Chinaunix首页 | 论坛 | 博客
  • 博客访问: 269148
  • 博文数量: 113
  • 博客积分: 446
  • 博客等级: 下士
  • 技术积分: 1244
  • 用 户 组: 普通用户
  • 注册时间: 2012-12-09 16:01
个人简介

Let's go!!!!!

文章分类

全部博文(113)

文章存档

2019年(5)

2018年(4)

2017年(9)

2016年(5)

2015年(39)

2014年(6)

2013年(28)

2012年(17)

分类: LINUX

2016-03-15 21:22:04

Network Working Group                                       B. Callaghan
Request for Comments: 1813                                  B. Pawlowski
Category: Informational                                      P. Staubach
                                                 Sun Microsystems, Inc.
                                                              June 1995

                 NFS Version 3 Protocol Specification

Status of this Memo

  This memo provides information for the Internet community.
  This memo does not specify an Internet standard of any kind.
  Distribution of this memo is unlimited.

IESG Note

  Internet Engineering Steering Group comment: please note that
  the IETF is not involved in creating or maintaining this
  specification.  This is the significance of the specification
  not being on the standards track.

Abstract

  This paper describes the NFS version 3 protocol.  This paper is
  provided so that people can write compatible implementations.

Table of Contents

  1.    Introduction . . . . . . . . . . . . . . . . . . . . . . .   3
  1.1     Scope of the NFS version 3 protocol  . . . . . . . . . .   4
  1.2     Useful terms . . . . . . . . . . . . . . . . . . . . . .   5
  1.3     Remote Procedure Call  . . . . . . . . . . . . . . . . .   5
  1.4     External Data Representation . . . . . . . . . . . . . .   5
  1.5     Authentication and Permission Checking . . . . . . . . .   7
  1.6     Philosophy . . . . . . . . . . . . . . . . . . . . . . .   8
  1.7     Changes from the NFS version 2 protocol  . . . . . . . .  11
  2.    RPC Information  . . . . . . . . . . . . . . . . . . . . .  14
  2.1     Authentication . . . . . . . . . . . . . . . . . . . . .  14
  2.2     Constants  . . . . . . . . . . . . . . . . . . . . . . .  14
  2.3     Transport address  . . . . . . . . . . . . . . . . . . .  14
  2.4     Sizes  . . . . . . . . . . . . . . . . . . . . . . . . .  14
  2.5     Basic Data Types . . . . . . . . . . . . . . . . . . . .  15
  2.6     Defined Error Numbers  . . . . . . . . . . . . . . . . .  17
  3.    Server Procedures  . . . . . . . . . . . . . . . . . . . .  27
  3.1     General comments on attributes . . . . . . . . . . . . .  29
  3.2     General comments on filenames  . . . . . . . . . . . . .  30
  3.3.0   NULL: Do nothing . . . . . . . . . . . . . . . . . . . .  31

  3.3.1   GETATTR: Get file attributes . . . . . . . . . . . . . .  32
  3.3.2   SETATTR: Set file attributes . . . . . . . . . . . . . .  33
  3.3.3   LOOKUP: Lookup filename  . . . . . . . . . . . . . . . .  37
  3.3.4   ACCESS: Check access permission  . . . . . . . . . . . .  40
  3.3.5   READLINK: Read from symbolic link  . . . . . . . . . . .  44
  3.3.6   READ: Read from file . . . . . . . . . . . . . . . . . .  46
  3.3.7   WRITE: Write to file . . . . . . . . . . . . . . . . . .  49
  3.3.8   CREATE: Create a file  . . . . . . . . . . . . . . . . .  54
  3.3.9   MKDIR: Create a directory  . . . . . . . . . . . . . . .  58
  3.3.10  SYMLINK: Create a symbolic link  . . . . . . . . . . . .  61
  3.3.11  MKNOD: Create a special device . . . . . . . . . . . . .  63
  3.3.12  REMOVE: Remove a file  . . . . . . . . . . . . . . . . .  67
  3.3.13  RMDIR: Remove a directory  . . . . . . . . . . . . . . .  69
  3.3.14  RENAME: Rename a file or directory . . . . . . . . . . .  71
  3.3.15  LINK: Create link to an object . . . . . . . . . . . . .  74
  3.3.16  READDIR: Read From directory . . . . . . . . . . . . . .  76
  3.3.17  READDIRPLUS: Extended read from directory  . . . . . . .  80
  3.3.18  FSSTAT: Get dynamic file system information  . . . . . .  84
  3.3.19  FSINFO: Get static file system information . . . . . . .  86
  3.3.20  PATHCONF: Retrieve POSIX information . . . . . . . . . .  90
  3.3.21  COMMIT: Commit cached data on a server to stable storage  92
  4.    Implementation issues  . . . . . . . . . . . . . . . . . .  96
  4.1     Multiple version support . . . . . . . . . . . . . . . .  96
  4.2     Server/client relationship . . . . . . . . . . . . . . .  96
  4.3     Path name interpretation . . . . . . . . . . . . . . . .  97
  4.4     Permission issues  . . . . . . . . . . . . . . . . . . .  98
  4.5     Duplicate request cache  . . . . . . . . . . . . . . . .  99
  4.6     File name component handling . . . . . . . . . . . . . . 101
  4.7     Synchronous modifying operations . . . . . . . . . . . . 101
  4.8     Stable storage . . . . . . . . . . . . . . . . . . . . . 101
  4.9     Lookups and name resolution  . . . . . . . . . . . . . . 102
  4.10    Adaptive retransmission  . . . . . . . . . . . . . . . . 102
  4.11    Caching policies . . . . . . . . . . . . . . . . . . . . 102
  4.12    Stable versus unstable writes. . . . . . . . . . . . . . 103
  4.13    32 bit clients/servers and 64 bit clients/servers. . . . 104
  5.    Appendix I: Mount protocol . . . . . . . . . . . . . . . . 106
  5.1     RPC Information  . . . . . . . . . . . . . . . . . . . . 106
  5.1.1     Authentication . . . . . . . . . . . . . . . . . . . . 106
  5.1.2     Constants  . . . . . . . . . . . . . . . . . . . . . . 106
  5.1.3     Transport address  . . . . . . . . . . . . . . . . . . 106
  5.1.4     Sizes  . . . . . . . . . . . . . . . . . . . . . . . . 106
  5.1.5     Basic Data Types . . . . . . . . . . . . . . . . . . . 106
  5.2     Server Procedures  . . . . . . . . . . . . . . . . . . . 107
  5.2.0     NULL: Do nothing . . . . . . . . . . . . . . . . . . . 108
  5.2.1     MNT: Add mount entry . . . . . . . . . . . . . . . . . 109
  5.2.2     DUMP: Return mount entries . . . . . . . . . . . . . . 110
  5.2.3     UMNT: Remove mount entry . . . . . . . . . . . . . . . 111
  5.2.4     UMNTALL: Remove all mount entries  . . . . . . . . . . 112

  5.2.5     EXPORT: Return export list . . . . . . . . . . . . . . 113
  6.    Appendix II: Lock manager protocol . . . . . . . . . . . . 114
  6.1     RPC Information  . . . . . . . . . . . . . . . . . . . . 114
  6.1.1     Authentication . . . . . . . . . . . . . . . . . . . . 114
  6.1.2     Constants  . . . . . . . . . . . . . . . . . . . . . . 114
  6.1.3     Transport Address  . . . . . . . . . . . . . . . . . . 115
  6.1.4     Basic Data Types . . . . . . . . . . . . . . . . . . . 115
  6.2     NLM Procedures . . . . . . . . . . . . . . . . . . . . . 118
  6.2.0     NULL: Do nothing . . . . . . . . . . . . . . . . . . . 120
  6.3     Implementation issues  . . . . . . . . . . . . . . . . . 120
  6.3.1     64-bit offsets and lengths . . . . . . . . . . . . . . 120
  6.3.2     File handles . . . . . . . . . . . . . . . . . . . . . 120
  7.    Appendix III: Bibliography . . . . . . . . . . . . . . . . 122
  8.    Security Considerations  . . . . . . . . . . . . . . . . . 125
  9.    Acknowledgements . . . . . . . . . . . . . . . . . . . . . 125
  10.   Authors' Addresses . . . . . . . . . . . . . . . . . . . . 126

1. Introduction

  Sun's NFS protocol provides transparent remote access to shared
  file systems across networks. The NFS protocol is designed to be
  machine, operating system, network architecture, and transport
  protocol independent. This independence is achieved through the
  use of Remote Procedure Call (RPC) primitives built on top of an
  eXternal Data Representation (XDR).  Implementations of the NFS
  version 2 protocol exist for a variety of machines, from personal
  computers to supercomputers. The initial version of the NFS
  protocol is specified in the Network File System Protocol
  Specification [RFC1094]. A description of the initial
  implementation can be found in [Sandberg].

  The supporting MOUNT protocol performs the operating
  system-specific functions that allow clients to attach remote
  directory trees to a point within the local file system. The
  mount process also allows the server to grant remote access
  privileges to a restricted set of clients via export control.

  The Lock Manager provides support for file locking when used in
  the NFS environment. The Network Lock Manager (NLM) protocol
  isolates the inherently stateful aspects of file locking into a
  separate protocol.

  A complete description of the above protocols and their
  implementation is to be found in [X/OpenNFS].

  The purpose of this document is to:

       o Specify the NFS version 3 protocol.

       o Describe semantics of the protocol through annotation
         and description of intended implementation.

       o Specify the MOUNT version 3 protocol.

       o Briefly describe the changes between the NLM version 3
         protocol and the NLM version 4 protocol.

  The normative text is the description of the RPC procedures and
  arguments and results, which defines the over-the-wire protocol,
  and the semantics of those procedures. The material describing
  implementation practice aids the understanding of the protocol
  specification and describes some possible implementation issues
  and solutions. It is not possible to describe all implementations
  and the UNIX operating system implementation of the NFS version 3
  protocol is most often used to provide examples. Given that, the
  implementation discussion does not bear the authority of the
  description of the over-the-wire protocol itself.

1.1 Scope of the NFS version 3 protocol

  This revision of the NFS protocol addresses new requirements.
  The need to support larger files and file systems has prompted
  extensions to allow 64 bit file sizes and offsets. The revision
  enhances security by adding support for an access check to be
  done on the server. Performance modifications are of three
  types:

  1. The number of over-the-wire packets for a given
     set of file operations is reduced by returning file
     attributes on every operation, thus decreasing the number
     of calls to get modified attributes.

  2. The write throughput bottleneck caused by the synchronous
     definition of write in the NFS version 2 protocol has been
     addressed by adding support so that the NFS server can do
     unsafe writes. Unsafe writes are writes which have not
     been committed to stable storage before the operation
     returns.  This specification defines a method for
     committing these unsafe writes to stable storage in a
     reliable way.

  3. Limitations on transfer sizes have been relaxed.

  The ability to support multiple versions of a protocol in RPC
  will allow implementors of the NFS version 3 protocol to define

  clients and servers that provide backwards compatibility with
  the existing installed base of NFS version 2 protocol
  implementations.

  The extensions described here represent an evolution of the
  existing NFS protocol and most of the design features of the
  NFS protocol described in [Sandberg] persist. See Changes
  from the NFS version 2 protocol on page 11 for a more
  detailed summary of the changes introduced by this revision.

1.2 Useful terms

  In this specification, a "server" is a machine that provides
  resources to the network; a "client" is a machine that accesses
  resources over the network; a "user" is a person logged in on a
  client; an "application" is a program that executes on a client.

1.3 Remote Procedure Call

  The Sun Remote Procedure Call specification provides a
  procedure-oriented interface to remote services. Each server
  supplies a program, which is a set of procedures. The NFS
  service is one such program. The combination of host address,
  program number, version number, and procedure number specify one
  remote service procedure.  Servers can support multiple versions
  of a program by using different protocol version numbers.

  The NFS protocol was designed to not require any specific level
  of reliability from its lower levels so it could potentially be
  used on many underlying transport protocols. The NFS service is
  based on RPC which provides the abstraction above lower level
  network and transport protocols.

  The rest of this document assumes the NFS environment is
  implemented on top of Sun RPC, which is specified in [RFC1057].
  A complete discussion is found in [Corbin].

1.4 External Data Representation

  The eXternal Data Representation (XDR) specification provides a
  standard way of representing a set of data types on a network.
  This solves the problem of different byte orders, structure
  alignment, and data type representation on different,
  communicating machines.

  In this document, the RPC Data Description Language is used to
  specify the XDR format parameters and results to each of the RPC
  service procedures that an NFS server provides. The RPC Data

  Description Language is similar to declarations in the C
  programming language. A few new constructs have been added.
  The notation:

     string  name[SIZE];
     string  data;

  defines name, which is a fixed size block of SIZE bytes, and
  data, which is a variable sized block of up to DSIZE bytes. This
  notation indicates fixed-length arrays and arrays with a
  variable number of elements up to a fixed maximum. A
  variable-length definition with no size specified means there is
  no maximum size for the field.

  The discriminated union definition:

     union example switch (enum status) {
          case OK:
             struct {
                filename      file1;
                filename      file2;
                integer       count;
             }
          case ERROR:
             struct {
                errstat       error;
                integer       errno;
             }
          default:
             void;
     }

  defines a structure where the first thing over the network is an
  enumeration type called status. If the value of status is OK,
  the next thing on the network will be the structure containing
  file1, file2, and count. Else, if the value of status is ERROR,
  the next thing on the network will be a structure containing
  error and errno.  If the value of status is neither OK nor
  ERROR, then there is no more data in the structure.

  The XDR type, hyper, is an 8 byte (64 bit) quantity. It is used
  in the same way as the integer type. For example:

     hyper          foo;
     unsigned hyper bar;

  foo is an 8 byte signed value, while bar is an 8 byte unsigned
  value.

  Although RPC/XDR compilers exist to generate client and server
  stubs from RPC Data Description Language input, NFS
  implementations do not require their use. Any software that
  provides equivalent encoding and decoding to the canonical
  network order of data defined by XDR can be used to interoperate
  with other NFS implementations.

  XDR is described in [RFC1014].

1.5 Authentication and Permission Checking

  The RPC protocol includes a slot for authentication parameters
  on every call. The contents of the authentication parameters are
  determined by the type of authentication used by the server and
  client. A server may support several different flavors of
  authentication at once. The AUTH_NONE flavor provides null
  authentication, that is, no authentication information is
  passed. The AUTH_UNIX flavor provides UNIX-style user ID, group
  ID, and groups with each call. The AUTH_DES flavor provides
  DES-encrypted authentication parameters based on a network-wide
  name, with session keys exchanged via a public key scheme. The
  AUTH_KERB flavor provides DES encrypted authentication
  parameters based on a network-wide name with session keys
  exchanged via Kerberos secret keys.

  The NFS server checks permissions by taking the credentials from
  the RPC authentication information in each remote request. For
  example, using the AUTH_UNIX flavor of authentication, the
  server gets the user's effective user ID, effective group ID and
  groups on each call, and uses them to check access. Using user
  ids and group ids implies that the client and server either
  share the same ID list or do local user and group ID mapping.
  Servers and clients must agree on the mapping from user to uid
  and from group to gid, for those sites that do not implement a
  consistent user ID and group ID space. In practice, such mapping
  is typically performed on the server, following a static mapping
  scheme or a mapping established by the user from a client at
  mount time.

  The AUTH_DES and AUTH_KERB style of authentication is based on a
  network-wide name. It provides greater security through the use
  of DES encryption and public keys in the case of AUTH_DES, and
  DES encryption and Kerberos secret keys (and tickets) in the
  AUTH_KERB case. Again, the server and client must agree on the
  identity of a particular name on the network, but the name to
  identity mapping is more operating system independent than the
  uid and gid mapping in AUTH_UNIX. Also, because the
  authentication parameters are encrypted, a malicious user must

  know another users network password or private key to masquerade
  as that user. Similarly, the server returns a verifier that is
  also encrypted so that masquerading as a server requires knowing
  a network password.

  The NULL procedure typically requires no authentication.

1.6 Philosophy

  This specification defines the NFS version 3 protocol, that is
  the over-the-wire protocol by which a client accesses a server.
  The protocol provides a well-defined interface to a server's
  file resources. A client or server implements the protocol and
  provides a mapping of the local file system semantics and
  actions into those defined in the NFS version 3 protocol.
  Implementations may differ to varying degrees, depending on the
  extent to which a given environment can support all the
  operations and semantics defined in the NFS version 3 protocol.
  Although implementations exist and are used to illustrate
  various aspects of the NFS version 3 protocol, the protocol
  specification itself is the final description of how clients
  access server resources.

  Because the NFS version 3 protocol is designed to be
  operating-system independent, it does not necessarily match the
  semantics of any existing system. Server implementations are
  expected to make a best effort at supporting the protocol.  If a
  server cannot support a particular protocol procedure, it may
  return the error, NFS3ERR_NOTSUP, that indicates that the
  operation is not supported.  For example, many operating systems
  do not support the notion of a hard link. A server that cannot
  support hard links should return NFS3ERR_NOTSUP in response to a
  LINK request. FSINFO describes the most commonly unsupported
  procedures in the properties bit map.  Alternatively, a server
  may not natively support a given operation, but can emulate it
  in the NFS version 3 protocol implementation to provide greater
  functionality.

  In some cases, a server can support most of the semantics
  described by the protocol but not all. For example, the ctime
  field in the fattr structure gives the time that a file's
  attributes were last modified. Many systems do not keep this
  information. In this case, rather than not support the GETATTR
  operation, a server could simulate it by returning the last
  modified time in place of ctime.  Servers must be careful when
  simulating attribute information because of possible side
  effects on clients. For example, many clients use file
  modification times as a basis for their cache consistency

  scheme.

  NFS servers are dumb and NFS clients are smart. It is the
  clients that do the work required to convert the generalized
  file access that servers provide into a file access method that
  is useful to applications and users. In the LINK example given
  above, a UNIX client that received an NFS3ERR_NOTSUP error from
  a server would do the recovery necessary to either make it look
  to the application like the link request had succeeded or return
  a reasonable error. In general, it is the burden of the client
  to recover.

  The NFS version 3 protocol assumes a stateless server
  implementation.  Statelessness means that the server does not
  need to maintain state about any of its clients in order to
  function correctly. Stateless servers have a distinct advantage
  over stateful servers in the event of a crash. With stateless
  servers, a client need only retry a request until the server
  responds; the client does not even need to know that the server
  has crashed. See additional comments in Duplicate request cache
  on page 99.

  For a server to be useful, it holds nonvolatile state: data
  stored in the file system. Design assumptions in the NFS version
  3 protocol regarding flushing of modified data to stable storage
  reduce the number of failure modes in which data loss can occur.
  In this way, NFS version 3 protocol implementations can tolerate
  transient failures, including transient failures of the network.
  In general, server implementations of the NFS version 3 protocol
  cannot tolerate a non-transient failure of the stable storage
  itself. However, there exist fault tolerant implementations
  which attempt to address such problems.

  That is not to say that an NFS version 3 protocol server can't
  maintain noncritical state. In many cases, servers will maintain
  state (cache) about previous operations to increase performance.
  For example, a client READ request might trigger a read-ahead of
  the next block of the file into the server's data cache in the
  anticipation that the client is doing a sequential read and the
  next client READ request will be satisfied from the server's
  data cache instead of from the disk. Read-ahead on the server
  increases performance by overlapping server disk I/O with client
  requests. The important point here is that the read-ahead block
  is not necessary for correct server behavior. If the server
  crashes and loses its memory cache of read buffers, recovery is
  simple on reboot - clients will continue read operations
  retrieving data from the server disk.

  Most data-modifying operations in the NFS protocol are
  synchronous.  That is, when a data modifying procedure returns
  to the client, the client can assume that the operation has
  completed and any modified data associated with the request is
  now on stable storage. For example, a synchronous client WRITE
  request may cause the server to update data blocks, file system
  information blocks, and file attribute information - the latter
  information is usually referred to as metadata. When the WRITE
  operation completes, the client can assume that the write data
  is safe and discard it.  This is a very important part of the
  stateless nature of the server. If the server did not flush
  dirty data to stable storage before returning to the client, the
  client would have no way of knowing when it was safe to discard
  modified data. The following data modifying procedures are
  synchronous: WRITE (with stable flag set to FILE_SYNC), CREATE,
  MKDIR, SYMLINK, MKNOD, REMOVE, RMDIR, RENAME, LINK, and COMMIT.

  The NFS version 3 protocol introduces safe asynchronous writes
  on the server, when the WRITE procedure is used in conjunction
  with the COMMIT procedure. The COMMIT procedure provides a way
  for the client to flush data from previous asynchronous WRITE
  requests on the server to stable storage and to detect whether
  it is necessary to retransmit the data. See the procedure
  descriptions of WRITE on page 49 and COMMIT on page 92.

  The LOOKUP procedure is used by the client to traverse
  multicomponent file names (pathnames). Each call to LOOKUP is
  used to resolve one segment of a pathname. There are two reasons
  for restricting LOOKUP to a single segment: it is hard to
  standardize a common format for hierarchical file names and the
  client and server may have different mappings of pathnames to
  file systems. This would imply that either the client must break
  the path name at file system attachment points, or the server
  must know about the client's file system attachment points. In
  NFS version 3 protocol implementations, it is the client that
  constructs the hierarchical file name space using mounts to
  build a hierarchy. Support utilities, such as the Automounter,
  provide a way to manage a shared, consistent image of the file
  name space while still being driven by the client mount
  process.

  Clients can perform caching in varied manner. The general
  practice with the NFS version 2 protocol was to implement a
  time-based client-server cache consistency mechanism. It is
  expected NFS version 3 protocol implementations will use a
  similar mechanism. The NFS version 3 protocol has some explicit
  support, in the form of additional attribute information to
  eliminate explicit attribute checks. However, caching is not

  required, nor is any caching policy defined by the protocol.
  Neither the NFS version 2 protocol nor the NFS version 3
  protocol provide a means of maintaining strict client-server
  consistency (and, by implication, consistency across client
  caches).

1.7 Changes from the NFS Version 2 Protocol

  The ROOT and WRITECACHE procedures have been removed. A MKNOD
  procedure has been defined to allow the creation of special
  files, eliminating the overloading of CREATE. Caching on the
  client is not defined nor dictated by the NFS version 3
  protocol, but additional information and hints have been added
  to the protocol to allow clients that implement caching to
  manage their caches more effectively. Procedures that affect the
  attributes of a file or directory may now return the new
  attributes after the operation has completed to optimize out a
  subsequent GETATTR used in validating attribute caches. In
  addition, operations that modify the directory in which the
  target object resides return the old and new attributes of the
  directory to allow clients to implement more intelligent cache
  invalidation procedures.  The ACCESS procedure provides access
  permission checking on the server, the FSSTAT procedure returns
  dynamic information about a file system, the FSINFO procedure
  returns static information about a file system and server, the
  READDIRPLUS procedure returns file handles and attributes in
  addition to directory entries, and the PATHCONF procedure
  returns POSIX pathconf information about a file.

  Below is a list of the important changes between the NFS version
  2 protocol and the NFS version 3 protocol.

  File handle size
        The file handle has been increased to a variable-length
        array of 64 bytes maximum from a fixed array of 32
        bytes. This addresses some known requirements for a
        slightly larger file handle size. The file handle was
        converted from fixed length to variable length to
        reduce local storage and network bandwidth requirements
        for systems which do not utilize the full 64 bytes of
        length.

  Maximum data sizes
        The maximum size of a data transfer used in the READ
        and WRITE procedures is now set by values in the FSINFO
        return structure. In addition, preferred transfer sizes
        are returned by FSINFO. The protocol does not place any
        artificial limits on the maximum transfer sizes.

        Filenames and pathnames are now specified as strings of
        variable length. The actual length restrictions are
        determined by the client and server implementations as
        appropriate.  The protocol does not place any
        artificial limits on the length. The error,
        NFS3ERR_NAMETOOLONG, is provided to allow the server to
        return an indication to the client that it received a
        pathname that was too long for it to handle.

  Error return
        Error returns in some instances now return data (for
        example, attributes). nfsstat3 now defines the full set
        of errors that can be returned by a server. No other
        values are allowed.

  File type
        The file type now includes NF3CHR and NF3BLK for
        special files. Attributes for these types include
        subfields for UNIX major and minor devices numbers.
        NF3SOCK and NF3FIFO are now defined for sockets and
        fifos in the file system.

  File attributes
        The blocksize (the size in bytes of a block in the
        file) field has been removed. The mode field no longer
        contains file type information. The size and fileid
        fields have been widened to eight-byte unsigned
        integers from four-byte integers. Major and minor
        device information is now presented in a distinct
        structure.  The blocks field name has been changed to
        used and now contains the total number of bytes used by
        the file. It is also an eight-byte unsigned integer.

  Set file attributes
        In the NFS version 2 protocol, the settable attributes
        were represented by a subset of the file attributes
        structure; the client indicated those attributes which
        were not to be modified by setting the corresponding
        field to -1, overloading some unsigned fields. The set
        file attributes structure now uses a discriminated
        union for each field to tell whether or how to set that
        field. The atime and mtime fields can be set to either
        the server's current time or a time supplied by the
        client.

  LOOKUP
        The LOOKUP return structure now includes the attributes
        for the directory searched.

  ACCESS
        An ACCESS procedure has been added to allow an explicit
        over-the-wire permissions check. This addresses known
        problems with the superuser ID mapping feature in many
        server implementations (where, due to mapping of root
        user, unexpected permission denied errors could occur
        while reading from or writing to a file).  This also
        removes the assumption which was made in the NFS
        version 2 protocol that access to files was based
        solely on UNIX style mode bits.

  READ
        The reply structure includes a Boolean that is TRUE if
        the end-of-file was encountered during the READ.  This
        allows the client to correctly detect end-of-file.

  WRITE
        The beginoffset and totalcount fields were removed from
        the WRITE arguments. The reply now includes a count so
        that the server can write less than the requested
        amount of data, if required. An indicator was added to
        the arguments to instruct the server as to the level of
        cache synchronization that is required by the client.

  CREATE
        An exclusive flag and a create verifier was added for
        the exclusive creation of regular files.

  MKNOD
        This procedure was added to support the creation of
        special files. This avoids overloading fields of CREATE
        as was done in some NFS version 2 protocol
        implementations.

  READDIR
        The READDIR arguments now include a verifier to allow
        the server to validate the cookie. The cookie is now a
        64 bit unsigned integer instead of the 4 byte array
        which was used in the NFS version 2 protocol.  This
        will help to reduce interoperability problems.

  READDIRPLUS
        This procedure was added to return file handles and
        attributes in an extended directory list.

  FSINFO
        FSINFO was added to provide nonvolatile information
        about a file system. The reply includes preferred and

        maximum read transfer size, preferred and maximum write
        transfer size, and flags stating whether links or
        symbolic links are supported.  Also returned are
        preferred transfer size for READDIR procedure replies,
        server time granularity, and whether times can be set
        in a SETATTR request.

  FSSTAT
        FSSTAT was added to provide volatile information about
        a file system, for use by utilities such as the Unix
        system df command. The reply includes the total size
        and free space in the file system specified in bytes,
        the total number of files and number of free file slots
        in the file system, and an estimate of time between
        file system modifications (for use in cache consistency
        checking algorithms).

  COMMIT
        The COMMIT procedure provides the synchronization
        mechanism to be used with asynchronous WRITE
        operations.

2. RPC Information

2.1 Authentication

  The NFS service uses AUTH_NONE in the NULL procedure. AUTH_UNIX,
  AUTH_DES, or AUTH_KERB are used for all other procedures. Other
  authentication types may be supported in the future.

2.2 Constants

  These are the RPC constants needed to call the NFS Version 3
  service.  They are given in decimal.

     PROGRAM  100003
     VERSION  3

2.3 Transport address

  The NFS protocol is normally supported over the TCP and UDP
  protocols.  It uses port 2049, the same as the NFS version 2
  protocol.

2.4 Sizes

  These are the sizes, given in decimal bytes, of various XDR
  structures used in the NFS version 3 protocol:

  NFS3_FHSIZE 64
     The maximum size in bytes of the opaque file handle.

  NFS3_COOKIEVERFSIZE 8
     The size in bytes of the opaque cookie verifier passed by
     READDIR and READDIRPLUS.

  NFS3_CREATEVERFSIZE 8
     The size in bytes of the opaque verifier used for
     exclusive CREATE.

  NFS3_WRITEVERFSIZE 8
     The size in bytes of the opaque verifier used for
     asynchronous WRITE.

2.5 Basic Data Types

  The following XDR definitions are basic definitions that are
  used in other structures.

  uint64
        typedef unsigned hyper uint64;

  int64
        typedef hyper int64;

  uint32
        typedef unsigned long uint32;

  int32
        typedef long int32;

  filename3
        typedef string filename3<>;

  nfspath3
        typedef string nfspath3<>;

  fileid3
        typedef uint64 fileid3;

  cookie3
        typedef uint64 cookie3;

  cookieverf3
        typedef opaque cookieverf3[NFS3_COOKIEVERFSIZE];

  createverf3
        typedef opaque createverf3[NFS3_CREATEVERFSIZE];

  writeverf3
        typedef opaque writeverf3[NFS3_WRITEVERFSIZE];

  uid3
        typedef uint32 uid3;

  gid3
        typedef uint32 gid3;

  size3
        typedef uint64 size3;

  offset3
        typedef uint64 offset3;

  mode3
        typedef uint32 mode3;

  count3
        typedef uint32 count3;

  nfsstat3
     enum nfsstat3 {
        NFS3_OK             = 0,
        NFS3ERR_PERM        = 1,
        NFS3ERR_NOENT       = 2,
        NFS3ERR_IO          = 5,
        NFS3ERR_NXIO        = 6,
        NFS3ERR_ACCES       = 13,
        NFS3ERR_EXIST       = 17,
        NFS3ERR_XDEV        = 18,
        NFS3ERR_NODEV       = 19,
        NFS3ERR_NOTDIR      = 20,
        NFS3ERR_ISDIR       = 21,
        NFS3ERR_INVAL       = 22,
        NFS3ERR_FBIG        = 27,
        NFS3ERR_NOSPC       = 28,
        NFS3ERR_ROFS        = 30,
        NFS3ERR_MLINK       = 31,
        NFS3ERR_NAMETOOLONG = 63,
        NFS3ERR_NOTEMPTY    = 66,
        NFS3ERR_DQUOT       = 69,
        NFS3ERR_STALE       = 70,
        NFS3ERR_REMOTE      = 71,
        NFS3ERR_BADHANDLE   = 10001,

        NFS3ERR_NOT_SYNC    = 10002,
        NFS3ERR_BAD_COOKIE  = 10003,
        NFS3ERR_NOTSUPP     = 10004,
        NFS3ERR_TOOSMALL    = 10005,
        NFS3ERR_SERVERFAULT = 10006,
        NFS3ERR_BADTYPE     = 10007,
        NFS3ERR_JUKEBOX     = 10008
     };

  The nfsstat3 type is returned with every procedure's results
  except for the NULL procedure. A value of NFS3_OK indicates that
  the call completed successfully. Any other value indicates that
  some error occurred on the call, as identified by the error
  code. Note that the precise numeric encoding must be followed.
  No other values may be returned by a server. Servers are
  expected to make a best effort mapping of error conditions to
  the set of error codes defined. In addition, no error
  precedences are specified by this specification.  Error
  precedences determine the error value that should be returned
  when more than one error applies in a given situation. The error
  precedence will be determined by the individual server
  implementation. If the client requires specific error
  precedences, it should check for the specific errors for
  itself.

2.6 Defined Error Numbers

  A description of each defined error follows:

  NFS3_OK
      Indicates the call completed successfully.

  NFS3ERR_PERM
      Not owner. The operation was not allowed because the
      caller is either not a privileged user (root) or not the
      owner of the target of the operation.

  NFS3ERR_NOENT
      No such file or directory. The file or directory name
      specified does not exist.

  NFS3ERR_IO
      I/O error. A hard error (for example, a disk error)
      occurred while processing the requested operation.

  NFS3ERR_NXIO
      I/O error. No such device or address.

  NFS3ERR_ACCES
      Permission denied. The caller does not have the correct
      permission to perform the requested operation. Contrast
      this with NFS3ERR_PERM, which restricts itself to owner
      or privileged user permission failures.

  NFS3ERR_EXIST
      File exists. The file specified already exists.

  NFS3ERR_XDEV
      Attempt to do a cross-device hard link.

  NFS3ERR_NODEV
      No such device.

  NFS3ERR_NOTDIR
      Not a directory. The caller specified a non-directory in
      a directory operation.

  NFS3ERR_ISDIR
      Is a directory. The caller specified a directory in a
      non-directory operation.

  NFS3ERR_INVAL
      Invalid argument or unsupported argument for an
      operation. Two examples are attempting a READLINK on an
      object other than a symbolic link or attempting to
      SETATTR a time field on a server that does not support
      this operation.

  NFS3ERR_FBIG
      File too large. The operation would have caused a file to
      grow beyond the server's limit.

  NFS3ERR_NOSPC
      No space left on device. The operation would have caused
      the server's file system to exceed its limit.

  NFS3ERR_ROFS
      Read-only file system. A modifying operation was
      attempted on a read-only file system.

  NFS3ERR_MLINK
      Too many hard links.

  NFS3ERR_NAMETOOLONG
      The filename in an operation was too long.

  NFS3ERR_NOTEMPTY

      An attempt was made to remove a directory that was not
      empty.

  NFS3ERR_DQUOT
      Resource (quota) hard limit exceeded. The user's resource
      limit on the server has been exceeded.

  NFS3ERR_STALE
      Invalid file handle. The file handle given in the
      arguments was invalid. The file referred to by that file
      handle no longer exists or access to it has been
      revoked.

  NFS3ERR_REMOTE
      Too many levels of remote in path. The file handle given
      in the arguments referred to a file on a non-local file
      system on the server.

  NFS3ERR_BADHANDLE
      Illegal NFS file handle. The file handle failed internal
      consistency checks.

  NFS3ERR_NOT_SYNC
      Update synchronization mismatch was detected during a
      SETATTR operation.

  NFS3ERR_BAD_COOKIE
      READDIR or READDIRPLUS cookie is stale.

  NFS3ERR_NOTSUPP
      Operation is not supported.

  NFS3ERR_TOOSMALL
      Buffer or request is too small.

  NFS3ERR_SERVERFAULT
      An error occurred on the server which does not map to any
      of the legal NFS version 3 protocol error values.  The
      client should translate this into an appropriate error.
      UNIX clients may choose to translate this to EIO.

  NFS3ERR_BADTYPE
      An attempt was made to create an object of a type not
      supported by the server.

  NFS3ERR_JUKEBOX
      The server initiated the request, but was not able to
      complete it in a timely fashion. The client should wait
      and then try the request with a new RPC transaction ID.
      For example, this error should be returned from a server
      that supports hierarchical storage and receives a request
      to process a file that has been migrated. In this case,
      the server should start the immigration process and
      respond to client with this error.

  ftype3

     enum ftype3 {
        NF3REG    = 1,
        NF3DIR    = 2,
        NF3BLK    = 3,
        NF3CHR    = 4,
        NF3LNK    = 5,
        NF3SOCK   = 6,
        NF3FIFO   = 7
     };

  The enumeration, ftype3, gives the type of a file. The type,
  NF3REG, is a regular file, NF3DIR is a directory, NF3BLK is a
  block special device file, NF3CHR is a character special device
  file, NF3LNK is a symbolic link, NF3SOCK is a socket, and
  NF3FIFO is a named pipe. Note that the precise enum encoding
  must be followed.

  specdata3

     struct specdata3 {
          uint32     specdata1;
          uint32     specdata2;
     };

  The interpretation of the two words depends on the type of file
  system object. For a block special (NF3BLK) or character special
  (NF3CHR) file, specdata1 and specdata2 are the major and minor
  device numbers, respectively.  (This is obviously a
  UNIX-specific interpretation.) For all other file types, these
  two elements should either be set to 0 or the values should be
  agreed upon by the client and server. If the client and server
  do not agree upon the values, the client should treat these
  fields as if they are set to 0. This data field is returned as
  part of the fattr3 structure and so is available from all
  replies returning attributes. Since these fields are otherwise
  unused for objects which are not devices, out of band

  information can be passed from the server to the client.
  However, once again, both the server and the client must agree
  on the values passed.

  nfs_fh3

     struct nfs_fh3 {
        opaque       data;
     };

  The nfs_fh3 is the variable-length opaque object returned by the
  server on LOOKUP, CREATE, SYMLINK, MKNOD, LINK, or READDIRPLUS
  operations, which is used by the client on subsequent operations
  to reference the file. The file handle contains all the
  information the server needs to distinguish an individual file.
  To the client, the file handle is opaque. The client stores file
  handles for use in a later request and can compare two file
  handles from the same server for equality by doing a
  byte-by-byte comparison, but cannot otherwise interpret the
  contents of file handles. If two file handles from the same
  server are equal, they must refer to the same file, but if they
  are not equal, no conclusions can be drawn. Servers should try
  to maintain a one-to-one correspondence between file handles and
  files, but this is not required. Clients should use file handle
  comparisons only to improve performance, not for correct
  behavior.

  Servers can revoke the access provided by a file handle at any
  time.  If the file handle passed in a call refers to a file
  system object that no longer exists on the server or access for
  that file handle has been revoked, the error, NFS3ERR_STALE,
  should be returned.

  nfstime3

     struct nfstime3 {
        uint32   seconds;
        uint32   nseconds;
     };

  The nfstime3 structure gives the number of seconds and
  nanoseconds since midnight January 1, 1970 Greenwich Mean Time.
  It is used to pass time and date information. The times
  associated with files are all server times except in the case of
  a SETATTR operation where the client can explicitly set the file
  time. A server converts to and from local time when processing
  time values, preserving as much accuracy as possible. If the
  precision of timestamps stored for a file is less than that

  defined by NFS version 3 protocol, loss of precision can occur.
  An adjunct time maintenance protocol is recommended to reduce
  client and server time skew.

  fattr3

     struct fattr3 {
        ftype3     type;
        mode3      mode;
        uint32     nlink;
        uid3       uid;
        gid3       gid;
        size3      size;
        size3      used;
        specdata3  rdev;
        uint64     fsid;
        fileid3    fileid;
        nfstime3   atime;
        nfstime3   mtime;
        nfstime3   ctime;
     };

  This structure defines the attributes of a file system object.
  It is returned by most operations on an object; in the case of
  operations that affect two objects (for example, a MKDIR that
  modifies the target directory attributes and defines new
  attributes for the newly created directory), the attributes for
  both may be returned. In some cases, the attributes are returned
  in the structure, wcc_data, which is defined below; in other
  cases the attributes are returned alone.  The main changes from
  the NFS version 2 protocol are that many of the fields have been
  widened and the major/minor device information is now presented
  in a distinct structure rather than being packed into a word.

  The fattr3 structure contains the basic attributes of a file.
  All servers should support this set of attributes even if they
  have to simulate some of the fields. Type is the type of the
  file. Mode is the protection mode bits. Nlink is the number of
  hard links to the file - that is, the number of different names
  for the same file. Uid is the user ID of the owner of the file.
  Gid is the group ID of the group of the file. Size is the size
  of the file in bytes. Used is the number of bytes of disk space
  that the file actually uses (which can be smaller than the size
  because the file may have holes or it may be larger due to
  fragmentation). Rdev describes the device file if the file type
  is NF3CHR or NF3BLK - see specdata3 on page 20. Fsid is the file
  system identifier for the file system. Fileid is a number which
  uniquely identifies the file within its file system (on UNIX

  this would be the inumber). Atime is the time when the file data
  was last accessed. Mtime is the time when the file data was last
  modified.  Ctime is the time when the attributes of the file
  were last changed.  Writing to the file changes the ctime in
  addition to the mtime.

  The mode bits are defined as follows:

     0x00800 Set user ID on execution.
     0x00400 Set group ID on execution.
     0x00200 Save swapped text (not defined in POSIX).
     0x00100 Read permission for owner.
     0x00080 Write permission for owner.
     0x00040 Execute permission for owner on a file. Or lookup
             (search) permission for owner in directory.
     0x00020 Read permission for group.
     0x00010 Write permission for group.
     0x00008 Execute permission for group on a file. Or lookup
             (search) permission for group in directory.
     0x00004 Read permission for others.
     0x00002 Write permission for others.
     0x00001 Execute permission for others on a file. Or lookup
             (search) permission for others in directory.

  post_op_attr

     union post_op_attr switch (bool attributes_follow) {
     case TRUE:
        fattr3   attributes;
     case FALSE:
        void;
     };

  This structure is used for returning attributes in those
  operations that are not directly involved with manipulating
  attributes. One of the principles of this revision of the NFS
  protocol is to return the real value from the indicated
  operation and not an error from an incidental operation. The
  post_op_attr structure was designed to allow the server to
  recover from errors encountered while getting attributes.

  This appears to make returning attributes optional. However,
  server implementors are strongly encouraged to make best effort
  to return attributes whenever possible, even when returning an
  error.

  wcc_attr

     struct wcc_attr {
        size3       size;
        nfstime3    mtime;
        nfstime3    ctime;
     };

  This is the subset of pre-operation attributes needed to better
  support the weak cache consistency semantics. Size is the file
  size in bytes of the object before the operation. Mtime is the
  time of last modification of the object before the operation.
  Ctime is the time of last change to the attributes of the object
  before the operation. See discussion in wcc_attr on page 24.

  The use of mtime by clients to detect changes to file system
  objects residing on a server is dependent on the granularity of
  the time base on the server.

  pre_op_attr

     union pre_op_attr switch (bool attributes_follow) {
     case TRUE:
          wcc_attr  attributes;
     case FALSE:
          void;
     };

  wcc_data

     struct wcc_data {
        pre_op_attr    before;
        post_op_attr   after;
     };

  When a client performs an operation that modifies the state of a
  file or directory on the server, it cannot immediately determine
  from the post-operation attributes whether the operation just
  performed was the only operation on the object since the last
  time the client received the attributes for the object. This is
  important, since if an intervening operation has changed the
  object, the client will need to invalidate any cached data for
  the object (except for the data that it just wrote).

  To deal with this, the notion of weak cache consistency data or
  wcc_data is introduced. A wcc_data structure consists of certain
  key fields from the object attributes before the operation,
  together with the object attributes after the operation. This

  information allows the client to manage its cache more
  accurately than in NFS version 2 protocol implementations. The
  term, weak cache consistency, emphasizes the fact that this
  mechanism does not provide the strict server-client consistency
  that a cache consistency protocol would provide.

  In order to support the weak cache consistency model, the server
  will need to be able to get the pre-operation attributes of the
  object, perform the intended modify operation, and then get the
  post-operation attributes atomically. If there is a window for
  the object to get modified between the operation and either of
  the get attributes operations, then the client will not be able
  to determine whether it was the only entity to modify the
  object. Some information will have been lost, thus weakening the
  weak cache consistency guarantees.

  post_op_fh3

     union post_op_fh3 switch (bool handle_follows) {
     case TRUE:
          nfs_fh3  handle;
     case FALSE:
          void;
     };

  One of the principles of this revision of the NFS protocol is to
  return the real value from the indicated operation and not an
  error from an incidental operation. The post_op_fh3 structure
  was designed to allow the server to recover from errors
  encountered while constructing a file handle.

  This is the structure used to return a file handle from the
  CREATE, MKDIR, SYMLINK, MKNOD, and READDIRPLUS requests. In each
  case, the client can get the file handle by issuing a LOOKUP
  request after a successful return from one of the listed
  operations. Returning the file handle is an optimization so that
  the client is not forced to immediately issue a LOOKUP request
  to get the file handle.

  sattr3

     enum time_how {
        DONT_CHANGE        = 0,
        SET_TO_SERVER_TIME = 1,
        SET_TO_CLIENT_TIME = 2
     };

     union set_mode3 switch (bool set_it) {

     case TRUE:
        mode3    mode;
     default:
        void;
     };

     union set_uid3 switch (bool set_it) {
     case TRUE:
        uid3     uid;
     default:
        void;
     };

     union set_gid3 switch (bool set_it) {
     case TRUE:
        gid3     gid;
     default:
        void;
     };

     union set_size3 switch (bool set_it) {
     case TRUE:
        size3    size;
     default:
        void;
     };

     union set_atime switch (time_how set_it) {
     case SET_TO_CLIENT_TIME:
        nfstime3  atime;
     default:
        void;
     };

     union set_mtime switch (time_how set_it) {
     case SET_TO_CLIENT_TIME:
        nfstime3  mtime;
     default:
        void;
     };

     struct sattr3 {
        set_mode3   mode;
        set_uid3    uid;
        set_gid3    gid;
        set_size3   size;
        set_atime   atime;
        set_mtime   mtime;

     };

  The sattr3 structure contains the file attributes that can be
  set from the client. The fields are the same as the similarly
  named fields in the fattr3 structure. In the NFS version 3
  protocol, the settable attributes are described by a structure
  containing a set of discriminated unions. Each union indicates
  whether the corresponding attribute is to be updated, and if so,
  how.

  There are two forms of discriminated unions used. In setting the
  mode, uid, gid, or size, the discriminated union is switched on
  a boolean, set_it; if it is TRUE, a value of the appropriate
  type is then encoded.

  In setting the atime or mtime, the union is switched on an
  enumeration type, set_it. If set_it has the value DONT_CHANGE,
  the corresponding attribute is unchanged. If it has the value,
  SET_TO_SERVER_TIME, the corresponding attribute is set by the
  server to its local time; no data is provided by the client.
  Finally, if set_it has the value, SET_TO_CLIENT_TIME, the
  attribute is set to the time passed by the client in an nfstime3
  structure. (See FSINFO on page 86, which addresses the issue of
  time granularity).

  diropargs3

     struct diropargs3 {
        nfs_fh3     dir;
        filename3   name;
     };

  The diropargs3 structure is used in directory operations. The
  file handle, dir, identifies the directory in which to
  manipulate or access the file, name. See additional comments in
  File name component handling on page 101.

3. Server Procedures

  The following sections define the RPC procedures that are
  supplied by an NFS version 3 protocol server. The RPC
  procedure number is given at the top of the page with the
  name. The SYNOPSIS provides the name of the procedure, the
  list of the names of the arguments, the list of the names of
  the results, followed by the XDR argument declarations and
  results declarations. The information in the SYNOPSIS is
  specified in RPC Data Description Language as defined in
  [RFC1014]. The DESCRIPTION section tells what the procedure

  is expected to do and how its arguments and results are used.
  The ERRORS section lists the errors returned for specific
  types of failures. These lists are not intended to be the
  definitive statement of all of the errors which can be
  returned by any specific procedure, but as a guide for the
  more common errors which may be returned.  Client
  implementations should be prepared to deal with unexpected
  errors coming from a server. The IMPLEMENTATION field gives
  information about how the procedure is expected to work and
  how it should be used by clients.

     program NFS_PROGRAM {
        version NFS_V3 {

           void
            NFSPROC3_NULL(void)                    = 0;

           GETATTR3res
            NFSPROC3_GETATTR(GETATTR3args)         = 1;

           SETATTR3res
            NFSPROC3_SETATTR(SETATTR3args)         = 2;

           LOOKUP3res
            NFSPROC3_LOOKUP(LOOKUP3args)           = 3;

           ACCESS3res
            NFSPROC3_ACCESS(ACCESS3args)           = 4;

           READLINK3res
            NFSPROC3_READLINK(READLINK3args)       = 5;

           READ3res
            NFSPROC3_READ(READ3args)               = 6;

           WRITE3res
            NFSPROC3_WRITE(WRITE3args)             = 7;

           CREATE3res
            NFSPROC3_CREATE(CREATE3args)           = 8;

           MKDIR3res
            NFSPROC3_MKDIR(MKDIR3args)             = 9;

           SYMLINK3res
            NFSPROC3_SYMLINK(SYMLINK3args)         = 10;

           MKNOD3res
            NFSPROC3_MKNOD(MKNOD3args)             = 11;

           REMOVE3res
            NFSPROC3_REMOVE(REMOVE3args)           = 12;

           RMDIR3res
            NFSPROC3_RMDIR(RMDIR3args)             = 13;

           RENAME3res
            NFSPROC3_RENAME(RENAME3args)           = 14;

           LINK3res
            NFSPROC3_LINK(LINK3args)               = 15;

           READDIR3res
            NFSPROC3_READDIR(READDIR3args)         = 16;

           READDIRPLUS3res
            NFSPROC3_READDIRPLUS(READDIRPLUS3args) = 17;

           FSSTAT3res
            NFSPROC3_FSSTAT(FSSTAT3args)           = 18;

           FSINFO3res
            NFSPROC3_FSINFO(FSINFO3args)           = 19;

           PATHCONF3res
            NFSPROC3_PATHCONF(PATHCONF3args)       = 20;

           COMMIT3res
            NFSPROC3_COMMIT(COMMIT3args)           = 21;

        } = 3;
     } = 100003;

  Out of range (undefined) procedure numbers result in RPC
  errors.  Refer to [RFC1057] for more detail.

3.1 General comments on attributes and consistency data on failure

  For those procedures that return either post_op_attr or wcc_data
  structures on failure, the discriminated union may contain the
  pre-operation attributes of the object or object parent
  directory.  This depends on the error encountered and may also
  depend on the particular server implementation. Implementors are
  strongly encouraged to return as much attribute data as possible
  upon failure, but client implementors need to be aware that

  their implementation must correctly handle the variant return
  instance where no attributes or consistency data is returned.

3.2 General comments on filenames

  The following comments apply to all NFS version 3 protocol
  procedures in which the client provides one or more filenames in
  the arguments: LOOKUP, CREATE, MKDIR, SYMLINK, MKNOD, REMOVE,
  RMDIR, RENAME, and LINK.

  1. The filename must not be null nor may it be the null
     string.  The server should return the error, NFS3ERR_ACCES, if
     it receives such a filename. On some clients, the filename, ``''
     or a null string, is assumed to be an alias for the current
     directory. Clients which require this functionality should
     implement it for themselves and not depend upon the server to
     support such semantics.

  2. A filename having the value of "." is assumed to be an
     alias for the current directory. Clients which require this
     functionality should implement it for themselves and not depend
     upon the server to support such semantics. However, the server
     should be able to handle such a filename correctly.

  3. A filename having the value of ".." is assumed to be an
     alias for the parent of the current directory, i.e. the
     directory which contains the current directory. The server
     should be prepared to handle this semantic, if it supports
     directories, even if those directories do not contain UNIX-style
     "." or ".." entries.

  4. If the filename is longer than the maximum for the file
     system (see PATHCONF on page 90, specifically name_max), the
     result depends on the value of the PATHCONF flag, no_trunc. If
     no_trunc is FALSE, the filename will be silently truncated to
     name_max bytes. If no_trunc is TRUE and the filename exceeds the
     server's file system maximum filename length, the operation will
     fail with the error, NFS3ERR_NAMETOOLONG.

  5. In general, there will be characters that a server will
     not be able to handle as part of a filename. This set of
     characters will vary from server to server and from
     implementation to implementation.  In most cases, it is the
     server which will control the client's view of the file system.
     If the server receives a filename containing characters that it
     can not handle, the error, NFS3ERR_EACCES, should be returned.
     Client implementations should be prepared to handle this side
     affect of heterogeneity.

  See also comments in File name component handling on page 101.

3.3.0 Procedure 0: NULL - Do nothing

  SYNOPSIS

     void NFSPROC3_NULL(void) = 0;

  DESCRIPTION

     Procedure NULL does not do any work. It is made available to
     allow server response testing and timing.

  IMPLEMENTATION

     It is important that this procedure do no work at all so
     that it can be used to measure the overhead of processing
     a service request. By convention, the NULL procedure
     should never require any authentication. A server may
     choose to ignore this convention, in a more secure
     implementation, where responding to the NULL procedure
     call acknowledges the existence of a resource to an
     unauthenticated client.

  ERRORS

     Since the NULL procedure takes no NFS version 3 protocol
     arguments and returns no NFS version 3 protocol response,
     it can not return an NFS version 3 protocol error.
     However, it is possible that some server implementations
     may return RPC errors based on security and authentication
     requirements.

3.3.1 Procedure 1: GETATTR - Get file attributes

  SYNOPSIS

     GETATTR3res NFSPROC3_GETATTR(GETATTR3args) = 1;

     struct GETATTR3args {
        nfs_fh3  object;
     };

     struct GETATTR3resok {
        fattr3   obj_attributes;
     };

     union GETATTR3res switch (nfsstat3 status) {
     case NFS3_OK:
        GETATTR3resok  resok;
     default:
        void;
     };

  DESCRIPTION

     Procedure GETATTR retrieves the attributes for a specified
     file system object. The object is identified by the file
     handle that the server returned as part of the response
     from a LOOKUP, CREATE, MKDIR, SYMLINK, MKNOD, or
     READDIRPLUS procedure (or from the MOUNT service,
     described elsewhere). On entry, the arguments in
     GETATTR3args are:

     object
        The file handle of an object whose attributes are to be
        retrieved.

     On successful return, GETATTR3res.status is NFS3_OK and
     GETATTR3res.resok contains:

     obj_attributes
        The attributes for the object.

     Otherwise, GETATTR3res.status contains the error on failure and
     no other results are returned.

  IMPLEMENTATION

     The attributes of file system objects is a point of major
     disagreement between different operating systems. Servers

     should make a best attempt to support all of the
     attributes in the fattr3 structure so that clients can
     count on this as a common ground. Some mapping may be
     required to map local attributes to those in the fattr3
     structure.

     Today, most client NFS version 3 protocol implementations
     implement a time-bounded attribute caching scheme to
     reduce over-the-wire attribute checks.

  ERRORS

     NFS3ERR_IO
     NFS3ERR_STALE
     NFS3ERR_BADHANDLE
     NFS3ERR_SERVERFAULT

  SEE ALSO

     ACCESS.

3.3.2 Procedure 2: SETATTR - Set file attributes

  SYNOPSIS

     SETATTR3res NFSPROC3_SETATTR(SETATTR3args) = 2;

     union sattrguard3 switch (bool check) {
     case TRUE:
        nfstime3  obj_ctime;
     case FALSE:
        void;
     };

     struct SETATTR3args {
        nfs_fh3      object;
        sattr3       new_attributes;
        sattrguard3  guard;
     };

     struct SETATTR3resok {
        wcc_data  obj_wcc;
     };

     struct SETATTR3resfail {
        wcc_data  obj_wcc;
     };

     union SETATTR3res switch (nfsstat3 status) {
     case NFS3_OK:
        SETATTR3resok   resok;
     default:
        SETATTR3resfail resfail;
     };

  DESCRIPTION

     Procedure SETATTR changes one or more of the attributes of
     a file system object on the server. The new attributes are
     specified by a sattr3 structure. On entry, the arguments
     in SETATTR3args are:

     object
        The file handle for the object.

     new_attributes
        A sattr3 structure containing booleans and
        enumerations describing the attributes to be set and the new
        values for those attributes.

     guard
        A sattrguard3 union:

        check
           TRUE if the server is to verify that guard.obj_ctime
           matches the ctime for the object; FALSE otherwise.

     A client may request that the server check that the object
     is in an expected state before performing the SETATTR
     operation. To do this, it sets the argument guard.check to
     TRUE and the client passes a time value in guard.obj_ctime.
     If guard.check is TRUE, the server must compare the value of
     guard.obj_ctime to the current ctime of the object. If the
     values are different, the server must preserve the object
     attributes and must return a status of NFS3ERR_NOT_SYNC.
     If guard.check is FALSE, the server will not perform this
     check.

     On successful return, SETATTR3res.status is NFS3_OK and
     SETATTR3res.resok contains:

        obj_wcc
           A wcc_data structure containing the old and new
           attributes for the object.

     Otherwise, SETATTR3res.status contains the error on
     failure and SETATTR3res.resfail contains the following:

        obj_wcc
           A wcc_data structure containing the old and new
           attributes for the object.

  IMPLEMENTATION

     The guard.check mechanism allows the client to avoid
     changing the attributes of an object on the basis of stale
     attributes. It does not guarantee exactly-once semantics.
     In particular, if a reply is lost and the server does not
     detect the retransmission of the request, the procedure
     can fail with the error, NFS3ERR_NOT_SYNC, even though the
     attribute setting was previously performed successfully.
     The client can attempt to recover from this error by
     getting fresh attributes from the server and sending a new
     SETATTR request using the new ctime.  The client can
     optionally check the attributes to avoid the second
     SETATTR request if the new attributes show that the
     attributes have already been set as desired (though it may
     not have been the issuing client that set the
     attributes).

     The new_attributes.size field is used to request changes
     to the size of a file. A value of 0 causes the file to be
     truncated, a value less than the current size of the file
     causes data from new size to the end of the file to be
     discarded, and a size greater than the current size of the
     file causes logically zeroed data bytes to be added to the
     end of the file.  Servers are free to implement this using
     holes or actual zero data bytes. Clients should not make
     any assumptions regarding a server's implementation of
     this feature, beyond that the bytes returned will be
     zeroed. Servers must support extending the file size via
     SETATTR.

     SETATTR is not guaranteed atomic. A failed SETATTR may
     partially change a file's attributes.

     Changing the size of a file with SETATTR indirectly
     changes the mtime. A client must account for this as size
     changes can result in data deletion.

     If server and client times differ, programs that compare
     client time to file times can break. A time maintenance
     protocol should be used to limit client/server time skew.

     In a heterogeneous environment, it is quite possible that
     the server will not be able to support the full range of
     SETATTR requests. The error, NFS3ERR_INVAL, may be
     returned if the server can not store a uid or gid in its
     own representation of uids or gids, respectively.  If the
     server can only support 32 bit offsets and sizes, a
     SETATTR request to set the size of a file to larger than
     can be represented in 32 bits will be rejected with this
     same error.

  ERRORS

     NFS3ERR_PERM
     NFS3ERR_IO
     NFS3ERR_ACCES
     NFS3ERR_INVAL
     NFS3ERR_NOSPC
     NFS3ERR_ROFS
     NFS3ERR_DQUOT
     NFS3ERR_NOT_SYNC
     NFS3ERR_STALE
     NFS3ERR_BADHANDLE
     NFS3ERR_SERVERFAULT

  SEE ALSO

     CREATE, MKDIR, SYMLINK, and MKNOD.

3.3.3 Procedure 3: LOOKUP -  Lookup filename

  SYNOPSIS

     LOOKUP3res NFSPROC3_LOOKUP(LOOKUP3args) = 3;

     struct LOOKUP3args {
          diropargs3  what;
     };

     struct LOOKUP3resok {
          nfs_fh3      object;
          post_op_attr obj_attributes;
          post_op_attr dir_attributes;
     };

     struct LOOKUP3resfail {
          post_op_attr dir_attributes;
     };

     union LOOKUP3res switch (nfsstat3 status) {
     case NFS3_OK:
          LOOKUP3resok    resok;
     default:
          LOOKUP3resfail  resfail;
     };

  DESCRIPTION

     Procedure LOOKUP searches a directory for a specific name
     and returns the file handle for the corresponding file
     system object. On entry, the arguments in LOOKUP3args
     are:

     what
        Object to look up:

        dir
           The file handle for the directory to search.

        name
           The filename to be searched for. Refer to General
           comments on filenames on page 30.

     On successful return, LOOKUP3res.status is NFS3_OK and
     LOOKUP3res.resok contains:

     object
        The file handle of the object corresponding to
        what.name.

     obj_attributes
        The attributes of the object corresponding to
        what.name.

     dir_attributes
        The post-operation attributes of the directory,
        what.dir.

     Otherwise, LOOKUP3res.status contains the error on failure and
     LOOKUP3res.resfail contains the following:

     dir_attributes
        The post-operation attributes for the directory,
        what.dir.

  IMPLEMENTATION

     At first glance, in the case where what.name refers to a
     mount point on the server, two different replies seem
     possible. The server can return either the file handle for
     the underlying directory that is mounted on or the file
     handle of the root of the mounted directory.  This
     ambiguity is simply resolved. A server will not allow a
     LOOKUP operation to cross a mountpoint to the root of a
     different filesystem, even if the filesystem is exported.
     This does not prevent a client from accessing a hierarchy
     of filesystems exported by a server, but the client must
     mount each of the filesystems individually so that the
     mountpoint crossing takes place on the client.  A given
     server implementation may refine these rules given
     capabilities or limitations particular to that
     implementation. Refer to [X/OpenNFS] for a discussion on
     exporting file systems.

     Two filenames are distinguished, as in the NFS version 2
     protocol.  The name, ".", is an alias for the current
     directory and the name, "..", is an alias for the parent
     directory; that is, the directory that includes the
     specified directory as a member. There is no facility for
     dealing with a multiparented directory and the NFS
     protocol assumes a hierarchical organization, organized as
     a single-rooted tree.

     Note that this procedure does not follow symbolic links.
     The client is responsible for all parsing of filenames
     including filenames that are modified by symbolic links
     encountered during the lookup process.

  ERRORS

     NFS3ERR_IO
     NFS3ERR_NOENT
     NFS3ERR_ACCES
     NFS3ERR_NOTDIR
     NFS3ERR_NAMETOOLONG
     NFS3ERR_STALE
     NFS3ERR_BADHANDLE
     NFS3ERR_SERVERFAULT

  SEE ALSO

     CREATE, MKDIR, SYMLINK, MKNOD, READDIRPLUS, and PATHCONF.

3.3.4 Procedure 4: ACCESS - Check Access Permission

  SYNOPSIS

     ACCESS3res NFSPROC3_ACCESS(ACCESS3args) = 4;

     const ACCESS3_READ    = 0x0001;
     const ACCESS3_LOOKUP  = 0x0002;
     const ACCESS3_MODIFY  = 0x0004;
     const ACCESS3_EXTEND  = 0x0008;
     const ACCESS3_DELETE  = 0x0010;
     const ACCESS3_EXECUTE = 0x0020;

     struct ACCESS3args {
          nfs_fh3  object;
          uint32   access;
     };

     struct ACCESS3resok {
          post_op_attr   obj_attributes;
          uint32         access;
     };

     struct ACCESS3resfail {
          post_op_attr   obj_attributes;
     };

     union ACCESS3res switch (nfsstat3 status) {
     case NFS3_OK:
          ACCESS3resok   resok;
     default:
          ACCESS3resfail resfail;
     };

  DESCRIPTION

     Procedure ACCESS determines the access rights that a user,
     as identified by the credentials in the request, has with
     respect to a file system object. The client encodes the
     set of permissions that are to be checked in a bit mask.
     The server checks the permissions encoded in the bit mask.
     A status of NFS3_OK is returned along with a bit mask
     encoded with the permissions that the client is allowed.

     The results of this procedure are necessarily advisory in
     nature.  That is, a return status of NFS3_OK and the
     appropriate bit set in the bit mask does not imply that
     such access will be allowed to the file system object in

     the future, as access rights can be revoked by the server
     at any time.

     On entry, the arguments in ACCESS3args are:

     object
        The file handle for the file system object to which
        access is to be checked.

     access
        A bit mask of access permissions to check.

     The following access permissions may be requested:

        ACCESS3_READ
           Read data from file or read a directory.

        ACCESS3_LOOKUP
           Look up a name in a directory (no meaning for
           non-directory objects).

        ACCESS3_MODIFY
           Rewrite existing file data or modify existing
           directory entries.

        ACCESS3_EXTEND
           Write new data or add directory entries.

        ACCESS3_DELETE
           Delete an existing directory entry.

        ACCESS3_EXECUTE
           Execute file (no meaning for a directory).

     On successful return, ACCESS3res.status is NFS3_OK. The
     server should return a status of NFS3_OK if no errors
     occurred that prevented the server from making the
     required access checks. The results in ACCESS3res.resok
     are:

     obj_attributes
        The post-operation attributes of object.

     access
        A bit mask of access permissions indicating access
        rights for the authentication credentials provided with
        the request.

     Otherwise, ACCESS3res.status contains the error on failure
     and ACCESS3res.resfail contains the following:

     obj_attributes
        The attributes of object - if access to attributes is
        permitted.

  IMPLEMENTATION

     In general, it is not sufficient for the client to attempt
     to deduce access permissions by inspecting the uid, gid,
     and mode fields in the file attributes, since the server
     may perform uid or gid mapping or enforce additional
     access control restrictions. It is also possible that the
     NFS version 3 protocol server may not be in the same ID
     space as the NFS version 3 protocol client. In these cases
     (and perhaps others), the NFS version 3 protocol client
     can not reliably perform an access check with only current
     file attributes.

     In the NFS version 2 protocol, the only reliable way to
     determine whether an operation was allowed was to try it
     and see if it succeeded or failed. Using the ACCESS
     procedure in the NFS version 3 protocol, the client can
     ask the server to indicate whether or not one or more
     classes of operations are permitted.  The ACCESS operation
     is provided to allow clients to check before doing a
     series of operations. This is useful in operating systems
     (such as UNIX) where permission checking is done only when
     a file or directory is opened. This procedure is also
     invoked by NFS client access procedure (called possibly
     through access(2)). The intent is to make the behavior of
     opening a remote file more consistent with the behavior of
     opening a local file.

     The information returned by the server in response to an
     ACCESS call is not permanent. It was correct at the exact
     time that the server performed the checks, but not
     necessarily afterwards. The server can revoke access
     permission at any time.

     The NFS version 3 protocol client should use the effective
     credentials of the user to build the authentication
     information in the ACCESS request used to determine access
     rights. It is the effective user and group credentials
     that are used in subsequent read and write operations. See
     the comments in Permission issues on page 98 for more
     information on this topic.

     Many implementations do not directly support the
     ACCESS3_DELETE permission. Operating systems like UNIX
     will ignore the ACCESS3_DELETE bit if set on an access
     request on a non-directory object. In these systems,
     delete permission on a file is determined by the access
     permissions on the directory in which the file resides,
     instead of being determined by the permissions of the file
     itself.  Thus, the bit mask returned for such a request
     will have the ACCESS3_DELETE bit set to 0, indicating that
     the client does not have this permission.

  ERRORS

     NFS3ERR_IO
     NFS3ERR_STALE
     NFS3ERR_BADHANDLE
     NFS3ERR_SERVERFAULT

  SEE ALSO

     GETATTR.

3.3.5 Procedure 5: READLINK - Read from symbolic link

  SYNOPSIS

     READLINK3res NFSPROC3_READLINK(READLINK3args) = 5;

     struct READLINK3args {
          nfs_fh3  symlink;
     };

     struct READLINK3resok {
          post_op_attr   symlink_attributes;
          nfspath3       data;
     };

     struct READLINK3resfail {
          post_op_attr   symlink_attributes;
     };

     union READLINK3res switch (nfsstat3 status) {
     case NFS3_OK:
          READLINK3resok   resok;
     default:
          READLINK3resfail resfail;
     };

  DESCRIPTION

     Procedure READLINK reads the data associated with a
     symbolic link.  The data is an ASCII string that is opaque
     to the server.  That is, whether created by the NFS
     version 3 protocol software from a client or created
     locally on the server, the data in a symbolic link is not
     interpreted when created, but is simply stored. On entry,
     the arguments in READLINK3args are:

     symlink
        The file handle for a symbolic link (file system object
        of type NF3LNK).

     On successful return, READLINK3res.status is NFS3_OK and
     READLINK3res.resok contains:

     data
        The data associated with the symbolic link.

     symlink_attributes
        The post-operation attributes for the symbolic link.

     Otherwise, READLINK3res.status contains the error on
     failure and READLINK3res.resfail contains the following:

     symlink_attributes
        The post-operation attributes for the symbolic link.

  IMPLEMENTATION

     A symbolic link is nominally a pointer to another file.
     The data is not necessarily interpreted by the server,
     just stored in the file.  It is possible for a client
     implementation to store a path name that is not meaningful
     to the server operating system in a symbolic link.  A
     READLINK operation returns the data to the client for
     interpretation. If different implementations want to share
     access to symbolic links, then they must agree on the
     interpretation of the data in the symbolic link.

     The READLINK operation is only allowed on objects of type,
     NF3LNK.  The server should return the error,
     NFS3ERR_INVAL, if the object is not of type, NF3LNK.
     (Note: The X/Open XNFS Specification for the NFS version 2
     protocol defined the error status in this case as
     NFSERR_NXIO. This is inconsistent with existing server
     practice.)

  ERRORS

     NFS3ERR_IO
     NFS3ERR_INVAL
     NFS3ERR_ACCES
     NFS3ERR_STALE
     NFS3ERR_BADHANDLE
     NFS3ERR_NOTSUPP
     NFS3ERR_SERVERFAULT

  SEE ALSO

     READLINK, SYMLINK.

3.3.6 Procedure 6: READ - Read From file

  SYNOPSIS

     READ3res NFSPROC3_READ(READ3args) = 6;

     struct READ3args {
          nfs_fh3  file;
          offset3  offset;
          count3   count;
     };

     struct READ3resok {
          post_op_attr   file_attributes;
          count3         count;
          bool           eof;
          opaque         data<>;
     };

     struct READ3resfail {
          post_op_attr   file_attributes;
     };

     union READ3res switch (nfsstat3 status) {
     case NFS3_OK:
          READ3resok   resok;
     default:
          READ3resfail resfail;
     };

  DESCRIPTION

     Procedure READ reads data from a file.  On entry, the
     arguments in READ3args are:

     file
        The file handle of the file from which data is to be
        read.  This must identify a file system object of type,
        NF3REG.

     offset
        The position within the file at which the read is to
        begin.  An offset of 0 means to read data starting at
        the beginning of the file. If offset is greater than or
        equal to the size of the file, the status, NFS3_OK, is
        returned with count set to 0 and eof set to TRUE,
        subject to access permissions checking.

     count
        The number of bytes of data that are to be read. If
        count is 0, the READ will succeed and return 0 bytes of
        data, subject to access permissions checking. count
        must be less than or equal to the value of the rtmax
        field in the FSINFO reply structure for the file system
        that contains file. If greater, the server may return
        only rtmax bytes, resulting in a short read.

     On successful return, READ3res.status is NFS3_OK and
     READ3res.resok contains:

     file_attributes
        The attributes of the file on completion of the read.

     count
        The number of bytes of data returned by the read.

     eof
        If the read ended at the end-of-file (formally, in a
        correctly formed READ request, if READ3args.offset plus
        READ3resok.count is equal to the size of the file), eof
        is returned as TRUE; otherwise it is FALSE. A
        successful READ of an empty file will always return eof
        as TRUE.

     data
        The counted data read from the file.

     Otherwise, READ3res.status contains the error on failure
     and READ3res.resfail contains the following:

     file_attributes
        The post-operation attributes of the file.

  IMPLEMENTATION

     The nfsdata type used for the READ and WRITE operations in
     the NFS version 2 protocol defining the data portion of a
     request or reply has been changed to a variable-length
     opaque byte array.  The maximum size allowed by the
     protocol is now limited by what XDR and underlying
     transports will allow. There are no artificial limits
     imposed by the NFS version 3 protocol. Consult the FSINFO
     procedure description for details.

     It is possible for the server to return fewer than count
     bytes of data. If the server returns less than the count
     requested and eof set to FALSE, the client should issue
     another READ to get the remaining data. A server may
     return less data than requested under several
     circumstances. The file may have been truncated by another
     client or perhaps on the server itself, changing the file
     size from what the requesting client believes to be the
     case. This would reduce the actual amount of data
     available to the client. It is possible that the server
     may back off the transfer size and reduce the read request
     return. Server resource exhaustion may also occur
     necessitating a smaller read return.

     Some NFS version 2 protocol client implementations chose
     to interpret a short read response as indicating EOF. The
     addition of the eof flag in the NFS version 3 protocol
     provides a correct way of handling EOF.

     Some NFS version 2 protocol server implementations
     incorrectly returned NFSERR_ISDIR if the file system
     object type was not a regular file. The correct return
     value for the NFS version 3 protocol is NFS3ERR_INVAL.

  ERRORS

     NFS3ERR_IO
     NFS3ERR_NXIO
     NFS3ERR_ACCES
     NFS3ERR_INVAL
     NFS3ERR_STALE
     NFS3ERR_BADHANDLE
     NFS3ERR_SERVERFAULT

  SEE ALSO

     READLINK.

3.3.7 Procedure 7: WRITE - Write to file

  SYNOPSIS

     WRITE3res NFSPROC3_WRITE(WRITE3args) = 7;

     enum stable_how {
          UNSTABLE  = 0,
          DATA_SYNC = 1,
          FILE_SYNC = 2
     };

     struct WRITE3args {
          nfs_fh3     file;
          offset3     offset;
          count3      count;
          stable_how  stable;
          opaque      data<>;
     };

     struct WRITE3resok {
          wcc_data    file_wcc;
          count3      count;
          stable_how  committed;
          writeverf3  verf;
     };

     struct WRITE3resfail {
          wcc_data    file_wcc;
     };

     union WRITE3res switch (nfsstat3 status) {
     case NFS3_OK:
          WRITE3resok    resok;
     default:
          WRITE3resfail  resfail;
     };

  DESCRIPTION

     Procedure WRITE writes data to a file. On entry, the
     arguments in WRITE3args are:

     file
        The file handle for the file to which data is to be
        written.  This must identify a file system object of
        type, NF3REG.

     offset
        The position within the file at which the write is to
        begin.  An offset of 0 means to write data starting at
        the beginning of the file.

     count
        The number of bytes of data to be written. If count is
        0, the WRITE will succeed and return a count of 0,
        barring errors due to permissions checking. The size of
        data must be less than or equal to the value of the
        wtmax field in the FSINFO reply structure for the file
        system that contains file. If greater, the server may
        write only wtmax bytes, resulting in a short write.

     stable
        If stable is FILE_SYNC, the server must commit the data
        written plus all file system metadata to stable storage
        before returning results. This corresponds to the NFS
        version 2 protocol semantics. Any other behavior
        constitutes a protocol violation. If stable is
        DATA_SYNC, then the server must commit all of the data
        to stable storage and enough of the metadata to
        retrieve the data before returning.  The server
        implementor is free to implement DATA_SYNC in the same
        fashion as FILE_SYNC, but with a possible performance
        drop.  If stable is UNSTABLE, the server is free to
        commit any part of the data and the metadata to stable
        storage, including all or none, before returning a
        reply to the client. There is no guarantee whether or
        when any uncommitted data will subsequently be
        committed to stable storage. The only guarantees made
        by the server are that it will not destroy any data
        without changing the value of verf and that it will not
        commit the data and metadata at a level less than that
        requested by the client. See the discussion on COMMIT
        on page 92 for more information on if and when
        data is committed to stable storage.

     data
        The data to be written to the file.

     On successful return, WRITE3res.status is NFS3_OK and
     WRITE3res.resok contains:

     file_wcc
        Weak cache consistency data for the file. For a client
        that requires only the post-write file attributes,
        these can be found in file_wcc.after.

     count
        The number of bytes of data written to the file. The
        server may write fewer bytes than requested. If so, the
        actual number of bytes written starting at location,
        offset, is returned.

     committed
        The server should return an indication of the level of
        commitment of the data and metadata via committed. If
        the server committed all data and metadata to stable
        storage, committed should be set to FILE_SYNC. If the
        level of commitment was at least as strong as
        DATA_SYNC, then committed should be set to DATA_SYNC.
        Otherwise, committed must be returned as UNSTABLE. If
        stable was FILE_SYNC, then committed must also be
        FILE_SYNC: anything else constitutes a protocol
        violation. If stable was DATA_SYNC, then committed may
        be FILE_SYNC or DATA_SYNC: anything else constitutes a
        protocol violation. If stable was UNSTABLE, then
        committed may be either FILE_SYNC, DATA_SYNC, or
        UNSTABLE.

     verf
        This is a cookie that the client can use to determine
        whether the server has changed state between a call to
        WRITE and a subsequent call to either WRITE or COMMIT.
        This cookie must be consistent during a single instance
        of the NFS version 3 protocol service and must be
        unique between instances of the NFS version 3 protocol
        server, where uncommitted data may be lost.

     Otherwise, WRITE3res.status contains the error on failure
     and WRITE3res.resfail contains the following:

     file_wcc
        Weak cache consistency data for the file. For a client
        that requires only the post-write file attributes,
        these can be found in file_wcc.after. Even though the
        write failed, full wcc_data is returned to allow the
        client to determine whether the failed write resulted
        in any change to the file.

     If a client writes data to the server with the stable
     argument set to UNSTABLE and the reply yields a committed
     response of DATA_SYNC or UNSTABLE, the client will follow
     up some time in the future with a COMMIT operation to
     synchronize outstanding asynchronous data and metadata
     with the server's stable storage, barring client error. It

     is possible that due to client crash or other error that a
     subsequent COMMIT will not be received by the server.

  IMPLEMENTATION

     The nfsdata type used for the READ and WRITE operations in
     the NFS version 2 protocol defining the data portion of a
     request or reply has been changed to a variable-length
     opaque byte array.  The maximum size allowed by the
     protocol is now limited by what XDR and underlying
     transports will allow. There are no artificial limits
     imposed by the NFS version 3 protocol. Consult the FSINFO
     procedure description for details.

     It is possible for the server to write fewer than count
     bytes of data. In this case, the server should not return
     an error unless no data was written at all. If the server
     writes less than count bytes, the client should issue
     another WRITE to write the remaining data.

     It is assumed that the act of writing data to a file will
     cause the mtime of the file to be updated. However, the
     mtime of the file should not be changed unless the
     contents of the file are changed.  Thus, a WRITE request
     with count set to 0 should not cause the mtime of the file
     to be updated.

     The NFS version 3 protocol introduces safe asynchronous
     writes.  The combination of WRITE with stable set to
     UNSTABLE followed by a COMMIT addresses the performance
     bottleneck found in the NFS version 2 protocol, the need
     to synchronously commit all writes to stable storage.

     The definition of stable storage has been historically a
     point of contention. The following expected properties of
     stable storage may help in resolving design issues in the
     implementation. Stable storage is persistent storage that
     survives:

     1. Repeated power failures.

     2. Hardware failures (of any board, power supply, and so on.).

     3. Repeated software crashes, including reboot cycle.

     This definition does not address failure of the stable
     storage module itself.

     A cookie, verf, is defined to allow a client to detect
     different instances of an NFS version 3 protocol server
     over which cached, uncommitted data may be lost. In the
     most likely case, the verf allows the client to detect
     server reboots. This information is required so that the
     client can safely determine whether the server could have
     lost cached data. If the server fails unexpectedly and the
     client has uncommitted data from previous WRITE requests
     (done with the stable argument set to UNSTABLE and in
     which the result committed was returned as UNSTABLE as
     well) it may not have flushed cached data to stable
     storage. The burden of recovery is on the client and the
     client will need to retransmit the data to the server.

     A suggested verf cookie would be to use the time that the
     server was booted or the time the server was last started
     (if restarting the server without a reboot results in lost
     buffers).

     The committed field in the results allows the client to do
     more effective caching. If the server is committing all
     WRITE requests to stable storage, then it should return
     with committed set to FILE_SYNC, regardless of the value
     of the stable field in the arguments. A server that uses
     an NVRAM accelerator may choose to implement this policy.
     The client can use this to increase the effectiveness of
     the cache by discarding cached data that has already been
     committed on the server.

     Some implementations may return NFS3ERR_NOSPC instead of
     NFS3ERR_DQUOT when a user's quota is exceeded.

     Some NFS version 2 protocol server implementations
     incorrectly returned NFSERR_ISDIR if the file system
     object type was not a regular file. The correct return
     value for the NFS version 3 protocol is NFS3ERR_INVAL.

  ERRORS

     NFS3ERR_IO
     NFS3ERR_ACCES
     NFS3ERR_FBIG
     NFS3ERR_DQUOT
     NFS3ERR_NOSPC
     NFS3ERR_ROFS
     NFS3ERR_INVAL
     NFS3ERR_STALE
     NFS3ERR_BADHANDLE

     NFS3ERR_SERVERFAULT

  SEE ALSO

     COMMIT.

3.3.8 Procedure 8: CREATE - Create a file

  SYNOPSIS

     CREATE3res NFSPROC3_CREATE(CREATE3args) = 8;

     enum createmode3 {
          UNCHECKED = 0,
          GUARDED   = 1,
          EXCLUSIVE = 2
     };

     union createhow3 switch (createmode3 mode) {
     case UNCHECKED:
     case GUARDED:
          sattr3       obj_attributes;
     case EXCLUSIVE:
          createverf3  verf;
     };

     struct CREATE3args {
          diropargs3   where;
          createhow3   how;
     };

     struct CREATE3resok {
          post_op_fh3   obj;
          post_op_attr  obj_attributes;
          wcc_data      dir_wcc;
     };

     struct CREATE3resfail {
          wcc_data      dir_wcc;
     };

     union CREATE3res switch (nfsstat3 status) {
     case NFS3_OK:
          CREATE3resok    resok;
     default:
          CREATE3resfail  resfail;
     };

  DESCRIPTION

     Procedure CREATE creates a regular file. On entry, the
     arguments in CREATE3args are:

     where
        The location of the file to be created:

        dir
           The file handle for the directory in which the file
           is to be created.

        name
           The name that is to be associated with the created
           file.  Refer to General comments on filenames on
           page 30.

     When creating a regular file, there are three ways to
     create the file as defined by:

     how
        A discriminated union describing how the server is to
        handle the file creation along with the appropriate
        attributes:

     mode
        One of UNCHECKED, GUARDED, and EXCLUSIVE. UNCHECKED
        means that the file should be created without checking
        for the existence of a duplicate file in the same
        directory. In this case, how.obj_attributes is a sattr3
        describing the initial attributes for the file. GUARDED
        specifies that the server should check for the presence
        of a duplicate file before performing the create and
        should fail the request with NFS3ERR_EXIST if a
        duplicate file exists. If the file does not exist, the
        request is performed as described for UNCHECKED.
        EXCLUSIVE specifies that the server is to follow
        exclusive creation semantics, using the verifier to
        ensure exclusive creation of the target. No attributes
        may be provided in this case, since the server may use
        the target file metadata to store the createverf3
        verifier.

     On successful return, CREATE3res.status is NFS3_OK and the
     results in CREATE3res.resok are:

     obj
        The file handle of the newly created regular file.

     obj_attributes
        The attributes of the regular file just created.

     dir_wcc
        Weak cache consistency data for the directory,
        where.dir. For a client that requires on the
        post-CREATE directory attributes, these can be found in
        dir_wcc.after.

     Otherwise, CREATE3res.status contains the error on failure
     and CREATE3res.resfail contains the following:

     dir_wcc
        Weak cache consistency data for the directory,
        where.dir. For a client that requires only the
        post-CREATE directory attributes, these can be found in
        dir_wcc.after. Even though the CREATE failed, full
        wcc_data is returned to allow the client to determine
        whether the failing CREATE resulted in any change to
        the directory.

  IMPLEMENTATION

     Unlike the NFS version 2 protocol, in which certain fields
     in the initial attributes structure were overloaded to
     indicate creation of devices and FIFOs in addition to
     regular files, this procedure only supports the creation
     of regular files. The MKNOD procedure was introduced in
     the NFS version 3 protocol to handle creation of devices
     and FIFOs. Implementations should have no reason in the
     NFS version 3 protocol to overload CREATE semantics.

     One aspect of the NFS version 3 protocol CREATE procedure
     warrants particularly careful consideration: the mechanism
     introduced to support the reliable exclusive creation of
     regular files. The mechanism comes into play when how.mode
     is EXCLUSIVE.  In this case, how.verf contains a verifier
     that can reasonably be expected to be unique.  A
     combination of a client identifier, perhaps the client
     network address, and a unique number generated by the
     client, perhaps the RPC transaction identifier, may be
     appropriate.

     If the file does not exist, the server creates the file
     and stores the verifier in stable storage. For file
     systems that do not provide a mechanism for the storage of
     arbitrary file attributes, the server may use one or more
     elements of the file metadata to store the verifier. The

     verifier must be stored in stable storage to prevent
     erroneous failure on retransmission of the request. It is
     assumed that an exclusive create is being performed
     because exclusive semantics are critical to the
     application. Because of the expected usage, exclusive
     CREATE does not rely solely on the normally volatile
     duplicate request cache for storage of the verifier. The
     duplicate request cache in volatile storage does not
     survive a crash and may actually flush on a long network
     partition, opening failure windows.  In the UNIX local
     file system environment, the expected storage location for
     the verifier on creation is the metadata (time stamps) of
     the file. For this reason, an exclusive file create may
     not include initial attributes because the server would
     have nowhere to store the verifier.

     If the server can not support these exclusive create
     semantics, possibly because of the requirement to commit
     the verifier to stable storage, it should fail the CREATE
     request with the error, NFS3ERR_NOTSUPP.

     During an exclusive CREATE request, if the file already
     exists, the server reconstructs the file's verifier and
     compares it with the verifier in the request. If they
     match, the server treats the request as a success. The
     request is presumed to be a duplicate of an earlier,
     successful request for which the reply was lost and that
     the server duplicate request cache mechanism did not
     detect. If the verifiers do not match, the request is
     rejected with the status, NFS3ERR_EXIST.

     Once the client has performed a successful exclusive
     create, it must issue a SETATTR to set the correct file
     attributes.  Until it does so, it should not rely upon any
     of the file attributes, since the server implementation
     may need to overload file metadata to store the verifier.

     Use of the GUARDED attribute does not provide exactly-once
     semantics.  In particular, if a reply is lost and the
     server does not detect the retransmission of the request,
     the procedure can fail with NFS3ERR_EXIST, even though the
     create was performed successfully.

     Refer to General comments on filenames on page 30.

  ERRORS

     NFS3ERR_IO
     NFS3ERR_ACCES
     NFS3ERR_EXIST
     NFS3ERR_NOTDIR
     NFS3ERR_NOSPC
     NFS3ERR_ROFS
     NFS3ERR_NAMETOOLONG
     NFS3ERR_DQUOT
     NFS3ERR_STALE
     NFS3ERR_BADHANDLE
     NFS3ERR_NOTSUPP
     NFS3ERR_SERVERFAULT

  SEE ALSO

     MKDIR, SYMLINK, MKNOD, and PATHCONF.

3.3.9 Procedure 9: MKDIR - Create a directory

  SYNOPSIS

     MKDIR3res NFSPROC3_MKDIR(MKDIR3args) = 9;

     struct MKDIR3args {
          diropargs3   where;
          sattr3       attributes;
     };

     struct MKDIR3resok {
          post_op_fh3   obj;
          post_op_attr  obj_attributes;
          wcc_data      dir_wcc;
     };

     struct MKDIR3resfail {
          wcc_data      dir_wcc;
     };

     union MKDIR3res switch (nfsstat3 status) {
     case NFS3_OK:
          MKDIR3resok   resok;
     default:
          MKDIR3resfail resfail;
     };

  DESCRIPTION

     Procedure MKDIR creates a new subdirectory. On entry, the
     arguments in MKDIR3args are:

     where
        The location of the subdirectory to be created:

        dir
           The file handle for the directory in which the
           subdirectory is to be created.

        name
           The name that is to be associated with the created
           subdirectory. Refer to General comments on filenames
           on page 30.

     attributes
        The initial attributes for the subdirectory.

     On successful return, MKDIR3res.status is NFS3_OK and the
     results in MKDIR3res.resok are:

     obj
        The file handle for the newly created directory.

     obj_attributes
        The attributes for the newly created subdirectory.

     dir_wcc
        Weak cache consistency data for the directory,
        where.dir. For a client that requires only the
        post-MKDIR directory attributes, these can be found in
        dir_wcc.after.

     Otherwise, MKDIR3res.status contains the error on failure
     and MKDIR3res.resfail contains the following:

     dir_wcc
        Weak cache consistency data for the directory,
        where.dir. For a client that requires only the
        post-MKDIR directory attributes, these can be found in
        dir_wcc.after. Even though the MKDIR failed, full
        wcc_data is returned to allow the client to determine
        whether the failing MKDIR resulted in any change to the
        directory.

  IMPLEMENTATION

     Many server implementations will not allow the filenames,
     "." or "..", to be used as targets in a MKDIR operation.
     In this case, the server should return NFS3ERR_EXIST.
     Refer to General comments on filenames on page 30.

  ERRORS

     NFS3ERR_IO
     NFS3ERR_ACCES
     NFS3ERR_EXIST
     NFS3ERR_NOTDIR
     NFS3ERR_NOSPC
     NFS3ERR_ROFS
     NFS3ERR_NAMETOOLONG
     NFS3ERR_DQUOT
     NFS3ERR_STALE
     NFS3ERR_BADHANDLE
     NFS3ERR_NOTSUPP
     NFS3ERR_SERVERFAULT

  SEE ALSO

     CREATE, SYMLINK, MKNOD, and PATHCONF.

3.3.10 Procedure 10: SYMLINK - Create a symbolic link

  SYNOPSIS

     SYMLINK3res NFSPROC3_SYMLINK(SYMLINK3args) = 10;

     struct symlinkdata3 {
          sattr3    symlink_attributes;
          nfspath3  symlink_data;
     };

     struct SYMLINK3args {
          diropargs3    where;
          symlinkdata3  symlink;
     };

     struct SYMLINK3resok {
          post_op_fh3   obj;
          post_op_attr  obj_attributes;
          wcc_data      dir_wcc;
     };

     struct SYMLINK3resfail {
          wcc_data      dir_wcc;
     };

     union SYMLINK3res switch (nfsstat3 status) {
     case NFS3_OK:
          SYMLINK3resok   resok;
     default:
          SYMLINK3resfail resfail;
     };

  DESCRIPTION

     Procedure SYMLINK creates a new symbolic link. On entry,
     the arguments in SYMLINK3args are:

     where
        The location of the symbolic link to be created:

        dir
           The file handle for the directory in which the
           symbolic link is to be created.

        name
           The name that is to be associated with the created
           symbolic link. Refer to General comments on
           filenames on page 30.

     symlink
        The symbolic link to create:

        symlink_attributes
           The initial attributes for the symbolic link.

        symlink_data
           The string containing the symbolic link data.

     On successful return, SYMLINK3res.status is NFS3_OK and
     SYMLINK3res.resok contains:

     obj
        The file handle for the newly created symbolic link.

     obj_attributes
        The attributes for the newly created symbolic link.

     dir_wcc
        Weak cache consistency data for the directory,
        where.dir. For a client that requires only the
        post-SYMLINK directory attributes, these can be found
        in dir_wcc.after.

     Otherwise, SYMLINK3res.status contains the error on
     failure and SYMLINK3res.resfail contains the following:

     dir_wcc
        Weak cache consistency data for the directory,
        where.dir. For a client that requires only the
        post-SYMLINK directory attributes, these can be found
        in dir_wcc.after. Even though the SYMLINK failed, full
        wcc_data is returned to allow the client to determine
        whether the failing SYMLINK changed the directory.

  IMPLEMENTATION

     Refer to General comments on filenames on page 30.

     For symbolic links, the actual file system node and its
     contents are expected to be created in a single atomic
     operation.  That is, once the symbolic link is visible,
     there must not be a window where a READLINK would fail or

     return incorrect data.

  ERRORS

     NFS3ERR_IO
     NFS3ERR_ACCES
     NFS3ERR_EXIST
     NFS3ERR_NOTDIR
     NFS3ERR_NOSPC
     NFS3ERR_ROFS
     NFS3ERR_NAMETOOLONG
     NFS3ERR_DQUOT
     NFS3ERR_STALE
     NFS3ERR_BADHANDLE
     NFS3ERR_NOTSUPP
     NFS3ERR_SERVERFAULT

  SEE ALSO

     READLINK, CREATE, MKDIR, MKNOD, FSINFO, and PATHCONF.

3.3.11 Procedure 11: MKNOD - Create a special device

  SYNOPSIS

     MKNOD3res NFSPROC3_MKNOD(MKNOD3args) = 11;

     struct devicedata3 {
          sattr3     dev_attributes;
          specdata3  spec;
     };

     union mknoddata3 switch (ftype3 type) {
     case NF3CHR:
     case NF3BLK:
          devicedata3  device;
     case NF3SOCK:
     case NF3FIFO:
          sattr3       pipe_attributes;
     default:
          void;
     };

     struct MKNOD3args {
          diropargs3   where;
          mknoddata3   what;
     };

     struct MKNOD3resok {
          post_op_fh3   obj;
          post_op_attr  obj_attributes;
          wcc_data      dir_wcc;
     };

     struct MKNOD3resfail {
          wcc_data      dir_wcc;
     };

     union MKNOD3res switch (nfsstat3 status) {
     case NFS3_OK:
          MKNOD3resok   resok;
     default:
          MKNOD3resfail resfail;
     };

  DESCRIPTION

     Procedure MKNOD creates a new special file of the type,
     what.type.  Special files can be device files or named
     pipes.  On entry, the arguments in MKNOD3args are:

     where
        The location of the special file to be created:

        dir
           The file handle for the directory in which the
           special file is to be created.

        name
           The name that is to be associated with the created
           special file. Refer to General comments on filenames
           on page 30.

     what
        A discriminated union identifying the type of the
        special file to be created along with the data and
        attributes appropriate to the type of the special
        file:

        type
           The type of the object to be created.

     When creating a character special file (what.type is
     NF3CHR) or a block special file (what.type is NF3BLK),
     what includes:

     device
        A structure devicedata3 with the following components:

        dev_attributes
           The initial attributes for the special file.

        spec
           The major number stored in device.spec.specdata1 and
           the minor number stored in device.spec.specdata2.

     When creating a socket (what.type is NF3SOCK) or a FIFO
     (what.type is NF3FIFO), what includes:

        pipe_attributes
           The initial attributes for the special file.

     On successful return, MKNOD3res.status is NFS3_OK and
     MKNOD3res.resok contains:

     obj
        The file handle for the newly created special file.

     obj_attributes
        The attributes for the newly created special file.

     dir_wcc
        Weak cache consistency data for the directory,
        where.dir. For a client that requires only the
        post-MKNOD directory attributes, these can be found in
        dir_wcc.after.

     Otherwise, MKNOD3res.status contains the error on failure
     and MKNOD3res.resfail contains the following:

     dir_wcc
        Weak cache consistency data for the directory,
        where.dir. For a client that requires only the
        post-MKNOD directory attributes, these can be found in
        dir_wcc.after. Even though the MKNOD failed, full
        wcc_data is returned to allow the client to determine
        whether the failing MKNOD changed the directory.

  IMPLEMENTATION

     Refer to General comments on filenames on page 30.

     Without explicit support for special file type creation in
     the NFS version 2 protocol, fields in the CREATE arguments

     were overloaded to indicate creation of certain types of
     objects.  This overloading is not necessary in the NFS
     version 3 protocol.

     If the server does not support any of the defined types,
     the error, NFS3ERR_NOTSUPP, should be returned. Otherwise,
     if the server does not support the target type or the
     target type is illegal, the error, NFS3ERR_BADTYPE, should
     be returned. Note that NF3REG, NF3DIR, and NF3LNK are
     illegal types for MKNOD. The procedures, CREATE, MKDIR,
     and SYMLINK should be used to create these file types,
     respectively, instead of MKNOD.

  ERRORS

     NFS3ERR_IO
     NFS3ERR_ACCES
     NFS3ERR_EXIST
     NFS3ERR_NOTDIR
     NFS3ERR_NOSPC
     NFS3ERR_ROFS
     NFS3ERR_NAMETOOLONG
     NFS3ERR_DQUOT
     NFS3ERR_STALE
     NFS3ERR_BADHANDLE
     NFS3ERR_NOTSUPP
     NFS3ERR_SERVERFAULT
     NFS3ERR_BADTYPE

  SEE ALSO

     CREATE, MKDIR, SYMLINK, and PATHCONF.

3.3.12 Procedure 12: REMOVE - Remove a File

  SYNOPSIS

     REMOVE3res NFSPROC3_REMOVE(REMOVE3args) = 12;

     struct REMOVE3args {
          diropargs3  object;
     };

     struct REMOVE3resok {
          wcc_data    dir_wcc;
     };

     struct REMOVE3resfail {
          wcc_data    dir_wcc;
     };

     union REMOVE3res switch (nfsstat3 status) {
     case NFS3_OK:
          REMOVE3resok   resok;
     default:
          REMOVE3resfail resfail;
     };

  DESCRIPTION

     Procedure REMOVE removes (deletes) an entry from a
     directory. If the entry in the directory was the last
     reference to the corresponding file system object, the
     object may be destroyed.  On entry, the arguments in
     REMOVE3args are:

     object
        A diropargs3 structure identifying the entry to be
        removed:

     dir
        The file handle for the directory from which the entry
        is to be removed.

     name
        The name of the entry to be removed. Refer to General
        comments on filenames on page 30.

     On successful return, REMOVE3res.status is NFS3_OK and
     REMOVE3res.resok contains:

     dir_wcc
        Weak cache consistency data for the directory,
        object.dir.  For a client that requires only the
        post-REMOVE directory attributes, these can be found in
        dir_wcc.after.

     Otherwise, REMOVE3res.status contains the error on failure
     and REMOVE3res.resfail contains the following:

     dir_wcc
        Weak cache consistency data for the directory,
        object.dir.  For a client that requires only the
        post-REMOVE directory attributes, these can be found in
        dir_wcc.after. Even though the REMOVE failed, full
        wcc_data is returned to allow the client to determine
        whether the failing REMOVE changed the directory.

  IMPLEMENTATION

     In general, REMOVE is intended to remove non-directory
     file objects and RMDIR is to be used to remove
     directories.  However, REMOVE can be used to remove
     directories, subject to restrictions imposed by either the
     client or server interfaces.  This had been a source of
     confusion in the NFS version 2 protocol.

     The concept of last reference is server specific. However,
     if the nlink field in the previous attributes of the
     object had the value 1, the client should not rely on
     referring to the object via a file handle. Likewise, the
     client should not rely on the resources (disk space,
     directory entry, and so on.) formerly associated with the
     object becoming immediately available. Thus, if a client
     needs to be able to continue to access a file after using
     REMOVE to remove it, the client should take steps to make
     sure that the file will still be accessible. The usual
     mechanism used is to use RENAME to rename the file from
     its old name to a new hidden name.

     Refer to General comments on filenames on page 30.

  ERRORS

     NFS3ERR_NOENT
     NFS3ERR_IO
     NFS3ERR_ACCES
     NFS3ERR_NOTDIR
     NFS3ERR_NAMETOOLONG

     NFS3ERR_ROFS
     NFS3ERR_STALE
     NFS3ERR_BADHANDLE
     NFS3ERR_SERVERFAULT

  SEE ALSO

     RMDIR and RENAME.

3.3.13 Procedure 13: RMDIR - Remove a Directory

  SYNOPSIS

     RMDIR3res NFSPROC3_RMDIR(RMDIR3args) = 13;

     struct RMDIR3args {
          diropargs3  object;
     };

     struct RMDIR3resok {
          wcc_data    dir_wcc;
     };

     struct RMDIR3resfail {
          wcc_data    dir_wcc;
     };

     union RMDIR3res switch (nfsstat3 status) {
     case NFS3_OK:
          RMDIR3resok   resok;
     default:
          RMDIR3resfail resfail;
     };

  DESCRIPTION

     Procedure RMDIR removes (deletes) a subdirectory from a
     directory. If the directory entry of the subdirectory is
     the last reference to the subdirectory, the subdirectory
     may be destroyed. On entry, the arguments in RMDIR3args
     are:

     object
        A diropargs3 structure identifying the directory entry
        to be removed:

        dir
           The file handle for the directory from which the
           subdirectory is to be removed.

        name
           The name of the subdirectory to be removed. Refer to
           General comments on filenames on page 30.

     On successful return, RMDIR3res.status is NFS3_OK and
     RMDIR3res.resok contains:

     dir_wcc
        Weak cache consistency data for the directory,
        object.dir.  For a client that requires only the
        post-RMDIR directory attributes, these can be found in
        dir_wcc.after.

     Otherwise, RMDIR3res.status contains the error on failure
     and RMDIR3res.resfail contains the following:

     dir_wcc
        Weak cache consistency data for the directory,
        object.dir.  For a client that requires only the
        post-RMDIR directory attributes, these can be found in
        dir_wcc.after. Note that even though the RMDIR failed,
        full wcc_data is returned to allow the client to
        determine whether the failing RMDIR changed the
        directory.

  IMPLEMENTATION

     Note that on some servers, removal of a non-empty
     directory is disallowed.

     On some servers, the filename, ".", is illegal. These
     servers will return the error, NFS3ERR_INVAL. On some
     servers, the filename, "..", is illegal. These servers
     will return the error, NFS3ERR_EXIST. This would seem
     inconsistent, but allows these servers to comply with
     their own specific interface definitions.  Clients should
     be prepared to handle both cases.

     The client should not rely on the resources (disk space,
     directory entry, and so on.) formerly associated with the
     directory becoming immediately available.

  ERRORS

     NFS3ERR_NOENT
     NFS3ERR_IO
     NFS3ERR_ACCES
     NFS3ERR_INVAL
     NFS3ERR_EXIST
     NFS3ERR_NOTDIR
     NFS3ERR_NAMETOOLONG
     NFS3ERR_ROFS
     NFS3ERR_NOTEMPTY
     NFS3ERR_STALE
     NFS3ERR_BADHANDLE
     NFS3ERR_NOTSUPP
     NFS3ERR_SERVERFAULT

  SEE ALSO

     REMOVE.

3.3.14 Procedure 14: RENAME - Rename a File or Directory

  SYNOPSIS

     RENAME3res NFSPROC3_RENAME(RENAME3args) = 14;

     struct RENAME3args {
          diropargs3   from;
          diropargs3   to;
     };

     struct RENAME3resok {
          wcc_data     fromdir_wcc;
          wcc_data     todir_wcc;
     };

     struct RENAME3resfail {
          wcc_data     fromdir_wcc;
          wcc_data     todir_wcc;
     };

     union RENAME3res switch (nfsstat3 status) {
     case NFS3_OK:
          RENAME3resok   resok;
     default:
          RENAME3resfail resfail;
     };

  DESCRIPTION

     Procedure RENAME renames the file identified by from.name
     in the directory, from.dir, to to.name in the di- rectory,
     to.dir. The operation is required to be atomic to the
     client. To.dir and from.dir must reside on the same file
     system and server. On entry, the arguments in RENAME3args
     are:

     from
        A diropargs3 structure identifying the source (the file
        system object to be re-named):

        from.dir
           The file handle for the directory from which the
           entry is to be renamed.

        from.name
           The name of the entry that identifies the object to
           be renamed. Refer to General comments on filenames
           on page 30.

     to
        A diropargs3 structure identifying the target (the new
        name of the object):

        to.dir
           The file handle for the directory to which the
           object is to be renamed.

        to.name
           The new name for the object. Refer to General
           comments on filenames on page 30.

     If the directory, to.dir, already contains an entry with
     the name, to.name, the source object must be compatible
     with the target: either both are non-directories or both
     are directories and the target must be empty. If
     compatible, the existing target is removed before the
     rename occurs. If they are not compatible or if the target
     is a directory but not empty, the server should return the
     error, NFS3ERR_EXIST.

     On successful return, RENAME3res.status is NFS3_OK and
     RENAME3res.resok contains:

     fromdir_wcc
        Weak cache consistency data for the directory,
        from.dir.

     todir_wcc
        Weak cache consistency data for the directory, to.dir.

     Otherwise, RENAME3res.status contains the error on failure
     and RENAME3res.resfail contains the following:

     fromdir_wcc
        Weak cache consistency data for the directory,
        from.dir.

     todir_wcc
        Weak cache consistency data for the directory, to.dir.

  IMPLEMENTATION
     The RENAME operation must be atomic to the client. The
     message "to.dir and from.dir must reside on the same file
     system on the server, [or the operation will fail]" means
     that the fsid fields in the attributes for the directories
     are the same. If they reside on different file systems,
     the error, NFS3ERR_XDEV, is returned. Even though the
     operation is atomic, the status, NFS3ERR_MLINK, may be
     returned if the server used a "unlink/link/unlink"
     sequence internally.

     A file handle may or may not become stale on a rename.
     However, server implementors are strongly encouraged to
     attempt to keep file handles from becoming stale in this
     fashion.

     On some servers, the filenames, "." and "..", are illegal
     as either from.name or to.name. In addition, neither
     from.name nor to.name can be an alias for from.dir. These
     servers will return the error, NFS3ERR_INVAL, in these
     cases.

     If from and to both refer to the same file (they might
     be hard links of each other), then RENAME should perform
     no action and return NFS3_OK.

     Refer to General comments on filenames on page 30.

  ERRORS

     NFS3ERR_NOENT
     NFS3ERR_IO
     NFS3ERR_ACCES
     NFS3ERR_EXIST
     NFS3ERR_XDEV
     NFS3ERR_NOTDIR
     NFS3ERR_ISDIR
     NFS3ERR_INVAL
     NFS3ERR_NOSPC
     NFS3ERR_ROFS
     NFS3ERR_MLINK
     NFS3ERR_NAMETOOLONG
     NFS3ERR_NOTEMPTY
     NFS3ERR_DQUOT
     NFS3ERR_STALE
     NFS3ERR_BADHANDLE
     NFS3ERR_NOTSUPP
     NFS3ERR_SERVERFAULT

  SEE ALSO

  REMOVE and LINK.

3.3.15 Procedure 15: LINK - Create Link to an object

  SYNOPSIS

     LINK3res NFSPROC3_LINK(LINK3args) = 15;

     struct LINK3args {
          nfs_fh3     file;
          diropargs3  link;
     };

     struct LINK3resok {
          post_op_attr   file_attributes;
          wcc_data       linkdir_wcc;
     };

     struct LINK3resfail {
          post_op_attr   file_attributes;
          wcc_data       linkdir_wcc;
     };

     union LINK3res switch (nfsstat3 status) {
     case NFS3_OK:

          LINK3resok    resok;
     default:
          LINK3resfail  resfail;
     };

  DESCRIPTION

     Procedure LINK creates a hard link from file to link.name,
     in the directory, link.dir. file and link.dir must reside
     on the same file system and server. On entry, the
     arguments in LINK3args are:

     file
        The file handle for the existing file system object.

     link
        The location of the link to be created:

        link.dir
           The file handle for the directory in which the link
           is to be created.

        link.name
           The name that is to be associated with the created
           link. Refer to General comments on filenames on page
           17.

     On successful return, LINK3res.status is NFS3_OK and
     LINK3res.resok contains:

     file_attributes
        The post-operation attributes of the file system object
        identified by file.

     linkdir_wcc
        Weak cache consistency data for the directory,
        link.dir.

     Otherwise, LINK3res.status contains the error on failure
     and LINK3res.resfail contains the following:

     file_attributes
        The post-operation attributes of the file system object
        identified by file.

     linkdir_wcc
        Weak cache consistency data for the directory,
        link.dir.

  IMPLEMENTATION

     Changes to any property of the hard-linked files are
     reflected in all of the linked files. When a hard link is
     made to a file, the attributes for the file should have a
     value for nlink that is one greater than the value before
     the LINK.

     The comments under RENAME regarding object and target
     residing on the same file system apply here as well. The
     comments regarding the target name applies as well. Refer
     to General comments on filenames on page 30.

  ERRORS

     NFS3ERR_IO
     NFS3ERR_ACCES
     NFS3ERR_EXIST
     NFS3ERR_XDEV
     NFS3ERR_NOTDIR
     NFS3ERR_INVAL
     NFS3ERR_NOSPC
     NFS3ERR_ROFS
     NFS3ERR_MLINK
     NFS3ERR_NAMETOOLONG
     NFS3ERR_DQUOT
     NFS3ERR_STALE
     NFS3ERR_BADHANDLE
     NFS3ERR_NOTSUPP
     NFS3ERR_SERVERFAULT

  SEE ALSO

     SYMLINK, RENAME and FSINFO.

3.3.16 Procedure 16: READDIR - Read From Directory

  SYNOPSIS

     READDIR3res NFSPROC3_READDIR(READDIR3args) = 16;

     struct READDIR3args {
          nfs_fh3      dir;
          cookie3      cookie;
          cookieverf3  cookieverf;
          count3       count;
     };

     struct entry3 {
          fileid3      fileid;
          filename3    name;
          cookie3      cookie;
          entry3       *nextentry;
     };

     struct dirlist3 {
          entry3       *entries;
          bool         eof;
     };

     struct READDIR3resok {
          post_op_attr dir_attributes;
          cookieverf3  cookieverf;
          dirlist3     reply;
     };

     struct READDIR3resfail {
          post_op_attr dir_attributes;
     };

     union READDIR3res switch (nfsstat3 status) {
     case NFS3_OK:
          READDIR3resok   resok;
     default:
          READDIR3resfail resfail;
     };

  DESCRIPTION

     Procedure READDIR retrieves a variable number of entries,
     in sequence, from a directory and returns the name and
     file identifier for each, with information to allow the
     client to request additional directory entries in a
     subsequent READDIR request. On entry, the arguments in
     READDIR3args are:

     dir
        The file handle for the directory to be read.

     cookie
        This should be set to 0 in the first request to read
        the directory. On subsequent requests, it should be a
        cookie as returned by the server.

     cookieverf
        This should be set to 0 in the first request to read
        the directory. On subsequent requests, it should be a
        cookieverf as returned by the server. The cookieverf
        must match that returned by the READDIR in which the
        cookie was acquired.

     count
        The maximum size of the READDIR3resok structure, in
        bytes.  The size must include all XDR overhead. The
        server is free to return less than count bytes of
        data.

     On successful return, READDIR3res.status is NFS3_OK and
     READDIR3res.resok contains:

     dir_attributes
        The attributes of the directory, dir.

     cookieverf
        The cookie verifier.

     reply
        The directory list:

        entries
           Zero or more directory (entry3) entries.

        eof
           TRUE if the last member of reply.entries is the last
           entry in the directory or the list reply.entries is
           empty and the cookie corresponded to the end of the
           directory. If FALSE, there may be more entries to
           read.

     Otherwise, READDIR3res.status contains the error on
     failure and READDIR3res.resfail contains the following:

     dir_attributes
        The attributes of the directory, dir.

  IMPLEMENTATION

     In the NFS version 2 protocol, each directory entry
     returned included a cookie identifying a point in the
     directory. By including this cookie in a subsequent
     READDIR, the client could resume the directory read at any
     point in the directory.  One problem with this scheme was

     that there was no easy way for a server to verify that a
     cookie was valid. If two READDIRs were separated by one or
     more operations that changed the directory in some way
     (for example, reordering or compressing it), it was
     possible that the second READDIR could miss entries, or
     process entries more than once. If the cookie was no
     longer usable, for example, pointing into the middle of a
     directory entry, the server would have to either round the
     cookie down to the cookie of the previous entry or round
     it up to the cookie of the next entry in the directory.
     Either way would possibly lead to incorrect results and
     the client would be unaware that any problem existed.

     In the NFS version 3 protocol, each READDIR request
     includes both a cookie and a cookie verifier. For the
     first call, both are set to 0.  The response includes a
     new cookie verifier, with a cookie per entry.  For
     subsequent READDIRs, the client must present both the
     cookie and the corresponding cookie verifier.  If the
     server detects that the cookie is no longer valid, the
     server will reject the READDIR request with the status,
     NFS3ERR_BAD_COOKIE. The client should be careful to
     avoid holding directory entry cookies across operations
     that modify the directory contents, such as REMOVE and
     CREATE.

     One implementation of the cookie-verifier mechanism might
     be for the server to use the modification time of the
     directory. This might be overly restrictive, however. A
     better approach would be to record the time of the last
     directory modification that changed the directory
     organization in a way that would make it impossible to
     reliably interpret a cookie. Servers in which directory
     cookies are always valid are free to use zero as the
     verifier always.

     The server may return fewer than count bytes of
     XDR-encoded entries.  The count specified by the client in
     the request should be greater than or equal to FSINFO
     dtpref.

     Since UNIX clients give a special meaning to the fileid
     value zero, UNIX clients should be careful to map zero
     fileid values to some other value and servers should try
     to avoid sending a zero fileid.

  ERRORS

     NFS3ERR_IO
     NFS3ERR_ACCES
     NFS3ERR_NOTDIR
     NFS3ERR_BAD_COOKIE
     NFS3ERR_TOOSMALL
     NFS3ERR_STALE
     NFS3ERR_BADHANDLE
     NFS3ERR_SERVERFAULT

  SEE ALSO

     READDIRPLUS and FSINFO.

3.3.17 Procedure 17: READDIRPLUS - Extended read from directory

  SYNOPSIS

     READDIRPLUS3res NFSPROC3_READDIRPLUS(READDIRPLUS3args) = 17;

     struct READDIRPLUS3args {
          nfs_fh3      dir;
          cookie3      cookie;
          cookieverf3  cookieverf;
          count3       dircount;
          count3       maxcount;
     };

     struct entryplus3 {
          fileid3      fileid;
          filename3    name;
          cookie3      cookie;
          post_op_attr name_attributes;
          post_op_fh3  name_handle;
          entryplus3   *nextentry;
     };

     struct dirlistplus3 {
          entryplus3   *entries;
          bool         eof;
     };

     struct READDIRPLUS3resok {
          post_op_attr dir_attributes;
          cookieverf3  cookieverf;
          dirlistplus3 reply;
     };

     struct READDIRPLUS3resfail {
          post_op_attr dir_attributes;
     };

     union READDIRPLUS3res switch (nfsstat3 status) {
     case NFS3_OK:
          READDIRPLUS3resok   resok;
     default:
          READDIRPLUS3resfail resfail;
     };

  DESCRIPTION

     Procedure READDIRPLUS retrieves a variable number of
     entries from a file system directory and returns complete
     information about each along with information to allow the
     client to request additional directory entries in a
     subsequent READDIRPLUS.  READDIRPLUS differs from READDIR
     only in the amount of information returned for each
     entry.  In READDIR, each entry returns the filename and
     the fileid.  In READDIRPLUS, each entry returns the name,
     the fileid, attributes (including the fileid), and file
     handle. On entry, the arguments in READDIRPLUS3args are:

     dir
        The file handle for the directory to be read.

     cookie
        This should be set to 0 on the first request to read a
        directory. On subsequent requests, it should be a
        cookie as returned by the server.

     cookieverf
        This should be set to 0 on the first request to read a
        directory. On subsequent requests, it should be a
        cookieverf as returned by the server. The cookieverf
        must match that returned by the READDIRPLUS call in
        which the cookie was acquired.

     dircount
        The maximum number of bytes of directory information
        returned. This number should not include the size of
        the attributes and file handle portions of the result.

     maxcount
        The maximum size of the READDIRPLUS3resok structure, in
        bytes. The size must include all XDR overhead. The

        server is free to return fewer than maxcount bytes of
        data.

     On successful return, READDIRPLUS3res.status is NFS3_OK
     and READDIRPLUS3res.resok contains:

     dir_attributes
        The attributes of the directory, dir.

     cookieverf
        The cookie verifier.

     reply
        The directory list:

        entries
           Zero or more directory (entryplus3) entries.

        eof
           TRUE if the last member of reply.entries is the last
           entry in the directory or the list reply.entries is
           empty and the cookie corresponded to the end of the
           directory. If FALSE, there may be more entries to
           read.

     Otherwise, READDIRPLUS3res.status contains the error on
     failure and READDIRPLUS3res.resfail contains the following:

     dir_attributes
        The attributes of the directory, dir.

  IMPLEMENTATION

     Issues that need to be understood for this procedure
     include increased cache flushing activity on the client
     (as new file handles are returned with names which are
     entered into caches) and over-the-wire overhead versus
     expected subsequent LOOKUP elimination. It is thought that
     this procedure may improve performance for directory
     browsing where attributes are always required as on the
     Apple Macintosh operating system and for MS-DOS.

     The dircount and maxcount fields are included as an
     optimization.  Consider a READDIRPLUS call on a UNIX
     operating system implementation for 1048 bytes; the reply
     does not contain many entries because of the overhead due
     to attributes and file handles. An alternative is to issue
     a READDIRPLUS call for 8192 bytes and then only use the

     first 1048 bytes of directory information. However, the
     server doesn't know that all that is needed is 1048 bytes
     of directory information (as would be returned by
     READDIR). It sees the 8192 byte request and issues a
     VOP_READDIR for 8192 bytes. It then steps through all of
     those directory entries, obtaining attributes and file
     handles for each entry.  When it encodes the result, the
     server only encodes until it gets 8192 bytes of results
     which include the attributes and file handles. Thus, it
     has done a larger VOP_READDIR and many more attribute
     fetches than it needed to. The ratio of the directory
     entry size to the size of the attributes plus the size of
     the file handle is usually at least 8 to 1. The server has
     done much more work than it needed to.

     The solution to this problem is for the client to provide
     two counts to the server. The first is the number of bytes
     of directory information that the client really wants,
     dircount.  The second is the maximum number of bytes in
     the result, including the attributes and file handles,
     maxcount. Thus, the server will issue a VOP_READDIR for
     only the number of bytes that the client really wants to
     get, not an inflated number.  This should help to reduce
     the size of VOP_READDIR requests on the server, thus
     reducing the amount of work done there, and to reduce the
     number of VOP_LOOKUP, VOP_GETATTR, and other calls done by
     the server to construct attributes and file handles.

  ERRORS

     NFS3ERR_IO
     NFS3ERR_ACCES
     NFS3ERR_NOTDIR
     NFS3ERR_BAD_COOKIE
     NFS3ERR_TOOSMALL
     NFS3ERR_STALE
     NFS3ERR_BADHANDLE
     NFS3ERR_NOTSUPP
     NFS3ERR_SERVERFAULT

  SEE ALSO

     READDIR.

3.3.18 Procedure 18: FSSTAT - Get dynamic file system information

  SYNOPSIS

     FSSTAT3res NFSPROC3_FSSTAT(FSSTAT3args) = 18;

     struct FSSTAT3args {
          nfs_fh3   fsroot;
     };

     struct FSSTAT3resok {
          post_op_attr obj_attributes;
          size3        tbytes;
          size3        fbytes;
          size3        abytes;
          size3        tfiles;
          size3        ffiles;
          size3        afiles;
          uint32       invarsec;
     };

     struct FSSTAT3resfail {
          post_op_attr obj_attributes;
     };

     union FSSTAT3res switch (nfsstat3 status) {
     case NFS3_OK:
          FSSTAT3resok   resok;
     default:
          FSSTAT3resfail resfail;
     };

  DESCRIPTION

     Procedure FSSTAT retrieves volatile file system state
     information. On entry, the arguments in FSSTAT3args are:

     fsroot
        A file handle identifying a object in the file system.
        This is normally a file handle for a mount point for a
        file system, as originally obtained from the MOUNT
        service on the server.

     On successful return, FSSTAT3res.status is NFS3_OK and
     FSSTAT3res.resok contains:

     obj_attributes
        The attributes of the file system object specified in
        fsroot.

     tbytes
        The total size, in bytes, of the file system.

     fbytes
        The amount of free space, in bytes, in the file
        system.

     abytes
        The amount of free space, in bytes, available to the
        user identified by the authentication information in
        the RPC.  (This reflects space that is reserved by the
        file system; it does not reflect any quota system
        implemented by the server.)

     tfiles
        The total number of file slots in the file system. (On
        a UNIX server, this often corresponds to the number of
        inodes configured.)

     ffiles
        The number of free file slots in the file system.

     afiles
        The number of free file slots that are available to the
        user corresponding to the authentication information in
        the RPC.  (This reflects slots that are reserved by the
        file system; it does not reflect any quota system
        implemented by the server.)

     invarsec
        A measure of file system volatility: this is the number
        of seconds for which the file system is not expected to
        change. For a volatile, frequently updated file system,
        this will be 0. For an immutable file system, such as a
        CD-ROM, this would be the largest unsigned integer. For
        file systems that are infrequently modified, for
        example, one containing local executable programs and
        on-line documentation, a value corresponding to a few
        hours or days might be used. The client may use this as
        a hint in tuning its cache management. Note however,
        this measure is assumed to be dynamic and may change at
        any time.

     Otherwise, FSSTAT3res.status contains the error on failure
     and FSSTAT3res.resfail contains the following:

     obj_attributes
        The attributes of the file system object specified in
        fsroot.

  IMPLEMENTATION

     Not all implementations can support the entire list of
     attributes. It is expected that servers will make a best
     effort at supporting all the attributes.

  ERRORS

     NFS3ERR_IO
     NFS3ERR_STALE
     NFS3ERR_BADHANDLE
     NFS3ERR_SERVERFAULT

  SEE ALSO

     FSINFO.

3.3.19 Procedure 19: FSINFO - Get static file system Information

  SYNOPSIS

     FSINFO3res NFSPROC3_FSINFO(FSINFO3args) = 19;

     const FSF3_LINK        = 0x0001;
     const FSF3_SYMLINK     = 0x0002;
     const FSF3_HOMOGENEOUS = 0x0008;
     const FSF3_CANSETTIME  = 0x0010;

     struct FSINFOargs {
          nfs_fh3   fsroot;
     };

     struct FSINFO3resok {
          post_op_attr obj_attributes;
          uint32       rtmax;
          uint32       rtpref;
          uint32       rtmult;
          uint32       wtmax;
          uint32       wtpref;
          uint32       wtmult;
          uint32       dtpref;

          size3        maxfilesize;
          nfstime3     time_delta;
          uint32       properties;
     };

     struct FSINFO3resfail {
          post_op_attr obj_attributes;
     };

     union FSINFO3res switch (nfsstat3 status) {
     case NFS3_OK:
          FSINFO3resok   resok;
     default:
          FSINFO3resfail resfail;
     };

  DESCRIPTION

     Procedure FSINFO retrieves nonvolatile file system state
     information and general information about the NFS version
     3 protocol server implementation. On entry, the arguments
     in FSINFO3args are:

     fsroot
        A file handle identifying a file object. Normal usage
        is to provide a file handle for a mount point for a
        file system, as originally obtained from the MOUNT
        service on the server.

     On successful return, FSINFO3res.status is NFS3_OK and
     FSINFO3res.resok contains:

     obj_attributes
        The attributes of the file system object specified in
        fsroot.

     rtmax
        The maximum size in bytes of a READ request supported
        by the server. Any READ with a number greater than
        rtmax will result in a short read of rtmax bytes or
        less.

     rtpref
        The preferred size of a READ request. This should be
        the same as rtmax unless there is a clear benefit in
        performance or efficiency.

     rtmult
        The suggested multiple for the size of a READ request.

     wtmax
        The maximum size of a WRITE request supported by the
        server.  In general, the client is limited by wtmax
        since there is no guarantee that a server can handle a
        larger write. Any WRITE with a count greater than wtmax
        will result in a short write of at most wtmax bytes.

     wtpref
        The preferred size of a WRITE request. This should be
        the same as wtmax unless there is a clear benefit in
        performance or efficiency.

     wtmult
        The suggested multiple for the size of a WRITE
        request.

     dtpref
        The preferred size of a READDIR request.

     maxfilesize
        The maximum size of a file on the file system.

     time_delta
        The server time granularity. When setting a file time
        using SETATTR, the server guarantees only to preserve
        times to this accuracy. If this is {0, 1}, the server
        can support nanosecond times, {0, 1000000} denotes
        millisecond precision, and {1, 0} indicates that times
        are accurate only to the nearest second.

     properties
        A bit mask of file system properties. The following
        values are defined:

        FSF_LINK
           If this bit is 1 (TRUE), the file system supports
           hard links.

        FSF_SYMLINK
           If this bit is 1 (TRUE), the file system supports
           symbolic links.

        FSF_HOMOGENEOUS
           If this bit is 1 (TRUE), the information returned by
           PATHCONF is identical for every file and directory

           in the file system. If it is 0 (FALSE), the client
           should retrieve PATHCONF information for each file
           and directory as required.

        FSF_CANSETTIME
           If this bit is 1 (TRUE), the server will set the
           times for a file via SETATTR if requested (to the
           accuracy indicated by time_delta). If it is 0
           (FALSE), the server cannot set times as requested.

     Otherwise, FSINFO3res.status contains the error on failure
     and FSINFO3res.resfail contains the following:

     attributes
        The attributes of the file system object specified in
        fsroot.

  IMPLEMENTATION

     Not all implementations can support the entire list of
     attributes. It is expected that a server will make a best
     effort at supporting all the attributes.

     The file handle provided is expected to be the file handle
     of the file system root, as returned to the MOUNT
     operation.  Since mounts may occur anywhere within an
     exported tree, the server should expect FSINFO requests
     specifying file handles within the exported file system.
     A server may export different types of file systems with
     different attributes returned to the FSINFO call. The
     client should retrieve FSINFO information for each mount
     completed. Though a server may return different FSINFO
     information for different files within a file system,
     there is no requirement that a client obtain FSINFO
     information for other than the file handle returned at
     mount.

     The maxfilesize field determines whether a server's
     particular file system uses 32 bit sizes and offsets or 64
     bit file sizes and offsets. This may affect a client's
     processing.

     The preferred sizes for requests are nominally tied to an
     exported file system mounted by a client. A surmountable
     issue arises in that the transfer size for an NFS version
     3 protocol request is not only dependent on
     characteristics of the file system but also on
     characteristics of the network interface, particularly the

     maximum transfer unit (MTU). A server implementation can
     advertise different transfer sizes (for the fields, rtmax,
     rtpref, wtmax, wtpref, and dtpref) depending on the
     interface on which the FSINFO request is received. This is
     an implementation issue.

  ERRORS

     NFS3ERR_STALE
     NFS3ERR_BADHANDLE
     NFS3ERR_SERVERFAULT

  SEE ALSO

     READLINK, WRITE, READDIR, FSSTAT and PATHCONF.

3.3.20 Procedure 20: PATHCONF - Retrieve POSIX information

  SYNOPSIS

     PATHCONF3res NFSPROC3_PATHCONF(PATHCONF3args) = 20;

     struct PATHCONF3args {
          nfs_fh3   object;
     };

     struct PATHCONF3resok {
          post_op_attr obj_attributes;
          uint32       linkmax;
          uint32       name_max;
          bool         no_trunc;
          bool         chown_restricted;
          bool         case_insensitive;
          bool         case_preserving;
     };

     struct PATHCONF3resfail {
          post_op_attr obj_attributes;
     };

     union PATHCONF3res switch (nfsstat3 status) {
     case NFS3_OK:
          PATHCONF3resok   resok;
     default:
          PATHCONF3resfail resfail;
     };

  DESCRIPTION

     Procedure PATHCONF retrieves the pathconf information for
     a file or directory. If the FSF_HOMOGENEOUS bit is set in
     FSFINFO3resok.properties, the pathconf information will be
     the same for all files and directories in the exported
     file system in which this file or directory resides. On
     entry, the arguments in PATHCONF3args are:

     object
        The file handle for the file system object.

     On successful return, PATHCONF3res.status is NFS3_OK and
     PATHCONF3res.resok contains:

     obj_attributes
        The attributes of the object specified by object.

     linkmax
        The maximum number of hard links to an object.

     name_max
        The maximum length of a component of a filename.

     no_trunc
        If TRUE, the server will reject any request that
        includes a name longer than name_max with the error,
        NFS3ERR_NAMETOOLONG. If FALSE, any length name over
        name_max bytes will be silently truncated to name_max
        bytes.

     chown_restricted
        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 the privileged user. (Uid 0.)

     case_insensitive
        If TRUE, the server file system does not distinguish
        case when interpreting filenames.

     case_preserving
        If TRUE, the server file system will preserve the case
        of a name during a CREATE, MKDIR, MKNOD, SYMLINK,
        RENAME, or LINK operation.

     Otherwise, PATHCONF3res.status contains the error on
     failure and PATHCONF3res.resfail contains the following:

     obj_attributes
        The attributes of the object specified by object.

  IMPLEMENTATION

     In some implementations of the NFS version 2 protocol,
     pathconf information was obtained at mount time through
     the MOUNT protocol.  The proper place to obtain it, is as
     here, in the NFS version 3 protocol itself.

  ERRORS

     NFS3ERR_STALE
     NFS3ERR_BADHANDLE
     NFS3ERR_SERVERFAULT

  SEE ALSO

     LOOKUP, CREATE, MKDIR, SYMLINK, MKNOD, RENAME, LINK and FSINFO.

3.3.21 Procedure 21: COMMIT - Commit cached data on a server to stable
      storage

  SYNOPSIS

     COMMIT3res NFSPROC3_COMMIT(COMMIT3args) = 21;

     struct COMMIT3args {
          nfs_fh3    file;
          offset3    offset;
          count3     count;
     };

     struct COMMIT3resok {
          wcc_data   file_wcc;
          writeverf3 verf;
     };

     struct COMMIT3resfail {
          wcc_data   file_wcc;
     };

     union COMMIT3res switch (nfsstat3 status) {
     case NFS3_OK:
          COMMIT3resok   resok;
     default:
          COMMIT3resfail resfail;
     };

  DESCRIPTION

     Procedure COMMIT forces or flushes data to stable storage
     that was previously written with a WRITE procedure call
     with the stable field set to UNSTABLE. On entry, the
     arguments in COMMIT3args are:

     file
        The file handle for the file to which data is to be
        flushed (committed). This must identify a file system
        object of type, NF3REG.

     offset
        The position within the file at which the flush is to
        begin.  An offset of 0 means to flush data starting at
        the beginning of the file.

     count
        The number of bytes of data to flush. If count is 0, a
        flush from offset to the end of file is done.

     On successful return, COMMIT3res.status is NFS3_OK and
     COMMIT3res.resok contains:

     file_wcc
        Weak cache consistency data for the file. For a client
        that requires only the post-operation file attributes,
        these can be found in file_wcc.after.

     verf
        This is a cookie that the client can use to determine
        whether the server has rebooted between a call to WRITE
        and a subsequent call to COMMIT. This cookie must be
        consistent during a single boot session and must be
        unique between instances of the NFS version 3 protocol
        server where uncommitted data may be lost.

     Otherwise, COMMIT3res.status contains the error on failure
     and COMMIT3res.resfail contains the following:

     file_wcc
        Weak cache consistency data for the file. For a client
        that requires only the post-write file attributes,
        these can be found in file_wcc.after. Even though the
        COMMIT failed, full wcc_data is returned to allow the
        client to determine whether the file changed on the
        server between calls to WRITE and COMMIT.

  IMPLEMENTATION

     Procedure COMMIT is similar in operation and semantics to
     the POSIX fsync(2) system call that synchronizes a file's
     state with the disk, that is it flushes the file's data
     and metadata to disk. COMMIT performs the same operation
     for a client, flushing any unsynchronized data and
     metadata on the server to the server's disk for the
     specified file. Like fsync(2), it may be that there is
     some modified data or no modified data to synchronize. The
     data may have been synchronized by the server's normal
     periodic buffer synchronization activity. COMMIT will
     always return NFS3_OK, unless there has been an unexpected
     error.

     COMMIT differs from fsync(2) in that it is possible for
     the client to flush a range of the file (most likely
     triggered by a buffer-reclamation scheme on the client
     before file has been completely written).

     The server implementation of COMMIT is reasonably simple.
     If the server receives a full file COMMIT request, that is
     starting at offset 0 and count 0, it should do the
     equivalent of fsync()'ing the file. Otherwise, it should
     arrange to have the cached data in the range specified by
     offset and count to be flushed to stable storage.  In both
     cases, any metadata associated with the file must be
     flushed to stable storage before returning. It is not an
     error for there to be nothing to flush on the server.
     This means that the data and metadata that needed to be
     flushed have already been flushed or lost during the last
     server failure.

     The client implementation of COMMIT is a little more
     complex.  There are two reasons for wanting to commit a
     client buffer to stable storage. The first is that the
     client wants to reuse a buffer. In this case, the offset
     and count of the buffer are sent to the server in the
     COMMIT request. The server then flushes any cached data
     based on the offset and count, and flushes any metadata
     associated with the file. It then returns the status of
     the flush and the verf verifier.  The other reason for the
     client to generate a COMMIT is for a full file flush, such
     as may be done at close. In this case, the client would
     gather all of the buffers for this file that contain
     uncommitted data, do the COMMIT operation with an offset
     of 0 and count of 0, and then free all of those buffers.
     Any other dirty buffers would be sent to the server in the

     normal fashion.

     This implementation will require some modifications to the
     buffer cache on the client. After a buffer is written with
     stable UNSTABLE, it must be considered as dirty by the
     client system until it is either flushed via a COMMIT
     operation or written via a WRITE operation with stable set
     to FILE_SYNC or DATA_SYNC. This is done to prevent the
     buffer from being freed and reused before the data can be
     flushed to stable storage on the server.

     When a response comes back from either a WRITE or a COMMIT
     operation that contains an unexpected verf, the client
     will need to retransmit all of the buffers containing
     uncommitted cached data to the server.  How this is to be
     done is up to the implementor. If there is only one buffer
     of interest, then it should probably be sent back over in
     a WRITE request with the appropriate stable flag. If there
     more than one, it might be worthwhile retransmitting all
     of the buffers in WRITE requests with stable set to
     UNSTABLE and then retransmitting the COMMIT operation to
     flush all of the data on the server to stable storage. The
     timing of these retransmissions is left to the
     implementor.

     The above description applies to page-cache-based systems
     as well as buffer-cache-based systems. In those systems,
     the virtual memory system will need to be modified instead
     of the buffer cache.

     See additional comments on WRITE on page 49.

  ERRORS

     NFS3ERR_IO
     NFS3ERR_STALE
     NFS3ERR_BADHANDLE
     NFS3ERR_SERVERFAULT

  SEE ALSO

     WRITE.

4. Implementation issues

  The NFS version 3 protocol was designed to allow different
  operating systems to share files. However, since it was
  designed in a UNIX environment, many operations have
  semantics similar to the operations of the UNIX file system.
  This section discusses some of the general
  implementation-specific details and semantic issues.
  Procedure descriptions have implementation comments specific
  to that procedure.

  A number of papers have been written describing issues
  encountered when constructing an NFS version 2 protocol
  implementation. The best overview paper is still [Sandberg].
  [Israel], [Macklem], and [Pawlowski] describe other
  implementations. [X/OpenNFS] provides a complete description
  of the NFS version 2 protocol and supporting protocols, as
  well as a discussion on implementation issues and procedure
  and error semantics. Many of the issues encountered when
  constructing an NFS version 2 protocol implementation will be
  encountered when constructing an NFS version 3 protocol
  implementation.

4.1 Multiple version support

  The RPC protocol provides explicit support for versioning of
  a service. Client and server implementations of NFS version 3
  protocol should support both versions, for full backwards
  compatibility, when possible. Default behavior of the RPC
  binding protocol is the client and server bind using the
  highest version number they both support. Client or server
  implementations that cannot easily support both versions (for
  example, because of memory restrictions) will have to choose
  what version to support. The NFS version 2 protocol would be
  a safe choice since fully capable clients and servers should
  support both versions. However, this choice would need to be
  made keeping all requirements in mind.

4.2 Server/client relationship

  The NFS version 3 protocol is designed to allow servers to be
  as simple and general as possible. Sometimes the simplicity
  of the server can be a problem, if the client implements
  complicated file system semantics.

  For example, some operating systems allow removal of open
  files.  A process can open a file and, while it is open,
  remove it from the directory. The file can be read and

  written as long as the process keeps it open, even though the
  file has no name in the file system.  It is impossible for a
  stateless server to implement these semantics.  The client
  can do some tricks such as renaming the file on remove (to a
  hidden name), and only physically deleting it on close. The
  NFS version 3 protocol provides sufficient functionality to
  implement most file system semantics on a client.

  Every NFS version 3 protocol client can also potentially be a
  server, and remote and local mounted file systems can be
  freely mixed. This leads to some problems when a client
  travels down the directory tree of a remote file system and
  reaches the mount point on the server for another remote file
  system. Allowing the server to follow the second remote mount
  would require loop detection, server lookup, and user
  revalidation. Instead, both NFS version 2 protocol and NFS
  version 3 protocol implementations do not typically let
  clients cross a server's mount point. When a client does a
  LOOKUP on a directory on which the server has mounted a file
  system, the client sees the underlying directory instead of
  the mounted directory.

  For example, if a server has a file system called /usr and
  mounts another file system on /usr/src, if a client mounts
  /usr, it does not see the mounted version of /usr/src. A
  client could do remote mounts that match the server's mount
  points to maintain the server's view.  In this example, the
  client would also have to mount /usr/src in addition to /usr,
  even if they are from the same server.

4.3 Path name interpretation

  There are a few complications to the rule that path names are
  always parsed on the client. For example, symbolic links
  could have different interpretations on different clients.
  There is no answer to this problem in this specification.

  Another common problem for non-UNIX implementations is the
  special interpretation of the pathname, "..", to mean the
  parent of a given directory. A future revision of the
  protocol may use an explicit flag to indicate the parent
  instead - however it is not a problem as many working
  non-UNIX implementations exist.

4.4 Permission issues

  The NFS version 3 protocol, strictly speaking, does not
  define the permission checking used by servers. However, it
  is expected that a server will do normal operating system
  permission checking using AUTH_UNIX style authentication as
  the basis of its protection mechanism, or another stronger
  form of authentication such as AUTH_DES or AUTH_KERB. With
  AUTH_UNIX authentication, the server gets the client's
  effective uid, effective gid, and groups on each call and
  uses them to check permission. These are the so-called UNIX
  credentials. AUTH_DES and AUTH_KERB use a network name, or
  netname, as the basis for identification (from which a UNIX
  server derives the necessary standard UNIX credentials).
  There are problems with this method that have been solved.

  Using uid and gid implies that the client and server share
  the same uid list. Every server and client pair must have the
  same mapping from user to uid and from group to gid. Since
  every client can also be a server, this tends to imply that
  the whole network shares the same uid/gid space. If this is
  not the case, then it usually falls upon the server to
  perform some custom mapping of credentials from one
  authentication domain into another. A discussion of
  techniques for managing a shared user space or for providing
  mechanisms for user ID mapping is beyond the scope of this
  specification.

  Another problem arises due to the usually stateful open
  operation.  Most operating systems check permission at open
  time, and then check that the file is open on each read and
  write request. With stateless servers, the server cannot
  detect that the file is open and must do permission checking
  on each read and write call. UNIX client semantics of access
  permission checking on open can be provided with the ACCESS
  procedure call in this revision, which allows a client to
  explicitly check access permissions without resorting to
  trying the operation. On a local file system, a user can open
  a file and then change the permissions so that no one is
  allowed to touch it, but will still be able to write to the
  file because it is open. On a remote file system, by
  contrast, the write would fail. To get around this problem,
  the server's permission checking algorithm should allow the
  owner of a file to access it regardless of the permission
  setting. This is needed in a practical NFS version 3 protocol
  server implementation, but it does depart from correct local
  file system semantics. This should not affect the return
  result of access permissions as returned by the ACCESS

  procedure, however.

  A similar problem has to do with paging in an executable
  program over the network. The operating system usually checks
  for execute permission before opening a file for demand
  paging, and then reads blocks from the open file. In a local
  UNIX file system, an executable file does not need read
  permission to execute (pagein). An NFS version 3 protocol
  server can not tell the difference between a normal file read
  (where the read permission bit is meaningful) and a demand
  pagein read (where the server should allow access to the
  executable file if the execute bit is set for that user or
  group or public). To make this work, the server allows
  reading of files if the uid given in the call has either
  execute or read permission on the file, through ownership,
  group membership or public access. Again, this departs from
  correct local file system semantics.

  In most operating systems, a particular user (on UNIX, the
  uid 0) has access to all files, no matter what permission and
  ownership they have. This superuser permission may not be
  allowed on the server, since anyone who can become superuser
  on their client could gain access to all remote files. A UNIX
  server by default maps uid 0 to a distinguished value
  (UID_NOBODY), as well as mapping the groups list, before
  doing its access checking. A server implementation may
  provide a mechanism to change this mapping. This works except
  for NFS version 3 protocol root file systems (required for
  diskless NFS version 3 protocol client support), where
  superuser access cannot be avoided.  Export options are used,
  on the server, to restrict the set of clients allowed
  superuser access.

4.5 Duplicate request cache

  The typical NFS version 3 protocol failure recovery model
  uses client time-out and retry to handle server crashes,
  network partitions, and lost server replies. A retried
  request is called a duplicate of the original.

  When used in a file server context, the term idempotent can
  be used to distinguish between operation types. An idempotent
  request is one that a server can perform more than once with
  equivalent results (though it may in fact change, as a side
  effect, the access time on a file, say for READ). Some NFS
  operations are obviously non-idempotent. They cannot be
  reprocessed without special attention simply because they may
  fail if tried a second time. The CREATE request, for example,

  can be used to create a file for which the owner does not
  have write permission. A duplicate of this request cannot
  succeed if the original succeeded. Likewise, a file can be
  removed only once.

  The side effects caused by performing a duplicate
  non-idempotent request can be destructive (for example, a
  truncate operation causing lost writes). The combination of a
  stateless design with the common choice of an unreliable
  network transport (UDP) implies the possibility of
  destructive replays of non-idempotent requests. Though to be
  more accurate, it is the inherent stateless design of the NFS
  version 3 protocol on top of an unreliable RPC mechanism that
  yields the possibility of destructive replays of
  non-idempotent requests, since even in an implementation of
  the NFS version 3 protocol over a reliable
  connection-oriented transport, a connection break with
  automatic reestablishment requires duplicate request
  processing (the client will retransmit the request, and the
  server needs to deal with a potential duplicate
  non-idempotent request).

  Most NFS version 3 protocol server implementations use a
  cache of recent requests (called the duplicate request cache)
  for the processing of duplicate non-idempotent requests. The
  duplicate request cache provides a short-term memory
  mechanism in which the original completion status of a
  request is remembered and the operation attempted only once.
  If a duplicate copy of this request is received, then the
  original completion status is returned.

  The duplicate-request cache mechanism has been useful in
  reducing destructive side effects caused by duplicate NFS
  version 3 protocol requests. This mechanism, however, does
  not guarantee against these destructive side effects in all
  failure modes. Most servers store the duplicate request cache
  in RAM, so the contents are lost if the server crashes.  The
  exception to this may possibly occur in a redundant server
  approach to high availability, where the file system itself
  may be used to share the duplicate request cache state. Even
  if the cache survives server reboots (or failovers in the
  high availability case), its effectiveness is a function of
  its size. A network partition can cause a cache entry to be
  reused before a client receives a reply for the corresponding
  request. If this happens, the duplicate request will be
  processed as a new one, possibly with destructive side
  effects.

  A good description of the implementation and use of a
  duplicate request cache can be found in [Juszczak].

4.6 File name component handling

  Server implementations of NFS version 3 protocol will
  frequently impose restrictions on the names which can be
  created. Many servers will also forbid the use of names that
  contain certain characters, such as the path component
  separator used by the server operating system. For example,
  the UFS file system will reject a name which contains "/",
  while "." and ".." are distinguished in UFS, and may not be
  specified as the name when creating a file system object.
  The exact error status values return for these errors is
  specified in the description of each procedure argument. The
  values (which conform to NFS version 2 protocol server
  practice) are not necessarily obvious, nor are they
  consistent from one procedure to the next.

4.7 Synchronous modifying operations

  Data-modifying operations in the NFS version 3 protocol are
  synchronous. When a procedure returns to the client, the
  client can assume that the operation has completed and any
  data associated with the request is now on stable storage.

4.8 Stable storage

  NFS version 3 protocol servers must be able to recover
  without data loss from multiple power failures (including
  cascading power failures, that is, several power failures in
  quick succession), operating system failures, and hardware
  failure of components other than the storage medium itself
  (for example, disk, nonvolatile RAM).

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

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

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

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

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

  Conversely, the following are not examples of stable
  storage:

  1. An immediate reply disk drive without battery-backed
     on-drive intermediate storage or uninterruptible power
     system (UPS).

  2. Cache commit without both uninterruptible power system
     (UPS) and recovery software.

  The only exception to this (introduced in this protocol
  revision) is as described under the WRITE procedure on the
  handling of the stable bit, and the use of the COMMIT
  procedure.  It is the use of the synchronous COMMIT procedure
  that provides the necessary semantic support in the NFS
  version 3 protocol.

4.9 Lookups and name resolution

  A common objection to the NFS version 3 protocol is the
  philosophy of component-by-component LOOKUP by the client in
  resolving a name. The objection is that this is inefficient,
  as latencies for component-by-component LOOKUP would be
  unbearable.

  Implementation practice solves this issue. A name cache,
  providing component to file-handle mapping, is kept on the
  client to short circuit actual LOOKUP invocations over the
  wire.  The cache is subject to cache timeout parameters that
  bound attributes.

4.10 Adaptive retransmission

  Most client implementations use either an exponential
  back-off strategy to some maximum retransmission value, or a
  more adaptive strategy that attempts congestion avoidance.
  Congestion avoidance schemes in NFS request retransmission
  are modelled on the work presented in [Jacobson]. [Nowicki]
  and [Macklem] describe congestion avoidance schemes to be
  applied to the NFS protocol over UDP.

4.11 Caching policies

  The NFS version 3 protocol does not define a policy for
  caching on the client or server. In particular, there is no

  support for strict cache consistency between a client and
  server, nor between different clients. See [Kazar] for a
  discussion of the issues of cache synchronization and
  mechanisms in several distributed file systems.

4.12 Stable versus unstable writes

  The setting of the stable field in the WRITE arguments, that
  is whether or not to do asynchronous WRITE requests, is
  straightforward on a UNIX client. If the NFS version 3
  protocol client receives a write request that is not marked
  as being asynchronous, it should generate the RPC with stable
  set to TRUE. If the request is marked as being asynchronous,
  the RPC should be generated with stable set to FALSE. If the
  response comes back with the committed field set to TRUE, the
  client should just mark the write request as done and no
  further action is required. If committed is set to FALSE,
  indicating that the buffer was not synchronized with the
  server's disk, the client will need to mark the buffer in
  some way which indicates that a copy of the buffer lives on
  the server and that a new copy does not need to be sent to
  the server, but that a commit is required.

  Note that this algorithm introduces a new state for buffers,
  thus there are now three states for buffers. The three states
  are dirty, done but needs to be committed, and done. This
  extra state on the client will likely require modifications
  to the system outside of the NFS version 3 protocol client.

  One proposal that was rejected was the addition of a boolean
  commit argument to the WRITE operation. It would be used to
  indicate whether the server should do a full file commit
  after doing the write. This seems as if it could be useful if
  the client knew that it was doing the last write on the file.
  It is difficult to see how this could be used, given existing
  client architectures though.

  The asynchronous write opens up the window of problems
  associated with write sharing. For example: client A writes
  some data asynchronously. Client A is still holding the
  buffers cached, waiting to commit them later. Client B reads
  the modified data and writes it back to the server. The
  server then crashes. When it comes back up, client A issues a
  COMMIT operation which returns with a different cookie as
  well as changed attributes. In this case, the correct action
  may or may not be to retransmit the cached buffers.
  Unfortunately, client A can't tell for sure, so it will need
  to retransmit the buffers, thus overwriting the changes from

  client B.  Fortunately, write sharing is rare and the
  solution matches the current write sharing situation. Without
  using locking for synchronization, the behaviour will be
  indeterminate.

  In a high availability (redundant system) server
  implementation, two cases exist which relate to the verf
  changing.  If the high availability server implementation
  does not use a shared-memory scheme, then the verf should
  change on failover, since the unsynchronized data is not
  available to the second processor and there is no guarantee
  that the system which had the data cached was able to flush
  it to stable storage before going down. The client will need
  to retransmit the data to be safe. In a shared-memory high
  availability server implementation, the verf would not need
  to change because the server would still have the cached data
  available to it to be flushed. The exact policy regarding the
  verf in a shared memory high availability implementation,
  however, is up to the server implementor.

4.13 32 bit clients/servers and 64 bit clients/servers

  The 64 bit nature of the NFS version 3 protocol introduces
  several compatibility problems. The most notable two are
  mismatched clients and servers, that is, a 32 bit client and
  a 64 bit server or a 64 bit client and a 32 bit server.

  The problems of a 64 bit client and a 32 bit server are easy
  to handle. The client will never encounter a file that it can
  not handle. If it sends a request to the server that the
  server can not handle, the server should reject the request
  with an appropriate error.

  The problems of a 32 bit client and a 64 bit server are much
  harder to handle. In this situation, the server does not have
  a problem because it can handle anything that the client can
  generate. However, the client may encounter a file that it
  can not handle. The client will not be able to handle a file
  whose size can not be expressed in 32 bits. Thus, the client
  will not be able to properly decode the size of the file into
  its local attributes structure. Also, a file can grow beyond
  the limit of the client while the client is accessing the
  file.

  The solutions to these problems are left up to the individual
  implementor. However, there are two common approaches used to
  resolve this situation. The implementor can choose between
  them or even can invent a new solution altogether.

  The most common solution is for the client to deny access to
  any file whose size can not be expressed in 32 bits. This is
  probably the safest, but does introduce some strange
  semantics when the file grows beyond the limit of the client
  while it is being access by that client. The file becomes
  inaccessible even while it is being accessed.

  The second solution is for the client to map any size greater
  than it can handle to the maximum size that it can handle.
  Effectively, it is lying to the application program. This
  allows the application access as much of the file as possible
  given the 32 bit offset restriction. This eliminates the
  strange semantic of the file effectively disappearing after
  it has been accessed, but does introduce other problems. The
  client will not be able to access the entire file.

  Currently, the first solution is the recommended solution.
  However, client implementors are encouraged to do the best
  that they can to reduce the effects of this situation.

5.0 Appendix I: Mount protocol

  The changes from the NFS version 2 protocol to the NFS version 3
  protocol have required some changes to be made in the MOUNT
  protocol.  To meet the needs of the NFS version 3 protocol, a
  new version of the MOUNT protocol has been defined. This new
  protocol satisfies the requirements of the NFS version 3
  protocol and addresses several other current market
  requirements.

5.1 RPC Information

5.1.1 Authentication

  The MOUNT service uses AUTH_NONE in the NULL procedure.
  AUTH_UNIX, AUTH_SHORT, AUTH_DES, or AUTH_KERB are used for all
  other procedures.  Other authentication types may be supported
  in the future.

5.1.2 Constants

  These are the RPC constants needed to call the MOUNT service.
  They are given in decimal.

     PROGRAM  100005
     VERSION  3

5.1.3 Transport address

  The MOUNT service is normally supported over the TCP and UDP
  protocols. The rpcbind daemon should be queried for the correct
  transport address.

5.1.4 Sizes

  const MNTPATHLEN = 1024;  /* Maximum bytes in a path name */
  const MNTNAMLEN  = 255;   /* Maximum bytes in a name */
  const FHSIZE3    = 64;    /* Maximum bytes in a V3 file handle */

5.1.5 Basic Data Types

  typedef opaque fhandle3;
  typedef string dirpath;
  typedef string name;

  enum mountstat3 {
     MNT3_OK = 0,                 /* no error */
     MNT3ERR_PERM = 1,            /* Not owner */
     MNT3ERR_NOENT = 2,           /* No such file or directory */
     MNT3ERR_IO = 5,              /* I/O error */
     MNT3ERR_ACCES = 13,          /* Permission denied */
     MNT3ERR_NOTDIR = 20,         /* Not a directory */
     MNT3ERR_INVAL = 22,          /* Invalid argument */
     MNT3ERR_NAMETOOLONG = 63,    /* Filename too long */
     MNT3ERR_NOTSUPP = 10004,     /* Operation not supported */
     MNT3ERR_SERVERFAULT = 10006  /* A failure on the server */
  };

5.2 Server Procedures

  The following sections define the RPC procedures  supplied by a
  MOUNT version 3 protocol server. The RPC procedure number is
  given at the top of the page with the name and version. The
  SYNOPSIS provides the name of the procedure, the list of the
  names of the arguments, the list of the names of the results,
  followed by the XDR argument declarations and results
  declarations. The information in the SYNOPSIS is specified in
  RPC Data Description Language as defined in [RFC1014]. The
  DESCRIPTION section tells what the procedure is expected to do
  and how its arguments and results are used. The ERRORS section
  lists the errors returned for specific types of failures. The
  IMPLEMENTATION field describes how the procedure is expected to
  work and how it should be used by clients.

     program MOUNT_PROGRAM {
        version MOUNT_V3 {
           void      MOUNTPROC3_NULL(void)    = 0;
           mountres3 MOUNTPROC3_MNT(dirpath)  = 1;
           mountlist MOUNTPROC3_DUMP(void)    = 2;
           void      MOUNTPROC3_UMNT(dirpath) = 3;
           void      MOUNTPROC3_UMNTALL(void) = 4;
           exports   MOUNTPROC3_EXPORT(void)  = 5;
        } = 3;
     } = 100005;

5.2.0 Procedure 0: Null - Do nothing

  SYNOPSIS

     void MOUNTPROC3_NULL(void) = 0;

  DESCRIPTION

     Procedure NULL does not do any work. It is made available
     to allow server response testing and timing.

  IMPLEMENTATION

     It is important that this procedure do no work at all so
     that it can be used to measure the overhead of processing
     a service request. By convention, the NULL procedure
     should never require any authentication. A server may
     choose to ignore this convention, in a more secure
     implementation, where responding to the NULL procedure
     call acknowledges the existence of a resource to an
     unauthenticated client.

  ERRORS

     Since the NULL procedure takes no MOUNT protocol arguments
     and returns no MOUNT protocol response, it can not return
     a MOUNT protocol error. However, it is possible that some
     server implementations may return RPC errors based on
     security and authentication requirements.

5.2.1 Procedure 1: MNT - Add mount entry

  SYNOPSIS

     mountres3 MOUNTPROC3_MNT(dirpath) = 1;

     struct mountres3_ok {
          fhandle3   fhandle;
          int        auth_flavors<>;
     };

     union mountres3 switch (mountstat3 fhs_status) {
     case MNT_OK:
          mountres3_ok  mountinfo;
     default:
          void;
     };

  DESCRIPTION

     Procedure MNT maps a pathname on the server to a file
     handle.  The pathname is an ASCII string that describes a
     directory on the server. If the call is successful
     (MNT3_OK), the server returns an NFS version 3 protocol
     file handle and a vector of RPC authentication flavors
     that are supported with the client's use of the file
     handle (or any file handles derived from it).  The
     authentication flavors are defined in Section 7.2 and
     section 9 of [RFC1057].

  IMPLEMENTATION

     If mountres3.fhs_status is MNT3_OK, then
     mountres3.mountinfo contains the file handle for the
     directory and a list of acceptable authentication
     flavors.  This file handle may only be used in the NFS
     version 3 protocol.  This procedure also results in the
     server adding a new entry to its mount list recording that
     this client has mounted the directory. AUTH_UNIX
     authentication or better is required.

  ERRORS

     MNT3ERR_NOENT
     MNT3ERR_IO
     MNT3ERR_ACCES
     MNT3ERR_NOTDIR
     MNT3ERR_NAMETOOLONG

5.2.2 Procedure 2: DUMP - Return mount entries

  SYNOPSIS

     mountlist MOUNTPROC3_DUMP(void) = 2;

     typedef struct mountbody *mountlist;

     struct mountbody {
          name       ml_hostname;
          dirpath    ml_directory;
          mountlist  ml_next;
     };

  DESCRIPTION

     Procedure DUMP returns the list of remotely mounted file
     systems. The mountlist contains one entry for each client
     host name and directory pair.

  IMPLEMENTATION

     This list is derived from a list maintained on the server
     of clients that have requested file handles with the MNT
     procedure.  Entries are removed from this list only when a
     client calls the UMNT or UMNTALL procedure. Entries may
     become stale if a client crashes and does not issue either
     UMNT calls for all of the file systems that it had
     previously mounted or a UMNTALL to remove all entries that
     existed for it on the server.

  ERRORS

     There are no MOUNT protocol errors which can be returned
     from this procedure. However, RPC errors may be returned
     for authentication or other RPC failures.

5.2.3 Procedure 3: UMNT - Remove mount entry

  SYNOPSIS

     void MOUNTPROC3_UMNT(dirpath) = 3;

  DESCRIPTION

     Procedure UMNT removes the mount list entry for the
     directory that was previously the subject of a MNT call
     from this client.  AUTH_UNIX authentication or better is
     required.

  IMPLEMENTATION

     Typically, server implementations have maintained a list
     of clients which have file systems mounted. In the past,
     this list has been used to inform clients that the server
     was going to be shutdown.

  ERRORS

     There are no MOUNT protocol errors which can be returned
     from this procedure. However, RPC errors may be returned
     for authentication or other RPC failures.

5.2.4 Procedure 4: UMNTALL - Remove all mount entries

  SYNOPSIS

     void MOUNTPROC3_UMNTALL(void) = 4;

  DESCRIPTION

     Procedure UMNTALL removes all of the mount entries for
     this client previously recorded by calls to MNT. AUTH_UNIX
     authentication or better is required.

  IMPLEMENTATION

     This procedure should be used by clients when they are
     recovering after a system shutdown. If the client could
     not successfully unmount all of its file systems before
     being shutdown or the client crashed because of a software
     or hardware problem, there may be servers which still have
     mount entries for this client. This is an easy way for the
     client to inform all servers at once that it does not have
     any mounted file systems.  However, since this procedure
     is generally implemented using broadcast RPC, it is only
     of limited usefullness.

  ERRORS

     There are no MOUNT protocol errors which can be returned
     from this procedure. However, RPC errors may be returned
     for authentication or other RPC failures.

5.2.5 Procedure 5: EXPORT - Return export list

  SYNOPSIS

     exports MOUNTPROC3_EXPORT(void) = 5;

     typedef struct groupnode *groups;

     struct groupnode {
          name     gr_name;
          groups   gr_next;
     };

     typedef struct exportnode *exports;

     struct exportnode {
          dirpath  ex_dir;
          groups   ex_groups;
          exports  ex_next;
     };

  DESCRIPTION

     Procedure EXPORT returns a list of all the exported file
     systems and which clients are allowed to mount each one.
     The names in the group list are implementation-specific
     and cannot be directly interpreted by clients. These names
     can represent hosts or groups of hosts.

  IMPLEMENTATION

     This procedure generally returns the contents of a list of
     shared or exported file systems. These are the file
     systems which are made available to NFS version 3 protocol
     clients.

  ERRORS

     There are no MOUNT protocol errors which can be returned
     from this procedure. However, RPC errors may be returned
     for authentication or other RPC failures.

6.0 Appendix II: Lock manager protocol

  Because the NFS version 2 protocol as well as the NFS version 3
  protocol is stateless, an additional Network Lock Manager (NLM)
  protocol is required to support locking of NFS-mounted files.
  The NLM version 3 protocol, which is used with the NFS version 2
  protocol, is documented in [X/OpenNFS].

  Some of the changes in the NFS version 3 protocol require a
  new version of the NLM protocol. This new protocol is the NLM
  version 4 protocol. The following table summarizes the
  correspondence between versions of the NFS protocol and NLM
  protocol.

      NFS and NLM protocol compatibility

              +---------+---------+
              |   NFS   |   NLM   |
              | Version | Version |
              +===================+
              |    2    |   1,3   |
              +---------+---------+
              |    3    |    4    |
              +---------+---------+

  This appendix only discusses the differences between the NLM
  version 3 protocol and the NLM version 4 protocol.  As in the
  NFS version 3 protocol, almost all the names in the NLM version
  4 protocol have been changed to include a version number. This
  appendix does not discuss changes that consist solely of a name
  change.

6.1 RPC Information

6.1.1 Authentication

  The NLM service uses AUTH_NONE in the NULL procedure.
  AUTH_UNIX, AUTH_SHORT, AUTH_DES, and AUTH_KERB are used for
  all other procedures. Other authentication types may be
  supported in the future.

6.1.2 Constants

  These are the RPC constants needed to call the NLM service.
  They are given in decimal.

     PROGRAM    100021
     VERSION    4

6.1.3 Transport Address

  The NLM service is normally supported over the TCP and UDP
  protocols.  The rpcbind daemon should be queried for the
  correct transport address.

6.1.4 Basic Data Types

  uint64
     typedef unsigned hyper uint64;

  int64
     typedef hyper int64;

  uint32
     typedef unsigned long uint32;

  int32
     typedef long int32;

  These types are new for the NLM version 4 protocol. They are
  the same as in the NFS version 3 protocol.

  nlm4_stats

     enum nlm4_stats {
        NLM4_GRANTED = 0,
        NLM4_DENIED = 1,
        NLM4_DENIED_NOLOCKS = 2,
        NLM4_BLOCKED = 3,
        NLM4_DENIED_GRACE_PERIOD = 4,
        NLM4_DEADLCK = 5,
        NLM4_ROFS = 6,
        NLM4_STALE_FH = 7,
        NLM4_FBIG = 8,
        NLM4_FAILED = 9
     };

  Nlm4_stats indicates the success or failure of a call. This
  version contains several new error codes, so that clients can
  provide more precise failure information to applications.

  NLM4_GRANTED
     The call completed successfully.

  NLM4_DENIED
     The call failed. For attempts to set a lock, this status
     implies that if the client retries the call later, it may

     succeed.

  NLM4_DENIED_NOLOCKS
     The call failed because the server could not allocate the
     necessary resources.

  NLM4_BLOCKED
     Indicates that a blocking request cannot be granted
     immediately. The server will issue an NLMPROC4_GRANTED
     callback to the client when the lock is granted.

  NLM4_DENIED_GRACE_PERIOD
     The call failed because the server is reestablishing old
     locks after a reboot and is not yet ready to resume normal
     service.

  NLM4_DEADLCK
     The request could not be granted and blocking would cause
     a deadlock.

  NLM4_ROFS
     The call failed because the remote file system is
     read-only.  For example, some server implementations might
     not support exclusive locks on read-only file systems.

  NLM4_STALE_FH
     The call failed because it uses an invalid file handle.
     This can happen if the file has been removed or if access
     to the file has been revoked on the server.

  NLM4_FBIG
     The call failed because it specified a length or offset
     that exceeds the range supported by the server.

  NLM4_FAILED
     The call failed for some reason not already listed.  The
     client should take this status as a strong hint not to
     retry the request.

  nlm4_holder

     struct nlm4_holder {
          bool     exclusive;
          int32    svid;
          netobj   oh;
          uint64   l_offset;
          uint64   l_len;
     };

  This structure indicates the holder of a lock. The exclusive
  field tells whether the holder has an exclusive lock or a
  shared lock. The svid field identifies the process that is
  holding the lock. The oh field is an opaque object that
  identifies the host or process that is holding the lock. The
  l_len and l_offset fields identify the region that is locked.
  The only difference between the NLM version 3 protocol and
  the NLM version 4 protocol is that in the NLM version 3
  protocol, the l_len and l_offset fields are 32 bits wide,
  while they are 64 bits wide in the NLM version 4 protocol.

  nlm4_lock

     struct nlm4_lock {
          string   caller_name;
          netobj   fh;
          netobj   oh;
          int32    svid;
          uint64   l_offset;
          uint64   l_len;
     };

  This structure describes a lock request. The caller_name
  field identifies the host that is making the request. The fh
  field identifies the file to lock. The oh field is an opaque
  object that identifies the host or process that is making the
  request, and the svid field identifies the process that is
  making the request.  The l_offset and l_len fields identify
  the region of the file that the lock controls.  A l_len of 0
  means "to end of file".

  There are two differences between the NLM version 3 protocol
  and the NLM version 4 protocol versions of this structure.
  First, in the NLM version 3 protocol, the length and offset
  are 32 bits wide, while they are 64 bits wide in the NLM
  version 4 protocol.  Second, in the NLM version 3 protocol,
  the file handle is a fixed-length NFS version 2 protocol file
  handle, which is encoded as a byte count followed by a byte
  array. In the NFS version 3 protocol, the file handle is
  already variable-length, so it is copied directly into the fh
  field.  That is, the first four bytes of the fh field are the
  same as the byte count in an NFS version 3 protocol nfs_fh3.
  The rest of the fh field contains the byte array from the NFS
  version 3 protocol nfs_fh3.

  nlm4_share

     struct nlm4_share {
          string      caller_name;
          netobj      fh;
          netobj      oh;
          fsh4_mode   mode;
          fsh4_access access;
     };

  This structure is used to support DOS file sharing. The
  caller_name field identifies the host making the request.
  The fh field identifies the file to be operated on. The oh
  field is an opaque object that identifies the host or process
  that is making the request. The mode and access fields
  specify the file-sharing and access modes. The encoding of fh
  is a byte count, followed by the file handle byte array. See
  the description of nlm4_lock for more details.

6.2 NLM Procedures

  The procedures in the NLM version 4 protocol are semantically
  the same as those in the NLM version 3 protocol. The only
  semantic difference is the addition of a NULL procedure that
  can be used to test for server responsiveness.  The procedure
  names with _MSG and _RES suffixes denote asynchronous
  messages; for these the void response implies no reply.  A
  syntactic change is that the procedures were renamed to avoid
  name conflicts with the values of nlm4_stats. Thus the
  procedure definition is as follows.

     version NLM4_VERS {
        void
           NLMPROC4_NULL(void)                  = 0;

        nlm4_testres
           NLMPROC4_TEST(nlm4_testargs)         = 1;

        nlm4_res
           NLMPROC4_LOCK(nlm4_lockargs)         = 2;

        nlm4_res
           NLMPROC4_CANCEL(nlm4_cancargs)       = 3;

        nlm4_res
           NLMPROC4_UNLOCK(nlm4_unlockargs)     = 4;

        nlm4_res
           NLMPROC4_GRANTED(nlm4_testargs)      = 5;

        void
           NLMPROC4_TEST_MSG(nlm4_testargs)     = 6;

        void
           NLMPROC4_LOCK_MSG(nlm4_lockargs)     = 7;

        void
           NLMPROC4_CANCEL_MSG(nlm4_cancargs)   = 8;

        void
           NLMPROC4_UNLOCK_MSG(nlm4_unlockargs) = 9;

        void
           NLMPROC4_GRANTED_MSG(nlm4_testargs) = 10;

        void
           NLMPROC4_TEST_RES(nlm4_testres)     = 11;

        void
           NLMPROC4_LOCK_RES(nlm4_res)         = 12;

        void
           NLMPROC4_CANCEL_RES(nlm4_res)       = 13;

        void
           NLMPROC4_UNLOCK_RES(nlm4_res)       = 14;

        void
           NLMPROC4_GRANTED_RES(nlm4_res)      = 15;

        nlm4_shareres
           NLMPROC4_SHARE(nlm4_shareargs)      = 20;

        nlm4_shareres
           NLMPROC4_UNSHARE(nlm4_shareargs)    = 21;

        nlm4_res
           NLMPROC4_NM_LOCK(nlm4_lockargs)     = 22;

        void
           NLMPROC4_FREE_ALL(nlm4_notify)      = 23;

     } = 4;

6.2.0 Procedure 0: NULL - Do nothing

  SYNOPSIS

     void NLMPROC4_NULL(void) = 0;

  DESCRIPTION

     The NULL procedure does no work. It is made available in
     all RPC services to allow server response testing and
     timing.

  IMPLEMENTATION

     It is important that this procedure do no work at all so
     that it can be used to measure the overhead of processing
     a service request. By convention, the NULL procedure
     should never require any authentication.

  ERRORS

     It is possible that some server implementations may return
     RPC errors based on security and authentication
     requirements.

6.3 Implementation issues

6.3.1 64-bit offsets and lengths

     Some NFS version 3 protocol servers can only support
     requests where the file offset or length fits in 32 or
     fewer bits.  For these servers, the lock manager will have
     the same restriction.  If such a lock manager receives a
     request that it cannot handle (because the offset or
     length uses more than 32 bits), it should return the
     error, NLM4_FBIG.

6.3.2 File handles

     The change in the file handle format from the NFS version
     2 protocol to the NFS version 3 protocol complicates the
     lock manager. First, the lock manager needs some way to
     tell when an NFS version 2 protocol file handle refers to
     the same file as an NFS version 3 protocol file handle.
     (This is assuming that the lock manager supports both NLM
     version 3 protocol clients and NLM version 4 protocol
     clients.) Second, if the lock manager runs the file handle
     through a hashing function, the hashing function may need

     to be retuned to work with NFS version 3 protocol file
     handles as well as NFS version 2 protocol file handles.

7.0 Appendix III: Bibliography

[Corbin]        Corbin, John, "The Art of Distributed
               Programming-Programming Techniques for Remote
               Procedure Calls." Springer-Verlag, New York, New
               York. 1991.  Basic description of RPC and XDR
               and how to program distributed applications
               using them.

[Glover]        Glover, Fred, "TNFS Protocol Specification,"
               Trusted System Interest Group, Work in
               Progress.

[Israel]        Israel, Robert K., Sandra Jett, James Pownell,
               George M. Ericson, "Eliminating Data Copies in
               UNIX-based NFS Servers," Uniforum Conference
               Proceedings, San Francisco, CA,
               February 27 - March 2, 1989.  Describes two
               methods for reducing data copies in NFS server
               code.

[Jacobson]      Jacobson, V., "Congestion Control and
               Avoidance," Proc. ACM SIGCOMM `88, Stanford, CA,
               August 1988.  The paper describing improvements
               to TCP to allow use over Wide Area Networks and
               through gateways connecting networks of varying
               capacity. This work was a starting point for the
               NFS Dynamic Retransmission work.

[Juszczak]      Juszczak, Chet, "Improving the Performance and
               Correctness of an NFS Server," USENIX Conference
               Proceedings, USENIX Association, Berkeley, CA,
               June 1990, pages 53-63.  Describes reply cache
               implementation that avoids work in the server by
               handling duplicate requests. More important,
               though listed as a side-effect, the reply cache
               aids in the avoidance of destructive
               non-idempotent operation re-application --
               improving correctness.

[Kazar]         Kazar, Michael Leon, "Synchronization and Caching
               Issues in the Andrew File System," USENIX Conference
               Proceedings, USENIX Association, Berkeley, CA,
               Dallas Winter 1988, pages 27-36.  A description
               of the cache consistency scheme in AFS.
               Contrasted with other distributed file systems.

[Macklem]       Macklem, Rick, "Lessons Learned Tuning the
               4.3BSD Reno Implementation of the NFS Protocol,"
               Winter USENIX Conference Proceedings, USENIX
               Association, Berkeley, CA, January 1991.
               Describes performance work in tuning the 4.3BSD
               Reno NFS implementation. Describes performance
               improvement (reduced CPU loading) through
               elimination of data copies.

[Mogul]         Mogul, Jeffrey C., "A Recovery Protocol for Spritely
               NFS," USENIX File System Workshop Proceedings,
               Ann Arbor, MI, USENIX Association, Berkeley, CA,
               May 1992.  Second paper on Spritely NFS proposes
               a lease-based scheme for recovering state of
               consistency protocol.

[Nowicki]       Nowicki, Bill, "Transport Issues in the Network
               File System," ACM SIGCOMM newsletter Computer
               Communication Review, April 1989.  A brief
               description of the basis for the dynamic
               retransmission work.

[Pawlowski]     Pawlowski, Brian, Ron Hixon, Mark Stein, Joseph
               Tumminaro, "Network Computing in the UNIX and
               IBM Mainframe Environment," Uniforum `89 Conf.
               Proc., (1989) Description of an NFS server
               implementation for IBM's MVS operating system.

[RFC1014]       Sun Microsystems, Inc., "XDR: External Data
               Representation Standard", RFC 1014,
               Sun Microsystems, Inc., June 1987.
               Specification for canonical format for data
               exchange, used with RPC.

[RFC1057]       Sun Microsystems, Inc., "RPC: Remote Procedure
               Call Protocol Specification", RFC 1057,
               Sun Microsystems, Inc., June 1988.
               Remote procedure protocol specification.

[RFC1094]       Sun Microsystems, Inc., "Network Filesystem
               Specification", RFC 1094, Sun Microsystems, Inc.,
               March 1989.  NFS version 2 protocol
               specification.

[Sandberg]      Sandberg, R., D. Goldberg, S. Kleiman, D. Walsh,
               B.  Lyon, "Design and Implementation of the Sun
               Network Filesystem," USENIX Conference
               Proceedings, USENIX Association, Berkeley, CA,
               Summer 1985.  The basic paper describing the
               SunOS implementation of the NFS version 2
               protocol, and discusses the goals, protocol
               specification and trade-offs.

[Srinivasan]    Srinivasan, V., Jeffrey C. Mogul, "Spritely
               NFS:  Implementation and Performance of Cache
               Consistency Protocols", WRL Research Report
               89/5, Digital Equipment Corporation Western
               Research Laboratory, 100 Hamilton Ave., Palo
               Alto, CA, 94301, May 1989.  This paper analyzes
               the effect of applying a Sprite-like consistency
               protocol applied to standard NFS. The issues of
               recovery in a stateful environment are covered
               in [Mogul].

[X/OpenNFS]     X/Open Company, Ltd., X/Open CAE Specification:
               Protocols for X/Open Internetworking: XNFS,
               X/Open Company, Ltd., Apex Plaza, Forbury Road,
               Reading Berkshire, RG1 1AX, United Kingdom,
               1991.  This is an indispensable reference for
               NFS version 2 protocol and accompanying
               protocols, including the Lock Manager and the
               Portmapper.

[X/OpenPCNFS]   X/Open Company, Ltd., X/Open CAE Specification:
               Protocols for X/Open Internetworking: (PC)NFS,
               Developer's Specification, X/Open Company, Ltd.,
               Apex Plaza, Forbury Road, Reading Berkshire, RG1
               1AX, United Kingdom, 1991.  This is an
               indispensable reference for NFS version 2
               protocol and accompanying protocols, including
               the Lock Manager and the Portmapper.

8. Security Considerations

  Since sensitive file data may be transmitted or received
  from a server by the NFS protocol, authentication, privacy,
  and data integrity issues should be addressed by implementations
  of this protocol.

  As with the previous protocol revision (version 2), NFS
  version 3 defers to the authentication provisions of the
  supporting RPC protocol [RFC1057], and assumes that data
  privacy and integrity are provided by underlying transport
  layers as available in each implementation of the protocol.
  See section 4.4 for a discussion relating to file access
  permissions.

9. Acknowledgements

  This description of the protocol is derived from an original
  document written by Brian Pawlowski and revised by Peter
  Staubach.  This protocol is the result of a co-operative
  effort that comprises the contributions of Geoff Arnold,
  Brent Callaghan, John Corbin, Fred Glover, Chet Juszczak,
  Mike Eisler, John Gillono, Dave Hitz, Mike Kupfer, Rick
  Macklem, Ron Minnich, Brian Pawlowski, David Robinson, Rusty
  Sandberg, Craig Schamp, Spencer Shepler, Carl Smith, Mark
  Stein, Peter Staubach, Tom Talpey, Rob Thurlow, and Mark
  Wittle.

10. Authors' Addresses

  Address comments related to this protocol to:

     nfs3@eng.sun.com

  Brent Callaghan
  Sun Microsystems, Inc.
  2550 Garcia Avenue
  Mailstop UMTV05-44
  Mountain View, CA 94043-1100

  Phone: 1-415-336-1051
  Fax:   1-415-336-6015
  EMail: brent.callaghan@eng.sun.com

  Brian Pawlowski
  Network Appliance Corp.
  319 North Bernardo Ave.
  Mountain View, CA 94043

  Phone: 1-415-428-5136
  Fax:   1-415-428-5151
  EMail: beepy@netapp.com

  Peter Staubach
  Sun Microsystems, Inc.
  2550 Garcia Avenue
  Mailstop UMTV05-44
  Mountain View, CA 94043-1100

  Phone: 1-415-336-5615
  Fax:   1-415-336-6015
  EMail: peter.staubach@eng.sun.com
阅读(781) | 评论(0) | 转发(0) |
0

上一篇:nfs 安装 配置

下一篇:gtk画矩形

给主人留下些什么吧!~~
评论热议
请登录后评论。

登录 注册