NFSv4 T. Haynes
Internet-Draft Primary Data
Intended status: Standards Track D. Noveck, Ed.
Expires: April 9, 2015
October 06, 2014
Minor versioning Rules for NFSv4
draft-haynes-nfsv4-versioning-00
Abstract
This document specifies the minor versioning rules for NFSv4. It
also specifies how those minor versioning rules may be modified.
Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
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
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Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
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This Internet-Draft will expire on April 9, 2015.
Copyright Notice
Copyright (c) 2014 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
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publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
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to this document. Code Components extracted from this document must
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described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 2
3. Modifying the minor version rules . . . . . . . . . . . . . . 3
4. The minor versioning rules . . . . . . . . . . . . . . . . . 3
5. Extensions within Minor Versions . . . . . . . . . . . . . . 6
5.1. Feature Specification Documents . . . . . . . . . . . . . 6
5.2. Additional Informational Documents . . . . . . . . . . . 9
5.3. Relationship Between Minor versioning and Extensions
within a Minor Version . . . . . . . . . . . . . . . . . 10
6. Security Considerations . . . . . . . . . . . . . . . . . . . 11
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 11
8.1. Normative References . . . . . . . . . . . . . . . . . . 11
8.2. Informative References . . . . . . . . . . . . . . . . . 11
Appendix A. Acknowledgments . . . . . . . . . . . . . . . . . . 11
Appendix B. RFC Editor Notes . . . . . . . . . . . . . . . . . . 11
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 12
1. Introduction
To address the requirement of an NFS protocol that can evolve as the
need arises, the Network File System (NFS) version 4 (NFSv4) protocol
contains the rules and framework to allow for future minor changes or
versioning.
The base assumption with respect to minor versioning is that any
future accepted minor version will be documented in one or more
Standards Track RFCs. Minor version 0 of the NFSv4 protocol is
represented by [RFC3530], minor version 1 by [RFC5661], and minor
version 2 by [NFSv42]. The COMPOUND (see Section 14.2 of [RFC3530])
and CB_COMPOUND (see Section 15.2 of [RFC3530]) procedures support
the encoding of the minor version being requested by the client.
2. Terminology
A basic familiarity with the NFSv4 terminology is assumed in this
document, the reader is pointed to [RFC3530].
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3. Modifying the minor version rules
The minor versioning rules had been being maintained inside the
various Standards Track RFCs, which had the impact of the minor
versioning rules being modified as needed per release of the minor
versions. The rules for minor versions SHOULD stand outside the
minor versions and be tracked by their own Standard Track RFCs. As
such, all modifications to the minor versioning rules MUST be
documented not in the minor version documents, but in Standard Track
RFCs which are focused entirely on the minor versioning rules
themselves.
4. The minor versioning rules
The following items represent the basic rules for the development of
minor versions.
1. Procedures are not added or deleted.
To maintain the general Remote Procedure Call (RPC) model, NFSv4
minor versions will not add to or delete procedures from the NFS
program.
2. Minor versions may add operations to the COMPOUND and
CB_COMPOUND procedures.
The addition of operations to the COMPOUND and CB_COMPOUND
procedures does not affect the RPC model.
* Minor versions may append attributes to the bitmap4 that
represents sets of attributes and to the fattr4 that
represents sets of attribute values.
This allows for the expansion of the attribute model to allow
for future growth or adaptation.
* Minor version X must append any new attributes after the last
documented attribute.
Since attribute results are specified as an opaque array of
per-attribute, XDR-encoded results, the complexity of adding
new attributes in the midst of the current definitions would
be too burdensome.
3. Minor versions must not modify the structure of an existing
operation's arguments or results.
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Again, the complexity of handling multiple structure definitions
for a single operation is too burdensome. New operations should
be added instead of modifying existing structures for a minor
version.
This rule does not preclude the following adaptations in a minor
version:
* adding bits to flag fields, such as new attributes to
GETATTR's bitmap4 data type, and providing corresponding
variants of opaque arrays, such as a notify4 used together
with such bitmaps
* adding bits to existing attributes like Access Control Lists
(ACL) that have flag words
* extending enumerated types (including NFS4ERR_*) with new
values
* adding cases to a switched union
4. Note that when adding new cases to a switched union, a minor
version must not make new cases be REQUIRED. While the
encapsulating operation may be REQUIRED, the new cases (the
specific arm of the discriminated union) is not. The error code
NFS4ERR_UNION_NOTSUPP is used to notify the client when the
server does not support such a case.
5. Minor versions must not modify the structure of existing
attributes.
6. Minor versions must not delete operations.
This prevents the potential reuse of a particular operation
"slot" in a future minor version.
7. Minor versions must not delete attributes.
8. Minor versions must not delete flag bits or enumeration values.
9. Minor versions may declare an operation MUST NOT be implemented.
Specifying that an operation MUST NOT be implemented is
equivalent to obsoleting an operation. For the client, it means
that the operation MUST NOT be sent to the server. For the
server, an NFS error can be returned as opposed to "dropping"
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the request as an XDR decode error. This approach allows for
the obsolescence of an operation while maintaining its structure
so that a future minor version can reintroduce the operation.
1. Minor versions may declare that an attribute MUST NOT be
implemented.
2. Minor versions may declare that a flag bit or enumeration
value MUST NOT be implemented.
10. Minor versions may declare an operation to be OBSOLESCENT, which
indicates an intention to remove the operation (i.e., make it
MANDATORY TO NOT implement) in a subsequent minor version. Such
labeling is separate from the question of whether the operation
is REQUIRED or RECOMMENDED or OPTIONAL in the current minor
version. An operation may be both REQUIRED for the given minor
version and marked OBSOLESCENT, with the expectation that it
will be MANDATORY TO NOT implement in the next (or other
subsequent) minor version.
11. Note that the early notification of operation obsolescence is
put in place to mitigate the effects of design and
implementation mistakes, and to allow protocol development to
adapt to unexpected changes in the pace of implementation. Even
if an operation is marked OBSOLESCENT in a given minor version,
it may end up not being marked MANDATORY TO NOT implement in the
next minor version. In unusual circumstances, it might not be
marked OBSOLESCENT in a subsequent minor version, and never
become MANDATORY TO NOT implement.
12. Minor versions may downgrade features from REQUIRED to
RECOMMENDED, from RECOMMENDED to OPTIONAL, or from OPTIONAL to
MANDATORY TO NOT implement. Also, if a feature was marked as
OBSOLESCENT in the prior minor version, it may be downgraded
from REQUIRED to OPTIONAL from RECOMMENDED to MANDATORY TO NOT
implement, or from REQUIRED to MANDATORY TO NOT implement.
13. Minor versions may upgrade features from OPTIONAL to
RECOMMENDED, or RECOMMENDED to REQUIRED. Also, if a feature was
marked as OBSOLESCENT in the prior minor version, it may be
upgraded to not be OBSOLESCENT.
14. A client and server that support minor version X SHOULD support
minor versions 0 through X-1 as well.
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15. Except for infrastructural changes, a minor version must not
introduce REQUIRED new features.
This rule allows for the introduction of new functionality and
forces the use of implementation experience before designating a
feature as REQUIRED. On the other hand, some classes of
features are infrastructural and have broad effects. Allowing
infrastructural features to be RECOMMENDED or OPTIONAL
complicates implementation of the minor version.
16. A client MUST NOT attempt to use a stateid, filehandle, or
similar returned object from the COMPOUND procedure with minor
version X for another COMPOUND procedure with minor version Y,
where X != Y.
5. Extensions within Minor Versions
An important goal of this document is to enable extensions to be made
to the features included in an existing minor version, without the
overhead attendant upon the creation of an entirely new minor
version.
5.1. Feature Specification Documents
Each such extension will be in the form of a working-group standards-
track document which defines a new optional feature. The definition
of the new feature may include one or more "feature elements" which
add to the existing XDR in ways already used in creating new minor
versions. Other sorts of XDR modification are not allowed. 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 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.
Such an 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 minorversion field within the
COMPOUND operation.
The working group has two occasions to make sure that such features
are appropriate ones:
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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 of the
feature.
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 in NFSv4.2, the feature
definition documents would each define a single feature.
Such feature definition documents would contain a number of 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]).
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 A summary description 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 operation 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 (always
OPTIONAL), and its relationship to the feature being described
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(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 it is restricted to
a single feature and expanded in scope to include all feature
elements.
o All of the sections required for RFC publication, such as
"Security Considerations", "IANA considerations", etc.
Such feature definition documents would contain a number of Addition
of features to an existing 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 the version number. This will enable compatibility with
existing clients and servers. In particular:
o Existing server implementations will return NFS4ERR_NOTSUPP or
NFS4ERR_OP_ILLEGAL in response to any use of the new operation,
allowing the client to determine that the requested (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 as the
value of the supported_attr attribute.
o New callbacks will only be sent to clients that have used the new
features associated with them, allowing existing clients to be
unaware of their existence.
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 will return will return NFS4ERR_INVAL or
NFS4ERR_UNION_NOTSUPP, enabling the client to determine that the
the new union arm is not supported by the server.
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 client uses a new feature will a previously invalid error
value be returned.
Given that some existing servers may have XDR parsing implementations
that cannot easily accommodate previously unknown operations or
switched union arms, clients should carefully determine whether
particular features are supported by the server before proceeding to
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use them and need to be prepared to treat NFS4ERR_BADXDR as
indicating non-support of a new operation or switched union arm where
server support for a particular feature is being tested.
5.2. Additional Informational Documents
Additional documents will be required from time to time. The purpose
of these documents will be to organize existing material so that an
implementer will not have to scan a large set of feature definition
document or minor version specification to find information being
sought.
The frequency of updates for such documents will be affected by
implementer needs and the ability to easily generate such documents,
preferably by automated means. These documents will be informational
documents whose purpose is to simplify use of the standards-track
documents. Some desirable elements would include:
o An updated XDR for the protocol as a whole including feature
elements from all features accepted as Proposed Standards.
o A consolidated list of XDR assignments of values (e.g., operation
codes, attribute numbers, error codes, new flag bits, enumeration
extensions) for all features under development (i.e., accepted as
working-group standards-track documents but not yet published or
abandoned).
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 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
OPTIONAL, REQUIRED, RECOMMENDED, 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
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material in section 14 of [NFSv42], expanded in scope to include
all feature elements, and updated to include all published
features that are part of the current NFSv4 minor version, at the
date of publication.
5.3. Relationship Between Minor versioning and Extensions within a
Minor Version
The 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 [RFC3530bis] 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 extension to a minor version may be made once the specification
document for a subsequent minor version becomes a working group
standards-track document.
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
operations 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 operations 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. I.e., when it is clear that existing client 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
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infer support for one operation from support for the other, in the
same way that had been done previously, invalidating logic in
existing clients.
6. Security Considerations
There are no security considerations in this document.
7. IANA Considerations
There are no IANA considerations in this document.
8. References
8.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", March 1997.
[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.
[RFC3530bis]
Haynes, T. and D. Noveck, "Network File System (NFS)
version 4 Protocol", draft-ietf-nfsv4-rfc3530bis-33 (Work
In Progress), April 2014.
[RFC5661] Shepler, S., Eisler, M., and D. Noveck, "Network File
System (NFS) Version 4 Minor Version 1 Protocol", RFC
5661, January 2010.
8.2. Informative References
[NFSv42] Haynes, T., "NFS Version 4 Minor Version 2", draft-ietf-
nfsv4-minorversion2-27 (Work In Progress), September 2014.
Appendix A. Acknowledgments
Appendix B. RFC Editor Notes
[RFC Editor: please remove this section prior to publishing this
document as an RFC]
[RFC Editor: prior to publishing this document as an RFC, please
replace all occurrences of RFCTBD10 with RFCxxxx where xxxx is the
RFC number of this document]
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Authors' Addresses
Thomas Haynes
Primary Data, Inc.
4300 El Camino Real Ste 100
Los Altos, CA 94022
USA
Phone: +1 408 215 1519
Email: thomas.haynes@primarydata.com
David Noveck (editor)
26 Locust Ave
Lexington, MA 02421
US
Phone: +1 781 572 8038
Email: davenoveck@gmail.com
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