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

NFSv4                                                          D. Noveck
Internet-Draft                                                       HPE
Updates: 5661, xxxx (if approved)                       October 22, 2016
Intended status: Standards Track
Expires: April 25, 2017


             Rules for NFSv4 Extensions and Minor Versions.
                     draft-ietf-nfsv4-versioning-07

Abstract

   This document describes the rules relating to the extension of 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 and
   other RFCs defining minor versions.

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 April 25, 2017.

Copyright Notice

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

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect



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   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   3
     2.1.  Use of Keywords Defined in RFC2119  . . . . . . . . . . .   3
     2.2.  Use of Feature Statuses . . . . . . . . . . . . . . . . .   4
     2.3.  NFSv4 Versions  . . . . . . . . . . . . . . . . . . . . .   5
   3.  Consolidation of Extension Rules  . . . . . . . . . . . . . .   6
   4.  XDR Considerations  . . . . . . . . . . . . . . . . . . . . .   7
     4.1.  XDR Extension . . . . . . . . . . . . . . . . . . . . . .   7
     4.2.  Rules for XDR Extension within NFSv4  . . . . . . . . . .   8
     4.3.  Handling of Protocol Elements . . . . . . . . . . . . . .   9
     4.4.  Inter-version Interoperability  . . . . . . . . . . . . .  10
       4.4.1.  Requirements for Knowledge of Protocol Elements . . .  10
       4.4.2.  Establishing Interoperability . . . . . . . . . . . .  12
       4.4.3.  Determining Knowledge of Protocol Elements  . . . . .  13
     4.5.  XDR Overlay . . . . . . . . . . . . . . . . . . . . . . .  14
   5.  Other NFSv4 Protocol Changes  . . . . . . . . . . . . . . . .  15
     5.1.  Field Interpretation and Use  . . . . . . . . . . . . . .  15
     5.2.  Behavioral Changes  . . . . . . . . . . . . . . . . . . .  16
   6.  Extending Existing Minor Versions . . . . . . . . . . . . . .  16
   7.  Minor Versions  . . . . . . . . . . . . . . . . . . . . . . .  16
     7.1.  Creation of New Minor Versions  . . . . . . . . . . . . .  16
   8.  Minor Version Interaction Rules . . . . . . . . . . . . . . .  17
     8.1.  Minor Version Identifier Transfer Issues  . . . . . . . .  17
     8.2.  Minor Version Compatibility . . . . . . . . . . . . . . .  18
   9.  Correction of Existing Minor Versions and Features  . . . . .  19
     9.1.  XDR Changes to Implement Protocol Corrections . . . . . .  19
     9.2.  XDR Corrections to required features  . . . . . . . . . .  21
   10. Security Considerations . . . . . . . . . . . . . . . . . . .  22
   11. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  22
   12. References  . . . . . . . . . . . . . . . . . . . . . . . . .  22
     12.1.  Normative References . . . . . . . . . . . . . . . . . .  22
     12.2.  Informative References . . . . . . . . . . . . . . . . .  23
   Appendix A.  Acknowledgements . . . . . . . . . . . . . . . . . .  23
   Appendix B.  Instructions for RFC Editor  . . . . . . . . . . . .  23
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .  23

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 a framework to allow for future changes via the creation of



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   new protocol versions including minor versions and certain forms of
   modification of existing minor versions.  The extension rules
   contained in this document allow extensions and other changes to be
   implemented in a way that maintains compatibility with existing
   clients and servers.

   Previously, all protocol 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 procedure (see Section 15.2 of [RFC7530]) specifies the
   minor version being used by the server on callback requests.

   Creation of a new minor version is no longer the only way in which
   protocol changes may be made.  Optional features may be added as
   extensions and protocol corrections can be proposed, specified and
   implemented within the context of a single minor version.  Creation
   of new minor versions remains available to make other sorts of
   changes.

   The goal of allowing extensions within the context of a minor version
   is provide more implementation flexibility while preserving
   interoperability on protocol upgrade.  As described in Section 4.4,
   two implementations can each choose to implement a subset of
   available extensions, enabling interoperation to proceed just as if
   both implementations supported only the parts of the protocol they
   both support.

2.  Terminology

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

   In this document, the term "version" is not limited to minor
   versions.  When minor versions are meant, the term "minor version" is
   used explicitly.  For more discussion of this and related terms, see
   Section 2.3

   A "feature package" is a set of features that are defined together,
   either as part of a minor version or as part of the same protocol
   extension.

2.1.  Use of Keywords Defined in RFC2119

   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:




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   o  Where this document does not directly specify implementation
      requirements, use of these capitalized terms is often not
      appropriate, since the guidance given in this document does not
      directly affect interoperability.

   o  In this document, what authors of RFCs defining features and minor
      versions need to do is stated without these specialized terms.
      Although it is necessary to follow this guidance to provide
      successful NFSv4 protocol extension, that sort of necessity is not
      of the sort defined as applicable to the use of the keywords
      defined in [RFC2119].

      The fact that these capitalized terms are not used should not be
      interpreted as indicating that this guidance does not need to be
      followed or is somehow not important.

   o  In speaking of the possible statuses of features and feature
      elements, the terms "OPTIONAL" and "REQUIRED" are used.  For
      further discussion, see Section 2.2.

   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, the status of a feature or
      protocol element, or in a quotation, sometimes indirect, from
      another document.

2.2.  Use of Feature Statuses

   There has been some confusion, during the history of NFSv4, about the
   correct use of these terms, and instances in which the keywords
   defined in [RFC2119] were used in ways that appear to be at variance
   with the definitions in that document.

   o  In [RFC3530], the lower-case terms "optional", "recommended", and
      "required" were used as feature statuses, Later, in [RFC5661] and
      [RFC7530], the corresponding upper-case keywords were used.  It is
      not clear why this change was made.

   o  In the case of "RECOMMENDED", its use as a feature status is
      inconsistent with [RFC2119] and it will not be used for this
      purpose in this document.

   o  The word "RECOMMENDED" to denote the status of attributes in
      [RFC7530] and [RFC5661] raises similar issues.  This has been
      recognized in [RFC7530] with regard to NFSV4.0, although the
      situation with regard to NFSv4.1 remains unresolved.





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   In this document, the keywords "OPTIONAL" and "REQUIRED" and the
   phrase "mandatory to not implement" are used to denote the status of
   features within a given minor version.  In using these terms, RFCs
   which specify the status of features inform:

   o  client implementations whether they need to deal with the absence
      of support for these features.

   o  server implementations whether they need to provide support for
      these features.

2.3.  NFSv4 Versions

   The term "version" denotes any valid protocol variant constructed
   according to the rules in this document.  It includes minor versions,
   but there are situations which allow multiple variant versions to be
   associated with and co-exist within a single minor version:

   o  When there are feature specification documents published as
      Proposed Standards extending a given minor version, then the
      protocol defined by the minor version specification document, when
      combined with any subset (not necessarily proper) of the feature
      specification documents, is a valid NFSv4 version variant which is
      part of the minor version in question.

   o  When there are protocol corrections published which update a given
      minor version, each set of published updates, up to the date of
      publication of the update, is a valid NFSv4 version variant which
      is part of the minor version in question.

   Because of the above, there can be multiple version variants that are
   part of a given minor version.  Two of these are worthy of special
   terms:

   o  The term "base minor version" denotes the version variant that
      corresponds to the minor version as originally defined, including
      all protocol elements specified in the minor version definition
      document but not incorporating any extensions or protocol
      corrections published subsequently.

   o  At any given time, the term "current minor version" denotes the
      minor version variant including all extensions of and corrections
      to the minor version made by standard-track documents published
      subsequently.

   Each version variant which is part of a given minor version is a
   subset of the current minor version and a superset of the base minor
   version.  When the term "minor version" is used without either of



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   these qualifiers, it should refer to something which is true of all
   variants within that minor version.  For example, in the case of a
   minor version that has not had a protocol correction, one may refer
   to the set of REQUIRED features for that minor version since it is
   the set is the same for all variants within the minor version.  See
   Section 9 for a discussion of correcting an existing minor version.

   Each client and server which implements a specific minor version will
   implement some particular variant of that minor version.  Each of
   these will be a superset of the appropriate base minor version.

3.  Consolidation of Extension Rules

   In the past, the only existing extension rules were the minor
   versioning rules that were being maintained and specified in the
   Standards Track RFCs which defined the individual minor versions.  In
   the past, 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 extension 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 extension rules, as was done in the
   minor versioning rules in [RFC5661], this document defines multiple
   sets of rules that deal with the various forms of protocol change
   provided for in the NFSv4 extension framework.

   o  The kinds of XDR changes that may be made to extend NFSv4 are
      addressed in the rules in Section 4.2.

   o  Minor version construction, including rules applicable to changes
      which cannot be made in extensions to existing minor versions are
      addressed in Section 7.1

   o  Minor version interaction rules are discussed in Sections 8.1 and
      8.2.

   This document supersedes minor versioning rules appearing in the
   minor version specification RFC's, including those in [RFC5661] and
   also the modification to those rules mentioned in [RFCv42].  As a




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   result, potential conflicts among documents should be addressed as
   follows:

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

   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 8 for a discussion of these issues,
      including how potential conflicts between rules are to be
      resolved.

   o  Otherwise, any conflict between the extension 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 9 for all
      previously specified minor versions and the extensibility of
      previously specified minor versions is to be handled in accord
      with Section 6.

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

4.  XDR Considerations

   As an extensible XDR-based protocol, NFSv4 has to ensure interversion
   compatibility in situations in which the client and server use
   different XDR descriptions.  For example, the client and server may
   implement different variants of the same minor version, in that they
   each might add different sets of extensions to the base minor
   version.

   The XDR extension paradigm, discussed in Section 4.1, assures that
   these descriptions are compatible, with clients and servers able to
   determine and use those portions of the protocol that they both share
   according to the method described in Section 4.4.2.

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




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   (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 XDR extension approach 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 extension not
      provided for.

   The use of XDR extension can facilitate compatibility between
   different versions of the NFSv4 protocol.  When XDR extension is used
   to implement OPTIONAL features, the greatest degree of inter-version
   compatibility is obtained.  In this case, no change in minor version
   number is needed and the extension may be effected in the context of
   a single minor version.

4.2.  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:





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

   o  Addition of previously unspecified RPC operation codes, for either
      the nfsv4 program or the callback program.

   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.

4.3.  Handling of Protocol Elements

   Implementations handle protocol elements in one of three ways.  Which
   of the following ways are valid depends on the status of the protocol
   element in the variant being implemented:

   o  The protocol element is not a part of definition of the variant in
      question and so is "unknown".  The responder, when it does not
      report an RPC XDR decode error, reports an error indicative of the
      element not being defined in the XDR such as NFS4ERR_OP_ILLEGAL,
      NFS4ERR_BADXDR, or NFS4ERR_INVAL.  See Section 4.4.3 for details.

   o  The protocol element is a known part of the variant but is not
      supported by the particular implementation.  The responder reports
      an error indicative of the element being recognized as one which
      is not supported such as NFS4ERR_NOTSUPP, NFS4ERR_UNION_NOTSUPP,
      or NFS4ERR_ATTRNOTSUPP.

   o  The protocol element is a known part of the variant which is
      supported by the particular implementation.  The responder reports
      success or an error other than the special ones discussed above.

   Which of these are validly returned by the responder depends on the
   status of the protocol element in the minor version specified in the
   COMPOUND or CB_COMPOUND.  The possibilities which can exist when
   dealing with minor versions that have not been subject to corrections
   are listed below.  See Sections 9.1 and 9.2 for a discussion of the
   effects of protocol correction.

   o  The protocol element is not known in the minor version.  In this
      case all implementations of the minor version MUST indicate that
      the protocol element is not known.

   o  The protocol element is part of a feature specified mandatory to
      not implement in the minor version.  In this case as well, all



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      implementations of the minor version MUST indicate that the
      protocol element is not known.

   o  The protocol element is defined as part of the current variant of
      the minor version but is not part of the corresponding base
      variant.  In this case, the requester can encounter situations in
      which the protocol element is either not known to the responder,
      is known to but not supported by the responder, or is both known
      to and supported by the responder.

   o  The protocol element is defined as an OPTIONAL part of the base
      minor version.  In this case, the requester can expect the
      protocol element to be known but must deal with cases in which it
      is supported or is not supported.

   o  The protocol element is defined as a REQUIRED part of the base
      minor version.  In this case, the requester can expect the
      protocol element to be both known and supported by the responder.

   The listing of possibilities above does not mean that a requester
   always needs to be prepared for all such possibilities.  Often,
   depending on the scope of the feature of which the protocol element
   is a part, handling of a previous request using the same or related
   protocol elements, will allow the requester to be sure that certain
   of these possibilities cannot occur.

   Requesters, typically clients, may test for knowledge of or support
   for protocol elements as part of connection establishment.  This may
   allow the requester to be aware of responder lack of knowledge of or
   support for problematic requests before they are actually used to
   effect user requests.

4.4.  Inter-version Interoperability

   Because of NFSv4's use of XDR extension, any communicating client and
   server versions have XDR definitions that are each valid extensions
   of a third version.  Once that version is determined, it may be used
   by both client and server to communicate.  Each party can
   successfully use a subset of protocol elements that are both known
   and supported by both parties.

4.4.1.  Requirements for Knowledge of Protocol Elements

   With regard to requirements for knowledge of protocol elements, the
   following rules apply.  These rules are the result of the use of the
   XDR extension paradigm combined with the way in which extensions are
   incorporated in existing minor versions (for details of which see
   Section 6).



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   o  Any protocol element defined as part of the base variant of
      particular minor version is required to be known by that minor
      version.  This occurs whether the specification happens in the
      body of the minor definition document or is in a feature
      definition document that is made part of the minor version by
      being normatively referenced by the minor version definition
      document.

   o  Any protocol element required to be known in a given minor version
      is required to be known in subsequent minor version, unless and
      until a minor version has made that protocol element as mandatory
      to not implement.

   o  When a protocol element is defined as part of an extension to an
      extensible minor version, it is not required to be known in that
      minor version but is required to be known by the next minor
      version.  In the earlier minor version, it might not be defined in
      the XDR definition document, while in the later version it needs
      to be defined in the XDR definition document.  In either case, if
      it is defined, it might or might not be supported.

   o  When knowledge of protocol elements is optional in a given minor
      version, the responder's knowledge of such optional elements must
      obey the rule that if one such element is known, then all the
      protocol elements defined in the same minor version definition
      document must be known as well.

   For many minor versions, all existing protocol elements, are required
   to be known by both the client and the server, and so requesters do
   not have to test for the presence or absence of knowledge regarding
   protocol elements for which knowledge might be optional.  This is the
   case if there has been no extension for the minor version in
   question.  Extensions can be added to extensible minor versions as
   described in Section 6 and can be used to correct protocol flaws as
   described in Section 9.

   Requesters can ascertain the knowledge of the responder in two ways:

   o  By issuing a request using the protocol element and looking at the
      response.  Note that, even if the protocol element used is not
      supported by the responder, the requester can still determine if
      the element is known by the responder.

   o  By receiving a request from the responder, acting in the role of
      requester.  For example, a client may issue a request enabling the
      server to infer that it is aware of a corresponding callback.





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   In making this determination, the requester can rely on two basic
   facts:

   o  If the responder is aware of a single protocol element within a
      feature package, it must be aware of all protocol elements within
      that feature package

   o  If a protocol element is one defined by the minor version
      specified by a request (and not in an extension), or in a previous
      minor version, the responder must be aware of it.

4.4.2.  Establishing Interoperability

   When a client and a server interact, they need to able to take
   advantage of the compatibility provided by NFSv4's use of XDR
   extension.

   In this context, the client and server would arrive at a common
   variant which the client would uses to send requests which the server
   would then accept.  The server would use that variant to send
   callbacks which the client would then accept.  This state of affairs
   could arise in a number of ways:

   o  Client and server have been built using XDR variants that belong
      to the same minor version

   o  The client's minor version is lower than that of the server.  In
      this case the server, in accord with Section 8.2, accepts the
      client's minor version, and acts as if it has no knowledge of
      extensions made in subsequent minor versions.  It has knowledge of
      protocol elements within the current (i.e. effectively final)
      variant of the lower minor version.

   o  The client's minor version is higher than that of the server.  In
      this case the client, in accord with Section 8.2, uses a lower
      minor version that the server will accept.  In this case, the
      server has no knowledge of extensions made in subsequent minor
      versions.

   There are a number of cases to consider based on the characteristics
   of the minor version chosen.

   o  The minor version consists of only a single variant (no extension
      or XDR corrections), so the client and the server are using the
      same XDR description and have knowledge of the same protocol
      elements.





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   o  When the minor version consists of multiple variants (i.e. there
      are one or more XDR extensions or XDR corrections), the client and
      the server are using compatible XDR descriptions.  The client is
      aware of some set of extensions while the server may be aware of a
      different set.  The client can determine which of the extensions
      that he is aware of, are also known to the server by using the
      approach described in Section 4.4.3.  Once this is done, the
      client and server will both be using a common variant.  The
      variants that the client and the server were built with will both
      either be identical to this variant or a valid extension of it.
      Similarly, the variants that the client and the server actually
      use will be a subset of this variant, in that certain OPTIONAL
      features will not be used.

   In either case, the client must determine which of the OPTIONAL
   protocol elements within the common version are supported by the
   server, just as it does for OPTIONAL features introduced as part of a
   minor version.

   It is best if client implementations make the determination as to the
   support provided by the server before acting on user requests.  This
   includes the determination of the common protocol variant and the
   level of support for OPTIONAL protocol elements.

4.4.3.  Determining Knowledge of Protocol Elements

   A requester may test the responder's knowledge of particular protocol
   elements as defined below, based on the type of protocol element.
   Note that in the case of attribute or flag bits, use of a request
   that refers to 2 or more bits of undetermined status (known versus
   unknown) may return results which are not particularly helpful.  In
   such cases, when the response is NFS4ERR_INVAL, the requester can
   only conclude that at least one of the bits is unknown.

   o  When a GETATTR request is made specifying an attribute bit to be
      tested and that attribute is not a set-only attribute, if the
      GETATTR returns with the error NFS4ERR_INVAL, then it can be
      concluded that the responder has no knowledge of the attribute in
      question.  Other responses, including NFS4ERR_ATTRNOTSUPP,
      indicate that the responder is aware of the attribute in question.

   o  When a SETATTR request is made specifying the attribute bit to be
      tested and that attribute is not a get-only attribute, if the
      SETATTR returns with the error NFS4ERR_INVAL, then it can be
      concluded that the responder has no knowledge of the attribute in
      question.  Other responses, including NFS4ERR_ATTRNOTSUPP,
      indicate that the responder is aware of the attribute in question.




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   o  When a request is made including an operation with a new flag bit,
      if the operation returns with the error NFS4ERR_INVAL,then it can
      generally be concluded that the responder has no knowledge of the
      flag bit in question, as long as the requester is careful to avoid
      other error situations in which the operation in question is
      defined as returning NFS4ERR_INVAL.  Other responses indicate that
      the responder is aware of the flag bit in question.

   o  When a request is made including the operation to be tested, if
      the responder returns an RPC XDR decode error, or a response
      indicating that the operation in question resulted in
      NFS4ERR_OP_ILLEGAL or NFS4ERR_BADXDR, then it can be concluded
      that the responder has no knowledge of the operation in question.
      Other responses, including NFS4ERR_NOTSUPP, indicate that the
      responder is aware of the operation in question.

   o  When a request is made including the switch arm to be tested, if
      the responder returns an RPC XDR decode error, or a response
      indicating that the operation in question resulted in
      NFS4ERR_BADXDR, then it can be concluded that the responder has no
      knowledge of the operation in question.  Other responses,
      including NFS4ERR_UNION_NOTSUPP, indicate that the responder is
      aware of the protocol element in question.

   A determination of the knowledge or lack of knowledge of a particular
   protocol element is expected to remain valid as long as the clientid
   associated with the request remains valid.

   The above assumes, as should be the case, that the server will accept
   the minor version used by the client.  For more detail regarding this
   issue, see Section 8.2.

4.5.  XDR Overlay

   XDR additions may also be made by defining XDR structures that
   overlay nominally opaque fields. defined to allow such incremental
   extensions.

   For example, each pNFS mapping type provides its own XDR definition
   for various pNFS-related fields defined in [RFC5661] as opaque
   arrays.

   Because such additions provide new interpretations of existing
   fields, they may be made outside of the extension framework as long
   as they obey the rules previously established when the nominally
   opaque protocol elements were added to the protocol.





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5.  Other NFSv4 Protocol Changes

   There are a number of types of protocol changes that are outside the
   XDR extension framework discussed in Section 4.  These changes are
   also managed within the NFSv4 versioning framework and may be of a
   number of types, which are discussed in the sections below

   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.

   All such changes that have been made in the past have been made as
   part of new minor version.  Future change of these sorts may not be
   done in an extension but can only be made in a new minor version.

5.1.  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-specified type of the element, 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 objects 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 8.1.

      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



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      "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.  Such cases are discussed in
      Section 4.5.

5.2.  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.

   One class of behavioral change involves changes in the set of errors
   to be returned in the event of various errors.  When the set of valid
   requests remain the same, and the behavior for each of them remains
   the same, such changes can be implemented with only limited
   disruption to existing clients.

   Many more substantial behavioral changes have occurred in connection
   with the addition of the session concept in NFSv4.1.  Even though
   there was no change to the XDR for existing operations, many existing
   operations and COMPOUNDs consisting only of them became invalid.

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

6.  Extending Existing Minor Versions

   Extensions to the most recently published NFSv4 minor version may be
   made by publishing the extension as a Proposed Standard, unless the
   minor version in question has been defined as non-extensible.  A
   document need not update the document defining the minor version,
   which remains a valid description of the base variant of the minor
   version in question.

   Corrections to protocol errors (see Section 9) may be accomplished by
   publishing an extension, including a compatible XDR change.  Such
   documents will update the defining documents for the corrected minor
   version.

7.  Minor Versions

7.1.  Creation of New Minor Versions

   It is important to note that this section, in describing situations
   that would require new minor versions to be created, does not thereby
   imply that situations will exist in the future.  Judgments regarding



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   desirability of future changes will be made by the working group or
   its successors and any guidance that can be offered at this point is
   necessarily quite limited.

   Creation of a new minor version is an option that the working group
   retains.  The listing of situations below that would prompt such
   actions is not meant to be exhaustive.

   The following sorts of features are not allowed as extensions and
   would require creation of a new minor version:

   o  Features that incorporate any of the non-XDR-based changes
      discussed in Sections 5.1 and 5.2.

   o  Addition of REQUIRED new features.

   o  Changes to the status of existing features including converting
      features to be mandatory to not implement.

8.  Minor Version Interaction Rules

   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.

8.1.  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 OPTONAL features will not change within the context
   of a single clientid.  Server implementations MUST ensure that the
   set of supported features and protocol elements does not change
   within such a context.







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8.2.  Minor Version Compatibility

   The goal of the NFSv4 extension model is to enable compatibility
   including compatibility between clients and servers implementing
   different minor versions.

   Within a set of minor versions that define the same set of features
   as REQUIRED and mandatory to not implement, it is relatively easy for
   clients and servers to provide the needed compatibility by adhering
   to the following practices.

   o  Servers supporting a given minor version should support earlier
      minor versions within that set and return appropriate errors for
      use of protocol elements that were not a valid part of that
      earlier minor version.  For details see below.

   o  Clients should deal with an NFS4ERR_MINOR_VERS_MISMATCH error by
      searching for a lower minor version number that the server will
      accept.

   Servers supporting a given minor version MUST, in returning errors
   for operations which were a valid part of the minor version, return
   the errors allowed for the current operation in the minor version
   actually being used.

   With regard to protocol elements not known in a given minor version,
   the appropriate error codes are given below.  Essentially, the
   server, although it has a more extensive XDR reflective of a newer
   minor version, must act as a server with a more limited XDR would.

   o  When an operation is used which is not known in the specified
      minor version, NFS4ERR_OP_ILLEGAL (as opposed to NFS4ERR_NOTSUPP)
      should be returned.

   o  When an attribute is used which is not known in the specified
      minor version, NFS4ERR_INVAL (as opposed to NFS4ERR_ATTRNOTSUPP)
      should be returned.

   o  When a switch case is used which is not known in the specified
      minor version, NFS4ERR_BADXDR (as opposed to
      NFS4ERR_UNION_NOTSUPP) should be returned.  Even though the
      message may be XDR-decodable by the server's current XDR, it is
      not so according to the minor version being used.

   o  When a flag bit is used which is not known in the specified minor
      version, NFS4ERR_INVAL (as opposed to NFS4ERR_NOTSUPP or any other
      error defined as indicated non-support a flag bit) should be
      returned.



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9.  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 document obsoleting or updating
   the RFC defining the relevant feature definition document or minor
   version specification.  In making such corrections, the working group
   will have to carefully consider how to assure interoperability with
   older clients and servers.

   Often, corrections can be done without changing the protocol XDR.  In
   many cases, a change in client and server behavior can be implemented
   without taking special provision with regard to interoperability with
   earlier implementations.  In those case, and in cases in which a
   revision merely clarifies an earlier protocol definition document, a
   new document can be published which simply updates the earlier
   protocol definition document.

   In other cases, it is best if client or server behavior needs to
   change in a way which raises interoperability concerns.  In such
   cases, incompatible changes in server or client behavior should not
   be mandated in order to avoid XDR changes.

9.1.  XDR Changes to Implement Protocol Corrections

   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 a minor version for
      which optional features may no longer be added, if the working
      group decides that it is an appropriate to compatibly effect a
      correction.

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



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   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
      OPTIONAL.  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.  The nature of such
      corrections is such that it may result in situations in which
      different variants of the same minor version may not support the
      same set of REQUIRED protocol elements.  See Section 9.2 for
      details.

   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.

   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
      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



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      that the feature cannot be used on that server.  In the case of
      OPTIONAL 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
   allows client and server implementers to adopt the new version of the
   feature at a reasonable pace.

9.2.  XDR Corrections to required features

   When protocol corrections are made to REQUIRED features, there can be
   situations in which different implementations of the minor version
   may implement distinct variants of that minor version.  As a result,
   they might not support (or have knowledge of) the same set of
   REQUIRED protocol elements.  In such situations, client and server
   implementations might:

   o  Implement only the earlier uncorrected version of the REQUIRED
      feature.

   o  Implement only the newer, corrected version of the REQUIRED
      feature.

   o  Implement both the uncorrected and corrected versions of the
      REQUIRED feature.

   In such situations, clients can attempt to use the techniques
   described in Sections 4.4.2 and 4.4.3 to arrive at a common protocol
   variant to serve as a basis for interoperation.  The fact that the
   set of REQUIRED protocol elements might not be the same gives rise to
   additional issues, since there might be cases in which the client and
   server do not share a common version of the REQUIRED feature being
   corrected.

   o  When the client implements only the uncorrected version of the
      feature, it can successfully interoperate with servers which
      support only the uncorrected version or both the corrected and
      uncorrected versions.

   o  When the client implements only the corrected version of the
      feature, it can successfully interoperate with servers which
      support only the corrected version or both the corrected and
      uncorrected versions.




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   o  When the client is able to use both the uncorrected and corrected
      versions of the feature, it can successfully interoperate with
      servers which support either version or both versions.

   o  When the client implements only the uncorrected version of the
      feature, it cannot successfully interoperate with servers which
      support only the corrected version.  In this situation, it can
      determine that the implementations are incompatible just as it
      would have done if the server did not support the minor version in
      question.

   o  When the client implements only the uncorrected version of the
      feature, it cannot successfully interoperate with servers which
      support only the uncorrected version.  In this situation, it can
      determine that the implementations are incompatible just as it
      would have done if the server did not support the minor version in
      question.

   In such situations, clients and servers implemented after the
   corrected version is defined are well advised to support both the
   corrected and uncorrected versions.  Nevertheless, once uncorrected
   implementations become uncommon, implementers have the option of only
   supporting the corrected version.

10.  Security Considerations

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

11.  IANA Considerations

   The current document does not require any actions by IANA.

12.  References

12.1.  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,
              <http://www.rfc-editor.org/info/rfc2119>.

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





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

   [RFCv42]   Haynes, T., Ed., "NFS Version 4 Minor Version 2", January
              2016, <http://www.ietf.org/id/
              draft-ietf-nfsv4-minorversion2-41.txt>.

12.2.  Informative References

   [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, DOI 10.17487/RFC3530,
              April 2003, <http://www.rfc-editor.org/info/rfc3530>.

Appendix A.  Acknowledgements

   The author wishes to thank Tom Haynes of Primary Data for his role in
   getting this effort started and his work in co-authoring the first
   version of the initial working group versioning document.

   The author also wishes to thank Chuck Lever and Mike Kupfer of Oracle
   and Bruce Fields of Red Hat for their helpful reviews of this and
   other versioning-related documents.

Appendix B.  Instructions for RFC Editor

   In a number of places, this document needs to refer to the RFC for
   NFSv4.2, which is in the process of being published as a Proposed
   Standard.  Because this process is not yet complete, the following
   changes need to be made to adapt to the eventual assignment of an RFC
   number for that document.

   o  Replacement of the string "xxxx" by the RFC number assigned, in
      the list of RFC's to be updated

   o  Replacement of the reference anchor "RFCv42" by a string which
      reflects the RFC number assigned.  Also, the bibliographic
      information associated with that reference will need to reflect
      the RFC publication.

Author's Address









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

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











































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