[Docs] [txt|pdf] [draft-ietf-nfsv4-...]



Internet Engineering Task Force (IETF)                         T. Haynes
Request for Comments: 7862                                  Primary Data
Category: Standards Track                                  November 2016
ISSN: 2070-1721


      Network File System (NFS) Version 4 Minor Version 2 Protocol

Abstract

   This document describes NFS version 4 minor version 2; it describes
   the protocol extensions made from NFS version 4 minor version 1.
   Major extensions introduced in NFS version 4 minor version 2 include
   the following: Server-Side Copy, Application Input/Output (I/O)
   Advise, Space Reservations, Sparse Files, Application Data Blocks,
   and Labeled NFS.

Status of This Memo

   This is an Internet Standards Track document.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Further information on
   Internet Standards is available in Section 2 of RFC 7841.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   http://www.rfc-editor.org/info/rfc7862.

Copyright Notice

   Copyright (c) 2016 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.






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Table of Contents

   1. Introduction ....................................................4
      1.1. Requirements Language ......................................4
      1.2. Scope of This Document .....................................5
      1.3. NFSv4.2 Goals ..............................................5
      1.4. Overview of NFSv4.2 Features ...............................6
           1.4.1. Server-Side Clone and Copy ..........................6
           1.4.2. Application Input/Output (I/O) Advise ...............6
           1.4.3. Sparse Files ........................................6
           1.4.4. Space Reservation ...................................7
           1.4.5. Application Data Block (ADB) Support ................7
           1.4.6. Labeled NFS .........................................7
           1.4.7. Layout Enhancements .................................7
      1.5. Enhancements to Minor Versioning Model .....................7
   2. Minor Versioning ................................................8
   3. pNFS Considerations for New Operations ..........................9
      3.1. Atomicity for ALLOCATE and DEALLOCATE ......................9
      3.2. Sharing of Stateids with NFSv4.1 ...........................9
      3.3. NFSv4.2 as a Storage Protocol in pNFS: The File
           Layout Type ................................................9
           3.3.1. Operations Sent to NFSv4.2 Data Servers .............9
   4. Server-Side Copy ...............................................10
      4.1. Protocol Overview .........................................10
           4.1.1. COPY Operations ....................................11
           4.1.2. Requirements for Operations ........................11
      4.2. Requirements for Inter-Server Copy ........................13
      4.3. Implementation Considerations .............................13
           4.3.1. Locking the Files ..................................13
           4.3.2. Client Caches ......................................14
      4.4. Intra-Server Copy .........................................14
      4.5. Inter-Server Copy .........................................16
      4.6. Server-to-Server Copy Protocol ............................19
           4.6.1. Considerations on Selecting a Copy Protocol ........19
           4.6.2. Using NFSv4.x as the Copy Protocol .................19
           4.6.3. Using an Alternative Copy Protocol .................20
      4.7. netloc4 - Network Locations ...............................21
      4.8. Copy Offload Stateids .....................................21
      4.9. Security Considerations for Server-Side Copy ..............22
           4.9.1. Inter-Server Copy Security .........................22
   5. Support for Application I/O Hints ..............................30
   6. Sparse Files ...................................................30
      6.1. Terminology ...............................................31
      6.2. New Operations ............................................32
           6.2.1. READ_PLUS ..........................................32
           6.2.2. DEALLOCATE .........................................32
   7. Space Reservation ..............................................32




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   8. Application Data Block Support .................................34
      8.1. Generic Framework .........................................35
           8.1.1. Data Block Representation ..........................36
      8.2. An Example of Detecting Corruption ........................36
      8.3. An Example of READ_PLUS ...................................38
      8.4. An Example of Zeroing Space ...............................39
   9. Labeled NFS ....................................................39
      9.1. Definitions ...............................................40
      9.2. MAC Security Attribute ....................................41
           9.2.1. Delegations ........................................41
           9.2.2. Permission Checking ................................42
           9.2.3. Object Creation ....................................42
           9.2.4. Existing Objects ...................................42
           9.2.5. Label Changes ......................................42
      9.3. pNFS Considerations .......................................43
      9.4. Discovery of Server Labeled NFS Support ...................43
      9.5. MAC Security NFS Modes of Operation .......................43
           9.5.1. Full Mode ..........................................44
           9.5.2. Limited Server Mode ................................45
           9.5.3. Guest Mode .........................................45
      9.6. Security Considerations for Labeled NFS ...................46
   10. Sharing Change Attribute Implementation Characteristics
       with NFSv4 Clients ............................................46
   11. Error Values ..................................................47
      11.1. Error Definitions ........................................47
           11.1.1. General Errors ....................................47
           11.1.2. Server-to-Server Copy Errors ......................47
           11.1.3. Labeled NFS Errors ................................48
      11.2. New Operations and Their Valid Errors ....................49
      11.3. New Callback Operations and Their Valid Errors ...........53
   12. New File Attributes ...........................................54
      12.1. New RECOMMENDED Attributes - List and Definition
            References ...............................................54
      12.2. Attribute Definitions ....................................54
   13. Operations: REQUIRED, RECOMMENDED, or OPTIONAL ................57
   14. Modifications to NFSv4.1 Operations ...........................61
      14.1. Operation 42: EXCHANGE_ID - Instantiate the client ID ....61
      14.2. Operation 48: GETDEVICELIST - Get all device
            mappings for a file system ...............................63
   15. NFSv4.2 Operations ............................................64
      15.1. Operation 59: ALLOCATE - Reserve space in a
            region of a file .........................................64
      15.2. Operation 60: COPY - Initiate a server-side copy .........65
      15.3. Operation 61: COPY_NOTIFY - Notify a source
            server of a future copy ..................................70
      15.4. Operation 62: DEALLOCATE - Unreserve space in a
            region of a file .........................................72




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      15.5. Operation 63: IO_ADVISE - Send client I/O access
            pattern hints to the server ..............................73
      15.6. Operation 64: LAYOUTERROR - Provide errors for
            the layout ...............................................79
      15.7. Operation 65: LAYOUTSTATS - Provide statistics
            for the layout ...........................................82
      15.8. Operation 66: OFFLOAD_CANCEL - Stop an offloaded
            operation ................................................84
      15.9. Operation 67: OFFLOAD_STATUS - Poll for the
            status of an asynchronous operation ......................85
      15.10. Operation 68: READ_PLUS - READ data or holes
             from a file .............................................86
      15.11. Operation 69: SEEK - Find the next data or hole .........91
      15.12. Operation 70: WRITE_SAME - WRITE an ADB multiple
             times to a file .........................................92
      15.13. Operation 71: CLONE - Clone a range of a file
             into another file .......................................96
   16. NFSv4.2 Callback Operations ...................................98
      16.1. Operation 15: CB_OFFLOAD - Report the results of
            an asynchronous operation ................................98
   17. Security Considerations .......................................99
   18. IANA Considerations ...........................................99
   19. References ...................................................100
      19.1. Normative References ....................................100
      19.2. Informative References ..................................101
   Acknowledgments ..................................................103
   Author's Address .................................................104

1.  Introduction

   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 [RFC7530], and the second minor
   version, NFSv4.1, is described in [RFC5661].

   As a minor version, NFSv4.2 is consistent with the overall goals for
   NFSv4, but NFSv4.2 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.

1.1.  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 [RFC2119].





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1.2.  Scope of This Document

   This document describes the NFSv4.2 protocol as a set of extensions
   to the specification for NFSv4.1.  That specification remains current
   and forms the basis for the additions defined herein.  The
   specification for NFSv4.0 remains current as well.

   It is necessary to implement all the REQUIRED features of NFSv4.1
   before adding NFSv4.2 features to the implementation.  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 -- that is, any
      clarifications made here apply only to NFSv4.2 and not to NFSv4.0
      or NFSv4.1

   NFSv4.2 is a superset of NFSv4.1, with all of the new features being
   optional.  As such, NFSv4.2 maintains the same compatibility that
   NFSv4.1 had with NFSv4.0.  Any interactions of a new feature with
   NFSv4.1 semantics is described in the relevant text.

   The full External Data Representation (XDR) [RFC4506] for NFSv4.2 is
   presented in [RFC7863].

1.3.  NFSv4.2 Goals

   A major goal of the enhancements provided in NFSv4.2 is to take
   common local file system features that have not been available
   through earlier versions of NFS and to 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 pulls in both
      SEEK_HOLE and SEEK_DATA

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

   NFSv4.2 provides means for clients to leverage these features on the
   server in cases in which such leveraging had previously not been
   possible within the confines of the NFS protocol.





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1.4.  Overview of NFSv4.2 Features

1.4.1.  Server-Side Clone and Copy

   A traditional file copy of a remotely accessed file, whether from one
   server to another or between locations in the same server, results in
   the data being put on the network twice -- source to client and then
   client to destination.  New operations are introduced to allow
   unnecessary traffic to be eliminated:

   o  The intra-server CLONE feature allows the client to request a
      synchronous cloning, perhaps by copy-on-write semantics.

   o  The intra-server COPY feature allows the client to request the
      server to perform the copy internally, avoiding unnecessary
      network traffic.

   o  The inter-server COPY feature allows the client to authorize the
      source and destination servers to interact directly.

   As such copies can be lengthy, asynchronous support is also provided.

1.4.2.  Application Input/Output (I/O) Advise

   Applications and clients want to advise the server as to expected I/O
   behavior.  Using IO_ADVISE (see Section 15.5) to communicate 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, allows servers to 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() [posix_fadvise] function.  In
   addition, it may be helpful to applications such as databases and
   video editors.

1.4.3.  Sparse Files

   Sparse files are files that have unallocated or uninitialized data
   blocks as holes in the file.  Such holes are typically transferred as
   zeros when read from the file.  READ_PLUS (see Section 15.10) allows
   a server to send back to the client metadata describing the hole, and
   DEALLOCATE (see Section 15.4) allows the client to punch holes into a
   file.  In addition, SEEK (see Section 15.11) is provided to scan for
   the next hole or data from a given location.








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1.4.4.  Space Reservation

   When a file is sparse, one concern that applications have is ensuring
   that there will always be enough data blocks available for the file
   during future writes.  ALLOCATE (see Section 15.1) allows a client to
   request a guarantee that space will be available.  Also, DEALLOCATE
   (see Section 15.4) allows the client to punch a hole into a file,
   thus releasing a space reservation.

1.4.5.  Application Data Block (ADB) Support

   Some applications treat a file as if it were a disk and as such want
   to initialize (or format) the file image.  The WRITE_SAME operation
   (see Section 15.12) is introduced to send this metadata to the server
   to allow it to write the block contents.

1.4.6.  Labeled NFS

   While both clients and servers can employ Mandatory Access Control
   (MAC) security models to enforce data access, there has been no
   protocol support for interoperability.  A new file object attribute,
   sec_label (see Section 12.2.4), allows the server to store MAC labels
   on files, which the client retrieves and uses to enforce data access
   (see Section 9.5.3).  The format of the sec_label accommodates any
   MAC security system.

1.4.7.  Layout Enhancements

   In the parallel NFS implementations of NFSv4.1 (see Section 12 of
   [RFC5661]), the client cannot communicate back to the metadata server
   any errors or performance characteristics with the storage devices.
   NFSv4.2 provides two new operations to do so: LAYOUTERROR (see
   Section 15.6) and LAYOUTSTATS (see Section 15.7), respectively.

1.5.  Enhancements to Minor Versioning Model

   In NFSv4.1, the only way to introduce new variants of an operation
   was to introduce a new operation.  For instance, READ would have to
   be replaced or supplemented by, say, either READ2 or READ_PLUS.  With
   the use of discriminated unions as parameters for such functions in
   NFSv4.2, it is possible to add a new "arm" (i.e., a new entry in the
   union and a corresponding new field in the structure) in a subsequent
   minor version.  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




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   versioning as operations in NFSv4.1 -- i.e., they may not be made
   REQUIRED.  To support this, a new error code, NFS4ERR_UNION_NOTSUPP,
   allows the server to communicate to the client that the operation is
   supported but the specific arm of the discriminated union is not.

2.  Minor Versioning

   NFSv4.2 is a minor version of NFSv4 and is built upon NFSv4.1 as
   documented in [RFC5661] and [RFC5662].

   NFSv4.2 does not modify the rules applicable to the NFSv4 versioning
   process and follows the rules set out in [RFC5661] or in
   Standards Track documents updating that document (e.g., in an RFC
   based on [NFSv4-Versioning]).

   NFSv4.2 only defines extensions to NFSv4.1, each of which may be
   supported (or not) independently.  It does not

   o  introduce infrastructural features

   o  make existing features MANDATORY to NOT implement

   o  change the status of existing features (i.e., by changing their
      status among OPTIONAL, RECOMMENDED, REQUIRED)

   The following versioning-related considerations should be noted.

   o  When a new case is added to an existing switch, servers need to
      report non-support of that new case by returning
      NFS4ERR_UNION_NOTSUPP.

   o  As regards the potential cross-minor-version transfer of stateids,
      Parallel NFS (pNFS) (see Section 12 of [RFC5661]) implementations
      of the file-mapping type may support the use of an NFSv4.2
      metadata server (see Sections 1.7.2.2 and 12.2.2 of [RFC5661])
      with NFSv4.1 data servers.  In this context, a stateid returned by
      an NFSv4.2 COMPOUND will be used in an NFSv4.1 COMPOUND directed
      to the data server (see Sections 3.2 and 3.3).













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3.  pNFS Considerations for New Operations

   The interactions of the new operations with non-pNFS functionality
   are straightforward and are covered in the relevant sections.
   However, the interactions of the new operations with pNFS are more
   complicated.  This section provides an overview.

3.1.  Atomicity for ALLOCATE and DEALLOCATE

   Both ALLOCATE (see Section 15.1) and DEALLOCATE (see Section 15.4)
   are sent to the metadata server, which is responsible for
   coordinating the changes onto the storage devices.  In particular,
   both operations must either fully succeed or fail; it cannot be the
   case that one storage device succeeds whilst another fails.

3.2.  Sharing of Stateids with NFSv4.1

   An NFSv4.2 metadata server can hand out a layout to an NFSv4.1
   storage device.  Section 13.9.1 of [RFC5661] discusses how the client
   gets a stateid from the metadata server to present to a storage
   device.

3.3.  NFSv4.2 as a Storage Protocol in pNFS: The File Layout Type

   A file layout provided by an NFSv4.2 server may refer to either (1) a
   storage device that only implements NFSv4.1 as specified in [RFC5661]
   or (2) a storage device that implements additions from NFSv4.2, in
   which case the rules in Section 3.3.1 apply.  As the file layout type
   does not provide a means for informing the client as to which minor
   version a particular storage device is providing, the client will
   have to negotiate this with the storage device via the normal Remote
   Procedure Call (RPC) semantics of major and minor version discovery.
   For example, as per Section 16.2.3 of [RFC5661], the client could try
   a COMPOUND with a minorversion field value of 2; if it gets
   NFS4ERR_MINOR_VERS_MISMATCH, it would drop back to 1.

3.3.1.  Operations Sent to NFSv4.2 Data Servers

   In addition to the commands listed in [RFC5661], NFSv4.2 data servers
   MAY accept a COMPOUND containing the following additional operations:
   IO_ADVISE (see Section 15.5), READ_PLUS (see Section 15.10),
   WRITE_SAME (see Section 15.12), and SEEK (see Section 15.11), which
   will be treated like the subset specified as "Operations Sent to
   NFSv4.1 Data Servers" in Section 13.6 of [RFC5661].

   Additional details on the implementation of these operations in a
   pNFS context are documented in the operation-specific sections.




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4.  Server-Side Copy

   The server-side copy features provide mechanisms that allow an NFS
   client to copy file data on a server or between two servers without
   the data being transmitted back and forth over the network through
   the NFS client.  Without these features, an NFS client would copy
   data from one location to another by reading the data from the source
   server over the network and then writing the data back over the
   network to the destination server.

   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.

   The copy feature allows the server to perform the copying either
   synchronously or asynchronously.  The client can request synchronous
   copying, but the server may not be able to honor this request.  If
   the server intends to perform asynchronous copying, it supplies the
   client with a request identifier that the client can use to monitor
   the progress of the copying and, if appropriate, cancel a request in
   progress.  The request identifier is a stateid representing the
   internal state held by the server while the copying is performed.
   Multiple asynchronous copies of all or part of a file may be in
   progress in parallel on a server; the stateid request identifier
   allows monitoring and canceling to be applied to the correct request.

4.1.  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.

   In addition, the CLONE operation provides COPY-like functionality in
   the intra-server case, which is both synchronous and atomic in that
   other operations may not see the target file in any state between the
   state before the CLONE operation and the state after it.

   Throughout the rest of this document, the NFS server containing the
   source file is referred to 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.



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   The new operations are designed to copy files or regions within them.
   Other file system objects can be copied by building on these
   operations or using other techniques.  For example, if a user wishes
   to copy a directory, the client can synthesize a directory COPY
   operation by first creating the destination directory and the
   individual (empty) files within it and then copying the contents of
   the source directory's files to files in the new destination
   directory.

   For the inter-server copy, the operations are defined to be
   compatible with the traditional copy authorization approach.  The
   client and user are authorized at the source for reading.  Then, they
   are authorized at the destination for writing.

4.1.1.  COPY Operations

   CLONE:  Used by the client to request a synchronous atomic COPY-like
      operation.  (Section 15.13)

   COPY_NOTIFY:  Used by the client to request the source server to
      authorize a future file copy that will be made by a given
      destination server on behalf of the given user.  (Section 15.3)

   COPY:  Used by the client to request a file copy.  (Section 15.2)

   OFFLOAD_CANCEL:  Used by the client to terminate an asynchronous file
      copy.  (Section 15.8)

   OFFLOAD_STATUS:  Used by the client to poll the status of an
      asynchronous file copy.  (Section 15.9)

   CB_OFFLOAD:  Used by the destination server to report the results of
      an asynchronous file copy to the client.  (Section 16.1)

4.1.2.  Requirements for Operations

   Inter-server copy, intra-server copy, and intra-server clone are each
   OPTIONAL features in the context of server-side copy.  A server may
   choose independently to implement any of them.  A server implementing
   any of these features may be REQUIRED to implement certain
   operations.  Other operations are OPTIONAL in the context of a
   particular feature (see Table 5 in Section 13) but may become
   REQUIRED, depending on server behavior.  Clients need to use these
   operations to successfully copy a file.







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   For a client to do an intra-server file copy, it needs to use either
   the COPY or the CLONE operation.  If COPY is used, the client MUST
   support the CB_OFFLOAD operation.  If COPY is used and it returns a
   stateid, then the client MAY use the OFFLOAD_CANCEL and
   OFFLOAD_STATUS operations.

   For a client to do an inter-server file copy, it needs to use the
   COPY and COPY_NOTIFY operations and MUST support the CB_OFFLOAD
   operation.  If COPY returns a stateid, then the client MAY use the
   OFFLOAD_CANCEL and OFFLOAD_STATUS operations.

   If a server supports the intra-server COPY feature, then the server
   MUST support the COPY operation.  If a server's COPY operation
   returns a stateid, then the server MUST also support these
   operations: CB_OFFLOAD, OFFLOAD_CANCEL, and OFFLOAD_STATUS.

   If a server supports the CLONE feature, then it MUST support the
   CLONE operation and the clone_blksize attribute on any file system on
   which CLONE is supported (as either source or destination file).

   If a source server supports the inter-server COPY feature, then it
   MUST support the COPY_NOTIFY and OFFLOAD_CANCEL operations.  If a
   destination server supports the inter-server COPY feature, then it
   MUST support the COPY operation.  If a destination server's COPY
   operation returns a stateid, then the destination server MUST also
   support these operations: CB_OFFLOAD, OFFLOAD_CANCEL, COPY_NOTIFY,
   and OFFLOAD_STATUS.

   Each operation is performed in the context of the user identified by
   the Open Network Computing (ONC) RPC credential in the RPC request
   containing the COMPOUND or CB_COMPOUND request.  For example, an
   OFFLOAD_CANCEL operation issued by a given user indicates that a
   specified COPY operation initiated by the same user is to be
   canceled.  Therefore, an OFFLOAD_CANCEL 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.













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4.2.  Requirements for Inter-Server Copy

   The specification of the inter-server copy is driven by several
   requirements:

   o  The specification MUST NOT mandate the server-to-server protocol.

   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
      the specification MUST address.

   o  The specification MUST NOT mandate preconfiguration between the
      source and destination servers.  Requiring that the source and
      destination servers first have a "copying relationship" increases
      the administrative burden.  However, the specification MUST NOT
      preclude implementations that require preconfiguration.

   o  The specification MUST NOT mandate a trust relationship between
      the source and destination servers.  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.

4.3.  Implementation Considerations

4.3.1.  Locking the Files

   Both the source file and the destination file may need to be locked
   to protect the content during the COPY operations.  A client can
   achieve this by a combination of OPEN and LOCK operations.  That is,
   either share locks or byte-range locks might be desired.

   Note that when the client establishes a lock stateid on the source,
   the context of that stateid is for the client and not the
   destination.  As such, there might already be an outstanding stateid,
   issued to the destination as the client of the source, with the same
   value as that provided for the lock stateid.  The source MUST
   interpret the lock stateid as that of the client, i.e., when the
   destination presents it in the context of an inter-server copy, it is
   on behalf of the client.










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4.3.2.  Client Caches

   In a traditional copy, if the client is in the process of writing to
   the file before the copy (and perhaps with a write delegation), it
   will be straightforward to update the destination server.  With an
   inter-server copy, the source has no insight into the changes cached
   on the client.  The client SHOULD write the data back to the source.
   If it does not do so, it is possible that the destination will
   receive a corrupt copy of the file.

4.4.  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_OFFLOAD callback operation.  If the copy is
   performed asynchronously, the client may poll the status of the copy
   using OFFLOAD_STATUS or cancel the copy using OFFLOAD_CANCEL.

   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
        +                                      +
        |                                      |
        |--- OPEN ---------------------------->| Client opens
        |<------------------------------------/| the source file
        |                                      |
        |--- OPEN ---------------------------->| Client opens
        |<------------------------------------/| the destination file
        |                                      |
        |--- COPY ---------------------------->| Client requests
        |<------------------------------------/| a file copy
        |                                      |
        |--- CLOSE --------------------------->| Client closes
        |<------------------------------------/| the destination file
        |                                      |
        |--- CLOSE --------------------------->| Client closes
        |<------------------------------------/| the source file
        |                                      |
        |                                      |

                 Figure 1: A Synchronous Intra-Server Copy





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   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 an OFFLOAD_CANCEL.  When the server completes
   the copy, the server performs a callback to the client and reports
   the results.

     Client                                  Server
        +                                      +
        |                                      |
        |--- OPEN ---------------------------->| Client opens
        |<------------------------------------/| the source file
        |                                      |
        |--- OPEN ---------------------------->| Client opens
        |<------------------------------------/| the destination file
        |                                      |
        |--- COPY ---------------------------->| Client requests
        |<------------------------------------/| a file copy
        |                                      |
        |                                      |
        |--- OFFLOAD_STATUS ------------------>| Client may poll
        |<------------------------------------/| for status
        |                                      |
        |                  .                   | Multiple OFFLOAD_STATUS
        |                  .                   | operations may be sent
        |                  .                   |
        |                                      |
        |<-- CB_OFFLOAD -----------------------| Server reports results
        |\------------------------------------>|
        |                                      |
        |--- CLOSE --------------------------->| Client closes
        |<------------------------------------/| the destination file
        |                                      |
        |--- CLOSE --------------------------->| Client closes
        |<------------------------------------/| the source file
        |                                      |
        |                                      |

                Figure 2: An Asynchronous Intra-Server Copy









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4.5.  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 192.0.2.0/24 in the diagram)
   that does not include the client.  The protocol allows the client to
   set up the copy between the servers (over network 203.0.113.0/24 in
   the diagram) and for the servers to communicate on the high-speed
   network if they choose to do so.

                             192.0.2.0/24
                 +-------------------------------------+
                 |                                     |
                 |                                     |
                 | 192.0.2.18                          | 192.0.2.56
         +-------+------+                       +------+------+
         |     Source   |                       | Destination |
         +-------+------+                       +------+------+
                 | 203.0.113.18                        | 203.0.113.56
                 |                                     |
                 |                                     |
                 |             203.0.113.0/24          |
                 +------------------+------------------+
                                    |
                                    |
                                    | 203.0.113.243
                              +-----+-----+
                              |   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.












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   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.

     Client                Source         Destination
        +                    +                 +
        |                    |                 |
        |--- OPEN        --->|                 | Returns
        |<------------------/|                 | open state os1
        |                    |                 |
        |--- COPY_NOTIFY --->|                 |
        |<------------------/|                 |
        |                    |                 |
        |--- OPEN ---------------------------->| Returns
        |<------------------------------------/| open state os2
        |                    |                 |
        |--- COPY ---------------------------->|
        |                    |                 |
        |                    |                 |
        |                    |<----- READ -----|
        |                    |\--------------->|
        |                    |                 |
        |                    |        .        | Multiple READs may
        |                    |        .        | be necessary
        |                    |        .        |
        |                    |                 |
        |                    |                 |
        |<------------------------------------/| Destination replies
        |                    |                 | to COPY
        |                    |                 |
        |--- CLOSE --------------------------->| Release os2
        |<------------------------------------/|
        |                    |                 |
        |--- CLOSE       --->|                 | Release os1
        |<------------------/|                 |

                 Figure 4: A Synchronous Inter-Server Copy














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   An asynchronous inter-server 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
       +                    +                 +
       |                    |                 |
       |--- OPEN        --->|                 | Returns
       |<------------------/|                 | open state os1
       |                    |                 |
       |--- LOCK        --->|                 | Optional; could be done
       |<------------------/|                 | with a share lock
       |                    |                 |
       |--- COPY_NOTIFY --->|                 | Need to pass in
       |<------------------/|                 | os1 or lock state
       |                    |                 |
       |                    |                 |
       |                    |                 |
       |--- OPEN ---------------------------->| Returns
       |<------------------------------------/| open state os2
       |                    |                 |
       |--- LOCK ---------------------------->| Optional ...
       |<------------------------------------/|
       |                    |                 |
       |--- COPY ---------------------------->| Need to pass in
       |<------------------------------------/| os2 or lock state
       |                    |                 |
       |                    |                 |
       |                    |<----- READ -----|
       |                    |\--------------->|
       |                    |                 |
       |                    |        .        | Multiple READs may
       |                    |        .        | be necessary
       |                    |        .        |
       |                    |                 |
       |                    |                 |
       |--- OFFLOAD_STATUS ------------------>| Client may poll
       |<------------------------------------/| for status
       |                    |                 |
       |                    |        .        | Multiple OFFLOAD_STATUS
       |                    |        .        | operations may be sent
       |                    |        .        |
       |                    |                 |
       |                    |                 |
       |                    |                 |
       |<-- CB_OFFLOAD -----------------------| Destination reports
       |\------------------------------------>| results
       |                    |                 |



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       |--- LOCKU --------------------------->| Only if LOCK was done
       |<------------------------------------/|
       |                    |                 |
       |--- CLOSE --------------------------->| Release os2
       |<------------------------------------/|
       |                    |                 |
       |--- LOCKU       --->|                 | Only if LOCK was done
       |<------------------/|                 |
       |                    |                 |
       |--- CLOSE       --->|                 | Release os1
       |<------------------/|                 |
       |                    |                 |

                Figure 5: An Asynchronous Inter-Server Copy

4.6.  Server-to-Server Copy Protocol

   The choice of what protocol to use in an inter-server copy is
   ultimately the destination server's decision.  However, the
   destination server has to be cognizant that it is working on behalf
   of the client.

4.6.1.  Considerations on Selecting a Copy Protocol

   The client can have requirements over both the size of transactions
   and error recovery semantics.  It may want to split the copy up such
   that each chunk is synchronously transferred.  It may want the copy
   protocol to copy the bytes in consecutive order such that upon an
   error the client can restart the copy at the last known good offset.
   If the destination server cannot meet these requirements, the client
   may prefer the traditional copy mechanism such that it can meet those
   requirements.

4.6.2.  Using NFSv4.x as the Copy Protocol

   The destination server MAY use standard NFSv4.x (where x >= 1)
   operations 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 source filehandle and ca_src_stateid provided in the COPY
   request with standard NFSv4.x operations to read data from the source
   server.  Note that the ca_src_stateid MUST be the cnr_stateid
   returned from the source via the COPY_NOTIFY (Section 15.3).









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4.6.3.  Using an Alternative 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;
   instead, ownership of the file and its contents might simply be
   reassigned 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 [RFC7230] or FTP [RFC959]) 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 pathnames is
   to use an ASCII hexadecimal representation of the source filehandle
   as the filename.

   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 filename 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 that 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.  One solution would be to construct
   unique URLs for each destination server.









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4.7.  netloc4 - Network Locations

   The server-side COPY operations specify network locations using the
   netloc4 data type shown below (see [RFC7863]):

   <CODE BEGINS>

   enum netloc_type4 {
           NL4_NAME        = 1,
           NL4_URL         = 2,
           NL4_NETADDR     = 3
   };

   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;
   };

   <CODE ENDS>

   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, the Lightweight Directory Access
   Protocol (LDAP), the Network Information Service (NIS), /etc/hosts,
   or some other means.  If the netloc4 is of type NL4_URL, a server URL
   [RFC3986] 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 [RFC5661].

   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.

4.8.  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, OFFLOAD_CANCEL,
   OFFLOAD_STATUS, and CB_OFFLOAD operations.

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



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   A copy offload stateid's seqid MUST NOT be zero.  In the context of a
   copy offload operation, it is inappropriate to indicate "the most
   recent copy offload operation" using a stateid with a seqid of zero
   (see Section 8.2.2 of [RFC5661]).  It is inappropriate because the
   stateid refers to internal state in the server and there may be
   several asynchronous COPY operations being performed in parallel on
   the same file by the server.  Therefore, a copy offload stateid with
   a seqid of zero MUST be considered invalid.

4.9.  Security Considerations for Server-Side Copy

   All security considerations pertaining to NFSv4.1 [RFC5661] apply to
   this section; as such, the standard security mechanisms used by the
   protocol can be used to secure the server-to-server operations.

   NFSv4 clients and servers supporting the inter-server COPY operations
   described in this section are REQUIRED to implement the mechanism
   described in Section 4.9.1.1 and to support rejecting COPY_NOTIFY
   requests that do not use the RPC security protocol (RPCSEC_GSS)
   [RFC7861] with privacy.  If the server-to-server copy protocol is
   based on ONC RPC, the servers are also REQUIRED to implement
   [RFC7861], including the RPCSEC_GSSv3 "copy_to_auth",
   "copy_from_auth", and "copy_confirm_auth" structured privileges.
   This requirement to implement is not a requirement to use; for
   example, a server may, depending on configuration, also allow
   COPY_NOTIFY requests that use only AUTH_SYS.

   If a server requires the use of an RPCSEC_GSSv3 copy_to_auth,
   copy_from_auth, or copy_confirm_auth privilege and it is not used,
   the server will reject the request with NFS4ERR_PARTNER_NO_AUTH.

4.9.1.  Inter-Server Copy Security

4.9.1.1.  Inter-Server Copy via ONC RPC 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, lets the source server properly authenticate the
   destination's copy, and does not allow the destination server to
   exceed this authorization is necessary.






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   An approach that sends delegated credentials of the client's user
   principal to the destination server is not used for the following
   reason.  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, a feature of the RPCSEC_GSSv3 protocol [RFC7861] can be
   used: RPC-application-defined structured privilege assertion.  This
   feature allows the destination server to authenticate to the source
   server as acting on behalf of the user principal and to authorize the
   destination server to perform READs of the file to be copied from the
   source on behalf of the user principal.  Once the copy is complete,
   the client can destroy the RPCSEC_GSSv3 handles to end the
   authorization of both the source and destination servers to copy.

   For each structured privilege assertion defined by an RPC
   application, RPCSEC_GSSv3 requires the application to define a name
   string and a data structure that will be encoded and passed between
   client and server as opaque data.  For NFSv4, the data structures
   specified below MUST be serialized using XDR.

   Three RPCSEC_GSSv3 structured privilege assertions that work together
   to authorize the copy are defined here.  For each of the assertions,
   the description starts with the name string passed in the rp_name
   field of the rgss3_privs structure defined in Section 2.7.1.4 of
   [RFC7861] and specifies the XDR encoding of the associated structured
   data passed via the rp_privilege field of the structure.


















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   copy_from_auth:  A user principal is authorizing a source principal
      ("nfs@<source>") to allow a destination principal
      ("nfs@<destination>") to set up the copy_confirm_auth privilege
      required to copy a file from the source to the destination on
      behalf of the user principal.  This privilege is established on
      the source server before the user principal sends a COPY_NOTIFY
      operation to the source server, and the resultant RPCSEC_GSSv3
      context is used to secure the COPY_NOTIFY operation.

      <CODE BEGINS>

   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;
   };

      <CODE ENDS>

      cfap_shared_secret is an automatically generated random number
      secret value.

   copy_to_auth:  A user principal is authorizing a destination
      principal ("nfs@<destination>") to set up a copy_confirm_auth
      privilege with a source principal ("nfs@<source>") to allow it to
      copy a file from the source to the destination on behalf of the
      user principal.  This privilege is established on the destination
      server before the user principal sends a COPY operation to the
      destination server, and the resultant RPCSEC_GSSv3 context is used
      to secure the COPY operation.

      <CODE BEGINS>

   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;
   };

      <CODE ENDS>

      ctap_shared_secret is the automatically generated secret value
      used to establish the copy_from_auth privilege with the source
      principal.  See Section 4.9.1.1.1.




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   copy_confirm_auth:  A destination principal ("nfs@<destination>") is
      confirming with the source principal ("nfs@<source>") that it is
      authorized to copy data from the source.  This privilege is
      established on the destination server before the file is copied
      from the source to the destination.  The resultant RPCSEC_GSSv3
      context is used to secure the READ operations from the source to
      the destination server.

      <CODE BEGINS>

   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;
   };

      <CODE ENDS>

4.9.1.1.1.  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 as follows:

   o  As noted in [RFC7861], the client uses an existing RPCSEC_GSSv3
      context termed the "parent" handle to establish and protect
      RPCSEC_GSSv3 structured privilege assertion exchanges.  The
      copy_from_auth privilege will use the context established between
      the user principal and the source server used to OPEN the source
      file as the RPCSEC_GSSv3 parent handle.  The copy_to_auth
      privilege will use the context established between the user
      principal and the destination server used to OPEN the destination
      file as the RPCSEC_GSSv3 parent handle.

   o  A random number is generated to use as a secret to be shared
      between the two servers.  Note that the random number SHOULD NOT
      be reused between establishing different security contexts.  The
      resulting shared secret will be placed in the copy_from_auth_priv
      cfap_shared_secret field and the copy_to_auth_priv
      ctap_shared_secret field.  Because of this shared_secret, the
      RPCSEC_GSS3_CREATE control messages for copy_from_auth and
      copy_to_auth MUST use a Quality of Protection (QoP) of
      rpc_gss_svc_privacy.







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   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 and is placed in rpc_gss3_create_args
      assertions[0].privs.privilege.  The string "copy_from_auth" is
      placed in assertions[0].privs.name.  The source server unwraps the
      rpc_gss_svc_privacy RPCSEC_GSS3_CREATE payload and 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 field "handle" in a successful reply is the
      RPCSEC_GSSv3 copy_from_auth "child" handle that the client will
      use in COPY_NOTIFY requests to the source server.

   o  An instance of copy_to_auth_priv is filled in with the shared
      secret, the cnr_source_server list returned by COPY_NOTIFY, and
      the NFSv4 user id of the user principal.  The copy_to_auth_priv
      instance is placed in rpc_gss3_create_args
      assertions[0].privs.privilege.  The string "copy_to_auth" is
      placed in assertions[0].privs.name.  The destination server
      unwraps the rpc_gss_svc_privacy RPCSEC_GSS3_CREATE payload and
      verifies that the NFSv4 user id being asserted matches the
      destination server's mapping of the user principal.  If it does,
      the privilege is established on the destination server as
      <copy_to_auth, user id, source list>.  The field "handle" in a
      successful reply is the RPCSEC_GSSv3 copy_to_auth child handle
      that the client will use in COPY requests to the destination
      server involving the source server.

   As noted in Section 2.7.1 of [RFC7861] ("New Control Procedure -
   RPCSEC_GSS_CREATE"), both the client and the source server should
   associate the RPCSEC_GSSv3 child handle with the parent RPCSEC_GSSv3
   handle used to create the RPCSEC_GSSv3 child handle.

4.9.1.1.2.  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 the COPY_NOTIFY MUST be the same as
   cfap_destination specified in copy_from_auth_priv.  Otherwise, the
   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, the COPY_NOTIFY will fail with NFS4ERR_ACCESS.





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   When the client sends a COPY request to the destination server, it
   uses the privileged copy_to_auth RPCSEC_GSSv3 handle.
   ca_source_server list in the COPY MUST be the same as ctap_source
   list specified in copy_to_auth_priv.  Otherwise, the COPY will fail
   with NFS4ERR_ACCESS.  The destination server verifies that the
   privilege <copy_to_auth, user id, source list> exists and annotates
   it with the source and destination filehandles.  If the COPY returns
   a wr_callback_id, then this is an asynchronous copy and the
   wr_callback_id must also must be annotated to the copy_to_auth
   privilege.  If the client has failed to establish the copy_to_auth
   privilege, it will reject the request with NFS4ERR_PARTNER_NO_AUTH.

   If either the COPY_NOTIFY operation or the COPY operations fail, the
   associated copy_from_auth and copy_to_auth RPCSEC_GSSv3 handles MUST
   be destroyed.

4.9.1.1.3.  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 prior to responding to the COPY
   operation, as follows:

   o  Before establishing an RPCSEC_GSSv3 context, a parent context
      needs to exist between nfs@<destination> as the initiator
      principal and nfs@<source> as the target principal.  If NFS is to
      be used as the copy protocol, this means that the destination
      server must mount the source server using RPCSEC_GSSv3.

   o  An instance of copy_confirm_auth_priv is filled in with
      information from the established copy_to_auth privilege.  The
      value of the ccap_shared_secret_mic field is a GSS_GetMIC() of the
      ctap_shared_secret in the copy_to_auth privilege using the parent
      handle context.  The ccap_username field is the mapping of the
      user principal to an NFSv4 user name ("user"@"domain" form) and
      MUST be the same as the ctap_username in the copy_to_auth
      privilege.  The copy_confirm_auth_priv instance is placed in
      rpc_gss3_create_args assertions[0].privs.privilege.  The string
      "copy_confirm_auth" is placed in assertions[0].privs.name.

   o  The RPCSEC_GSS3_CREATE copy_from_auth message is sent to the
      source server with a QoP of rpc_gss_svc_privacy.  The source
      server unwraps the rpc_gss_svc_privacy RPCSEC_GSS3_CREATE payload
      and verifies the cap_shared_secret_mic by calling GSS_VerifyMIC()
      using the parent context on the cfap_shared_secret from the
      established copy_from_auth privilege, and verifies that the
      ccap_username equals the cfap_username.



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   o  If all verifications succeed, the copy_confirm_auth privilege is
      established on the source server as <copy_confirm_auth,
      shared_secret_mic, user id>.  Because the shared secret has been
      verified, the resultant copy_confirm_auth RPCSEC_GSSv3 child
      handle is noted to be acting on behalf of the user principal.

   o  If the source server fails to verify the copy_from_auth privilege,
      the COPY_NOTIFY operation will be rejected with
      NFS4ERR_PARTNER_NO_AUTH.

   o  If the destination server fails to verify the copy_to_auth or
      copy_confirm_auth privilege, the COPY will be rejected with
      NFS4ERR_PARTNER_NO_AUTH, causing the client to destroy the
      associated copy_from_auth and copy_to_auth RPCSEC_GSSv3 structured
      privilege assertion handles.

   o  All subsequent ONC RPC READ requests sent from the destination to
      copy data from the source to the destination will use the
      RPCSEC_GSSv3 copy_confirm_auth child handle.

   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, the
      export policies can be overridden if the destination server is not
      authorized to act as an NFS client.

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

4.9.1.1.4.  Maintaining a Secure Inter-Server Copy

   If the client determines that either the copy_from_auth or the
   copy_to_auth handle becomes invalid during a copy, then the copy MUST
   be aborted by the client sending an OFFLOAD_CANCEL to both the source
   and destination servers and destroying the respective copy-related
   context handles as described in Section 4.9.1.1.5.

4.9.1.1.5.  Finishing or Stopping a Secure Inter-Server Copy

   Under normal operation, the client MUST destroy the copy_from_auth
   and the copy_to_auth RPCSEC_GSSv3 handle once the COPY operation
   returns for a synchronous inter-server copy or a CB_OFFLOAD reports
   the result of an asynchronous copy.







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   The copy_confirm_auth privilege is constructed from information held
   by the copy_to_auth privilege and MUST be destroyed by the
   destination server (via an RPCSEC_GSS3_DESTROY call) when the
   copy_to_auth RPCSEC_GSSv3 handle is destroyed.

   The copy_confirm_auth RPCSEC_GSS3 handle is associated with a
   copy_from_auth RPCSEC_GSS3 handle on the source server via the shared
   secret and MUST be locally destroyed (there is no
   RPCSEC_GSS3_DESTROY, as the source server is not the initiator) when
   the copy_from_auth RPCSEC_GSSv3 handle is destroyed.

   If the client sends an OFFLOAD_CANCEL to the source server to rescind
   the destination server's synchronous copy privilege, it uses the
   privileged copy_from_auth RPCSEC_GSSv3 handle, and the
   cra_destination_server in the OFFLOAD_CANCEL 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.
   The client MUST destroy both the copy_from_auth and the copy_to_auth
   RPCSEC_GSSv3 handles.

   If the client sends an OFFLOAD_STATUS to the destination server to
   check on the status of an asynchronous copy, it uses the privileged
   copy_to_auth RPCSEC_GSSv3 handle, and the osa_stateid in the
   OFFLOAD_STATUS MUST be the same as the wr_callback_id specified in
   the copy_to_auth privilege stored on the destination server.

   If the client sends an OFFLOAD_CANCEL to the destination server to
   cancel an asynchronous copy, it uses the privileged copy_to_auth
   RPCSEC_GSSv3 handle, and the oaa_stateid in the OFFLOAD_CANCEL MUST
   be the same as the wr_callback_id specified in the copy_to_auth
   privilege stored on the destination server.  The destination server
   will then delete the <copy_to_auth, user id, source list> privilege
   and the associated copy_confirm_auth RPCSEC_GSSv3 handle.  The client
   MUST destroy both the copy_to_auth and copy_from_auth RPCSEC_GSSv3
   handles.

4.9.1.2.  Inter-Server Copy via ONC RPC without RPCSEC_GSS

   ONC RPC security flavors other than RPCSEC_GSS MAY be used with the
   server-side copy offload operations described in this section.  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.





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   The biggest issue is that there is a lack of a strong security method
   to allow the source server and destination server to identify
   themselves to each other.  A further complication is that in a
   multihomed environment the destination server might not contact the
   source server from the same network address specified by the client
   in the COPY_NOTIFY.  The cnr_stateid returned from the COPY_NOTIFY
   can be used to uniquely identify the destination server to the source
   server.  The use of the cnr_stateid provides initial authentication
   of the destination server but cannot defend against man-in-the-middle
   attacks after authentication or against an eavesdropper that observes
   the opaque stateid on the wire.  Other secure communication
   techniques (e.g., IPsec) are necessary to block these attacks.

   Servers SHOULD reject COPY_NOTIFY requests that do not use RPCSEC_GSS
   with privacy, thus ensuring that the cnr_stateid in the COPY_NOTIFY
   reply is encrypted.  For the same reason, clients SHOULD send COPY
   requests to the destination using RPCSEC_GSS with privacy.

5.  Support for Application I/O Hints

   Applications can issue client I/O hints via posix_fadvise()
   [posix_fadvise] to the NFS client.  While this can help the NFS
   client optimize I/O and caching for a file, it does not allow the NFS
   server and its exported file system to do likewise.  The IO_ADVISE
   procedure (Section 15.5) is used to communicate the client file
   access patterns to the NFS server.  The NFS server, upon receiving an
   IO_ADVISE operation, MAY choose to alter its I/O and caching behavior
   but is under no obligation to do so.

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

6.  Sparse Files

   A sparse file is a common way of representing a large file without
   having to utilize all of the disk space for it.  Consequently, a
   sparse file uses less physical space than its size indicates.  This
   means the file contains "holes", byte ranges within the file that
   contain no data.  Most modern file systems support sparse files,
   including most UNIX file systems and Microsoft's New Technology File
   System (NTFS); however, it should be noted that Apple's Hierarchical
   File System Plus (HFS+) does not.  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
   High-Performance Computing (HPC) community.





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   In addition, many modern file systems support the concept of
   "unwritten" or "uninitialized" blocks, which have uninitialized space
   allocated to them on disk but will return zeros until data is written
   to them.  Such functionality is already present in the data model of
   the pNFS block/volume layout (see [RFC5663]).  Uninitialized blocks
   can be thought of as holes inside a space reservation window.

   If an application reads a hole in a sparse file, the file system must
   return all zeros to the application.  For local data access there is
   little penalty, but with NFS these zeros must be transferred back to
   the client.  If an application uses the NFS client to read data into
   memory, this wastes time and bandwidth as the application waits for
   the zeros to be transferred.

   A sparse file is typically created by initializing the file to be all
   zeros.  Nothing is written to the data in the file; instead, the hole
   is recorded in the metadata for the file.  So, an 8G disk image might
   be represented initially by a few hundred bits in the metadata (on
   UNIX file systems, the inode) and nothing on the disk.  If the VM
   then writes 100M to a file in the middle of the image, there would
   now be two holes represented in the metadata and 100M in the data.

   No new operation is needed to allow the creation of a sparsely
   populated file; when a file is created and a write occurs past the
   current size of the file, the non-allocated region will either be a
   hole or be filled with zeros.  The choice of behavior is dictated by
   the underlying file system and is transparent to the application.
   However, the abilities to read sparse files and to punch holes to
   reinitialize the contents of a file are needed.

   Two new operations -- DEALLOCATE (Section 15.4) and READ_PLUS
   (Section 15.10) -- are introduced.  DEALLOCATE allows for the hole
   punching, where an application might want to reset the allocation and
   reservation status of a range of the file.  READ_PLUS supports all
   the features of READ but includes an extension to support sparse
   files.  READ_PLUS is guaranteed to perform no worse than READ and can
   dramatically improve performance with sparse files.  READ_PLUS does
   not depend on pNFS protocol features but can be used by pNFS to
   support sparse files.

6.1.  Terminology

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

   Sparse file:  A regular file that contains one or more holes.

   Hole:  A byte range within a sparse file that contains all zeros.  A
      hole might or might not have space allocated or reserved to it.



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6.2.  New Operations

6.2.1.  READ_PLUS

   READ_PLUS is a new variant of the NFSv4.1 READ operation [RFC5661].
   Besides being able to support all of the data semantics of the READ
   operation, it can also be used by the client and server to
   efficiently transfer holes.  Because the client does not know in
   advance whether a hole is present or not, if the client supports
   READ_PLUS and so does the server, then it should always use the
   READ_PLUS operation in preference to the READ operation.

   READ_PLUS extends the response with a new arm representing holes to
   avoid returning data for portions of the file that are initialized to
   zero and may or may not contain a backing store.  Returning actual
   data blocks corresponding to holes wastes computational and network
   resources, thus reducing performance.

   When a client sends a READ operation, it is not prepared to accept a
   READ_PLUS-style response providing a compact encoding of the scope of
   holes.  If a READ occurs on a sparse file, then the server must
   expand such data to be raw bytes.  If a READ occurs in the middle of
   a hole, the server can only send back bytes starting from that
   offset.  By contrast, if a READ_PLUS occurs in the middle of a hole,
   the server can send back a range that starts before the offset and
   extends past the requested length.

6.2.2.  DEALLOCATE

   The client can use the DEALLOCATE operation on a range of a file as a
   hole punch, which allows the client to avoid the transfer of a
   repetitive pattern of zeros across the network.  This hole punch is a
   result of the unreserved space returning all zeros until overwritten.

7.  Space Reservation

   Applications want to be able to reserve space for a file, report the
   amount of actual disk space a file occupies, and free up the backing
   space of a file when it is not required.

   One example is the posix_fallocate() operation [posix_fallocate],
   which allows applications to ask for space reservations from the
   operating system, usually to provide a better file layout and reduce
   overhead for random or slow-growing file-appending workloads.







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   Another example is space reservation for virtual disks in a
   hypervisor.  In virtualized environments, virtual disk files are
   often stored on NFS-mounted volumes.  When a hypervisor creates a
   virtual disk file, it often tries to preallocate the space for the
   file so that there are no future allocation-related errors during the
   operation of the VM.  Such errors prevent a VM from continuing
   execution and result in downtime.

   Currently, in order to achieve such a guarantee, applications 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 only inefficient in terms of the amount of I/O
   done; it is also not guaranteed to work on file systems that are
   log-structured or deduplicated.  An efficient way of guaranteeing
   space reservation would be beneficial to such applications.

   The new ALLOCATE operation (see Section 15.1) allows a client to
   request a guarantee that space will be available.  The ALLOCATE
   operation guarantees that any future writes to the region it was
   successfully called for will not fail with NFS4ERR_NOSPC.

   Another useful feature is the ability to report the number of blocks
   that would be freed when a file is deleted.  Currently, NFS reports
   two size attributes:

   size  The logical file size of the file.

   space_used  The size in bytes that the file occupies on disk.

   While these attributes are sufficient for space accounting in
   traditional file systems, they prove to be inadequate in modern file
   systems that support block-sharing.  In such file systems, multiple
   inodes (the metadata portion of the file system object) can point to
   a single block with a block reference count to guard against
   premature freeing.  Having a way to tell the number of blocks that
   would be freed if the 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 hard drive in a VM, a virtual disk
   can be viewed as a file system within a file.  Since not all blocks
   within a file system 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; less space might be consumed for
   backups after block deallocation.






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   The following attribute and operation can be used to resolve these
   issues:

   space_freed  This attribute reports the space that would be freed
      when a file is deleted, taking block-sharing into consideration.

   DEALLOCATE  This operation deallocates the blocks backing a region of
      the file.

   If space_used of a file is interpreted to mean the size in bytes of
   all disk blocks pointed to by the inode of the file, then shared
   blocks get double-counted, over-reporting the space utilization.
   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 to mean the size in
   bytes of those disk blocks unique to the inode of the file, then
   shared blocks are not counted in any file, resulting in
   under-reporting of the space utilization.

   For example, two files, A and B, have 10 blocks each.  Let six 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 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 that the space utilization is only
   8 * BLOCK_SIZE.

   Using the space_freed attribute (see Section 12.2.2) is helpful in
   solving this problem.  space_freed is the number of blocks that are
   allocated to the given file that would 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 A is deleted, B will report
   space_freed as 10 * BLOCK_SIZE, as the deletion of B would result in
   the deallocation of all 10 blocks.

   Using the space_freed attribute does not solve the problem of space
   being over-reported.  However, over-reporting is better than
   under-reporting.

8.  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
   thus 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 [Strohm11]).  An ADB is typically



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   comprised of two sections: 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 Application Data Block Number (ADBN), which allows the
       application to determine which data block is being referenced.
       This is useful when the client is not storing the blocks in
       contiguous memory, i.e., a logical block number.

   2.  Fields to describe the state of the ADB and a means to detect
       block corruption.  For both pieces of data, a useful property
       would be that the allowed values are specially selected so that,
       if passed across the network, corruption due to translation
       between big-endian and little-endian architectures is detectable.
       For example, 0xf0dedef0 has the same (32 wide) bit pattern in
       both architectures, making it inappropriate.

   Applications already impose structures on files [Strohm11] and detect
   corruption in data blocks [Ashdown08].  What they are not able to do
   is efficiently transfer and store ADBs.  To initialize a file with
   ADBs, the client must send each full ADB to the server, and that must
   be stored on the server.

   This section defines a framework for transferring the ADB from client
   to server and presents one approach to detecting corruption in a
   given ADB implementation.

8.1.  Generic Framework

   The representation of the ADB needs to be flexible enough to support
   many different applications.  The most basic approach is no
   imposition of a block at all, which entails 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 [McDougall07].  The next
   might store the ADBN at an offset of 100 bytes within the block and
   have no guard pattern at all, 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.



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

8.1.1.  Data Block Representation

   <CODE BEGINS>

   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<>;
   };

   <CODE ENDS>

   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.  The adb_block_num is used 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 ADBs.

8.2.  An Example of Detecting Corruption

   In this section, an example ADB format is defined 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 an indirect block that allows for
   files that are 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; this would enable the OS
   application in question to undelete a file.









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   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 starting at byte 16 that
   applies to the remaining contents of the block (see [Baira08] for an
   example of using checksums to detect data corruption).  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 [Ashdown08] for an example of checksums used
   to detect corruption in application data blocks).

   Corruption in each ADB can thus be detected:

   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 can
   detect corruption based on the state and the contents of the ADB.



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   This last point is important in validating the minimum amount of data
   incorporated into the generic framework.  That is, 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 cases where the application
   detects corruption.

8.3.  An Example of READ_PLUS

   The hypothetical application presented in Section 8.2 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 with the
   WRITE_SAME operation (see Section 15.12):

      WRITE_SAME {0, 4K, 100, 0, 0, 8, 0xfeedface}

   Further, assume that the application writes a single ADB at 16K,
   changing the guard pattern to 0xcafedead; then there would be in
   memory:

       0K ->   (4K - 1) : 00 00 00 00 ... fe ed fa ce 00 00 ... 00
       4K ->   (8K - 1) : 00 00 00 01 ... fe ed fa ce 00 00 ... 00
       8K ->  (12K - 1) : 00 00 00 02 ... fe ed fa ce 00 00 ... 00
      12K ->  (16K - 1) : 00 00 00 03 ... fe ed fa ce 00 00 ... 00
      16K ->  (20K - 1) : 00 00 00 04 ... ca fe de ad 00 00 ... 00
      20K ->  (24K - 1) : 00 00 00 05 ... fe ed fa ce 00 00 ... 00
      24K ->  (28K - 1) : 00 00 00 06 ... fe ed fa ce 00 00 ... 00
         ...
     396K -> (400K - 1) : 00 00 00 63 ... fe ed fa ce 00 00 ... 00

   And when the client did a READ_PLUS of 64K at the start of the file,
   it could get back a result of data:

       0K ->   (4K - 1) : 00 00 00 00 ... fe ed fa ce 00 00 ... 00
       4K ->   (8K - 1) : 00 00 00 01 ... fe ed fa ce 00 00 ... 00
       8K ->  (12K - 1) : 00 00 00 02 ... fe ed fa ce 00 00 ... 00
      12K ->  (16K - 1) : 00 00 00 03 ... fe ed fa ce 00 00 ... 00
      16K ->  (20K - 1) : 00 00 00 04 ... ca fe de ad 00 00 ... 00
      20K ->  (24K - 1) : 00 00 00 05 ... fe ed fa ce 00 00 ... 00
      24K ->  (28K - 1) : 00 00 00 06 ... fe ed fa ce 00 00 ... 00
         ...
      62K ->  (64K - 1) : 00 00 00 15 ... fe ed fa ce 00 00 ... 00





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8.4.  An Example of Zeroing Space

   A simpler use case for WRITE_SAME is applications that want to
   efficiently zero out a file, but do not want to modify space
   reservations.  This can easily be achieved by a call to WRITE_SAME
   without an ADB block numbers and pattern, e.g.:

      WRITE_SAME {0, 1K, 10000, 0, 0, 0, 0}

9.  Labeled NFS

   Access control models such as UNIX permissions or Access Control
   Lists (ACLs) 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
   [RFC4949].  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 -- that the users do
   not have the ability to override.  In this section, a MAC model is
   added to NFSv4.2.

   First, a method is provided 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 is done through a combination of two mechanisms.
   As with other recommended attributes on file objects, the usual DAC
   checks, based on the 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.

   Second, a method is described for the client to determine if an NFSv4
   file object security label has changed.  A client that needs to know
   if a label on a file or set of files is going to change SHOULD
   request a delegation on each labeled file.  In order to change such a
   security label, the server will have to recall delegations on any
   file affected by the label change, so informing clients of the label
   change.







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   An additional useful feature would be modification to the RPC layer
   used by NFSv4 to allow RPCs to assert client process subject security
   labels and enable the enforcement of Full Mode as described in
   Section 9.5.1.  Such modifications are outside the scope of this
   document (see [RFC7861]).

9.1.  Definitions

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

   Security Label Format Selection Registry:  the IANA registry (see
      [RFC7569]) containing all registered LFSs, along with references
      to the documents that describe the syntactic format and semantics
      of the security label.

   Policy Identifier (PI):  an optional part of the definition of an
      LFS.  The PI allows clients and servers to identify specific
      security policies.

   Object:  a passive resource within the system that is 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:  an active entity, usually a process that is requesting
      access to an object.

   MAC-Aware:  a server that can transmit and store object labels.

   MAC-Functional:  a client or server that is Labeled NFS enabled.
      Such a system can interpret labels and apply policies based on the
      security system.

   Multi-Level Security (MLS):  a traditional model where objects are
      given a sensitivity level (Unclassified, Secret, Top Secret, etc.)
      and a category set (see [LB96], [RFC1108], [RFC2401], and
      [RFC4949]).

      (Note: RFC 2401 has been obsoleted by RFC 4301, but we list
      RFC 2401 here because RFC 4301 does not discuss MLS.)







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9.2.  MAC Security Attribute

   MAC models base access decisions on security attributes bound to
   subjects (usually processes) and objects (for NFS, file objects).
   This information can range from a user identity for an identity-based
   MAC model, sensitivity levels for MLS, 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 attribute are listed
   below:

   o  MUST provide flexibility with respect to the 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 on
      both the client and the server.

   o  MUST NOT expose an object to either the client or server namespace
      before its security information has been bound to it.

   NFSv4 implements the MAC security attribute as a recommended
   attribute.  This attribute has a fixed format and semantics, which
   conflicts with the flexible nature of security attributes in general.
   To resolve this, the MAC security attribute consists of two
   components.  The first component is an LFS, as defined in [RFC7569],
   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 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 listed above.  The
   recommended attribute FATTR4_SEC_LABEL (see Section 12.2.4) will be
   used to satisfy this requirement.

9.2.1.  Delegations

   In the event that a security attribute is changed on the server while
   a client holds a delegation on the file, both the server and the
   client MUST follow the NFSv4.1 protocol (see Section 10 of [RFC5661])
   with respect to attribute changes.  It SHOULD flush all changes back
   to the server and relinquish the delegation.




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9.2.2.  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 9.5 gives a
   specific example of how the security attribute is handled under a
   particular MAC model.

9.2.3.  Object Creation

   When creating files in NFSv4, the OPEN and CREATE operations are
   used.  One of the parameters for 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-Functional, it must always
   provide the initial security attribute upon file creation.  In the
   event that the server is MAC-Functional as well, it should determine
   by policy whether it will accept the attribute from the client or
   instead make the determination itself.  If the client is not
   MAC-Functional, then the MAC-Functional server must decide on a
   default label.  A more in-depth explanation can be found in
   Section 9.5.

9.2.4.  Existing Objects

   Note that under the MAC model, all objects must have labels.
   Therefore, if an existing server is upgraded to include Labeled NFS
   support, then it is the responsibility of the security system to
   define the behavior for existing objects.

9.2.5.  Label Changes

   Consider a Guest Mode system (Section 9.5.3) in which the clients
   enforce MAC checks and the server has only a DAC security system that
   stores the labels along with the file data.  In this type of system,
   a user with the appropriate DAC credentials on a client with poorly
   configured or disabled MAC labeling enforcement is allowed access to
   the file label (and data) on the server and can change the label.









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   Clients that need to know if a label on a file or set of files has
   changed SHOULD request a delegation on each labeled file so that a
   label change by another client will be known via the process
   described in Section 9.2.1, which must be followed: the delegation
   will be recalled, which effectively notifies the client of the
   change.

   Note that the MAC security policies on a client can be such that the
   client does not have access to the file unless it has a delegation.

9.3.  pNFS Considerations

   The new FATTR4_SEC_LABEL attribute is metadata information, and as
   such the storage device is not aware of the value contained on the
   metadata server.  Fortunately, the NFSv4.1 protocol [RFC5661] already
   has provisions for doing access-level checks from the storage device
   to the metadata server.  In order for the storage device to validate
   the subject label presented by the client, it SHOULD utilize this
   mechanism.

9.4.  Discovery of Server Labeled NFS Support

   The server can easily determine that a client supports Labeled NFS
   when it queries for the FATTR4_SEC_LABEL label for an object.
   Further, it can then determine which LFS the client understands.  The
   client might want to discover whether the server supports Labeled NFS
   and which LFS the server supports.

   The following COMPOUND MUST NOT be denied by any MAC label check:

        PUTROOTFH, GETATTR {FATTR4_SEC_LABEL}

   Note that the server might have imposed a security flavor on the root
   that precludes such access.  That is, 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.

9.5.  MAC Security NFS Modes of Operation

   A system using Labeled NFS may operate in three modes (see Section 4
   of [RFC7204]).  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 second mode is a subset of the Full Mode and is called
   "Limited Server Mode".  In this mode, the server cannot enforce the



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   labels, but it can store and transmit them.  The remaining mode is
   called the "Guest Mode"; in this mode, one end of the connection is
   not implementing a MAC model and thus offers less protection than
   Full Mode.

9.5.1.  Full Mode

   Full Mode environments consist of MAC-Functional 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 9.2.

   Fully MAC-Functional NFSv4 servers are not possible in the absence of
   RPCSEC_GSSv3 [RFC7861] support for client process subject label
   assertion.  However, servers may make decisions based on the RPC
   credential information available.

9.5.1.1.  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 attribute 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
   outside the scope of this document.  If a translation is unavailable
   for a given LFS, then the request MUST be denied.  Another recourse
   is to allow the host to provide a fallback mapping for unknown
   security attributes.

9.5.1.2.  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



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   object it is trying to access.  If the client denies that access, an
   RPC 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 uses any
   credential information conveyed in the RPC request and the attributes
   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.

   Future protocol extensions may also allow the server to factor into
   the decision a security label extracted from the RPC request.

   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.

9.5.2.  Limited Server Mode

   A Limited Server mode (see Section 4.2 of [RFC7204]) consists of a
   server that is label aware but does not enforce policies.  Such a
   server will store and retrieve all object labels presented by clients
   and will utilize the methods described in Section 9.2.5 to allow the
   clients to detect changing labels, but may not factor the label into
   access decisions.  Instead, it will expect the clients to enforce all
   such access locally.

9.5.3.  Guest Mode

   Guest Mode implies that either the client or the server does not
   handle labels.  If the client is not Labeled NFS 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 Labeled NFS aware, then
   it will not return object labels to the client.  Clients in this
   environment may consist of groups implementing different MAC model
   policies.  The system requires that all clients in the environment be
   responsible for access control checks.







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9.6.  Security Considerations for Labeled NFS

   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 that does not present
   one.  This will prevent a non-Labeled NFS client from mixing entries
   in the directory cache.

10.  Sharing Change Attribute Implementation Characteristics with NFSv4
     Clients

   Although both the NFSv4 [RFC7530] and NFSv4.1 [RFC5661] protocols
   define the change attribute as being mandatory to implement, there is
   little in the way of guidance as to its construction.  The only
   mandated constraint is that the value must change whenever the file
   data or metadata changes.

   While this allows for a wide range of implementations, it also leaves
   the client with no way to determine which is the most recent value
   for the change attribute in a case where several RPCs 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 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 serialized 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.  change_attr_type is defined as a new recommended attribute
   (see Section 12.2.3) and is a per-file system attribute.








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11.  Error Values

   NFS error numbers are assigned to failed operations within a COMPOUND
   (COMPOUND or CB_COMPOUND) request.  A COMPOUND request contains a
   number of NFS operations that have their results encoded in sequence
   in a COMPOUND reply.  The results of successful operations will
   consist of an NFS4_OK status followed by the encoded results of the
   operation.  If an NFS operation fails, an error status will be
   entered in the reply and the COMPOUND request will be terminated.

11.1.  Error Definitions

          +-------------------------+--------+------------------+
          | Error                   | Number | Description      |
          +-------------------------+--------+------------------+
          | NFS4ERR_BADLABEL        | 10093  | Section 11.1.3.1 |
          | NFS4ERR_OFFLOAD_DENIED  | 10091  | Section 11.1.2.1 |
          | NFS4ERR_OFFLOAD_NO_REQS | 10094  | Section 11.1.2.2 |
          | NFS4ERR_PARTNER_NO_AUTH | 10089  | Section 11.1.2.3 |
          | NFS4ERR_PARTNER_NOTSUPP | 10088  | Section 11.1.2.4 |
          | NFS4ERR_UNION_NOTSUPP   | 10090  | Section 11.1.1.1 |
          | NFS4ERR_WRONG_LFS       | 10092  | Section 11.1.3.2 |
          +-------------------------+--------+------------------+

                    Table 1: Protocol Error Definitions

11.1.1.  General Errors

   This section deals with errors that are applicable to a broad set of
   different purposes.

11.1.1.1.  NFS4ERR_UNION_NOTSUPP (Error Code 10090)

   One of the arguments to the operation is a discriminated union, and
   while the server supports the given operation, it does not support
   the selected arm of the discriminated union.

11.1.2.  Server-to-Server Copy Errors

   These errors deal with the interaction between server-to-server
   copies.

11.1.2.1.  NFS4ERR_OFFLOAD_DENIED (Error Code 10091)

   The COPY offload operation is supported by both the source and the
   destination, but the destination is not allowing it for this file.
   If the client sees this error, it should fall back to the normal copy
   semantics.



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11.1.2.2.  NFS4ERR_OFFLOAD_NO_REQS (Error Code 10094)

   The COPY offload operation is supported by both the source and the
   destination, but the destination cannot meet the client requirements
   for either consecutive byte copy or synchronous copy.  If the client
   sees this error, it should either relax the requirements (if any) or
   fall back to the normal copy semantics.

11.1.2.3.  NFS4ERR_PARTNER_NO_AUTH (Error Code 10089)

   The source server does not authorize a server-to-server COPY offload
   operation.  This may be due to the client's failure to send the
   COPY_NOTIFY operation to the source server, the source server
   receiving a server-to-server copy offload request after the copy
   lease time expired, or some other permission problem.

   The destination server does not authorize a server-to-server COPY
   offload operation.  This may be due to an inter-server COPY request
   where the destination server requires RPCSEC_GSSv3 and it is not
   used, or some other permissions problem.

11.1.2.4.  NFS4ERR_PARTNER_NOTSUPP (Error Code 10088)

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

11.1.3.  Labeled NFS Errors

   These errors are used in Labeled NFS.

11.1.3.1.  NFS4ERR_BADLABEL (Error Code 10093)

   The label specified is invalid in some manner.

11.1.3.2.  NFS4ERR_WRONG_LFS (Error Code 10092)

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













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11.2.  New Operations and Their Valid Errors

   This section contains a table that gives the valid error returns for
   each new NFSv4.2 protocol operation.  The error code NFS4_OK
   (indicating no error) is not listed but should be understood to be
   returnable by all new operations.  The error values for all other
   operations are defined in Section 15.2 of [RFC5661].

   +----------------+--------------------------------------------------+
   | Operation      | Errors                                           |
   +----------------+--------------------------------------------------+
   | ALLOCATE       | NFS4ERR_ACCESS, NFS4ERR_ADMIN_REVOKED,           |
   |                | NFS4ERR_BADXDR, NFS4ERR_BAD_STATEID,             |
   |                | NFS4ERR_DEADSESSION, NFS4ERR_DELAY,              |
   |                | NFS4ERR_DELEG_REVOKED, NFS4ERR_DQUOT,            |
   |                | NFS4ERR_EXPIRED, NFS4ERR_FBIG,                   |
   |                | NFS4ERR_FHEXPIRED, NFS4ERR_GRACE, NFS4ERR_INVAL, |
   |                | NFS4ERR_IO, NFS4ERR_ISDIR, NFS4ERR_MOVED,        |
   |                | NFS4ERR_NOFILEHANDLE, NFS4ERR_NOSPC,             |
   |                | NFS4ERR_NOTSUPP, NFS4ERR_OLD_STATEID,            |
   |                | NFS4ERR_OPENMODE, NFS4ERR_OP_NOT_IN_SESSION,     |
   |                | NFS4ERR_REP_TOO_BIG,                             |
   |                | NFS4ERR_REP_TOO_BIG_TO_CACHE,                    |
   |                | NFS4ERR_REQ_TOO_BIG, NFS4ERR_RETRY_UNCACHED_REP, |
   |                | NFS4ERR_ROFS, NFS4ERR_SERVERFAULT,               |
   |                | NFS4ERR_STALE, NFS4ERR_SYMLINK,                  |
   |                | NFS4ERR_TOO_MANY_OPS, NFS4ERR_WRONG_TYPE         |
   +----------------+--------------------------------------------------+
   | CLONE          | NFS4ERR_ACCESS, NFS4ERR_ADMIN_REVOKED,           |
   |                | NFS4ERR_BADXDR, NFS4ERR_BAD_STATEID,             |
   |                | NFS4ERR_DEADSESSION, NFS4ERR_DELAY,              |
   |                | NFS4ERR_DELEG_REVOKED, NFS4ERR_DQUOT,            |
   |                | NFS4ERR_EXPIRED, NFS4ERR_FBIG,                   |
   |                | NFS4ERR_FHEXPIRED, NFS4ERR_GRACE, NFS4ERR_INVAL, |
   |                | NFS4ERR_IO, NFS4ERR_ISDIR, NFS4ERR_MOVED,        |
   |                | NFS4ERR_NOFILEHANDLE, NFS4ERR_NOSPC,             |
   |                | NFS4ERR_NOTSUPP, NFS4ERR_OLD_STATEID,            |
   |                | NFS4ERR_OPENMODE, NFS4ERR_OP_NOT_IN_SESSION,     |
   |                | NFS4ERR_REP_TOO_BIG,                             |
   |                | NFS4ERR_REP_TOO_BIG_TO_CACHE,                    |
   |                | NFS4ERR_REQ_TOO_BIG, NFS4ERR_RETRY_UNCACHED_REP, |
   |                | NFS4ERR_ROFS, NFS4ERR_SERVERFAULT,               |
   |                | NFS4ERR_STALE, NFS4ERR_SYMLINK,                  |
   |                | NFS4ERR_TOO_MANY_OPS, NFS4ERR_WRONG_TYPE,        |
   |                | NFS4ERR_XDEV                                     |






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   +----------------+--------------------------------------------------+
   | COPY           | NFS4ERR_ACCESS, NFS4ERR_ADMIN_REVOKED,           |
   |                | NFS4ERR_BADXDR, NFS4ERR_BAD_STATEID,             |
   |                | NFS4ERR_DEADSESSION, NFS4ERR_DELAY,              |
   |                | NFS4ERR_DELEG_REVOKED, NFS4ERR_DQUOT,            |
   |                | NFS4ERR_EXPIRED, NFS4ERR_FBIG,                   |
   |                | NFS4ERR_FHEXPIRED, NFS4ERR_GRACE, NFS4ERR_INVAL, |
   |                | NFS4ERR_IO, NFS4ERR_ISDIR, NFS4ERR_LOCKED,       |
   |                | NFS4ERR_MOVED, NFS4ERR_NOFILEHANDLE,             |
   |                | NFS4ERR_NOSPC, NFS4ERR_OFFLOAD_DENIED,           |
   |                | NFS4ERR_OLD_STATEID, NFS4ERR_OPENMODE,           |
   |                | NFS4ERR_OP_NOT_IN_SESSION,                       |
   |                | NFS4ERR_PARTNER_NO_AUTH,                         |
   |                | NFS4ERR_PARTNER_NOTSUPP, NFS4ERR_PNFS_IO_HOLE,   |
   |                | NFS4ERR_PNFS_NO_LAYOUT, NFS4ERR_REP_TOO_BIG,     |
   |                | NFS4ERR_REP_TOO_BIG_TO_CACHE,                    |
   |                | NFS4ERR_REQ_TOO_BIG, NFS4ERR_RETRY_UNCACHED_REP, |
   |                | NFS4ERR_ROFS, NFS4ERR_SERVERFAULT,               |
   |                | NFS4ERR_STALE, NFS4ERR_SYMLINK,                  |
   |                | NFS4ERR_TOO_MANY_OPS, NFS4ERR_WRONG_TYPE         |
   +----------------+--------------------------------------------------+
   | COPY_NOTIFY    | NFS4ERR_ACCESS, NFS4ERR_ADMIN_REVOKED,           |
   |                | NFS4ERR_BADXDR, NFS4ERR_BAD_STATEID,             |
   |                | NFS4ERR_DEADSESSION, NFS4ERR_DELAY,              |
   |                | NFS4ERR_DELEG_REVOKED, NFS4ERR_EXPIRED,          |
   |                | NFS4ERR_FHEXPIRED, NFS4ERR_GRACE, NFS4ERR_INVAL, |
   |                | NFS4ERR_IO, NFS4ERR_ISDIR, NFS4ERR_LOCKED,       |
   |                | NFS4ERR_MOVED, NFS4ERR_NOFILEHANDLE,             |
   |                | NFS4ERR_OLD_STATEID, NFS4ERR_OPENMODE,           |
   |                | NFS4ERR_OP_NOT_IN_SESSION, NFS4ERR_PNFS_IO_HOLE, |
   |                | NFS4ERR_PNFS_NO_LAYOUT, NFS4ERR_REP_TOO_BIG,     |
   |                | NFS4ERR_REP_TOO_BIG_TO_CACHE,                    |
   |                | NFS4ERR_REQ_TOO_BIG, NFS4ERR_RETRY_UNCACHED_REP, |
   |                | NFS4ERR_SERVERFAULT, NFS4ERR_STALE,              |
   |                | NFS4ERR_SYMLINK, NFS4ERR_TOO_MANY_OPS,           |
   |                | NFS4ERR_WRONG_TYPE                               |
   +----------------+--------------------------------------------------+
   | DEALLOCATE     | NFS4ERR_ACCESS, NFS4ERR_ADMIN_REVOKED,           |
   |                | NFS4ERR_BADXDR, NFS4ERR_BAD_STATEID,             |
   |                | NFS4ERR_DEADSESSION, NFS4ERR_DELAY,              |
   |                | NFS4ERR_DELEG_REVOKED, NFS4ERR_EXPIRED,          |
   |                | NFS4ERR_FBIG, NFS4ERR_FHEXPIRED, NFS4ERR_GRACE,  |
   |                | NFS4ERR_INVAL, NFS4ERR_IO, NFS4ERR_ISDIR,        |
   |                | NFS4ERR_MOVED, NFS4ERR_NOFILEHANDLE,             |
   |                | NFS4ERR_NOTSUPP, NFS4ERR_OLD_STATEID,            |
   |                | NFS4ERR_OPENMODE, NFS4ERR_OP_NOT_IN_SESSION,     |
   |                | NFS4ERR_REP_TOO_BIG,                             |
   |                | NFS4ERR_REP_TOO_BIG_TO_CACHE,                    |



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   |                | NFS4ERR_REQ_TOO_BIG, NFS4ERR_RETRY_UNCACHED_REP, |
   |                | NFS4ERR_ROFS, NFS4ERR_SERVERFAULT,               |
   |                | NFS4ERR_STALE, NFS4ERR_SYMLINK,                  |
   |                | NFS4ERR_TOO_MANY_OPS, NFS4ERR_WRONG_TYPE         |
   +----------------+--------------------------------------------------+
   | GETDEVICELIST  | NFS4ERR_NOTSUPP                                  |
   +----------------+--------------------------------------------------+
   | IO_ADVISE      | NFS4ERR_ACCESS, NFS4ERR_ADMIN_REVOKED,           |
   |                | NFS4ERR_BADXDR, NFS4ERR_BAD_STATEID,             |
   |                | NFS4ERR_DEADSESSION, NFS4ERR_DELAY,              |
   |                | NFS4ERR_DELEG_REVOKED, NFS4ERR_EXPIRED,          |
   |                | NFS4ERR_FBIG, NFS4ERR_FHEXPIRED, NFS4ERR_GRACE,  |
   |                | NFS4ERR_INVAL, NFS4ERR_IO, NFS4ERR_ISDIR,        |
   |                | NFS4ERR_MOVED, NFS4ERR_NOFILEHANDLE,             |
   |                | NFS4ERR_NOTSUPP, NFS4ERR_OLD_STATEID,            |
   |                | NFS4ERR_OP_NOT_IN_SESSION,                       |
   |                | NFS4ERR_RETRY_UNCACHED_REP, NFS4ERR_SERVERFAULT, |
   |                | NFS4ERR_STALE, NFS4ERR_SYMLINK,                  |
   |                | NFS4ERR_TOO_MANY_OPS, NFS4ERR_WRONG_TYPE         |
   +----------------+--------------------------------------------------+
   | LAYOUTERROR    | NFS4ERR_ADMIN_REVOKED, NFS4ERR_BADXDR,           |
   |                | NFS4ERR_BAD_STATEID, NFS4ERR_DEADSESSION,        |
   |                | NFS4ERR_DELAY, NFS4ERR_DELEG_REVOKED,            |
   |                | NFS4ERR_EXPIRED, NFS4ERR_FHEXPIRED,              |
   |                | NFS4ERR_GRACE, NFS4ERR_INVAL, NFS4ERR_ISDIR,     |
   |                | NFS4ERR_MOVED, NFS4ERR_NOFILEHANDLE,             |
   |                | NFS4ERR_NOTSUPP, NFS4ERR_NO_GRACE,               |
   |                | NFS4ERR_OLD_STATEID, NFS4ERR_OP_NOT_IN_SESSION,  |
   |                | NFS4ERR_REP_TOO_BIG,                             |
   |                | NFS4ERR_REP_TOO_BIG_TO_CACHE,                    |
   |                | NFS4ERR_REQ_TOO_BIG, NFS4ERR_RETRY_UNCACHED_REP, |
   |                | NFS4ERR_SERVERFAULT, NFS4ERR_STALE,              |
   |                | NFS4ERR_TOO_MANY_OPS,                            |
   |                | NFS4ERR_UNKNOWN_LAYOUTTYPE, NFS4ERR_WRONG_CRED,  |
   |                | NFS4ERR_WRONG_TYPE                               |
   +----------------+--------------------------------------------------+
   | LAYOUTSTATS    | NFS4ERR_ADMIN_REVOKED, NFS4ERR_BADXDR,           |
   |                | NFS4ERR_BAD_STATEID, NFS4ERR_DEADSESSION,        |
   |                | NFS4ERR_DELAY, NFS4ERR_DELEG_REVOKED,            |
   |                | NFS4ERR_EXPIRED, NFS4ERR_FHEXPIRED,              |
   |                | NFS4ERR_GRACE, NFS4ERR_INVAL, NFS4ERR_ISDIR,     |
   |                | NFS4ERR_MOVED, NFS4ERR_NOFILEHANDLE,             |
   |                | NFS4ERR_NOTSUPP, NFS4ERR_NO_GRACE,               |
   |                | NFS4ERR_OLD_STATEID, NFS4ERR_OP_NOT_IN_SESSION,  |
   |                | NFS4ERR_REP_TOO_BIG,                             |
   |                | NFS4ERR_REP_TOO_BIG_TO_CACHE,                    |
   |                | NFS4ERR_REQ_TOO_BIG, NFS4ERR_RETRY_UNCACHED_REP, |
   |                | NFS4ERR_SERVERFAULT, NFS4ERR_STALE,              |



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   |                | NFS4ERR_TOO_MANY_OPS,                            |
   |                | NFS4ERR_UNKNOWN_LAYOUTTYPE, NFS4ERR_WRONG_CRED,  |
   |                | NFS4ERR_WRONG_TYPE                               |
   +----------------+--------------------------------------------------+
   | OFFLOAD_CANCEL | NFS4ERR_ADMIN_REVOKED, NFS4ERR_BADXDR,           |
   |                | NFS4ERR_BAD_STATEID, NFS4ERR_COMPLETE_ALREADY,   |
   |                | NFS4ERR_DEADSESSION, NFS4ERR_DELAY,              |
   |                | NFS4ERR_EXPIRED, NFS4ERR_GRACE, NFS4ERR_NOTSUPP, |
   |                | NFS4ERR_OLD_STATEID, NFS4ERR_OP_NOT_IN_SESSION,  |
   |                | NFS4ERR_SERVERFAULT, NFS4ERR_TOO_MANY_OPS        |
   +----------------+--------------------------------------------------+
   | OFFLOAD_STATUS | NFS4ERR_ADMIN_REVOKED, NFS4ERR_BADXDR,           |
   |                | NFS4ERR_BAD_STATEID, NFS4ERR_COMPLETE_ALREADY,   |
   |                | NFS4ERR_DEADSESSION, NFS4ERR_DELAY,              |
   |                | NFS4ERR_EXPIRED, NFS4ERR_GRACE, NFS4ERR_NOTSUPP, |
   |                | NFS4ERR_OLD_STATEID, NFS4ERR_OP_NOT_IN_SESSION,  |
   |                | NFS4ERR_SERVERFAULT, NFS4ERR_TOO_MANY_OPS        |
   +----------------+--------------------------------------------------+
   | READ_PLUS      | NFS4ERR_ACCESS, NFS4ERR_ADMIN_REVOKED,           |
   |                | NFS4ERR_BADXDR, NFS4ERR_BAD_STATEID,             |
   |                | NFS4ERR_DEADSESSION, NFS4ERR_DELAY,              |
   |                | NFS4ERR_DELEG_REVOKED, NFS4ERR_EXPIRED,          |
   |                | NFS4ERR_FHEXPIRED, NFS4ERR_GRACE, NFS4ERR_INVAL, |
   |                | NFS4ERR_IO, NFS4ERR_ISDIR, NFS4ERR_LOCKED,       |
   |                | NFS4ERR_MOVED, NFS4ERR_NOFILEHANDLE,             |
   |                | NFS4ERR_NOTSUPP, NFS4ERR_OLD_STATEID,            |
   |                | NFS4ERR_OPENMODE, NFS4ERR_OP_NOT_IN_SESSION,     |
   |                | NFS4ERR_PARTNER_NO_AUTH, NFS4ERR_PNFS_IO_HOLE,   |
   |                | NFS4ERR_PNFS_NO_LAYOUT, NFS4ERR_REP_TOO_BIG,     |
   |                | NFS4ERR_REP_TOO_BIG_TO_CACHE,                    |
   |                | NFS4ERR_REQ_TOO_BIG, NFS4ERR_RETRY_UNCACHED_REP, |
   |                | NFS4ERR_SERVERFAULT, NFS4ERR_STALE,              |
   |                | NFS4ERR_SYMLINK, NFS4ERR_TOO_MANY_OPS,           |
   |                | NFS4ERR_WRONG_TYPE                               |
   +----------------+--------------------------------------------------+
   | SEEK           | NFS4ERR_ACCESS, NFS4ERR_ADMIN_REVOKED,           |
   |                | NFS4ERR_BADXDR, NFS4ERR_BAD_STATEID,             |
   |                | NFS4ERR_DEADSESSION, NFS4ERR_DELAY,              |
   |                | NFS4ERR_DELEG_REVOKED, NFS4ERR_EXPIRED,          |
   |                | NFS4ERR_FHEXPIRED, NFS4ERR_GRACE, NFS4ERR_INVAL, |
   |                | NFS4ERR_IO, NFS4ERR_ISDIR, NFS4ERR_LOCKED,       |
   |                | NFS4ERR_MOVED, NFS4ERR_NOFILEHANDLE,             |
   |                | NFS4ERR_NOTSUPP, NFS4ERR_OLD_STATEID,            |
   |                | NFS4ERR_OPENMODE, NFS4ERR_OP_NOT_IN_SESSION,     |
   |                | NFS4ERR_PNFS_IO_HOLE, NFS4ERR_PNFS_NO_LAYOUT,    |
   |                | NFS4ERR_REP_TOO_BIG,                             |
   |                | NFS4ERR_REP_TOO_BIG_TO_CACHE,                    |
   |                | NFS4ERR_REQ_TOO_BIG, NFS4ERR_RETRY_UNCACHED_REP, |



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   |                | NFS4ERR_SERVERFAULT, NFS4ERR_STALE,              |
   |                | NFS4ERR_SYMLINK, NFS4ERR_TOO_MANY_OPS,           |
   |                | NFS4ERR_UNION_NOTSUPP, NFS4ERR_WRONG_TYPE        |
   +----------------+--------------------------------------------------+
   | WRITE_SAME     | NFS4ERR_ACCESS, NFS4ERR_ADMIN_REVOKED,           |
   |                | NFS4ERR_BADXDR, NFS4ERR_BAD_STATEID,             |
   |                | NFS4ERR_DEADSESSION, NFS4ERR_DELAY,              |
   |                | NFS4ERR_DELEG_REVOKED, NFS4ERR_DQUOT,            |
   |                | NFS4ERR_EXPIRED, NFS4ERR_FBIG,                   |
   |                | NFS4ERR_FHEXPIRED, NFS4ERR_GRACE, NFS4ERR_INVAL, |
   |                | NFS4ERR_IO, NFS4ERR_ISDIR, NFS4ERR_LOCKED,       |
   |                | NFS4ERR_MOVED, NFS4ERR_NOFILEHANDLE,             |
   |                | NFS4ERR_NOSPC, NFS4ERR_NOTSUPP,                  |
   |                | NFS4ERR_OLD_STATEID, NFS4ERR_OPENMODE,           |
   |                | NFS4ERR_OP_NOT_IN_SESSION, NFS4ERR_PNFS_IO_HOLE, |
   |                | NFS4ERR_PNFS_NO_LAYOUT, NFS4ERR_REP_TOO_BIG,     |
   |                | NFS4ERR_REP_TOO_BIG_TO_CACHE,                    |
   |                | NFS4ERR_REQ_TOO_BIG, NFS4ERR_RETRY_UNCACHED_REP, |
   |                | NFS4ERR_ROFS, NFS4ERR_SERVERFAULT,               |
   |                | NFS4ERR_STALE, NFS4ERR_SYMLINK,                  |
   |                | NFS4ERR_TOO_MANY_OPS, NFS4ERR_WRONG_TYPE         |
   +----------------+--------------------------------------------------+

       Table 2: Valid Error Returns for Each New Protocol Operation

11.3.  New Callback Operations and Their Valid Errors

   This section contains a table that gives the valid error returns for
   each new NFSv4.2 callback operation.  The error code NFS4_OK
   (indicating no error) is not listed but should be understood to be
   returnable by all new callback operations.  The error values for all
   other callback operations are defined in Section 15.3 of [RFC5661].

   +------------+------------------------------------------------------+
   | Callback   | Errors                                               |
   | Operation  |                                                      |
   +------------+------------------------------------------------------+
   | CB_OFFLOAD | NFS4ERR_BADHANDLE, NFS4ERR_BADXDR,                   |
   |            | NFS4ERR_BAD_STATEID, NFS4ERR_DELAY,                  |
   |            | NFS4ERR_OP_NOT_IN_SESSION, NFS4ERR_REP_TOO_BIG,      |
   |            | NFS4ERR_REP_TOO_BIG_TO_CACHE, NFS4ERR_REQ_TOO_BIG,   |
   |            | NFS4ERR_RETRY_UNCACHED_REP, NFS4ERR_SERVERFAULT,     |
   |            | NFS4ERR_TOO_MANY_OPS                                 |
   +------------+------------------------------------------------------+

   Table 3: Valid Error Returns for Each New Protocol Callback Operation





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12.  New File Attributes

12.1.  New RECOMMENDED Attributes - List and Definition References

   The list of new RECOMMENDED attributes appears in Table 4.  The
   meanings of the columns of the table are:

   Name:  The name of the attribute.

   Id:  The number assigned to the attribute.  In the event of conflicts
      between the assigned number and [RFC7863], the latter is
      authoritative, but in such an event, it should be resolved with
      errata to this document and/or [RFC7863].  See [IESG08] 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.

   +------------------+----+-------------------+-----+----------------+
   | Name             | Id | Data Type         | Acc | Defined in     |
   +------------------+----+-------------------+-----+----------------+
   | clone_blksize    | 77 | uint32_t          | R   | Section 12.2.1 |
   | space_freed      | 78 | length4           | R   | Section 12.2.2 |
   | change_attr_type | 79 | change_attr_type4 | R   | Section 12.2.3 |
   | sec_label        | 80 | sec_label4        | R W | Section 12.2.4 |
   +------------------+----+-------------------+-----+----------------+

                    Table 4: New RECOMMENDED Attributes

12.2.  Attribute Definitions

12.2.1.  Attribute 77: clone_blksize

   The clone_blksize attribute indicates the granularity of a CLONE
   operation.






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12.2.2.  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.

12.2.3.  Attribute 79: change_attr_type

   <CODE BEGINS>

   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
   };

   <CODE ENDS>

   change_attr_type is a per-file system attribute that 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.  While Section 5.4 of [RFC5661] discusses
   per-file system attributes, it is expected that the value of
   change_attr_type will not depend on the value of "homogeneous" and
   will only change in the event of a migration.

   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 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
      the file attributes, data, or directory contents.  In the case
      where the client is writing to pNFS data servers, the number of
      increments is not guaranteed to exactly match the number of
      WRITEs.








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   NFS4_CHANGE_TYPE_IS_TIME_METADATA:  The change attribute is
      implemented as suggested in [RFC7530] in terms of the
      time_metadata attribute.

   NFS4_CHANGE_TYPE_IS_UNDEFINED:  The change attribute 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 is set, then the client knows at
   the very least that the change attribute is monotonically increasing,
   which is sufficient to resolve the question of which value is the
   most recent.

   If the client sees the value NFS4_CHANGE_TYPE_IS_TIME_METADATA, then
   by inspecting the value of the "time_delta" attribute it additionally
   has the option of detecting rogue server implementations that use
   time_metadata in violation of the specification.

   If the client sees NFS4_CHANGE_TYPE_IS_VERSION_COUNTER, it has the
   ability to predict what the resulting change attribute value should
   be after a COMPOUND containing a SETATTR, WRITE, or CREATE.  This
   again allows it to detect changes made in parallel by another client.
   The value NFS4_CHANGE_TYPE_IS_VERSION_COUNTER_NOPNFS permits the
   same, but only if the client is not doing pNFS WRITEs.

   Finally, if the server does not support change_attr_type or if
   NFS4_CHANGE_TYPE_IS_UNDEFINED is set, then the server SHOULD make an
   effort to implement the change attribute in terms of the
   time_metadata attribute.

12.2.4.  Attribute 80: sec_label

   <CODE BEGINS>

   typedef uint32_t  policy4;

   struct labelformat_spec4 {
           policy4 lfs_lfs;
           policy4 lfs_pi;
   };

   struct sec_label4 {
           labelformat_spec4       slai_lfs;
           opaque                  slai_data<>;
   };

   <CODE ENDS>



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   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 the Security Label
   Format Selection Registry are described in detail in [RFC7569].  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 that 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 and server being part of a specific MAC
   model, the client will be aware of the size.

13.  Operations: REQUIRED, RECOMMENDED, or OPTIONAL

   Tables 5 and 6 summarize the operations of the NFSv4.2 protocol and
   the corresponding designations of REQUIRED, RECOMMENDED, and OPTIONAL
   to implement or MUST NOT implement.  The "MUST NOT implement"
   designation 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 that 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 forechannel 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.









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   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 regarding implementation requirements, the
   operation descriptions themselves must be consulted, along with other
   relevant explanatory text within either this specification or the
   NFSv4.1 specification [RFC5661].

   The abbreviations used in the second and third columns of Tables 5
   and 6 are defined as follows:

   REQ:  REQUIRED to implement

   REC:  RECOMMENDED to implement

   OPT:  OPTIONAL to implement

   MNI:  MUST NOT implement

   For the NFSv4.2 features that are OPTIONAL, the operations that
   support those features are OPTIONAL, and the server MUST return
   NFS4ERR_NOTSUPP in response to the client's use of those operations
   when those operations are not implemented by the server.  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 tables 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

   COPYra:  Intra-server Server-Side Copy

   COPYer:  Inter-server Server-Side Copy

   ADB:  Application Data Blocks









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   +----------------------+--------------------+-----------------------+
   | Operation            | REQ, REC, OPT, or  | Feature (REQ, REC, or |
   |                      | MNI                | OPT)                  |
   +----------------------+--------------------+-----------------------+
   | ACCESS               | REQ                |                       |
   | ALLOCATE             | OPT                |                       |
   | BACKCHANNEL_CTL      | REQ                |                       |
   | BIND_CONN_TO_SESSION | REQ                |                       |
   | CLONE                | OPT                |                       |
   | CLOSE                | REQ                |                       |
   | COMMIT               | REQ                |                       |
   | COPY                 | OPT                | COPYer (REQ), COPYra  |
   |                      |                    | (REQ)                 |
   | COPY_NOTIFY          | OPT                | COPYer (REQ)          |
   | CREATE               | REQ                |                       |
   | CREATE_SESSION       | REQ                |                       |
   | DEALLOCATE           | OPT                |                       |
   | 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        | MNI                | pNFS (MNI)            |
   | GETFH                | REQ                |                       |
   | GET_DIR_DELEGATION   | OPT                | DDELG (REQ)           |
   | ILLEGAL              | REQ                |                       |
   | IO_ADVISE            | OPT                |                       |
   | LAYOUTCOMMIT         | OPT                | pNFS (REQ)            |
   | LAYOUTERROR          | OPT                | pNFS (OPT)            |
   | LAYOUTGET            | OPT                | pNFS (REQ)            |
   | LAYOUTRETURN         | OPT                | pNFS (REQ)            |
   | LAYOUTSTATS          | OPT                | pNFS (OPT)            |
   | LINK                 | OPT                |                       |
   | LOCK                 | REQ                |                       |
   | LOCKT                | REQ                |                       |
   | LOCKU                | REQ                |                       |
   | LOOKUP               | REQ                |                       |
   | LOOKUPP              | REQ                |                       |
   | NVERIFY              | REQ                |                       |
   | OFFLOAD_CANCEL       | OPT                | COPYer (OPT), COPYra  |
   |                      |                    | (OPT)                 |
   | OFFLOAD_STATUS       | OPT                | COPYer (OPT), COPYra  |
   |                      |                    | (OPT)                 |




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   | OPEN                 | REQ                |                       |
   | OPENATTR             | OPT                |                       |
   | OPEN_CONFIRM         | MNI                |                       |
   | OPEN_DOWNGRADE       | REQ                |                       |
   | PUTFH                | REQ                |                       |
   | PUTPUBFH             | REQ                |                       |
   | PUTROOTFH            | REQ                |                       |
   | READ                 | REQ                |                       |
   | READDIR              | REQ                |                       |
   | READLINK             | OPT                |                       |
   | READ_PLUS            | OPT                |                       |
   | 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)                 |
   | SEEK                 | OPT                |                       |
   | SEQUENCE             | REQ                |                       |
   | SETATTR              | REQ                |                       |
   | SETCLIENTID          | MNI                |                       |
   | SETCLIENTID_CONFIRM  | MNI                |                       |
   | SET_SSV              | REQ                |                       |
   | TEST_STATEID         | REQ                |                       |
   | VERIFY               | REQ                |                       |
   | WANT_DELEGATION      | OPT                | FDELG (OPT)           |
   | WRITE                | REQ                |                       |
   | WRITE_SAME           | OPT                | ADB (REQ)             |
   +----------------------+--------------------+-----------------------+

                            Table 5: Operations
















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   +-------------------------+------------------+----------------------+
   | Operation               | REQ, REC, OPT,   | Feature (REQ, REC,   |
   |                         | or MNI           | or OPT)              |
   +-------------------------+------------------+----------------------+
   | CB_GETATTR              | OPT              | FDELG (REQ)          |
   | CB_ILLEGAL              | REQ              |                      |
   | CB_LAYOUTRECALL         | OPT              | pNFS (REQ)           |
   | CB_NOTIFY               | OPT              | DDELG (REQ)          |
   | CB_NOTIFY_DEVICEID      | OPT              | pNFS (OPT)           |
   | CB_NOTIFY_LOCK          | OPT              |                      |
   | CB_OFFLOAD              | OPT              | COPYer (REQ), COPYra |
   |                         |                  | (REQ)                |
   | 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)                |
   +-------------------------+------------------+----------------------+

                       Table 6: Callback Operations

14.  Modifications to NFSv4.1 Operations

14.1.  Operation 42: EXCHANGE_ID - Instantiate the client ID

14.1.1.  ARGUMENT

   <CODE BEGINS>

      /* new */
      const EXCHGID4_FLAG_SUPP_FENCE_OPS      = 0x00000004;

   <CODE ENDS>

14.1.2.  RESULT

      Unchanged








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14.1.3.  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 that the previous operation has completed.
   However, if the session is lost, there is no way to know when any
   operations in progress have aborted or completed.  In hindsight, the
   NFSv4.1 specification should have mandated that DESTROY_SESSION
   either abort or complete all outstanding operations.

14.1.4.  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.  It is the server's return that determines whether this
   capability is in effect.  When it is in effect, the following will
   occur:

   o  The server will not reply to any DESTROY_SESSION invoked with the
      client ID until all operations in progress are completed or
      aborted.

   o  The server will not reply to subsequent EXCHANGE_ID operations
      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  In implementations where the NFS server is deployed as a cluster,
      it does support client ID trunking, 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 affect all sessions,
      regardless of what node the sessions were created on.














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14.2.  Operation 48: GETDEVICELIST - Get all device mappings for a file
       system

14.2.1.  ARGUMENT

   <CODE BEGINS>

   struct GETDEVICELIST4args {
           /* CURRENT_FH: object belonging to the file system */
           layouttype4     gdla_layout_type;

           /* number of device IDs to return */
           count4          gdla_maxdevices;

           nfs_cookie4     gdla_cookie;
           verifier4       gdla_cookieverf;
   };

   <CODE ENDS>

14.2.2.  RESULT

   <CODE BEGINS>

   struct GETDEVICELIST4resok {
           nfs_cookie4             gdlr_cookie;
           verifier4               gdlr_cookieverf;
           deviceid4               gdlr_deviceid_list<>;
           bool                    gdlr_eof;
   };

   union GETDEVICELIST4res switch (nfsstat4 gdlr_status) {
   case NFS4_OK:
           GETDEVICELIST4resok     gdlr_resok4;
   default:
           void;
   };

   <CODE ENDS>

14.2.3.  MOTIVATION

   The GETDEVICELIST operation was introduced in [RFC5661] specifically
   to request a list of devices at file system mount time from block
   layout type servers.  However, the use of the GETDEVICELIST operation
   introduces a race condition versus notification about changes to pNFS
   device IDs as provided by CB_NOTIFY_DEVICEID.  Implementation
   experience with block layout servers has shown that there is no need



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   for GETDEVICELIST.  Clients have to be able to request new devices
   using GETDEVICEINFO at any time in response to either a new deviceid
   in LAYOUTGET results or the CB_NOTIFY_DEVICEID callback operation.

14.2.4.  DESCRIPTION

   Clients and servers MUST NOT implement the GETDEVICELIST operation.

15.  NFSv4.2 Operations

15.1.  Operation 59: ALLOCATE - Reserve space in a region of a file

15.1.1.  ARGUMENT

   <CODE BEGINS>

   struct ALLOCATE4args {
           /* CURRENT_FH: file */
           stateid4        aa_stateid;
           offset4         aa_offset;
           length4         aa_length;
   };

   <CODE ENDS>

15.1.2.  RESULT

   <CODE BEGINS>

   struct ALLOCATE4res {
           nfsstat4        ar_status;
   };

   <CODE ENDS>

15.1.3.  DESCRIPTION

   Whenever a client wishes to reserve space for a region in a file, it
   calls the ALLOCATE operation with the current filehandle set to the
   filehandle of the file in question, and with the start offset and
   length in bytes of the region set in aa_offset and aa_length,
   respectively.

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






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   The aa_stateid MUST refer to a stateid that is valid for a WRITE
   operation and follows the rules for stateids in Sections 8.2.5 and
   18.32.3 of [RFC5661].

   The server will ensure that backing blocks are reserved to the region
   specified by aa_offset and aa_length, and that no future writes into
   this region will return NFS4ERR_NOSPC.  If the region lies partially
   or fully outside the current file size, the file size will be set to
   aa_offset + aa_length implicitly.  If the server cannot guarantee
   this, it must return NFS4ERR_NOSPC.

   The ALLOCATE operation can also be used to extend the size of a file
   if the region specified by aa_offset and aa_length extends beyond the
   current file size.  In that case, any data outside of the previous
   file size will return zeros when read before data is written to it.

   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
   deferral does not result in an asynchronous reply.

   The ALLOCATE operation will result in the space_used and space_freed
   attributes being increased by the number of bytes reserved, unless
   they were previously reserved or written and not shared.

15.2.  Operation 60: COPY - Initiate a server-side copy

15.2.1.  ARGUMENT

   <CODE BEGINS>

   struct COPY4args {
           /* SAVED_FH: source file */
           /* CURRENT_FH: destination file */
           stateid4        ca_src_stateid;
           stateid4        ca_dst_stateid;
           offset4         ca_src_offset;
           offset4         ca_dst_offset;
           length4         ca_count;
           bool            ca_consecutive;
           bool            ca_synchronous;
           netloc4         ca_source_server<>;
   };

   <CODE ENDS>






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15.2.2.  RESULT

   <CODE BEGINS>

   struct write_response4 {
           stateid4        wr_callback_id<1>;
           length4         wr_count;
           stable_how4     wr_committed;
           verifier4       wr_writeverf;
   };

   struct copy_requirements4 {
           bool            cr_consecutive;
           bool            cr_synchronous;
   };

   struct COPY4resok {
           write_response4         cr_response;
           copy_requirements4      cr_requirements;
   };

   union COPY4res switch (nfsstat4 cr_status) {
   case NFS4_OK:
           COPY4resok              cr_resok4;
   case NFS4ERR_OFFLOAD_NO_REQS:
           copy_requirements4      cr_requirements;
   default:
           void;
   };

   <CODE ENDS>

15.2.3.  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 range in the file specified by SAVED_FH be copied to a range
   in the file specified by CURRENT_FH.

   Both SAVED_FH and CURRENT_FH must be regular files.  If either
   SAVED_FH or CURRENT_FH is not a regular file, the operation MUST fail
   and return NFS4ERR_WRONG_TYPE.

   SAVED_FH and CURRENT_FH must be different files.  If SAVED_FH and
   CURRENT_FH refer to the same file, the operation MUST fail with
   NFS4ERR_INVAL.




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   If the request is for an inter-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.

   If a server supports the inter-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.
   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 filehandle at that point.

   The ca_dst_stateid MUST refer to a stateid that is valid for a WRITE
   operation and follows the rules for stateids in Sections 8.2.5 and
   18.32.3 of [RFC5661].  For an inter-server copy, the ca_src_stateid
   MUST be the cnr_stateid returned from the earlier COPY_NOTIFY
   operation, while for an intra-server copy ca_src_stateid MUST refer
   to a stateid that is valid for a READ operation and follows the rules
   for stateids in Sections 8.2.5 and 18.22.3 of [RFC5661].  If either
   stateid is invalid, then 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 EOF 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).











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   If the source offset or the source offset plus count is greater than
   the size of the source file, the operation MUST fail with
   NFS4ERR_INVAL.  The destination offset or destination offset plus
   count may be greater than the size of the destination file.  This
   allows the client to issue parallel copies to implement operations
   such as

   <CODE BEGINS>

      % cat file1 file2 file3 file4 > dest

   <CODE ENDS>

   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 MUST 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 that specifies both a
   protocol service and server name.  Server-to-server copy protocol
   considerations are described in Sections 4.6 and 4.9.1.

   If ca_consecutive is set, then the client has specified that the copy
   protocol selected MUST copy bytes in consecutive order from
   ca_src_offset to ca_count.  If the destination server cannot meet
   this requirement, then it MUST return an error of
   NFS4ERR_OFFLOAD_NO_REQS and set cr_consecutive to be FALSE.
   Likewise, if ca_synchronous is set, then the client has required that
   the copy protocol selected MUST perform a synchronous copy.  If the
   destination server cannot meet this requirement, then it MUST return
   an error of NFS4ERR_OFFLOAD_NO_REQS and set cr_synchronous to be
   FALSE.

   If both are set by the client, then the destination SHOULD try to
   determine if it can respond to both requirements at the same time.
   If it cannot make that determination, it must set to TRUE the one it
   can and set to FALSE the other.  The client, upon getting an
   NFS4ERR_OFFLOAD_NO_REQS error, has to examine both cr_consecutive and
   cr_synchronous against the respective values of ca_consecutive and
   ca_synchronous to determine the possible requirement not met.  It
   MUST be prepared for the destination server not being able to
   determine both requirements at the same time.






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   Upon receiving the NFS4ERR_OFFLOAD_NO_REQS error, the client has to
   determine whether it wants to re-request the copy with a relaxed set
   of requirements or revert to manually copying the data.  If it
   decides to manually copy the data and this is a remote copy, then the
   client is responsible for informing the source that the earlier
   COPY_NOTIFY is no longer valid by sending it an OFFLOAD_CANCEL.

   If the operation does not result in an immediate failure, the server
   will return NFS4_OK.

   If the wr_callback_id is returned, this indicates that an
   asynchronous COPY operation was initiated and a CB_OFFLOAD callback
   will deliver the final results of the operation.  The wr_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 wr_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 files differently.

   If a failure does occur for a synchronous copy, wr_count will be set
   to the number of bytes copied to the destination file before the
   error occurred.  If cr_consecutive is TRUE, then the bytes were
   copied in order.  If the failure occurred for an asynchronous copy,
   then the client will have gotten the notification of the consecutive
   copy order when it got the copy stateid.  It will be able to
   determine the bytes copied from the coa_bytes_copied in the
   CB_OFFLOAD argument.

   In either case, if cr_consecutive was not TRUE, there is no assurance
   as to exactly which bytes in the range were copied.  The client MUST
   assume that there exists a mixture of the original contents of the
   range and the new bytes.  If the COPY wrote past the end of the file
   on the destination, then the last byte written to will determine the
   new file size.  The contents of any block not written to and past
   the original size of the file will be as if a normal WRITE extended
   the file.





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

15.3.1.  ARGUMENT

   <CODE BEGINS>

   struct COPY_NOTIFY4args {
           /* CURRENT_FH: source file */
           stateid4        cna_src_stateid;
           netloc4         cna_destination_server;
   };

   <CODE ENDS>

15.3.2.  RESULT

   <CODE BEGINS>

   struct COPY_NOTIFY4resok {
           nfstime4        cnr_lease_time;
           stateid4        cnr_stateid;
           netloc4         cnr_source_server<>;
   };

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

   <CODE ENDS>

15.3.3.  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_src_stateid MUST refer to either open or locking states
   provided earlier by the server.  If it is invalid, then the operation
   MUST fail.

   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.



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   If this operation succeeds, the source server will allow the
   cna_destination_server to copy the specified file on behalf of the
   given user 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.  If the
      cnr_lease_time expires before the destination server uses READ or
      READ_PLUS to begin the transfer, the source server can use
      NFS4ERR_PARTNER_NO_AUTH to inform the destination server that the
      cnr_lease_time has expired.

   o  The client has not issued an OFFLOAD_CANCEL 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 avoid the need for
   synchronized clocks, copy lease times are granted by the server as a
   time delta.  To renew the copy lease time, the client should resend
   the same copy notification request to the source server.

   The cnr_stateid is a copy stateid that uniquely describes the state
   needed on the source server to track the proposed COPY.  As defined
   in Section 8.2 of [RFC5661], a stateid is tied to the current
   filehandle, and if the same stateid is presented by two different
   clients, it may refer to different states.  As the source does not
   know which netloc4 network location the destination might use to
   establish the COPY operation, it can use the cnr_stateid to identify
   that the destination is operating on behalf of the client.  Thus, the
   source server MUST construct copy stateids such that they are
   distinct from all other stateids handed out to clients.  These copy
   stateids MUST denote the same set of locks as each of the earlier
   delegation, locking, and open states for the client on the given file
   (see Section 4.3.1).

   A successful response will also contain a list of netloc4 network
   location formats 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.

   This operation is unnecessary for an intra-server copy.








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15.4.  Operation 62: DEALLOCATE - Unreserve space in a region of a file

15.4.1.  ARGUMENT

   <CODE BEGINS>

   struct DEALLOCATE4args {
           /* CURRENT_FH: file */
           stateid4        da_stateid;
           offset4         da_offset;
           length4         da_length;
   };

   <CODE ENDS>

15.4.2.  RESULT

   <CODE BEGINS>

   struct DEALLOCATE4res {
           nfsstat4        dr_status;
   };

   <CODE ENDS>

15.4.3.  DESCRIPTION

   Whenever a client wishes to unreserve space for a region in a file,
   it calls the DEALLOCATE operation with the current filehandle set to
   the filehandle of the file in question, and with the start offset and
   length in bytes of the region set in da_offset and da_length,
   respectively.  If no space was allocated or reserved for all or parts
   of the region, the DEALLOCATE operation will have no effect for the
   region that already is in unreserved state.  All further READs from
   the region passed to DEALLOCATE MUST return zeros until overwritten.

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

   The da_stateid MUST refer to a stateid that is valid for a WRITE
   operation and follows the rules for stateids in Sections 8.2.5 and
   18.32.3 of [RFC5661].









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   Situations may arise where da_offset and/or da_offset + da_length
   will not be aligned to a boundary for which the server does
   allocations or deallocations.  For most file systems, 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.

   DEALLOCATE 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.

15.5.  Operation 63: IO_ADVISE - Send client I/O access pattern hints to
       the server

15.5.1.  ARGUMENT

   <CODE BEGINS>

   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        iaa_stateid;
           offset4         iaa_offset;
           length4         iaa_count;
           bitmap4         iaa_hints;
   };

   <CODE ENDS>








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15.5.2.  RESULT

   <CODE BEGINS>

   struct IO_ADVISE4resok {
           bitmap4 ior_hints;
   };

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

   <CODE ENDS>

15.5.3.  DESCRIPTION

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

   The following are the allowed hints for a stateid holder:

   IO_ADVISE4_NORMAL  There is no advice to give.  This is the default
      behavior.

   IO_ADVISE4_SEQUENTIAL  Expects to access the specified data
      sequentially from lower offsets to higher offsets.

   IO_ADVISE4_SEQUENTIAL_BACKWARDS  Expects to access the specified data
      sequentially from higher offsets to lower offsets.

   IO_ADVISE4_RANDOM  Expects to access the specified data in a random
      order.

   IO_ADVISE4_WILLNEED  Expects to access the specified data in the near
      future.

   IO_ADVISE4_WILLNEED_OPPORTUNISTIC  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.



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   IO_ADVISE_DONTNEED  Expects that it will not access the specified
      data in the near future.

   IO_ADVISE_NOREUSE  Expects to access the specified data once and then
      not reuse it thereafter.

   IO_ADVISE4_READ  Expects to read the specified data in the near
      future.

   IO_ADVISE4_WRITE  Expects to write the specified data in the near
      future.

   IO_ADVISE4_INIT_PROXIMITY  Informs the server that the data in the
      byte range remains important to the client.

   Since IO_ADVISE is a hint, a server SHOULD NOT return an error and
   invalidate an entire COMPOUND request if one of the sent hints in
   iar_hints is not supported by the server.  Also, the server MUST NOT
   return an error 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 these cases, the server MUST return success
   and an ior_hints value that indicates the hint it intends to
   implement.  This may mean simply returning IO_ADVISE4_NORMAL.

   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, the server may need to change its handling of a given file
   -- for example, because of memory pressure, additional IO_ADVISE
   hints sent by other clients, or heuristically detected file access
   patterns.

   The server MAY return different advice than what the client
   requested.  Some examples include another client advising of a
   different I/O access pattern, another client employing a different
   I/O access pattern, or inability of the server to support the
   requested I/O access pattern.

   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 stateid and
   byte range.

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





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15.5.4.  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.

15.5.5.  IO_ADVISE4_INIT_PROXIMITY

   The IO_ADVISE4_INIT_PROXIMITY hint is non-POSIX in origin and can be
   used to convey that the client has recently accessed the byte range
   in its own cache.  That is, it has not accessed it on the server but
   has accessed it locally.  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 as to
   which delegations are more important, because if delegations are
   working correctly, once delegated to a client and the client has read
   the content for that byte range, a server might never receive another
   READ request for that byte range.

   The IO_ADVISE4_INIT_PROXIMITY hint can also be used in a pNFS setting
   to let the client inform the metadata server as to the I/O statistics
   between the client and the storage devices.  The metadata server is
   then free to use this information about client I/O to optimize the
   data storage location.

   This hint is also useful in the case of NFS clients that are network-
   booting from a server.  If the first client to be booted sends this
   hint, then it keeps the cache warm for the remaining clients.

15.5.6.  pNFS File Layout Data Type Considerations

   The IO_ADVISE considerations for pNFS are very similar to the COMMIT
   considerations for pNFS (see Section 13.7 of [RFC5661]).  That is, as
   with COMMIT, some NFS server implementations prefer that IO_ADVISE be
   done on the storage device, and some prefer that it be done on the
   metadata server.

   For the file's layout type, NFSv4.2 includes an additional hint,
   NFL42_CARE_IO_ADVISE_THRU_MDS, which is valid only on metadata
   servers running NFSv4.2 or higher.  ("NFL" stands for "NFS File
   Layout".)  Any file's layout obtained from an NFSv4.1 metadata server
   MUST NOT have NFL42_UFLG_IO_ADVISE_THRU_MDS set.  Any file's layout




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   obtained with an NFSv4.2 metadata server MAY have
   NFL42_UFLG_IO_ADVISE_THRU_MDS set.  However, if the layout utilizes
   NFSv4.1 storage devices, the IO_ADVISE operation cannot be sent
   to them.

   If NFL42_UFLG_IO_ADVISE_THRU_MDS is set, the client MUST send the
   IO_ADVISE operation to the metadata server in order for it to be
   honored by the storage device.  Once the metadata server receives the
   IO_ADVISE operation, it will communicate the advice to each storage
   device.

   If NFL42_UFLG_IO_ADVISE_THRU_MDS is not set, then the client SHOULD
   send an IO_ADVISE operation to the appropriate storage device for the
   specified byte range.  While the client MAY always send IO_ADVISE to
   the metadata server, 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 storage device for the same
   open file reference.

   The server is not required to support different advice for different
   storage devices with the same open file reference.

15.5.6.1.  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 (see
   Section 13.4.4 of [RFC5661]).

   For example, if NFL4_UFLG_DENSE is present, then (1) a READ or WRITE
   to the storage device for iaa_offset 0 really means iaa_offset 10000
   in the logical file and (2) an IO_ADVISE for iaa_offset 0 means
   iaa_offset 10000 in the logical file.

   For example, if NFL4_UFLG_DENSE is absent, then (1) a READ or WRITE
   to the storage device for iaa_offset 0 really means iaa_offset 0 in
   the logical file and (2) an IO_ADVISE for iaa_offset 0 means
   iaa_offset 0 in the logical file.













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   For example, if NFL4_UFLG_DENSE is present, the stripe unit is
   1000 bytes and the stripe count is 10, and the dense storage device
   file is serving iar_offset 0.  A READ or WRITE to the storage device
   for iaa_offsets 0, 1000, 2000, and 3000 really means iaa_offsets
   10000, 20000, 30000, and 40000 (implying a stripe count of 10 and a
   stripe unit of 1000), and then an IO_ADVISE sent to the same storage
   device with an iaa_offset of 500 and an iaa_count of 3000 means that
   the IO_ADVISE applies to these byte ranges of the dense storage
   device file:

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

   That is, 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)

   For example, if NFL4_UFLG_DENSE is absent, the stripe unit is
   250 bytes, the stripe count is 4, and the sparse storage device file
   is serving iaa_offset 0.  Then, a READ or WRITE to the storage device
   for iaa_offsets 0, 1000, 2000, and 3000 really means iaa_offsets 0,
   1000, 2000, and 3000 in the logical file, keeping in mind that in the
   storage device 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 storage device with an iaa_offset of 500 and an iaa_count
   of 3000 means that the IO_ADVISE applies to these byte ranges of the
   logical file and the sparse storage device 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





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   If neither the NFL42_UFLG_IO_ADVISE_THRU_MDS flag nor the
   NFL4_UFLG_DENSE flag is set in the layout, then any IO_ADVISE request
   sent to the data server with a byte range that overlaps stripe units
   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.

15.6.  Operation 64: LAYOUTERROR - Provide errors for the layout

15.6.1.  ARGUMENT

   <CODE BEGINS>

   struct device_error4 {
           deviceid4       de_deviceid;
           nfsstat4        de_status;
           nfs_opnum4      de_opnum;
   };

   struct LAYOUTERROR4args {
           /* CURRENT_FH: file */
           offset4                 lea_offset;
           length4                 lea_length;
           stateid4                lea_stateid;
           device_error4           lea_errors<>;
   };

   <CODE ENDS>

15.6.2.  RESULT

   <CODE BEGINS>

   struct LAYOUTERROR4res {
           nfsstat4        ler_status;
   };

   <CODE ENDS>

15.6.3.  DESCRIPTION

   The client can use LAYOUTERROR to inform the metadata server about
   errors in its interaction with the layout (see Section 12 of
   [RFC5661]) represented by the current filehandle, client ID (derived
   from the session ID in the preceding SEQUENCE operation), byte range
   (lea_offset + lea_length), and lea_stateid.



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   Each individual device_error4 describes a single error associated
   with a storage device, which is identified via de_deviceid.  If the
   layout type (see Section 12.2.7 of [RFC5661]) supports NFSv4
   operations, then the operation that returned the error is identified
   via de_opnum.  If the layout type does not support NFSv4 operations,
   then either (1) it MAY choose to map the operation onto one of the
   allowed operations that can be sent to a storage device with the file
   layout type (see Section 3.3) or (2) it can signal no support for
   operations by marking de_opnum with the ILLEGAL operation.  Finally,
   the NFS error value (nfsstat4) encountered is provided via de_status
   and may consist of the following error codes:

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

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

   Note that while the metadata server may return an error associated
   with the layout stateid or the open file, it MUST NOT return an error
   in the processing of the errors.  If LAYOUTERROR is in a COMPOUND
   before LAYOUTRETURN, it MUST NOT introduce an error other than what
   LAYOUTRETURN would already encounter.

15.6.4.  IMPLEMENTATION

   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 metadata server to consider
   such issues to be transient.  A prime example of this is if the
   metadata server fences off a client from either a stateid or a
   filehandle.  The client will get an error from the storage device and
   might relay either NFS4ERR_ACCESS or NFS4ERR_BAD_STATEID back to the
   metadata server, with the belief that this is a hard error.  If the
   metadata server is informed by the client that there is an error, it
   can safely ignore that.  For the metadata server, the mission is
   accomplished in that the client has returned a layout that the
   metadata server had most likely recalled.










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   The client might also need to inform the metadata server that it
   cannot reach one or more of the storage devices.  While the metadata
   server can detect the connectivity of both of these paths:

   o  metadata server to storage device

   o  metadata server to client

   it cannot determine if the client and storage device path is working.
   As with the case of the storage device passing errors to the client,
   it must be prepared for the metadata server to consider such outages
   as being transitory.

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

   When an I/O to a storage device fails, the client SHOULD retry the
   failed I/O via the metadata server.  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
   storage device 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 metadata server.  If the client
   does not do this, the metadata server 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 metadata server, the metadata server may silently
   ignore this functionality.  Also, as the metadata server may consider
   some issues the client reports to be expected, the client might find
   it difficult to detect a metadata server that has not implemented
   error handling via LAYOUTERROR.

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



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   Also, in the case of existing files, the metadata server might have
   no choice regarding which storage devices to hand out to clients.

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

15.7.  Operation 65: LAYOUTSTATS - Provide statistics for the layout

15.7.1.  ARGUMENT

   <CODE BEGINS>

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

   struct io_info4 {
           uint64_t        ii_count;
           uint64_t        ii_bytes;
   };

   struct LAYOUTSTATS4args {
           /* CURRENT_FH: file */
           offset4                 lsa_offset;
           length4                 lsa_length;
           stateid4                lsa_stateid;
           io_info4                lsa_read;
           io_info4                lsa_write;
           deviceid4               lsa_deviceid;
           layoutupdate4           lsa_layoutupdate;
   };

   <CODE ENDS>

15.7.2.  RESULT

   <CODE BEGINS>

   struct LAYOUTSTATS4res {
           nfsstat4        lsr_status;
   };

   <CODE ENDS>




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15.7.3.  DESCRIPTION

   The client can use LAYOUTSTATS to inform the metadata server about
   its interaction with the layout (see Section 12 of [RFC5661])
   represented by the current filehandle, client ID (derived from the
   session ID in the preceding SEQUENCE operation), byte range
   (lsa_offset and lsa_length), and lsa_stateid.  lsa_read and lsa_write
   allow non-layout-type-specific statistics to be reported.
   lsa_deviceid allows the client to specify to which storage device the
   statistics apply.  The remaining information the client is presenting
   is specific to the layout type and presented in the lsa_layoutupdate
   field.  Each layout type MUST define the contents of lsa_layoutupdate
   in their respective specifications.

   LAYOUTSTATS can be combined with IO_ADVISE (see Section 15.5) to
   augment the decision-making process of how the metadata server
   handles a file.  That is, IO_ADVISE lets the server know that a byte
   range has a certain characteristic, but not necessarily the intensity
   of that characteristic.

   The statistics are cumulative, i.e., multiple LAYOUTSTATS updates can
   be in flight at the same time.  The metadata server can examine the
   packet's timestamp to order the different calls.  The first
   LAYOUTSTATS sent by the client SHOULD be from the opening of the
   file.  The choice of how often to update the metadata server is made
   by the client.

   Note that while the metadata server may return an error associated
   with the layout stateid or the open file, it MUST NOT return an error
   in the processing of the statistics.





















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15.8.  Operation 66: OFFLOAD_CANCEL - Stop an offloaded operation

15.8.1.  ARGUMENT

   <CODE BEGINS>

   struct OFFLOAD_CANCEL4args {
           /* CURRENT_FH: file to cancel */
           stateid4        oca_stateid;
   };

   <CODE ENDS>

15.8.2.  RESULT

   <CODE BEGINS>

   struct OFFLOAD_CANCEL4res {
           nfsstat4        ocr_status;
   };

   <CODE ENDS>

15.8.3.  DESCRIPTION

   OFFLOAD_CANCEL is used by the client to terminate an asynchronous
   operation, which is identified by both CURRENT_FH and the
   oca_stateid.  That is, there can be multiple OFFLOAD_CANCEL
   operations acting on the file, and the stateid will identify to the
   server exactly which one is to be stopped.  Currently, there are only
   two operations that can decide to be asynchronous: COPY and
   WRITE_SAME.

   In the context of server-to-server copy, the client can send
   OFFLOAD_CANCEL to either the source or destination server, albeit
   with a different stateid.  The client uses OFFLOAD_CANCEL to inform
   the destination to stop the active transfer and uses the stateid it
   got back from the COPY operation.  The client uses OFFLOAD_CANCEL and
   the stateid it used in the COPY_NOTIFY to inform the source to not
   allow any more copying from the destination.

   OFFLOAD_CANCEL is also 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.






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15.9.  Operation 67: OFFLOAD_STATUS - Poll for the status of an
       asynchronous operation

15.9.1.  ARGUMENT

   <CODE BEGINS>

   struct OFFLOAD_STATUS4args {
           /* CURRENT_FH: destination file */
           stateid4        osa_stateid;
   };

   <CODE ENDS>

15.9.2.  RESULT

   <CODE BEGINS>

   struct OFFLOAD_STATUS4resok {
           length4         osr_count;
           nfsstat4        osr_complete<1>;
   };

   union OFFLOAD_STATUS4res switch (nfsstat4 osr_status) {
   case NFS4_OK:
           OFFLOAD_STATUS4resok            osr_resok4;
   default:
           void;
   };

   <CODE ENDS>

15.9.3.  DESCRIPTION

   OFFLOAD_STATUS can be used by the client to query the progress of an
   asynchronous operation, which is identified by both CURRENT_FH and
   the osa_stateid.  If this operation is successful, the number of
   bytes processed is returned to the client in the osr_count field.

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

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




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15.10.  Operation 68: READ_PLUS - READ data or holes from a file

15.10.1.  ARGUMENT

   <CODE BEGINS>

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

   <CODE ENDS>

15.10.2.  RESULT

   <CODE BEGINS>

   enum data_content4 {
           NFS4_CONTENT_DATA = 0,
           NFS4_CONTENT_HOLE = 1
   };

   struct data_info4 {
           offset4         di_offset;
           length4         di_length;
   };

   struct data4 {
           offset4         d_offset;
           opaque          d_data<>;
   };

   union read_plus_content switch (data_content4 rpc_content) {
   case NFS4_CONTENT_DATA:
           data4           rpc_data;
   case NFS4_CONTENT_HOLE:
           data_info4      rpc_hole;
   default:
           void;
   };









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   /*
    * 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 rp_status) {
   case NFS4_OK:
           read_plus_res4  rp_resok4;
   default:
           void;
   };

   <CODE ENDS>

15.10.3.  DESCRIPTION

   The READ_PLUS operation is based upon the NFSv4.1 READ operation (see
   Section 18.22 of [RFC5661]) and similarly reads data from the regular
   file identified by the current filehandle.

   The client provides an rpa_offset of where the READ_PLUS is to start
   and an rpa_count of how many bytes are to be read.  An rpa_offset of
   zero means that data will be read 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.

   The READ_PLUS result is comprised of an array of rpr_contents, each
   of which describes a data_content4 type of data.  For NFSv4.2, the
   allowed values are data and hole.  A server MUST support both the
   data type and the hole if it uses READ_PLUS.  If it does not want to
   support a hole, it MUST use READ.  The array contents MUST be
   contiguous in the file.

   Holes SHOULD be returned in their entirety -- clients must be
   prepared to get more information than they requested.  Both the start
   and the end of the hole may exceed what was requested.  If data to be
   returned is comprised entirely of zeros, then the server SHOULD
   return that data as a hole instead.

   The server may elect to return adjacent elements of the same type.
   For example, 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.




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   If the client specifies an rpa_count value of zero, the READ_PLUS
   succeeds and returns zero bytes of 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 data that is entirely contained within a hole
   of the file (i.e., both rpa_offset and rpa_offset + rpa_count are
   within the hole), then the di_offset and di_length returned MAY be
   for the entire hole.  If the owner has a locked byte range covering
   rpa_offset and rpa_count entirely, the di_offset and di_length MUST
   NOT be extended outside the locked byte range.  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 zeros; the implied
   hole's contents lifetime MUST be exactly the same as any other
   read data.

   If the client specifies data by an rpa_offset that begins in a
   non-hole of the file but extends into a hole (the rpa_offset +
   rpa_count is in the 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,
   to 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 the 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.





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   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.

15.10.3.1.  Note on Client Support of Arms of the Union

   It was decided not to add a means for the client to inform the server
   as to which arms of READ_PLUS it would support.  In a later minor
   version, it may become necessary for the introduction of a new
   operation that would allow the client to inform the server as to
   whether it supported the new arms of the union of data types
   available in READ_PLUS.

15.10.4.  IMPLEMENTATION

   In general, the IMPLEMENTATION notes for READ in Section 18.22.4 of
   [RFC5661] also apply to READ_PLUS.

15.10.4.1.  Additional pNFS Implementation Information

   With pNFS, the semantics of using READ_PLUS remains the same.  Any
   data server MAY return a hole result for a READ_PLUS request that it
   receives.  When a data server chooses to return such a result, it has
   the option of returning 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.

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















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15.10.5.  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 will only create a hole if it is greater
   than 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 7: Sparse File

   Under the given circumstances, if a client was to read from the file
   with a maximum read size of 64K, the following will be the results
   for the given READ_PLUS calls.  This assumes that 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
       minimum hole size, the first 32K of the file is returned as data
       and the remaining 32K is returned as a hole that 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
       that there is no more data in the file.





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15.11.  Operation 69: SEEK - Find the next data or hole

15.11.1.  ARGUMENT

   <CODE BEGINS>

   enum data_content4 {
           NFS4_CONTENT_DATA = 0,
           NFS4_CONTENT_HOLE = 1
   };

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

   <CODE ENDS>

15.11.2.  RESULT

   <CODE BEGINS>

   struct seek_res4 {
           bool            sr_eof;
           offset4         sr_offset;
   };

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

   <CODE ENDS>

15.11.3.  DESCRIPTION

   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 the lseek(2) function to allow clients to
   determine the next hole whilst in data or the next data whilst in
   a hole.






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   From the given sa_offset, find the next data_content4 of type sa_what
   in the file.  If the server cannot find a corresponding sa_what, then
   the status will still be NFS4_OK, but sr_eof would be TRUE.  If the
   server can find the sa_what, then the sr_offset is the start of that
   content.  If the sa_offset is beyond the end of the file, then SEEK
   MUST return NFS4ERR_NXIO.

   All files MUST have a virtual hole at the end of the file.  That is,
   if a file system does not support sparse files, then a COMPOUND with
   {SEEK 0 NFS4_CONTENT_HOLE;} would return a result of {SEEK 1 X;},
   where "X" was the size of the file.

   SEEK must follow the same rules for stateids as READ_PLUS
   (Section 15.10.3).

15.12.  Operation 70: WRITE_SAME - WRITE an ADB multiple times to a file

15.12.1.  ARGUMENT

   <CODE BEGINS>

   enum stable_how4 {
           UNSTABLE4       = 0,
           DATA_SYNC4      = 1,
           FILE_SYNC4      = 2
   };

   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<>;
   };

   struct WRITE_SAME4args {
           /* CURRENT_FH: file */
           stateid4        wsa_stateid;
           stable_how4     wsa_stable;
           app_data_block4 wsa_adb;
   };

   <CODE ENDS>






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15.12.2.  RESULT

   <CODE BEGINS>

   struct write_response4 {
           stateid4        wr_callback_id<1>;
           length4         wr_count;
           stable_how4     wr_committed;
           verifier4       wr_writeverf;
   };

   union WRITE_SAME4res switch (nfsstat4 wsr_status) {
   case NFS4_OK:
           write_response4         resok4;
   default:
           void;
   };

   <CODE ENDS>

15.12.3.  DESCRIPTION

   The WRITE_SAME operation writes an application data block to the
   regular file identified by the current filehandle (see
   WRITE SAME (10) in [T10-SBC2]).  The target file is specified by the
   current filehandle.  The data to be written is specified by an
   app_data_block4 structure (Section 8.1.1).  The client specifies with
   the wsa_stable parameter the method of how the data is to be
   processed by the server.  It is treated like the stable parameter in
   the NFSv4.1 WRITE operation (see Section 18.32.3 of [RFC5661]).

   A successful WRITE_SAME will construct a reply for wr_count,
   wr_committed, and wr_writeverf as per the NFSv4.1 WRITE operation
   results.  If wr_callback_id is set, it indicates an asynchronous
   reply (see Section 15.12.3.1).

   As it is an OPTIONAL operation, WRITE_SAME has to support
   NFS4ERR_NOTSUPP.  As it is an extension of WRITE, it has to support
   all of the errors returned by WRITE.  If the client supports
   WRITE_SAME, it MUST support CB_OFFLOAD.

   If the server supports ADBs, then it MUST support the WRITE_SAME
   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 WRITE_SAME.




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   When the client invokes the WRITE_SAME operation, it wants to record
   the block structure described by the app_data_block4 into the file.

   When the server receives the WRITE_SAME operation, it MUST populate
   adb_block_count ADBs in the file, starting at adb_offset.  The block
   size will be given by adb_block_size.  The ADBN (if provided) will
   start at adb_reloff_blocknum, and each block will be monotonically
   numbered, starting from adb_block_num in the first block.  The
   pattern (if provided) will be at adb_reloff_pattern of each block and
   will be provided in adb_pattern.

   The server SHOULD return an asynchronous result if it can determine
   that the operation will be long-running (see Section 15.12.3.1).
   Once either the WRITE_SAME finishes synchronously or the server uses
   CB_OFFLOAD to inform the client of the asynchronous completion of the
   WRITE_SAME, the server MUST return the ADBs to clients as data.

15.12.3.1.  Asynchronous Transactions

   ADB initialization may cause a server to decide to service the
   operation asynchronously.  If it decides to do so, it sets the
   stateid in wr_callback_id to be that of the wsa_stateid.  If it does
   not set the wr_callback_id, then the result is synchronous.

   When the client determines that the reply will be given
   asynchronously, it should not assume anything about the contents of
   what it wrote until it is informed by the server that the operation
   is complete.  It can use OFFLOAD_STATUS (Section 15.9) to monitor the
   operation and OFFLOAD_CANCEL (Section 15.8) to cancel the operation.
   An example of an asynchronous WRITE_SAME is shown in Figure 6.  Note
   that, as with the COPY operation, WRITE_SAME must provide a stateid
   for tracking the asynchronous operation.



















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     Client                                  Server
        +                                      +
        |                                      |
        |--- OPEN ---------------------------->| Client opens
        |<------------------------------------/| the file
        |                                      |
        |--- WRITE_SAME ---------------------->| Client initializes
        |<------------------------------------/| an ADB
        |                                      |
        |                                      |
        |--- OFFLOAD_STATUS ------------------>| Client may poll
        |<------------------------------------/| for status
        |                                      |
        |                  .                   | Multiple OFFLOAD_STATUS
        |                  .                   | operations may be sent.
        |                  .                   |
        |                                      |
        |<-- CB_OFFLOAD -----------------------| Server reports results
        |\------------------------------------>|
        |                                      |
        |--- CLOSE --------------------------->| Client closes
        |<------------------------------------/| the file
        |                                      |
        |                                      |

                   Figure 6: An Asynchronous WRITE_SAME

   When CB_OFFLOAD informs the client of the successful WRITE_SAME, the
   write_response4 embedded in the operation will provide the necessary
   information that a synchronous WRITE_SAME would have provided.

   Regardless of whether the operation is asynchronous or synchronous,
   it MUST still support the COMMIT operation semantics as outlined in
   Section 18.3 of [RFC5661].  That is, COMMIT works on one or more
   WRITE operations, and the WRITE_SAME operation can appear as several
   WRITE operations to the server.  The client can use locking
   operations to control the behavior on the server with respect to
   long-running asynchronous WRITE_SAME operations.

15.12.3.2.  Error Handling of a Partially Complete WRITE_SAME

   WRITE_SAME will clone adb_block_count copies of the given ADB in
   consecutive order in the file, starting at adb_offset.  An error can
   occur after writing the Nth ADB to the file.  WRITE_SAME MUST appear
   to populate the range of the file as if the client used WRITE to
   transfer the instantiated ADBs.  That is, the contents of the range
   will be easy for the client to determine in the case of a partially
   complete WRITE_SAME.



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15.13.  Operation 71: CLONE - Clone a range of a file into another file

15.13.1.  ARGUMENT

   <CODE BEGINS>

   struct CLONE4args {
           /* SAVED_FH: source file */
           /* CURRENT_FH: destination file */
           stateid4        cl_src_stateid;
           stateid4        cl_dst_stateid;
           offset4         cl_src_offset;
           offset4         cl_dst_offset;
           length4         cl_count;
   };

   <CODE ENDS>

15.13.2.  RESULT

   <CODE BEGINS>

   struct CLONE4res {
           nfsstat4        cl_status;
   };

   <CODE ENDS>

15.13.3.  DESCRIPTION

   The CLONE operation is used to clone file content from a source file
   specified by the SAVED_FH value into a destination file specified by
   CURRENT_FH without actually copying the data, e.g., by using a
   copy-on-write mechanism.

   Both SAVED_FH and CURRENT_FH must be regular files.  If either
   SAVED_FH or CURRENT_FH is not a regular file, the operation MUST fail
   and return NFS4ERR_WRONG_TYPE.

   The ca_dst_stateid MUST refer to a stateid that is valid for a WRITE
   operation and follows the rules for stateids in Sections 8.2.5 and
   18.32.3 of [RFC5661].  The ca_src_stateid MUST refer to a stateid
   that is valid for a READ operation and follows the rules for stateids
   in Sections 8.2.5 and 18.22.3 of [RFC5661].  If either stateid is
   invalid, then the operation MUST fail.






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   The cl_src_offset is the starting offset within the source file from
   which the data to be cloned will be obtained, and the cl_dst_offset
   is the starting offset of the target region into which the cloned
   data will be placed.  An offset of 0 (zero) indicates the start of
   the respective file.  The number of bytes to be cloned is obtained
   from cl_count, except that a cl_count of 0 (zero) indicates that the
   number of bytes to be cloned is the count of bytes between
   cl_src_offset and the EOF of the source file.  Both cl_src_offset and
   cl_dst_offset must be aligned to the clone block size
   (Section 12.2.1).  The number of bytes to be cloned must be a
   multiple of the clone block size, except in the case in which
   cl_src_offset plus the number of bytes to be cloned is equal to the
   source file size.

   If the source offset or the source offset plus count is greater than
   the size of the source file, the operation MUST fail with
   NFS4ERR_INVAL.  The destination offset or destination offset plus
   count may be greater than the size of the destination file.

   If SAVED_FH and CURRENT_FH refer to the same file and the source and
   target ranges overlap, the operation MUST fail with NFS4ERR_INVAL.

   If the target area of the CLONE operation ends beyond the end of the
   destination file, the offset at the end of the target area will
   determine the new size of the destination file.  The contents of any
   block not part of the target area will be the same as if the file
   size were extended by a WRITE.

   If the area to be cloned is not a multiple of the clone block size
   and the size of the destination file is past the end of the target
   area, the area between the end of the target area and the next
   multiple of the clone block size will be zeroed.

   The CLONE operation is atomic in that other operations may not see
   any intermediate states between the state of the two files before the
   operation and after the operation.  READs of the destination file
   will never see some blocks of the target area cloned without all of
   them being cloned.  WRITEs of the source area will either have no
   effect on the data of the target file or be fully reflected in the
   target area of the destination file.

   The completion status of the operation is indicated by cr_status.









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16.  NFSv4.2 Callback Operations

16.1.  Operation 15: CB_OFFLOAD - Report the results of an asynchronous
       operation

16.1.1.  ARGUMENT

   <CODE BEGINS>

   struct write_response4 {
           stateid4        wr_callback_id<1>;
           length4         wr_count;
           stable_how4     wr_committed;
           verifier4       wr_writeverf;
   };

   union offload_info4 switch (nfsstat4 coa_status) {
   case NFS4_OK:
           write_response4 coa_resok4;
   default:
           length4         coa_bytes_copied;
   };

   struct CB_OFFLOAD4args {
           nfs_fh4         coa_fh;
           stateid4        coa_stateid;
           offload_info4   coa_offload_info;
   };

   <CODE ENDS>

16.1.2.  RESULT

   <CODE BEGINS>

   struct CB_OFFLOAD4res {
           nfsstat4        cor_status;
   };

   <CODE ENDS>











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16.1.3.  DESCRIPTION

   CB_OFFLOAD is used to report to the client the results of an
   asynchronous operation, e.g., server-side COPY or WRITE_SAME.  The
   coa_fh and coa_stateid identify the transaction, and the coa_status
   indicates success or failure.  The coa_resok4.wr_callback_id MUST NOT
   be set.  If the transaction failed, then the coa_bytes_copied
   contains the number of bytes copied before the failure occurred.  The
   coa_bytes_copied value indicates the number of bytes copied but not
   which specific bytes have been copied.

   If the client supports any of the following operations:

   COPY:  for both intra-server and inter-server asynchronous copies

   WRITE_SAME:  for ADB initialization

   then the client is REQUIRED to support the CB_OFFLOAD operation.

   There is a potential race between the reply to the original
   transaction on the forechannel and the CB_OFFLOAD callback on the
   backchannel.  Section 2.10.6.3 of [RFC5661] describes how to handle
   this type of issue.

   Upon success, the coa_resok4.wr_count presents for each operation:

   COPY:  the total number of bytes copied

   WRITE_SAME:  the same information that a synchronous WRITE_SAME would
      provide

17.  Security Considerations

   NFSv4.2 has all of the security concerns present in NFSv4.1 (see
   Section 21 of [RFC5661]), as well as those present in the server-side
   copy (see Section 4.9) and in Labeled NFS (see Section 9.6).

18.  IANA Considerations

   The IANA considerations for Labeled NFS are addressed in [RFC7569].











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19.  References

19.1.  Normative References

   [posix_fadvise]
              The Open Group, "Section 'posix_fadvise()' of System
              Interfaces of The Open Group Base Specifications Issue 7",
              IEEE Std 1003.1, 2016 Edition (HTML Version),
              ISBN 1937218812, September 2016,
              <http://www.opengroup.org/>.

   [posix_fallocate]
              The Open Group, "Section 'posix_fallocate()' of System
              Interfaces of The Open Group Base Specifications Issue 7",
              IEEE Std 1003.1, 2016 Edition (HTML Version),
              ISBN 1937218812, September 2016,
              <http://www.opengroup.org/>.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <http://www.rfc-editor.org/info/rfc2119>.

   [RFC3986]  Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
              Resource Identifier (URI): Generic Syntax", STD 66,
              RFC 3986, DOI 10.17487/RFC3986, January 2005,
              <http://www.rfc-editor.org/info/rfc3986>.

   [RFC5661]  Shepler, S., Ed., Eisler, M., Ed., and D. Noveck, Ed.,
              "Network File System (NFS) Version 4 Minor Version 1
              Protocol", RFC 5661, DOI 10.17487/RFC5661, January 2010,
              <http://www.rfc-editor.org/info/rfc5661>.

   [RFC5662]  Shepler, S., Ed., Eisler, M., Ed., and D. Noveck, Ed.,
              "Network File System (NFS) Version 4 Minor Version 1
              External Data Representation Standard (XDR) Description",
              RFC 5662, DOI 10.17487/RFC5662, January 2010,
              <http://www.rfc-editor.org/info/rfc5662>.

   [RFC7569]  Quigley, D., Lu, J., and T. Haynes, "Registry
              Specification for Mandatory Access Control (MAC) Security
              Label Formats", RFC 7569, DOI 10.17487/RFC7569, July 2015,
              <http://www.rfc-editor.org/info/rfc7569>.








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RFC 7862                         NFSv4.2                   November 2016


   [RFC7861]  Adamson, A. and N. Williams, "Remote Procedure Call (RPC)
              Security Version 3", RFC 7861, DOI 10.17487/RFC7861,
              November 2016, <http://www.rfc-editor.org/info/rfc7861>.

   [RFC7863]  Haynes, T., "Network File System (NFS) Version 4 Minor
              Version 2 External Data Representation Standard (XDR)
              Description", RFC 7863, DOI 10.17487/RFC7863,
              November 2016, <http://www.rfc-editor.org/info/rfc7863>.

19.2.  Informative References

   [Ashdown08]
              Ashdown, L., "Chapter 15: Validating Database Files and
              Backups", Oracle Database Backup and Recovery User's
              Guide 11g Release 1 (11.1), August 2008,
              <http://download.oracle.com/docs/cd/B28359_01/backup.111/
              b28270/rcmvalid.htm>.

   [Baira08]  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,
              <http://www.usenix.org/events/fast08/tech/full_papers/
              bairavasundaram/bairavasundaram.pdf>.

   [IESG08]   IESG, "IESG Processing of RFC Errata for the IETF Stream",
              July 2008, <https://www.ietf.org/iesg/statement/
              errata-processing.html>.

   [LB96]     LaPadula, L. and D. Bell, "MITRE Technical Report 2547,
              Volume II", Journal of Computer Security, Volume 4,
              Issue 2-3, 239-263, IOS Press, Amsterdam, The Netherlands,
              January 1996.

   [McDougall07]
              McDougall, R. and J. Mauro, "Section 11.4.3: Detecting
              Memory Corruption", Solaris Internals: Solaris 10 and
              OpenSolaris Kernel Architecture, 2nd Edition, 2007.

   [NFSv4-Versioning]
              Noveck, D., "Rules for NFSv4 Extensions and Minor
              Versions", Work in Progress,
              draft-ietf-nfsv4-versioning-07, October 2016.

   [RFC959]   Postel, J. and J. Reynolds, "File Transfer Protocol",
              STD 9, RFC 959, DOI 10.17487/RFC0959, October 1985,
              <http://www.rfc-editor.org/info/rfc959>.



Haynes                       Standards Track                  [Page 101]


RFC 7862                         NFSv4.2                   November 2016


   [RFC1108]  Kent, S., "U.S. Department of Defense Security Options for
              the Internet Protocol", RFC 1108, DOI 10.17487/RFC1108,
              November 1991, <http://www.rfc-editor.org/info/rfc1108>.

   [RFC2401]  Kent, S. and R. Atkinson, "Security Architecture for the
              Internet Protocol", RFC 2401, DOI 10.17487/RFC2401,
              November 1998, <http://www.rfc-editor.org/info/rfc2401>.

   [RFC4506]  Eisler, M., Ed., "XDR: External Data Representation
              Standard", STD 67, RFC 4506, DOI 10.17487/RFC4506,
              May 2006, <http://www.rfc-editor.org/info/rfc4506>.

   [RFC4949]  Shirey, R., "Internet Security Glossary, Version 2",
              FYI 36, RFC 4949, DOI 10.17487/RFC4949, August 2007,
              <http://www.rfc-editor.org/info/rfc4949>.

   [RFC5663]  Black, D., Fridella, S., and J. Glasgow, "Parallel NFS
              (pNFS) Block/Volume Layout", RFC 5663,
              DOI 10.17487/RFC5663, January 2010,
              <http://www.rfc-editor.org/info/rfc5663>.

   [RFC7204]  Haynes, T., "Requirements for Labeled NFS", RFC 7204,
              DOI 10.17487/RFC7204, April 2014,
              <http://www.rfc-editor.org/info/rfc7204>.

   [RFC7230]  Fielding, R., Ed., and J. Reschke, Ed., "Hypertext
              Transfer Protocol (HTTP/1.1): Message Syntax and Routing",
              RFC 7230, DOI 10.17487/RFC7230, June 2014,
              <http://www.rfc-editor.org/info/rfc7230>.

   [RFC7530]  Haynes, T., Ed., and D. Noveck, Ed., "Network File System
              (NFS) Version 4 Protocol", RFC 7530, DOI 10.17487/RFC7530,
              March 2015, <http://www.rfc-editor.org/info/rfc7530>.

   [Strohm11] Strohm, R., "Chapter 2: Data Blocks, Extents, and
              Segments", Oracle Database Concepts 11g Release 1 (11.1),
              January 2011,
              <http://download.oracle.com/docs/cd/B28359_01/server.111/
              b28318/logical.htm>.

   [T10-SBC2] Elliott, R., Ed., "ANSI INCITS 405-2005, Information
              Technology - SCSI Block Commands - 2 (SBC-2)",
              November 2004,
              <ftp://www.t10.org/t10/document.05/05-344r0.pdf>.







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Acknowledgments

   Tom Haynes would like to thank NetApp, Inc. for its funding of his
   time on this project.

   For the topic "sharing change attribute implementation
   characteristics with NFSv4 clients", the original document was by
   Trond Myklebust.

   For the NFS server-side copy, the original document 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 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.  Anna Schumaker's early prototyping experience helped us
   avoid some traps.  Also, both Olga Kornievskaia and Andy Adamson
   brought implementation experience to the use of copy stateids in the
   inter-server copy.  Jorge Mora was able to optimize the handling of
   errors for the result of COPY.

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

   For the sparse file support, the original document 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 I/O hints, the original document was by Dean
   Hildebrand, Mike Eisler, Trond Myklebust, and Sam Falkner.  Some
   early reviewers included Benny Halevy and Pranoop Erasani.

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

   Christoph Hellwig was very helpful in getting the WRITE_SAME
   semantics to model more of what T10 was doing for WRITE SAME (10)
   [T10-SBC2].  And he led the push to get space reservations to more
   closely model the posix_fallocate() operation.

   Andy Adamson picked up the RPCSEC_GSSv3 work, which enabled both
   Labeled NFS and server-side copy to provide more secure options.

   Christoph Hellwig provided the update to GETDEVICELIST.




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   Jorge Mora provided a very detailed review and caught some important
   issues with the tables.

   During the review process, Talia Reyes-Ortiz helped the sessions run
   smoothly.  While many people contributed here and there, the core
   reviewers were Andy Adamson, Pranoop Erasani, Bruce Fields, Chuck
   Lever, Trond Myklebust, David Noveck, Peter Staubach, and Mike
   Kupfer.

   Elwyn Davies was the General Area Reviewer for this document, and his
   insights as to the relationship of this document and both [RFC5661]
   and [RFC7530] were very much appreciated!

Author's Address

   Thomas Haynes
   Primary Data, Inc.
   4300 El Camino Real Ste 100
   Los Altos, CA  94022
   United States of America

   Phone: +1 408 215 1519
   Email: thomas.haynes@primarydata.com




























Haynes                       Standards Track                  [Page 104]


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