draft-ietf-nfsv4-versioning-05.txt   draft-ietf-nfsv4-versioning-06.txt 
es
NFSv4 D. Noveck NFSv4 D. Noveck
Internet-Draft HPE Internet-Draft HPE
Updates: 5661 (if approved) July 28, 2016 Updates: 5661 (if approved) September 7, 2016
Intended status: Standards Track Intended status: Standards Track
Expires: January 29, 2017 Expires: March 11, 2017
NFSv4 Version Management Rules for NFSv4 Extensions and Minor Versions.
draft-ietf-nfsv4-versioning-05 draft-ietf-nfsv4-versioning-06
Abstract Abstract
This document describes the management of versioning within the NFSv4 This document describes the rules relating to the extension of the
family of protocols. It covers the creation of minor versions, the NFSv4 family of protocols. It covers the creation of minor versions,
addition of optional features to existing minor versions, and the the addition of optional features to existing minor versions, and the
correction of flaws in features already published as Proposed correction of flaws in features already published as Proposed
Standards. The rules relating to the construction of minor versions Standards. The rules relating to the construction of minor versions
and the interaction of minor version implementations that appear in and the interaction of minor version implementations that appear in
this document supersede the minor versioning rules in RFC5661. this document supersede the minor versioning rules in RFC5661.
Status of This Memo Status of This Memo
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provisions of BCP 78 and BCP 79. provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on January 29, 2017. This Internet-Draft will expire on March 11, 2017.
Copyright Notice Copyright Notice
Copyright (c) 2016 IETF Trust and the persons identified as the Copyright (c) 2016 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
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Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Existing Minor Versions . . . . . . . . . . . . . . . . . 4 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.2. Updated NFSv4 Version Management Framework . . . . . . . 4 2.1. Use of Keywords Defined in RFC2119 . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5 2.2. Use of Feature Statuses . . . . . . . . . . . . . . . . . 4
2.1. Use of Keywords Defined in RFC2119 . . . . . . . . . . . 6 2.3. NFSv4 Versions . . . . . . . . . . . . . . . . . . . . . 5
2.2. Use of Feature Statuses . . . . . . . . . . . . . . . . . 7 3. Consolidation of Extension Rules . . . . . . . . . . . . . . 6
2.3. NFSv4 Versions . . . . . . . . . . . . . . . . . . . . . 8 4. XDR Considerations . . . . . . . . . . . . . . . . . . . . . 7
3. Consolidation of Version Management Rules . . . . . . . . . . 9 4.1. XDR Extension . . . . . . . . . . . . . . . . . . . . . . 7
4. XDR Considerations . . . . . . . . . . . . . . . . . . . . . 11 4.2. Rules for XDR Extension within NFSv4 . . . . . . . . . . 8
4.1. XDR Extension . . . . . . . . . . . . . . . . . . . . . . 11 4.3. Handling of Protocol Elements . . . . . . . . . . . . . . 9
4.1.1. XDR Extension in General . . . . . . . . . . . . . . 11 4.4. Inter-version Interoperability . . . . . . . . . . . . . 10
4.1.2. Particulars of XDR Extension within NFSv4 . . . . . . 12 4.4.1. Requirements for Knowledge of Protocol Elements . . . 10
4.1.3. Rules for XDR Extension within NFSv4 . . . . . . . . 13 4.4.2. Establishing Interoperability . . . . . . . . . . . . 12
4.2. Handling of Protocol Elements . . . . . . . . . . . . . . 13 4.4.3. Determining Knowledge of Protocol Elements . . . . . 13
4.3. Organization of Protocol Elements . . . . . . . . . . . . 15 4.5. XDR Overlay . . . . . . . . . . . . . . . . . . . . . . . 14
4.4. Inter-version Interoperability . . . . . . . . . . . . . 15 5. Other NFSv4 Protocol Changes . . . . . . . . . . . . . . . . 14
4.4.1. Requirements for Knowledge of Protocol Elements . . . 15 5.1. Field Interpretation and Use . . . . . . . . . . . . . . 15
4.4.2. Establishing Interoperability . . . . . . . . . . . . 17 5.2. Behavioral Changes . . . . . . . . . . . . . . . . . . . 15
4.4.3. Determining Knowledge of Protocol Elements . . . . . 18 6. Extending Existing Minor Versions . . . . . . . . . . . . . . 16
4.4.4. Interoperability Between Version Groups . . . . . . . 19 7. Minor Versions . . . . . . . . . . . . . . . . . . . . . . . 16
5. Other NFSv4 Protocol Changes . . . . . . . . . . . . . . . . 19 7.1. Creation of New Minor Versions . . . . . . . . . . . . . 16
5.1. Non-XDR Protocol Changes . . . . . . . . . . . . . . . . 20 8. Minor Version Interaction Rules . . . . . . . . . . . . . . . 17
5.1.1. Field Interpretation and Use . . . . . . . . . . . . 20 8.1. Minor Version Identifier Transfer Issues . . . . . . . . 17
5.1.2. Behavioral Changes . . . . . . . . . . . . . . . . . 21 8.2. Minor Version Compatibility . . . . . . . . . . . . . . . 17
5.1.3. Rules for non-XDR changes . . . . . . . . . . . . . . 22 9. Correction of Existing Minor Versions and Features . . . . . 18
5.2. Specification of Associated Protocols . . . . . . . . . . 22 9.1. XDR Changes to Implement Protocol Corrections . . . . . . 19
5.2.1. Associated Protocols via pNFS Mapping Types . . . . . 23 10. Security Considerations . . . . . . . . . . . . . . . . . . . 20
5.2.2. Additional Forms of Associated Protocols . . . . . . 23 11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 21
6. NFSv4 Protocol Features . . . . . . . . . . . . . . . . . . . 24 12. References . . . . . . . . . . . . . . . . . . . . . . . . . 21
6.1. Previous Uses of the Feature Concept . . . . . . . . . . 25 12.1. Normative References . . . . . . . . . . . . . . . . . . 21
6.2. Rules for Protocol Feature Construction . . . . . . . . . 26 12.2. Informative References . . . . . . . . . . . . . . . . . 21
6.3. Statuses of Features . . . . . . . . . . . . . . . . . . 26 Appendix A. Acknowledgements . . . . . . . . . . . . . . . . . . 21
6.4. Statuses of Protocol Elements Within Features . . . . . . 27 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 21
6.5. Determining Protocol Element Support . . . . . . . . . . 29
6.6. Feature Discovery . . . . . . . . . . . . . . . . . . . . 30
6.7. Feature Incorporation . . . . . . . . . . . . . . . . . . 32
7. Extensions within Minor Versions . . . . . . . . . . . . . . 32
7.1. Adding Features to Extensible Minor Versions . . . . . . 32
7.2. Use of Feature Specification Documents . . . . . . . . . 33
7.3. Compatibility Issues . . . . . . . . . . . . . . . . . . 34
7.3.1. Compatibility Issues for Messages Sent to Servers . . 34
7.3.2. Compatibility Issues for Messages Sent to Clients . . 35
7.4. Relationship Between Minor Versioning and Extensions
within a Minor Version . . . . . . . . . . . . . . . . . 36
8. Minor Versions . . . . . . . . . . . . . . . . . . . . . . . 37
8.1. Creation of New Minor Versions . . . . . . . . . . . . . 37
8.1.1. New Minor Versions within an Existing Group . . . . . 37
8.1.2. New Minor Version Groups . . . . . . . . . . . . . . 37
8.1.3. Limits on Minor Version Groups . . . . . . . . . . . 40
8.2. Role of Minor Versions . . . . . . . . . . . . . . . . . 41
8.3. Minor Version Interaction Rules . . . . . . . . . . . . . 41
8.3.1. Minor Version Identifier Transfer Issues . . . . . . 42
8.3.2. Minor Version Intra-Group Compatibility . . . . . . . 42
8.3.3. Minor Version Inter-Group Compatibility . . . . . . . 43
9. Correction of Existing Minor Versions and Features . . . . . 44
9.1. XDR Changes to Implement Protocol Corrections . . . . . . 45
10. Documentation of Features, Extensions, Minor Versions, and
Protocol Corrections . . . . . . . . . . . . . . . . . . . . 47
10.1. Documentation Approach . . . . . . . . . . . . . . . . . 47
10.2. Indexing material . . . . . . . . . . . . . . . . . . . 47
10.3. Feature Specification Documents . . . . . . . . . . . . 48
10.4. XDR File Considerations . . . . . . . . . . . . . . . . 50
10.5. Additional Documents to Support Protocol Extension . . . 51
10.5.1. Minor Version Indexing Document . . . . . . . . . . 51
10.5.2. Consolidated XDR Document . . . . . . . . . . . . . 52
10.5.3. XDR Assignment Document . . . . . . . . . . . . . . 52
10.5.4. Transition of Documents to RFC's . . . . . . . . . . 53
10.6. Documentation of New Minor Versions . . . . . . . . . . 54
10.7. Documentation of XDR Changes for Corrections . . . . . . 54
11. Security Considerations . . . . . . . . . . . . . . . . . . . 55
12. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 55
13. References . . . . . . . . . . . . . . . . . . . . . . . . . 55
13.1. Normative References . . . . . . . . . . . . . . . . . . 55
13.2. Informative References . . . . . . . . . . . . . . . . . 56
Appendix A. Acknowledgements . . . . . . . . . . . . . . . . . . 57
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 57
1. Introduction 1. Introduction
To address the requirement for an NFS protocol that can evolve as the To address the requirement for an NFS protocol that can evolve as the
need arises, the Network File System (NFS) version 4 (NFSv4) protocol need arises, the Network File System (NFS) version 4 (NFSv4) protocol
provides a framework to allow for future changes via the creation of provides a framework to allow for future changes via the creation of
new protocol versions including minor versions and certain forms of new protocol versions including minor versions and certain forms of
modification of existing minor versions. The version management modification of existing minor versions. The extension rules
rules contained in this document allow extensions and other changes contained in this document allow extensions and other changes to be
to be implemented in a way that maintains compatibility with existing implemented in a way that maintains compatibility with existing
clients and servers. clients and servers.
1.1. Existing Minor Versions
Previously, all protocol changes had been part of new minor versions. Previously, all protocol changes had been part of new minor versions.
The COMPOUND procedure (see Section 14.2 of [RFC7530]) specifies the The COMPOUND procedure (see Section 14.2 of [RFC7530]) specifies the
minor version being used by the client in making requests. The minor version being used by the client in making requests. The
CB_COMPOUND procedure (see Section 15.2 of [RFC7530]) specifies the CB_COMPOUND procedure (see Section 15.2 of [RFC7530]) specifies the
minor version being used by the server on callback requests. minor version being used by the server on callback requests.
Each existing minor version has been specified by one or more Creation of a new minor version is no longer the only way in which
standards track RFCs: protocol changes may be made. Optional features may be added as
extensions and protocol corrections can be proposed, specified and
o Minor version 0 (NFSv4.0) is specified by [RFC7530] with the XDR implemented within the context of a single minor version. Creation
description appearing in [RFC7531]. of new minor versions remains available to make other sorts of
changes.
o Minor version 1 (NFSv4.1) is specified by [RFC5661] with the XDR
description appearing in [RFC5662].
o Minor version 2 (NFSv4.2) is specified by [NFSv42] (in terms of
changes from [RFC5661]). The XDR description appears in
[NFSv42-dot-x]
Existing minor versions can be divided into two groups, based on
compatibility considerations. NFSv4.0 is one group, while NFSv4.1,
NFSv4.2, and potentially other minor versions, form a second group.
The definition of NFSv4 minor version groups is explained in more
detail in Section 2.3, as is the concept of variants within minor
versions and version groups.
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. Added optional features 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.
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 10 should be used.
After dealing with some preliminary matters, this document focuses on
presenting the conceptual framework on which NFSv4 versioning is
built.
o First we discuss (in Section 4) how the XDR descriptions for
various NFSv4 versions can be extended to produce the XDR
descriptions for other versions while allowing clients and servers
using the XDR descriptions associated with different versions to
communicate.
o We then complete the discussion (in Section 5) of 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 and feature packages.
Using this framework, we look at the ways that those changes can be
incorporated into the NFSv4 protocol.
o The addition of new feature packages to existing minor versions is
discussed in Section 7.
o New Minor versions can be constructed, as described in Section 8.
o Issues relating to the correction of protocol errors in existing
features and minor versions are discussed in Section 9.
We then discuss (in Section 10) how features, minor versions, and The goal of allowing extensions within the context of a minor version
protocol corrections will be documented. 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 2. Terminology
A basic familiarity with NFSv4 terminology is assumed in this A basic familiarity with NFSv4 terminology is assumed in this
document and the reader is pointed to [RFC7530]. document and the reader is pointed to [RFC7530].
In this document, the term "version" is not limited to minor In this document, the term "version" is not limited to minor
versions. When minor versions are meant, the term "minor version" is versions. When minor versions are meant, the term "minor version" is
used explicitly. For more discussion of this and related terms, see used explicitly. For more discussion of this and related terms, see
Section 2.3 Section 2.3
In this document, the word "feature" is used, except in the case of
quotations, to denote a key structuring concept. By organizing
changes into features, defining RFCs can clearly specify what
protocol elements a server must be able to recognize and what
protocol elements a server must support. See Section 6 for details
about how features are specified and how the structuring information
provided is used.
A feature contains one or more "feature elements". Often, at least
one feature element will be a protocol extension that can help a
sender determine whether the receiver supports a given feature. See
Section 4.1.3 for more details. A feature element may also be one of
a set of other types of protocol change as described in Section 5.
A "feature package" is a set of features that are defined together, 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 either as part of a minor version or as part of the same protocol
extension. extension.
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 10.6) or implicitly
(see Section 7.1).
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 10.5.
o The term "feature definition document" denotes a document
describing a single feature or a set of closely related features,
forming a feature package.
o The term "protocol definition document" denotes a minor version
definition document, a feature definition document or any
standards-track document updating one of these.
2.1. Use of Keywords Defined in RFC2119 2.1. Use of Keywords Defined in RFC2119
The keywords defined by [RFC2119] have special meanings which this The keywords defined by [RFC2119] have special meanings which this
document intends to adhere to. However, due to the nature of this document intends to adhere to. However, due to the nature of this
document and some special circumstances, there are some complexities document and some special circumstances, there are some complexities
to take note of: to take note of:
o Where this document does not directly specify implementation o Where this document does not directly specify implementation
requirements, use of these capitalized terms is often not requirements, use of these capitalized terms is often not
appropriate, since the guidance given in this document does not appropriate, since the guidance given in this document does not
directly affect interoperability. directly affect interoperability.
o In this document, what authors of RFCs defining features and minor o In this document, what authors of RFCs defining features and minor
versions need to do is stated without these specialized terms. versions need to do is stated without these specialized terms.
Although it is necessary to follow this guidance to provide Although it is necessary to follow this guidance to provide
successful NFSv4 version management, that sort of necessity is not successful NFSv4 protocol extension, that sort of necessity is not
of the sort defined as applicable to the use of the keywords of the sort defined as applicable to the use of the keywords
defined in [RFC2119]. defined in [RFC2119].
The fact that these capitalized terms are not used should not be The fact that these capitalized terms are not used should not be
interpreted as indicating that this guidance does not need to be interpreted as indicating that this guidance does not need to be
followed or is somehow not important. followed or is somehow not important.
o In speaking of the possible statuses of features and feature o In speaking of the possible statuses of features and feature
elements, the terms "OPTIONAL" and "REQUIRED" are used. For elements, the terms "OPTIONAL" and "REQUIRED" are used. For
further discussion, see Section 2.2. further discussion, see Section 2.2.
skipping to change at page 7, line 37 skipping to change at page 4, line 37
2.2. Use of Feature Statuses 2.2. Use of Feature Statuses
There has been some confusion, during the history of NFSv4, about the There has been some confusion, during the history of NFSv4, about the
correct use of these terms, and instances in which the keywords correct use of these terms, and instances in which the keywords
defined in [RFC2119] were used in ways that appear to be at variance defined in [RFC2119] were used in ways that appear to be at variance
with the definitions in that document. with the definitions in that document.
o In [RFC3530], the lower-case terms "optional", "recommended", and o In [RFC3530], the lower-case terms "optional", "recommended", and
"required" were used as feature statuses, Later, in [RFC5661] and "required" were used as feature statuses, Later, in [RFC5661] and
[RFC7530], the corresponding upper-case keywords were used. [RFC7530], the corresponding upper-case keywords were used. It is
However, it is not clear why this change was made. not clear why this change was made.
o In the case of "RECOMMENDED", its use as a feature status is o In the case of "RECOMMENDED", its use as a feature status is
inconsistent with [RFC2119] and it will not be used for this inconsistent with [RFC2119] and it will not be used for this
purpose in this document. purpose in this document.
o The word "RECOMMENDED" to denote the status of attributes in o The word "RECOMMENDED" to denote the status of attributes in
[RFC3530] and [RFC5661] raises similar issues. This has been [RFC7530] and [RFC5661] raises similar issues. This has been
recognized in [RFC7530] with regard to NFSV4.0, although the recognized in [RFC7530] with regard to NFSV4.0, although the
situation with regard to NFSv4.1 remains unresolved. situation with regard to NFSv4.1 remains unresolved.
In this document, the keywords "OPTIONAL" and "REQUIRED" and the In this document, the keywords "OPTIONAL" and "REQUIRED" and the
phrase "mandatory to not implement" are used to denote the status of phrase "mandatory to not implement" are used to denote the status of
features and individual protocol elements within a given minor features within a given minor version. In using these terms, RFCs
version. In using these terms, RFCs which specify the status of which specify the status of features inform:
features or protocol elements inform:
o client implementations whether they need to deal with the absence o client implementations whether they need to deal with the absence
of support for the protocol elements of support for these features.
o server implementations whether they need to provide support for o server implementations whether they need to provide support for
the protocol elements these features.
When the status of a protocol feature is specified, the support
requirements for associated protocol elements are defined by the
status of the protocol elements with regard to the feature in
question as described in Section 6.4.
The fact that such statuses and the organization of protocol features
may change between minor version groups may raise interoperability
issues which the authors of minor version RFCs and the working group
need to carefully consider. See Section 8.1.2 for guidance in this
regard.
2.3. NFSv4 Versions 2.3. NFSv4 Versions
The term "version" denotes any valid protocol variant constructed The term "version" denotes any valid protocol variant constructed
according to the rules in this document. It includes minor versions, according to the rules in this document. It includes minor versions,
but there are situations which allow multiple variant versions to be but there are situations which allow multiple variant versions to be
associated with and co-exist within a single minor version: associated with and co-exist within a single minor version:
o When there are feature specification documents published as o When there are feature specification documents published as
Proposed Standards extending a given minor version, then the Proposed Standards extending a given minor version, then the
protocol defined by the minor version specification document, when protocol defined by the minor version specification document, when
combined with any subset (not necessarily proper) of the feature combined with any subset (not necessarily proper) of the feature
specification documents, is a valid NFSv4 version variant which is specification documents, is a valid NFSv4 version variant which is
part of the minor version in question. part of the minor version in question.
o When there are protocol corrections published which update a given o When there are protocol corrections published which update a given
minor version, each set of published updates, up to the date of minor version, each set of published updates, up to the date of
publication of the update, is a valid NFSv4 version variant which publication of the update, is a valid NFSv4 version variant which
is part of the minor version in question. is part of the minor version in question.
Whether the above situations arise depend on the need for protocol
and whether extensions are allowed within a particular minor version.
Protocol corrections are always allowed although it is hoped that
they will be rare.
Whether extensions are allowed depends on whether the minor version
in question is specified as an extensible one. For a description of
rules regarding minor version extensibility, see Section 7.4.
Because of the above, there can be multiple version variants that are 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 part of a given minor version. Two of these are worthy of special
terms: terms:
o The term "base minor version" denotes the version variant that o The term "base minor version" denotes the version variant that
corresponds to the minor version as originally defined, including corresponds to the minor version as originally defined, including
all protocol elements specified in the minor version definition all protocol elements specified in the minor version definition
document but not incorporating any extensions or protocol document but not incorporating any extensions or protocol
corrections published subsequently. corrections published subsequently.
skipping to change at page 9, line 32 skipping to change at page 6, line 11
version. When the term "minor version" is used without either of version. When the term "minor version" is used without either of
these qualifiers, it should refer to something which is true of all these qualifiers, it should refer to something which is true of all
variants within that minor version. For example, one may refer to variants within that minor version. For example, one may refer to
the set of REQUIRED features in a given minor version since it is the the set of REQUIRED features in a given minor version since it is the
same for all variants within the minor version. same for all variants within the minor version.
Each client and server which implements a specific minor version will Each client and server which implements a specific minor version will
implement some particular variant of that minor version. Each of implement some particular variant of that minor version. Each of
these will be a superset of the appropriate base minor version. these will be a superset of the appropriate base minor version.
A minor version group is defined as a successive set of minor 3. Consolidation of Extension Rules
versions having exactly the same set of REQUIRED and mandatory to not
implement protocol elements. The union of the sets of variants for
all these minor versions provides a high degree of inter-variant
compatibility. Clients and servers which implement variants within
this group should be compatible as long as each takes proper care, as
it should, to properly deal with the case in which the other party
does not know of or has no support for OPTIONAL protocol elements.
3. Consolidation of Version Management Rules
In the past, the only existing version management rules were the In the past, the only existing extension rules were the minor
minor versioning rules that had been being maintained and specified versioning rules that were being maintained and specified in the
in the Standards Track RFCs which defined the individual minor Standards Track RFCs which defined the individual minor versions. In
versions. In the past, these minor versioning rules were modified on the past, these minor versioning rules were modified on an ad hoc
an ad hoc basis for each new minor version. basis for each new minor version.
More recently, minor versioning rules were specified in [RFC5661] More recently, minor versioning rules were specified in [RFC5661]
while modifications to those rules were allowed in subsequent minor while modifications to those rules were allowed in subsequent minor
versions. versions.
This document defines a set of version management rules, including This document defines a set of extension rules, including rules for
rules for minor version construction. These rules apply to all minor version construction. These rules apply to all future changes
future changes to the NFSv4 protocol. The rules are subject to to the NFSv4 protocol. The rules are subject to change but any such
change but any such change should be part of a standards track RFC change should be part of a standards track RFC obsoleting or updating
obsoleting or updating this document. 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, 5.1.3, 5.2.1, and 5.2.2.
o Rules relating to the composition of changes into protocol Rather than a single list of extension rules, as was done in the
features are addressed in Section 6.2 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 Rules limiting the protocol features which may be effected as an o The kinds of XDR changes that may be made to extend NFSv4 are
extension to an existing minor version appear in Section 7. addressed in the rules in Section 4.2.
o Minor version construction, including rules applicable to protocol o Minor version construction, including rules applicable to changes
features which cannot be used as extensions to existing minor which cannot be made in extensions to existing minor versions are
versions are addressed in Sections 8.1.1 and 8.1.2. addressed in Section 7.1
o Minor version interaction rules are discussed in Sections 8.3.2, o Minor version interaction rules are discussed in Sections 8.1 and
8.3.3, and 8.3.1. 8.2.
This document supersedes minor versioning rules appearing in the This document supersedes minor versioning rules appearing in the
minor version specification RFC's, including those in [RFC5661]. As minor version specification RFC's, including those in [RFC5661]. As
a result, potential conflicts among these documents should be a result, potential conflicts among documents should be addressed as
addressed as follows: follows:
o The specification of the actual protocols for minor versions o The specification of the actual protocols for minor versions
previously published as Proposed Standards take precedence over previously published as Proposed Standards take precedence over
minor versioning rules in either this document or in the minor minor versioning rules in either this document or in the minor
version specification RFC's. In other words, if the transition version specification RFC's. In other words, if the transition
from version A to version B violates a minor versioning rule, the from version A to version B violates a minor versioning rule, the
version B protocol stays as it is. In particular, many of the version B protocol stays as it is.
changes made for NFSV4.1 would not be allowed in the version
management framework defined here. See Section 5.1.3 for details.
o Since minor versioning rules #11 and #13 from [RFC5661] deal with o Since minor versioning rules #11 and #13 from [RFC5661] deal with
the interactions between multiple minor versions, the situation is the interactions between multiple minor versions, the situation is
more complicated. See Section 8.3 for a discussion of these more complicated. See Section 8 for a discussion of these issues,
issues, including how potential conflicts between rules are to be including how potential conflicts between rules are to be
resolved. resolved.
o Otherwise, any conflict between the version management rules in o Otherwise, any conflict between the extension rules in this
this document and those in minor version specification RFC's are document and those in minor version specification RFC's are to be
to be resolved based on the treatment in this document. In resolved based on the treatment in this document. In particular,
particular, corrections may be made as specified in Section 9 for corrections may be made as specified in Section 9 for all
all previously specified minor versions and the extensibility of previously specified minor versions and the extensibility of
previously specified minor versions is to be handled in accord previously specified minor versions is to be handled in accord
with Section 7.1. with Section 6.
Future minor version specification documents should avoid specifying Future minor version specification documents should avoid specifying
minor versioning rules. Instead, this document should be referenced rules relating to minor versioning and reference this document in
in connection with rules for NFSv4 version management. connection with rules for NFSv4 extension.
4. XDR Considerations 4. XDR Considerations
As an extensible XDR-based protocol, NFSv4 has to ensure interversion As an extensible XDR-based protocol, NFSv4 has to ensure interversion
compatibility, in situations in which the client and server use compatibility in situations in which the client and server use
different XDR descriptions. For example, the client may implement different XDR descriptions. For example, the client and server may
different variants of the same minor version or different variants implement different variants of the same minor version, in that they
that are part of the same minor version group. The XDR extension each might add different sets of extensions to the base minor
paradigm, discussed in Section 4.1, assures that these descriptions version.
are compatible, with clients and servers able to determine and use
those portions of the protocol that they both share according to the The XDR extension paradigm, discussed in Section 4.1, assures that
methods described in Sections 4.4.2 and 4.4.4. 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 4.1. XDR Extension
When an NFSv4 version change requires a modification to the protocol When an NFSv4 version change requires a modification to the protocol
XDR, this is effected within a framework based on the idea of XDR XDR, this is effected within a framework based on the idea of XDR
extension. This is opposed to transitions between major NFS versions extension. This is opposed to transitions between major NFS versions
(including that between NFSv3 and NFSv4.0) in which the XDR for one (including that between NFSv3 and NFSv4.0) in which the XDR for one
version was replaced by a different XDR for a newer version. version was replaced by a different XDR for a newer version.
The use of XDR extension can facilitate compatibility between The XDR extension approach allows an XDR description to be extended
different versions of the NFSv4 protocol. When XDR extension is used in a way which retains the structure of all previously valid
to implement OPTIONAL features, the greatest degree of inter-version messages. If a base XDR description is extended to create a second
compatibility is obtained. For specifics regarding rules for XDR description, the following will be true for the second
interversion compatibility, see Section 8.3.2. For a discussion of
compatibility issues that might arise between different version
groups, see Sections 8.1.2 and 8.3.3.
4.1.1. XDR Extension in General
The XDR extension approach provides a way for 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: description to be a valid extension of the first:
o The set of valid messages described by the extended definition is o The set of valid messages described by the extended definition is
a superset of that described by the first. a superset of that described by the first.
o Each message within the set of valid messages described by the o Each message within the set of valid messages described by the
base definition is recognized as having exactly the same base definition is recognized as having exactly the same
structure/interpretation using the extended definition. structure/interpretation using the extended definition.
o Each message within the set of messages described as valid by the o Each message within the set of messages described as valid by the
extended definition but not the base definition must be extended definition but not the base definition must be
recognized, using the base definition, as part of an unsupported recognized, using the base definition, as part of an extension not
extension. provided for.
In general, an extension of a given XDR description consists of any
set of the following changes:
o Addition of previously unspecified RPC procedures.
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 procedures, 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.
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 been structured around compound requests and
callbacks, addition of previously unspecified RPC procedures 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 value sets are represented within NFSv4 by The use of XDR extension can facilitate compatibility between
nominally opaque arrays calls for special handling. 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.
4.1.3. Rules for XDR Extension within NFSv4 4.2. Rules for XDR Extension within NFSv4
In the context of NFSv4, an extension of a given XDR description In the context of NFSv4, an extension of a given XDR description
consists of one or more of the following: consists of one or more of the following:
o Addition of previously unspecified operation codes, within the o Addition of previously unspecified operation codes, within the
framework established by COMPOUND and CB_COMPOUND. framework established by COMPOUND and CB_COMPOUND.
o Addition of previously unspecified attributes. o Addition of previously unspecified attributes.
o Addition of new, previously unused, values to existing enums. o Addition of new, previously unused, values to existing enums.
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o Addition of previously unassigned bit values to a flag word. o Addition of previously unassigned bit values to a flag word.
o Addition of new cases to existing switches, provided that the o Addition of new cases to existing switches, provided that the
existing switch did not contain a default case. existing switch did not contain a default case.
However, none of the following is allowed to happen: However, none of the following is allowed to happen:
o Any change to the structure of existing requests or replies other o Any change to the structure of existing requests or replies other
than those listed above. than those listed above.
o Addition of previously unspecified RPC procedures, for either the o Addition of previously unspecified RPC operation codes, for either
nfsv4 program or the callback program, is not allowed. the nfsv4 program or the callback program, is not allowed.
o Deletion of existing RPC procedures, enum values, flag bit values o Deletion of existing RPC operations, enum values, flag bit values
and switch cases. Note that changes may be made to define use of 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 any of these as causing an error, as long as the XDR is
unaffected. unaffected.
o Similarly, none of these items may be reused for a new purpose. o Similarly, none of these items may be reused for a new purpose.
4.2. Handling of Protocol Elements 4.3. Handling of Protocol Elements
Implementations handle protocol elements in one of three ways. Which Implementations handle protocol elements in one of three ways. Which
of the following ways are valid depends on the status of the protocol of the following ways are valid depends on the status of the protocol
element in the variant being implemented: element in the variant being implemented:
o The protocol element is not a part of definition of the variant in 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 question and so is "unknown". The responder, when it does not
report an RPC XDR decode error, reports an error indicative of the report an RPC XDR decode error, reports an error indicative of the
element not being defined in the XDR such as NFS4ERR_OP_ILLEGAL, element not being defined in the XDR such as NFS4ERR_OP_ILLEGAL,
NFS4ERR_BADXDR, or NFS4ERR_INVAL. See Section 4.4.3 for details. 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 o The protocol element is a known part of the variant but is not
supported by the particular implementation. The responder reports supported by the particular implementation. The responder reports
an error indicative of the element being recognized as one which an error indicative of the element being recognized as one which
is not supported such as NFS4ERR_NOTSUPP, NFS4ERR_UNION_NOTSUPP, is not supported such as NFS4ERR_NOTSUPP, NFS4ERR_UNION_NOTSUPP,
or NFS4ERR_ATTRNOTSUPP. See Section 6.5 for details. or NFS4ERR_ATTRNOTSUPP.
o The protocol element is a known part of the variant which is o The protocol element is a known part of the variant which is
supported by the particular implementation. The responder reports supported by the particular implementation. The responder reports
success or an error other than the special ones discussed above. success or an error other than the special ones discussed above.
Which of these are validly returned by the responder depends on the Which of these are validly returned by the responder depends on the
status of the feature element in the minor version specified in the status of the protocol element in the minor version specified in the
COMPOUND or CB_COMPOUND. The possibilities which can exist are COMPOUND or CB_COMPOUND. The possibilities which can exist are
listed below. listed below.
o The protocol element is not known in the current variant of the o The protocol element is not known in the minor version. In this
minor version. In this case all implementations of the minor case all implementations of the minor version MUST indicate that
version MUST indicate that the protocol element is not known. the protocol element is not known.
o The protocol element is specified mandatory to not implement in o The protocol element is part of a feature specified mandatory to
the minor version. In this case as well, all implementations of not implement in the minor version. In this case as well, all
the minor version MUST indicate that the protocol element is not implementations of the minor version MUST indicate that the
known. protocol element is not known.
o The protocol element is defined as part of the current variant of o The protocol element is defined as part of the current variant of
the minor version but is not part of the corresponding base the minor version but is not part of the corresponding base
variant. In this case, the requester can encounter situations in variant. In this case, the requester can encounter situations in
which the protocol element is either not known to the responder , which the protocol element is either not known to the responder,
is known but not supported by the responder, or is both known to is known to but not supported by the responder, or is both known
and supported by the responder. to and supported by the responder.
o The protocol element is defined as an OPTIONAL part of the base o The protocol element is defined as an OPTIONAL part of the base
minor version. In this case, the requester can expect the minor version. In this case, the requester can expect the
protocol element to be known but must deal with cases in which it protocol element to be known but must deal with cases in which it
is supported or is not supported. is supported or is not supported.
o The protocol element is defined as a REQUIRED part of the base o The protocol element is defined as a REQUIRED part of the base
minor version. In this case, the requester can expect the minor version. In this case, the requester can expect the
protocol element to be both known and supported by the responder. protocol element to be both known and supported by the responder.
The listing of possibilities above does not mean that a requester The listing of possibilities above does not mean that a requester
always needs to be prepared for all such possibilities. Often, always needs to be prepared for all such possibilities. Often,
depending on the scope of the feature of which the protocol element 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 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 protocol elements, will allow the requester to be sure that certain
these possibilities cannot occur. Section 6.6 discusses this subject of these possibilities cannot occur.
in detail.
Requesters, typically clients, may test for knowledge of or support Requesters, typically clients, may test for knowledge of or support
for protocol elements as part of connection establishment. This may for protocol elements as part of connection establishment. This may
allow the requester to be aware of responder lack of knowledge of or allow the requester to be aware of responder lack of knowledge of or
support for problematic requests before they are actually issued. support for problematic requests before they are actually used to
effect user requests.
4.3. Organization of Protocol Elements
To enable compatible operation within a version group, all of the
protocol elements within an NFSv4 minor version are organized as
follows:
o Each protocol element is defined as a member of exactly one
feature. One important reason for this organization (see
Section 6 for others) is to regularize and simplify the
determination by the client and server as to what protocol
elements the other party supports.
o Each feature is defined as a member of a feature package, based on
how it was defined. Features established as part of a minor
version at the same time belong to the same feature package.
4.4. Inter-version Interoperability 4.4. Inter-version Interoperability
Because of NFSv4's use of XDR extension, there will always be, for Because of NFSv4's use of XDR extension, any communicating client and
any communicating client and server versions, a version such the server versions have XDR definitions that are each valid extensions
client and server versions are each either identical to that common of a third version. Once that version is determined, it may be used
base version or a valid extension of it. Once that base version is by both client and server to communicate. Each party can
determined, it may be used by both client and server to communicate. successfully use a subset of protocol elements that are both known
Each party can successfully use a subset of protocol elements that and supported by both parties.
are both known and supported by both parties.
4.4.1. Requirements for Knowledge of Protocol Elements 4.4.1. Requirements for Knowledge of Protocol Elements
With regard to requirements for knowledge of protocol elements, the With regard to requirements for knowledge of protocol elements, the
following rules apply. These rules are the result of the use of 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 XDR extension paradigm combined with the way in which extensions are
incorporated in existing minor versions (for details of which see incorporated in existing minor versions (for details of which see
Section 7.1). For information about the rules regarding the Section 6).
extensibility of minor versions, see Section 7.4.
o Any protocol element defined as part of the base variant of a o Any protocol element defined as part of the base variant of
particular minor version is required to be known by that minor particular minor version is required to be known by that minor
version. This occurs whether the specification happens in the version. This occurs whether the specification happens in the
body of the minor definition document or is in a feature body of the minor definition document or is in a feature
definition document that is made part of the minor version by definition document that is made part of the minor version by
being normatively referenced by the minor version definition being normatively referenced by the minor version definition
document. document.
o Any protocol element required to be known in a given minor version o Any protocol element required to be known in a given minor version
is required to be known in subsequent minor versions, unless and is required to be known in subsequent minor version, unless and
until a minor version has made that protocol element as mandatory until a minor version has made that protocol element as mandatory
to not implement. to not implement.
o When a protocol element is defined as pahttp://conf.meetecho.com/ o When a protocol element is defined as part of an extension to an
presenter/?id=nfsv4rt of an extension to an extensible minor extensible minor version, it is not required to be known in that
version, it is not required to be known in that minor version but minor version but is required to be known by the next minor
is required to be known by the next minor version. In the earlier version. In the earlier minor version, it might not be defined in
minor version, it might not be defined in the XDR definition the XDR definition document, while in the later version it needs
document for that minor, while in the later minor version it needs
to be defined in the XDR definition document. In either case, if to be defined in the XDR definition document. In either case, if
it is defined, it might or might not be supported. it is defined, it might or might not be supported.
o When knowledge of protocol elements is optional in a given minor o When knowledge of protocol elements is optional in a given minor
version, the responder's knowledge of such optional elements must version, the responder's knowledge of such optional elements must
obey the rule that if one such element is known, then all the obey the rule that if one such element is known, then all the
protocol elements defined in the same minor version definition protocol elements defined in the same minor version definition
document must be known as well. document must be known as well.
For many minor versions, all existing protocol elements are required For many minor versions, all existing protocol elements, are required
to be known by both the client and the server, and so requesters do 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 not have to test for the presence or absence of knowledge regarding
protocol elements for which knowledge might be optional. This is the protocol elements for which knowledge might be optional. This is the
case if there has been no extension for the minor version in case if there has been no extension for the minor version in
question. Extensions can be added to extensible minor versions as question. Extensions can be added to extensible minor versions as
described in Section 7.1 and can be used to correct protocol flaws as described in Section 6 and can be used to correct protocol flaws as
described in Section 9. described in Section 9.
Requesters can ascertain the knowledge of the responder in two ways: Requesters can ascertain the knowledge of the responder in two ways:
o By issuing a request using the protocol element and looking at the o By issuing a request using the protocol element and looking at the
response. Note that, even if the protocol element used is not response. Note that, even if the protocol element used is not
supported by the responder, the requester can still determine if supported by the responder, the requester can still determine if
the element is known by the responder. the element is known by the responder.
o By receiving a request from the responder, acting in the role of o By receiving a request from the responder, acting in the role of
requester. For example, a client may issue a request enabling the requester. For example, a client may issue a request enabling the
server to infer that it is aware of a corresponding callback. server to infer that it is aware of a corresponding callback.
In making this determination, the requester can rely on two basic In making this determination, the requester can rely on two basic
facts: facts:
o If the responder is aware of a single protocol element within a o If the responder is aware of a single protocol element within a
feature package, it must be aware of all protocol elements within feature package, it must be aware of all protocol elements within
that feature package. that feature package
o If a protocol element is one defined by the minor version 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 specified by a request (and not in an extension), or in a previous
minor version, the responder must be aware of it. minor version, the responder must be aware of it.
4.4.2. Establishing Interoperability 4.4.2. Establishing Interoperability
When a client and a server interact, they need to able to take When a client and a server interact, they need to able to take
advantage of the compatibility provided by NFSv4's use of XDR advantage of the compatibility provided by NFSv4's use of XDR
extension. extension.
In this section, we will deal with situation in which the client and
server are of the same version group. Later, in Section 4.4.4, we
will discuss possible extensions to the inter-version-group case.
In this context, the client and server would arrive at a common In this context, the client and server would arrive at a common
variant which the client would uses to send requests which the server variant which the client would uses to send requests which the server
would then accept. The server would use that variant to send would then accept. The server would use that variant to send
callbacks which the client would then accept. This state of affairs callbacks which the client would then accept. This state of affairs
could arise in a number of ways: could arise in a number of ways:
o Client and server have been built using XDR variants that belong o Client and server have been built using XDR variants that belong
to the same minor version to the same minor version
o The client's minor version is lower than that of the server. In o The client's minor version is lower than that of the server. In
this case the server, in accord with Section 8.3.2, accepts the 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 client's minor version, and acts as if it has no knowledge of
extensions made in subsequent minor versions. It has knowledge of extensions made in subsequent minor versions. It has knowledge of
protocol elements within the current (i.e. effectively final) protocol elements within the current (i.e. effectively final)
variant of the lower minor version. variant of the lower minor version.
o The client's minor version is higher than that of the server. In o The client's minor version is higher than that of the server. In
this case the client, in accord with Section 8.3.2, uses a lower this case the client, in accord with Section 8.2, uses a lower
minor version that the server will accept. In this case, the minor version that the server will accept. In this case, the
server has no knowledge of extensions made in subsequent minor server has no knowledge of extensions made in subsequent minor
versions. versions.
There are a number of cases to consider based on the characteristics There are a number of cases to consider based on the characteristics
of the minor version chosen. of the minor version chosen.
o The minor version consists of only a single variant (no extension o The minor version consists of only a single variant (no extension
or XDR corrections), so the client and the server are using the or XDR corrections), so the client and the server are using the
same XDR description and have knowledge of the same protocol same XDR description and have knowledge of the same protocol
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approach described in Section 4.4.3. Once this is done, the approach described in Section 4.4.3. Once this is done, the
client and server will both be using a common variant. The client and server will both be using a common variant. The
variants that the client and the server were built with will both variants that the client and the server were built with will both
either be identical to this variant or a valid extension of it. either be identical to this variant or a valid extension of it.
Similarly, the variants that the client and the server actually Similarly, the variants that the client and the server actually
use will be a subset of this variant, in that certain OPTIONAL use will be a subset of this variant, in that certain OPTIONAL
features will not be used. features will not be used.
In either case, the client must determine which of the OPTIONAL In either case, the client must determine which of the OPTIONAL
protocol elements within the common version are supported by the protocol elements within the common version are supported by the
server as described in Section 6.6. server, just as it does for OPTIONAL features introduced as part of a
minor version.
4.4.3. Determining Knowledge of Protocol Elements 4.4.3. Determining Knowledge of Protocol Elements
A requester may test the responder's knowledge of particular protocol A requester may test the responder's knowledge of particular protocol
elements as defined below, based on the type of protocol element. elements as defined below, based on the type of protocol element.
o When a GETATTR request is made specifying an attribute bit to be 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 tested and that attribute is not a set-only attribute, if the
GETATTR returns with the error NFS4ERR_INVAL, then it can be GETATTR returns with the error NFS4ERR_INVAL, then it can be
concluded that the responder has no knowledge of the attribute in concluded that the responder has no knowledge of the attribute in
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indicate that the responder is aware of the attribute in question. indicate that the responder is aware of the attribute in question.
o When a SETATTR request is made specifying the attribute bit to be 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 tested and that attribute is not a get-only attribute, if the
SETATTR returns with the error NFS4ERR_INVAL, then it can be SETATTR returns with the error NFS4ERR_INVAL, then it can be
concluded that the responder has no knowledge of the attribute in concluded that the responder has no knowledge of the attribute in
question. Other responses, including NFS4ERR_ATTRNOTSUPP, question. Other responses, including NFS4ERR_ATTRNOTSUPP,
indicate that the responder is aware of the attribute in question. indicate that the responder is aware of the attribute in question.
o When a request is made including an operation with a new flag bit, 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 if the operation returns with the error NFS4ERR_INVAL,then it can
generally be concluded that the responder has no knowledge of the generally be concluded that the responder has no knowledge of the
flag bit in question, as long as the requester is careful to avoid flag bit in question, as long as the requester is careful to avoid
other error situations in which the operation in question is other error situations in which the operation in question is
defined as returning NFS4ERR_INVAL. Other responses indicate that defined as returning NFS4ERR_INVAL. Other responses indicate that
the responder is aware of the flag bit in question. the responder is aware of the flag bit in question.
o When a request is made including the operation to be tested, if o When a request is made including the operation to be tested, if
the responder returns an RPC XDR decode error, or a response the responder returns an RPC XDR decode error, or a response
indicating that the operation in question resulted in indicating that the operation in question resulted in
NFS4ERR_OP_ILLEGAL or NFS4ERR_BADXDR, then it can be concluded NFS4ERR_OP_ILLEGAL or NFS4ERR_BADXDR, then it can be concluded
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knowledge of the operation in question. Other responses, knowledge of the operation in question. Other responses,
including NFS4ERR_UNION_NOTSUPP, indicate that the responder is including NFS4ERR_UNION_NOTSUPP, indicate that the responder is
aware of the protocol element in question. aware of the protocol element in question.
A determination of the knowledge or lack of knowledge of a particular A determination of the knowledge or lack of knowledge of a particular
protocol element is expected to remain valid as long as the clientid protocol element is expected to remain valid as long as the clientid
associated with the request remains valid. associated with the request remains valid.
The above assumes, as should be the case, that the server will accept 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 the minor version used by the client. For more detail regarding this
issue, see Section 8.3.2. issue, see Section 8.2.
4.4.4. Interoperability Between Version Groups
Within a minor version group, we have complete compatibility in the 4.5. XDR Overlay
sense that:
o Servers are REQUIRED to implement a core set of features which XDR additions may also be made by defining XDR structures that
cannot change within the minor version group, allowing clients to overlay nominally opaque fields. defined to allow such incremental
depend on the continued existence of and support for these extensions.
features as long as one remains within the minor version group.
o The set of OPTIONAL features supported or known by servers may For example, each pNFS mapping type provides its own XDR definition
change but clients, in using such OPTIONAL features need to be for various pNFS-related fields defined in [RFC5661] as opaque
prepared for the fact that they might not be implemented on all arrays.
servers implementing a minor version within the same version
group.
The same level of compatibility is not provided between different Because such additions provide new interpretations of existing
minor version groups. Nevertheless, the same guarantees of inter-XDR fields, they may be made outside of the extension framework as long
comprehensibility apply across minor version groups. For a as they obey the rules previously established when the nominally
discussion of how this comprehensibility can be used between minor opaque protocol elements were added to the protocol.
version groups, see Section 8.3.3.
5. Other NFSv4 Protocol Changes 5. Other NFSv4 Protocol Changes
There are a number of types of protocol changes that are outside the There are a number of types of protocol changes that are outside the
XDR extension framework discussed in Section 4. These changes are XDR extension framework discussed in Section 4. These changes are
also managed within the NFSv4 versioning framework and may be of a also managed within the NFSv4 versioning framework and may be of a
number of types, which are discussed in the sections below number of types, which are discussed in the sections below
Each such change will be organized, documented and effected as part
of a given feature, just as changes discussed in Section 4 are. The
way such features will be incorporated in the NFSv4 protocol depends
on a number of factors, including the types of changes included in
the feature. This subject is discussed in Sections 6.7 and 7.
5.1. Non-XDR Protocol Changes
Despite the previous emphasis on XDR changes, additions and changes Despite the previous emphasis on XDR changes, additions and changes
to the NFSv4 protocols have not been limited to those that involve to the NFSv4 protocols have not been limited to those that involve
changes (in the form of extensions) to the protocol XDR. Examples of changes (in the form of extensions) to the protocol XDR. Examples of
other sorts of changes have been taken from NFSv4.1. other sorts of changes have been taken from NFSv4.1.
Because these sorts of changes do not involve XDR extensions, it is All such changes that have been made in the past have been made as
not possible to use the techniques discussed in Section 4.4.3 to part of new minor version. Future change of these sorts may not be
distinguish responders which have the change those which do not. To done in an extension but can only be made in a new minor version.
avoid this situation resulting in implementation incompatibility, all
such changes need to be made in a minor version, rather than in an
extension with to an existing minor version.
5.1.1. Field Interpretation and Use 5.1. Field Interpretation and Use
The XDR description of a protocol does not constitute a complete The XDR description of a protocol does not constitute a complete
description of the protocol. Therefore, versioning needs to consider description of the protocol. Therefore, versioning needs to consider
the role of changes in the use of fields, even when there is no the role of changes in the use of fields, even when there is no
change to the underlying XDR. change to the underlying XDR.
Although any XDR element is potentially subject to a change in its Although any XDR element is potentially subject to a change in its
interpretation and use, the likelihood of such change will vary with interpretation and use, the likelihood of such change will vary with
the XDR-specified type of the element, as discussed below: the XDR-specified type of the element, as discussed below:
skipping to change at page 20, line 45 skipping to change at page 15, line 29
definition documents. Some types of strings within NFS4 are used definition documents. Some types of strings within NFS4 are used
in server names (in location-related attributes), user and group in server names (in location-related attributes), user and group
names, and in the names of file objects within directories. Rules names, and in the names of file objects within directories. Rules
regarding what strings are acceptable appear in [RFC7530] and regarding what strings are acceptable appear in [RFC7530] and
[RFC5661] with the role of the XDR limited to hints regarding [RFC5661] with the role of the XDR limited to hints regarding
UTF-8 and capitalization issues via XDR typedefs. UTF-8 and capitalization issues via XDR typedefs.
o Fields that are XDR-defined as opaque elements and which are truly o Fields that are XDR-defined as opaque elements and which are truly
opaque, do not raise versioning issues, except as regards inter- opaque, do not raise versioning issues, except as regards inter-
version use, which is effectively foreclosed by the rules in version use, which is effectively foreclosed by the rules in
Section 8.3.1. Section 8.1.
Note that sometimes a field will seem to be opaque but not Note that sometimes a field will seem to be opaque but not
actually be fully opaque when considered carefully. For example, actually be fully opaque when considered carefully. For example,
the "other" field of stateids is defined as an opaque array, while the "other" field of stateids is defined as an opaque array, while
the specification text specially defines appropriate treatment the specification text specially defines appropriate treatment
when the "other" field within it is either all zeros or all ones. when the "other" field within it is either all zeros or all ones.
Given this context, creation or deletion of reserved values for Given this context, creation or deletion of reserved values for
"special" stateids will be a protocol change which versioning "special" stateids will be a protocol change which versioning
rules need to deal with. rules need to deal with.
o Some nominally opaque elements have external XDR definitions that o Some nominally opaque elements have external XDR definitions that
overlay the nominally opaque arrays. This technique is useful overlay the nominally opaque arrays. Such cases are discussed in
when the same element may be used in several ways when a switched Section 4.5.
union is not appropriate.
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 5.2.1.
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.
5.1.2. Behavioral Changes 5.2. Behavioral Changes
Changes in the behavior of NFSv4 operations are possible, even if Changes in the behavior of NFSv4 operations are possible, even if
there is no change in the underlying XDR or change to field there is no change in the underlying XDR or change to field
interpretation and use. interpretation and use.
One class of behavioral change involves changes in the set of errors 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 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 requests remain the same, and the behavior for each of them remains
the same, such changes can be implemented with only limited the same, such changes can be implemented with only limited
disruption to existing clients. disruption to existing clients.
Many more substantial behavioral changes have occurred in connection Many more substantial behavioral changes have occurred in connection
with the addition of the session concept in NFSv4.1. with the addition of the session concept in NFSv4.1. Even though
there was no change to the XDR for existing operations, many existing
o Because exactly-once is semantics provided by sessions, the use of operations and COMPOUNDs consisting only of them became invalid.
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 Also, changes were made regarding the required server behavior as to
the interaction of the MODE and ACL attributes. the interaction of the MODE and ACL attributes.
5.1.3. Rules for non-XDR changes 6. Extending Existing Minor Versions
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 9.
o A protocol improvement relevant to a new minor version or feature,
to be documented as described in Section 10.3.
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. As specified in Section 5.1, such changes may not be made
in an extension.
Also, to provide greater clarity about such changes, the following
rules apply to features which include the sort non-XDR changes
described in Sections 5.1.1 and 5.1.2.
o Except for features that only change the set of valid error codes
or prescribe that different error codes are to be returned in
particular situations, feature that include such non-XDR changes
cannot be made REQUIRED at initial introduction.
Since such features are to be OPTIONAL, there needs to be some way
that requester can determine whether the feature is supported by
the responder. This normally take the form of an associated XDR
change, such as an attribute which can be interrogated to
determine if support is present.
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.
5.2. 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 5.2.2
5.2.1. Associated Protocols via pNFS Mapping Types
pNFS is structured around the ability to define alternative 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
version. As explained in Section 7, if a feature consists only of
that single change, it is available in multiple minor versions upon
publication.
Such a feature has a file system scope and the attribute
fs_layout_type can used to determine whether support is present.
5.2.2. 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 of 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 template feature establishing the requirements
that the associated protocols are to meet.
o That the template feature is defined as an integral part of a
particular minor version and not as an extension. This does not
exclude this feature being defined in a separate document to which
the minor version specification has a normative reference.
o The template feature defines the scope that the individual feature
instances will have.
o The template feature defines a means by which support for
particular feature instances might be determined by a client.
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 (an instance
of the template feature) should be defined in separate documents.
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
specify further restrictions governing as to when minor versions are
allowed to incorporate particular instances of that extension
mechanism. In the absence of such restrictions, particular
extensions will be incorporated, as is the case with pNFS mapping
types, in all minor versions upon publication of the instance as a
Proposed Standard.
6. NFSv4 Protocol Features
Individual changes, whether they are XDR extensions or other sorts of
changes, are organized in term of protocol 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.
o help the client determine which particular changes are present and
implemented by the server.
o support the independent development and specification of changes
to the protocol, without artificially tying features together in a
paradigm solely based on minor versions.
o provide support for a feature-based documentation structure, as
described in Section 10.3.
In contrast with some previous uses of the feature concept, every
protocol element is defined as a member of exactly one protocol
feature.
Because support for particular protocol features may depend on
facilities provided by the underlying file systems, or may vary based
on characteristics of the session within which communication is
occurring, each protocol feature will be defined as having a
particular scope, which may be any of the following:
o Client scope in which case support for a given feature is assumed
to be uniform between given client and server as long as neither
reboots.
o Session scope in which case different sessions associated with the
same client may have differences as to feature support but
otherwise support is uniform.
o file system scope in which case different file systems may have
differences as to feature support but otherwise support is
uniform.
6.1. Previous Uses of the Feature Concept
The word "feature" has been used inconsistently in previous documents
bearing on issues related NFSv4 versioning, making it necessary to
offer some clarification here.
o In some cases, the term "feature" is used colloquially
o In some cases, the word "feature" is used to refer to protocol
extensions which are incorporated in the protocol that we refer to
as "protocol elements." The term "feature elements" is similar
but it differs in that it includes changes in field interpretation
and use (Section 5.1.1) and protocol behavior (See Section 5.1.2).
o In some cases the word is used to refer to groups of feature
elements, as defined by tables in [RFC5661] and [NFSv42]. This is
similar to, but not exactly the same as the way we use the word
"feature" is used in this document.
Often, as in previous minor versioning rules, it is not always clear
which sense of the word "feature" is meant.
6.2. Rules for Protocol Feature Construction
A protocol 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 5 although the specific types
of changes will affect how the feature can be integrated in the NFSv4
protocol.
A critical distinction in this regard is the one between features
which can added to the protocol without a new minor version and those
which require a new minor version. In this document:
o Features which do not require a new minor version are discussed in
Section 7, while the process of incorporation depends on the type
of features and is discussed in Sections 7.1, 9, 5.2.1, and 5.2.2,
o For handling of the remaining features which do require a new
minor version, see Section 8.
6.3. Statuses of Features
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, i.e. it is OPTIONAL
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 not being undefined.
These statuses define whether a client implementing the minor version
has to be prepared for the protocol feature's non-support by a server
implementation, even if the feature in question is known 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.
Particular protocol elements have similar statuses, which are derived
from a combination of the status of feature of which the protocol
element, the status of that protocol element within its feature, and,
in some cases, within other supported features. See Section 6.4 for
details.
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.
6.4. Statuses of Protocol Elements Within Features
This section discusses three classes of information that a requester
might use in order to allow it to avoid individually testing the
responder's knowledge of and support for each possible protocol
element. This information includes:
o The grouping of feature elements within features and features
within feature packages. If two feature elements are part of the
same feature or of features within the same feature package, then
each responder which is aware of one must be aware of the other,
o The assignment of status values that allow support for the feature
in which the feature element is defined to be inferred based on
support for the protocol element. This is referred to as the
protocol element's E-to-F status.
o The assignment of status values that allows support for a feature
element to be inferred based on support for the feature. This is
referred to as the protocol element's F-to-E status with regard to
the feature.
The purpose of specifying this information is to allow the knowledge
of and support for one protocol element to be determined based on
responses for others, avoiding the complexity that a client would
have to deal with if each such support decision were independent. A
simpler model would have been to simply assign protocol elements to
feature-based support equivalence classes and require all protocol
elements in a feature to be supported or not supported together.
This approach was not adopted because it is not compatible with many
current and expected feature patterns:
o Many existing protocol features contain protocol elements that are
optional in the context of the feature.
o Some existing protocol elements are used by more than one feature.
o Boolean attributes that indicate the presence of support for a
given feature are tied to that feature, even though the attribute
can be supported when the feature is not, in which case the
attribute is supported and has the value FALSE.
The following are noteworthy E-to-F statuses.
o Support or non-support for the feature is always the same as that
for the protocol element. This is represented as an "IFF" value.
o Lack of support for the feature can be inferred from lack of
support for the protocol element but the reverse can be determined
by using the protocol element to determine whether support for the
feature is present. An example would be a Boolean attribute
indicating whether support for the feature is present. This is
represented as an "SVAL" value.
It needs to be clear how a client may determine whether any
particular OPTIONAL feature is supported. Typically there will be
one or more protocol elements belonging to the feature whose E-F
status is "IFF" or "SVAL". In these cases, support for the protocol
elements in question can be determined as described in Section 6.5
In more complicated cases, the feature specification should clearly
specify how to determine whether support is present.
The following are possible F-to-E statuses.
o Support for the protocol element is REQUIRED when support for the
feature is present.
o Support for the protocol element is OPTIONAL when support for the
feature is present.
o Support for the protocol element is unaffected by the presence of
support for the feature.
The overall status of a feature element within a minor version is
generally determined as follows:
o If there are one or more REQUIRED features which give the protocol
element an F-to-E status of REQUIRED, then the overall status of
the protocol element within the minor version is REQUIRED.
o Otherwise, if there are one or more REQUIRED or OPTIONAL features
which give the protocol element an F-to-E status of REQUIRED or
OPTIONAL, then the overall status of the protocol element within
the minor version is OPTIONAL.
o If neither of the above is true, the protocol element is treated
as not a part of the minor version. That is, it is treated as
mandatory to not implement.
In some cases the overall status may be different from that specified
above. For example, it could be that there were two features, each
of which is OPTIONAL, and it is specified that exactly one of these
must always me supported. In such a case, if both features assign a
protocol element an F-to-E status of REQUIRED, then the overall
status of the protocol element is REQUIRED.
6.5. Determining Protocol Element Support
If it has already been determined that a particular protocol element
is known to the server, the client can determine whether it is
supported based on its type, as follows:
o If the protocol element is an attribute, the supported_attr
attribute can be interrogated to determine if support is present.
o If the protocol element is an operation, the operation can be
attempted, with an error of NFS4ERR_NOTSUPP indicating the
operation is known but not supported.
o If the protocol element is a switch case, use of that case can be
attempted, with an error of NFS4ERR_UNION_NOTSUPP indicating t the
operation is known but not supported.
o If the protocol element is an operation flag bit and the operation
is REQUIRED, use of that flag bit can be attempted with an error
of NFS4ERR_NOTSUPP indicating the protocol element is known but
not supported.
o If the protocol element is an operation flag bit and the operation
defines an error to return in the case of unsupported flag bits,
use if that flag bit can be attempted with the specified error
indicating the operation is known but not supported.
Once this is done, all of the protocol elements the client is aware
of can be divided into three sets:
o Those that the server is unaware of and thus cannot support.
o Those that the server knows about but does not support.
o Those that the server supports.
Information obtained in the process of determining knowledge of
protocol elements (see Section 4.4.3) may be saved and used in
connection with the interrogations above. For example, in testing
for knowledge of a given operation, the specific error code returned
will indicate support or non-support as well as indicating support or
non-support, as well as knowledge of the corresponding operation.
Note that in doing so care needs to be taken regarding protocol
elements associated with features whose scope is more limited than
that of an entire client, since support may be different for
different sessions or different file systems.
6.6. Feature Discovery
In many cases, a client will need to determine whether particular
features are supported before using protocol elements that are part
of those features. While some clients may choose to defer this
determination until the features in question are actually needed,
others may make the determination as part of first connecting with a
server, using a session or accessing a file system, depending on the
scope of the feature in question.
Once such a determination of feature support or non-support are made,
the client may assume that it remains valid and will not change so
long as the object defining the feature scope remains valid.
o For features of client scope as long as the clientid remains
valid.
o For features of session scope as long as the sessionid remains
valid.
o For features of file system scope as long as the clientid and fsid
both remain valid.
In making this determination, the client is entitled to rely on, and
the server is REQUIRED to obey any inter-feature constraints that are
specified as applying to the minor version being used.
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, the
client can treat the fact that the server accepted a request with
that minor version (and did not return
NFS4ERR_MINOR_VERSION_MISMATCH) as indicating that support is
present.
o For features which consist only of the addition of a pNFS layout
type, the fs_layout_type attribute for the fs in question can be
interrogated and scanned for the layout type.
o For features which consist only of the addition of an instance of
a feature template as defined in Section 5.2.2, the template
feature definition will describe the means by which the presence
of support for particular feature instances is to be determined.
For the remaining features, which are all OPTIONAL and contain an
XDR-extending protocol element, the E-to-F statuses of the
constituent protocol elements (see Section 6.4) can be used to
determine if support is present within the scope defined by the
feature in question. In most cases, support for the protocol element
is tested as described in Section 6.5.
o If there are one or more protocol elements whose status is "IFF",
support for any of these may be tested, with the result
determining support for the feature
o If there are one or more protocol elements whose status is "SVAL",
support for it can be tested, and if present the value returned
can be tested as described by the feature specification, resulting
in a determination of support for the feature.
o If there are protocol elements with statuses of "SINF" and
"NSINF", testing of these protocol elements can be used, although,
it is not always certain that testing all such will always resolve
the question.
o If none of these approaches are determinative, the feature
specification should define a method of resolving the question.
Once the set of supported features is determined:
o For protocol elements which have an F-to-E status of REQUIRED for
at least one supported feature, it can be assumed that support is
present.
o For other protocol elements which have an F-to-E status of
OPTIONAL for at least one supported feature, support needs to be
tested for as described in Section 6.5.
o For the remaining protocol elements, it can be assumed that
support is not present.
6.7. 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 8.
o In separately documented new features. When new features are
OPTIONAL and do not include any non-XDR-based changes, they may be
incorporated in an extensible minor version under construction.
See Section 7.1 for details.
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 9 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 5.2.2).
o Minor versions designated as extensible (see Section 7.1) may be
extended by the publication of a standards-track document defining
the additional feature. Details are set out below. The features
to be added are considered OPTIONAL in the extensible minor
version and must consist only of valid XDR-based extensions
7.1. 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.
7.2. 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 OPTIONAL 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.
Also, certain additional documents may be produced at this time to
simplify the process of using new versions that contain the
extension, and to help co-ordinate the process of making further
extensions. See Section 10.5 for details.
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.
7.3. 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 7.3.1.
o Issues related to messages sent to the client are discussed in
Section 7.3.2.
7.3.1. 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
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 known or known but 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
NFS4ERR_ATTRNOTSUPP 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.
7.3.2. 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.
7.4. 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 OPTIONAL 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.
o No new feature may be added to a minor version 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 9 for details.
While making minor versions extensible will decrease the frequency of
new minor versions, it will not eliminate the need for them.
Protocol features that cannot be used as extensions (see
Section 8.1.1 require a new minor version.
In addition, change which involve modifications to the set of Extensions to the most recently published NFSv4 minor version may be
protocol elements which are REQUIRED or mandatory to not implement made by publishing the extension as a Proposed Standard, unless the
requires a new minor version which starts a new minor version group. 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.
Changes to the organization of protocol features are treated Corrections to protocol errors (see Section 9) may be accomplished by
similarly, since they have a similar potential to cause interversion publishing an extension, including a compatible XDR change. Such
incompatibility. See Section 8.1.2 for details. documents will update the defining documents for the corrected minor
version.
8. Minor Versions 7. Minor Versions
8.1. Creation of New Minor Versions 7.1. Creation of New Minor Versions
It is important to note that this section, in describing situations It is important to note that this section, in describing situations
that would require new minor versions or minor version groups to be that would require new minor versions to be created, does not thereby
created, does not thereby imply that situations will exist in the imply that situations will exist in the future. Judgments regarding
future. Judgments regarding desirability of future changes will be desirability of future changes will be made by the working group or
made by the working group or its successors and any guidance that can its successors and any guidance that can be offered at this point is
be offered at this point is necessarily quite limited. necessarily quite limited.
Creation of a new minor version or minor version group is an option
that the working group retains. The listing of situations below that
would prompt such actions is not meant to be exhaustive.
New minor versions are to be documented as described in Section 10.6.
8.1.1. New Minor Versions within an Existing Group 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 The following sorts of features are not allowed as extensions and
would require creation of a new minor version: would require creation of a new minor version:
o Features that incorporate any of the non-XDR-based changes o Features that incorporate any of the non-XDR-based changes
discussed in Sections 5.1.1 and 5.1.2. discussed in Sections 5.1 and 5.2.
o Any feature which includes a new mapping type (as described in
Section 5.2.1) and includes any other change.
To prevent new mapping types from evading this restriction by
splitting the mapping type and other changes into two separate
changes, if new mapping type makes a reference to protocol changes
in an extension, it may not be incorporated in minor versions in
which that extension is defined but only in later minor versions.
o Any feature that creates a new expansion mechanism as described in
in Section 5.2.2.
8.1.2. New Minor Version Groups
The following sorts of changes can only occur in the context of a new
minor version group:
o Addition of REQUIRED new features. o Addition of REQUIRED new features.
o Changes to the status of existing features including converting o Changes to the status of existing features including converting
features to be mandatory to not implement. features to be mandatory to not implement.
o Changes to the status of existing feature elements within 8. Minor Version Interaction Rules
features, causing those feature elements to be required or
optional when they previously had not been.
o Changes to the scope of existing features.
o Changes to feature organization or to inter-feature constraints.
Such changes may have the effect of making support for some change
element required or optional in circumstances in which it
previously had not been
Changes to the status or organization of features will, in most case,
result in changes to the status of individual protocol elements,
changing them between REQUIRED and OPTIONAL, or making them mandatory
to not implement.
Conversion of protocol elements to be mandatory to not implement,
will not, as had previously been the practice, result in their
deletion from the protocol XDR. However, the server will be REQUIRED
to treat such protocol elements as not known when responding to
requests within minor versions in which they are not to be
implemented. See Sections 4.4.3 and 8.3.2 for details.
Such changes give rise to potential compatibility issues. In most
cases in which such changes will actually be made, careful
consideration of compatibility issues can limit the scope of such
issues or ensure that compatibility issues actually experienced are
quite limited.
This is opposed to the first new minor version group, that associated
with minor version one, which resulted in a situation in which
clients for minor version zero could not interoperate with servers
for minor version one and vice versa. Issues related to the question
of what to do about such situations are discussed in Section 8.1.3
The addition of REQUIRED features may serve to illustrate the issues.
Such additions pose no compatibility issue for existing clients. On
the other hand, all servers will need to be updated to support the
new features. The effort required and any potential for disruption
depend on the scope of the feature being added.
A number of features introduced as REQUIRED in NFSv4.1 can serve to
illustrate the issues.
o suppattr_exclattr was added as a REQUIRED attribute. This was
very simple for servers to implement.
o RECLAIM_COMPLETE was added as a REQUIRED operation.
o TEST_STATEID and FREE_STATEID were added as REQUIRED operations.
Some examples of potential feature status changes may be helpful in
illustrating compatibility issues
o Converting a REQUIRED feature to be mandatory to not implement
poses the greatest level of difficulty from an interoperability
point of view. Clients need to change to use an alternative means
of providing the functionality provided by the feature. Existing
servers need to be updated, even if there is a replacement feature
available.
Such a transition is only possible without disruption if the
feature in question has already fallen into disuse.
o Converting an OPTIONAL feature to be mandatory to not implement
poses similar difficulties. If clients have ceased to use the
feature, after they have become aware, formally or informally,
that it is moribund, the difficulties can be quite limited.
o Converting a REQUIRED feature to be OPTIONAL poses no difficulty
for existing server implementations. It may pose difficulties for
clients who have not made preparations for server non-support of
the feature.
The degree of such difficulties and the readiness of clients to
make such changes should be key considerations in making such a
state transition.
o Converting an OPTIONAL feature to be REQUIRED poses no difficulty
for existing client implementations. The difficulties for
existing server implementations depend on the scope of the feature
involved and the set of implementations without support for the
feature in question. The degree of such difficulties and the
readiness of servers to make such changes should be key
considerations in making such a state transition. Nevertheless,
it should not be the only consideration. If all existing servers
support the feature, it does not thereby follow that the
transition should be made. The possible effect of making server
development more complicated should also be considered.
A number of other changes allowed only in a new minor version group,
raise analogous issues.
o In the case of inter-feature constraints or similar
reorganizations, the basic issue is whether the client has to deal
with the absence of a protocol element when it previously had not
had to deal with that or the server has to provide support for a
protocol element in situations in which it previously had not had
to. When a set of changes cause both sorts of issues, the
greatest interoperability difficulties arise, making such a set of
changes hard to implement.
o If a feature scope is changed to be more fine-grained, the client
has to deal with combinations of support and non-support it
previously had not had to deal with, while the reverse forces the
server to maintain a unity of support it had previously not had
to. The unlikely case of conversion between session and file
system scope causes difficulties for both parties.
The tradeoff between interoperability issues and desirable changes to
the protocol is one for the working group to make. If the decision
is made to create a new minor version group, the working group has
decided that absolute compatibility is not required. Nevertheless,
it should strive to make necessary changes as non-disruptive as
possible.
8.1.3. Limits on Minor Version Groups
The guidance that needs to be offered with regard to appropriate
limits on changes that form new version groups does not appear
reducible to specific rules.
Instead it is appropriate to return to the basic goal of allowing the
NFSv4 protocol to adapt to future circumstances as they develop.
Although this was not explicitly stated, it seems to be intended that
this would not involve generation of an essentially a new protocol,
even if that were, in some sense, a better one.
So the best way we can address the question of limits on new version
groups is to state that the purpose of the rules in this document,
including the creation of new minor version groups is not the
creation of a successor protocol to NFSv4.
If this or a future working group does find itself defining a new
file access protocol, it would be helpful if proper care were taken
to retain what is valuable in the intellectual heritage of NFSv4.
Nevertheless, in doing so, it is important not to assume that
adherence to the rules in this document, is, in and of itself, a
guarantee that the new protocol is thereby a version of NFSv4.
In dealing with such a future changed situation, the better option
would be to face the issue of necessary change forthrightly and
acknowledge that such a large change creates a fundamentally new
situation. Appropriate responses might include replacing the XDR in
whole or in part, using a successor to XDR, or other means.
8.2. Role of Minor Versions
Clearly, the ability to provide protocol extensions without creation
of a new minor version, has lessened the role of minor versions in
extending the NFSv4 protocol to meet future needs.
We have gone from a situation in which there was a single mechanism,
creation of a new minor version, to extend the protocol, to a three-
level approach:
o OPTIONAL features which extend but do not change protocol
semantics may be added without creating a new minor version.
o Other OPTIONAL features may be added by creating a new minor
version within an existing version group, as long as the sets of
protocol elements which are REQUIRED and mandatory to not
implement.
o Changes which do as the sets of protocol elements which are
REQUIRED and mandatory to not implement are only allowed in a new
minor version group.
This document does explore the situations that, if they arise, would
require the creation of new minor versions or version groups. This
does not imply that such situations will exist or that the working
will choose to address things in that way. Such choices are left for
future decision by the working group and the IESG.
The discussion in Section 8.1.3 raises similar issues. It is
possible that situations might arise that would cause NFSv4
development to be done outside the framework established here.
Nevertheless, this does not imply that such situations will arise.
8.3. Minor Version Interaction Rules
This section addresses issues related to rules #11 and #13 in the This section addresses issues related to rules #11 and #13 in the
minor versioning rules in [RFC5661]. With regard to the supersession minor versioning rules in [RFC5661]. With regard to the supersession
of minor versioning rules, the treatment here overrides that in of minor versioning rules, the treatment here overrides that in
[RFC5661] when either of the potentially interacting minor versions [RFC5661] when either of the potentially interacting minor versions
has not yet been published as a Proposed Standard. has not yet been published as a Proposed Standard.
Note that these rules are the only ones directed to minor version Note that these rules are the only ones directed to minor version
implementers, rather than to those specifying new minor versions. implementers, rather than to those specifying new minor versions.
8.3.1. Minor Version Identifier Transfer Issues 8.1. Minor Version Identifier Transfer Issues
Each relationship between a client instance and a server instance, as Each relationship between a client instance and a server instance, as
represented by a clientid, is to be devoted to a single minor represented by a clientid, is to be devoted to a single minor
version. If a server detects that a COMPOUND with an inappropriate version. If a server detects that a COMPOUND with an inappropriate
minor version is being used, it MUST reject the request. In doing minor version is being used, it MUST reject the request. In doing
so, it may return either NFS4ERR_BAD_CLIENTID or so, it may return either NFS4ERR_BAD_CLIENTID or
NFS4RR_MINOR_VERS_MISMATCH. NFS4RR_MINOR_VERS_MISMATCH.
As a result of the above, the client has the assurance that the set 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 REQUIRED and OPTONAL features will not change within the context
of a single clientid. Server implementations MUST ensure that the of a single clientid. Server implementations MUST ensure that the
set of supported features and protocol elements does not change set of supported features and protocol elements does not change
within such a context. within such a context.
8.3.2. Minor Version Intra-Group Compatibility 8.2. Minor Version Compatibility
Within a set of minor versions that belong to the same minor version The goal of the NFSv4 extension model is to enable compatibility
group, it is relatively easy for clients and servers to provides the including compatibility between clients and servers implementing
needed compatibility by following the following rules. different minor versions.
o Servers supporting a given minor version SHOULD support any Within a set of minor versions that define the same set of features
earlier minor version in the same minor version group. If a as REQUIRED and mandatory to not implement, it is relatively easy for
server does not do so it will be unable to interoperate with clients and servers to provide the needed compatibility by adhering
clients built to interoperate with servers supporting earlier to the following practices.
minor versions, despite the fact that all features expected by the
client are still required of the server and the client is unaware
of added OPTIONAL server added since then.
Servers that do so MUST return appropriate errors for use of o Servers supporting a given minor version should support earlier
protocol elements that were not a valid part of that earlier minor minor versions within that set and return appropriate errors for
version. For details see below. use of protocol elements that were not a valid part of that
earlier minor version. For details see below.
o Servers supporting a given minor version MUST, in returning errors o Clients should deal with an NFS4ERR_MINOR_VERS_MISMATCH error by
for operation which were a valid part of the minor version, return searching for a lower minor version number that the server will
the errors allowed for the current operation in the minor version accept.
actually being used.
o Clients MUST deal with an NFS4ERR_MINOR_VERS_MISMATCH error by a Servers supporting a given minor version MUST, in returning errors
searching for a lower minor version number in the same minor for operation which were a valid part of the minor version, return
version group that the server will accept. 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, With regard to protocol elements not known in a given minor version,
the appropriate error codes are given below. Essentially, the the appropriate error codes are given below. Essentially, the
server, although it has a more extensive XDR reflective of a newer 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. 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 o When an operation is used which is not known in the specified
minor version, NFS4ERR_OP_ILLEGAL (as opposed to NFS4ERR_NOTSUPP) minor version, NFS4ERR_OP_ILLEGAL (as opposed to NFS4ERR_NOTSUPP)
should be returned. should be returned.
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minor version, NFS4ERR_BADXDR (as opposed to minor version, NFS4ERR_BADXDR (as opposed to
NFS4ERR_UNION_NOTSUPP) should be returned. Even though the NFS4ERR_UNION_NOTSUPP) should be returned. Even though the
message may be XDR-decodable by the server's current XDR, it is message may be XDR-decodable by the server's current XDR, it is
not so according to the minor version being used. not so according to the minor version being used.
o When a flag bit is used which is not known in the specified minor 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 version, NFS4ERR_INVAL (as opposed to NFS4ERR_NOTSUPP Or any other
error defined as indicated non-support a flag bit) should be error defined as indicated non-support a flag bit) should be
returned. returned.
8.3.3. Minor Version Inter-Group Compatibility
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, and the particulars of the changes made which establish new
version groups.
Options for compatibility are affected by the scale and frequency of
the changes which require a new minor version group and the working
group needs to take needs for inter-group compatibility into account
when making such changes. In all cases, the following rules apply:
o Servers supporting a given minor version SHOULD support minor
versions in earlier minor version groups. When doing so, it MUST
behave appropriately given the definition of the minor version
used. For details see below.
o Clients SHOULD deal with an NFS4ERR_MINOR_VERS_MISMATCH error by a
searching for a lower minor version number within the appropriate
minor version range until it finds one that the server will
accept.
In some cases, the server needs to behave as a more restricted one
for an earlier minor version might, despite it having extensions for
protocol elements added in later minor versions. In these cases, the
errors described in Section 8.3.2 should be returned in this case as
well.
In the case in which the earlier version contains protocol elements
subsequently made mandatory to not implement, the server needs to
know of those protocol elements and not return the errors that would
appropriate if the most up-to-date minor version were used. In cases
in which support for these protocol elements is REQUIRED, support
will have to be provided by the server and if it cannot do that, it
MUST return NFS4ERR_MINOR_VERS_MISMATCH for any requests using that
minor version.
In addition to using an appropriate subset of the protocol XDR
definition, the server needs to respect the non-XDR elements of the
earlier minor version group as well. In particular, the serve needs
to:
o Support REQUIRED features as specified by the earlier minor
version group.
o Support (or not) features according to E-to-F statuses specified
by the earlier minor version group.
o Respect the inter-feature constraints specified by the earlier
minor version group.
o Respect the feature scopes specified by the earlier minor version
group.
o Support (or not) protocol elements according to the F-to-E
statuses specified in the earlier minor version group.
9. Correction of Existing Minor Versions and Features 9. Correction of Existing Minor Versions and Features
The possibility always exists that there will be a need to correct an 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 existing feature in some way, after the acceptance of that feature or
a minor version containing it, as a Proposed Standard. While the a minor version containing it, as a Proposed Standard. While the
working group can reduce the probability of such situations arising working group can reduce the probability of such situations arising
by waiting for running code before considering a feature as done, it by waiting for running code before considering a feature as done, it
cannot reduce the probability to zero. As features are used more cannot reduce the probability to zero. As features are used more
extensively and interact with other features, previously unseen flaws extensively and interact with other features, previously unseen flaws
may be discovered and will need to be corrected. may be discovered and will need to be corrected.
Such corrections are best done in a document obsoleting or updating Such corrections are best done in a document obsoleting or updating
the RFC defining the relevant feature definition document or minor the RFC defining the relevant feature definition document or minor
version specification. In making such corrections, the working will version specification. In making such corrections, the working group
have to carefully consider how to assure interoperability with older will have to carefully consider how to assure interoperability with
clients and servers. older clients and servers.
Often, corrections can be done without changing the protocol XDR. In Often, corrections can be done without changing the protocol XDR. In
many cases, a change in client and server behavior can be implemented many cases, a change in client and server behavior can be implemented
without taking special provision with regard to interoperability with without taking special provision with regard to interoperability with
earlier implementations. In those case, and in cases in which a earlier implementations. In those case, and in cases in which a
revision merely clarifies an earlier protocol definition document, a revision merely clarifies an earlier protocol definition document, a
new document can be published which simply updates the earlier new document can be published which simply updates the earlier
protocol definition document. Subsequently, the indexing material protocol definition document.
would be updated to reflect the existence of the newer document.
In other cases, it is best if client or server behavior needs to In other cases, it is best if client or server behavior needs to
change in a way which raises interoperability concerns. In such change in a way which raises interoperability concerns. In such
cases, incompatible changes in server or client behavior should not cases, incompatible changes in server or client behavior should not
be mandated in order to avoid XDR changes. be mandated in order to avoid XDR changes.
9.1. XDR Changes to Implement Protocol Corrections 9.1. XDR Changes to Implement Protocol Corrections
When XDR changes are necessary as part of correcting a flaw, these 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 should be done in a manner similar to that used when implementing new
minor versions or features within them. In particular, minor versions or features within them. In particular,
o Existing XDR structures may not be modified or deleted. o Existing XDR structures may not be modified or deleted.
o XDR extensions may be used to correct existing protocol facilities o XDR extensions may be used to correct existing protocol facilities
in a manner similar to those used to add additional optional in a manner similar to those used to add additional optional
features. Such corrections may be done in an otherwise non- features. Such corrections may be done in a minor version for
extensible minor version, if the working group judges it which optional features may no longer be added, if the working
appropriate. 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 o When a correction is made to an OPTIONAL feature, the result is
similar to a situation in which there are two independent OPTIONAL similar to a situation in which there are two independent OPTIONAL
features. A server may choose to implement either or both. features. A server may choose to implement either or both.
o When a correction is made to a required feature, the situation 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 becomes one in which neither the old nor the new version of the
feature is required. Instead, it is required that a server feature is required. Instead, it is required that a server
support at least one of the two, while each is individually support at least one of the two, while each is individually
OPTIONAL. Although use of the corrected version is ultimately OPTIONAL. Although use of the corrected version is ultimately
better, and may be recommended, it should not be described as better, and may be recommended, it should not be described as
"RECOMMENDED", since the choice of which version to support if "RECOMMENDED", since the choice of which version to support if
only one is supported will depend on the needs of clients, which only one is supported will depend on the needs of clients, which
may be slow to adopt the updated version. may be slow to adopt the updated version.
o In all of the cases above, it is appropriate that the old version o In all of the cases above, it is appropriate that the old version
of the feature, be considered obsolescent, with the expectation of the feature, be considered obsolescent, with the expectation
that the working group might, in a later minor version, decide that the working group might, in a later minor version, decide
that the older version is to become mandatory to not implement. 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 10.7.
By doing things this way, the protocol with the XDR modification can By doing things this way, the protocol with the XDR modification can
accommodate clients and servers that support either the corrected or accommodate clients and servers that support either the corrected or
the uncorrected version of the protocol and also clients and servers the uncorrected version of the protocol and also clients and servers
aware of and capable of supporting both alternatives. aware of and capable of supporting both alternatives.
o A client that supports only the earlier version of the feature o A client that supports only the earlier version of the feature
(i.e., an older unfixed client) can determine whether the server (i.e., an older unfixed client) can determine whether the server
it is connecting to supports the older version of feature. It is it is connecting to supports the older version of feature. It is
capable of interoperating with older servers that support only the capable of interoperating with older servers that support only the
unfixed protocol as well as ones that support both versions. unfixed protocol as well as ones that support both versions.
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support of that particular feature. support of that particular feature.
o A server that supports both the older and newer versions of the o A server that supports both the older and newer versions of the
feature can interoperate with all client variants. feature can interoperate with all client variants.
By using extensions in this manner, the protocol creates a clear path By using extensions in this manner, the protocol creates a clear path
which preserves the functioning of existing clients and servers and which preserves the functioning of existing clients and servers and
allows client and server implementers to adopt the new version of the allows client and server implementers to adopt the new version of the
feature at a reasonable pace. feature at a reasonable pace.
10. Documentation of Features, Extensions, Minor Versions, and Protocol 10. Security Considerations
Corrections
As mentioned previously, NFSv4 is evolving towards a finer-grained
documentation model. This trend will be continued by:
o The use of extensions within minor versions.
o Features that are added by a minor version being documented in
feature definition documents rather than within the minor version
specification itself.
10.1. Documentation Approach
Documentation of future changes to the NFSv4 protocol will use
feature specification documents as described in Section 10.3. There
are a number of ways in which such documents may be used, which
reflect the different ways in which features are incorporated in the
NFSv4 protocol, as discussed in Section 6.7
This documentation approach is intended to avoid the unnecessary
production of large documents in which many unrelated features are
tied together because either:
o The entire protocol is described in a single document, as happened
with NFSv4.0 (in [RFC7530]) and NFSv4.1 (in [RFC5661]).
o Many unrelated features are described in a single document as
occurred with NFSv4.2 (in [NFSv42]).
The production of a larger number of smaller documents will
streamline document production and review. A potential problem is
that a profusion of smaller documents might cause difficulty for
those learning about and implementing the protocol.
The production of indexing material described in Section 10.2 is
intended to limit such difficulties. The result will be that, for
operations and attributes, we will have essentially a single table of
contents, referencing material from multiple minor version definition
documents and feature specification documents.
10.2. Indexing material
The items listed below, 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
protocol definition document containing a description of that
operation.
o A table mapping attributes to the most recent protocol definition
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, OPTIONAL, or mandatory-to-not implement), the name of
the feature of which it is a part, its associated E-to-F and
F-to-E status values and information about other features for
which it has a non-empty F-to-E status value. This would be
similar to the material in Section 14 of [NFSv42], expanded to
include all feature elements.
10.3. 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 5. Feature elements include new operations,
attributes, and enumeration values. Note that in this context,
"Operations" include both forward and callback operations. 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(s) in question,
the items to be included in such feature definition documents would
be as listed below. In some cases these items, in addition to
descriptive text, would contain fragments of XDR code, to aid in
preparation of XDR files that include the additions defined by the
feature added to the base protocol that is being extended. For
information regarding preparation of such XDR files, see
Section 10.4.
o Description of new operations (corresponding to Sections 15 and 16
of [NFSv42]). Such descriptions will contain XDR code defining
the structure the arguments and results of the new operation along
with preparatory XDR definitions used only by that operation.
o Description of any modified operations (corresponding to
Section 15 of [NFSv42]). Such description may contain XDR code
defining the new flag bits, enum values, and cases to be added to
existing switched unions. Note that addition of new attributes is
not considered an extension of GETATTR, SETATTR, VERIFY, or
NVERIFY.
o Description of new attributes (corresponding to Section 13 of
[NFSv42]). XDR code defining the types of the attributes would be
part of this description.
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 set of XDR code fragments giving the numeric values of added
operation codes, attribute numbers, and error codes.
o Descriptions of all other extensions made to existing flag words,
enums and switched unions used by existing operations. Such
descriptions will contain XDR code defining the new flag bits,
enum values, and cases to be added to existing switched unions.
o Descriptions of all new structures, enums, flag words, and
switched unions that are used by more than one new operation, or
which are available for future use by multiple operations. Such
descriptions will contain XDR code defining the new structures/
union and assigning the new numeric values for enum and flag bits.
o A listing giving the valid errors for each new operation and
callback (corresponds to Sections 12.2 and 12.3 of [NFSv42]).
o For each feature, a table giving for each feature element that is
part of the feature, its overall status within the minor version
and its E-to-F and F-to-E status values. This would be similar to
the material in Section 14 of [NFSv42] but restricted to the
feature(s) defined in the document and expanded to include all
feature elements.
o A table presenting support requirement for each protocol element
which is either a part of a feature defined in the document or has
an F-to-E status with relation with a feature defined in the
document. This could present the F-to-E status value for each
relevant combination of feature element and feature. An
alternative presentation would give, for each protocol element,
boolean expressions in term of supported features, that allows or
that guarantees support for the specified element.
o All of the additional Sections required for RFC publication, such
as "Security Considerations", "IANA considerations", etc.
Note that the listing above is not intended to define, in detail, the
structure of the specification. Rather, the intention is to define
the things it needs to contain. If there would be no content for a
particular element, there is no need for an empty section
corresponding to that list element. If it makes more sense to
describe a new structure together with an extended one, then the need
for a readily understandable document is primary.
10.4. XDR File Considerations
As mentioned previously, feature specification documents will
contain, in addition to description of XDR extensions, XDR code
fragments that embody those extensions. There will be various
occasions on which people will have occasion to produce XDR files
that combine one or more extensions together with the XDR for an
existing minor version.
o When a minor version is specified by a number of feature
specification documents, there will be a need to produce, in as
simple fashion as possible, the corresponding XDR specification
document for the new minor version.
o Within an extensible minor version, there will be a need for those
developing and testing the feature to have an XDR file that
incorporates XDR definitions from early drafts of the feature
specification document.
o Also, for an extensible minor version, there will be a need to
periodically produce Consolidated XDR documents that reflect all
features approved as Proposed Standards and thus incorporated in
the current minor version.
o Developers may need to be able to produce XDR files that reflect
particular combination of approved features, features under
development or experimental features not yet ready for working
group consideration.
We are assuming here that the primary task is producing XDR files and
that corresponding XDR documents can be produced relatively easily if
there is a well understood process to produce the underlying XDR
files.
The Feature specification document should contain all of the
necessary lines of XDR codes to be added to a base XDR file to effect
the extension. The only remaining issue is where to place each
addition to arrive at the correct consolidated file.
o One could rely on those preparing updated XDR file to place the
additional XDR code lines in the appropriate place, based on
inference from the document text.
o One could rely on the Feature Specification Document to indicate,
in the descriptive text, where each XDR extension is to be placed.
o One could formalize a set of conventions whereby the appropriate
placements are indicated by specific instructions embedded within
comments within the XDR code fragments to be placed.
10.5. Additional Documents to Support Protocol Extension
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.
10.5.1. 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 10.2)
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.
10.5.2. 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.
10.5.3. 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 implement.
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:
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.
10.5.4. 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 10.7
10.6. Documentation of New Minor Versions
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 OPTIONAL 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 10.2.
10.7. Documentation of XDR Changes for Corrections
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.
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 Since no substantive protocol changes are proposed here, no security
considerations apply. considerations apply.
As features and minor versions are designed and specified in 11. IANA Considerations
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. The current document does not require any actions by IANA.
Depending on decisions that the working group makes about how to 12. References
address the issues raised in this document, future documents may
require actions by IANA.
13. References
13.1. Normative References 12.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997, DOI 10.17487/RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>. <http://www.rfc-editor.org/info/rfc2119>.
13.2. Informative References
[NFSv42] Haynes, T., Ed., "NFS Version 4 Minor Version 2", January
2016, <http://www.ietf.org/id/
draft-ietf-nfsv4-minorversion2-41.txt>.
Work in progress.
[NFSv42-dot-x]
Haynes, T., Ed., "NFS Version 4 Minor Version 2 Protocol
External Data Representation Standard (XDR) Description",
January 2016, <http://www.ietf.org/id/
draft-ietf-nfsv4-minorversion2-dot-x-41.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, DOI 10.17487/RFC3530,
April 2003, <http://www.rfc-editor.org/info/rfc3530>.
[RFC5661] Shepler, S., Ed., Eisler, M., Ed., and D. Noveck, Ed., [RFC5661] Shepler, S., Ed., Eisler, M., Ed., and D. Noveck, Ed.,
"Network File System (NFS) Version 4 Minor Version 1 "Network File System (NFS) Version 4 Minor Version 1
Protocol", RFC 5661, DOI 10.17487/RFC5661, January 2010, Protocol", RFC 5661, DOI 10.17487/RFC5661, January 2010,
<http://www.rfc-editor.org/info/rfc5661>. <http://www.rfc-editor.org/info/rfc5661>.
[RFC5662] Shepler, S., Ed., Eisler, M., Ed., and D. Noveck, Ed.,
"Network File System (NFS) Version 4 Minor Version 1
External Data Representation Standard (XDR) Description",
RFC 5662, DOI 10.17487/RFC5662, January 2010,
<http://www.rfc-editor.org/info/rfc5662>.
[RFC5663] Black, D., Fridella, S., and J. Glasgow, "Parallel NFS
(pNFS) Block/Volume Layout", RFC 5663,
DOI 10.17487/RFC5663, January 2010,
<http://www.rfc-editor.org/info/rfc5663>.
[RFC5664] Halevy, B., Welch, B., and J. Zelenka, "Object-Based
Parallel NFS (pNFS) Operations", RFC 5664,
DOI 10.17487/RFC5664, January 2010,
<http://www.rfc-editor.org/info/rfc5664>.
[RFC7530] Haynes, T., Ed. and D. Noveck, Ed., "Network File System [RFC7530] Haynes, T., Ed. and D. Noveck, Ed., "Network File System
(NFS) Version 4 Protocol", RFC 7530, DOI 10.17487/RFC7530, (NFS) Version 4 Protocol", RFC 7530, DOI 10.17487/RFC7530,
March 2015, <http://www.rfc-editor.org/info/rfc7530>. March 2015, <http://www.rfc-editor.org/info/rfc7530>.
[RFC7531] Haynes, T., Ed. and D. Noveck, Ed., "Network File System 12.2. Informative References
(NFS) Version 4 External Data Representation Standard
(XDR) Description", RFC 7531, DOI 10.17487/RFC7531, March [RFC3530] Shepler, S., Callaghan, B., Robinson, D., Thurlow, R.,
2015, <http://www.rfc-editor.org/info/rfc7531>. 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 Appendix A. Acknowledgements
The author wishes to thank Tom Haynes of Primary Data for his role in 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 getting this effort started and his work in co-authoring the first
version of this document. version of the initial working group versioning document.
The author also wishes to thank Chuck Lever and Mike Kepfer of Oracle The author also wishes to thank Chuck Lever and Mike Kupfer of Oracle
for their thorough document reviews and many helpful suggestions. and Bruce Fields of Red Hat for their helpful reviews of this and
other versioning-related documents.
Author's Address Author's Address
David Noveck David Noveck
Hewlett Packard Enterprise Hewlett Packard Enterprise
165 Dascomb Road 165 Dascomb Road
Andover, MA 01810 Andover, MA 01810
US US
Phone: +1 978 474 2011 Phone: +1 978 474 2011
Email: davenoveck@gmail.com Email: davenoveck@gmail.com
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