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By submitting this Internet-Draft, each author represents that any applicable patent or other IPR claims of which he or she is aware have been or will be disclosed, and any of which he or she becomes aware will be disclosed, in accordance with Section 6 of BCP 79.
Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet-Drafts.
Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as “work in progress.”
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The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html.
This Internet-Draft will expire on January 2, 2008.
Copyright © The IETF Trust (2007).
This Internet-Draft describes NFSv4 minor version one, including features retained from the base protocol and protocol extensions made subsequently. The current draft includes description of the major extensions, Sessions, Directory Delegations, and parallel NFS (pNFS). This Internet-Draft is an active work item of the NFSv4 working group. Active and resolved issues may be found in the issue tracker at: http://www.nfsv4-editor.org/cgi-bin/roundup/nfsv4. New issues related to this document should be raised with the NFSv4 Working Group nfsv4@ietf.org and logged in the issue tracker.
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 (Bradner, S., “Key words for use in RFCs to Indicate Requirement Levels,” March 1997.) [1].
1.
Introduction
1.1.
The NFSv4.1 Protocol
1.2.
NFS Version 4 Goals
1.3.
Minor Version 1 Goals
1.4.
Overview of NFS version 4.1 Features
1.4.1.
RPC and Security
1.4.2.
Protocol Structure
1.4.3.
File System Model
1.4.4.
Locking Facilities
1.5.
General Definitions
1.6.
Differences from NFSv4.0
2.
Core Infrastructure
2.1.
Introduction
2.2.
RPC and XDR
2.2.1.
RPC-based Security
2.3.
COMPOUND and CB_COMPOUND
2.4.
Client Identifiers and Client Owners
2.4.1.
Server Release of Client ID
2.4.2.
Resolving Client Owner Conflicts
2.5.
Server Owners
2.6.
Security Service Negotiation
2.6.1.
NFSv4.1 Security Tuples
2.6.2.
SECINFO and SECINFO_NO_NAME
2.6.3.
Security Error
2.7.
Minor Versioning
2.8.
Non-RPC-based Security Services
2.8.1.
Authorization
2.8.2.
Auditing
2.8.3.
Intrusion Detection
2.9.
Transport Layers
2.9.1.
Required and Recommended Properties of Transports
2.9.2.
Client and Server Transport Behavior
2.9.3.
Ports
2.10.
Session
2.10.1.
Motivation and Overview
2.10.2.
NFSv4 Integration
2.10.3.
Channels
2.10.4.
Trunking
2.10.5.
Exactly Once Semantics
2.10.6.
RDMA Considerations
2.10.7.
Sessions Security
2.10.8.
Session Mechanics - Steady State
2.10.9.
Session Mechanics - Recovery
2.10.10.
Parallel NFS and Sessions
3.
Protocol Data Types
3.1.
Basic Data Types
3.2.
Structured Data Types
4.
Filehandles
4.1.
Obtaining the First Filehandle
4.1.1.
Root Filehandle
4.1.2.
Public Filehandle
4.2.
Filehandle Types
4.2.1.
General Properties of a Filehandle
4.2.2.
Persistent Filehandle
4.2.3.
Volatile Filehandle
4.3.
One Method of Constructing a Volatile Filehandle
4.4.
Client Recovery from Filehandle Expiration
5.
File Attributes
5.1.
Mandatory Attributes
5.2.
Recommended Attributes
5.3.
Named Attributes
5.4.
Classification of Attributes
5.5.
Mandatory Attributes - Definitions
5.6.
Recommended Attributes - Definitions
5.7.
Time Access
5.8.
Interpreting owner and owner_group
5.9.
Character Case Attributes
5.10.
Quota Attributes
5.11.
mounted_on_fileid
5.12.
Directory Notification Attributes
5.12.1.
dir_notif_delay
5.12.2.
dirent_notif_delay
5.13.
PNFS Attributes
5.13.1.
fs_layout_type
5.13.2.
layout_alignment
5.13.3.
layout_blksize
5.13.4.
layout_hint
5.13.5.
layout_type
5.13.6.
mdsthreshold
5.14.
Retention Attributes
6.
Security Related Attributes
6.1.
Goals
6.2.
File Attributes Discussion
6.2.1.
ACL Attributes
6.2.2.
dacl and sacl Attributes
6.2.3.
mode Attribute
6.2.4.
mode_set_masked Attribute
6.3.
Common Methods
6.3.1.
Interpreting an ACL
6.3.2.
Computing a Mode Attribute from an ACL
6.4.
Requirements
6.4.1.
Setting the mode and/or ACL Attributes
6.4.2.
Retrieving the mode and/or ACL Attributes
6.4.3.
Creating New Objects
7.
Single-server Namespace
7.1.
Server Exports
7.2.
Browsing Exports
7.3.
Server Pseudo File System
7.4.
Multiple Roots
7.5.
Filehandle Volatility
7.6.
Exported Root
7.7.
Mount Point Crossing
7.8.
Security Policy and Namespace Presentation
8.
State Management
8.1.
Client and Session ID
8.2.
Stateid Definition
8.2.1.
Stateid Types
8.2.2.
Stateid Structure
8.2.3.
Special Stateids
8.2.4.
Stateid Lifetime and Validation
8.3.
Lease Renewal
8.4.
Crash Recovery
8.4.1.
Client Failure and Recovery
8.4.2.
Server Failure and Recovery
8.4.3.
Network Partitions and Recovery
8.5.
Server Revocation of Locks
8.6.
Short and Long Leases
8.7.
Clocks, Propagation Delay, and Calculating Lease Expiration
8.8.
Vestigial Locking Infrastructure From V4.0
9.
File Locking and Share Reservations
9.1.
Opens and Byte-range Locks
9.1.1.
State-owner Definition
9.1.2.
Use of the Stateid and Locking
9.2.
Lock Ranges
9.3.
Upgrading and Downgrading Locks
9.4.
Blocking Locks
9.5.
Share Reservations
9.6.
OPEN/CLOSE Operations
9.7.
Open Upgrade and Downgrade
9.8.
Reclaim of Open and Byte-range Locks
10.
Client-Side Caching
10.1.
Performance Challenges for Client-Side Caching
10.2.
Delegation and Callbacks
10.2.1.
Delegation Recovery
10.3.
Data Caching
10.3.1.
Data Caching and OPENs
10.3.2.
Data Caching and File Locking
10.3.3.
Data Caching and Mandatory File Locking
10.3.4.
Data Caching and File Identity
10.4.
Open Delegation
10.4.1.
Open Delegation and Data Caching
10.4.2.
Open Delegation and File Locks
10.4.3.
Handling of CB_GETATTR
10.4.4.
Recall of Open Delegation
10.4.5.
Clients that Fail to Honor Delegation Recalls
10.4.6.
Delegation Revocation
10.4.7.
Delegations via WANT_DELEGATION
10.5.
Data Caching and Revocation
10.5.1.
Revocation Recovery for Write Open Delegation
10.6.
Attribute Caching
10.7.
Data and Metadata Caching and Memory Mapped Files
10.8.
Name Caching
10.9.
Directory Caching
11.
Multi-Server Namespace
11.1.
Location attributes
11.2.
File System Presence or Absence
11.3.
Getting Attributes for an Absent File System
11.3.1.
GETATTR Within an Absent File System
11.3.2.
READDIR and Absent File Systems
11.4.
Uses of Location Information
11.4.1.
File System Replication
11.4.2.
File System Migration
11.4.3.
Referrals
11.5.
Additional Client-side Considerations
11.6.
Effecting File System Transitions
11.6.1.
File System Transitions and Simultaneous Access
11.6.2.
Simultaneous Use and Transparent Transitions
11.6.3.
Filehandles and File System Transitions
11.6.4.
Fileid's and File System Transitions
11.6.5.
Fsids and File System Transitions
11.6.6.
The Change Attribute and File System Transitions
11.6.7.
Lock State and File System Transitions
11.6.8.
Write Verifiers and File System Transitions
11.7.
Effecting File System Referrals
11.7.1.
Referral Example (LOOKUP)
11.7.2.
Referral Example (READDIR)
11.8.
The Attribute fs_absent
11.9.
The Attribute fs_locations
11.10.
The Attribute fs_locations_info
11.10.1.
The fs_locations_server4 Structure
11.10.2.
The fs_locations_info4 Structure
11.10.3.
The fs_locations_item4 Structure
11.11.
The Attribute fs_status
12.
Directory Delegations
12.1.
Introduction to Directory Delegations
12.2.
Directory Delegation Design
12.3.
Attributes in Support of Directory Notifications
12.4.
Delegation Recall
12.5.
Directory Delegation Recovery
13.
Parallel NFS (pNFS)
13.1.
Introduction
13.2.
pNFS Definitions
13.2.1.
Metadata
13.2.2.
Metadata Server
13.2.3.
pNFS Client
13.2.4.
Storage Device
13.2.5.
Storage Protocol
13.2.6.
Control Protocol
13.2.7.
Layout Types
13.2.8.
Layout
13.2.9.
Layout Iomode
13.2.10.
Device IDs
13.3.
pNFS Operations
13.4.
pNFS Attributes
13.5.
Layout Semantics
13.5.1.
Guarantees Provided by Layouts
13.5.2.
Getting a Layout
13.5.3.
Committing a Layout
13.5.4.
Recalling a Layout
13.5.5.
Metadata Server Write Propagation
13.6.
pNFS Mechanics
13.7.
Recovery
13.7.1.
Client Recovery
13.7.2.
Dealing with Lease Expiration on the Client
13.7.3.
Dealing with Loss of Layout State on the Metadata Server
13.7.4.
Recovery from Metadata Server Restart
13.7.5.
Operations During Metadata Server Grace Period
13.7.6.
Storage Device Recovery
13.8.
Metadata and Storage Device Roles
13.9.
Security Considerations
14.
PNFS: NFSv4.1 File Layout Type
14.1.
Client ID and Session Considerations
14.2.
File Layout Definitions
14.3.
File Layout Data Types
14.4.
Interpreting the File Layout
14.5.
Sparse and Dense Stripe Unit Packing
14.6.
Data Server Multipathing
14.7.
Operations Issued to NFSv4.1 Data Servers
14.8.
COMMIT Through Metadata Server
14.9.
The Layout Iomode
14.10.
Metadata and Data Server State Coordination
14.10.1.
Global Stateid Requirements
14.10.2.
Data Server State Propagation
14.11.
Data Server Component File Size
14.12.
Recovery from Loss of Layout
14.13.
Security Considerations for the File Layout Type
15.
Internationalization
15.1.
Stringprep profile for the utf8str_cs type
15.2.
Stringprep profile for the utf8str_cis type
15.3.
Stringprep profile for the utf8str_mixed type
15.4.
UTF-8 Related Errors
16.
Error Values
16.1.
Error Definitions
16.2.
Operations and their valid errors
16.3.
Callback operations and their valid errors
16.4.
Errors and the operations that use them
17.
NFS version 4.1 Procedures
17.1.
Procedure 0: NULL - No Operation
17.2.
Procedure 1: COMPOUND - Compound Operations
18.
NFS version 4.1 Operations
18.1.
Operation 3: ACCESS - Check Access Rights
18.2.
Operation 4: CLOSE - Close File
18.3.
Operation 5: COMMIT - Commit Cached Data
18.4.
Operation 6: CREATE - Create a Non-Regular File Object
18.5.
Operation 7: DELEGPURGE - Purge Delegations Awaiting Recovery
18.6.
Operation 8: DELEGRETURN - Return Delegation
18.7.
Operation 9: GETATTR - Get Attributes
18.8.
Operation 10: GETFH - Get Current Filehandle
18.9.
Operation 11: LINK - Create Link to a File
18.10.
Operation 12: LOCK - Create Lock
18.11.
Operation 13: LOCKT - Test For Lock
18.12.
Operation 14: LOCKU - Unlock File
18.13.
Operation 15: LOOKUP - Lookup Filename
18.14.
Operation 16: LOOKUPP - Lookup Parent Directory
18.15.
Operation 17: NVERIFY - Verify Difference in Attributes
18.16.
Operation 18: OPEN - Open a Regular File
18.17.
Operation 19: OPENATTR - Open Named Attribute Directory
18.18.
Operation 21: OPEN_DOWNGRADE - Reduce Open File Access
18.19.
Operation 22: PUTFH - Set Current Filehandle
18.20.
Operation 23: PUTPUBFH - Set
Public Filehandle
18.21.
Operation 24: PUTROOTFH - Set Root Filehandle
18.22.
Operation 25: READ - Read from File
18.23.
Operation 26: READDIR - Read Directory
18.24.
Operation 27: READLINK - Read Symbolic Link
18.25.
Operation 28: REMOVE - Remove File System Object
18.26.
Operation 29: RENAME - Rename Directory Entry
18.27.
Operation 31: RESTOREFH - Restore Saved Filehandle
18.28.
Operation 32: SAVEFH - Save Current Filehandle
18.29.
Operation 33: SECINFO - Obtain Available Security
18.30.
Operation 34: SETATTR - Set Attributes
18.31.
Operation 37: VERIFY - Verify Same Attributes
18.32.
Operation 38: WRITE - Write to File
18.33.
Operation 40: BACKCHANNEL_CTL - Backchannel control
18.34.
Operation 41: BIND_CONN_TO_SESSION
18.35.
Operation 42: EXCHANGE_ID - Instantiate Client ID
18.36.
Operation 43: CREATE_SESSION - Create New Session and Confirm Client ID
18.37.
Operation 44: DESTROY_SESSION - Destroy existing session
18.38.
Operation 45: FREE_STATEID - Free stateid with no locks
18.39.
Operation 46: GET_DIR_DELEGATION - Get a directory delegation
18.40.
Operation 47: GETDEVICEINFO - Get Device Information
18.41.
Operation 48: GETDEVICELIST
18.42.
Operation 49: LAYOUTCOMMIT - Commit writes made using a layout
18.43.
Operation 50: LAYOUTGET - Get Layout Information
18.44.
Operation 51: LAYOUTRETURN - Release Layout Information
18.45.
Operation 52: SECINFO_NO_NAME - Get Security on Unnamed Object
18.46.
Operation 53: SEQUENCE - Supply per-procedure sequencing and control
18.47.
Operation 54: SET_SSV
18.48.
Operation 55: TEST_STATEID - Test stateids for validity
18.49.
Operation 56: WANT_DELEGATION
18.50.
Operation 57: DESTROY_CLIENTID - Destroy existing client ID
18.51.
Operation 58: RECLAIM_COMPLETE - Indicates Reclaims Finished
18.52.
Operation 10044: ILLEGAL - Illegal operation
19.
NFS version 4.1 Callback Procedures
19.1.
Procedure 0: CB_NULL - No Operation
19.2.
Procedure 1: CB_COMPOUND - Compound Operations
20.
NFS version 4.1 Callback Operations
20.1.
Operation 3: CB_GETATTR - Get Attributes
20.2.
Operation 4: CB_RECALL - Recall an Open Delegation
20.3.
Operation 5: CB_LAYOUTRECALL
20.4.
Operation 6: CB_NOTIFY - Notify directory changes
20.5.
Operation 7: CB_PUSH_DELEG
20.6.
Operation 8: CB_RECALL_ANY - Keep any N delegations
20.7.
Operation 9: CB_RECALLABLE_OBJ_AVAIL
20.8.
Operation 10: CB_RECALL_SLOT - change flow control limits
20.9.
Operation 11: CB_SEQUENCE - Supply backchannel sequencing and control
20.10.
Operation 12: CB_WANTS_CANCELLED
20.11.
Operation 13: CB_NOTIFY_LOCK - Notify of possible lock availability
20.12.
Operation 10044: CB_ILLEGAL - Illegal Callback Operation
21.
Security Considerations
22.
IANA Considerations
22.1.
Defining new layout types
23.
References
23.1.
Normative References
23.2.
Informative References
Appendix A.
Acknowledgments
§
Authors' Addresses
§
Intellectual Property and Copyright Statements
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The NFSv4.1 protocol is a minor version of the NFSv4 protocol described in [2] (Shepler, S., Callaghan, B., Robinson, D., Thurlow, R., Beame, C., Eisler, M., and D. Noveck, “Network File System (NFS) version 4 Protocol,” April 2003.). It generally follows the guidelines for minor versioning model laid in Section 10 of RFC 3530. However, it diverges from guidelines 11 ("a client and server that supports minor version X must support minor versions 0 through X-1"), and 12 ("no features may be introduced as mandatory in a minor version"). These divergences are due to the introduction of the sessions model for managing non-idempotent operations and the RECLAIM_COMPLETE operation. These two new features are infrastructural in nature and simplify implementation of existing and other new features. Making them optional would add undue complexity to protocol definition and implementation. NFSv4.1 accordingly updates the Minor Versioning guidelines (Minor Versioning).
NFSv4.1, as a minor version, is consistent with the overall goals for NFS Version 4, but extends the protocol so as to better meet those goals, based on experiences with NFSv4.0. In addition, NFSv4.1 has adopted some additional goals, which motivate some of the major extensions in minor version 1.
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The NFS version 4 protocol is a further revision of the NFS protocol defined already by versions 2 [21] (Nowicki, B., “NFS: Network File System Protocol specification,” March 1989.) and 3 [22] (Callaghan, B., Pawlowski, B., and P. Staubach, “NFS Version 3 Protocol Specification,” June 1995.). It retains the essential characteristics of previous versions: design for easy recovery, independent of transport protocols, operating systems and file systems, simplicity, and good performance. The NFS version 4 revision has the following goals:
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Minor version one has the following goals, within the framework established by the overall version 4 goals.
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To provide a reasonable context for the reader, the major features of NFS version 4.1 protocol will be reviewed in brief. This will be done to provide an appropriate context for both the reader who is familiar with the previous versions of the NFS protocol and the reader that is new to the NFS protocols. For the reader new to the NFS protocols, there is still a set of fundamental knowledge that is expected. The reader should be familiar with the XDR and RPC protocols as described in [3] (Eisler, M., “XDR: External Data Representation Standard,” May 2006.) and [4] (Srinivasan, R., “RPC: Remote Procedure Call Protocol Specification Version 2,” August 1995.). A basic knowledge of file systems and distributed file systems is expected as well.
This description of version 4.1 features will not distinguish those added in minor version one from those present in the base protocol but will treat minor version 1 as a unified whole. See Section 1.6 (Differences from NFSv4.0) for a description of the differences between the two minor versions.
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As with previous versions of NFS, the External Data Representation (XDR) and Remote Procedure Call (RPC) mechanisms used for the NFS version 4.1 protocol are those defined in [3] (Eisler, M., “XDR: External Data Representation Standard,” May 2006.) and [4] (Srinivasan, R., “RPC: Remote Procedure Call Protocol Specification Version 2,” August 1995.). To meet end-to-end security requirements, the RPCSEC_GSS framework [5] (Eisler, M., Chiu, A., and L. Ling, “RPCSEC_GSS Protocol Specification,” September 1997.) will be used to extend the basic RPC security. With the use of RPCSEC_GSS, various mechanisms can be provided to offer authentication, integrity, and privacy to the NFS version 4 protocol. Kerberos V5 will be used as described in [6] (Linn, J., “The Kerberos Version 5 GSS-API Mechanism,” June 1996.) to provide one security framework. The LIPKEY and SPKM-3 GSS-API mechanisms described in [7] (Eisler, M., “LIPKEY - A Low Infrastructure Public Key Mechanism Using SPKM,” June 2000.) will be used to provide for the use of user password and client/server public key certificates by the NFS version 4 protocol. With the use of RPCSEC_GSS, other mechanisms may also be specified and used for NFS version 4.1 security.
To enable in-band security negotiation, the NFS version 4.1 protocol has operations which provide the client a method of querying the server about its policies regarding which security mechanisms must be used for access to the server's file system resources. With this, the client can securely match the security mechanism that meets the policies specified at both the client and server.
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Unlike NFS Versions 2 and 3, which used a series of ancillary protocols (e.g. NLM, NSM, MOUNT), within all minor versions of NFS version 4 only a single RPC protocol is used to make requests of the server. Facilities that had been separate protocols, such as locking, are now integrated within a single unified protocol.
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Minor version one supports high-performance data access to a clustered server implementation by enabling a separation of metadata access and data access, with the latter done to multiple servers in parallel.
Such parallel data access is controlled by recallable objects known as "layouts", which are integrated into the protocol locking model. Clients direct requests for data access to a set of data servers specified by the layout via a data storage protocol which may be NFSv4.1 or may be another protocol.
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The general file system model used for the NFS version 4.1 protocol is the same as previous versions. The server file system is hierarchical with the regular files contained within being treated as opaque octet streams. In a slight departure, file and directory names are encoded with UTF-8 to deal with the basics of internationalization.
The NFS version 4.1 protocol does not require a separate protocol to provide for the initial mapping between path name and filehandle. All file systems exported by a server are presented as a tree so that all file systems are reachable from a special per-server global root filehandle. This allows LOOKUP operations to be used to perform functions previously provided by the MOUNT protocol. The server provides any necessary pseudo file systems to bridge any gaps that arise due to unexported gaps between exported file systems.
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As in previous versions of the NFS protocol, opaque filehandles are used to identify individual files and directories. Lookup-type and create operations are used to go from file and directory names to the filehandle which is then used to identify the object to subsequent operations.
The NFS version 4.1 protocol provides support for persistent filehandles, guaranteed to be valid for the lifetime of the file system object designated. In addition it provides support to servers to provide filehandles with more limited validity guarantees, called volatile filehandles.
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The NFS version 4.1 protocol has a rich and extensible attribute structure. Only a small set of the defined attributes are mandatory and must be provided by all server implementations. The other attributes are known as "recommended" attributes.
The acl, sacl, and dacl attributes are a significant set of file attributes that make up the Access Control List (ACL) of a file. These attributes provide for directory and file access control beyond the model used in NFS Versions 2 and 3. The ACL definition allows for specification of specific sets of permissions for individual users and groups. In addition, ACL inheritance allows propagation of access permissions and restriction down a directory tree as file system objects are created.
One other type of attribute is the named attribute. A named attribute is an opaque octet 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.
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NFS Version 4.1 contains a number of features to allow implementation of namespaces that cross server boundaries and that allow and facilitate a non-disruptive transfer of support for individual file systems between servers. They are all based upon attributes that allow one file system to specify alternate or new locations for that file system.
These attributes may be used together with the concept of absent file system which provide specifications for additional locations but no actual file system content. This allows a number of important facilities:
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As mentioned previously, NFS v4.1, is a single protocol which includes locking facilities. These locking facilities include support for many types of locks including a number of sorts of recallable locks. Recallable locks such as delegations allow the client to be assured that certain events will not occur so long as that lock is held. When circumstances change, the lock is recalled via a callback request. The assurances provided by delegations allow more extensive caching to be done safely when circumstances allow it.
All locks for a given client are tied together under a single client-wide lease. All requests made on sessions associated with the client renew that lease. When leases are not promptly renewed lock are subject to revocation. In the event of server reinitialization, clients have the opportunity to safely reclaim their locks within a special grace period.
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The following definitions are provided for the purpose of providing an appropriate context for the reader.
- Client
- The "client" is the entity that accesses the NFS server's resources. The client may be an application which contains the logic to access the NFS server directly. The client may also be the traditional operating system client remote file system services for a set of applications.
A client is uniquely identified by a Client Owner.
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 connection and multiple clients may exist on the same network node.- Client ID
- A 64-bit quantity used as a unique, short-hand reference to a client supplied Verifier and client owner. The server is responsible for supplying the client ID.
- Client Owner
- The client owner is a unique string, opaque to the server, which identifies a client. Multiple network connections and source network addresses originating those connections may share a client owner. The server is expected to treat requests from connnections with the same client owner has coming from the same client.
- 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 any of record (octet-range) locks, share reservations, delegations or layouts unless specifically stated otherwise.
- Server
- The "Server" is the entity responsible for coordinating client access to a set of file systems. A server can span multiple network addresses. In NFSv4.1, a server is a two tiered entity allows for servers consisting of multiple components the flexibility to tightly or loosely couple their components without requiring tight synchronization among the components. Every server has a "Server Owner" which reflects the two tiers of a server entity.
- Server Owner
- The "Server Owner" identifies the server to the client. The server owner consists of a major and minor identifier. When the client has two connections each to a peer with the same major and minor identifier, the client assumes both peers are the same server (the server namespace is the same via each connection), and further assumes session and lock state is sharable across both connections. When each peer has the same major identifier but different minor identifier, the client assumes both peers can serve the same namespace, but session and lock state is not sharable across both connections.
- 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:
- Media commit of data, that is, the modified data has been successfully written to the disk media, for example, the disk platter.
- An immediate reply disk drive with battery-backed on- drive intermediate storage or uninterruptible power system (UPS).
- Server commit of data with battery-backed intermediate storage and recovery software.
- 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 and type of lock.
- 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.
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The following summarizes the differences between minor version one and the base protocol:
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NFS version 4.1 (NFSv4.1) relies on core infrastructure common to nearly every operation. This core infrastructure is described in the remainder of this section.
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The NFS version 4.1 (NFSv4.1) protocol is a Remote Procedure Call (RPC) application that uses RPC version 2 and the corresponding eXternal Data Representation (XDR) as defined in [4] (Srinivasan, R., “RPC: Remote Procedure Call Protocol Specification Version 2,” August 1995.) and [3] (Eisler, M., “XDR: External Data Representation Standard,” May 2006.).
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Previous NFS versions have been thought of as having a host-based authentication model, where the NFS server authenticates the NFS client, and trust the client to authenticate all users. Actually, NFS has always depended on RPC for authentication. The first form of RPC authentication which required a host-based authentication approach. NFSv4.1 also depends on RPC for basic security services, and mandates RPC support for a user-based authentication model. The user-based authentication model has user principals authenticated by a server, and in turn the server authenticated by user principals. RPC provides some basic security services which are used by NFSv4.
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As described in section 7.2 "Authentication" of [4] (Srinivasan, R., “RPC: Remote Procedure Call Protocol Specification Version 2,” August 1995.), RPC security is encapsulated in the RPC header, via a security or authentication flavor, and information specific to the specification of the security flavor. Every RPC header conveys information used to identify and authenticate a client and server. As discussed in Section 2.2.1.1.1 (RPCSEC_GSS and Security Services), some security flavors provide additional security services.
NFSv4.1 clients and servers MUST implement RPCSEC_GSS. (This requirement to implement is not a requirement to use.) Other flavors, such as AUTH_NONE, and AUTH_SYS, MAY be implemented as well.
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RPCSEC_GSS ([5] (Eisler, M., Chiu, A., and L. Ling, “RPCSEC_GSS Protocol Specification,” September 1997.)) uses the functionality of GSS-API [8] (Linn, J., “Generic Security Service Application Program Interface Version 2, Update 1,” January 2000.). This allows for the use of various security mechanisms by the RPC layer without the additional implementation overhead of adding RPC security flavors.
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Via the GSS-API, RPCSEC_GSS can be used to identify and authenticate users on clients to servers, and servers to users. It can also perform integrity checking on the entire RPC message, including the RPC header, and the arguments or results. Finally, privacy, usually via encryption, is a service available with RPCSEC_GSS. Privacy is performed on the arguments and results. Note that if privacy is selected, integrity, authentication, and identification are enabled. If privacy is not selected, but integrity is selected, authentication and identification are enabled. If integrity and privacy are not selected, but authentication is enabled, identification is enabled. RPCSEC_GSS does not provide identification as a separate service.
Although GSS-API has an authentication service distinct from its privacy and integrity services, GSS-API's authentication service is not used for RPCSEC_GSS's authentication service. Instead, each RPC request and response header is integrity protected with the GSS-API integrity service, and this allows RPCSEC_GSS to offer per-RPC authentication and identity. See [5] (Eisler, M., Chiu, A., and L. Ling, “RPCSEC_GSS Protocol Specification,” September 1997.) for more information.
NFSv4.1 client and servers MUST support RPCSEC_GSS's integrity and authentication service. NFSv4.1 servers MUST support RPCSEC_GSS's privacy service.
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RPCSEC_GSS, via GSS-API, normalizes access to mechanisms that provide security services. Therefore NFSv4.1 clients and servers MUST support three security mechanisms: Kerberos V5, SPKM-3, and LIPKEY.
The use of RPCSEC_GSS requires selection of: mechanism, quality of protection (QOP), and service (authentication, integrity, privacy). For the mandated security mechanisms, NFSv4.1 specifies that a QOP of zero (0) is used, leaving it up to the mechanism or the mechanism's configuration to use an appropriate level of protection that QOP zero maps to. Each mandated mechanism specifies minimum set of cryptographic algorithms for implementing integrity and privacy. NFSv4.1 clients and servers MUST be implemented on operating environments that comply with the mandatory cryptographic algorithms of each mandated mechanism.
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The Kerberos V5 GSS-API mechanism as described in [6] (Linn, J., “The Kerberos Version 5 GSS-API Mechanism,” June 1996.) ( [Comment.1] (need new Kerberos RFC) ) MUST be implemented with the RPCSEC_GSS services as specified in the following table:
column descriptions: 1 == number of pseudo flavor 2 == name of pseudo flavor 3 == mechanism's OID 4 == RPCSEC_GSS service 5 == NFSv4.1 clients MUST support 6 == NFSv4.1 servers MUST support 1 2 3 4 5 6 ------------------------------------------------------------------ 390003 krb5 1.2.840.113554.1.2.2 rpc_gss_svc_none yes yes 390004 krb5i 1.2.840.113554.1.2.2 rpc_gss_svc_integrity yes yes 390005 krb5p 1.2.840.113554.1.2.2 rpc_gss_svc_privacy no yes
Note that the number and name of the pseudo flavor is presented here as a mapping aid to the implementor. Because the NFSv4.1 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 the NFS version 3 since the security negotiation is done via the MOUNT protocol as described in [23] (Eisler, M., “NFS Version 2 and Version 3 Security Issues and the NFS Protocol's Use of RPCSEC_GSS and Kerberos V5,” June 1999.).
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The LIPKEY V5 GSS-API mechanism as described in [7] (Eisler, M., “LIPKEY - A Low Infrastructure Public Key Mechanism Using SPKM,” June 2000.) MUST be implemented with the RPCSEC_GSS services as specified in the following table:
1 2 3 4 5 6 ------------------------------------------------------------------ 390006 lipkey 1.3.6.1.5.5.9 rpc_gss_svc_none yes yes 390007 lipkey-i 1.3.6.1.5.5.9 rpc_gss_svc_integrity yes yes 390008 lipkey-p 1.3.6.1.5.5.9 rpc_gss_svc_privacy no yes
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The SPKM-3 GSS-API mechanism as described in [7] (Eisler, M., “LIPKEY - A Low Infrastructure Public Key Mechanism Using SPKM,” June 2000.) MUST be implemented with the RPCSEC_GSS services as specified in the following table:
1 2 3 4 5 6 ------------------------------------------------------------------ 390009 spkm3 1.3.6.1.5.5.1.3 rpc_gss_svc_none yes yes 390010 spkm3i 1.3.6.1.5.5.1.3 rpc_gss_svc_integrity yes yes 390011 spkm3p 1.3.6.1.5.5.1.3 rpc_gss_svc_privacy no yes
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Regardless of what security mechanism under RPCSEC_GSS is being used, the NFS server, MUST identify itself in GSS-API via a GSS_C_NT_HOSTBASED_SERVICE name type. GSS_C_NT_HOSTBASED_SERVICE names are of the form:
service@hostname
For NFS, the "service" element is
nfs
Implementations of security mechanisms will convert nfs@hostname to various different forms. For Kerberos V5, LIPKEY, and SPKM-3, the following form is RECOMMENDED:
nfs/hostname
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A significant departure from the versions of the NFS protocol before version 4 is the introduction of the COMPOUND procedure. For the NFSv4 protocol, in all minor versions, there are exactly two RPC procedures, NULL and COMPOUND. The COMPOUND procedure is defined as a series of individual operations and these operations perform the sorts of functions performed by traditional NFS procedures.
The operations combined within a COMPOUND request are evaluated in order by the server, without any atomicity guarantees. A limited set of facilities exist to pass results from one operation to another. Once an operation returns a failing result, the evaluation ends and the results of all evaluated operations are returned to the client.
With the use of the COMPOUND procedure, the client is able to build simple or complex requests. These COMPOUND requests allow for a reduction in the number of RPCs needed for logical file system operations. For example, multi-component lookup requests can be constructed by combining multiple LOOKUP operations. Those can be further combined with operations such as GETATTR, READDIR, or OPEN plus READ to do more complicated sets of operation without incurring additional latency.
NFSv4.1 also contains a considerable set of callback operations in which the server makes an RPC directed at the client. Callback RPC's have a similar structure to that of the normal server requests. For the NFS version 4 protocol callbacks in all minor versions, there are two RPC procedures, NULL and CB_COMPOUND. The CB_COMPOUND procedure is defined in an analogous fashion to that of COMPOUND with its own set of callback operations.
Addition of new server and callback operation within the COMPOUND and CB_COMPOUND request framework provide means of extending the protocol in subsequent minor versions.
Except for a small number of operations needed for session creation, server requests and callback requests are performed within the context of a session. Sessions provide a client context for every request and support robust reply protection for non-idempotent requests.
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For each operation that obtains or depends on locking state, the specific client must be determinable by the server. In NFSv4, each distinct client instance is represented by a client ID, which is a 64-bit identifier that identifies a specific client at a given time and which is changed whenever the client re-initializes, and may change when the server re-initializes. Client IDs are used to support lock identification and crash recovery.
In NFSv4.1, during steady state operation, the client ID associated with each operation is derived from the session (see Section 2.10 (Session)) on which the operation is issued. Each session is associated with a specific client ID at session creation and that client ID then becomes the client ID associated with all requests issued using it. Therefore, unlike NFSv4.0, the only NFSv4.1 operations possible before a client ID is established are those needed to establish the client ID.
A sequence of an EXCHANGE_ID operation followed by a CREATE_SESSION operation using that client ID (eir_clientid as returned from EXCHANGE_ID) is required to establish the identification on the server. Establishment of identification by a new incarnation of the client also has the effect of immediately releasing any locking state that a previous incarnation of that same client might have had on the server. Such released state would include all lock, share reservation, layout state, and where the server is not supporting the CLAIM_DELEGATE_PREV claim type, all delegation state associated with same client with the same identity. For discussion of delegation state recovery, see Section 10.2.1 (Delegation Recovery). For discussion of layout state recovery see Section 13.7.1 (Client Recovery).
Releasing such state requires that the server be able to determine that one client instance is the successor of another. Where this cannot be done, for any of a number of reasons, the locking state will remain for a time subject to lease expiration (see Section 8.3 (Lease Renewal)) and the new client will need to wait for such state to be removed, if it makes conflicting lock requests.
Client identification is encapsulated in the following Client Owner structure:
struct client_owner4 {
verifier4 co_verifier;
opaque co_ownerid<NFS4_OPAQUE_LIMIT>;
};
The first field, co_verifier, is a client incarnation verifier that is used to detect client reboots. Only if the co_verifier is different from that the server had previously recorded for the client (as identified by the second field of the structure, co_ownerid) does the server start the process of canceling the client's leased state.
The second field, co_ownerid is a variable length string that uniquely defines the client so that subsequent instances of the same client bear the same co_ownerid with a different verifier.
There are several considerations for how the client generates the co_ownerid string:
Given the above considerations, an example of a well generated co_ownerid string is one that includes:
A server may compare a client_owner4 in an EXCHANGE_ID with an nfs_client_id4 established using SETCLIENTID using NFSv4 minor version 0, so that an NFSv4.1 client is not forced to delay until lease expiration for locking state established by the earlier client using minor version 0. This requires the client_owner4 be constructed the same way as the nfs_client_id4. If the latter's contents included the server's network address, and the NFSv4.1 client does not wish to use a client ID that prevents trunking, it should issue two EXCHANGE_ID operations. The first EXCHANGE_ID will have a client_owner4 equal to the nfs_client_id4. This will clear the state created by the NFSv4.0 client. The second EXCHANGE_ID will not have the server's network address. The state created for the second EXCHANGE_ID will not have to wait for lease expiration, because there will be no state to expire.
Once an EXCHANGE_ID has been done, and the resulting client ID established as associated with a session, all requests made on that session implicitly identify that client ID, which in turn designates the client specified using the long-form client_owner4 structure. The shorthand client identifier (a client ID) is assigned by the server (the eir_clientid result from EXCHANGE_ID) and should be chosen so that it will not conflict with a client ID previously assigned by the server. This applies across server restarts or reboots.
In the event of a server restart, a client may find out that its current client ID is no longer valid when receives a NFS4ERR_STALE_CLIENTID error. The precise circumstances depend of the characteristics of the sessions involved, specifically whether the session is persistent (see Section 2.10.5.5 (Persistence)).
When a session is not persistent, the client will need to create a new session. When the existing client ID is presented to a server as part of creating a session and that client ID is not recognized, as would happen after a server reboot, the server will reject the request with the error NFS4ERR_STALE_CLIENTID. When this happens, the client must obtain a new client ID by use of the EXCHANGE_ID operation and then use that client ID as the basis of the basis of a new session and then proceed to any other necessary recovery for the server reboot case (See Section 8.4.2 (Server Failure and Recovery)).
In the case of the session being persistent, the client will re-establish communication using the existing session after the reboot. This session will be associated with a client ID that has had state revoked (but the persistent session is never associated with a stale client ID, because if the session is persistent, the client ID MUST persist), and the client will receive an indication of that fact in the sr_status_flags field returned by the SEQUENCE operation (see Section 18.46.4 (DESCRIPTION)). The client can then use the existing session to do whatever operations are necessary to determine the status of requests outstanding at the time of reboot, while avoiding issuing new requests, particularly any involving locking on that session. Such requests would fail with an NFS4ERR_STALE_STATEID error, if attempted.
See the detailed descriptions of EXCHANGE_ID (Section 18.35 (Operation 42: EXCHANGE_ID - Instantiate Client ID) and CREATE_SESSION (Section 18.36 (Operation 43: CREATE_SESSION - Create New Session and Confirm Client ID)) for a complete specification of these operations.
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NFSv4.1 introduces a new operation called DESTROY_CLIENTID (Section 18.50 (Operation 57: DESTROY_CLIENTID - Destroy existing client ID)) which the client SHOULD use to destroy a client ID it no longer needs. This permits graceful, bilateral release of a client ID.
If the server determines that the client holds no associated state for its client ID (including sessions, opens, locks, delegations, layouts, and wants), the server may choose to unilaterally release the client ID. The server may make this choice for an inactive client so that resources are not consumed by those intermittently active clients. If the client contacts the server after this release, the server must ensure the client receives the appropriate error so that it will use the EXCHANGE_ID/CREATE_SESSION sequence to establish a new identity. It should be clear that the server must be very hesitant to release a client ID since the resulting work on the client to recover from such an event will be the same burden as if the server had failed and restarted. Typically a server would not release a client ID unless there had been no activity from that client for many minutes. As long as there are sessions, opens, locks, delegations, layouts, or wants, the server MUST not release the client ID. See Section 2.10.9.1.4 (Loss of Session) for discussion on releasing inactive sessions.
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When the server gets an EXCHANGE_ID for a client owner that currently has no state, or if it has state, but the lease has expired, server MUST allow the EXCHANGE_ID, and confirm the new client ID if followed by the appropriate CREATE_SESSION.
When the server gets an EXCHANGE_ID for a client owner that currently has state and an unexpired lease, the server MUST NOT destroy any state that currently exists for the client owner unless one of the following are true:
If the none of the above situations apply, the server MUST return NFS4ERR_CLID_INUSE.
Even the server accepts the principal and co_ownerid as matching that which created the client ID, it MUST NOT delete any state unless the co_verifier in the EXCHANGE_ID does not match the co_verifier used when client ID was created. If the co_verifier matches, then the client is either updating properties of the client ID, or possibly attempting trunking opportunity (Section 2.10.4 (Trunking)).
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The Server Owner is somewhat similar to a Client Owner (Section 2.4 (Client Identifiers and Client Owners)), but unlike the Client Owner, there is no shorthand serverid. The Server Owner is defined in the following structure:
struct server_owner4 {
uint64_t so_minor_id;
opaque so_major_id<NFS4_OPAQUE_LIMIT>;
};
The Server Owner is returned in the results of EXCHANGE_ID. When the so_major_id fields are the same in two EXCHANGE_ID results, the connections each EXCHANGE_ID are sent over can be assumed to address the same Server (as defined in Section 1.5 (General Definitions)). If the so_minor_id fields are also the same, then not only do both connections connect to the same server, but the session and other state can be shared across both connections. The reader is cautioned that multiple servers may deliberately or accidentally claim to have the same so_major_id or so_major_id/so_minor_id; the reader should examine Section 2.10.4 (Trunking) and Section 18.35 (Operation 42: EXCHANGE_ID - Instantiate Client ID).
The considerations for generating a so_major_id are similar to that for generating a co_ownerid string (see Section 2.4 (Client Identifiers and Client Owners)). The consequences of two servers generating conflicting so_major_id values are less dire than they are for co_ownerid conflicts because the client can use RPCSEC_GSS to compare the authenticity of each server (see Section 2.10.4 (Trunking)).
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With the NFS version 4 server potentially offering multiple security mechanisms, the client needs a method to determine or negotiate which mechanism is to be used for its communication with the server. The NFS server may have multiple points within its file system namespace that are available for use by NFS clients. These points can be considered security policy boundaries, and in some NFS implementations are tied to NFS export points. In turn the NFS server may be configured such that each of these security policy boundaries may have different or multiple security mechanisms in use.
The security negotiation between client and server must be done with a secure channel to eliminate the possibility of a third party intercepting the negotiation sequence and forcing the client and server to choose a lower level of security than required or desired. See Section 21 (Security Considerations) for further discussion.
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An NFS server can assign one or more "security tuples" to each security policy boundary in its namespace. Each security tuple consists of a security flavor (see Section 2.2.1.1 (RPC Security Flavors)), and if the flavor is RPCSEC_GSS, a GSS-API mechanism OID, a GSS-API quality of protection, and an RPCSEC_GSS service.
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The SECINFO and SECINFO_NO_NAME operations allow the client to determine, on a per filehandle basis, what security tuple is to be used for server access. In general, the client will not have to use either operation except during initial communication with the server or when the client crosses security policy boundaries at the server. It is possible that the server's policies change during the client's interaction therefore forcing the client to negotiate a new security tuple.
Where the use of different security tuples would affect the type of access that would be allowed if a request was issued over the same connection used for the SECINFO or SECINFO_NO_NAME operation (e.g. read-only vs. read-write) access, security tuples that allow greater access should be presented first. Where the general level of access is the same and different security flavors limit the range of principals whose privileges are recognized (e.g. allowing or disallowing root access), flavors supporting the greatest range of principals should be listed first.
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Based on the assumption that each NFS version 4 client and server must support a minimum set of security (i.e., LIPKEY, SPKM-3, and Kerberos-V5 all under RPCSEC_GSS), the NFS client will initiate file access to the server with one of the minimal security tuples. During communication with the server, the client may receive an NFS error of NFS4ERR_WRONGSEC. This error allows the server to notify the client that the security tuple currently being used contravenes the server's security policy. The client is then responsible for determining (see Section 2.6.3.1 (Using NFS4ERR_WRONGSEC, SECINFO, and SECINFO_NO_NAME)) what security tuples are available at the server and choosing one which is appropriate for the client.
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This section explains of the mechanics of NFSv4.1 security negotiation. The term "put filehandle operation" refers to PUTROOTFH, PUTPUBFH, PUTFH, and RESTOREFH.
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The client is saving a filehandle for a future RESTOREFH. The server MUST NOT return NFS4ERR_WRONGSEC to either the put filehandle operation or SAVEFH.
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For a series of N put filehandle operations, the server MUST NOT return NFS4ERR_WRONGSEC to the first N-1 put filehandle operations. The Nth put filehandle operation is handled as if it is the first in a series of operations, and the second in the series of operations is not a put filehandle operation. For example if the server received PUTFH, PUTROOTFH, LOOKUP, then the PUTFH is ignored for NFS4ERR_WRONGSEC purposes, and the PUTROOTFH, LOOKUP subseries is processed as according to Section 2.6.3.1.3 (Put Filehandle Operation + LOOKUP (or OPEN by Name)).
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This situation also applies to a put filehandle operation followed by a LOOKUP or an OPEN operation that specifies a component name.
In this situation, the client is potentially crossing a security policy boundary, and the set of security tuples the parent directory supports differ from those of the child. The server implementation may decide whether to impose any restrictions on security policy administration. There are at least three approaches (sec_policy_child is the tuple set of the child export, sec_policy_parent is that of the parent).
- a)
- sec_policy_child <= sec_policy_parent (<= for subset). This means that the set of security tuples specified on the security policy of a child directory is always a subset of that of its parent directory.
- b)
- sec_policy_child ^ sec_policy_parent != {} (^ for intersection, {} for the empty set). This means that the security tuples specified on the security policy of a child directory always has a non empty intersection with that of the parent.
- c)
- sec_policy_child ^ sec_policy_parent == {}. This means that the set of tuples specified on the security policy of a child directory may not intersect with that of the parent. In other words, there are no restrictions on how the system administrator may set up these tuples.
For a server to support approach (b) (when client chooses a flavor that is not a member of sec_policy_parent) and (c), the put filehandle operation must NOT return NFS4ERR_WRONGSEC in case of security mismatch. Instead, it should be returned from the LOOKUP (or OPEN by component name) that follows.
Since the above guideline does not contradict approach (a), it should be followed in general. Even if approach (a) is implemented, it is possible for the security tuple used to be acceptable for the target of LOOKUP but not for the filehandles used in the put filehandle operation. The put filehandle operation could be a PUTROOTFH or PUTPUBFH, where the client cannot know the security tuples for the root or public filehandle. Or the security policy for the filehandle used by the put filehandle operation could have changed since the time the filehandle was obtained.
Therefore, an NFSv4.1 server MUST NOT return NFS4ERR_WRONGSEC in response to the put filehandle operation if the operation is immediately followed by a LOOKUP or an OPEN by component name.
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Since SECINFO only works its way down, there is no way LOOKUPP can return NFS4ERR_WRONGSEC without SECINFO_NO_NAME. SECINFO_NO_NAME solves this issue because via style SECINFO_STYLE4_PARENT, it works in the opposite direction as SECINFO. As with Section 2.6.3.1.3 (Put Filehandle Operation + LOOKUP (or OPEN by Name)), the put filehandle operation must not return NFS4ERR_WRONGSEC whenever it is followed by LOOKUPP. If the server does not support SECINFO_NO_NAME, the client's only recourse is to issue the put filehandle operation, LOOKUPP, GETFH sequence of operations with every security tuple it supports.
Regardless whether SECINFO_NO_NAME is supported, an NFSv4.1 server MUST NOT return NFS4ERR_WRONGSEC in response to a put filehandle operation if the operation is immediately followed by a LOOKUPP.
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A security sensitive client is allowed to choose a strong security tuple when querying a server to determine a file object's permitted security tuples. The security tuple chosen by the client does not have to be included in the tuple list of the security policy of the either parent directory indicated in the put filehandle operation, or the child file object indicated in SECINFO (or any parent directory indicated in SECINFO_NO_NAME). Of course the server has to be configured for whatever security tuple the client selects, otherwise the request will fail at RPC layer with an appropriate authentication error.
In theory, there is no connection between the security flavor used by SECINFO or SECINFO_NO_NAME and those supported by the security policy. But in practice, the client may start looking for strong flavors from those supported by the security policy, followed by those in the mandatory set.
The NFSv4.1 server MUST NOT return NFS4ERR_WRONGSEC to a put filehandle operation whenever it is immediately followed by SECINFO or SECINFO_NO_NAME. The NFSv4.1 server MUST NOT return NFS4ERR_WRONGSEC from SECINFO or SECINFO_NO_NAME.
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The NFSv4.1 server MUST NOT return NFS4ERR_WRONGSEC.
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"Anything Else" includes OPEN by filehandle.
The security policy enforcement applies to the filehandle specified in the put filehandle operation. Therefore PUTFH must return NFS4ERR_WRONGSEC in case of security tuple on the part of the mismatch. This avoids the complexity adding NFS4ERR_WRONGSEC as an allowable error to every other operation.
A COMPOUND containing the series put filehandle operation + SECINFO_NO_NAME (style SECINFO_STYLE4_CURRENT_FH) is an efficient way for the client to recover from NFS4ERR_WRONGSEC.
The NFSv4.1 server MUST not return NFS4ERR_WRONGSEC to any operation other than a put filehandle operation, LOOKUP, LOOKUPP, and OPEN (by component name).
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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 [2] (Shepler, S., Callaghan, B., Robinson, D., Thurlow, R., Beame, C., Eisler, M., and D. Noveck, “Network File System (NFS) version 4 Protocol,” April 2003.), and minor version one is represented by this document [Comment.2] (change "document" to "RFC" when we publish) . The COMPOUND and CB_COMPOUND procedures support the encoding of the minor version being requested by the client.
The following items represent the basic rules for the development of minor versions. Note that a future minor version may decide to modify or add to the following rules as part of the minor version definition.
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As described in Section 2.2.1.1.1.1 (Identification, Authentication, Integrity, Privacy), NFSv4.1 relies on RPC for identification, authentication, integrity, and privacy. NFSv4.1 itself provides additional security services as described in the next several subsections.
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Authorization to access a file object via an NFSv4.1 operation is ultimately determined by the NFSv4.1 server. A client can predetermine its access to a file object via the OPEN (Section 18.16 (Operation 18: OPEN - Open a Regular File)) and the ACCESS (Section 18.1 (Operation 3: ACCESS - Check Access Rights)) operations.
Principals with appropriate access rights can modify the authorization on a file object via the SETATTR (Section 18.30 (Operation 34: SETATTR - Set Attributes)) operation. Four attributes that affect access rights are: mode, owner, owner_group, and acl. See Section 5 (File Attributes).
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NFSv4.1 provides auditing on a per file object basis, via the ACL attribute as described in Section 6 (Security Related Attributes). It is outside the scope of this specification to specify audit log formats or management policies.
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NFSv4.1 provides alarm control on a per file object basis, via the ACL attribute as described in Section 6 (Security Related Attributes). Alarms may serve as the basis for intrusion detection. It is outside the scope of this specification to specify heuristics for detecting intrusion via alarms.
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NFSv4.1 works over RDMA and non-RDMA_based transports with the following attributes:
Where an NFS version 4 implementation supports operation over the IP network protocol, any transport used between NFS and IP MUST be among the IETF-approved congestion control transport protocols. At the time this document was written, the only two transports that had the above attributes were TCP and SCTP. To enhance the possibilities for interoperability, an NFS version 4 implementation MUST support operation over the TCP transport protocol.
Even if NFS version 4 is used over a non-IP network protocol, it is RECOMMENDED that the transport support congestion control.
It is permissible for a connectionless transport to be used under NFSv4.1, however reliable and in-order delivery of data by the connectionless transport are still required. NFSv4.1 assumes that a client transport address and server transport address used to send data over a transport together constitute a connection, even if the underlying transport eschews the concept of a connection.
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If a connection-oriented transport (e.g. TCP) is used the client and server SHOULD use long lived connections for at least three reasons:
In order to reduce congestion, if a connection-oriented transport is used, and the request is not the NULL procedure,
When using RDMA transports there are other reasons for not tolerating retries over the same connection:
In addition, the NFSv4.1 requester is not allowed to stop waiting for a reply, as described in Section 2.10.5.2 (Retry and Replay of Reply).
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Historically, NFS version 2 and version 3 servers have listened over TCP port 2049. The registered port 2049 [25] (Reynolds, J., “Assigned Numbers: RFC 1700 is Replaced by an On-line Database,” January 2002.) for the NFS protocol should be the default configuration. NFSv4.1 clients SHOULD NOT use the RPC binding protocols as described in [26] (Srinivasan, R., “Binding Protocols for ONC RPC Version 2,” August 1995.).
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Previous versions and minor versions of NFS have suffered from the following:
Through the introduction of a session, NFSv4.1 addresses the above shortfalls with practical solutions:
A session is a dynamically created, long-lived server object created by a client, used over time from one or more transport connections. Its function is to maintain the server's state relative to the connection(s) belonging to a client instance. This state is entirely independent of the connection itself, and indeed the state exists whether the connection exists or not. A client may have one or more sessions associated with it so that client-associated state may be accessed using any of the sessions associated with that client's client ID, when connections are associated with those sessions. When no connections are associated for any of the sessions associated with the client ID for an extended time such objects as locks, opens, delegations, layouts, etc. are subject to expiration. The session serves as an object representing a means of access by a client to the associated client state on the server, independent of the physical means of access to that state.
A single client may create multiple sessions. A single session MUST NOT serve multiple clients.
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Sessions are part of NFSv4.1 and not NFSv4.0. Normally, a major infrastructure change such as sessions would require a new major version number to an ONC RPC program like NFS. However, because NFSv4 encapsulates its functionality in a single procedure, COMPOUND, and because COMPOUND can support an arbitrary number of operations, sessions have been added to NFSv4.1 with little difficulty. COMPOUND includes a minor version number field, and for NFSv4.1 this minor version is set to 1. When the NFSv4 server processes a COMPOUND with the minor version set to 1, it expects a different set of operations than it does for NFSv4.0. NFSv4.1 defines the SEQUENCE operation, which is required for every COMPOUND that operates over an established session, with the exception of some session administration operations, such as DESTROY_SESSION (Section 18.37 (Operation 44: DESTROY_SESSION - Destroy existing session)).
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In NFSv4.1, when the SEQUENCE operation is present, it MUST be the first operation in the COMPOUND procedure. The primary purpose of SEQUENCE is to carry the session identifier. The session identifier associates all other operations in the COMPOUND procedure with a particular session. SEQUENCE also contains required information for maintaining EOS (see Section 2.10.5 (Exactly Once Semantics)). Session-enabled NFSv4.1 COMPOUND requests thus have the form:
+-----+--------------+-----------+------------+-----------+----
| tag | minorversion | numops |SEQUENCE op | op + args | ...
| | (== 1) | (limited) | + args | |
+-----+--------------+-----------+------------+-----------+----
and the reply's structure is:
+------------+-----+--------+-------------------------------+--//
|last status | tag | numres |status + SEQUENCE op + results | //
+------------+-----+--------+-------------------------------+--//
//-----------------------+----
// status + op + results | ...
//-----------------------+----
A CB_COMPOUND procedure request and reply has a similar form to COMPOUND, but instead of a SEQUENCE operation, there is a CB_SEQUENCE operation. CB_COMPOUND also has an additional field called "callback_ident", which is superfluous in NFSv4.1 and MUST be ignored by the client. CB_SEQUENCE has the same information as SEQUENCE, and also includes other information needed to resolve callback races (Section 2.10.5.3 (Resolving Server Callback Races)).
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Each client ID (Section 2.4 (Client Identifiers and Client Owners)) can have zero or more active sessions. A client ID, and a session associated with it are required to perform file access in NFSv4.1. Each time a session is used (whether by a client sending a request to the server, or the client replying to a callback request from the server), the state leased to its associated client ID is automatically renewed.
State such as share reservations, locks, delegations, and layouts (Section 1.4.4 (Locking Facilities)) is tied to the client ID. Client state is not tied to the sessions of the client ID. Successive state changing operations from a given state owner MAY go over different sessions, provided the session is associated with the same client ID. A callback MAY arrive over a different session than from the session that originally acquired the state pertaining to the callback. For example, if session A is used to acquire a delegation, a request to recall the delegation MAY arrive over session B if both sessions are associated with the same client ID. Section 2.10.7.1 (Session Callback Security) and Section 2.10.7.2 (Backchannel RPC Security) discuss the security considerations around callbacks.
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A channel is not a connection. A channel represents the direction ONC RPC requests are sent to.
Each session has one or two channels: the fore channel and the backchannel. Because there are at most two channels per session, and because each channel has a distinct purpose, channels are not assigned identifiers.
The fore channel is used for ordinary requests from the client to the server, and carries COMPOUND requests and responses. A session always has a fore channel.
The backchannel used for callback requests from server to client, and carries CB_COMPOUND requests and responses. Whether there is a backchannel or not is a decision by the client, however many features of NFSv4.1 require a backchannel. NFSv4.1 servers MUST support backchannels.
Each session has resources for each channel, including separate reply caches (see Section 2.10.5.1 (Slot Identifiers and Reply Cache)). Note that even the backchannel requires a reply cache because some callback operations are nonidempotent.
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Each channel is associated with zero or more transport connections. A connection can be associated with one channel or both channels of a session; the client and server negotiate whether a connection will carry traffic for one channel or both channels via the CREATE_SESSION (Section 18.36 (Operation 43: CREATE_SESSION - Create New Session and Confirm Client ID)) and the BIND_CONN_TO_SESSION (Section 18.34 (Operation 41: BIND_CONN_TO_SESSION)) operations. When a session is created via CREATE_SESSION, the connection that transported the CREATE_SESSION request is automatically associated with the fore channel, and optionally the backchannel. If the client specifies no state protection (Section 18.35 (Operation 42: EXCHANGE_ID - Instantiate Client ID)). when the session is created, then when SEQUENCE is transmitted on a different connection, the connection is automatically associated with the fore channel of the session specified in the SEQUENCE operation.
A connection's association with a session is not exclusive. A connection associated with the channel(s) of one session may be simultaneously associated with the channel(s) of other sessions including sessions associated with other client IDs.
It is permissible for connections of multiple transport types to be associated with the same channel. For example both a TCP and RDMA connection can be associated with the fore channel. In the event an RDMA and non-RDMA connection are associated with the same channel, the maximum number of slots SHOULD be at least one more than the total number of credits (Section 2.10.5.1 (Slot Identifiers and Reply Cache). This way if all RDMA credits are used, the non-RDMA connection can have at least one outstanding request. If a server supports multiple transport types, it MUST allow a client to associate connections from each transport to a channel.
It is permissible for a connection of type of transport to be associated with the fore channel, and a connection of a different type to be associated with the backchannel.
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Trunking is the use of multiple connections between a client and server in order to increase the speed of data transfer. NFSv4.1 supports two types of trunking: session trunking and client ID trunking. NFSv4.1 servers MUST support trunking.
Session trunking is essentially the association of multiple connections, each with a potentially different target network address, to the same session.
Client ID trunking is the association of multiple sessions to the same client ID, major server owner ID (Section 2.5 (Server Owners)), and server scope (Section 11.6.7 (Lock State and File System Transitions)). When two servers return the same major server owner and server scope it means the two servers are cooperating on locking state management which is a prerequisite for client ID trunking.
Understanding and distinguishing session and client ID trunking requires understanding how the results of the EXCHANGE_ID (Section 18.35 (Operation 42: EXCHANGE_ID - Instantiate Client ID)) operation identify a server. Suppose a client issues EXCHANGE_ID over two different connections each with a possibly different target network address but each EXCHANGE_ID with the same value in the eia_clientowner field. If the same NFSv4.1 server is listening over each connection, then each EXCHANGE_ID result MUST return the same values of eir_clientid, eir_server_owner.so_major_id and eir_server_scope. The client can then treat each connection as referring to the same server (subject to verification, see Paragraph 5 later in this section), and it can use each connection to trunk requests and replies. The question is whether session trunking and/or client ID trunking applies.
- Session Trunking
- If the eia_clientowner argument is the same in two different EXCHANGE_ID requests, and the eir_clientid, eir_server_owner.so_major_id, eir_server_owner.so_minor_id, and eir_server_scope results match in both EXCHANGE_ID results, then the client is permitted to perform session trunking. If the client has no session mapping to the tuple of eir_clientid, eir_server_owner.so_major_id, eir_server_scope, eir_server_owner.so_minor_id, then it creates the session via a CREATE_SESSION operation over one of the connections, which associates the connection to the session. If there is a session for the tuple, the client can issue BIND_CONN_TO_SESSION to associate the connection to the session. The client can invoke CREATE_SESSION regardless whether there is session for the tuple. The second connection is associated with the same session as the first connection via the BIND_CONN_TO_SESSION operation.
- Client ID Trunking
- If the eia_clientowner argument is the same in two different EXCHANGE_ID requests, and the eir_clientid, eir_server_owner.so_major_id, and eir_server_scope results match in both EXCHANGE_ID results, but the eir_server_owner.so_minor_id results do not match then the client is permitted to perform client ID trunking. The client can associate each connection with different sessions, where each session is associated with the same server. Of course, even if the eir_server_owner.so_minor_id fields do match, the client is free to employ client ID trunking instead of sessiond trunking. The client completes the act of client ID trunking by invoking CREATE_SESSION on each connection, using the same client ID that was returned in eir_clientid. These invocations create two sessions and also associate each connection with each session.
When doing client ID trunking, locking state is shared across sessions associated with the same client ID. This requires the server to coordinate state across sessions.
When two servers over two connections claim matching or partially matching eir_server_owner, eir_server_scope, and eir_clientid values, the client does not have to trust the servers' claims. The client may verify these claims before trunking traffic in the following ways:
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Via the session, NFSv4.1 offers exactly once semantics (EOS) for requests sent over a channel. EOS is supported on both the fore and back channels.
Each COMPOUND or CB_COMPOUND request that is issued with a leading SEQUENCE or CB_SEQUENCE operation MUST be executed by the receiver exactly once. This requirement is regardless whether the request is issued with reply caching specified (see Section 2.10.5.1.2 (Optional Reply Caching)). The requirement holds even if the requester is issuing the request over a session created between a pNFS data client and pNFS data server. The rationale for this requirement is understood by categorizing requests into three classifications:
An example of a non-idempotent request is RENAME. If is obvious that if a replier executes the same RENAME request twice, and the first execution succeeds, the re-execution will fail. If the replier returns the result from the re-execution, this result is incorrect. Therefore, EOS is required for nonidempotent requests.
An example of an idempotent modifying request is a COMPOUND request containing a WRITE operation. Repeated execution of the same WRITE has the same effect as execution of that write once. Nevertheless, putting enforcing EOS for WRITEs and other idempotent modifying requests is necessary to avoid data corruption.
Suppose a client issues WRITEs A, and B to a noncompliant server that does not enforce EOS, and receives no response, perhaps due to a network partition. The client reconnects to the server and re-issues both WRITEs. Now, the server has outstanding two instances of each of A and B. The server can be in a situation in which it executes and replies to the retries of A and B, while the first A and B are still waiting in the server's I/O system for some resource. Upon receiving the replies to the second attempts of WRITEs A and B, the client believes its writes are done so it is free to issue WRITE D which overlaps the range of one or both of A and B. If A or B are subsequently executed for the second time, then what has been written by D can be overwritten and thus corrupted.
An example of an idempotent non-modifying request is a COMPOUND containing SEQUENCE, PUTFH, READLINK and nothing else. The re-execution of a such a request will not cause data corruption, or produce an incorrect result. Nonetheless, to keep the implementation simple, the replier MUST enforce EOS for all requests whether idempotent and non-modifying or not.
Note that true and complete EOS is not possible unless the server persists the reply cache in stable storage, unless the server is somehow implemented to never require a restart (indeed if such a server exists, the distinction between a reply cache kept in stable storage versus one that is not is one without meaning). See Section 2.10.5.5 (Persistence) for a discussion of persistence in the reply cache. Regardless, even if the server does not persist the reply cache, EOS improves robustness and correctness over previous versions of NFS because the legacy duplicate request/reply caches were based on the ONC RPC transaction identifier (XID). Section 2.10.5.1 (Slot Identifiers and Reply Cache) explains the shortcomings of the XID as a basis for a reply cache and describes how NFSv4.1 sessions improve upon the XID.
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The RPC layer provides a transaction ID (XID), which, while required to be unique, is not convenient for tracking requests for two reasons. First, the XID is only meaningful to the requester; it cannot be interpreted by the replier except to test for equality with previously issued requests. When consulting an RPC-based duplicate request cache, the opaqueness of the XID requires a computationally expensive lookup (often via a hash that includes XID and source address). NFSv4.1 requests use a non-opaque slot id which is an index into a slot table, which is far more efficient. Second, because RPC requests can be executed by the replier in any order, there is no bound on the number of requests that may be outstanding at any time. To achieve perfect EOS using ONC RPC would require storing all replies in the reply cache. XIDs are 32 bits; storing over four billion (2^32) replies in the reply cache is not practical. In practice, previous versions of NFS have chosen to store a fixed number of replies in the cache, and use a least recently used (LRU) approach to replacing cache entries with new entries when the cache is full. In NFSv4.1, the number of outstanding requests is bounded by the size of the slot table, and a sequence id per slot is used to tell the replier when it is safe to delete a cached reply.
In the NFSv4.1 reply cache, when the requester issues a new request, it selects a slot id in the range 0..N, where N is the replier's current maximum slot id granted to the requester on the session over which the request is to be issued. The value of N starts out as equal to ca_maxrequests - 1 (Section 18.36 (Operation 43: CREATE_SESSION - Create New Session and Confirm Client ID)), but can be adjusted by the response to SEQUENCE or CB_SEQUENCE as described later in this section. The slot id must be unused by any of the requests which the requester has already active on the session. "Unused" here means the requester has no outstanding request for that slot id.
A slot contains a sequence id and the cached reply corresponding to the request send with that sequence id. The sequence id is a 32 bit unsigned value, and is therefore in the range 0..0xFFFFFFFF (2^32 - 1). The first time a slot is used, the requester must specify a sequence id of one (1) (Section 18.36 (Operation 43: CREATE_SESSION - Create New Session and Confirm Client ID)). Each time a slot is re-used, the request MUST specify a sequence id that is one greater than that of the previous request on the slot. If the previous sequence id was 0xFFFFFFFF, then the next request for the slot MUST have the sequence id set to zero (i.e. (2^32 - 1) + 1 mod 2^32).
The sequence id accompanies the slot id in each request. It is for the critical check at the server: it used to efficiently determine whether a request using a certain slot id is a retransmit or a new, never-before-seen request. It is not feasible for the client to assert that it is retransmitting to implement this, because for any given request the client cannot know whether the server has seen it unless the server actually replies. Of course, if the client has seen the server's reply, the client would not retransmit.
The replier compares each received request's sequence id with the last one previously received for that slot id, to see if the new request is:
Unlike the XID, the slot id is always within a specific range; this has two implications. The first implication is that for a given session, the replier need only cache the results of a limited number of COMPOUND requests . The second implication derives from the first, which is unlike XID-indexed reply caches (also known as duplicate request caches - DRCs), the slot id-based reply cache cannot be overflowed. Through use of the sequence id to identify retransmitted requests, the replier does not need to actually cache the request itself, reducing the storage requirements of the reply cache further. These facilities make it practical to maintain all the required entries for an effective reply cache.
The slot id and sequence id therefore take over the traditional role of the XID and source network address in the replier's reply cache implementation. This approach is considerably more portable and completely robust - it is not subject to the reassignment of ports as clients reconnect over IP networks. In addition, the RPC XID is not used in the reply cache, enhancing robustness of the cache in the face of any rapid reuse of XIDs by the requester. While the replier does not care about the XID for the purposes of reply cache management (but the replier MUST return the same XID that was in the request), nonetheless there are considerations for the XID in NFSv4.1 that are the same as all other previous versions of NFS. The RPC XID remains in each message and must be formulated in NFSv4.1 requests as it any other ONC RPC request. The reasons include:
Givem that well formulated XIDs continue to be required, this begs the question why SEQUENCE and CB_SEQUENCE replies have a sessionid, slot id and sequence id? Having the sessionid in the reply means the requester does not have to use the XID to lookup the sessionid, which would be necessary if the connection were associated with multiple sessions. Having the slot id and sequence id in the reply means requester does not have to use the XID to lookup the slot id and sequence id. Furhermore, since the XID is only 32 bits, it is too small to guarantee the re-association of a reply with its request ([27] (Werme, R., “RPC XID Issues,” February 1996.)); having sessionid, slot id, and sequence id in the reply allows the client to validate that the reply in fact belongs to the matched request.
The SEQUENCE (and CB_SEQUENCE) operation also carries a "highest_slotid" value which carries additional requester slot usage information. The requester must always provide a slot id representing the outstanding request with the highest-numbered slot value. The requester should in all cases provide the most conservative value possible, although it can be increased somewhat above the actual instantaneous usage to maintain some minimum or optimal level. This provides a way for the requester to yield unused request slots back to the replier, which in turn can use the information to reallocate resources.
The replier responds with both a new target highest_slotid, and an enforced highest_slotid, described as follows:
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Any time SEQUENCE or CB_SEQUENCE return an error, the sequence id of the slot MUST NOT change. The replier MUST NOT modify the reply cache entry for the slot whenever an error is returned from SEQUENCE or CB_SEQUENCE.
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On a per-request basis the requester can choose to direct the replier to cache the reply to all operations after the first operation (SEQUENCE or CB_SEQUENCE) via the sa_cachethis or csa_cachethis fields of the arguments to SEQUENCE or CB_SEQUENCE. The reason it would not direct the replier to cache the entire reply is that the request is composed of all idempotent operations [24] (Juszczak, C., “Improving the Performance and Correctness of an NFS Server,” June 1990.). Caching the reply may offer little benefit. If the reply is too large (see Section 2.10.5.4 (COMPOUND and CB_COMPOUND Construction Issues)), it may not be cacheable anyway. Even if the reply to idempotent request is small enough to cache, unnecessarily caching the reply slows down the server and increases RPC latency.
Whether the requester requests the reply to be cached or not has no effect on the slot processing. If the results of SEQUENCE or CB_SEQUENCE are NFS4_OK, then the slot's sequence id MUST be incremented by one. If a requester does not direct the replier to cache the reply, the replier MUST do one of following:
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A requester MUST NOT retry a request, unless the connection it used to send the request disconnects. The requester can then reconnect and resend the request, or it can resend the request over a different connection that is associated with the same session.
If the requester is a server wanting to resend a callback operation over the backchannel of session, the requester of course cannot reconnect because only the client can associate connections with the backchannel. The server can resend the request over another connection that is bound to the same session's backchannel. If there is no such connection, the server MUST indicate that the session has no backchannel by setting the SEQ4_STATUS_CB_PATH_DOWN_SESSION flag bit in the response to the next SEQUENCE operation from the client. The client MUST then associate a connection with the session (or destroy the session).
Note that it is not fatal for a client to retry without a disconnect between the request and retry. However the retry does consume resources, especially with RDMA, where each request, retry or not, consumes a credit. Retries for no reason, especially retries issued shortly after the previous attempt, are a poor use of network bandwidth and defeat the purpose of a transport's inherent congestion control system.
A client MUST wait for a reply to a request before using the slot for another request. If it does not wait for a reply, then the client does not know what sequence id to use for the slot on its next request. For example, suppose a client sends a request with sequence id 1, and does not wait for the response. The next time it uses the slot, it sends the new request with sequence id 2. If the server has not seen the request with sequence id 1, then the server is not expecting sequence id 2, and rejects the client's new request with NFS4ERR_SEQ_MISORDERED (as the result from SEQUENCE or CB_SEQUENCE).
RDMA fabrics do not guarantee that the memory handles (Steering Tags) within each RPC/RDMA "chunk" ([9] (Talpey, T. and B. Callaghan, “RDMA Transport for ONC RPC - A Work in Progress,” May 2007.)) are valid on a scope outside that of a single connection. Therefore, handles used by the direct operations become invalid after connection loss. The server must ensure that any RDMA operations which must be replayed from the reply cache use the newly provided handle(s) from the most recent request.
A retry might be issued while the original request is still in progress on the replier. The replier SHOULD deal with issue by by returning NFS4ERR_DELAY as the reply to SEQUENCE or CB_SEQUENCE operation, but implementations MAY return NFS4ERR_MISORDERED. Since errors from SEQUENCE and CB_SEQUENCE are never recorded in the reply cache, this approach allows the results of the execution of the original request to be properly recorded in the reply cache (assuming the requester specified the reply to be cached).
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It is possible for server callbacks to arrive at the client before the reply from related fore channel operations. For example, a client may have been granted a delegation to a file it has opened, but the reply to the OPEN (informing the client of the granting of the delegation) may be delayed in the network. If a conflicting operation arrives at the server, it will recall the delegation using the backchannel, which may be on a different transport connection, perhaps even a different network, or even a different session associated with the same client ID
The presence of a session between client and server alleviates this issue. When a session is in place, each client request is uniquely identified by its { sessionid, slot id, sequence id } triple. By the rules under which slot entries (reply cache entries) are retired, the server has knowledge whether the client has "seen" each of the server's replies. The server can therefore provide sufficient information to the client to allow it to disambiguate between an erroneous or conflicting callback race condition.
For each client operation which might result in some sort of server callback, the server SHOULD "remember" the { sessionid, slot id, sequence id } triple of the client request until the slot id retirement rules allow the server to determine that the client has, in fact, seen the server's reply. Until the time the { sessionid, slot id, sequence id } request triple can be retired, any recalls of the associated object MUST carry an array of these referring identifiers (in the CB_SEQUENCE operation's arguments), for the benefit of the client. After this time, it is not necessary for the server to provide this information in related callbacks, since it is certain that a race condition can no longer occur.
The CB_SEQUENCE operation which begins each server callback carries a list of "referring" { sessionid, slot id, sequence id } triples. If the client finds the request corresponding to the referring sessionid, slot id and sequence id to be currently outstanding (i.e. the server's reply has not been seen by the client), it can determine that the callback has raced the reply, and act accordingly. If the client does not find the request corresponding the referring triple to be outstanding (including the case of a sessionid referring to a destroyed session), then there is no race with respect to this triple. The server SHOULD limit the referring triples to requests that refer to just those that apply to the objects referred to in the CB_COMPOUND procedure.
The client must not simply wait forever for the expected server reply to arrive before responding to the CB_COMPOUND that won the race, because it is possible that it will be delayed indefinitely. The client should assume the likely case that the reply will arrive within the average round trip time for COMPOUND requests to the server, and wait that period of time. If that period of expires it can respond to the CB_COMPOUND with NFS4ERR_DELAY.
There are other scenarios under which callbacks may race replies, among them pNFS layout recalls, described in Section 13.5.4.2 (Serialization of Layout Operations).
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Very large requests and replies may pose both buffer management issues (especially with RDMA) and reply cache issues. When the session is created, (Section 18.36 (Operation 43: CREATE_SESSION - Create New Session and Confirm Client ID)), for each channel (fore and back), the client and server negotiate the maximum sized request they will send or process (ca_maxrequestsize), the maximum sized reply they will return or process (ca_maxresponsesize), and the maximum sized reply they will store in the reply cache (ca_maxresponsesize_cached).
If a request exceeds ca_maxrequestsize, the reply will have the status NFS4ERR_REQ_TOO_BIG. A replier MAY return NFS4ERR_REQ_TOO_BIG as the status for first operation (SEQUENCE or CB_SEQUENCE) in the request (which means no operations in the request executed, and the state of the slot in the reply cache is unchanged), or it MAY chose to return it on a subsequent operation in the same COMPOUND or CB_COMPOUND request (which means at least one operation did execute and the state of the slot in reply cache does change). The replier SHOULD set NFS4ERR_REQ_TOO_BIG on the operation that exceeds ca_maxrequestsize.
If a reply exceeds ca_maxresponsesize, the reply will have the status NFS4ERR_REP_TOO_BIG. A replier MAY return NFS4ERR_REP_TOO_BIG as the status for first operation (SEQUENCE or CB_SEQUENCE) in the request, or it MAY chose to return it on a subsequent operation (in the same COMPOUND or CB_COMPOUND reply). A replier MAY return NFS4ERR_REP_TOO_BIG in the reply to SEQUENCE or CB_SEQUENCE, even if the response would still exceed ca_maxresponsesize.
If sa_cachethis or csa_cachethis are TRUE, then the replier MUST cache a reply except if an error is returned by the SEQUENCE or CB_SEQUENCE operation (see Section 2.10.5.1.1 (Errors from SEQUENCE and CB_SEQUENCE)). If the reply exceeds ca_maxresponsesize_cached, (and sa_cachethis or csa_cachethis are TRUE) then the server MUST return NFS4ERR_REP_TOO_BIG_TO_CACHE. Even if NFS4ERR_REP_TOO_BIG_TO_CACHE (or any other error for that matter) is returned on a operation other than first operation (SEQUENCE or CB_SEQUENCE), then the reply MUST be cached if sa_cachethis or csa_cachethis are TRUE. For example, if a COMPOUND has eleven operations, including SEQUENCE, the fifth operation is a RENAME, and the tenth operation is a READ for one million octets, the server may return NFS4ERR_REP_TOO_BIG_TO_CACHE on the tenth operation. Since the server executed several operations, especially the non-idempotent RENAME, the client's request to cache the reply needs to be honored in order for correct operation of exactly once semantics. If the client retries the request, the server will have cached a reply that contains results for ten of the eleven requested operations, with the tenth operation having a status of NFS4ERR_REP_TOO_BIG_TO_CACHE.
A client needs to take care that when sending operations that change the current filehandle (except for PUTFH, PUTPUBFH, and PUTROOTFH) that it not exceed the maximum reply buffer before the GETFH operation. Otherwise the client will have to retry the operation that changed the current filehandle, in order to obtain the desired filehandle. For the OPEN operation (see Section 18.16 (Operation 18: OPEN - Open a Regular File)), retry is not always available as an option. The following guidelines for the handling of filehandle changing operations are advised:
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Since the reply cache is bounded, it is practical for the reply cache to persist across server restarts. The replier MUST persist the following information if it agreed to persist the session (when the session was created; see Section 18.36 (Operation 43: CREATE_SESSION - Create New Session and Confirm Client ID)):
The above are sufficient for a replier to provide EOS semantics for any requests that were sent and executed before the server restarted. If the replier is a client then there is no need for it to persist any more information, unless the client will be persisting all other state across client restart. In which case, the server will never see any NFSv4.1-level protocol manifestation of a client restart. If the replier is a server, with just the slot table and sessionid persisting, any requests the client retries after the server restart will return the results that are cached in reply cache. and any new requests (i.e. the sequence id is one (1) greater than the slot's sequence id) MUST be rejected with NFS4ERR_DEADSESSION (returned by SEQUENCE). Such a session is considered: dead. A server MAY re-animate a session after a server restart so that the session will accept new requests as well as retries. To re-animate a session the server needs to persist additional information through server restart:
A persistent reply cache places certain demands on the server. The execution of the sequence of operations (starting with SEQUENCE) and placement of its results in the persistent cache MUST be atomic. If a client retries an sequence of operations that was previously executed on the server the only acceptable outcomes are either the original cached reply or an indication that client ID or session has been lost (indicating a catastrophic loss of the reply cache or a session that has been deleted because the client failed to use the session for an extended period of time).
A server could fail and restart in the middle of a COMPOUND procedure that contains one or more non-idempotent or idempotent-but-modifying operations. This creates an even higher challenge for atomic execution and placement of results in the reply cache. One way to view the problem is as a single transaction consisting of each operation in the COMPOUND followed by storing the result in persistent storage, then finally a transaction commit. If there is a failure before the transaction is committed, then the server rolls back the transaction. If server itself fails, then when it restarts, its recovery logic could roll back the transaction before starting the NFSv4.1 server.
While the description of the implementation for atomic execution of the request and caching of the reply is beyond the scope of this document, an example implementation for NFS version 2 is described in [28] (Bhide, A., Elnozahy, E., and S. Morgan, “A Highly Available Network Server,” January 1991.).
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A complete discussion of the operation of RPC-based protocols over RDMA transports is in [9] (Talpey, T. and B. Callaghan, “RDMA Transport for ONC RPC - A Work in Progress,” May 2007.). A discussion of the operation of NFSv4, including NFSv4.1, over RDMA is in [10] (Talpey, T. and B. Callaghan, “NFS Direct Data Placement - A Work in Progress,” May 2007.). Where RDMA is considered, this specification assumes the use of such a layering; it addresses only the upper layer issues relevant to making best use of RPC/RDMA.
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RDMA requires its consumers to register memory and post buffers of a specific size and number for receive operations.
Registration of memory can be a relatively high-overhead operation, since it requires pinning of buffers, assignment of attributes (e.g. readable/writable), and initialization of hardware translation. Preregistration is desirable to reduce overhead. These registrations are specific to hardware interfaces and even to RDMA connection endpoints, therefore negotiation of their limits is desirable to manage resources effectively.
Following basic registration, these buffers must be posted by the RPC layer to handle receives. These buffers remain in use by the RPC/NFSv4.1 implementation; the size and number of them must be known to the remote peer in order to avoid RDMA errors which would cause a fatal error on the RDMA connection.
NFSv4.1 manages slots as resources on a per session basis (see Section 2.10 (Session)), while RDMA connections manage credits on a per connection basis. This means that in order for a peer to send data over RDMA to a remote buffer, it has to have both an NFSv4.1 slot, and an RDMA credit. If multiple RDMA connections are associated with a session, then if the total number of credits across all RDMA connections associated with the session is X, and the number slots in the session is Y, then the maximum number of outstanding requests is lesser of X and Y.
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Previous versions of NFS do not provide flow control; instead they rely on the windowing provided by transports like TCP to throttle requests. This does not work with RDMA, which provides no operation flow control and will terminate a connection in error when limits are exceeded. Limits such as maximum number of requests outstanding are therefore negotiated when a session is created (see the ca_maxrequests field in Section 18.36 (Operation 43: CREATE_SESSION - Create New Session and Confirm Client ID)). These limits then provide the maxima which each connection associated with the session's channel(s) must remain within. RDMA connections are managed within these limits as described in section 3.3 ("Flow Control"[Comment.4] (RFC Editor: please verify section and title of the RPCRDMA document)) of [9] (Talpey, T. and B. Callaghan, “RDMA Transport for ONC RPC - A Work in Progress,” May 2007.); if there are multiple RDMA connections, then the maximum number of requests for a channel will be divided among the RDMA connections. Put a different way, the onus is on the replier to ensure that total number of RDMA credits across all connections associated with the replier's channel does exceed the channel's maximum number of outstanding requests.
The limits may also be modified dynamically at the replier's choosing by manipulating certain parameters present in each NFSv4.1 reply. In addition, the CB_RECALL_SLOT callback operation (see Section 20.8 (Operation 10: CB_RECALL_SLOT - change flow control limits)) can be issued by a server to a client to return RDMA credits to the server, thereby lowering the maximum number of requests a client can have outstanding to the server.
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Header padding is requested by each peer at session initiation (see the ca_headerpadsize argument to CREATE_SESSION in Section 18.36 (Operation 43: CREATE_SESSION - Create New Session and Confirm Client ID)), and subsequently used by the RPC RDMA layer, as described in [9] (Talpey, T. and B. Callaghan, “RDMA Transport for ONC RPC - A Work in Progress,” May 2007.). Zero padding is permitted.
Padding leverages the useful property that RDMA preserve alignment of data, even when they are placed into anonymous (untagged) buffers. If requested, client inline writes will insert appropriate pad octets within the request header to align the data payload on the specified boundary. The client is encouraged to add sufficient padding (up to the negotiated size) so that the "data" field of the NFSv4.1 WRITE operation is aligned. Most servers can make good use of such padding, which allows them to chain receive buffers in such a way that any data carried by client requests will be placed into appropriate buffers at the server, ready for file system processing. The receiver's RPC layer encounters no overhead from skipping over pad octets, and the RDMA layer's high performance makes the insertion and transmission of padding on the sender a significant optimization. In this way, the need for servers to perform RDMA Read to satisfy all but the largest client writes is obviated. An added benefit is the reduction of message round trips on the network - a potentially good trade, where latency is present.
The value to choose for padding is subject to a number of criteria. A primary source of variable-length data in the RPC header is the authentication information, the form of which is client-determined, possibly in response to server specification. The contents of COMPOUNDs, sizes of strings such as those passed to RENAME, etc. all go into the determination of a maximal NFSv4.1 request size and therefore minimal buffer size. The client must select its offered value carefully, so as not to overburden the server, and vice- versa. The payoff of an appropriate padding value is higher performance. [Comment.5] (RFC editor please keep this diagram on one page.)
Sender gather:
|RPC Request|Pad octets|Length| -> |User data...|
\------+----------------------/ \
\ \
\ Receiver scatter: \-----------+- ...
/-----+----------------\ \ \
|RPC Request|Pad|Length| -> |FS buffer|->|FS buffer|->...
In the above case, the server may recycle unused buffers to the next posted receive if unused by the actual received request, or may pass the now-complete buffers by reference for normal write processing. For a server which can make use of it, this removes any need for data copies of incoming data, without resorting to complicated end-to-end buffer advertisement and management. This includes most kernel-based and integrated server designs, among many others. The client may perform similar optimizations, if desired.
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Some RDMA transports (for example [11] (Recio, P., Culley, P., Garcia, D., Hilland, J., and B. Metzler, “A Remote Direct Memory Access Protocol Specification - A Work in Progress,” September 2006.)), permit a "streaming" (non-RDMA) phase, where ordinary traffic might flow before "stepping up" to RDMA mode, commencing RDMA traffic. Some RDMA transports start connections always in RDMA mode. NFSv4.1 allows, but does not assume, a streaming phase before RDMA mode. When a connection is associated with a session, the client and server negotiate whether the connection is used in RDMA or non-RDMA mode (see Section 18.36 (Operation 43: CREATE_SESSION - Create New Session and Confirm Client ID) and Section 18.34 (Operation 41: BIND_CONN_TO_SESSION)).
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Via session / connection association, NFSv4.1 improves security over that provided by NFSv4.0 for the backchannel. The connection is client-initiated (see Section 18.34 (Operation 41: BIND_CONN_TO_SESSION)), and subject to the same firewall and routing checks as the fore channel. The connection cannot be hijacked by an attacker who connects to the client port prior to the intended server as is possible with NFSv4.0. At the client's option (see Section 18.35 (Operation 42: EXCHANGE_ID - Instantiate Client ID)), connection association is fully authenticated before being activated (see Section 18.34 (Operation 41: BIND_CONN_TO_SESSION)). Traffic from the server over the backchannel is authenticated exactly as the client specifies (see Section 2.10.7.2 (Backchannel RPC Security)).
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When the NFSv4.1 client establishes the backchannel, it informs the server of the security flavors and principals to use when sending requests. If the security flavor is RPCSEC_GSS, the client expresses the principal in the form of an established RPCSEC_GSS context. The server is free to use any of the flavor/principal combinations the client offers, but it MUST NOT use unoffered combinations. This way, the client need not provide a target GSS principal for the backchannel as it did with NFSv4.0, nor the server have to implement an RPCSEC_GSS initiator as it did with NFSv4.0 [2] (Shepler, S., Callaghan, B., Robinson, D., Thurlow, R., Beame, C., Eisler, M., and D. Noveck, “Network File System (NFS) version 4 Protocol,” April 2003.).
The CREATE_SESSION (Section 18.36 (Operation 43: CREATE_SESSION - Create New Session and Confirm Client ID)) and BACKCHANNEL_CTL (Section 18.33 (Operation 40: BACKCHANNEL_CTL - Backchannel control)) operations allow the client to specify flavor/principal combinations.
Also note that the SP4_SSV state protection mode (see Section 18.35 (Operation 42: EXCHANGE_ID - Instantiate Client ID) and Section 2.10.7.3 (Protection from Unauthorized State Changes)) has the side benefit of providing SSV-derived RPCSEC_GSS contexts (Section 2.10.7.4 (The SSV GSS Mechanism)).
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As described to this point in the specification, the state model of NFSv4.1 is vulnerable to an attacker that issues a SEQUENCE operation with a forged sessionid and with a slot id that it expects the legitimate client to use next. When the legitimate client uses the slot id with the same sequence number, the server returns the attacker's result from the reply cache which disrupts the legitimate client and thus denies service to it. Similarly an attacker could issue a CREATE_SESSION with a forged client ID to create a new session associated with the client ID. The attacker could issue requests using the new session that change locking state, such as LOCKU operations to release locks the legitimate client has acquired. Setting a security policy on the file which requires RPCSEC_GSS credentials when manipulating the file's state is one potential work around, but has the disadvantage of preventing a legitimate client from releasing state when RPCSEC_GSS is required to do so, but a GSS context cannot be obtained (possibly because the user has logged off the client).
NFSv4.1 provides three options to a client for state protection which are specified when a client creates a client ID via EXCHANGE_ID (Section 18.35 (Operation 42: EXCHANGE_ID - Instantiate Client ID)).
The first (SP4_NONE) is to simply waive state protection.
The other two options (SP4_MACH_CRED and SP4_SSV) share several traits:
The SP4_MACH_CRED state protection option uses a machine credential where the principal that creates the client ID, must also be the principal that performs client ID and session maintenance operations. The security of the machine credential state protection approach depends entirely on safe guarding the per-machine credential. Assuming a proper safe guard, using the per-machine credential for operations like CREATE_SESSION, BIND_CONN_TO_SESSION, DESTROY_SESSION, and DESTROY_CLIENTID will prevent an attacker from associating a rogue connection with a session, or associating a rogue session with a client ID.
There are at least three scenarios for the SP4_MACH_CRED option:
The SP4_SSV protection option uses a Secret State Verifier (SSV) which is shared between a client and server. The SSV serves as the secret key for an internal (that is, internal to NFSv4.1) GSS mechanism that uses the secret key for Message Integrity Code (MIC) and Wrap tokens (Section 2.10.7.4 (The SSV GSS Mechanism)). The SP4_SSV protection option is intended for the client that has multiple users, and the system administrator does not wish to configure a permanent machine credential for each client. The SSV is established on the server via SET_SSV (see Section 18.47 (Operation 54: SET_SSV)). To prevent eavesdropping, a client SHOULD issue SET_SSV via RPCSEC_GSS with the privacy service. Several aspects of the SSV make it intractable for an attacker to guess the SSV, and thus associate rogue connections with a session, and rogue sessions with a client ID:
Here are the types of attacks that can be attempted by an attacker named Eve on a victim named Bob, and how SP4_SSV protection foils each attack:
In summary an attacker's disruption of state when SP4_SSV protection is in use is limited to the formative period of a client ID, its first session, and the establishment of the SSV. Once a non-malicious user uses the client ID, the client quickly detects any hijack and rectifies the situation. Once a non-malicious user successfully modifies the SSV, the attacker cannot use NFSv4.1 operations to disrupt the non-malicious user.
Note that neither the SP4_MACH_CRED nor SP4_SSV protection approaches prevent hijacking of a transport connection that has previously been associated with a session. If the goal of a counter threat strategy is to prevent connection hijacking, the use of IPsec is RECOMMENDED. If the goal of a counter threat strategy is to prevent a connection hijacker from making unauthorized state changes, then the SP4_MACH_CRED protection approach can be used with a client ID per user (i.e. the aforementioned third scenario for machine credential state protection). Each EXCHANGE_ID can specify the all operations MUST be protected with the machine credential. The server will then reject any subsequent operations on the client ID that do not use RPCSEC_GSS with privacy or integrity and do not use the same credential that created the client ID.
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The SSV provides the secret key for a mechanism that NFSv4.1 uses for state protection. Contexts for this mechanism are not established via the RPCSEC_GSS protocol. Instead, the contexts are automatically created when EXCHANGE_ID specifies SP4_SSV protection. The only tokens defined are the PerMsgToken (emitted by GSS_GetMIC) and the SealedMessage (emitted by GSS_Wrap).
The mechanism OID for the SSV mechanism is: iso.org.dod.internet.private.enterprise.Michael Eisler.nfs.ssv_mech (1.3.6.1.4.1.28882.1.1). While the SSV mechanisms does not define any initial context tokens, the OID can be used to let servers indicate that the SSV mechanism is acceptable whenever the client issues a SECINFO or SECINFO_NO_NAME operation (see Section 2.6 (Security Service Negotiation)).
The PerMsgToken description is based on an XDR definition:
/* Input for computing smt_hmac */
struct ssv_mic_plain_tkn4 {
uint32_t smpt_ssv_seq;
opaque smpt_orig_plain<>;
};
/* SSV GSS PerMsgToken token */
struct ssv_mic_tkn4 {
uint32_t smt_ssv_seq;
opaque smt_hmac<>;
};
The token emitted by GSS_GetMIC() is XDR encoded and of XDR data type ssv_mic_tkn4. The field smt_ssv_seq comes from the SSV sequence number which is equal to 1 after SET_SSV is called the first time on a client ID. Thereafter, it is incremented on each SET_SSV. Thus smt_ssv_seq represents the version of the SSV at the time GSS_GetMIC() was called. This allows the SSV to be changed without serializing all RPC calls that use the SSV mechanism with SET_SSV operations.
The field smt_hmac is an HMAC ([12] (Krawczyk, H., Bellare, M., and R. Canetti, “HMAC: Keyed-Hashing for Message Authentication,” February 1997.)), calculated by using the current SSV as the key, the one way hash algorithm as negotiated by EXCHANGE_ID, and the input text as represented by data of type ssv_mic_plain_tkn4. The field smpt_ssv_seq is the same as smt_ssv_seq. The field smt_orig_plain is the input text as passed into GSS_GetMIC().
The SealedMessage description is based on an XDR definition:
/* Input for computing ssct_encr_data and ssct_hmac */
struct ssv_seal_plain_tkn4 {
opaque sspt_confounder<>;
uint32_t sspt_ssv_seq;
opaque sspt_orig_plain<>;
opaque sspt_pad<>;
};
/* SSV GSS SealedMessage token */
struct ssv_seal_cipher_tkn4 {
uint32_t ssct_ssv_seq;
opaque ssct_iv<>;
opaque ssct_encr_data<>;
opaque ssct_hmac<>;
};
The token emitted by GSS_Wrap() is XDR encoded and of XDR data type ssv_seal_cipher_tkn4.
The ssct_ssv_seq field has the same meaning as smt_ssv_seq.
The ssct_encr_data field is the result of encrypting a value of the XDR encoded data type ssv_seal_plain_tkn4. The encryption key is the SSV, and the encryption algorithm is that negotiated by EXCHANGE_ID.
The ssct_iv field is the initialization vector (IV) for the encryption algorithm (if applicable) and is sent in clear text. The content and size of the IV MUST comply with specification of the encryption algorithm. For example, the id-aes256-CBC algorithm MUST use a 16 octet initialization vector (IV) which MUST be unpredictable for each instance of a value of type ssv_seal_plain_tkn4 that is encrypted with a particular SSV key.
The ssct_hmac field is the result of computing an HMAC using value of the XDR encoded data type ssv_seal_plain_tkn4 as the input text. The key is the SSV, and the one way hash algorithm is that negotiated by EXCHANGE_ID.
The sspt_confounder field is a random value.
The sspt_ssv_seq field is the same as ssvt_ssv_seq.
The sspt_orig_plain field is the original plaintext as passed to GSS_Wrap().
The sspt_pad field is present to support encryption algorithms that require inputs to be in fixed sized blocks. The content of sspt_pad is zero filled except for the length. Beware that the XDR encoding of ssv_seal_plain_tkn4 contains three variable length arrays, and so each array consumes 4 octets for an array length, and each array that follows the length is always padded to a multiple of 4 octets per the XDR standard.
For example suppose the encryption algorithm uses 16 octet blocks, and the sspt_confounder is 3 octets long, and the sspt_orig_plain field is 15 octets long. The XDR encoding of sspt_confounder uses 8 octets (4 + 3 + 1 octet pad), the XDR encoding of sspt_ssv_seq uses 4 octets, the XDR encoding of sspt_orig_plain uses 20 octets (4 + 15 + 1 octet pad), and the smallest XDR encoding of the sspt_pad field is 4 octets. This totals 36 octets. The next multiple of 16 is 48, thus the length field of sspt_pad needs to be set to 12 octets, or a total encoding of 16 octets. The total number of XDR encoded octets is thus 8 + 4 + 20 + 16 = 48.
GSS_Wrap() emits a token that is an XDR encoding of a value of data type ssv_seal_cipher_tkn4. Note that regardless whether the caller of GSS_Wrap() requests confidentiality or not, the token always has confidentiality. This is because the SSV mechanism is for RPCSEC_GSS, and RPCSEC_GSS never produces GSS_wrap() tokens without confidentiality.
Effectively there is a single GSS context for all RPCSEC_GSS handles that have been created on a session. And all sessions associated with a a client ID share the same SSV. SSV GSS contexts do not expire except when the SSV is destroyed (causes would include the client ID being destroyed or a server restart). Since one purpose of context expiration is to replace keys that have been in use for "too long" hence vulnerable to compromise by brute force or accident, the client can issue periodic SET_SSV operations, by cycling through different users' RPCSEC_GSS credentials. This way the SSV is replaced without destroying the SSV's GSS contexts. If for some reason SSV RPCSEC_GSS handles expire, the EXCHANGE_ID operation can be used to create more SSV RPCSEC_GSS handles.
The client MUST establish an SSV via SET_SSV before the GSS context can be used to emit tokens from GSS_Wrap() and GSS_GetMIC(). If SET_SSV has not been successfully called, attempts to emit tokens MUST fail.
The SSV mechanism does not support replay detection and sequencing in its tokens because RPCSEC_GSS does not use those features (Section 5.2.2 "Context Creation Requests" in [5] (Eisler, M., Chiu, A., and L. Ling, “RPCSEC_GSS Protocol Specification,” September 1997.)).
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The server has the primary obligation to monitor the state of backchannel resources that the client has created for the server (RPCSEC_GSS contexts and backchannel connections). If these resources vanish, the server takes action as specified in Section 2.10.9.2 (Events Requiring Server Action).
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The client SHOULD honor the following obligations in order to utilize the session:
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If the client does not have a client ID, the client issues EXCHANGE_ID to establish a client ID. If it opts for SP4_MACH_CRED or SP4_SSV protection, in the spo_must_enforce list of operations, it SHOULD at minimum specify: CREATE_SESSION, DESTROY_SESSION, BIND_CONN_TO_SESSION, BACKCHANNEL_CTL, and DESTROY_CLIENTID. If opts for SP4_SSV protection, the client needs to ask for SSV-based RPCSEC_GSS handles.
The client uses the client ID to issue a CREATE_SESSION on a connection to the server. The results of CREATE_SESSION indicate whether the server will persist the session reply cache through a server reboot or not, and the client notes this for future reference.
If the client specified SP4_SSV state protection when the client ID was created, then it SHOULD issue SET_SSV in the first COMPOUND after the session is created. Each time a new principal goes to use the client ID, it SHOULD issue a SET_SSV again.
If the client wants to use delegations, layouts, directory notifications, or any other state that requires a backchannel, then it must add a connection to the backchannel if CREATE_SESSION did not already do so. The client creates a connection, and calls BIND_CONN_TO_SESSION to associate the connection with the session and the session's backchannel. If CREATE_SESSION did not already do so, the client MUST tell the server what security is required in order for the client to accept callbacks. The client does this via BACKCHANNEL_CTL. If the client selected SP4_MACH_CRED or SP4_SSV protection when it called EXCHANGE_ID, then the client SHOULD specify that the backchannel use RPCSEC_GSS contexts for security.
If the client wants to use additional connections for the backchannel, then it must call BIND_CONN_TO_SESSION on each connection it wants to use with the session. If the client wants to use additional connections for the fore channel, then it must call BIND_CONN_TO_SESSION if it specified SP4_SSV or SP4_MACH_CRED state protection when the client ID was created.
At this point the session has reached steady state.
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The following events require client action to recover.
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If all RPCSEC_GSS contexts granted by the client to the server for callback use have expired, the client MUST establish a new context via BACKCHANNEL_CTL. The sr_status_flags field of the SEQUENCE results indicates when callback contexts are nearly expired, or fully expired (see Section 18.46.4 (DESCRIPTION)).
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If the client loses the last connection of the session, and if wants to retain the session, then it must create a new connection, and if, when the client ID was created, BIND_CONN_TO_SESSION was specified in the spo_must_enforce list, the client MUST use BIND_CONNN_TO_SESSION to associate the connection with the session.
If there was a request outstanding at the time the of connection loss, then if client wants to continue to use the session it MUST retry the request, as described in Section 2.10.5.2 (Retry and Replay of Reply). Note that it is not necessary to retry requests over a connection with the same source network address or the same destination network address as the lost connection. As long as the sessionid, slot id, and sequence id in the retry match that of the original request, the server will recognize the request as a retry if it executed the request prior to disconnect.
If the connection that was lost was the last one associated with the backchannel, and the client wants to retain the backchannel and/or not put recallable state subject to revocation, the client must reconnect, and if it does, it MUST associate the connection to the session and backchannel via BIND_CONN_TO_SESSION. The server SHOULD indicate when it has no callback connection via the sr_status_flags result from SEQUENCE.
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Via the sr_status_flags result of the SEQUENCE operation or other means, the client will learn if some or all of the RPCSEC_GSS contexts it assigned to the backchannel have been lost. If the client wants to the retain the backchannel and/or not put recallable state subjection to revocation, the client must use BACKCHANNEL_CTL to assign new contexts.
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The replier might lose a record of the session. Causes include:
Loss of reply cache is equivalent to loss of session. The replier indicates loss of session to the requester by returning NFS4ERR_BADSESSION on the next operation that uses the sessionid that refers to the lost session.
After an event like a server reboot, the client may have lost its connections. The client assumes for the moment that the session has not been lost. It reconnects, and if it specified connection association enforcement when the session was created, it invokes BIND_CONN_TO_SESSION using the sessionid. Otherwise, it invokes SEQUENCE. If BIND_CONN_TO_SESSION or SEQUENCE returns NFS4ERR_BADSESSION, the client knows the session was lost. If the connection survives session loss, then the next SEQUENCE operation the client issues over the connection will get back NFS4ERR_BADSESSION. The client again knows the session was lost.
When the client detects session loss, it must call CREATE_SESSION to recover. Any non-idempotent operations that were in progress may have been performed on the server at the time of session loss. The client has no general way to recover from this.
Note that loss of session does not imply loss of lock, open, delegation, or layout state because locks, opens, delegations, and layouts are tied to the client ID and depend on the client ID, not the session. Nor does loss of lock, open, delegation, or layout state imply loss of session state, because the session depends on the client ID; loss of client ID however does imply loss of session, lock, open, delegation, and layout state. See Section 8.4.2 (Server Failure and Recovery). A session can survive a server reboot, but lock recovery may still be needed.
It is possible CREATE_SESSION will fail with NFS4ERR_STALE_CLIENTID (for example the server reboots and does not preserve client ID state). If so, the client needs to call EXCHANGE_ID, followed by CREATE_SESSION.
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The following events require server action to recover.
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As described in Section 18.35 (Operation 42: EXCHANGE_ID - Instantiate Client ID), a rebooted client issues EXCHANGE_ID in such a way it causes the server to delete any sessions it had.
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If a client crashes and never comes back, it will never issue EXCHANGE_ID with its old client owner. Thus the server has session state that will never be used again. After an extended period of time and if the server has resource constraints, it MAY destroy the old session as well as locking state.
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To the server, the extended network partition may be no different from a client crash with no reboot (see Section 2.10.9.2.2 (Client Crash with No Reboot)). Unless the server can discern that there is a network partition, it is free to treat the situation as if the client has crashed permanently.
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If there were callback requests outstanding at the time of a connection loss, then the server MUST retry the request, as described in Section 2.10.5.2 (Retry and Replay of Reply). Note that it is not necessary to retry requests over a connection with the same source network address or the same destination network address as the lost connection. As long as the sessionid, slot id, and sequence id in the retry match that of the original request, the callback target will recognize the request as a retry even if it did see the request prior to disconnect.
If the connection lost is the last one associated with the backchannel, then the server MUST indicate that in the sr_status_flags field of every SEQUENCE reply until the backchannel is reestablished. There are two situations each of which use different status flags: no connectivity for the session's backchannel, and no connectivity for any session backchannel of the client. See Section 18.46 (Operation 53: SEQUENCE - Supply per-procedure sequencing and control) for a description of the appropriate flags in sr_status_flags.
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The server SHOULD monitor when the number RPCSEC_GSS contexts assigned to the backchannel reaches one, and that one context is near expiry (i.e. between one and two periods of lease time), and indicate so in the sr_status_flags field of all SEQUENCE replies. The server MUST indicate when the all of the backchannel's assigned RPCSEC_GSS contexts have expired in the sr_status_flags field of all SEQUENCE replies.
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A client and server can potentially be a non-pNFS implementation, a metadata server implementation, a data server implementation, or two or three types of implementations. The EXCHGID4_FLAG_USE_NON_PNFS, EXCHGID4_FLAG_USE_PNFS_MDS, and EXCHGID4_FLAG_USE_PNFS_DS flags (not mutually exclusive) are passed in the EXCHANGE_ID arguments and results to allow the client to indicate how it wants to use sessions created under the client ID, and to allow the server to indicate how it will allow the sessions to be used. See Section 14.1 (Client ID and Session Considerations) for pNFS sessions considerations.
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The syntax and semantics to describe the data types of the NFS version 4 protocol are defined in the XDR RFC4506 (Eisler, M., “XDR: External Data Representation Standard,” May 2006.) [3] and RPC RFC1831 (Srinivasan, R., “RPC: Remote Procedure Call Protocol Specification Version 2,” August 1995.) [4] documents. The next sections build upon the XDR data types to define types and structures specific to this protocol.
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These are the base NFSv4 data types.
| Data Type | Definition |
|---|---|
| int32_t | typedef int int32_t; |
| uint32_t | typedef unsigned int uint32_t; |
| int64_t | typedef hyper int64_t; |
| uint64_t | typedef unsigned hyper uint64_t; |
| attrlist4<> | typedef opaque attrlist4<>; |
| Used for file/directory attributes | |
| bitmap4<> | typedef uint32_t bitmap4<>; |
| Used in attribute array encoding. | |
| changeid4 | typedef uint64_t changeid4; |
| Used in definition of change_info | |
| clientid4 | typedef uint64_t clientid4; |
| Shorthand reference to client identification | |
| 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<NFS4_FHSIZE> | typedef opaque nfs_fh4<NFS4_FHSIZE>; |
| Filehandle definition; NFS4_FHSIZE is defined as 128 | |
| nfs_ftype4 | enum nfs_ftype4; |
| Various defined file types | |
| nfsstat4 | enum nfsstat4; |
| Return value for operations | |
| offset4 | typedef uint64_t offset4; |
| Various offset designations (READ, WRITE, LOCK, COMMIT) | |
| 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 ASN.1 OBJECT IDENTIFIER as used by GSS-API in the mech_type argument to GSS_Init_sec_context. See [8] (Linn, J., “Generic Security Service Application Program Interface Version 2, Update 1,” January 2000.) for details. | |
| sequenceid4 | typedef uint32_t sequenceid4; |
| sequence number used for various session operations (EXCHANGE_ID, CREATE_SESSION, SEQUENCE, CB_SEQUENCE). | |
| seqid4 | typedef uint32_t seqid4; |
| Sequence identifier used for file locking | |
| sessionid4 | typedef opaque sessionid4[16]; |
| Session identifier | |
| slotid4 | typedef uint32_t slotid4; |
| sequencing artifact for various session operations (SEQUENCE, CB_SEQUENCE). | |
| utf8string<> | typedef opaque utf8string<>; |
| UTF-8 encoding for strings | |
| utf8str_cis | typedef utf8string utf8str_cis; |
| Case-insensitive UTF-8 string | |
| utf8str_cs | typedef utf8string utf8str_cs; |
| Case-sensitive UTF-8 string | |
| utf8str_mixed | typedef utf8string utf8str_mixed; |
| UTF-8 strings with a case sensitive prefix and a case insensitive suffix. | |
| component4 | typedef utf8str_cs component4; |
| Represents path name components | |
| linktext4 | typedef utf8str_cs linktext4; |
| Symbolic link contents | |
| pathname4<> | typedef component4 pathname4<>; |
| Represents path name for fs_locations | |
| 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 |
| TOC |
| TOC |
struct nfstime4 {
int64_t seconds;
uint32_t nseconds;
};
The nfstime4 structure gives the number of seconds and nanoseconds since midnight or 0 hour January 1, 1970 Coordinated Universal Time (UTC). Values greater than zero for the seconds field denote dates after the 0 hour January 1, 1970. Values less than zero for the seconds field denote dates before the 0 hour January 1, 1970. In both cases, the nseconds field is to be added to the seconds field for the final time representation. For example, if the time to be represented is one-half second before 0 hour January 1, 1970, the seconds field would have a value of negative one (-1) and the nseconds fields would have a value of one-half second (500000000). Values greater than 999,999,999 for nseconds are considered invalid.
This data type is used to pass time and date information. A server converts to and from its local representation of time when processing time values, preserving as much accuracy as possible. If the precision of timestamps stored for a file system object is less than defined, loss of precision can occur. An adjunct time maintenance protocol is recommended to reduce client and server time skew.
| TOC |
enum time_how4 {
SET_TO_SERVER_TIME4 = 0,
SET_TO_CLIENT_TIME4 = 1
};
| TOC |
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.
| TOC |
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.
| TOC |
struct fsid4 {
uint64_t major;
uint64_t minor;
};
| TOC |
struct fs_location4 {
utf8str_cis server<>;
pathname4 rootpath;
};
| TOC |
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.
| TOC |
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 | +-----------+-----------+-----------+--
| TOC |
struct change_info4 {
bool atomic;
changeid4 before;
changeid4 after;
};
This structure is used with the CREATE, LINK, REMOVE, RENAME operations to let the client know the value of the change attribute for the directory in which the target file system object resides.
| TOC |
struct netaddr4 {
/* see struct rpcb in RFC 1833 */
string na_r_netid<>; /* network id */
string na_r_addr<>; /* universal address */
};
The netaddr4 structure is used to identify TCP/IP based endpoints. The r_netid and r_addr fields are specified in RFC1833 (Srinivasan, R., “Binding Protocols for ONC RPC Version 2,” August 1995.) [26], but they are underspecified in RFC1833 (Srinivasan, R., “Binding Protocols for ONC RPC Version 2,” August 1995.) [26] as far as what they should look like for specific protocols.
For TCP over IPv4 and for UDP over IPv4, the format of r_addr is the US-ASCII string:
h1.h2.h3.h4.p1.p2
The prefix, "h1.h2.h3.h4", is the standard textual form for representing an IPv4 address, which is always four octets long. Assuming big-endian ordering, h1, h2, h3, and h4, are respectively, the first through fourth octets each converted to ASCII-decimal. Assuming big-endian ordering, p1 and p2 are, respectively, the first and second octets each converted to ASCII-decimal. For example, if a host, in big-endian order, has an address of 0x0A010307 and there is a service listening on, in big endian order, port 0x020F (decimal 527), then complete universal address is "10.1.3.7.2.15".
For TCP over IPv4 the value of r_netid is the string "tcp". For UDP over IPv4 the value of r_netid is the string "udp". That this document specifies the universal address and netid for UDP/IPv6 does not imply that UDP/IPv4 is a legal transport for NFSv4.1 (see Section 2.9 (Transport Layers)).
For TCP over IPv6 and for UDP over IPv6, the format of r_addr is the US-ASCII string:
x1:x2:x3:x4:x5:x6:x7:x8.p1.p2
The suffix "p1.p2" is the service port, and is computed the same way as with universal addresses for TCP and UDP over IPv4. The prefix, "x1:x2:x3:x4:x5:x6:x7:x8", is the standard textual form for representing an IPv6 address as defined in Section 2.2 of RFC1884 (Hinden, R. and S. Deering, “IP Version 6 Addressing Architecture,” December 1995.) [13]. Additionally, the two alternative forms specified in Section 2.2 of RFC1884 (Hinden, R. and S. Deering, “IP Version 6 Addressing Architecture,” December 1995.) [13] 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". That this document specifies the universal address and netid for UDP/IPv6 does not imply that UDP/IPv6 is a legal transport for NFSv4.1 (see Section 2.9 (Transport Layers)).
| TOC |
struct state_owner4 {
clientid4 clientid;
opaque owner<NFS4_OPAQUE_LIMIT>;
};
typedef state_owner4 open_owner4;
typedef state_owner4 lock_owner4;
The state_owner4 data type is the base type for the open_owner4 Section 3.2.11.1 (open_owner4) and lock_owner4 Section 3.2.11.2 (lock_owner4). NFS4_OPAQUE_LIMIT is defined as 1024.
| TOC |
This structure is used to identify the owner of open state.
| TOC |
This structure is used to identify the owner of file locking state.
| TOC |
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.
| TOC |
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.
| TOC |
enum layouttype4 {
LAYOUT4_NFSV4_1_FILES = 1,
LAYOUT4_OSD2_OBJECTS = 2,
LAYOUT4_BLOCK_VOLUME = 3
};
A layout type specifies the layout being used. The implication is that clients have "layout drivers" that support one or more layout types. The file server advertises the layout types it supports through the fs_layout_type file system attribute (Section 5.13.1 (fs_layout_type)). A client asks for layouts of a particular type in LAYOUTGET, and passes those layouts to its layout driver.
The layouttype4 structure is 32 bits in length. The range represented by the layout type is split into three parts. Type 0x0 is reserved. Types within the range 0x00000001-0x7FFFFFFF are globally unique and are assigned according to the description in Section 22.1 (Defining new layout types); they are maintained by IANA. Types within the range 0x80000000-0xFFFFFFFF are site specific and for "private use" only.
The LAYOUT4_NFSV4_1_FILES enumeration specifies that the NFSv4.1 file layout type is to be used. The LAYOUT4_OSD2_OBJECTS enumeration specifies that the object layout, as defined in [29] (Zelenka, J., Welch, B., and B. Halevy, “Object-based pNFS Operations,” July 2005.), is to be used. Similarly, the LAYOUT4_BLOCK_VOLUME enumeration that the block/volume layout, as defined in [30] (Black, D., “pNFS Block/Volume Layout,” July 2005.), is to be used.
| TOC |
typedef uint32_t deviceid4;
Layout information includes device IDs that specify a storage device through a compact handle. Addressing and type information is obtained with the GETDEVICEINFO operation. A client must not assume that device IDs are valid across metadata server reboots. The device ID is qualified by the layout type and are unique per file system (FSID). See Section 13.2.10 (Device IDs) for more details.
| TOC |
struct device_addr4 {
layouttype4 da_layout_type;
opaque da_addr_body<>;
};
The device address is used to set up a communication channel with the storage device. Different layout types will require different types of structures to define how they communicate with storage devices. The opaque da_addr_body field must be interpreted based on the specified da_layout_type field.
This document defines the device address for the NFSv4.1 file layout ([Comment.7] (need xref)), which identifies a storage device by network IP address and port number. This is sufficient for the clients to communicate with the NFSv4.1 storage devices, and may be sufficient for other layout types as well. Device types for object storage devices and block storage devices (e.g., SCSI volume labels) will be defined by their respective layout specifications.
| TOC |
struct devlist_item4 {
deviceid4 dli_id;
device_addr4 dli_device_addr<>;
};
An array of these values is returned by the GETDEVICELIST operation. They define the set of devices associated with a file system for the layout type specified in the GETDEVICELIST4args.
| TOC |
struct layout_content4 {
layouttype4 loc_type;
opaque loc_body<>;
};
The loc_body field must be interpreted based on the layout type (loc_type). This document defines the loc_body for the NFSv4.1 file layout type is defined; see Section 14.3 (File Layout Data Types) for its definition.
| TOC |
struct layout4 {
offset4 lo_offset;
length4 lo_length;
layoutiomode4 lo_iomode;
layout_content4 lo_content;
};
The layout4 structure defines a layout for a file. The layout type specific data is opaque within lo_content. Since layouts are sub-dividable, the offset and length together with the file's filehandle, the client ID, iomode, and layout type, identifies the layout.
| TOC |
struct layoutupdate4 {
layouttype4 lou_type;
opaque lou_body<>;
};
The layoutupdate4 structure is used by the client to return 'updated' layout information to the metadata server at LAYOUTCOMMIT time. This structure provides a channel to pass layout type specific information (in field lou_body) back to the metadata server. E.g., for block/volume layout types this could include the list of reserved blocks that were written. The contents of the opaque lou_body argument are determined by the layout type and are defined in their context. The NFSv4.1 file-based layout does not use this structure, thus the lou_body field should have a zero length.
| TOC |
struct layouthint4 {
layouttype4 loh_type;
opaque loh_body<>;
};
The layouthint4 structure is used by the client to pass in a hint about the type of layout it would like created for a particular file. It is the structure specified by the layout_hint attribute described in Section 5.13.4 (layout_hint). The metadata server may ignore the hint, or may selectively ignore fields within the hint. This hint should be provided at create time as part of the initial attributes within OPEN. The loh_body field is specific to the type of layout (loh_type). The NFSv4.1 file-based layout uses the nfsv4_1_file_layouthint4 structure as defined in Section 14.3 (File Layout Data Types).
| TOC |
enum layoutiomode4 {
LAYOUTIOMODE4_READ = 1,
LAYOUTIOMODE4_RW = 2,
LAYOUTIOMODE4_ANY = 3
};
The iomode specifies whether the client intends to read or write (with the possibility of reading) the data represented by the layout. The ANY iomode MUST NOT be used for LAYOUTGET, however, it can be used for LAYOUTRETURN and LAYOUTRECALL. The ANY iomode specifies that layouts pertaining to both READ and RW iomodes are being returned or recalled, respectively. The metadata server's use of the iomode may depend on the layout type being used. The storage devices may validate I/O accesses against the iomode and reject invalid accesses.
| TOC |
struct nfs_impl_id4 {
utf8str_cis nii_domain;
utf8str_cs nii_name;
nfstime4 nii_date;
};
This structure is used to identify client and server implementation detail. The nii_domain field is the DNS domain name that the implementer is associated with. The nii_name field is the product name of the implementation and is completely free form. It is recommended that the nii_name be used to distinguish machine architecture, machine platforms, revisions, versions, and patch levels. The nii_date field is the timestamp of when the software instance was published or built.
| TOC |
struct threshold_item4 {
layouttype4 thi_layout_type;
bitmap4 thi_hintset;
opaque thi_hintlist<>;
};
This structure contains a list of hints specific to a layout type for helping the client determine when it should issue I/O directly through the metadata server vs. the data servers. The hint structure consists of the layout type (thi_layout_type), a bitmap (thi_hintset) describing the set of hints supported by the server (they may differ based on the layout type), and a list of hints (thi_hintlist), whose structure is determined by the hintset bitmap. See the mdsthreshold attribute for more details.
The thi_hintset field is a bitmap of the following values:
| name | # | Data Type | Description |
|---|---|---|---|
| threshold4_read_size | 0 | length4 | The file size below which it is recommended to read data through the MDS. |
| threshold4_write_size | 1 | length4 | The file size below which it is recommended to write data through the MDS. |
| threshold4_read_iosize | 2 | length4 | For read I/O sizes below this threshold it is recommended to read data through the MDS |
| threshold4_write_iosize | 3 | length4 | For write I/O sizes below this threshold it is recommended to write data through the MDS |
| TOC |
struct mdsthreshold4 {
threshold_item4 mth_hints<>;
};
This structure holds an array of threshold_item4 structures each of which is valid for a particular layout type. An array is necessary since a server can support multiple layout types for a single file.
| TOC |
The filehandle in the NFS protocol is a per server unique identifier for a file system object. The contents of the filehandle are opaque to the client. Therefore, the server is responsible for translating the filehandle to an internal representation of the file system object.
| TOC |
The operations of the NFS protocol are defined in terms of one or more filehandles. Therefore, the client needs a filehandle to initiate communication with the server. With the NFS version 2 protocol RFC1094 (Nowicki, B., “NFS: Network File System Protocol specification,” March 1989.) [21] and the NFS version 3 protocol RFC1813 (Callaghan, B., Pawlowski, B., and P. Staubach, “NFS Version 3 Protocol Specification,” June 1995.) [22], there exists an ancillary protocol to obtain this first filehandle. The MOUNT protocol, RPC program number 100005, provides the mechanism of translating a string based file system path name to a filehandle which can then be used by the NFS protocols.
The MOUNT protocol has deficiencies in the area of security and use via firewalls. This is one reason that the use of the public filehandle was introduced in RFC2054 (Callaghan, B., “WebNFS Client Specification,” October 1996.) [31] and RFC2055 (Callaghan, B., “WebNFS Server Specification,” October 1996.) [32]. 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.
| TOC |
The first of the special filehandles is the ROOT filehandle. The ROOT filehandle is the "conceptual" root of the file system name space at the NFS server. The client uses or starts with the ROOT filehandle by employing the PUTROOTFH operation. The PUTROOTFH operation instructs the server to set the "current" filehandle to the ROOT of the server's file tree. Once this PUTROOTFH operation is used, the client can then traverse the entirety of the server's file tree with the LOOKUP operation. A complete discussion of the server name space is in the section "NFS Server Name Space".
| TOC |
The second special filehandle is the PUBLIC filehandle. Unlike the ROOT filehandle, the PUBLIC filehandle may be bound or represent an arbitrary file system object at the server. The server is responsible for this binding. It may be that the PUBLIC filehandle and the ROOT filehandle refer to the same file system object. However, it is up to the administrative software at the server and the policies of the server administrator to define the binding of the PUBLIC filehandle and server file system object. The client may not make any assumptions about this binding. The client uses the PUBLIC filehandle via the PUTPUBFH operation.
| TOC |
In the NFS version 2 and 3 protocols, there was one type of filehandle with a single set of semantics. This type of filehandle is termed "persistent" in NFS Version 4. The semantics of a persistent filehandle remain the same as before. A new type of filehandle introduced in NFS Version 4 is the "volatile" filehandle, which attempts to accommodate certain server environments.
The volatile filehandle type was introduced to address server functionality or implementation issues which make correct implementation of a persistent filehandle infeasible. Some server environments do not provide a file system level invariant that can be used to construct a persistent filehandle. The underlying server file system may not provide the invariant or the server's file system programming interfaces may not provide access to the needed invariant. Volatile filehandles may ease the implementation of server functionality such as hierarchical storage management or file system reorganization or migration. However, the volatile filehandle increases the implementation burden for the client.
Since the client will need to handle persistent and volatile filehandles differently, a file attribute is defined which may be used by the client to determine the filehandle types being returned by the server.
| TOC |
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 an octet-by-octet comparison. However, the client MUST NOT otherwise interpret the contents of filehandles. If two filehandles from the same server are equal, they MUST refer to the same file. Servers SHOULD try to maintain a one-to-one correspondence between filehandles and files but this is not required. Clients MUST use filehandle comparisons only to improve performance, not for correct behavior. All clients need to be prepared for situations in which it cannot be determined whether two filehandles denote the same object and in such cases, avoid making invalid assumptions which might cause incorrect behavior. Further discussion of filehandle and attribute comparison in the context of data caching is presented in the section "Data Caching and File Identity".
As an example, in the case that two different path names when traversed at the server terminate at the same file system object, the server SHOULD return the same filehandle for each path. This can 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.
| TOC |
A persistent filehandle is defined as having a fixed value for the lifetime of the file system object to which it refers. Once the server creates the filehandle for a file system object, the server MUST accept the same filehandle for the object for the lifetime of the object. If the server restarts or reboots the NFS server must honor the same filehandle value as it did in the server's previous instantiation. Similarly, if the file system is migrated, the new NFS server must honor the same filehandle as the old NFS server.
The persistent filehandle will be become stale or invalid when the file system object is removed. When the server is presented with a persistent filehandle that refers to a deleted object, it MUST return an error of NFS4ERR_STALE. A filehandle may become stale when the file system containing the object is no longer available. The file system may become unavailable if it exists on removable media and the media is no longer available at the server or the file system in whole has been destroyed or the file system has simply been removed from the server's name space (i.e. unmounted in a UNIX environment).
| TOC |
A volatile filehandle does not share the same longevity characteristics of a persistent filehandle. The server may determine that a volatile filehandle is no longer valid at many different points in time. If the server can definitively determine that a volatile filehandle refers to an object that has been removed, the server should return NFS4ERR_STALE to the client (as is the case for persistent filehandles). In all other cases where the server determines that a volatile filehandle can no longer be used, it should return an error of NFS4ERR_FHEXPIRED.
The mandatory attribute "fh_expire_type" is used by the client to determine what type of filehandle the server is providing for a particular file system. This attribute is a bitmask with the following values:
- FH4_PERSISTENT
- The value of FH4_PERSISTENT is used to indicate a persistent filehandle, which is valid until the object is removed from the file system. The server will not return NFS4ERR_FHEXPIRED for this filehandle. FH4_PERSISTENT is defined as a value in which none of the bits specified below are set.
- FH4_VOLATILE_ANY
- The filehandle may expire at any time, except as specifically excluded (i.e. FH4_NO_EXPIRE_WITH_OPEN).
- FH4_NOEXPIRE_WITH_OPEN
- May only be set when FH4_VOLATILE_ANY is set. If this bit is set, then the meaning of FH4_VOLATILE_ANY is qualified to exclude any expiration of the filehandle when it is open.
- FH4_VOL_MIGRATION
- The filehandle will expire as a result of a file system transition (migration or replication), in those case in which the continuity of filehandle use is not specified by handle class information within the fs_locations_info attribute. When this bit is set, clients without access to fs_locations_info information should assume filehandles will expire on file system transitions.
- FH4_VOL_RENAME
- The filehandle will expire during rename. This includes a rename by the requesting client or a rename by any other client. If FH4_VOL_ANY is set, FH4_VOL_RENAME is redundant.
Servers which provide volatile filehandles that may expire while open (i.e. if FH4_VOL_MIGRATION or FH4_VOL_RENAME is set or if FH4_VOLATILE_ANY is set and FH4_NOEXPIRE_WITH_OPEN not set), should deny a RENAME or REMOVE that would affect an OPEN file of any of the components leading to the OPEN file. In addition, the server should deny all RENAME or REMOVE requests during the grace period upon server restart.
Servers which provide volatile filehandles that may expire while open require special care as regards handling of RENAMESs and REMOVEs. This situation can arise if FH4_VOL_MIGRATION or FH4_VOL_RENAME is set, if FH4_VOLATILE_ANY is set and FH4_NOEXPIRE_WITH_OPEN not set, or if a non-readonly file system has a transition target in a different handle class. In these cases, the server should deny a RENAME or REMOVE that would affect an OPEN file of any of the components leading to the OPEN file. In addition, the server should deny all RENAME or REMOVE requests during the grace period, in order to make sure that reclaims of files where filehandles may have expired do not do a reclaim for the wrong file.
Volatile filehandles are especialy suitable for implementation of the pseudo file systems used to bridge exports. See Section 7.5 (Filehandle Volatility) for a discussion of this.
| TOC |
A volatile filehandle, while opaque to the client could contain:
[volatile bit = 1 | server boot time | slot | generation number]
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.
| TOC |
If possible, the client SHOULD recover from the receipt of an NFS4ERR_FHEXPIRED error. The client must take on additional responsibility so that it may prepare itself to recover from the expiration of a volatile filehandle. If the server returns persistent filehandles, the client does not need these additional steps.
For volatile filehandles, most commonly the client will need to store the component names leading up to and including the file system object in question. With these names, the client should be able to recover by finding a filehandle in the name space that is still available or by starting at the root of the server's file system name space.
If the expired filehandle refers to an object that has been removed from the file system, obviously the client will not be able to recover from the expired filehandle.
It is also possible that the expired filehandle refers to a file that has been renamed. If the file was renamed by another client, again it is possible that the original client will not be able to recover. However, in the case that the client itself is renaming the file and the file is open, it is possible that the client may be able to recover. The client can determine the new path name based on the processing of the rename request. The client can then regenerate the new filehandle based on the new path name. The client could also use the compound operation mechanism to construct a set of operations like:
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.
| TOC |
To meet the requirements of extensibility and increased interoperability with non-UNIX platforms, attributes must be handled in a flexible manner. The NFS version 3 fattr3 structure contains a fixed list of attributes that not all clients and servers are able to support or care about. The fattr3 structure can not be extended as new needs arise and it provides no way to indicate non-support. With the NFS version 4 protocol, the client is able query what attributes the server supports and construct requests with only those supported attributes (or a subset thereof).
To this end, attributes are divided into three groups: mandatory, recommended, and named. Both mandatory and recommended attributes are supported in the NFS version 4 protocol by a specific and well-defined encoding and are identified by number. They are requested by setting a bit in the bit vector sent in the GETATTR request; the server response includes a bit vector to list what attributes were returned in the response. New mandatory or recommended attributes may be added to the NFS protocol between major revisions by publishing a standards-track RFC which allocates a new attribute number value and defines the encoding for the attribute. See the section "Minor Versioning" for further discussion.
Named attributes are accessed by the new OPENATTR operation, which accesses a hidden directory of attributes associated with a file system object. OPENATTR takes a filehandle for the object and returns the filehandle for the attribute hierarchy. The filehandle for the named attributes is a directory object accessible by LOOKUP or READDIR and contains files whose names represent the named attributes and whose data bytes are the value of the attribute. For example:
| LOOKUP | "foo" | ; look up file |
| GETATTR | attrbits | |
| OPENATTR | ; access foo's named attributes | |
| LOOKUP | "x11icon" | ; look up specific attribute |
| READ | 0,4096 | ; read stream of bytes |
Named attributes are intended for data needed by applications rather than by an NFS client implementation. NFS implementors are strongly encouraged to define their new attributes as recommended attributes by bringing them to the IETF standards-track process.
The set of attributes which are classified as mandatory is deliberately small since servers must do whatever it takes to support them. A server should support as many of the recommended attributes as possible but by their definition, the server is not required to support all of them. Attributes are deemed mandatory if the data is both needed by a large number of clients and is not otherwise reasonably computable by the client when support is not provided on the server.
Note that the hidden directory returned by OPENATTR is a convenience for protocol processing. The client should not make any assumptions about the server's implementation of named attributes and whether the underlying file system at the server has a named attribute directory or not. Therefore, operations such as SETATTR and GETATTR on the named attribute directory are undefined.
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These MUST be supported by every NFS version 4 client and server in order to ensure a minimum level of interoperability. The server must store and return these attributes and the client must be able to function with an attribute set limited to these attributes. With just the mandatory attributes some client functionality may be impaired or limited in some ways. A client may ask for any of these attributes to be returned by setting a bit in the GETATTR request and the server must return their value.
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These attributes are understood well enough to warrant support in the NFS version 4 protocol. However, they may not be supported on all clients and servers. A client may ask for any of these attributes to be returned by setting a bit in the GETATTR request but must handle the case where the server does not return them. A client may ask for the set of attributes the server supports and should not request attributes the server does not support. A server should be tolerant of requests for unsupported attributes and simply not return them rather than considering the request an error. It is expected that servers will support all attributes they comfortably can and only fail to support attributes which are difficult to support in their operating environments. A server should provide attributes whenever they don't have to "tell lies" to the client. For example, a file modification time should be either an accurate time or should not be supported by the server. This will not always be comfortable to clients but the client is better positioned decide whether and how to fabricate or construct an attribute or whether to do without the attribute.
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These attributes are not supported by direct encoding in the NFS Version 4 protocol but are accessed by string names rather than numbers and correspond to an uninterpreted stream of bytes which are stored with the file system object. The name space for these attributes may be accessed by using the OPENATTR operation. The OPENATTR operation returns a filehandle for a virtual "attribute directory" and further perusal of the name space may be done using READDIR and LOOKUP operations on this filehandle. Named attributes may then be examined or changed by normal READ and WRITE and CREATE operations on the filehandles returned from READDIR and LOOKUP. Named attributes may have attributes.
It is recommended that servers support arbitrary named attributes. A client should not depend on the ability to store any named attributes in the server's file system. If a server does support named attributes, a client which is also able to handle them should be able to copy a file's data and meta-data with complete transparency from one location to another; this would imply that names allowed for regular directory entries are valid for named attribute names as well.
Names of attributes will not be controlled by this document or other IETF standards track documents. See the section "IANA Considerations" for further discussion.
| TOC |
Each of the Mandatory and Recommended attributes can be classified in one of three categories: per server, per file system, or per file system object. Note that it is possible that some per file system attributes may vary within the file system. See the "homogeneous" attribute for its definition. Note that the attributes time_access_set and time_modify_set are not listed in this section because they are write-only attributes corresponding to time_access and time_modify, and are used in a special instance of SETATTR.
lease_time
supp_attr, fh_expire_type, link_support, symlink_support, unique_handles, aclsupport, cansettime, case_insensitive, case_preserving, chown_restricted, files_avail, files_free, files_total, fs_locations, homogeneous, maxfilesize, maxname, maxread, maxwrite, no_trunc, space_avail, space_free, space_total, time_delta, fs_status, fs_layout_type, fs_locations_info
type, change, size, named_attr, fsid, rdattr_error, filehandle, ACL, archive, fileid, hidden, maxlink, mimetype, mode, numlinks, owner, owner_group, rawdev, space_used, system, time_access, time_backup, time_create, time_metadata, time_modify, mounted_on_fileid, dir_notif_delay, dirent_notif_delay, dacl, sacl, layout_type, layout_hint, layout_blksize, layout_alignment, mdsthreshold, retention_get, retention_set, retentevt_get, retentevt_set, retention_hold, mode_set_masked
For quota_avail_hard, quota_avail_soft, and quota_used see their definitions below for the appropriate classification.
| TOC |
| name | # | Data Type | Access | Description |
|---|---|---|---|---|
| supp_attr | 0 | bitmap | READ | The bit vector which would retrieve all mandatory and recommended attributes that are supported for this object. The scope of this attribute applies to all objects with a matching fsid. |
| type | 1 | nfs_ftype4 | READ | The type of the object (file, directory, symlink, etc.) |
| fh_expire_type | 2 | uint32 | READ | Server uses this to specify filehandle expiration behavior to the client. See the section "Filehandles" for additional description. |
| change | 3 | uint64 | READ | A value created by the server that the client can use to determine if file data, directory contents or attributes of the object have been modified. The server may return the object's time_metadata attribute for this attribute's value but only if the file system object can not be updated more frequently than the resolution of time_metadata. |
| size | 4 | uint64 | R/W | The size of the object in bytes. |
| link_support | 5 | bool | READ | True, if the object's file system supports hard links. |
| symlink_support | 6 | bool | READ | True, if the object's file system supports symbolic links. |
| named_attr | 7 | bool | READ | True, if this object has named attributes. In other words, object has a non-empty named attribute directory. |
| fsid | 8 | fsid4 | READ | Unique file system identifier for the file system holding this object. fsid contains major and minor components each of which are uint64. |
| unique_handles | 9 | bool | READ | True, if two distinct filehandles guaranteed to refer to two different file system objects. |
| lease_time | 10 | nfs_lease4 | READ | Duration of leases at server in seconds. |
| rdattr_error | 11 | enum | READ | Error returned from getattr during readdir. |
| filehandle | 19 | nfs_fh4 | READ | The filehandle of this object (primarily for readdir requests). |
| TOC |
| name | # | Data Type | Access | Description |
|---|---|---|---|---|
| ACL | 12 | nfsace4<> | R/W | The access control list for the object. |
| aclsupport | 13 | uint32 | READ | Indicates what types of ACLs are supported on the current file system. |
| archive | 14 | bool | R/W | True, if this file has been archived since the time of last modification (deprecated in favor of time_backup). |
| cansettime | 15 | bool | READ | True, if the server able to change the times for a file system object as specified in a SETATTR operation. |
| case_insensitive | 16 | bool | READ | True, if filename comparisons on this file system are case insensitive. |
| case_preserving | 17 | bool | READ | True, if filename case on this file system are preserved. |
| chown_restricted | 18 | bool | READ | If TRUE, the server will reject any request to change either the owner or the group associated with a file if the caller is not a privileged user (for example, "root" in UNIX operating environments or in Windows 2000 the "Take Ownership" privilege). |
| dacl | 58 | nfsacl41 | R/W | Access Control List used for determining access to file system objects. |
| dir_notif_delay | 56 | nfstime4 | READ | notification delays on directory attributes |
| dirent_ notif_delay | 57 | nfstime4 | READ | notification delays on child attributes |
| fileid | 20 | uint64 | READ | A number uniquely identifying the file within the file system. |
| files_avail | 21 | uint64 | READ | File slots available to this user on the file system containing this object - this should be the smallest relevant limit. |
| files_free | 22 | uint64 | READ | Free file slots on the file system containing this object - this should be the smallest relevant limit. |
| files_total | 23 | uint64 | READ | Total file slots on the file system containing this object. |
| fs_absent | 60 | bool | READ | Is current file system present or absent. |
| fs_layout_type | 62 | layouttype4<> | READ | Layout types available for the file system. |
| fs_locations | 24 | fs_locations | READ | Locations where this file system may be found. If the server returns NFS4ERR_MOVED as an error, this attribute MUST be supported. |
| fs_locations_info | 67 | READ | Full function file system location. | |
| fs_status | 61 | fs4_status | READ | Generic file system type information. |
| hidden | 25 | bool | R/W | True, if the file is considered hidden with respect to the Windows API? |
| homogeneous | 26 | bool | READ | True, if this object's file system is homogeneous, i.e. are per file system attributes the same for all file system's objects. |
| layout_alignment | 66 | uint32_t | READ | Preferred alignment for layout related I/O. |
| layout_blksize | 65 | uint32_t | READ | Preferred block size for layout related I/O. |
| layout_hint | 63 | layouthint4 | WRITE | Client specified hint for file layout. |
| layout_type | 64 | layouttype4<> | READ | Layout types available for the file. |
| maxfilesize | 27 | uint64 | READ | Maximum supported file size for the file system of this object. |
| maxlink | 28 | uint32 | READ | Maximum number of links for this object. |
| maxname | 29 | uint32 | READ | Maximum filename size supported for this object. |
| maxread | 30 | uint64 | READ | Maximum read size supported for this object. |
| maxwrite | 31 | uint64 | READ | Maximum write size supported for this object. This attribute SHOULD be supported if the file is writable. Lack of this attribute can lead to the client either wasting bandwidth or not receiving the best performance. |
| mdsthreshold | 68 | mdsthreshold4 | READ | Hint to client as to when to write through the pnfs metadata server. |
| mimetype | 32 | utf8<> | R/W | MIME body type/subtype of this object. |
| mode | 33 | mode4 | R/W | UNIX-style mode including permission bits for this object. |
| mode_set_masked | 74 | mode_masked4 | WRITE | Allows setting or resetting a subset of the bits in a UNIX-style mode |
| mounted_on_fileid | 55 | uint64 | READ | Like fileid, but if the target filehandle is the root of a file system return the fileid of the underlying directory. |
| no_trunc | 34 | bool | READ | True, if a name longer than name_max is used, an error be returned and name is not truncated. |
| numlinks | 35 | uint32 | READ | Number of hard links to this object. |
| owner | 36 | utf8<> | R/W | The string name of the owner of this object. |
| owner_group | 37 | utf8<> | R/W | The string name of the group ownership of this object. |
| quota_avail_hard | 38 | uint64 | READ | For definition see "Quota Attributes" section below. |
| quota_avail_soft | 39 | uint64 | READ | For definition see "Quota Attributes" section below. |
| quota_used | 40 | uint64 | READ | For definition see "Quota Attributes" section below. |
| rawdev | 41 | specdata4 | READ | Raw device identifier. UNIX device major/minor node information. If the value of type is not NF4BLK or NF4CHR, the value return SHOULD NOT be considered useful. |
| retentevt_get | 71 | retention_get4 | READ | Get the event-based retention duration, and if enabled, the event-based retention begin time of the file object. GETATTR use only. |
| retentevt_set | 72 | retention_set4 | WRITE | Set the event-based retention duration, and optionally enable event-based retention on the file object. SETATTR use only. |
| retention_get | 69 | retention_get4 | READ | Get the retention duration, and if enabled, the retention begin time of the file object. GETATTR use only. |
| retention_hold | 73 | uint64_t | R/W | Get or set administrative retention holds, one hold per bit position. |
| retention_set | 70 | retention_set4 | WRITE | Set the retention duration, and optionally enable retention on the file object. SETATTR use only. |
| sacl | 59 | nfsacl41 | R/W | Access Control List used for auditing access to file system objects. |
| space_avail | 42 | uint64 | READ | Disk space in bytes available to this user on the file system containing this object - this should be the smallest relevant limit. |
| space_free | 43 | uint64 | READ | Free disk space in bytes on the file system containing this object - this should be the smallest relevant limit. |
| space_total | 44 | uint64 | READ | Total disk space in bytes on the file system containing this object. |
| space_used | 45 | uint64 | READ | Number of file system bytes allocated to this object. |
| system | 46 | bool | R/W | True, if this file is a "system" file with respect to the Windows API? |
| time_access | 47 | nfstime4 | READ | The time of last access to the object by a read that was satisfied by the server. |
| time_access_set | 48 | settime4 | WRITE | Set the time of last access to the object. SETATTR use only. |
| time_backup | 49 | nfstime4 | R/W | The time of last backup of the object. |
| time_create | 50 | nfstime4 | R/W | The time of creation of the object. This attribute does not have any relation to the traditional UNIX file attribute "ctime" or "change time". |
| time_delta | 51 | nfstime4 | READ | Smallest useful server time granularity. |
| time_metadata | 52 | nfstime4 | READ | The time of last meta-data modification of the object. |
| time_modify | 53 | nfstime4 | READ | The time of last modification to the object. |
| time_modify_set | 54 | settime4 | WRITE | Set the time of last modification to the object. SETATTR use only. |
| TOC |
As defined above, the time_access attribute represents the time of last access to the object by a read that was satisfied by the server. The notion of what is an "access" depends on server's operating environment and/or the server's file system semantics. For example, for servers obeying POSIX semantics, time_access would be updated only by the READLINK, READ, and READDIR operations and not any of the operations that modify the content of the object. Of course, setting the corresponding time_access_set attribute is another way to modify the time_access attribute.
Whenever the file object resides on a writable file system, the server should make best efforts to record time_access into stable storage. However, to mitigate the performance effects of doing so, and most especially whenever the server is satisfying the read of the object's content from its cache, the server MAY cache access time updates and lazily write them to stable storage. It is also acceptable to give administrators of the server the option to disable time_access updates.
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The recommended attributes "owner" and "owner_group" (and also users and groups within the "acl" attribute) are represented in terms of a UTF-8 string. To avoid a representation that is tied to a particular underlying implementation at the client or server, the use of the UTF-8 string has been chosen. Note that section 6.1 of RFC2624 (Shepler, S., “NFS Version 4 Design Considerations,” June 1999.) [33] provides additional rationale. It is expected that the client and server will have their own local representation of owner and owner_group that is used for local storage or presentation to the end user. Therefore, it is expected that when these attributes are transferred between the client and server that the local representation is translated to a syntax of the form "user@dns_domain". This will allow for a client and server that do not use the same local representation the ability to translate to a common syntax that can be interpreted by both.
Similarly, security principals may be represented in different ways by different security mechanisms. Servers normally translate these representations into a common format, generally that used by local storage, to serve as a means of identifying the users corresponding to these security principals. When these local identifiers are translated to the form of the owner attribute, associated with files created by such principals they identify, in a common format, the users associated with each corresponding set of security principals.
The translation used to interpret owner and group strings is not specified as part of the protocol. This allows various solutions to be employed. For example, a local translation table may be consulted that maps between a numeric id to the user@dns_domain syntax. A name service may also be used to accomplish the translation. A server may provide a more general service, not limited by any particular translation (which would only translate a limited set of possible strings) by storing the owner and owner_group attributes in local storage without any translation or it may augment a translation method by storing the entire string for attributes for which no translation is available while using the local representation for those cases in which a translation is available.
Servers that do not provide support for all possible values of the owner and owner_group attributes, should return an error (NFS4ERR_BADOWNER) when a string is presented that has no translation, as the value to be set for a SETATTR of the owner, owner_group, or acl attributes. When a server does accept an owner or owner_group value as valid on a SETATTR (and similarly for the owner and group strings in an acl), it is promising to return that same string when a corresponding GETATTR is done. Configuration changes and ill-constructed name translations (those that contain aliasing) may make that promise impossible to honor. Servers should make appropriate efforts to avoid a situation in which these attributes have their values changed when no real change to ownership has occurred.
The "dns_domain" portion of the owner string is meant to be a DNS domain name. For example, user@ietf.org. Servers should accept as valid a set of users for at least one domain. A server may treat other domains as having no valid translations. A more general service is provided when a server is capable of accepting users for multiple domains, or for all domains, subject to security constraints.
In the case where there is no translation available to the client or server, the attribute value must be constructed without the "@". Therefore, the absence of the @ from the owner or owner_group attribute signifies that no translation was available at the sender and that the receiver of the attribute should not use that string as a basis for translation into its own internal format. Even though the attribute value can not be translated, it may still be useful. In the case of a client, the attribute string may be used for local display of ownership.
To provide a greater degree of compatibility with previous versions of NFS (i.e. v2 and v3), which identified users and groups by 32-bit unsigned uid's and gid's, owner and group strings that consist of decimal numeric values with no leading zeros can be given a special interpretation by clients and servers which choose to provide such support. The receiver may treat such a user or group string as representing the same user as would be represented by a v2/v3 uid or gid having the corresponding numeric value. A server is not obligated to accept such a string, but may return an NFS4ERR_BADOWNER instead. To avoid this mechanism being used to subvert user and group translation, so that a client might pass all of the owners and groups in numeric form, a server SHOULD return an NFS4ERR_BADOWNER error when there is a valid translation for the user or owner designated in this way. In that case, the client must use the appropriate name@domain string and not the special form for compatibility.
The owner string "nobody" may be used to designate an anonymous user, which will be associated with a file created by a security principal that cannot be mapped through normal means to the owner attribute.
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With respect to the case_insensitive and case_preserving attributes, each UCS-4 character (which UTF-8 encodes) has a "long descriptive name" RFC1345 (Simonsen, K., “Character Mnemonics and Character Sets,” June 1992.) [34] which may or may not included the word "CAPITAL" or "SMALL". The presence of SMALL or CAPITAL allows an NFS server to implement unambiguous and efficient table driven mappings for case insensitive comparisons, and non-case-preserving storage. For general character handling and internationalization issues, see the section "Internationalization".
| TOC |
For the attributes related to file system quotas, the following definitions apply:
- quota_avail_soft
- The value in bytes which represents the amount of additional disk space that can be allocated to this file or directory before the user may reasonably be warned. It is understood that this space may be consumed by allocations to other files or directories though there is a rule as to which other files or directories.
- quota_avail_hard
- The value in bytes which represent the amount of additional disk space beyond the current allocation that can be allocated to this file or directory before further allocations will be refused. It is understood that this space may be consumed by allocations to other files or directories.
- quota_used
- The value in bytes which represent the amount of disc space used by this file or directory and possibly a number of other similar files or directories, where the set of "similar" meets at least the criterion that allocating space to any file or directory in the set will reduce the "quota_avail_hard" of every other file or directory in the set.
Note that there may be a number of distinct but overlapping sets of files or directories for which a quota_used value is maintained. E.g. "all files with a given owner", "all files with a given group owner". etc.
The server is at liberty to choose any of those sets but should do so in a repeatable way. The rule may be configured per file system or may be "choose the set with the smallest quota".
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UNIX-based operating environments connect a file system into the namespace by connecting (mounting) the file system onto the existing file object (the mount point, usually a directory) of an existing file system. When the mount point's parent directory is read via an API like readdir(), the return results are directory entries, each with a component name and a fileid. The fileid of the mount point's directory entry will be different from the fileid that the stat() system call returns. The stat() system call is returning the fileid of the root of the mounted file system, whereas readdir() is returning the fileid stat() would have returned before any file systems were mounted on the mount point.
Unlike NFS version 3, NFS version 4 allows a client's LOOKUP request to cross other file systems. The client detects the file system crossing whenever the filehandle argument of LOOKUP has an fsid attribute different from that of the filehandle returned by LOOKUP. A UNIX-based client will consider this a "mount point crossing". UNIX has a legacy scheme for allowing a process to determine its current working directory. This relies on readdir() of a mount point's parent and stat() of the mount point returning fileids as previously described. The mounted_on_fileid attribute corresponds to the fileid that readdir() would have returned as described previously.
While the NFS version 4 client could simply fabricate a fileid corresponding to what mounted_on_fileid provides (and if the server does not support mounted_on_fileid, the client has no choice), there is a risk that the client will generate a fileid that conflicts with one that is already assigned to another object in the file system. Instead, if the server can provide the mounted_on_fileid, the potential for client operational problems in this area is eliminated.
If the server detects that there is no mounted point at the target file object, then the value for mounted_on_fileid that it returns is the same as that of the fileid attribute.
The mounted_on_fileid attribute is RECOMMENDED, so the server SHOULD provide it if possible, and for a UNIX-based server, this is straightforward. Usually, mounted_on_fileid will be requested during a READDIR operation, in which case it is trivial (at least for UNIX-based servers) to return mounted_on_fileid since it is equal to the fileid of a directory entry returned by readdir(). If mounted_on_fileid is requested in a GETATTR operation, the server should obey an invariant that has it returning a value that is equal to the file object's entry in the object's parent directory, i.e. what readdir() would have returned. Some operating environments allow a series of two or more file systems to be mounted onto a single mount point. In this case, for the server to obey the aforementioned invariant, it will need to find the base mount point, and not the intermediate mount points.
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As described in Section 18.39 (Operation 46: GET_DIR_DELEGATION - Get a directory delegation), the client can request a minimum delay for notifications of changes to attributes, but the server is free ignore what the client requests. The client can determine in advance what notification delays the server will accept by issuing a GETATTR for either or both of two directory notification attributes. When the client calls the GET_DIR_DELEGATION operation and asks^M for attribute change notifications, it should request^M notification delays that are no less than the values in the^M server-provided attributes.
| TOC |
The dir_notify_delay attribute is the minimum number of seconds the server will delay before notifying the client of a change to the directory's attributes.
| TOC |
The dirent_notif_delay attribute is the minimum number of seconds the server will delay before notifying the client of a change to a file object that has an entry in the directory.
| TOC |
| TOC |
The fs_layout_type attribute (data type layouttype4, see Section 3.2.14 (layouttype4)) applies to a file system and indicates what layout types are supported by the file system. This attribute is expected be queried when a client encounters a new fsid. This attribute is used by the client to determine if it supports the layout type.
| TOC |
The layout_alignment attribute indicates the preferred alignment for I/O to files on the file system the client has layouts for. Where possible, the client should issue READ and WRITE operations with offsets are whole multiples of the layout_alignment attribute.
| TOC |
The layout_blksize attribute indicates the preferred block size for I/O to files on the file system the client has layouts for. Where possible, the client should issue READ operations with a count argument that is a whole multiple of layout_blksize, and WRITE operations with a data argument of size that is a whole multiple of layout_blksize.
| TOC |
The layout_hint attribute (data type layouthint4, see Section 3.2.21 (layouthint4)) may be set on newly created files to influence the metadata server's choice for the file's layout. It is suggested that this attribute is set as one of the initial attributes within the OPEN call. The metadata server may ignore this attribute. This attribute is a sub-set of the layout structure returned by LAYOUTGET. For example, instead of specifying particular devices, this would be used to suggest the stripe width of a file. It is up to the server implementation to determine which fields within the layout it uses.
| TOC |
This attribute indicates the particular layout type(s) used for a file. This is for informational purposes only. The client needs to use the LAYOUTGET operation in order to get enough information (e.g., specific device information) in order to perform I/O.
| TOC |
This attribute is a server provided hint used to communicate to the client when it is more efficient to issue read and write requests to the metadata server or the data server. The two types of thresholds described are file size thresholds and I/O size thresholds. If a file's size is smaller than the file size threshold, data accesses should be issued to the metadata server. If an I/O is below the I/O size threshold, the I/O should be issued to the metadata server. As defined, each threshold type is specified separately for read and write.
The server may provide both types of thresholds for a file. If both file size and I/O size are provided, the client should exceed both thresholds before issuing its read or write requests to the data server. Alternatively, if only one of the specified thresholds is exceeded, the I/O requests are issued to the metadata server.
For each threshold type, a value of 0 indicates no read or write should be issued to the metadata server, while a value of all 1s indicates all reads or writes should be issued to the metadata server.
The attribute is available on a per filehandle basis. If the current filehandle refers to a non-pNFS file or directory, the metadata server should return an attribute that is representative of the filehandle's file system. It is suggested that this attribute is queried as part of the OPEN operation. Due to dynamic system changes, the client should not assume that the attribute will remain constant for any specific time period, thus it should be periodically refreshed.
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Retention is a concept whereby a file object can be placed in an immutable, undeletable, unrenamable state for a fixed or infinite duration of time. Once in this "retained" state, the file cannot be moved out of the state until the duration of retention has been reached.
When retention is enabled, retention MUST extend to the data of the file, and the name of file. The server MAY extend retention any other property of the file, including any subset of mandatory, recommended, and named attributes, with the exceptions noted in this section.
Servers MAY support or not support retention on any file object type.
There are five retention attributes:
const RET4_DURATION_INFINITE = 0xffffffffffffffff;
struct retention_get4 {
uint64_t rg_duration;
nfstime4 rg_begin_time<1>;
};
struct retention_set4 {
bool rs_enable;
uint64_t rs_duration<1>;
};
| TOC |
Access Control Lists (ACLs) are file attributes that specify fine grained access control. This chapter covers the "acl", "dacl", "sacl", "aclsupport", "mode", "mode_set_masked" file attributes, and their interactions. Note that file attributes may apply to any file system objects.
| TOC |
ACLs and modes represent two well established but different models for specifying permissions. This chapter specifies requirements that attempt to meet the following goals:
| TOC |
| TOC |
The NFS version 4 ACL attributes contain an array of access control entries (ACEs). Although the client can read and write the acl attribute, the server is responsible for using the ACL to perform access control. The client can use the OPEN or ACCESS operations to check access without modifying or reading data or metadata.
The NFS ACE 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 who;
};
To determine if a request succeeds, the server processes each nfsace4 entry in order. Only ACEs which have a "who" that matches the requester are considered. Each ACE is processed until all of the bits of the requester's access have been ALLOWED. Once a bit (see below) has been ALLOWED by an ACCESS_ALLOWED_ACE, it is no longer considered in the processing of later ACEs. If an ACCESS_DENIED_ACE is encountered where the requester's access still has unALLOWED bits in common with the "access_mask" of the ACE, the request is denied. When the ACL is fully processed, if there are bits in the requester's mask that have not been ALLOWED or DENIED, access is denied.
Unlike the ALLOW and DENY ACE types, the ALARM and AUDIT ACE types do not affect a requester's access, and instead are for triggering events as a result of a requester's access attempt. Therefore, AUDIT and ALARM ACEs are processed only after processing ALLOW and DENY ACEs.
The NFS version 4 ACL model is quite rich. Some server platforms may provide access control functionality that goes beyond the UNIX-style mode attribute, but which is not as rich as the NFS ACL model. So that users can take advantage of this more limited functionality, the server may indicate that it supports ACLs as long as it follows the guidelines for mapping between its ACL model and the NFS version 4 ACL model.
The situation is complicated by the fact that a server may have multiple modules that enforce ACLs. For example, the enforcement for NFS version 4 access may be different from, 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 the file more secure than it really is.
| TOC |
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;
Only the ALLOWED and DENIED bits types may be used in the dacl attribute, and only the AUDIT and ALARM bits may be used in the sacl attribute. All four are permitted in the acl attribute.
| Value | Abbreviation | Description |
|---|---|---|
| ACE4_ACCESS_ALLOWED_ACE_TYPE | ALLOW | Explicitly grants the access defined in acemask4 to the file or directory. |
| ACE4_ACCESS_DENIED_ACE_TYPE | DENY | Explicitly denies the access defined in acemask4 to the file or directory. |
| ACE4_SYSTEM_AUDIT_ACE_TYPE | AUDIT | LOG (system dependent) any access attempt to a file or directory which uses any of the access methods specified in acemask4. |
| ACE4_SYSTEM_ALARM_ACE_TYPE | ALARM | Generate a system ALARM (system dependent) when any access attempt is made to a file or directory for the access methods specified in acemask4. |
The "Abbreviation" column denotes how the types will be referred to throughout the rest of this document.
| TOC |
A server need not support all of the above ACE types. The bitmask constants used to represent the above definitions within the aclsupport attribute are as follows:
const ACL4_SUPPORT_ALLOW_ACL = 0x00000001;
const ACL4_SUPPORT_DENY_ACL = 0x00000002;
const ACL4_SUPPORT_AUDIT_ACL = 0x00000004;
const ACL4_SUPPORT_ALARM_ACL = 0x00000008;
Servers which support either the ALLOW or DENY ACE type 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.
Support for any of the ACL attributes is optional. However, a server that supports either of the new ACL attributes (dacl or sacl) must allow use of the new ACL attributes to access all of the ACE types which it supports. In more detail: if such a server supports ALLOW or DENY ACEs, then it must support the dacl attribute, and if it supports AUDIT or ALARM ACEs, then it must support the sacl attribute.
| TOC |
The bitmask constants used for the access mask field are as follows:
const ACE4_READ_DATA = 0x00000001;
const ACE4_LIST_DIRECTORY = 0x00000001;
const ACE4_WRITE_DATA = 0x00000002;
const ACE4_ADD_FILE = 0x00000002;
const ACE4_APPEND_DATA = 0x00000004;
const ACE4_ADD_SUBDIRECTORY = 0x00000004;
const ACE4_READ_NAMED_ATTRS = 0x00000008;
const ACE4_WRITE_NAMED_ATTRS = 0x00000010;
const ACE4_EXECUTE = 0x00000020;
const ACE4_TRAVERSE = 0x00000020;
const ACE4_DELETE_CHILD = 0x00000040;
const ACE4_READ_ATTRIBUTES = 0x00000080;
const ACE4_WRITE_ATTRIBUTES = 0x00000100;
const ACE4_WRITE_RETENTION = 0x00000200;
const ACE4_WRITE_RETENTION_HOLD = 0x00000400;
const ACE4_DELETE = 0x00010000;
const ACE4_READ_ACL = 0x00020000;
const ACE4_WRITE_ACL = 0x00040000;
const ACE4_WRITE_OWNER = 0x00080000;
const ACE4_SYNCHRONIZE = 0x00100000;
Note that some masks have coincident values, for example, ACE4_READ_DATA and ACE4_LIST_DIRECTORY. The mask entries ACE4_LIST_DIRECTORY, ACE4_ADD_SUBDIRECTORY, and ACE4_TRAVERSE are intended to be used with directory objects, while ACE4_READ_DATA, ACE4_WRITE_DATA, and ACE4_EXECUTE are intended to be used with non-directory objects.
| TOC |
ACE4_READ_DATA
Operation(s) affected:
READ
OPEN
Discussion:
Permission to read the data of the file.
Servers SHOULD allow a user the ability to read the data
of the file when only the ACE4_EXECUTE access mask bit is
allowed.
ACE4_LIST_DIRECTORY
Operation(s) affected:
READDIR
Discussion:
Permission to list the contents of a directory.
ACE4_WRITE_DATA
Operation(s) affected:
WRITE
OPEN
SETATTR of size
Discussion:
Permission to modify a file's data.
ACE4_ADD_FILE
Operation(s) affected:
CREATE
LINK
OPEN
RENAME
Discussion:
Permission to add a new file in a directory. The CREATE
operation is affected when nfs_ftype4 is NF4LNK, NF4BLK,
NF4CHR, NF4SOCK, or NF4FIFO. (NF4DIR is not listed because
it is covered by ACE4_ADD_SUBDIRECTORY.) OPEN is affected
when used to create a regular file. LINK and RENAME are
always affected.
ACE4_APPEND_DATA
Operation(s) affected:
WRITE
OPEN
SETATTR of size
Discussion:
The ability to modify a file's data, but only starting at
EOF. This allows for the notion of append-only files, by
allowing ACE4_APPEND_DATA and denying ACE4_WRITE_DATA to
the same user or group. If a file has an ACL such as the
one described above and a WRITE request is made for
somewhere other than EOF, the server SHOULD return
NFS4ERR_ACCESS.
ACE4_ADD_SUBDIRECTORY
Operation(s) affected:
CREATE
RENAME
Discussion:
Permission to create a subdirectory in a directory. The
CREATE operation is 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 named attributes of a file or to
lookup the named attributes directory. OPENATTR is
affected when it is not used to create a named attribute
directory. This is when 1.) createdir is TRUE, but a
named attribute directory already exists, or 2.) createdir
is FALSE.
ACE4_WRITE_NAMED_ATTRS
Operation(s) affected:
OPENATTR
Discussion:
Permission to write the named attributes of a file or
to create a named attribute directory. OPENATTR is
affected when it is used to create a named attribute
directory. This is when createdir is TRUE and no named
attribute directory exists. The ability to check whether
or not a named attribute directory exists depends on the
ability to look it up, therefore, users also need the
ACE4_READ_NAMED_ATTRS permission in order to create a
named attribute directory.
ACE4_EXECUTE
Operation(s) affected:
READ
OPEN
Discussion:
Permission to execute a file.
Servers SHOULD allow a user the ability to read the data
of the file when only the ACE4_EXECUTE access mask bit is
allowed. This is because there is no way to execute a
file without reading the contents. Though a server may
treat ACE4_EXECUTE and ACE4_READ_DATA bits identically
when deciding to permit a READ operation, it SHOULD still
allow the two bits to be set independently in ACLs, and
MUST distinguish between them when replying to ACCESS
operations. In particular, servers SHOULD NOT silently
turn on one of the two bits when the other is set, as
that would make it impossible for the client to correctly
enforce the distinction between read and execute
permissions.
As an example, following a SETATTR of the following ACL:
nfsuser:ACE4_EXECUTE:ALLOW
A subsequent GETATTR of ACL for that file SHOULD return:
nfsuser:ACE4_EXECUTE:ALLOW
Rather than:
nfsuser:ACE4_EXECUTE/ACE4_READ_DATA:ALLOW
ACE4_EXECUTE
Operation(s) affected:
LOOKUP
Discussion:
Permission to traverse/search a directory.
ACE4_DELETE_CHILD
Operation(s) affected:
REMOVE
RENAME
Discussion:
Permission to delete a file or directory within a
directory. See section "ACE4_DELETE vs. ACE4_DELETE_CHILD"
for information on how these two access mask bits interact.
ACE4_READ_ATTRIBUTES
Operation(s) affected:
GETATTR of file system object attributes
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 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 allowed for the READDIR to succeed.
ACE4_WRITE_ATTRIBUTES
Operation(s) affected:
SETATTR of time_access_set, time_backup,
time_create, time_modify_set, mimetype, hidden, system
Discussion:
Permission to change the times associated with a file or
directory to an arbitrary value. Also permission to change
the mimetype, hidden and system attributes. A user having
ACE4_WRITE_DATA or ACE4_WRITE_ATTRIBUTES will be allowed to
set the times associated with a file to the current server
time.
ACE4_WRITE_RETENTION
Operation(s) affected:
SETATTR of retention_set, retentevt_set.
Discussion:
Permission to modify the durations of event and
non-event-based retention. Also permission to enable event and
non-event-based retention. A server MAY behave such that
setting ACE4_WRITE_ATTRIBUTES allows ACE4_WRITE_RETENTION.
ACE4_WRITE_RETENTION_HOLD
Operation(s) affected:
SETATTR of retention_hold.
Discussion:
Permission to modify the administration retention holds.
A server MAY map ACE4_WRITE_ATTRIBUTES to
ACE_WRITE_RETENTION_HOLD.
ACE4_DELETE
Operation(s) affected:
REMOVE
Discussion:
Permission to delete the file or directory. See section
"ACE4_DELETE vs. ACE4_DELETE_CHILD" for information on how
these two access mask bits interact.
ACE4_READ_ACL
Operation(s) affected:
GETATTR of acl, dacl, or sacl
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
Discussions:
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 provide the granularity of control that is implied by this list of masks. For example, POSIX-based systems might not distinguish ACE4_APPEND_DATA (the ability to append to a file) from ACE4_WRITE_DATA (the ability to modify existing contents); both masks would be tied to a single "write" permission. When such a server returns attributes to the client, it would show both ACE4_APPEND_DATA and ACE4_WRITE_DATA if and only if the write permission is enabled.
If a server receives a SETATTR request that it cannot accurately implement, it should 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 ACE where ACE4_APPEND_DATA is set but ACE4_WRITE_DATA is not (or vice versa), the server should reject the request with NFS4ERR_ATTRNOTSUPP. Nonetheless, if the ACE has type DENY, the server may silently turn on the other bit, so that both ACE4_APPEND_DATA and ACE4_WRITE_DATA are denied.
| TOC |
Two access mask bits govern the ability to delete a file or directory object: ACE4_DELETE on the object itself, and ACE4_DELETE_CHILD on the object's parent directory.
Many systems also consult the "sticky bit" (MODE4_SVTX) and write mode bit on the parent directory when determining whether to allow a file to be deleted. The mode bit for write corresponds to ACE4_WRITE_DATA, which is the same physical bit as ACE4_ADD_FILE. Therefore, ACE4_WRITE_DATA can come into play when determining permission to delete.
In the algorithm below, the strategy is that ACE4_DELETE and ACE4_DELETE_CHILD take precedence over the sticky bit, and the sticky bit takes precedence over the "write" mode bits (reflected in ACE4_ADD_FILE).
Server implementations SHOULD grant or deny permission to delete based on the following algorithm.
if ACE4_TRAVERSE is denied by the parent directory ACL {
deny delete
} else if ACE4_DELETE is allowed by the target object ACL {
allow delete
} else if ACE4_DELETE_CHILD is allowed by the parent
directory ACL {
allow delete
} else if ACE4_DELETE_CHILD is denied by the
parent directory ACL {
deny delete
} else if ACE4_ADD_FILE is allowed by the parent directory ACL {
if MODE4_SVTX is set for the parent directory {
if the principal owns the parent directory OR
the principal owns the target object OR
ACE4_WRITE_DATA is allowed by the target
object ACL {
allow delete
} else {
deny delete
}
} else {
allow delete
}
} else {
deny delete
}
| TOC |
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;
const ACE4_INHERITED_ACE = 0x00000080;
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.
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.
| TOC |
- 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_INHERITED_ACE
- Indicates that this ACE is inherited from a parent directory. A server that supports automatic inheritance will place this flag on any ACEs inherited from the parent directory when creating a new object. Client applications will use this to perform automatic inheritance. Clients and servers MUST clear this bit in the acl attribute; it may only be used in the dacl and sacl attributes.
- ACE4_SUCCESSFUL_ACCESS_ACE_FLAG
- ACE4_FAILED_ACCESS_ACE_FLAG
- The ACE4_SUCCESSFUL_ACCESS_ACE_FLAG (SUCCESS) and ACE4_FAILED_ACCESS_ACE_FLAG (FAILED) flag bits relate only to ACE4_SYSTEM_AUDIT_ACE_TYPE (AUDIT) and ACE4_SYSTEM_ALARM_ACE_TYPE (ALARM) ACE types. If during the processing of the file's ACL, the server encounters an AUDIT or ALARM ACE that matches the principal attempting the OPEN, the server notes that fact, and the presence, if any, of the SUCCESS and FAILED flags encountered in the AUDIT or ALARM ACE. Once the server completes the ACL processing, it then notes if the operation succeeded or failed. If the operation succeeded, and if the SUCCESS flag was set for a matching AUDIT or ALARM ACE, then the appropriate AUDIT or ALARM event occurs. If the operation failed, and if the FAILED flag was set for the matching AUDIT or ALARM ACE, then the appropriate AUDIT or ALARM event occurs. Either or both of the SUCCESS or FAILED can be set, but if neither is set, the AUDIT or ALARM ACE is not useful.
- The previously described processing applies to that of the ACCESS operation as well, the difference being that "success" or "failure" does not mean whether ACCESS returns NFS4_OK or not. Success means whether ACCESS returns all requested and supported bits. Failure means whether ACCESS failed to return at least one 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 (ACE Who).
| TOC |
The "who" field of an ACE is an identifier that specifies the principal or principals to whom the ACE applies. It may refer to a user or a group, with the flag bit ACE4_IDENTIFIER_GROUP specifying which.
There are several special identifiers which need to be understood universally, rather than in the context of a particular DNS domain. Some of these identifiers cannot be understood when an NFS client accesses the server, but have meaning when a local process accesses the file. The ability to display and modify these permissions is permitted over NFS, even if none of the access methods on the server understands the identifiers.
| Who | Description |
|---|---|
| OWNER | The owner of the file |
| GROUP | The group associated with the file. |
| EVERYONE | The world, including the owner and owning group. |
| INTERACTIVE | Accessed from an interactive terminal. |
| NETWORK | Accessed via the network. |
| DIALUP | Accessed as a dialup user to the server. |
| BATCH | Accessed from a batch job. |
| ANONYMOUS | Accessed without any authentication. |
| AUTHENTICATED | Any authenticated user (opposite of ANONYMOUS) |
| SERVICE | Access from a system service. |
| Table 7 |
To avoid conflict, these special identifiers are distinguish by an appended "@" and should appear in the form "xxxx@" (note: no domain name after the "@"). For example: ANONYMOUS@.
The ACE4_IDENTIFIER_GROUP flag MUST be ignored on entries with these special identifiers. When encoding entries with these special identifiers, the ACE4_IDENTIFIER_GROUP flag SHOULD be set to zero.
| TOC |
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.
| TOC |
The dacl and sacl attributes are like the acl attribute, but dacl and sacl each allow only certain types of ACEs. The dacl attribute allows just ALLOW and DENY ACEs. The sacl attribute allows just AUDIT and ALARM ACEs. The dacl and sacl attributes also support automatic inheritance (see Section 6.4.3.2 (Automatic Inheritance)).
| TOC |
The NFS version 4 mode attribute is based on the UNIX mode bits. The following bits are defined:
const MODE4_SUID = 0x800; /* set user id on execution */
const MODE4_SGID = 0x400; /* set group id on execution */
const MODE4_SVTX = 0x200; /* save text even after use */
const MODE4_RUSR = 0x100; /* read permission: owner */
const MODE4_WUSR = 0x080; /* write permission: owner */
const MODE4_XUSR = 0x040; /* execute permission: owner */
const MODE4_RGRP = 0x020; /* read permission: group */
const MODE4_WGRP = 0x010; /* write permission: group */
const MODE4_XGRP = 0x008; /* execute permission: group */
const MODE4_ROTH = 0x004; /* read permission: other */
const MODE4_WOTH = 0x002; /* write permission: other */
const MODE4_XOTH = 0x001; /* execute permission: other */
Bits MODE4_RUSR, MODE4_WUSR, and MODE4_XUSR apply to the principal identified in the owner attribute. Bits MODE4_RGRP, MODE4_WGRP, and MODE4_XGRP apply to principals identified in the owner_group attribute but who are not identified in the owner attribute. Bits MODE4_ROTH, MODE4_WOTH, MODE4_XOTH apply to any principal that does not match that in the owner attribute, and does not have a group matching that of the owner_group attribute.
Bits within the mode other than those specified above are not defined by this protocol. A server MUST NOT return bits other than those defined above in a GETATTR or READDIR operation, and it MUST return NFS4ERR_INVAL if bits other than those defined above are set in a SETATTR, CREATE, OPEN, VERIFY or NVERIFY operation.
| TOC |
The mode_set_masked attribute is a write-only attribute that allows individual bits in the mode attribute to be set or reset, without changing others. It allows, for example, the bits MODE4_SUID, MODE4_SGID, and MODE4_SVTX to be modified while leaving unmodified any of the nine low-order mode bits devoted to permissions.
In such instances that the nine low-order bits are left unmodified, then neither the acl nor the dacl attribute should be automatically modified as discussed in Section 6.4.1 (Setting the mode and/or ACL Attributes).
The mode_set_masked attribute consists of two words each in the form of a mode4. The first consists of the value to be applied to the current mode value and the second is a mask. Only bits set to one in the mask word are changed (set or reset) in the file's mode. All other bits in the mode remain unchanged. Bits in the first word that correspond to bits which are zero in the mask are ignored, except that undefined bits are checked for validity and can result in NFS4ERR_INVAL as described below.
The mode_set_masked attribute is only valid in a SETATTR operation. If it is used in a CREATE or OPEN operation, the server MUST return NFS4ERR_INVAL.
Bits not defined as valid in the mode attribute are not valid in either word of the mode_set_masked attribute. The server MUST return NFS4ERR_INVAL if any of those are on in a SETATTR. If the mode and mode_set_masked attributes are both specified in the same SETATTR, the server MUST also return NFS4ERR_INVAL.
| TOC |
The requirements in this section will be referred to in future sections, especially Section 6.4 (Requirements).
| TOC |
| TOC |
The server uses the algorithm described in Section 6.2.1 (ACL Attributes) to determine whether an ACL allows access to an object. However, the ACL may not be the sole determiner of access. For example:
| TOC |
Clients SHOULD NOT do their own access checks based on their interpretation the ACL, but rather use the OPEN and ACCESS operations to do access checks. This allows the client to act on the results of having the server determine whether or not access should be granted based on its interpretation of the ACL.
Clients must be aware of situations in which an object's ACL will define a certain access even though the server will not enforce it. In general, but especially in these situations, the client needs to do its part in the enforcement of access as defined by the ACL. To do this, the client MAY issue the appropriate ACCESS operation prior to servicing the request of the user or application in order to determine whether the user or application should be granted the access requested. For examples in which the ACL may define accesses that the server doesn't enforce see Section 6.3.1.1 (Server Considerations).
| TOC |
The following method can be used to calculate the MODE4_R*, MODE4_W* and MODE4_X* bits of a mode attribute, based upon an ACL.
- A.
- If the special identifier EVERYONE@ is granted ACE4_READ_DATA, then the bit MODE4_ROTH SHOULD be set. Otherwise, MODE4_ROTH SHOULD NOT be set.
- B.
- If the special identifier EVERYONE@ is granted ACE4_WRITE_DATA or ACE4_APPEND_DATA, then the bit MODE4_WOTH SHOULD be set. Otherwise, MODE4_WOTH SHOULD NOT be set.
- C.
- If the special identifier EVERYONE@ is granted ACE4_EXECUTE, then the bit MODE4_XOTH SHOULD be set. Otherwise, MODE4_XOTH SHOULD NOT be set.
- A.
- If the special identifier GROUP@ is granted ACE4_READ_DATA, then the bit MODE4_RGRP SHOULD be set. Otherwise, MODE4_RGRP SHOULD NOT be set.
- B.
- If the special identifier GROUP@ is granted ACE4_WRITE_DATA or ACE4_APPEND_DATA, then the bit MODE4_WGRP SHOULD be set. Otherwise, MODE4_WGRP SHOULD NOT be set.
- C.
- If the special identifier GROUP@ is granted ACE4_EXECUTE, then the bit MODE4_XGRP SHOULD be set. Otherwise, MODE4_XGRP SHOULD NOT be set.
- A.
- If the special identifier OWNER@ is granted ACE4_READ_DATA, then the bit MODE4_RUSR SHOULD be set. Otherwise, MODE4_RUSR SHOULD NOT be set.
- B.
- If the special identifier OWNER@ is granted ACE4_WRITE_DATA or ACE4_APPEND_DATA, then the bit MODE4_WUSR SHOULD be set. Otherwise, MODE4_WUSR SHOULD NOT be set.
- C.
- If the special identifier OWNER@ is granted ACE4_EXECUTE, then the bit MODE4_XUSR SHOULD be set. Otherwise, MODE4_XUSR SHOULD NOT be set.
| TOC |
The nine low-order mode bits (MODE4_R*, MODE4_W*, MODE4_X*) correspond to ACE4_READ_DATA, ACE4_WRITE_DATA/ACE4_APPEND_DATA, and ACE4_EXECUTE for OWNER@, GROUP@, and EVERYONE@. On some implementations, mode bits may represent a superset of these permissions, e.g. if a specific user is granted ACE4_WRITE_DATA, then MODE4_WGRP will be set, even though the file's owner_group is not granted ACE4_WRITE_DATA.
Server implementations are discouraged from doing this, as experience has shown that this is confusing and annoying to end users. The specifications above also discourage this practice to enforce the semantic that setting the mode attribute effectively specifies read, write, and execute for owner, group, and other.
| TOC |
The server that supports both mode and ACL must take care to synchronize the MODE4_*USR, MODE4_*GRP, and MODE4_*OTH bits with the ACEs which have respective who fields of "OWNER@", "GROUP@", and "EVERYONE@" so that the client can see semantically equivalent access permissions exist whether the client asks for owner, owner_group and mode attributes, or for just the ACL.
In this section, much is made of the methods in Section 6.3.2 (Computing a Mode Attribute from an ACL). Many requirements refer to this section. But note that the methods have behaviors specified with "SHOULD". This is intentional, to avoid invalidating existing implementations that compute the mode according to the withdrawn POSIX ACL draft (1003.1e draft 17), rather than by actual permissions on owner, group, and other.
| TOC |
In the case where a server supports the sacl or dacl attribute, in addition to the acl attribute, the server MUST fail a request to set the acl attribute simultaneously with a dacl or sacl attribute. The error to be given is NFS4ERR_ATTRNOTSUP.
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When any of the nine low-order mode permission bits are subject to change, either because the mode attribute was set or because the mode_set_masked attribute was set and the mask included one or more bits from the low-order nine mode bits that control permissions, and no ACL attribute is explicitly set, the acl and dacl attributes must be modified in accordance with the updated value of the permissions bits within the mode. This must happen even if the value of the permission bits within the mode is the same after the mode is set as before.
Note that any AUDIT or ALARM ACEs (hence any ACEs in the sacl attribute) are unaffected by changes to the mode.
In cases in which the permissions bits are subject to change, the acl and dacl attributes MUST be modified such that the mode computed via the method in Section 6.3.2 (Computing a Mode Attribute from an ACL) yields the low-order nine bits (MODE4_R*, MODE4_W*, MODE4_X*) of the mode attribute as modified by the attribute change. The ACL attributes SHOULD also be modified such that:
Access mask bits other those listed above, appearing in ALLOW ACEs, MAY also be disabled.
Note that ACEs with the flag ACE4_INHERIT_ONLY_ACE set do not affect the permissions of the ACL itself, nor do ACEs of the type AUDIT and ALARM. As such, it is desirable to leave these ACEs unmodified when modifying the ACL attributes.
Also note that the requirement may be met by discarding the acl and dacl, in favor of an ACL that represents the mode and only the mode. This is permitted, but it is preferable for a server to preserve as much of the ACL as possible without violating the above requirements. Discarding the ACL makes it effectively impossible for a file created with a mode attribute to inherit an ACL (see Section 6.4.3 (Creating New Objects)).
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When setting the acl or dacl and not setting the mode or mode_set_masked attributes, the permission bits of the mode need to be derived from the ACL. In this case, the ACL attribute SHOULD be set as given. The nine low-order bits of the mode attribute (MODE4_R*, MODE4_W*, MODE4_X*) MUST be modified to match the result of the method Section 6.3.2 (Computing a Mode Attribute from an ACL). The three high-order bits of the mode (MODE4_SUID, MODE4_SGID, MODE4_SVTX) SHOULD remain unchanged.
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When setting both the mode (includes use of either the mode attribute or the mode_set_masked attribute) and the acl or dacl attributes in the same operation, the attributes MUST be applied in this order: mode (or mode_set_masked), then ACL. The mode-related attribute is set as given, then the ACL attribute is set as given, possibly changing the final mode, as described above in Section 6.4.1.2 (Setting ACL and not mode).
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This section applies only to servers that support both the mode and ACL attributes.
Some server implementations may have a concept of "objects without ACLs", meaning that all permissions are granted and denied according to the mode attribute, and that no ACL attribute is stored for that object. If an ACL attribute is requested of such a server, the server SHOULD return an ACL that does not conflict with the mode; that is to say, the ACL returned SHOULD represent the nine low-order bits of the mode attribute (MODE4_R*, MODE4_W*, MODE4_X*) as described in Section 6.3.2 (Computing a Mode Attribute from an ACL).
For other server implementations, the ACL attribute is always present for every object. Such servers SHOULD store at least the three high-order bits of the mode attribute (MODE4_SUID, MODE4_SGID, MODE4_SVTX). The server SHOULD return a mode attribute if one is requested, and the low-order nine bits of the mode (MODE4_R*, MODE4_W*, MODE4_X*) MUST match the result of applying the method in Section 6.3.2 (Computing a Mode Attribute from an ACL) to the ACL attribute.
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If a server supports any ACL attributes, it may use the ACL attributes on the parent directory to compute an initial ACL attribute for a newly created object. This will be referred to as the inherited ACL within this section. The act of adding one or more ACEs to the inherited ACL that are based upon ACEs in the parent directory's ACL will be referred to as inheriting an ACE within this section.
Implementors should standardize on what the behavior of CREATE and OPEN must be depending on the presence or absence of the mode and ACL attributes.
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If the object being created is not a directory, the inherited ACL SHOULD NOT inherit ACEs from the parent directory ACL unless the ACE4_FILE_INHERIT_FLAG is set.
If the object being created is a directory, the inherited ACL should inherit all inheritable ACEs from the parent directory, those that have ACE4_FILE_INHERIT_ACE or ACE4_DIRECTORY_INHERIT_ACE flag set. If the inheritable ACE has ACE4_FILE_INHERIT_ACE set, but ACE4_DIRECTORY_INHERIT_ACE is clear, the inherited ACE on the newly created directory MUST have the ACE4_INHERIT_ONLY_ACE flag set to prevent the directory from being affected by ACEs meant for non-directories.
If when a new directory is created and it inherits ACEs from its parent, for each inheritable ACE which affects the directory's permissions, a server MAY create two ACEs on the directory being created; one effective and one which is only inheritable (i.e. has ACE4_INHERIT_ONLY_ACE flag set). In the case of a dacl or sacl attribute, both of these ACEs SHOULD have the ACE4_INHERITED_ACE flag set. This gives the user and the server, in the cases which it must mask certain permissions upon creation, the ability to modify the effective permissions without modifying the ACE which is to be inherited to the new directory's children.
When a newly created object is created with attributes, and those attributes contain an ACL attribute and/or a mode attribute, the server MUST apply those attributes to the newly created object, as described in Section 6.4.1 (Setting the mode and/or ACL Attributes).
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The acl attribute consists only of an array of ACEs, but the sacl and dacl attributes (see Section 6.2.2 (dacl and sacl Attributes)) also include an additional flag field. The flag field applies to the entire sacl or dacl; three flag values are defined:
const ACL4_AUTO_INHERIT = 0x00000001;
const ACL4_PROTECTED = 0x00000002;
const ACL4_DEFAULTED = 0x00000004;
and all other bits must be cleared. The ACE4_INHERITED_ACE flag may be set in the ACEs of the sacl or dacl (whereas it must always be cleared in the acl).
Together these features allow a server to support automatic inheritance, which we now explain in more detail.
Inheritable ACEs are normally inherited by child objects only at the time that the child objects are created; later modifications to inheritable ACEs do not result in modifications to inherited ACEs on descendents.
However, the dacl and sacl provide an optional mechanism which allows a client application to propagate changes to inheritable ACEs to an entire directory hierarchy.
A server that supports this performs inheritance at object creation time in the normal way, and SHOULD set the ACE4_INHERITED_ACE flag on any inherited ACEs as they are added to the new object.
A client application such as an ACL editor may then propagate changes to inheritable ACEs on a directory by recursively traversing that directory's descendants and modifying each ACL encountered to remove any ACEs with the ACE4_INHERITED_ACE flag and to replace them by the new inheritable ACEs (also with the ACE4_INHERITED_ACE flag set). It uses the existing ACE inheritance flags in the obvious way to decide which ACEs to propagate. (Note that it may encounter further inheritable ACEs when descending the directory hierarchy, and that those will also need to be taken into account when propagating inheritable ACEs to further descendants.)
The reach of this propagation may be limited in two ways: first, automatic inheritance is not performed from any directory ACL that has the ACL4_AUTO_INHERIT flag cleared; and second, automatic inheritance stops wherever an ACL with the ACL4_PROTECTED flag is set, preventing modification of that ACL and also (if the ACL is set on a directory) of the ACL on any of the object's descendants.
This propagation is performed independently for the sacl and the dacl attributes; thus the ACL4_AUTO_INHERIT and ACL4_PROTECTED flags may be independently set for the sacl and the dacl, and propagation of one type of acl may continue down a hierarchy even where propagation of the other acl has stopped.
New objects should be created with a dacl and a sacl that both have the ACL4_PROTECTED flag cleared and the ACL4_AUTO_INHERIT flag set to the same value as that on, respectively, the sacl or dacl of the parent object.
Both the dacl and sacl attributes are RECOMMENDED, and a server may support one without supporting the other.
A server that supports both the old acl attribute and one or both of the new dacl or sacl attributes must do so in such a way as to keep all three attributes consistent with each other. Thus the ACEs reported in the acl attribute should be the union of the ACEs reported in the dacl and sacl attributes, except that the ACE4_INHERITED_ACE flag must be cleared from the ACEs in the acl. And of course a client that queries only the acl will be unable to determine the values of the sacl or dacl flag fields.
When a client performs a SETATTR for the acl attribute, the server SHOULD set the ACL4_PROTECTED flag to true on both the sacl and the dacl. By using the acl attribute, as opposed to the dacl or sacl attributes, the client signals that it may not understand automatic inheritance, and thus cannot be trusted to set an ACL for which automatic inheritance would make sense.
When a client application queries an ACL, modifies it, and sets it again, it should leave any ACEs marked with ACE4_INHERITED_ACE unchanged, in their original order, at the end of the ACL. If the application is unable to do this, it should set the ACL4_PROTECTED flag. This behavior is not enforced by servers, but violations of this rule may lead to unexpected results when applications perform automatic inheritance.
If a server also supports the mode attribute, it SHOULD set the mode in such a way that leaves inherited ACEs unchanged, in their original order, at the end of the ACL. If it is unable to do so, it SHOULD set the ACL4_PROTECTED flag on the file's dacl.
Finally, in the case where the request that creates a new file or directory does not also set permissions for that file or directory, and there are also no ACEs to inherit from the parent's directory, then the server's choice of ACL for the new object is implementation-dependent. In this case, the server SHOULD set the ACL4_DEFAULTED flag on the ACL it chooses for the new object. An application performing automatic inheritance takes the ACL4_DEFAULTED flag as a sign that the ACL should be completely replaced by one generated using the automatic inheritance rules.
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This chapter describes the NFSv4 single-server namespace. Single-server namespaces may be presented directly to clients, or they may be used as a basis to form larger multi-server namespaces (e.g. site-wide or organization-wide) to be presented to clients, as described in Section 11 (Multi-Server Namespace).
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On a UNIX server, the namespace describes all the files reachable by pathnames under the root directory or "/". On a Windows NT server the namespace constitutes all the files on disks named by mapped disk letters. NFS server administrators rarely make the entire server's file system namespace available to NFS clients. More often portions of the namespace are made available via an "export" feature. In previous versions of the NFS protocol, the root filehandle for each export is obtained through the MOUNT protocol; the client sends a string that identifies the export of namespace and the server returns the root filehandle for it. The MOUNT protocol supports an EXPORTS procedure that will enumerate the server's exports.
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The NFS version 4 protocol provides a root filehandle that clients can use to obtain filehandles for the exports of a particular server, via a series of LOOKUP operations within a COMPOUND, to traverse a path. A common user experience is to use a graphical user interface (perhaps a file "Open" dialog window) to find a file via progressive browsing through a directory tree. The client must be able to move from one export to another export via single-component, progressive LOOKUP operations.
This style of browsing is not well supported by the NFS version 2 and 3 protocols. The client expects all LOOKUP operations to remain within a single server file system. For example, the device attribute will not change. This prevents a client from taking namespace paths that span exports.
In the case of Veriosn 2 and 3, an automounter on the client can obtain a snapshot of the server's namespace using the EXPORTS procedure of the MOUNT protocol. If it understands the server's pathname syntax, it can create an image of the server's namespace on the client. The parts of the namespace that are not exported by the server are filled in with directories that might be arrange similarly to a version 4 "pseudo file system" that allows the user to browse from one mounted file system to another. There is a drawback to this representation of the server's namespace on the client: it is static. If the server administrator adds a new export the client will be unaware of it.
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NFS version 4 servers avoid this namespace inconsistency by presenting all the exports for a given server within the framework of a single namespace, for that server. An NFS version 4 client uses LOOKUP and READDIR operations to browse seamlessly from one export to another.
Where there are portions of the server namespace that are not exported, clients require some way of traversing those portions to reach actual exported file systems. A technique that servers may use to provide for this is to bridge unexported portion of the namespace via a "pseudo file system" that provides a view of exported directories only. A pseudo file system has a unique fsid and behaves like a normal, read only file system.
Based on the construction of the server's namespace, it is possible that multiple pseudo file systems may exist. For example,
/a pseudo file system
/a/b real file system
/a/b/c pseudo file system
/a/b/c/d real file system
Each of the pseudo file systems are considered separate entities and therefore MUST have its own unique fsid.
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Certain operating environments are sometimes described as having "multiple roots". In such environments individual file systems are commonly represented by disk or volume names. NFS version 4 servers for these platforms can construct a pseudo file system above these root names so that disk letters or volume names are simply directory names in the pseudo root.
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The nature of the server's pseudo file system is that it is a logical representation of file system(s) available from the server. Therefore, the pseudo file system is most likely constructed dynamically when the server is first instantiated. It is expected that the pseudo file system may not have an on disk counterpart from which persistent filehandles could be constructed. Even though it is preferable that the server provide persistent filehandles for the pseudo file system, the NFS client should expect that pseudo file system filehandles are volatile. This can be confirmed by checking the associated "fh_expire_type" attribute for those filehandles in question. If the filehandles are volatile, the NFS client must be prepared to recover a filehandle value (e.g. with a series of LOOKUP operations) when receiving an error of NFS4ERR_FHEXPIRED.
Because it is quite likely that servers will implement pseudo file systems using volative filehandles, clients need to be prepared for them, rather than assuming that all filehandles will be persistent.
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If the server's root file system is exported, one might conclude that a pseudo-file system is unneeded. This not necessarily so. Assume the following file systems on a server:
/ fs1 (exported)
/a fs2 (not exported)
/a/b fs3 (exported)
Because fs2 is not exported, fs3 cannot be reached with simple LOOKUPs. The server must bridge the gap with a pseudo-file system.
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The server file system environment may be constructed in such a way that one file system contains a directory which is 'covered' or mounted upon by a second file system. For example:
/a/b (file system 1)
/a/b/c/d (file system 2)
The pseudo file system for this server may be constructed to look like:
/ (place holder/not exported)
/a/b (file system 1)
/a/b/c/d (file system 2)
It is the server's responsibility to present the pseudo file system that is complete to the client. If the client sends a lookup request for the path "/a/b/c/d", the server's response is the filehandle of the file system "/a/b/c/d". In previous versions of the NFS protocol, the server would respond with the filehandle of directory "/a/b/c/d" within the file system "/a/b".
The NFS client will be able to determine if it crosses a server mount point by a change in the value of the "fsid" attribute.
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Because NFSv4 clients possess the ability to change the security mechanisms used, after determining what is allowed, by using SECINFO and SECINFO_NONAME, the server SHOULD NOT present a different view of the namespace based on the security mechanism being used by a client. Instead, it should present a consistent view and return NFS4ERR_WRONGSEC if an attempt is made to access data with an inappropriate security mechanism.
If security considerations make it necessary to hide the existence of a particular file system, as opposed to all of the data within it, the server can apply the security policy of a shared resource in the server's namespace to components of the resource's ancestors. For example:
/
/a/b
/a/b/MySecretProject
The /a/b/MySecretProject directory is a real file system and is the shared resource. Suppose the security policy for /a/b/MySecretProject is Kerberos with integrity and it desired to prevent knowledge of the existence of this file system to be very limited. In this case the server should apply the same security policy to /a/b. This allows for knowledge the existence of a filesystem to be secured in cases where this is desirable.
For the case of the use of multiple, disjoint security mechanisms in the server's resources, the security for a particular object in the server's namespace should be the union of all security mechanisms of all direct descendants. A common and convenient practice, unless strong security requirements dictate otherwise, is to make all of the pseudo file system accessible by all of the valid security mechanisms.
Where there is concern about the security of data on the wire, clients should use strong security mechanisms to access the pseudo file system in order to prevent man-in-the-middle-attacks from directing LOOKUP's within the pseudo-fs from compromising the existence of sensitive data, or getting access to data that the client is sending by directing the client to send it using weak security mechanisms.
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Integrating locking into the NFS protocol necessarily causes it to be stateful. With the inclusion of such features as share reservations, file and directory delegations, recallable layouts, and support for mandatory record locking the protocol becomes substantially more dependent on state than the traditional combination of NFS and NLM [XNFS]. There are three components to making this state manageable:
In this model, the server owns the state information. The client requests changes in locks and the server responds with the changes made. Non-client-initiated changes in locking state are infrequent and the client receives prompt notification of them and can adjust its view of the locking state to reflect the server's changes.
Individual pieces of state created by the server and passed to the client at its request are represented by 128-bit stateids. These stateids may represent a particular open file, a set of byte-range locks held by a particular owner, or a recallable delegation of privileges to access a file in particular ways, or at a particular location.
In all cases, there is a transition from the largest-gauge information which represents a client as a whole to the eventual lightweight stateid used for most client and server locking interactions. The details of this transition will vary with the type of object but it always starts with a client_id.
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A client must establish a client ID (see Section 2.4 (Client Identifiers and Client Owners)) and then one or more sessionids (see Section 2.10 (Session)) before performing any operations to open, lock, delegate, or obtain a layout for a file object. The sessionid serves as a shorthand reference to an NFSv4.1 client.
For some types of locking interactions, the client will represent some number of internal locking entities called "owners", which normally correspond to processes internal to the client. For other types of locking-related objects, such as delegations and layouts, no such intermediate entities are provided for, and the locking-related objects are considered to be transferred directly between the server and a unitary client.
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When the server grants a lock of any type (including opens, record locks, delegations, and layouts) it responds with a unique stateid, that represents a set of locks (often a single lock) for the same file, of the same type, and sharing the same ownership characteristics. Thus opens of the same file by different open-owners each have an identifying stateid. Similarly, each set of record locks on a file owned by a specific lock-owner and gotten via an open for a specific open-owner, has its own identifying stateid. Delegations and layouts also have associated stateids by which they may be referenced. The stateid is used as a shorthand reference to a lock or set of locks and given a stateid the server can determine the associated state-owner or state-owners (in the case of an open-owner/lock-owner pair) and the associated filehandle. When stateids are used, the current filehandle must be the one associated with that stateid.
The server may assign stateids independently for different clients and a stateid with the same bit pattern for one client may designate an entirely different set of locks for a different client. The stateid is always interpreted with respect to the client ID associated with the current session. Stateids apply to all sessions associated with the given client ID and the client may use a stateid obtained from one session on another session associated with the same client ID.
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Besides special stateids, to be discussed later, each stateid represents locking objects of one of set of types defined by the NFSv4.1 protocol. Note that in all these cases, where we speak of guarantee, there is always an implied codicil that any situation such as a client reboot, or lock revocation, allows the guarantee to be voided.
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Stateids are divided into two fields, a 96-bit "other" field identifying the specific set of locks and a 32-bit "seqid" sequence value. Except in the case of special stateids, to be discussed below, a particular value of the "other" field denotes a set of locks of the same type (for example byte-range lock, opens, delegations, or layouts), for a specific file or directory, and sharing the same ownership characteristics. The seqid designates a specific instance of such a set of locks, and is incremented to indicate changes in such a set of locks, either by the addition or deletion of locks from the, a change in the byte-range they apply to, or an upgrade or downgrade in the type of one or more locks.
When such a set of locks is first created the server returns a stateid with seqid value of one. On subsequent operations which modify the set of locks the server is required to increment the seqid field by one (1) whenever it returns a stateid for the same state owner/file/type combination and there is some change in the set of locks actually designated. In this case the server will return a stateid with an other field the same as previously used for that state owner/file/type combination, with an incremented seqid field.
The purpose of the incrementing of the seqid is to allow the replier to communicate to the requester the order in which operations that modified locking state associated with a stateid have been processed and to make it possible for the client to issue requests that are conditional on the set of locks not having changed since the stateid in question was returned.
When stateids are sent to the server by the client, it has two choices with regard to the seqid sent. It may set the seqid to zero to indicate to the server that it wishes the most up-to-date seqid for that stateid's "other" field to be used. This would be the common choice in the case of stateid sent with a READ or WRITE operation. It also may set a non-zero value in which case the server checks if that seqid is the correct one. In that case the server is required to return NFS4ERR_OLD_STATEID if the seqid is lower than the most current value and NFS4ERR_BAD_STATEID if the seqid is greater than the most current value. This would be the common choice in the case if stateids sent with a CLOSE or OPEN_DOWNGRADE. Because OPENs may be sent in parallel for the same owner, a client might close a file without knowing that an OPEN upgrade had been done by the server, changing the lock in question. If CLOSE were sent with a zero seqid, the OPEN upgrade would be canceled before the client even received an indication that it had happened.
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Stateid values whose "other" field is either all zeros or all ones are reserved. They may not be assigned by the server but have special meanings defined by the protocol. The particular meaning depends on whether the "other" field is all zeros or all ones and the specific value of the "seqid" field.
The following combinations of "other" and "seqid" are defined in NFSv4.1:
If a stateid value is used which has all zero or all ones in the "other" field, but does not match one of the cases above, the server MUST return the error NFS4ERR_BAD_STATEID.
Special stateids, unlike other stateids, are not associated with individual client ID's or filehandles and can be used with all valid client ID's and filehandles. In the case of a special stateid designating the current stateid, the current stateid value substituted for the special stateid is associated with a particular client ID and filehandle.
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Stateids must remain valid until either a client reboot or a server reboot or until the client returns all of the locks associated with the stateid by means of an operation such as CLOSE or DELEGRETURN. If the locks are lost due to revocation the stateid remains a valid designation of that revoked state until the client frees it by using FREE_STATEID. Stateids associated with record locks are an exception. They remain valid even if a LOCKU frees all remaining locks, so long as the open file with which they are associated remains open, unless the client does a FREE_STATEID to cause the stateid to be freed.
An "other" value must never be reused for a different purpose (i.e. different filehandle, owner, or type of locks) within the context of a single client ID. A server may retain the "other" value for the same purpose beyond the point where it may otherwise be freed but if it does so, it must maintain "seqid" continuity with previous values.
One mechanism that may be used to satisfy the requirement that the server recognize invalid and out-of-date stateids is for the server to divide the "other" field of the stateid into two fields.
And then store in each table entry,
With this information, the following procedure would be used to validate an incoming stateid and return an appropriate error, when necessary:
Note that a stateid may be valid in general, as would be reported by the TEST_STATEID operation, but be invalid for a particular operation, as, for example, when a stateid which doesn't represent byte-range locks is passed to non-from_open case of LOCK or to LOCKU, or when a stateid which does not represent an open is passed to CLOSE or OPEN_DOWNGRADE. In such cases, the server MUST return NFS4ERR_BAD_STATEID.
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The purpose of a lease is to allow a server to remove stale locking-related objects that are held by a client that has crashed or is otherwise unreachable. It is not a mechanism for cache consistency and lease renewals may not be denied if the lease interval has not expired.
Since each session is associated with a specific client, any operation issued on that session is an indication that the associated client is reachable. When a request is issued for a given session, successful execution of a SEQUENCE operation (or successful retrieval of the result of SEQUENCE from the reply cache) will result in all leases for the associated client to be implicitly renewed. In addition, whenever a new stateid is created ot updated (i.e. returned with a new seqid value), all leases for the associate client are also renewed. This approach allows for low overhead lease renewal which scales well. In the typical case no extra RPC calls are required for lease renewal and in the worst case one RPC is required every lease period, via a COMPOUND that consists solely of a single SEQUENCE operation. The number of locks held by the client is not a factor since all state for the client is involved with the lease renewal action.
Since all operations that create a new lease also renew existing leases, the server must maintain a common lease expiration time for all valid leases for a given client. This lease time can then be easily updated upon implicit lease renewal actions.
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The important requirement in crash recovery is that both the client and the server know when the other has failed. Additionally, it is required that a client sees a consistent view of data across server restarts or reboots. All READ and WRITE operations that may have been queued within the client or network buffers must wait until the client has successfully recovered the locks protecting the READ and WRITE operations. Any that reach the server before it can safely determine that it has re-established enough locking state to be sure that such requests can be safely processed must be rejected, either because the state presented is no longer valid (NFS4ERR_STALE_CLIENTID or NFS4ERR_STALE_STATEID) or because subsequent recovery of locks may make execution of the operation inappropriate (NFS4ERR_GRACE).
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In the event that a client fails, the server may release the client's locks when the associated leases have expired. Conflicting locks from another client may only be granted after this lease expiration. When a client has not failed and re-establishes his lease before expiration occurs, requests for conflicting locks will not be granted.
To minimize client delay upon restart, lock requests are associated with an instance of the client by a client-supplied verifier. This verifier is part of the client_owner4 sent in the initial EXCHANGE_ID call made by the client. The server returns a client ID as a result of the EXCHANGE_ID operation. The client then confirms the use of the client ID by establishing a session associated with that client ID. All locks, including opens, record locks, delegations, and layout obtained by sessions using that client ID are associated with that client ID.
Since the verifier will be changed by the client upon each initialization, the server can compare a new verifier to the verifier associated with currently held locks and determine that they do not match. This signifies the client's new instantiation and subsequent loss of locking state. As a result, the server is free to release all locks held which are associated with the old client ID which was derived from the old verifier. At this point conflicting locks from other clients, kept waiting while the lease had not yet expired, can be granted.
Note that the verifier must have the same uniqueness properties of the verifier for the COMMIT operation.
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If the server loses locking state (usually as a result of a restart or reboot), it must allow clients time to discover this fact and re-establish the lost locking state. The client must be able to re-establish the locking state without having the server deny valid requests because the server has granted conflicting access to another client. Likewise, if there is a possibility that clients have not yet re-established their locking state for a file, and that such locking state might make it invalid to perform READ or WRITE operations, for example though the establishment of mandatory locks, the server must disallow READ and WRITE operations for that file.
A client can determine that loss of locking state has occurred via several methods.
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When state information and the associated locks are lost as a result of a server reboot, the protocol must provide a way to cause that state to be re-established. The approach used is to define, for most type of locking state (layouts are an exception, a request whose function is to allow the client to re-establish on the server a lock first gotten on a previous instance. Generally these requests are variants of the requests normally used to create locks of that type and are referred to as "reclaim-type" requests and the process of re-establishing such locks is referred to as "reclaiming" them.
Because each client must have an opportunity to reclaim all of the locks that it has without the possibility that some other client will be granted a conflicting lock, a special period called the "grace period" is devoted to the reclaim process. During this period, only reclaim-type locking requests are allowed, unless the server is able to reliably determine (through state persistently maintained across reboot instances), that granting any such lock cannot possibly conflict with a subsequent reclaim. When a request is made to obtain a new lock (i.e. not a reclaim-type request) during the grace period and such a determination cannot be made, the server must return the error NFS4ERR_GRACE.
Once a session is established using the new client ID, the client will use reclaim-type locking requests (e.g. LOCK requests with reclaim set to true and OPEN operations with a claim type of CLAIM_PREVIOUS. See Section 9.8 (Reclaim of Open and Byte-range Locks)) to re-establish its locking state. Once this is done, or if there is no such locking state to reclaim, the client does a global RECLAIM_COMPLETE operation, i.e. one with the one_fs argument set to false, to indicate that it has reclaimed all of the locking state that it will reclaim. Once a client does such a RECLAIM_COMPLETE operation, it may attempt non-reclaim locking operations, although it may get NFS4ERR_GRACE errors on these until the period of special handling is over. See Section 11.6.7 (Lock State and File System Transitions) for a discussion of the analogous handling lock reclamation in the case of filesystems transitioning from server to server.
Note that if the client ID persisted through a server reboot (which will be self-evident if the client never received a NFS4ERR_STALE_CLIENTID error, and instead got SEQ4_STATUS_RESTART_RECLAIM_NEEDED status from SEQUENCE (Section 18.46.4 (DESCRIPTION)), no client ID was re-established. See Paragraph 2 of Section 9.8 (Reclaim of Open and Byte-range Locks) for discussion of some restrictions on use of upgrade semantics in connection with reclaim that are the result of some issues that apply to this situation.
During the grace period, the server must reject READ and WRITE operations and non-reclaim locking requests (i.e. other LOCK and OPEN operations) with an error of NFS4ERR_GRACE, unless it is able to guarantee that these may be done safely, as described below.
The grace period may last until all clients who are known to possibly have had locks have done a global RECLAIM_COMPLETE operation, indicating that they have finished reclaiming the locks they held before the server reboot. The server is assumed to maintain in stable storage a list of clients who may have such locks. The server may also terminate the grace period before all clients have done a global RECLAIM_COMPLETE. The server SHOULD NOT terminate the grace period before a time equal to the lease period in order to give clients an opportunity to find out about the server reboot. Some additional time in order to allow time to establish a new client ID and session and to effect lock reclaims may be added. Note that analogous rules apply to filesystem-specific grace periods discussed in Section 11.6.7 (Lock State and File System Transitions).
If the server can reliably determine that granting a non-reclaim request will not conflict with reclamation of locks by other clients, the NFS4ERR_GRACE error does not have to be returned even within the grace period, although NFS4ERR_GRACE must always be returned to clients attempting a non-reclaim lock request before doing their own global RECLAIM_COMPLETE. For the server to be able to service READ and WRITE operations during the grace period, it must again be able to guarantee that no possible conflict could arise between a potential reclaim locking request and the READ or WRITE operation. If the server is unable to offer that guarantee, the NFS4ERR_GRACE error must be returned to the client.
For a server to provide simple, valid handling during the grace period, the easiest method is to simply reject all non-reclaim locking requests and READ and WRITE operations by returning the NFS4ERR_GRACE error. However, a server may keep information about granted locks in stable storage. With this information, the server could determine if a regular lock or READ or WRITE operation can be safely processed.
For example, if the server maintained on stable storage summary information on whether mandatory locks exist, either mandatory record locks, or share reservations specifying deny modes, many requests could be allowed during the grace period. If it is known that no such share reservations exist, OPEN request that do not specify deny modes may be safely granted. If, in addition, it is known that no mandatory record locks exist, either through information stored on stable storage or simply because the server does not support such locks, READ and WRITE requests may be safely processed during the grace period.
Another important case is where it is known that no mandatory byte-range locks exist, either because the server does not provide support for them, or because their absence is known from persistently recorded data. In this case, READ and WRITE operations specifying stateids derived from reclaim-type operation may be validly processed during the grace period because the fact of the valid reclaim ensures that no lock subsequently granted can prevent the IO.
To reiterate, for a server that allows non-reclaim lock and I/O requests to be processed during the grace period, it MUST determine that no lock subsequently reclaimed will be rejected and that no lock subsequently reclaimed would have prevented any I/O operation processed during the grace period.
Clients should be prepared for the return of NFS4ERR_GRACE errors for non-reclaim lock and I/O requests. In this case the client should employ a retry mechanism for the request. A delay (on the order of several seconds) between retries should be used to avoid overwhelming the server. Further discussion of the general issue is included in [Floyd]. The client must account for the server that is able to perform I/O and non-reclaim locking requests within the grace period as well as those that can not do so.
A reclaim-type locking request outside the server's grace period can only succeed if the server can guarantee that no conflicting lock or I/O request has been granted since reboot or restart.
A server may, upon restart, establish a new value for the lease period. Therefore, clients should, once a new client ID is established, refetch the lease_time attribute and use it as the basis for lease renewal for the lease associated with that server. However, the server must establish, for this restart event, a grace period at least as long as the lease period for the previous server instantiation. This allows the client state obtained during the previous server instance to be reliably re-established.
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If the duration of a network partition is greater than the lease period provided by the server, the server will have not received a lease renewal from the client. If this occurs, the server may free all locks held for the client, or it may allow the lock state to remain for a considerable period, subject to the constraint that if a request for a conflicting lock is made, locks associated with expired leases do not prevent such a conflicting lock from being granted but are revoked as necessary so as not to interfere with such conflicting requests.
If the server chooses to delay freeing of lock state until there is a conflict, it may either free all of the clients locks once there is a conflict, or it may only revoke the minimum set of locks necessary to allow conflicting requests. When it adopts the finer-grained approach, it must revoke all locks associated with a given stateid, as long as it revokes a single such lock.
When the server chooses to free all of a client's lock state, either immediately upon lease expiration, or a result of the first attempt to get a lock, all stateids held by the client will become invalid or stale. Once the client is able to reach the server after such a network partition, the status returned by the SEQUENCE operation will indicate a loss of locking state. In addition all I/O submitted by the client with the now invalid stateids will fail with the server returning the error NFS4ERR_EXPIRED. Once the client learns of the loss of locking state, it will suitably notify the applications that held the invalidated locks. The client should then take action to free invalidated stateids, either by establishing a new client ID using a new verifier or by doing a FREE_STATEID operation to release each of the invalidated stateids.
When the server adopts a finer-grained approach to revocation of locks when lease have expired, only a subset of stateids will normally become invalid during a network partition. When the client is able to communicate with the server after such a network partition, the status returned by the SEQUENCE operation will indicate a partial loss of locking state. In addition, operations, including I/O submitted by the client with the now invalid stateids will fail with the server returning the error NFS4ERR_EXPIRED. Once the client learns of the loss of locking state, it will use the TEST_STATEID operation on all of its stateids to determine which locks have been lost and them suitably notify the applications that held the invalidated locks. The client can then release the invalidated locking state and acknowledge the revocation of the associated locks by doing a FREE_STATEID operation on each of the invalidated stateids.
When a network partition is combined with a server reboot, there are edge conditions that place requirements on the server in order to avoid silent data corruption following the server reboot. Two of these edge conditions are known, and are discussed below.
The first edge condition arises as a result of the scenarios such as the following:
Thus, at the final step, the server has erroneously granted client A's lock reclaim. If client B modified the object the lock was protecting, client A will experience object corruption.
The second known edge condition arises in situations such as the following:
As with the first edge condition, the final step of the scenario of the second edge condition has the server erroneously granting client A's lock reclaim.
Solving the first and second edge conditions requires that the server either always assumes after it reboots that some edge condition occurs, and thus return NFS4ERR_NO_GRACE for all reclaim attempts, or that the server record some information in stable storage. The amount of information the server records in stable storage is in inverse proportion to how harsh the server intends to be whenever edge conditions arise. The server that is completely tolerant of all edge conditions will record in stable storage every lock that is acquired, removing the lock record from stable storage only when the lock is released. For the two edge conditions discussed above, the harshest a server can be, and still support a grace period for reclaims, requires that the server record in stable storage information some minimal information. For example, a server implementation could, for each client, save in stable storage a record containing:
Assuming the above record keeping, for the first edge condition, after the server reboots, the record that client A's lease expired means that another client could have acquired a conflicting record lock, share reservation, or delegation. Hence the server must reject a reclaim from client A with the error NFS4ERR_NO_GRACE.
For the second edge condition, after the server reboots for a second time, the indication that the client had not completed its reclaims at the time at which the grace period ended means that the server must reject a reclaim from client A with the error NFS4ERR_NO_GRACE.
When either edge condition occurs, the client's attempt to reclaim locks will result in the error NFS4ERR_NO_GRACE. When this is received, or after the client reboots with no lock state, the client will issue a global RECLAIM_COMPLETE. When the RECLAIM_COMPLETE is received, the server and client are again in agreement regarding reclaimable locks and both booleans in persistent storage can be reset, to be set again only when there is a subsequent event that causes lock reclaim operations to be questionable.
Regardless of the level and approach to record keeping, the server MUST implement one of the following strategies (which apply to reclaims of share reservations, record locks, and delegations):
A mandate for the client's handling of the NFS4ERR_NO_GRACE error is outside the scope of this specification, since the strategies for such handling are very dependent on the client's operating environment. However, one potential approach is described below.
When the client receives NFS4ERR_NO_GRACE, it could examine the change attribute of the objects the client is trying to reclaim state for, and use that to determine whether to re-establish the state via normal OPEN or LOCK requests. This is acceptable provided the client's operating environment allows it. In other words, the client implementor is advised to document for his users the behavior. The client could also inform the application that its record lock or share reservations (whether they were delegated or not) have been lost, such as via a UNIX signal, a GUI pop-up window, etc. See Section 10.5 (Data Caching and Revocation) for a discussion of what the client should do for dealing with unreclaimed delegations on client state.
For further discussion of revocation of locks see Section 8.5 (Server Revocation of Locks).
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At any point, the server can revoke locks held by a client and the client must be prepared for this event. When the client detects that its locks have been or may have been revoked, the client is responsible for validating the state information between itself and the server. Validating locking state for the client means that it must verify or reclaim state for each lock currently held.
The first occasion of lock revocation is upon server reboot or restart. In this instance the client will receive an error (NFS4ERR_STALE_STATEID on an operation that takes a stateid as an argument or NFS4ERR_STALE_CLIENTID on an operation that takes a sessionid or client ID) and the client will proceed with normal crash recovery as described in the Section 8.4.2.1 (State Reclaim).
The second occasion of lock revocation is the inability to renew the lease before expiration, as discussed above. While this is considered a rare or unusual event, the client must be prepared to recover. The server is responsible for determining lease expiration, and deciding exactly how to deal with it, informing the client of the scope of the lock revocation. The client then uses the status information provided by the server in the SEQUENCE results (field sr_status_flags, see Section 18.46.4 (DESCRIPTION)) to synchronize its locking state with that of the server, in order to recover.
The third occasion of lock revocation can occur as a result of revocation of locks within the lease period, either because of administrative intervention, or because a recallable lock (a delegation or layout) was not returned within the lease period after having been recalled. While these are considered rare events, they are possible and the client must be prepared to deal with them. When either of these events occur, the client finds out about the situation through the status returned by the SEQUENCE operation. Any use of stateids associated with locks revoked during the lease period will receive the error NFS4ERR_ADMIN_REVOKED or NFS4ERR_DELEG_REVOKED, as appropriate. </