Internet DRAFT - draft-dnoveck-nfsv4-rpcrdma-rtrext
draft-dnoveck-nfsv4-rpcrdma-rtrext
Network File System Version 4 D. Noveck
Internet-Draft NetApp
Intended status: Informational December 5, 2017
Expires: June 8, 2018
RPC-over-RDMA Extensions to Reduce Internode Round-trips
draft-dnoveck-nfsv4-rpcrdma-rtrext-03
Abstract
It is expected that a future version of the RPC-over-RDMA transport
will allow protocol extensions to be defined. This would provide for
the specification of OPTIONAL features allowing participants who
implement such features to cooperate as specified by that extension,
while still interoperating with participants who do not support that
extension.
A particular extension is described herein, whose motivation is to
reduce the latency due to inter-node round-trips needed to effect
operations which involve direct data placement or which transfer RPC
messages longer than the fixed inline buffer size limit.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on June 8, 2018.
Copyright Notice
Copyright (c) 2017 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(https://trustee.ietf.org/license-info) in effect on the date of
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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
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described in the Simplified BSD License.
Table of Contents
1. Preliminaries . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 3
1.2. Introduction . . . . . . . . . . . . . . . . . . . . . . 3
1.3. Role of this Document . . . . . . . . . . . . . . . . . . 3
1.4. Prerequisites . . . . . . . . . . . . . . . . . . . . . . 4
1.5. Participant Terminology . . . . . . . . . . . . . . . . . 5
2. Extension Overview . . . . . . . . . . . . . . . . . . . . . 5
3. Data Placement Features . . . . . . . . . . . . . . . . . . . 6
3.1. Current Situation . . . . . . . . . . . . . . . . . . . . 6
3.2. RDMA_MSGP . . . . . . . . . . . . . . . . . . . . . . . . 6
3.3. Send-based Data Placement . . . . . . . . . . . . . . . . 8
3.4. Other Extensions Relating to Data Placement . . . . . . . 8
4. Message Continuation Feature . . . . . . . . . . . . . . . . 9
4.1. Current Situation . . . . . . . . . . . . . . . . . . . . 9
4.2. Message Continuation Changes . . . . . . . . . . . . . . 10
4.3. Message Continuation and Credits . . . . . . . . . . . . 10
5. Using Protocol Additions . . . . . . . . . . . . . . . . . . 11
5.1. New Operation Support . . . . . . . . . . . . . . . . . . 12
5.2. Message Continuation Support . . . . . . . . . . . . . . 12
5.3. Support for Send-based Data Placement . . . . . . . . . . 13
5.4. Error Reporting . . . . . . . . . . . . . . . . . . . . . 14
6. XDR Preliminaries . . . . . . . . . . . . . . . . . . . . . . 15
6.1. Message Continuation Preliminaries . . . . . . . . . . . 15
6.2. Data Placement Preliminaries . . . . . . . . . . . . . . 15
7. Data Placement Structures . . . . . . . . . . . . . . . . . . 18
7.1. Data Placement Overview . . . . . . . . . . . . . . . . . 18
7.2. Buffer Structure Definition . . . . . . . . . . . . . . . 19
7.3. Message Data Placement Structures . . . . . . . . . . . . 21
7.4. Response Direction Data Placement Structures . . . . . . 23
8. Transport Properties . . . . . . . . . . . . . . . . . . . . 25
8.1. Property List . . . . . . . . . . . . . . . . . . . . . . 25
8.2. RTR Support Property . . . . . . . . . . . . . . . . . . 26
8.3. Receive Buffer Structure Property . . . . . . . . . . . . 26
8.4. Request Transmission Receive Limit Property . . . . . . . 27
8.5. Response Transmission Send Limit Property . . . . . . . . 27
9. New Operations . . . . . . . . . . . . . . . . . . . . . . . 28
9.1. Operations List . . . . . . . . . . . . . . . . . . . . . 28
9.2. Transmit Request Operation . . . . . . . . . . . . . . . 29
9.3. Transmit Response Operation . . . . . . . . . . . . . . . 29
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9.4. Transmit Continue Operation . . . . . . . . . . . . . . . 30
9.5. Error Reporting Operation . . . . . . . . . . . . . . . . 31
10. XDR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
10.1. Code Component License . . . . . . . . . . . . . . . . . 35
10.2. XDR Proper for Extension . . . . . . . . . . . . . . . . 37
11. Security Considerations . . . . . . . . . . . . . . . . . . . 42
12. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 43
13. References . . . . . . . . . . . . . . . . . . . . . . . . . 43
13.1. Normative References . . . . . . . . . . . . . . . . . . 43
13.2. Informative References . . . . . . . . . . . . . . . . . 43
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 44
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 44
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 describes a potential extension to the RPC-over-RDMA
protocol, which would allow participating implementations to have
more flexibility in how they use RDMA sends and receives to effect
necessary transmission of RPC requests and replies.
In contrast to existing facilities defined in RPC-over-RDMA Version
One in which the mapping between RPC messages and RPC-over-RDMA
messages is strictly one-to-one and placement of bulk data is
effected only through use of explicit RDMA operations, the following
features are made available through this extension:
o The ability to effect data placement in the context of a single
RPC-over-RDMA transmission, rather than requiring explicit RDMA
operations to effect the necessary placement.
o The ability to continue an RPC request or reply over multiple RPC-
over-RDMA transmissions.
1.3. Role of this Document
This is not a standards-track document, despite the fact that it
contains many of the sorts of items (e.g. proposed XDR, detailed
field descriptions) that normally appear in such documents.
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Although this document is in the informational category it is not
expected to result in an Informational RFC, as the material within it
is not expected to be of interest to the internet community in
general. Its target audience is the nfsv4 working group itself and
it is not expected to evolve into an RFC.
The function of this document is essentially exploratory, in that it
looks at a number of possible ways that the RPC-over-RDMA transport
could be extended. Although many of these might well be followed up
on eventually with standards-track documents, it should not be
assumed that all will or that the relation among the various elements
of any extension to address these issue will be the same as laid out
here.
1.4. Prerequisites
This document is written assuming that certain underlying facilities
will be made available to build upon, in the context of a future
version of RPC-over-RDMA. It is most likely that such facilities
will be first available in Version Two of RPC-over-RDMA.
o A protocol extension mechanism is needed to enable the extensions
to RPC-over-RDMA described here.
This document is currently written to conform to the extension
model for the proposed RPC-over-RDMA Version Two as described in
[I-D.cel-nfsv4-rpcrdma-version-two].
o An existing means of communicating transport properties between
the RPC-over-RDMA endpoints is assumed.
This document is currently written assuming the transport property
model defined in [I-D.cel-nfsv4-rpcrdma-version-two]. will be
available and can be extended to meet the needs of this extension.
As the document referred to above is currently a personal Internet
Draft, and subject to change, adjustments to this document are
expected to be necessary when and if the needed facilities are
defined in one or more working group documents leading to the
potential publication of Standards-track RFCs.
Such an RFC for a new RPC-over-RDMA version might differ from
[I-D.cel-nfsv4-rpcrdma-version-two] in significant ways even if it
provides the prerequisites listed above. For example,
o The extension model might be significantly different. For
example, it might use an approach more like that used in [RFC8178]
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rather than using a single message type as a vehicle for OPTIONAL
extensions.
o There is the possibility of significant change in the credit
model. While [I-D.cel-nfsv4-rpcrdma-version-two] contains support
for one-way messages, much of the text regarding credits is
inherited from [RFC8166] which assumes a one-to-one mapping
between requests and responses. It is not clear whether this
mismatch will be resolved by changing (only) the description of
the credit mechanism or whether a more basic protocol change is
required. Whichever approach is taken, the treatment of message
continuation is likely to follow.
1.5. Participant 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 for different requests issued
on the same connection.
The roles of sender and receiver vary from message to messages. With
regard to the messages described in this document, the sender may act
as a requester by sending RPC requests or a responder by sending RPC
requests or as both at the same time by sending a mix of the two.
2. Extension Overview
This extension is intended to function as part of RPC-over-RDMA and
implementations should successfully interoperate with existing RPC-
over-RDMA Version One implementations. Nevertheless, this extension
seeks to take a somewhat different approach to high-performance RPC
operation than has been used previously in that it seeks to de-
emphasize the use of explicit RDMA operations. It does this in two
ways:
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o By implementing a send-based form of data placement (see
Section 3), use of explicit RDMA operations can be avoided in many
common cases in which data is to be placed at an appropriate
location in the receiver's memory.
o Use of explicit RDMA to support reply chunks and position-zero
read chunks can be avoided by allowing a single message to be
split into multiple transmissions. This can be used to avoid many
instances of the only existing use of explicit RDMA operations not
associated with Direct Data Placement.
While use of explicit RDMA operations allows the cost of the actual
data transfer to be offloaded from the client and server CPUs to the
RNIC, there are ancillary costs in setting up the transfer that
cannot be ignored. As a result, send-based functions are often
preferable, since the RNIC also uses DMA to effect these operations.
In addition, the cost of the additional inter-node round trips
required by explicit RDMA operation can be an issue, which can
becomes increasingly troublesome as internode distances increase.
Once one moves from in-machine-room to campus-wide or metropolitan-
area distances the additional round-trip delay of 16 microseconds per
mile becomes an issue impeding use of explicit RDMA operations.
3. Data Placement Features
3.1. Current Situation
Although explicit RDMA operations are used in the existing RPC-over-
RDMA protocol for purposes unrelated to Direct Data Placement, all
placement of bulk data is effected using explicit RDMA operations.
As a result, many operations requiring placement of bulk data involve
multiple internode round trips.
3.2. RDMA_MSGP
Although this was not stated explicitly, it appears that RDMA_MSGP
(defined in [RFC5666], removed from RPC-over-RDMA Version One by
[RFC8166]), was an early attempt to effect correct placement of bulk
data within a single RPC-over-RDMA transmission.
As things turned out, the fields within the RDMA_MSGP header were not
described in [RFC5666] in a way that allowed this message type to be
implemented.
In attempting to provide the appropriate data placement
functionality, we have to keep in mind and avoid the problems that
led to failure of RDMA_MSGP. It appears that the problems go deeper
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than neglecting to write a few relevant sentences. It is helpful to
note that:
o The inline message size limits eventually adopted were too small
to allow RDMA_MSGP to be used effectively. This is true of both
the 1K limit in Version One [RFC8166] and the 4K limit specified
in [I-D.cel-nfsv4-rpcrdma-version-two].
On the other hand, there is text within [RFC5667] that suggests
that much longer messages were anticipated at some points during
the evolution of RPC-over-RDMA.
o The fact that NFSv4 COMPOUNDs often have additional operations
beyond the one including the bulk data means that the RDMA_MSGP
model cannot be extended to NFSv4. As a result, the bulk data
needs to be excised from the data stream just as chunks are, so
that the payload stream can include non-bulk data both before and
after the logical position of the excised bulk data.
o In order for the sender to determine the appropriate amount of
padding necessary within a transmission to place the bulk data at
the proper position within receive buffer, the server must know
more about the structure of the receiver's buffers. Since the
padding needs to bring the bulk data to a position within the
buffer that is appropriate to receive the bulk data, the sender
needs to know where within the receive buffers such placement-
eligible areas are located.
o While appropriate padding could place the bulk data within a large
WRITE into an appropriately aligned buffer or set of buffer, there
is no corresponding provision for the bulk data associated with a
READ. In short, there is no way to indicate to the responder that
it should use RDMA_MSGP to appropriately place bulk data in the
response.
o There is no explicit discussion of the required padding's use in
effecting proper data placement or connection with the ULB's
specification of DDP-eligible XDR items.
To summarize, RDMA_MSGP was an attempt to properly place bulk data
which was thought of as a local optimization and insufficient
attention was given to it to make it successful. As a result, as
RPC-over-RDMA Version One was developed, data placement was
identified with the use of explicit RDMA operations providing DDP and
the possibility of data placement within sends was not recognized.
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3.3. Send-based Data Placement
In this extension we will describe a more complete way to provide
send-based data placement, as follows:
o By defining the structure of receive buffers as a transport
property available to be interrogated by the peer implementation.
o By treating positioning of bulk data within a message as an
instance of data placement, causing the bulk data to be excised
from the payload XDR stream, as is the case with other forms of
bulk data placement (e.g. DDP).
o By defining new data structures to control placement of bulk data
that support both send-based data placement and DDP using explicit
RDMA operations that was an integral part in RPC-over-RDMA Version
One. These new control structures, described in Section 7.1 are
organized differently from the chunk-based structures described in
[RFC8166].
In making these changes, we will retain certain aspects of the DDP
model:
o The set of bulk data items eligible for special data placement is
exactly the same as with DDP, as defined by the RPC protocol's
upper-layer binding document.
o The concept of an inline XDR stream is retained, with specially
placed items appearing outside it, but with references to them
retained so that the receiver has access to all of the message
data.
3.4. Other Extensions Relating to Data Placement
In order to support send-based data placement, new placement-related
data structures have been defined, as described in Sections 7.3 and
7.4.
These new data structures support both send-based and RDMA-operation-
based data placement. In addition, because of the restructuring
described in Section 7.1, a number of additional facilities are made
available:
o The ability to restrict entries regarding data placement in
response data to XDR data items generated in response to
performing particular constituent operations within a given RPC
request (e.g. specific operations within an NFSv4 COMPOUND).
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o The ability to make use of special data placement contingent on
the actual length of a placement-eligible data item in the
response.
o The ability to specify whether use of data placement for a
particular placement-eligible data item is required or optional.
These additional facilities will be available to implementations that
do not support send-based data placement, as long as both parties
support the OPTIONAL Header types that include these new structures.
For more information about the relationships among, the new transport
properties, operations, and features, see Section 5.
4. Message Continuation Feature
4.1. Current Situation
Within RPC-over-RDMA Version One [RFC8166], each transmission of a
request or reply involves sending a single RDMA send message and
conversely each message-related transmission involves only a single
RPC request or reply.
This strict one-to-one model leads to some potential performance
issues.
o Because of RDMA's use of fixed-size receives, some requests and
replies will inevitably not fit in the limited space available,
even if they do not contain any DDP-eligible bulk data.
Such cases will raise performance issues because, to deal with
them, the server is interrupted twice to receive a single request
and all the necessary transfers are serialized. In particular,
there are two server interrupt latencies involved before the
server can process the actual request, in addition to the OTW
round-trip latencies.
o In the case of replies, there may be cases in which reply chucks
need to be allocated and registered even if the actual reply would
fit within the fixed receive-size limit. Because the decision to
create a reply chunk is made at the time the request is sent, even
an extremely low probability of a longer reply will trigger
allocation of a reply chunk.
Because this decision is made in conformance with ULB rules,
which, by their nature, may only reference a limited set of data,
a reply chunk may be required even when the actual probability of
a long reply is exactly zero. For example a GETATTR request can
generate a long reply due to a long ACL, and thus COMPOUND with
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this operation might allocate a reply chunk, even if the specific
file system being interrogated only supports ACLs of limited
sizes, or the GETATTR in question does not interrogate one of the
ACL attributes. Also, the OWNER attribute is a string and it may
be impossible to determine a priori that the owner of any
particular file has no chance of requiring more than 4K bytes of
space, for example. The assumption that there are no such user
names, while it probably is valid, is not a fact that RPC-over-
RDMA implementations can depend on.
4.2. Message Continuation Changes
Continuing a single RPC request or reply is addressed by defining
separate optional header types to begin and to continue sending a
single RPC message. This is instead of creating a header with a
continuation bit. In this approach, all of the fields relating to
data placement, which include support for send-based data placement,
appear in the starting header (of types ROPT_XMTREQ and ROPT_XMTRESP)
and apply to the RPC message as a whole.
Later RPC-over-RDMA messages (of type ROPT_XMTCONT) may extend the
payload stream and/or provide additional buffers to which bulk data
can be directed.
In this case, all of the RPC-over-RDMA messages used together are
referred to as a transmission group and must be received in order
without any intervening message.
In implementations using this optional facility, those decoding RPC
messages received using RPC-over-RDMA no longer have the assurance
that that each RPC message is in a contiguous buffer. As most XDR
implementations are built based on the assumption that input will not
be contiguous, this will not affect performance in most cases.
4.3. Message Continuation and Credits
Using multiple transmissions to send a single request or response can
complicate credit management. In the case of the message
continuation feature, deadlocks can be avoided because use of message
continuation is not obligatory. The requester or responder can use
explicit RDMA operations if sufficient credits to use message
continuation are not available.
A requester is well positioned to make this choice with regard to the
sending of requests. The requester must know, before sending a
request, how long it will be, and therefore, how many credits it
would require to send the request using message continuation. If
these are not available, it can avoid message continuation by either
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creating read chunks sufficient to make the payload stream fit in a
single transmission or by creating a position-zero read chunk.
With regard to the response, the requester is not in position to know
exactly how long the response will be. However, the ULB will allow
the maximum response length to be determined based on the request.
This value can be used:
o To determine the maximum number of receive buffers that might be
required to receive any response sent.
o To allocate and register a reply chunk to hold a possible large
reply.
The requester can avoid doing the second of these if the responder
has indicated it can use message continuation to send the response.
In this case, it makes sure that the buffers will be available and
indicates to the responder how many additional buffers (in the form
of pre-posted reads have been made available to accommodate
continuation transmissions.
When the responder processes the request, those additional receive
buffers may be used or not, or used only in part. This may be
because the response is shorter than the maximum possible response,
or because a reply chunk was used to transmit the response.
After the first or only transmission associated with the response is
received by the requester, it can be determined how many of the
additional buffers were used for the response. Any unused buffers
can be made available for other uses such as expanding the pool of
receive buffers available for the initial transmissions of response
or for receiving opposite direction requests. Alternatively, they
can be kept in reserve for future uses, such as being made available
to future requests which have potentially long responses.
5. Using Protocol Additions
In using existing RPC-over-RDMA facilities for protocol extension,
interoperability with existing implementations needs to be assured.
Because this document describes support for multiple features, we
need to clearly specify the various possible extensions and how peers
can determine whether certain facilities are supported by both ends
of the connection.
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5.1. New Operation Support
Note that most of the new operations defined in this extension are
not tightly tied to a specific feature. XOPT_XMTREQ and XOPT_XMTRESP
are designed to support implementations that support either or both
Send-based data placement or message continuation. However, the
converse is not the case and these header types can be implemented by
those not supporting either of these features. For example,
implementations may only need support for the facilities described in
Section 3.4.
Implementations may determine whether a peer implementation supports
XOPT_XMTREQ, XOPT_XMTREQ, or XOPT_XMTCONT by attempting these
operations. An alternative is to interrogate the RTR Support
Property for information about which operations are supported.
5.2. Message Continuation Support
Implementations may determine and act based on the level of peer
implementation of support for message continuation as follows:
o To deal with issues relating to sending the peer multi-
transmission requests, the requester can interrogate the peer's
value of the Request Transmission Receive Limit (Section 8.4). In
cases in which the property is not provided or has the value one,
the requester implementation can avoid sending multi-transmission
requests, and use the equivalent of position-zero read chunks to
convey a request larger than the receive buffer limit.
Similarly, if the request is longer than can fit in a set of
transmissions given that limit, the request can be conveyed in the
same fashion,
o To deal with issues relating to sending the peer multi-
transmission responses, responders will only send multi-
transmission responses for requests conveyed using XOPT_XMTREQ
where the number of response transmissions is less than or equal
to buffer reservation count (in the field optxrq_rsbuf). The
requester can avoid receiving a message consisting of too many
transmissions by setting this field appropriately. This includes
the case in which the requester cannot handle any multi-
transmission responses.
o To avoid reserving receive buffers that the responder is not
prepared to use, the requester can interrogate the peer's value of
the Response Transmission Send Receive Limit (Section 8.5). In
cases in which it is possible that a request might result in a
response too large for this set of buffers, the requester, the
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requester can provide a reply chunk to receive the response, which
the responder can use if the count of buffers provided is
insufficient.
5.3. Support for Send-based Data Placement
Implementations may determine and adapt to the level of peer
implementation support for send-based data placement as described
below. Note that an implementation may be able to send messages
containing bulk data items placed using send-based data placement
while not being prepared to receive them, or the reverse.
o The requester can interrogate the responder's Receive Buffer
Structure Property. In cases in which the property is not
provided or shows no placement-targetable buffer segments, an
implementation knows that messages containing bulk data may not be
sent using send-based data placement. In such cases, when
XOPT_XMTREQ is used to send a request, bulk items may be
transferred by setting the associated placement information to
indicate that the bulk data is to be fetched using explicit RDMA
operations.
o In cases in which a requester is unprepared to accept messages
using send-based data placement, its Receive Buffer Structure
Property will make this clear to the responder. Nevertheless, the
requester will generally indicate to the responder that bulk data
items are to be returned using explicit RDMA operations. As a
result, requesters may use XOPT_XMTREQ (and get the benefit of the
placement-related features discussed in Section 3.4 even if they
support neither message continuation nor send-based data
placement.
o Since it is possible for a responder to generate responses
containing bulk data using send-based data placement even if it is
not prepared to send such message, a requester who is prepared to
accept such messages should specify in the request that the
responses are to contain (or may contain) bulk data placed in this
way. In deciding whether this is to be done the requester can
interrogate the responder's RTR Support Property for information
about which whether the peer can send responses in this form. It
can do this without regard to whether the responder can accept
messages containing bulk data items placed using send-based data
placement.
In determining whether bulk data will be placed using send-based data
placement or via explicit RDMA operations, the level of support for
message continuation will have a role. This is because DDP using
explicit RDMA will reduce message size while send-based data
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placement reduces the size of the payload stream by rearranging the
message, leaving the message size the same. As a result, the
considerations discussed in Section 4.3 will have to be attended to
by the sender in determining which form of data placement is to be
used.
5.4. Error Reporting
The more extensive transport layer functionality described in this
document requires its own means of reporting errors, to deal with
issues that are distinct from:
o Errors (including XDR errors) in the XDR stream as received by
responder or requester.
o XDR errors detected in the XDR headers defined by the base
protocol.
o XDR errors detected in the new operations defined in this
document.
Beyond the above, the following sorts of errors will have to be dealt
with, depending on which of the features of the extension are
implemented.
o Information associated with send-based data placement may be
inconsistent or otherwise invalid, even though it conforms to the
XDR definition.
o There may be problems with the organization of transmission groups
in that there are missing or extraneous transmissions.
In each of the above cases, the problem will be reported to the
sender using the Error Reporting operation which needs to be
supported by every endpoint that sends ROPT_XMTREQ, ROPT_XMTRESP, or
ROPT_XMTCONT. This includes cases in which the problem is one with a
reply. The function of the Error Reporting operation is to aid in
diagnosing transport protocol errors and allowing the sender to
recover or decide recovery is not possible. Reporting failure to the
requesting process is dealt with indirectly. For example,
o When the transmissions used to send a request are ill-formed, the
requestor can respond to the error indication by proceeding to
send the request using existing (i.e. non-extended) facilities.
If it chooses not to do so, the requestor can report an RPC
request failure to the initiator of the RPC.
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o When the transmissions used to send a response are ill-formed, the
responder need to know about the problem since it will otherwise
assume that the transmissions succeeded. It can proceed to resend
the reply using existing (i.e. non-extended) facilities. If it
chooses not to do so, the requester will not see a response and
eventually an RPC timeout will occur.
6. XDR Preliminaries
6.1. Message Continuation Preliminaries
In order to implement message continuation, we have occasion to refer
to particular RPC-over-RDMA transmissions within a transmission group
or to characteristics of a later transmission group.
<CODE BEGINS>
typedef uint32 xms_grpxn;
typedef uint32 xms_grpxc;
struct xms_id {
uint32 xmsi_xid;
msg_type xmsi_dir;
xms_grpxn xmsi_seq;
}
<CODE ENDS>
An xms_grpxn designates a particular RPC-over-RDMA transmission
within a set of transmissions devoted to sending a single RPC
message.
An xms_grpxc specifies the number of RPC-over-RDMA transmissions in a
potential group of transmissions devoted to sending a single RPC
message.
6.2. Data Placement Preliminaries
Data structures related to data placement use a number of XDR
typedefs to help clarify the meaning of fields in the data structures
which use these typedefs.
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<CODE BEGINS>
typedef uint32 xmdp_itemlen;
typedef uint32 xmdp_pldisp;
typedef uint32 xmdp_vsdisp;
typedef uint32 xmdp_tbsn;
enum xmdp_type {
XMPTYPE_EXRW = 1,
XMPTYPE_TBSN = 2,
XMPTYPE_CHOOSE = 3,
XMPTYPE_BYSIZE = 4,
XMPTYPE_TOOSHORT = 5,
XMPTYPE_NOITEM = 6
};
<CODE ENDS>
An xmdp_itemlen specifies the length of XDR item. Because items
excised from the XDR stream are XDR items, lengths of items excised
from the XDR stream are denoted by xmdp_itemlens.
An xmdp_pldisp specifies a specific displacement with the payload
stream associated with a single RPC-over-RDNA transmission or a group
of such transmissions. Note that when multiple transmissions are
used for a single message, all of the payload streams within a
transmission group are considered concatenated.
An xmdp_vsdisp specifies a displacement within the virtual XDR stream
associates with the set of RPC messages transferred by single RPC-
over-RDNA transmission or a group of such transmissions. The virtual
XDR stream includes bulk data excised from the payload stream and so
displacements within it reflect those of the corresponding objects in
the XDR stream that might be sent and received if no bulk data
excision facilities were involved in the RPC transmission.
An xmdp_tbsn designates a particular target buffer segment within a
(trivial or non-trivial) RPC-over-RDMA transmission group. Each
placement-targetable buffer segment is assigned a number starting
with zero and proceeding through all the buffer segments for all the
RPC-over-RDMA transmissions in the group. This includes buffer
segments not actually used because transmission are shorter than the
maximum size and those in which a placement-targetable buffer segment
is used to hold part of the payload XDR stream rather than bulk data.
An xmdp_type allows a selection between placement using explicit RDMA
operations (i.e. DDP) and send-based data placement. Fields of this
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type are used in a number of contexts. The specific context governs
which subset of the types is valid:
o In request messages, they indicate where each of the specially
placed data items within the request has been placed. In this
case, xmdp_type appears as the discriminator within an xmdp_loc
which is part of an xmdp_mitem that is an element within a
request's optxrq_dp field.
o In request messages, they direct the responder as to where
potential specially placed items are to be placed. In this case,
xmdp_type appears as the discriminator within an xmdp_rsdloc which
is part of an xmdp_rsditem that is an element within a request's
optxrq_rsd field.
o In response messages, they indicate how each of the potential
specially placed items has been dealt with. A subset of these
specially placed data items and are presented in the same form as
that used for specially placed data items within a request. In
this case, xmdp_type appears as the discriminator within an
xmdp_loc which is part of an xmdp_mitem that is an element within
a response's optxrs_dp field.
A number of these type are valid in all of these contexts, since they
specify use of a specific mode of data placement which is to be used
or has been used.
o XMPTYPE_EXRW selects DDP using explicit RDMA reads and writes.
o XMPTYPE_TBSN selects use of send-based data placement in which
placement-eligible data is located in placement-targetable buffer
segments.
Another set of types is used to direct the use of specific sets of
types but cannot specify an actual choice that has been made.
o XMPTYPE_CHOICE indicates that the responder may use either send-
based data placement or chunk-based DDP using explicit RDMA
operations, with a target location for the latter having been
provided by the requester.
o XMPTYPE_BYSIZE indicates that the responder is to use either send-
based data placement or chunk-based DDP using explicit RDMA
operations, with the choice between the two governed by the actual
size of the associated DDP-eligible XDR item.
The following types are used when no actual special placement has
occurred. They are used in responses to indicate ways in which a
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direction to govern data placement in a reply was responded to
without resulting in special placement.
o XMPTYPE_TOOSHORT indicates that the corresponding entry in an
xmdp_rsdset was matched with a DDP-eligible item which was too
small to be handled using special placement, resulting in the DDP-
eligible item being placed inline.
o XMPTYPE_NOITEM indicates that the corresponding entry in an
xmdp_rsdset was not matched with a DDP-eligible item in the reply.
The following table indicates which of the above types is valid in
each of the contexts in which these types may appear. For valid
occurrences, it distinguishes those which give sender-generated
information about the message, and those that direct reply
construction, from those that indicate how those directions governed
the construction of a reply. For invalid occurrences, we distinguish
between those that result in XDR decode errors and those which are
valid from the XDR point of view but are semantically invalid.
+------------------+--------------+-----------------+---------------+
| Type | xmdp_loc in | xmdp_rsdloc in | xmdp_loc in |
| | request | request | response |
+------------------+--------------+-----------------+---------------+
| XMPTYPE_EXRW | Valid Info | Valid Direction | Valid Result |
| XMPTYPE_TBSN | Valid Info | Valid Direction | Valid Result |
| XMPTYPE_BYSIZE | XDR Invalid | Valid Direction | XDR Invalid |
| XMPTYPE_CHOICE | XDR Invalid | Valid Direction | XDR Invalid |
| XMPTYPE_TOOSHORT | Sem. Invalid | XDR Invalid | Valid Result |
| XMPTYPE_NOITEM | Sem. Invalid | XDR Invalid | Valid Result |
+------------------+--------------+-----------------+---------------+
Table 1
7. Data Placement Structures
7.1. Data Placement Overview
To understand the new data placement structures defined here, it is
necessary to review the existing DDP structures used in RPC-over-RDMA
Version One and look at the corresponding structures in the new
message transmission headers defined in this document.
We look first at the existing structures.
o Read chunks are specified on requests to indicate data items to be
excised from the payload stream and fetched from the requester's
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memory by the responder. As such, they serve as a means of
supplying data excised from the payload XDR stream.
Read chunks appear in replies but they have no clear function
there.
o Write chunks are specified on requests to provide locations in
requester memory to which DDP-eligible items in the corresponding
reply are to be transferred. They do not describe data in the
request but serve to direct reply construction.
When write chunks appear in replies they serve to indicate the
length of the data transferred. The addresses to which the bulk
reply data has been transferred is available, but this information
is already known to the requester.
o Reply chunks are specified to provide a location in the
requester's memory to which the responder can transfer the
response using RDMA Write. Like write chunks, they do not
describe data in the request but serve to direct reply
construction.
When reply chunks appear in reply message headers, they serve
mainly to indicate whether the reply chunk was actually used.
Within the data placement structures defined here a different
organization is used, even where DDP using explicit RDMA operations
in supported.
o All messages that contain bulk data contain structures that
indicate where the excised data is located. See Section 7.3 for
details.
o Requests that might generate replies containing bulk data contain
structures that provide guidance as to where the bulk data is to
be placed. See Section 7.4 for details.
Both sets of data structure are defined at the granularity of an RPC-
over-RDMA transmission group. That is, they describe the placement
of data within an RPC message and the scope of description is not
limited to a single RPC-over-RDMA transmission.
7.2. Buffer Structure Definition
Buffer structure definition information is used to allow the sender
to know how receive buffers are constructed, to allow it to
appropriately pad messages being sent so that bulk data will be
received into a memory area with the appropriate characteristics.
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In this case, data placement will not place data in a specific
address, picked and registered in advance as is done to effect DDP
using explicit RDMA operations. Instead, a message is sent so that
when it is matched with one of the preposted receives, the bulk data
will be received into a memory area with the appropriate
characteristics, including:
o size
o alignment
o placement-targetability and potentially other memory
characteristics such as speed, persistence.
<CODE BEGINS>
struct xmrbs_seg {
uint32 xmrseg_length;
uint32 xmrseg_align;
uint32 xmrseg_flags;
};
const uint32 XMRSFLAG_PLT = 0x01;
struct xmrbs_group {
uint32 xmrgrp_count;
xmrbs_seg xmrgrp_info;
};
struct xmrbs_buf {
uint32 xmrbuf_length;
xmrbs_group xmrbuf_groups<>;
};
<CODE ENDS>
Buffers can be, and typically are, structured to contain multiple
segments. Preposted receives that target a buffer uses a scatter
list to place received messages in successive buffer segments.
An xmrbs_seg defines a single buffer segment. The fields included
are:
o xmrseg_length is the length of this contiguous buffer segment
o xmrseg_align specifies the guaranteed alignment for the
corresponding buffer segment.
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o xmrseg_flags which specify some noteworthy characteristics of the
associated buffer segment.
The following flag bit is the only one currently defined:
o XMRSFLAG_PLT indicates that the buffer segment in question is to
be considered suitable as a target for data placement.
An xmrgs_group designates a set of buffer segment all with the same
buffer segment characteristics as indicated by xmr_grpinfo. The
buffer segments are contiguous within the buffer although they are
likely not to be physically contiguous.
An xmrbs_buf defines a receiver's buffer structure and consists of
multiple xmrbs_groups. This buffer structure, when made available as
a transport property, allows the sender to structure transmissions so
as to place DDP-eligible data in appropriate target buffer segments.
7.3. Message Data Placement Structures
These data structures show where in the virtual XDR stream for the
set of messages, data is to be excised from that XDR stream and where
that excised bulk data is to be found instead.
<CODE BEGINS>
union xmdp_loc switch(xmdp_type type)
case XMPTYPE_EXRW:
rpcrdma1_segment xmdl_ex<>;
case XMPTYPE_TBSN:
xmdp_itemlen xmdl_offset;
xmdp_tbsn xmdl_bsnum<>;
case XMPTYPE_TOOSHORT:
case XMPTYPE_NOITEM:
void;
};
struct xmdp_mitem {
xmdp_vsdisp xmdmi_disp;
xmdp_itemlen xmdmi_length;
xmdp_loc xmdmi_where;
};
typedef xmdp_mitem xmdp_grpinfo<>;
<CODE ENDS>
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An xmdp_loc shows where a particular piece of bulk data is located.
This information exists in multiple forms.
o The case for DDP using explicit RDMA operations, contains, in
xmdl_ex an array of rpcrdma1_segments showing where bulk data is
to be fetched from or has been transferred to.
o The case for send-based data placement contains, in xmdl_tbsn an
array placement-targetable buffer segments, indicating where bulk
data, excised from the payload stream, is actually located. The
bulk data starts xmdl_offset bytes into the buffer segment
designated by xmdl_bsnum[0] and then proceeds through buffer
segments denoted by successive xmdl_bsnum entries until the length
of the data item is exhausted.
o The cases for XMPTYPE_TOOSHORT and XMPTYPE_NOITEM are only valid
in responses
An xmdp_mitem denotes a specific item of bulk data. It consists of:
o The XDR stream displacement of the bulk data excised from the
payload stream, in xmdmi_disp.
o The length of the data item, in xmdmi_length.
o The actual location of the bulk data, in xmdmi_loc.
An xmdp_grpinfo consists of an array of xmdp_mitems describing all of
the bulk data excised from all RPC messages sent in a single RPC-
over-RDMA transmission group. Some possible cases:
o The array is of length zero, indicating that there is no DDP-
eligible data excised from the virtual XDR stream. In this case,
the virtual XDR stream and the payload stream are identical.
o The array consists of one or more xmdp_mitems, each of whose
xmdmi_where fields is of type XMPTYPE_EXRW. In this case, the
placement data corresponds to read chunks in the case in which a
request is being sent and to write chunks in the case in which a
reply is being sent.
o The array consists of one or more xmdp_mitems, each of whose
xmdmi_where fields is of type XMPTYPE_TBSN. In this case, each
entry, whether it applies to bulk data in a request or a reply,
describes data logically part of the message being sent, which may
be part of any RPC-over-RDMA transmissions in the same
transmission group.
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o The array consists of one or more xmdp_mitems, with xmdmi_where
fields of a mixture of types, In this case, each entry, whether it
applies to bulk data in a request or a reply, describes data
logically part of the message being sent, although the method of
getting access to that data may vary from entry to entry.
7.4. Response Direction Data Placement Structures
These data structures, when sent as part of the request, instruct the
responder how to use data placement to place response data subject to
special data placement.
<CODE BEGINS>
union xmdp_rsdloc switch(xmdp_type type)
case XMPTYPE_EXRW:
case XMPTYPE_CHOICE:
rpcrdma1_segment xmdrsdl_ex<>;
case XMPTYPE_BYSIZE:
xmdp_itemlen xmdrsdl_dsdov;
rpcrdma1_segment xmdrsdl_bsex<>;
case XMPTYPE_TBSN:
void;
};
struct xmdp_rsdrange {
xmdp_vsdisp xmdrsdr_begin;
xmdp_vsdisp xmdrsdr_end;
};
struct xmdp_rsditem {
xmdp_itemlen xmdrsdi_minlen;
xmdp_rsdloc xmdrsdi_loc;
};
struct xmdp_rsdset {
xmdp_rsdrange xmdrsds_range;
xmdp_rsditem xmdrsds_items<>;
};
typedef xmdp_rsdset xmdp_rsdgroup<>;
<CODE ENDS>
An xmdp_rsdloc contains information specifying where bulk data
generated as part of a reply is to be placed. This information is
defined as a union with the following cases:
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o The case for DDP using explicit RDMA operations, XMPTYPE_EXRW,
contains, in xmrsdl_ex, an array of rpcrdma1_segments showing
where bulk data generated by the corresponding reply is to be
transferred to.
o The case allowing the responder to freely choose the data
placement method, XMPTYPE_CHOICE, is identical. It also contains,
in xmrsdl_ex, an array of rpcrdma1_segments showing where bulk
data generated by the corresponding reply is to be transferred to
if explicit RDMA requests are to be used.
o The case for send-based data placement, XMPTYPE_TBSN, is void,
since the decisions as to where bulk data is to be placed are made
by the responder.
o In the case directing the responder to choose the data placement
method based on item size, XMPTYPE_BYSIZE, an array of
rpcrdma1_segments is in xmrsdl_bsex.
In all cases, each xmdp_rsdloc sent as part of a request has a
corresponding xmdp_loc in the associated response. The xmdp_type
specified in the request will affect the type in the response, but
the types are not necessarily the same. The table below describes
the valid combinations of request and response xmdp_type values.
In this table, rows correspond to types in requests directing, the
responder as to the desired placement in the response while the
columns correspond to types in the ensuing response. Invalid
combinations are labelled "Inv" while valid combination are labelled
either "NDR" denoting no need to deregister memory, or "DR" to
indicate that memory previously registered will need to be
deregistered.
+---------+--------+--------+-----------+---------+
| Type | EXRW | TBSN | TOOSHORT | NOITEM |
+---------+--------+--------+-----------+---------+
| EXRW | DR | Inv. | DR | DR |
| TBSN | Inv. | NDR | NDR | NDR |
| CHOICE | DR | NDR | DR | DR |
| BYSIZE | DR | NDR | DR | DR |
+---------+--------+--------+-----------+---------+
Table 2
An xmdp_rsdrange denotes a range of positions in the XDR stream
associated with a request. Particular directions regarding bulk data
in the corresponding response are limited to such ranges, where
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response XDR stream positions and request XDR stream positions can be
reliably tied together.
When the ULP supports multiple individual operations per RPC request
(e.g., COMPOUND and CB_COMPOUND in NFSv4), an xmd_rsdrange can
isolate elements of the reply due to particular operations.
An xmdp_rsditem specifies the handling of one potential item of bulk
data. The handling specified is qualified by a length range. If the
item is smaller than xmdrsdi_minlen, it is not treated as bulk data
and the corresponding data item appears in the payload stream, while
that particular xmdp_rsditem is considered used up, making the next
xmdp_rsditem in the xmdp_rsdset the target of the next DDP-eligible
data item in the reply. Note that in the case in which xmdrsdi_loc
specifies use of explicit RDMA operations, the area specified is not
used and the requester is responsible for deregistering it.
For each xmdp_rsditem, there will be a corresponding xmdp_mitem
An xmdp_rsdset contains a set of xmdp_rsditems applicable to a given
xmdp_range in the request.
An xmdp_rsdgroup designates a set of xmdp_rsdsets applicable to a
particular RPC-over-RDMA transmission group. The xmdrsds_range
fields of successive xmdp_rsdsets must be disjoint and in strictly
increasing order.
8. Transport Properties
8.1. Property List
In this document we take advantage of the fact that the set of
transport properties defined in [I-D.cel-nfsv4-rpcrdma-version-two].
is subject to later extension. The additional transport properties
are summarized below in Table 3.
In that table the columns have the following values:
o The column labeled "property" identifies the transport property
described by the current row.
o The column labeled "#" specifies the propid value used to identify
this property.
o The column labeled "XDR type" gives XDR type of the data used to
communicate the value of this property. This data overlays the
nominally opaque field pv_data in a 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.
+------------------------------+----+-----------+---------+---------+
| property | # | XDR type | default | section |
+------------------------------+----+-----------+---------+---------+
| RTR Support | 3 | uint32 | 0 | 8.2 |
| Receive Buffer Structure | 4 | xmrbs_buf | Note1 | 8.3 |
| Request Transmission Receive | 5 | xms_grpxc | 1 | 8.4 |
| Limit | | | | |
| Response Transmission Send | 6 | xms_grpxc | 1 | 8.5 |
| Limit | | | | |
+------------------------------+----+-----------+---------+---------+
Table 3
The following notes apply to the above table:
1. The default value for the Receive Buffer Structure always
consists of a single buffer segment, without any alignment
restrictions and not targetable for DDP. The length of that
buffer segment derives from the Receive Buffer Size Property if
available, and from the default receive buffer size otherwise.
8.2. RTR Support Property
<CODE BEGINS>
const uint32 XPROP_RTRSUPP = 3;
typedef uint32 xpr_rtrs;
const uint32 RTRS_XREQ = 1;
const uint32 RTRS_XRESP = 2;
const uint32 RTRS_XCONT = 4;
<CODE ENDS>
8.3. Receive Buffer Structure Property
This property defines the structure of the endpoint's receive
buffers, in order to give a sender the ability to place bulk data in
specific DDP-targetable buffer segments.
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<CODE BEGINS>
const uint32 XPROP_RBSTRUCT = 4;
typedef xmrbs_buf xpr_rbs;
<CODE ENDS>
Normally, this property, if specified, should be in agreement with
Receive Buffer Size Property. However, the following rules apply.
o If the value of Receive Buffer Structure Property is not
specified, it is derived from the Receive Buffer Size Property, if
known, and the default buffer size otherwise. The buffer is
considered to consist of a single non-DDP-targetable segment whose
size is the buffer size.
o If the value of Receive Buffer Size Property is not specified and
the Receive Buffer Structure Property is specified, the value of
the former is derived from the latter, by adding up the length of
all buffer segments specified.
8.4. Request Transmission Receive Limit Property
This property specifies the length of the longest request messages
(in terms of number of transmissions) that a responder will accept.
<CODE BEGINS>
const uint32 XPROP_REQRXLIM = 5;
typedef uint32 xpr_rqrxl;
<CODE ENDS>
A requester can use this property to determine whether to send long
requests by using message continuation or by using a position-zero
read chunk.
8.5. Response Transmission Send Limit Property
This property specifies the length of the longest response message
(in terms of number of transmissions) that a responder will generate.
<CODE BEGINS>
const uint32 XPROP_RESPSXLIM = 6;
typedef uint32 xpr_rssxl;
<CODE ENDS>
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9. New Operations
9.1. Operations List
The proposed new operation are set for in Table 4 below. In that
table, the columns have the following values:
o The column labeled "operation" specifies the particular operation.
o The column labeled "#" specifies the value of opttype for this
operation.
o The column labeled "XDR type" gives XDR type of the data structure
used to describe the information in this new message 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 (or something else).
o The column labeled "section" indicates the section (within this
document) that explains the semantics and use of this optional
operation.
+--------------------+----+--------------+--------+----------+
| operation | # | XDR type | msg | section |
+--------------------+----+--------------+--------+----------+
| Transmit Request | 5 | optxmt_req | Note1 | 9.2 |
| Transmit Response | 6 | optxmt_resp | Note1 | 9.3 |
| Transmit Continue | 7 | optxmt_cont | Note2 | 9.4 |
| Report Error | 8 | optrept_err | No. | 9.5 |
+--------------------+----+--------------+--------+----------+
Table 4
The following notes apply to the above table:
1. Contains an initial segment of the message payload stream for an
RPC message, or the entre payload stream. The optxr[qs]_pslen
field, indicates the length of the section present
2. May contain a part of a message payload stream for an RPC
message, although not the entre payload stream. The optxc_pslen
field, if non-zero, indicates that this portion is present, and
the length of the section.
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9.2. Transmit Request Operation
The message definition for this operation is as follows:
<CODE BEGINS>
const uint32 ROPT_XMTREQ = 1;
struct optxmt_req {
xmdp_grpinfo optxrq_dp;
xmdp_rsdgroup optxrq_rsd;
xms_grpxc optxrq_count;
xms_grpxc optxrq_rsbuf;
xmdp_pldisp optxrq_pslen;
};
<CODE ENDS>
The field optxrq_dp describes the fields in virtual XDR stream which
have been excised in forming the payload stream, and information
about where the corresponding bulk data is located.
The field optxrq_rsd consists of information directing the responder
as to how to construct the reply, in terms of DDP. of length zero.
The field optrq_count specifies the count of transmissions in this
group of transmissions used to send a request.
The field optrq_repch serves as a way to transfer a reply chunk to
the responder to serve as a way in which a reply longer than the
inline size limit may be transferred. Although, not prohibited by
the protocol, it is unlikely to be used in environments in which
message continuation is supported.
The field optrq_pslen gives the length of the payload stream for the
RPC transmitted. The payload stream begins right after the end of
the optxmt_msg and proceeds for optxm_pslen bytes. This can include
crossing buffer segment boundaries.
9.3. Transmit Response Operation
The message definition for this operation is as follows:
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<CODE BEGINS>
const uint32 ROPT_XMTRESP = 2;
struct optxmt_resp {
xmdp_grpinfo optxrs_dp;
xms_grpxn optxrs_count;
xmdp_pldisp optxrs_pslen;
};
<CODE ENDS>
The field optxrs_dp describes the fields in virtual XDR stream which
have been excised in forming the payload stream, and information
about where the corresponding bulk data is located.
The field optrs_count specifies the count of transmissions in this
group of transmissions used to send a reply.
The field optrq_pslen gives the length of the payload stream for the
RPC transmitted. The payload stream begins right after the end of
the optxmt_msg and proceeds for optxm_pslen bytes. This can include
crossing buffer segment boundaries.
9.4. Transmit Continue Operation
RPC-over-RDMA headers of this type are used to continue RPC messages
begun by RPC-over-RDMA message of type ROPT_XMTREQ or ROPT_XMTRESP.
The xid field of this message must match that in the initial
transmission.
This operation needs to be supported for the message continuation
feature to be used.
The message definition for this operation is as follows:
<CODE BEGINS>
const uint32 ROPT_XMTCONT = 3;
struct optxmt_cont {
xms_grpxn optxc_xnum;
uint32 optxc_itype;
xmdp_pldisp; optxc_pslen;
};
<CODE ENDS>
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The field optxc_xnum indicates the transmission number of this
transmission within its transmission group.
The field optxc_pslen gives the length of the section of the payload
stream which is located in the current RPC-over-RDMA transmission.
It is valid for this length to be zero, indicating that there is no
portion of the payload stream in this transmission. Except when the
length is zero, the payload stream begins right after the end of the
optxmt_cont and proceeds for optxc_pslen bytes. This can include
crossing buffer segment boundaries. In any case, the payload streams
for all transmissions within the same group are considered
concatenated.
9.5. Error Reporting Operation
This RPC-over-RDMA message type is used to signal the occurrence of
errors that do not involve:
1. Transmission of a message that violates the rules specified in
[I-D.cel-nfsv4-rpcrdma-version-two].
2. Transmission of a message described in this document which does
not conform to the XDR specified here.
3. The transmission of a message, which, when assembled according to
the rules here, cannot be decoded according to the XDR for the
ULP.
Such errors can arise if the rules specified in this document are not
followed and can be the result of a mismatch between multiple, each
of which is valid when considered on its own.
The preliminary error-related definition is as follows:
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<CODE BEGINS>
enum optr_err {
OPTRERR_BADHMT = 1,
OPTRERR_BADOMT = 2,
OPTRERR_BADCONT = 3,
OPTRERR_BADSEQ = 4,
OPTRERR_BADXID = 5,
OPTRERR_BADOFF = 6,
OPTRERR_BADTBSN = 7,
OPTRERR_BADPL = 8
}
union optr_info switch(optr_err optre_which) {
case OPTRERR_BADHMT:
case OPTRERR_BADOMT:
case OPTRERR_BADSEQ:
case OPTRERR_BADXID:
uint32 optri_expect;
uint32 optri_current;
case OPTRERR_BADCONT:
void;
case OPTRERR_BADTBSN:
case OPTRERR_BADOFF:
case OPTRERR_BADPL:
uint32 optri_value;
uint32 optri_min;
uint32 optri_max;
};
<CODE ENDS>
optr_err enumerates the various error conditions that might be
reported.
o OPTRERR_BADHMT indicates that a header message type other than the
one expected was received. In this context, a particular message
type can be considered "expected" only because of message or group
continuation.
o OPTRERR_BADOMT indicates that an optional message type other than
the one expected was received. In this context, a particular
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message type can be considered "expected" only because of message
or group continuation.
o OPTRERR_BADCONT indicates that a continuation messages was
received when there was no reason to expect one.
o OPTRERR_BADSEQ indicate that a transmission sequence number other
than the one expected was received.
o OPTRERR_BADXID indicate that an xid other than the one expected in
a continuation context.
o OPTRERR_BADTBSN indicate that an invalid target buffer sequence
number was received.
o OPTRERR_BADOFF indicate that a bad offset was received as part of
an xmdp_loc. This is typically because the offset is larger than
the buffer segment size.
o OPTRERR_BADPL indicates that a bad offset was received for the
payload length. This is typically because the length would make
the area devoted to the payload stream not a subset of the actual
transmission.
The optr_info gives error about the specific invalid field being
reported. The additional information given depends on the specific
error.
o For the errors OPTRERR_BADHMT, OPTRERR_BADOMT, OPTRERR_BADSEQ, and
OPTRERR_BADXID, the expected and actual values of the field are
reported
o For the error OPTRERR_CONT, no additional information is provided.
o For the errors OPTRERR_BADTBSN, OPTRERR_BADOFF, and OPTRERR_BADPL,
the actual value together with a range of valid values is
provided. When the actual value is with the valid range, it can
be inferred that the actual value is not properly aligned (e.g.
not on a 32-bit boundary)
The message definition for this operation is as follows:
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<CODE BEGINS>
const uint32 ROPT_REPTERR = 4;
struct optrept_err {
xms_id optre_bad;
xms_id *optre_lead;
optr_info optre_info;
};
<CODE ENDS>
The field optre_bad is a description of the transmission on which the
error was actually detected.
The optional field optre_lead is a description of an earlier
transmission that might have led to the error reported.
The field optre_info provides information about the
10. 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 includes the base protocol together 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:
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<CODE BEGINS>
sh extract.sh < ext.txt > xmitext.x
<CODE ENDS>
The XDR description for this extension can be combined with that for
other extensions and that for the base protocol. While this is a
complete description and can be processed by the XDR compiler, the
result might not be usable to process the extended protocol, for a
number of reasons:
The RPC-over-RDMA transport headers do not constitute an RPC
program and version negotiation and message selection part of the
XDR, rather than being external to it.
Headers used for requests and replies are not necessarily paired,
as they would be in an RPC program.
Header types defined as optional extensions overlay existing
nominally opaque fields in the base protocol. While this overlay
architecture allows code aware of the overlay relationships to
have a more complete view of header structure, this overlay
relationship cannot be expressed within the XDR language
10.1. 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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10.2. XDR Proper for Extension
<CODE BEGINS>
/// /*******************************************************************
/// *******************************************************************
/// **
/// ** XDR for OPTIONAL protocol extension.
/// **
/// ** Includes support for both message continuation and send-based
/// ** DDP. The latter is supported by a new structure for the
/// ** specification of data placements which can be used for both
/// ** send-based data placement and DDP using explicit RDMA
/// ** operations.
/// **
/// ** Extensions include:
/// **
/// ** o Four new transport properties.
/// ** o Four new OPTIONAL message types
/// **
/// *******************************************************************
/// ******************************************************************/
///
/// /*******************************************************************
/// *
/// * Core XDR Definitions
/// *
/// ******************************************************************/
/// /*
/// * General XDR preliminaries for these features,
/// */
/// typedef uint32 xms_grpxn;
/// typedef uint32 xms_grpxc;
///
/// /*
/// * Basic XDR typedefs for the new approach to the specification of
/// 8 data placement.
/// */
/// typedef uint32 xmdp_itemlen;
/// typedef uint32 xmdp_pldisp;
/// typedef uint32 xmdp_vsdisp;
/// typedef uint32 xmdp_tbsn;
///
/// /*
/// * Define the possible types of data placement items.
/// */
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/// enum xmdp_type {
/// XMPTYPE_EXRW = 1,
/// XMPTYPE_TBSN = 2,
/// XMPTYPE_CHOOSE = 3,
/// XMPTYPE_BYSIZE = 4,
/// XMPTYPE_TOOSHORT = 5,
/// XMPTYPE_NOITEM = 6
/// };
///
/// /*
/// * XDR defining the placement of bulk items in the message being
/// * sent.
/// */
/// union xmdp_loc switch(xmdp_type type)
///
/// case XMPTYPE_EXRW:
/// rpcrdma1_segment xmdl_ex<>;
/// case XMPTYPE_TBSN:
/// xmdp_itemlen xmdl_offset;
/// xmdp_tbsn xmdl_bsnum<>;
/// case XMPTYPE_TOOSHORT:
/// case XMPTYPE_NOITEM:
/// void;
/// };
///
///
///
/// struct xmdp_mitem {
/// xmdp_vsdisp xmdmi_disp;
/// xmdp_itemlen xmdmi_length;
/// xmdp_loc xmdmi_where;
/// };
///
/// typedef xmdp_mitem xmdp_grpinfo<>;
///
/// /*
/// * XDR defining the placement of bulk items in the response to the
/// * message being sent.
/// */
/// union xmdp_rsdloc switch(xmdp_type type)
///
/// case XMPTYPE_EXRW:
/// case XMPTYPE_CHOICE:
/// rpcrdma1_segment xmdrsdl_ex<>;
/// case XMPTYPE_BYSIZE:
/// xmdp_itemlen xmdrsdl_dsdov;
/// rpcrdma1_segment xmdrsdl_bsex<>;
/// case XMPTYPE_TBSN:
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/// void;
/// };
///
/// struct xmdp_rsdrange {
/// xmdp_vsdisp xmdrsdr_begin;
/// xmdp_vsdisp xmdrsdr_end;
/// };
///
/// struct xmdp_rsditem {
/// xmdp_itemlen xmdrsdi_minlen;
/// xmdp_rsdloc xmdrsdi_loc;
/// };
///
/// struct xmdp_rsdset {
/// xmdp_rsdrange xmdrsds_range;
/// xmdp_rsditem xmdrsds_items<>;
/// };
///
/// typedef xmdp_rsdset xmdp_rsdgroup<>;
///
/// /*******************************************************************
/// *
/// * New Transport Properties
/// *
/// ******************************************************************/
///
/// /*
/// * New Transport Property codes
/// */
/// const uint32 XPROP_RTRSUPP = 3;
/// const uint32 XPROP_RBSTRUCT = 4;
/// const uint32 XPROP_REQRXLIM = 5;
/// const uint32 XPROP_RESPSXLIM = 6;
///
/// /*
/// * XDR relating to RTR Support Property
/// */
/// typedef uint32 xpr_rtrs;
///
/// const uint32 RTRS_XREQ = 1;
/// const uint32 RTRS_XRESP = 2;
/// const uint32 RTRS_XCONT = 4;
///
/// /*
/// * Items related to Receive Buffer Structure Property
/// */
/// struct xmrbs_seg {
/// uint32 xmrseg_length;
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/// uint32 xmrseg_align;
/// uint32 xmrseg_flags;
/// };
///
/// const uint32 XMRSFLAG_PLT = 0x01;
///
/// struct xmrbs_group {
/// uint32 xmrgrp_count;
/// xmrbs_seg xmrgrp_info;
/// };
///
/// struct xmrbs_buf {
/// uint32 xmrbuf_length;
/// xmrbs_group xmrbuf_groups<>;
/// };
/// typedef xmrbs_buf xpr_rbs;
///
/// /*
/// * XDR relating to transmission limit properties
/// */
/// typedef uint32 xpr_rqrxl;
///
/// typedef uint32 xpr_rssxl;
///
/// /*******************************************************************
/// *
/// * New OPTIONAL Message Types
/// *
/// ******************************************************************/
///
/// /*
/// * New message type codes
/// */
/// const uint32 ROPT_XMTREQ = 1;
/// const uint32 ROPT_XMTRESP = 2;
/// const uint32 ROPT_XMTCONT = 3;
/// const uint32 ROPT_REPTERR = 4;
///
///
/// /*
/// * New message type to do the initial transmission of a request.
/// */
/// struct optxmt_req {
/// xmdp_grpinfo optxrq_dp;
/// xmdp_rsdgroup optxrq_rsd;
/// xms_grpxc optxrq_count;
/// xms_grpxc optxrq_rsbuf;
/// xmdp_pldisp optxrq_pslen;
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///
/// };
///
/// /*
/// * New message type to do the initial transmission of a response.
/// */
/// struct optxmt_resp {
/// xmdp_grpinfo optxrs_dp;
/// xms_grpxn optxrs_count;
/// xmdp_pldisp optxrs_pslen;
///
/// };
///
/// /*
/// * New message type to transmit the continuation of a request or
/// * response.
/// */
/// struct optxmt_cont {
/// xms_grpxn optxc_xnum;
/// uint32 optxc_itype;
/// xmdp_pldisp; optxc_pslen;
/// };
///
/// /*
/// * XDR definitions to support error reporting.
/// */
/// enum optr_err {
/// OPTRERR_BADHMT = 1,
/// OPTRERR_BADOMT = 2,
/// OPTRERR_BADCONT = 3,
/// OPTRERR_BADSEQ = 4,
/// OPTRERR_BADXID = 5,
/// OPTRERR_BADOFF = 6,
/// OPTRERR_BADTBSN = 7,
/// OPTRERR_BADPL = 8
/// }
///
/// union optr_info switch(optr_err optre_which) {
///
/// case OPTRERR_BADHMT:
/// case OPTRERR_BADOMT:
/// case OPTRERR_BADSEQ:
/// case OPTRERR_BADXID:
/// uint32 optri_expect;
/// uint32 optri_current;
///
/// case OPTRERR_BADCONT:
/// void;
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///
///
/// case OPTRERR_BADTBSN:
/// case OPTRERR_BADOFF:
/// case OPTRERR_BADPL:
/// uint32 optri_value;
/// uint32 optri_min;
/// uint32 optri_max;
///
/// };
///
/// struct xms_id {
/// uint32 xmsi_xid;
/// msg_type xmsi_dir;
/// xms_grpxn xmsi_seq;
/// };
///
/// /*
/// * New message type for error reporting.
/// */
/// struct optrept_err {
/// xms_id optre_bad;
/// xms_id *optre_lead;
/// optr_info optre_info;
/// };
///
///
<CODE ENDS>
11. Security Considerations
The extension described has the same security considerations
described in [RFC8166] and [I-D.cel-nfsv4-rpcrdma-version-two]. With
regard to the transport properties introduced in this document, it is
possible that a man-in-the-middle could interfere with the
communication of transport properties with possible negative effects.
To prevent such interference, the steps described in
[I-D.cel-nfsv4-rpcrdma-version-two] should be attended to.
The use of the techniques described in this document to reduce use of
explicit RDMA operations raise important issues which implementers
should consider:
While the use of these techniques may be expedient in certain
cases, their use is not likely to be universal, at least for a
considerable time. As a result, implementers should remain aware
of the issues discussed in Section 9.1 of [RFC8166], unless and
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until it is certain that none of a requesters memory can be
registered for remote access.
Extra care needs to be taken in cases in which padding needs to be
inserted in a transmission to ensure that DDP-targetable data item
will be received in an appropriately aligned buffer segment. In
some implementations, sensitive data could be inadvertently sent
within the padding. To prevent this, the padding can be zeroed or
it can be sent from a pre-zeroed area using a gather list.
12. IANA Considerations
This document does not require any actions by IANA.
13. References
13.1. 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,
<https://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, <https://www.rfc-editor.org/info/rfc4506>.
[RFC8166] Lever, C., Ed., Simpson, W., and T. Talpey, "Remote Direct
Memory Access Transport for Remote Procedure Call Version
1", RFC 8166, DOI 10.17487/RFC8166, June 2017,
<https://www.rfc-editor.org/info/rfc8166>.
13.2. Informative References
[I-D.cel-nfsv4-rpcrdma-version-two]
Lever, C. and D. Noveck, "RPC-over-RDMA Version 2
Protocol", draft-cel-nfsv4-rpcrdma-version-two-05 (work in
progress), July 2017.
[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,
<https://www.rfc-editor.org/info/rfc5662>.
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[RFC5666] Talpey, T. and B. Callaghan, "Remote Direct Memory Access
Transport for Remote Procedure Call", RFC 5666,
DOI 10.17487/RFC5666, January 2010,
<https://www.rfc-editor.org/info/rfc5666>.
[RFC5667] Talpey, T. and B. Callaghan, "Network File System (NFS)
Direct Data Placement", RFC 5667, DOI 10.17487/RFC5667,
January 2010, <https://www.rfc-editor.org/info/rfc5667>.
[RFC8178] Noveck, D., "Rules for NFSv4 Extensions and Minor
Versions", RFC 8178, DOI 10.17487/RFC8178, July 2017,
<https://www.rfc-editor.org/info/rfc8178>.
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 [RFC8166], for clarifying the relationshp
between RDMA and direct data placement, and for beginning the work on
RPC-over-RDMA Version Two.
The extract.sh shell script and formatting conventions were first
described by the authors of the NFSv4.1 XDR specification [RFC5662].
Author's Address
David Noveck
NetApp
1601 Trapelo Road
Waltham, MA 02451
US
Phone: +1 781 572 8038
Email: davenoveck@gmail.com
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