RPC-over-RDMA Extension to Manage Transport Characteristics
draft-dnoveck-nfsv4-rpcrdma-xcharext-02
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draft-dnoveck-nfsv4-rpcrdma-xcharext-02
Network File System Version 4 D. Noveck
Internet-Draft HPE
Intended status: Standards Track August 18, 2016
Expires: February 19, 2017
RPC-over-RDMA Extension to Manage Transport Characteristics
draft-dnoveck-nfsv4-rpcrdma-xcharext-02
Abstract
This document specifies an extension to RPC-over-RDMA Version Two.
The extension enables endpoints of an RPC-over-RDMA connection to
exchange information which can be used to optimize message transfer.
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 February 19, 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
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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.
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Table of Contents
1. Preliminaries . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 2
1.2. Introduction . . . . . . . . . . . . . . . . . . . . . . 2
1.3. Role Terminology . . . . . . . . . . . . . . . . . . . . 3
2. Transport Characteristics . . . . . . . . . . . . . . . . . . 4
2.1. Characteristics Model . . . . . . . . . . . . . . . . . . 4
2.2. Transport Characteristics Groups . . . . . . . . . . . . 5
2.3. Operations Related to Transport Characteristics . . . . . 6
3. Initial Transport Characteristics . . . . . . . . . . . . . . 6
3.1. Receive Buffer Size . . . . . . . . . . . . . . . . . . . 8
3.2. Requester Remote Invalidation . . . . . . . . . . . . . . 9
3.3. Backward Request Support . . . . . . . . . . . . . . . . 9
4. New Operations . . . . . . . . . . . . . . . . . . . . . . . 10
4.1. ROPT_INITXCH: Specify Initial Characteristics . . . . . . 11
4.2. ROPT_REQXCH: Request Modification of Characteristics . . 12
4.3. ROPT_RESPXCH: Respond to Request to Modify Transport
Characteristics . . . . . . . . . . . . . . . . . . . . . 13
4.4. ROPT_UPDXCH: Update Transport Characteristics . . . . . . 14
5. XDR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
5.1. Code Component License . . . . . . . . . . . . . . . . . 16
5.2. XDR Proper for Extension . . . . . . . . . . . . . . . . 18
6. Extensibility . . . . . . . . . . . . . . . . . . . . . . . . 19
6.1. Additional Characteristics . . . . . . . . . . . . . . . 19
6.2. Experimental Characteristics . . . . . . . . . . . . . . 20
7. Security Considerations . . . . . . . . . . . . . . . . . . . 21
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 21
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 21
9.1. Normative References . . . . . . . . . . . . . . . . . . 21
9.2. Informative References . . . . . . . . . . . . . . . . . 22
Appendix A. Acknowledgments . . . . . . . . . . . . . . . . . . 22
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 22
1. Preliminaries
1.1. 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].
1.2. Introduction
This document specifies an extension to RPC-over-RDMA Version Two.
It allows each participating endpoint on a single connection to
communicate various characteristics of its implementation, to request
changes in characteristics of the other endpoint, and to effect
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changes and notify the other endpoint of changes to these
characteristics during operation.
The extension described herein specifies OPTIONAL message header
types to implement this mechanism. The means by which the
implementation support status of these OPTIONAL types is ascertained
is described in [rpcrmdav2].
Although this document specifies the new OPTIONAL message header
types to implement these functions, the precise means by which the
presence of support for these OPTIONAL functions will be ascertained
is not described here, as would be done more appropriately by the RFC
defining a version of RPC-over-RDMA which supports protocol
extension.
This document is currently written to conform to the extension model
for RPC-over-RDMA Version Two as described in [rpcrdmav2].
1.3. Role Terminology
A number of different terms are used regarding the roles of the two
participants in an RPC-over-RMA connection. Some of these roles last
for the duration of a connection while others vary from request to
request or from message to message.
The roles of the client and server are fixed for the lifetime of the
connection, with the client defined as the endpoint which initiated
the connection.
The roles of requester and responder often parallel those of client
and server, although this is not always the case. Most requests are
made in the forward direction, in which the client is the requester
and the server is the responder. However, backward-direction
requests are possible, in which case the server is the requester and
the client is the responder. As a result, clients and servers may
both act as requesters and responders.
The roles of sender and receiver vary from message. With regard to
the messages described in this document, both the client and the
server can act as sender and receiver. With regard to messages used
to transfer RPC requests and replies, the requester sends requests
and receives replies while the responder receives requests and sends
replies.
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2. Transport Characteristics
2.1. Characteristics Model
An initial set of receiver and sender characteristics are specified
in this document. An extensible approach is used, allowing new
characteristics to be defined in future standards track documents.
Such characteristics are specified using:
o A code identifying the particular transport characteristic being
specified.
o A nominally opaque array which contains within it the XDR encoding
of the specific characteristic indicated by the associated code.
The following XDR types are used by operations that deal with
transport characteristics:
<CODE BEGINS>
typedef xcharid uint32;
struct xcharval {
xcharid xchv_which;
opaque xchv_data<>;
};
typedef xcharspec xcharval<>;
typedef uint32 xcharsubset<>;
<CODE ENDS>
An xcharid specifies a particular transport characteristic. In order
to allow easier XDR extension of the set of characteristics by
concatenating XDR files, specific characteristics are defined as
const values rather than as elements in an enum.
An xcharval specifies a value of a particular transport
characteristic with the particular characteristic identified by
xchv_which, while the associated value of that characteristic is
contained within xchv_data.
While xchv_data is defined as opaque within the XDR, the contents are
interpreted using the XDR typedef associated with the characteristic
specified by xchv_which. The receiver of a message containing an
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xcharval MUST report an XDR error if the length of xchv_data is such
that it extends beyond the bounds of the message transferred.
In cases in which the xcharid specified by xchv_which is understood
by the receiver, the receiver also MUST report an XDR error if either
of the following occur:
o The nominally opaque data within xchv_data is not valid when
interpreted using the characteristic-associated typedef.
o The length of xchv_data is insufficient to contain the data
represented by the characteristic-associated typedef.
Note that no error is to be reported if xchv_which is unknown to the
receiver. In that case, that xcharval is not processed and
processing continues using the next xcharval, if any.
An xcharspec specifies a set of transport characteristics. No
particular ordering of the xcharvals within it is imposed.
An xcharsubset identifies a subset of the characteristics in a
previously specified xcharspec. Each bit in the mask denotes a
particular element in a previously specified xcharspec. If a
particular xcharval is at position N in the array, then bit number N
mod 32 in word N div 32 specifies whether that particular xcharval is
included in the defined subset. Words beyond the last one specified
are treated as containing zero.
xcharsubsets are useful in a number of contexts:
o In an initial specification of transport characteristics, 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
characteristics, allows the responding endpoint to specify the
subset of those characteristics that have been performed, have
been requested, or have been accepted for later change, with
notification of that change to be done asynchronously.
2.2. Transport Characteristics Groups
Transport characteristics are divided into a number of groups
o An initial set of transport characteristics defined in this
document. See Section 3 for the complete list.
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o Additional transport characteristics defined in future standards
track documents as specified in Section 6.1.
o Experimental transport characteristics being explored preparatory
to being considered for standards track definition. See the
description in Section 6.2.
2.3. Operations Related to Transport Characteristics
There are a number of operations defined in Section 4 which are used
to communicate and manage transport characteristics.
Prime among these is ROPT_INITXCH (defined in Section 4.1 which
serves as a means by which an endpoints transport characteristics 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
characteristics:
o ROPT_REQXCH (defined in Section 4.2 which serves as a way for an
endpoint to request that a peer change the value of a set of
transport characteristics.
o ROPT_RESPXCH (defined in Section 4.3 is used to report on the
disposition of each of the individual transport characteristic
changes requested in a previous ROPT_REQXCH.
o ROPT_UPDXCH (defined in Section 4.4 is used to report a change in
a transport characteristic. This may be one requested by a
previous ROPT_REQXCH, or an unsolicited one, not being requested
by a peer.
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 ROPT_REQXCH and the corresponding ROPT_RESPXCH
do constitute an RPC-like remote call. The other operations are not
part of a remote call transaction, although one or more asynchronous
ROPT_UPDXCH operations may result from a ROPT_REQXCH.
3. Initial Transport Characteristics
Although the set of transport characteristics is subject to later
extension, an initial set of transport characteristics is defined
below in Table 1.
In that table, the columns contain the following information:
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o The column labeled "characteristic" identifies the transport
characteristic described by the current row.
o The column labeled "code" specifies the xcharid value used to
identify this characteristic.
o The column labeled "XDR type" gives the XDR type of the data used
to communicate the value of this characteristic. This data type
overlays the nominally opaque field xchv_data in an xcharval.
o The column labeled "default" gives the default value for the
characteristic which is to be assumed by those who do not receive,
or are unable to interpret, information about the actual value of
the characteristic.
o The column labeled "section" indicates the section (within this
document) that explains the semantics and use of this transport
characteristic.
+--------------------+------+-----------+-----------------+---------+
| characteristic | code | XDR type | default | section |
+--------------------+------+-----------+-----------------+---------+
| Receive Buffer | 1 | uint32 | 4096 | 3.1 |
| Size | | | | |
| Requester Remote | 2 | bool | false | 3.2 |
| Invalidation | | | | |
| Backward Request | 3 | enum | BKREQSUP_INLINE | 3.3 |
| Support | | bkreqsup | | |
+--------------------+------+-----------+-----------------+---------+
Table 1
Note that there is no explicit indication regarding whether a
particular characteristic can change or whether a change in the value
may be requested (see Section 4.2). Such matters are not addressed
by the protocol definition. A partner implementation can always
request a change but peers MAY reject a request to change a
characteristic 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 characteristics:
o If an endpoint does not wish to accept request to change
particular characteristics, it may reject such requests as
described in Section 4.3.
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o If an endpoint does not support the ROPT_REQXCH operation, the
effect would be the same as if every request to change a set of
characteristic were rejected.
With regard to unrequested changes in transport characteristics, 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 3.1).
3.1. 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 XCHAR_RBSIZ = 1;
typedef uint32 xchrbsiz;
<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 characteristic, changing
this characteristics 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.
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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
response to an explicit request by the other endpoint (See
Section 4.2). The participant making the request should use that
lower size as the send size limit until the request is rejected
(See Section 4.3) or an update to a size larger than the requested
value becomes effective and the requested change is no longer
pending (See Section 4.4).
3.2. Requester Remote Invalidation
The Requester Remote Invalidation characteristic indicates that the
current endpoint, when in the role of a requester, is prepared for
the responder to use RDMA Send With Invalidate when replying to an
RPC-over-RDMA request containing non-empty chuck lists.
As RPC-over-RDMA is currently used, memory registrations exposed to
peers are not established by the server and explicit RDMA operations
are not done to satisfy backward direction requests. This makes it
unlikely that servers will present non-default values of the
XCHAR_REQREMINV characteristic or that clients will take note of that
value when presented by servers.
<CODE BEGINS>
const uint32 XCHAR_REQREMINV = 2;
typedef bool xchrreqrem;
<CODE ENDS>
When the Requester Remote Invalidate characteristic is set to false,
a responder MUST use Send to convey RPC reply messages to the
requester. When the Requester Remote Invalidate characteristic is
set to true, a responder MAY use Send With Invalidate instead of Send
to convey RPC replies to the requester.
The value of the Requester Remote Invalidate characteristic is not
likely to change from the value reported by ROPT_INITXCH (see
Section 4.2).
3.3. Backward Request Support
The value of this characteristic is used to indicate a client
implementation's readiness to accept and process messages that are
part of backward-direction RPC requests.
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<CODE BEGINS>
enum bkreqsup {
BKREQSUP_NONE = 0,
BKREQSUP_INLINE = 1,
BKREQSUP_GENL = 2
};
const uint32 XCHAR_BRS = 3;
typedef bkreqsup xchrbrs;
<CODE ENDS>
Multiple levels of support are distinguished:
o The value BKREQSUP_NONE indicates that receipt of backward-
direction requests and replies is not supported.
o The value BKREQSUP_INLINE indicates that receipt of backward-
direction requests or replies is only supported using inline
messages and that use of explicit RDMA operations for backward
direction requests or responses is not supported.
o The value BKREQSUP_GENL that receipt of backward-direction
requests or replies is supported in the same ways that forward-
direction requests or replies typically are.
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 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.
4. New Operations
The proposed new operation 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
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type. This data overlays 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 Initial | 1 | optinfo_initxch | No | 4.1 |
| Characteristics | | | | |
| Request Characteristic | 2 | optinfo_reqxch | No | 4.2 |
| Modification | | | | |
| Respond to Modification | 3 | optinfo_respxch | No | 4.3 |
| Request | | | | |
| Report Updated | 4 | optinfo_updxch | No | 4.4 |
| Characteristics | | | | |
+--------------------------+------+-----------------+-----+---------+
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 as specified in [rpcrdmav2]
The only operation support requirements are as follows:
o Implementations which send ROPT_REQXCH messages must support
ROPT_RESPXCH and ROPT_UPDXCH messages.
o Implementations which support ROPT_RESPXCH or ROPT_UPDXCH messages
must also support ROPT_INITXCH messages.
4.1. ROPT_INITXCH: Specify Initial Characteristics
The ROPT_INITXCH message type allows an RPC-over-RDMA participant,
whether client or server, to indicate to its partner relevant
transport characteristics that the partner might need to be aware of.
The message definition for this operation is as follows:
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<CODE BEGINS>
const uint32 ROPT_INITXCH = 1;
struct optinfo_initxch {
xcharspec optixch_start;
xcharsubset optixch_nochg;
};
<CODE ENDS>
All relevant transport characteristics that the sender is aware of
should be included in optixch_start. Since support of this request
is OPTIONAL, and since each of the characteristics is OPTIONAL as
well, the sender cannot assume that the receiver will necessarily
take note of these characteristics and so the sender should be
prepared for cases in which the partner continues to assume that the
default value for a particular characteristic is still in effect.
The subset of transport characteristic specified by optixch_nochg is
not expected to change during the lifetime of the connection.
Generally, a participant will send a ROPT_INITXCH 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.
Those receiving an ROPT_INITXCH may encounter characteristics that
they do not support or are unaware of. In such cases, these
characteristics are simply ignored without any error response being
generated.
4.2. ROPT_REQXCH: Request Modification of Characteristics
The ROPT_REQXCH message type allows an RPC-over-RDMA participant,
whether client or server, to request of its partner that relevant
transport characteristics be changed.
The partner need not change the characteristics as requested by the
sender but if it does support the message type, it will generate a
ROPT_RESPXCH message, indicating the disposition of the request.
The message definition for this operation is as follows:
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<CODE BEGINS>
const uint32 ROPT_REQXCH = 2;
struct optinfo_reqxch {
xcharspec optreqxch_want;
};
<CODE ENDS>
The xcharspec optreqxch_want is a set of transport characteristics
together with the desired values requested by the sender.
4.3. ROPT_RESPXCH: Respond to Request to Modify Transport
Characteristics
The ROPT_RESPXCH message type allows an RPC-over-RDMA participant to
respond to a request to change characteristics by its partner,
indicating how the request was dealt with.
The message definition for this operation is as follows:
<CODE BEGINS>
const uint32 ROPT_RESPXCH = 3;
struct optinfo_respxch {
xcharsubset optrespxch_done;
xcharsubset optrespxch_rej;
xcharsubset optrespxch_pend;
};
<CODE ENDS>
The rdma_xid field of this message must match that used in the
ROPT_REQXCH message to which this message is responding.
The optrespxch_done field indicates which of the requested transport
characteristic changes have been immediately effected. For each such
characteristic, 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 optrespxch_rej field indicates which of the requested transport
characteristic changes have been rejected by the sender. This may be
because of any of the following reasons:
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o The particular characteristic specified is not known or supported
by the receiver of the ROPT_REQXCH message.
o The implementation receiving the ROPT_REQXCH message does not
support modification of this characteristic.
o The implementation receiving the ROPT_REQXCHG message has rejected
the modification for another reason.
The optrespxch_pend field indicates which of the requested transport
characteristic modifications remain pending, since they were neither
rejected nor effected immediately. The receiver can expect the
modification to be effected by a later ROPT_UPDXCH message, although
there is no way to determine when this will happen. For each
characteristic bit set in this field, one or more ROPT_UPXCH can be
expected, the last of which will have optupdxch_pendclr flag set.
The subsets of characteristics specified by optrespxch_done,
optrespxch_rej, optrespxch_pend should not overlap and, when ored
together, should cover the entire set of characteristics specified by
optreqxch_want in the corresponding request.
4.4. ROPT_UPDXCH: Update Transport Characteristics
The ROPT_UPDXCH message type allows an RPC-over-RDMA participant to
notify the other participant that a change to the transport
characteristics has occurred.
This may be because:
o A change requested by a ROPT_REQXCH message, has, after some
delay, been effected.
o The sender has decided, independently, to modify the transport
characteristic and is notifying the receiver of this change.
One should pay particular attention to the fact that there is no
there no way to tie a message reporting a change to the specific
request which asked for the change. In particular, the rdma_xid
field in this message is independent of that for any earlier
ROPT_REQXCH message.
The message definition for this operation is as follows:
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<CODE BEGINS>
const uint32 ROPT_UPDXCH = 4;
struct optinfo_updxch {
xcharval optupdxch_now;
bool optupdxch_pendclr;
};
<CODE ENDS>
optupdxch_now defines the new characteristic value to be used.
optupdxch_pendclr, if true, indicates that a previous request to
update the characteristic specified by optupdxch_now.xchv_which is no
longer to be considered pending. This may be set true even if the
characteristic value is not changed from the previous value.
Some instances of ROPT_UPDXCH are the result of a previous a previous
ROPT_REQXCH while others are unsolicited. This distinction relates
to the setting of optupdxch_pendclr as follows:
o If a characteristic update is unsolicited, then optupdxch_pendclr
will always be false.
o If a characteristic update is prompted by a previous ROPT_REQXCH
and optupdxch_pendclr is true, then the current message indicates
the (asynchronous) completion of that previous change request.
In this case the disposition of the change request can be
determined using optupdxch_now. If the value is that requested by
the associated ROPT_REQXCH then the request was successful, while
if the value is unchanged from the original value, the change can
be considered rejected.
In cases in which the characteristic has a range of values,
intermediate value are possible, indicating a partial satisfaction
of the original request.
o If a characteristic update is prompted by a previous ROPT_REQXCH
and optupdxch_pendclr is false, then the current message does not
indicate completion of a previous change request.
In such cases, the characteristic value indicates the current
value of the characteristic, which the receiver is entitled to
rely upon, just as would have been the case if the change had been
unsolicited.
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Nevertheless, the change request is still active and will remain
so until a ROPT_UPDXCH with optupdxch_pendclr is received.
5. XDR
This section contains an XDR [RFC4506] description of the proposed
extension.
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>
#!/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 "ext.txt" then the reader can
do the following to extract an XDR description file for this
extension:
<CODE BEGINS>
sh extract.sh < ext.txt > charext.x
<CODE ENDS>
5.1. 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 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>
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5.2. XDR Proper for Extension
<CODE BEGINS>
///
////*
/// * Basic transport characteristic types
/// */
///typedef xcharid uint32;
///
///struct xcharval {
/// xcharid xchv_which;
/// opaque xchv_data<>;
///};
///
///typedef xcharspec xcharval<>;
///
///typedef xcharsubset uint32<>;
///
////*
/// * Transport characteristic codes
/// */
///const uint32 XCHAR_RBSIZ = 1;
///const uint32 XCHAR_REQREMINV = 2;
///const uint32 XCHAR_BRS = 3;
///
////*
/// * Other transport characteristic types
/// */
///enum bkreqsup {
/// BKREQSUP_NONE = 0,
/// BKREQSUP_INLINE = 1,
/// BKREQSUP_GENL = 2
///};
///
////*
/// * Transport characteristic typedefs
/// */
///typedef uint32 xchrbsiz;
///typedef bool xchrreqrem;
///typedef bkreqsup xchrbrs;
///
////*
/// * Optional operation codes
/// */
///const uint32 ROPT_INITXCH = 1;
///const uint32 ROPT_REQXCH = 2;
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///const uint32 ROPT_RESPXCH = 3;
///const uint32 ROPT_UPDXCH = 4;
///
////*
/// * Optional operation message structures
/// */
///struct optinfo_initxch {
/// xcharspec optixch_start;
/// xcharsubset optixch_nochg;
///};
///
///struct optinfo_reqxch {
/// xcharspec optreqxch_want;
///};
///
///struct optinfo_respxch {
/// xcharsubset optrespxch_done;
/// xcharsubset optrespxch_rej;
/// xcharsubset optrespxch_pend;
///};
///
///struct optinfo_updxch {
/// xcharval optupdxch_now;
/// bool optupdxch_pendclr;
///};
<CODE ENDS>
6. Extensibility
6.1. Additional Characteristics
The set of transport characteristics is designed to be extensible.
As a result, once new characteristics are defined in standards track
documents, the operations defined in this document may reference
these new transport characteristics, as well as the ones described in
this document.
A standards track document defining a new transport characteristic
should include the following information paralleling that provided in
this document for the transport characteristics defined herein.
o The xcharid value used to identify this characteristic.
o The XDR typedef specifying the form in which the characteristic
value is communicated.
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o A description of the transport characteristic that is communicated
by the sender of ROPT_INITXCH and ROPT_UPDXCH and requested by the
sender of ROP_REQXCH.
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 characteristic.
The definition of transport characteristic 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 The xcharids specified in the document do not conflict with those
currently assigned or in use by other pending working group
documents defining transport characteristics.
o The xcharids specified in the document do not conflict with the
range reserved for experimental use, as defined in Section 6.2.
Documents defining new characteristics fall into a number of
categories.
o Those defining new characteristics and explaining (only) how they
affect use of existing message types.
o Those defining new OPTIONAL message types and new characteristics
applicable to the operation of those new message types.
o Those defining new OPTIONAL message types and new characteristics
applicable both to new and existing message types.
When additional transport characteristics are proposed, the review of
the associated standards track document should deal with possible
security issues raised by those new transport characteristics.
6.2. Experimental Characteristics
Given the design of the transport characteristics data structure, it
possible to use the operations to implement experimental, possibly
unpublished, transport characteristics.
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xcharids 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 characteristics 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,
characteristic 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, <http://www.ietf.org/id/
draft-ietf-nfsv4-rpcrdma-bidirection-02.txt>.
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,
<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>.
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[rfc5666bis]
Lever, C., Ed., Simpson, W., and T. Talpey, "Remote Direct
Memory Access Transport for Remote Procedure Call", May
2016, <http://www.ietf.org/id/
draft-ietf-nfsv4-rfc5666bis-07.txt>.
Work in progress.
[rpcrdmav2]
Lever, C., Ed. and D. Noveck, "RPC-over-RDMA Version Two",
June 2016, <http://www.ietf.org/id/
draft-cel-nfsv4-rpcrdma-version-two-01.txt>.
Work in progress.
9.2. Informative References
[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 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
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David Noveck
Hewlett Packard Enterprise
165 Dascomb Road
Andover, MA 01810
USA
Phone: +1 781-572-8038
Email: davenoveck@gmail.com
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