NFSv4 Version Management
draft-ietf-nfsv4-versioning-01
The information below is for an old version of the document.
| Document | Type |
This is an older version of an Internet-Draft that was ultimately published as RFC 8178.
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|---|---|---|---|
| Author | David Noveck | ||
| Last updated | 2015-07-12 | ||
| RFC stream | Internet Engineering Task Force (IETF) | ||
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draft-ietf-nfsv4-versioning-01
NFSv4 D. Noveck
Internet-Draft HP
Intended status: Standards Track July 2, 2015
Expires: January 3, 2016
NFSv4 Version Management
draft-ietf-nfsv4-versioning-01
Abstract
This document describes the management of versioning within the NFSv4
family of protocols. It covers the creation of minor versions, the
addition of optional features to existing minor versions, and the
correction of flaws in features already published as Proposed
Standards. The rules relating to the construction of minor versions
and the interaction of minor version implementations that appear in
this document supersede the minor versioning rules in RFC5661.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on January 3, 2016.
Copyright Notice
Copyright (c) 2015 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
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the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Existing Minor Versions . . . . . . . . . . . . . . . . . 3
1.2. Updated NFSv4 Version Management Framework . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Consolidation of Version Management Rules . . . . . . . . . . 6
4. NFSv4 Protocol Changes . . . . . . . . . . . . . . . . . . . 7
4.1. XDR Extension . . . . . . . . . . . . . . . . . . . . . . 7
4.1.1. XDR Extension in General . . . . . . . . . . . . . . 8
4.1.2. Particulars of XDR Extension within NFSv4 . . . . . . 9
4.1.3. Rules for XDR Extension within NFSv4 . . . . . . . . 9
4.2. Non-XDR Protocol Changes . . . . . . . . . . . . . . . . 10
4.2.1. Field Interpretation and Use . . . . . . . . . . . . 10
4.2.2. Behavioral Changes . . . . . . . . . . . . . . . . . 11
4.2.3. Rules for non-XDR changes . . . . . . . . . . . . . . 11
4.3. Specification of Associated Protocols . . . . . . . . . . 12
4.3.1. Associated Protocols via pNFS Mapping Types . . . . . 12
4.3.2. Additional Forms of Associated Protocols . . . . . . 13
5. Documentation Approach . . . . . . . . . . . . . . . . . . . 14
5.1. Indexing material . . . . . . . . . . . . . . . . . . . . 14
6. NFSv4 Features . . . . . . . . . . . . . . . . . . . . . . . 14
6.1. Rules for Feature Construction . . . . . . . . . . . . . 15
6.2. Feature Statuses . . . . . . . . . . . . . . . . . . . . 15
6.3. Feature Discovery . . . . . . . . . . . . . . . . . . . . 16
6.4. Feature Specification Documents . . . . . . . . . . . . . 16
6.5. Feature Incorporation . . . . . . . . . . . . . . . . . . 17
7. Extensions within Minor Versions . . . . . . . . . . . . . . 18
8. Adding Features to Extensible Minor Versions . . . . . . . . 18
8.1. Use of Feature Specification Documents . . . . . . . . . 18
8.2. Compatibility Issues . . . . . . . . . . . . . . . . . . 19
8.2.1. Compatibility Issues for Messages Sent to Servers . . 19
8.2.2. Compatibility Issues for Messages Sent to Clients . . 21
8.3. Additional Documents to be Produced . . . . . . . . . . . 22
8.3.1. Minor Version Indexing Document . . . . . . . . . . . 22
8.3.2. Consolidated XDR Document . . . . . . . . . . . . . . 22
8.3.3. XDR Assignment Document . . . . . . . . . . . . . . . 23
8.3.4. Transition of Documents to RFC's . . . . . . . . . . 24
8.4. Relationship Between Minor Versioning and Extensions
within a Minor Version . . . . . . . . . . . . . . . . . 24
9. Minor Versions . . . . . . . . . . . . . . . . . . . . . . . 25
9.1. Minor Version Construction . . . . . . . . . . . . . . . 25
9.2. Minor Version Interaction . . . . . . . . . . . . . . . . 26
9.2.1. Minor Version Identifier Transfer Issues . . . . . . 26
9.2.2. Minor Version Compatibility Issues . . . . . . . . . 26
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9.3. Minor Version Documentation . . . . . . . . . . . . . . . 27
10. Correction of Existing Minor Versions and Features . . . . . 27
10.1. Documentation of XDR Changes . . . . . . . . . . . . . . 29
11. Security Considerations . . . . . . . . . . . . . . . . . . . 30
12. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 30
13. References . . . . . . . . . . . . . . . . . . . . . . . . . 31
13.1. Normative References . . . . . . . . . . . . . . . . . . 31
13.2. Informative References . . . . . . . . . . . . . . . . . 31
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 32
1. Introduction
To address the requirement for an NFS protocol that can evolve as the
need arises, the Network File System (NFS) version 4 (NFSv4) protocol
provides rules and a framework to allow for future changes via the
creation of new protocol versions and certain forms of modification
of existing versions. These version management rules allow changes
to be implemented in a way that maintains compatibility with existing
clients and servers.
1.1. Existing Minor Versions
Previously, all such changes had been part of new minor versions.
The COMPOUND procedure (see Section 14.2 of [RFC7530]) specifies the
minor version being used by the client in making requests. The
CB_COMPOUND (see Section 15.2 of [RFC7530]) procedure specifies the
minor version being used by the server on callback requests.
Each existing minor version has been specified by one or more
standards track RFCs:
o Minor version 0 is specified by [RFC7530] with the XDR description
appearing in [RFC7531].
o Minor version 1 is specified by [RFC5661]) with the XDR
description appearing in [RFC5662].
o Minor version 2 is specified by [NFSv42] (in terms of changes from
[RFC5661]). The XDR description appears in [NFSv42-dot-x]
1.2. Updated NFSv4 Version Management Framework
A number of significant changes from previous version management
practices should be noted here:
o Creation of a new minor version is no longer the only way in which
protocol changes may be made. Many changes can be done within the
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context of a single minor version. Creation of new minor versions
remains available to make other sorts of changes.
o Specification of future minor versions in the way that was done
for NFSv4.0 and NFSv4.1 (i.e. as a single document defining the
entire protocol) is no longer practical and should not be
attempted. All future minor versions will be documented by
specifying the differences between the minor version being
documented and the previous minor version. The documentation
framework discussed in Section 5 should be used.
This document starts by presenting the conceptual framework on which
NFSv4 versioning is built.
o First we discuss (in Section 4) the range of protocol changes that
NFSv4 versioning is to deal with.
o Then we discuss (in Section 6) how those changes are organized
into features.
Using this framework, we then look at the ways the NFSv4 protocol can
be changed.
o The addition of new features to existing minor versions is
discussed in Sections 7 and 8.
o New Minor versions can be constructed, as described in Section 9.
o Issues relating to the correction of protocol errors in existing
features and minor versions are discussed in Section 10.
2. Terminology
A basic familiarity with the NFSv4 terminology is assumed in this
document and the reader is pointed to [RFC7530].
The word "feature" has been used inconsistently in previous
treatments of NFSv4 versioning. Sometimes it is used to indicate a
specific XDR extension, while at other times it has been used to
indicate a set of multiple such extensions which are either supported
or not supported together.
In this document, we use the word "feature" in the second sense,
while individual protocol extensions which are incorporated in a
feature are referred to as "protocol elements." The term "feature
elements" is similar but it differs in that it includes changes in
field interpretation and use (Section 4.2.1) and protocol behavior
(See Section 4.2.2). See Section 6 for more details.
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We also need to introduce our vocabulary regarding specification of
features and minor versions. Given the ongoing shift to a finer-
grained documentation model, it is important to be clear here.
o The term "minor version definition document" denotes the principal
document defining a specific NFSv4 minor version. It may be in
the form of a complete protocol definition (e.g. [RFC7530],
[RFC5661]), a specification of changes relative to the previous
minor version (e.g. [NFSv42]), or in a document that specifies
the features to be included, either by referencing their
definition document normatively (see Section 9.3) or implicitly
(see Section 8).
o The term "minor version documentation" includes the minor version
definition document but also includes any corresponding XDR
definition documents if they are published separately (e.g.
[RFC7531], [RFC5662]), [NFSv42-dot-x]). Also included are
documents separately specifying features newly incorporated in the
minor version and the ancillary documents described in
Section 8.3.
o The term "feature definition document" denotes a document
describing a single feature or a set of closely related features.
As noted above, the keywords defined by [RFC2119] have special
meanings which this document intends to adhere to. However, due to
the nature of this document and some special circumstances, there are
some complexities to take note of:
o Where this document does not directly specify implementation
requirements, use of these capitalized term is often not
appropriate. Instead, what document writers need to do is stated
without these specialized terms. In any case, one should not
conclude that the normative character of this document is
compromised by this.
o In speaking of the previously existing possible statuses of
feature elements, the lower-case versions of these terms are used,
following the practice of [RFC3530]. This is despite the fact
that the corresponding uses of these terms in [RFC5661] was
switched to upper-case, for no clear reason, and similarly in the
case [RFC7530], presumably due to inertia.
o In speaking of the potential statuses of features, the words
"required" and "non-required" are used. By using the latter term,
we focus on the fact that the feature in question is not required
to be supported, while treating any potential recommendation for
support as out-of-scope.
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o When one of these upper-case keywords defined in [RFC2119] is used
in this document, it is in the context of a rule directed to an
implementer of NFSV4 minor versions, or in a quotation, sometimes
indirect, from another document.
3. Consolidation of Version Management Rules
In the past, the only existing version management rules were the
minor versioning rules that had been being maintained and specified
in the Standards Track RFCs which defined the individual minor
versions. As a result, these minor versioning rules were modified on
an ad hoc basis for each new minor version.
More recently, minor versioning rules were specified in [RFC5661]
while modifications to those rules were allowed in subsequent minor
versions.
This document defines a set of version management rules, including
rules for minor version construction. These rules apply to all
future changes to the NFSv4 protocol. The rules are subject to
change but any such change should be part of a standards track RFC
obsoleting or updating this document.
Rather than a single list of minor versioning rules, as in [RFC5661],
this document defines multiple sets of rules that deal with the
various forms of versioning provided for in the NFSv4 version
management framework.
o The kinds of changes that may be made are addressed in the rules
in Sections 4.1.3, 4.2.3, 4.3.1, and 4.3.2.
o Rules relating to the composition of changes into features are
addressed in Section 6.1
o Minor version construction, including rules applicable to features
which cannot be used as extensions to existing minor versions are
addressed in Section 9.1
o Minor version interaction rules are discussed in Sections 9.2.2
and 9.2.1.
This document supersedes minor versioning rules appearing in the
minor version specification RFC's, including those in [RFC5661]. As
a result, potential conflicts among these documents should be
addressed as follows:
o The specification of the actual protocols for minor versions
previously published as Proposed Standards take precedence over
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minor versioning rules in either this document or in the minor
version specification RFC's. In other words, if the transition
from version A to version B violates a minor versioning rule, the
version B protocol stays as it is. In particular, many of the
changes made for NFSV4.1 would not be allowed in the version
management framework defined here. See Section 4.2.3 for details.
o Since minor versioning rules #11 and #13 from [RFC5661] deal with
the interactions between multiple minor versions, the situation is
more complicated. See Section 9.2 for a discussion of these
issues, including how potential conflicts between rules are to be
resolved.
o Otherwise, any conflict between the version management rules in
this document and those in minor version specification RFC's are
to be resolved based on the treatment in this document. In
particular, corrections may be made as specified in Section 10 for
all previously specified minor versions and extensibility of
previously specified minor versions is to be handled in accord
with Section 8.
Future minor version specification documents should avoid specifying
minor versioning rules and reference this document in connection with
rules for NFSv4 version management.
4. NFSv4 Protocol Changes
Protocol changes that are to be managed within the NFSv4 versioning
framework may be of a number of types, which are discussed in the
sections below. Such changes include, but are not limited to,
changes in the underlying protocol XDR.
Each such change will be organized, documented and effected as part
of a given feature. The way this will be done depends on a number of
factors, including the types of changes included in the feature.
This subject is discussed in Section 6.5.
4.1. XDR Extension
When an NFSv4 version change requires a modification to the protocol
XDR, this is effected within a framework based on the idea of XDR
extension. This is opposed to transitions between major NFS versions
(including that between NFSv3 and NFSv4.0) in which the XDR for one
version was replaced by a different XDR for a newer version.
The use of XDR extension can facilitate compatibility between
different versions of the NFSv4 protocol. When XDR extension is used
to implement non-required features, the greatest degree of inter-
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version compatibility is obtained. For specifics regarding rules for
interversion compatibility, see Section 9.2.2.
4.1.1. XDR Extension in General
XDR extension allows an XDR description to be extended in a way which
retains the structure of all previously valid messages. If a base
XDR description is extended to create a second XDR description, the
following will be true for the second description to be a valid
extension of the first:
o The set of valid messages described by the extended definition is
a superset of that described by the first.
o Each message within the set of valid messages described by the
base definition is recognized as having exactly the same
structure/interpretation using the extended definition.
o Each message within the set of messages described as valid by the
extended definition but not the base definition must be
recognized, using the base definition, as part of an unsupported
extension.
An extension of a given XDR description consists of any of the
following:
o Addition of previously unspecified RPC operation codes.
o Addition of new, previously unused, values to existing enums.
o Addition of previously unassigned bit values to a flag word.
o Addition of new cases to existing switches, provided that the
existing switch did not contain a default case.
However, none of the following may happen:
o Deletion of existing RPC operations, enum values, flag bit values
and switch cases. Note that changes may be made to define use of
any of these as causing an error, as long as the XDR is
unaffected.
o Similarly, none of these items may be reused for a new purpose.
o Any change to the XDR-defined structure of existing requests or
replies other than those listed above.
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4.1.2. Particulars of XDR Extension within NFSv4
There are issues, particular to NFSv4, that affect the definition of
a valid XDR extension within NFSv4.
o Because NFSv4 has chosen to structure itself around compound
requests and callbacks, addition of previously unspecified RPC
operation codes is not allowed.
o Although they fit under the general category of enumerations,
operation codes (including those for callbacks) are so central to
the structure of NFSv4, that they merit special treatment.
o The fact that attribute sets are represented within nominally
opaque arrays calls for special handling.
4.1.3. Rules for XDR Extension within NFSv4
In the context of NFSv4, an extension of a given XDR description
consists of one or more of the following:
o Addition of previously unspecified operation codes, within the
framework established by COMPOUND and CB_COMPOUND.
o Addition of previously unspecified attributes.
o Addition of new, previously unused, values to existing enums.
o Addition of previously unassigned bit values to a flag word.
o Addition of new cases to existing switches, provided that the
existing switch did not contain a default case.
However, none of the following is allowed to happen:
o Deletion of existing RPC operations, enum values, flag bit values
and switch cases. Note that changes may be made to define use of
any of these as causing an error, as long as the XDR is
unaffected.
o Similarly, none of these items may be reused for a new purpose.
o Any change to the structure of existing requests or replies other
than those listed above.
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4.2. Non-XDR Protocol Changes
Despite the previous emphasis on XDR changes, additions and changes
to the NFSv4 protocols have not been limited to those that involve
changes (in the form of extensions) to the protocol XDR. Examples of
other sorts of changes have been taken from NFSv4.1.
4.2.1. Field Interpretation and Use
The XDR description of a protocol does not constitute a complete
description of the protocol. Therefore, versioning needs to consider
the role of changes in the use of fields, even when there is no
change to the underlying XDR.
Although any XDR element is potentially subject to a change in its
interpretation and use the likelihood of such change will vary with
the XDR type, as discussed below:.
o When XDR elements are defined as strings, rules regarding the
appropriate string values are specified in protocol specification
text with changes in such rules documented in minor version
definition documents.
Some types of strings within NFS4 are used in server names (in
location-related attributes), user and group names, and in the
names of file object within directories. Rules regarding what
strings are acceptable appear in [RFC7530] and [RFC5661] with the
role of the XDR limited to hints regarding UTF-8 and
capitalization issues via XDR typedefs.
o Fields that are XDR-defined as opaque elements and which are truly
opaque, do not raise versioning issues, except as regards inter-
version use, which is effectively foreclosed by the rules in
Section 9.2.
Note that sometimes a field will seem to be opaque but not
actually be fully opaque when considered carefully. For example,
the "other" field of stateids is defined as an opaque array, while
the specification text specially defines appropriate treatment
when the "other" field within it is either all zeros or all ones.
Given this context, creation or deletion of reserved values for
"special" stateids will be a protocol change which versioning
rules need to deal with.
o Some nominally opaque elements have external XDR definitions that
overlay the nominally opaque arrays. This technique is useful
when the same element may be used in several ways when a switched
union is not appropriate.
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For example, each pNFS mapping type provides its own XDR
definition for various pNFS-related fields defined in [RFC5661] as
opaque arrays. For more information about the handling of pNFS
within the NFSv4 versioning framework, see Section 4.3.1.
Another form of protocol change that changes how fields are
presented, without affecting the XDR occurs when there is a change in
the data elements which may be presented as RDMA chunks.
4.2.2. Behavioral Changes
Changes in the behavior of NFSv4 operations are possible, even if
there is no change in the underlying XDR or change to field
interpretation and use.
Many such behavioral changes have occurred in connection with the
addition of the session concept in NFSv4.1.
o Because exactly-once is semantics provided by sessions, the use of
owner-based sequence values in such operations as OPEN, LOCK,
LOCKU are now longer needed and the server is to ignore them.
o Because of the requirement to begin almost all COMPOUNDs with a
SEQUENCE operation, the semantics of previously defined operations
was changed and all formerly valid COMPOUNDs were defined as
resulting in errors.
o Because the clientid is inferable from a previous SEQUENCE
operation, the clientid is not needed in operations such as OPEN
and LOCK, and the client is required to pass a value of zero.
Also changes were made regarding the required server behavior as to
the interaction of the MODE and ACL attributes.
4.2.3. Rules for non-XDR changes
In the past (e.g. in [RFC5661]) there was often uncertainty about
whether any particular difference from NFSv4.0 was:
o A purely editorial change, which may be relevant to other minor
versions.
o The correction of a protocol mistake, best handled as described in
Section 10.
o A protocol improvement relevant to a new minor version or feature,
to be documented as described in Section 6.4.
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In order to avoid such situations, all such changes will be
documented as part of a feature, specifying the specific changes
relative to protocol versions that do not incorporate that new
feature. Also, to provide greater clarity about such changes, the
following rules apply:
o Any such change must be part of a feature in which there is also
an XDR extension present, to enable testing for presence of the
feature.
o No feature including such a change can be made required at initial
introduction.
o No feature including such a change can be introduced as an
extension. While the feature may be documented in a separate
feature definition document in such cases, that document should be
referenced normatively by the minor version specification.
o While it is allowed to include multiple such changes in the same
feature this should only be done if there is a good reason for all
of these to be included or not included together. Such changes
should not be included in the same feature simply because all such
changes were introduced in the same minor version.
4.3. Specification of Associated Protocols
The definition of ancillary protocols is a form of protocol extension
that is provided as part of pNFS and might be made available for
other uses in the future.
As in the case of pNFS, the NFSv4 protocol proper would provide the
basic framework for performing some protocol-related task, while
allowing multiple independent means of performing that task to be
defined. The version management considerations appropriate to
creating such additional forms of protocol extension are discussed in
Section 4.3.2
4.3.1. Associated Protocols via pNFS Mapping Types
pNFS is structured around the ability to define alternate mapping
types in addition to the one defined in [RFC5661], (e.g. [RFC5663],
[RFC5664]). Each mapping type specifies the data-transfer protocol
to be used to access data represented by layouts as well as mapping-
type-specific XDR definitions of layout-related data structures.
Specifying a new mapping type is an additional form of protocol
change within the NFSv4 version management framework. A feature
consisting of the new mapping type is not tied to a specific minor
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version. As explained in Section 7, it is available in multiple
minor versions upon publication.
4.3.2. Additional Forms of Associated Protocols
The same sort of approach used for pNFS might be used in other
circumstances where there is a clear need to standardize a set of
protocol-related requirements and where it is desirable, for various
reasons, to leave open the choice of mechanism by which those
requirements might be met.
Such cases might arise where the function to be performed is likely
to be too enmeshed with the structure of the file system
implementation to allow a single protocol mechanism to be specified.
In such cases, multiple approaches might themselves be standardized,
each fitting into a template established previously using any or all
of the elements used by pNFS:
o The establishment of a registry of identifiers for the
standardized mechanisms to satisfy the established requirements.
o Definition of data structures related to the function to be
performed to include both a mechanism identifier, and a nominally
opaque portion, the real format of which is to have a mechanism-
specific definition.
o The ability to specify multiple protocols to perform the same
function, which may include a minor version of NFSv4, a particular
use an established protocol, or a new protocol designed for the
purpose.
New instances of such a two-level approach might be established in
the future, subject to the following restrictions:
o That there is a feature establishing the requirements that the
associated protocols are to meet.
o That that feature is defined as an integral feature of a
particular minor version and not as an extension. This does not
exclude the feature being defined in a separate document to which
the minor version specification has a normative reference.
o That there be at least one instance of a specific protocol
mechanism meeting the established requirements. To limit
confusion, the requirements and the initial mechanism should be
defined in separate documents.
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The above are a minimal set of restrictions for establishing such an
additional extension mechanism. The working group may, as part of
defining the core feature establishing the extension mechanism may
specify further restrictions governing when minor versions may
incorporate particular instances of that extension mechanism.
5. Documentation Approach
Documentation of future changes to the NFSv4 protocol will use
feature specification documents as described in Section 6.4. There
are a number of ways in which such documents may be used, as
discussed in Section 6.5
5.1. Indexing material
The following items, referred to collectively as "Indexing material"
will be useful in many contexts. The reason for frequently
publishing such material is to prevent a situation in which large
numbers of documents must be scanned to find the most current
description of a particular protocol element.
o A table mapping operations and callbacks to the most recent
document containing a description of that operation.
o A table mapping attributes to the most recent document containing
a description of that attribute.
o A table giving, for each operation in the protocol, the errors
that may validly be returned for that operation. If possible, it
would be desirable to give, as does [RFC5661], the operations
which may validly return each particular error.
o A table giving for each operation, callback, and attribute and for
each feature element in a published extension giving its status
(required or not, or mandatory-to-not implement), and its
relationship to the feature which allows its inclusion (i.e.,
required for every implementation of the feature, or optional in
the presence of the feature). This would be similar to the
material in Section 14 of [NFSv42], expanded in scope to include
all feature elements.
6. NFSv4 Features
Individual changes, whether they are XDR extensions or other sorts of
changes, are organized in term of features. This is in order to
o allow the protocol documentation to more clearly specify what XDR
extensions and other changes must be supported together.
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o help the client determine which particular changes are present and
implemented by the server.
o to support the independent development and specification of
changes to the protocol, without artificially tying features
together in a paradigm based on minor versions.
o provide support for a feature-based documentation structure, as
described in Section 6.4.
6.1. Rules for Feature Construction
A feature consists of one or more valid NFSv4 changes, which work
together as a functional whole. The change elements may be of any of
the types described in Section 4 although the specific types of
changes will affect how the feature can be integrated in the NFSv4
protocol.
6.2. Feature Statuses
Each feature has one of three statuses with regard to each minor
version of which it might be a part.
o The feature is a required part of the minor version.
o The feature is not a required part of the minor version, but may
be implemented as part of that version..
o The feature is not a valid part of the minor version.
For features which have been previously defined as valid, this is
represented as being "mandatory to not implement" as opposed to
simply being undefined.
These statuses define whether a client implementing the minor version
has to be prepared for the existence of the feature and/or its non-
support by the server.
The working group is still free to make recommendations regarding the
desirability of server and client support for particular features in
particular minor versions in the minor version definition document,
or in other, presumably informational, documents.
In addition to feature status, there may be other constraints that
define when an implementation must or may support a feature. In
particular, support for one feature may require support for another,
or the presence of one feature may require that another feature not
be supported.
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6.3. Feature Discovery
The presence or absence of particular features may be determined in a
number of ways:
o For features which are required within a given minor version, a
client can determine whether the feature is supported by seeing if
the minor version is supported.
o For non-required features that contain an XDR-extending protocol
element, a client can try to use techniques described in
Section 8.2.1 to determine what features the server supports.
o For non-required features that do not contain an XDR-extending
protocol element, appropriate feature discovery facilities can be
constructed on an ad hoc basis by defining a non-required per-
server or per-fs boolean attribute to serve as an indication of
support. To address compatibility issues with earlier servers, an
appropriate default value to assume when the attribute is not
supported should be specified.
6.4. Feature Specification Documents
Features will be documented in the form of a working-group standards-
track document which define one or more features. Generally, only
closely related features should be defined in the same document.
The definition of each of the new features may include one or more
"feature elements" which change the protocol in any of the ways
discussed in Section 4. Feature elements include new operations,
callbacks, attributes, and enumeration values. The functionality of
some existing operations may be extended by the addition of new flags
bits in existing flag words, by new cases in existing switched
unions, and by valid semantic changes to existing operations.
Such feature definition documents would contain a number of items,
following the pattern of the NFSv4.2 specification. The only
difference would be that while the NFSv4.2 specification defines a
number of features to be incorporated into NFSv4.2, the feature
definition documents would each define a single feature, or a small
set of closely related features.
In addition to a general explanation of the feature in question, the
items to be included in such feature definition documents would be:
o Description of new operations (corresponding to Sections 16 and 17
of [NFSv42]).
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o Description of any modified operations (corresponding to
Section 15 of [NFSv42]).
o Description of new attributes (corresponding to Section 13 of
[NFSv42]).
o Description of any added error codes (corresponding to
Section 12.1 of [NFSv42]).
o All operation descriptions, whether for new or modified
operations, should indicate when operations or the corresponding
results may be presented as RDMA chunks.
o A summary description of all changes made by this feature to the
XDR definition of the protocol, including operation codes,
attribute numbers, added flag bits and enumeration values, and
request and response structures for new operations together with
the other XDR extensions needed to support them.
o A listing giving the valid errors for each new operation and
callback (corresponds to Sections 12.2 and 12.3 of [NFSv42]).
o A table giving for each new feature element its status (required
or not) and its relationship to the feature(s) being described
(i.e., required for every implementation of the feature, or
optional in the presence of the feature). This would be similar
to the material in Section 14 of [NFSv42] but restricted to the
feature(s) defined in the document and expanded in scope to
include all feature elements.
o All of the additional Sections required for RFC publication, such
as "Security Considerations", "IANA considerations", etc.
6.5. Feature Incorporation
All protocol changes will be organized, documented and effected as
part of a given feature. This includes XDR extension and the various
sorts of non-XDR-based changes allowed.
Such features may be made part of the protocol in a number of ways:
o In new minor versions, as discussed in Section 9.
o In separately documented new features. When new features are non-
required and do not include any non-XDR-based changes, they may be
incorporated in an extensible minor version under construction.
See Section 8 for details.
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o When appropriate compatibility arrangement are in effect, they may
be used to correct protocol problems in already approved minor
versions and features. See Section 10 for details.
7. Extensions within Minor Versions
The NFSv4 version management framework allows, with certain
restrictions, features to be added to existing minor versions
o In the case of features which consist only of a pNFS mapping type,
the protocol may be extended by publishing the new mapping type
definition as a Proposed Standard. This effects an extension to
all minor versions in which pNFS is a valid feature.
Similar extension facilities could be made available if additional
pNFS-like extension frameworks were created (See Section 4.3.2).
o Minor versions designated as extensible (see Section 8) may be
extended by the publication of a standards-track document defining
the additional feature. Details are set out in Section 8. The
features to be added are considered non-required in the extensible
minor version and must consist only of valid XDR-based extensions
8. Adding Features to Extensible Minor Versions
Addition of features to an extensible minor version will take
advantage of the existing NFSv4 infrastructure that allows optional
features to be added to new minor versions, but without in this case
requiring any change in the minor version number. Adding features in
this way will enable compatibility with existing clients and servers,
who may be unaware of the new feature.
8.1. Use of Feature Specification Documents
Each such extension will be in the form of a working-group standards-
track document which defines one or more new non-required features.
The definition of each of the new feature may include one or more
"protocol elements" which extend the existing XDR as already
discussed (in Section 4.1). Other sorts of XDR modification are not
allowed. Protocol elements include new operations, callbacks,
attributes, and enumeration values. The functionality of some
existing operations may be extended by the addition of new flags bits
in existing flag words and new cases in existing switched unions.
New error codes may be added but the set of valid error codes to be
returned by an operation is fixed, except that existing operations
may return new errors to respond to situations that only arise when
previously unused flag bits are set or when extensions to a switched
union are used.
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Each such additional feature will become, for all intents and
purposes, part of the current NFSv4 minor version upon publication of
the description as a Proposed Standard, enabling such extensions to
be used by new client and server implementations without, as
previously required, a change in the value of the minor version field
within the COMPOUND operation.
The working group has two occasions to make sure that such features
are appropriate ones:
o At the time the feature definition document becomes a working
group document, the working group needs to determine, in addition
to the feature's general compatibility with NFSv4, that the XDR
assignments (i.e. additional values for operation callback and
attribute numbers, and for new flags and switch values to be added
to existing operations) associated with the new feature are
complete and do not conflict with those in the existing protocol
or those currently under development.
o At the time the working group document is complete, the working
group, in addition to normal document review, can and should look
at what prototype implementations of the feature have been done
and use that information to determine the work-ability and
maturity of the feature.
8.2. Compatibility Issues
Because the receiver of a message may be unaware of the existence of
a specific extension, certain compatibility rules need to be
observed. In some cases (e.g., addition of new operations or
callbacks or addition of new arms to an existing switched union)
older clients or servers may be unable to do XDR parsing on an
extension of whose existence they are unaware. In other cases (e.g.,
error returns) there are no XDR parsing issues but existing clients
and servers may have expectations as to what may validly be returned.
Detailed discussion of these compatibility issues appears below:
o Issues related to messages sent to the server are discussed in
Section 8.2.1.
o Issues related to messages sent to the client are discussed in
Section 8.2.2.
8.2.1. Compatibility Issues for Messages Sent to Servers
This section deals with compatibility issues that relate to messages
sent to the server, i.e., requests and replies to callbacks. In the
case of requests, it is the responsibility of the client to determine
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whether the server supports the extension in question before sending
a request containing it for any purpose other than determining
whether the server is aware of the extension. In the case of
callback replies, the server demonstrates its awareness of proper
parsing for callback replies by sending the associated callback.
Regarding the handling of requests:
o Existing server implementations will return NFS4ERR_NOTSUPP or
NFS4ERR_OP_ILLEGAL in response to any use of a new operation,
allowing the client to determine that the requested operation (and
potentially the feature in question) is not supported by the
server.
o Clients can determine whether particular new attributes are
supported by a given server by examining the value returned when
the supported_attr attribute is interrogated. Clients need to do
this before attempting to use attributes defined in an extension
since they cannot depend on the server returning
NFS4ERRATTRNOTSUPP for requests which include a mask bit
corresponding to a previously unspecified attribute number (as
opposed to one which is defined but unsupported).
o Existing server implementations that do not recognize new flag
bits will return NFS4ERR_INVAL, enabling the client to determine
that the new flag value is not supported by the server.
o Existing server implementations that do not recognize the new arm
of a switched union in a request will return NFS4ERR_INVAL or
NFS4ERR_UNION_NOTSUPP, enabling the client to determine that the
new union arm is not supported by the server.
Regarding the handling of responses to callbacks:
o Error values returned to the server for all callbacks that do not
use new features will only be those previously allowed. Only when
the server uses a new extension feature can a previously invalid
error value be returned.
o Callback replies may only include a new arm of an existing
switched union when the server, typically in the callback being
responded to, has used a feature element associated with the
feature that defined the new switched union arm.
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8.2.2. Compatibility Issues for Messages Sent to Clients
This sections deals with compatibility issues that relate to messages
sent to clients, i.e., request replies and callbacks. In both cases,
extensions are only sent to clients that have demonstrated awareness
of the extensions in question by using an extension associated with
the same feature.
Regarding the handling of request replies:
o Error values returned to the client for all requests that do not
use new features will only be those previously allowed. Only when
the server uses a new extension feature can a previously invalid
error value be returned.
o Replies may only include a new arm of an existing switched union
when the server, typically in the request being responded to, has
used a feature element associated with the feature that defined
the new switched union arm.
Regarding the handling of callback requests, the server needs to be
sure that it only sends callbacks to those clients prepared to
receive and parse them.
o In most cases, the new callback will be part of a feature that
contains new (forward) operations as well. When this is the case,
the feature specification will specify the operations whose
receipt by a server is sufficient to indicate that the client
issuing them is prepared to accept and parse the associated
callbacks.
o For callbacks associated with features that have no new operations
defined, the feature specification should define some way for a
client to indicate that it is prepared to accept and parse
callbacks that are part of the extension. For example, a flag bit
in the EXCHANGE_ID request may serve this purpose.
o In both of the above cases, the ability to accept and parse the
specified callback is considered separate from support for the
callback. The feature specification will indicate whether support
for the callback is required whenever the feature is used by the
client. In cases in which support is not required, the client is
free to return NFS4ERR_NOTSUPP upon receiving the callback.
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8.3. Additional Documents to be Produced
Additional documents will be required from time to time. These
documents will eventually become RFC's (informational or standards
track as described below), but the work of the working group and of
implementers developing features will be facilitated by a progression
of document drafts that incorporate information about new features
that are being developed or have been approved as Proposed Standards.
8.3.1. Minor Version Indexing Document
One document will organize existing material for a minor version
undergoing extension so that implementers will not have to scan a
large set of feature definition documents or minor version
specifications to find information being sought. Successive drafts
of this document will serve as an index to the current state of the
extensible minor version. Some desirable elements of this indexing
document would include:
o A list of all feature definition documents that have been approved
as working group documents but have not yet been approved as
Proposed Standards.
o All of the items of indexing material (see Section 5.1)
appropriately adjusted to reflect the contents of all extensions
accepted as Proposed Standards.
The frequency of updates for this document will be affected by
implementer needs and the ability to easily generate document drafts,
preferably by automated means. The most desirable situation is one
in which a new draft is available soon after each feature reaches the
status of a Proposed Standard.
8.3.2. Consolidated XDR Document
This document will consist of an updated XDR for the protocol as a
whole including feature elements from all features and minor versions
accepted as Proposed Standards.
A new draft should be prepared whenever a new feature within an
extensible minor version is accepted as a Proposed Standard. In most
cases, feature developers will be using a suitable XDR which can then
be reviewed and published. In cases in which multiple features reach
Proposed Standard status at approximately the same time, a merge of
the XDR changes made by each feature may be necessary.
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8.3.3. XDR Assignment Document
This document will contain consolidated lists of XDR value
assignments that are relevant to the protocol extension process. It
should contain lists of assignments for:
o operation codes (separate lists for forward operations and for
callbacks)
o attribute numbers
o error codes
o bits within flag words that have been extended since they were
first introduced.
o enumeration values for enumerations which have been extended since
they were first introduced.
For each set of assignments, the individual assignments may be of
three types:
1. permanent assignments associated with a minor version or a
feature extension that has achieved Proposed Standard status.
These assignments are permanent in that the assigned value will
never be re-used. However, a subsequent minor version may define
some or all feature elements associated with a feature to be
Mandatory to NOT support.
2. provisional assignments associated with a feature under
development (i.e., one which has been approved as a working group
document but has not been approved as a Proposed Standard).
Provisional assignments are not are not permanent and the values
assigned can be re-used in certain circumstances. In particular,
when a feature with provisional assignments is not progressing
toward the goal of eventual Proposed Standard status, the working
group can judge the feature effort to have been abandoned,
allowing the codes formerly provisionally allocated to be
reclaimed and reassigned.
3. definition of individual assignments or ranges reserved for
experimental use.
A new draft of this document should be produced, whenever:
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o A minor version or feature specification is accepted as a Proposed
Standard.
o A new feature is accepted for development and a draft of the
corresponding working-group standards-track document is produced
o A feature previously accepted for development is abandoned.
o The working group decides to make some change in assignments for
experimental use.
8.3.4. Transition of Documents to RFC's
Each of these documents should be published as an RFC soon after the
minor version in question ceases to be considered extensible.
Typically this will happen when the working group makes the
specification for the subsequent minor version into a working group
document. Some specifics about the individual documents are listed
below:
o The most current draft of the indexing document for the minor
version would be published as an informational RFC.
o The most current draft of the consolidated XDR document should be
published as a standards-track RFC. It would update the initial
specification of the minor version
o The most recent draft of the XDR assignment document should be
published as an informational RFC.
Handling of these documents in the event of a post-approval XDR
correction is discussed in Section 10.1
8.4. Relationship Between Minor Versioning and Extensions within a
Minor Version
Extensibility of minor versions are governed by the following rules:
o Minor versions zero and one are not extensible. Each has a fixed
set of non-required features as described in [RFC7530] and
[RFC5661].
o Minor versions beyond one are presumed extensible as discussed
herein. However, any statement within the minor version
specification disallowing extension will cause that minor version
to be considered non-extensible.
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o No new feature may be added to a minor version may be made once
the specification document for a subsequent minor version becomes
a working group standards-track document.
Even when a minor version is non-extensible, or when a previous minor
version is closed to further extension, the features that it contains
are still subject to updates to effect protocol corrections. In many
cases, making an XDR change, in the form of an extension will be the
best way of correcting an issue. See Section 10 for details.
While making minor versions extensible will decrease the frequency of
new minor versions, it will not eliminate the need for them. In
particular:
o A new minor version will be required for any change in the status
of a feature element (i.e., an operation, callback, attribute,
added flag or switch case). For example, changes which make
feature elements Recommended, Required or Mandatory to Not
Implement will require a minor version.
o Any incompatible semantic change in the required or allowed
processing of an existing operation or attribute will require a
minor version.
o Any change that extends the set of errors returned that an
existing operation, with the exception noted above. New errors
may be added when the conditions that give rise to these new
errors cannot arise as long as new flag bits or switched union
arms are not used. In these cases, it is clear that existing
clients cannot receive these errors.
o Any change in the mapping of feature elements to features will
require a minor version. For example, if a feature is to be split
into two separate features clients would no longer be able to
infer support for one operation from support for the other, in the
same way that had been done previously, invalidating logic in
existing clients
9. Minor Versions
9.1. Minor Version Construction
In addition to the sorts of non-required features that may be made in
the context of extensible minor version, a number of other sorts of
changes may be made in a new minor version. Because such changes
have the potential to disrupt inter-version such changes should only
be made after careful consideration of the effects on interversion
interoperability.
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o Addition of new features that incorporate any of the non-XDR-based
changes discussed in Sections 4.2.1 and 4.2.2. Such features must
always be introduced as non-required.
o Addition of required new features.
o Changes to the status of existing features or to inter-feature
constraints.
o Changes to feature organization. Such changes may have the effect
of making support for some change element obligatory in
circumstances when it had not been previously.
9.2. Minor Version Interaction
This section addresses issues related to rules #11 and #13 in the
minor versioning rules in [RFC5661]. With regard to the supersession
of minor versioning rules, the treatment here overrides that in
[RFC5661] when either of the potentially interacting minor versions
has not yet been published as a Proposed Standard.
Note that these rules are the only ones directed to minor version
implementers, rather than to those specifying new minor versions.
9.2.1. Minor Version Identifier Transfer Issues
Each relationship between a client instance and a server instance, as
represented by a clientid, is to be devoted to a single minor
version. If a server detects that a COMPOUND with an inappropriate
minor version is being used, it MUST reject the request. In doing
so, it may return either NFS4ERR_BAD_CLIENTID or
NFS4RR_MINOR_VERS_MISMATCH.
As a result of the above, the client has the assurance that the set
of required and allowed features will not change within the context
of a single clientid. Server implementations MUST ensure that the
set of supported features does not change within such a context.
9.2.2. Minor Version Compatibility Issues
It is desirable for client and server implementations to support a
wide range of minor versions. The difficulty of doing so can be
affected by choices made by the working group in defining those minor
versions.
Within a set of minor versions that have exactly the same set of
required features, it is relatively easy for clients and servers to
provide appropriate compatibility and they are well-advised to do so.
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Servers SHOULD accept any minor version number within the range and
return NFS4ERR_OPNOTSUPP or NFS4ERR_OP_ILLEGAL for non-supported
operations based on the version number.
Clients SHOULD deal with an NFS4ERR_MINOR_VERS_MISMATCH error by
searching the appropriate minor version range for one the server will
accept.
Servers and clients MAY deal with changes in the set of required
features by supporting at least the union of the set of required
features for all minor versions within the range to be supported.
This may involve logic to specifically withhold support for features
when not allowed for a particular minor version.
9.3. Minor Version Documentation
Minor versions should be documented by specifying and explaining the
changes made relative to the previous minor version.
Features added to the minor version should be documented in their own
feature specification documents and normatively referenced.
Changes to the status or organization of existing features should be
documented by presenting a summary of the status of all existing
protocol elements, their relationship to non-required features, and
any relevant feature dependencies.
In addition, to avoid situation where a large number of minor
versions must be scanned to find the most recent valid treatment of a
specific protocol element, minor version definition documents will
contain the indexing material described in Section 5.1.
10. Correction of Existing Minor Versions and Features
The possibility always exists that there will be a need to correct an
existing feature in some way, after the acceptance of that feature or
a minor version containing it, as a Proposed Standard. While the
working group can reduce the probability of such situations arising
by waiting for running code before considering a feature as done, it
cannot reduce the probability to zero. As features are used more
extensively and interact with other features, previously unseen flaws
may be discovered and will need to be corrected.
Such corrections are best done in a bis document updating the RFC
defining the relevant feature definition document or minor version
specification. In making such a correction, the working will have to
carefully consider how to assure interoperability with older clients
and servers.
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Often, corrections can be done without changing the protocol XDR.
However, incompatible changes in server or client behavior should not
be mandated in order to avoid XDR changes. When XDR changes are
necessary as part of correcting a flaw, these should be done in a
manner similar to that used when implementing new minor versions or
features within them. In particular,
o Existing XDR structures may not be modified or deleted.
o XDR extensions may be used to correct existing protocol facilities
in a manner similar to those used to add additional optional
features. Such corrections may be done in an otherwise non-
extensible minor version, if the working group judges it
appropriate.
o When a correction is made to a non-required feature, the result is
similar to a situation in which there are two independent non-
required features. A server may choose to implement either or
both.
o When a correction is made to a required feature, the situation
becomes one in which neither the old nor the new version of the
feature is required. Instead, it is required that a server
support at least one of the two, while each is individually non-
required. Although use of the corrected version is ultimately
better, and may be recommended, it should not be described as
"RECOMMENDED", since the choice of which version to support if
only one is supported will depend on the needs of clients, which
may be slow to adopt the updated version.
o In all of the cases above, it is appropriate that the old version
of the feature, be considered obsolescent, with the expectation
that the working group might, in a later minor version, decide
that the older version is to become mandatory to not implement.
Issues related to the effect of XDR corrections on existing
documents, including co-ordination with other minor versions, are
discussed in Section 10.1.
By doing things this way, the protocol with the XDR modification can
accommodate clients and servers that support either the corrected or
the uncorrected version of the protocol and also clients and servers
aware of and capable of supporting both alternatives.
o A client that supports only the earlier version of the feature
(i.e., an older unfixed client) can determine whether the server
it is connecting to supports the older version of feature. It is
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capable of interoperating with older servers that support only the
unfixed protocol as well as ones that support both versions.
o A client that supports only the corrected version of the feature
(i.e., a new or updated client) can determine whether the server
it is connecting to supports the newer version of the feature. It
is capable of interoperating with newer servers that support only
the updated feature as well as ones that support both versions.
o A client that supports both the older and newer version of the
feature can determine which version of the particular feature is
supported by the server it is working with.
o A server that supports only the earlier version of the feature
(i.e., an older unfixed server) can only successfully interoperate
with older clients. However newer clients can easily determine
that the feature cannot be used on that server.
o A server that supports only the newer version of the feature
(i.e., a new or updated server) can only successfully interoperate
with newer clients. However, older clients can easily determine
that the feature cannot be used on that server. In the case of
non-required features, clients can be expected to deal with non-
support of that particular feature.
o A server that supports both the older and newer versions of the
feature can interoperate with all client variants.
By using extensions in this manner, the protocol creates a clear path
which preserves the functioning of existing clients and servers and
allowing client and server implementers to adopt the new version of
the feature at a reasonable pace.
10.1. Documentation of XDR Changes
In the event of an XDR correction, as discussed above, some document
updates will be required. For the purposes of this discussion we
call the minor version for which XDR correction is required minor
version X and the minor version on which development is occurring
minor version Y.
The following discusses the specific updated documents which could be
required:
o The specification of the feature in question will have to be
updated to explain the issue, how it was fixed, and the
compatibility and upgrade strategy. Normally this will require an
RFC updating the associated feature specification document.
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However, in the case of a correction to a feature documented in a
minor version definition document, the RFC will update that
document instead.
o An updated XDR for minor version X will be produced and will be
published as a updated to the minor version specification RFC for
minor version X.
When the correction is to feature documented in a minor version
definition, a single RFC will contain both updates to the minor
version specification RFC.
o An updated minor version indexing document for minor version X is
desirable but not absolutely necessary.
The question of updated minor version indexing documents for minor
versions between X and Y should be addressed by the working group
on a case-by-case basis.
o An updated XDR assignment document will be required. It should be
based on the most recent such document associated with minor
version Y and will serve as the basis for later XDR assignment
drafts for minor version Y.
The informational RFC's associated with minor version Y (version
indexing document and XDR assignment document) will contain the
effects of the correction when published. Similarly, the minor
version specification RFC will contain the XDR changes associated
with the correction.
11. Security Considerations
Since no substantive protocol changes are proposed here, no security
considerations apply.
As features and minor versions are designed and specified in
standards-track documents, their security issues will be addressed
and each RFC candidate will receive the appropriate security review
from the NFSv4 working group and IESG.
12. IANA Considerations
The current document does not require any actions by IANA.
Depending on decisions that the working group makes about how to
address the issues raised in this document, future documents may
require actions by IANA.
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13. References
13.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
13.2. Informative References
[NFSv42] Haynes, T., Ed., "NFS Version 4 Minor Version 2", April
2015, <http://www.ietf.org/id/
draft-ietf-nfsv4-minorversion2-38.txt>.
Work in progress.
[NFSv42-dot-x]
Haynes, T., Ed., "NFS Version 4 Minor Version 2 Protocol
External Data Representation Standard (XDR) Description",
April 2015, <http://www.ietf.org/id/
draft-ietf-nfsv4-minorversion2-dot-x-38.txt>.
Work in progress.
[RFC3530] Shepler, S., Callaghan, B., Robinson, D., Thurlow, R.,
Beame, C., Eisler, M., and D. Noveck, "Network File System
(NFS) version 4 Protocol", RFC 3530, April 2003.
[RFC5661] Shepler, S., Eisler, M., and D. Noveck, "Network File
System (NFS) Version 4 Minor Version 1 Protocol", RFC
5661, January 2010.
[RFC5662] Shepler, S., Eisler, M., and D. Noveck, "Network File
System (NFS) Version 4 Minor Version 1 External Data
Representation Standard (XDR) Description", RFC 5662,
January 2010.
[RFC5663] Black, D., Fridella, S., and J. Glasgow, "Parallel NFS
(pNFS) Block/Volume Layout", RFC 5663, January 2010.
[RFC5664] Halevy, B., Welch, B., and J. Zelenka, "Object-Based
Parallel NFS (pNFS) Operations", RFC 5664, January 2010.
[RFC7530] Haynes, T. and D. Noveck, "Network File System (NFS)
Version 4 Protocol", RFC 7530, March 2015.
[RFC7531] Haynes, T. and D. Noveck, "Network File System (NFS)
Version 4 External Data Representation Standard (XDR)
Description", RFC 7531, March 2015.
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Author's Address
David Noveck
Hewlett-Packard
165 Dascomb Road
Andover, MA 01810
US
Phone: +1 978 474 2011
Email: davenoveck@gmail.com
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