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Network File System Version 4                                   C. Lever
Internet-Draft                                                    Oracle
Intended status: Standards Track                             4 July 2020
Expires: 5 January 2021


Network File System (NFS) Upper-Layer Binding To RPC-Over-RDMA Version 2
                     draft-ietf-nfsv4-nfs-ulb-v2-02

Abstract

   This document specifies Upper-Layer Bindings of Network File System
   (NFS) protocol versions to RPC-over-RDMA version 2.

Note

   Discussion of this draft takes place on the NFSv4 working group
   mailing list (nfsv4@ietf.org), which is archived at
   https://mailarchive.ietf.org/arch/browse/nfsv4/. Working Group
   information can be found at https://datatracker.ietf.org/wg/nfsv4/
   about/.

   This note is to be removed before publishing as an RFC.

   The source for this draft is maintained in GitHub.  Suggested changes
   can be submitted as pull requests at https://github.com/chucklever/
   i-d-nfs-ulb-v2.  Instructions are on that page as well.

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 https://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 5 January 2021.







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Copyright Notice

   Copyright (c) 2020 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 (https://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 the Trust Legal Provisions and are
   provided without warranty as described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Requirements Language . . . . . . . . . . . . . . . . . . . .   3
   3.  Reply Size Estimation . . . . . . . . . . . . . . . . . . . .   4
   4.  Upper-Layer Binding for NFS Versions 2 and 3  . . . . . . . .   4
     4.1.  Reply Size Estimation . . . . . . . . . . . . . . . . . .   4
     4.2.  RPC Binding Considerations  . . . . . . . . . . . . . . .   5
     4.3.  Transport Considerations  . . . . . . . . . . . . . . . .   5
   5.  Upper-Layer Bindings for NFS Version 2 and 3 Auxiliary
           Protocols . . . . . . . . . . . . . . . . . . . . . . . .   6
     5.1.  MOUNT, NLM, and NSM Protocols . . . . . . . . . . . . . .   6
     5.2.  NFSACL Protocol . . . . . . . . . . . . . . . . . . . . .   7
   6.  Upper-Layer Binding For NFS Version 4 . . . . . . . . . . . .   7
     6.1.  DDP-Eligibility . . . . . . . . . . . . . . . . . . . . .   7
     6.2.  Reply Size Estimation . . . . . . . . . . . . . . . . . .   8
     6.3.  RPC Binding Considerations  . . . . . . . . . . . . . . .   9
     6.4.  NFS COMPOUND Requests . . . . . . . . . . . . . . . . . .   9
     6.5.  NFS Callback Requests . . . . . . . . . . . . . . . . . .  12
     6.6.  Session-Related Considerations  . . . . . . . . . . . . .  13
     6.7.  Transport Considerations  . . . . . . . . . . . . . . . .  14
   7.  Extending NFS Upper-Layer Bindings  . . . . . . . . . . . . .  15
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .  16
   9.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  16
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .  16
     10.1.  Normative References . . . . . . . . . . . . . . . . . .  16
     10.2.  Informative References . . . . . . . . . . . . . . . . .  17
   Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . .  18
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .  18








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1.  Introduction

   The RPC-over-RDMA version 2 transport may employ direct data
   placement to convey data payloads associated with RPC transactions
   [I-D.ietf-nfsv4-rpcrdma-version-two].  RPC client and server
   implementations using RPC-over-RDMA version 2 must agree which XDR
   data items and RPC procedures are eligible to use direct data
   placement (DDP) to ensure successful interoperation.

   An Upper-Layer Binding specifies this agreement for one or more
   versions of one RPC program.  Other operational details, such as RPC
   binding assignments, pairing Write chunks with result data items, and
   reply size estimation, are also specified by this Binding.

   This document contains material required of Upper-Layer Bindings, as
   specified in [I-D.ietf-nfsv4-rpcrdma-version-two], for the following
   NFS protocol versions:

   *  NFS version 2 [RFC1094]

   *  NFS version 3 [RFC1813]

   *  NFS version 4.0 [RFC7530]

   *  NFS version 4.1 [RFC5661]

   *  NFS version 4.2 [RFC7862]

   The current document also provides Upper-Layer Bindings for auxiliary
   protocols used with NFS versions 2 and 3 (see Section 5).

   This document assumes the reader is already familiar with concepts
   and terminology defined in [I-D.ietf-nfsv4-rpcrdma-version-two] and
   the documents it references.

2.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in
   BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.









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3.  Reply Size Estimation

   During the construction of each RPC Call message, a Requester is
   responsible for allocating appropriate resources for receiving the
   corresponding Reply message.  If the Requester expects that the RPC
   Reply message could be larger than its inline threshold, it MAY
   provide Write chunks wherein the Responder can place results and
   Reply chunks wherein the Responder can place the reply's Payload
   stream.  A message continuation facility is also available in RPC-
   over-RDMA version 2 to convey RPC messages that are larger than the
   transport's inline threshold.

4.  Upper-Layer Binding for NFS Versions 2 and 3

   The Upper-Layer Binding specification in this section applies to NFS
   version 2 [RFC1094] and NFS version 3 [RFC1813].  For brevity, in
   this document, a "Legacy NFS client" refers to an NFS client using
   version 2 or version 3 of the NFS RPC program (100003) to communicate
   with an NFS server.  Likewise, a "Legacy NFS server" is an NFS server
   communicating with clients using NFS version 2 or NFS version 3.

   The following XDR data items in NFS versions 2 and 3 are DDP-
   eligible:

   *  The opaque file data argument in the NFS WRITE procedure

   *  The pathname argument in the NFS SYMLINK procedure

   *  The opaque file data result in the NFS READ procedure

   *  The pathname result in the NFS READLINK procedure

   All other argument or result data items in NFS versions 2 and 3 are
   not DDP-eligible.

   Whether or not an NFS operation is considered non-idempotent, a
   transport error might not indicate whether the server has processed
   the arguments of the RPC Call, or whether the server has accessed or
   modified client memory associated with that RPC.

4.1.  Reply Size Estimation

   A Legacy NFS client determines the maximum reply size for each
   operation using the criteria outlined in Section 3.







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4.2.  RPC Binding Considerations

   Legacy NFS servers traditionally listen for clients on UDP and TCP
   port 2049.  Additionally, they register these ports with a local
   portmapper service [RFC1833].

   A Legacy NFS server supporting RPC-over-RDMA version 2 and
   registering itself with the RPC portmapper MAY choose an arbitrary
   port, or MAY use the alternative well-known port number for its RPC-
   over-RDMA service (see Section 9).  The chosen port MAY be registered
   with the RPC portmapper using the netids assigned in
   [I-D.ietf-nfsv4-rpcrdma-version-two].

4.3.  Transport Considerations

   Legacy NFS client implementations often rely on a transport-layer
   keep-alive mechanism to detect when a legacy server has become
   unresponsive.  When an NFS server is no longer responsive, client-
   side keep-alive terminates the connection, which in turn triggers
   reconnection and retransmission of outstanding RPC transactions.

4.3.1.  Keep-Alive

   Some RDMA transports (such as the Reliable Connected QP type on
   InfiniBand) have no keep-alive mechanism.  Without a disconnect or
   new RPC traffic, such connections can remain alive long after an NFS
   server has become unresponsive or unreachable.  Once an NFS client
   has consumed all available RPC-over-RDMA version 2 credits on that
   transport connection, it awaits a reply indefinitely before sending
   another RPC request.

   Legacy NFS clients SHOULD reserve one RPC-over-RDMA version 2 credit
   to use for periodic server or connection health assessment.  Either
   peer can use this credit to drive an RPC request on an otherwise idle
   connection, triggering either an affirmative server response or a
   connection termination.

4.3.2.  Replay Detection

   Legacy NFS servers typically employ request replay detection to
   reduce the risk of data corruption that could result when an NFS
   client retransmits a non-idempotent NFS request.  A legacy NFS server
   can send a cached response when a replay is detected, rather than
   executing the request again.  Replay detection is not perfect, but it
   is usually adequate.






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   For legacy NFS servers, replay detection commonly utilizes heuristic
   indicators such as the IP address of the NFS client, the source port
   of the connection, the transaction ID of the request, and the
   contents of the request's RPC and upper-layer protocol headers.  In
   short, replay detection is typically based on a connection tuple and
   the request's XID.  A legacy NFS client is careful to re-use the same
   source port, if practical, when reconnecting so that legacy NFS
   servers are better able to detect retransmissions.

   However, a legacy NFS client operating over an RDMA transport has no
   control over connection source ports.  It is almost certain that an
   RPC request that is retransmitted on a new connection can never be
   detected as a replay if the legacy NFS server includes the connection
   source port in its replay detection heuristics.

   Therefore a legacy NFS server using an RDMA transport should never
   use a legacy NFS client connection's source port as part of its NFS
   request replay detection mechanism.

5.  Upper-Layer Bindings for NFS Version 2 and 3 Auxiliary Protocols

   Storage administrators typically deploy NFS versions 2 and 3 with
   several other protocols, sometimes referred to as "NFS auxiliary
   protocols."  These are distinct RPC programs that define procedures
   that are not part of the NFS RPC program (100003).  The Upper-Layer
   Bindings in this section apply to:

   *  Versions 2 and 3 of the MOUNT RPC program (100005) [RFC1813]

   *  Versions 1, 3, and 4 of the NLM RPC program (100021) [RFC1813]

   *  Version 1 of the NSM RPC program (100024), described in Chapter 11
      of [XNFS]

   *  Version 1 of the NFSACL RPC program (100227), which does not have
      a public definition.  NFSACL is treated in this document as a de
      facto standard, as there are several interoperating
      implementations.

5.1.  MOUNT, NLM, and NSM Protocols

   Historically, NFS/RDMA implementations have chosen to convey the
   MOUNT, NLM, and NSM protocols via TCP.  A legacy NFS server
   implementation MUST provide support for these protocols via TCP to
   enable interoperation of these protocols when NFS/RDMA is in use.






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5.2.  NFSACL Protocol

   Often legacy clients and servers that support the NFSACL RPC program
   convey NFSACL procedures on the same connection as the NFS RPC
   program (100003).  Utilizing the same connection obviates the need
   for separate rpcbind queries to discover server support for this RPC
   program.

   ACLs are typically small, but even large ACLs must be encoded and
   decoded to some degree before being made available to users.  Thus no
   data item in this Upper-Layer Protocol is DDP-eligible.

   For procedures whose replies do not include an ACL object, the size
   of a reply is determined directly from the NFSACL RPC program's XDR
   definition.  Legacy client implementations should choose a maximum
   size for ACLs based on internal limits.

6.  Upper-Layer Binding For NFS Version 4

   The Upper-Layer Binding specification in this section applies to
   versions of the NFS RPC program defined in NFS version 4.0 [RFC7530]
   NFS version 4.1 [RFC5661] and NFS version 4.2 [RFC7862].

6.1.  DDP-Eligibility

   Only the following XDR data items in the COMPOUND procedure of all
   NFS version 4 minor versions are DDP-eligible:

   *  The opaque data field in the WRITE4args structure

   *  The linkdata field of the NF4LNK arm in the createtype4 union

   *  The opaque data field in the READ4resok structure

   *  The linkdata field in the READLINK4resok structure

6.1.1.  The NFSv4.2 READ_PLUS operation

   NFS version 4.2 introduces an enhanced READ operation called
   READ_PLUS [RFC7862].  READ_PLUS enables an NFS server to perform
   inline data reduction of READ results so that the returned READ data
   is more compact.

   In a READ_PLUS result, returned file content appears as a list of one
   or more of the following items:

   *  Regular data content: the same as the result of a traditional READ
      operation.



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   *  Unallocated space in a file: where no data has yet been written or
      previously-written data has been removed via a hole-punch
      operation.

   *  A counted pattern.

   Upon receipt of a READ_PLUS result, an NFSv4.2 client expands the
   returned list into a preferred local representation of the original
   file content.

   Before receiving that result, an NFSv4.2 client typically does not
   know how the file's content is organized on the NFS server.  Thus it
   is not possible to predict the size or structure of a READ_PLUS Reply
   in advance.  The use of direct data placement is therefore
   challenging.

   A READ_PLUS content list containing more than one segment of regular
   file data could be conveyed using multiple Write chunks, but only if
   the client knows in advance where those chunks appear in the Reply
   Payload stream.  Moreover, the usual benefits of hardware-assisted
   data placement are entirely waived if the client-side transport must
   parse the result of each read I/O.

   Therefore this Upper Layer Binding does not make any element of an
   NFSv4.2 READ_PLUS Reply DDP-eligible.  Further, this Upper Layer
   Binding recommends that implementers disable the use of the READ_PLUS
   operation on NFS/RDMA mount points.

6.2.  Reply Size Estimation

   Within NFS version 4, there are certain variable-length result data
   items whose maximum size cannot be estimated by clients reliably
   because there is no protocol-specified size limit on these result
   arrays.  These include:

   *  The attrlist4 field

   *  Fields containing ACLs such as fattr4_acl, fattr4_dacl, and
      fattr4_sacl

   *  Fields in the fs_locations4 and fs_locations_info4 data structures

   *  Fields which pertain to pNFS layout metadata, such as loc_body,
      loh_body, da_addr_body, lou_body, lrf_body, fattr_layout_types,
      and fs_layout_types






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6.2.1.  Reply Size Estimation for Minor Version 0

   The NFS version 4.0 protocol itself does not impose any bound on the
   size of NFS calls or replies.

   Some of the data items enumerated in Section 6.2 (in particular, the
   items related to ACLs and fs_locations) make it difficult to predict
   the maximum size of NFS version 4.0 replies that interrogate
   variable-length fattr4 attributes.  Client implementations might rely
   upon internal architectural limits to constrain the reply size, but
   such limits are not always guaranteed to be reliable.

   When an NFS version 4.0 client expects an especially sizeable fattr4
   result, it can provide a Reply chunk to enable that server to return
   that result via explicit RDMA.  An NFS version 4.0 client can use
   short Reply chunk retry when an NFS COMPOUND containing a GETATTR
   operation encounters a transport error.

6.2.2.  Reply Size Estimation for Minor Version 1 and Newer

   In NFS version 4.1 and newer minor versions, the csa_fore_chan_attrs
   argument of the CREATE_SESSION operation contains a
   ca_maxresponsesize field.  The value in this field can be taken as
   the absolute maximum size of replies generated by an NFS version 4.1
   server.

   An NFS version 4 client can use this value in cases where it is not
   possible to estimate a reply size upper bound precisely.  In
   practice, objects such as ACLs, named attributes, layout bodies, and
   security labels are much smaller than this maximum.

6.3.  RPC Binding Considerations

   NFS version 4 servers are required to listen on TCP port 2049, and
   they are not required to register with a rpcbind service [RFC7530].

   Therefore, an NFS version 4 server supporting RPC-over-RDMA version 2
   MUST use the alternative well-known port number for its RPC-over-RDMA
   service (see Section 9 Clients SHOULD connect to this well-known port
   without consulting the RPC portmapper (as for NFS version 4 on TCP
   transports).

6.4.  NFS COMPOUND Requests








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6.4.1.  Multiple DDP-eligible Data Items

   An NFS version 4 COMPOUND procedure can contain more than one
   operation that carries a DDP-eligible data item.  An NFS version 4
   client provides XDR Position values in each Read chunk to
   disambiguate which chunk is associated with which argument data item.
   However, NFS version 4 server and client implementations must agree
   in advance on how to pair Write chunks with returned result data
   items.

   In the following lists, a "READ operation" refers to any NFS version
   4 operation that has a DDP-eligible result data item.  An NFS version
   4 client applies the mechanism specified in Section 4.3.2 of
   [I-D.ietf-nfsv4-rpcrdma-version-two] is applied to this class of
   operations as follows:

   *  If an NFS version 4 client wishes all DDP-eligible items in an NFS
      reply to be conveyed inline, it leaves the Write list empty.

   An NFS version 4 server applies that mechanism as follows:

   *  The first chunk in the Write list MUST be used by the first READ
      operation in an NFS version 4 COMPOUND procedure.  The next Write
      chunk is used by the next READ operation, and so on.

   *  If an NFS version 4 client has provided a matching non-empty Write
      chunk, then the corresponding READ operation MUST return its DDP-
      eligible data item using that chunk.

   *  If an NFS version 4 client has provided an empty matching Write
      chunk, then the corresponding READ operation MUST return all of
      its result data items inline.

   *  If a READ operation returns a union arm which does not contain a
      DDP-eligible result, and the NFS version 4 client has provided a
      matching non-empty Write chunk, an NFS version 4 server MUST
      return an empty Write chunk in that Write list position.

   *  If there are more READ operations than Write chunks, then
      remaining NFS Read operations in an NFS version 4 COMPOUND that
      have no matching Write chunk MUST return their results inline.










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6.4.2.  Chunk List Complexity

   The RPC-over-RDMA version 2 protocol does not place any limit on the
   number of chunks or segments that may appear in Read or Write lists.
   However, for various reasons, NFS version 4 server implementations
   often have practical limits on the number of chunks or segments they
   can process in a single RPC transaction conveyed via RPC-over-RDMA
   version 2.

   These implementation limits are especially important when Kerberos
   integrity or privacy is in use [RFC7861].  GSS services increase the
   size of credential material in RPC headers, potentially requiring the
   use of a Long message, which increases the complexity of chunk lists
   independent of the particular NFS version 4 COMPOUND being conveyed.

   In the absence of explicit knowledge of the server's limits, NFS
   version 4 clients SHOULD follow the prescriptions listed below when
   constructing RPC-over-RDMA version 2 messages.  NFS version 4 servers
   MUST accept and process all such requests.

   *  The Read list can contain either a Position-Zero Read chunk, one
      Read chunk with a non-zero Position, or both.

   *  The Write list can contain no more than one Write chunk.

   *  Any chunk can contain up to sixteen RDMA segments.

   NFS version 4 clients wishing to send more complex chunk lists can
   provide configuration interfaces to bound the complexity of NFS
   version 4 COMPOUNDs, limit the number of elements in scatter-gather
   operations, and avoid other sources of chunk overruns at the
   receiving peer.

   If an NFS version 4 server receives an RPC request via RPC-over-RDMA
   version 2 that it cannot process due to chunk list complexity limits,
   it SHOULD return one of the following responses to the client:

   *  A problem is detected by the transport layer while parsing the
      transport header in an RPC Call message.  The server responds with
      an RDMA2_ERROR message with the err field set to ERR_CHUNK.

   *  A problem is detected during XDR decoding of the RPC Call message
      while the RPC layer reassembles the call's XDR stream.  The server
      responds with an RPC reply with its "reply_stat" field set to
      MSG_ACCEPTED and its "accept_stat" field set to GARBAGE_ARGS.






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   After receiving one of these errors, an NFS version 4 client SHOULD
   NOT retransmit the failing request, as the result would be the same
   error.  It SHOULD immediately terminate the RPC transaction
   associated with the XID in the reply.

6.4.3.  NFS Version 4 COMPOUND Example

   The following example shows a Write list with three Write chunks, A,
   B, and C.  The NFS version 4 server consumes the provided Write
   chunks by writing the results of the designated operations in the
   compound request (READ and READLINK) back to each chunk.

      Write list:

         A --> B --> C

      NFS version 4 COMPOUND request:

         PUTFH LOOKUP READ PUTFH LOOKUP READLINK PUTFH LOOKUP READ
                       |                   |                   |
                       v                   v                   v
                       A                   B                   C

   If the NFS version 4 client does not want to have the READLINK result
   returned via RDMA, it provides an empty Write chunk for buffer B to
   indicate that the READLINK result must be returned inline.

6.5.  NFS Callback Requests

   The NFS version 4 family of protocols support server-initiated
   callbacks to notify NFS version 4 clients of events such as recalled
   delegations.

6.5.1.  NFS Version 4.0 Callback

   NFS version 4.0 implementations typically employ a separate TCP
   connection to handle callback operations, even when the forward
   channel uses an RPC-over-RDMA version 2 transport.

   No operation in the NFS version 4.0 callback RPC program conveys a
   data payload of significant size.  Therefore, no XDR data items in
   this RPC program is DDP-eligible.

   A CB_RECALL reply is small and fixed in size.  The CB_GETATTR reply
   contains a variable-length fattr4 data item.  See Section 6.2.1 for a
   discussion of reply size prediction for this data item.





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   An NFS version 4.0 client advertises netids and ad hoc port addresses
   for contacting its NFS version 4.0 callback service using the
   SETCLIENTID operation.

6.5.2.  NFS Version 4.1 Callback

   In NFS version 4.1 and newer minor versions, callback operations may
   appear on the same connection as is used for NFS version 4 forward
   channel client requests.  NFS version 4 clients and servers MUST use
   the approach described in [RFC8167] to convey backchannel operations
   on an RPC-over-RDMA version 2 transport.

   The csa_back_chan_attrs argument of the CREATE_SESSION operation
   contains a ca_maxresponsesize field.  The value in this field is the
   absolute maximum size of backchannel replies generated by a replying
   NFS version 4 client.

   There are no DDP-eligible data items in callback procedures defined
   in NFS version 4.1 or NFS version 4.2.  However, some callback
   operations, such as messages that convey device ID information, can
   be sizeable.  A sender can use Message Continuation or a Long message
   in this situation.

   When an NFS version 4.1 client can support Long Calls in its
   backchannel, it reports a backchannel ca_maxrequestsize that is
   larger than the connection's inline thresholds.  Otherwise, an NFS
   version 4 server MUST use only Short messages to convey backchannel
   operations.

6.6.  Session-Related Considerations

   The presence of an NFS version 4 session (as defined in [RFC5661])
   does not effect the operation of RPC-over-RDMA version 2.  None of
   the operations introduced to support NFS sessions (e.g., the SEQUENCE
   operation) contain DDP-eligible data items.  There is no need to
   match the number of session slots with the number of available RPC-
   over-RDMA version 2 credits.

   However, there are a few new cases where an RPC transaction can fail.
   For example, a Requester might receive, in response to an RPC
   request, an RDMA2_ERROR message with a rdma_err value of ERR_CHUNK.
   These situations are not different from existing RPC errors, which an
   NFS session implementation can already handle for other transport
   types.  Moreover, there might be no SEQUENCE result available to the
   Requester to distinguish whether failure occurred before or after the
   Responder executed the requested operations.





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   When a transport error occurs (e.g., an RDMA2_ERROR type message is
   received), the Requester proceeds, as usual, to match the incoming
   XID value to a waiting RPC Call.  The Requester terminates the RPC
   transaction and reports the result status to the RPC consumer.  The
   Requester's session implementation then determines the session ID and
   slot for the failed request and performs slot recovery to make that
   slot usable again.  Otherwise, that slot could be rendered
   permanently unavailable.

   When an NFS session is not present (for example, when NFS version 4.0
   is in use), a transport error does not indicate whether the server
   has processed the arguments of the RPC Call, or whether the server
   has accessed or modified client memory associated with that RPC.

6.7.  Transport Considerations

6.7.1.  Congestion Avoidance

   Section 3.1 of [RFC7530] states:

      Where an NFS version 4 implementation supports operation over the
      IP network protocol, the supported transport layer between NFS and
      IP MUST be an IETF standardized transport protocol that is
      specified to avoid network congestion; such transports include TCP
      and the Stream Control Transmission Protocol (SCTP).

   Section 2.9.1 of [RFC5661] further states:

      Even if NFS version 4.1 is used over a non-IP network protocol, it
      is RECOMMENDED that the transport support congestion control.

      It is permissible for a connectionless transport to be used under
      NFS version 4.1; however, reliable and in-order delivery of data
      combined with congestion control by the connectionless transport
      is REQUIRED.  As a consequence, UDP by itself MUST NOT be used as
      an NFS version 4.1 transport.

   RPC-over-RDMA version 2 utilizes only RDMA Reliable Connected QP type
   connections [I-D.ietf-nfsv4-rpcrdma-version-two].  RDMA Reliable
   Connected QPs are reliable, connection-oriented transports that
   guarantee in-order delivery, meeting all the above requirements.










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6.7.2.  Retransmission and Keep-alive

   NFS version 4 client implementations often rely on a transport-layer
   keep-alive mechanism to detect when an NFS version 4 server has
   become unresponsive.  When an NFS server is no longer responsive,
   client-side keep-alive terminates the connection, which in turn
   triggers reconnection and RPC retransmission.

   Some RDMA transports (such as the Reliable Connected QP type on
   InfiniBand) have no keep-alive mechanism.  Without a disconnect or
   new RPC traffic, such connections can remain alive long after an NFS
   server has become unresponsive.  Once an NFS client has consumed all
   available RPC-over-RDMA version 2 credits on that transport
   connection, it indefinitely awaits a reply before sending another RPC
   request.

   NFS version 4 clients SHOULD reserve one RPC-over-RDMA version 2
   credit to use for periodic server or connection health assessment.
   Either peer can use this credit to drive an RPC request on an
   otherwise idle connection, triggering either a quick affirmative
   server response or immediate connection termination.

   In addition to network partition and request loss scenarios, RPC-
   over-RDMA version 2 transport connections can be terminated when a
   Transport header is malformed, Reply messages exceed receive
   resources, or when too many RPC-over-RDMA messages are sent at once.
   In such cases:

   *  If a transport error occurs (e.g., an RDMA2_ERROR type message is
      received) before the disconnect or instead of a disconnect, the
      Requester MUST respond to that error as prescribed by the
      specification of the RPC transport.  Then the NFS version 4 rules
      for handling retransmission apply.

   *  If there is a transport disconnect and the Responder has provided
      no other response for a request, then only the NFS version 4 rules
      for handling retransmission apply.

7.  Extending NFS Upper-Layer Bindings

   RPC programs such as NFS are required to have an Upper-Layer Binding
   specification to interoperate on RPC-over-RDMA version 2 transports
   [I-D.ietf-nfsv4-rpcrdma-version-two].  Via standards action, the
   Upper-Layer Binding specified in this document can be extended to
   cover versions of the NFS version 4 protocol specified after NFS
   version 4 minor version 2, or to cover separately published
   extensions to an existing NFS version 4 minor version, as described
   in [RFC8178].



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8.  Security Considerations

   RPC-over-RDMA version 2 supports all RPC security models, including
   RPCSEC_GSS security and transport-level security [RFC7861].  The
   choice of what Direct Data Placement mechanism to convey RPC argument
   and results does not affect this since it changes only the method of
   data transfer.  Because the current document defines only the binding
   of the NFS protocols atop [I-D.ietf-nfsv4-rpcrdma-version-two], all
   relevant security considerations are, therefore, described at that
   layer.

9.  IANA Considerations

   The use of direct data placement in NFS introduces a need for an
   additional port number assignment for networks that share traditional
   UDP and TCP port spaces with RDMA services.  The iWARP protocol is
   such an example [RFC5040] [RFC5041].

   For this purpose, the current document specifies a set of transport
   protocol port number assignments.  IANA has assigned the following
   ports for NFS/RDMA in the IANA port registry, according to the
   guidelines described in [RFC6335].

     nfsrdma 20049/tcp Network File System (NFS) over RDMA
     nfsrdma 20049/udp Network File System (NFS) over RDMA
     nfsrdma 20049/sctp Network File System (NFS) over RDMA

   The current document should be added as a reference for the nfsrdma
   port assignments.  The current document does not alter these
   assignments.

10.  References

10.1.  Normative References

   [I-D.ietf-nfsv4-rpcrdma-version-two]
              Lever, C. and D. Noveck, "RPC-over-RDMA Version 2
              Protocol", Work in Progress, Internet-Draft, draft-ietf-
              nfsv4-rpcrdma-version-two-02, 3 July 2020,
              <https://tools.ietf.org/html/draft-ietf-nfsv4-rpcrdma-
              version-two-02>.

   [RFC1833]  Srinivasan, R., "Binding Protocols for ONC RPC Version 2",
              RFC 1833, DOI 10.17487/RFC1833, August 1995,
              <https://www.rfc-editor.org/info/rfc1833>.






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   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

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

   [RFC6335]  Cotton, M., Eggert, L., Touch, J., Westerlund, M., and S.
              Cheshire, "Internet Assigned Numbers Authority (IANA)
              Procedures for the Management of the Service Name and
              Transport Protocol Port Number Registry", BCP 165,
              RFC 6335, DOI 10.17487/RFC6335, August 2011,
              <https://www.rfc-editor.org/info/rfc6335>.

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

   [RFC7861]  Adamson, A. and N. Williams, "Remote Procedure Call (RPC)
              Security Version 3", RFC 7861, DOI 10.17487/RFC7861,
              November 2016, <https://www.rfc-editor.org/info/rfc7861>.

   [RFC7862]  Haynes, T., "Network File System (NFS) Version 4 Minor
              Version 2 Protocol", RFC 7862, DOI 10.17487/RFC7862,
              November 2016, <https://www.rfc-editor.org/info/rfc7862>.

   [RFC8167]  Lever, C., "Bidirectional Remote Procedure Call on RPC-
              over-RDMA Transports", RFC 8167, DOI 10.17487/RFC8167,
              June 2017, <https://www.rfc-editor.org/info/rfc8167>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

10.2.  Informative References

   [RFC1094]  Nowicki, B., "NFS: Network File System Protocol
              specification", RFC 1094, DOI 10.17487/RFC1094, March
              1989, <https://www.rfc-editor.org/info/rfc1094>.

   [RFC1813]  Callaghan, B., Pawlowski, B., and P. Staubach, "NFS
              Version 3 Protocol Specification", RFC 1813,
              DOI 10.17487/RFC1813, June 1995,
              <https://www.rfc-editor.org/info/rfc1813>.




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   [RFC5040]  Recio, R., Metzler, B., Culley, P., Hilland, J., and D.
              Garcia, "A Remote Direct Memory Access Protocol
              Specification", RFC 5040, DOI 10.17487/RFC5040, October
              2007, <https://www.rfc-editor.org/info/rfc5040>.

   [RFC5041]  Shah, H., Pinkerton, J., Recio, R., and P. Culley, "Direct
              Data Placement over Reliable Transports", RFC 5041,
              DOI 10.17487/RFC5041, October 2007,
              <https://www.rfc-editor.org/info/rfc5041>.

   [RFC8178]  Noveck, D., "Rules for NFSv4 Extensions and Minor
              Versions", RFC 8178, DOI 10.17487/RFC8178, July 2017,
              <https://www.rfc-editor.org/info/rfc8178>.

   [XNFS]     The Open Group, "Protocols for Interworking: XNFS, Version
              3W", February 1998.

Acknowledgments

   Thanks to Tom Talpey, who contributed the text of Section 6.4.2.
   David Noveck contributed the text of Section 6.6 and Section 7.  The
   author also wishes to thank Bill Baker and Greg Marsden for their
   support of this work.

   Special thanks go to Transport Area Director Magnus Westerlund, NFSV4
   Working Group Chairs Spencer Shepler, Brian Pawlowski, and David
   Noveck, and NFSV4 Working Group Secretary Thomas Haynes for their
   support.

Author's Address

   Charles Lever
   Oracle Corporation
   United States of America

   Email: chuck.lever@oracle.com















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