operation	code	XDR type	msg	section
Specify Properties at Connection	1	optinfo_connprop	No	4.1
Request Property Modification	2	optinfo_reqprop	No	4.2
Respond to Modification Request	3	optinfo_resprop	No	4.3
Report Updated Properties	4	optinfo_updprop	No	4.4

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 as specified in [rpcrdmav2]

The only operation support requirements are as follows:

• Implementations which send ROPT_REQPROP messages must support ROPT_RESPROP messages.
• Implementations which support ROPT_RESPROP or ROPT_UPDPROP messages must also support ROPT_CONNPROP messages.

4.1. ROPT_CONNPROP: Specify Properties at Connection

The ROPT_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.

<CODE BEGINS>

const uint32     ROPT_CONNPROP= 1;

struct optinfo_connprop {
        propvalset      opticonnpr_start;
        propvalsubset   opticonnpr_nochg;
};        
 
<CODE ENDS>
          

The message definition for this operation is as follows:

All relevant transport properties that the sender is aware of should be included in opticonnpr_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 opticonnpr_nochg is not expected to change during the lifetime of the connection.

Generally, a participant will send a ROPT_CONNPR 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. See [rpcrdmav2] for details.

Properties not included in opticonnpr_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.

Those receiving an ROPT_CONNPR 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.

4.2. ROPT_REQPROP: Request Modification of Properties

The ROPT_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 ROPT_RESPROP (See Section 4.3.) In assigning the value of this field, the sender does not need to avoid conflict with xid's associated with RPC messages or with ROPT_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 ROPT_RESPROP message, indicating the disposition of the request.

<CODE BEGINS>

const uint32     ROPT_REQPROP = 2;

struct optinfo_reqprop {
       propvalset      optreqpr_want;
                       
};        
 
<CODE ENDS>
          

The message definition for this operation is as follows:

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

4.3. ROPT_RESPROP: Respond to Request to Modify Transport Properties

The ROPT_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.

<CODE BEGINS>

const uint32     ROPT_RESPROP = 3;

struct optinfo_resprop {
        propvalsubset   optrespr_done;
        propvalsubset   optrespr_rej;
        propvalset      optrespr_other;                        
};        
 
<CODE ENDS>
          

The message definition for this operation is as follows:

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

The optrespr_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 optrespr_rej 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:

• The particular property specified is not known or supported by the receiver of the ROPT_REQPROP message.
• The implementation receiving the ROPT_REQPROP message does not support modification of this property.
• The implementation receiving the ROPT_REQPROP message has chosen to reject the modification for another reason.

The optrespr_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 propvals within optrespr_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 propvals.

The subsets of properties specified by optrespr_done, optrespr_rej, and included in optrespr_other MUST NOT overlap, and when ored together, should cover the entire set of properties specified by optreqpr_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.

4.4. ROPT_UPDPROP: Update Transport Properties

The ROPT_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.

<CODE BEGINS>
 
const uint32     ROPT_UPDPROP = 4;

struct optinfo_updprop {
        propvalset        optupdpr_now;
};        

<CODE ENDS>

          

The message definition for this operation is as follows:

optupdpr_now defines the new property values to be used.

5. XDR

This section contains an XDR [RFC4506] description of the proposed extension.

<CODE BEGINS>

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

<CODE ENDS>

       

This description is provided in a way that makes it simple to extract into ready-to-use form. The reader can apply the following shell script to this document to produce a machine-readable XDR description of extension which can be combined with XDR for the base protocol to produce an XDR that combines the base protocol with the optional extensions.

<CODE BEGINS>

sh extract.sh < ext.txt > charext.x

<CODE ENDS>

        

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

5.1. Code Component License

<CODE BEGINS>

/// /*
///  * Copyright (c) 2010, 2016 IETF Trust and the persons
///  * identified as authors of the code.  All rights reserved.
///  *
///  * The author of the code is: 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>

          

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.

5.2. XDR Proper for Extension

<CODE BEGINS>

///
////*
/// * Core transport property types
/// */ 
///typedef propid          uint32;
///
///struct propval {
///        propid          pv_which;
///        opaque          pv_data<>;
///};
///
///typedef propval         propvalset<>;
///
///typedef uint32          propvalsubset<>;
///
////*
/// * Transport property codes for basic properties
/// */
///const uint32    PROP_RBSIZ = 1;
///const uint32    PROP_REQREMINV = 2;
///const uint32    PROP_BRS = 3;
///
////*
/// * Other transport property types
/// */
///enum bkreqsup {
///        BKREQSUP_NONE    = 0,
///        BKREQSUP_INLINE  = 1,
///        BKREQSUP_GENL    = 2
///};
///
////*
/// * Transport property typedefs
/// */
///typedef uint32   prop_bsiz;
///typedef bool     prop_reqreminv;
///typedef bkreqsup prop_brs;                
///
////*
/// * Optional operation codes
/// */
///const uint32     ROPT_CONNPROP = 1;
///const uint32     ROPT_REQPROP = 2;
///const uint32     ROPT_RESPRO = 3;
///const uint32     ROPT_UPDPROP = 4;
///
////*
/// * Optional operation message structures
/// */
///struct optinfo_connprop {
///        propvalset      opticonnpr_start;
///        propvalsubset   opticonnpr_nochg;
///};        
///
///struct optinfo_reqprop {
///       propvalset      optreqpr_want;
///                       
///};                
///
///struct optinfo_resprop {
///        propvalsubset   optrespr_done;
///        propvalsubset   optrespr_rej;
///        propvalset      optrespr_other;                        
///};                
///
///struct optinfo_updprop {
///        propvalset      optupdpr_now;
///};        

<CODE ENDS>
          

6. Extensibility

6.1. 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.

• The propid value used to identify this property.
• The XDR typedef specifying the form in which the property value is communicated.
• A description of the transport property that is communicated by the sender of ROPT_INITXCH and ROPT_UPDXCH and requested by the sender of ROP_REQXCH.
• An explanation of how this knowledge could be used by the participant receiving this information.
• 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:

• The propids specified in the document do not conflict with those currently assigned or in use by other pending working group documents defining transport properties.
• The propids specified in the document do not conflict with the range reserved for experimental use, as defined in Section 6.2.

Documents defining new properties fall into a number of categories.

• Those defining new properties and explaining (only) how they affect use of existing message types.
• Those defining new OPTIONAL message types and new properties applicable to the operation of those new message types.
• 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.

6.2. Experimental Properties

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

propids 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.

7. Security Considerations

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

8. IANA Considerations

This document does not require any actions by IANA.

9. References

9.1. Normative References

[bidir]	Lever, C., "Size-Limited Bi-directional Remote Procedure Call On Remote Direct Memory Access Transports", April 2016. Work in progress.
[RFC2119]	Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997.
[RFC4506]	Eisler, M., "XDR: External Data Representation Standard", STD 67, RFC 4506, DOI 10.17487/RFC4506, May 2006.
[rfc5666bis]	Lever, C., Simpson, W. and T. Talpey, "Remote Direct Memory Access Transport for Remote Procedure Call", May 2016. Work in progress.
[rpcrdmav2]	Lever, C. and D. Noveck, "RPC-over-RDMA Version Two", June 2016. Work in progress.

9.2. Informative References

[RFC5662]	Shepler, S., Eisler, M. and D. Noveck, "Network File System (NFS) Version 4 Minor Version 1 External Data Representation Standard (XDR) Description", RFC 5662, DOI 10.17487/RFC5662, January 2010.
[RFC5666]	Talpey, T. and B. Callaghan, "Remote Direct Memory Access Transport for Remote Procedure Call", RFC 5666, DOI 10.17487/RFC5666, January 2010.

Appendix A. Acknowledgments

The author gratefully acknowledges the work of Brent Callaghan and Tom Talpey producing the original RPC-over-RDMA Version One specification [RFC5666] and also Tom's work in helping to clarify that specification.

The author also wishes to thank Chuck Lever for his work resurrecting NFS support for RDMA in [rfc5666bis] and for his helpful review of and suggestions for this document.

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

Author's Address