence of mandatory file locking for a given
   file is indicated when client should be prepared to receive this error, and if
   appropriate, report the error to the requesting application.

   If a client gets back NFS4ERR_LOCKED from has a
   READ or WRITE read lock on a file record, it has can request an appropriate share reservation for.
   When mandatory locking is in effect for a file, atomic
   upgrade of the client must check
   for an appropriate file lock for data being read or written.  If to a write lock exists for the range being read or written, the client may
   satisfy via the LOCK request using by setting
   the client's validated cache. type to WRITE_LT or WRITEW_LT.  If an
   appropriate file lock is the server does not held for support
   atomic upgrade, it will return NFS4ERR_LOCK_NOTSUPP.  If the range of upgrade
   can be achieved without an existing conflict, the read or write, request will
   succeed.  Otherwise, the read server will return either NFS4ERR_DENIED or write request must not be satisfied by
   NFS4ERR_DEADLOCK.  The error NFS4ERR_DEADLOCK is returned if the client's cache
   and
   client issued the LOCK request must be sent with the type set to WRITEW_LT and the
   server for processing.  When a
   read or write request partially overlaps has detected a locked region, the request deadlock.  The client should be subdivided into multiple pieces with each region (locked or
   not) treated appropriately.

9.3.4.  Data Caching prepared to
   receive such errors and File Identity

   When clients cache data, if appropriate, report the file data needs to be organized
   according error to the filesystem object to which
   requesting application.

9.4.  Blocking Locks

   Some clients require the data belongs.  For support of blocking locks.  The NFS version 3 clients, the typical practice
   4 protocol must not rely on a callback mechanism and therefore is
   unable to notify a client when a previously denied lock has been
   granted.  Clients have no choice but to assume continually poll for the purpose of caching
   lock.  This presents a fairness problem.  Two new lock types are
   added, READW and WRITEW, and are used to indicate to the server that distinct filehandles represent distinct
   filesystem objects.  The client then has
   the choice to organize and client is requesting a blocking lock.  The server should maintain
   an ordered list of pending blocking locks.  When the data cache on this basis.

   In the NFS version 4 protocol, there conflicting lock
   is now released, the possibility to have
   significant deviations from a "one filehandle per object" model
   because a filehandle server may be constructed on wait the basis of lease period for the object's
   pathname.  Therefore, clients need a reliable method first
   waiting client to determine if
   two filehandles designate re-request the same filesystem object.  If clients
   were simply to assume that all distinct filehandles denote distinct
   objects and proceed to do data caching on this basis, caching
   inconsistencies would arise between lock.  After the distinct lease period
   expires the next waiting client side objects
   which mapped to request is allowed the same server side object.

   By providing a method lock.  Clients
   are required to differentiate filehandles, poll at an interval sufficiently small that it is
   likely to acquire the NFS version 4
   protocol alleviates a potential functional regression lock in comparison
   with the NFS version 3 protocol.  Without this method, caching
   inconsistencies within the same client could occur and this has a timely manner.  The server is not
   been present in previous versions
   required to maintain a list of the NFS protocol.  Note that pending blocked locks as it is possible used to have such inconsistencies with applications executing
   on multiple clients but that is
   increase fairness and not correct operation.  Because of the issue being addressed here.

   For
   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 purposes lock types and delay returning denial of data caching,
   the following steps request to allow an NFS
   version 4 client extra time for a conflicting lock to determine whether two distinct filehandles denote be
   released, allowing a successful return.  In this way, clients can
   avoid the same burden of needlessly frequent polling for blocking locks.
   The server side object:

   o  If GETATTR directed to two filehandles returns different values should take care in the length of delay in the fsid attribute, then event the filehandles represent distinct
      objects.

   o  If GETATTR for any file with an fsid that matches
   client retransmits the fsid request.

9.5.  Lease Renewal

   The purpose of the
      two filehandles in question returns a unique_handles attribute
      with lease is to allow a value of TRUE, then the two objects are distinct.

   o  If GETATTR directed server to the two filehandles does remove stale locks
   that are held by a client that has crashed or is otherwise
   unreachable.  It is not return the
      fileid attribute a mechanism for both of the handles, then it cannot cache consistency and lease
   renewals may not be
      determined whether the two objects are denied if the same.  Therefore,
      operations which depend on that knowledge (e.g., client side data
      caching) cannot be done reliably.

   o  If GETATTR directed to lease interval has not expired.

   The following events cause implicit renewal of all of the two filehandles returns different
      values leases for the fileid attribute, then they are distinct objects.

   o  Otherwise they are the same object.

9.4.  Open Delegation

   When
   a file given client (i.e., all those sharing a given clientid).  Each of
   these is being OPENed, a positive indication that the server may delegate further handling
   of opens client is still active and closes for
   that file to the opening client.  Any such
   delegation is recallable, since associated state held at the circumstances that allowed server, 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
   still valid.

   o  An OPEN either will or
   will not result in an open delegation.  The following is with a typical
   set valid clientid.

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

      Note that servers might use in deciding whether OPEN
   should be delegated:

   o  The if the client must had restarted or rebooted, the client
      would not be able to respond to making these requests without issuing the server's callback
      requests.
      SETCLIENTID/SETCLIENTID_CONFIRM sequence.  The server will use the CB_NULL procedure for a test of
      callback ability.

   o  The the
      SETCLIENTID/SETCLIENTID_CONFIRM sequence (one that changes the
      client must have responded properly verifier) notifies the server to previous recalls.

   o  There must be no current open conflicting with drop the requested
      delegation.

   o  There should be no current delegation that conflicts locking state
      associated with the
      delegation being requested.

   o  The probability of future conflicting open requests should client.  SETCLIENTID/SETCLIENTID_CONFIRM never
      renews a lease.

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

   This approach allows for low
      based on overhead lease renewal which scales
   well.  In the recent history of typical case no extra RPC calls are required for lease
   renewal and in the file.

   o worst case one RPC is required every lease period
   (i.e., a RENEW operation).  The existence of any server-specific semantics number of OPEN/CLOSE that
      would make locks held by the required handling incompatible client is
   not a factor since all state for the client is involved with the prescribed
      handling
   lease renewal action.

   Since all operations that the delegated client would apply (see below).

   There are two types of open delegations, read and write.  A read open
   delegation allows create a client to handle, on its own, requests to open new lease also renew existing
   leases, the server must maintain a
   file common lease expiration time 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 valid leases for a given file at a given client.  This lease time and it can then be
   easily updated upon implicit lease renewal actions.

9.6.  Crash Recovery

   The important requirement in crash recovery is inconsistent with any read open
   delegations.

   When a that both the client has a read open delegation, it may not make any changes
   to
   and the contents or attributes of server know when the file but other has failed.  Additionally, it is assured
   required that no
   other client may do so.  When a client has sees a write open delegation,
   it consistent view of data across server
   restarts or reboots.  All READ and WRITE operations that may modify have
   been queued within the file data since no other client will be accessing or network buffers must wait until the file's data.  The
   client holding a write delegation may only
   affect file attributes which are intimately connected with has successfully recovered the file
   data: size, time_modify, change.

   When locks protecting the READ and
   WRITE operations.

9.6.1.  Client Failure and Recovery

   In the event that a client has an open delegation, it does not send OPENs or
   CLOSEs to fails, the server but updates may recover the appropriate status internally.
   For a read open delegation, opens that cannot client's
   locks when the associated leases have expired.  Conflicting locks
   from another client may only be handled locally
   (opens for write granted after this lease expiration.
   If the client is able to restart or that deny read access) must reinitialize within the lease
   period the client may be sent forced to wait the
   server.

   When remainder of the lease
   period before obtaining new locks.

   To minimize client delay upon restart, lock requests are associated
   with an open delegation instance of the client by a client supplied verifier.  This
   verifier is made, part of the response to initial SETCLIENTID call made by the OPEN contains an
   open delegation structure which specifies client.
   The server returns a clientid as a result of the following:

   o SETCLIENTID
   operation.  The client then confirms the type of delegation (read or write)

   o  space limitation information to control flushing use of data on close
      (write open delegation only, see Section 9.4.1 "Open Delegation
      and Data Caching")

   o  an nfsace4 specifying read and write permissions

   o  a stateid to represent the delegation for READ and WRITE clientid with
   SETCLIENTID_CONFIRM.  The delegation stateid clientid in combination with an opaque
   owner field is separate and distinct from the stateid for then used by the OPEN proper.  The standard stateid, unlike client to identify the delegation
   stateid, lock owner for
   OPEN.  This chain of associations is associated with then used to identify all locks
   for a particular lock_owner and client.

   Since the verifier will continue
   to be valid after changed by the delegation is recalled and client upon each
   initialization, the file remains
   open.

   When server can compare a request internal new verifier to the client is made to open a file verifier
   associated with currently held locks and open
   delegation is in effect, it will be accepted or rejected solely on determine that they do not
   match.  This signifies the basis client's new instantiation and subsequent
   loss of locking state.  As a result, the following conditions.  Any requirement for other
   checks server is free to be made by release
   all locks held which are associated with the delegate should result in open delegation
   being denied so old clientid which was
   derived from the old verifier.

   Note that the checks can be made by verifier must have the server itself.

   o  The access and deny bits same uniqueness properties of
   the verifier for the request COMMIT operation.

9.6.2.  Server Failure and Recovery

   If the file server loses locking state (usually as described
      in Section 8.9 "Share Reservations".

   o  The read a result of a restart
   or reboot), it must allow clients time to discover this fact and write permissions as determined below. re-
   establish the lost locking state.  The nfsace4 passed with delegation can client must be used able to avoid frequent
   ACCESS calls.  The permission check should be as follows:

   o  If re-
   establish the nfsace4 indicates that locking state without having the open may be done, then it should
      be server deny valid
   requests because the server has granted without reference conflicting access to another
   client.  Likewise, if there is the server.

   o  If the nfsace4 indicates possibility that the open may clients have not be done, then an
      ACCESS request must be sent to the server to obtain
   yet re-established their locking state for a file, the definitive
      answer.

   The server may return an nfsace4 must
   disallow READ and WRITE operations for that file.  The duration of
   this recovery period is more restrictive than equal to the
   actual ACL duration of the file.  This includes an nfsace4 lease period.

   A client can determine that specifies
   denial server failure (and thus loss of all access.  Note that some common practices such as
   mapping the traditional user "root" to the user "nobody" may make locking
   state) has occurred, when it
   incorrect to return the actual ACL receives one of the file in the delegation
   response. two errors.  The use of delegation together with various other forms of caching
   creates the possibility that no server authentication will ever be
   performed for
   NFS4ERR_STALE_STATEID error indicates a given user since all stateid invalidated by a
   reboot or restart.  The NFS4ERR_STALE_CLIENTID error indicates a
   clientid invalidated by reboot or restart.  When either of the user's requests might be
   satisfied locally.  Where these are
   received, the client is depending on the server for
   authentication, must establish a new clientid (see
   Section 9.1.1) and re-establish the client should be sure authentication occurs for
   each user by use locking state as discussed below.

   The period of special handling of locking and READs and WRITEs, equal
   in duration to the ACCESS operation.  This should be lease period, is referred to as the case
   even if an ACCESS operation would not be required otherwise.  As
   mentioned before, "grace
   period".  During the server may enforce frequent authentication grace period, clients recover locks and the
   associated state by
   returning an nfsace4 denying all access reclaim-type locking requests (i.e., LOCK
   requests with every open delegation.

9.4.1.  Open Delegation reclaim set to true and Data Caching OPEN delegation allows much operations with a claim
   type of CLAIM_PREVIOUS).  During the message overhead associated with grace period, the opening server must
   reject READ and closing files to be eliminated.  An open when WRITE operations and non-reclaim locking requests
   (i.e., other LOCK and OPEN operations) with an open
   delegation is in effect does not require that a validation message be
   sent to the server.  The continued endurance error of
   NFS4ERR_GRACE.

   If the "read open
   delegation" provides a guarantee server can reliably determine that no OPEN for write and thus no
   write has occurred.  Similarly, when closing granting a file opened for write
   and if write open delegation is in effect, non-reclaim
   request will not conflict with reclamation of locks by other clients,
   the data written NFS4ERR_GRACE error does not have to be flushed to returned and the server until non-
   reclaim client request can be serviced.  For the open delegation is
   recalled.  The continued endurance of server to be able to
   service READ and WRITE operations during the open delegation provides a grace period, it must
   again be able to guarantee that no open possible conflict could arise
   between an impending reclaim locking request and thus no read the READ or write has been done by
   another client.

   For WRITE
   operation.  If 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 server is unable to the READs and WRITEs offer that use guarantee, 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
   NFS4ERR_GRACE error must be returned to the client.

   For a server to recall a write open delegation.  A provide simple, valid handling during the grace
   period, the easiest method is to simply reject all non-reclaim
   locking requests and READ and WRITE with a special stateid done operations by another client will force returning the
   NFS4ERR_GRACE error.  However, a
   recall of read open delegations. server may keep information about
   granted locks in stable storage.  With delegations, a client is able to avoid writing data to this information, the server when the CLOSE
   could determine if a regular lock or READ or WRITE operation can be
   safely processed.

   For example, if a count of locks on a given file is serviced.  The file close system
   call is the usual point at which the client is notified of a lack of available in
   stable storage for the modified file data generated by storage, the
   application.  At server can track reclaimed locks for the close, file data is written to and
   when all reclaims have been processed, non-reclaim locking requests
   may be processed.  This way the server and
   through normal accounting can ensure that non-reclaim
   locking requests will not conflict with potential reclaim requests.
   With respect to I/O requests, if the server is able to determine if that
   there are no outstanding reclaim requests for a file by information
   from stable storage or another similar mechanism, the
   available filesystem space processing of
   I/O requests could proceed normally for the data has been exceeded (i.e., file.

   To reiterate, for a server returns NFS4ERR_NOSPC or NFS4ERR_DQUOT).  This accounting
   includes quotas.  The introduction of delegations requires that a
   alternative method allows non-reclaim lock and I/O
   requests to be in place 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 same type return of communication to
   occur between client NFS4ERR_GRACE errors for
   non-reclaim lock and server. I/O requests.  In this case the delegation response, client should
   employ a retry mechanism for the server provides either request.  A delay (on the limit order of
   several seconds) between retries should be used to avoid overwhelming
   the size server.  Further discussion of the file or the number of modified blocks and associated
   block size. general issue is included in
   [20].  The server client must ensure that account for the client will be server that is able to
   flush data to perform
   I/O and non-reclaim locking requests within the server of a size equal to grace period as well
   as those that provided in can not do so.

   A reclaim-type locking request outside the
   original delegation.  The server must make this assurance for all
   outstanding delegations.  Therefore, server's grace period can
   only succeed if the server must be careful in
   its management of available space for new can guarantee that no conflicting lock or modified data taking
   into account available filesystem space and any applicable quotas.
   The
   I/O request has been granted since reboot or restart.

   A server can recall delegations as may, upon restart, establish a result of managing new value for the
   available filesystem space.  The client should abide by lease
   period.  Therefore, clients should, once a new clientid is
   established, refetch the server's
   state space limits lease_time attribute and use it as the basis
   for lease renewal for delegations.  If the client exceeds lease associated with that server.
   However, the stated
   limits server must establish, for this restart event, a grace
   period at least as long as the delegation, lease period for the server's behavior is undefined.

   Based on previous server conditions, quotas or available filesystem space,
   instantiation.  This allows 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 client state obtained during the
   previous server on close.

   With respect to authentication, flushing modified data instance to the server
   after a CLOSE has occurred may be problematic.  For example, reliably re-established.

9.6.3.  Network Partitions and Recovery

   If the user duration of a network partition is greater than the application may have logged off lease
   period provided by the client and unexpired
   authentication credentials may server, the server will have not be present.  In received a
   lease renewal from the client.  If this case, occurs, the
   client may need to take special care to ensure that local unexpired
   credentials will in fact be available.  This server may be accomplished free
   all locks held for the client.  As a result, all stateids held by
   tracking the expiration time of credentials and flushing data well in
   advance of their expiration
   client will become invalid or by making private copies of
   credentials to assure their availability when needed.

9.4.2.  Open Delegation and File Locks

   When a stale.  Once the client holds a write open delegation, lock operations may be
   performed locally.  This includes those required for mandatory file
   locking.  This can be done since is able to
   reach the delegation implies that there
   can be no conflicting locks.  Similarly, server after such a network partition, all of I/O submitted by
   the revalidations
   that would normally be associated client with obtaining locks and the
   flushing of data associated now invalid stateids will fail with the releasing of locks need not be
   done.

   When a client holds a read open delegation, lock operations are not
   performed locally.  All lock operations, including those requesting
   non-exclusive locks, are sent to the server for resolution.

9.4.3.  Handling of CB_GETATTR

   The server needs to employ special handling for a GETATTR where
   returning the
   target is a file that has a write open delegation in effect.  The
   reason for error NFS4ERR_EXPIRED.  Once this error is that received,
   the client holding the write delegation may
   have modified will suitably notify the data and application that held the server needs to reflect this change lock.

   As a courtesy to the second client that submitted the GETATTR.  Therefore, or as an optimization, the server may
   continue to hold locks on behalf of a client
   holding for which recent
   communication has extended beyond the write delegation needs to be interrogated.  The server
   will use lease period.  If the CB_GETATTR operation.  The only attributes server
   receives a lock or I/O request that conflicts with one of these
   courtesy locks, the server can reliably query via CB_GETATTR are size must free the courtesy lock 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 grant the
   delegation has
   new request.

   When a modified version of network partition is combined with a server reboot, there are
   edge conditions that place requirements on the file.  If server in order to
   avoid silent data corruption following the client's copy server reboot.  Two of
   these edge conditions are known, and are discussed below.

   The first edge condition has the delegated file following scenario:

   1.  Client A acquires a lock.

   2.  Client A and server experience mutual network partition, such
       that client A is not modified (data or size), the unable to renew its lease.

   3.  Client A's lease expires, so server can
   satisfy releases lock.

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

   5.  Client B releases the second client's GETATTR request from lock

   6.  Server reboots

   7.  Network partition between client A and server heals.

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

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

   Thus, at the server.  If the file is modified, final step, the server
   only needs to know about this modified state. 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 follows:

   1.   Client A acquires a lock.

   2.   Server reboots.

   3.   Client A and server
   determines experience mutual network partition, such
        that the file client A is currently modified, it will respond unable to reclaim its lock within the grace
        period.

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

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

   6.   Client B releases the lock.

   7.   Server reboots a second client's GETATTR as if time.

   8.   Network partition between client A and server heals.

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

   10.  Client A reclaims its lock within the file had been modified locally
   at server's grace period.

   As with the server.

   Since first edge condition, the form final step of the change attribute is determined by scenario of
   the second edge condition has the server erroneously granting client
   A's lock reclaim.

   Solving the first and second edge conditions requires that the server
   either assume after it reboots that edge condition occurs, and thus
   return NFS4ERR_NO_GRACE for all reclaim attempts, or that the server
   record some information stable storage.  The amount of information
   the server records in stable storage is opaque in inverse proportion to how
   harsh the client, the client and server need wants to agree on a
   method of communicating be whenever the modified state edge conditions occur.  The
   server that is completely tolerant of all edge conditions will record
   in stable storage every lock that is acquired, removing the file.  For lock
   record from stable storage only when the size
   attribute, lock is unlocked by the
   client will report its current view of and the file size.

   For lock's lockowner advances the change attribute, sequence number such
   that the handling lock release is more involved. not the last stateful event for the
   lockowner's sequence.  For the client, two aforementioned edge conditions,
   the following steps will be taken when receiving harshest a
   write delegation:

   o  The value of the change attribute will be obtained from the server can be, and cached.  Let this value be represented by c.

   o  The client will create still support a value greater than c that will be used grace period for communicating modified data is held at the client.  Let this
      value be represented by d.

   o  When
   reclaims, requires that the client is queried via CB_GETATTR 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 change
      attribute, it checks to see client's id string

   o  a boolean that indicates if it holds modified data.  If the
      file client's lease expired or if there
      was administrative intervention (see Section 9.8) to revoke a
      record lock, share reservation, or delegation

   o  a timestamp that is modified, updated the value d is returned for first time after a server boot or
      reboot the change attribute
      value.  If this file is client acquires record locking, share reservation, or
      delegation state on the server.  The timestamp need not currently modified, be updated
      on subsequent lock requests until the client returns server reboots.

   The server implementation would also record in the value c for stable storage the change attribute.

   For simplicity of implementation,
   timestamps from the client MAY two most recent server reboots.

   Assuming the above record keeping, for each CB_GETATTR
   return the same value d.  This is true even if, between successive
   CB_GETATTR operations, first edge condition,
   after the client again modifies in server reboots, the file's data record that client A's lease expired
   means that another client could have acquired a conflicting record
   lock, share reservation, or metadata in its cache.  The delegation.  Hence the server must reject
   a reclaim from client can return A with the same value
   because error NFS4ERR_NO_GRACE.

   For the only requirement is second edge condition, after the server reboots for a second
   time, the record that the client be able to indicate
   to had an unexpired record lock, share
   reservation, or delegation established before the server server's previous
   incarnation means that the server must reject a reclaim from client holds modified data.  Therefore, A
   with the
   value error NFS4ERR_NO_GRACE.

   Regardless of d may always be c + 1.

   While the change attribute is opaque level and approach to record keeping, the client in server
   MUST implement one of the sense that
   it has no idea what units following strategies (which apply to
   reclaims of time, share reservations, record locks, and delegations):

   1.  Reject all reclaims with NFS4ERR_NO_GRACE.  This is superharsh,
       but necessary if any, the server is counting
   change with, it is does not opaque want to record lock state in
       stable storage.

   2.  Record sufficient state in stable storage such that all known
       edge conditions involving server reboot, including the client has to treat two noted
       in this section, are detected.  False positives are acceptable.
       Note that at this time, it as
   an unsigned integer, and is not known if there are other edge
       conditions.  In the event, after a server reboot, the server has to be able
       determines that there is unrecoverable damage or corruption to see
       the results
   of the client's changes to that integer.  Therefore, stable storage, then for all clients and/or locks
       affected, the server MUST
   encode return NFS4ERR_NO_GRACE.

   A mandate for 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 client's handling of octets.

   For the server, the following steps will be taken when providing a
   write delegation:

   o  Upon providing a write delegation, NFS4ERR_NO_GRACE error is
   outside the server will cache a copy scope 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 specification, since the same file to strategies for
   such handling are very dependent on the server, client's operating
   environment.  However, one potential approach is described below.

   When the server obtains client receives NFS4ERR_NO_GRACE, it could examine the
   change attribute from of the first
      client.  Let this value be cc.

   o  If objects the value cc client is equal trying to sc, the file is not modified and the
      server returns the current values for change, time_metadata, reclaim state
   for, and
      time_modify (for example) use that to the second client.

   o  If the value cc is NOT equal determine whether to sc, re-establish the file state via
   normal OPEN or LOCK requests.  This is currently modified
      at acceptable provided the first client and most likely will be modified at
   client's operating environment allows it.  In otherwords, 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, client
   implementor is computed by the
      server, such that nsc >= sc + 1.  The server then returns the
      constructed time_metadata, time_modify, and nsc values advised to document for his users the
      requester. behavior.  The server replaces sc in
   client could also inform the delegation application that its record with
      nsc.  To prevent 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
   Section 10.5, for a discussion of what the possibility client should do for
   dealing with unreclaimed delegations on client state.

   For further discussion of time_modify, time_metadata,
      and change revocation of locks see Section 9.8.

9.7.  Recovery from appearing a Lock Request Timeout or Abort

   In the event a lock request times out, a client may decide to go backward (which would happen if not
   retry the request.  The client holding may also abort the delegation fails to write its modified data request when the
   process for which it was issued is terminated (e.g., in UNIX due to a
   signal).  It is possible though that the server before received the delegation is revoked or returned), request
   and acted upon it.  This would change the
      server SHOULD update state on the file's metadata record with server without
   the
      constructed attribute values.  For reasons client being aware of reasonable
      performance, committing the constructed attribute values to stable
      storage change.  It is OPTIONAL.

      As discussed earlier in this section, paramount that the
   client MAY return re-synchronize state with server before it attempts any other
   operation that takes a seqid and/or a stateid with the same cc value on subsequent CB_GETATTR calls, even if
   lock_owner.  This is straightforward to do without a special re-
   synchronize operation.

   Since the file was
      modified in server maintains the client's last lock request and response
   received on the lock_owner, for each lock_owner, the client should
   cache yet again between successive
      CB_GETATTR calls.  Therefore, the server must assume last lock request it sent such that the file
      has been modified yet again, and MUST take care to ensure that lock request did
   not receive a response.  From this, the
      new nsc it constructs and returns is greater than next time the previous nsc
      it returned.  An example implementation's delegation record would
      satisfy this mandate by including client does a boolean field (let us call
   lock operation for the lock_owner, it
      "modified") that is set to false when can send the delegation cached request, if
   there is granted, one, and an sc value set at if the time of grant to request was one that established state
   (e.g., a LOCK or OPEN operation), the change attribute
      value. server will return the cached
   result or if never saw the request, perform it.  The modified field would be set client can
   follow up with a request to true remove the first time cc
      != sc, state (e.g., a LOCKU or CLOSE
   operation).  With this approach, the sequencing and would stay true until stateid
   information on the delegation is returned or
      revoked.  The processing for constructing nsc, time_modify, client and
      time_metadata would use this pseudo code:

   if (!modified) {
       do CB_GETATTR server for change the given lock_owner will
   re-synchronize 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) in turn the attributes
      it requested, but make sure size comes from what
      CB_GETATTR returned.  Do not update lock state will re-synchronize.

9.8.  Server Revocation of Locks

   At any point, the file's metadata
      with server can revoke locks held by a client and the client's modified size.

   o  In
   client must be prepared for this event.  When the case client detects that
   its locks have been or may have been revoked, the file attribute size client is different than
   responsible for validating the
      server's current value, state information between itself and
   the server treats this as a modification
      regardless of server.  Validating locking state for the value client means that it
   must verify or reclaim state for each lock currently held.

   The first instance of lock revocation is upon server reboot or re-
   initialization.  In this instance the change attribute retrieved via
      CB_GETATTR client will receive an error
   (NFS4ERR_STALE_STATEID or NFS4ERR_STALE_CLIENTID) and responds to the second client will
   proceed with normal crash recovery as described in the last step.

   This methodology resolves issues of clock differences between client
   and server and other scenarios where previous
   section.

   The second lock revocation event is the use of CB_GETATTR break
   down.

   It should be noted that inability to renew the server lease
   before expiration.  While this is under no obligation considered a rare or unusual event,
   the client must be prepared to use
   CB_GETATTR and therefore recover.  Both the server MAY simply recall and client
   will be able to detect the delegation failure to avoid its use.

9.4.4.  Recall of Open Delegation

   The following events necessitate recall renew the lease and are capable
   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 recovering without data corruption.  For the server, it tracks the
   last renewal event serviced for the file

   o  RENAME client and knows when the lease
   will expire.  Similarly, the client must track operations which will
   renew the lease period.  Using the time that each such request for was
   sent and the file as either source or target of time that the
      RENAME

   Whether a RENAME of a directory in corresponding reply was received, the path leading to
   client should bound the file
   results in recall of an open delegation depends on time that the semantics of corresponding renewal could
   have occurred on the server filesystem.  If and thus determine if it is possible that filesystem denies such RENAMEs when
   a
   file lease period expiration could have occurred.

   The third lock revocation event can occur as a result of
   administrative intervention within the lease period.  While this is open,
   considered a rare event, it is possible that the recall must be performed server's
   administrator has decided to determine whether release or revoke a particular lock held
   by the
   file in question is, in fact, open. client.  As a result of revocation, the client will receive an
   error of NFS4ERR_ADMIN_REVOKED.  In addition to this instance the situations above, client may
   assume that only the server lock_owner's locks have been lost.  The client
   notifies the lock holder appropriately.  The client may choose to recall
   open delegations at any time if resource constraints make it
   advisable to do so.  Clients should always be prepared for not assume
   the
   possibility lease period has been renewed as a result of recall.

   When a failed operation.

   When the client receives a recall determines the lease period may have expired, the
   client must mark all locks held for an open delegation, it needs the associated lease as
   "unvalidated".  This means the client has been unable to
   update re-establish
   or confirm the appropriate lock state on with the server.  As described
   in Section 9.6, there are scenarios in which the server before returning may grant
   conflicting locks after the delegation.  These
   same updates must be done whenever lease period has expired for a client.
   When it is possible that the lease period has expired, the client chooses
   must validate each lock currently held to return ensure that a
   delegation voluntarily. conflicting
   lock has not been granted.  The following items of state need to be
   dealt with:

   o  If client may accomplish this task by
   issuing an I/O request, either a pending I/O or a zero-length read,
   specifying the file stateid associated with the delegation lock in question.  If the
   response to the request is no longer open and
      no previous CLOSE operation success, the client has been sent to validated all of
   the server, a CLOSE
      operation must be sent to locks governed by that stateid and re-established the appropriate
   state between itself and the server.

   o

   If a file has other open references at the client, I/O request is not successful, then OPEN
      operations must be sent to one or more of the server.  The appropriate stateids
      will be provided locks
   associated with the stateid was revoked by the server for subsequent use by and the client
      since
   must notify the delegation stateid will not longer be valid.  These owner.

9.9.  Share Reservations

   A share reservation is a mechanism to control access to a file.  It
   is a separate and independent mechanism from record locking.  When a
   client opens a file, it issues an OPEN
      requests are done with operation to the server
   specifying the claim type of CLAIM_DELEGATE_CUR.  This
      will allow access required (READ, WRITE, or BOTH) and the presentation
   type of access to deny others (deny NONE, READ, WRITE, or BOTH).  If
   the delegation stateid so that OPEN fails the client can establish will fail the appropriate rights to perform application's open request.

   Pseudo-code definition of the OPEN.
      (see Section 14.18"Operation 18: OPEN" 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 details.)

   o  If there are granted file locks, the corresponding LOCK same open_owner.

   The constants used for the OPEN and OPEN_DOWNGRADE operations
      need to be performed.  This applies to for the write open delegation
      case only.

   o  For
   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;

9.10.  OPEN/CLOSE Operations

   To provide correct share semantics, a write open delegation, 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 at the time client intends to
   use a stateid of recall all 0's or all 1's, it must still obtain the
   filehandle for the regular file is 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 write, all modified data for regular files as used in previous versions of the file must be flushed NFS
   protocol.  This allows a create with a share to be done atomically.

   The CLOSE operation removes all share reservations held by the server.
   lock_owner on that file.  If the delegation had not existed, record locks are held, the client
      would have done this data flush 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 operation.

   o  For a write open delegation when
   of a file is that still open at the time
      of recall, has record locks held.  The server MUST return
   failure, NFS4ERR_LOCKS_HELD, if any modified data for locks would exist after the file needs to be flushed to
   CLOSE.

   The LOOKUP operation will return a filehandle without establishing
   any lock state on the server.

   o  With the write open delegation in place, it is possible that  Without a valid stateid, the
      file was truncated during server
   will assume the duration of client has the delegation. least access.  For example, the truncation could have occurred as a result of an OPEN
      UNCHECKED file
   opened with deny READ/WRITE cannot be accessed using a size attribute value of zero.  Therefore, if filehandle
   obtained through LOOKUP because it would not have a
      truncation valid stateid
   (i.e., using a stateid of the file has occurred all bits 0 or all bits 1).

9.10.1.  Close and this Retention of State Information

   Since a CLOSE operation has not
      been propagated to the server, the truncation must occur before
      any modified data is written to the server.

   In the case requests deallocation 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 stateid, dealing
   with retransmission of the write delegation was in
   effect.  However, because CLOSE, may pose special difficulties,
   since the write open delegation implies no other
   locking by other clients, a simpler implementation is state information, which normally would be used to flush all
   modified data for
   determine the file (as described just above) if any write
   lock has been released while state of the write open delegation was file being designated, might be
   deallocated, resulting in an NFS4ERR_BAD_STATEID error.

   Servers may deal with this problem in effect.

   An implementation need not wait until delegation recall (or deciding
   to voluntarily return a delegation) to perform any number of ways.  To provide
   the above
   actions, if implementation considerations (e.g., resource
   availability constraints) make that desirable.  Generally, however,
   the fact greatest degree assurance that the actual open state of protocol is being used
   properly, a server should, rather than deallocate the file may continue to
   change makes stateid, mark
   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 close-pending, and retain the
   delegation would clients be likely to do stateid with 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 status, until
   later deallocation.  In this way, a retransmitted CLOSE can be performed
   before the delegation is returned, including (when applicable)
   recognized since the
   close that corresponds stateid points to the open state information with this
   distinctive status, so that resulted in the delegation.
   These actions it can be performed either in previous requests or in
   previous operations in handled without error.

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

   o  Another validly sequenced request for the same COMPOUND request.

9.4.5.  Clients lockowner, that Fail to Honor Delegation Recalls

   A client may fail to respond to is
      not a recall for various reasons, such as retransmission.

   o  The time that a failure of lockowner is freed by the callback path from server due to period
      with no activity.

   o  All locks for the client.  The client
   may be unaware are freed as a result of a failure in SETCLIENTID.

   Servers may avoid this complexity, at the callback path.  This lack cost of
   awareness could result less complete
   protocol error checking, by simply responding NFS4_OK 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 event of
   a problem CLOSE for the client that held a write delegation.

   The server also has a dilemma in that deallocated stateid, on the client assumption that fails to
   respond to the recall might also this case
   must be sending other NFS requests,
   including those that renew the lease before the lease expires.
   Without returning caused by a retransmitted close.  When adopting this
   approach, it is desirable to at least log an error for those lease renewing operations, when returning a
   no-error indication in this situation.  If the server leads the client to believe that the delegation maintains a
   reply-cache mechanism, it has can verify the CLOSE is indeed a
   retransmission and avoid error logging in
   force.

   This difficulty most cases.

9.11.  Open Upgrade and Downgrade

   When an OPEN is solved by done for a file and the following rules:

   o  When lockowner for which the callback path open
   is down, being done already has the server MUST NOT revoke file open, the
      delegation if one of result is to upgrade the following occurs:

      *  The client has issued a RENEW operation and
   open file status maintained on the server has
         returned an NFS4ERR_CB_PATH_DOWN error.  The server MUST renew to include the lease for any record locks access and share reservations
   deny bits specified by the
         client has new OPEN as well as those for the existing
   OPEN.  The result is that there is one open file, as far as the server has known about (as opposed to those
         locks
   protocol is concerned, and share reservations the client has established but not
         yet sent to it includes the server, due to union of the delegation).  The server
         SHOULD give access and
   deny bits for all of the client OPEN requests completed.  Only a reasonable time to return its
         delegations single
   CLOSE will be done to reset the server before revoking effects of both OPENs.  Note that the client's
         delegations.

      *  The client has
   client, when issuing the OPEN, may not issued a RENEW operation for some period of
         time after 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 attempted chooses to export multiple filehandles corresponding
   to recall the delegation.  This
         period same file object and returns different filehandles on two
   different OPENs of time the same file object, the server MUST NOT be less than "OR"
   together the value of access and deny bits and coalesce the
         lease_time attribute.

   o  When two open files.
   Instead 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 server must use RENEW maintain separate OPENs with separate
   stateids and will require separate CLOSEs to do so.

9.4.6.  Delegation Revocation

   At free them.

   When multiple open files on the point a delegation is revoked, if there client are associated opens merged into a single open
   file object on the client, server, 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 of one of the open file.

   If no opens exist for the file at the point files (on the delegation is
   revoked, then notification
   client) may necessitate change of the revocation is unnecessary.
   However, if there is modified data present at access and deny status of the client for
   open file on the
   file, server.  This is because the user union of the application should be notified.  Unfortunately,
   it may not be possible to notify access and
   deny bits for the user since active applications remaining opens may not be present at smaller (i.e., a proper
   subset) than previously.  The OPEN_DOWNGRADE operation is used to
   make the client.  See Section 9.5.1 "Revocation
   Recovery for Write Open Delegation" for additional details.

9.5.  Data Caching and Revocation

   When locks necessary change 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 client should use it to be notified.  This notification includes applications with a
   file open update the
   server so that has a corresponding delegation which has been revoked.
   Cached data associated with share reservation requests by other clients are
   handled properly.

9.12.  Short and Long Leases

   When determining the revocation must be removed from time period for the
   client.  In server lease, the case usual
   lease tradeoffs apply.  Short leases are good for fast server
   recovery at a cost of modified data existing increased RENEW or READ (with zero length)
   requests.  Longer leases are certainly kinder and gentler to servers
   trying to handle very large numbers of clients.  The number of RENEW
   requests drop in proportion to the client's cache,
   that data lease time.  The disadvantages of
   long leases are slower recovery after server failure (the server must be removed from
   wait for the leases to expire and the grace period to elapse before
   granting new lock requests) and increased file contention (if client without it being written
   fails to transmit an unlock request then server must wait for lease
   expiration before granting new locks).

   Long leases are usable if the server is able to store lease state in
   non-volatile memory.  Upon recovery, the server.  As mentioned, server can reconstruct the assumptions made by
   lease state from its non-volatile memory and continue operation with
   its clients and therefore long leases would not be an issue.

9.13.  Clocks, Propagation Delay, and Calculating Lease Expiration

   To avoid the client need for synchronized clocks, lease times are no
   longer valid at granted by
   the point when server as a lock or delegation has been revoked.
   For example, another client may have been granted time delta.  However, there is a conflicting lock
   after requirement that the revocation
   client and server clocks do not drift excessively over the duration
   of the lock at lock.  There is also the first client.  Therefore, issue of propagation delay across the
   data within
   network which could easily be several hundred milliseconds as well as
   the lock range may have been modified by possibility that requests will be lost and need to be
   retransmitted.

   To take propagation delay into account, the other
   client.  Obviously, client should subtract it
   from lease times (e.g., if the first client estimates the one-way
   propagation delay as 200 msec, then it can assume that the lease is unable to guarantee
   already 200 msec old when it gets it).  In addition, it will take
   another 200 msec to the
   application what has occurred get a response back to the file in server.  So the case of revocation.

   Notification to client
   must send 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 renewal or on write data back to the close.  Where server 400 msec
   before 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. lease would expire.

   The justification for
   this is server's lease period configuration should take into account the
   network distance of the clients that an invariant for which an application depends on may will be
   violated.  Depending on how errors are typically treated for accessing the
   client operating environment, further levels of notification
   including logging, console messages, server's
   resources.  It is expected that the lease period will take into
   account the network propagation delays and GUI pop-ups may be
   appropriate.

9.5.1.  Revocation Recovery for Write Open Delegation

   Revocation recovery other network delay
   factors for a write open delegation poses the special
   issue of modified data in the client cache while population.  Since the file is not
   open.  In this situation, any client which protocol does not flush modified
   data allow
   for an automatic method to the server on each close must ensure that the user receives determine an appropriate notification of the failure as a result of lease period, the
   revocation.  Since such situations
   server's administrator may require human action have to
   correct problems, notification schemes in which tune the appropriate user
   or administrator is notified may be necessary.  Logging lease period.

9.14.  Migration, Replication and console
   messages are typical examples.

   If there State

   When responsibility for handling a given file system is modified data on the client, it must not be flushed
   normally transferred
   to a new server (migration) or the server.  A client may attempt chooses to provide a copy of
   the file data as modified during the delegation under a different
   name use an alternate
   server (e.g., in the filesystem name space response 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 server unresponsiveness) in question, such a saved copy of the client's view context
   of the file may
   be of particular value for recovery.  In other case, recovery using a
   copy of system replication, the file based partially on appropriate handling of state shared
   between the client's cached data client and
   partially on the server copy (i.e., locks, leases, stateids, and
   clientids) is 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 described below.  The handling differs between
   migration and replication.  For related discussion of possible problems.

   Saving file server
   state and recover of such modified data in delegation revocation situations may
   be limited to files of see the sections under Section 9.6.

   If server replica or a certain size server immigrating a filesystem agrees to, or might be used only when
   sufficient disk space
   is available within the target filesystem.
   Such saving may also be restricted to situations when expected to, accept opaque values from the client has
   sufficient buffering resources to keep the cached copy available
   until that originated
   from another server, then it is properly stored a wise implementation practice for
   the servers to encode the target filesystem.

9.6.  Attribute Caching

   The attributes discussed "opaque" values 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 network byte order.
   This way, servers acting as data
   caching replicas or immigrating filesystems will
   be able to parse values like stateids, directory cookies,
   filehandles, etc. even if their native byte order is for ordinary files.  Similarly, LOOKUP results different from an
   OPENATTR directory are to be cached on the same basis as any
   other
   pathnames servers cooperating in the replication and similarly for directory contents.

   Clients may cache file attributes obtained from migration of the server
   filesystem.

9.14.1.  Migration and use
   them to avoid subsequent GETATTR requests.  Such caching is write
   through State

   In the case of migration, the servers involved in that modification to file attributes is always done by
   means the migration of requests a
   filesystem SHOULD transfer all server state from the original to the server and should not
   new server.  This must be done locally and
   cached.  The exception to this are modifications to attributes that
   are intimately connected with data caching.  Therefore, extending in a
   file by writing data way that is transparent to the local data cache is reflected immediately
   in
   client.  This state transfer will ease the size as seen on client's transition when a
   filesystem migration occurs.  If the servers are successful in
   transferring all state, the client without this change being
   immediately reflected on will continue to use stateids
   assigned by the original server.  Normally such changes are not
   propagated directly to  Therefore the new server but when must
   recognize these stateids as valid.  This holds true for the modified data clientid
   as well.  Since responsibility for an entire filesystem is
   flushed to the server, analogous attribute changes are made on the
   server.  When open delegation
   transferred with a migration event, there is in effect, the modified attributes
   may be returned to no possibility that
   conflicts will arise on the new server in the response to as a CB_RECALL call.

   The result of local caching the transfer of
   locks.

   As part of attributes is that the attribute
   caches maintained on individual clients will not transfer of information between servers, leases would
   be coherent.
   Changes made in one order on transferred as well.  The leases being transferred to the new
   server may be seen in a different
   order on one client and in a third order on will typically have a different client.

   The typical filesystem application programming interfaces do not
   provide means to atomically modify or interrogate attributes expiration time from those for
   multiple files at
   the same time.  The following rules provide an
   environment where client, previously on the potential incoherences mentioned above can be
   reasonably managed.  These rules are derived from old server.  To maintain the practice of
   previous NFS protocols.

   o  All attributes for
   property that all leases on a given file (per-fsid attributes excepted) are
      cached as server for a unit at the given client so that no non-serializability can
      arise within expire
   at 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 same time, the server.

   o  When operations are performed that change attributes at server should advance the
      server, expiration time to
   the updated attribute set is requested as part later of the
      containing RPC. leases being transferred or the leases already
   present.  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 allows the GETATTR client to update the client's cached attributes.

   Note that if the full set maintain lease renewal of attributes both
   classes without special effort.

   The servers may choose not to be cached transfer the state information upon
   migration.  However, this choice is requested by
   READDIR, discouraged.  In this case, when
   the results can be cached by client presents state information from the original server (e.g.
   in a RENEW op or a READ op of zero length), the client on must be
   prepared to receive either NFS4ERR_STALE_CLIENTID or
   NFS4ERR_STALE_STATEID from the same basis as
   attributes obtained via GETATTR.

   A new server.  The client may validate should then
   recover its cached version of attributes for state information as it normally would in response to a file by
   fetching just both the change and time_access attributes and assuming
   that if the change attribute has
   server failure.  The new server must take care to allow for the same value
   recovery of state information 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 would in environments where the operation event of server
   restart.

   A client SHOULD re-establish new callback information with the new
   server as soon as possible, according to sequences described in
   Section 15.35 and Section 15.36.  This ensures that updates
   change does not update time_access.  For example, POSIX file
   semantics do server operations
   are not update access time when a file is modified blocked 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 inability to recall delegations.

9.14.2.  Replication and update its cached time_access.

   The State

   Since client may maintain a cache switch-over in the case of modified attributes for those
   attributes intimately connected with data replication is not under
   server control, the handling of modified regular files
   (size, time_modify, state is different.  In this case,
   leases, stateids and change).  Other than those three attributes,
   the client MUST NOT maintain clientids do not have validity across a cache of modified attributes.
   Instead, attribute changes are immediately sent
   transition from one server to another.  The client must re-establish
   its locks on the new server.

   In some operating environments, the equivalent to time_access is
   expected to  This can be implicitly updated by each read of compared to the content re-
   establishment of the
   file object.  If an NFS client is caching the content locks by means of reclaim-type requests after a file
   object, whether it
   server reboot.  The difference is a regular file, directory, that the server has no provision to
   distinguish requests reclaiming locks from those obtaining new locks
   or symbolic link, to defer the latter.  Thus, a client SHOULD NOT update the time_access attribute (via SETATTR
   or re-establishing a small READ or READDIR request) lock on the
   new 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 (by means of time_access a LOCK or OPEN request), may alter the change attribute on the server.
   If the change attribute changes, clients that are caching have the content
   will think the content has changed, and will re-read unmodified data
   from the server.  Nor is the client encouraged
   requests denied due to maintain a modified
   version conflicting lock.  Since replication is
   intended for read-only use of time_access filesystems, such denial of locks
   should not pose large difficulties in its cache, since this would mean that practice.  When an attempt to
   re-establish a lock on a new server is denied, the client will either eventually have to write should
   treat the access time to situation as if his original lock had been revoked.

9.14.3.  Notification of Migrated Lease

   In the
   server with bad performance effects, or it would never update case of lease renewal, the
   server's time_access, thereby resulting in client may not be submitting
   requests for a situation where an
   application filesystem that caches access time between a close and open has been migrated to another server.
   This can occur because of the
   same file observes the access time oscillating between the past and
   present. implicit lease renewal mechanism.  The time_access attribute always means
   client renews leases for all filesystems when submitting a request to
   any one filesystem at the time server.

   In order for the client to schedule renewal of last
   access 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 implicitly renew leases for a file by a read that was satisfied by 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
   way clients condition will tend to see only time_access changes that go forward
   in time.

9.7.  Data and Metadata Caching and Memory Mapped Files

   Some operating environments include
   continue until the capability for client receives an application
   to map a file's content into NFS4ERR_MOVED error and the application's address space.  Each
   time
   server receives the application accesses a memory location that corresponds subsequent GETATTR(fs_locations) for an access to
   each filesystem for which a
   block that lease has not been loaded into the address space, moved to a page fault
   occurs and the file is read (or if new server.

   When a client receives an NFS4ERR_LEASE_MOVED error, it should
   perform an operation on each filesystem associated with the block does not exist server in
   question.  When the
   file, client receives an NFS4ERR_MOVED error, the block is allocated and then instantiated in
   client can follow the
   application's address space).

   As long as each memory mapped access normal process to obtain the file requires a page
   fault, new server
   information (through the relevant attributes fs_locations attribute) and perform renewal
   of those leases on 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 new server.  If the server has not required these attributes had state
   transferred to it transparently, the client will not be
   updated on reads receive either
   NFS4ERR_STALE_CLIENTID or updates to NFS4ERR_STALE_STATEID from the file via memory access (regardless
   whether new server,
   as described above, and the file is local file or is being access remotely).  A client or server MAY fail to update attributes can then recover state information
   as it does in the event 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 failure.

9.14.4.  Migration and the Lease_time Attribute

   In order that has memory mapped a
      file that a client is also accessing, the client may not be able
      to get a consistent value appropriately manage its leases in the
   case of migration, the change attribute to determine
      whether its cache is stale or not.  A destination server that knows that the
      file is memory mapped could always pessimistically return updated must establish proper
   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 lease_time attribute.

   When state is transferred transparently, that state should include
   the negative performance implications correct value of this, such behavior is
      OPTIONAL.

   o  If the memory mapped file is not being modified lease_time attribute.  The lease_time
   attribute on the server, and
      instead is just being read by an application via the memory mapped
      interface, destination server must never be less than that on
   the client will not see an updated time_access
      attribute.  However, source since this would result in many operating environments, neither will
      any process running on premature expiration of leases
   granted by the source server.  Thus NFS clients are at no
      disadvantage with respect to local processes.

   o  If there  Upon migration in which state is another
   transferred transparently, the client that is memory mapping under no obligation to re-
   fetch the file, lease_time attribute and if
      that client is holding a write delegation, may continue to use the same set of issues
      as discussed in value
   previously fetched (on the previous two bullet items apply.  So, when source server).

   If state has not been transferred transparently (i.e., the client
   sees a real or simulated server does a CB_GETATTR to a file that reboot), 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 should fetch the file has been modified since
   value of lease_time on the delegation was
      granted, not whether it has been modified again between successive
      CB_GETATTR calls, new (i.e., destination) server, and use it
   for subsequent locking requests.  However the server MUST assume that any file must respect a
   grace period at least as long as the
      client has modified in cache has been modified again between
      successive CB_GETATTR calls.  Depending lease_time on the nature of the
      client's memory management system, this weak obligation may not be
      possible.  A client MAY return stale information source server,
   in CB_GETATTR
      whenever the file is memory mapped.

   o order to ensure that clients have ample time to reclaim their
   locks before potentially conflicting non-reclaimed locks are granted.
   The mixture means by which the new server obtains the value of memory mapping and file locking lease_time on
   the same file old server is
      problematic.  Consider the following scenario, where left to the page size
      on each client server implementations.  It is 8192 bytes.

      *  Client A memory maps first page (8192 bytes) not
   specified by the NFS version 4 protocol.

10.  Client-Side Caching

   Client-side caching of data, of file X

      *  Client B memory maps first page (8192 bytes) attributes, and 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 names is
   essential to client A, client B issues a STORE on part of
         its locked region.

   Here providing good performance with the challenge NFS protocol.
   Providing distributed cache coherence is for each client to resynchronize to get a
   correct view difficult problem and
   previous versions of the first page.  In many operating environments, the
   virtual memory management systems on each client only know a page is
   modified, NFS protocol have not attempted it.
   Instead, several NFS client implementation techniques have been used
   to reduce the problems that a subset lack of the page corresponding to the
   respective lock regions has coherence poses for users.
   These techniques have not been modified.  So clearly defined by earlier protocol
   specifications and it is not possible for
   each often unclear what is valid or invalid
   client behavior.

   The NFS version 4 protocol uses many techniques similar to do the right thing, which is 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 only write 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 that portion to
   be made locally by clients.  This mechanism provides efficient
   support 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 common cases where sharing is lost.

   Moreover, if mandatory locking infrequent or where
   sharing is enabled on read-only.

10.1.  Performance Challenges for Client-Side Caching

   Caching techniques used in previous versions of the file, then we NFS protocol have a
   different problem.  When
   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 A and B issue the STORE
   instructions, are geographically distributed which classically increases
   the resulting page faults require a record lock on latency for cache revalidation requests.

   The previous versions of the
   entire page.  Each client then tries to extend NFS protocol repeat their locked range to file data
   cache validation requests at the entire page, which results time the file is opened.  This
   behavior can have serious performance drawbacks.  A common case is
   one in which a deadlock.

   Communicating file is only accessed by a single client.  Therefore,
   sharing is infrequent.

   In this case, repeated reference to the NFS4ERR_DEADLOCK error server to a STORE instruction find that no
   conflicts exist is
   difficult at best.

   If expensive.  A better option with regards to
   performance is to allow a client is locking that repeatedly opens a file to do
   so without reference to the entire memory mapped file, there server.  This is no
   problem with advisory or mandatory record locking, at least done until the potentially
   conflicting operations from another client unlocks a region actually occur.

   A similar situation arises in connection with file locking.  Sending
   file lock and unlock requests to the middle of the file.

   Given the above issues server as well as the following are permitted:

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

   o  Clients read 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
   write requests necessary to make data caching consistent with the
   locking for I/O. If mandatory semantics (see Section 10.3.2) can severely limit
   performance.  When locking is enabled after used to provide protection against
   infrequent conflicts, a large penalty is incurred.  This penalty may
   discourage the use of file is opened and mapped, locking by applications.

   The NFS version 4 protocol provides more aggressive caching
   strategies with the client MAY deny following design goals:

   o  Compatibility with a large range of server semantics.

   o  Provide the application
      further access to its mapped file.

9.8.  Name Caching

   The results same caching benefits as previous versions of LOOKUP and READDIR operations may be cached the NFS
      protocol when unable to avoid provide the cost more aggressive model.

   o  Requirements for aggressive caching are organized so that a large
      portion of subsequent LOOKUP operations.  Just as in the case benefit can be obtained even when not all of
   attribute caching, inconsistencies may arise among the various client
   caches.  To mitigate
      requirements can be met.

   The appropriate requirements for the effects server are discussed in later
   sections in which specific forms of these inconsistencies caching are covered (see
   Section 10.4).

10.2.  Delegation and given
   the context Callbacks

   Recallable delegation of typical filesystem APIs, an upper time boundary is
   maintained on how long server responsibilities for a file to a
   client name cache entry can be kept without
   verifying that the entry has not been made invalid improves performance by avoiding repeated requests to the
   server in the absence of inter-client conflict.  With the use of a directory
   change operation performed by another client.

   When
   "callback" RPC from server to client, a server recalls delegated
   responsibilities when another client is not making changes to engages in sharing of a directory for which there
   exist name cache entries,
   delegated file.

   A delegation is passed from the client needs to periodically fetch
   attributes for that directory server to ensure that it is not being
   modified.  After determining that no modification has occurred, the
   expiration time for client, specifying the associated name cache entries may be updated
   to be
   object of the current time plus delegation and the name cache staleness bound.

   When a client is making changes to type of delegation.  There are
   different types of delegations but each type contains a given directory, it needs stateid to
   determine whether there have been changes made be
   used to represent the directory by
   other clients.  It does this by using delegation when performing operations that
   depend on the change attribute as
   reported before delegation.  This stateid is similar to those
   associated with locks and after the directory operation share reservations but differs in that the associated
   change_info4 value returned
   stateid for the operation.  The server a delegation is able to
   communicate to associated with a clientid and may be
   used on behalf of all the client whether open_owners for the change_info4 data given client.  A
   delegation is provided
   atomically with respect made to the directory operation.  If the change
   values are provided atomically, the client is then able as a whole and not to compare
   the pre-operation change value with the change value 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 client's
   name cache.  If continuity of the comparison indicates 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 directory was
   updated by another client, granting of a
   delegation is always conditional upon the name cache 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 with the
   modified directory lease that is purged from subject to renewal together with all
   of the other leases held by that client.  If the comparison
   indicates no modification,

   Unlike locks, an operation by a second client to a delegated file
   will cause the name cache can be updated on server to recall a delegation through a callback.

   On recall, the client holding the delegation must flush modified
   state (such as modified data) to reflect the directory operation server and return the associated timeout
   extended.
   delegation.  The post-operation change value needs to be saved as the
   basis for future change_info4 comparisons.

   As demonstrated by conflicting request will not receive a response
   until the scenario above, name caching requires that recall is complete.  The recall is considered complete when
   the client revalidate name cache data by inspecting returns the change attribute
   of a directory at delegation or the point when server times out on the name cache item was cached.
   This requires that
   recall and revokes the server update delegation as a result of the change attribute for
   directories when timeout.
   Following the contents resolution of the corresponding directory is
   modified.  For a client to use recall, the server has the change_info4
   information
   appropriately and correctly, necessary to grant or deny the server must report second client's request.

   At the pre and post
   operation change attribute values atomically.  When time the server is
   unable client receives a delegation recall, it may have
   substantial state that needs to report the before and after values atomically with respect be flushed to the directory operation, server.  Therefore,
   the server must indicate that fact in should allow sufficient time for the
   change_info4 return value.  When delegation to be
   returned since it may involve numerous RPCs to the information is not atomically
   reported, server.  If the client should not assume
   server is able to determine that other clients have not
   changed the directory.

9.9.  Directory Caching

   The results of READDIR operations may be used client is diligently flushing
   state to avoid subsequent
   READDIR operations.  Just as in the cases server as a result of attribute and name
   caching, inconsistencies may arise among the various client caches.
   To mitigate recall, the effects of these inconsistencies, and given server may extend
   the
   context of typical filesystem APIs, usual time allowed for a recall.  However, the following rules time allowed for
   recall completion should not be
   followed:

   o  Cached READDIR information for a directory which unbounded.

   An example of this is not obtained
      in a single READDIR operation must always be when responsibility to mediate opens on a consistent snapshot
      of directory contents.  This given
   file is determined by using delegated to a GETATTR
      before client (see Section 10.4).  The server will
   not know what opens are in effect on the first READDIR and after client.  Without this
   knowledge the last of READDIR that
      contributes server will be unable to determine if the cache.

   o  An upper time boundary is maintained to indicate access and
   deny state for the length of
      time a directory cache entry is considered valid before file allows any particular open until the
   delegation for the file has been returned.

   A client
      must revalidate failure or a network partition can result in failure to
   respond to a recall callback.  In this case, the cached information.

   The revalidation technique parallels that discussed server will revoke
   the delegation which in turn will render useless any modified state
   still on the case of
   name caching.  When client.

10.2.1.  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 is not changing reboots or restarts, the directory failure to renew
   leases will result in
   question, checking the change attribute of the directory with GETATTR
   is adequate.  The lifetime revocation of the cache entry can record locks and share
   reservations.  Delegations, however, may be extended at
   these checkpoints.  When 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 modifying the directory, client may have file data stored locally and this data
   was associated with the previously held delegations.  The client needs will
   need to use reestablish the change_info4 data to determine whether there
   are other clients modifying appropriate file state on the directory.  If it is determined 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
   no requests from other client modifications are occurring, clients that conflict
   with these delegations will need to wait.  Because the client normal recall
   process may update
   its directory cache to reflect its own changes.

   As demonstrated previously, directory caching requires that require significant time for the client revalidate directory cache data by inspecting to flush changed
   state to the change
   attribute server, other clients need be prepared for delays that
   occur because of a directory at the point when the directory was cached. conflicting delegation.  This requires that the server update longer interval
   would increase the change attribute window for
   directories when the contents of clients to reboot and consult stable
   storage so that the corresponding directory is
   modified. delegations can be reclaimed.  For open
   delegations, such delegations are reclaimed using OPEN with a client to use the change_info4 information
   appropriately claim
   type of CLAIM_DELEGATE_PREV.  (See Section 10.5 and correctly, the server must report the pre Section 15.18 for
   discussion of open delegation and post
   operation change attribute values atomically.  When the details of OPEN respectively).

   A server is
   unable to report the before MAY support a claim type of CLAIM_DELEGATE_PREV, but if it
   does, it MUST NOT remove delegations upon SETCLIENTID_CONFIRM, and after values atomically with respect
   to
   instead MUST, for a period of time no less than that of the directory operation, 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 must indicate that fact in supports CLAIM_DELEGATE_PREV MUST support the
   change_info4 return value. DELEGPURGE
   operation.

   When the information 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 not atomically
   reported, a slight
   semantic difference.  In the client should not assume normal case if the server decides that other clients have a
   delegation should not
   changed be granted, it performs the directory.

10.  Minor Versioning

   To address requested action
   (e.g., OPEN) without granting any delegation.  For reclaim, the requirement of an NFS protocol
   server grants the delegation but a special designation is applied so
   that can evolve the client treats the delegation as having been granted but
   recalled by the
   need arises, server.  Because of this, the NFS version 4 protocol contains client has the rules and
   framework duty to allow for future minor changes or versioning.

   The base assumption with respect
   write all modified state to minor versioning is that any
   future accepted minor version must follow the IETF process server and be
   documented in a standards track RFC.  Therefore, each minor version
   number will correspond to an RFC.  Minor version zero then return the
   delegation.  This process of handling delegation reclaim reconciles
   three principles of the NFS version 4 protocol is represented protocol:

   o  Upon reclaim, a client reporting resources assigned to it by this RFC. an
      earlier server instance must be granted those resources.

   o  The COMPOUND
   procedure will support the encoding 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 minor version being
   requested client
      has proven its ability to receive them.

   When a network partition occurs, delegations are subject to freeing
   by the client.

   The following items represent server when the basic rules lease renewal period expires.  This is similar
   to the behavior for locks and share reservations.  For delegations,
   however, the development of
   minor versions.  Note that a future minor version server may decide to
   modify or add to the following rules as part of extend the minor version
   definition.

   1.   Procedures period in which conflicting
   requests are not added or deleted

        To maintain held off.  Eventually the general RPC model, NFS version 4 minor versions
        will not add to or delete procedures occurrence of a conflicting
   request from another client will cause revocation of the NFS program.

   2.   Minor versions may add operations to delegation.
   A loss of the COMPOUND callback path (e.g., by later network configuration
   change) will have the same effect.  A recall request will fail and
        CB_COMPOUND procedures.

        The addition
   revocation of operations to the COMPOUND delegation will result.

   A client normally finds out about revocation of a delegation when it
   uses a stateid associated with a delegation and CB_COMPOUND
        procedures does not affect receives the RPC model.

        1.  Minor versions error
   NFS4ERR_EXPIRED.  It also may append attributes find out about delegation revocation
   after a client reboot when it attempts to GETATTR4args,
            bitmap4, reclaim a delegation and GETATTR4res.

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

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

            Since attribute results are specified as an opaque array of
            per-attribute XDR encoded results,
   receives that same error.  Note that in the complexity case of adding
            new attributes in a revoked write
   open delegation, there are issues because data may have been modified
   by the midst client whose delegation is revoked and separately by other
   clients.  See Section 10.5.1 for a discussion of such issues.  Note
   also that when delegations are revoked, information about the current definitions revoked
   delegation will be too burdensome.

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

        Again server to stable storage (as
   described in Section 9.6).  This is done to deal with the complexity of handling multiple structure definitions
        for case in
   which a single operation is too burdensome.  New operations should
        be added instead of modifying existing structures for server reboots after revoking a minor
        version.

        This rule does not preclude delegation but before the following adaptations in
   client holding the revoked delegation is notified about the
   revocation.

10.3.  Data Caching

   When applications share access to a minor
        version.

        *  adding bits set of files, they need to flag fields such be
   implemented so as new attributes to
           GETATTR's bitmap4 data type

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

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

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

   5.   Minor versions may not delete operations. conflicting
   access by another application.  This prevents is true whether the potential reuse of a particular operation
        "slot" applications
   in a future minor version.

   6.   Minor versions may not delete attributes.

   7.   Minor versions may not delete flag bits question execute on different clients or enumeration values.

   8.   Minor versions may declare an operation as mandatory reside on the same
   client.

   Share reservations and record locks are the facilities the NFS
   version 4 protocol provides to NOT
        implement.

        Specifying an operation as "mandatory 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 implement" is
        equivalent to obsoleting an operation.  For
   invalidate the client, it means assumptions that those using these facilities depend
   upon.

10.3.1.  Data Caching and OPENs

   In order to avoid invalidating the operation sharing assumptions that
   applications rely on, NFS version 4 clients should not be sent provide cached
   data to the server.  For the
        server, applications or modify it on behalf of an NFS error can application when it
   would not be returned as opposed valid to "dropping"
        the request as an XDR decode error.  This approach allows for obtain or modify that same data via a READ or
   WRITE operation.

   Furthermore, in the obsolescence absence of an operation while maintaining its structure
        so open delegation (see Section 10.4) two
   additional rules apply.  Note that a future minor these rules are obeyed in practice
   by many NFS version can reintroduce 2 and version 3 clients.

   o  First, cached data present on a client must be revalidated after
      doing an OPEN.  Revalidating means that the operation.

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

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

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

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

   11.  A client fetches the
      change attribute from the server, compares it with the cached
      change attribute, and server that support minor version X must support
        minor versions 0 (zero) through X-1 if different, declares the cached data (as
      well as well.

   12.  No new features may be introduced the cached attributes) as mandatory in a minor
        version. invalid.  This rule allows is to ensure that
      the data for the introduction of new functionality and
        forces OPENed file is still correctly reflected in the use of implementation experience before designating a
        feature as mandatory.

   13.  A client MUST NOT attempt to use a stateid, filehandle, or
        similar returned object from
      client's cache.  This validation must be done at least when the COMPOUND procedure with minor
        version X for another COMPOUND procedure with minor version Y,
        where X != Y.

11.  Internationalization

   The primary issue
      client's OPEN operation includes DENY=WRITE or BOTH thus
      terminating a period in which NFS version 4 needs other clients may have had the
      opportunity to deal with
   internationalization, or I18N, is open the file with respect WRITE access.  Clients may
      choose to file names and
   other strings as used within do the protocol.  The choice of string
   representation must allow reasonable name/string access revalidation more often (i.e., at OPENs
      specifying DENY=NONE) to clients
   which use various languages.  The UTF-8 encoding of parallel the UCS as
   defined by [7] allows NFS version 3 protocol's
      practice for the benefit of users assuming this type degree of access cache
      revalidation.  Since the change attribute is updated for data and follows
      metadata modifications, some client implementors may be tempted to
      use the policy
   described in "IETF Policy on Character Sets time_modify attribute and Languages", [8].

   [9], otherwise know as "stringprep", documents a framework for using
   Unicode/UTF-8 in networking protocols, not change to validate cached
      data, so as "to increase the
   likelihood that string input and string comparison work metadata changes do not spuriously invalidate clean
      data.  The implementor is cautioned in ways that
   make sense this approach.  The change
      attribute is guaranteed to change for typical users throughout each update to the world."  A protocol must
   define a profile of stringprep "in order file,
      whereas time_modify is guaranteed to fully specify change only at the
   processing options."  The remainder
      granularity of this Internationalization
   section defines the NFS version 4 stringprep profiles.  Much of
   terminology used for time_delta attribute.  Use by the remainder client's data
      cache validation logic of this section comes from
   stringprep.

   There are three UTF-8 string types defined for NFS version 4:
   utf8str_cs, utf8str_cis, time_modify and utf8str_mixed.  Separate profiles are
   defined for each.  Each profile defines not change runs the following, as required by
   stringprep:

   o  The intended applicability risk
      of the profile client incorrectly marking stale data as valid.

   o  The character repertoire that is  Second, modified data must be flushed to the input and output server before closing
      a file OPENed for write.  This is complementary to
      stringprep (which the first rule.
      If the data is Unicode 3.2 for referenced version of
      stringprep)

   o  The mapping tables from stringprep used (as described in section 3
      of stringprep)

   o  Any additional mapping tables specific to not flushed at CLOSE, the profile

   o  The Unicode normalization used, if any (as described in section 4
      of stringprep)

   o  The tables from stringprep listing of characters that are
      prohibited revalidation done after
      client OPENs as output (as described in section 5 of stringprep)

   o file is unable to achieve its purpose.  The bidirectional string testing used, if any (as described in
      section 6 of stringprep)

   o  Any additional characters that are prohibited as output specific other
      aspect to flushing the profile

   Stringprep discusses Unicode characters, whereas NFS version 4
   renders UTF-8 characters.  Since there data before close is a one to one mapping from
   UTF-8 to Unicode, where ever that the remainder of this document refers to data must be
      committed to Unicode, the reader should assume UTF-8.

   Much of the text for the profiles comes from [9].

11.1.  Stringprep profile for the utf8str_cs type

   Every use of stable storage, at the utf8str_cs type definition in server, before the NFS version 4
   protocol specification follows CLOSE
      operation is requested by the profile named nfs4_cs_prep.

11.1.1.  Intended applicability of client.  In the nfs4_cs_prep profile

   The utf8str_cs type is a case sensitive string of UTF-8 characters.
   Its primary use in NFS Version 4 is for naming components and
   pathnames.  Components a server
      reboot or restart and pathnames are stored on the server's
   filesystem.  Two valid distinct UTF-8 strings might be the same after
   processing via the utf8str_cs profile.  If the strings are two names
   inside a directory, CLOSEd file, it may not be possible to
      retransmit the NFS version 4 server will need data to be written to either:

   o  disallow the creation of a second name if it's post processed form
      collides with file.  Hence, this
      requirement.

10.3.2.  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 existing name, or

   o  allow the creation
   analogous set of the second name, but arrange so constraints that after
      post processing, apply to client side data caching.
   These rules are effective only if the second name file locking is different than the post
      processed form of the first name.

11.1.2.  Character repertoire of nfs4_cs_prep

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

11.1.3.  Mapping used by nfs4_cs_prep

   The nfs4_cs_prep profile specifies mapping using in a way
   that matches in an equivalent way the following tables
   from stringprep:

   o  Table B.1

   Table B.2 actual READ and WRITE
   operations executed.  This is normally not part of the nfs4_cs_prep profile as opposed to file locking that is
   based on pure convention.  For example, it is
   primarily for dealing with case-insensitive comparisons.  However, if possible to manipulate
   a two-megabyte file by dividing the NFS version 4 file server supports into two one-megabyte
   regions and protecting access to the case_insensitive
   filesystem attribute, two regions by file locks on
   bytes zero and if case_insensitive is true, one.  A lock for write on byte zero of the NFS
   version 4 server MUST use Table B.2 (in addition file would
   represent the right to Table B1) when
   processing utf8str_cs strings, do READ and WRITE operations on the NFS version 4 client MUST
   assume Table B.2 (in addition to Table B.1) are being used.

   If first
   region.  A lock for write on byte one of the case_preserving attribute is present and set to false, then file would represent the NFS version 4 server MUST use table B.2
   right to map case when
   processing utf8str_cs strings.  Whether do READ and WRITE operations on the server maps from lower to
   upper case or second region.  As long
   as all applications manipulating the upper to lower case is an implementation
   dependency.

11.1.4.  Normalization used by nfs4_cs_prep

   The nfs4_cs_prep profile does not specify a normalization form.  A
   later revision of file obey this specification may specify convention, they
   will work on a particular
   normalization form.  Therefore, the server and client can expect that local filesystem.  However, they may receive unnormalized characters within not work with the
   NFS version 4 protocol requests and
   responses.  If unless clients refrain from data caching.

   The rules for data caching in the operating file locking environment requires normalization, then are:

   o  First, when a client obtains a file lock for a particular region,
      the implementation data cache corresponding to that region (if any cached data
      exists) must normalize utf8str_cs strings within be revalidated.  If the
   protocol before presenting change attribute indicates
      that the information to an application (at file may have been updated since the
   client) cached data was
      obtained, the client must flush or local filesystem (at invalidate the server).

11.1.5.  Prohibited output cached data for nfs4_cs_prep

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

   o  Table C.3

   o  Table C.4

   o  Table C.5

   o  Table C.6

   o  Table C.7

   o  Table C.8

   o  Table C.9

11.1.6.  Bidirectional output for nfs4_cs_prep

   The nfs4_cs_prep profile does not specify any checking newly locked region.  A client might choose to invalidate all
      of
   bidirectional strings.

11.2.  Stringprep profile non-modified cached data that it has for the utf8str_cis type

   Every use of the utf8str_cis type definition in the NFS version 4
   protocol specification follows the profile named nfs4_cis_prep.

11.2.1.  Intended applicability of file but the nfs4_cis_prep profile

   The utf8str_cis type is a case insensitive string of UTF-8
   characters.  Its primary use in NFS Version 4 is only
      requirement for naming NFS
   servers.

11.2.2.  Character repertoire correct operation is to invalidate all of nfs4_cis_prep

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

11.2.3.  Mapping used by nfs4_cis_prep

   The nfs4_cis_prep profile specifies mapping using the following
   tables from stringprep:

   o  Table B.1

   o  Table B.2

11.2.4.  Normalization used by nfs4_cis_prep

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

11.2.5.  Prohibited output for nfs4_cis_prep

   The nfs4_cis_prep profile specifies prohibiting using the following
   tables from stringprep:

   o  Table C.1.2

   o  Table C.2.2

   o  Table C.3

   o  Table C.4

   o  Table C.5

   o  Table C.6

   o  Table C.7

   o  Table C.8 newly locked region.

   o  Table C.9

11.2.6.  Bidirectional output  Second, before releasing a write lock for nfs4_cis_prep

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

11.3.  Stringprep profile a region, all modified
      data for that region must be flushed to the utf8str_mixed type

   Every use of the utf8str_mixed type definition in server.  The modified
      data must also be written to stable storage.

   Note that flushing data to the NFS version 4
   protocol specification follows server and the profile named nfs4_mixed_prep.

11.3.1.  Intended applicability invalidation of cached
   data must reflect the nfs4_mixed_prep profile

   The utf8str_mixed type is 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 string
   modified block when only half of UTF-8 characters, with a prefix that block is case sensitive, a separator equal within an area being
   unlocked may cause invalid modification to '@', and the region outside the
   unlocked area.  This, in turn, may be part of a suffix 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 fully qualified domain name.  Its primary use in NFS Version 4 not a full block.  Similarly, invalidating
   a locked area which is
   for naming principals identified in not an Access Control Entry.

11.3.2.  Character repertoire of nfs4_mixed_prep

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

11.3.3.  Mapping used by nfs4_cis_prep

   For the prefix and the separator integral number of a utf8str_mixed string, the
   nfs4_mixed_prep profile specifies mapping using full buffer blocks
   would require the following table client to read one or two partial blocks from stringprep:

   o  Table B.1

   For the suffix of a utf8str_mixed string, the nfs4_mixed_prep profile
   specifies mapping using
   server if the following tables from stringprep:

   o  Table B.1

   o  Table B.2

11.3.4.  Normalization used by nfs4_mixed_prep

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

11.3.5.  Prohibited output for nfs4_mixed_prep

   The nfs4_mixed_prep profile specifies prohibiting using revalidation procedure shows that the following
   tables from stringprep:

   o  Table C.1.2

   o  Table C.2.2

   o  Table C.3

   o  Table C.4

   o  Table C.5

   o  Table C.6

   o  Table C.7

   o  Table C.8

   o  Table C.9

11.3.6.  Bidirectional output for nfs4_mixed_prep

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

11.4.  UTF-8 Related Errors

   Where data which the
   client sends an invalid UTF-8 string, possesses may not be valid.

   The data that is written to the server should
   return an NFS4ERR_INVAL error.  This includes cases in which
   inappropriate prefixes are detected and where as a prerequisite to the count includes
   trailing bytes that do not constitute
   unlocking of a full UCS character.

   Where region must be written, at the server, to stable
   storage.  The client supplied string is valid UTF-8 but contains
   characters that are not supported 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 as reboot might conflict with a value for that
   string lock held by another client.

   A client implementation may choose to accommodate applications which
   use record locking in non-standard ways (e.g., names containing characters that have more than two
   octets on using a filesystem that supports Unicode characters only), record lock as
   a global semaphore) by flushing to the server should return more data upon an NFS4ERR_BADCHAR error.

   Where a UTF-8 string LOCKU
   than is used as a file name, and the filesystem,
   while supporting all of covered by the characters locked range.  This may include modified data
   within files other than the name, does not
   allow that particular name to be used, one for which the server should return unlocks are being done.
   In such cases, the
   error NFS4ERR_BADNAME.  This includes situations in client must not interfere with applications whose
   READs and WRITEs are being done only within the bounds of record
   locks which the server
   filesystem imposes application holds.  For example, an application locks
   a normalization constraint on name strings, but
   will also include such situations as filesystem prohibitions single byte of "."
   and ".." as a file names for certain operations, and other such
   constraints.

12.  Error Definitions

   NFS error numbers are assigned proceeds to failed operations within a compound
   request. write that single byte.  A compound request contains a number of NFS operations
   client that
   have their results encoded in sequence in chose to handle a compound reply.  The
   results of successful operations will consist of an NFS4_OK status
   followed LOCKU by flushing all modified data to
   the encoded results of the operation.  If server could validly write that single byte in response to an NFS
   operation fails, an error status will
   unrelated unlock.  However, it would not be entered in valid to write the reply entire
   block in which that single written byte was located since it includes
   an area that is not locked and the
   compound request will might be terminated.

   A description of each defined error follows:

   NFS4_OK  Indicates the operation completed successfully.

   NFS4ERR_ACCESS  Permission denied.  The caller does not have the
      correct permission to perform the requested operation.  Contrast locked by another client.
   Client implementations can avoid this problem by dividing files with NFS4ERR_PERM,
   modified data into those for which restricts itself all modifications are done to owner or
      privileged user permission failures.

   NFS4ERR_ATTRNOTSUPP  An attribute specified is not supported
   areas covered by the
      server.  Does not apply to the GETATTR operation.

   NFS4ERR_ADMIN_REVOKED  Due to administrator intervention, the
      lockowner's an appropriate record locks, share reservations, lock and delegations have
      been revoked by the server.

   NFS4ERR_BADCHAR  A UTF-8 string contains a character those for which is there
   are modifications not
      supported covered by a record lock.  Any writes done for
   the server in former class of files must not include areas not locked and thus
   not modified on the context in which client.

10.3.3.  Data Caching and Mandatory File Locking

   Client side data caching needs to respect mandatory file locking when
   it being used.

   NFS4ERR_BAD_COOKIE  READDIR cookie is stale.

   NFS4ERR_BADHANDLE  Illegal NFS filehandle.  The filehandle failed
      internal consistency checks.

   NFS4ERR_BADNAME  A name string in a request consists effect.  The presence of valid UTF-8
      characters supported by the server but the name mandatory file locking for a given
   file is not supported
      by indicated when the server as client gets back NFS4ERR_LOCKED from a valid name for current operation.

   NFS4ERR_BADOWNER  An owner, owner_group,
   READ or ACL attribute value can
      not be translated to local representation.

   NFS4ERR_BADTYPE  An attempt was made to create WRITE on a file it has an object of appropriate share reservation for.
   When mandatory locking is in effect for a type
      not supported by file, the server.

   NFS4ERR_BAD_RANGE  The range client must check
   for an appropriate file lock for data being read or written.  If a LOCK, LOCKT,
   lock exists for the range being read or LOCKU operation written, the client may
   satisfy the request using the client's validated cache.  If an
   appropriate file lock is not appropriate to held for the allowable range of offsets for the server.

   NFS4ERR_BAD_SEQID  The sequence number in a locking request is
      neither the next expected number read or write,
   the last number processed.

   NFS4ERR_BAD_STATEID  A stateid generated by the current server
      instance, but which does not designate any locking state (either
      current read or superseded) for a current lockowner-file pair, was
      used.

   NFS4ERR_BADXDR  The server encountered an XDR decoding error while
      processing an operation.

   NFS4ERR_CLID_INUSE  The SETCLIENTID operation has found that a client
      id is already in use write request must not be satisfied by another client.

   NFS4ERR_DEADLOCK  The server has been able to determine a file
      locking deadlock condition for a blocking lock request.

   NFS4ERR_DELAY  The server initiated the request, but was not able to
      complete it in a timely fashion.  The client should wait client's cache
   and then
      try the request with a new RPC transaction ID.  For example, this
      error should must be returned from a sent to the server that supports hierarchical
      storage and receives for processing.  When a
   read or write request to process partially overlaps a file that has been
      migrated.  In this case, locked region, the server request
   should start the immigration
      process and respond to client be subdivided into multiple pieces with this error.  This error may
      also occur when a necessary delegation recall makes processing a
      request in a timely fashion impossible.

   NFS4ERR_DENIED  An attempt to lock a each region (locked or
   not) treated appropriately.

10.3.4.  Data Caching and File Identity

   When clients cache data, the file is denied.  Since this may data needs to be a temporary condition, the client is encouraged organized
   according to retry the
      lock request until filesystem object to which the lock is accepted.

   NFS4ERR_DQUOT  Resource (quota) hard limit exceeded.  The user's
      resource limit on data belongs.  For
   NFS version 3 clients, the server typical practice has been exceeded.

   NFS4ERR_EXIST  File exists. to assume for
   the purpose of caching that distinct filehandles represent distinct
   filesystem objects.  The file specified already exists.

   NFS4ERR_EXPIRED  A lease client then has expired that is being used in the
      current operation.

   NFS4ERR_FBIG  File too large.  The operation would have caused a file choice to grow beyond organize and
   maintain the server's limit.

   NFS4ERR_FHEXPIRED  The filehandle provided data cache on this basis.

   In the NFS version 4 protocol, there is volatile and has
      expired at now the server.

   NFS4ERR_FILE_OPEN  The operation can not be successfully processed possibility to have
   significant deviations from a "one filehandle per object" model
   because a file involved in the operation is currently open.

   NFS4ERR_GRACE  The server is in its recovery or grace period which
      should match filehandle may be constructed on the lease period basis of the server.

   NFS4ERR_INVAL  Invalid argument or unsupported argument for an
      operation.  Two examples are attempting a READLINK on an object
      other than a symbolic link or specifying object's
   pathname.  Therefore, clients need a value for an enum field reliable method to determine if
   two filehandles designate the same filesystem object.  If clients
   were simply to assume that is not defined in all distinct filehandles denote distinct
   objects and proceed to do data caching on this basis, caching
   inconsistencies would arise between the protocol (e.g., nfs_ftype4).

   NFS4ERR_IO  I/O error.  A hard error (for example, a disk error)
      occurred while processing distinct client side objects
   which mapped to the requested operation.

   NFS4ERR_ISDIR  Is same server side object.

   By providing a directory.  The caller specified method to differentiate filehandles, the NFS version 4
   protocol alleviates a directory potential functional regression in a
      non-directory operation.

   NFS4ERR_LEASE_MOVED  A lease being renewed is associated comparison
   with a
      filesystem that the NFS version 3 protocol.  Without this method, caching
   inconsistencies within the same client could occur and this has been migrated to a new server.

   NFS4ERR_LOCKE  A read or write operation was attempted on a locked
      file.

   NFS4ERR_LOCK_NOTSUPP  Server does not support atomic upgrade or
      downgrade
   been present in previous versions of locks.

   NFS4ERR_LOCK_RANGE  A lock request the NFS protocol.  Note that it
   is operating possible to have such inconsistencies with applications executing
   on a sub-range of a
      current lock for multiple clients but that is not the lock owner and issue being addressed here.

   For the server does not support
      this type purposes of request.

   NFS4ERR_LOCKS_HELD  A CLOSE was attempted and file locks would exist
      after data caching, the CLOSE.

   NFS4ERR_MINOR_VERS_MISMATCH  The server has received a request that
      specifies following steps allow an unsupported minor version.  The server must return a
      COMPOUND4res with a zero length operations result array.

   NFS4ERR_MLINK  Too many hard links.

   NFS4ERR_MOVED  The filesystem which contains NFS
   version 4 client to determine whether two distinct filehandles denote
   the current filehandle
      object has been relocated or migrated same server side object:

   o  If GETATTR directed to another server.  The
      client may obtain two filehandles returns different values of
      the new filesystem location by obtaining fsid attribute, then the
      "fs_locations" attribute filehandles represent distinct
      objects.

   o  If GETATTR for any file with an fsid that matches the current filehandle.  For further
      discussion, refer to fsid of the section "Filesystem Migration or
      Relocation".

   NFS4ERR_NAMETOOLONG  The filename
      two filehandles in an operation was too long.

   NFS4ERR_NOENT  No such file or directory.  The file or directory name
      specified does not exist.

   NFS4ERR_NOFILEHANDLE  The logical current filehandle question returns a unique_handles attribute
      with a value (or, in
      the case of RESTOREFH, TRUE, then the saved filehandle value) has two objects are distinct.

   o  If GETATTR directed to the two filehandles does not been
      set properly.  This may be a result return the
      fileid attribute for both of a malformed COMPOUND
      operation (i.e., no PUTFH or PUTROOTFH before an operation that
      requires the current filehandle handles, then it cannot be set).

   NFS4ERR_NO_GRACE  A reclaim of
      determined whether the two objects are the same.  Therefore,
      operations which depend on that knowledge (e.g., client state has fallen outside of side data
      caching) cannot be done reliably.

   o  If GETATTR directed to the
      grace period of two filehandles returns different
      values for the server.  As fileid attribute, then they are distinct objects.

   o  Otherwise they are the same object.

10.4.  Open Delegation

   When a result, file is being OPENed, the server can not
      guarantee may delegate further handling
   of opens and closes for that conflicting state has not been provided file to another the opening client.

   NFS4ERR_NOSPC  No space left on device.  The operation would have
      caused  Any such
   delegation is recallable, since the server's filesystem to exceed its limit.

   NFS4ERR_NOTDIR  Not a directory.  The caller specified a non-
      directory in a directory operation.

   NFS4ERR_NOTEMPTY  An attempt was made to remove a directory circumstances that was
      not empty.

   NFS4ERR_NOTSUPP  Operation is not supported.

   NFS4ERR_NOT_SAME  This error is returned by allowed for
   the VERIFY operation delegation are subject to
      signify that change.  In particular, the attributes compared were not server may
   receive a conflicting OPEN from another client, the same as provided
      in server must
   recall the client's request.

   NFS4ERR_NXIO  I/O error.  No such device or address.

   NFS4ERR_OLD_STATEID  A stateid which designates delegation before deciding whether the locking state for
      a lockowner-file at an earlier time was used.

   NFS4ERR_OPENMODE  The OPEN from the other
   client attempted may be granted.  Making a READ, WRITE, LOCK or SETATTR
      operation not sanctioned by the stateid passed (e.g., writing delegation is up to a
      file opened only for read).

   NFS4ERR_OP_ILLEGAL  An illegal operation value has been specified in the argop field of a COMPOUND or CB_COMPOUND procedure.

   NFS4ERR_PERM  Not owner.  The operation was server and
   clients should not allowed because the
      caller is assume that any particular OPEN either not a privileged user (root) will or
   will not the owner of
      the target of the operation.

   NFS4ERR_RECLAIM_BAD result in an open delegation.  The reclaim provided by the client does not
      match any following is a typical
   set of the conditions that servers might use in deciding whether OPEN
   should be delegated:

   o  The client must be able to respond to the server's state consistency checks and is bad.

   NFS4ERR_RECLAIM_CONFLICT callback
      requests.  The reclaim provided by server will use the CB_NULL procedure for a test of
      callback ability.

   o  The client has
      encountered 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 conflict 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 can 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 provided.  Potentially
      indicates accessing
   the file's data.  The client holding a misbehaving client.

   NFS4ERR_RESOURCE 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 processing
   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 Section 10.4.1)

   o  an nfsace4 specifying read and write permissions

   o  a stateid to represent the COMPOUND procedure, delegation for READ and WRITE

   The delegation stateid is separate and distinct from the
      server may exhaust available resources stateid for
   the OPEN proper.  The standard stateid, unlike the delegation
   stateid, is associated with a particular lock_owner and can not will continue
      processing operations within
   to be valid after the COMPOUND procedure.  This error 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 returned from accepted or rejected solely on
   the server in those instances basis of resource
      exhaustion related to the processing of following conditions.  Any requirement for other
   checks to be made by the COMPOUND procedure. 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 Section 9.9.

   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.

10.4.1.  Open Delegation and Data Caching

   OPEN delegation allows much of the message overhead associated with
   the opening and closing files to be eliminated.  An open when an open
   delegation is in effect does not require that a validation message be
   sent to the server.  The continued endurance of the "read open
   delegation" provides a guarantee that no OPEN for write and thus no
   write has occurred.  Similarly, when closing a file opened for write
   and if write open delegation is in effect, the data written does not
   have to be flushed to the server until the open delegation is
   recalled.  The continued endurance of the open delegation provides a
   guarantee that no open and thus no read or write has been done by
   another client.

   For the purposes of open delegation, READs and WRITEs done without an
   OPEN are treated as the functional equivalents of a corresponding
   type of OPEN.  This refers to the READs and WRITEs that use the
   special stateids consisting of all zero bits or all one bits.
   Therefore, READs or WRITEs with a special stateid done by another
   client will force the server to recall a write open delegation.  A
   WRITE with a special stateid done by another client will force a
   recall of read open delegations.

   With delegations, a client is able to avoid writing data to the
   server when the CLOSE of a file is serviced.  The file close system
   call is the usual point at which the client is notified of a lack of
   stable storage for the modified file data generated by the
   application.  At the close, file data is written to the server and
   through normal accounting the server is able to determine if the
   available filesystem space for the data has been exceeded (i.e.,
   server returns NFS4ERR_NOSPC or NFS4ERR_DQUOT).  This accounting
   includes quotas.  The introduction of delegations requires that a
   alternative method be in place for the same type of communication to
   occur between client and server.

   In the delegation response, the server provides either the limit of
   the size of the file or the number of modified blocks and associated
   block size.  The server must ensure that the client will be able to
   flush data to the server of a size equal to that provided in the
   original delegation.  The server must make this assurance for all
   outstanding delegations.  Therefore, the server must be careful in
   its management of available space for new or modified data taking
   into account available filesystem space and any applicable quotas.
   The server can recall delegations as a result of managing the
   available filesystem space.  The client should abide by the server's
   state space limits for delegations.  If the client exceeds the stated
   limits for the delegation, the server's behavior is undefined.

   Based on server conditions, quotas or available filesystem space, the
   server may grant write open delegations with very restrictive space
   limitations.  The limitations may be defined in a way that will
   always force modified data to be flushed to the server on close.

   With respect to authentication, flushing modified data to the server
   after a CLOSE has occurred may be problematic.  For example, the user
   of the application may have logged off the client and unexpired
   authentication credentials may not be present.  In this case, the
   client may need to take special care to ensure that local unexpired
   credentials will in fact be available.  This may be accomplished by
   tracking the expiration time of credentials and flushing data well in
   advance of their expiration or by making private copies of
   credentials to assure their availability when needed.

10.4.2.  Open Delegation and File Locks

   When a client holds a write open delegation, lock operations may be
   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.

10.4.3.  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.

   o  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.

10.4.4.  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 filesystem.  If that filesystem denies such RENAMEs when a
   file is open, the recall must be performed to determine whether the
   file in question is, in fact, open.

   In addition to the situations above, the server may choose to recall
   open delegations at any time if resource constraints make it
   advisable to do so.  Clients should always be prepared for the
   possibility of recall.

   When a client receives a recall for an open delegation, it needs to
   update state on the server before returning the delegation.  These
   same updates must be done whenever a client chooses to return a
   delegation voluntarily.  The following items of state need to be
   dealt with:

   o  If the file associated with the delegation is no longer open and
      no previous CLOSE operation has been sent to the server, a CLOSE
      operation must be sent to the server.

   o  If a file has other open references at the client, then OPEN
      operations must be sent to the server.  The appropriate stateids
      will be provided by the server for subsequent use by the client
      since the delegation stateid will not longer be valid.  These OPEN
      requests are done with the claim type of CLAIM_DELEGATE_CUR.  This
      will allow the presentation of the delegation stateid so that the
      client can establish the appropriate rights to perform the OPEN.
      (see Section 15.18 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.

10.4.5.  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.

10.4.6.  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 Section 10.5.1 for additional
   details.

10.5.  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.

10.5.1.  Revocation Recovery for Write Open Delegation

   Revocation recovery for a write open delegation poses the special
   issue of modified data in the client cache while the file is not
   open.  In this situation, any client which does not flush modified
   data to the server on each close must ensure that the user receives
   appropriate notification of the failure as a result of the
   revocation.  Since such situations may require human action to
   correct problems, notification schemes in which the appropriate user
   or administrator is notified may be necessary.  Logging and console
   messages are typical examples.

   If there is modified data on the client, it must not be flushed
   normally to the server.  A client may attempt to provide a copy of
   the file data as modified during the delegation under a different
   name in the filesystem name space to ease recovery.  Note that when
   the client can determine that the file has not been modified by any
   other client, or when the client has a complete cached copy of file
   in question, such a saved copy of the client's view of the file may
   be of particular value for recovery.  In other case, recovery using a
   copy of the file based partially on the client's cached data and
   partially on the server copy as modified by other clients, will be
   anything but straightforward, so clients may avoid saving file
   contents in these situations or mark the results specially to warn
   users of possible problems.

   Saving of such modified data in delegation revocation situations may
   be limited to files of a certain size or might be used only when
   sufficient disk space is available within the target filesystem.
   Such saving may also be restricted to situations when the client has
   sufficient buffering resources to keep the cached copy available
   until it is properly stored to the target filesystem.

10.6.  Attribute Caching

   The attributes discussed in this section do not include named
   attributes.  Individual named attributes are analogous to files and
   caching of the data for these needs to be handled just as data
   caching is for ordinary files.  Similarly, LOOKUP results from an
   OPENATTR directory are to be cached on the same basis as any other
   pathnames and similarly for directory contents.

   Clients may cache file attributes obtained from the server and use
   them to avoid subsequent GETATTR requests.  Such caching is write
   through in that modification to file attributes is always done by
   means of requests to the server and should not be done locally and
   cached.  The exception to this are modifications to attributes that
   are intimately connected with data caching.  Therefore, extending a
   file by writing data to the local data cache is reflected immediately
   in the size as seen on the client without this change being
   immediately reflected on the server.  Normally such changes are not
   propagated directly to the server but when the modified data is
   flushed to the server, analogous attribute changes are made on the
   server.  When open delegation is in effect, the modified attributes
   may be returned to the server in the response to a CB_RECALL call.

   The result of local caching of attributes is that the attribute
   caches maintained on individual clients will not be coherent.
   Changes made in one order on the server may be seen in a different
   order on one client and in a third order on a different client.

   The typical filesystem application programming interfaces do not
   provide means to atomically modify or interrogate attributes for
   multiple files at the same time.  The following rules provide an
   environment where the potential incoherences mentioned above can be
   reasonably managed.  These rules are derived from the practice of
   previous NFS protocols.

   o  All attributes for a given file (per-fsid attributes excepted) are
      cached as a unit at the client so that no non-serializability can
      arise within the context of a single file.

   o  An upper time boundary is maintained on how long a client cache
      entry can be kept without being refreshed from the server.

   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.

10.7.  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 the 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.

10.8.  Name Caching

   The results of LOOKUP and READDIR operations may be cached to avoid
   the cost of subsequent LOOKUP operations.  Just as in the case of
   attribute caching, inconsistencies may arise among the various client
   caches.  To mitigate the effects of these inconsistencies and given
   the context of typical filesystem APIs, an upper time boundary is
   maintained on how long a client name cache entry can be kept without
   verifying that the entry has not been made invalid by a directory
   change operation performed by another client.

   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.

10.9.  Directory Caching

   The results of READDIR operations may be used to avoid subsequent
   READDIR operations.  Just as in the cases of attribute and name
   caching, inconsistencies may arise among the various client caches.
   To mitigate the effects of these inconsistencies, and given the
   context of typical filesystem APIs, the following rules should be
   followed:

   o  Cached READDIR information for a directory which is not obtained
      in a single READDIR operation must always be a consistent snapshot
      of directory contents.  This is determined by using a GETATTR
      before the first READDIR and after the last of READDIR that
      contributes to the cache.

   o  An upper time boundary is maintained to indicate the length of
      time a directory cache entry is considered valid before the client
      must revalidate the cached information.

   The revalidation technique parallels that discussed in the case of
   name caching.  When the client is not changing the directory in
   question, checking the change attribute of the directory with GETATTR
   is adequate.  The lifetime of the cache entry can be extended at
   these checkpoints.  When a client is modifying the directory, the
   client needs to use the change_info4 data to determine whether there
   are other clients modifying the directory.  If it is determined that
   no other client modifications are occurring, the client may update
   its directory cache to reflect its own changes.

   As demonstrated previously, directory caching requires that the
   client revalidate directory cache data by inspecting the change
   attribute of a directory at the point when the directory was cached.
   This requires that the server update the change attribute for
   directories when the contents of the corresponding directory is
   modified.  For a client to use the change_info4 information
   appropriately and correctly, the server must report the pre and post
   operation change attribute values atomically.  When the server is
   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.

11.  Minor Versioning

   To address the requirement of an NFS protocol that can evolve as the
   need arises, the NFS version 4 protocol contains the rules and
   framework to allow for future minor changes or versioning.

   The base assumption with respect to minor versioning is that any
   future accepted minor version must follow the IETF process and be
   documented in a standards track RFC.  Therefore, each minor version
   number will correspond to an RFC.  Minor version zero of the NFS
   version 4 protocol is represented by this RFC.  The COMPOUND
   procedure will support the encoding of the minor version being
   requested by the client.

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

   1.   Procedures are not added or deleted

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

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

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

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

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

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

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

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

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

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

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

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

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

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

   5.   Minor versions may not delete operations.

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

   6.   Minor versions may not delete attributes.

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

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

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

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

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

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

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

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

   12.  No new features may be introduced as mandatory in a minor
        version.

        This rule allows for the introduction of new functionality and
        forces the use of implementation experience before designating a
        feature as mandatory.

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

12.  Internationalization

   This chapter describes the string-handling aspects of the NFS version
   4 protocol, and how they address issues related to
   internationalization, including issues related to UTF-8,
   normalization, string preparation, case folding, and handling of
   internationalization issues related to domains.

   The NFS version 4 protocol needs to deal with internationalization,
   or I18N, with respect to file names and other strings as used within
   the protocol.  The choice of string representation must allow for
   reasonable name/string access to clients, applications, and users
   which use various languages.  The UTF-8 encoding of the UCS as
   defined by [7] allows for this type of access and follows the policy
   described in "IETF Policy on Character Sets and Languages", [8].

   In implementing such policies, it is important to understand and
   respect the nature of NFS version 4 as a means by which client
   implementations may invoke operations on remote file systems.  Server
   implementations act as a conduit to a range of file system
   implementations that the NFS version 4 server typically invokes
   through a virtual-file-system interface.

   Keeping this context in mind, one needs to understand that the file
   systems with which clients will be interacting will generally not be
   devoted solely to access using NFS version 4.  Local access and its
   requirements will generally be important and often access over other
   remote file access protocols will be as well.  It is generally a
   functional requirement in practice for the users of the NFS version 4
   protocol (although it may be formally out of scope for this document)
   for the implementation to allow files created by other protocols and
   by local operations on the file system to be accessed using NFS
   version 4 as well.

   It also needs to be understood that a considerable portion of file
   name processing will occur within the implementation of the file
   system rather than within the limits of the NFS version 4 server
   implementation per se.  As a result, cetain aspects of name
   processing may change as the locus of processing moves from file
   system to file system.  As a result of these factors, the protocol
   does not enforce uniformity of processing NFS version 4 server
   requests on the server as a whole.  Because the server interacts with
   existing file system implementations, the same server handling will
   produce different behavior when interacting with different file
   system implementations.  To attempt to require uniform behavior, and
   treat the the protocol server and the file system as a unified
   application, would considerably limit the usefulness of the protocol.

12.1.  Use of UTF-8

   As mentioned above, UTF-8 is used as a convenient way to encode
   Unicode which allows clients that have no internationalization
   requirements to avoid these issues since the mapping of ASCII names
   to UTF-8 is the identity.

12.1.1.  Relation to Stringprep

   RFC 3454 [9], otherwise known as "stringprep", documents a framework
   for using Unicode/UTF-8 in networking protocols, intended "to
   increase the likelihood that string input and string comparison work
   in ways that make sense for typical users throughout the world."  A
   protocol conforming to this framework must define a profile of
   stringprep "in order to fully specify the processing options."  NFS
   version 4, while it does make normative references to stringprep and
   uses elements of that framework, it does not, for reasons that are
   explained below, conform to that framework, for all of the strings
   that are used within it.

   In addition to some specific issues which have caused stringprep to
   add confusion in handling certain characters for certain languages,
   there are a number of reasons why stringprep profiles are not
   suitable for describing NFS version 4.

   o  Restricting the character repertoire to Unicode 3.2, as required
      by stringprep is unduly constricting.

   o  Many of the character tables in stringprep are inappropriate
      because of this limited character repertoire, so that normative
      reference to stringprep is not desirable in many case and instead,
      we allow more flexibility in the definition of case mapping
      tables.

   o  Because of the presence of different file systems, the specifics
      of processing are not fully defined and some aspects that are are
      RECOMMENDED, rather than REQUIRED.

   Despite these issues, in many cases the general structure of
   stringprep profiles, consisting of sections which deal with the
   applicability of the description, the character repertoire, charcter
   mapping, normalization, prohibited characters, and issues of the
   handling (i.e. possible prohibition) of bidirectional strings, is a
   convenient way to describe the string handling which is needed and
   will be used where appropriate.

12.1.2.  Normalization, Equivalence, and Confusability

   Unicode has defined several equivalence relationships among the set
   of possible strings.  Understanding the nature and purpose of these
   equivalence relations is important to understand the handling of
   unicode strings within NFS version 4.

   o  Some string pairs are thought as only differing in the way accents
      and other diacritics are encoded.  Such string pairs are called
      "canonically equivalent".  For example, the character LATIN SMALL
      LETTER E WITH ACUTE (U+00E9) is defined as equivalent to the
      string consisting of LATIN SMALL LETTER E followed by COMBINING
      ACUTE ACCENT (U+0065, U+0301).

   o  Additionally there is an equvalence relation of "compatibility
      equivalence".  Two canonically equivalent strings are necessarily
      compatibility equivalent, although not the converse.  An example
      of compatibility equivalent strings which are not canonically
      equivalent are GREEK CAPITAL LETTER OMEGA (U+03A9) and OHM SIGN
      (U+2129).  These are identical in appearance while other
      compatibility equivalent strings are not.  Another example would
      be "x2" and the two character string denoting x-squared which are
      clearly differnt in appearance although compatibility equivalent
      and not canonically equivalent.  These have Unicode encodings
      LATIN SMALL LETTER X, DIGIT TWO (U+0078, U+0032) and LATIN SMALL
      LETTER X, SUPERSCRIPT TWO (U+0078, U+00B2),

   One way to deal with these equivalence relations is via
   normalization.  A normalization form maps all strings to correspond
   normalized string in such a fashion that all strings that are
   equivalent (canonically or compatibly, depending on the form) are
   mapped to the same value.  Thus the image of the mapping is a subset
   of Unicode strings conceived as the representives of the equivalence
   classes defined by the chosed equivalence relation.

   In the NFS version 4 protocol, handling of issues related to
   internationalization with regard to normalization follows one of two
   basic patterns:

   o  For strings whose function is related to other internet standards,
      such as server and domain naming, the normalization form defined
      by the appropriate internet standards is used.  For server and
      domain naming, this involves normalization form NKFC as specified
      in [10]

   o  For other strings, particular those passed by the server to file
      system implementations, normalization requirements are the
      province of the file system and the job of this specification is
      not to specify a particular form but to make sure that
      interoperability is maximmized, even when clients and server-based
      file systems may have different preferences.

   A related but distinct issue concerns string confusability.  This can
   occur when two strings (including single-charcter strings) having a
   similar appearance.  There have been attempts to define uniform
   processing in an attempt to avoid such confusion (see stringprep [9])
   but the results have often added to confusion.

   Some examples of possible confusions and proposed processing intended
   to reduce/avoid confusions:

   o  Deletion of characters supposed to be invisible and appropriately
      ignored, justifying their deletion, including, WORD JOINER
      (U+2060), and the ZERO WIDTH SPACE (U+200B).

   o  Deletion of characters supposed to not bear semantics and only
      affect glyph choice, including the ZERO WIDTH NON-JOINER (U+200C)
      and the ZERO WIDTH JOINER (U+200D), where the deletion turns out
      to be a problem for Farsi speakers.

   o  Prohibition of space characters such as the EM SPACE (U+2003), the
      EN SPACE (U+2002), and the THIN SPACE (U+2009).

   In addition, character pairs which apprear very similar and could and
   often do result in confusion.  In addition to what Unicode defines as
   "compatibility equivalence", there are a considerable number of
   additional character pairs that could cause confusion.  This includes
   characters such as LATIN CAPITAL LETTER O (U+004F) and DIGIT ZERO
   (U+0030), and CYRILLIC SMALL LETTER ER (U+0440) LATIN SMALL LETTER P
   (U+0070) (also with MATHEMATICAL BOLD SMALL P (U+1D429) and GREEK
   SMALL LETTER RHO (U+1D56, for good measure).

   NFS version 4, as it does with normalization, takes a two-part
   approach to this issue:

   o  For strings whose function is related to other internet standards,
      such as server and domain naming, any string processing to address
      the confusability issue is defined by the appropriate internet
      standards is used.  For server and domain naming, this is the
      responsibility of IDNA as described in [10].

   o  For other strings, particularly those passed by the server to file
      system implementations, any such preparation requirements
      including the choice of how, or whether to address the
      confusability issue, are the responsibility of the file system to
      define, and for this specification to try to add its own set would
      add unacceptably to complexity, and make many files accessible
      locally and by other remote file access protocols, inaccessible by
      NFS version 4.  This specification defines how the protocol
      maximizes interoperability in the face of different file system
      implementations.

      NFS version 4 does allow file systems to map and to reject
      characters, including those likely to result in confusion, since
      file systems may choose to do such things.  It defines what the
      client will see in such cases, in order to limit problems that can
      arise when a file name is created and it appears to have a
      different name from the one it is assigned when the name is
      created.

12.2.  String Type Overview

12.2.1.  Overall String Class Divisions

   NFS version 4 has to deal with with a large set of diffreent types of
   strings and because of the different role of each,
   internationalization issues will be different for each:

   o  For some types of strings, the fundamental internationalization-
      related decisions are the province of the file system or the
      security-handling functions of the server and the protocol's job
      is to establish the rules under which file systems and servers are
      allowed to exercise this freedom, to avoid adding to confusion.

   o  In other cases, the fundamental internationalization issues are
      the responsibility of other IETF groups and our jobis simply to
      reference those and perhaps make a few choices as to how they are
      to be used (e.g.  U-labels vs. A-labels).

   o  There are also cases in which a string has a small amount of NFS
      version 4 processing which results in one or more strings being
      referred to one of the other categories.

   We will divide strings to be dealt with into the following classes:

   MIX  indicating that there is small amount of preparatory processing
      that either picks an appropriate modes of internationalization
      handling or divides the string into a set of (two) strings with a
      different mode internationalization handling for each.  The
      details are discussed in the section "Types with Pre-processing to
      Resolve Mixture Issues".

   NIP  indicating that, for various reasons, there is no need for
      internationalization-specific processing to be performed.  The
      specifics of the various string types handled in this way are
      described in the section "String Types without
      Internationalization Processing".

   INET  indicating that the string needs to be processed in a fashion
      is goverened by non-NFS-specific internet specifications.  The
      details are discussed in the section "Types with Processing
      Defined by Other Internet Areas".

   NFS  indicating that the string needs to be processed in a fashion is
      goverened by NFSv4-specific consideration.  The primary focus is
      on enabling flexibility for the various file systems to be
      accessed and is described in the section "String Types with NFS-
      specific Processing".

12.2.2.  Divisions by Typedef Parent types

   There are a number of different string types within NFS version 4 and
   internationalization handling will be different for different types
   of strings.  Each the types will be in one of four groups based on
   the parent type that specifies the nature of its relationship to utf8
   and ascii.

   utf8_should/SHOULD:  indicating that strings of this type should be
      UTF-8 but clients and servers will not check for valid UTF-8
      encoding.

   utf8val_should/VSHOULD:  indicating that strings of this type should
      be and generally will be in the form of the UTF-8 encoding of
      Unicode.  Strings in most cases will be checked by the server for
      valid UTF-8 but for certain file systems, such checking may be
      inhibited.

   utf8val_must/VMUST:  indicating that strings of this type must be in
      the form of the UTF-8 encoding of Unicode.  Strings will be
      checked by the server for valid UTF-8 and the server should ensure
      that when sent to the client, they are valid UTF-8.

   ascii_must/ASCII:  indicating that strings of this type must be pure
      ASCII, and thus automatically UTF-8.  The processing of these
      string must ensure that they are only have ASCII characters but
      this need not be a separate step if any normally required check
      for validity inherently assures that only ASCII characters are
      present.

12.2.3.  Individual Types and Their Handling

   The first table outlines the handling for the primary string types,
   i.e. those not derived as a prefix or a suffix from a mixture type.

   +-----------------+---------+-------+-------------------------------+
   | Type            | Parent  | Class | Explanation                   |
   +-----------------+---------+-------+-------------------------------+
   | comptag4        | SHOULD  | NIP   | Should be utf8 but no         |
   |                 |         |       | validation by server or       |
   |                 |         |       | client is to be done.         |
   | component4      | VSHOULD | NFS   | Should be utf8 but clients    |
   |                 |         |       | may need to access file       |
   |                 |         |       | systems with a different name |
   |                 |         |       | structure. files systems with |
   |                 |         |       | non-utf8 names.               |
   | linktext4       | VSHOULD | NFS   | Should be utf8 since text may |
   |                 |         |       | include name components.      |
   |                 |         |       | Because of the need to access |
   |                 |         |       | existing file systems, this   |
   |                 |         |       | check may be inhibited.       |
   | fattr4_mimetype | ASCII   | NIP   | All mime types are ascii so   |
   |                 |         |       | no specific utf8 processing   |
   |                 |         |       | is required, given that you   |
   |                 |         |       | are comparing to that list.   |
   +-----------------+---------+-------+-------------------------------+

                                  Table 5

   There are a number of string types that are compound in that they may
   consist of multiple conjoined strings with different utf8-related
   processing for each.

   +---------+--------+-------+----------------------------------------+
   | Type    | Parent | Class | Explanation                            |
   +---------+--------+-------+----------------------------------------+
   | prin4   | VMUST  | MIX   | Consists of two parts separated by an  |
   |         |        |       | at-sign, a prinpfx4 and a prinsfx4.    |
   |         |        |       | These are described in the next table. |
   | server4 | VMUST  | MIX   | Is either an IP address (serveraddr4)  |
   |         |        |       | which has to be pure ascii or a server |
   |         |        |       | name svrname4, which is described      |
   |         |        |       | immediately below.                     |
   +---------+--------+-------+----------------------------------------+

                                  Table 6

   The last table describes the components of the compound types
   described above.

   +----------+-------+------+-----------------------------------------+
   | Type     | Class | Def  | Explanation                             |
   +----------+-------+------+-----------------------------------------+
   | svraddr4 | ASCII | NIP  | Server as IP address, whether IPv4 or   |
   |          |       |      | IPv6,                                   |
   | svrname4 | VMUST | INET | Server name as returned by server.  Not |
   |          |       |      | sent by client, except in               |
   |          |       |      | VERIFY/NVERIFY.                         |
   | prinsfx4 | VMUST | INET | Suffix part of principal, in the form   |
   |          |       |      | of a domain name.                       |
   | prinpfx4 | VMUST | NFS  | Must match one of a list of valid users |
   |          |       |      | or groups for that particular domain.   |
   +----------+-------+------+-----------------------------------------+

                                  Table 7

12.3.  Errors Related to Strings

   When the client sends an invalid UTF-8 string in a context in which
   UTF-8 is required, the server MUST return an NFS4ERR_INVAL error.
   When the client sends an invalid UTF-8 string in a context in which
   UTF-8 is recommended, the server SHOULD return an NFS4ERR_INVAL
   error.  These situations apply to cases in which inappropriate
   prefixes are detected and where the count includes trailing bytes
   that do not constitute a full UCS character.

   Where the client supplied string is valid UTF-8 but contains
   characters that are not supported by the server file system as a
   value for that string (e.g., names containing characters that have
   more than two octets on a file system that supports UCS-2 characters
   only, file name components containing slashes on file systems that do
   not allow them in filename file name components), the server should
   MUST return an NFS4ERR_BADCHAR error.

   Where a UTF-8 string is used as a file name component, and the file
   system, while supporting all of the characters within the name, does
   not allow that particular name to be used, the server should return
   the error NFS4ERR_BADNAME.  This includes file system prohibitions of
   "." and ".." as file names for certain operations, and other such
   similar constraints.  It does not include use of strings with non-
   preferred normalization modes.

   Where a UTF-8 string is used as a file name component, the file
   system implementation MUST NOT return NFS4ERR_BADNAME, simply due to
   a normalization mismatch.  In such cases the implementation MAY
   convert the string to its own preferred normalization mode before
   performing the operation.  As a result, a client cannot assume that a
   file created with a name it specifies will have that name when the
   directory is read.  It may have instead, the name converted to the
   file system's preferred normalization form.

   Where a UTF-8 string is used as other than a file name component and
   the string does not meet the normalization requirements specified for
   it, the error NFS4ERR_INVAL is returned.

12.4.  Types with Pre-processing to Resolve Mixture Issues

12.4.1.  Processing of Principal Strings

   Strings denoting principals (users or groups) MUST be UTF-8 but since
   they consist of a principal prefix, an at-sign, and a domain, all
   three of which either are checked for being UTF-8, or inherently are
   UTF-8, checking the string as a whole for being UTF-8 is not
   required.  Although a server implementation may choose to make this
   check on the string as whole, for example in converting it to
   Unicode, the description within this document, will reflect a
   processing model in which such checking happens after the division
   into a principal prefix and suffix, the latter being in the form of a
   domain name.

   The string should be scanned for at-signs.  If there is more that one
   at-sign, the string is considered invalid.  For cases in which there
   are no at-signs or the at-sign appears at the start of end of the
   string see Interpreting owner and owner_group Otherwise, the portion
   before the at-sign is dealt with as a prinpfx4 and the portion after
   is dealt with as a prinsfx4.

12.4.2.  Processing of Server Id Strings

   Server id strings typically appear in responses (as attribute values)
   and only appear in requests as attribute value presented to VERIFY
   and NVERIFY.  With that exception, they are not subject to server
   validation and posible rejection.  It is not expected that clients
   will typically do such validation on receipt of responses but they
   may as a way to check for proper server behavior.  The responsibility
   for sending correct UTF-8 strings is with the server.

   Servers are identified by either server names of IP addresses.  Once
   an id has been identified as an IP address, then there is no
   processing specific to internationalization to be done, since such an
   address must be ASCII to be valid.

   Identifiers which are not valid IP addresses are treated as server
   names for which see below.  There are fifteen top-level domains that
   consist of two characters, each within the range a-f.  Given that, it
   is possible to have a string such as bb.bb.bb.bb, which might be
   either an IP address or a server name.  It is recommended that in
   such cases, a check for a valid server name be done first and the
   string interpreted as an IP address only if it found that the string
   is not a server name.

12.5.  String Types without Internationalization Processing

   There are a number of types of strings which, for a number of
   different reasons, do not require any internationalization-specific
   handling, such as valdiation of UTF-8, normaliztion, or character
   mapping or checking.  This does not necessarily mean that the strings
   need not be UTF-8.  In some case, other checking on the string
   ensures that they are valid UTF-8, without doing any checking
   specific to internationalization.

   The following are the specific types:

   comptag4  strings are an aid to debugging and the sender should avoid
      confusion by not using anything but valid UTF-8.  But any work
      validating the string or modifying it would just add complication
      to a mechanism whose basic function is best supported by making it
      not subject to any checking and having data maximally available to
      be looked at in a network trace.

   fattr4_mimetype  strings need to be validated by matching against a
      list of valid mime types.  Since these are all ASCII, no
      processing specific to internationaliztion is required since
      anything that does not match is invalid and anything which does
      not obey the rules of UTF-8 will not be ASCII and consequently
      will not match, and will be invalid.

   svraddr4  strings, in order to be valid, need to be ASCII, but if you
      check them for validity, you have inherently checked that that
      they are ASCII and thus UTF-8.

12.6.  Types with Processing Defined by Other Internet Areas

   There are two types of strings which NFS version 4 deals with whose
   processing is defined by other Internet standards, and where issues
   related to different handling choices by server operating systems or
   server file systems do not apply.

   These are as follows:

   o  Server names as they appear in the fs_locations attribute.  Note
      that for most purposes, such server names will only be sent by the
      server to the client.  The exception is use of the fs_locations
      attribute in a VERIFY or NVERIFY operation.

   o  Principal suffixes which are used to denote sets of users and
      groups, and are in the form of domain names.

   The general rules for handling all of these domain-related strings
   are similar and independent of role of the sender or receiver as
   client or sender, although the consequences of failure to obey these
   rules may be different for client or server.

   The string sent SHOULD be in the form of a U-label although it MAY be
   in the form of an A-label or a UTF-8 string that would not map to
   itself when canonicalized by applying ToUnicode(ToASCII(...)).  The
   receiver needs to be able to accept domain and server names in any of
   the formats allowed.  The server MUST reject, using the the error
   NFS4ERR_INVAL, a string which is not valid UTF-8 or which begins with
   "xn--" and violates the rules for a valid A-label.

   When a domain string is part of id@domain or group@domain, the server
   SHOULD map domain strings which are A-labels or are UTF-8 domain
   names which are not U-labels, to the corresponding U-label, using
   ToUnicode(domain) or ToUnicode(ToASCII(domain)).  As a result, the
   domain name returned within a userid on a GETATTR may not match that
   sent when the userid is set using SETATTR, although when this
   happens, the domain will be in the form of a U-label.  When the
   server does not map domain strings which are not U-labels into a
   U-label, which it MAY do, it MUST NOT modify the domain and the
   domain returned on a GETATTR of the userid MUST be the same as that
   using when setting the userid by the SETATTTR.

   The server MAY implement VERIFY and NVERIFY without translating
   internal state to a string form, so that, for example, a user
   principal which represents a specific numeric user id, will match a
   different principal string which represents the same numeric user id.

12.7.  String Types with NFS-specific Processing

   For a number of data types within NFSv4, the primary responsbibility
   for internationalization-related handling is that of some entity
   other than the server itself (see below for details).  In these
   situations, the primary responsibility of NFS version 4 is to provide
   a framework in which that other entity (file system and server
   operating system principal naming framework) to implement its own
   decisions while establishing rules to limit interoperability issues.

   This pattern applies to the following data types:

   o  In the case of name components (strings of type component4), the
      server-side file system implementation (of which there may be more
      than one for a particular server) deals with internationalization
      issues, in a fashion that is appropriate to NFS version 4, other
      remote file access protocols, and local file access methods.  See
      "Handling of File Came Components" for the detailed treatment.

   o  In the case of link text strings (strings of type lintext4), the
      issues are similar, but file systems are restricted in the set of
      acceptable internationalization-related processing that they may
      do, principally because symbolic links may contain name componetns
      that, when used, are presented to other file systems and/or other
      servers.  See "Processing of Link Text" for the detailed
      treatment.

   o  In the case of principal prefix strings, any decisions regarding
      internationalization are the responsibility of the server
      operating systems which may make its own rules regarding user and
      group name encoding.  See "Processing of Principal Prefixes" for
      the detailed treatment.

12.7.1.  Handling of File Came Components

   There are a number of places within client and server where file name
   components are processed:

   o  On the client, file names may be processed as part of forming NFS
      version 4 requests.  Any such processing will reflect specific
      needs of the client's environment and will be treated as out-of-
      scope from the viewpoint of this specification.

   o  On the server, file names are processed as part of processing NFS
      version 4 requests.  In practice, parts of the processing will be
      implemented within the NFS version 4 server while other parts will
      be implemented within the file system.  This processing is
      described in the sections below.  These sections are organized in
      a fashion parallel to a stringprep profile.  The same sorts of
      topics are dealt with but they differ in that there is a wider
      range of possible processing choices.

   o  On the server, file name components might potentially be subject
      to processing as part of generating NFS version 4 responses.  This
      specification assumes that this processing will be empty and that
      file name components will be copied verbatim at this point.  The
      file name components may be modified as they appear in responses,
      relative to the values used in the request but this is only
      treated as reflecting changes made as part of request processing.
      For example, a change to a file name component made in processing
      a CREATE operation will be reflected in the READDIR since the
      files created will have names that reflect CREATE-time processing.

   o  On the client, responses will need to be properly dealt with and
      the relevant issues will be discussed in the sections below.
      Primarily, this will involve dealing with the fact that file name
      components received in responses may need to be processed to meet
      the requirements of the client's internal environment.  This will
      mainly involve dealing with changes in name components possibly
      made by server processing.  It also addresses other sorts of
      expected behavior that do not involve a returned component4, such
      as whether a LOOKUP finds a given component4 or whether a CREATE
      or OPEN finds that a specified name already exists.

12.7.1.1.  Nature of Server Processing of Name Components in Request

   The component4 type defines a potentially case sensitive string,
   typically of UTF-8 characters.  Its use in NFS version 4 is for
   representing file name components.  Since file systems can implement
   case insensitive file name handling, it can be used for both case
   sensitive and case insensitive file name handling, based on the
   attributes of the file system.

   It may be the case that two valid distinct UTF-8 strings will be the
   same after the processing described below.  In such a case, a server
   may either,

   o  disallow the creation of a second name if its post-processed form
      collides with that of an existing name, or

   o  allow the creation of the second name, but arrange so that after
      post processing, the second name is different than the post-
      processed form of the first name.

12.7.1.2.  Character Repertoire for the Component4 Type

   The RECOMMENDED character repertoire for file name components is a
   recent/current version of Unicode, as encoded via UTF-8.  There are a
   number of alternate character repertoires which may be chosen by the
   server based on implementation constraints including the requirements
   of the file system being accessed.

   Two important alternative repertoires are:

   o  One alternate character repertoire is to represent file name
      components as strings of bytes with no protocol-defined encoding
      of multi-byte characters.  Most typically, implementations that
      support this single-byte alternative will make it available as an
      option set by an administrator for all file systems within a
      server or for some particular file systems.  If a server accepts
      non-UTF-8 strings anywhere within a specific file system, then it
      MUST do so throughout the entire file system.

   o  Another alternate character repertoires is the set of codepoints,
      representable by the file system, most typically UCS-4.

   Individual file system implementations may have more restricted
   character repertoires, as for example file system that only are
   capable of storing names consisting of UCS-2 characters.  When this
   is the case, and the character repertoire is not restricted to
   single-byte characters, characters not within that repertoire are
   treated as prohibited and the error NFS4ERR_BADCHAR is returned by
   the server when that character is encountered.

   Strings are intended to be in UTF-8 format and servers SHOULD return
   NFS4ERR_INVAL, as discussed above, when the characters sent are not
   valid UTF-8.  When the character repertoire consists of single-byte
   characters, UTF-8 is not enforced.  Such situations should be
   restricted to those where use is within a restricted environment
   where a single character mapping locale can be administratively
   enforced, allowing a file name to be treated as string of bytes,
   rather than as a string of characters.  Such an arrangement might be
   necessary when NFS version 4 access to a file system containing names
   which are not valid UTF-8 needs to be provided.

   However, in any of the following situations, file names have to be
   treated as strings of characters and servers MUST return
   NFS4ERR_INVAL when file names that are not in UTF-8 format:

   o  Case-insensitive comparisons are specified by the file system and
      any characters sent contain non-ASCII byte codes.

   o  Any normalization constraints are enforced by the server or file
      system implementation.

   o  The server accepts a given name when creating a file and reports a
      different one when the directory is being examined.

   Much of the discussion below regarding normalization and silent
   deletion of characters within component4 strings is not applicable
   when the server does not enforce UTF-8 component4 strings and treats
   them as strings of bytes.  A client may determine that a given
   filesystem is operating in this mode by performing a LOOKUP using a
   non-UTF-8 string, if NFS4ERR_INVAL is not returned, then name
   components will be treated as opaque and those sorts of modifications
   will not be seen.

12.7.1.3.  Case-based Mapping Used for Component4 Strings

   Case-based mapping is not always a required part of server processing
   of name components.  However, if the NFS version 4 file server
   supports the case_insensitive file system attribute, and if the
   case_insensitive attribute is true for a given file system, the NFS
   version 4 server must use the Unicode case mapping tables for the
   version of Unicode corresponding to the character repertoire.  In the
   case where the character repertoire is UCS-2 or UCS-4, the case
   mapping tables from the latest available version of Unicode should be
   used.

   If the case_preserving attribute is present and set to false, then
   the NFS version 4 server MUST use the corresponding Unicode case
   mapping table to map case when processing component4 strings.
   Whether the server maps from lower to upper case or the upper to
   lower case is a matter for implementation choice.

   Stringprep Table B.2 should not be used for these purpose since it is
   limited to Unicode version 3.2 and also because it erroneously maps
   the German ligature eszett to the string "ss", whereas later versions
   of Unicode contain both lower-case and upper-case versions of Eszett
   (SMALL LETTER SHARP S and CAPITAL LETTER SHARP S).

   Clients should be aware that servers may have mapped SMALL LETTER
   SHARP S to the string "ss" when case-insensitive mapping is in
   effect, with result that file whose name contains SMALL LETTER SHARP
   S may have that character replaced by "ss" or "SS".

12.7.1.4.  Other Mapping Used for Component4 Strings

   Other than for issues of case mapping, an NFS version 4 server SHOULD
   limit visible (i.e. those that change the name of file to reflect
   those mappings to those from from a subset of the stringprep table
   B.1.  Note particularly, the mapings from U+200C and U+200D to the
   empty string should be avoided, due to their undesirable effect on
   some strings in Farsi.

   Table B.1 may be used but it should be used only if required by the
   local file system implementation.  For example, if the file system in
   question accepts file names containing the MONGOLIAN TODO SOFT HYPHEN
   character (U+1806) and they are distinct from the corresponding file
   names with this character removed, then using Table B.1 will cause
   functional problems when clients attempt to interact with that file
   system.  The NFS version 4 server implementation including the
   filesystem MUST NOT silently remove characters not within Table B.1.

   If an implementation wishes to eliminate other characters because it
   is believed that allowing component name versions that both include
   the character and not have while otherwise the same, will contribute
   to confusion, it has two options:

   o  Treat the characters as prohibited and return NFS4ERR_BADCHAR.

   o  Eliminate the character as part of the name matching processing,
      while retaining it when a file is created.  This would be
      analogous to file systems that are both case-insensitive and case-
      preserving,as dicussed above, or those which are both
      normalization-insensitive and normalization-preserving, as
      discussed below.  The handling will be insensitive to presence of
      the chosen characters while preserving the presence or absence of
      such chatacters within names.

   Note that the second of these choices is a desirable way to handle
   characters within table B.1, again with the exception of U+200C and
   U+200D, which can cause issues for Farsi.

   In addition to modification due to normalization, discussed below,
   clients have to be able to deal with name modifications and other
   consequences of character mapping on the server, as discussed above.

12.7.1.5.  Normalization Issues for Component Strings

   The issues are best discussed separately for the server and the
   client.  It is important to note that the server and client may have
   different approaches to this area, and that the server choice may not
   match the client operating environment so the issue of mismatches and
   how they will be dealt with by the client is discussed in a later
   section.

12.7.1.5.1.  Server Normalization Issues for Component Strings

   The NFS version 4 does not specify required use of a particular
   normalization form for component4 strings.  Therefore, the server may
   receive unnormalized strings or strings that reflect either
   normalization form within protocol requests and responses.  If the
   operating environment requires normalization, then the server
   implementation must normalize component4 strings within the protocol
   server before presenting the information to the local file system.

   With regard to normalization, servers have the following choices,
   with the possibility that different choices may be selected for
   different file systems.

   o  Implement a particular normalization form, either NFC, or NFD, in
      which case file names received from a client are converted to that
      normalization form and as a consequence, the client will always
      receive names in that normalization form.  If this option is
      chosen, then it is impossible to create two files in the same
      directory that have different names which map to the same name
      when normalized.

   o  Implement handling which is both normalization-insensitive and
      normalization-preserving.  This makes it impossible to create two
      files in the same directory that have two different canonically
      equivalent name, i.e. names which map to the same name when
      normalized.  However, unlike the previous option, clients will not
      have the names that they present modified to meet the server's
      normalization constraints.

   o  Implement normalization-sensitive handling without enforcing a
      normalization form constraint on file names.  This exposes the
      client to the possibility that two files can be created in the
      same directory which have different names which map to the same
      name when normalized.  This may be a significant issue when client
      which use different normalization forms are used on the same file
      system, but this issue needs to be set against the difficulty of
      providing other sorts of normalization handling for some existing
      file systems.

12.7.1.5.2.  Client Normalization Issues for Component Strings

   The client, in processing name components, needs to deal with the
   fact that the server may impose normalization on file name components
   presented to it.  As a result, a file can be created within a
   directory and that name may have different name due to normalization
   at the server.

   Client operating environments differ in their handling of canonically
   equivalent name.  Some environments treat canonically equivalent
   strings as essentially equal and we will call these environments
   normalization-aware.  Others, because of the pattern of their
   development with regard to these issues treat different strings as
   different, even if they are canonically equivalent.  We call these
   normalization-unaware.

   Normalization-aware environments interoperate most normally with
   servers that either impose a given normalization form or those that
   implement name handling which is both normalization-insensitive and
   normalization-preserving name handling.  However, clients need to be
   prepared to interoperate with servers that have normalization-
   sensitive file naming.  In this situation, the client needs to be
   prepared for the fact that a directory may contain multiple names
   that it considers equivalent.

   Normalization-unaware environments interoperate most normally with
   servers that implement normalization-sensitive file naming.  However,
   clients need to be prepared to interoperate with servers that impose
   a given normalization form or that implement name handling which is
   both normalization-insensitive and normalization-preserving.  In the
   former case, a file created with a given name may find it changed to
   a different (although related name).  In both cases, the client will
   have to deal with the fact that it is unable to create two names
   within a directory that are canonically equivalent.

12.7.1.6.  Prohibited Characters for Component Names

   The NFS version 4 protocol does not specify particular characters
   that may not appear in component names.  File systems may have their
   own set of prohibited characters for which the error NFS4ERR_BADCHAR
   should be returned by the server.  Clients need to be prepared for
   this error to occur whenever file name components are presented to
   the server.

   Clients whose character repertoire for acceptable characters in file
   name components is smaller than the entire scope of UCS-4 may need to
   deal with names returned by the server that contain characters
   outside that repertoire.  It is up to the client whether it simply
   ignores these files or modifies the name to meet its own rules for
   acceptable names.

   Clients may encounter names that do not consist of valid UTF-8, if
   they interact with servers configured to allow this option.  They are
   not required to deal with this case and may treat the server as not
   functioning correctly, or they may handle this as normal.  Clients
   will normally make this a configuration option.  As discussed above,
   a client can determine whether a particular file system is being
   supported by the server in this mode by issuing a LOOKUP specifying a
   name which is not valid UTF-8 and seeing if NFS4ERR_INVAL is
   returned.

12.7.1.7.  Bidirectional String Checking for Component Names

   The NFS version 4 protocol does not require processing of component
   names to check for and reject bidirectional strings.  Such processing
   may be a part of the file system implementation but if so, its
   particular form will be defined by the file system implementation.
   When strings are rejected on this basis, the error NFS4ERR_BADNAME
   would be returned.

   Clients need to be prepared for the fact that the server may reject a
   file name component if it consists of a bidirectional string,
   returning NFS4ERR_BADNAME.

   Clients may encounter names with bidirectional strings returned in
   responses from the server.  If clients treat such strings as not
   valid file name components, it is up to the client whether it simply
   ignores these files or modifies the name component to meet its own
   rules for acceptable name component strings.

12.7.2.  Processing of Link Text

   Symbolic link text is defined as utf8_should and therefore the server
   SHOULD validate link text on a CREATE and return NFS4ERR_INVAL if it
   is is not valid UTF-8.  Note that file systems which treat names as
   strings of byte are an exception for which such validation need not
   be done.  One other situation in which an NFS version 4 might choose
   (or be configured) not to make such a check is when links within file
   system reference names in another which is configured to treat names
   as strings of bytes.

   On the other hand, UTF-8 validation of symbolic link text need not be
   done on the data resulting from a READLINK.  Such data might have
   been stored by an NFS Version 4 server configured to allow non-UTF-8
   link text or it might have resulted from symbolic link text stored
   via local file system access or access via another remote file access
   protocol.

   Note that because of the role of the symbolic link, as data stored
   and read by the user, other sorts of validations or modifications
   should not be done.  Note that when component names with the symbolic
   link text are used, such checks and modifications will be done at
   that time.  In particular,

   o  Limitation of the character repertoire MUST NOT be done.  This
      includes limitations to reflect a particular version of unicode,
      or the inability of any particualr file system to store characters
      beyond UCS-2.

   o  Name mapping, whether for case folding or otherwise MUST NOT be
      done.

   o  Checks for a type of normalization or normalization to a
      particular form MUST NOT be done.

   o  Checks for specific characters excluded by the server or file
      system MUST NOT be done.

   o  Checks for bidrectional strings MUST NOT be done.

12.7.3.  Processing of Principal Prefixes

   As mentioned above, users and groups are designated as a particular
   string at a specified domain.  Servers will recognize a set of valid
   principals for one or more domains.  With regard to the handling of
   these strings, the following rules MUST be followed

   o  The string MUST be checked by the server for valid UTF-8 and the
      error NFS4ERR_INVAL returned if it is not valid.

   o  The character repertoire for the principal prefix string should be
      limited to a current version of Unicode when the server is
      implemented.  However, the client cannot be assured that all
      characters it receives as part of a user or group attribute are
      those that are defined in the Unicode version it expects to work
      with.

   o  No character mapping is to be done, as for example table B.1 in
      stringprep, and no case mapping is to be done.  The user and group
      names are to be treated as case-sensitive.

   o  Strings must not be rejected based on their normalization.
      Servers should do normalization insensitive matching in converting
      a user to group to an internal id.  The client cannot assume that
      the server preserves normalization so a user set to one string
      value may be returned as a string which differs in nomralization
      and the client must be prepared to deal with that, by, for
      example, normalizing the string to the client's prferred form.

   o  There are no checks for specific invalid characters but servers
      may limit the characters, with the result that any principal
      presented by the client which has such a characters is treated as
      invalid.

   o  Specific checks for bidrectional strings are not done but servers
      may limit the principal prefix strings to those which are
      unidirectional or are of a certain direction, with the result that
      any principal presented by the client which done not meet that
      criterion will be treated as invaid.

13.  Error Values

   NFS error numbers are assigned to failed operations within a Compound
   (COMPOUND or CB_COMPOUND) request.  A Compound request contains a
   number of NFS operations that have their results encoded in sequence
   in a Compound reply.  The results of successful operations will
   consist of an NFS4_OK status followed by the encoded results of the
   operation.  If an NFS operation fails, an error status will be
   entered in the reply and the Compound request will be terminated.

13.1.  Error Definitions

                        Protocol Error Definitions

       +-----------------------------+--------+-------------------+
       | Error                       | Number | Description       |
       +-----------------------------+--------+-------------------+
       | NFS4_OK                     | 0      | Section 13.1.3.1  |
       | NFS4ERR_ACCESS              | 13     | Section 13.1.6.1  |
       | NFS4ERR_ATTRNOTSUPP         | 10032  | Section 13.1.11.1 |
       | NFS4ERR_ADMIN_REVOKED       | 10047  | Section 13.1.5.1  |
       | NFS4ERR_BADCHAR             | 10040  | Section 13.1.7.1  |
       | NFS4ERR_BADHANDLE           | 10001  | Section 13.1.2.1  |
       | NFS4ERR_BADNAME             | 10041  | Section 13.1.7.2  |
       | NFS4ERR_BADOWNER            | 10039  | Section 13.1.11.2 |
       | NFS4ERR_BADTYPE             | 10007  | Section 13.1.4.1  |
       | NFS4ERR_BADXDR              | 10036  | Section 13.1.1.1  |
       | NFS4ERR_BAD_COOKIE          | 10003  | Section 13.1.1.2  |
       | NFS4ERR_BAD_RANGE           | 10042  | Section 13.1.8.1  |
       | NFS4ERR_BAD_SEQID           | 10026  | Section 13.1.8.2  |
       | NFS4ERR_BAD_STATEID         | 10025  | Section 13.1.5.2  |
       | NFS4ERR_CLID_INUSE          | 10017  | Section 13.1.10.1 |
       | NFS4ERR_DEADLOCK            | 10045  | Section 13.1.8.3  |
       | NFS4ERR_DELAY               | 10008  | Section 13.1.1.3  |
       | NFS4ERR_DENIED              | 10010  | Section 13.1.8.4  |
       | NFS4ERR_DQUOT               | 69     | Section 13.1.4.2  |
       | NFS4ERR_EXIST               | 17     | Section 13.1.4.3  |
       | NFS4ERR_EXPIRED             | 10011  | Section 13.1.5.3  |
       | NFS4ERR_FBIG                | 27     | Section 13.1.4.4  |
       | NFS4ERR_FHEXPIRED           | 10014  | Section 13.1.2.2  |
       | NFS4ERR_FILE_OPEN           | 10046  | Section 13.1.4.5  |
       | NFS4ERR_GRACE               | 10013  | Section 13.1.9.1  |
       | NFS4ERR_INVAL               | 22     | Section 13.1.1.4  |
       | NFS4ERR_IO                  | 5      | Section 13.1.4.6  |
       | NFS4ERR_ISDIR               | 21     | Section 13.1.2.3  |
       | NFS4ERR_LEASE_MOVED         | 10031  | Section 13.1.5.4  |
       | NFS4ERR_LOCKED              | 10012  | Section 13.1.8.5  |
       | NFS4ERR_LOCKS_HELD          | 10037  | Section 13.1.8.6  |
       | NFS4ERR_LOCK_NOTSUPP        | 10043  | Section 13.1.8.7  |
       | NFS4ERR_LOCK_RANGE          | 10028  | Section 13.1.8.8  |
       | NFS4ERR_MINOR_VERS_MISMATCH | 10021  | Section 13.1.3.2  |
       | NFS4ERR_MLINK               | 31     | Section 13.1.4.7  |
       | NFS4ERR_MOVED               | 10019  | Section 13.1.2.4  |
       | NFS4ERR_NAMETOOLONG         | 63     | Section 13.1.7.3  |
       | NFS4ERR_NOENT               | 2      | Section 13.1.4.8  |
       | NFS4ERR_NOFILEHANDLE        | 10020  | Section 13.1.2.5  |
       | NFS4ERR_NOSPC               | 28     | Section 13.1.4.9  |
       | NFS4ERR_NOTDIR              | 20     | Section 13.1.2.6  |
       | NFS4ERR_NOTEMPTY            | 66     | Section 13.1.4.10 |
       | NFS4ERR_NOTSUPP             | 10004  | Section 13.1.1.5  |
       | NFS4ERR_NOT_SAME            | 10027  | Section 13.1.11.3 |
       | NFS4ERR_NO_GRACE            | 10033  | Section 13.1.9.2  |
       | NFS4ERR_NXIO                | 6      | Section 13.1.4.11 |
       | NFS4ERR_OLD_STATEID         | 10024  | Section 13.1.5.5  |
       | NFS4ERR_OPENMODE            | 10038  | Section 13.1.8.9  |
       | NFS4ERR_OP_ILLEGAL          | 10044  | Section 13.1.3.3  |
       | NFS4ERR_PERM                | 1      | Section 13.1.6.2  |
       | NFS4ERR_RECLAIM_BAD         | 10034  | Section 13.1.9.3  |
       | NFS4ERR_RECLAIM_CONFLICT    | 10035  | Section 13.1.9.4  |
       | NFS4ERR_RESOURCE            | 10018  | Section 13.1.3.4  |
       | NFS4ERR_RESTOREFH           | 10030  | Section 13.1.4.12 |
       | NFS4ERR_ROFS                | 30     | Section 13.1.4.13 |
       | NFS4ERR_SAME                | 10009  | Section 13.1.11.4 |
       | NFS4ERR_SERVERFAULT         | 10006  | Section 13.1.1.6  |
       | NFS4ERR_STALE               | 70     | Section 13.1.2.7  |
       | NFS4ERR_STALE_CLIENTID      | 10022  | Section 13.1.10.2 |
       | NFS4ERR_STALE_STATEID       | 10023  | Section 13.1.5.6  |
       | NFS4ERR_SYMLINK             | 10029  | Section 13.1.2.8  |
       | NFS4ERR_TOOSMALL            | 10005  | Section 13.1.1.7  |
       | NFS4ERR_WRONGSEC            | 10016  | Section 13.1.6.3  |
       | NFS4ERR_XDEV                | 18     | Section 13.1.4.14 |
       +-----------------------------+--------+-------------------+

                                  Table 8

13.1.1.  General Errors

   This section deals with errors that are applicable to a broad set of
   different purposes.

13.1.1.1.  NFS4ERR_BADXDR (Error Code 10036)

   The arguments for this operation do not match those specified in the
   XDR definition.  This includes situations in which the request ends
   before all the arguments have been seen.  Note that this error
   applies when fixed enumerations (these include booleans) have a value
   within the input stream which is not valid for the enum.  A replier
   may pre-parse all operations for a Compound procedure before doing
   any operation execution and return RPC-level XDR errors in that case.

13.1.1.2.  NFS4ERR_BAD_COOKIE (Error Code 10003)

   Used for operations that provide a set of information indexed by some
   quantity provided by the client or cookie sent by the server for an
   earlier invocation.  Where the value cannot be used for its intended
   purpose, this error results.

13.1.1.3.  NFS4ERR_DELAY (Error Code 10008)

   For any of a number of reasons, the replier could not process this
   operation in what was deemed a reasonable time.  The client should
   wait and then try the request with a new RPC transaction ID.

   Some example of situations that might lead to this situation:

   o  A server that supports hierarchical storage receives a request to
      process a file that had been migrated.

   o  An operation requires a delegation recall to proceed and waiting
      for this delegation recall makes processing this request in a
      timely fashion impossible.

   In such cases, the error NFS4ERR_DELAY allows these preparatory
   operations to proceed without holding up client resources such as a
   session slot.  After delaying for period of time, the client can then
   re-send the operation in question.

13.1.1.4.  NFS4ERR_INVAL (Error Code 22)

   The arguments for this operation are not valid for some reason, even
   though they do match those specified in the XDR definition for the
   request.

13.1.1.5.  NFS4ERR_NOTSUPP (Error Code 10004)

   Operation not supported, either because the operation is an OPTIONAL
   one and is not supported by this server or because the operation MUST
   NOT be implemented in the current minor version.

13.1.1.6.  NFS4ERR_SERVERFAULT (Error Code 10006)

   An error occurred on the server which does not map to any of the
   specific legal NFSv4.1 protocol error values.  The client should
   translate this into an appropriate error.  UNIX clients may choose to
   translate this to EIO.

13.1.1.7.  NFS4ERR_TOOSMALL (Error Code 10005)

   Used where an operation returns a variable amount of data, with a
   limit specified by the client.  Where the data returned cannot be fit
   within the limit specified by the client, this error results.

13.1.2.  Filehandle Errors

   These errors deal with the situation in which the current or saved
   filehandle, or the filehandle passed to PUTFH intended to become the
   current filehandle, is invalid in some way.  This includes situations
   in which the filehandle is a valid filehandle in general but is not
   of the appropriate object type for the current operation.

   Where the error description indicates a problem with the current or
   saved filehandle, it is to be understood that filehandles are only
   checked for the condition if they are implicit arguments of the
   operation in question.

13.1.2.1.  NFS4ERR_BADHANDLE (Error Code 10001)

   Illegal NFS filehandle for the current server.  The current file
   handle failed internal consistency checks.  Once accepted as valid
   (by PUTFH), no subsequent status change can cause the filehandle to
   generate this error.

13.1.2.2.  NFS4ERR_FHEXPIRED (Error Code 10014)

   A current or saved filehandle which is an argument to the current
   operation is volatile and has expired at the server.

13.1.2.3.  NFS4ERR_ISDIR (Error Code 21)

   The current or saved filehandle designates a directory when the
   current operation does not allow a directory to be accepted as the
   target of this operation.

13.1.2.4.  NFS4ERR_MOVED (Error Code 10019)

   The file system which contains the current filehandle object is not
   present at the server.  It may have been relocated, migrated to
   another server or may have never been present.  The client may obtain
   the new file system location by obtaining the "fs_locations" or
   attribute for the current filehandle.  For further discussion, refer
   to Section 7

13.1.2.5.  NFS4ERR_NOFILEHANDLE (Error Code 10020)

   The logical current or saved filehandle value is required by the
   current operation and is not set.  This may be a result of a
   malformed COMPOUND operation (i.e. no PUTFH or PUTROOTFH before an
   operation that requires the current filehandle be set).

13.1.2.6.  NFS4ERR_NOTDIR (Error Code 20)

   The current (or saved) filehandle designates an object which is not a
   directory for an operation in which a directory is required.

13.1.2.7.  NFS4ERR_STALE (Error Code 70)

   The current or saved filehandle value designating an argument to the
   current operation is invalid The file referred to by that filehandle
   no longer exists or access to it has been revoked.

13.1.2.8.  NFS4ERR_SYMLINK (Error Code 10029)

   The current filehandle designates a symbolic link when the current
   operation does not allow a symbolic link as the target.

13.1.3.  Compound Structure Errors

   This section deals with errors that relate to overall structure of a
   Compound request (by which we mean to include both COMPOUND and
   CB_COMPOUND), rather than to particular operations.

   There are a number of basic constraints on the operations that may
   appear in a Compound request.

13.1.3.1.  NFS_OK (Error code 0)

   Indicates the operation completed successfully, in that all of the
   constituent operations completed without error.

13.1.3.2.  NFS4ERR_MINOR_VERS_MISMATCH (Error code 10021)

   The minor version specified is not one that the current listener
   supports.  This value is returned in the overall status for the
   Compound but is not associated with a specific operation since the
   results must specify a result count of zero.

13.1.3.3.  NFS4ERR_OP_ILLEGAL (Error Code 10044)

   The operation code is not a valid one for the current Compound
   procedure.  The opcode in the result stream matched with this error
   is the ILLEGAL value, although the value that appears in the request
   stream may be different.  Where an illegal value appears and the
   replier pre-parses all operations for a Compound procedure before
   doing any operation execution, an RPC-level XDR error may be returned
   in this case.

13.1.3.4.  NFS4ERR_RESOURCE (Error Code 10018)

   For the processing of the Compound procedure, the server may exhaust
   available resources and can not continue processing operations within
   the Compound procedure.  This error will be returned from the server
   in those instances of resource exhaustion related to the processing
   of the Compound procedure.

13.1.4.  File System Errors

   These errors describe situations which occurred in the underlying
   file system implementation rather than in the protocol or any NFSv4.x
   feature.

13.1.4.1.  NFS4ERR_BADTYPE (Error Code 10007)

   An attempt was made to create an object with an inappropriate type
   specified to CREATE.  This may be because the type is undefined,
   because it is a type not supported by the server, or because it is a
   type for which create is not intended such as a regular file or named
   attribute, for which OPEN is used to do the file creation.

13.1.4.2.  NFS4ERR_DQUOT (Error Code 19)

   Resource (quota) hard limit exceeded.  The user's resource limit on
   the server has been exceeded.

13.1.4.3.  NFS4ERR_EXIST (Error Code 17)

   A file of the specified target name (when creating, renaming or
   linking) already exists.

13.1.4.4.  NFS4ERR_FBIG (Error Code 27)

   File too large.  The operation would have caused a file to grow
   beyond the server's limit.

13.1.4.5.  NFS4ERR_FILE_OPEN (Error Code 10046)

   The operation is not allowed because a file involved in the operation
   is currently open.  Servers may, but are not required to disallow
   linking-to, removing, or renaming open files.

13.1.4.6.  NFS4ERR_IO (Error Code 5)

   Indicates that an I/O error occurred for which the file system was
   unable to provide recovery.

13.1.4.7.  NFS4ERR_MLINK (Error Code 31)

   The request would have caused the server's limit for the number of
   hard links a file may have to be exceeded.

13.1.4.8.  NFS4ERR_NOENT (Error Code 2)

   Indicates no such file or directory.  The file or directory name
   specified does not exist.

13.1.4.9.  NFS4ERR_NOSPC (Error Code 28)

   Indicates no space left on device.  The operation would have caused
   the server's file system to exceed its limit.

13.1.4.10.  NFS4ERR_NOTEMPTY (Error Code 66)

   An attempt was made to remove a directory that was not empty.

13.1.4.11.  NFS4ERR_NXIO (Error Code 5)

   I/O error.  No such device or address.

13.1.4.12.  NFS4ERR_RESTOREFH (Error Code 10030)

   The RESTOREFH operation does not have a saved filehandle (identified
   by SAVEFH) to operate upon.

13.1.4.13.  NFS4ERR_ROFS (Error Code 30)

   Indicates a read-only file system.  A modifying operation was
   attempted on a read-only file system.

13.1.4.14.  NFS4ERR_XDEV (Error Code 18)

   Indicates an attempt to do an operation, such as linking, that
   inappropriately crosses a boundary.  This may be due to such
   boundaries as:

   o  That between file systems (where the fsids are different).

   o  That between different named attribute directories or between a
      named attribute directory and an ordinary directory.

   o  That between regions of a file system that the file system
      implementation treats as separate (for example for space
      accounting purposes), and where cross-connection between the
      regions are not allowed.

13.1.5.  State Management Errors

   These errors indicate problems with the stateid (or one of the
   stateids) passed to a given operation.  This includes situations in
   which the stateid is invalid as well as situations in which the
   stateid is valid but designates revoked locking state.  Depending on
   the operation, the stateid when valid may designate opens, byte-range
   locks, file or directory delegations, layouts, or device maps.

13.1.5.1.  NFS4ERR_ADMIN_REVOKED (Error Code 10047)

   A stateid designates locking state of any type that has been revoked
   due to administrative interaction, possibly while the lease is valid.

13.1.5.2.  NFS4ERR_BAD_STATEID (Error Code 10026)

   A stateid generated by the current server instance, but which does
   not designate any locking state (either current or superseded) for a
   current lockowner-file pair, was used.

13.1.5.3.  NFS4ERR_EXPIRED (Error Code 10011)

   A stateid designates locking state of any type that has been revoked
   due to expiration of the client's lease, either immediately upon
   lease expiration, or following a later request for a conflicting
   lock.

13.1.5.4.  NFS4ERR_LEASE_MOVED (Error Code 10031)

   A lease being renewed is associated with a file system that has been
   migrated to a new server.

13.1.5.5.  NFS4ERR_OLD_STATEID (Error Code 10024)

   A stateid with a non-zero seqid value does match the current seqid
   for the state designated by the user.

13.1.5.6.  NFS4ERR_STALE_STATEID (Error Code 10023)

   A stateid generated by an earlier server instance was used.

13.1.6.  Security Errors

   These are the various permission-related errors in NFSv4.1.

13.1.6.1.  NFS4ERR_ACCESS (Error Code 13)

   Indicates permission denied.  The caller does not have the correct
   permission to perform the requested operation.  Contrast this with
   NFS4ERR_PERM (Section 13.1.6.2), which restricts itself to owner or
   privileged user permission failures.

13.1.6.2.  NFS4ERR_PERM (Error Code 1)

   Indicates requester is not the owner.  The operation was not allowed
   because the caller is neither a privileged user (root) nor the owner
   of the target of the operation.

13.1.6.3.  NFS4ERR_WRONGSEC (Error Code 10016)

   Indicates that the security mechanism being used by the client for
   the operation does not match the server's security policy.  The
   client should change the security mechanism being used and re-send
   the operation.  SECINFO can be used to determine the appropriate
   mechanism.

13.1.7.  Name Errors

   Names in NFSv4 are UTF-8 strings.  When the strings are not are of
   length zero, the error NFS4ERR_INVAL results.  When they are not
   valid UTF-8 the error NFS4ERR_INVAL also results, but servers may
   accommodate file systems with different character formats and not
   return this error.  Besides this, there are a number of other errors
   to indicate specific problems with names.

13.1.7.1.  NFS4ERR_BADCHAR (Error Code 10040)

   A UTF-8 string contains a character which is not supported by the
   server in the context in which it being used.

13.1.7.2.  NFS4ERR_BADNAME (Error Code 10041)

   A name string in a request consisted of valid UTF-8 characters
   supported by the server but the name is not supported by the server
   as a valid name for current operation.  An example might be creating
   a file or directory named ".." on a server whose file system uses
   that name for links to parent directories.

   This error should not be returned due a normalization issue in a
   string.  When a file system keeps names in a particular normalization
   form, it is the server's responsiblity to do the approproriate
   normalization, rather than rejecting the name.

13.1.7.3.  NFS4ERR_NAMETOOLONG (Error Code 63)

   Returned when the filename in an operation exceeds the server's
   implementation limit.

13.1.8.  Locking Errors

   This section deal with errors related to locking, both as to share
   reservations and byte-range locking.  It does not deal with errors
   specific to the process of reclaiming locks.  Those are dealt with in
   the next section.

13.1.8.1.  NFS4ERR_BAD_RANGE (Error Code 10042)

   The range for a LOCK, LOCKT, or LOCKU operation is not appropriate to
   the allowable range of offsets for the server.  E.g., this error
   results when a server which only supports 32-bit ranges receives a
   range that cannot be handled by that server.  (See Section 15.12.4).

13.1.8.2.  NFS4ERR_BAD_SEQID (Error Code 10026)

   The sequence number (seqid) in a locking request is neither the next
   expected number or the last number processed.

13.1.8.3.  NFS4ERR_DEADLOCK (Error Code 10045)

   The server has been able to determine a file locking deadlock
   condition for a blocking lock request.

13.1.8.4.  NFS4ERR_DENIED (Error Code 10010)

   An attempt to lock a file is denied.  Since this may be a temporary
   condition, the client is encouraged to re-send the lock request until
   the lock is accepted.  See Section 9.4 for a discussion of the re-
   send.

13.1.8.5.  NFS4ERR_LOCKED (Error Code 10012)

   A read or write operation was attempted on a file where there was a
   conflict between the I/O and an existing lock:

   o  There is a share reservation inconsistent with the I/O being done.

   o  The range to be read or written intersects an existing mandatory
      byte range lock.

13.1.8.6.  NFS4ERR_LOCKS_HELD (Error Code 10037)

   An operation was prevented by the unexpected presence of locks.

13.1.8.7.  NFS4ERR_LOCK_NOTSUPP (Error Code 10043)

   A locking request was attempted which would require the upgrade or
   downgrade of a lock range already held by the owner when the server
   does not support atomic upgrade or downgrade of locks.

13.1.8.8.  NFS4ERR_LOCK_RANGE (Error Code 10028)

   A lock request is operating on a range that overlaps in part a
   currently held lock for the current lock owner and does not precisely
   match a single such lock where the server does not support this type
   of request, and thus does not implement POSIX locking semantics.  See
   Section 15.12.5, Section 15.13.5, and Section 15.14.5 for a
   discussion of how this applies to LOCK, LOCKT, and LOCKU
   respectively.

13.1.8.9.  NFS4ERR_OPENMODE (Error Code 10038)

   The client attempted a READ, WRITE, LOCK or other operation not
   sanctioned by the stateid passed (e.g. writing to a file opened only
   for read).

13.1.9.  Reclaim Errors

   These errors relate to the process of reclaiming locks after a server
   restart.

13.1.9.1.  NFS4ERR_GRACE (Error Code 10013)

   The server is in its recovery or grace period which should at least
   match the lease period of the server.  A locking request other than a
   reclaim could not be granted during that period.

13.1.9.2.  NFS4ERR_NO_GRACE (Error Code 10033)

   A reclaim of client state was attempted in circumstances in which the
   server cannot guarantee that conflicting state has not been provided
   to another client.  As a result, the server can not guarantee that
   conflicting state has not been provided to another client.

13.1.9.3.  NFS4ERR_RECLAIM_BAD (Error Code 10034)

   A reclaim attempted by the client does not match the server's state
   consistency checks and has been rejected therefore as invalid.

13.1.9.4.  NFS4ERR_RECLAIM_CONFLICT (Error Code 10035)

   The reclaim attempted by the client has encountered a conflict and
   cannot be satisfied.  Potentially indicates a misbehaving client,
   although not necessarily the one receiving the error.  The
   misbehavior might be on the part of the client that established the
   lock with which this client conflicted.

13.1.10.  Client Management Errors

   This sections deals with errors associated with requests used to
   create and manage client IDs.

13.1.10.1.  NFS4ERR_CLID_INUSE (Error Code 10017)

   The SETCLIENTID operation has found that a client id is already in
   use by another client.

13.1.10.2.  NFS4ERR_STALE_CLIENTID (Error Code 10022)

   A clientid not recognized by the server was used in a locking or
   SETCLIENTID_CONFIRM request.

13.1.11.  Attribute Handling Errors

   This section deals with errors specific to attribute handling within
   NFSv4.

13.1.11.1.  NFS4ERR_ATTRNOTSUPP (Error Code 10032)

   An attribute specified is not supported by the server.  This error
   MUST NOT be returned by the GETATTR operation.

13.1.11.2.  NFS4ERR_BADOWNER (Error Code 10039)

   Returned when an owner or owner_group attribute value or the who
   field of an ace within an ACL attribute value cannot be translated to
   a local representation.

13.1.11.3.  NFS4ERR_NOT_SAME (Error Code 10027)

   This error is returned by the VERIFY operation to signify that the
   attributes compared were not the same as those provided in the
   client's request.

13.1.11.4.  NFS4ERR_SAME (Error Code 10009)

   This error is returned by the NVERIFY operation to signify that the
   attributes compared were the same as those provided in the client's
   request.

13.2.  Operations and their valid errors

   This section contains a table which gives the valid error returns for
   each protocol operation.  The error code NFS4_OK (indicating no
   error) is not listed but should be understood to be returnable by all
   operations except ILLEGAL.

              Valid error returns for each protocol operation

   +---------------------+---------------------------------------------+
   | Operation           | Errors                                      |
   +---------------------+---------------------------------------------+
   | ACCESS              | NFS4ERR_ACCESS, NFS4ERR_BADHANDLE,          |
   |                     | NFS4ERR_BADXDR, NFS4ERR_DELAY,              |
   |                     | NFS4ERR_FHEXPIRED, NFS4ERR_INVAL,           |
   |                     | NFS4ERR_IO, NFS4ERR_MOVED,                  |
   |                     | NFS4ERR_NOFILEHANDLE, NFS4ERR_RESOURCE,     |
   |                     | NFS4ERR_SERVERFAULT, NFS4ERR_STALE          |
   | CLOSE               | NFS4ERR_ADMIN_REVOKED, NFS4ERR_BADHANDLE,   |
   |                     | NFS4ERR_BAD_SEQID, NFS4ERR_BAD_STATEID,     |
   |                     | NFS4ERR_BADXDR, NFS4ERR_DELAY,              |
   |                     | NFS4ERR_EXPIRED, NFS4ERR_FHEXPIRED,         |
   |                     | NFS4ERR_INVAL, NFS4ERR_ISDIR,               |
   |                     | NFS4ERR_LEASE_MOVED, NFS4ERR_LOCKS_HELD,    |
   |                     | NFS4ERR_MOVED, NFS4ERR_NOFILEHANDLE,        |
   |                     | NFS4ERR_OLD_STATEID, NFS4ERR_RESOURCE,      |
   |                     | NFS4ERR_SERVERFAULT, NFS4ERR_STALE,         |
   |                     | NFS4ERR_STALE_STATEID                       |
   | COMMIT              | NFS4ERR_ACCESS, NFS4ERR_BADHANDLE,          |
   |                     | NFS4ERR_BADXDR, NFS4ERR_FHEXPIRED,          |
   |                     | NFS4ERR_INVAL, NFS4ERR_IO, NFS4ERR_ISDIR,   |
   |                     | NFS4ERR_MOVED, NFS4ERR_NOFILEHANDLE,        |
   |                     | NFS4ERR_RESOURCE, NFS4ERR_ROFS,             |
   |                     | NFS4ERR_SERVERFAULT, NFS4ERR_STALE,         |
   |                     | NFS4ERR_SYMLINK                             |
   | CREATE              | NFS4ERR_ACCESS, NFS4ERR_ATTRNOTSUPP,        |
   |                     | NFS4ERR_BADCHAR, NFS4ERR_BADHANDLE,         |
   |                     | NFS4ERR_BADNAME, NFS4ERR_BADOWNER,          |
   |                     | NFS4ERR_BADTYPE, NFS4ERR_BADXDR,            |
   |                     | NFS4ERR_DELAY, NFS4ERR_DQUOT,               |
   |                     | NFS4ERR_EXIST, NFS4ERR_FHEXPIRED,           |
   |                     | NFS4ERR_INVAL, NFS4ERR_IO, NFS4ERR_MOVED,   |
   |                     | NFS4ERR_NAMETOOLONG, NFS4ERR_NOFILEHANDLE,  |
   |                     | NFS4ERR_NOSPC, NFS4ERR_NOTDIR,              |
   |                     | NFS4ERR_PERM, NFS4ERR_RESOURCE,             |
   |                     | NFS4ERR_ROFS, NFS4ERR_SERVERFAULT,          |
   |                     | NFS4ERR_STALE                               |
   | DELEGPURGE          | NFS4ERR_BADXDR, NFS4ERR_NOTSUPP,            |
   |                     | NFS4ERR_LEASE_MOVED, NFS4ERR_RESOURCE,      |
   |                     | NFS4ERR_SERVERFAULT, NFS4ERR_STALE_CLIENTID |
   | DELEGRETURN         | NFS4ERR_ADMIN_REVOKED, NFS4ERR_BAD_STATEID, |
   |                     | NFS4ERR_BADXDR, NFS4ERR_EXPIRED,            |
   |                     | NFS4ERR_INVAL, NFS4ERR_LEASE_MOVED,         |
   |                     | NFS4ERR_MOVED, NFS4ERR_NOFILEHANDLE,        |
   |                     | NFS4ERR_NOTSUPP, NFS4ERR_OLD_STATEID,       |
   |                     | NFS4ERR_RESOURCE, NFS4ERR_SERVERFAULT,      |
   |                     | NFS4ERR_STALE, NFS4ERR_STALE_STATEID        |
   | GETATTR             | NFS4ERR_ACCESS, NFS4ERR_BADHANDLE,          |
   |                     | NFS4ERR_BADXDR, NFS4ERR_DELAY,              |
   |                     | NFS4ERR_FHEXPIRED, NFS4ERR_GRACE,           |
   |                     | NFS4ERR_INVAL, NFS4ERR_IO, NFS4ERR_MOVED,   |
   |                     | NFS4ERR_NOFILEHANDLE, NFS4ERR_RESOURCE,     |
   |                     | NFS4ERR_SERVERFAULT, NFS4ERR_STALE          |
   | GETFH               | NFS4ERR_BADHANDLE, NFS4ERR_FHEXPIRED,       |
   |                     | NFS4ERR_MOVED, NFS4ERR_NOFILEHANDLE,        |
   |                     | NFS4ERR_RESOURCE, NFS4ERR_SERVERFAULT,      |
   |                     | NFS4ERR_STALE                               |
   | ILLEGAL             | NFS4ERR_BADXDR, NFS4ERR_OP_ILLEGAL          |
   | LINK                | NFS4ERR_ACCESS, NFS4ERR_BADCHAR,            |
   |                     | NFS4ERR_BADHANDLE, NFS4ERR_BADNAME,         |
   |                     | NFS4ERR_BADXDR, NFS4ERR_DELAY,              |
   |                     | NFS4ERR_DQUOT, NFS4ERR_EXIST,               |
   |                     | NFS4ERR_FHEXPIRED, NFS4ERR_FILE_OPEN,       |
   |                     | NFS4ERR_INVAL, NFS4ERR_IO, NFS4ERR_ISDIR,   |
   |                     | NFS4ERR_MLINK, NFS4ERR_MOVED,               |
   |                     | NFS4ERR_NAMETOOLONG, NFS4ERR_NOENT,         |
   |                     | NFS4ERR_NOFILEHANDLE, NFS4ERR_NOSPC,        |
   |                     | NFS4ERR_NOTDIR, NFS4ERR_NOTSUPP,            |
   |                     | NFS4ERR_RESOURCE, NFS4ERR_ROFS,             |
   |                     | NFS4ERR_SERVERFAULT, NFS4ERR_STALE,         |
   |                     | NFS4ERR_WRONGSEC, NFS4ERR_XDEV              |
   | LOCK                | NFS4ERR_ACCESS, NFS4ERR_ADMIN_REVOKED,      |
   |                     | NFS4ERR_BADHANDLE, NFS4ERR_BAD_RANGE,       |
   |                     | NFS4ERR_BAD_SEQID, NFS4ERR_BAD_STATEID,     |
   |                     | NFS4ERR_BADXDR, NFS4ERR_DEADLOCK,           |
   |                     | NFS4ERR_DELAY, NFS4ERR_DENIED,              |
   |                     | NFS4ERR_EXPIRED, NFS4ERR_FHEXPIRED,         |
   |                     | NFS4ERR_GRACE, NFS4ERR_INVAL,               |
   |                     | NFS4ERR_ISDIR, NFS4ERR_LEASE_MOVED,         |
   |                     | NFS4ERR_LOCK_NOTSUPP, NFS4ERR_LOCK_RANGE,   |
   |                     | NFS4ERR_MOVED, NFS4ERR_NOFILEHANDLE,        |
   |                     | NFS4ERR_NO_GRACE, NFS4ERR_OLD_STATEID,      |
   |                     | NFS4ERR_OPENMODE, NFS4ERR_RECLAIM_BAD,      |
   |                     | NFS4ERR_RECLAIM_CONFLICT, NFS4ERR_RESOURCE, |
   |                     | NFS4ERR_SERVERFAULT, NFS4ERR_STALE,         |
   |                     | NFS4ERR_STALE_CLIENTID,                     |
   |                     | NFS4ERR_STALE_STATEID                       |
   | LOCKT               | NFS4ERR_ACCESS, NFS4ERR_BADHANDLE,          |
   |                     | NFS4ERR_BAD_RANGE, NFS4ERR_BADXDR,          |
   |                     | NFS4ERR_DELAY, NFS4ERR_DENIED,              |
   |                     | NFS4ERR_FHEXPIRED, NFS4ERR_GRACE,           |
   |                     | NFS4ERR_INVAL, NFS4ERR_ISDIR,               |
   |                     | NFS4ERR_LEASE_MOVED, NFS4ERR_LOCK_RANGE,    |
   |                     | NFS4ERR_MOVED, NFS4ERR_NOFILEHANDLE,        |
   |                     | NFS4ERR_RESOURCE, NFS4ERR_SERVERFAULT,      |
   |                     | NFS4ERR_STALE, NFS4ERR_STALE_CLIENTID       |
   | LOCKU               | NFS4ERR_ACCESS, NFS4ERR_ADMIN_REVOKED,      |
   |                     | NFS4ERR_BADHANDLE, NFS4ERR_BAD_RANGE,       |
   |                     | NFS4ERR_BAD_SEQID, NFS4ERR_BAD_STATEID,     |
   |                     | NFS4ERR_BADXDR, NFS4ERR_EXPIRED,            |
   |                     | NFS4ERR_FHEXPIRED, NFS4ERR_GRACE,           |
   |                     | NFS4ERR_INVAL, NFS4ERR_ISDIR,               |
   |                     | NFS4ERR_LEASE_MOVED, NFS4ERR_LOCK_RANGE,    |
   |                     | NFS4ERR_MOVED, NFS4ERR_NOFILEHANDLE,        |
   |                     | NFS4ERR_OLD_STATEID, NFS4ERR_RESOURCE,      |
   |                     | NFS4ERR_SERVERFAULT, NFS4ERR_STALE,         |
   |                     | NFS4ERR_STALE_STATEID                       |
   | LOOKUP              | NFS4ERR_ACCESS, NFS4ERR_BADCHAR,            |
   |                     | NFS4ERR_BADHANDLE, NFS4ERR_BADNAME,         |
   |                     | NFS4ERR_BADXDR, NFS4ERR_FHEXPIRED,          |
   |                     | NFS4ERR_INVAL, NFS4ERR_IO, NFS4ERR_MOVED,   |
   |                     | NFS4ERR_NAMETOOLONG, NFS4ERR_NOENT,         |
   |                     | NFS4ERR_NOFILEHANDLE, NFS4ERR_NOTDIR,       |
   |                     | NFS4ERR_RESOURCE, NFS4ERR_SERVERFAULT,      |
   |                     | NFS4ERR_STALE, NFS4ERR_SYMLINK,             |
   |                     | NFS4ERR_WRONGSEC                            |
   | LOOKUPP             | NFS4ERR_ACCESS, NFS4ERR_BADHANDLE,          |
   |                     | NFS4ERR_DELAY, NFS4ERR_FHEXPIRED,           |
   |                     | NFS4ERR_IO, NFS4ERR_MOVED, NFS4ERR_NOENT,   |
   |                     | NFS4ERR_NOFILEHANDLE, NFS4ERR_NOTDIR,       |
   |                     | NFS4ERR_RESOURCE, NFS4ERR_SERVERFAULT,      |
   |                     | NFS4ERR_STALE, NFS4ERR_SYMLINK,             |
   |                     | NFS4ERR_WRONGSEC                            |
   | NVERIFY             | NFS4ERR_ACCESS, NFS4ERR_ATTRNOTSUPP,        |
   |                     | NFS4ERR_BADCHAR, NFS4ERR_BADHANDLE,         |
   |                     | NFS4ERR_BADXDR, NFS4ERR_DELAY,              |
   |                     | NFS4ERR_FHEXPIRED, NFS4ERR_GRACE,           |
   |                     | NFS4ERR_INVAL, NFS4ERR_IO, NFS4ERR_MOVED,   |
   |                     | NFS4ERR_NOFILEHANDLE, NFS4ERR_SAME,         |
   |                     | NFS4ERR_SERVERFAULT, NFS4ERR_STALE          |
   | OPEN                | NFS4ERR_ACCESS, NFS4ERR_ADMIN_REVOKED,      |
   |                     | NFS4ERR_ATTRNOTSUPP, NFS4ERR_BADCHAR,       |
   |                     | NFS4ERR_BADHANDLE, NFS4ERR_BADNAME,         |
   |                     | NFS4ERR_BADOWNER, NFS4ERR_BADXDR,           |
   |                     | NFS4ERR_BAD_SEQID, NFS4ERR_BAD_STATEID,     |
   |                     | NFS4ERR_DELAY, NFS4ERR_DQUOT,               |
   |                     | NFS4ERR_EXIST, NFS4ERR_EXPIRED,             |
   |                     | NFS4ERR_FBIG, NFS4ERR_FHEXPIRED,            |
   |                     | NFS4ERR_GRACE, NFS4ERR_INVAL, NFS4ERR_IO,   |
   |                     | NFS4ERR_ISDIR, NFS4ERR_MOVED,               |
   |                     | NFS4ERR_NAMETOOLONG, NFS4ERR_NOENT,         |
   |                     | NFS4ERR_NOFILEHANDLE, NFS4ERR_NOSPC,        |
   |                     | NFS4ERR_NOTDIR, NFS4ERR_NOTSUP,             |
   |                     | NFS4ERR_NO_GRACE, NFS4ERR_OLD_STATEID,      |
   |                     | NFS4ERR_PERM, NFS4ERR_RECLAIM_BAD,          |
   |                     | NFS4ERR_RECLAIM_CONFLICT, NFS4ERR_RESOURCE, |
   |                     | NFS4ERR_ROFS, NFS4ERR_SERVERFAULT,          |
   |                     | NFS4ERR_SHARE_DENIED, NFS4ERR_STALE,        |
   |                     | NFS4ERR_STALE_CLIENTID, NFS4ERR_SYMLINK,    |
   |                     | NFS4ERR_WRONGSEC                            |
   | OPENATTR            | NFS4ERR_ACCESS, NFS4ERR_BADHANDLE,          |
   |                     | NFS4ERR_BADXDR, NFS4ERR_DELAY,              |
   |                     | NFS4ERR_DQUOT, NFS4ERR_FHEXPIRED,           |
   |                     | NFS4ERR_IO, NFS4ERR_MOVED, NFS4ERR_NOENT,   |
   |                     | NFS4ERR_NOFILEHANDLE, NFS4ERR_NOSPC,        |
   |                     | NFS4ERR_NOTSUPP, NFS4ERR_RESOURCE,          |
   |                     | NFS4ERR_ROFS, NFS4ERR_SERVERFAULT,          |
   |                     | NFS4ERR_STALE                               |
   | OPEN_CONFIRM        | NFS4ERR_ADMIN_REVOKED, NFS4ERR_BADHANDLE,   |
   |                     | NFS4ERR_BAD_SEQID, NFS4ERR_BAD_STATEID,     |
   |                     | NFS4ERR_BADXDR, NFS4ERR_EXPIRED,            |
   |                     | NFS4ERR_FHEXPIRED, NFS4ERR_INVAL,           |
   |                     | NFS4ERR_ISDIR, NFS4ERR_MOVED,               |
   |                     | NFS4ERR_NOFILEHANDLE, NFS4ERR_OLD_STATEID,  |
   |                     | NFS4ERR_RESOURCE, NFS4ERR_SERVERFAULT,      |
   |                     | NFS4ERR_STALE, NFS4ERR_STALE_STATEID        |
   | OPEN_DOWNGRADE      | NFS4ERR_ADMIN_REVOKED, NFS4ERR_BADHANDLE,   |
   |                     | NFS4ERR_BADXDR, NFS4ERR_BAD_SEQID,          |
   |                     | NFS4ERR_BAD_STATEID, NFS4ERR_DELAY,         |
   |                     | NFS4ERR_EXPIRED, NFS4ERR_FHEXPIRED,         |
   |                     | NFS4ERR_INVAL, NFS4ERR_MOVED,               |
   |                     | NFS4ERR_NOFILEHANDLE, NFS4ERR_OLD_STATEID,  |
   |                     | NFS4ERR_RESOURCE, NFS4ERR_ROFS,             |
   |                     | NFS4ERR_SERVERFAULT, NFS4ERR_STALE,         |
   |                     | NFS4ERR_STALE_STATEID                       |
   | PUTFH               | NFS4ERR_BADHANDLE, NFS4ERR_BADXDR,          |
   |                     | NFS4ERR_DELAY, NFS4ERR_FHEXPIRED,           |
   |                     |