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 working documents as Internet-Drafts. The list of current Internet- Drafts is at http://datatracker.ietf.org/drafts/current/. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." This Internet-Draft will expire on April 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 (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 Haynes & Noveck Expires April 9, 2015 [Page 1] Internet-Draft NFSv4 October 2014 to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 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]. Haynes & Noveck Expires April 9, 2015 [Page 2] Internet-Draft NFSv4 October 2014 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. Haynes & Noveck Expires April 9, 2015 [Page 3] Internet-Draft NFSv4 October 2014 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" Haynes & Noveck Expires April 9, 2015 [Page 4] Internet-Draft NFSv4 October 2014 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. Haynes & Noveck Expires April 9, 2015 [Page 5] Internet-Draft NFSv4 October 2014 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: Haynes & Noveck Expires April 9, 2015 [Page 6] Internet-Draft NFSv4 October 2014 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 Haynes & Noveck Expires April 9, 2015 [Page 7] Internet-Draft NFSv4 October 2014 (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 Haynes & Noveck Expires April 9, 2015 [Page 8] Internet-Draft NFSv4 October 2014 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 Haynes & Noveck Expires April 9, 2015 [Page 9] Internet-Draft NFSv4 October 2014 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 Haynes & Noveck Expires April 9, 2015 [Page 10] Internet-Draft NFSv4 October 2014 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] Haynes & Noveck Expires April 9, 2015 [Page 11] Internet-Draft NFSv4 October 2014 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 Haynes & Noveck Expires April 9, 2015 [Page 12]