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NFSv4                                                          T. Haynes
Internet-Draft                                                    Editor
Intended status: Standards Track                          April 18, 2011
Expires: October 20, 2011


                     NFS Version 4 Minor Version 2
                draft-haynes-nfsv4-minorversion2-01.txt

Abstract

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

Requirements Language

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

Status of this Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
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   This Internet-Draft will expire on October 20, 2011.

Copyright Notice

   Copyright (c) 2011 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



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   publication of this document.  Please review these documents
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   it for publication as an RFC or to translate it into languages other
   than English.

































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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  5
     1.1.  The NFS Version 4 Minor Version 2 Protocol . . . . . . . .  5
     1.2.  Scope of This Document . . . . . . . . . . . . . . . . . .  5
     1.3.  NFSv4.2 Goals  . . . . . . . . . . . . . . . . . . . . . .  5
     1.4.  Overview of NFSv4.2 Features . . . . . . . . . . . . . . .  5
     1.5.  Differences from NFSv4.1 . . . . . . . . . . . . . . . . .  5
   2.  pNFS LAYOUTRETURN Error Handling . . . . . . . . . . . . . . .  5
     2.1.  Introduction . . . . . . . . . . . . . . . . . . . . . . .  5
     2.2.  Changes to Operation 51: LAYOUTRETURN  . . . . . . . . . .  6
       2.2.1.  ARGUMENT . . . . . . . . . . . . . . . . . . . . . . .  6
       2.2.2.  RESULT . . . . . . . . . . . . . . . . . . . . . . . .  6
       2.2.3.  DESCRIPTION  . . . . . . . . . . . . . . . . . . . . .  6
       2.2.4.  IMPLEMENTATION . . . . . . . . . . . . . . . . . . . .  7
   3.  Sharing change attribute implementation details with NFSv4
       clients  . . . . . . . . . . . . . . . . . . . . . . . . . . .  8
     3.1.  Abstract . . . . . . . . . . . . . . . . . . . . . . . . .  8
     3.2.  Introduction . . . . . . . . . . . . . . . . . . . . . . .  9
     3.3.  Definition of the 'change_attr_type' per-file system
           attribute  . . . . . . . . . . . . . . . . . . . . . . . .  9
   4.  NFS Server-side Copy . . . . . . . . . . . . . . . . . . . . . 10
     4.1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . 11
     4.2.  Protocol Overview  . . . . . . . . . . . . . . . . . . . . 11
       4.2.1.  Intra-Server Copy  . . . . . . . . . . . . . . . . . . 13
       4.2.2.  Inter-Server Copy  . . . . . . . . . . . . . . . . . . 14
       4.2.3.  Server-to-Server Copy Protocol . . . . . . . . . . . . 17
     4.3.  Operations . . . . . . . . . . . . . . . . . . . . . . . . 19
       4.3.1.  netloc4 - Network Locations  . . . . . . . . . . . . . 19
       4.3.2.  Operation 61: COPY_NOTIFY - Notify a source server
               of a future copy . . . . . . . . . . . . . . . . . . . 20
       4.3.3.  Operation 62: COPY_REVOKE - Revoke a destination
               server's copy privileges . . . . . . . . . . . . . . . 22
       4.3.4.  Operation 59: COPY - Initiate a server-side copy . . . 23
       4.3.5.  Operation 60: COPY_ABORT - Cancel a server-side
               copy . . . . . . . . . . . . . . . . . . . . . . . . . 31
       4.3.6.  Operation 63: COPY_STATUS - Poll for status of a
               server-side copy . . . . . . . . . . . . . . . . . . . 32
       4.3.7.  Operation 15: CB_COPY - Report results of a
               server-side copy . . . . . . . . . . . . . . . . . . . 33
       4.3.8.  Copy Offload Stateids  . . . . . . . . . . . . . . . . 35
     4.4.  Security Considerations  . . . . . . . . . . . . . . . . . 35
       4.4.1.  Inter-Server Copy Security . . . . . . . . . . . . . . 35
     4.5.  IANA Considerations  . . . . . . . . . . . . . . . . . . . 43
   5.  Space Reservation  . . . . . . . . . . . . . . . . . . . . . . 43
     5.1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . 43
     5.2.  Use Cases  . . . . . . . . . . . . . . . . . . . . . . . . 45
       5.2.1.  Space Reservation  . . . . . . . . . . . . . . . . . . 45



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       5.2.2.  Space freed on deletes . . . . . . . . . . . . . . . . 45
       5.2.3.  Operations and attributes  . . . . . . . . . . . . . . 46
       5.2.4.  Attribute 77: space_reserve  . . . . . . . . . . . . . 46
       5.2.5.  Attribute 78: space_freed  . . . . . . . . . . . . . . 47
       5.2.6.  Attribute 79: max_hole_punch . . . . . . . . . . . . . 47
       5.2.7.  Operation 64: HOLE_PUNCH - Zero and deallocate
               blocks backing the file in the specified range.  . . . 47
     5.3.  Security Considerations  . . . . . . . . . . . . . . . . . 49
     5.4.  IANA Considerations  . . . . . . . . . . . . . . . . . . . 49
   6.  Simple and Efficient Read Support for Sparse Files . . . . . . 49
     6.1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . 49
     6.2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . 50
     6.3.  Applications and Sparse Files  . . . . . . . . . . . . . . 50
     6.4.  Overview of Sparse Files and NFSv4 . . . . . . . . . . . . 51
     6.5.  Operation 65: READPLUS . . . . . . . . . . . . . . . . . . 52
       6.5.1.  ARGUMENT . . . . . . . . . . . . . . . . . . . . . . . 53
       6.5.2.  RESULT . . . . . . . . . . . . . . . . . . . . . . . . 54
       6.5.3.  DESCRIPTION  . . . . . . . . . . . . . . . . . . . . . 54
       6.5.4.  IMPLEMENTATION . . . . . . . . . . . . . . . . . . . . 56
       6.5.5.  READPLUS with Sparse Files Example . . . . . . . . . . 57
     6.6.  Related Work . . . . . . . . . . . . . . . . . . . . . . . 58
     6.7.  Other Proposed Designs . . . . . . . . . . . . . . . . . . 59
       6.7.1.  Multi-Data Server Hole Information . . . . . . . . . . 59
       6.7.2.  Data Result Array  . . . . . . . . . . . . . . . . . . 59
       6.7.3.  User-Defined Sparse Mask . . . . . . . . . . . . . . . 60
       6.7.4.  Allocated flag . . . . . . . . . . . . . . . . . . . . 60
       6.7.5.  Dense and Sparse pNFS File Layouts . . . . . . . . . . 60
     6.8.  Security Considerations  . . . . . . . . . . . . . . . . . 60
     6.9.  IANA Considerations  . . . . . . . . . . . . . . . . . . . 60
   7.  Security Considerations  . . . . . . . . . . . . . . . . . . . 60
   8.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 60
   9.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 60
     9.1.  Normative References . . . . . . . . . . . . . . . . . . . 60
     9.2.  Informative References . . . . . . . . . . . . . . . . . . 61
   Appendix A.  Acknowledgments . . . . . . . . . . . . . . . . . . . 62
   Appendix B.  RFC Editor Notes  . . . . . . . . . . . . . . . . . . 63
   Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 63














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1.  Introduction

1.1.  The NFS Version 4 Minor Version 2 Protocol

   The NFS version 4 minor version 2 (NFSv4.2) protocol is the third
   minor version of the NFS version 4 (NFSv4) protocol.  The first minor
   version, NFSv4.0, is described in [10] and the second minor version,
   NFSv4.1, is described in [2].  It follows the guidelines for minor
   versioning that are listed in Section 11 of RFC 3530bis.

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

1.2.  Scope of This Document

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

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

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

   o  clarify the NFSv4.0 or NFSv4.1 protocols.

1.3.  NFSv4.2 Goals

1.4.  Overview of NFSv4.2 Features

1.5.  Differences from NFSv4.1


2.  pNFS LAYOUTRETURN Error Handling

2.1.  Introduction

   In the pNFS description provided in [2], the client is not enabled to
   relay an error code from the DS to the MDS.  In the specification of
   the Objects-Based Layout protocol [3], use is made of the opaque
   lrf_body field of the LAYOUTRETURN argument to do such a relaying of
   error codes.  In this section, we define a new data structure to
   enable the passing of error codes back to the MDS and provide some
   guidelines on what both the client and MDS should expect in such
   circumstances.




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

2.2.  Changes to Operation 51: LAYOUTRETURN

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

2.2.1.  ARGUMENT

   The ARGUMENT specification of the LAYOUTRETURN operation in section
   18.44.1 of [2] is augmented by the following XDR code [11]:

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

   struct layoutreturn_error_report4 {
           layoutreturn_device_error4      lrer_errors<>;
   };

2.2.2.  RESULT

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

2.2.3.  DESCRIPTION

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

   When a client used LAYOUTRETURN with a type of LAYOUTRETURN4_FILE,
   then if the lrf_body field is NULL, it indicates to the MDS that the



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   client experienced no errors.  If lrf_body is non-NULL, then the
   field references error information which is layout type specific.
   I.e., the Objects-Based Layout protocol can continue to utilize
   lrf_body as specified in [3].  For both Files-Based Layouts, the
   field references a layoutreturn_device_error4, which contains an
   array of layoutreturn_device_error4.

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

   NFS4_OKAY:  No issues were found for this device.

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

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

2.2.4.  IMPLEMENTATION

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

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

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

   When an I/O fails to a storage device, the client SHOULD retry the
   failed I/O via the MDS.  In this situation, before retrying the I/O,
   the client SHOULD return the layout, or the affected portion thereof,
   and SHOULD indicate which storage device or devices was problematic.
   If the client does not do this, the MDS may issue a layout recall



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   callback in order to perform the retried I/O.

   The client needs to be cognizant that since this error handling is
   optional in the MDS, the MDS may silently ignore this functionality.
   Also, as the MDS may consider some issues the client reports to be
   expected (see Section 2.1), the client might find it difficult to
   detect a MDS which has not implemented error handling via
   LAYOUTRETURN.

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

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

   An MDS SHOULD react to a client return of layouts with errors by not
   using the problematic storage devices in layouts for that client, but
   the MDS is not required to indefinitely retain per-client storage
   device error information.  An MDS is also not required to
   automatically reinstate use of a previously problematic storage
   device; administrative intervention may be required instead.

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


3.  Sharing change attribute implementation details with NFSv4 clients

3.1.  Abstract

   This document describes an extension to the NFSv4 protocol that
   allows the server to share information about the implementation of
   its change attribute with the client.  The aim is to improve the
   client's ability to determine the order in which parallel updates to
   the same file were processed.







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3.2.  Introduction

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

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

   In order to avoid this kind of inefficiency, we propose a method to
   allow 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.

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

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

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

   The proposed solution is to enable the NFS server to provide
   additional information about how it expects the change attribute
   value to evolve after the file data or metadata has changed.  To do
   so, we define a new recommended attribute, 'change_attr_type', which
   may take values from enum change_attr_typeinfo as follows:





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   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.

   NFS4_CHANGE_TYPE_IS_TIME_METADATA:  The change attribute is
      implemented as suggested in the NFSv4 spec [10] 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 are 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 spec.

   Finally, 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.


4.  NFS Server-side Copy







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4.1.  Introduction

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

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

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

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

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

4.2.  Protocol Overview

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

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

   The operations described below are designed to copy files.  Other
   file system objects can be copied by building on these operations or
   using other techniques.  For example if the user wishes to copy a
   directory, the client can synthesize a directory copy by first



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   creating the destination directory and then copying the source
   directory's files to the new destination directory.  If the user
   wishes to copy a namespace junction [12] [13], the client can use the
   ONC RPC Federated Filesystem protocol [13] to perform the copy.
   Specifically the client can determine the source junction's
   attributes using the FEDFS_LOOKUP_FSN procedure and create a
   duplicate junction using the FEDFS_CREATE_JUNCTION procedure.

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

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

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

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

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

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

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

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






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

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

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

   These operations are described in detail in Section 4.3.  This
   section provides an overview of how these operations are used to
   perform server-side copies.

4.2.1.  Intra-Server Copy

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

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

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

                Figure 1: A synchronous intra-server copy.

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





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

               Figure 2: An asynchronous intra-server copy.

4.2.2.  Inter-Server Copy

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




















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

            Figure 3: An example inter-server network topology.

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

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

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
















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

                Figure 4: A synchronous inter-server copy.





























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

               Figure 5: An asynchronous inter-server copy.

4.2.3.  Server-to-Server Copy Protocol

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

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

   The destination server MAY use standard NFSv4.x (where x >= 1) to
   read the data from the source server.  If NFSv4.x is used for the
   server-to-server copy protocol, the destination server can use the
   filehandle contained in the COPY request with standard NFSv4.x



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   operations to read data from the source server.  Specifically, the
   destination server may use the NFSv4.x OPEN operation's CLAIM_FH
   facility to open the file being copied and obtain an open stateid.
   Using the stateid, the destination server may then use NFSv4.x READ
   operations to read the file.

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

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

   In a heterogeneous environment, using a protocol other than NFSv4.x
   (e.g.  HTTP [14] or FTP [15]) presents some challenges.  In
   particular, the destination server is presented with the challenge of
   accessing the source file given only an NFSv4.x filehandle.

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

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

   Authenticating and identifying the destination server to the source
   server is also a challenge.  Recommendations for how to accomplish
   this are given in Section 4.4.1.2.4 and Section 4.4.1.4.



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4.3.  Operations

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

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

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

4.3.1.  netloc4 - Network Locations

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

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

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

   When netloc4 values are used for an inter-server copy as shown in
   Figure 3, their values may be evaluated on the source server,
   destination server, and client.  The network environment in which



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   these systems operate should be configured so that the netloc4 values
   are interpreted as intended on each system.

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

4.3.2.1.  ARGUMENT


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


4.3.2.2.  RESULT

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

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


4.3.2.3.  DESCRIPTION

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

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

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





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

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

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

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

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

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

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




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

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

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

   NFS4ERR_MOVED:  The file system which contains the source file is not
      present on the source server.  The client can determine the
      correct location and reissue the operation with the correct
      location.

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

   NFS4ERR_WRONGSEC:  The security mechanism being used by the client
      does not match the server's security policy.

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

4.3.3.1.  ARGUMENT

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


4.3.3.2.  RESULT

   struct COPY_REVOKE4res {
           nfsstat4        crr_status;
   };


4.3.3.3.  DESCRIPTION

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



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

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

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

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

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

   NFS4ERR_MOVED:  The file system which contains the source file is not
      present on the source server.  The client can determine the
      correct location and reissue the operation with the correct
      location.

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

4.3.4.  Operation 59: COPY - Initiate a server-side copy

4.3.4.1.  ARGUMENT


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

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






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4.3.4.2.  RESULT

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


4.3.4.3.  DESCRIPTION

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

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

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

                           PUTFH source-fh
                           SAVEFH

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

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

   The CURRENT_FH and ca_destination together specify the destination of
   the copy operation.  If ca_destination is of 0 (zero) length, then



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

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

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

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

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




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   If the ca_source_server list is specified, then this is an inter-
   server copy operation and the source file is on a remote server.  The
   client is expected to have previously issued a successful COPY_NOTIFY
   request to the remote source server.  The ca_source_server list
   SHOULD be the same as the COPY_NOTIFY response's cnr_source_server
   list.  If the client includes the entries from the COPY_NOTIFY
   response's cnr_source_server list in the ca_source_server list, the
   source server can indicate a specific copy protocol for the
   destination server to use by returning a URL, which specifies both a
   protocol service and server name.  Server-to-server copy protocol
   considerations are described in Section 4.2.3 and Section 4.4.1.

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

   [NOTE: Earlier versions of this document defined a
   COPY4_SPACE_RESERVED flag for controlling space reservations on the
   destination file.  This flag has been removed with the expectation
   that the space_reserve attribute defined in XXX_TDH_XXX will be
   adopted.]

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

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

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

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










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

                                  Table 1

          +--------------------+----+---------------------------+
          | Name               | Id | Copy to destination file? |
          +--------------------+----+---------------------------+
          | acl                | 12 | MUST                      |
          | aclsupport         | 13 | no                        |
          | archive            | 14 | no                        |
          | cansettime         | 15 | no                        |
          | case_insensitive   | 16 | no                        |
          | case_preserving    | 17 | no                        |
          | change_policy      | 60 | no                        |
          | chown_restricted   | 18 | MUST                      |
          | dacl               | 58 | MUST                      |
          | dir_notif_delay    | 56 | no                        |
          | dirent_notif_delay | 57 | no                        |
          | fileid             | 20 | no                        |
          | files_avail        | 21 | no                        |
          | files_free         | 22 | no                        |
          | files_total        | 23 | no                        |
          | fs_charset_cap     | 76 | no                        |
          | fs_layout_type     | 62 | no                        |
          | fs_locations       | 24 | no                        |
          | fs_locations_info  | 67 | no                        |
          | fs_status          | 61 | no                        |
          | hidden             | 25 | MUST                      |
          | homogeneous        | 26 | no                        |
          | layout_alignment   | 66 | no                        |
          | layout_blksize     | 65 | no                        |



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          | layout_hint        | 63 | no                        |
          | layout_type        | 64 | no                        |
          | maxfilesize        | 27 | no                        |
          | maxlink            | 28 | no                        |
          | maxname            | 29 | no                        |
          | maxread            | 30 | no                        |
          | maxwrite           | 31 | no                        |
          | mdsthreshold       | 68 | no                        |
          | mimetype           | 32 | MUST                      |
          | mode               | 33 | MUST                      |
          | mode_set_masked    | 74 | no                        |
          | mounted_on_fileid  | 55 | no                        |
          | no_trunc           | 34 | no                        |
          | numlinks           | 35 | no                        |
          | owner              | 36 | MUST                      |
          | owner_group        | 37 | MUST                      |
          | quota_avail_hard   | 38 | no                        |
          | quota_avail_soft   | 39 | no                        |
          | quota_used         | 40 | no                        |
          | rawdev             | 41 | no                        |
          | retentevt_get      | 71 | MUST                      |
          | retentevt_set      | 72 | no                        |
          | retention_get      | 69 | MUST                      |
          | retention_hold     | 73 | MUST                      |
          | retention_set      | 70 | no                        |
          | sacl               | 59 | MUST                      |
          | space_avail        | 42 | no                        |
          | space_free         | 43 | no                        |
          | space_total        | 44 | no                        |
          | space_used         | 45 | no                        |
          | system             | 46 | MUST                      |
          | time_access        | 47 | MUST                      |
          | time_access_set    | 48 | no                        |
          | time_backup        | 49 | no                        |
          | time_create        | 50 | MUST                      |
          | time_delta         | 51 | no                        |
          | time_metadata      | 52 | SHOULD                    |
          | time_modify        | 53 | MUST                      |
          | time_modify_set    | 54 | no                        |
          +--------------------+----+---------------------------+

                                  Table 2

   [NOTE: The space_reserve attribute XXX_TDH_XXX will be in the MUST
   set.]

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



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

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

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

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

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

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

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

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

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

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



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

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

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

   NFS4ERR_MOVED:  The file system which contains the source file, or
      the destination file or directory is not present.  The client can
      determine the correct location and reissue the operation with the
      correct location.

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

   NFS4ERR_PARTNER_NOTSUPP:  The remote server does not support the
      server-to-server copy offload protocol.

   NFS4ERR_PARTNER_NO_AUTH:  The remote 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 remote
      server, the remote server receiving a server-to-server copy
      offload request after the copy lease time expired, or for some
      other permission problem.

   NFS4ERR_FBIG:  The copy operation would have caused the file to grow
      beyond the server's limit.

   NFS4ERR_NOTDIR:  The CURRENT_FH is a file and ca_destination has non-
      zero length.

   NFS4ERR_WRONG_TYPE:  The SAVED_FH is not a regular file.

   NFS4ERR_ISDIR:  The CURRENT_FH is a directory and ca_destination has
      zero length.







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   NFS4ERR_INVAL:  The source offset or offset plus count are greater
      than or equal to the size of the source file.

   NFS4ERR_DELAY:  The server does not have the resources to perform the
      copy operation at the current time.  The client should retry the
      operation sometime in the future.

   NFS4ERR_METADATA_NOTSUPP:  The destination file cannot support the
      same metadata as the source file.

   NFS4ERR_WRONGSEC:  The security mechanism being used by the client
      does not match the server's security policy.

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

4.3.5.1.  ARGUMENT

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


4.3.5.2.  RESULT

   struct COPY_ABORT4res {
           nfsstat4        car_status;
   };

4.3.5.3.  DESCRIPTION

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

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

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




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

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

   NFS4ERR_NOTSUPP:  The abort operation is not supported by the NFS
      server receiving this request.

   NFS4ERR_RETRY:  The abort failed, but a retry at some time in the
      future MAY succeed.

   NFS4ERR_COMPLETE_ALREADY:  The abort failed, and a callback will
      deliver the results of the copy operation.

   NFS4ERR_SERVERFAULT:  An error occurred on the server that does not
      map to a specific error code.

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

4.3.6.1.  ARGUMENT


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


4.3.6.2.  RESULT

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

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








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4.3.6.3.  DESCRIPTION

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

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

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

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

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

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

   NFS4ERR_NOTSUPP:  The copy status operation is not supported by the
      NFS server receiving this request.

   NFS4ERR_BAD_STATEID:  The stateid is not valid (see Section 4.3.8
      below).

   NFS4ERR_EXPIRED:  The stateid has expired (see Copy Offload Stateid
      section below).

4.3.7.  Operation 15: CB_COPY - Report results of a server-side copy














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4.3.7.1.  ARGUMENT

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

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

4.3.7.2.  RESULT

   struct CB_COPY4res {
           nfsstat4        ccr_status;
   };

4.3.7.3.  DESCRIPTION

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

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

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

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




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

4.3.8.  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, COPY_ABORT, COPY_STATUS,
   and CB_COPY operations.

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

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

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

4.4.  Security Considerations

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

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

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

4.4.1.  Inter-Server Copy Security

4.4.1.1.  Requirements for Secure Inter-Server Copy

   Inter-server copy is driven by several requirements:





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

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

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

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

4.4.1.2.  Inter-Server Copy with RPCSEC_GSSv3

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

   An approach that sends delegated credentials of the client's user
   principal to the destination server is not used for the following
   reasons.  If the client's user delegated its credentials, the
   destination would authenticate as the user principal.  If the



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   destination were using the NFSv4 protocol to perform the copy, then
   the source server would authenticate the destination server as the
   user principal, and the file copy would securely proceed.  However,
   this approach would allow the destination server to copy other files.
   The user principal would have to trust the destination server to not
   do so.  This is counter to the requirements, and therefore is not
   considered.  Instead an approach using RPCSEC_GSSv3 [5] privileges is
   proposed.

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

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

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


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


      cap_shared_secret is a secret value the user principal generates.

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









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


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

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


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

4.4.1.2.1.  Establishing a Security Context

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

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

   o  An instance of copy_from_auth_priv is filled in with the shared
      secret, the destination server, and the NFSv4 user id of the user
      principal.  It will be sent with an RPCSEC_GSS3_CREATE procedure,



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      and so cfap_seq_num is set to the seq_num of the credential of the
      RPCSEC_GSS3_CREATE procedure.  Because cfap_shared_secret is a
      secret, after XDR encoding copy_from_auth_priv, GSS_Wrap() (with
      privacy) is invoked on copy_from_auth_priv.  The
      RPCSEC_GSS3_CREATE procedure's arguments are:


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


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


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


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

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



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      are:


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


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


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


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

4.4.1.2.2.  Starting a Secure Inter-Server Copy

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



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

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

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

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

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

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

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





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

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

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

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

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

   For protocols that authenticate user names with passwords (e.g.  HTTP
   [14] and FTP [15]), the nfsv4 user id could be used as the user name,
   and an ASCII hexadecimal representation of the RPCSEC_GSSv3 shared
   secret could be used as the user password or as input into non-
   password authentication methods like CHAP [16].

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

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

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

   When the client sends the source server the COPY_NOTIFY operation,
   the source server may reply to the client with a list of target
   addresses, names, and/or URLs and assign them to the unique triple:
   <source fh, user ID, destination address Y>.  If the destination uses
   one of these target netlocs to contact the source server, the source



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   server will be able to uniquely identify the destination server, even
   if the destination server does not connect from the address specified
   by the client in COPY_NOTIFY.

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

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

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

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

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

   The source server will therefore know that these NFSv4.1 operations
   are being issued by the destination server identified in the
   COPY_NOTIFY.

4.4.1.4.  Inter-Server Copy without ONC RPC and RPCSEC_GSSv3

   The same techniques as Section 4.4.1.3, using unique URLs for each
   destination server, can be used for other protocols (e.g.  HTTP [14]
   and FTP [15]) as well.

4.5.  IANA Considerations

   This section has no actions for IANA.


5.  Space Reservation

5.1.  Introduction

   This section describes a set of operations that allow applications
   such as hypervisors to reserve space for a file, report the amount of
   actual disk space a file occupies and freeup the backing space of a
   file when it is not required.

   In virtualized environments, virtual disk files are often stored on
   NFS mounted volumes.  Since virtual disk files represent the hard



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   disks of virtual machines, hypervisors often have to guarantee
   certain properties for the file.

   One such example is space reservation.  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 virtual machine.  Such errors prevent a virtual
   machine from continuing execution and result in downtime.

   Another useful feature would be 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 filesystems, they prove to be inadequate in modern
   filesystems that support block sharing.  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 virtual machine, a
   virtual disk can be viewed as a filesystem within a file.  Since not
   all blocks within a filesystem are in use, there is an opportunity to
   reclaim blocks that are no longer in use.  A call to deallocate
   blocks could result in better space efficiency.  Lesser space MAY be
   consumed for backups after block deallocation.

   We propose the following operations and attributes for the
   aforementioned use cases:

   space_reserve  This attribute specifies whether the blocks backing
      the file have been preallocated.

   space_freed  This attribute specifies the space freed when a file is
      deleted, taking block sharing into consideration.

   max_hole_punch  This attribute specifies the maximum sized hole that
      can be punched on the filesystem.

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






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5.2.  Use Cases

5.2.1.  Space Reservation

   Some applications require that once a file of a certain size is
   created, writes to that file never fail with an out of space
   condition.  One such example is that of a hypervisor writing to a
   virtual disk.  An out of space condition while writing to virtual
   disks would mean that the virtual machine would need to be frozen.

   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 filesystems that are log
   structured or deduplicated.  An efficient way of guaranteeing space
   reservation would be beneficial to such applications.

   If the space_reserved attribute is set on a file, it is guaranteed
   that writes that do not grow the file will not fail with
   NFSERR_NOSPC.

5.2.2.  Space freed on deletes

   Currently, files in NFS have 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 filesystems, they prove to be inadequate in modern
   filesystems that support block sharing.  In such filesystems,
   multiple inodes can point to a single block with a block reference
   count to guard against premature freeing.

   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 6 of these



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   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.

   Adding another size attribute, space_freed, 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.

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

5.2.3.  Operations and attributes

   In the sections that follow, one operation and three attributes are
   defined that together provide the space management facilities
   outlined earlier in the document.  The operation is intended to be
   OPTIONAL and the attributes RECOMMENDED as defined in section 17 of
   [2].

5.2.4.  Attribute 77: space_reserve

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

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

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

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



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

5.2.5.  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.

5.2.6.  Attribute 79: max_hole_punch

   max_hole_punch specifies the maximum size of a hole that the
   HOLE_PUNCH operation can handle.  This attribute is read only and of
   type length4.  It is a per filesystem attribute.  This attribute MUST
   be implemented if HOLE_PUNCH is implemented.

5.2.7.  Operation 64: HOLE_PUNCH - Zero and deallocate blocks backing
        the file in the specified range.

5.2.7.1.  ARGUMENT


   struct HOLE_PUNCH4args {
           /* CURRENT_FH: file */
           offset4        hpa_offset;
           length4        hpa_count;
   };


5.2.7.2.  RESULT


   struct HOLE_PUNCH4res {
           nfsstat4        hpr_status;
   };


5.2.7.3.  DESCRIPTION

   Whenever a client wishes to deallocate the blocks backing a
   particular region in the file, it calls the HOLE_PUNCH operation with
   the current filehandle set to the filehandle of the file in question,
   start offset and length in bytes of the region set in hpa_offset and
   hpa_count respectively.  All further reads to this region MUST return



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   zeros until overwritten.  The filehandle specified must be that of a
   regular file.

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

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

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

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

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

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

   NFS4ERR_DIR  The current filehandle is of type NF4DIR.

   NFS4ERR_SYMLINK  The current filehandle is of type NF4LNK.

   NFS4ERR_WRONG_TYPE  The current filehandle does not designate an
      ordinary file.








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5.3.  Security Considerations

   There are no security considerations for this section.

5.4.  IANA Considerations

   This section has no actions for IANA.


6.  Simple and Efficient Read Support for Sparse Files

6.1.  Introduction

   NFS is now used in many data centers as the sole or primary method of
   data access.  Consequently, more types of applications are using NFS
   than ever before, each with their own requirements and generated
   workloads.  As part of this, sparse files are increasing in number
   while NFS continues to lack any specific knowledge of a sparse file's
   layout.  This document puts forth a proposal for the NFSv4.2 protocol
   to support efficient reading of sparse files.

   A sparse file is a common way of representing a large file without
   having to reserve 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 NTFS, but notably not Apple's HFS+.  Common
   examples of sparse files include VM OS/disk images, database files,
   log files, and even checkpoint recovery files most commonly used by
   the HPC community.

   If an application reads a hole in a sparse file, the file system must
   returns all zeros to the application.  For local data access there is
   little penalty, but with NFS these zeroes 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 zeroes to be transferred.  Once the zeroes arrive, they then
   steal memory or cache space from real data.  To make matters worse,
   if an application then proceeds to write data to another file system,
   the zeros are written into the file, expanding the sparse file into a
   full sized regular file.  Beyond wasting disk space, this can
   actually prevent large sparse files from ever being copied to another
   storage location due to space limitations.

   This document adds a new READPLUS operation to efficiently read from
   sparse files by avoiding the transfer of all zero regions from the
   server to the client.  READPLUS supports all the features of READ but
   includes a minimal extension to support sparse files.  In addition,



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   the return value of READPLUS is now compatible with NFSv4.1 minor
   versioning rules and could support other future extensions without
   requiring yet another operation.  READPLUS is guaranteed to perform
   no worse than READ, and can dramatically improve performance with
   sparse files.  READPLUS does not depend on pNFS protocol features,
   but can be used by pNFS to support sparse files.

6.2.  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 regions of all
      zeroes.  For block-based file systems, this could also be an
      unallocated region of the file.

   Hole Threshold  The minimum length of a Hole as determined by the
      server.  If a server chooses to define a Hole Threshold, then it
      would not return hole information (nfs_readplusreshole) with a
      hole_offset and hole_length that specify a range shorter than the
      Hole Threshold.

6.3.  Applications and Sparse Files

   Applications may cause an NFS client to read holes in a file for
   several reasons.  This section describes three different application
   workloads that cause the NFS client to transfer data unnecessarily.
   These workloads are simply examples, and there are probably many more
   workloads that are negatively impacted by sparse files.

   The first workload that can cause holes to be read is sequential
   reads within a sparse file.  When this happens, the NFS client may
   perform read requests ("readahead") into sections of the file not
   explicitly requested by the application.  Since the NFS client cannot
   differentiate between holes and non-holes, the NFS client may
   prefetch empty sections of the file.

   This workload is exemplified by Virtual Machines and their associated
   file system images, e.g., VMware .vmdk files, which are large sparse
   files encapsulating an entire operating system.  If a VM reads files
   within the file system image, this will translate to sequential NFS
   read requests into the much larger file system image file.  Since NFS
   does not understand the internals of the file system image, it ends
   up performing readahead file holes.

   The second workload is generated by copying a file from a directory
   in NFS to either the same NFS server, to another file system, e.g.,



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   another NFS or Samba server, to a local ext3 file system, or even a
   network socket.  In this case, bandwidth and server resources are
   wasted as the entire file is transferred from the NFS server to the
   NFS client.  Once a byte range of the file has been transferred to
   the client, it is up to the client application, e.g., rsync, cp, scp,
   on how it writes the data to the target location.  For example, cp
   supports sparse files and will not write all zero regions, whereas
   scp does not support sparse files and will transfer every byte of the
   file.

   The third workload is generated by applications that do not utilize
   the NFS client cache, but instead use direct I/O and manage cached
   data independently, e.g., databases.  These applications may perform
   whole file caching with sparse files, which would mean that even the
   holes will be transferred to the clients and cached.

6.4.  Overview of Sparse Files and NFSv4

   This proposal seeks to provide sparse file support to the largest
   number of NFS client and server implementations, and as such proposes
   to add a new return code to the mandatory NFSv4.1 READPLUS operation
   instead of proposing additions or extensions of new or existing
   optional features (such as pNFS).

   As well, this document seeks to ensure that the proposed extensions
   are simple and do not transfer data between the client and server
   unnecessarily.  For example, one possible way to implement sparse
   file read support would be to have the client, on the first hole
   encountered or at OPEN time, request a Data Region Map from the
   server.  A Data Region Map would specify all zero and non-zero
   regions in a file.  While this option seems simple, it is less useful
   and can become inefficient and cumbersome for several reasons:

   o  Data Region Maps can be large, and transferring them can reduce
      overall read performance.  For example, VMware's .vmdk files can
      have a file size of over 100 GBs and have a map well over several
      MBs.

   o  Data Region Maps can change frequently, and become invalidated on
      every write to the file.  NFSv4 has a single change attribute,
      which means any change to any region of a file will invalidate all
      Data Region Maps.  This can result in the map being transferred
      multiple times with each update to the file.  For example, a VM
      that updates a config file in its file system image would
      invalidate the Data Region Map not only for itself, but for all
      other clients accessing the same file system image.





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   o  Data Region Maps do not handle all zero-filled sections of the
      file, reducing the effectiveness of the solution.  While it may be
      possible to modify the maps to handle zero-filled sections (at
      possibly great effort to the server), it is almost impossible with
      pNFS.  With pNFS, the owner of the Data Region Map is the metadata
      server, which is not in the data path and has no knowledge of the
      contents of a data region.

   Another way to handle holes is compression, but this not ideal since
   it requires all implementations to agree on a single compression
   algorithm and requires a fair amount of computational overhead.

   Note that supporting writing to a sparse file does not require
   changes to the protocol.  Applications and/or NFS implementations can
   choose to ignore WRITE requests of all zeroes to the NFS server
   without consequence.

6.5.  Operation 65: READPLUS

   The section introduces a new read operation, named READPLUS, which
   allows NFS clients to avoid reading holes in a sparse file.  READPLUS
   is guaranteed to perform no worse than READ, and can dramatically
   improve performance with sparse files.

   READPLUS supports all the features of the existing NFSv4.1 READ
   operation [2] and adds a simple yet significant extension to the
   format of its response.  The change allows the client to avoid
   returning all zeroes from a file hole, wasting computational and
   network resources and reducing performance.  READPLUS uses a new
   result structure that tells the client that the result is all zeroes
   AND the byte-range of the hole in which the request was made.
   Returning the hole's byte-range, and only upon request, avoids
   transferring large Data Region Maps that may be soon invalidated and
   contain information about a file that may not even be read in its
   entirely.

   A new read operation is required due to NFSv4.1 minor versioning
   rules that do not allow modification of existing operation's
   arguments or results.  READPLUS is designed in such a way to allow
   future extensions to the result structure.  The same approach could
   be taken to extend the argument structure, but a good use case is
   first required to make such a change.









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6.5.1.  ARGUMENT

   struct READPLUS4args {
           /* CURRENT_FH: file */
           stateid4        rpa_stateid;
           offset4         rpa_offset;
           count4          rpa_count;
   };











































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6.5.2.  RESULT

   struct readplus_hole_info {
           offset4         rphi_offset;
           length4         rphi_length;
   };

   enum holeres4 {
           HOLE_NOINFO = 0,
           HOLE_INFO = 1
   };

   union readplus_hole switch (holeres4 resop) {
           case HOLE_INFO:
                   readplus_hole_info      rph_info;
           case HOLE_NOINFO:
                   void;
   };

   enum readplusrestype4 {
           READ_OK = 0,
           READ_HOLE = 1
   };

   union readplus_data switch (readplusrestype4 resop) {
           case READ_OK:
                   opaque          rpd_data<>;
           case READ_HOLE:
                   readplus_hole   rpd_hole4;
   };

   struct READPLUS4resok {
           bool            rpr_eof;
           readplus_data   rpr_data;
   };

   union READPLUS4res switch (nfsstat4 status) {
           case NFS4_OK:
                   READPLUS4resok  resok4;
           default:
                   void;
   };

6.5.3.  DESCRIPTION

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



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   The client provides an offset of where the READPLUS is to start and a
   count of how many bytes are to be read.  An offset of zero means to
   read data starting at the beginning of the file.  If offset is
   greater than or equal to the size of the file, the status NFS4_OK is
   returned with nfs_readplusrestype4 set to READ_OK, data length set to
   zero, and eof set to TRUE.  The READPLUS is subject to access
   permissions checking.

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

   If the client specifies an offset and count value that is entirely
   contained within a hole of the file, the status NFS4_OK is returned
   with nfs_readplusresok4 set to READ_HOLE, and if information is
   available regarding the hole, a nfs_readplusreshole structure
   containing the offset and range of the entire hole.  The
   nfs_readplusreshole structure is considered valid until the file is
   changed (detected via the change attribute).  The server MUST provide
   the same semantics for nfs_readplusreshole as if the client read the
   region and received zeroes; the implied holes contents lifetime MUST
   be exactly the same as any other read data.

   If the client specifies an offset and count value that begins in a
   non-hole of the file but extends into hole the server should return a
   short read with status NFS4_OK, nfs_readplusresok4 set to READ_OK,
   and data length set to the number of bytes returned.  The client will
   then issue another READPLUS for the remaining bytes, which the server
   will respond with information about the hole in the file.

   If the server knows that the requested byte range is into a hole of
   the file, but has no further information regarding the hole, it
   returns a nfs_readplusreshole structure with holeres4 set to
   HOLE_NOINFO.

   If hole information is available and can be returned to the client,
   the server returns a nfs_readplusreshole structure with the value of
   holeres4 to HOLE_INFO.  The values of hole_offset and hole_length
   define the byte-range for the current hole in the file.  These values
   represent the information known to the server and may describe a
   byte-range smaller than the true size of the hole.

   Except when special stateids are used, the stateid value for a
   READPLUS 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



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   any and is used by the server to verify that the associated locks are
   still valid (e.g., have not been revoked).

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

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

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

   On success, the current filehandle retains its value.

6.5.4.  IMPLEMENTATION

   If the server returns a "short read" (i.e., fewer data than requested
   and eof is set to FALSE), the client should send another READPLUS to
   get the remaining data.  A server may return less data than requested
   under several circumstances.  The file may have been truncated by
   another client or perhaps on the server itself, changing the file
   size from what the requesting client believes to be the case.  This
   would reduce the actual amount of data available to the client.  It
   is possible that the server reduce the transfer size and so return a
   short read result.  Server resource exhaustion may also occur in a
   short read.

   If mandatory byte-range locking is in effect for the file, and if the
   byte-range corresponding to the data to be read from the file is
   WRITE_LT locked by an owner not associated with the stateid, the
   server will return the NFS4ERR_LOCKED error.  The client should try
   to get the appropriate READ_LT via the LOCK operation before re-
   attempting the READPLUS.  When the READPLUS completes, the client
   should release the byte-range lock via LOCKU.  In addition, the
   server MUST return a nfs_readplusreshole structure with values of
   hole_offset and hole_length that are within the owner's locked byte
   range.




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   If another client has an OPEN_DELEGATE_WRITE delegation for the file
   being read, the delegation must be recalled, and the operation cannot
   proceed until that delegation is returned or revoked.  Except where
   this happens very quickly, one or more NFS4ERR_DELAY errors will be
   returned to requests made while the delegation remains outstanding.
   Normally, delegations will not be recalled as a result of a READPLUS
   operation since the recall will occur as a result of an earlier OPEN.
   However, since it is possible for a READPLUS to be done with a
   special stateid, the server needs to check for this case even though
   the client should have done an OPEN previously.

6.5.4.1.  Additional pNFS Implementation Information

   With pNFS, the semantics of using READPLUS remains the same.  Any
   data server MAY return a READ_HOLE result for a READPLUS request that
   it receives.

   When a data server chooses to return a READ_HOLE result, it has the
   option of returning hole information for the data stored on that data
   server (as defined by the data layout), but it MUST not return a
   nfs_readplusreshole structure with a byte range that includes data
   managed by another data server.

   1.  Data servers that cannot determine hole information SHOULD return
       HOLE_NOINFO.

   2.  Data servers that can obtain hole information for the parts of
       the file stored on that data server, the data server SHOULD
       return HOLE_INFO and the byte range of the hole stored on that
       data server.

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

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

6.5.5.  READPLUS with Sparse Files Example

   To see how the return value READ_HOLE will work, the following table
   describes a sparse file.  For each byte range, the file contains
   either non-zero data or a hole.  In addition, the server in this
   example uses a hole threshold of 32K.





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                        +-------------+----------+
                        | 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 3

   Under the given circumstances, if a client was to read the file from
   beginning to end with a max read size of 64K, the following will be
   the result.  This assumes the client has already opened the file and
   acquired a valid stateid and just needs to issue READPLUS requests.

   1.  READPLUS(s, 0, 64K) --> NFS_OK, readplusrestype4 = READ_OK, eof =
       false, data<>[32K].  Return a short read, as the last half of the
       request was all zeroes.  Note that the first hole is read back as
       all zeros as it is below the hole threshhold.

   2.  READPLUS(s, 32K, 64K) --> NFS_OK, readplusrestype4 = READ_HOLE,
       nfs_readplusreshole(HOLE_INFO)(32K, 224K).  The requested range
       was all zeros, and the current hole begins at offset 32K and is
       224K in length.

   3.  READPLUS(s, 256K, 64K) --> NFS_OK, readplusrestype4 = READ_OK,
       eof = false, data<>[32K].  Return a short read, as the last half
       of the request was all zeroes.

   4.  READPLUS(s, 288K, 64K) --> NFS_OK, readplusrestype4 = READ_HOLE,
       nfs_readplusreshole(HOLE_INFO)(288K, 66K).

   5.  READPLUS(s, 354K, 64K) --> NFS_OK, readplusrestype4 = READ_OK,
       eof = true, data<>[64K].

6.6.  Related Work

   Solaris and ZFS support an extension to lseek(2) that allows
   applications to discover holes in a file.  The values, SEEK_HOLE and
   SEEK_DATA, allow clients to seek to the next hole or beginning of
   data, respectively.

   XFS supports the XFS_IOC_GETBMAP extended attribute, which returns
   the Data Region Map for a file.  Clients can then use this
   information to avoid reading holes in a file.



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   NTFS and CIFS support the FSCTL_SET_SPARSE attribute, which allows
   applications to control whether empty regions of the file are
   preallocated and filled in with zeros or simply left unallocated.

6.7.  Other Proposed Designs

6.7.1.  Multi-Data Server Hole Information

   The current design prohibits pnfs data servers from returning hole
   information for regions of a file that are not stored on that data
   server.  Having data servers return information regarding other data
   servers changes the fundamental principal that all metadata
   information comes from the metadata server.

   Here is a brief description if we did choose to support multi-data
   server hole information:

   For a data server that can obtain hole information for the entire
   file without severe performance impact, it MAY return HOLE_INFO and
   the byte range of the entire file hole.  When a pNFS client receives
   a READ_HOLE result and a non-empty nfs_readplusreshole structure, it
   MAY use this information in conjunction with a valid layout for the
   file to determine the next data server for the next region of data
   that is not in a hole.

6.7.2.  Data Result Array

   If a single read request contains one or more Holes with a length
   greater than the Sparse Threshold, the current design would return
   results indicating a short read to the client.  A client would then
   send a series of read requests to the server to retrieve information
   for the Holes and the remaining data.  To avoid turning a single read
   request into several exchanges between the client and server, the
   server may need to choose a relatively large Sparse Threshold in
   order to decrease the number of short reads it creates.  A large
   Sparse Threshold may miss many smaller holes, which in turn may
   negate the benefits of sparse read support.

   To avoid this situation, one option is to have the READPLUS operation
   return information for multiple holes in a single return value.  This
   would allow several small holes to be described in a single read
   response without requiring multliple exchanges between the client and
   server.

   One important item to consider with returning an array of data chunks
   is its impact on RDMA, which may use different block sizes on the
   client and server (among other things).




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6.7.3.  User-Defined Sparse Mask

   Add mask (instead of just zeroes).  Specified by server or client?

6.7.4.  Allocated flag

   A Hole on the server may be an allocated byte-range consisting of all
   zeroes or may not be allocated at all.  To ensure this information is
   properly communicated to the client, it may be beneficial to add a
   'alloc' flag to the HOLE_INFO section of nfs_readplusreshole.  This
   would allow an NFS client to copy a file from one file system to
   another and have it more closely resemble the original.

6.7.5.  Dense and Sparse pNFS File Layouts

   The hole information returned form a data server must be understood
   by pNFS clients using both Dense or Sparse file layout types.  Does
   the current READPLUS return value work for both layout types?  Does
   the data server know if it is using dense or sparse so that it can
   return the correct hole_offset and hole_length values?

6.8.  Security Considerations

   The additions to the NFS protocol for supporting sparse file reads
   does not alter the security considerations of the NFSv4.1 protocol
   [2].

6.9.  IANA Considerations

   There are no IANA considerations in this section.


7.  Security Considerations


8.  IANA Considerations

   This section uses terms that are defined in [17].


9.  References

9.1.  Normative References

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

   [2]   Shepler, S., Eisler, M., and D. Noveck, "Network File System



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         (NFS) Version 4 Minor Version 1 Protocol", RFC 5661,
         January 2010.

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

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

   [5]   Williams, N., "Remote Procedure Call (RPC) Security Version 3",
         draft-williams-rpcsecgssv3 (work in progress), 2008.

   [6]   Shepler, S., Eisler, M., and D. Noveck, "Network File System
         (NFS) Version 4 Minor Version 1 External Data Representation
         Standard (XDR) Description", RFC 5662, January 2010.

   [7]   Black, D., Glasgow, J., and S. Fridella, "Parallel NFS (pNFS)
         Block/Volume Layout", RFC 5663, January 2010.

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

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

9.2.  Informative References

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

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

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

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

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



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

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

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

   [18]  Nowicki, B., "NFS: Network File System Protocol specification",
         RFC 1094, March 1989.

   [19]  Callaghan, B., Pawlowski, B., and P. Staubach, "NFS Version 3
         Protocol Specification", RFC 1813, June 1995.

   [20]  Srinivasan, R., "Binding Protocols for ONC RPC Version 2",
         RFC 1833, August 1995.

   [21]  Eisler, M., "NFS Version 2 and Version 3 Security Issues and
         the NFS Protocol's Use of RPCSEC_GSS and Kerberos V5",
         RFC 2623, June 1999.

   [22]  Callaghan, B., "NFS URL Scheme", RFC 2224, October 1997.

   [23]  Shepler, S., "NFS Version 4 Design Considerations", RFC 2624,
         June 1999.

   [24]  Reynolds, J., "Assigned Numbers: RFC 1700 is Replaced by an On-
         line Database", RFC 3232, January 2002.

   [25]  Linn, J., "The Kerberos Version 5 GSS-API Mechanism", RFC 1964,
         June 1996.

   [26]  Shepler, S., Callaghan, B., Robinson, D., Thurlow, R., Beame,
         C., Eisler, M., and D. Noveck, "Network File System (NFS)
         version 4 Protocol", RFC 3530, April 2003.


Appendix A.  Acknowledgments

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

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




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

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

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


Appendix B.  RFC Editor Notes

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

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


Author's Address

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

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













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