NFSv4                                                          T. Haynes
Internet-Draft                                                    Editor
Intended status: Standards Track                            May 02, 08, 2012
Expires: November 3, 9, 2012

                     NFS Version 4 Minor Version 2
                 draft-ietf-nfsv4-minorversion2-09.txt
                 draft-ietf-nfsv4-minorversion2-10.txt

Abstract

   This Internet-Draft describes NFS version 4 minor version two,
   focusing mainly on the protocol extensions made from NFS version 4
   minor version 0 and NFS version 4 minor version 1.  Major extensions
   introduced in NFS version 4 minor version two include: Server-side
   Copy, Application I/O Advise, Space Reservations, and Support for Sparse Files. Files,
   Application Data Blocks, and Labeled NFS.

Requirements Language

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

Status of this Memo

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   provisions of BCP 78 and BCP 79.

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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  6
     1.1.   The NFS Version 4 Minor Version 2 Protocol  . . . . . . .  6
     1.2.   Scope of This Document  . . . . . . . . . . . . . . . . .  6
     1.3.   NFSv4.2 Goals . . . . . . . . . . . . . . . . . . . . . .  6
     1.4.   Overview of NFSv4.2 Features  . . . . . . . . . . . . . .  6  7
       1.4.1.  Sparse Files . . . . . . . . . . . . . . . . . . . . .  6  7
       1.4.2.  Application I/O Advise . . . . . . . . . . . . . . . .  7
     1.5.   Differences from NFSv4.1  . . . . . . . . . . . . . . . .  7
   2.  NFS Server-side Copy . . . . . . . . . . . . . . . . . . . . .  7
     2.1.   Introduction  . . . . . . . . . . . . . . . . . . . . . .  7
     2.2.   Protocol Overview . . . . . . . . . . . . . . . . . . . .  8
       2.2.1.  Intra-Server Copy  . . . . . . . . . . . . . . . . . .  9 10
       2.2.2.  Inter-Server Copy  . . . . . . . . . . . . . . . . . . 11
       2.2.3.  Server-to-Server Copy Protocol . . . . . . . . . . . . 13 14
     2.3.   Operations  . . . . . . . . . . . . . . . . . . . . . . . 15 16
       2.3.1.  netloc4 - Network Locations  . . . . . . . . . . . . . 15 16
       2.3.2.  Copy Offload Stateids  . . . . . . . . . . . . . . . . 16 17
     2.4.   Security Considerations . . . . . . . . . . . . . . . . . 16 17
       2.4.1.  Inter-Server Copy Security . . . . . . . . . . . . . . 16 17
   3.  Sparse Files  Support for Application IO Hints . . . . . . . . . . . . . . . 26
     3.1.   Introduction  . . . . . . . . . . 25
     3.1.   Introduction . . . . . . . . . . . . 26
     3.2.   POSIX Requirements  . . . . . . . . . . 25
     3.2.   Terminology . . . . . . . . . 26
     3.3.   Additional Requirements . . . . . . . . . . . . . . 25
   4.  Space Reservation . . . 27
     3.4.   Security Considerations . . . . . . . . . . . . . . . . . 28
     3.5.   IANA Considerations . . 26
     4.1.   Introduction . . . . . . . . . . . . . . . . . 28
   4.  Sparse Files . . . . . 26
   5.  Support for Application IO Hints . . . . . . . . . . . . . . . 28
     5.1.   Introduction . . . . . 28
     4.1.   Introduction  . . . . . . . . . . . . . . . . . 28
     5.2.   POSIX Requirements . . . . . 29
     4.2.   Terminology . . . . . . . . . . . . . . 29
     5.3.   Additional Requirements . . . . . . . . . 29
   5.  Space Reservation  . . . . . . . . 30
     5.4.   Security Considerations . . . . . . . . . . . . . . 30
     5.1.   Introduction  . . . 31
     5.5.   IANA Considerations . . . . . . . . . . . . . . . . . . . 31 30
   6.  Application Data Block Support . . . . . . . . . . . . . . . . 31 32
     6.1.   Generic Framework . . . . . . . . . . . . . . . . . . . . 32 33
       6.1.1.  Data Block Representation  . . . . . . . . . . . . . . 32 33
       6.1.2.  Data Content . . . . . . . . . . . . . . . . . . . . . 33 34
     6.2.   pNFS Considerations . . . . . . . . . . . . . . . . . . . 33 34
     6.3.   An Example of Detecting Corruption  . . . . . . . . . . . 34
     6.4.   Example of READ_PLUS  . . . . . . . . . . . . . . . . . . 35 36
     6.5.   Zero Filled Holes . . . . . . . . . . . . . . . . . . . . 36
   7.  Labeled NFS  . . . . . . . . . . . . . . . . . . . . . . . . . 36
     7.1.   Introduction  . . . . . . . . . . . . . . . . . . . . . . 36 37
     7.2.   Definitions . . . . . . . . . . . . . . . . . . . . . . . 37 38
     7.3.   MAC Security Attribute  . . . . . . . . . . . . . . . . . 37
       7.3.1.  Interpreting FATTR4_SEC_LABEL  . . . . . . . . . . . . 38
       7.3.2.
       7.3.1.  Delegations  . . . . . . . . . . . . . . . . . . . . . 39
       7.3.3.
       7.3.2.  Permission Checking  . . . . . . . . . . . . . . . . . 39
       7.3.4.
       7.3.3.  Object Creation  . . . . . . . . . . . . . . . . . . . 39
       7.3.5.
       7.3.4.  Existing Objects . . . . . . . . . . . . . . . . . . . 40
       7.3.6.
       7.3.5.  Label Changes  . . . . . . . . . . . . . . . . . . . . 40
     7.4.   pNFS Considerations . . . . . . . . . . . . . . . . . . . 41 40
     7.5.   Discovery of Server LNFS Support  . . . . . . . . . . . . 41
     7.6.   MAC Security NFS Modes of Operation . . . . . . . . . . . 41
       7.6.1.  Full Mode  . . . . . . . . . . . . . . . . . . . . . . 42
       7.6.2.  Guest Mode . . . . . . . . . . . . . . . . . . . . . . 43
     7.7.   Security Considerations . . . . . . . . . . . . . . . . . 43
   8.  Sharing change attribute implementation details with NFSv4
       clients  . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
     8.1.   Introduction  . . . . . . . . . . . . . . . . . . . . . . 44
     8.2.   Definition of the 'change_attr_type' per-file system
            attribute . . . . . . . . . . . . . . . . . . . . . . . . 44
   9.  Security Considerations  . . . . . . . . . . . . . . . . . . . 46 44
   10. Error Values . . . . . . . . . . . . . . . . . . . . . . . . . 46 44
     10.1.  Error Definitions . . . . . . . . . . . . . . . . . . . . 46 45
       10.1.1. General Errors . . . . . . . . . . . . . . . . . . . . 46 45
       10.1.2. Server to Server Copy Errors . . . . . . . . . . . . . 46 45
       10.1.3. Labeled NFS Errors . . . . . . . . . . . . . . . . . . 47 46
   11. New File Attributes  . . . . . . . . . . . . . . . . . . . . . 46
     11.1.  New RECOMMENDED Attributes - List and Definition
            References  . . . . . . 47
     11.1. . . . . . . . . . . . . . . . . . 46
     11.2.  Attribute Definitions . . . . . . . . . . . . . . . . . . 47
   12. Operations: REQUIRED, RECOMMENDED, or OPTIONAL . . . . . . . . 48 50
   13. NFSv4.2 Operations . . . . . . . . . . . . . . . . . . . . . . 52 53
     13.1.  Operation 59: COPY - Initiate a server-side copy  . . . . 52 53
     13.2.  Operation 60: COPY_ABORT - Cancel a server-side copy  . . 59 61
     13.3.  Operation 61: COPY_NOTIFY - Notify a source server of
            a future copy . . . . . . . . . . . . . . . . . . . . . . 60 62
     13.4.  Operation 62: COPY_REVOKE - Revoke a destination
            server's copy privileges  . . . . . . . . . . . . . . . . 62 64
     13.5.  Operation 63: COPY_STATUS - Poll for status of a
            server-side copy  . . . . . . . . . . . . . . . . . . . . 63 65
     13.6.  Modification to Operation 42: EXCHANGE_ID -
            Instantiate Client ID . . . . . . . . . . . . . . . . . . 64 66
     13.7.  Operation 64: INITIALIZE  . . . . . . . . . . . . . . . . 65 67
     13.8.  Operation 67: IO_ADVISE - Application I/O access
            pattern hints . . . . . . . . . . . . . . . . . . . . . . 69 71
     13.9.  Changes to Operation 51: LAYOUTRETURN . . . . . . . . . . 75 77
     13.10. Operation 65: READ_PLUS . . . . . . . . . . . . . . . . . 78 80
     13.11. Operation 66: SEEK  . . . . . . . . . . . . . . . . . . . 83 85
   14. NFSv4.2 Callback Operations  . . . . . . . . . . . . . . . . . 84 86
     14.1.  Procedure 16: CB_ATTR_CHANGED - Notify Client that
            the File's Attributes Changed . . . . . . . . . . . . . . 84 86
     14.2.  Operation 15: CB_COPY - Report results of a
            server-side copy  . . . . . . . . . . . . . . . . . . . . 85 87
   15. IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 87 89
   16. References . . . . . . . . . . . . . . . . . . . . . . . . . . 87 89
     16.1.  Normative References  . . . . . . . . . . . . . . . . . . 87 89
     16.2.  Informative References  . . . . . . . . . . . . . . . . . 88 90
   Appendix A.  Acknowledgments . . . . . . . . . . . . . . . . . . . 89 91
   Appendix B.  RFC Editor Notes  . . . . . . . . . . . . . . . . . . 90 92
   Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 90 92

1.  Introduction

1.1.  The NFS Version 4 Minor Version 2 Protocol

   The NFS version 4 minor version 2 (NFSv4.2) protocol is the third
   minor version of the NFS version 4 (NFSv4) protocol.  The first minor
   version, NFSv4.0, is described in [10] and the second minor version,
   NFSv4.1, is described in [2].  It follows the guidelines for minor
   versioning that are listed in Section 11 of [10].

   As a minor version, NFSv4.2 is consistent with the overall goals for
   NFSv4, but extends the protocol so as to better meet those goals,
   based on experiences with NFSv4.1.  In addition, NFSv4.2 has adopted
   some additional goals, which motivate some of the major extensions in
   NFSv4.2.

1.2.  Scope of This Document

   This document describes the NFSv4.2 protocol.  With respect to
   NFSv4.0 and NFSv4.1, this document does not:

   o  describe the NFSv4.0 or NFSv4.1 protocols, except where needed to
      contrast with NFSv4.2.

   o  modify the specification of the NFSv4.0 or NFSv4.1 protocols.

   o  clarify the NFSv4.0 or NFSv4.1 protocols.  I.e., any
      clarifications made here apply to NFSv4.2 and neither of the prior
      protocols.

   The full XDR for NFSv4.2 is presented in [3].

1.3.  NFSv4.2 Goals

   [[Comment.1: This needs fleshing out! --TH]]

   The goal of the design of NFSv4.2 is to take common local filesystem
   features and offer them remotely.  These features might

   o  already be available on the servers, e.g., sparse files

   o  be under development as a new standard, e.g., SEEK_HOLE and
      SEEK_DATA

   o  be used by clients with the servers via some proprietary means,
      e.g., Labeled NFS

   but the clients are not able to leverage them on the server within
   the confines of the NFS protocol.

1.4.  Overview of NFSv4.2 Features

   [[Comment.2:

   [[Comment.1: This needs fleshing out! --TH]]

1.4.1.  Sparse Files

   Two new operations are defined to support the reading of sparse files
   (READ_PLUS) and the punching of holes to remove backing storage
   (INITIALIZE).

1.4.2.  Application I/O Advise

   We propose a new IO_ADVISE operation for NFSv4.2 that clients can use
   to communicate expected I/O behavior to the server.  By communicating
   future I/O behavior such as whether a file will be accessed
   sequentially or randomly, and whether a file will or will not be
   accessed in the near future, servers can optimize future I/O requests
   for a file by, for example, prefetching or evicting data.  This
   operation can be used to support the posix_fadvise function as well
   as other applications such as databases and video editors.

1.5.  Differences from NFSv4.1

   In NFSv4.1, the only way to introduce new variants of an operation
   was to introduce a new operation.  I.e., READ becomes either READ2 or
   READ_PLUS.  With the use of discriminated unions as parameters to
   such functions in NFSv4.2, it is possible to add a new arm in a
   subsequent minor version.  And it is also possible to move such an
   operation from OPTIONAL/RECOMMENDED to REQUIRED.  Forcing an
   implementation to adopt each arm of a discriminated union at such a
   time does not meet the spirit of the minor versioning rules.  As
   such, new arms of a discriminated union MUST follow the same
   guidelines for minor versioning as operations in NFSv4.1 - i.e., they
   may not be made REQUIRED.  To support this, a new error code,
   NFS4ERR_UNION_NOTSUPP, is introduced which allows the server to
   communicate to the client that the operation is supported, but the
   specific arm of the discriminated union is not.

2.  NFS Server-side Copy

2.1.  Introduction

   This section describes a server-side copy feature for the NFS
   protocol.

   The server-side copy feature provides a mechanism for the NFS client
   to perform a file copy on the server without the data being
   transmitted back and forth over the network.

   Without this feature, an NFS client copies data from one location to
   another by reading the data from the server over the network, and
   then writing the data back over the network to the server.  Using
   this server-side copy operation, the client is able to instruct the
   server to copy the data locally without the data being sent back and
   forth over the network unnecessarily.

   In general, this feature is useful whenever data is copied from one
   location to another on the server.  It is particularly useful when
   copying the contents of a file from a backup.  Backup-versions of a
   file are copied for a number of reasons, including restoring and
   cloning data.

   If the source object and destination object are on different file
   servers, the file servers will communicate with one another to
   perform the copy operation.  The server-to-server protocol by which
   this is accomplished is not defined in this document.

2.2.  Protocol Overview

   The server-side copy offload operations support both intra-server and
   inter-server file copies.  An intra-server copy is a copy in which
   the source file and destination file reside on the same server.  In
   an inter-server copy, the source file and destination file are on
   different servers.  In both cases, the copy may be performed
   synchronously or asynchronously.

   Throughout the rest of this document, we refer to the NFS server
   containing the source file as the "source server" and the NFS server
   to which the file is transferred as the "destination server".  In the
   case of an intra-server copy, the source server and destination
   server are the same server.  Therefore in the context of an intra-
   server copy, the terms source server and destination server refer to
   the single server performing the copy.

   The operations described below are designed to copy files.  Other
   file system objects can be copied by building on these operations or
   using other techniques.  For example if the user wishes to copy a
   directory, the client can synthesize a directory copy by first
   creating the destination directory and then copying the source
   directory's files to the new destination directory.  If the user
   wishes to copy a namespace junction [11] [12], the client can use the
   ONC RPC Federated Filesystem protocol [12] to perform the copy.
   Specifically the client can determine the source junction's
   attributes using the FEDFS_LOOKUP_FSN procedure and create a
   duplicate junction using the FEDFS_CREATE_JUNCTION procedure.

   For the inter-server copy protocol, the operations are defined to be
   compatible with a server-to-server copy protocol in which the
   destination server reads the file data from the source server.  This
   model in which the file data is pulled from the source by the
   destination has a number of advantages over a model in which the
   source pushes the file data to the destination.  The advantages of
   the pull model include:

   o  The pull model only requires a remote server (i.e., the
      destination server) to be granted read access.  A push model
      requires a remote server (i.e., the source server) to be granted
      write access, which is more privileged.

   o  The pull model allows the destination server to stop reading if it
      has run out of space.  In a push model, the destination server
      must flow control the source server in this situation.

   o  The pull model allows the destination server to easily flow
      control the data stream by adjusting the size of its read
      operations.  In a push model, the destination server does not have
      this ability.  The source server in a push model is capable of
      writing chunks larger than the destination server has requested in
      attributes and session parameters.  In theory, the destination
      server could perform a "short" write in this situation, but this
      approach is known to behave poorly in practice.

   The following operations are provided to support server-side copy:

   COPY_NOTIFY:  For inter-server copies, the client sends this
      operation to the source server to notify it of a future file copy
      from a given destination server for the given user.

   COPY_REVOKE:  Also for inter-server copies, the client sends this
      operation to the source server to revoke permission to copy a file
      for the given user.

   COPY:  Used by the client to request a file copy.

   COPY_ABORT:  Used by the client to abort an asynchronous file copy.

   COPY_STATUS:  Used by the client to poll the status of an
      asynchronous file copy.

   CB_COPY:  Used by the destination server to report the results of an
      asynchronous file copy to the client.

   These operations are described in detail in Section 2.3.  This
   section provides an overview of how these operations are used to
   perform server-side copies.

2.2.1.  Intra-Server Copy

   To copy a file on a single server, the client uses a COPY operation.
   The server may respond to the copy operation with the final results
   of the copy or it may perform the copy asynchronously and deliver the
   results using a CB_COPY operation callback.  If the copy is performed
   asynchronously, the client may poll the status of the copy using
   COPY_STATUS or cancel the copy using COPY_ABORT.

   A synchronous intra-server copy is shown in Figure 1.  In this
   example, the NFS server chooses to perform the copy synchronously.
   The copy operation is completed, either successfully or
   unsuccessfully, before the server replies to the client's request.
   The server's reply contains the final result of the operation.

     Client                                  Server
        +                                      +
        |                                      |
        |--- COPY ---------------------------->| Client requests
        |<------------------------------------/| a file copy
        |                                      |
        |                                      |

                Figure 1: A synchronous intra-server copy.

   An asynchronous intra-server copy is shown in Figure 2.  In this
   example, the NFS server performs the copy asynchronously.  The
   server's reply to the copy request indicates that the copy operation
   was initiated and the final result will be delivered at a later time.
   The server's reply also contains a copy stateid.  The client may use
   this copy stateid to poll for status information (as shown) or to
   cancel the copy using a COPY_ABORT.  When the server completes the
   copy, the server performs a callback to the client and reports the
   results.

     Client                                  Server
        +                                      +
        |                                      |
        |--- COPY ---------------------------->| Client requests
        |<------------------------------------/| a file copy
        |                                      |
        |                                      |
        |--- COPY_STATUS --------------------->| Client may poll
        |<------------------------------------/| for status
        |                                      |
        |                  .                   | Multiple COPY_STATUS
        |                  .                   | operations may be sent.
        |                  .                   |
        |                                      |
        |<-- CB_COPY --------------------------| Server reports results
        |\------------------------------------>|
        |                                      |

               Figure 2: An asynchronous intra-server copy.

2.2.2.  Inter-Server Copy

   A copy may also be performed between two servers.  The copy protocol
   is designed to accommodate a variety of network topologies.  As shown
   in Figure 3, the client and servers may be connected by multiple
   networks.  In particular, the servers may be connected by a
   specialized, high speed network (network 192.168.33.0/24 in the
   diagram) that does not include the client.  The protocol allows the
   client to setup the copy between the servers (over network
   10.11.78.0/24 in the diagram) and for the servers to communicate on
   the high speed network if they choose to do so.

                             192.168.33.0/24
                 +-------------------------------------+
                 |                                     |
                 |                                     |
                 | 192.168.33.18                       | 192.168.33.56
         +-------+------+                       +------+------+
         |     Source   |                       | Destination |
         +-------+------+                       +------+------+
                 | 10.11.78.18                         | 10.11.78.56
                 |                                     |
                 |                                     |
                 |             10.11.78.0/24           |
                 +------------------+------------------+
                                    |
                                    |
                                    | 10.11.78.243
                              +-----+-----+
                              |   Client  |
                              +-----------+

            Figure 3: An example inter-server network topology.

   For an inter-server copy, the client notifies the source server that
   a file will be copied by the destination server using a COPY_NOTIFY
   operation.  The client then initiates the copy by sending the COPY
   operation to the destination server.  The destination server may
   perform the copy synchronously or asynchronously.

   A synchronous inter-server copy is shown in Figure 4.  In this case,
   the destination server chooses to perform the copy before responding
   to the client's COPY request.

   An asynchronous copy is shown in Figure 5.  In this case, the
   destination server chooses to respond to the client's COPY request
   immediately and then perform the copy asynchronously.

     Client                Source         Destination
        +                    +                 +
        |                    |                 |
        |--- COPY_NOTIFY --->|                 |
        |<------------------/|                 |
        |                    |                 |
        |                    |                 |
        |--- COPY ---------------------------->|
        |                    |                 |
        |                    |                 |
        |                    |<----- read -----|
        |                    |\--------------->|
        |                    |                 |
        |                    |        .        | Multiple reads may
        |                    |        .        | be necessary
        |                    |        .        |
        |                    |                 |
        |                    |                 |
        |<------------------------------------/| Destination replies
        |                    |                 | to COPY

                Figure 4: A synchronous inter-server copy.

     Client                Source         Destination
        +                    +                 +
        |                    |                 |
        |--- COPY_NOTIFY --->|                 |
        |<------------------/|                 |
        |                    |                 |
        |                    |                 |
        |--- COPY ---------------------------->|
        |<------------------------------------/|
        |                    |                 |
        |                    |                 |
        |                    |<----- read -----|
        |                    |\--------------->|
        |                    |                 |
        |                    |        .        | Multiple reads may
        |                    |        .        | be necessary
        |                    |        .        |
        |                    |                 |
        |                    |                 |
        |--- COPY_STATUS --------------------->| Client may poll
        |<------------------------------------/| for status
        |                    |                 |
        |                    |        .        | Multiple COPY_STATUS
        |                    |        .        | operations may be sent
        |                    |        .        |
        |                    |                 |
        |                    |                 |
        |                    |                 |
        |<-- CB_COPY --------------------------| Destination reports
        |\------------------------------------>| results
        |                    |                 |

               Figure 5: An asynchronous inter-server copy.

2.2.3.  Server-to-Server Copy Protocol

   During an inter-server copy, the destination server reads the file
   data from the source server.  The source server and destination
   server are not required to use a specific protocol to transfer the
   file data.  The choice of what protocol to use is ultimately the
   destination server's decision.

2.2.3.1.  Using NFSv4.x as a Server-to-Server Copy Protocol

   The destination server MAY use standard NFSv4.x (where x >= 1) to
   read the data from the source server.  If NFSv4.x is used for the
   server-to-server copy protocol, the destination server can use the
   filehandle contained in the COPY request with standard NFSv4.x
   operations to read data from the source server.  Specifically, the
   destination server may use the NFSv4.x OPEN operation's CLAIM_FH
   facility to open the file being copied and obtain an open stateid.
   Using the stateid, the destination server may then use NFSv4.x READ
   operations to read the file.

2.2.3.2.  Using an alternative Server-to-Server Copy Protocol

   In a homogeneous environment, the source and destination servers
   might be able to perform the file copy extremely efficiently using
   specialized protocols.  For example the source and destination
   servers might be two nodes sharing a common file system format for
   the source and destination file systems.  Thus the source and
   destination are in an ideal position to efficiently render the image
   of the source file to the destination file by replicating the file
   system formats at the block level.  Another possibility is that the
   source and destination might be two nodes sharing a common storage
   area network, and thus there is no need to copy any data at all, and
   instead ownership of the file and its contents might simply be re-
   assigned to the destination.  To allow for these possibilities, the
   destination server is allowed to use a server-to-server copy protocol
   of its choice.

   In a heterogeneous environment, using a protocol other than NFSv4.x
   (e.g,.  HTTP [13] or FTP [14]) presents some challenges.  In
   particular, the destination server is presented with the challenge of
   accessing the source file given only an NFSv4.x filehandle.

   One option for protocols that identify source files with path names
   is to use an ASCII hexadecimal representation of the source
   filehandle as the file name.

   Another option for the source server is to use URLs to direct the
   destination server to a specialized service.  For example, the
   response to COPY_NOTIFY could include the URL
   ftp://s1.example.com:9999/_FH/0x12345, where 0x12345 is the ASCII
   hexadecimal representation of the source filehandle.  When the
   destination server receives the source server's URL, it would use
   "_FH/0x12345" as the file name to pass to the FTP server listening on
   port 9999 of s1.example.com.  On port 9999 there would be a special
   instance of the FTP service that understands how to convert NFS
   filehandles to an open file descriptor (in many operating systems,
   this would require a new system call, one which is the inverse of the
   makefh() function that the pre-NFSv4 MOUNT service needs).

   Authenticating and identifying the destination server to the source
   server is also a challenge.  Recommendations for how to accomplish
   this are given in Section 2.4.1.2.4 and Section 2.4.1.4.

2.3.  Operations

   In the sections that follow, several operations are defined that
   together provide the server-side copy feature.  These operations are
   intended to be OPTIONAL operations as defined in section 17 of [2].
   The COPY_NOTIFY, COPY_REVOKE, COPY, COPY_ABORT, and COPY_STATUS
   operations are designed to be sent within an NFSv4 COMPOUND
   procedure.  The CB_COPY operation is designed to be sent within an
   NFSv4 CB_COMPOUND procedure.

   Each operation is performed in the context of the user identified by
   the ONC RPC credential of its containing COMPOUND or CB_COMPOUND
   request.  For example, a COPY_ABORT operation issued by a given user
   indicates that a specified COPY operation initiated by the same user
   be canceled.  Therefore a COPY_ABORT MUST NOT interfere with a copy
   of the same file initiated by another user.

   An NFS server MAY allow an administrative user to monitor or cancel
   copy operations using an implementation specific interface.

2.3.1.  netloc4 - Network Locations

   The server-side copy operations specify network locations using the
   netloc4 data type shown below:

   enum netloc_type4 {
           NL4_NAME        = 0,
           NL4_URL         = 1,
           NL4_NETADDR     = 2
   };
   union netloc4 switch (netloc_type4 nl_type) {
           case NL4_NAME:          utf8str_cis nl_name;
           case NL4_URL:           utf8str_cis nl_url;
           case NL4_NETADDR:       netaddr4    nl_addr;
   };

   If the netloc4 is of type NL4_NAME, the nl_name field MUST be
   specified as a UTF-8 string.  The nl_name is expected to be resolved
   to a network address via DNS, LDAP, NIS, /etc/hosts, or some other
   means.  If the netloc4 is of type NL4_URL, a server URL [4]
   appropriate for the server-to-server copy operation is specified as a
   UTF-8 string.  If the netloc4 is of type NL4_NETADDR, the nl_addr
   field MUST contain a valid netaddr4 as defined in Section 3.3.9 of
   [2].

   When netloc4 values are used for an inter-server copy as shown in
   Figure 3, their values may be evaluated on the source server,
   destination server, and client.  The network environment in which
   these systems operate should be configured so that the netloc4 values
   are interpreted as intended on each system.

2.3.2.  Copy Offload Stateids

   A server may perform a copy offload operation asynchronously.  An
   asynchronous copy is tracked using a copy offload stateid.  Copy
   offload stateids are included in the COPY, COPY_ABORT, COPY_STATUS,
   and CB_COPY operations.

   Section 8.2.4 of [2] specifies that stateids are valid until either
   (A) the client or server restart or (B) the client returns the
   resource.

   A copy offload stateid will be valid until either (A) the client or
   server restarts or (B) the client returns the resource by issuing a
   COPY_ABORT operation or the client replies to a CB_COPY operation.

   A copy offload stateid's seqid MUST NOT be 0 (zero).  In the context
   of a copy offload operation, it is ambiguous to indicate the most
   recent copy offload operation using a stateid with seqid of 0 (zero).
   Therefore a copy offload stateid with seqid of 0 (zero) MUST be
   considered invalid.

2.4.  Security Considerations

   The security considerations pertaining to NFSv4 [10] apply to this
   document.

   The standard security mechanisms provide by NFSv4 [10] may be used to
   secure the protocol described in this document.

   NFSv4 clients and servers supporting the the inter-server copy
   operations described in this document are REQUIRED to implement [5],
   including the RPCSEC_GSSv3 privileges copy_from_auth and
   copy_to_auth.  If the server-to-server copy protocol is ONC RPC
   based, the servers are also REQUIRED to implement the RPCSEC_GSSv3
   privilege copy_confirm_auth.  These requirements to implement are not
   requirements to use.  NFSv4 clients and servers are RECOMMENDED to
   use [5] to secure server-side copy operations.

2.4.1.  Inter-Server Copy Security

2.4.1.1.  Requirements for Secure Inter-Server Copy

   Inter-server copy is driven by several requirements:

   o  The specification MUST NOT mandate an inter-server copy protocol.
      There are many ways to copy data.  Some will be more optimal than
      others depending on the identities of the source server and
      destination server.  For example the source and destination
      servers might be two nodes sharing a common file system format for
      the source and destination file systems.  Thus the source and
      destination are in an ideal position to efficiently render the
      image of the source file to the destination file by replicating
      the file system formats at the block level.  In other cases, the
      source and destination might be two nodes sharing a common storage
      area network, and thus there is no need to copy any data at all,
      and instead ownership of the file and its contents simply gets re-
      assigned to the destination.

   o  The specification MUST provide guidance for using NFSv4.x as a
      copy protocol.  For those source and destination servers willing
      to use NFSv4.x there are specific security considerations that
      this specification can and does address.

   o  The specification MUST NOT mandate pre-configuration between the
      source and destination server.  Requiring that the source and
      destination first have a "copying relationship" increases the
      administrative burden.  However the specification MUST NOT
      preclude implementations that require pre-configuration.

   o  The specification MUST NOT mandate a trust relationship between
      the source and destination server.  The NFSv4 security model
      requires mutual authentication between a principal on an NFS
      client and a principal on an NFS server.  This model MUST continue
      with the introduction of COPY.

2.4.1.2.  Inter-Server Copy with RPCSEC_GSSv3

   When the client sends a COPY_NOTIFY to the source server to expect
   the destination to attempt to copy data from the source server, it is
   expected that this copy is being done on behalf of the principal
   (called the "user principal") that sent the RPC request that encloses
   the COMPOUND procedure that contains the COPY_NOTIFY operation.  The
   user principal is identified by the RPC credentials.  A mechanism
   that allows the user principal to authorize the destination server to
   perform the copy in a manner that lets the source server properly
   authenticate the destination's copy, and without allowing the
   destination to exceed its authorization is necessary.

   An approach that sends delegated credentials of the client's user
   principal to the destination server is not used for the following
   reasons.  If the client's user delegated its credentials, the
   destination would authenticate as the user principal.  If the
   destination were using the NFSv4 protocol to perform the copy, then
   the source server would authenticate the destination server as the
   user principal, and the file copy would securely proceed.  However,
   this approach would allow the destination server to copy other files.
   The user principal would have to trust the destination server to not
   do so.  This is counter to the requirements, and therefore is not
   considered.  Instead an approach using RPCSEC_GSSv3 [5] privileges is
   proposed.

   One of the stated applications of the proposed RPCSEC_GSSv3 protocol
   is compound client host and user authentication [+ privilege
   assertion].  For inter-server file copy, we require compound NFS
   server host and user authentication [+ privilege assertion].  The
   distinction between the two is one without meaning.

   RPCSEC_GSSv3 introduces the notion of privileges.  We define three
   privileges:

   copy_from_auth:  A user principal is authorizing a source principal
      ("nfs@<source>") to allow a destination principal ("nfs@
      <destination>") to copy a file from the source to the destination.
      This privilege is established on the source server before the user
      principal sends a COPY_NOTIFY operation to the source server.

   struct copy_from_auth_priv {
           secret4             cfap_shared_secret;
           netloc4             cfap_destination;
           /* the NFSv4 user name that the user principal maps to */
           utf8str_mixed       cfap_username;
           /* equal to seq_num of rpc_gss_cred_vers_3_t */
           unsigned int        cfap_seq_num;
   };

      cfp_shared_secret is a secret value the user principal generates.

   copy_to_auth:  A user principal is authorizing a destination
      principal ("nfs@<destination>") to allow it to copy a file from
      the source to the destination.  This privilege is established on
      the destination server before the user principal sends a COPY
      operation to the destination server.

   struct copy_to_auth_priv {
           /* equal to cfap_shared_secret */
           secret4              ctap_shared_secret;
           netloc4              ctap_source;
           /* the NFSv4 user name that the user principal maps to */
           utf8str_mixed        ctap_username;
           /* equal to seq_num of rpc_gss_cred_vers_3_t */
           unsigned int         ctap_seq_num;
   };

      ctap_shared_secret is a secret value the user principal generated
      and was used to establish the copy_from_auth privilege with the
      source principal.

   copy_confirm_auth:  A destination principal is confirming with the
      source principal that it is authorized to copy data from the
      source on behalf of the user principal.  When the inter-server
      copy protocol is NFSv4, or for that matter, any protocol capable
      of being secured via RPCSEC_GSSv3 (i.e., any ONC RPC protocol),
      this privilege is established before the file is copied from the
      source to the destination.

   struct copy_confirm_auth_priv {
           /* equal to GSS_GetMIC() of cfap_shared_secret */
           opaque              ccap_shared_secret_mic<>;
           /* the NFSv4 user name that the user principal maps to */
           utf8str_mixed       ccap_username;
           /* equal to seq_num of rpc_gss_cred_vers_3_t */
           unsigned int        ccap_seq_num;
   };

2.4.1.2.1.  Establishing a Security Context

   When the user principal wants to COPY a file between two servers, if
   it has not established copy_from_auth and copy_to_auth privileges on
   the servers, it establishes them:

   o  The user principal generates a secret it will share with the two
      servers.  This shared secret will be placed in the
      cfap_shared_secret and ctap_shared_secret fields of the
      appropriate privilege data types, copy_from_auth_priv and
      copy_to_auth_priv.

   o  An instance of copy_from_auth_priv is filled in with the shared
      secret, the destination server, and the NFSv4 user id of the user
      principal.  It will be sent with an RPCSEC_GSS3_CREATE procedure,
      and so cfap_seq_num is set to the seq_num of the credential of the
      RPCSEC_GSS3_CREATE procedure.  Because cfap_shared_secret is a
      secret, after XDR encoding copy_from_auth_priv, GSS_Wrap() (with
      privacy) is invoked on copy_from_auth_priv.  The
      RPCSEC_GSS3_CREATE procedure's arguments are:

      struct {
         rpc_gss3_gss_binding    *compound_binding;
         rpc_gss3_chan_binding   *chan_binding_mic;
         rpc_gss3_assertion      assertions<>;
         rpc_gss3_extension      extensions<>;
      } rpc_gss3_create_args;

      The string "copy_from_auth" is placed in assertions[0].privs.  The
      output of GSS_Wrap() is placed in extensions[0].data.  The field
      extensions[0].critical is set to TRUE.  The source server calls
      GSS_Unwrap() on the privilege, and verifies that the seq_num
      matches the credential.  It then verifies that the NFSv4 user id
      being asserted matches the source server's mapping of the user
      principal.  If it does, the privilege is established on the source
      server as: <"copy_from_auth", user id, destination>.  The
      successful reply to RPCSEC_GSS3_CREATE has:

      struct {
         opaque                  handle<>;
         rpc_gss3_chan_binding   *chan_binding_mic;
         rpc_gss3_assertion      granted_assertions<>;
         rpc_gss3_assertion      server_assertions<>;
         rpc_gss3_extension      extensions<>;
      } rpc_gss3_create_res;

      The field "handle" is the RPCSEC_GSSv3 handle that the client will
      use on COPY_NOTIFY requests involving the source and destination
      server. granted_assertions[0].privs will be equal to
      "copy_from_auth".  The server will return a GSS_Wrap() of
      copy_to_auth_priv.

   o  An instance of copy_to_auth_priv is filled in with the shared
      secret, the source server, and the NFSv4 user id.  It will be sent
      with an RPCSEC_GSS3_CREATE procedure, and so ctap_seq_num is set
      to the seq_num of the credential of the RPCSEC_GSS3_CREATE
      procedure.  Because ctap_shared_secret is a secret, after XDR
      encoding copy_to_auth_priv, GSS_Wrap() is invoked on
      copy_to_auth_priv.  The RPCSEC_GSS3_CREATE procedure's arguments
      are:

      struct {
         rpc_gss3_gss_binding    *compound_binding;
         rpc_gss3_chan_binding   *chan_binding_mic;
         rpc_gss3_assertion      assertions<>;
         rpc_gss3_extension      extensions<>;
      } rpc_gss3_create_args;

      The string "copy_to_auth" is placed in assertions[0].privs.  The
      output of GSS_Wrap() is placed in extensions[0].data.  The field
      extensions[0].critical is set to TRUE.  After unwrapping,
      verifying the seq_num, and the user principal to NFSv4 user ID
      mapping, the destination establishes a privilege of
      <"copy_to_auth", user id, source>.  The successful reply to
      RPCSEC_GSS3_CREATE has:

      struct {
         opaque                  handle<>;
         rpc_gss3_chan_binding   *chan_binding_mic;
         rpc_gss3_assertion      granted_assertions<>;
         rpc_gss3_assertion      server_assertions<>;
         rpc_gss3_extension      extensions<>;
      } rpc_gss3_create_res;

      The field "handle" is the RPCSEC_GSSv3 handle that the client will
      use on COPY requests involving the source and destination server.
      The field granted_assertions[0].privs will be equal to
      "copy_to_auth".  The server will return a GSS_Wrap() of
      copy_to_auth_priv.

2.4.1.2.2.  Starting a Secure Inter-Server Copy

   When the client sends a COPY_NOTIFY request to the source server, it
   uses the privileged "copy_from_auth" RPCSEC_GSSv3 handle.
   cna_destination_server in COPY_NOTIFY MUST be the same as the name of
   the destination server specified in copy_from_auth_priv.  Otherwise,
   COPY_NOTIFY will fail with NFS4ERR_ACCESS.  The source server
   verifies that the privilege <"copy_from_auth", user id, destination>
   exists, and annotates it with the source filehandle, if the user
   principal has read access to the source file, and if administrative
   policies give the user principal and the NFS client read access to
   the source file (i.e., if the ACCESS operation would grant read
   access).  Otherwise, COPY_NOTIFY will fail with NFS4ERR_ACCESS.

   When the client sends a COPY request to the destination server, it
   uses the privileged "copy_to_auth" RPCSEC_GSSv3 handle.
   ca_source_server in COPY MUST be the same as the name of the source
   server specified in copy_to_auth_priv.  Otherwise, COPY will fail
   with NFS4ERR_ACCESS.  The destination server verifies that the
   privilege <"copy_to_auth", user id, source> exists, and annotates it
   with the source and destination filehandles.  If the client has
   failed to establish the "copy_to_auth" policy it will reject the
   request with NFS4ERR_PARTNER_NO_AUTH.

   If the client sends a COPY_REVOKE to the source server to rescind the
   destination server's copy privilege, it uses the privileged
   "copy_from_auth" RPCSEC_GSSv3 handle and the cra_destination_server
   in COPY_REVOKE MUST be the same as the name of the destination server
   specified in copy_from_auth_priv.  The source server will then delete
   the <"copy_from_auth", user id, destination> privilege and fail any
   subsequent copy requests sent under the auspices of this privilege
   from the destination server.

2.4.1.2.3.  Securing ONC RPC Server-to-Server Copy Protocols

   After a destination server has a "copy_to_auth" privilege established
   on it, and it receives a COPY request, if it knows it will use an ONC
   RPC protocol to copy data, it will establish a "copy_confirm_auth"
   privilege on the source server, using nfs@<destination> as the
   initiator principal, and nfs@<source> as the target principal.

   The value of the field ccap_shared_secret_mic is a GSS_VerifyMIC() of
   the shared secret passed in the copy_to_auth privilege.  The field
   ccap_username is the mapping of the user principal to an NFSv4 user
   name ("user"@"domain" form), and MUST be the same as ctap_username
   and cfap_username.  The field ccap_seq_num is the seq_num of the
   RPCSEC_GSSv3 credential used for the RPCSEC_GSS3_CREATE procedure the
   destination will send to the source server to establish the
   privilege.

   The source server verifies the privilege, and establishes a
   <"copy_confirm_auth", user id, destination> privilege.  If the source
   server fails to verify the privilege, the COPY operation will be
   rejected with NFS4ERR_PARTNER_NO_AUTH.  All subsequent ONC RPC
   requests sent from the destination to copy data from the source to
   the destination will use the RPCSEC_GSSv3 handle returned by the
   source's RPCSEC_GSS3_CREATE response.

   Note that the use of the "copy_confirm_auth" privilege accomplishes
   the following:

   o  if a protocol like NFS is being used, with export policies, export
      policies can be overridden in case the destination server as-an-
      NFS-client is not authorized

   o  manual configuration to allow a copy relationship between the
      source and destination is not needed.

   If the attempt to establish a "copy_confirm_auth" privilege fails,
   then when the user principal sends a COPY request to destination, the
   destination server will reject it with NFS4ERR_PARTNER_NO_AUTH.

2.4.1.2.4.  Securing Non ONC RPC Server-to-Server Copy Protocols

   If the destination won't be using ONC RPC to copy the data, then the
   source and destination are using an unspecified copy protocol.  The
   destination could use the shared secret and the NFSv4 user id to
   prove to the source server that the user principal has authorized the
   copy.

   For protocols that authenticate user names with passwords (e.g., HTTP
   [13] and FTP [14]), the nfsv4 user id could be used as the user name,
   and an ASCII hexadecimal representation of the RPCSEC_GSSv3 shared
   secret could be used as the user password or as input into non-
   password authentication methods like CHAP [15].

2.4.1.3.  Inter-Server Copy via ONC RPC but without RPCSEC_GSSv3

   ONC RPC security flavors other than RPCSEC_GSSv3 MAY be used with the
   server-side copy offload operations described in this document.  In
   particular, host-based ONC RPC security flavors such as AUTH_NONE and
   AUTH_SYS MAY be used.  If a host-based security flavor is used, a
   minimal level of protection for the server-to-server copy protocol is
   possible.

   In the absence of strong security mechanisms such as RPCSEC_GSSv3,
   the challenge is how the source server and destination server
   identify themselves to each other, especially in the presence of
   multi-homed source and destination servers.  In a multi-homed
   environment, the destination server might not contact the source
   server from the same network address specified by the client in the
   COPY_NOTIFY.  This can be overcome using the procedure described
   below.

   When the client sends the source server the COPY_NOTIFY operation,
   the source server may reply to the client with a list of target
   addresses, names, and/or URLs and assign them to the unique
   quadruple: <random number, source fh, user ID, destination address
   Y>.  If the destination uses one of these target netlocs to contact
   the source server, the source server will be able to uniquely
   identify the destination server, even if the destination server does
   not connect from the address specified by the client in COPY_NOTIFY.
   The level of assurance in this identification depends on the
   unpredictability, strength and secrecy of the random number.

   For example, suppose the network topology is as shown in Figure 3.
   If the source filehandle is 0x12345, the source server may respond to
   a COPY_NOTIFY for destination 10.11.78.56 with the URLs:

      nfs://10.11.78.18//_COPY/FvhH1OKbu8VrxvV1erdjvR7N/10.11.78.56/_FH/
      0x12345

      nfs://192.168.33.18//_COPY/FvhH1OKbu8VrxvV1erdjvR7N/10.11.78.56/
      _FH/0x12345

   The name component after _COPY is 24 characters of base 64, more than
   enough to encode a 128 bit random number.

   The client will then send these URLs to the destination server in the
   COPY operation.  Suppose that the 192.168.33.0/24 network is a high
   speed network and the destination server decides to transfer the file
   over this network.  If the destination contacts the source server
   from 192.168.33.56 over this network using NFSv4.1, it does the
   following:

   COMPOUND  { PUTROOTFH, LOOKUP "_COPY" ; LOOKUP
      "FvhH1OKbu8VrxvV1erdjvR7N" ; LOOKUP "10.11.78.56"; LOOKUP "_FH" ;
      OPEN "0x12345" ; GETFH }

   Provided that the random number is unpredictable and has been kept
   secret by the parties involved, the source server will therefore know
   that these NFSv4.x operations are being issued by the destination
   server identified in the COPY_NOTIFY.  This random number technique
   only provides initial authentication of the destination server, and
   cannot defend against man-in-the-middle attacks after authentication
   or an eavesdropper that observes the random number on the wire.
   Other secure communication techniques (e.g., IPsec) are necessary to
   block these attacks.

2.4.1.4.  Inter-Server Copy without ONC RPC and RPCSEC_GSSv3

   The same techniques as Section 2.4.1.3, using unique URLs for each
   destination server, can be used for other protocols (e.g., HTTP [13]
   and FTP [14]) as well.

3.  Sparse Files  Support for Application IO Hints

3.1.  Introduction

   A sparse file is a common way of representing a large file without
   having to utilize all of the disk space

   Applications currently have several options for it.  Consequently, a
   sparse file uses less physical space than its size indicates.  This
   means communicating I/O
   access patterns to the file contains 'holes', byte ranges within NFS client.  While this can help the file that
   contain no data.  Most modern file systems support sparse files,
   including most UNIX file systems and NTFS, but notably not Apple's
   HFS+.  Common examples of sparse files include Virtual Machine (VM)
   OS/disk images, database files, log files, NFS
   client optimize I/O and even checkpoint
   recovery files most commonly used by the HPC community.

   If an application reads a hole in caching for a sparse file, it does not allow the NFS
   server and its exported file system must
   return all zeros to do likewise.  Therefore, here
   we put forth a proposal for the application.  For local data access there is
   little penalty, but with NFS these zeroes must be transferred back NFSv4.2 protocol to
   the client.  If an application uses the NFS client allow
   applications to read communicate their expected behavior to the server.

   By communicating expected access pattern, e.g., sequential or random,
   and data into
   memory, this wastes time re-use behavior, e.g., data range will be read multiple
   times and bandwidth as the application waits for
   the zeroes to should be transferred.

   A sparse file is typically created by initializing cached, the file to server will be all
   zeros - nothing is written able to the data in the file, instead the hole
   is recorded in the metadata better
   understand what optimizations it should implement for the file.  So access to a 8G disk image might
   be represented initially by
   file.  For example, if a couple hundred bits in application indicates it will never read the inode
   data more than once, then the file system can avoid polluting the
   data cache and
   nothing on not cache the disk.  If data.

   The first application that can issue client I/O hints is the VM then writes 100M
   posix_fadvise operation.  For example, on Linux, when an application
   uses posix_fadvise to specify a file in will be read sequentially, Linux
   doubles the
   middle readahead buffer size.

   Another instance where applications provide an indication of their
   desired I/O behavior is the image, there would now be two holes represented in the
   metadata and 100M in use of direct I/O. By specifying direct
   I/O, clients will no longer cache data, but this information is not
   passed to the server, which will continue caching data.

   Application specific NFS clients such as those used by hypervisors
   and databases can also leverage application hints to communicate
   their specialized requirements.

   This section introduces adds a new IO_ADVISE operation READ_PLUS (Section 13.10)
   which supports all to communicate the features of READ client
   file access patterns to the NFS server.  The NFS server upon
   receiving a IO_ADVISE operation MAY choose to alter its I/O and
   caching behavior, but includes an extension is under no obligation to
   support sparse pattern files.  READ_PLUS do so.

3.2.  POSIX Requirements

   The first key requirement of the IO_ADVISE operation is guaranteed to perform no
   worse than READ, support
   the posix_fadvise function [6], which is supported in Linux and can dramatically many
   other operating systems.  Examples and guidance on how to use
   posix_fadvise to improve performance with sparse
   files.  READ_PLUS does not depend on pNFS protocol features, but can be used by pNFS to support sparse files.

3.2.  Terminology

   Regular file:  An object found here [16].
   posix_fadvise is defined as follows,

      int posix_fadvise(int fd, off_t offset, off_t len, int advice);

   The posix_fadvise() function shall advise the implementation on the
   expected behavior of the application with respect to the data in the
   file type NF4REG or NF4NAMEDATTR.

   Sparse file:  A Regular associated with the open file that contains one or more Holes.

   Hole:  A byte descriptor, fd, starting at offset
   and continuing for len bytes.  The specified range within a Sparse file that contains regions of need not currently
   exist in the file.  If len is zero, all
      zeroes.  For block-based file systems, data following offset is
   specified.  The implementation may use this could also be an
      unallocated region information to optimize
   handling of the file.

   Hole Threshold: specified data.  The minimum length posix_fadvise() function shall
   have no effect on the semantics of a Hole as determined by other operations on the
      server.  If a server chooses to define a Hole Threshold, then specified
   data, although it
      would not return hole information about holes with a length
      shorter than may affect the Hole Threshold.

4.  Space Reservation

4.1.  Introduction

   This section describes a set performance of operations that allow applications
   such as hypervisors other operations.

   The advice to be applied to reserve space for a file, report the amount of
   actual disk space a file occupies and freeup the backing space of a
   file when it data is not required.  In virtualized environments, virtual
   disk files are often stored on NFS mounted volumes.  Since virtual
   disk files represent specified by the hard disks advice
   parameter and may be one of virtual machines, hypervisors
   often have the following values:

   POSIX_FADV_NORMAL -  Specifies that the application has no advice to
      give on its behavior with respect to guarantee certain properties for the file.

   One such example specified data.  It is space reservation.  When a hypervisor creates a
   virtual disk file, it often tries to preallocate
      the space default characteristic if no advice is given for the
   file so an open file.

   POSIX_FADV_SEQUENTIAL -  Specifies that there are no future allocation related errors during the
   operation of application expects to
      access the virtual machine.  Such errors prevent a virtual
   machine specified data sequentially from continuing execution and result in downtime.

   Currently, in order lower offsets to achieve such a guarantee, applications zero
      higher offsets.

   POSIX_FADV_RANDOM -  Specifies that the entire file.  The initial zeroing allocates application expects to access
      the backing blocks
   and all subsequent writes are overwrites of already allocated blocks.
   This approach is not only inefficient specified data in terms of a random order.

   POSIX_FADV_WILLNEED -  Specifies that the amount of I/O
   done, application expects to
      access the specified data in the near future.

   POSIX_FADV_DONTNEED -  Specifies that the application expects that it is also
      will not guaranteed to work on filesystems access the specified data in the near future.

   POSIX_FADV_NOREUSE -  Specifies that are log
   structured or deduplicated.  An efficient way of guaranteeing space
   reservation would the application expects to
      access the specified data once and then not reuse it thereafter.

   Upon successful completion, posix_fadvise() shall return zero;
   otherwise, an error number shall be beneficial returned to such applications.

   If indicate the space_reserved attribute error.

3.3.  Additional Requirements

   Many use cases exist for sending application I/O hints to the server
   that cannot utilize the POSIX supported interface.  This is set on because
   some applications may benefit from additional hints not specified by
   posix_fadvise, and some applications may not use POSIX altogether.

   One use case is "Opportunistic Prefetch", which allows a file, stateid
   holder to tell the server that it is guaranteed
   that writes possible that do not grow the file it will not fail with
   NFSERR_NOSPC.

   Another useful feature would be access the ability
   specified data in the near future.  This is similar to report
   POSIX_FADV_WILLNEED, but the number of
   blocks that would client is unsure it will in fact read
   the specified data, so the server should only prefetch the data if it
   can be freed done at a marginal cost.  For example, when a server receives
   this hint, it could prefetch only the indirect blocks for a file is deleted.  Currently, NFS
   reports two size attributes:

   size  The logical file size
   instead of all the file.

   space_used  The size data.  This would still improve performance if the
   client does read the data, but with less pressure on server memory.

   An example use case for this hint is a database that reads in bytes a
   single record that points to additional records in either other areas
   of the same file occupies or different files located on disk the same or different
   server.  While these attributes are sufficient it is likely that the application may access the
   additional records, it is far from guaranteed.  Therefore, the
   database may issue an opportunistic prefetch (instead of
   POSIX_FADV_WILLNEED) for space accounting in
   traditional filesystems, they prove to be inadequate the data in modern
   filesystems that support block sharing.  In such filesystems,
   multiple inodes can point the other files pointed to by
   the record.

   Another use case is "Direct I/O", which allows a single block with a block reference
   count stated holder to guard against premature freeing.  Having a way
   inform the server that it does not wish to tell cache data.  Today, for
   applications that only intend to read data once, the
   number use of blocks direct
   I/O disables client caching, but does not affect server caching.  By
   caching data that would will not be freed if re-read, the file was deleted would be server is polluting its
   cache and possibly causing useful cached data to applications that wish to migrate files when a volume is
   low on space.

   Since virtual disks represent a hard drive in a virtual machine, a
   virtual disk be evicted.  By
   informing the server of its expected I/O access, this situation can
   be viewed as a filesystem within a file.  Since not
   all blocks within a filesystem are in use, there is an opportunity to
   reclaim blocks that are no longer in use.  A call to deallocate
   blocks could result in better space efficiency.  Lesser space MAY be
   consumed for backups after block deallocation.

   The following operations and attributes avoid.  Direct I/O can be used to resolve this
   issues:

   space_reserved  This attribute specifies whether in Linux and AIX via the blocks backing open()
   O_DIRECT parameter, in Solaris via the file have been preallocated.

   space_freed  This attribute specifies directio() function, and in
   Windows via the space freed when a file CreateFile() FILE_FLAG_NO_BUFFERING flag.

   Another use case is
      deleted, taking block sharing into consideration.

   INITIALIZED  This operation zeroes and/or deallocates the blocks
      backing a region of the file.

   If space_used of "Backward Sequential Read", which allows a file is interpreted stated
   holder to mean inform the size in bytes of
   all disk blocks pointed server that it intends to by read the inode of specified
   data backwards, i.e., back the file, then shared
   blocks get double counted, over-reporting end to the space utilization. beginning.  This also has the adverse effect that the deletion of a file with
   shared blocks frees up less than space_used bytes.

   On the other hand, if space_used is interpreted
   different than POSIX_FADV_SEQUENTIAL, whose implied intention was
   that data will be read from beginning to mean the size in
   bytes of those disk blocks unique end.  This hint allows
   servers to prefetch data at the inode end of the file, range first, and then
   shared blocks are not counted in any file, resulting
   prefetch data sequentially in under-
   reporting a backwards manner to the start of the space utilization.

   For example, two files A and B have 10 blocks each.  Let 6 of these
   blocks be shared between them.  Thus, the combined space utilized by
   the two files is 14 * BLOCK_SIZE bytes.  In the former case, the
   combined space utilization
   data range.  One example of the two files would be reported as 20 *
   BLOCK_SIZE.  However, deleting either would only result in 4 *
   BLOCK_SIZE being freed.  Conversely, the latter interpretation would
   report an application that the space utilization is only 8 * BLOCK_SIZE.

   Adding another size attribute, space_freed, is helpful in solving can make use of this problem. space_freed
   hint is the number of blocks that are allocated
   to the given file that would video editing.

3.4.  Security Considerations

   None.

3.5.  IANA Considerations

   The IO_ADVISE_type4 will be freed on its deletion.  In the
   example, both A and B would report space_freed as 4 * BLOCK_SIZE and
   space_used as 10 * BLOCK_SIZE.  If extended through an IANA registry.

4.  Sparse Files
4.1.  Introduction

   A sparse file is deleted, B will report
   space_freed as 10 * BLOCK_SIZE as the deletion of B would result in
   the deallocation a common way of representing a large file without
   having to utilize all 10 blocks.

   The addition of this problem doesn't solve the problem of disk space being
   over-reported.  However, over-reporting is better than under-
   reporting.

5.  Support for Application IO Hints

5.1.  Introduction

   Applications currently have several options for communicating I/O
   access patterns to the NFS client.  While this can help the NFS
   client optimize I/O and caching for it.  Consequently, a file, it does not allow the NFS
   server and its exported
   sparse file system to do likewise.  Therefore, here
   we put forth a proposal for the NFSv4.2 protocol to allow
   applications to communicate their expected behavior to the server.

   By communicating expected access pattern, e.g., sequential or random,
   and data re-use behavior, e.g., data range will be read multiple
   times and should be cached, the server will be able to better
   understand what optimizations it should implement for access to a
   file.  For example, if a application indicates it will never read the
   data more uses less physical space than once, then its size indicates.  This
   means the file system can avoid polluting contains 'holes', byte ranges within the
   data cache file that
   contain no data.  Most modern file systems support sparse files,
   including most UNIX file systems and NTFS, but notably not cache the data.

   The first application that can issue client I/O hints is Apple's
   HFS+.  Common examples of sparse files include Virtual Machine (VM)
   OS/disk images, database files, log files, and even checkpoint
   recovery files most commonly used by the
   posix_fadvise operation.  For example, on Linux, when HPC community.

   If an application
   uses posix_fadvise to specify reads a hole in a sparse file, the file will be read sequentially, Linux
   doubles system must
   return all zeros to the readahead buffer size.

   Another instance where applications provide an indication of their
   desired I/O behavior application.  For local data access there is the use of direct I/O. By specifying direct
   I/O, clients will no longer cache data,
   little penalty, but this information is not
   passed with NFS these zeroes must be transferred back to
   the server, which will continue caching data.

   Application specific NFS clients such as those used by hypervisors
   and databases can also leverage client.  If an application hints to communicate
   their specialized requirements.

   This section adds a new IO_ADVISE operation to communicate uses the NFS client
   file access patterns to read data into
   memory, this wastes time and bandwidth as the NFS server.  The NFS server upon
   receiving a IO_ADVISE operation MAY choose application waits for
   the zeroes to alter its I/O and
   caching behavior, but be transferred.

   A sparse file is under no obligation to do so.

5.2.  POSIX Requirements

   The first key requirement of typically created by initializing the IO_ADVISE operation file to be all
   zeros - nothing is written to support the posix_fadvise function [6], which is supported data in Linux and many
   other operating systems.  Examples and guidance on how to use
   posix_fadvise to improve performance can be found here [16].
   posix_fadvise the file, instead the hole
   is defined as follows,

      int posix_fadvise(int fd, off_t offset, off_t len, int advice);

   The posix_fadvise() function shall advise recorded in the metadata for the file.  So a 8G disk image might
   be represented initially by a couple hundred bits in the implementation inode and
   nothing on the
   expected behavior of disk.  If the application with respect VM then writes 100M to a file in the data
   middle of the image, there would now be two holes represented in the
   file associated with
   metadata and 100M in the open data.

   Two new operations INITIALIZE (Section 13.7) and READ_PLUS
   (Section 13.10) are introduced.  INITIALIZE allows for the creation
   of a sparse file descriptor, fd, starting at offset and continuing for len bytes.  The specified hole punching.  An application might want to
   zero out a range need not currently
   exist in of the file.  If len is zero,  READ_PLUS supports all data following offset is
   specified.  The implementation may use this information to optimize
   handling of the specified data.  The posix_fadvise() function shall
   have no effect on the semantics of other operations on the specified
   data, although it may affect the performance features of other operations.

   The advice to be applied
   READ but includes an extension to the data support sparse pattern files
   (Section 6.1.2).  READ_PLUS is specified by the advice
   parameter and may be one of the following values:

   POSIX_FADV_NORMAL -  Specifies that the application has no advice guaranteed to
      give on its behavior perform no worse than
   READ, and can dramatically improve performance with respect sparse files.
   READ_PLUS does not depend on pNFS protocol features, but can be used
   by pNFS to the specified data.  It is
      the default characteristic if no advice is given for an open file.

   POSIX_FADV_SEQUENTIAL -  Specifies support sparse files.

4.2.  Terminology

   Regular file:  An object of file type NF4REG or NF4NAMEDATTR.

   Sparse file:  A Regular file that the application expects to
      access the specified data sequentially from lower offsets to
      higher offsets.

   POSIX_FADV_RANDOM -  Specifies contains one or more Holes.

   Hole:  A byte range within a Sparse file that contains regions of all
      zeroes.  For block-based file systems, this could also be an
      unallocated region of the application expects file.

   Hole Threshold:  The minimum length of a Hole as determined by the
      server.  If a server chooses to access define a Hole Threshold, then it
      would not return hole information about holes with a length
      shorter than the specified data in Hole Threshold.

5.  Space Reservation

5.1.  Introduction

   This section describes a random order.

   POSIX_FADV_WILLNEED -  Specifies set of operations that the application expects allow applications
   such as hypervisors to
      access the specified data in reserve space for a file, report the near future.

   POSIX_FADV_DONTNEED -  Specifies that amount of
   actual disk space a file occupies and freeup the application expects that backing space of a
   file when it
      will is not access the specified data in the near future.

   POSIX_FADV_NOREUSE -  Specifies that required.  In virtualized environments, virtual
   disk files are often stored on NFS mounted volumes.  Since virtual
   disk files represent the application expects hard disks of virtual machines, hypervisors
   often have to
      access guarantee certain properties for the specified data once and then not reuse file.

   One such example is space reservation.  When a hypervisor creates a
   virtual disk file, it thereafter.

   Upon successful completion, posix_fadvise() shall return zero;
   otherwise, an error number shall be returned often tries to indicate preallocate the error.

5.3.  Additional Requirements

   Many use cases exist space for sending application I/O hints to the server
   file so that cannot utilize there are no future allocation related errors during the POSIX supported interface.  This is because
   some applications may benefit
   operation of the virtual machine.  Such errors prevent a virtual
   machine from additional hints not specified by
   posix_fadvise, continuing execution and some result in downtime.

   Currently, in order to achieve such a guarantee, applications may zero
   the entire file.  The initial zeroing allocates the backing blocks
   and all subsequent writes are overwrites of already allocated blocks.
   This approach is not use POSIX altogether.

   One use case only inefficient in terms of the amount of I/O
   done, it is "Opportunistic Prefetch", which allows a stateid
   holder also not guaranteed to tell the server work on filesystems that are log
   structured or deduplicated.  An efficient way of guaranteeing space
   reservation would be beneficial to such applications.

   If the space_reserved attribute (see Section 11.2.3) is set on a
   file, it is possible guaranteed that it will access writes that do not grow the
   specified data in file will not
   fail with NFSERR_NOSPC.

   Another useful feature would be the near future.  This is similar ability to
   POSIX_FADV_WILLNEED, but report the client number of
   blocks that would be freed when a file is unsure it will in fact read
   the specified data, so deleted.  Currently, NFS
   reports two size attributes:

   size  The logical file size of the server should only prefetch file.

   space_used  The size in bytes that the data if it
   can file occupies on disk

   While these attributes are sufficient for space accounting in
   traditional filesystems, they prove to be done at inadequate in modern
   filesystems that support block sharing.  In such filesystems,
   multiple inodes can point to a marginal cost.  For example, when single block with a server receives
   this hint, it could prefetch only the indirect blocks for block reference
   count to guard against premature freeing.  Having a file
   instead of all way to tell the data.  This
   number of blocks that would still improve performance be freed if the
   client does read the data, but with less pressure on server memory.

   An example use case for this hint file was deleted would be
   useful to applications that wish to migrate files when a volume is
   low on space.

   Since virtual disks represent a database that reads hard drive in a
   single record virtual machine, a
   virtual disk can be viewed as a filesystem within a file.  Since not
   all blocks within a filesystem are in use, there is an opportunity to
   reclaim blocks that points are no longer in use.  A call to additional records deallocate
   blocks could result in either other areas
   of better space efficiency.  Lesser space MAY be
   consumed for backups after block deallocation.

   The following operations and attributes can be used to resolve this
   issues:

   space_reserved  This attribute specifies whether the blocks backing
      the same file or different files located on have been preallocated.

   space_freed  This attribute specifies the same or different
   server.  While it space freed when a file is likely that the application may access
      deleted, taking block sharing into consideration.

   INITIALIZED  This operation zeroes and/or deallocates the
   additional records, it is far from guaranteed.  Therefore, blocks
      backing a region of the
   database may issue an opportunistic prefetch (instead file.

   If space_used of
   POSIX_FADV_WILLNEED) for a file is interpreted to mean the data size in the other files bytes of
   all disk blocks pointed to by the record.

   Another use case is "Direct I/O", which allows a stated holder to
   inform inode of the server file, then shared
   blocks get double counted, over-reporting the space utilization.
   This also has the adverse effect that it does not wish the deletion of a file with
   shared blocks frees up less than space_used bytes.

   On the other hand, if space_used is interpreted to cache data.  Today, for
   applications that only intend mean the size in
   bytes of those disk blocks unique to read data once, the use inode of direct
   I/O disables client caching, but does not affect server caching.  By
   caching data that will the file, then
   shared blocks are not be re-read, counted in any file, resulting in under-
   reporting of the server is polluting its
   cache space utilization.

   For example, two files A and possibly causing useful cached data to B have 10 blocks each.  Let 6 of these
   blocks be evicted.  By
   informing shared between them.  Thus, the server combined space utilized by
   the two files is 14 * BLOCK_SIZE bytes.  In the former case, the
   combined space utilization of its expected I/O access, this situation can
   be avoid.  Direct I/O can be used in Linux and AIX via the open()
   O_DIRECT parameter, two files would be reported as 20 *
   BLOCK_SIZE.  However, deleting either would only result in Solaris via 4 *
   BLOCK_SIZE being freed.  Conversely, the directio() function, and in
   Windows via latter interpretation would
   report that the CreateFile() FILE_FLAG_NO_BUFFERING flag.

   Another use case space utilization is only 8 * BLOCK_SIZE.

   Adding another size attribute, space_freed (see Section 11.2.4), is
   helpful in solving this problem. space_freed is "Backward Sequential Read", which allows a stated
   holder to inform the server number of blocks
   that it intends to read the specified
   data backwards, i.e., back the end are allocated to the beginning.  This is
   different than POSIX_FADV_SEQUENTIAL, whose implied intention was given file that data will would be read from beginning to end.  This hint allows
   servers to prefetch data at the end of freed on its
   deletion.  In the range first, example, both A and then
   prefetch data sequentially in a backwards manner to B would report space_freed as 4
   * BLOCK_SIZE and space_used as 10 * BLOCK_SIZE.  If A is deleted, B
   will report space_freed as 10 * BLOCK_SIZE as the start deletion of B would
   result in the
   data range.  One example deallocation of an application that can make use all 10 blocks.

   The addition of this
   hint problem doesn't solve the problem of space being
   over-reported.  However, over-reporting is video editing.

5.4.  Security Considerations

   None.

5.5.  IANA Considerations

   The IO_ADVISE_type4 will be extended through an IANA registry. better than under-
   reporting.

6.  Application Data Block Support

   At the OS level, files are contained on disk blocks.  Applications
   are also free to impose structure on the data contained in a file and
   we can define an Application Data Block (ADB) to be such a structure.
   From the application's viewpoint, it only wants to handle ADBs and
   not raw bytes (see [17]).  An ADB is typically comprised of two
   sections: a header and data.  The header describes the
   characteristics of the block and can provide a means to detect
   corruption in the data payload.  The data section is typically
   initialized to all zeros.

   The format of the header is application specific, but there are two
   main components typically encountered:

   1.  An ADB Number (ADBN), which allows the application to determine
       which data block is being referenced.  The ADBN is a logical
       block number and is useful when the client is not storing the
       blocks in contiguous memory.

   2.  Fields to describe the state of the ADB and a means to detect
       block corruption.  For both pieces of data, a useful property is
       that allowed values be unique in that if passed across the
       network, corruption due to translation between big and little
       endian architectures are detectable.  For example, 0xF0DEDEF0 has
       the same bit pattern in both architectures.

   Applications already impose structures on files [17] and detect
   corruption in data blocks [18].  What they are not able to do is
   efficiently transfer and store ADBs.  To initialize a file with ADBs,
   the client must send the full ADB to the server and that must be
   stored on the server.  When the application is initializing a file to
   have the ADB structure, it could compress the ADBs to just the
   information to necessary to later reconstruct the header portion of
   the ADB when the contents are read back.  Using sparse file
   techniques, the disk blocks described by would not be allocated.
   Unlike sparse file techniques, there would be a small cost to store
   the compressed header data.

   In this section, we are going to define a generic framework for an
   ADB, present one approach to detecting corruption in a given ADB
   implementation, and describe the model for how the client and server
   can support efficient initialization of ADBs, reading of ADB holes,
   punching holes in ADBs, and space reservation.  Further, we need to
   be able to extend this model to applications which do not support
   ADBs, but wish to be able to handle sparse files, hole punching, and
   space reservation.

6.1.  Generic Framework

   We want the representation of the ADB to be flexible enough to
   support many different applications.  The most basic approach is no
   imposition of a block at all, which means we are working with the raw
   bytes.  Such an approach would be useful for storing holes, punching
   holes, etc.  In more complex deployments, a server might be
   supporting multiple applications, each with their own definition of
   the ADB.  One might store the ADBN at the start of the block and then
   have a guard pattern to detect corruption [19].  The next might store
   the ADBN at an offset of 100 bytes within the block and have no guard
   pattern at all.  The point is that  I.e., existing applications might already have well
   defined formats for their data blocks.

   The guard pattern can be used to represent the state of the block, to
   protect against corruption, or both.  Again, it needs to be able to
   be placed anywhere within the ADB.

   We need to be able to represent the starting offset of the block and
   the size of the block.  Note that nothing prevents the application
   from defining different sized blocks in a file.

6.1.1.  Data Block Representation

   struct app_data_block4 {
           offset4         adb_offset;
           length4         adb_block_size;
           length4         adb_block_count;
           length4         adb_reloff_blocknum;
           count4          adb_block_num;
           length4         adb_reloff_pattern;
           opaque          adb_pattern<>;
   };

   The app_data_block4 structure captures the abstraction presented for
   the ADB.  The additional fields present are to allow the transmission
   of adb_block_count ADBs at one time.  We also use adb_block_num to
   convey the ADBN of the first block in the sequence.  Each ADB will
   contain the same adb_pattern string.

   As both adb_block_num and adb_pattern are optional, if either
   adb_reloff_pattern or adb_reloff_blocknum is set to NFS4_UINT64_MAX,
   then the corresponding field is not set in any of the ADB.

6.1.2.  Data Content

   /*
    * Use an enum such that we can extend new types.
    */
   enum data_content4 {
           NFS4_CONTENT_DATA = 0,
           NFS4_CONTENT_APP_BLOCK = 1,
           NFS4_CONTENT_HOLE = 2
   };

   New operations might need to differentiate between wanting to access
   data versus an ADB.  Also, future minor versions might want to
   introduce new data formats.  This enumeration allows that to occur.

6.2.  pNFS Considerations

   While this document does not mandate how sparse ADBs are recorded on
   the server, it does make the assumption that such information is not
   in the file.  I.e., the information is metadata.  As such, the
   INITIALIZE operation is defined to be not supported by the DS - it
   must be issued to the MDS.  But since the client must not assume a
   priori whether a read is sparse or not, the READ_PLUS operation MUST
   be supported by both the DS and the MDS.  I.e., the client might
   impose on the MDS to asynchronously read the data from the DS.

   Furthermore, each DS MUST not report to a client either a sparse ADB
   or data which
   belongs to another DS.  One implication of this requirement is that
   the app_data_block4's adb_block_size MUST be either be the stripe
   width or the stripe width must be an even multiple of it.  The second
   implication here is that the DS must be able to use the
   Control Protocol to determine from the MDS where the sparse ADBs
   occur.  [[Comment.3: Need to discuss what happens if after the file
   is being written to and an INITIALIZE occurs? --TH]] Perhaps instead
   of the DS pulling from the MDS, the MDS pushes to the DS?  Thus an
   INITIALIZE causes a new push?  [[Comment.4: Still need to consider
   race cases of to use the DS getting a WRITE and Control
   Protocol to determine from the MDS getting an
   INITIALIZE. --TH]] where the sparse ADBs occur.

6.3.  An Example of Detecting Corruption

   In this section, we define an ADB format in which corruption can be
   detected.  Note that this is just one possible format and means to
   detect corruption.

   Consider a very basic implementation of an operating system's disk
   blocks.  A block is either data or it is an indirect block which
   allows for files to be larger than one block.  It is desired to be
   able to initialize a block.  Lastly, to quickly unlink a file, a
   block can be marked invalid.  The contents remain intact - which
   would enable this OS application to undelete a file.

   The application defines 4k sized data blocks, with an 8 byte block
   counter occurring at offset 0 in the block, and with the guard
   pattern occurring at offset 8 inside the block.  Furthermore, the
   guard pattern can take one of four states:

   0xfeedface -   This is the FREE state and indicates that the ADB
      format has been applied.

   0xcafedead -   This is the DATA state and indicates that real data
      has been written to this block.

   0xe4e5c001 -   This is the INDIRECT state and indicates that the
      block contains block counter numbers that are chained off of this
      block.

   0xba1ed4a3 -   This is the INVALID state and indicates that the block
      contains data whose contents are garbage.

   Finally, it also defines an 8 byte checksum [20] starting at byte 16
   which applies to the remaining contents of the block.  If the state
   is FREE, then that checksum is trivially zero.  As such, the
   application has no need to transfer the checksum implicitly inside
   the ADB - it need not make the transfer layer aware of the fact that
   there is a checksum (see [18] for an example of checksums used to
   detect corruption in application data blocks).

   Corruption in each ADB can be detected thusly:

   o  If the guard pattern is anything other than one of the allowed
      values, including all zeros.

   o  If the guard pattern is FREE and any other byte in the remainder
      of the ADB is anything other than zero.

   o  If the guard pattern is anything other than FREE, then if the
      stored checksum does not match the computed checksum.

   o  If the guard pattern is INDIRECT and one of the stored indirect
      block numbers has a value greater than the number of ADBs in the
      file.

   o  If the guard pattern is INDIRECT and one of the stored indirect
      block numbers is a duplicate of another stored indirect block
      number.

   As can be seen, the application can detect errors based on the
   combination of the guard pattern state and the checksum.  But also,
   the application can detect corruption based on the state and the
   contents of the ADB.  This last point is important in validating the
   minimum amount of data we incorporated into our generic framework.

   I.e., the guard pattern is sufficient in allowing applications to
   design their own corruption detection.

   Finally, it is important to note that none of these corruption checks
   occur in the transport layer.  The server and client components are
   totally unaware of the file format and might report everything as
   being transferred correctly even in the case the application detects
   corruption.

6.4.  Example of READ_PLUS

   The hypothetical application presented in Section 6.3 can be used to
   illustrate how READ_PLUS would return an array of results.  A file is
   created and initialized with 100 4k ADBs in the FREE state:

      INITIALIZE {0, 4k, 100, 0, 0, 8, 0xfeedface}

   Further, assume the application writes a single ADB at 16k, changing
   the guard pattern to 0xcafedead, we would then have in memory:

      0 -> (16k - 1)   : 4k, 4, 0, 0, 8, 0xfeedface
      16k -> (20k - 1) : 00 00 00 05 ca fe de ad XX XX ... XX XX
      20k -> 400k      : 4k, 95, 0, 6, 0xfeedface

   And when the client did a READ_PLUS of 64k at the start of the file,
   it would get back a result of an ADB, some data, and a final ADB:

      ADB {0, 4, 0, 0, 8, 0xfeedface}
      data 4k
      ADB {20k, 4k, 59, 0, 6, 0xfeedface}

6.5.  Zero Filled Holes

   As applications are free to define the structure of an ADB, it is
   trivial to define an ADB which supports zero filled holes.  Such a
   case would encompass the traditional definitions of a sparse file and
   hole punching.  For example, to punch a 64k hole, starting at 100M,
   into an existing file which has no ADB structure:

      INITIALIZE {100M, 64k, 1, NFS4_UINT64_MAX,
                  0, NFS4_UINT64_MAX, 0x0}

7.  Labeled NFS
7.1.  Introduction

   Access control models such as Unix permissions or Access Control
   Lists are commonly referred to as Discretionary Access Control (DAC)
   models.  These systems base their access decisions on user identity
   and resource ownership.  In contrast Mandatory Access Control (MAC)
   models base their access control decisions on the label on the
   subject (usually a process) and the object it wishes to access [7].
   These labels may contain user identity information but usually
   contain additional information.  In DAC systems users are free to
   specify the access rules for resources that they own.  MAC models
   base their security decisions on a system wide policy established by
   an administrator or organization which the users do not have the
   ability to override.  In this section, we add a MAC model to NFSv4.

   The first change necessary is to devise a method for transporting and
   storing security label data on NFSv4 file objects.  Security labels
   have several semantics that are met by NFSv4 recommended attributes
   such as the ability to set the label value upon object creation.
   Access control on these attributes are done through a combination of
   two mechanisms.  As with other recommended attributes on file objects
   the usual DAC checks (ACLs and permission bits) will be performed to
   ensure that proper file ownership is enforced.  In addition a MAC
   system MAY be employed on the client, server, or both to enforce
   additional policy on what subjects may modify security label
   information.

   The second change is to provide a method for the server to notify the
   client that the attribute changed on an open file on the server.  If
   the file is closed, then during the open attempt, the client will
   gather the new attribute value.  The server MUST not communicate the
   new value of the attribute, the client MUST query it.  This
   requirement stems from the need for the client to provide sufficient
   access rights to the attribute.

   The final change necessary is a modification to the RPC layer used in
   NFSv4 in the form of a new version of the RPCSEC_GSS [8] framework.
   In order for an NFSv4 server to apply MAC checks it must obtain
   additional information from the client.  Several methods were
   explored for performing this and it was decided that the best
   approach was to incorporate the ability to make security attribute
   assertions through the RPC mechanism.  RPCSECGSSv3 [5] outlines a
   method to assert additional security information such as security
   labels on gss context creation and have that data bound to all RPC
   requests that make use of that context.

7.2.  Definitions

   Label Format Specifier (LFS):  is an identifier used by the client to
      establish the syntactic format of the security label and the
      semantic meaning of its components.  These specifiers exist in a
      registry associated with documents describing the format and
      semantics of the label.

   Label Format Registry:  is the IANA registry containing all
      registered LFS along with references to the documents that
      describe the syntactic format and semantics of the security label.

   Policy Identifier (PI):  is an optional part of the definition of a
      Label Format Specifier which allows for clients and server to
      identify specific security policies.

   Object:  is a passive resource within the system that we wish to be
      protected.  Objects can be entities such as files, directories,
      pipes, sockets, and many other system resources relevant to the
      protection of the system state.

   Subject:  A subject is an active entity usually a process which is
      requesting access to an object.

   Multi-Level Security (MLS):  is a traditional model where objects are
      given a sensitivity level (Unclassified, Secret, Top Secret, etc)
      and a category set [21].

7.3.  MAC Security Attribute

   MAC models base access decisions on security attributes bound to
   subjects and objects.  This information can range from a user
   identity for an identity based MAC model, sensitivity levels for
   Multi-level security, or a type for Type Enforcement.  These models
   base their decisions on different criteria but the semantics of the
   security attribute remain the same.  The semantics required by the
   security attributes are listed below:

   o  Must provide flexibility with respect to MAC model.

   o  Must provide the ability to atomically set security information
      upon object creation.

   o  Must provide the ability to enforce access control decisions both
      on the client and the server.

   o  Must not expose an object to either the client or server name
      space before its security information has been bound to it.

   NFSv4 implements the security attribute as a recommended attribute.
   These attributes have a fixed format and semantics, which conflicts
   with the flexible nature of the security attribute.  To resolve this
   the security attribute consists of two components.  The first
   component is a LFS as defined in [22] to allow for interoperability
   between MAC mechanisms.  The second component is an opaque field
   which is the actual security attribute data.  To allow for various
   MAC models NFSv4 should be used solely as a transport mechanism for
   the security attribute.  It is the responsibility of the endpoints to
   consume the security attribute and make access decisions based on
   their respective models.  In addition, creation of objects through
   OPEN and CREATE allows for the security attribute to be specified
   upon creation.  By providing an atomic create and set operation for
   the security attribute it is possible to enforce the second and
   fourth requirements.  The recommended attribute FATTR4_SEC_LABEL will
   be used to satisfy this requirement.

7.3.1.  Interpreting FATTR4_SEC_LABEL

   The XDR [23] necessary to implement Labeled NFSv4 is presented below:

   const FATTR4_SEC_LABEL   = 81;

   typedef uint32_t  policy4;

                                 Figure 6

   struct labelformat_spec4 {
           policy4 lfs_lfs;
           policy4 lfs_pi;
   };

   struct sec_label_attr_info {
           labelformat_spec4       slai_lfs;
           opaque                  slai_data<>;
   };
   The FATTR4_SEC_LABEL contains an array of two components with the
   first component being an LFS.  It serves to provide the receiving end
   with the information necessary to translate the security attribute
   into a form that is usable by the endpoint.  Label Formats assigned
   an LFS may optionally choose to include a Policy Identifier field to
   allow for complex policy deployments.  The LFS and Label Format
   Registry are described in detail in [22].  The translation used to
   interpret the security attribute is not specified as part of the
   protocol as it may depend on various factors.  The second component
   is an opaque section which contains the data of the attribute.  This
   component is dependent on the MAC model to interpret and enforce.

   In particular, it is the responsibility of the LFS specification to
   define a maximum size for the opaque section, slai_data<>.  When
   creating or modifying a label for an object, the client needs to be
   guaranteed that the server will accept a label that is sized
   correctly.  By both client an atomic create and server being part of a specific MAC
   model, set operation for
   the client security attribute it is possible to enforce the second and
   fourth requirements.  The recommended attribute FATTR4_SEC_LABEL (see
   Section 11.2.2) will be aware of the size.

7.3.2. used to satisfy this requirement.

7.3.1.  Delegations

   In the event that a security attribute is changed on the server while
   a client holds a delegation on the file, the client should follow the
   existing protocol with respect to attribute changes.  It should flush
   all changes back to the server and relinquish the delegation.

7.3.3.

7.3.2.  Permission Checking

   It is not feasible to enumerate all possible MAC models and even
   levels of protection within a subset of these models.  This means
   that the NFSv4 client and servers cannot be expected to directly make
   access control decisions based on the security attribute.  Instead
   NFSv4 should defer permission checking on this attribute to the host
   system.  These checks are performed in addition to existing DAC and
   ACL checks outlined in the NFSv4 protocol.  Section 7.6 gives a
   specific example of how the security attribute is handled under a
   particular MAC model.

7.3.4.

7.3.3.  Object Creation

   When creating files in NFSv4 the OPEN and CREATE operations are used.
   One of the parameters to these operations is an fattr4 structure
   containing the attributes the file is to be created with.  This
   allows NFSv4 to atomically set the security attribute of files upon
   creation.  When a client is MAC aware it must always provide the
   initial security attribute upon file creation.  In the event that the
   server is the only MAC aware entity in the system it should ignore
   the security attribute specified by the client and instead make the
   determination itself.  A more in depth explanation can be found in
   Section 7.6.

7.3.5.

7.3.4.  Existing Objects

   Note that under the MAC model, all objects must have labels.
   Therefore, if an existing server is upgraded to include LNFS support,
   then it is the responsibility of the security system to define the
   behavior for existing objects.  For example, if the security system
   is LFS 0, which means the server just stores and returns labels, then
   existing files should return labels which are set to an empty value.

7.3.6.

7.3.5.  Label Changes

   As per the requirements, when a file's security label is modified,
   the server must notify all clients which have the file opened of the
   change in label.  It does so with CB_ATTR_CHANGED.  There are
   preconditions to making an attribute change imposed by NFSv4 and the
   security system might want to impose others.  In the process of
   meeting these preconditions, the server may chose to either serve the
   request in whole or return NFS4ERR_DELAY to the SETATTR operation.

   If there are open delegations on the file belonging to client other
   than the one making the label change, then the process described in
   Section 7.3.2 7.3.1 must be followed.

   As the server is always presented with the subject label from the
   client, it does not necessarily need to communicate the fact that the
   label has changed to the client.  In the cases where the change
   outright denies the client access, the client will be able to quickly
   determine that there is a new label in effect.  It is in cases where
   the client may share the same object between multiple subjects or a
   security system which is not strictly hierarchical that the
   CB_ATTR_CHANGED callback is very useful.  It allows the server to
   inform the clients that the cached security attribute is now stale.

   Consider a system in which the clients enforce MAC checks and and the
   server has a very simple security system which just stores the
   labels.  In this system, the MAC label check always allows access,
   regardless of the subject label.

   The way in which MAC labels are enforced is by the client.  So if
   client A changes a security label on a file, then the server MUST
   inform all clients that have the file opened that the label has
   changed via CB_ATTR_CHANGED.  Then the clients MUST retrieve the new
   label and MUST enforce access via the new attribute values.

7.4.  pNFS Considerations

   This section examines the issues in deploying LNFS in a pNFS
   community of servers.

7.4.1.  MAC Label Checks

   The new FATTR4_SEC_LABEL attribute is metadata information and as
   such the DS is not aware of the value contained on the MDS.
   Fortunately, the NFSv4.1 protocol [2] already has provisions for
   doing access level checks from the DS to the MDS.  In order for the
   DS to validate the subject label presented by the client, it SHOULD
   utilize this mechanism.

   If a file's FATTR4_SEC_LABEL is changed, then the MDS should utilize
   CB_ATTR_CHANGED to inform the client of that fact.  If the MDS is
   maintaining

7.5.  Discovery of Server LNFS Support

   The server can easily determine that a client supports LNFS when it
   queries for the FATTR4_SEC_LABEL label for an object.  Note that it
   cannot assume that the presence of RPCSEC_GSSv3 indicates LNFS
   support.  The client might need to discover which LFS the server
   supports.

   A server which supports LNFS MUST allow a client with any subject
   label to retrieve the FATTR4_SEC_LABEL attribute for the root
   filehandle, ROOTFH.  The following compound must always succeed as
   far as a MAC label check is concerned:

        PUTROOTFH, GETATTR {FATTR4_SEC_LABEL}

   Note that the server might have imposed a security flavor on the root
   that precludes such access.  I.e., if the server requires kerberized
   access and the client presents a compound with AUTH_SYS, then the
   server is allowed to return NFS4ERR_WRONGSEC in this case.  But if
   the client presents a correct security flavor, then the server MUST
   return the FATTR4_SEC_LABEL attribute with the supported LFS filled
   in.

7.6.  MAC Security NFS Modes of Operation

   A system using Labeled NFS may operate in two modes.  The first mode
   provides the most protection and is called "full mode".  In this mode
   both the client and server implement a MAC model allowing each end to
   make an access control decision.  The remaining mode is called the
   "guest mode" and in this mode one end of the connection is not
   implementing a MAC model and thus offers less protection than full
   mode.

7.6.1.  Full Mode

   Full mode environments consist of MAC aware NFSv4 servers and clients
   and may be composed of mixed MAC models and policies.  The system
   requires that both the client and server have an opportunity to
   perform an access control check based on all relevant information
   within the network.  The file object security attribute is provided
   using the mechanism described in Section 7.3.  The security attribute
   of the subject making the request is transported at the RPC layer
   using the mechanism described in RPCSECGSSv3 [5].

7.6.1.1.  Initial Labeling and Translation

   The ability to create a file is an action that a MAC model may wish
   to mediate.  The client is given the responsibility to determine the
   initial security attribute to be placed on a file.  This allows the
   client to make a decision as to the acceptable security attributes to
   create a file with before sending the request to the server.  Once
   the server receives the creation request from the client it may
   choose to evaluate if the security attribute is acceptable.

   Security attributes on the client and server may vary based on MAC
   model and policy.  To handle this the security attribute field has an
   LFS component.  This component is a mechanism for the host to
   identify the format and meaning of the opaque portion of the security
   attribute.  A full mode environment may contain hosts operating in
   several different LFSs.  In this case a mechanism for translating the
   opaque portion of the security attribute is needed.  The actual
   translation function will vary based on MAC model and policy and is
   out of the scope of this document.  If a translation is unavailable
   for a given LFS then the request SHOULD be denied.  Another recourse
   is to allow the host to provide a fallback mapping for unknown
   security attributes.

7.6.1.2.  Policy Enforcement

   In full mode access control decisions are made by both the clients
   and servers.  When a client makes a request it takes the security
   attribute from the requesting process and makes an access control
   decision based on that attribute and the security attribute of the
   object it is trying to access.  If the client denies that access an
   RPC call to the server is never made.  If however the access is
   allowed the client will make a call to the NFS server.

   When the server receives the request from the client it extracts the
   security attribute conveyed in the RPC request.  The server then uses
   this security attribute and the attribute of the object the client is
   trying to access to make an access control decision.  If the server's
   policy allows this access it will fulfill the client's request,
   otherwise it will return NFS4ERR_ACCESS.

   Implementations MAY validate security attributes supplied over the
   network to ensure that they are within a set of attributes permitted
   from a specific peer, and if not, reject them.  Note that a system
   may permit a different set of attributes to be accepted from each
   peer.

7.6.1.3.  Label Aware Only Server

   If the LFS is 0, then it indicates a server which is label aware, but
   does not enforce policies.  Such a server will store and retrieve all
   object labels presented by clients, notify the clients of any label
   changes via CB_ATTR_CHANGED, but will not restrict access via the
   subject label.  Instead, it will expect the clients to enforce all
   such access locally.

7.6.2.  Guest Mode

   Guest mode implies that either the client or the server does not
   handle labels.  If the client is not LNFS aware, then it will not
   offer subject labels to the server.  The server is the only entity
   enforcing policy, and may selectively provide standard NFS services
   to clients based on their authentication credentials and/or
   associated network attributes (e.g., IP address, network interface).
   The level of trust and access extended to a client in this mode is
   configuration-specific.  If the server is not LNFS aware, then it
   will not return object labels to the client.  Clients in this
   environment are may consist of groups implementing different MAC
   model policies.  The system requires that all clients in the
   environment be responsible for access control checks.

7.7.  Security Considerations

   This entire document deals with security issues.

   Depending on the level of protection the MAC system offers there may
   be a requirement to tightly bind the security attribute to the data.

   When only one of the client or server enforces labels, it is
   important to realize that the other side is not enforcing MAC
   protections.  Alternate methods might be in use to handle the lack of
   MAC support and care should be taken to identify and mitigate threats
   from possible tampering outside of these methods.

   An example of this is that a server that modifies READDIR or LOOKUP
   results based on the client's subject label might want to always
   construct the same subject label for a client which does not present
   one.  This will prevent a non-LNFS client from mixing entries in the
   directory cache.

8.  Sharing change attribute implementation details with NFSv4 clients

8.1.  Introduction

   Although both the NFSv4 [10] and NFSv4.1 protocol [2], define the
   change attribute as being mandatory to implement, there is little in
   the way of guidance.  The only feature that is mandated by them is
   that the value must change whenever the file data or metadata change.

   While this allows for a wide range of implementations, it also leaves
   the client with a conundrum: how does it determine which is the most
   recent value for the change attribute in a case where several RPC
   calls have been issued in parallel?  In other words if two COMPOUNDs,
   both containing WRITE and GETATTR requests for the same file, have
   been issued in parallel, how does the client determine which of the
   two change attribute values returned in the replies to the GETATTR
   requests corresponds correspond to the most recent state of the file?  In some
   cases, the only recourse may be to send another COMPOUND containing a
   third GETATTR that is fully serialised with the first two.

   NFSv4.2 avoids this kind of inefficiency by allowing the server to
   share details about how the change attribute is expected to evolve,
   so that the client may immediately determine which, out of the
   several change attribute values returned by the server, is the most
   recent.

8.2.  Definition of the 'change_attr_type' per-file system attribute

   enum change_attr_typeinfo {
              NFS4_CHANGE_TYPE_IS_MONOTONIC_INCR         = 0,
              NFS4_CHANGE_TYPE_IS_VERSION_COUNTER        = 1,
              NFS4_CHANGE_TYPE_IS_VERSION_COUNTER_NOPNFS = 2,
              NFS4_CHANGE_TYPE_IS_TIME_METADATA          = 3,
              NFS4_CHANGE_TYPE_IS_UNDEFINED              = 4
   };

        +------------------+----+---------------------------+-----+
        | Name             | Id | Data Type                 | Acc |
        +------------------+----+---------------------------+-----+
        | change_attr_type | XX | enum change_attr_typeinfo | R   |
        +------------------+----+---------------------------+-----+

   The solution enables the NFS server to provide additional information
   about how it expects the change attribute value to evolve after the
   file data or metadata has changed. 'change_attr_type' is defined as a new recommended attribute, and takes values from enum
   change_attr_typeinfo as follows:

   NFS4_CHANGE_TYPE_IS_MONOTONIC_INCR:  The change attribute value MUST
      monotonically increase for every atomic change to the file
      attributes, data or directory contents.

   NFS4_CHANGE_TYPE_IS_VERSION_COUNTER:  The change attribute value MUST
      be incremented by one unit for every atomic change to the file
      attributes, data or directory contents.  This property
   (see Section 11.2.1), and is
      preserved when writing per filesystem.

9.  Security Considerations

10.  Error Values

   NFS error numbers are assigned to pNFS data servers.

   NFS4_CHANGE_TYPE_IS_VERSION_COUNTER_NOPNFS: failed operations within a Compound
   (COMPOUND or CB_COMPOUND) request.  A Compound request contains a
   number of NFS operations that have their results encoded in sequence
   in a Compound reply.  The change attribute
      value MUST be incremented results of successful operations will
   consist of an NFS4_OK status followed by one unit for every atomic change to the file attributes, data or directory contents.  In encoded results of the case
      where
   operation.  If an NFS operation fails, an error status will be
   entered in the client is writing to pNFS data servers, reply and the number Compound request will be terminated.

10.1.  Error Definitions

                        Protocol Error Definitions

         +--------------------------+--------+------------------+
         | Error                    | Number | Description      |
         +--------------------------+--------+------------------+
         | NFS4ERR_BADLABEL         | 10093  | Section 10.1.3.1 |
         | NFS4ERR_METADATA_NOTSUPP | 10090  | Section 10.1.2.1 |
         | NFS4ERR_OFFLOAD_DENIED   | 10091  | Section 10.1.2.2 |
         | NFS4ERR_PARTNER_NO_AUTH  | 10089  | Section 10.1.2.3 |
         | NFS4ERR_PARTNER_NOTSUPP  | 10088  | Section 10.1.2.4 |
         | NFS4ERR_UNION_NOTSUPP    | 10094  | Section 10.1.1.1 |
         | NFS4ERR_WRONG_LFS        | 10092  | Section 10.1.3.2 |
         +--------------------------+--------+------------------+

                                  Table 1

10.1.1.  General Errors

   This section deals with errors that are applicable to a broad set of
      increments is not guaranteed
   different purposes.

10.1.1.1.  NFS4ERR_UNION_NOTSUPP (Error Code 10094)

   One of the arguments to exactly match the number of
      writes.

   NFS4_CHANGE_TYPE_IS_TIME_METADATA:  The change attribute operation is
      implemented as suggested in a discriminated union and
   while the NFSv4 spec [10] in terms of server supports the
      time_metadata attribute.

   NFS4_CHANGE_TYPE_IS_UNDEFINED:  The change attribute given operation, it does not take
      values that fit into any of these categories.

   If either NFS4_CHANGE_TYPE_IS_MONOTONIC_INCR,
   NFS4_CHANGE_TYPE_IS_VERSION_COUNTER, or
   NFS4_CHANGE_TYPE_IS_TIME_METADATA are set, then the client knows at support
   the very least that selected arm of the change attribute is monotonically increasing,
   which is sufficient discriminated union.  For an example, see
   READ_PLUS (Section 13.10).

10.1.2.  Server to resolve the question of which value is Server Copy Errors

   These errors deal with the
   most recent.

   If interaction between server to server
   copies.

10.1.2.1.  NFS4ERR_METADATA_NOTSUPP (Error Code 10090)

   The destination file cannot support the client sees same metadata as the value NFS4_CHANGE_TYPE_IS_TIME_METADATA, then source
   file.

10.1.2.2.  NFS4ERR_OFFLOAD_DENIED (Error Code 10091)

   The copy offload operation is supported by inspecting the value of both the 'time_delta' attribute it additionally
   has source and the option of detecting rogue server implementations that use
   time_metadata in violation of
   destination, but the spec.

   Finally, if destination is not allowing it for this file.
   If the client sees NFS4_CHANGE_TYPE_IS_VERSION_COUNTER, this error, it
   has the ability should fall back to predict what the resulting change attribute value
   should be after a COMPOUND containing normal copy
   semantics.

10.1.2.3.  NFS4ERR_PARTNER_NO_AUTH (Error Code 10089)

   The remote server does not authorize a SETATTR, WRITE, or CREATE. server-to-server copy offload
   operation.  This again allows it may be due to detect changes made in parallel by another
   client.  The value NFS4_CHANGE_TYPE_IS_VERSION_COUNTER_NOPNFS permits the same, but only if client's failure to send the client is not doing pNFS WRITEs.

9.  Security Considerations

10.  Error Values

   NFS error numbers are assigned
   COPY_NOTIFY operation to failed operations within the remote server, the remote server
   receiving a Compound
   (COMPOUND or CB_COMPOUND) request.  A Compound server-to-server copy offload request contains a
   number of after the copy
   lease time expired, or for some other permission problem.

10.1.2.4.  NFS4ERR_PARTNER_NOTSUPP (Error Code 10088)

   The remote server does not support the server-to-server copy offload
   protocol.

10.1.3.  Labeled NFS operations that have their results encoded Errors

   These errors are used in sequence LNFS.

10.1.3.1.  NFS4ERR_BADLABEL (Error Code 10093)

   The label specified is invalid in some manner.

10.1.3.2.  NFS4ERR_WRONG_LFS (Error Code 10092)

   The LFS specified in the subject label is not compatible with the LFS
   in object label.

11.  New File Attributes

11.1.  New RECOMMENDED Attributes - List and Definition References

   The list of new RECOMMENDED attributes appears in a Compound reply. Table 2.  The results
   meaning of successful operations will
   consist the columns of an NFS4_OK status followed by the encoded results table are:

   Name:  The name of the
   operation.  If an NFS operation fails, an error status will be
   entered in attribute.

   Id:  The number assigned to the reply attribute.  In the event of conflicts
      between the assigned number and [3], the Compound request will latter is likely
      authoritative, but should be terminated.

10.1.  Error Definitions

                        Protocol Error Definitions

         +--------------------------+--------+------------------+ resolved with Errata to this document
      and/or [3].  See [23] for the Errata process.

   Data Type:  The XDR data type of the attribute.

   Acc:  Access allowed to the attribute.

      R  means read-only (GETATTR may retrieve, SETATTR may not set).

      W  means write-only (SETATTR may set, GETATTR may not retrieve).

      R W   means read/write (GETATTR may retrieve, SETATTR may set).

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

   +------------------+----+-------------------+-----+----------------+
   | Error Name             | Number Id | Description Data Type         |
         +--------------------------+--------+------------------+ Acc | NFS4ERR_BADLABEL Defined in     | 10093
   +------------------+----+-------------------+-----+----------------+
   | Section 10.1.3.1 change_attr_type | 79 | NFS4ERR_METADATA_NOTSUPP change_attr_type4 | 10090 R   | Section 10.1.2.1 11.2.1 |
   | NFS4ERR_OFFLOAD_DENIED   | 10091  | Section 10.1.2.2 sec_label        | 80 | NFS4ERR_PARTNER_NO_AUTH sec_label4        | 10089 R W | Section 10.1.2.3 11.2.2 |
   | NFS4ERR_PARTNER_NOTSUPP space_reserved   | 10088 77 | Section 10.1.2.4 boolean           | R W | NFS4ERR_UNION_NOTSUPP Section 11.2.3 | 10094
   | Section 10.1.1.1 space_freed      | 78 | NFS4ERR_WRONG_LFS length4           | 10092 R   | Section 10.1.3.2 11.2.4 |
         +--------------------------+--------+------------------+
   +------------------+----+-------------------+-----+----------------+

                                  Table 1

10.1.1.  General Errors 2

11.2.  Attribute Definitions

11.2.1.  Attribute 79: change_attr_type

   enum change_attr_type4 {
              NFS4_CHANGE_TYPE_IS_MONOTONIC_INCR         = 0,
              NFS4_CHANGE_TYPE_IS_VERSION_COUNTER        = 1,
              NFS4_CHANGE_TYPE_IS_VERSION_COUNTER_NOPNFS = 2,
              NFS4_CHANGE_TYPE_IS_TIME_METADATA          = 3,
              NFS4_CHANGE_TYPE_IS_UNDEFINED              = 4
   };

   change_attr_type is a per filesystem attribute which enables the
   NFSv4.2 server to provide additional information about how it expects
   the change attribute value to evolve after the file data or metadata
   has changed.

   NFS4_CHANGE_TYPE_IS_MONOTONIC_INCR:  The change attribute value MUST
      monotonically increase for every atomic change to the file
      attributes, data or directory contents.

   NFS4_CHANGE_TYPE_IS_VERSION_COUNTER:  The change attribute value MUST
      be incremented by one unit for every atomic change to the file
      attributes, data or directory contents.  This section deals with errors that are applicable property is
      preserved when writing to pNFS data servers.

   NFS4_CHANGE_TYPE_IS_VERSION_COUNTER_NOPNFS:  The change attribute
      value MUST be incremented by one unit for every atomic change to a broad set of
   different purposes.

10.1.1.1.  NFS4ERR_UNION_NOTSUPP (Error Code 10094)

   One of
      the arguments file attributes, data or directory contents.  In the case
      where the client is writing to pNFS data servers, the operation number of
      increments is a discriminated union and
   while not guaranteed to exactly match the server supports number of
      writes.

   NFS4_CHANGE_TYPE_IS_TIME_METADATA:  The change attribute is
      implemented as suggested in the given operation, it NFSv4 spec [10] in terms of the
      time_metadata attribute.

   NFS4_CHANGE_TYPE_IS_UNDEFINED:  The change attribute does not support
   the selected arm take
      values that fit into any of these categories.

   If either NFS4_CHANGE_TYPE_IS_MONOTONIC_INCR,
   NFS4_CHANGE_TYPE_IS_VERSION_COUNTER, or
   NFS4_CHANGE_TYPE_IS_TIME_METADATA are set, then the discriminated union.  For an example, see
   READ_PLUS (Section 13.10).

10.1.2.  Server to Server Copy Errors

   These errors deal with client knows at
   the interaction between server to server
   copies.

10.1.2.1.  NFS4ERR_METADATA_NOTSUPP (Error Code 10090)

   The destination file cannot support very least that the same metadata as change attribute is monotonically increasing,
   which is sufficient to resolve the source
   file.

10.1.2.2.  NFS4ERR_OFFLOAD_DENIED (Error Code 10091)

   The copy offload operation question of which value is supported by both the source and
   most recent.

   If the
   destination, but client sees the destination is not allowing value NFS4_CHANGE_TYPE_IS_TIME_METADATA, then
   by inspecting the value of the 'time_delta' attribute it for this file.
   If additionally
   has the option of detecting rogue server implementations that use
   time_metadata in violation of the spec.

   Finally, if the client sees this error, NFS4_CHANGE_TYPE_IS_VERSION_COUNTER, it should fall back
   has the ability to predict what the normal copy
   semantics.

10.1.2.3.  NFS4ERR_PARTNER_NO_AUTH (Error Code 10089)

   The remote server does not authorize resulting change attribute value
   should be after a server-to-server copy offload
   operation. COMPOUND containing a SETATTR, WRITE, or CREATE.
   This may be due again allows it to detect changes made in parallel by another
   client.  The value NFS4_CHANGE_TYPE_IS_VERSION_COUNTER_NOPNFS permits
   the client's failure to send same, but only if the
   COPY_NOTIFY operation to client is not doing pNFS WRITEs.

11.2.2.  Attribute 80: sec_label

   typedef uint32_t  policy4;

   struct labelformat_spec4 {
           policy4 lfs_lfs;
           policy4 lfs_pi;
   };

   struct sec_label4 {
           labelformat_spec4       slai_lfs;
           opaque                  slai_data<>;
   };
   The FATTR4_SEC_LABEL contains an array of two components with the remote server,
   first component being an LFS.  It serves to provide the remote server receiving end
   with the information necessary to translate the security attribute
   into a server-to-server copy offload request after form that is usable by the copy
   lease time expired, or endpoint.  Label Formats assigned
   an LFS may optionally choose to include a Policy Identifier field to
   allow for some other permission problem.

10.1.2.4.  NFS4ERR_PARTNER_NOTSUPP (Error Code 10088) complex policy deployments.  The remote server does not support the server-to-server copy offload
   protocol.

10.1.3.  Labeled NFS Errors

   These errors LFS and Label Format
   Registry are used described in LNFS.

10.1.3.1.  NFS4ERR_BADLABEL (Error Code 10093) detail in [22].  The label translation used to
   interpret the security attribute is not specified as part of the
   protocol as it may depend on various factors.  The second component
   is an opaque section which contains the data of the attribute.  This
   component is dependent on the MAC model to interpret and enforce.

   In particular, it is invalid in some manner.

10.1.3.2.  NFS4ERR_WRONG_LFS (Error Code 10092)

   The the responsibility of the LFS specified in specification to
   define a maximum size for the subject opaque section, slai_data<>.  When
   creating or modifying a label for an object, the client needs to be
   guaranteed that the server will accept a label that is not compatible with sized
   correctly.  By both client and server being part of a specific MAC
   model, the LFS
   in object label.

11.  File Attributes

11.1.  Attribute Definitions

11.1.1. client will be aware of the size.

11.2.3.  Attribute 77: space_reserved

   The space_reserve attribute is a read/write attribute of type
   boolean.  It is a per file attribute.  When the space_reserved
   attribute is set via SETATTR, the server must ensure that there is
   disk space to accommodate every byte in the file before it can return
   success.  If the server cannot guarantee this, it must return
   NFS4ERR_NOSPC.

   If the client tries to grow a file which has the space_reserved
   attribute set, the server must guarantee that there is disk space to
   accommodate every byte in the file with the new size before it can
   return success.  If the server cannot guarantee this, it must return
   NFS4ERR_NOSPC.

   It is not required that the server allocate the space to the file
   before returning success.  The allocation can be deferred, however,
   it must be guaranteed that it will not fail for lack of space.

   The value of space_reserved can be obtained at any time through
   GETATTR.

   In order to avoid ambiguity, the space_reserve bit cannot be set
   along with the size bit in SETATTR.  Increasing the size of a file
   with space_reserve set will fail if space reservation cannot be
   guaranteed for the new size.  If the file size is decreased, space
   reservation is only guaranteed for the new size and the extra blocks
   backing the file can be released.

11.1.2.

11.2.4.  Attribute 78: space_freed

   space_freed gives the number of bytes freed if the file is deleted.
   This attribute is read only and is of type length4.  It is a per file
   attribute.

12.  Operations: REQUIRED, RECOMMENDED, or OPTIONAL

   The following tables summarize the operations of the NFSv4.2 protocol
   and the corresponding designation of REQUIRED, RECOMMENDED, and
   OPTIONAL to implement or either OBSOLETE if implemented or MUST NOT
   implement.  The designation of OBSOLETE if implemented is reserved
   for those operations which are defined in either NFSv4.0 or NFSV4.1,
   can be implemented in NFSv4.2, and are intended to be MUST NOT be
   implemented in NFSv4.3.  The designation of MUST NOT implement is
   reserved for those operations that were defined in either NFSv4.0 or
   NFSV4.1 and MUST NOT be implemented in NFSv4.2.

   For the most part, the REQUIRED, RECOMMENDED, or OPTIONAL designation
   for operations sent by the client is for the server implementation.
   The client is generally required to implement the operations needed
   for the operating environment for which it serves.  For example, a
   read-only NFSv4.2 client would have no need to implement the WRITE
   operation and is not required to do so.

   The REQUIRED or OPTIONAL designation for callback operations sent by
   the server is for both the client and server.  Generally, the client
   has the option of creating the backchannel and sending the operations
   on the fore channel that will be a catalyst for the server sending
   callback operations.  A partial exception is CB_RECALL_SLOT; the only
   way the client can avoid supporting this operation is by not creating
   a backchannel.

   Since this is a summary of the operations and their designation,
   there are subtleties that are not presented here.  Therefore, if
   there is a question of the requirements of implementation, the
   operation descriptions themselves must be consulted along with other
   relevant explanatory text within this either specification or that of
   NFSv4.1 [2].

   The abbreviations used in the second and third columns of the table
   are defined as follows.

   REQ  REQUIRED to implement

   REC  RECOMMEND to implement

   OPT  OPTIONAL to implement

   OBS  MUST NOT implement

   MNI  MUST NOT implement

   For the NFSv4.2 features that are OPTIONAL, the operations that
   support those features are OPTIONAL, and the server would return
   NFS4ERR_NOTSUPP in response to the client's use of those operations.
   If an OPTIONAL feature is supported, it is possible that a set of
   operations related to the feature become REQUIRED to implement.  The
   third column of the table designates the feature(s) and if the
   operation is REQUIRED or OPTIONAL in the presence of support for the
   feature.

   The OPTIONAL features identified and their abbreviations are as
   follows:

   pNFS  Parallel NFS

   FDELG  File Delegations

   DDELG  Directory Delegations

   COPY  Server Side Copy

   ADB  Application Data Blocks

                                Operations

   +----------------------+--------------------+-----------------------+
   | Operation            | REQ, REC, OPT, or  | Feature (REQ, REC, or |
   |                      | MNI                | OPT)                  |
   +----------------------+--------------------+-----------------------+
   | ACCESS               | REQ                |                       |
   | BACKCHANNEL_CTL      | REQ                |                       |
   | BIND_CONN_TO_SESSION | REQ                |                       |
   | CLOSE                | REQ                |                       |
   | COMMIT               | REQ                |                       |
   | COPY                 | OPT                | COPY (REQ)            |
   | COPY_ABORT           | OPT                | COPY (REQ)            |
   | COPY_NOTIFY          | OPT                | COPY (REQ)            |
   | COPY_REVOKE          | OPT                | COPY (REQ)            |
   | COPY_STATUS          | OPT                | COPY (REQ)            |
   | CREATE               | REQ                |                       |
   | CREATE_SESSION       | REQ                |                       |
   | DELEGPURGE           | OPT                | FDELG (REQ)           |
   | DELEGRETURN          | OPT                | FDELG, DDELG, pNFS    |
   |                      |                    | (REQ)                 |
   | DESTROY_CLIENTID     | REQ                |                       |
   | DESTROY_SESSION      | REQ                |                       |
   | EXCHANGE_ID          | REQ                |                       |
   | FREE_STATEID         | REQ                |                       |
   | GETATTR              | REQ                |                       |
   | GETDEVICEINFO        | OPT                | pNFS (REQ)            |
   | GETDEVICELIST        | OPT                | pNFS (OPT)            |
   | GETFH                | REQ                |                       |
   | INITIALIZE           | OPT                | ADB (REQ)             |
   | GET_DIR_DELEGATION   | OPT                | DDELG (REQ)           |
   | LAYOUTCOMMIT         | OPT                | pNFS (REQ)            |
   | LAYOUTGET            | OPT                | pNFS (REQ)            |
   | LAYOUTRETURN         | OPT                | pNFS (REQ)            |
   | LINK                 | OPT                |                       |
   | LOCK                 | REQ                |                       |
   | LOCKT                | REQ                |                       |
   | LOCKU                | REQ                |                       |
   | LOOKUP               | REQ                |                       |
   | LOOKUPP              | REQ                |                       |
   | NVERIFY              | REQ                |                       |
   | OPEN                 | REQ                |                       |
   | OPENATTR             | OPT                |                       |
   | OPEN_CONFIRM         | MNI                |                       |
   | OPEN_DOWNGRADE       | REQ                |                       |
   | PUTFH                | REQ                |                       |
   | PUTPUBFH             | REQ                |                       |
   | PUTROOTFH            | REQ                |                       |
   | READ                 | OPT OBS                |                       |
   | READDIR              | REQ                |                       |
   | READLINK             | OPT                |                       |
   | READ_PLUS            | OPT                | ADB (REQ)             |
   | RECLAIM_COMPLETE     | REQ                |                       |
   | RELEASE_LOCKOWNER    | MNI                |                       |
   | REMOVE               | REQ                |                       |
   | RENAME               | REQ                |                       |
   | RENEW                | MNI                |                       |
   | RESTOREFH            | REQ                |                       |
   | SAVEFH               | REQ                |                       |
   | SECINFO              | REQ                |                       |
   | SECINFO_NO_NAME      | REC                | pNFS file layout      |
   |                      |                    | (REQ)                 |
   | SEQUENCE             | REQ                |                       |
   | SETATTR              | REQ                |                       |
   | SETCLIENTID          | MNI                |                       |
   | SETCLIENTID_CONFIRM  | MNI                |                       |
   | SET_SSV              | REQ                |                       |
   | TEST_STATEID         | REQ                |                       |
   | VERIFY               | REQ                |                       |
   | WANT_DELEGATION      | OPT                | FDELG (OPT)           |
   | WRITE                | REQ                |                       |
   +----------------------+--------------------+-----------------------+

                            Callback Operations

   +-------------------------+-------------------+---------------------+
   | Operation               | REQ, REC, OPT, or | Feature (REQ, REC,  |
   |                         | MNI               | or OPT)             |
   +-------------------------+-------------------+---------------------+
   | CB_COPY                 | OPT               | COPY (REQ)          |
   | CB_GETATTR              | OPT               | FDELG (REQ)         |
   | CB_LAYOUTRECALL         | OPT               | pNFS (REQ)          |
   | CB_NOTIFY               | OPT               | DDELG (REQ)         |
   | CB_NOTIFY_DEVICEID      | OPT               | pNFS (OPT)          |
   | CB_NOTIFY_LOCK          | OPT               |                     |
   | CB_PUSH_DELEG           | OPT               | FDELG (OPT)         |
   | CB_RECALL               | OPT               | FDELG, DDELG, pNFS  |
   |                         |                   | (REQ)               |
   | CB_RECALL_ANY           | OPT               | FDELG, DDELG, pNFS  |
   |                         |                   | (REQ)               |
   | CB_RECALL_SLOT          | REQ               |                     |
   | CB_RECALLABLE_OBJ_AVAIL | OPT               | DDELG, pNFS (REQ)   |
   | CB_SEQUENCE             | OPT               | FDELG, DDELG, pNFS  |
   |                         |                   | (REQ)               |
   | CB_WANTS_CANCELLED      | OPT               | FDELG, DDELG, pNFS  |
   |                         |                   | (REQ)               |
   +-------------------------+-------------------+---------------------+

13.  NFSv4.2 Operations

13.1.  Operation 59: COPY - Initiate a server-side copy
13.1.1.  ARGUMENT

   const COPY4_GUARDED     = 0x00000001;
   const COPY4_METADATA    = 0x00000002;

   struct COPY4args {
           /* SAVED_FH: source file */
           /* CURRENT_FH: destination file or */
           /*             directory           */
           offset4         ca_src_offset;
           offset4         ca_dst_offset;
           length4         ca_count;
           uint32_t        ca_flags;
           component4      ca_destination;
           netloc4         ca_source_server<>;
   };

13.1.2.  RESULT

   union COPY4res switch (nfsstat4 cr_status) {
           case NFS4_OK:
                   stateid4        cr_callback_id<1>;
           default:
                   length4         cr_bytes_copied;
   };

13.1.3.  DESCRIPTION

   The COPY operation is used for both intra-server and inter-server
   copies.  In both cases, the COPY is always sent from the client to
   the destination server of the file copy.  The COPY operation requests
   that a file be copied from the location specified by the SAVED_FH
   value to the location specified by the combination of CURRENT_FH and
   ca_destination.

   The SAVED_FH must be a regular file.  If SAVED_FH is not a regular
   file, the operation MUST fail and return NFS4ERR_WRONG_TYPE.

   In order to set SAVED_FH to the source file handle, the compound
   procedure requesting the COPY will include a sub-sequence of
   operations such as

      PUTFH source-fh
      SAVEFH

   If the request is for a server-to-server copy, the source-fh is a
   filehandle from the source server and the compound procedure is being
   executed on the destination server.  In this case, the source-fh is a
   foreign filehandle on the server receiving the COPY request.  If
   either PUTFH or SAVEFH checked the validity of the filehandle, the
   operation would likely fail and return NFS4ERR_STALE.

   In order to avoid this problem, the minor version incorporating the
   COPY operations will need to make a few small changes in the handling
   of existing operations.  If a server supports the server-to-server
   COPY feature, a PUTFH followed by a SAVEFH MUST NOT return
   NFS4ERR_STALE for either operation.  These restrictions do not pose
   substantial difficulties for servers.  The CURRENT_FH and SAVED_FH
   may be validated in the context of the operation referencing them and
   an NFS4ERR_STALE error returned for an invalid file handle at that
   point.

   The CURRENT_FH and ca_destination together specify the destination of
   the copy operation.  If ca_destination is of 0 (zero) length, then
   CURRENT_FH specifies the target file.  In this case, CURRENT_FH MUST
   be a regular file and not a directory.  If ca_destination is not of 0
   (zero) length, the ca_destination argument specifies the file name to
   which the data will be copied within the directory identified by
   CURRENT_FH.  In this case, CURRENT_FH MUST be a directory and not a
   regular file.

   If the file named by ca_destination does not exist and the operation
   completes successfully, the file will be visible in the file system
   namespace.  If the file does not exist and the operation fails, the
   file MAY be visible in the file system namespace depending on when
   the failure occurs and on the implementation of the NFS server
   receiving the COPY operation.  If the ca_destination name cannot be
   created in the destination file system (due to file name
   restrictions, such as case or length), the operation MUST fail.

   The ca_src_offset is the offset within the source file from which the
   data will be read, the ca_dst_offset is the offset within the
   destination file to which the data will be written, and the ca_count
   is the number of bytes that will be copied.  An offset of 0 (zero)
   specifies the start of the file.  A count of 0 (zero) requests that
   all bytes from ca_src_offset through EOF be copied to the
   destination.  If concurrent modifications to the source file overlap
   with the source file region being copied, the data copied may include
   all, some, or none of the modifications.  The client can use standard
   NFS operations (e.g., OPEN with OPEN4_SHARE_DENY_WRITE or mandatory
   byte range locks) to protect against concurrent modifications if the
   client is concerned about this.  If the source file's end of file is
   being modified in parallel with a copy that specifies a count of 0
   (zero) bytes, the amount of data copied is implementation dependent
   (clients may guard against this case by specifying a non-zero count
   value or preventing modification of the source file as mentioned
   above).

   If the source offset or the source offset plus count is greater than
   or equal to the size of the source file, the operation will fail with
   NFS4ERR_INVAL.  The destination offset or destination offset plus
   count may be greater than the size of the destination file.  This
   allows for the client to issue parallel copies to implement
   operations such as "cat file1 file2 file3 file4 > dest".

   If the destination file is created as a result of this command, the
   destination file's size will be equal to the number of bytes
   successfully copied.  If the destination file already existed, the
   destination file's size may increase as a result of this operation
   (e.g. if ca_dst_offset plus ca_count is greater than the
   destination's initial size).

   If the ca_source_server list is specified, then this is an inter-
   server copy operation and the source file is on a remote server.  The
   client is expected to have previously issued a successful COPY_NOTIFY
   request to the remote source server.  The ca_source_server list
   SHOULD be the same as the COPY_NOTIFY response's cnr_source_server
   list.  If the client includes the entries from the COPY_NOTIFY
   response's cnr_source_server list in the ca_source_server list, the
   source server can indicate a specific copy protocol for the
   destination server to use by returning a URL, which specifies both a
   protocol service and server name.  Server-to-server copy protocol
   considerations are described in Section 2.2.3 and Section 2.4.1.

   The ca_flags argument allows the copy operation to be customized in
   the following ways using the guarded flag (COPY4_GUARDED) and the
   metadata flag (COPY4_METADATA).

   If the guarded flag is set and the destination exists on the server,
   this operation will fail with NFS4ERR_EXIST.

   If the guarded flag is not set and the destination exists on the
   server, the behavior is implementation dependent.

   If the metadata flag is set and the client is requesting a whole file
   copy (i.e., ca_count is 0 (zero)), a subset of the destination file's
   attributes MUST be the same as the source file's corresponding
   attributes and a subset of the destination file's attributes SHOULD
   be the same as the source file's corresponding attributes.  The
   attributes in the MUST and SHOULD copy subsets will be defined for
   each NFS version.

   For NFSv4.1, NFSv4.2, Table 2 3 and Table 3 4 list the REQUIRED and RECOMMENDED
   attributes respectively.  A "MUST" in the "Copy to destination file?"
   column indicates that the attribute is part of the MUST copy set.  A
   "SHOULD" in the "Copy to destination file?" column indicates that the
   attribute is part of the SHOULD copy set.

          +--------------------+----+---------------------------+
          | Name               | Id | Copy to destination file? |
          +--------------------+----+---------------------------+
          | supported_attrs    | 0  | no                        |
          | type               | 1  | MUST                      |
          | fh_expire_type     | 2  | no                        |
          | change             | 3  | SHOULD                    |
          | size               | 4  | MUST                      |
          | link_support       | 5  | no                        |
          | symlink_support    | 6  | no                        |
          | named_attr         | 7  | no                        |
          | fsid               | 8  | no                        |
          | unique_handles     | 9  | no                        |
          | lease_time         | 10 | no                        |
          | rdattr_error       | 11 | no                        |
          | filehandle         | 19 | no                        |
          | suppattr_exclcreat | 75 | no                        |
          +--------------------+----+---------------------------+

                                  Table 2 3

          +--------------------+----+---------------------------+
          | Name               | Id | Copy to destination file? |
          +--------------------+----+---------------------------+
          | acl                | 12 | MUST                      |
          | aclsupport         | 13 | no                        |
          | archive            | 14 | no                        |
          | cansettime         | 15 | no                        |
          | case_insensitive   | 16 | no                        |
          | case_preserving    | 17 | no                        |
          | change_attr_type   | 79 | no                        |
          | change_policy      | 60 | no                        |
          | chown_restricted   | 18 | MUST                      |
          | dacl               | 58 | MUST                      |
          | dir_notif_delay    | 56 | no                        |
          | dirent_notif_delay | 57 | no                        |
          | fileid             | 20 | no                        |
          | files_avail        | 21 | no                        |
          | files_free         | 22 | no                        |
          | files_total        | 23 | no                        |
          | fs_charset_cap     | 76 | no                        |
          | fs_layout_type     | 62 | no                        |
          | fs_locations       | 24 | no                        |
          | fs_locations_info  | 67 | no                        |
          | fs_status          | 61 | no                        |
          | hidden             | 25 | MUST                      |
          | homogeneous        | 26 | no                        |
          | layout_alignment   | 66 | no                        |
          | layout_blksize     | 65 | no                        |
          | layout_hint        | 63 | no                        |
          | layout_type        | 64 | no                        |
          | maxfilesize        | 27 | no                        |
          | maxlink            | 28 | no                        |
          | maxname            | 29 | no                        |
          | maxread            | 30 | no                        |
          | maxwrite           | 31 | no                        |
          | mdsthreshold       | 68 | no                        |
          | mimetype           | 32 | MUST                      |
          | mode               | 33 | MUST                      |
          | mode_set_masked    | 74 | no                        |
          | mounted_on_fileid  | 55 | no                        |
          | no_trunc           | 34 | no                        |
          | numlinks           | 35 | no                        |
          | owner              | 36 | MUST                      |
          | owner_group        | 37 | MUST                      |
          | quota_avail_hard   | 38 | no                        |
          | quota_avail_soft   | 39 | no                        |
          | quota_used         | 40 | no                        |
          | rawdev             | 41 | no                        |
          | retentevt_get      | 71 | MUST                      |
          | retentevt_set      | 72 | no                        |
          | retention_get      | 69 | MUST                      |
          | retention_hold     | 73 | MUST                      |
          | retention_set      | 70 | no                        |
          | sacl               | 59 | MUST                      |
          | sec_label          | 80 | MUST                      |
          | space_avail        | 42 | no                        |
          | space_free         | 43 | no                        |
          | space_freed        | 78 | no                        |
          | space_reserved     | 77 | MUST                      |
          | space_total        | 44 | no                        |
          | space_used         | 45 | no                        |
          | system             | 46 | MUST                      |
          | time_access        | 47 | MUST                      |
          | time_access_set    | 48 | no                        |
          | time_backup        | 49 | no                        |
          | time_create        | 50 | MUST                      |
          | time_delta         | 51 | no                        |
          | time_metadata      | 52 | SHOULD                    |
          | time_modify        | 53 | MUST                      |
          | time_modify_set    | 54 | no                        |
          +--------------------+----+---------------------------+

                                  Table 3 4

   [NOTE: The source file's attribute values will take precedence over
   any attribute values inherited by the destination file.]

   In the case of an inter-server copy or an intra-server copy between
   file systems, the attributes supported for the source file and
   destination file could be different.  By definition,the REQUIRED
   attributes will be supported in all cases.  If the metadata flag is
   set and the source file has a RECOMMENDED attribute that is not
   supported for the destination file, the copy MUST fail with
   NFS4ERR_ATTRNOTSUPP.

   Any attribute supported by the destination server that is not set on
   the source file SHOULD be left unset.

   Metadata attributes not exposed via the NFS protocol SHOULD be copied
   to the destination file where appropriate.

   The destination file's named attributes are not duplicated from the
   source file.  After the copy process completes, the client MAY
   attempt to duplicate named attributes using standard NFSv4
   operations.  However, the destination file's named attribute
   capabilities MAY be different from the source file's named attribute
   capabilities.

   If the metadata flag is not set and the client is requesting a whole
   file copy (i.e., ca_count is 0 (zero)), the destination file's
   metadata is implementation dependent.

   If the client is requesting a partial file copy (i.e., ca_count is
   not 0 (zero)), the client SHOULD NOT set the metadata flag and the
   server MUST ignore the metadata flag.

   If the operation does not result in an immediate failure, the server
   will return NFS4_OK, and the CURRENT_FH will remain the destination's
   filehandle.

   If an immediate failure does occur, cr_bytes_copied will be set to
   the number of bytes copied to the destination file before the error
   occurred.  The cr_bytes_copied value indicates the number of bytes
   copied but not which specific bytes have been copied.

   A return of NFS4_OK indicates that either the operation is complete
   or the operation was initiated and a callback will be used to deliver
   the final status of the operation.

   If the cr_callback_id is returned, this indicates that the operation
   was initiated and a CB_COPY callback will deliver the final results
   of the operation.  The cr_callback_id stateid is termed a copy
   stateid in this context.  The server is given the option of returning
   the results in a callback because the data may require a relatively
   long period of time to copy.

   If no cr_callback_id is returned, the operation completed
   synchronously and no callback will be issued by the server.  The
   completion status of the operation is indicated by cr_status.

   If the copy completes successfully, either synchronously or
   asynchronously, the data copied from the source file to the
   destination file MUST appear identical to the NFS client.  However,
   the NFS server's on disk representation of the data in the source
   file and destination file MAY differ.  For example, the NFS server
   might encrypt, compress, deduplicate, or otherwise represent the on
   disk data in the source and destination file differently.

   In the event of a failure the state of the destination file is
   implementation dependent.  The COPY operation may fail for the
   following reasons (this is a partial list).

   o  NFS4ERR_MOVED

   o  NFS4ERR_NOTSUPP

   o  NFS4ERR_PARTNER_NOTSUPP

   o  NFS4ERR_OFFLOAD_DENIED

   o  NFS4ERR_PARTNER_NO_AUTH

   o  NFS4ERR_FBIG

   o  NFS4ERR_NOTDIR

   o  NFS4ERR_WRONG_TYPE

   o  NFS4ERR_ISDIR

   o  NFS4ERR_INVAL

   o  NFS4ERR_DELAY
   o  NFS4ERR_METADATA_NOTSUPP

   o  NFS4ERR_WRONGSEC

13.2.  Operation 60: COPY_ABORT - Cancel a server-side copy

13.2.1.  ARGUMENT

   struct COPY_ABORT4args {
           /* CURRENT_FH: desination file */
           stateid4        caa_stateid;
   };

13.2.2.  RESULT

   struct COPY_ABORT4res {
           nfsstat4        car_status;
   };

13.2.3.  DESCRIPTION

   COPY_ABORT is used for both intra- and inter-server asynchronous
   copies.  The COPY_ABORT operation allows the client to cancel a
   server-side copy operation that it initiated.  This operation is sent
   in a COMPOUND request from the client to the destination server.
   This operation may be used to cancel a copy when the application that
   requested the copy exits before the operation is completed or for
   some other reason.

   The request contains the filehandle and copy stateid cookies that act
   as the context for the previously initiated copy operation.

   The result's car_status field indicates whether the cancel was
   successful or not.  A value of NFS4_OK indicates that the copy
   operation was canceled and no callback will be issued by the server.
   A copy operation that is successfully canceled may result in none,
   some, or all of the data copied.

   If the server supports asynchronous copies, the server is REQUIRED to
   support the COPY_ABORT operation.

   The COPY_ABORT operation may fail for the following reasons (this is
   a partial list):

   o  NFS4ERR_NOTSUPP
   o  NFS4ERR_RETRY

   o  NFS4ERR_COMPLETE_ALREADY

   o  NFS4ERR_SERVERFAULT

13.3.  Operation 61: COPY_NOTIFY - Notify a source server of a future
       copy

13.3.1.  ARGUMENT

   struct COPY_NOTIFY4args {
           /* CURRENT_FH: source file */
           netloc4         cna_destination_server;
   };

13.3.2.  RESULT

   struct COPY_NOTIFY4resok {
           nfstime4        cnr_lease_time;
           netloc4         cnr_source_server<>;
   };

   union COPY_NOTIFY4res switch (nfsstat4 cnr_status) {
           case NFS4_OK:
                   COPY_NOTIFY4resok       resok4;
           default:
                   void;
   };

13.3.3.  DESCRIPTION

   This operation is used for an inter-server copy.  A client sends this
   operation in a COMPOUND request to the source server to authorize a
   destination server identified by cna_destination_server to read the
   file specified by CURRENT_FH on behalf of the given user.

   The cna_destination_server MUST be specified using the netloc4
   network location format.  The server is not required to resolve the
   cna_destination_server address before completing this operation.

   If this operation succeeds, the source server will allow the
   cna_destination_server to copy the specified file on behalf of the
   given user.  If COPY_NOTIFY succeeds, the destination server is
   granted permission to read the file as long as both of the following
   conditions are met:

   o  The destination server begins reading the source file before the
      cnr_lease_time expires.  If the cnr_lease_time expires while the
      destination server is still reading the source file, the
      destination server is allowed to finish reading the file.

   o  The client has not issued a COPY_REVOKE for the same combination
      of user, filehandle, and destination server.

   The cnr_lease_time is chosen by the source server.  A cnr_lease_time
   of 0 (zero) indicates an infinite lease.  To renew the copy lease
   time the client should resend the same copy notification request to
   the source server.

   To avoid the need for synchronized clocks, copy lease times are
   granted by the server as a time delta.  However, there is a
   requirement that the client and server clocks do not drift
   excessively over the duration of the lease.  There is also the issue
   of propagation delay across the network which could easily be several
   hundred milliseconds as well as the possibility that requests will be
   lost and need to be retransmitted.

   To take propagation delay into account, the client should subtract it
   from copy lease times (e.g., if the client estimates the one-way
   propagation delay as 200 milliseconds, then it can assume that the
   lease is already 200 milliseconds old when it gets it).  In addition,
   it will take another 200 milliseconds to get a response back to the
   server.  So the client must send a lease renewal or send the copy
   offload request to the cna_destination_server at least 400
   milliseconds before the copy lease would expire.  If the propagation
   delay varies over the life of the lease (e.g., the client is on a
   mobile host), the client will need to continuously subtract the
   increase in propagation delay from the copy lease times.

   The server's copy lease period configuration should take into account
   the network distance of the clients that will be accessing the
   server's resources.  It is expected that the lease period will take
   into account the network propagation delays and other network delay
   factors for the client population.  Since the protocol does not allow
   for an automatic method to determine an appropriate copy lease
   period, the server's administrator may have to tune the copy lease
   period.

   A successful response will also contain a list of names, addresses,
   and URLs called cnr_source_server, on which the source is willing to
   accept connections from the destination.  These might not be
   reachable from the client and might be located on networks to which
   the client has no connection.

   If the client wishes to perform an inter-server copy, the client MUST
   send a COPY_NOTIFY to the source server.  Therefore, the source
   server MUST support COPY_NOTIFY.

   For a copy only involving one server (the source and destination are
   on the same server), this operation is unnecessary.

   The COPY_NOTIFY operation may fail for the following reasons (this is
   a partial list):

   o  NFS4ERR_MOVED

   o  NFS4ERR_NOTSUPP

   o  NFS4ERR_WRONGSEC

13.4.  Operation 62: COPY_REVOKE - Revoke a destination server's copy
       privileges

13.4.1.  ARGUMENT

   struct COPY_REVOKE4args {
           /* CURRENT_FH: source file */
           netloc4         cra_destination_server;
   };

13.4.2.  RESULT

   struct COPY_REVOKE4res {
           nfsstat4        crr_status;
   };

13.4.3.  DESCRIPTION

   This operation is used for an inter-server copy.  A client sends this
   operation in a COMPOUND request to the source server to revoke the
   authorization of a destination server identified by
   cra_destination_server from reading the file specified by CURRENT_FH
   on behalf of given user.  If the cra_destination_server has already
   begun copying the file, a successful return from this operation
   indicates that further access will be prevented.

   The cra_destination_server MUST be specified using the netloc4
   network location format.  The server is not required to resolve the
   cra_destination_server address before completing this operation.

   The COPY_REVOKE operation is useful in situations in which the source
   server granted a very long or infinite lease on the destination
   server's ability to read the source file and all copy operations on
   the source file have been completed.

   For a copy only involving one server (the source and destination are
   on the same server), this operation is unnecessary.

   If the server supports COPY_NOTIFY, the server is REQUIRED to support
   the COPY_REVOKE operation.

   The COPY_REVOKE operation may fail for the following reasons (this is
   a partial list):

   o  NFS4ERR_MOVED

   o  NFS4ERR_NOTSUPP

13.5.  Operation 63: COPY_STATUS - Poll for status of a server-side copy

13.5.1.  ARGUMENT

   struct COPY_STATUS4args {
           /* CURRENT_FH: destination file */
           stateid4        csa_stateid;
   };

13.5.2.  RESULT

   struct COPY_STATUS4resok {
           length4         csr_bytes_copied;
           nfsstat4        csr_complete<1>;
   };

   union COPY_STATUS4res switch (nfsstat4 csr_status) {
           case NFS4_OK:
                   COPY_STATUS4resok       resok4;
           default:
                   void;
   };

13.5.3.  DESCRIPTION

   COPY_STATUS is used for both intra- and inter-server asynchronous
   copies.  The COPY_STATUS operation allows the client to poll the
   server to determine the status of an asynchronous copy operation.
   This operation is sent by the client to the destination server.

   If this operation is successful, the number of bytes copied are
   returned to the client in the csr_bytes_copied field.  The
   csr_bytes_copied value indicates the number of bytes copied but not
   which specific bytes have been copied.

   If the optional csr_complete field is present, the copy has
   completed.  In this case the status value indicates the result of the
   asynchronous copy operation.  In all cases, the server will also
   deliver the final results of the asynchronous copy in a CB_COPY
   operation.

   The failure of this operation does not indicate the result of the
   asynchronous copy in any way.

   If the server supports asynchronous copies, the server is REQUIRED to
   support the COPY_STATUS operation.

   The COPY_STATUS operation may fail for the following reasons (this is
   a partial list):

   o  NFS4ERR_NOTSUPP

   o  NFS4ERR_BAD_STATEID

   o  NFS4ERR_EXPIRED

13.6.  Modification to Operation 42: EXCHANGE_ID - Instantiate Client ID

13.6.1.  ARGUMENT

      /* new */
      const EXCHGID4_FLAG_SUPP_FENCE_OPS      = 0x00000004;

13.6.2.  RESULT

      Unchanged

13.6.3.  MOTIVATION

   Enterprise applications require guarantees that an operation has
   either aborted or completed.  NFSv4.1 provides this guarantee as long
   as the session is alive: simply send a SEQUENCE operation on the same
   slot with a new sequence number, and the successful return of
   SEQUENCE indicates the previous operation has completed.  However, if
   the session is lost, there is no way to know when any in progress
   operations have aborted or completed.  In hindsight, the NFSv4.1
   specification should have mandated that DESTROY_SESSION abort/
   complete all outstanding operations.

13.6.4.  DESCRIPTION

   A client SHOULD request the EXCHGID4_FLAG_SUPP_FENCE_OPS capability
   when it sends an EXCHANGE_ID operation.  The server SHOULD set this
   capability in the EXCHANGE_ID reply whether the client requests it or
   not.  If the client ID is created with this capability then the
   following will occur:

   o  The server will not reply to DESTROY_SESSION until all operations
      in progress are completed or aborted.

   o  The server will not reply to subsequent EXCHANGE_ID invoked on the
      same Client Owner with a new verifier until all operations in
      progress on the Client ID's session are completed or aborted.

   o  When DESTROY_CLIENTID is invoked, if there are sessions (both idle
      and non-idle), opens, locks, delegations, layouts, and/or wants
      (Section 18.49) 18.49 of [2]) associated with the client ID are removed.
      Pending operations will be completed or aborted before the
      sessions, opens, locks, delegations, layouts, and/or wants are
      deleted.

   o  The NFS server SHOULD support client ID trunking, and if it does
      and the EXCHGID4_FLAG_SUPP_FENCE_OPS capability is enabled, then a
      session ID created on one node of the storage cluster MUST be
      destroyable via DESTROY_SESSION.  In addition, DESTROY_CLIENTID
      and an EXCHANGE_ID with a new verifier affects all sessions
      regardless what node the sessions were created on.

13.7.  Operation 64: INITIALIZE

   This operation can be used to initialize the structure imposed by an
   application onto a file, i.e., ADBs, and to punch a hole into a file.

13.7.1.  ARGUMENT

   /*
    * We use data_content4 in case we wish to
    * extend new types later. Note that we
    * are explicitly disallowing data.
    */
   union initialize_arg4 switch (data_content4 content) {
   case NFS4_CONTENT_APP_BLOCK:
           app_data_block4 ia_adb;
   case NFS4_CONTENT_HOLE:
           data_info4      ia_hole;
   default:
           void;
   };

   struct INITIALIZE4args {
           /* CURRENT_FH: file */
           stateid4        ia_stateid;
           stable_how4     ia_stable;
           initialize_arg4 ia_data<>;
   };

13.7.2.  RESULT

   struct INITIALIZE4resok {
           count4          ir_count;
           stable_how4     ir_committed;
           verifier4       ir_writeverf;
           data_content4   ir_sparse;
   };

   union INITIALIZE4res switch (nfsstat4 status) {
   case NFS4_OK:
           INITIALIZE4resok        resok4;
   default:
           void;
   };

13.7.3.  DESCRIPTION

   Using the data_content4 (Section 6.1.2), INITIALIZE can be used
   either to punch holes or to impose ADB structure on a file.

13.7.3.1.  Hole punching

   Whenever a client wishes to zero the blocks backing a particular
   region in the file, it calls the INITIALIZE operation with the
   current filehandle set to the filehandle of the file in question, and
   the equivalent of start offset and length in bytes of the region set
   in ia_hole.di_offset and ia_hole.di_length respectively.  If the
   ia_hole.di_allocated is set to TRUE, then the blocks will be zeroed
   and if it is set to FALSE, then they will be deallocated.  All
   further reads to this region MUST return zeros until overwritten.
   The filehandle specified must be that of a regular file.

   Situations may arise where di_offset and/or di_offset + di_length
   will not be aligned to a boundary that the server does allocations/
   deallocations in.  For most filesystems, this is the block size of
   the file system.  In such a case, the server can deallocate as many
   bytes as it can in the region.  The blocks that cannot be deallocated
   MUST be zeroed.  Except for the block deallocation and maximum hole
   punching capability, a INITIALIZE operation is to be treated similar
   to a write of zeroes.

   The server is not required to complete deallocating the blocks
   specified in the operation before returning.  It is acceptable to
   have the deallocation be deferred.  In fact, INITIALIZE is merely a
   hint; it is valid for a server to return success without ever doing
   anything towards deallocating the blocks backing the region
   specified.  However, any future reads to the region MUST return
   zeroes.

   If used to hole punch, INITIALIZE will result in the space_used
   attribute being decreased by the number of bytes that were
   deallocated.  The space_freed attribute may or may not decrease,
   depending on the support and whether the blocks backing the specified
   range were shared or not.  The size attribute will remain unchanged.

   The INITIALIZE operation MUST NOT change the space reservation
   guarantee of the file.  While the server can deallocate the blocks
   specified by di_offset and di_length, future writes to this region
   MUST NOT fail with NFSERR_NOSPC.

   The INITIALIZE operation may fail for the following reasons (this is
   a partial list):

   NFS4ERR_NOTSUPP  The Hole punch operations are not supported by the
      NFS server receiving this request.

   NFS4ERR_DIR  The current filehandle is of type NF4DIR.

   NFS4ERR_SYMLINK  The current filehandle is of type NF4LNK.

   NFS4ERR_WRONG_TYPE  The current filehandle does not designate an
      ordinary file.

13.7.3.2.  ADBs

   If the server supports ADBs, then it MUST support the
   NFS4_CONTENT_APP_BLOCK arm of the INITIALIZE operation.  The server
   has no concept of the structure imposed by the application.  It is
   only when the application writes to a section of the file does order
   get imposed.  In order to detect corruption even before the
   application utilizes the file, the application will want to
   initialize a range of ADBs using INITIALIZE.

   For ADBs, when the client invokes the INITIALIZE operation, it has
   two desired results:

   1.  The structure described by the app_data_block4 be imposed on the
       file.

   2.  The contents described by the app_data_block4 be sparse.

   If the server supports the INITIALIZE operation, it still might not
   support sparse files.  So if it receives the INITIALIZE operation,
   then it MUST populate the contents of the file with the initialized
   ADBs.

   If the data was already initialized, there are two interesting
   scenarios:

   1.  The data blocks are allocated.

   2.  Initializing in the middle of an existing ADB.

   If the data blocks were already allocated, then the INITIALIZE is a
   hole punch operation.  If INITIALIZE supports sparse files, then the
   data blocks are to be deallocated.  If not, then the data blocks are
   to be rewritten in the indicated ADB format.

   Since the server has no knowledge of ADBs, it should not report
   misaligned creation of ADBs.  Even while it can detect them, it
   cannot disallow them, as the application might be in the process of
   changing the size of the ADBs.  Thus the server must be prepared to
   handle an INITIALIZE into an existing ADB.

   This document does not mandate the manner in which the server stores
   ADBs sparsely for a file.  It does assume that if ADBs are stored
   sparsely, then the server can detect when an INITIALIZE arrives that
   will force a new ADB to start inside an existing ADB.  For example,
   assume that ADBi has a adb_block_size of 4k and that an INITIALIZE
   starts 1k inside ADBi.  The server should [[Comment.5: [[Comment.2: Need to flesh
   this out. --TH]]

13.8.  Operation 67: IO_ADVISE - Application I/O access pattern hints

   This section introduces a new operation, named IO_ADVISE, which
   allows NFS clients to communicate application I/O access pattern
   hints to the NFS server.  This new operation will allow hints to be
   sent to the server when applications use posix_fadvise, direct I/O,
   or at any other point at which the client finds useful.

13.8.1.  ARGUMENT

   enum IO_ADVISE_type4 {
           IO_ADVISE4_NORMAL                       = 0,
           IO_ADVISE4_SEQUENTIAL                   = 1,
           IO_ADVISE4_SEQUENTIAL_BACKWARDS         = 2,
           IO_ADVISE4_RANDOM                       = 3,
           IO_ADVISE4_WILLNEED                     = 4,
           IO_ADVISE4_WILLNEED_OPPORTUNISTIC       = 5,
           IO_ADVISE4_DONTNEED                     = 6,
           IO_ADVISE4_NOREUSE                      = 7,
           IO_ADVISE4_READ                         = 8,
           IO_ADVISE4_WRITE                        = 9,
           IO_ADVISE4_INIT_PROXIMITY               = 10
   };

   struct IO_ADVISE4args {
           /* CURRENT_FH: file */
           stateid4        iar_stateid;
           offset4         iar_offset;
           length4         iar_count;
           bitmap4         iar_hints;
   };

13.8.2.  RESULT

   struct IO_ADVISE4resok {
           bitmap4 ior_hints;
   };

   union IO_ADVISE4res switch (nfsstat4 _status) {
   case NFS4_OK:
           IO_ADVISE4resok resok4;
   default:
           void;
   };

13.8.3.  DESCRIPTION

   The IO_ADVISE operation sends an I/O access pattern hint to the
   server for the owner of stated for a given byte range specified by
   iar_offset and iar_count.  The byte range specified by iar_offset and
   iar_count need not currently exist in the file, but the iar_hints
   will apply to the byte range when it does exist.  If iar_count is 0,
   all data following iar_offset is specified.  The server MAY ignore
   the advice.

   The following are the possible hints:

   IO_ADVISE4_NORMAL  Specifies that the application has no advice to
      give on its behavior with respect to the specified data.  It is
      the default characteristic if no advice is given.

   IO_ADVISE4_SEQUENTIAL  Specifies that the stated holder expects to
      access the specified data sequentially from lower offsets to
      higher offsets.

   IO_ADVISE4_SEQUENTIAL BACKWARDS  Specifies that the stated holder
      expects to access the specified data sequentially from higher
      offsets to lower offsets.

   IO_ADVISE4_RANDOM  Specifies that the stated holder expects to access
      the specified data in a random order.

   IO_ADVISE4_WILLNEED  Specifies that the stated holder expects to
      access the specified data in the near future.

   IO_ADVISE4_WILLNEED_OPPORTUNISTIC  Specifies that the stated holder
      expects to possibly access the data in the near future.  This is a
      speculative hint, and therefore the server should prefetch data or
      indirect blocks only if it can be done at a marginal cost.

   IO_ADVISE_DONTNEED  Specifies that the stated holder expects that it
      will not access the specified data in the near future.

   IO_ADVISE_NOREUSE  Specifies that the stated holder expects to access
      the specified data once and then not reuse it thereafter.

   IO_ADVISE4_READ  Specifies that the stated holder expects to read the
      specified data in the near future.

   IO_ADVISE4_WRITE  Specifies that the stated holder expects to write
      the specified data in the near future.

   IO_ADVISE4_INIT_PROXIMITY  The client has recently accessed the byte
      range in its own cache.  This informs the server that the data in
      the byte range remains important to the client.  When the server
      reaches resource exhaustion, knowing which data is more important
      allows the server to make better choices about which data to, for
      example purge from a cache, or move to secondary storage.  It also
      informs the server which delegations are more important, since if
      delegations are working correctly, once delegated to a client, a
      server might never receive another I/O request for the file.

   The server will return success if the operation is properly formed,
   otherwise the server will return an error.  The server MUST NOT
   return an error if it does not recognize or does not support the
   requested advice.  This is also true even if the client sends
   contradictory hints to the server, e.g., IO_ADVISE4_SEQUENTIAL and
   IO_ADVISE4_RANDOM in a single IO_ADVISE operation.  In this case, the
   server MUST return success and a ior_hints value that indicates the
   hint it intends to optimize.  For contradictory hints, this may mean
   simply returning IO_ADVISE4_NORMAL for example.

   The ior_hints returned by the server is primarily for debugging
   purposes since the server is under no obligation to carry out the
   hints that it describes in the ior_hints result.  In addition, while
   the server may have intended to implement the hints returned in
   ior_hints, as time progresses, the server may need to change its
   handling of a given file due to several reasons including, but not
   limited to, memory pressure, additional IO_ADVISE hints sent by other
   clients, and heuristically detected file access patterns.

   The server MAY return different advice than what the client
   requested.  If it does, then this might be due to one of several
   conditions, including, but not limited to another client advising of
   a different I/O access pattern; a different I/O access pattern from
   another client that that the server has heuristically detected; or
   the server is not able to support the requested I/O access pattern,
   perhaps due to a temporary resource limitation.

   Each issuance of the IO_ADVISE operation overrides all previous
   issuances of IO_ADVISE for a given byte range.  This effectively
   follows a strategy of last hint wins for a given stated and byte
   range.

   Clients should assume that hints included in an IO_ADVISE operation
   will be forgotten once the file is closed.

13.8.4.  IMPLEMENTATION

   The NFS client may choose to issue an IO_ADVISE operation to the
   server in several different instances.

   The most obvious is in direct response to an application's execution
   of posix_fadvise.  In this case, IO_ADVISE4_WRITE and IO_ADVISE4_READ
   may be set based upon the type of file access specified when the file
   was opened.

   Another useful point would be when an application indicates it is
   using direct I/O. Direct I/O may be specified at file open, in which
   case a IO_ADVISE may be included in the same compound as the OPEN
   operation with the IO_ADVISE4_NOREUSE flag set.  Direct I/O may also
   be specified separately, in which case a IO_ADVISE operation can be
   sent to the server separately.  As above, IO_ADVISE4_WRITE and
   IO_ADVISE4_READ may be set based upon the type of file access
   specified when the file was opened.

13.8.5.  pNFS File Layout Data Type Considerations

   The IO_ADVISE considerations for pNFS are very similar to the COMMIT
   considerations for pNFS.  That is, as with COMMIT, some NFS server
   implementations prefer IO_ADVISE be done on the DS, and some prefer
   it be done on the MDS.

   So for the file's layout type, it is proposed that NFSv4.2 include an
   additional hint NFL42_CARE_IO_ADVISE_THRU_MDS which is valid only on
   NFSv4.2 or higher.  Any file's layout obtained with NFSv4.1 MUST NOT
   have NFL42_UFLG_IO_ADVISE_THRU_MDS set.  Any file's layout obtained
   with NFSv4.2 MAY have NFL42_UFLG_IO_ADVISE_THRU_MDS set.  If the
   client does not implement IO_ADVISE, then it MUST ignore
   NFL42_UFLG_IO_ADVISE_THRU_MDS.

   If NFL42_UFLG_IO_ADVISE_THRU_MDS is set, then if the client
   implements IO_ADVISE, then if it wants the DS to honor IO_ADVISE, the
   client MUST send the operation to the MDS, and the server will
   communicate the advice back each DS.  If the client sends IO_ADVISE
   to the DS, then the server MAY return NFS4ERR_NOTSUPP.

   If NFL42_UFLG_IO_ADVISE_THRU_MDS is not set, then this indicates to
   client that if wants to inform the server via IO_ADVISE of the
   client's intended use of the file, then the client SHOULD send an
   IO_ADVISE to each DS.  While the client MAY always send IO_ADVISE to
   the MDS, if the server has not set NFL42_UFLG_IO_ADVISE_THRU_MDS, the
   client should expect that such an IO_ADVISE is futile.  Note that a
   client SHOULD use the same set of arguments on each IO_ADVISE sent to
   a DS for the same open file reference.

   The server is not required to support different advice for different
   DS's with the same open file reference.

13.8.5.1.  Dense and Sparse Packing Considerations

   The IO_ADVISE operation MUST use the iar_offset and byte range as
   dictated by the presence or absence of NFL4_UFLG_DENSE.

   E.g., if NFL4_UFLG_DENSE is present, and a READ or WRITE to the DS
   for iar_offset 0 really means iar_offset 10000 in the logical file,
   then an IO_ADVISE for iar_offset 0 means iar_offset 10000.

   E.g., if NFL4_UFLG_DENSE is absent, then a READ or WRITE to the DS
   for iar_offset 0 really means iar_offset 0 in the logical file, then
   an IO_ADVISE for iar_offset 0 means iar_offset 0 in the logical file.

   E.g., if NFL4_UFLG_DENSE is present, the stripe unit is 1000 bytes
   and the stripe count is 10, and the dense DS file is serving
   iar_offset 0.  A READ or WRITE to the DS for iar_offsets 0, 1000,
   2000, and 3000, really mean iar_offsets 10000, 20000, 30000, and
   40000 (implying a stripe count of 10 and a stripe unit of 1000), then
   an IO_ADVISE sent to the same DS with an iar_offset of 500, and a
   iar_count of 3000 means that the IO_ADVISE applies to these byte
   ranges of the dense DS file:

     - 500 to 999
     - 1000 to 1999
     - 2000 to 2999
     - 3000 to 3499

   I.e., the contiguous range 500 to 3499 as specified in IO_ADVISE.

   It also applies to these byte ranges of the logical file:

     - 10500 to 10999 (500 bytes)
     - 20000 to 20999 (1000 bytes)
     - 30000 to 30999 (1000 bytes)
     - 40000 to 40499 (500 bytes)
     (total            3000 bytes)

   E.g., if NFL4_UFLG_DENSE is absent, the stripe unit is 250 bytes, the
   stripe count is 4, and the sparse DS file is serving iar_offset 0.
   Then a READ or WRITE to the DS for iar_offsets 0, 1000, 2000, and
   3000, really mean iar_offsets 0, 1000, 2000, and 3000 in the logical
   file, keeping in mind that on the DS file,. byte ranges 250 to 999,
   1250 to 1999, 2250 to 2999, and 3250 to 3999 are not accessible.
   Then an IO_ADVISE sent to the same DS with an iar_offset of 500, and
   a iar_count of 3000 means that the IO_ADVISE applies to these byte
   ranges of the logical file and the sparse DS file:

     - 500 to 999 (500 bytes)   - no effect
     - 1000 to 1249 (250 bytes) - effective
     - 1250 to 1999 (750 bytes) - no effect
     - 2000 to 2249 (250 bytes) - effective
     - 2250 to 2999 (750 bytes) - no effect
     - 3000 to 3249 (250 bytes) - effective
     - 3250 to 3499 (250 bytes) - no effect
     (subtotal      2250 bytes) - no effect
     (subtotal       750 bytes) - effective
     (grand total   3000 bytes) - no effect + effective

   If neither of the flags NFL42_UFLG_IO_ADVISE_THRU_MDS and
   NFL4_UFLG_DENSE are set in the layout, then any IO_ADVISE request
   sent to the data server with a byte range that overlaps stripe unit
   that the data server does not serve MUST NOT result in the status
   NFS4ERR_PNFS_IO_HOLE.  Instead, the response SHOULD be successful and
   if the server applies IO_ADVISE hints on any stripe units that
   overlap with the specified range, those hints SHOULD be indicated in
   the response.

13.8.6.  Number of Supported File Segments

   In theory IO_ADVISE allows a client and server to support multiple
   file segments, meaning that different, possibly overlapping, byte
   ranges of the same open file reference will support different hints.
   This is not practical, and in general the server will support just
   one set of hints, and these will apply to the entire file.  However,
   there are some hints that very ephemeral, and are essentially amount
   to one time instructions to the NFS server, which will be forgotten
   momentarily after IO_ADVISE is executed.

   The following hints will always apply to the entire file, regardless
   of the specified byte range:

   o  IO_ADVISE4_NORMAL

   o  IO_ADVISE4_SEQUENTIAL

   o  IO_ADVISE4_SEQUENTIAL_BACKWARDS

   o  IO_ADVISE4_RANDOM

   The following hints will always apply to specified byte range, and
   will treated as one time instructions:

   o  IO_ADVISE4_WILLNEED

   o  IO_ADVISE4_WILLNEED_OPPORTUNISTIC

   o  IO_ADVISE4_DONTNEED

   o  IO_ADVISE4_NOREUSE

   The following hints are modifiers to all other hints, and will apply
   to the entire file and/or to a one time instruction on the specified
   byte range:

   o  IO_ADVISE4_READ

   o  IO_ADVISE4_WRITE

13.9.  Changes to Operation 51: LAYOUTRETURN

13.9.1.  Introduction

   In the pNFS description provided in [2], the client is not enabled capable to
   relay an error code from the DS to the MDS.  In the specification of
   the Objects-Based Layout protocol [9], use is made of the opaque
   lrf_body field of the LAYOUTRETURN argument to do such a relaying of
   error codes.  In this section, we define a new data structure to
   enable the passing of error codes back to the MDS and provide some
   guidelines on what both the client and MDS should expect in such
   circumstances.

   There are two broad classes of errors, transient and persistent.  The
   client SHOULD strive to only use this new mechanism to report
   persistent errors.  It MUST be able to deal with transient issues by
   itself.  Also, while the client might consider an issue to be
   persistent, it MUST be prepared for the MDS to consider such issues
   to be persistent. transient.  A prime example of this is if the MDS fences off a
   client from either a stateid or a filehandle.  The client will get an
   error from the DS and might relay either NFS4ERR_ACCESS or
   NFS4ERR_STALE_STATEID
   NFS4ERR_BAD_STATEID back to the MDS, with the belief that this is a
   hard error.  If the MDS is informed by the client that there is an
   error, it can safely ignore that.  For it, the mission is
   accomplished in that the client has returned a layout that the MDS
   had most likley recalled.

   The client might also need to inform the MDS on that it cannot reach one
   or more of the DSes.  While the MDS can detect the connectivity of
   both of these paths:

   o  MDS to DS

   o  MDS to client

   it cannot determine if the other hand, client and DS path is waiting for working.  As with
   the client to
   report such an error.  For it, case of the mission is accomplished in that DS passing errors to the client has returned a layout that client, it must be prepared
   for the MDS had most likley
   recalled. to consider such outages as being transistory.

   The existing LAYOUTRETURN operation is extended by introducing a new
   data structure to report errors, layoutreturn_device_error4.  Also,
   layoutreturn_device_error4 is introduced to enable an array of errors
   to be reported.

13.9.2.  ARGUMENT

   The ARGUMENT specification of the LAYOUTRETURN operation in section
   18.44.1 of [2] is augmented by the following XDR code [23]: [24]:

   struct layoutreturn_device_error4 {
           deviceid4       lrde_deviceid;
           nfsstat4        lrde_status;
           nfs_opnum4      lrde_opnum;
   };

   struct layoutreturn_error_report4 {
           layoutreturn_device_error4      lrer_errors<>;
   };

13.9.3.  RESULT

   The RESULT of the LAYOUTRETURN operation is unchanged; see section
   18.44.2 of [2].

13.9.4.  DESCRIPTION

   The following text is added to the end of the LAYOUTRETURN operation
   DESCRIPTION in section 18.44.3 of [2].

   When a client used uses LAYOUTRETURN with a type of LAYOUTRETURN4_FILE,
   then if the lrf_body field is NULL, it indicates to the MDS that the
   client experienced no errors.  If lrf_body is non-NULL, then the
   field references error information which is layout type specific.
   I.e., the Objects-Based Layout protocol can continue to utilize
   lrf_body as specified in [9].  For both Files-Based and Block-Based
   Layouts, the field references a layoutreturn_device_error4, which
   contains an array of layoutreturn_device_error4.

   Each individual layoutreturn_device_error4 descibes a single error
   associated with a DS, which is identfied via lrde_deviceid.  The
   operation which returned the error is identified via lrde_opnum.
   Finally the NFS error value (nfsstat4) encountered is provided via
   lrde_status and may consist of the following error codes:

   NFS4_OKAY:  No issues were found for this device.

   NFS4ERR_NXIO:  The client was unable to establish any communication
      with the DS.

   NFS4ERR_*:  The client was able to establish communication with the
      DS and is returning one of the allowed error codes for the
      operation denoted by lrde_opnum.

13.9.5.  IMPLEMENTATION

   The following text is added to the end of the LAYOUTRETURN operation
   IMPLEMENTATION in section 18.4.4 of [2].

   A client that expects to use pNFS for a mounted filesystem SHOULD
   check for pNFS support at mount time.  This check SHOULD be performed
   by sending a GETDEVICELIST operation, followed by layout-type-
   specific checks for accessibility of each storage device returned by
   GETDEVICELIST.  If the NFS server does not support pNFS, the
   GETDEVICELIST operation will be rejected with an NFS4ERR_NOTSUPP
   error; in this situation it is up to the client to determine whether
   it is acceptable to proceed with NFS-only access.

   Clients are expected to tolerate transient storage device errors, and
   hence clients SHOULD NOT use the LAYOUTRETURN error handling for
   device access problems that may be transient.  The methods by which a
   client decides whether an a device access problem is transient vs.
   persistent are implementation-specific, but may include retrying I/Os
   to a data server under appropriate conditions.

   When an I/O fails to a storage device, the client SHOULD retry the
   failed I/O via the MDS.  In this situation, before retrying the I/O,
   the client SHOULD return the layout, or the affected portion thereof,
   and SHOULD indicate which storage device or devices was problematic.
   The client needs to do this when the DS is being unresponsive in
   order to fence off any failed write attempts, and ensure that they do
   not end up overwriting any later data being written through the MDS.
   If the client does not do this, the MDS may MAY issue a layout recall
   callback in order to perform the retried I/O.

   The client needs to be cognizant that since this error handling is
   optional in the MDS, the MDS may silently ignore this functionality.
   Also, as the MDS may consider some issues the client reports to be
   expected (see Section 13.9.1), the client might find it difficult to
   detect a MDS which has not implemented error handling via
   LAYOUTRETURN.

   If an MDS is aware that a storage device is proving problematic to a
   client, the MDS SHOULD NOT include that storage device in any pNFS
   layouts sent to that client.  If the MDS is aware that a storage
   device is affecting many clients, then the MDS SHOULD NOT include
   that storage device in any pNFS layouts sent out.  Clients must still  If a client asks
   for a new layout for the file from the MDS, it MUST be aware prepared for
   the MDS to return that storage device in the layout.  The MDS might
   not have any choice in using the storage device, i.e., there might
   only be one possible layout for the system.

   Another interesting complication is that for existing files, the MDS
   might have no choice  Also, in which storage devices to hand out to clients.
   The MDS might try to restripe a file across a different storage
   device, but clients need to be aware that not all implementations
   have restriping support.

   An MDS SHOULD react to a client return the case of layouts with errors by not
   using
   existing files, the problematic MDS might have no choice in which storage devices in layouts for that client, but
   the
   to hand out to clients.

   The MDS is not required to indefinitely retain per-client storage
   device error information.  An MDS is also not required to
   automatically reinstate use of a previously problematic storage
   device; administrative intervention may be required instead.

   A client MAY perform I/O via the MDS even when the client holds a
   layout that covers the I/O; servers MUST support this client
   behavior, and MAY recall layouts as needed to complete I/Os.

13.10.  Operation 65: READ_PLUS

   READ_PLUS is a new read operation which allows NFS clients to avoid
   reading holes in a sparse file and to efficiently transfer ADBs.
   READ_PLUS supports all the features variant of the existing NFSv4.1 READ operation [2] but [2].
   Besides being able to support all of the data semantics of READ, it
   can also be used by the server to return either holes or ADBs to the
   client.  For holes, READ_PLUS extends the response to avoid returning
   data for portions of the file which are either initialized and
   contain no backing store or if the result would appear to be so.
   I.e., if the result was a data block composed entirely of zeros, then
   it is easier to return a hole.  Returning data blocks of unitialized
   data wastes computational and network resources, thus reducing
   performance.  For ADBs, READ_PLUS uses a new result structure that tells the client that the
   result is all zeroes AND used to return the byte-range metadata
   describing the portions of the hole in file which the
   request was made. are either initialized and
   contain no backing store.

   If the client sends a READ operation, it is explicitly stating that
   it is neither supporting sparse files nor ADBs.  So if a READ occurs
   on a sparse ADB or file, then the server must expand such data to be
   raw bytes.  If a READ occurs in the middle of a hole or ADB, the
   server can only send back bytes starting from that offset.

   Such an operation  In
   contrast, if a READ_PLUS occurs in the middle of a hole or ADB, the
   server can send back a range which starts before the offset and
   extends past the range.

   READ is inefficient for transfer of sparse sections of the file.  As
   such, READ is marked as OBSOLETE in NFSv4.2.  Instead, a client
   should issue READ_PLUS.  Note that as the client has no a priori
   knowledge of whether either an ADB or a hole is present or not, it
   should always use READ_PLUS.

13.10.1.  ARGUMENT

   struct READ_PLUS4args {
           /* CURRENT_FH: file */
           stateid4        rpa_stateid;
           offset4         rpa_offset;
           count4          rpa_count;
   };

13.10.2.  RESULT

   union read_plus_content switch (data_content4 content) {
   case NFS4_CONTENT_DATA:
           opaque          rpc_data<>;
   case NFS4_CONTENT_APP_BLOCK:
           app_data_block4 rpc_block;
   case NFS4_CONTENT_HOLE:
           data_info4      rpc_hole;
   default:
           void;
   };

   /*
    * Allow a return of an array of contents.
    */
   struct read_plus_res4 {
           bool                    rpr_eof;
           read_plus_content       rpr_contents<>;
   };

   union READ_PLUS4res switch (nfsstat4 status) {
   case NFS4_OK:
           read_plus_res4  resok4;
   default:
           void;
   };

13.10.3.  DESCRIPTION

   The READ_PLUS operation is based upon the NFSv4.1 READ operation [2]
   and similarly reads data from the regular file identified by the
   current filehandle.

   The client provides a rpa_offset of where the READ_PLUS is to start
   and a rpa_count of how many bytes are to be read.  A rpa_offset of
   zero means to read data starting at the beginning of the file.  If
   rpa_offset is greater than or equal to the size of the file, the
   status NFS4_OK is returned with di_length (the data length) set to
   zero and eof set to TRUE.  READ_PLUS is subject to access permissions
   checking.

   The READ_PLUS result is comprised of an array of rpr_contents, each
   of which describe a data_content4 type of data. data (Section 6.1.2).  For
   NFSv4.2, the allowed values are data, ADB, and hole.  A server is
   required to support the data type, but neither ADB nor hole.  Both an
   ADB and a hole must be returned in its entirety - clients must be
   prepared to get more information than they requested.

   READ_PLUS has to support all of the errors which are returned by READ
   plus NFS4ERR_UNION_NOTSUPP.  If the client asks for a hole and the
   server does not support that arm of the discriminated union, but does
   support one or more additional arms, it can signal to the client that
   it supports the operation, but not the arm with
   NFS4ERR_UNION_NOTSUPP.

   If the data to be returned is comprised entirely of zeros, then the
   server may elect to return that data as a hole.  The server
   differentiates this to the client by setting di_allocated to TRUE in
   this case.  Note that in such a scenario, the server is not required
   to determine the full extent of the "hole" - it does not need to
   determine where the zeros start and end.

   The server may elect to return adjacent elements of the same type.
   For example, the guard pattern or block size of an ADB might change,
   which would require adjacent elements of type ADB.  Likewise if the
   server has a range of data comprised entirely of zeros and then a
   hole, it might want to return two adjacent holes to the client.

   If the client specifies a rpa_count value of zero, the READ_PLUS
   succeeds and returns zero bytes of data, again subject to access
   permissions checking. data.  In all situations, the
   server may choose to return fewer bytes than specified by the client.
   The client needs to check for this condition and handle the condition
   appropriately.

   If the client specifies an rpa_offset and rpa_count value that is
   entirely contained within a hole of the file, then the di_offset and
   di_length returned must be for the entire hole.  This result is
   considered valid until the file is changed (detected via the change
   attribute).  The server MUST provide the same semantics for the hole
   as if the client read the region and received zeroes; the implied
   holes contents lifetime MUST be exactly the same as any other read
   data.

   If the client specifies an rpa_offset and rpa_count value that begins
   in a non-hole of the file but extends into hole the server should
   return an array comprised of both data and a hole.  The client MUST
   be prepared for the server to return a short read describing just the
   data.  The client will then issue another READ_PLUS for the remaining
   bytes, which the server will respond with information about the hole
   in the file.

   Except when special stateids are used, the stateid value for a
   READ_PLUS request represents a value returned from a previous byte-
   range lock or share reservation request or the stateid associated
   with a delegation.  The stateid identifies the associated owners if
   any and is used by the server to verify that the associated locks are
   still valid (e.g., have not been revoked).

   If the read ended at the end-of-file (formally, in a correctly formed
   READ_PLUS operation, if rpa_offset + rpa_count is equal to the size
   of the file), or the READ_PLUS operation extends beyond the size of
   the file (if rpa_offset + rpa_count is greater than the size of the
   file), eof is returned as TRUE; otherwise, it is FALSE.  A successful
   READ_PLUS of an empty file will always return eof as TRUE.

   If the current filehandle is not an ordinary file, an error will be
   returned to the client.  In the case that the current filehandle
   represents an object of type NF4DIR, NFS4ERR_ISDIR is returned.  If
   the current filehandle designates a symbolic link, NFS4ERR_SYMLINK is
   returned.  In all other cases, NFS4ERR_WRONG_TYPE is returned.

   For a READ_PLUS with a stateid value of all bits equal to zero, the
   server MAY allow the READ_PLUS to be serviced subject to mandatory
   byte-range locks or the current share deny modes for the file.  For a
   READ_PLUS with a stateid value of all bits equal to one, the server
   MAY allow READ_PLUS operations to bypass locking checks at the
   server.

   On success, the current filehandle retains its value.

13.10.4.  IMPLEMENTATION

   In general, the IMPLEMENTATION notes for READ in Section 18.22.4 of
   [2] also apply to READ_PLUS.  One delta is that when the owner has a
   locked byte range, the server MUST return an array of rpr_contents
   with values inside that range.

13.10.4.1.  Additional pNFS Implementation Information

   With pNFS, the semantics of using READ_PLUS remains the same.  Any
   data server MAY return a hole or ADB result for a READ_PLUS request
   that it receives.  When a data server chooses to return such a hole
   result, it has the option of returning hole information for the data
   stored on that data server (as defined by the data layout), but it
   MUST not return results for a byte range that includes data managed
   by another data server.  Data
   servers that can obtain hole information for the parts of the file
   stored on that data server, the data server SHOULD return HOLE_INFO
   and the byte range of the hole stored on that data server.

   A data server should do its best to return as much information about
   a hole ADB as is feasible without having to contact the metadata
   server.  If communication with the metadata server is required, then
   every attempt should be taken to minimize the number of requests.

   If mandatory locking is enforced, then the data server must also
   ensure that to return only information for a Hole that is within the owner's
   locked byte range.

13.10.5.  READ_PLUS with Sparse Files Example

   The following table describes a sparse file.  For each byte range,
   the file contains either non-zero data or a hole.  In addition, the
   server in this example uses a Hole Threshold of 32K.

                        +-------------+----------+
                        | Byte-Range  | Contents |
                        +-------------+----------+
                        | 0-15999     | Hole     |
                        | 16K-31999   | Non-Zero |
                        | 32K-255999  | Hole     |
                        | 256K-287999 | Non-Zero |
                        | 288K-353999 | Hole     |
                        | 354K-417999 | Non-Zero |
                        +-------------+----------+

                                  Table 4 5

   Under the given circumstances, if a client was to read from the file
   with a max read size of 64K, the following will be the results for
   the given READ_PLUS calls.  This assumes the client has already
   opened the file, acquired a valid stateid ('s' in the example), and
   just needs to issue READ_PLUS requests.

   1.  READ_PLUS(s, 0, 64K) --> NFS_OK, eof = false, <data[0,32K],
       hole[32K,224K]>.  Since the first hole is less than the server's
       Hole Threshhold, the first 32K of the file is returned as data
       and the remaining 32K is returned as a hole which actually
       extends to 256K.

   2.  READ_PLUS(s, 32K, 64K) --> NFS_OK, eof = false, <hole[32K,224K]>
       The requested range was all zeros, and the current hole begins at
       offset 32K and is 224K in length.  Note that the client should
       not have followed up the previous READ_PLUS request with this one
       as the hole information from the previous call extended past what
       the client was requesting.

   3.  READ_PLUS(s, 256K, 64K) --> NFS_OK, eof = false, <data[256K,
       288K], hole[288K, 354K]>.  Returns an array of the 32K data and
       the hole which extends to 354K.

   4.  READ_PLUS(s, 354K, 64K) --> NFS_OK, eof = true, <data[354K,
       418K]>.  Returns the final 64K of data and informs the client
       there is no more data in the file.

13.11.  Operation 66: SEEK

   SEEK is an operation that allows a client to determine the location
   of the next data_content4 in a file.  It allows an implementation of
   the emerging extension to lseek(2) to allow clients to determine
   SEEK_HOLE and SEEK_DATA.

13.11.1.  ARGUMENT

   struct SEEK4args {
           /* CURRENT_FH: file */
           stateid4        sa_stateid;
           offset4         sa_offset;
           data_content4   sa_what;
   };

13.11.2.  RESULT

   union seek_content switch (data_content4 content) {
   case NFS4_CONTENT_DATA:
           data_info4      sc_data;
   case NFS4_CONTENT_APP_BLOCK:
           app_data_block4 sc_block;
   case NFS4_CONTENT_HOLE:
           data_info4      sc_hole;
   default:
           void;
   };

   struct seek_res4 {
           bool                    sr_eof;
           seek_content            sr_contents;
   };

   union SEEK4res switch (nfsstat4 status) {
   case NFS4_OK:
           seek_res4       resok4;
   default:
           void;
   };

13.11.3.  DESCRIPTION

   From the given sa_offset, find the next data_content4 of type sa_what
   in the file.  For either a hole or ADB, this must return the
   data_content4 in its entirety.  For data, it must not return the
   actual data.

   SEEK must follow the same rules for stateids as READ_PLUS
   (Section 13.10.3).

   If the server could not find a corresponding sa_what, then the status
   would still be NFS4_OK, but sr_eof would be TRUE.  The sr_contents
   would contain a zero-ed out content of the appropriate type.

14.  NFSv4.2 Callback Operations

14.1.  Procedure 16: CB_ATTR_CHANGED - Notify Client that the File's
       Attributes Changed

14.1.1.  ARGUMENTS

   struct CB_ATTR_CHANGED4args {
           nfs_fh4         acca_fh;
           bitmap4         acca_critical;
           bitmap4         acca_info;
   };

14.1.2.  RESULTS

   struct CB_ATTR_CHANGED4res {
           nfsstat4        accr_status;
   };

14.1.3.  DESCRIPTION

   The CB_ATTR_CHANGED callback operation is used by the server to
   indicate to the client that the file's attributes have been modified
   on the server.  The server does not convey how the attributes have
   changed, just that they have been modified.  The server can inform
   the client about both critical and informational attribute changes in
   the bitmask arguments.  The client SHOULD query the server about all
   attributes set in acca_critical.  For all changes reflected in
   acca_info, the client can decide whether or not it wants to poll the
   server.

   The CB_ATTR_CHANGED callback operation with the FATTR4_SEC_LABEL set
   in acca_critical is the method used by the server to indicate that
   the MAC label for the file referenced by acca_fh has changed.  In
   many ways, the server does not care about the result returned by the
   client.

14.2.  Operation 15: CB_COPY - Report results of a server-side copy
14.2.1.  ARGUMENT

   union copy_info4 switch (nfsstat4 cca_status) {
           case NFS4_OK:
                   void;
           default:
                   length4         cca_bytes_copied;
   };

   struct CB_COPY4args {
           nfs_fh4         cca_fh;
           stateid4        cca_stateid;
           copy_info4      cca_copy_info;
   };

14.2.2.  RESULT

   struct CB_COPY4res {
           nfsstat4        ccr_status;
   };

14.2.3.  DESCRIPTION

   CB_COPY is used for both intra- and inter-server asynchronous copies.
   The CB_COPY callback informs the client of the result of an
   asynchronous server-side copy.  This operation is sent by the
   destination server to the client in a CB_COMPOUND request.  The copy
   is identified by the filehandle and stateid arguments.  The result is
   indicated by the status field.  If the copy failed, cca_bytes_copied
   contains the number of bytes copied before the failure occurred.  The
   cca_bytes_copied value indicates the number of bytes copied but not
   which specific bytes have been copied.

   In the absence of an established backchannel, the server cannot
   signal the completion of the COPY via a CB_COPY callback.  The loss
   of a callback channel would be indicated by the server setting the
   SEQ4_STATUS_CB_PATH_DOWN flag in the sr_status_flags field of the
   SEQUENCE operation.  The client must re-establish the callback
   channel to receive the status of the COPY operation.  Prolonged loss
   of the callback channel could result in the server dropping the COPY
   operation state and invalidating the copy stateid.

   If the client supports the COPY operation, the client is REQUIRED to
   support the CB_COPY operation.

   The CB_COPY operation may fail for the following reasons (this is a
   partial list):

   NFS4ERR_NOTSUPP:  The copy offload operation is not supported by the
      NFS client receiving this request.

15.  IANA Considerations

   This section uses terms that are defined in [24]. [25].

16.  References

16.1.  Normative References

   [1]   Bradner, S., "Key words for use in RFCs to Indicate Requirement
         Levels", March 1997.

   [2]   Shepler, S., Eisler, M., and D. Noveck, "Network File System
         (NFS) Version 4 Minor Version 1 Protocol", RFC 5661,
         January 2010.

   [3]   Haynes, T., "Network File System (NFS) Version 4 Minor Version
         2 External Data Representation Standard (XDR) Description",
         March 2011.

   [4]   Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
         Resource Identifier (URI): Generic Syntax", STD 66, RFC 3986,
         January 2005.

   [5]   Haynes, T. and N. Williams, "Remote Procedure Call (RPC)
         Security Version 3", draft-williams-rpcsecgssv3 (work in
         progress), 2011.

   [6]   The Open Group, "Section 'posix_fadvise()' of System Interfaces
         of The Open Group Base Specifications Issue 6, IEEE Std 1003.1,
         2004 Edition", 2004.

   [7]   Haynes, T., "Requirements for Labeled NFS",
         draft-ietf-nfsv4-labreqs-00 (work in progress).

   [8]   Eisler, M., Chiu, A., and L. Ling, "RPCSEC_GSS Protocol
         Specification", RFC 2203, September 1997.

   [9]   Halevy, B., Welch, B., and J. Zelenka, "Object-Based Parallel
         NFS (pNFS) Operations", RFC 5664, January 2010.

16.2.  Informative References

   [10]  Haynes, T. and D. Noveck, "Network File System (NFS) version 4
         Protocol", draft-ietf-nfsv4-rfc3530bis-09 (Work In Progress),
         March 2011.

   [11]  Lentini, J., Everhart, C., Ellard, D., Tewari, R., and M. Naik,
         "NSDB Protocol for Federated Filesystems",
         draft-ietf-nfsv4-federated-fs-protocol (Work In Progress),
         2010.

   [12]  Lentini, J., Everhart, C., Ellard, D., Tewari, R., and M. Naik,
         "Administration Protocol for Federated Filesystems",
         draft-ietf-nfsv4-federated-fs-admin (Work In Progress), 2010.

   [13]  Fielding, R., Gettys, J., Mogul, J., Frystyk, H., Masinter, L.,
         Leach, P., and T. Berners-Lee, "Hypertext Transfer Protocol --
         HTTP/1.1", RFC 2616, June 1999.

   [14]  Postel, J. and J. Reynolds, "File Transfer Protocol", STD 9,
         RFC 959, October 1985.

   [15]  Simpson, W., "PPP Challenge Handshake Authentication Protocol
         (CHAP)", RFC 1994, August 1996.

   [16]  VanDeBogart, S., Frost, C., and E. Kohler, "Reducing Seek
         Overhead with Application-Directed Prefetching", Proceedings of
         USENIX Annual Technical Conference , June 2009.

   [17]  Strohm, R., "Chapter 2, Data Blocks, Extents, and Segments, of
         Oracle Database Concepts 11g Release 1 (11.1)", January 2011.

   [18]  Ashdown, L., "Chapter 15, Validating Database Files and
         Backups, of Oracle Database Backup and Recovery User's Guide
         11g Release 1 (11.1)", August 2008.

   [19]  McDougall, R. and J. Mauro, "Section 11.4.3, Detecting Memory
         Corruption of Solaris Internals", 2007.

   [20]  Bairavasundaram, L., Goodson, G., Schroeder, B., Arpaci-
         Dusseau, A., and R. Arpaci-Dusseau, "An Analysis of Data
         Corruption in the Storage Stack", Proceedings of the 6th USENIX
         Symposium on File and Storage Technologies (FAST '08) , 2008.

   [21]  "Section 46.6. Multi-Level Security (MLS) of Deployment Guide:
         Deployment, configuration and administration of Red Hat
         Enterprise Linux 5, Edition 6", 2011.

   [22]  Quigley, D. and J. Lu, "Registry Specification for MAC Security
         Label Formats", draft-quigley-label-format-registry (work in
         progress), 2011.

   [23]  ISEG, "IESG Processing of RFC Errata for the IETF Stream",
         2008.

   [24]  Eisler, M., "XDR: External Data Representation Standard",
         RFC 4506, May 2006.

   [24]

   [25]  Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA
         Considerations Section in RFCs", BCP 26, RFC 5226, May 2008.

Appendix A.  Acknowledgments

   For the pNFS Access Permissions Check, the original draft was by
   Sorin Faibish, David Black, Mike Eisler, and Jason Glasgow.  The work
   was influenced by discussions with Benny Halevy and Bruce Fields.  A
   review was done by Tom Haynes.

   For the Sharing change attribute implementation details with NFSv4
   clients, the original draft was by Trond Myklebust.

   For the NFS Server-side Copy, the original draft was by James
   Lentini, Mike Eisler, Deepak Kenchammana, Anshul Madan, and Rahul
   Iyer.  Tom Talpey co-authored an unpublished version of that
   document.  It was also was reviewed by a number of individuals:
   Pranoop Erasani, Tom Haynes, Arthur Lent, Trond Myklebust, Dave
   Noveck, Theresa Lingutla-Raj, Manjunath Shankararao, Satyam Vaghani,
   and Nico Williams.

   For the NFS space reservation operations, the original draft was by
   Mike Eisler, James Lentini, Manjunath Shankararao, and Rahul Iyer.

   For the sparse file support, the original draft was by Dean
   Hildebrand and Marc Eshel.  Valuable input and advice was received
   from Sorin Faibish, Bruce Fields, Benny Halevy, Trond Myklebust, and
   Richard Scheffenegger.

   For the Application IO Hints, the original draft was by Dean
   Hildebrand, Mike Eisler, Trond Myklebust, and Sam Falkner.  Some
   early reviwers included Benny Halevy and Pranoop Erasani.

   For Labeled NFS, the original draft was by David Quigley, James
   Morris, Jarret Lu, and Tom Haynes.  Peter Staubach, Trond Myklebust,
   Stephen Smalley, Sorrin Faibish, Nico Williams, and David Black also
   contributed in the final push to get this accepted.

Appendix B.  RFC Editor Notes

   [RFC Editor: please remove this section prior to publishing this
   document as an RFC]

   [RFC Editor: prior to publishing this document as an RFC, please
   replace all occurrences of RFCTBD10 with RFCxxxx where xxxx is the
   RFC number of this document]

Author's Address

   Thomas Haynes
   NetApp
   9110 E 66th St
   Tulsa, OK  74133
   USA

   Phone: +1 918 307 1415
   Email: thomas@netapp.com
   URI:   http://www.tulsalabs.com