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Network File System Version 4                              C. Lever, Ed.
Internet-Draft                                                    Oracle
Intended status: Standards Track                               D. Noveck
Expires: June 4, 2017                                                HPE
                                                        December 1, 2016


                   RPC-over-RDMA Version Two Protocol
                 draft-cel-nfsv4-rpcrdma-version-two-03

Abstract

   This document specifies an improved protocol for conveying Remote
   Procedure Call (RPC) messages on physical transports capable of
   Remote Direct Memory Access (RDMA), based on RPC-over-RDMA Version
   One.

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 [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 June 4, 2017.

Copyright Notice

   Copyright (c) 2016 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



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   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  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Inline Threshold  . . . . . . . . . . . . . . . . . . . . . .   4
     2.1.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   4
     2.2.  Motivation  . . . . . . . . . . . . . . . . . . . . . . .   4
     2.3.  Default Values  . . . . . . . . . . . . . . . . . . . . .   5
   3.  Remote Invalidation . . . . . . . . . . . . . . . . . . . . .   5
     3.1.  Backward-Direction Remote Invalidation  . . . . . . . . .   6
   4.  Protocol Extensibility  . . . . . . . . . . . . . . . . . . .   6
     4.1.  Optional Features . . . . . . . . . . . . . . . . . . . .   6
     4.2.  Message Direction . . . . . . . . . . . . . . . . . . . .   7
     4.3.  Documentation Requirements  . . . . . . . . . . . . . . .   7
   5.  Transport Properties  . . . . . . . . . . . . . . . . . . . .   8
     5.1.  Introduction To Transport Properties  . . . . . . . . . .   8
     5.2.  Basic Transport Properties  . . . . . . . . . . . . . . .  11
     5.3.  New Operations  . . . . . . . . . . . . . . . . . . . . .  15
     5.4.  Extensibility . . . . . . . . . . . . . . . . . . . . . .  19
   6.  XDR Protocol Definition . . . . . . . . . . . . . . . . . . .  21
     6.1.  Code Component License  . . . . . . . . . . . . . . . . .  22
     6.2.  RPC-Over-RDMA Version Two XDR . . . . . . . . . . . . . .  24
   7.  Protocol Version Negotiation  . . . . . . . . . . . . . . . .  30
     7.1.  Server Does Support RPC-over-RDMA Version Two . . . . . .  31
     7.2.  Server Does Not Support RPC-over-RDMA Version Two . . . .  31
     7.3.  Client Does Not Support RPC-over-RDMA Version Two . . . .  31
     7.4.  Security Considerations . . . . . . . . . . . . . . . . .  31
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  32
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  32
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .  32
     9.2.  Informative References  . . . . . . . . . . . . . . . . .  32
   Appendix A.  Acknowledgments  . . . . . . . . . . . . . . . . . .  33
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  33

1.  Introduction

   Remote Direct Memory Access (RDMA) [RFC5040] [RFC5041] [IB] is a
   technique for moving data efficiently between end nodes.  By
   directing data into destination buffers as it is sent on a network
   and placing it via direct memory access by hardware, the
   complementary benefits of faster transfers and reduced host overhead
   are obtained.



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   A protocol already exists that enables ONC RPC [RFC5531] messages to
   be conveyed on RDMA transports.  That protocol is RPC-over-RDMA
   Version One, specified in [I-D.ietf-nfsv4-rfc5666bis].  RPC-over-RDMA
   Version One is deployed and in use, though there are some
   shortcomings to this protocol, such as:

   o  The use of small Receive buffers force the use of RDMA Read and
      Write transfers for small payloads, and limit the size of
      backchannel messages.

   o  Lack of support for potential optimizations, such as remote
      invalidation, that require changes to on-the-wire behavior.

   To address these issues in a way that is compatible with existing
   RPC-over-RDMA Version One deployments, a new version of RPC-over-RDMA
   is presented in this document.  RPC-over-RDMA Version Two contains
   only incremental changes over RPC-over-RDMA Version One to facilitate
   adoption of Version Two by existing Version One implementations.

   The major new feature in RPC-over-RDMA Version Two is extensibility
   of the RPC-over-RDMA header.  Extensibility enables narrow changes to
   RPC-over-RDMA Version Two so that new optional capabilities can be
   introduced without a protocol version change and while maintaining
   interoperability with existing implementations.

   New capabilities can be proposed and developed independently of each
   other, and implementaters can choose among them, making it
   straightforward to create and document experimental features and then
   bring them through the standards process.

   As part of this new extensibility feature set, a mechanism for
   exchanging transport properties is introduced.  This mechanism allows
   RPC-over-RDMA Version Two connection endpoints to communicate
   properties of their implementations, to request changes in properties
   of the other endpoint, and to notify peer endpoints of changes to
   properties that occur during operation.

   In addition to extensibility, the default inline threshold value is
   larger in RPC-over-RDMA Version Two.  This change is driven by the
   increase in average size of RPC messages containing common NFS
   operations.  With NFSv4.1 [RFC5661] and later, compound operations
   convey more data per RPC message.  The default 1KB inline threshold
   in RPC-over-RDMA Version One prevents attaining the best possible
   performance.

   Support for Remote Invalidation has been introduced into RPC-over-
   RDMA Version Two.  An RPC-over-RDMA responder can now request
   invalidation of an STag as part of sending an RPC Reply, saving the



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   requester the effort of invalidating after message receipt.  This new
   feature is general enough to enable a requester to control precisely
   when Remote Invalidation may be utilized by responders.

   RPC-over-RDMA Version Two expands the repertoire of error codes to
   enable extensibility, support debugging, and to prevent requester
   retries when an error is permanent.

2.  Inline Threshold

2.1.  Terminology

   The term "inline threshold" is defined in Section 4 of
   [I-D.ietf-nfsv4-rfc5666bis].  An "inline threshold" value is the
   largest message size (in octets) that can be conveyed in one
   direction on an RDMA connection using only RDMA Send and Receive.
   Each connection has two inline threshold values: one for messages
   flowing from requester-to-responder (referred to as the "call inline
   threshold"), and one for messages flowing from responder-to-requester
   (referred to as the "reply inline threshold").  Inline threshold
   values are not advertised to peers via the base RPC-over-RDMA Version
   Two protocol.

   A connection's inline threshold determines when RDMA Read or Write
   operations are required because the RPC message to be sent cannot be
   conveyed via RDMA Send and Receive.  When an RPC message does not
   contain DDP-eligible data items, a requester prepares a Long Call or
   Reply to convey the whole RPC message using RDMA Read or Write
   operations.

2.2.  Motivation

   RDMA Read and Write operations require that each data payload resides
   in a region of memory that is registered with the RNIC.  When an RPC
   is complete, that region is invalidated, fencing it from the
   responder.

   Both registration and invalidation have a latency cost which is
   insignificant compared to data handling costs.  When a data payload
   is small, however, the cost of registering and invalidating the
   memory where the payload resides becomes a relatively significant
   part of total RPC latency.  Therefore the most efficient operation of
   RPC-over-RDMA occurs when RDMA Read and Write operations are used for
   large payloads, and avoided for small payloads.

   When RPC-over-RDMA Version One was conceived, the typical size of RPC
   messages that did not involve a significant data payload was under




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   500 bytes.  A 1024-byte inline threshold adequately minimized the
   frequency of inefficient Long Calls and Replies.

   Starting with NFSv4.1 [RFC5661], NFS COMPOUND RPC messages are larger
   and more complex than before.  With a 1024-byte inline threshold,
   RDMA Read or Write operations are needed for frequent operations that
   do not bear a data payload, such as GETATTR and LOOKUP, reducing the
   efficiency of the transport.

   To reduce the need to use Long Calls and Replies, RPC-over-RDMA
   Version Two increases the default inline threshold size.  This also
   increases the maximum size of backward direction RPC messages.

2.3.  Default Values

   RPC-over-RDMA Version Two receiver implementations MUST support an
   inline threshold of 4096 bytes, but MAY support larger inline
   threshold values.  A mechanism for discovering a peer's preferred
   inline threshold value (not defined in this document) may be used to
   optimize RDMA Send operations further.  In the absense of such a
   mechanism, senders MUST assume a receiver's inline threshold is 4096
   bytes.

   The new default inline threshold size is no larger than the size of a
   hardware page on typical platforms.  This conserves the resources
   needed to Send and Receive base level RPC-over-RDMA Version Two
   messages, enabling RPC-over-RDMA Version Two to be used on a broad
   variety of hardware.

3.  Remote Invalidation

   An STag that is registered using the FRWR mechanism (in a privileged
   execution context), or is registered via a Memory Window (in user
   space), may be invalidated remotely [RFC5040].  These mechanisms are
   available only when a requester's RNIC supports MEM_MGT_EXTENSIONS.

   For the purposes of this discussion, there are two classes of STags.
   Dynamically-registered STags are used in a single RPC, then
   invalidated.  Persistently-registered STags live longer than one RPC.
   They may persist for the life of an RPC-over-RDMA connection, or
   longer.

   An RPC-over-RDMA requester may provide more than one STag in one
   transport header.  It may provide a combination of dynamically- and
   persistently-registered STags in one RPC message, or any combination
   of these in a series of RPCs on the same connection.  Only
   dynamically-registered STags using Memory Windows or FRWR (ie.
   registered via MEM_MGT_EXTENSIONS) may be invalidated remotely.



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   There is no transport-level mechanism by which a responder can
   determine how a requester-provided STag was registered, nor whether
   it is eligible to be invalidated remotely.  A requester that mixes
   persistently- and dynamically-registered STags in one RPC, or mixes
   them across RPCs on the same connection, must therefore indicate
   which handles may be invalidated via a mechanism provided in the
   Upper Layer Protocol.  RPC-over-RDMA Version Two provides such a
   mechanism.

   The RDMA Send With Invalidate operation is used to invalidate an STag
   on a remote system.  It is available only when a responder's RNIC
   supports MEM_MGT_EXTENSIONS, and must be utilized only when a
   requester's RNIC supports MEM_MGT_EXTENSIONS (can receive and
   recognize an IETH).

3.1.  Backward-Direction Remote Invalidation

   Existing RPC-over-RDMA protocol specifications
   [I-D.ietf-nfsv4-rfc5666bis] [I-D.ietf-nfsv4-rpcrdma-bidirection] do
   not forbid direct data placement in the backward-direction, even
   though there is currently no Upper Layer Protocol that may use it.

   When chunks are present in a backward-direction RPC request, Remote
   Invalidation allows the responder to trigger invalidation of a
   requester's STags as part of sending a reply, the same as in the
   forward direction.

   However, in the backward direction, the server acts as the requester,
   and the client is the responder.  The server's RNIC, therefore, must
   support receiving an IETH, and the server must have registered the
   STags with an appropriate registration mechanism.

4.  Protocol Extensibility

   The core RPC-over-RDMA Version Two header format is specified in
   Section 6 as a complete and stand-alone piece of XDR.  Any change to
   this XDR description requires a protocol version number change.

4.1.  Optional Features

   RPC-over-RDMA Version Two introduces the ability to extend the core
   protocol via optional features.  Extensibility enables minor protocol
   issues to be addressed and incremental enhancements to be made
   without the need to change the protocol version.  The key capability
   is that both sides can detect whether a feature is supported by their
   peer or not.  With this ability, OPTIONAL features can be introduced
   over time to an otherwise stable protocol.




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   The rdma_opttype field carries a 32-bit unsigned integer.  The value
   in this field denotes an optional operation that MAY be supported by
   the receiver.  The values of this field and their meaning are defined
   in other Standards Track documents.

   The rdma_optinfo field carries opaque data.  The content of this
   field is data meaningful to the optional operation denoted by the
   value in rdma_opttype.  The content of this field is not defined in
   the base RPC-over-RDMA Version Two protocol, but is defined in other
   Standards Track documents

   When an implementation does not recognize or support the value
   contained in the rdma_opttype field, it MUST send an RPC-over-RDMA
   message with the rdma_xid field set to the same value as the
   erroneous message, the rdma_proc field set to RDMA2_ERROR, and the
   rdma_err field set to RDMA2_ERR_INVAL_OPTION.

4.2.  Message Direction

   Backward direction operation depends on the ability of the receiver
   to distinguish between incoming forward and backward direction calls
   and replies.  This needs to be done because both the XID field and
   the flow control value (RPC-over-RDMA credits) in the RPC-over-RDMA
   header are interpreted in the context of each message's direction.

   A receiver typically distinguishes message direction by examining the
   mtype field in the RPC header of each incoming payload message.
   However, RDMA2_OPTIONAL type messages may not carry an RPC message
   payload.

   To enable RDMA2_OPTIONAL type messages that do not carry an RPC
   message payload to be interpreted unambiguously, the rdma2_optional
   structure contains a field that identifies the message direction.  A
   similar field has been added to the rpcrdma2_chunk_lists and
   rpcrdma2_error structures to simplify parsing the RPC-over-RDMA
   header at the receiver.

4.3.  Documentation Requirements

   RPC-over-RDMA Version Two may be extended by defining a new
   rdma_opttype value, and then by providing an XDR description of the
   rdma_optinfo content that corresponds with the new rdma_opttype
   value.  As a result, a new header type is effectively created.

   A Standards Track document introduces each set of such protocol
   elements.  Together these elements are considered an OPTIONAL
   feature.  Each implementation is either aware of all the protocol
   elements introduced by that feature, or is aware of none of them.



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   Documents describing extensions to RPC-over-RDMA Version Two should
   contain:

   o  An explanation of the purpose and use of each new protocol element
      added

   o  An XDR description of the protocol elements, and a script to
      extract it

   o  A mechanism for reporting errors when the error is outside the
      available choices already available in the base protocol or in
      other extensions

   o  An indication of whether a Payload stream must be present, and a
      description of its contents

   o  A description of interactions with existing extensions

   The last bullet includes requirements that another OPTIONAL feature
   needs to be present for new protocol elements to work, or that a
   particular level of support be provided for some particular facility
   for the new extension to work.

   Implementers combine the XDR descriptions of the new features they
   intend to use with the XDR description of the base protocol in this
   document.  This may be necessary to create a valid XDR input file
   because extensions are free to use XDR types defined in the base
   protocol, and later extensions may use types defined by earlier
   extensions.

   The XDR description for the RPC-over-RDMA Version Two protocol
   combined with that for any selected extensions should provide an
   adequate human-readable description of the extended protocol.

5.  Transport Properties

5.1.  Introduction To Transport Properties

5.1.1.  Property Model

   A basic set of receiver and sender properties is specified in this
   document.  An extensible approach is used, allowing new properties to
   be defined in future standards track documents.

   Such properties are specified using:

   o  A code identifying the particular transport property being
      specified.



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   o  A nominally opaque array which contains within it the XDR encoding
      of the specific property indicated by the associated code.

   The following XDR types are used by operations that deal with
   transport properties:


   <CODE BEGINS>

   typedef rpcrdma2_propid uint32;

   struct rpcrdma2_propval {
           rpcrdma2_propid rdma_which;
           opaque          rdma_data<>;
   };

   typedef rpcrdma2_propval rpcrdma2_propset<>;

   typedef uint32 rpcrdma2_propsubset<>;

   <CODE ENDS>


   An rpcrdma2_propid specifies a particular transport property.  In
   order to allow easier XDR extension of the set of properties by
   concatenating XDR files, specific properties are defined as const
   values rather than as elements in an enum.

   An rpcrdma2_propval specifies a value of a particular transport
   property with the particular property identified by rdma_which, while
   the associated value of that property is contained within rdma_data.

   A rdma_data field which is of zero length is interpreted as
   indicating the default value or the property indicated by rdma_which.

   While rdma_data is defined as opaque within the XDR, the contents are
   interpreted (except when of length zero) using the XDR typedef
   associated with the property specified by rdma_which.  The receiver
   of a message containing an rpcrdma2_propval MUST report an XDR error
   [ cel: which error?  BAD_XDR, or do we want to add a new one? ] if
   the length of rdma_data is such that it extends beyond the bounds of
   the message transferred.

   In cases in which the rpcrdma2_propid specified by rdma_which is
   understood by the receiver, the receiver also MUST report an XDR
   error if either of the following occur: [ cel: which error?  BAD_XDR,
   or do we want to add a new one? ]




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   o  The nominally opaque data within rdma_data is not valid when
      interpreted using the property-associated typedef.

   o  The length of rdma_data is insufficient to contain the data
      represented by the property-associated typedef.

   Note that no error is to be reported if rdma_which is unknown to the
   receiver.  In that case, that rpcrdma2_propval is not processed and
   processing continues using the next rpcrdma2_propval, if any.

   A rpcrdma2_propset specifies a set of transport properties.  No
   particular ordering of the rpcrdma2_propval items within it is
   imposed.

   A rpcrdma2_propsubset identifies a subset of the properties in a
   previously specified rpcrdma2_propset.  Each bit in the mask denotes
   a particular element in a previously specified rpcrdma2_propset.  If
   a particular rpcrdma2_propval is at position N in the array, then bit
   number N mod 32 in word N div 32 specifies whether that particular
   rpcrdma2_propval is included in the defined subset.  Words beyond the
   last one specified are treated as containing zero.

   Propvalsubsets are useful in a number of contexts:

   o  In the specification of transport properties at connection, they
      allow the sender to specify what subset of those are subject to
      later change.

   o  In responding to a request to modify a set of transport
      properties, they allow the responding endpoint to specify the
      subsets of those properties for which the requested change has
      been performed or been rejected.

5.1.2.  Transport Property Groups

   Transport properties are divided into a number of groups

   o  A basic set of transport properties defined in this document.  See
      Section 5.2 for the complete list.

   o  Additional transport properties defined in future standards track
      documents as specified in Section 5.4.1.

   o  Experimental transport properties being explored preparatory to
      being considered for standards track definition.  See the
      description in Section 5.4.2.





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5.1.3.  Operations Related to Transport Properties

   There are a number of operations defined in Section 5.3 which are
   used to communicate and manage transport properties.

   Prime among these is RDMA2_CONNPROP (defined in Section 5.3.1 which
   serves as a means by which an endpoint's transport properties may be
   presented to its peer, typically upon establishing a connection.

   In addition, there are a set of related operations concerned with
   requesting, effecting and reporting changes in transport properties:

   o  RDMA2_REQPROP (defined in Section 5.3.2 which serves as a way for
      an endpoint to request that a peer change the values for a set of
      transport properties.

   o  RDMA2_RESPROP (defined in Section 5.3.3 is used to report on the
      disposition of each of the individual transport property changes
      requested in a previous RDMA2_REQPROP.

   o  RDMA2_UPDPROP (defined in Section 5.3.4 is used to report an
      unsolicited change in a transport property.

   Unlike many other operation types, the above are not used to effect
   transfer of RPC requests but are internal one-way information
   transfers.  However, a RDMA2_REQPROP and the corresponding
   RDMA2_RESPROP do constitute an RPC-like remote call.  The other
   operations are not part of a remote call transaction.

5.2.  Basic Transport Properties

   Although the set of transport properties is subject to later
   extension, a basic set of transport properties is defined below in
   Table 1.

   In that table, the columns contain the following information:

   o  The column labeled "property" identifies the transport property
      described by the current row.

   o  The column labeled "code" specifies the rpcrdma2_propid value used
      to identify this property.

   o  The column labeled "XDR type" gives the XDR type of the data used
      to communicate the value of this property.  This data type
      overlays the data portion of the nominally opaque field rdma_data
      in a rpcrdma2_propval.




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   o  The column labeled "default" gives the default value for the
      property which is to be assumed by those who do not receive, or
      are unable to interpret, information about the actual value of the
      property.

   o  The column labeled "section" indicates the section (within this
      document) that explains the semantics and use of this transport
      property.

   +---------+-----+------------------+----------------------+---------+
   | propert | cod | XDR type         | default              | section |
   | y       | e   |                  |                      |         |
   +---------+-----+------------------+----------------------+---------+
   | Receive | 1   | uint32           | 4096                 | 5.2.1   |
   | Buffer  |     |                  |                      |         |
   | Size    |     |                  |                      |         |
   | Backwar | 2   | enum rpcrdma2_bk | RDMA2_BKREQSUP_INLIN | 5.2.2   |
   | d       |     | reqsup           | E                    |         |
   | Request |     |                  |                      |         |
   | Support |     |                  |                      |         |
   +---------+-----+------------------+----------------------+---------+

                                  Table 1

   Note that this table does not provide any indication regarding
   whether a particular property can change or whether a change in the
   value may be requested (see Section 5.3.2).  Such matters are not
   addressed by the protocol definition.  An implementation may provide
   information about its readiness to make changed in a particular
   property using the rdma_nochg field in the RDMA2_CONNPROP message.

   A partner implementation can always request a change but peers MAY
   reject a request to change a property for any reason.
   Implementations are always free to reject such requests if they
   cannot or do not wish to effect the requested change.

   Either of the following will result in effective rejection requests
   to change specific properties:

   o  If an endpoint does not wish to accept request to change
      particular properties, it may reject such requests as described in
      Section 5.3.3.

   o  If an endpoint does not support the RDMA2_REQPROP operation, the
      effect would be the same as if every request to change a set of
      property were rejected.





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   With regard to unrequested changes in transport properties, it is the
   responsibility of the implementation making the change to do so in a
   fashion that which does not interfere with the other partner's
   continued correct operation (see Section 5.2.1).

5.2.1.  Receive Buffer Size

   The Receive Buffer Size specifies the minimum size, in octets, of
   pre-posted receive buffers.  It is the responsibility of the
   participant sending this value to ensure that its pre-posted receives
   are at least the size specified, allowing the participant receiving
   this value to send messages that are of this size.


   <CODE BEGINS>

   const uint32 RDMA2_PROPID_RBSIZ = 1;
   typedef uint32 rpcrdma2_prop_rbsiz;

   <CODE ENDS>


   The sender may use his knowledge of the receiver's buffer size to
   determine when the message to be sent will fit in the preposted
   receive buffers that the receiver has set up.  In particular,

   o  Requesters may use the value to determine when it is necessary to
      provide a Position-Zero read chunk when sending a request.

   o  Requesters may use the value to determine when it is necessary to
      provide a Reply chunk when sending a request, based on the maximum
      possible size of the reply.

   o  Responders may use the value to determine when it is necessary,
      given the actual size of the reply, to actually use a Reply chunk
      provided by the requester.

   Because there may be pre-posted receives with buffer sizes that
   reflect earlier values of the buffer size property, changing this
   property poses special difficulties:

   o  When the size is being raised, the partner should not be informed
      of the change until all pending receives using the older value
      have been eliminated.

   o  The size should not be reduced until the partner is aware of the
      need to reduce the size of future sends to conform to this reduced
      value.  To ensure this, such a change should only occur in



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      response to an explicit request by the other endpoint (See
      Section 5.3.2).  The participant making the request should use
      that lower size as the send size limit until the request is
      rejected (See Section 5.3.3) or an update to a size larger than
      the requested value becomes effective and the requested change is
      no longer pending (See Section 5.3.4).

5.2.2.  Backward Request Support

   The value of this property is used to indicate a client
   implementation's readiness to accept and process messages that are
   part of backward-direction RPC requests.


   <CODE BEGINS>

   enum rpcrdma2_bkreqsup {
           RDMA2_BKREQSUP_NONE    = 0,
           RDMA2_BKREQSUP_INLINE  = 1,
           RDMA2_BKREQSUP_GENL    = 2
   };

   const uint32 RDMA2_PROPID_BRS = 2;
   typedef rpcrdma2_bkreqsup rpcrdma2_prop_brs;

   <CODE ENDS>


   Multiple levels of support are distinguished:

   o  The value RDMA2_BKREQSUP_NONE indicates that receipt of backward-
      direction requests and replies is not supported.

   o  The value RDMA2_BKREQSUP_INLINE indicates that receipt of
      backward-direction requests or replies is only supported using
      inline messages and that use of explicit RDMA operations or other
      form of Direct Data Placement for backward direction requests or
      responses is not supported.

   o  The value RDMA2_BKREQSUP_GENL that receipt of backward-direction
      requests or replies is supported in the same ways that forward-
      direction requests or replies typically are.

   When information about this property is not provided, the support
   level of servers can be inferred from the backward- direction
   requests that they issue, assuming that issuing a request implicitly
   indicates support for receiving the corresponding reply.  On this
   basis, support for receiving inline replies can be assumed when



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   requests without read chunks, write chunks, or Reply chunks are
   issued, while requests with any of these elements allow the client to
   assume that general support for backward-direction replies is present
   on the server.

5.3.  New Operations

   The proposed new operations are set forth in Table 2 below.  In that
   table, the columns contain the following information:

   o  The column labeled "operation" specifies the particular operation.

   o  The column labeled "code" specifies the value of opttype for this
      operation.

   o  The column labeled "XDR type" gives the XDR type of the data
      structure used to describe the information in this new message
      type.  This data overlays the data portion of the nominally opaque
      field optinfo in an RDMA_OPTIONAL message.

   o  The column labeled "msg" indicates whether this operation is
      followed (or not) by an RPC message payload.

   o  The column labeled "section" indicates the section (within this
      document) that explains the semantics and use of this optional
      operation.

   +------------------------+------+------------------+------+---------+
   | operation              | code | XDR type         | msg  | section |
   +------------------------+------+------------------+------+---------+
   | Specify Properties at  | 1    | optinfo_connprop | No   | 5.3.1   |
   | Connection             |      |                  |      |         |
   | Request Property       | 2    | rpcrdma2_reqprop | No   | 5.3.2   |
   | Modification           |      |                  |      |         |
   | Respond to             | 3    | rpcrdma2_resprop | No   | 5.3.3   |
   | Modification Request   |      |                  |      |         |
   | Report Updated         | 4    | rpcrdma2_updprop | No   | 5.3.4   |
   | Properties             |      |                  |      |         |
   +------------------------+------+------------------+------+---------+

                                  Table 2

   Support for all of the operations above is OPTIONAL.  RPC-over-RDMA
   Version Two implementations that receive an operation that is not
   supported MUST respond with RDMA_ERROR message with an error code of
   RDMA_ERR_INVAL_OPTION.

   The only operation support requirements are as follows:



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   o  Implementations which send RDMA2_REQPROP messages must support
      RDMA2_RESPROP messages.

   o  Implementations which support RDMA2_RESPROP or RDMA2_UPDPROP
      messages must also support RDMA2_CONNPROP messages.

5.3.1.  RDMA2_CONNPROP: Specify Properties at Connection

   The RDMA2_CONNPROP message type allows an RPC-over-RDMA participant,
   whether client or server, to indicate to its partner relevant
   transport properties that the partner might need to be aware of.

   The message definition for this operation is as follows:


   <CODE BEGINS>

   struct rpcrdma2_connprop {
           rpcrdma2_propset rdma_start;
           rpcrdma2_propsubset rdma_nochg;
   };

   <CODE ENDS>


   All relevant transport properties that the sender is aware of should
   be included in rdma_start.  Since support of this request is
   OPTIONAL, and since each of the properties is OPTIONAL as well, the
   sender cannot assume that the receiver will necessarily take note of
   these properties and so the sender should be prepared for cases in
   which the partner continues to assume that the default value for a
   particular property is still in effect.

   Values of the subset of transport properties specified by rdma_nochg
   is not expected to change during the lifetime of the connection.

   Generally, a participant will send a RDMA2_CONNPROP message as the
   first message after a connection is established.  Given that fact,
   the sender should make sure that the message can be received by
   partners who use the default Receive Buffer Size.  The connection's
   initial receive buffer size is typically 1KB, but it depends on the
   initial connection state of the RPC-over-RDMA version in use.

   Properties not included in rdma_start are to be treated by the peer
   endpoint as having the default value and are not allowed to change
   subsequently.  The peer should not request changes in such
   properties.




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   Those receiving an RDMA2_CONNPROP may encounter properties that they
   do not support or are unaware of.  In such cases, these properties
   are simply ignored without any error response being generated.

5.3.2.  RDMA2_REQPROP: Request Modification of Properties

   The RDMA2_REQPROP message type allows an RPC-over-RDMA participant,
   whether client or server, to request of its partner that relevant
   transport properties be changed.

   The rdma_xid field allows the request to be tied to a corresponding
   response of type RDMA2_RESPROP (See Section 5.3.3.)  In assigning the
   value of this field, the sender does not need to avoid conflict with
   xid's associated with RPC messages or with RDMA2_REQPROP messages
   sent by the peer endpoint.

   The partner need not change the properties as requested by the sender
   but if it does support the message type, it will generate a
   RDMA2_RESPROP message, indicating the disposition of the request.

   The message definition for this operation is as follows:


   <CODE BEGINS>

   struct rpcrdma2_reqprop {
          rpcrdma2_propset rdma_want;
   };

   <CODE ENDS>


   The rpcrdma2_propset rdma_want is a set of transport properties
   together with the desired values requested by the sender.

5.3.3.  RDMA2_RESPROP: Respond to Request to Modify Transport Properties

   The RDMA2_RESPROP message type allows an RPC-over-RDMA participant to
   respond to a request to change properties by its partner, indicating
   how the request was dealt with.

   The message definition for this operation is as follows:









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   <CODE BEGINS>

   struct rpcrdma2_resprop {
           rpcrdma2_propsubset rdma_done;
           rpcrdma2_propsubset rdma_rejected;
           rpcrdma2_propset rdma_other;
   };

   <CODE ENDS>


   The rdma_xid field of this message must match that used in the
   RDMA2_REQPROP message to which this message is responding.

   The rdma_done field indicates which of the requested transport
   property changes have been effected as requested.  For each such
   property, the receiver is entitled to conclude that the requested
   change has been made and that future transmissions may be made based
   on the new value.

   The rdma_rejected field indicates which of the requested transport
   property changes have been rejected by the sender.  This may be
   because of any of the following reasons:

   o  The particular property specified is not known or supported by the
      receiver of the RDMA2_REQPROP message.

   o  The implementation receiving the RDMA2_REQPROP message does not
      support modification of this property.

   o  The implementation receiving the RDMA2_REQPROP message has chosen
      to reject the modification for another reason.

   The rdma_other field contains new values for properties where a
   change is requested.  The new value of the property is included and
   may be a value different from the original value in effect when the
   change was requested and from the requested value.  This is useful
   when the new value of some property is not as large as requested but
   still different from the original value, indicating a partial
   satisfaction of the peer's property change request.

   The sender MUST NOT include rpcrdma2_propval items within rdma_other
   that are for properties other than the ones for which the
   corresponding property request has requested a change.  If the
   receiver finds such a situation, it MUST ignore the erroneous
   rpcrdma2_propval items.





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   The subsets of properties specified by rdma_done, rdma_rejected, and
   included in rdma_other MUST NOT overlap, and when ored together,
   should cover the entire set of properties specified by rdma_want in
   the corresponding request.  If the receiver finds such an overlap or
   mismatch, it SHOULD treat properties missing or within the overlap as
   having been rejected.

5.3.4.  RDMA2_UPDPROP: Update Transport Properties

   The RDMA2_UPDPROP message type allows an RPC-over-RDMA participant to
   notify the other participant that a change to the transport
   properties has occurred.  This is because the sender has decided,
   independently, to modify one or more transport properties and is
   notifying the receiver of these changes.

   The message definition for this operation is as follows:


   <CODE BEGINS>

   struct rpcrdma2_updprop {
           rpcrdma2_propset rdma_now;
   };

   <CODE ENDS>


   rdma_now defines the new property values to be used.

5.4.  Extensibility

5.4.1.  Additional Properties

   The set of transport properties is designed to be extensible.  As a
   result, once new properties are defined in standards track documents,
   the operations defined in this document may reference these new
   transport properties, as well as the ones described in this document.

   A standards track document defining a new transport property should
   include the following information paralleling that provided in this
   document for the transport properties defined herein.

   o  The rpcrdma2_propid value used to identify this property.

   o  The XDR typedef specifying the form in which the property value is
      communicated.





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   o  A description of the transport property that is communicated by
      the sender of RDMA2_CONNPROP and RDMA2_UPDPROP and requested by
      the sender of RDMA2_REQPROP.

   o  An explanation of how this knowledge could be used by the
      participant receiving this information.

   o  Information giving rules governing possible changes of values of
      this property.

   The definition of transport property structures is such as to make it
   easy to assign unique values.  There is no requirement that a
   continuous set of values be used and implementations should not rely
   on all such values being small integers.  A unique value should be
   selected when the defining document is first published as an internet
   draft.  When the document becomes a standards track document working
   group should insure that:

   o  rpcrdma2_propid values specified in the document do not conflict
      with those currently assigned or in use by other pending working
      group documents defining transport properties.

   o  rpcrdma2_propid values specified in the document do not conflict
      with the range reserved for experimental use, as defined in
      Section 5.4.2.

   Documents defining new properties fall into a number of categories.

   o  Those defining new properties and explaining (only) how they
      affect use of existing message types.

   o  Those defining new OPTIONAL message types and new properties
      applicable to the operation of those new message types.

   o  Those defining new OPTIONAL message types and new properties
      applicable both to new and existing message types.

   When additional transport properties are proposed, the review of the
   associated standards track document should deal with possible
   security issues raised by those new transport properties.

5.4.2.  Experimental Properties

   Given the design of the transport properties data structure, it
   possible to use the operations to implement experimental, possibly
   unpublished, transport properties.





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   rpcrdma2_propid values in the range from 4,294,967,040 to
   4,294,967,295 are reserved for experimental use and these values
   should not be assigned to new properties in standards track
   documents.

   When values in this range are used there is no guarantee if
   successful interoperation among independent implementations.

6.  XDR Protocol Definition

   This section contains a description of the core features of the RPC-
   over-RDMA Version Two protocol, expressed in the XDR language
   [RFC4506].

   This description is provided in a way that makes it simple to extract
   into ready-to-compile form.  The reader can apply the following shell
   script to this document to produce a machine-readable XDR description
   of the RPC-over-RDMA Version One protocol without any OPTIONAL
   extensions.


   <CODE BEGINS>

   #!/bin/sh
   grep '^ *///' | sed 's?^ /// ??' | sed 's?^ *///$??'

   <CODE ENDS>


   That is, if the above script is stored in a file called "extract.sh"
   and this document is in a file called "spec.txt" then the reader can
   do the following to extract an XDR description file:


   <CODE BEGINS>

   sh extract.sh < spec.txt > rpcrdma_corev2.x

   <CODE ENDS>


   Optional extensions to RPC-over-RDMA Version Two, published as
   Standards Track documents, will have similar means of providing XDR
   that describes those extensions.  Once XDR for all desired extensions
   is also extracted, it can be appended to the XDR description file
   extracted from this document to produce a consolidated XDR
   description file reflecting all extensions selected for an RPC-over-
   RDMA implementation.



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6.1.  Code Component License

   Code components extracted from this document must include the
   following license text.  When the extracted XDR code is combined with
   other complementary XDR code which itself has an identical license,
   only a single copy of the license text need be preserved.













































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   <CODE BEGINS>

   /// /*
   ///  * Copyright (c) 2010, 2016 IETF Trust and the persons
   ///  * identified as authors of the code.  All rights reserved.
   ///  *
   ///  * The authors of the code are:
   ///  * B. Callaghan, T. Talpey, C. Lever, and D. Noveck.
   ///  *
   ///  * Redistribution and use in source and binary forms, with
   ///  * or without modification, are permitted provided that the
   ///  * following conditions are met:
   ///  *
   ///  * - Redistributions of source code must retain the above
   ///  *   copyright notice, this list of conditions and the
   ///  *   following disclaimer.
   ///  *
   ///  * - Redistributions in binary form must reproduce the above
   ///  *   copyright notice, this list of conditions and the
   ///  *   following disclaimer in the documentation and/or other
   ///  *   materials provided with the distribution.
   ///  *
   ///  * - Neither the name of Internet Society, IETF or IETF
   ///  *   Trust, nor the names of specific contributors, may be
   ///  *   used to endorse or promote products derived from this
   ///  *   software without specific prior written permission.
   ///  *
   ///  *   THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS
   ///  *   AND CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED
   ///  *   WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
   ///  *   IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
   ///  *   FOR A PARTICULAR PURPOSE ARE DISCLAIMED.  IN NO
   ///  *   EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
   ///  *   LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
   ///  *   EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
   ///  *   NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
   ///  *   SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
   ///  *   INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
   ///  *   LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
   ///  *   OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING
   ///  *   IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
   ///  *   ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
   ///  */

   <CODE ENDS>






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6.2.  RPC-Over-RDMA Version Two XDR

   The XDR defined in this section is used to encode the Transport
   Header Stream in each RPC-over-RDMA Version Two message.  The terms
   "Transport Header Stream" and "RPC Payload Stream" are defined in
   Section 4 of [I-D.ietf-nfsv4-rfc5666bis].


   <CODE BEGINS>

   /// /* From RFC 5531, Section 9 */
   /// enum msg_type {
   ///         CALL = 0,
   ///         REPLY = 1
   /// };
   ///
   /// struct rpcrdma2_segment {
   ///         uint32 rdma_handle;
   ///         uint32 rdma_length;
   ///         uint64 rdma_offset;
   /// };
   ///
   /// struct rpcrdma2_read_segment {
   ///         uint32                  rdma_position;
   ///         struct rpcrdma2_segment rdma_target;
   /// };
   ///
   /// struct rpcrdma2_read_list {
   ///         struct rpcrdma2_read_segment rdma_entry;
   ///         struct rpcrdma2_read_list    *rdma_next;
   /// };
   ///
   /// struct rpcrdma2_write_chunk {
   ///         struct rpcrdma2_segment rdma_target<>;
   /// };
   ///
   /// struct rpcrdma2_write_list {
   ///         struct rpcrdma2_write_chunk rdma_entry;
   ///         struct rpcrdma2_write_list  *rdma_next;
   /// };
   ///
   /// struct rpcrdma2_chunk_lists {
   ///         enum msg_type               rdma_direction;
   ///         uint32                      rdma_inv_handle;
   ///         struct rpcrdma2_read_list   *rdma_reads;
   ///         struct rpcrdma2_write_list  *rdma_writes;
   ///         struct rpcrdma2_write_chunk *rdma_reply;
   /// };



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   ///
   /// enum rpcrdma2_errcode {
   ///         RDMA2_ERR_VERS = 1,
   ///         RDMA2_ERR_BAD_XDR = 2,
   ///         RDMA2_ERR_REPLY_RESOURCE = 3,
   ///         RDMA2_ERR_INVAL_PROC = 4,
   ///         RDMA2_ERR_INVAL_OPTION = 5
   ///         RDMA2_ERR_SYSTEM = 6,
   /// };
   ///
   /// struct rpcrdma2_err_vers {
   ///         uint32 rdma_vers_low;
   ///         uint32 rdma_vers_high;
   /// };
   ///
   /// struct rpcrdma2_err_reply {
   ///         uint32 rdma_segment_index;
   ///         uint32 rdma_length_needed;
   /// };
   ///
   /// union rpcrdma2_error switch (rpcrdma2_errcode rdma_err) {
   ///         case RDMA2_ERR_VERS:
   ///           rpcrdma2_err_vers rdma_vrange;
   ///         case RDMA2_ERR_BAD_XDR:
   ///           void;
   ///         case RDMA2_ERR_REPLY_RESOURCE:
   ///           rpcrdma2_err_reply rdma_reply;
   ///         case RDMA2_ERR_INVAL_PROC:
   ///           void;
   ///         case RDMA2_ERR_INVAL_OPTION:
   ///           void;
   ///         case RDMA2_ERR_SYSTEM:
   ///           void;
   /// };
   ///
   /// struct rpcrdma2_optional {
   ///         enum msg_type rdma_optdir;
   ///         uint32 rdma_opttype;
   ///         opaque rdma_optinfo<>;
   /// };
   ///
   /// typedef rpcrdma2_propid uint32;
   ///
   /// struct rpcrdma2_propval {
   ///         rpcrdma2_propid rdma_which;
   ///         opaque          rdma_data<>;
   /// };
   ///



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   /// typedef rpcrdma2_propval rpcrdma2_propset<>;
   /// typedef uint32 rpcrdma2_propsubset<>;
   ///
   /// struct rpcrdma2_connprop {
   ///         rpcrdma2_propset rdma_start;
   ///         rpcrdma2_propsubset rdma_nochg;
   /// };
   ///
   /// struct rpcrdma2_reqprop {
   ///        rpcrdma2_propset rdma_want;
   /// };
   ///
   /// struct rpcrdma2_resprop {
   ///        rpcrdma2_propsubset rdma_done;
   ///        rpcrdma2_propsubset rdma_rejected;
   ///        rpcrdma2_propset rdma_other;
   /// };
   ///
   /// struct rpcrdma2_updprop {
   ///        rpcrdma2_propset rdma_now;
   /// };

   /// enum rpcrdma2_proc {
   ///         RDMA2_MSG = 0,
   ///         RDMA2_NOMSG = 1,
   ///         RDMA2_ERROR = 4,
   ///         RDMA2_OPTIONAL = 5,
   ///         RDMA2_CONNPROP = 6,
   ///         RDMA2_REQPROP = 7,
   ///         RDMA2_RESPROP = 8,
   ///         RDMA2_UPDPROP = 9
   /// };
   ///
   /// union rpcrdma2_body switch (rpcrdma2_proc rdma_proc) {
   ///         case RDMA2_MSG:
   ///           rpcrdma2_chunk_lists rdma_chunks;
   ///         case RDMA2_NOMSG:
   ///           rpcrdma2_chunk_lists rdma_chunks;
   ///         case RDMA2_ERROR:
   ///           rpcrdma2_error rdma_error;
   ///         case RDMA2_OPTIONAL:
   ///           rpcrdma2_optional rdma_optional;
   ///         case RDMA2_CONNPROP:
   ///           rpcrdma2_connprop rdma_connprop;
   ///         case RDMA2_REQPROP:
   ///           rpcrdma2_reqprop rdma_reqprop;
   ///         case RDMA2_RESPROP:
   ///           rpcrdma2_resprop rdma_resprop;



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   ///         case RDMA2_UPDPROP:
   ///           rpcrdma2_updprop rdma_updprop;
   /// };
   ///
   /// struct rpcrdma2_xprt_hdr {
   ///           uint32 rdma_xid;
   ///           uint32 rdma_vers;
   ///           uint32 rdma_credit;
   ///           rpcrdma2_body rdma_body;
   /// };
   ///
   /// /*
   ///  * Transport propid values for basic properties
   ///  */
   /// const uint32 RDMA2_PROPID_RBSIZ = 1;
   /// const uint32 RDMA2_PROPID_BRS = 2;
   ///
   /// /*
   ///  * Transport property typedefs
   ///  */
   /// typedef uint32 rpcrdma2_prop_rbsiz;
   /// typedef rpcrdma2_bkreqsup rpcrdma2_prop_brs;
   ///
   /// enum rpcrdma2_bkreqsup {
   ///         RDMA2_BKREQSUP_NONE = 0,
   ///         RDMA2_BKREQSUP_INLINE = 1,
   ///         RDMA2_BKREQSUP_GENL = 2
   /// };

   <CODE ENDS>


6.2.1.  Presence Of Payload

   o  When the rdma_proc field has the value RDMA2_MSG, an RPC Payload
      Stream MUST follow the Transport Header Stream in the Send buffer.

   o  When the rdma_proc field has the value RDMA2_ERROR, an RPC Payload
      Stream MUST NOT follow the Transport Header Stream.

   o  When the rdma_proc field has the value RDMA2_OPTIONAL, all, part
      of, or no RPC Payload Stream MAY follow the Transport header
      Stream in the Send buffer.








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6.2.2.  Message Direction

   Implementations of RPC-over-RDMA Version Two are REQUIRED to support
   backwards direction operation as described in
   [I-D.ietf-nfsv4-rpcrdma-bidirection].  RPC-over-RDMA Version Two
   introduces the rdma_direction field in its transport header to
   optimize the process of distinguishing between forward- and
   backwards-direction messages.

   The rdma_direction field qualifies the value contained in the
   transport header's rdma_xid field.  This enables a receiver to
   reliably avoid performing an XID lookup on incoming backwards-
   direction Call messages.

   In general, when a message carries an XID that was generated by the
   message's receiver (that is, the receiver is acting as a requester),
   the message's sender sets the rdma_direction field to REPLY (1).
   Otherwise the rdma_direction field is set to CALL (0).  For example:

   o  When the rdma_proc field has the value RDMA2_MSG or RDMA2_NOMSG,
      the value of the rdma_direction field MUST be the same as the
      value of the associated RPC message's msg_type field.

   o  When the rdma_proc field has the value RDMA2_OPTIONAL and a whole
      or partial RPC message payload is present, the value of the
      rdma_optdir field MUST be the same as the value of the associated
      RPC message's msg_type field.

   o  When the rdma_proc field has the value RDMA2_OPTIONAL and no RPC
      message payload is present, a Requester MUST set the value of the
      rdma_optdir field to CALL, and a Responder MUST set the value of
      the rdma_optdir field to REPLY.  The Requester chooses a value for
      the rdma_xid field from the XID space that matches the message's
      direction.  Requesters and Responders set the rdma_credit field in
      a similar fashion: a value is set that is appropriate for the
      direction of the message.

   o  When the rdma_proc field has the value RDMA2_ERROR, the direction
      of the message is always Responder-to-Requester (REPLY).

6.2.3.  Remote Invalidation

   To request Remote Invalidation, a requester MUST set the value of the
   rdma_inv_handle field in an RPC Call's transport header to a non-zero
   value that matches one of the rdma_handle fields in that header.  If
   none of the rdma_handle values in the Call may be invalidated by the
   responder, the requester MUST set the RPC Call's rdma_inv_handle
   field to the value zero.



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   If the responder chooses not to use Remote Invalidation for this
   particular RPC Reply, or the RPC Call's rdma_inv_handle field
   contains the value zero, the responder MUST use RDMA Send to transmit
   the matching RPC reply.

   If a requester has provided a non-zero value in the RPC Call's
   rdma_inv_handle field and the responder chooses to use Remote
   Invalidation for the matching RPC Reply, the responder MUST use RDMA
   Send With Invalidate to transmit that RPC reply, and MUST use the
   value in the RPC Call's rdma_inv_handle field to construct the Send
   With Invalidate Work Request.

6.2.4.  Transport Errors

   Error handling works the same way in RPC-over-RDMA Version Two as it
   does in RPC-over-RDMA Version One, with the addition of several new
   error codes.  Version One error handling is described in Section 5 of
   [I-D.ietf-nfsv4-rfc5666bis].

   In all cases below, the sender copies the values of the rdma_xid and
   rdma_vers fields from the incoming transport header that generated
   the error to transport header of the error response.  The rdma_proc
   field is set to RDMA2_ERROR.

   RDMA2_ERR_VERS
      This is the equivalent of ERR_VERS in RPC-over-RDMA Version One.
      The error code value, semantics, and utilization are the same.

   RDMA2_ERR_INVAL_PROC
      This is a new error code in RPC-over-RDMA Version Two.  If a
      receiver recognizes the value in the rdma_vers field, but it does
      not recognize the value in the rdma_proc field, it MUST send
      RDMA2_ERR_INVAL_PROC.

   RDMA2_ERR_BAD_XDR
      This is the equivalent of ERR_CHUNK in RPC-over-RDMA Version One,
      with a few extra restrictions.  The error code value is the same.

      If a receiver recognizes the values in the rdma_vers and rdma_proc
      fields, but the incoming RPC-over-RDMA transport header cannot be
      parsed, the receiver MUST send RDMA2_ERR_BAD_XDR before Upper
      Layer Protocol processing starts.

   RDMA2_ERR_REPLY_RESOURCE
      This is a new error code in RPC-over-RDMA Version Two.  If the
      RPC-over-RDMA transport header is otherwise correct, but the
      requester has not provided enough Write or Reply chunk resources




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      to transmit the reply, the responder MUST send
      RDMA2_ERR_REPLY_RESOURCE.

      The responder MUST set the rdma_segment_index field to point to
      the first segment in the transport header that is too short, or to
      zero to indicate that it was not possible to determine which
      segment was too small.  Indexing starts at one (1), which
      represents the first segment in the first Write chunk (in either
      the Write list or Reply chunk).  The responder MUST set the
      rdma_length_needed to the number of bytes needed in that segment
      in order to convey the reply.

      Upon receipt of this error code, a responder MAY choose to
      terminate the operation (for instance, if the responder set the
      index and length fields to zero), or it MAY send the request again
      using the same XID and larger reply resources.

   RDMA2_ERR_INVAL_OPTION
      This is a new error code in RPC-over-RDMA Version Two.  A receiver
      MUST send RDMA2_ERR_INVAL_OPTION when an RDMA2_OPTIONAL message is
      received and the receiver does not recognize the value in the
      rdma_opttype field.

   RDMA2_ERR_SYSTEM
      This is a new error code in RPC-over-RDMA Version Two.  If some
      problem occurs on a receiver that does not fit into the above
      categories, the receiver MAY report it to the sender using the
      error code RDMA2_ERR_SYSTEM.  This is a permanent error: a
      requester that receives this error MUST terminate the RPC
      transaction associated with the XID value in the rdma_xid field.

7.  Protocol Version Negotiation

   When an RPC-over-RDMA Version Two client establishes a connection to
   a server, the first order of business is to determine the server's
   highest supported protocol version.

   As with RPC-over-RDMA Version One, a client MUST assume the ability
   to exchange only a single RPC-over-RDMA message at a time until it
   receives a valid non-error RPC-over-RDMA message from the server that
   reports the server's credit limit.

   First, the client sends a single valid RPC-over-RDMA message with the
   value two (2) in the rdma_vers field.  Because the server might
   support only RPC-over-RDMA Version One, this initial message can be
   no larger than the Version One default inline threshold of 1024
   bytes.




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7.1.  Server Does Support RPC-over-RDMA Version Two

   If the server does support RPC-over-RDMA Version Two, it sends RPC-
   over-RDMA messages back to the client with the value two (2) in the
   rdma_vers field.  Both peers may use the default inline threshold
   value for RPC-over-RDMA Version Two connections (4096 bytes).

7.2.  Server Does Not Support RPC-over-RDMA Version Two

   If the server does not support RPC-over-RDMA Version Two, it MUST
   send an RPC-over-RDMA message to the client with the same XID, with
   RDMA2_ERROR in the rdma_proc field, and with the error code
   RDMA2_ERR_VERS.  This message also reports a range of protocol
   versions that the server supports.  To continue operation, the client
   selects a protocol version in the range of server-supported versions
   for subsequent messages on this connection.

   If the connection is lost immediately after an RDMA2_ERROR /
   RDMA2_ERR_VERS message is received, a client can avoid a possible
   version negotiation loop when re-establishing another connection by
   assuming that particular server does not support RPC-over-RDMA
   Version Two.  A client can assume the same situation (no server
   support for RPC-over-RDMA Version Two) if the initial negotiation
   message is lost or dropped.  Once the negotiation exchange is
   complete, both peers may use the default inline threshold value for
   the transport protocol version that has been selected.

7.3.  Client Does Not Support RPC-over-RDMA Version Two

   If the server supports the RPC-over-RDMA protocol version used in
   Call messages from a client, it MUST send Replies with the same RPC-
   over-RDMA protocol version that the client uses to send its Calls.

7.4.  Security Considerations

   The security considerations for RPC-over-RDMA Version Two are the
   same as those for RPC-over-RDMA Version One.

7.4.1.  Security Considerations (Transport Properties)

   Like other fields that appear in each RPC-over-RDMA header, property
   information is sent in the clear on the fabric with no integrity
   protection, making it vulnerable to man-in-the-middle attacks.

   For example, if a man-in-the-middle were to change the value of the
   Receive buffer size or the Requester Remote Invalidation boolean, it
   could reduce connection performance or trigger loss of connection.
   Repeated connection loss can impact performance or even prevent a new



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   connection from being established.  Recourse is to deploy on a
   private network or use link-layer encryption.

8.  IANA Considerations

   There are no IANA considerations at this time.

9.  References

9.1.  Normative References

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

   [RFC4506]  Eisler, M., Ed., "XDR: External Data Representation
              Standard", STD 67, RFC 4506, DOI 10.17487/RFC4506, May
              2006, <http://www.rfc-editor.org/info/rfc4506>.

   [RFC5531]  Thurlow, R., "RPC: Remote Procedure Call Protocol
              Specification Version 2", RFC 5531, DOI 10.17487/RFC5531,
              May 2009, <http://www.rfc-editor.org/info/rfc5531>.

9.2.  Informative References

   [I-D.ietf-nfsv4-rfc5666bis]
              Lever, C., Simpson, W., and T. Talpey, "Remote Direct
              Memory Access Transport for Remote Procedure Call, Version
              One", draft-ietf-nfsv4-rfc5666bis-08 (work in progress),
              November 2016.

   [I-D.ietf-nfsv4-rpcrdma-bidirection]
              Lever, C., "Bi-directional Remote Procedure Call On RPC-
              over-RDMA Transports", draft-ietf-nfsv4-rpcrdma-
              bidirection-05 (work in progress), June 2016.

   [IB]       InfiniBand Trade Association, "InfiniBand Architecture
              Specifications", <http://www.infinibandta.org>.

   [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, <http://www.rfc-editor.org/info/rfc5040>.







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

   [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,
              <http://www.rfc-editor.org/info/rfc5661>.

   [RFC5662]  Shepler, S., Ed., Eisler, M., Ed., and D. Noveck, Ed.,
              "Network File System (NFS) Version 4 Minor Version 1
              External Data Representation Standard (XDR) Description",
              RFC 5662, DOI 10.17487/RFC5662, January 2010,
              <http://www.rfc-editor.org/info/rfc5662>.

   [RFC5666]  Talpey, T. and B. Callaghan, "Remote Direct Memory Access
              Transport for Remote Procedure Call", RFC 5666,
              DOI 10.17487/RFC5666, January 2010,
              <http://www.rfc-editor.org/info/rfc5666>.

Appendix A.  Acknowledgments

   The authors gratefully acknowledge the work of Brent Callaghan and
   Tom Talpey on the original RPC-over-RDMA Version One specification
   [RFC5666].  The authors also wish to thank Bill Baker, Greg Marsden,
   and Matt Benjamin for their support of this work.

   The extract.sh shell script and formatting conventions were first
   described by the authors of the NFSv4.1 XDR specification [RFC5662].

   Special thanks go to nfsv4 Working Group Chair Spencer Shepler and
   nfsv4 Working Group Secretary Thomas Haynes for their support.

Authors' Addresses

   Charles Lever (editor)
   Oracle Corporation
   1015 Granger Avenue
   Ann Arbor, MI  48104
   USA

   Phone: +1 248 816 6463
   Email: chuck.lever@oracle.com







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   David Noveck
   Hewlett Packard Enterprise
   165 Dascomb Road
   Andover, MA  01810
   USA

   Phone: +1 978 474 2011
   Email: davenoveck@gmail.com











































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