Extending the Opening of Files in NFSv4.2
draft-ietf-nfsv4-delstid-02

Network File System Version 4                                  T. Haynes
Internet-Draft                                              T. Myklebust
Updates: 8881 (if approved)                                  Hammerspace
Intended status: Standards Track                        15 February 2023
Expires: 19 August 2023

               Extending the Opening of Files in NFSv4.2
                      draft-ietf-nfsv4-delstid-02

Abstract

   The Network File System v4 (NFSv4) allows a client to both open a
   file and be granted a delegation of that file.  This provides the
   client the right to cache metadata on the file locally.  This
   document presents several refinements to RFC8881 for both the opening
   and delegating of the file to the client.

Note

   This note is to be removed before publishing as an RFC.

   Discussion of this draft takes place on the NFSv4 working group
   mailing list (nfsv4@ietf.org), which is archived at
   https://mailarchive.ietf.org/arch/browse/nfsv4/.  Working Group
   information can be found at https://datatracker.ietf.org/wg/nfsv4/
   about/.

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 https://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on 19 August 2023.

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Copyright Notice

   Copyright (c) 2023 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 (https://trustee.ietf.org/
   license-info) in effect on the date of publication of this document.
   Please review these documents carefully, as they describe your rights
   and restrictions with respect to this document.  Code Components
   extracted from this document must include Revised BSD License text as
   described in Section 4.e of the Trust Legal Provisions and are
   provided without warranty as described in the Revised BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Definitions . . . . . . . . . . . . . . . . . . . . . . .   3
     1.2.  Requirements Language . . . . . . . . . . . . . . . . . .   3
   2.  Offline Files . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  OPEN grants only one of Open or Delegation Stateid  . . . . .   4
   4.  Proxying of Times . . . . . . . . . . . . . . . . . . . . . .   5
     4.1.  Use case  . . . . . . . . . . . . . . . . . . . . . . . .   6
     4.2.  XDR for Proxying of Times . . . . . . . . . . . . . . . .   6
   5.  Determining OPEN Feature Support  . . . . . . . . . . . . . .   7
   6.  Extraction of XDR . . . . . . . . . . . . . . . . . . . . . .  10
     6.1.  Code Components Licensing Notice  . . . . . . . . . . . .  11
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .  11
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  11
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  11
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .  11
     9.2.  Informative References  . . . . . . . . . . . . . . . . .  12
   Appendix A.  Acknowledgments  . . . . . . . . . . . . . . . . . .  12
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  12

1.  Introduction

   In the Network File System version4 (NFSv4) a client may be granted a
   delegation for a file.  This allows the client to act as the
   authority of the file's metadata and data.  In this document, we
   introduce some new semantics to both the open and the delegation
   process which allows the client to:

   *  detect an offline file, which may be located off premise.

   *  determine the extension of OPEN (see Section 18.16 of [RFC8881])
      flags.

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   *  during the OPEN procedure, get either the open or delegation
      stateids, but not both.

   *  cache both the access and modify times, reducing the number of
      times the client needs to go to the server to get that
      information.

   Using the process detailed in [RFC8178], the revisions in this
   document become an extension of NFSv4.2 [RFC7862].  They are built on
   top of the external data representation (XDR) [RFC4506] generated
   from [RFC7863].

1.1.  Definitions

   delegation:  A file delegation, which is a recall-able lock that
      assures the holder that inconsistent opens and file changes cannot
      occur so long as the delegation is held.

   proxy:  A proxy of attributes occurs when the client has the
      authority to represent the server's attributes.

   stateid:  A stateid is a 128-bit quantity returned by a server that
      uniquely defines state held by the server for the client.  (See
      Section 8 of [RFC8881])

1.2.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in
   BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

2.  Offline Files

   If a file is offline, then the server has immediate high-performance
   access to the file's attributes, but not to the file's content.  The
   cost of retrieving the data content is expensive, to the extent that
   the content should only be retrieved if it is going to be used.  For
   example, a graphical file manager (such as OSX's Finder) may want to
   access the beginning of the file to preview it for an user who is
   hovering their pointer over the file name.  If the file is retrieved,
   it will most likely either be immediately thrown away or returned.

   A compound with a GETATTR or READDIR can report the file's attributes
   without bringing the file online.  However, either an OPEN or a
   LAYOUTGET might cause the file server to retrieve the archived data
   contents, bringing the file online.  For non-pNFS systems, the OPEN

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   operation requires a filehandle to the data content.  For pNFS
   systems, the filehandle retrieved from an OPEN need not cause the
   data content to be retrieved.  But when the LAYOUTGET operation is
   processed, a layout type specific mapping will cause the data content
   to be retrieved from offline storage.

   If an operating system is not aware that the file is offline, it
   might inadvertently open the file to determine what type of file it
   is accessing.  By adding the new attribute FATTR4_OFFLINE, a client
   can predetermine the availability of the file, avoiding the need to
   open it at all.  Being offline might also involve situations in which
   the file is archived in the cloud, i.e., there can be an expense in
   both retrieving the file to bring online and in sending the file back
   to offline status.

   <CODE BEGINS>
   ///
   /// typedef bool            fattr4_offline;
   ///
   <CODE ENDS>

   <CODE BEGINS>
   ///
   /// const FATTR4_OFFLINE            = 83;
   ///
   <CODE ENDS>

3.  OPEN grants only one of Open or Delegation Stateid

   The OPEN (See Section 18.16 of [RFC8881]) procedure returns an open
   stateid to the client to reference the state of the file.  The client
   could also request a delegation stateid in the OPEN arguments.  The
   file is said to be "open" to the client as long as the count of open
   and delegated stateids is greater than 0.  Either type of stateid is
   sufficient to enable the server to treat the file as if it were open,
   which allows READ (See Section 18.25 of [RFC8881]), WRITE (See
   Section 18.38 of [RFC8881]), LOCK (See Section 18.12 of [RFC8881]),
   and LAYOUTGET (see Section 18.50 of [RFC8881]) operations to proceed.
   If the client gets both a open and a delegation stateid as part of
   the OPEN, then it has to return them both.  And during each
   operation, the client can send a costly GETATTR (See Section 18.9 of
   [RFC8881]).

   If the client knows that the server supports the
   OPEN4_SHARE_ACCESS_WANT_OPEN_XOR_DELEGATION flag (as determined by an
   earlier GETATTR operation which queried for the FATTR4_OPEN_ARGUMENTS
   attribute), then the client can supply that flag during the OPEN and
   only get either an open or delegation stateid.

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   The client is already prepared to not get a delegation stateid even
   if requested.  In order to not send an open stateid, the server can
   indicate that fact with the result flag of
   OPEN4_RESULT_NO_OPEN_STATEID.  The open stateid field,
   OPEN4resok.stateid (see Section 18.16.2 of [RFC8881]), will also be
   set to the special all zero stateid.

4.  Proxying of Times

   When a client is granted a write delegation on a file, it is the
   authority for the file.  If the server queries the client as to the
   state of the file via a CB_GETATTR (see Section 20.1 of [RFC8881]),
   then it can only determine the size of the file.  Likewise, if the
   client holding the delegation wants to know either of the access,
   modify, or change times, it has to send a GETATTR to the server.
   While it is the authority for these values, it has no way to transfer
   these values to the server when the delegation is being returned and
   the server reclaims its authority with regard to these values.  And
   as such, it can not pass these times up to an application expecting
   posix compliance.

   With the addition of the new flag:
   OPEN4_SHARE_ACCESS_WANT_DELEG_TIMESTAMPS, the client and server can
   negotiate that the client will be the authority for these values and
   upon return of the delegation stateid via a DELEGRETURN (see section
   18.6 of [RFC8881]), the times will be passed back to the server.  If
   the server is queried by another client for either the size or the
   times, it will need to use a CB_GETATTR to query the client which
   holds the delegation (see Section 20.1 of [RFC8881]).

   If a server informs the client via the FATTR4_OPEN_ARGUMENTS
   attribute that it supports
   OPEN_ARGS_SHARE_ACCESS_WANT_DELEG_TIMESTAMPS and it returns a valid
   delegation stateid for an OPEN operation which sets the
   OPEN4_SHARE_ACCESS_WANT_DELEG_TIMESTAMPS flag, then it MUST query the
   client via a CB_GETATTR for the FATTR4_TIME_DELEG_ACCESS attribute
   and FATTR4_TIME_DELEG_MODIFY attribute.  (The change time can be
   derived from the modify time.)  Further, when it gets a SETATTR (see
   Section 18.34 of [RFC8881]) in the same compound as the DELEGRETURN,
   then it MUST accept those FATTR4_TIME_DELEG_ACCESS attribute and
   FATTR4_TIME_DELEG_MODIFY attribute changes and derive the change time
   or reject the changes with NFS4ERR_DELAY.

   Note that the SETATTR SHOULD either be in a separate compound before
   the one containing the DELEGRETURN or if in the same compound, as an
   operation before the DELEGRETURN.  Failure to properly sequence the
   operations may lead to race cases.

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   A key prerequisite of this approach is that the server and client are
   in time synchronization with each other.  Note that while the base
   NFSv4.2 does not require such synchronization, the use of RPCSEC_GSS
   typically makes such a requirement.  When the client presents either
   FATTR4_TIME_DELEG_ACCESS or FATTR4_TIME_DELEG_MODIFY attributes to
   the server, the server MUST decide whether the times presented are
   before the old times or past the current time.  If the time presented
   is before the original time, then the update is ignored.  If the time
   presented is in the future, the server can either clamp the new time
   to the current time, or it may return NFS4ERR_DELAY to the client,
   allowing it to retry.  Note that if the clock skew is large, this
   policy will result in access to the file being denied until such time
   that the clock skew is exceeded.

   A change in the access time MUST NOT advance the change time, also
   known as the time_metadata attribute (see Section 5.8.2.42 of
   [RFC8881]), but a change in the modify time might advance the change
   time (and in turn the change attribute (See Section 5.8.1.4 of
   [RFC8881]).  If the modify time is greater than the change time and
   before the current time, then the change time is adjusted to the
   modify time and not the current time (as is most likely done on most
   SETATTR calls that change the metadata).  If the modify time is in
   the future, it will be clamped to the current time.

   Note that each of the possible times, access, modify, and change, are
   compared to the current time.  They should all be compared against
   the same time value for the current time.  I.e., do not retrieve a
   different value of the current time for each calculation.

   If the client sets the OPEN4_SHARE_ACCESS_WANT_DELEG_TIMESTAMPS flag
   in an OPEN operation, then it MUST support the
   FATTR4_TIME_DELEG_ACCESS and FATTR4_TIME_DELEG_MODIFY attributes both
   in the CB_GETATTR and SETATTR operations.

4.1.  Use case

   When a server is a proxy for a NFSv4 server, it is a client to the
   NFSv4 server and during file I/O, it may get a delegation on a file.
   The client of the proxy would be querying the proxy for attributes
   and not the NFSv4 server.  Each GETATTR from that client would result
   in at least one additional GETATTR being sent across the wire.

4.2.  XDR for Proxying of Times

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   <CODE BEGINS>
   ///
   /// /*
   ///  * attributes for the delegation times being
   ///  * cached and served by the "client"
   ///  */
   /// typedef nfstime4        fattr4_time_deleg_access;
   /// typedef nfstime4        fattr4_time_deleg_modify;
   ///
   <CODE ENDS>

   <CODE BEGINS>
   ///
   /// %/*
   /// % * New RECOMMENDED Attribute for
   /// % * delegation caching of times
   /// % */
   /// const FATTR4_TIME_DELEG_ACCESS  = 84;
   /// const FATTR4_TIME_DELEG_MODIFY  = 85;
   ///
   <CODE ENDS>

   <CODE BEGINS>
   ///
   /// const OPEN4_SHARE_ACCESS_WANT_DELEG_TIMESTAMPS = 0x100000;
   ///
   <CODE ENDS>

5.  Determining OPEN Feature Support

   [RFC8178] (see Section 4.4.2) allows for extending a particular minor
   version of the NFSv4 protocol without requiring the definition of a
   new minor version.  The client can probe the capabilities of the
   server and based on the result, determine if both it and the server
   support optional features not previously specified as part of the
   minor version.

   The XDR extensions presented in this section provide helpful support
   when the OPEN procedure is extended in such a fashion.  It models all
   of the parameters via bitmap4 data structures, which allows for the
   addition of a new flag to any of the OPEN arguments (see
   Section 18.16.1 of [RFC8881]).  Two new flags are provided:

   *  OPEN4_SHARE_ACCESS_WANT_OPEN_XOR_DELEGATION (see Section 3)

   *  OPEN4_SHARE_ACCESS_WANT_DELEG_TIMESTAMPS (see Section 4)

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   Subsequent extensions can use this framework when introducing new
   OPTIONAL functionality to OPEN, by creating a new flags for each
   OPTIONAL parameter.

   <CODE BEGINS>
   ///
   /// struct open_arguments4 {
   ///   bitmap4  oa_share_access;
   ///   bitmap4  oa_share_deny;
   ///   bitmap4  oa_share_access_want;
   ///   bitmap4  oa_open_claim;
   ///   bitmap4  oa_create_mode;
   /// };
   ///
   <CODE ENDS>

   <CODE BEGINS>
   ///
   /// enum open_args_share_access4 {
   ///    OPEN_ARGS_SHARE_ACCESS_READ  = 1,
   ///    OPEN_ARGS_SHARE_ACCESS_WRITE = 2,
   ///    OPEN_ARGS_SHARE_ACCESS_BOTH  = 3
   /// };
   ///
   <CODE ENDS>

   <CODE BEGINS>
   ///
   /// enum open_args_share_deny4 {
   ///    OPEN_ARGS_SHARE_DENY_NONE  = 0,
   ///    OPEN_ARGS_SHARE_DENY_READ  = 1,
   ///    OPEN_ARGS_SHARE_DENY_WRITE = 2,
   ///    OPEN_ARGS_SHARE_DENY_BOTH  = 3
   /// };
   ///
   <CODE ENDS>

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   <CODE BEGINS>
   ///
   /// enum open_args_share_access_want4 {
   ///    OPEN_ARGS_SHARE_ACCESS_WANT_ANY_DELEG           = 3,
   ///    OPEN_ARGS_SHARE_ACCESS_WANT_NO_DELEG            = 4,
   ///    OPEN_ARGS_SHARE_ACCESS_WANT_CANCEL              = 5,
   ///    OPEN_ARGS_SHARE_ACCESS_WANT_SIGNAL_DELEG_WHEN_RESRC_AVAIL
   ///                                                    = 17,
   ///    OPEN_ARGS_SHARE_ACCESS_WANT_PUSH_DELEG_WHEN_UNCONTENDED
   ///                                                    = 18,
   ///    OPEN_ARGS_SHARE_ACCESS_WANT_DELEG_TIMESTAMPS    = 20,
   ///    OPEN_ARGS_SHARE_ACCESS_WANT_OPEN_XOR_DELEGATION = 21
   /// };
   ///
   <CODE ENDS>

   <CODE BEGINS>
   ///
   /// enum open_args_open_claim4 {
   ///    OPEN_ARGS_OPEN_CLAIM_NULL          = 0,
   ///    OPEN_ARGS_OPEN_CLAIM_PREVIOUS      = 1,
   ///    OPEN_ARGS_OPEN_CLAIM_DELEGATE_CUR  = 2,
   ///    OPEN_ARGS_OPEN_CLAIM_DELEGATE_PREV = 3,
   ///    OPEN_ARGS_OPEN_CLAIM_FH            = 4,
   ///    OPEN_ARGS_OPEN_CLAIM_DELEG_CUR_FH  = 5,
   ///    OPEN_ARGS_OPEN_CLAIM_DELEG_PREV_FH = 6
   /// };
   ///
   <CODE ENDS>

   <CODE BEGINS>
   ///
   /// enum open_args_createmode4 {
   ///    OPEN_ARGS_CREATEMODE_UNCHECKED4     = 0,
   ///    OPEN_ARGS_CREATE_MODE_GUARDED       = 1,
   ///    OPEN_ARGS_CREATEMODE_EXCLUSIVE4     = 2,
   ///    OPEN_ARGS_CREATE_MODE_EXCLUSIVE4_1  = 3
   /// };
   ///
   <CODE ENDS>

   <CODE BEGINS>
   ///
   /// typedef open_arguments4 fattr4_open_arguments;
   ///
   <CODE ENDS>

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   <CODE BEGINS>
   ///
   /// %/*
   /// % * Determine what OPEN supports.
   /// % */
   /// const FATTR4_OPEN_ARGUMENTS     = 86;
   ///
   <CODE ENDS>

   <CODE BEGINS>
   ///
   /// const OPEN4_SHARE_ACCESS_WANT_OPEN_XOR_DELEGATION = 0x200000;
   ///
   <CODE ENDS>

   <CODE BEGINS>
   ///
   /// const OPEN4_RESULT_NO_OPEN_STATEID = 0x00000010;
   ///
   <CODE ENDS>

6.  Extraction of XDR

   This document contains the external data representation (XDR)
   [RFC4506] description of the new open flags for delegating the file
   to the client.  The XDR description is embedded in this document in a
   way that makes it simple for the reader to extract into a ready-to-
   compile form.  The reader can feed this document into the following
   shell script to produce the machine readable XDR description of the
   new flags:

   <CODE BEGINS>
   #!/bin/sh
   grep '^ *///' $* | sed 's?^ */// ??' | sed 's?^ *///$??'
   <CODE ENDS>

   That is, if the above script is stored in a file called "extract.sh",
   and this document is in a file called "spec.txt", then the reader can
   do:

   <CODE BEGINS>
   sh extract.sh < spec.txt > delstid_prot.x
   <CODE ENDS>

   The effect of the script is to remove leading white space from each
   line, plus a sentinel sequence of "///".  XDR descriptions with the
   sentinel sequence are embedded throughout the document.

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   Note that the XDR code contained in this document depends on types
   from the NFSv4.2 nfs4_prot.x file (generated from [RFC7863]).  This
   includes both nfs types that end with a 4, such as offset4, length4,
   etc., as well as more generic types such as uint32_t and uint64_t.

   While the XDR can be appended to that from [RFC7863], the various
   code snippets belong in their respective areas of the that XDR.

6.1.  Code Components Licensing Notice

   Both the XDR description and the scripts used for extracting the XDR
   description are Code Components as described in Section 4 of "Legal
   Provisions Relating to IETF Documents" [LEGAL].  These Code
   Components are licensed according to the terms of that document.

7.  Security Considerations

   There are no new security considerations beyond those in [RFC7862].

8.  IANA Considerations

   IANA should use the current document (RFC-TBD) as the reference for
   the new entries.

9.  References

9.1.  Normative References

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

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

   [RFC7862]  Haynes, T., "Network File System (NFS) Version 4 Minor
              Version 2 Protocol", RFC 7862, DOI 10.17487/RFC7862,
              November 2016, <https://www.rfc-editor.org/info/rfc7862>.

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

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   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

   [RFC8178]  Noveck, D., "Rules for NFSv4 Extensions and Minor
              Versions", RFC 8178, DOI 10.17487/RFC8178, July 2017,
              <https://www.rfc-editor.org/info/rfc8178>.

   [RFC8881]  Noveck, D., Ed. and C. Lever, "Network File System (NFS)
              Version 4 Minor Version 1 Protocol", RFC 8881,
              DOI 10.17487/RFC8881, August 2020,
              <https://www.rfc-editor.org/info/rfc8881>.

9.2.  Informative References

   [LEGAL]    IETF Trust, "Legal Provisions Relating to IETF Documents",
              November 2008, <http://trustee.ietf.org/docs/IETF-Trust-
              License-Policy.pdf>.

Appendix A.  Acknowledgments

   Trond Myklebust and David Flynn all worked on the prototype at
   Hammerspace.

   Dave Noveck provided reviews of the document.

Authors' Addresses

   Thomas Haynes
   Hammerspace
   Email: loghyr@hammerspace.com

   Trond Myklebust
   Hammerspace
   Email: trondmy@hammerspace.com

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