[Docs] [txt|pdf|xml|html] [Tracker] [WG] [Email] [Diff1] [Diff2] [Nits]

Versions: (draft-haynes-nfsv4-versioning) 00 01 02 03 04 05 06 07 08 09 10 11 RFC 8178

NFSv4                                                          D. Noveck
Internet-Draft                                                        HP
Intended status: Standards Track                            July 2, 2015
Expires: January 3, 2016


                        NFSv4 Version Management
                     draft-ietf-nfsv4-versioning-01

Abstract

   This document describes the management of versioning within the NFSv4
   family of protocols.  It covers the creation of minor versions, the
   addition of optional features to existing minor versions, and the
   correction of flaws in features already published as Proposed
   Standards.  The rules relating to the construction of minor versions
   and the interaction of minor version implementations that appear in
   this document supersede the minor versioning rules in RFC5661.

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
   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 January 3, 2016.

Copyright Notice

   Copyright (c) 2015 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of



Noveck                   Expires January 3, 2016                [Page 1]


Internet-Draft               next-versioning                   July 2015


   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.1.  Existing Minor Versions . . . . . . . . . . . . . . . . .   3
     1.2.  Updated NFSv4 Version Management Framework  . . . . . . .   3
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   4
   3.  Consolidation of Version Management Rules . . . . . . . . . .   6
   4.  NFSv4 Protocol Changes  . . . . . . . . . . . . . . . . . . .   7
     4.1.  XDR Extension . . . . . . . . . . . . . . . . . . . . . .   7
       4.1.1.  XDR Extension in General  . . . . . . . . . . . . . .   8
       4.1.2.  Particulars of XDR Extension within NFSv4 . . . . . .   9
       4.1.3.  Rules for XDR Extension within NFSv4  . . . . . . . .   9
     4.2.  Non-XDR Protocol Changes  . . . . . . . . . . . . . . . .  10
       4.2.1.  Field Interpretation and Use  . . . . . . . . . . . .  10
       4.2.2.  Behavioral Changes  . . . . . . . . . . . . . . . . .  11
       4.2.3.  Rules for non-XDR changes . . . . . . . . . . . . . .  11
     4.3.  Specification of Associated Protocols . . . . . . . . . .  12
       4.3.1.  Associated Protocols via pNFS Mapping Types . . . . .  12
       4.3.2.  Additional Forms of Associated Protocols  . . . . . .  13
   5.  Documentation Approach  . . . . . . . . . . . . . . . . . . .  14
     5.1.  Indexing material . . . . . . . . . . . . . . . . . . . .  14
   6.  NFSv4 Features  . . . . . . . . . . . . . . . . . . . . . . .  14
     6.1.  Rules for Feature Construction  . . . . . . . . . . . . .  15
     6.2.  Feature Statuses  . . . . . . . . . . . . . . . . . . . .  15
     6.3.  Feature Discovery . . . . . . . . . . . . . . . . . . . .  16
     6.4.  Feature Specification Documents . . . . . . . . . . . . .  16
     6.5.  Feature Incorporation . . . . . . . . . . . . . . . . . .  17
   7.  Extensions within Minor Versions  . . . . . . . . . . . . . .  18
   8.  Adding Features to Extensible Minor Versions  . . . . . . . .  18
     8.1.  Use of Feature Specification Documents  . . . . . . . . .  18
     8.2.  Compatibility Issues  . . . . . . . . . . . . . . . . . .  19
       8.2.1.  Compatibility Issues for Messages Sent to Servers . .  19
       8.2.2.  Compatibility Issues for Messages Sent to Clients . .  21
     8.3.  Additional Documents to be Produced . . . . . . . . . . .  22
       8.3.1.  Minor Version Indexing Document . . . . . . . . . . .  22
       8.3.2.  Consolidated XDR Document . . . . . . . . . . . . . .  22
       8.3.3.  XDR Assignment Document . . . . . . . . . . . . . . .  23
       8.3.4.  Transition of Documents to RFC's  . . . . . . . . . .  24
     8.4.  Relationship Between Minor Versioning and Extensions
           within a Minor Version  . . . . . . . . . . . . . . . . .  24
   9.  Minor Versions  . . . . . . . . . . . . . . . . . . . . . . .  25
     9.1.  Minor Version Construction  . . . . . . . . . . . . . . .  25
     9.2.  Minor Version Interaction . . . . . . . . . . . . . . . .  26
       9.2.1.  Minor Version Identifier Transfer Issues  . . . . . .  26
       9.2.2.  Minor Version Compatibility Issues  . . . . . . . . .  26



Noveck                   Expires January 3, 2016                [Page 2]


Internet-Draft               next-versioning                   July 2015


     9.3.  Minor Version Documentation . . . . . . . . . . . . . . .  27
   10. Correction of Existing Minor Versions and Features  . . . . .  27
     10.1.  Documentation of XDR Changes . . . . . . . . . . . . . .  29
   11. Security Considerations . . . . . . . . . . . . . . . . . . .  30
   12. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  30
   13. References  . . . . . . . . . . . . . . . . . . . . . . . . .  31
     13.1.  Normative References . . . . . . . . . . . . . . . . . .  31
     13.2.  Informative References . . . . . . . . . . . . . . . . .  31
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .  32

1.  Introduction

   To address the requirement for an NFS protocol that can evolve as the
   need arises, the Network File System (NFS) version 4 (NFSv4) protocol
   provides rules and a framework to allow for future changes via the
   creation of new protocol versions and certain forms of modification
   of existing versions.  These version management rules allow changes
   to be implemented in a way that maintains compatibility with existing
   clients and servers.

1.1.  Existing Minor Versions

   Previously, all such changes had been part of new minor versions.
   The COMPOUND procedure (see Section 14.2 of [RFC7530]) specifies the
   minor version being used by the client in making requests.  The
   CB_COMPOUND (see Section 15.2 of [RFC7530]) procedure specifies the
   minor version being used by the server on callback requests.

   Each existing minor version has been specified by one or more
   standards track RFCs:

   o  Minor version 0 is specified by [RFC7530] with the XDR description
      appearing in [RFC7531].

   o  Minor version 1 is specified by [RFC5661]) with the XDR
      description appearing in [RFC5662].

   o  Minor version 2 is specified by [NFSv42] (in terms of changes from
      [RFC5661]).  The XDR description appears in [NFSv42-dot-x]

1.2.  Updated NFSv4 Version Management Framework

   A number of significant changes from previous version management
   practices should be noted here:

   o  Creation of a new minor version is no longer the only way in which
      protocol changes may be made.  Many changes can be done within the




Noveck                   Expires January 3, 2016                [Page 3]


Internet-Draft               next-versioning                   July 2015


      context of a single minor version.  Creation of new minor versions
      remains available to make other sorts of changes.

   o  Specification of future minor versions in the way that was done
      for NFSv4.0 and NFSv4.1 (i.e. as a single document defining the
      entire protocol) is no longer practical and should not be
      attempted.  All future minor versions will be documented by
      specifying the differences between the minor version being
      documented and the previous minor version.  The documentation
      framework discussed in Section 5 should be used.

   This document starts by presenting the conceptual framework on which
   NFSv4 versioning is built.

   o  First we discuss (in Section 4) the range of protocol changes that
      NFSv4 versioning is to deal with.

   o  Then we discuss (in Section 6) how those changes are organized
      into features.

   Using this framework, we then look at the ways the NFSv4 protocol can
   be changed.

   o  The addition of new features to existing minor versions is
      discussed in Sections 7 and 8.

   o  New Minor versions can be constructed, as described in Section 9.

   o  Issues relating to the correction of protocol errors in existing
      features and minor versions are discussed in Section 10.

2.  Terminology

   A basic familiarity with the NFSv4 terminology is assumed in this
   document and the reader is pointed to [RFC7530].

   The word "feature" has been used inconsistently in previous
   treatments of NFSv4 versioning.  Sometimes it is used to indicate a
   specific XDR extension, while at other times it has been used to
   indicate a set of multiple such extensions which are either supported
   or not supported together.

   In this document, we use the word "feature" in the second sense,
   while individual protocol extensions which are incorporated in a
   feature are referred to as "protocol elements."  The term "feature
   elements" is similar but it differs in that it includes changes in
   field interpretation and use (Section 4.2.1) and protocol behavior
   (See Section 4.2.2).  See Section 6 for more details.



Noveck                   Expires January 3, 2016                [Page 4]


Internet-Draft               next-versioning                   July 2015


   We also need to introduce our vocabulary regarding specification of
   features and minor versions.  Given the ongoing shift to a finer-
   grained documentation model, it is important to be clear here.

   o  The term "minor version definition document" denotes the principal
      document defining a specific NFSv4 minor version.  It may be in
      the form of a complete protocol definition (e.g.  [RFC7530],
      [RFC5661]), a specification of changes relative to the previous
      minor version (e.g.  [NFSv42]), or in a document that specifies
      the features to be included, either by referencing their
      definition document normatively (see Section 9.3) or implicitly
      (see Section 8).

   o  The term "minor version documentation" includes the minor version
      definition document but also includes any corresponding XDR
      definition documents if they are published separately (e.g.
      [RFC7531], [RFC5662]), [NFSv42-dot-x]).  Also included are
      documents separately specifying features newly incorporated in the
      minor version and the ancillary documents described in
      Section 8.3.

   o  The term "feature definition document" denotes a document
      describing a single feature or a set of closely related features.

   As noted above, the keywords defined by [RFC2119] have special
   meanings which this document intends to adhere to.  However, due to
   the nature of this document and some special circumstances, there are
   some complexities to take note of:

   o  Where this document does not directly specify implementation
      requirements, use of these capitalized term is often not
      appropriate.  Instead, what document writers need to do is stated
      without these specialized terms.  In any case, one should not
      conclude that the normative character of this document is
      compromised by this.

   o  In speaking of the previously existing possible statuses of
      feature elements, the lower-case versions of these terms are used,
      following the practice of [RFC3530].  This is despite the fact
      that the corresponding uses of these terms in [RFC5661] was
      switched to upper-case, for no clear reason, and similarly in the
      case [RFC7530], presumably due to inertia.

   o  In speaking of the potential statuses of features, the words
      "required" and "non-required" are used.  By using the latter term,
      we focus on the fact that the feature in question is not required
      to be supported, while treating any potential recommendation for
      support as out-of-scope.



Noveck                   Expires January 3, 2016                [Page 5]


Internet-Draft               next-versioning                   July 2015


   o  When one of these upper-case keywords defined in [RFC2119] is used
      in this document, it is in the context of a rule directed to an
      implementer of NFSV4 minor versions, or in a quotation, sometimes
      indirect, from another document.

3.  Consolidation of Version Management Rules

   In the past, the only existing version management rules were the
   minor versioning rules that had been being maintained and specified
   in the Standards Track RFCs which defined the individual minor
   versions.  As a result, these minor versioning rules were modified on
   an ad hoc basis for each new minor version.

   More recently, minor versioning rules were specified in [RFC5661]
   while modifications to those rules were allowed in subsequent minor
   versions.

   This document defines a set of version management rules, including
   rules for minor version construction.  These rules apply to all
   future changes to the NFSv4 protocol.  The rules are subject to
   change but any such change should be part of a standards track RFC
   obsoleting or updating this document.

   Rather than a single list of minor versioning rules, as in [RFC5661],
   this document defines multiple sets of rules that deal with the
   various forms of versioning provided for in the NFSv4 version
   management framework.

   o  The kinds of changes that may be made are addressed in the rules
      in Sections 4.1.3, 4.2.3, 4.3.1, and 4.3.2.

   o  Rules relating to the composition of changes into features are
      addressed in Section 6.1

   o  Minor version construction, including rules applicable to features
      which cannot be used as extensions to existing minor versions are
      addressed in Section 9.1

   o  Minor version interaction rules are discussed in Sections 9.2.2
      and 9.2.1.

   This document supersedes minor versioning rules appearing in the
   minor version specification RFC's, including those in [RFC5661].  As
   a result, potential conflicts among these documents should be
   addressed as follows:

   o  The specification of the actual protocols for minor versions
      previously published as Proposed Standards take precedence over



Noveck                   Expires January 3, 2016                [Page 6]


Internet-Draft               next-versioning                   July 2015


      minor versioning rules in either this document or in the minor
      version specification RFC's.  In other words, if the transition
      from version A to version B violates a minor versioning rule, the
      version B protocol stays as it is.  In particular, many of the
      changes made for NFSV4.1 would not be allowed in the version
      management framework defined here.  See Section 4.2.3 for details.

   o  Since minor versioning rules #11 and #13 from [RFC5661] deal with
      the interactions between multiple minor versions, the situation is
      more complicated.  See Section 9.2 for a discussion of these
      issues, including how potential conflicts between rules are to be
      resolved.

   o  Otherwise, any conflict between the version management rules in
      this document and those in minor version specification RFC's are
      to be resolved based on the treatment in this document.  In
      particular, corrections may be made as specified in Section 10 for
      all previously specified minor versions and extensibility of
      previously specified minor versions is to be handled in accord
      with Section 8.

   Future minor version specification documents should avoid specifying
   minor versioning rules and reference this document in connection with
   rules for NFSv4 version management.

4.  NFSv4 Protocol Changes

   Protocol changes that are to be managed within the NFSv4 versioning
   framework may be of a number of types, which are discussed in the
   sections below.  Such changes include, but are not limited to,
   changes in the underlying protocol XDR.

   Each such change will be organized, documented and effected as part
   of a given feature.  The way this will be done depends on a number of
   factors, including the types of changes included in the feature.
   This subject is discussed in Section 6.5.

4.1.  XDR Extension

   When an NFSv4 version change requires a modification to the protocol
   XDR, this is effected within a framework based on the idea of XDR
   extension.  This is opposed to transitions between major NFS versions
   (including that between NFSv3 and NFSv4.0) in which the XDR for one
   version was replaced by a different XDR for a newer version.

   The use of XDR extension can facilitate compatibility between
   different versions of the NFSv4 protocol.  When XDR extension is used
   to implement non-required features, the greatest degree of inter-



Noveck                   Expires January 3, 2016                [Page 7]


Internet-Draft               next-versioning                   July 2015


   version compatibility is obtained.  For specifics regarding rules for
   interversion compatibility, see Section 9.2.2.

4.1.1.  XDR Extension in General

   XDR extension allows an XDR description to be extended in a way which
   retains the structure of all previously valid messages.  If a base
   XDR description is extended to create a second XDR description, the
   following will be true for the second description to be a valid
   extension of the first:

   o  The set of valid messages described by the extended definition is
      a superset of that described by the first.

   o  Each message within the set of valid messages described by the
      base definition is recognized as having exactly the same
      structure/interpretation using the extended definition.

   o  Each message within the set of messages described as valid by the
      extended definition but not the base definition must be
      recognized, using the base definition, as part of an unsupported
      extension.

   An extension of a given XDR description consists of any of the
   following:

   o  Addition of previously unspecified RPC operation codes.

   o  Addition of new, previously unused, values to existing enums.

   o  Addition of previously unassigned bit values to a flag word.

   o  Addition of new cases to existing switches, provided that the
      existing switch did not contain a default case.

   However, none of the following may happen:

   o  Deletion of existing RPC operations, enum values, flag bit values
      and switch cases.  Note that changes may be made to define use of
      any of these as causing an error, as long as the XDR is
      unaffected.

   o  Similarly, none of these items may be reused for a new purpose.

   o  Any change to the XDR-defined structure of existing requests or
      replies other than those listed above.





Noveck                   Expires January 3, 2016                [Page 8]


Internet-Draft               next-versioning                   July 2015


4.1.2.  Particulars of XDR Extension within NFSv4

   There are issues, particular to NFSv4, that affect the definition of
   a valid XDR extension within NFSv4.

   o  Because NFSv4 has chosen to structure itself around compound
      requests and callbacks, addition of previously unspecified RPC
      operation codes is not allowed.

   o  Although they fit under the general category of enumerations,
      operation codes (including those for callbacks) are so central to
      the structure of NFSv4, that they merit special treatment.

   o  The fact that attribute sets are represented within nominally
      opaque arrays calls for special handling.

4.1.3.  Rules for XDR Extension within NFSv4

   In the context of NFSv4, an extension of a given XDR description
   consists of one or more of the following:

   o  Addition of previously unspecified operation codes, within the
      framework established by COMPOUND and CB_COMPOUND.

   o  Addition of previously unspecified attributes.

   o  Addition of new, previously unused, values to existing enums.

   o  Addition of previously unassigned bit values to a flag word.

   o  Addition of new cases to existing switches, provided that the
      existing switch did not contain a default case.

   However, none of the following is allowed to happen:

   o  Deletion of existing RPC operations, enum values, flag bit values
      and switch cases.  Note that changes may be made to define use of
      any of these as causing an error, as long as the XDR is
      unaffected.

   o  Similarly, none of these items may be reused for a new purpose.

   o  Any change to the structure of existing requests or replies other
      than those listed above.







Noveck                   Expires January 3, 2016                [Page 9]


Internet-Draft               next-versioning                   July 2015


4.2.  Non-XDR Protocol Changes

   Despite the previous emphasis on XDR changes, additions and changes
   to the NFSv4 protocols have not been limited to those that involve
   changes (in the form of extensions) to the protocol XDR.  Examples of
   other sorts of changes have been taken from NFSv4.1.

4.2.1.  Field Interpretation and Use

   The XDR description of a protocol does not constitute a complete
   description of the protocol.  Therefore, versioning needs to consider
   the role of changes in the use of fields, even when there is no
   change to the underlying XDR.

   Although any XDR element is potentially subject to a change in its
   interpretation and use the likelihood of such change will vary with
   the XDR type, as discussed below:.

   o  When XDR elements are defined as strings, rules regarding the
      appropriate string values are specified in protocol specification
      text with changes in such rules documented in minor version
      definition documents.

      Some types of strings within NFS4 are used in server names (in
      location-related attributes), user and group names, and in the
      names of file object within directories.  Rules regarding what
      strings are acceptable appear in [RFC7530] and [RFC5661] with the
      role of the XDR limited to hints regarding UTF-8 and
      capitalization issues via XDR typedefs.

   o  Fields that are XDR-defined as opaque elements and which are truly
      opaque, do not raise versioning issues, except as regards inter-
      version use, which is effectively foreclosed by the rules in
      Section 9.2.

      Note that sometimes a field will seem to be opaque but not
      actually be fully opaque when considered carefully.  For example,
      the "other" field of stateids is defined as an opaque array, while
      the specification text specially defines appropriate treatment
      when the "other" field within it is either all zeros or all ones.
      Given this context, creation or deletion of reserved values for
      "special" stateids will be a protocol change which versioning
      rules need to deal with.

   o  Some nominally opaque elements have external XDR definitions that
      overlay the nominally opaque arrays.  This technique is useful
      when the same element may be used in several ways when a switched
      union is not appropriate.



Noveck                   Expires January 3, 2016               [Page 10]


Internet-Draft               next-versioning                   July 2015


      For example, each pNFS mapping type provides its own XDR
      definition for various pNFS-related fields defined in [RFC5661] as
      opaque arrays.  For more information about the handling of pNFS
      within the NFSv4 versioning framework, see Section 4.3.1.

   Another form of protocol change that changes how fields are
   presented, without affecting the XDR occurs when there is a change in
   the data elements which may be presented as RDMA chunks.

4.2.2.  Behavioral Changes

   Changes in the behavior of NFSv4 operations are possible, even if
   there is no change in the underlying XDR or change to field
   interpretation and use.

   Many such behavioral changes have occurred in connection with the
   addition of the session concept in NFSv4.1.

   o  Because exactly-once is semantics provided by sessions, the use of
      owner-based sequence values in such operations as OPEN, LOCK,
      LOCKU are now longer needed and the server is to ignore them.

   o  Because of the requirement to begin almost all COMPOUNDs with a
      SEQUENCE operation, the semantics of previously defined operations
      was changed and all formerly valid COMPOUNDs were defined as
      resulting in errors.

   o  Because the clientid is inferable from a previous SEQUENCE
      operation, the clientid is not needed in operations such as OPEN
      and LOCK, and the client is required to pass a value of zero.

   Also changes were made regarding the required server behavior as to
   the interaction of the MODE and ACL attributes.

4.2.3.  Rules for non-XDR changes

   In the past (e.g. in [RFC5661]) there was often uncertainty about
   whether any particular difference from NFSv4.0 was:

   o  A purely editorial change, which may be relevant to other minor
      versions.

   o  The correction of a protocol mistake, best handled as described in
      Section 10.

   o  A protocol improvement relevant to a new minor version or feature,
      to be documented as described in Section 6.4.




Noveck                   Expires January 3, 2016               [Page 11]


Internet-Draft               next-versioning                   July 2015


   In order to avoid such situations, all such changes will be
   documented as part of a feature, specifying the specific changes
   relative to protocol versions that do not incorporate that new
   feature.  Also, to provide greater clarity about such changes, the
   following rules apply:

   o  Any such change must be part of a feature in which there is also
      an XDR extension present, to enable testing for presence of the
      feature.

   o  No feature including such a change can be made required at initial
      introduction.

   o  No feature including such a change can be introduced as an
      extension.  While the feature may be documented in a separate
      feature definition document in such cases, that document should be
      referenced normatively by the minor version specification.

   o  While it is allowed to include multiple such changes in the same
      feature this should only be done if there is a good reason for all
      of these to be included or not included together.  Such changes
      should not be included in the same feature simply because all such
      changes were introduced in the same minor version.

4.3.  Specification of Associated Protocols

   The definition of ancillary protocols is a form of protocol extension
   that is provided as part of pNFS and might be made available for
   other uses in the future.

   As in the case of pNFS, the NFSv4 protocol proper would provide the
   basic framework for performing some protocol-related task, while
   allowing multiple independent means of performing that task to be
   defined.  The version management considerations appropriate to
   creating such additional forms of protocol extension are discussed in
   Section 4.3.2

4.3.1.  Associated Protocols via pNFS Mapping Types

   pNFS is structured around the ability to define alternate mapping
   types in addition to the one defined in [RFC5661], (e.g.  [RFC5663],
   [RFC5664]).  Each mapping type specifies the data-transfer protocol
   to be used to access data represented by layouts as well as mapping-
   type-specific XDR definitions of layout-related data structures.

   Specifying a new mapping type is an additional form of protocol
   change within the NFSv4 version management framework.  A feature
   consisting of the new mapping type is not tied to a specific minor



Noveck                   Expires January 3, 2016               [Page 12]


Internet-Draft               next-versioning                   July 2015


   version.  As explained in Section 7, it is available in multiple
   minor versions upon publication.

4.3.2.  Additional Forms of Associated Protocols

   The same sort of approach used for pNFS might be used in other
   circumstances where there is a clear need to standardize a set of
   protocol-related requirements and where it is desirable, for various
   reasons, to leave open the choice of mechanism by which those
   requirements might be met.

   Such cases might arise where the function to be performed is likely
   to be too enmeshed with the structure of the file system
   implementation to allow a single protocol mechanism to be specified.
   In such cases, multiple approaches might themselves be standardized,
   each fitting into a template established previously using any or all
   of the elements used by pNFS:

   o  The establishment of a registry of identifiers for the
      standardized mechanisms to satisfy the established requirements.

   o  Definition of data structures related to the function to be
      performed to include both a mechanism identifier, and a nominally
      opaque portion, the real format of which is to have a mechanism-
      specific definition.

   o  The ability to specify multiple protocols to perform the same
      function, which may include a minor version of NFSv4, a particular
      use an established protocol, or a new protocol designed for the
      purpose.

   New instances of such a two-level approach might be established in
   the future, subject to the following restrictions:

   o  That there is a feature establishing the requirements that the
      associated protocols are to meet.

   o  That that feature is defined as an integral feature of a
      particular minor version and not as an extension.  This does not
      exclude the feature being defined in a separate document to which
      the minor version specification has a normative reference.

   o  That there be at least one instance of a specific protocol
      mechanism meeting the established requirements.  To limit
      confusion, the requirements and the initial mechanism should be
      defined in separate documents.





Noveck                   Expires January 3, 2016               [Page 13]


Internet-Draft               next-versioning                   July 2015


   The above are a minimal set of restrictions for establishing such an
   additional extension mechanism.  The working group may, as part of
   defining the core feature establishing the extension mechanism may
   specify further restrictions governing when minor versions may
   incorporate particular instances of that extension mechanism.

5.  Documentation Approach

   Documentation of future changes to the NFSv4 protocol will use
   feature specification documents as described in Section 6.4.  There
   are a number of ways in which such documents may be used, as
   discussed in Section 6.5

5.1.  Indexing material

   The following items, referred to collectively as "Indexing material"
   will be useful in many contexts.  The reason for frequently
   publishing such material is to prevent a situation in which large
   numbers of documents must be scanned to find the most current
   description of a particular protocol element.

   o  A table mapping operations and callbacks to the most recent
      document containing a description of that operation.

   o  A table mapping attributes to the most recent document containing
      a description of that attribute.

   o  A table giving, for each operation in the protocol, the errors
      that may validly be returned for that operation.  If possible, it
      would be desirable to give, as does [RFC5661], the operations
      which may validly return each particular error.

   o  A table giving for each operation, callback, and attribute and for
      each feature element in a published extension giving its status
      (required or not, or mandatory-to-not implement), and its
      relationship to the feature which allows its inclusion (i.e.,
      required for every implementation of the feature, or optional in
      the presence of the feature).  This would be similar to the
      material in Section 14 of [NFSv42], expanded in scope to include
      all feature elements.

6.  NFSv4 Features

   Individual changes, whether they are XDR extensions or other sorts of
   changes, are organized in term of features.  This is in order to

   o  allow the protocol documentation to more clearly specify what XDR
      extensions and other changes must be supported together.



Noveck                   Expires January 3, 2016               [Page 14]


Internet-Draft               next-versioning                   July 2015


   o  help the client determine which particular changes are present and
      implemented by the server.

   o  to support the independent development and specification of
      changes to the protocol, without artificially tying features
      together in a paradigm based on minor versions.

   o  provide support for a feature-based documentation structure, as
      described in Section 6.4.

6.1.  Rules for Feature Construction

   A feature consists of one or more valid NFSv4 changes, which work
   together as a functional whole.  The change elements may be of any of
   the types described in Section 4 although the specific types of
   changes will affect how the feature can be integrated in the NFSv4
   protocol.

6.2.  Feature Statuses

   Each feature has one of three statuses with regard to each minor
   version of which it might be a part.

   o  The feature is a required part of the minor version.

   o  The feature is not a required part of the minor version, but may
      be implemented as part of that version..

   o  The feature is not a valid part of the minor version.

      For features which have been previously defined as valid, this is
      represented as being "mandatory to not implement" as opposed to
      simply being undefined.

   These statuses define whether a client implementing the minor version
   has to be prepared for the existence of the feature and/or its non-
   support by the server.

   The working group is still free to make recommendations regarding the
   desirability of server and client support for particular features in
   particular minor versions in the minor version definition document,
   or in other, presumably informational, documents.

   In addition to feature status, there may be other constraints that
   define when an implementation must or may support a feature.  In
   particular, support for one feature may require support for another,
   or the presence of one feature may require that another feature not
   be supported.



Noveck                   Expires January 3, 2016               [Page 15]


Internet-Draft               next-versioning                   July 2015


6.3.  Feature Discovery

   The presence or absence of particular features may be determined in a
   number of ways:

   o  For features which are required within a given minor version, a
      client can determine whether the feature is supported by seeing if
      the minor version is supported.

   o  For non-required features that contain an XDR-extending protocol
      element, a client can try to use techniques described in
      Section 8.2.1 to determine what features the server supports.

   o  For non-required features that do not contain an XDR-extending
      protocol element, appropriate feature discovery facilities can be
      constructed on an ad hoc basis by defining a non-required per-
      server or per-fs boolean attribute to serve as an indication of
      support.  To address compatibility issues with earlier servers, an
      appropriate default value to assume when the attribute is not
      supported should be specified.

6.4.  Feature Specification Documents

   Features will be documented in the form of a working-group standards-
   track document which define one or more features.  Generally, only
   closely related features should be defined in the same document.

   The definition of each of the new features may include one or more
   "feature elements" which change the protocol in any of the ways
   discussed in Section 4.  Feature elements include new operations,
   callbacks, attributes, and enumeration values.  The functionality of
   some existing operations may be extended by the addition of new flags
   bits in existing flag words, by new cases in existing switched
   unions, and by valid semantic changes to existing operations.

   Such feature definition documents would contain a number of items,
   following the pattern of the NFSv4.2 specification.  The only
   difference would be that while the NFSv4.2 specification defines a
   number of features to be incorporated into NFSv4.2, the feature
   definition documents would each define a single feature, or a small
   set of closely related features.

   In addition to a general explanation of the feature in question, the
   items to be included in such feature definition documents would be:

   o  Description of new operations (corresponding to Sections 16 and 17
      of [NFSv42]).




Noveck                   Expires January 3, 2016               [Page 16]


Internet-Draft               next-versioning                   July 2015


   o  Description of any modified operations (corresponding to
      Section 15 of [NFSv42]).

   o  Description of new attributes (corresponding to Section 13 of
      [NFSv42]).

   o  Description of any added error codes (corresponding to
      Section 12.1 of [NFSv42]).

   o  All operation descriptions, whether for new or modified
      operations, should indicate when operations or the corresponding
      results may be presented as RDMA chunks.

   o  A summary description of all changes made by this feature to the
      XDR definition of the protocol, including operation codes,
      attribute numbers, added flag bits and enumeration values, and
      request and response structures for new operations together with
      the other XDR extensions needed to support them.

   o  A listing giving the valid errors for each new operation and
      callback (corresponds to Sections 12.2 and 12.3 of [NFSv42]).

   o  A table giving for each new feature element its status (required
      or not) and its relationship to the feature(s) being described
      (i.e., required for every implementation of the feature, or
      optional in the presence of the feature).  This would be similar
      to the material in Section 14 of [NFSv42] but restricted to the
      feature(s) defined in the document and expanded in scope to
      include all feature elements.

   o  All of the additional Sections required for RFC publication, such
      as "Security Considerations", "IANA considerations", etc.

6.5.  Feature Incorporation

   All protocol changes will be organized, documented and effected as
   part of a given feature.  This includes XDR extension and the various
   sorts of non-XDR-based changes allowed.

   Such features may be made part of the protocol in a number of ways:

   o  In new minor versions, as discussed in Section 9.

   o  In separately documented new features.  When new features are non-
      required and do not include any non-XDR-based changes, they may be
      incorporated in an extensible minor version under construction.
      See Section 8 for details.




Noveck                   Expires January 3, 2016               [Page 17]


Internet-Draft               next-versioning                   July 2015


   o  When appropriate compatibility arrangement are in effect, they may
      be used to correct protocol problems in already approved minor
      versions and features.  See Section 10 for details.

7.  Extensions within Minor Versions

   The NFSv4 version management framework allows, with certain
   restrictions, features to be added to existing minor versions

   o  In the case of features which consist only of a pNFS mapping type,
      the protocol may be extended by publishing the new mapping type
      definition as a Proposed Standard.  This effects an extension to
      all minor versions in which pNFS is a valid feature.

      Similar extension facilities could be made available if additional
      pNFS-like extension frameworks were created (See Section 4.3.2).

   o  Minor versions designated as extensible (see Section 8) may be
      extended by the publication of a standards-track document defining
      the additional feature.  Details are set out in Section 8.  The
      features to be added are considered non-required in the extensible
      minor version and must consist only of valid XDR-based extensions

8.  Adding Features to Extensible Minor Versions

   Addition of features to an extensible minor version will take
   advantage of the existing NFSv4 infrastructure that allows optional
   features to be added to new minor versions, but without in this case
   requiring any change in the minor version number.  Adding features in
   this way will enable compatibility with existing clients and servers,
   who may be unaware of the new feature.

8.1.  Use of Feature Specification Documents

   Each such extension will be in the form of a working-group standards-
   track document which defines one or more new non-required features.
   The definition of each of the new feature may include one or more
   "protocol elements" which extend the existing XDR as already
   discussed (in Section 4.1).  Other sorts of XDR modification are not
   allowed.  Protocol elements include new operations, callbacks,
   attributes, and enumeration values.  The functionality of some
   existing operations may be extended by the addition of new flags bits
   in existing flag words and new cases in existing switched unions.
   New error codes may be added but the set of valid error codes to be
   returned by an operation is fixed, except that existing operations
   may return new errors to respond to situations that only arise when
   previously unused flag bits are set or when extensions to a switched
   union are used.



Noveck                   Expires January 3, 2016               [Page 18]


Internet-Draft               next-versioning                   July 2015


   Each such additional feature will become, for all intents and
   purposes, part of the current NFSv4 minor version upon publication of
   the description as a Proposed Standard, enabling such extensions to
   be used by new client and server implementations without, as
   previously required, a change in the value of the minor version field
   within the COMPOUND operation.

   The working group has two occasions to make sure that such features
   are appropriate ones:

   o  At the time the feature definition document becomes a working
      group document, the working group needs to determine, in addition
      to the feature's general compatibility with NFSv4, that the XDR
      assignments (i.e. additional values for operation callback and
      attribute numbers, and for new flags and switch values to be added
      to existing operations) associated with the new feature are
      complete and do not conflict with those in the existing protocol
      or those currently under development.

   o  At the time the working group document is complete, the working
      group, in addition to normal document review, can and should look
      at what prototype implementations of the feature have been done
      and use that information to determine the work-ability and
      maturity of the feature.

8.2.  Compatibility Issues

   Because the receiver of a message may be unaware of the existence of
   a specific extension, certain compatibility rules need to be
   observed.  In some cases (e.g., addition of new operations or
   callbacks or addition of new arms to an existing switched union)
   older clients or servers may be unable to do XDR parsing on an
   extension of whose existence they are unaware.  In other cases (e.g.,
   error returns) there are no XDR parsing issues but existing clients
   and servers may have expectations as to what may validly be returned.
   Detailed discussion of these compatibility issues appears below:

   o  Issues related to messages sent to the server are discussed in
      Section 8.2.1.

   o  Issues related to messages sent to the client are discussed in
      Section 8.2.2.

8.2.1.  Compatibility Issues for Messages Sent to Servers

   This section deals with compatibility issues that relate to messages
   sent to the server, i.e., requests and replies to callbacks.  In the
   case of requests, it is the responsibility of the client to determine



Noveck                   Expires January 3, 2016               [Page 19]


Internet-Draft               next-versioning                   July 2015


   whether the server supports the extension in question before sending
   a request containing it for any purpose other than determining
   whether the server is aware of the extension.  In the case of
   callback replies, the server demonstrates its awareness of proper
   parsing for callback replies by sending the associated callback.

   Regarding the handling of requests:

   o  Existing server implementations will return NFS4ERR_NOTSUPP or
      NFS4ERR_OP_ILLEGAL in response to any use of a new operation,
      allowing the client to determine that the requested operation (and
      potentially the feature in question) is not supported by the
      server.

   o  Clients can determine whether particular new attributes are
      supported by a given server by examining the value returned when
      the supported_attr attribute is interrogated.  Clients need to do
      this before attempting to use attributes defined in an extension
      since they cannot depend on the server returning
      NFS4ERRATTRNOTSUPP for requests which include a mask bit
      corresponding to a previously unspecified attribute number (as
      opposed to one which is defined but unsupported).

   o  Existing server implementations that do not recognize new flag
      bits will return NFS4ERR_INVAL, enabling the client to determine
      that the new flag value is not supported by the server.

   o  Existing server implementations that do not recognize the new arm
      of a switched union in a request will return NFS4ERR_INVAL or
      NFS4ERR_UNION_NOTSUPP, enabling the client to determine that the
      new union arm is not supported by the server.

   Regarding the handling of responses to callbacks:

   o  Error values returned to the server for all callbacks that do not
      use new features will only be those previously allowed.  Only when
      the server uses a new extension feature can a previously invalid
      error value be returned.

   o  Callback replies may only include a new arm of an existing
      switched union when the server, typically in the callback being
      responded to, has used a feature element associated with the
      feature that defined the new switched union arm.








Noveck                   Expires January 3, 2016               [Page 20]


Internet-Draft               next-versioning                   July 2015


8.2.2.  Compatibility Issues for Messages Sent to Clients

   This sections deals with compatibility issues that relate to messages
   sent to clients, i.e., request replies and callbacks.  In both cases,
   extensions are only sent to clients that have demonstrated awareness
   of the extensions in question by using an extension associated with
   the same feature.

   Regarding the handling of request replies:

   o  Error values returned to the client for all requests that do not
      use new features will only be those previously allowed.  Only when
      the server uses a new extension feature can a previously invalid
      error value be returned.

   o  Replies may only include a new arm of an existing switched union
      when the server, typically in the request being responded to, has
      used a feature element associated with the feature that defined
      the new switched union arm.

   Regarding the handling of callback requests, the server needs to be
   sure that it only sends callbacks to those clients prepared to
   receive and parse them.

   o  In most cases, the new callback will be part of a feature that
      contains new (forward) operations as well.  When this is the case,
      the feature specification will specify the operations whose
      receipt by a server is sufficient to indicate that the client
      issuing them is prepared to accept and parse the associated
      callbacks.

   o  For callbacks associated with features that have no new operations
      defined, the feature specification should define some way for a
      client to indicate that it is prepared to accept and parse
      callbacks that are part of the extension.  For example, a flag bit
      in the EXCHANGE_ID request may serve this purpose.

   o  In both of the above cases, the ability to accept and parse the
      specified callback is considered separate from support for the
      callback.  The feature specification will indicate whether support
      for the callback is required whenever the feature is used by the
      client.  In cases in which support is not required, the client is
      free to return NFS4ERR_NOTSUPP upon receiving the callback.








Noveck                   Expires January 3, 2016               [Page 21]


Internet-Draft               next-versioning                   July 2015


8.3.  Additional Documents to be Produced

   Additional documents will be required from time to time.  These
   documents will eventually become RFC's (informational or standards
   track as described below), but the work of the working group and of
   implementers developing features will be facilitated by a progression
   of document drafts that incorporate information about new features
   that are being developed or have been approved as Proposed Standards.

8.3.1.  Minor Version Indexing Document

   One document will organize existing material for a minor version
   undergoing extension so that implementers will not have to scan a
   large set of feature definition documents or minor version
   specifications to find information being sought.  Successive drafts
   of this document will serve as an index to the current state of the
   extensible minor version.  Some desirable elements of this indexing
   document would include:

   o  A list of all feature definition documents that have been approved
      as working group documents but have not yet been approved as
      Proposed Standards.

   o  All of the items of indexing material (see Section 5.1)
      appropriately adjusted to reflect the contents of all extensions
      accepted as Proposed Standards.

   The frequency of updates for this document will be affected by
   implementer needs and the ability to easily generate document drafts,
   preferably by automated means.  The most desirable situation is one
   in which a new draft is available soon after each feature reaches the
   status of a Proposed Standard.

8.3.2.  Consolidated XDR Document

   This document will consist of an updated XDR for the protocol as a
   whole including feature elements from all features and minor versions
   accepted as Proposed Standards.

   A new draft should be prepared whenever a new feature within an
   extensible minor version is accepted as a Proposed Standard.  In most
   cases, feature developers will be using a suitable XDR which can then
   be reviewed and published.  In cases in which multiple features reach
   Proposed Standard status at approximately the same time, a merge of
   the XDR changes made by each feature may be necessary.






Noveck                   Expires January 3, 2016               [Page 22]


Internet-Draft               next-versioning                   July 2015


8.3.3.  XDR Assignment Document

   This document will contain consolidated lists of XDR value
   assignments that are relevant to the protocol extension process.  It
   should contain lists of assignments for:

   o  operation codes (separate lists for forward operations and for
      callbacks)

   o  attribute numbers

   o  error codes

   o  bits within flag words that have been extended since they were
      first introduced.

   o  enumeration values for enumerations which have been extended since
      they were first introduced.

   For each set of assignments, the individual assignments may be of
   three types:

   1.  permanent assignments associated with a minor version or a
       feature extension that has achieved Proposed Standard status.

       These assignments are permanent in that the assigned value will
       never be re-used.  However, a subsequent minor version may define
       some or all feature elements associated with a feature to be
       Mandatory to NOT support.

   2.  provisional assignments associated with a feature under
       development (i.e., one which has been approved as a working group
       document but has not been approved as a Proposed Standard).

       Provisional assignments are not are not permanent and the values
       assigned can be re-used in certain circumstances.  In particular,
       when a feature with provisional assignments is not progressing
       toward the goal of eventual Proposed Standard status, the working
       group can judge the feature effort to have been abandoned,
       allowing the codes formerly provisionally allocated to be
       reclaimed and reassigned.

   3.  definition of individual assignments or ranges reserved for
       experimental use.

   A new draft of this document should be produced, whenever:





Noveck                   Expires January 3, 2016               [Page 23]


Internet-Draft               next-versioning                   July 2015


   o  A minor version or feature specification is accepted as a Proposed
      Standard.

   o  A new feature is accepted for development and a draft of the
      corresponding working-group standards-track document is produced

   o  A feature previously accepted for development is abandoned.

   o  The working group decides to make some change in assignments for
      experimental use.

8.3.4.  Transition of Documents to RFC's

   Each of these documents should be published as an RFC soon after the
   minor version in question ceases to be considered extensible.
   Typically this will happen when the working group makes the
   specification for the subsequent minor version into a working group
   document.  Some specifics about the individual documents are listed
   below:

   o  The most current draft of the indexing document for the minor
      version would be published as an informational RFC.

   o  The most current draft of the consolidated XDR document should be
      published as a standards-track RFC.  It would update the initial
      specification of the minor version

   o  The most recent draft of the XDR assignment document should be
      published as an informational RFC.

   Handling of these documents in the event of a post-approval XDR
   correction is discussed in Section 10.1

8.4.  Relationship Between Minor Versioning and Extensions within a
      Minor Version

   Extensibility of minor versions are governed by the following rules:

   o  Minor versions zero and one are not extensible.  Each has a fixed
      set of non-required features as described in [RFC7530] and
      [RFC5661].

   o  Minor versions beyond one are presumed extensible as discussed
      herein.  However, any statement within the minor version
      specification disallowing extension will cause that minor version
      to be considered non-extensible.





Noveck                   Expires January 3, 2016               [Page 24]


Internet-Draft               next-versioning                   July 2015


   o  No new feature may be added to a minor version may be made once
      the specification document for a subsequent minor version becomes
      a working group standards-track document.

   Even when a minor version is non-extensible, or when a previous minor
   version is closed to further extension, the features that it contains
   are still subject to updates to effect protocol corrections.  In many
   cases, making an XDR change, in the form of an extension will be the
   best way of correcting an issue.  See Section 10 for details.

   While making minor versions extensible will decrease the frequency of
   new minor versions, it will not eliminate the need for them.  In
   particular:

   o  A new minor version will be required for any change in the status
      of a feature element (i.e., an operation, callback, attribute,
      added flag or switch case).  For example, changes which make
      feature elements Recommended, Required or Mandatory to Not
      Implement will require a minor version.

   o  Any incompatible semantic change in the required or allowed
      processing of an existing operation or attribute will require a
      minor version.

   o  Any change that extends the set of errors returned that an
      existing operation, with the exception noted above.  New errors
      may be added when the conditions that give rise to these new
      errors cannot arise as long as new flag bits or switched union
      arms are not used.  In these cases, it is clear that existing
      clients cannot receive these errors.

   o  Any change in the mapping of feature elements to features will
      require a minor version.  For example, if a feature is to be split
      into two separate features clients would no longer be able to
      infer support for one operation from support for the other, in the
      same way that had been done previously, invalidating logic in
      existing clients

9.  Minor Versions

9.1.  Minor Version Construction

   In addition to the sorts of non-required features that may be made in
   the context of extensible minor version, a number of other sorts of
   changes may be made in a new minor version.  Because such changes
   have the potential to disrupt inter-version such changes should only
   be made after careful consideration of the effects on interversion
   interoperability.



Noveck                   Expires January 3, 2016               [Page 25]


Internet-Draft               next-versioning                   July 2015


   o  Addition of new features that incorporate any of the non-XDR-based
      changes discussed in Sections 4.2.1 and 4.2.2.  Such features must
      always be introduced as non-required.

   o  Addition of required new features.

   o  Changes to the status of existing features or to inter-feature
      constraints.

   o  Changes to feature organization.  Such changes may have the effect
      of making support for some change element obligatory in
      circumstances when it had not been previously.

9.2.  Minor Version Interaction

   This section addresses issues related to rules #11 and #13 in the
   minor versioning rules in [RFC5661].  With regard to the supersession
   of minor versioning rules, the treatment here overrides that in
   [RFC5661] when either of the potentially interacting minor versions
   has not yet been published as a Proposed Standard.

   Note that these rules are the only ones directed to minor version
   implementers, rather than to those specifying new minor versions.

9.2.1.  Minor Version Identifier Transfer Issues

   Each relationship between a client instance and a server instance, as
   represented by a clientid, is to be devoted to a single minor
   version.  If a server detects that a COMPOUND with an inappropriate
   minor version is being used, it MUST reject the request.  In doing
   so, it may return either NFS4ERR_BAD_CLIENTID or
   NFS4RR_MINOR_VERS_MISMATCH.

   As a result of the above, the client has the assurance that the set
   of required and allowed features will not change within the context
   of a single clientid.  Server implementations MUST ensure that the
   set of supported features does not change within such a context.

9.2.2.  Minor Version Compatibility Issues

   It is desirable for client and server implementations to support a
   wide range of minor versions.  The difficulty of doing so can be
   affected by choices made by the working group in defining those minor
   versions.

   Within a set of minor versions that have exactly the same set of
   required features, it is relatively easy for clients and servers to
   provide appropriate compatibility and they are well-advised to do so.



Noveck                   Expires January 3, 2016               [Page 26]


Internet-Draft               next-versioning                   July 2015


   Servers SHOULD accept any minor version number within the range and
   return NFS4ERR_OPNOTSUPP or NFS4ERR_OP_ILLEGAL for non-supported
   operations based on the version number.

   Clients SHOULD deal with an NFS4ERR_MINOR_VERS_MISMATCH error by
   searching the appropriate minor version range for one the server will
   accept.

   Servers and clients MAY deal with changes in the set of required
   features by supporting at least the union of the set of required
   features for all minor versions within the range to be supported.
   This may involve logic to specifically withhold support for features
   when not allowed for a particular minor version.

9.3.  Minor Version Documentation

   Minor versions should be documented by specifying and explaining the
   changes made relative to the previous minor version.

   Features added to the minor version should be documented in their own
   feature specification documents and normatively referenced.

   Changes to the status or organization of existing features should be
   documented by presenting a summary of the status of all existing
   protocol elements, their relationship to non-required features, and
   any relevant feature dependencies.

   In addition, to avoid situation where a large number of minor
   versions must be scanned to find the most recent valid treatment of a
   specific protocol element, minor version definition documents will
   contain the indexing material described in Section 5.1.

10.  Correction of Existing Minor Versions and Features

   The possibility always exists that there will be a need to correct an
   existing feature in some way, after the acceptance of that feature or
   a minor version containing it, as a Proposed Standard.  While the
   working group can reduce the probability of such situations arising
   by waiting for running code before considering a feature as done, it
   cannot reduce the probability to zero.  As features are used more
   extensively and interact with other features, previously unseen flaws
   may be discovered and will need to be corrected.

   Such corrections are best done in a bis document updating the RFC
   defining the relevant feature definition document or minor version
   specification.  In making such a correction, the working will have to
   carefully consider how to assure interoperability with older clients
   and servers.



Noveck                   Expires January 3, 2016               [Page 27]


Internet-Draft               next-versioning                   July 2015


   Often, corrections can be done without changing the protocol XDR.
   However, incompatible changes in server or client behavior should not
   be mandated in order to avoid XDR changes.  When XDR changes are
   necessary as part of correcting a flaw, these should be done in a
   manner similar to that used when implementing new minor versions or
   features within them.  In particular,

   o  Existing XDR structures may not be modified or deleted.

   o  XDR extensions may be used to correct existing protocol facilities
      in a manner similar to those used to add additional optional
      features.  Such corrections may be done in an otherwise non-
      extensible minor version, if the working group judges it
      appropriate.

   o  When a correction is made to a non-required feature, the result is
      similar to a situation in which there are two independent non-
      required features.  A server may choose to implement either or
      both.

   o  When a correction is made to a required feature, the situation
      becomes one in which neither the old nor the new version of the
      feature is required.  Instead, it is required that a server
      support at least one of the two, while each is individually non-
      required.  Although use of the corrected version is ultimately
      better, and may be recommended, it should not be described as
      "RECOMMENDED", since the choice of which version to support if
      only one is supported will depend on the needs of clients, which
      may be slow to adopt the updated version.

   o  In all of the cases above, it is appropriate that the old version
      of the feature, be considered obsolescent, with the expectation
      that the working group might, in a later minor version, decide
      that the older version is to become mandatory to not implement.

   Issues related to the effect of XDR corrections on existing
   documents, including co-ordination with other minor versions, are
   discussed in Section 10.1.

   By doing things this way, the protocol with the XDR modification can
   accommodate clients and servers that support either the corrected or
   the uncorrected version of the protocol and also clients and servers
   aware of and capable of supporting both alternatives.

   o  A client that supports only the earlier version of the feature
      (i.e., an older unfixed client) can determine whether the server
      it is connecting to supports the older version of feature.  It is




Noveck                   Expires January 3, 2016               [Page 28]


Internet-Draft               next-versioning                   July 2015


      capable of interoperating with older servers that support only the
      unfixed protocol as well as ones that support both versions.

   o  A client that supports only the corrected version of the feature
      (i.e., a new or updated client) can determine whether the server
      it is connecting to supports the newer version of the feature.  It
      is capable of interoperating with newer servers that support only
      the updated feature as well as ones that support both versions.

   o  A client that supports both the older and newer version of the
      feature can determine which version of the particular feature is
      supported by the server it is working with.

   o  A server that supports only the earlier version of the feature
      (i.e., an older unfixed server) can only successfully interoperate
      with older clients.  However newer clients can easily determine
      that the feature cannot be used on that server.

   o  A server that supports only the newer version of the feature
      (i.e., a new or updated server) can only successfully interoperate
      with newer clients.  However, older clients can easily determine
      that the feature cannot be used on that server.  In the case of
      non-required features, clients can be expected to deal with non-
      support of that particular feature.

   o  A server that supports both the older and newer versions of the
      feature can interoperate with all client variants.

   By using extensions in this manner, the protocol creates a clear path
   which preserves the functioning of existing clients and servers and
   allowing client and server implementers to adopt the new version of
   the feature at a reasonable pace.

10.1.  Documentation of XDR Changes

   In the event of an XDR correction, as discussed above, some document
   updates will be required.  For the purposes of this discussion we
   call the minor version for which XDR correction is required minor
   version X and the minor version on which development is occurring
   minor version Y.

   The following discusses the specific updated documents which could be
   required:

   o  The specification of the feature in question will have to be
      updated to explain the issue, how it was fixed, and the
      compatibility and upgrade strategy.  Normally this will require an
      RFC updating the associated feature specification document.



Noveck                   Expires January 3, 2016               [Page 29]


Internet-Draft               next-versioning                   July 2015


      However, in the case of a correction to a feature documented in a
      minor version definition document, the RFC will update that
      document instead.

   o  An updated XDR for minor version X will be produced and will be
      published as a updated to the minor version specification RFC for
      minor version X.

      When the correction is to feature documented in a minor version
      definition, a single RFC will contain both updates to the minor
      version specification RFC.

   o  An updated minor version indexing document for minor version X is
      desirable but not absolutely necessary.

      The question of updated minor version indexing documents for minor
      versions between X and Y should be addressed by the working group
      on a case-by-case basis.

   o  An updated XDR assignment document will be required.  It should be
      based on the most recent such document associated with minor
      version Y and will serve as the basis for later XDR assignment
      drafts for minor version Y.

   The informational RFC's associated with minor version Y (version
   indexing document and XDR assignment document) will contain the
   effects of the correction when published.  Similarly, the minor
   version specification RFC will contain the XDR changes associated
   with the correction.

11.  Security Considerations

   Since no substantive protocol changes are proposed here, no security
   considerations apply.

   As features and minor versions are designed and specified in
   standards-track documents, their security issues will be addressed
   and each RFC candidate will receive the appropriate security review
   from the NFSv4 working group and IESG.

12.  IANA Considerations

   The current document does not require any actions by IANA.

   Depending on decisions that the working group makes about how to
   address the issues raised in this document, future documents may
   require actions by IANA.




Noveck                   Expires January 3, 2016               [Page 30]


Internet-Draft               next-versioning                   July 2015


13.  References

13.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

13.2.  Informative References

   [NFSv42]   Haynes, T., Ed., "NFS Version 4 Minor Version 2", April
              2015, <http://www.ietf.org/id/
              draft-ietf-nfsv4-minorversion2-38.txt>.

              Work in progress.

   [NFSv42-dot-x]
              Haynes, T., Ed., "NFS Version 4 Minor Version 2 Protocol
              External Data Representation Standard (XDR) Description",
              April 2015, <http://www.ietf.org/id/
              draft-ietf-nfsv4-minorversion2-dot-x-38.txt>.

              Work in progress.

   [RFC3530]  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.

   [RFC5661]  Shepler, S., Eisler, M., and D. Noveck, "Network File
              System (NFS) Version 4 Minor Version 1 Protocol", RFC
              5661, January 2010.

   [RFC5662]  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.

   [RFC5663]  Black, D., Fridella, S., and J. Glasgow, "Parallel NFS
              (pNFS) Block/Volume Layout", RFC 5663, January 2010.

   [RFC5664]  Halevy, B., Welch, B., and J. Zelenka, "Object-Based
              Parallel NFS (pNFS) Operations", RFC 5664, January 2010.

   [RFC7530]  Haynes, T. and D. Noveck, "Network File System (NFS)
              Version 4 Protocol", RFC 7530, March 2015.

   [RFC7531]  Haynes, T. and D. Noveck, "Network File System (NFS)
              Version 4 External Data Representation Standard (XDR)
              Description", RFC 7531, March 2015.



Noveck                   Expires January 3, 2016               [Page 31]


Internet-Draft               next-versioning                   July 2015


Author's Address

   David Noveck
   Hewlett-Packard
   165 Dascomb Road
   Andover, MA  01810
   US

   Phone: +1 978 474 2011
   Email: davenoveck@gmail.com









































Noveck                   Expires January 3, 2016               [Page 32]


Html markup produced by rfcmarkup 1.129b, available from https://tools.ietf.org/tools/rfcmarkup/