wdiff draft-ietf-nfsv4-rfc5666bis-02.txt draft-ietf-nfsv4-rfc5666bis-03.txt

Network File System Version 4 C. Lever, Ed.
Internet-Draft Oracle
Obsoletes: 5666 (if approved) W. Simpson
Intended status: Standards Track DayDreamer
Expires: July 14, 28, 2016 T. Talpey
Microsoft
January 11, 25, 2016

Remote Direct Memory Access Transport for Remote Procedure Call
draft-ietf-nfsv4-rfc5666bis-02
draft-ietf-nfsv4-rfc5666bis-03

Abstract

This document specifies a protocol for conveying Remote Procedure
Call (RPC) messages on physical transports capable of Remote Direct
Memory Access (RDMA). It requires no revision to application RPC
protocols or the RPC protocol itself. This document obsoletes RFC
5666.

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
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This Internet-Draft will expire on July 14, 28, 2016.

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Table of Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 3
1.2. RPC Remote Procedure Calls On RDMA Transports . . . . . . . . . . . . . . . . . 3
2. Changes Since RFC 5666 . . . . . . . . . . . . . . . . . . . 4
2.1. Changes To The Specification . . . . . . . . . . . . . . 4
2.2. Changes To The Protocol . . . . . . . . . . . . . . . . . 4 5
3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5
3.1. Remote Procedure Calls . . . . . . . . . . . . . . . . . 5
3.2. Remote Direct Memory Access . . . . . . . . . . . . . . . 8
4. RPC-Over-RDMA Protocol Framework . . . . . . . . . . . . . . 10
4.1. Transfer Models . . . . . . . . . . . . . . . . . . . . . 10
4.2. RPC Message Framing . . . . . . . . . . . . . . . . . . . 11
4.3. Flow Control . . . . . . . 11
4.3. Managing Receiver Resources . . . . . . . . . . . . . . . 11 12
4.4. XDR Encoding With Chunks . . . . . . . . . . . . . . . . 13 14
4.5. Message Size . . . . . . . . . . . . . . . . . . . . . . 19 20
5. RPC-Over-RDMA In Operation . . . . . . . . . . . . . . . . . 20 21
5.1. XDR Protocol Definition . . . . . . . . . . . . . . . . . 21 22
5.2. Fixed Header Fields . . . . . . . . . . . . . . . . . . . 23 24
5.3. Chunk Lists . . . . . . . . . . . . . . . . . . . . . . . 25 26
5.4. Memory Registration . . . . . . . . . . . . . . . . . . . 26 28
5.5. Error Handling . . . . . . . . . . . . . . . . . . . . . 28 30
5.6. Protocol Elements No Longer Supported . . . . . . . . . . 30 32
5.7. XDR Examples . . . . . . . . . . . . . . . . . . . . . . 31 33
6. RPC Bind Parameters . . . . . . . . . . . . . . . . . . . . . 32 34
7. Bi-Directional RPC-Over-RDMA . . . . . . . . . . . . . . . . 34 35
7.1. RPC Direction . . . . . . . . . . . . . . . . . . . . . . 34 36
7.2. Backward Direction Flow Control . . . . . . . . . . . . . 35 37
7.3. Conventions For Backward Operation . . . . . . . . . . . 36 38
7.4. Backward Direction Upper Layer Binding . . . . . . . . . 38 40
8. Upper Layer Binding Specifications . . . . . . . . . . . . . 39 41
8.1. DDP-Eligibility . . . . . . . . . . . . . . . . . . . . . 39 41
8.2. Maximum Reply Size . . . . . . . . . . . . . . . . . . . 41 42
8.3. Additional Considerations . . . . . . . . . . . . . . . . 42 43
8.4. Upper Layer Protocol Extensions . . . . . . . . . . . . . 42 43
9. Transport Protocol Extensibility Guidelines . . . . . . . . . . . . . . 42 . . . . 43
9.1. Extending RPC-over-RDMA Header XDR . . . . . . . . . . . 44
9.2. RPC-over-RDMA Version Numbering . . . . . . . . . . . . . 43 45
10. Security Considerations . . . . . . . . . . . . . . . . . . . 43 46
10.1. Memory Protection . . . . . . . . . . . . . . . . . . . 43 46
10.2. Using GSS With RPC-Over-RDMA . . . . . . . . . . . . . . 44 46
11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 45 47
12. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 46 48
13. References . . . . . . . . . . . . . . . . . . . . . . . . . 46 48
13.1. Normative References . . . . . . . . . . . . . . . . . . 46 48
13.2. Informative References . . . . . . . . . . . . . . . . . 47 49
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 48 51

1. Introduction

This document obsoletes RFC 5666; however, 5666. However, the protocol specified by
this document is based on existing interoperating implementations of
the RPC-over-RDMA Version One protocol.

The new specification clarifies text that is subject to multiple interpretations
interpretations, and removes support for unimplemented RPC-over-RDMA
Version One protocol elements. This document It makes the role of Upper Layer
Bindings an explicit part of the protocol specification.

In addition, this document introduces conventions that enable bi-directional bi-
directional RPC-over-RDMA
operation to allow operation, enabling operation of NFSv4.1
[RFC5661] on RDMA transports.

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. RPC Remote Procedure Calls On RDMA Transports

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

Open Network Computing Remote Procedure Call (ONC RPC, or simply,
RPC) [RFC5531] is a remote procedure call protocol that runs over a
variety of transports. Most RPC implementations today use UDP
[RFC0768] or
TCP. TCP [RFC0793]. On UDP, RPC messages are encapsulated
inside datagrams, while on a TCP byte stream, RPC messages are
delineated by a record marking protocol. An RDMA transport also
conveys RPC messages in a specific fashion that must be fully
described if RPC implementations are to interoperate.

RDMA transports present semantics different from either UDP or TCP.
They retain message delineations like UDP, but provide a reliable and
sequenced data transfer like TCP. They also provide an offloaded
bulk transfer service not provided by UDP or TCP. RDMA transports
are therefore appropriately viewed as a new transport type by RPC.

In this context, the Network File System (NFS) protocols as described
in [RFC1094], [RFC1813], [RFC7530], [RFC5661], and future NFSv4 minor
verions are obvious beneficiaries of RDMA transports. A complete
problem statement is discussed in [RFC5532], and NFSv4-related issues
are discussed in [RFC5661]. Many other RPC-based protocols can also
benefit.

Although the RDMA transport described here can provide relatively
transparent support for any RPC application, this document also
describes mechanisms that can optimize data transfer further, given
more active participation by RPC applications.

2. Changes Since RFC 5666

2.1. Changes To The Specification

The following alterations have been made to the RPC-over-RDMA Version
One specification. The section numbers below refer to [RFC5666].

o Section 2 has been expanded to introduce and explain key RPC, XDR,
and RDMA terminology. These terms are now used consistently
throughout the specification. This change was necesssary because
implementers familiar with RDMA are often not familiar with the
mechanics of RPC, and vice versa.

o Section 3 has been re-organized and split into sub-sections to
help implementers readers locate specific requirements and definitions.

o Sections 4 and 5 have been combined for clarity and to improve the organization of
this information.

o The XDR definition of RPC-over-RDMA Version One has been updated
(without on-the-wire changes) to align with the terms and concepts
introduced in this specification. document.

o The specification of the optional Connection Configuration
Protocol has been removed from the specification, as there are no
known implementations of the this protocol.

o A section outlining consolidating requirements for Upper Layer Bindings has
been added.

o A section discussing RPC-over-RDMA protocol extensibility has been
added.

2.2. Changes To The Protocol

While

Although the protocol described herein interoperates with existing
implementations of [RFC5666], the following changes have been made
relative to the protocol described in that document:

o Support for the Read-Read transfer model has been removed. Read-
Read is a slower transfer model than Read-Write, thus implementers
have chosen not to support it. This Removal simplifies explanatory
text, and support for the RDMA_DONE message type procedure is no longer
necessary.

o The specification of RDMA_MSGP in [RFC5666] and current
implementations of it are incomplete. Even if completed, benefit
for protocols such as NFSv4.0 [RFC7530] is doubtful. Therefore
the RDMA_MSGP message type is no longer supported.

o Technical errors with regard to handling RPC-over-RDMA header
errors have been corrected.

o Specific requirements related to handling XDR round-up and
abstract complex
XDR data types have been added. Responders are now forbidden from
writing Write chunk round-up bytes.

o Explicit guidance is provided for sizing Write chunks, managing
multiple chunks in the Write list, and handling unused Write
chunks.

o Clear guidance about Send and Receive buffer size has been added.
This enables better decisions about when to provide and use the
Reply chunk.

o A section specifying bi-directional RPC operation on RPC-over-RDMA
has been added. This enables the NFSv4.1 [RFC5661] backchannel on
RPC-over-RDMA Version One transports when both endpoints support
the new functionality.

The protocol version number has not been changed because the protocol
specified in this document fully interoperates with implementations
of the RPC-over-RDMA Version One protocol specified in [RFC5666].

3. Terminology

3.1. Remote Procedure Calls

This section introduces key elements of the Remote Procedure Call
[RFC5531] and External Data Representation [RFC4506] protocols, upon
which RPC-over-RDMA Version One is constructed.

3.1.1. Upper Layer Protocols

Remote Procedure Calls are an abstraction used to implement the
operations of an "Upper Layer Protocol," sometimes referred to as a or ULP. The term Upper
Layer Protocol refers to an RPC Program and Version tuple, which is a
versioned set of procedure calls that comprise a single well-defined
API. One example of an Upper Layer Protocol is the Network File
System Version 4.0 [RFC7530].

3.1.2. Requesters And Responders

Like a local procedure call, every Remote Procedure Call (RPC) has a
set of "arguments" and a set of "results". A calling context is not
allowed to proceed until the procedure's results are available to it.
Unlike a local procedure call, the called procedure is executed
remotely rather than in the local application's context.

The RPC protocol as described in [RFC5531] is fundamentally a
message-passing protocol between one server and one or more clients.
ONC RPC transactions are made up of two types of messages:

CALL Message
A CALL message, or "Call", requests that work be done. A Call is
designated by the value CALL zero (0) in the message's msg_type field.
An arbitrary unique value is placed in the message's xid field. field in
order to match this CALL message to a corresponding REPLY message.

REPLY Message
A REPLY message, or "Reply", reports the results of work requested
by a Call. A Reply is designated by the value REPLY one (1) in the
message's msg_type field. The value contained in the message's
xid field is copied from the Call whose results are being
reported.

The RPC client endpoint, or "requester", serializes an RPC call's Call's
arguments and conveys them to a server endpoint via an RPC call Call
message. This message contains an RPC protocol header, a header
describing the requested upper layer operation, and all arguments.

The RPC server endpoint, or "responder", deserializes the arguments
and processes the requested operation. It then serializes the
operation's results into another byte stream. This byte stream is
conveyed back to the requester via an RPC reply Reply message. This
message contains an RPC protocol header, a header describing the
upper layer reply, and all results.

The requester deserializes the results and allows the original caller
to proceed. At this point the RPC transaction designated by the xid
in the call Call message is terminated complete, and the xid is retired.

3.1.3. RPC Transports

The role of an "RPC transport" is to mediate the exchange of RPC
messages between requesters and responders. An RPC transport bridges
the gap between the RPC message abstraction and the native operations
of a particular network transport.

RPC-over-RDMA is a connection-oriented RPC transport. When a
connection-oriented transport is used, ONC RPC client endpoints are
responsible for initiating requesters initiate transport
connections, while ONC RPC
service endpoints responders wait passively for incoming connection
requests.

3.1.4. External Data Representation

In a heterogenous environment, one

One cannot assume that all requesters and responders internally
represent data objects the same way. RPC uses eXternal Data
Representation, or XDR, to translate data types and serialize
arguments and results [RFC4506].

The XDR protocol encodes data independent of the endianness or size
of host-native data types, allowing unambiguous decoding of data on
the receiving end. RPC programs Programs are specified by writing an XDR
definition of their procedures, argument data types, and result data
types.

XDR assumes that the number of bits in a byte (octet) and their order
are the same on both endpoints and on the physical network. The
smallest indivisible unit of XDR encoding is a group of four octets
in little-endian order. XDR also flattens lists, arrays, and other
complex data types so they can be conveyed as a stream of bytes.

A serialized stream of bytes that is the result of XDR encoding is
referred to as an "XDR stream." A sending endpoint encodes native
data into an XDR stream and then transmits that stream to a receiver.
A receiving endpoint decodes incoming XDR byte streams into its
native data representation format.

3.1.4.1. XDR Opaque Data

Sometimes a data item must be transferred as-is, without encoding or
decoding. Such a data item is referred to as "opaque data." XDR
encoding places opaque data items directly into an XDR stream without
altering its their content in any way. Upper Layer Protocols or
applications perform any needed data translation in this case.

Examples of opaque data items include the contents content of files, and or
generic byte strings.

3.1.4.2. XDR Round-up

The number of octets in a variable-size opaque data item precedes
that item in the encoding an XDR stream. If the size of an encoded data item is
not a multiple of four octets, octets containing zero are added to
the end of the item as it is encoded so that the next encoded data
item starts on a four-octet boundary. The encoded size of the item
is not changed by the addition of the extra octets, and the zero
bytes are not exposed to the Upper Layer.

This technique is referred to as "XDR round-up," and the extra octets
are referred to as "XDR padding".

3.2. Remote Direct Memory Access

RPC requesters and responders can be made more efficient if large RPC
messages are transferred by a third party such as intelligent network
interface hardware (data movement offload), and placed in the
receiver's memory so that no additional adjustment of data alignment
has to be made (direct data placement). Remote Direct Memory Access
enables both optimizations.

3.2.1. Direct Data Placement

Typically, RPC implementations copy the contents of RPC messages into
a buffer before being sent. An efficient RPC implementation sends
bulk data without copying it into a separate send buffer first.

However, socket-based RPC implementations are often unable to receive
data directly into its final place in memory. Receivers often need
to copy incoming data to finish an RPC operation; sometimes, only to
adjust data alignment.

In this document, "RDMA" refers to the physical mechanism an RDMA
transport utilizes when moving data. Although this may not be
efficient, before an RDMA transfer a sender may copy data into an
intermediate buffer before an RDMA transfer. After an RDMA transfer,
a receiver may copy that data again to its final destination.

This document uses the term "direct data placement" (or DDP) to refer
specifically to an optimized data transfer where it is unnecessary
for a receiving host's CPU to copy transferred data to another
location after it has been received. Not all RDMA-based data
transfer qualifies as Direct Data Placement, and DDP can be achieved
using non-RDMA mechanisms.

3.2.2. RDMA Transport Requirements

The RPC-over-RDMA Version One protocol assumes the physical transport
provides the following abstract operations. A more complete
discussion of these operations is found in [RFC5040].

Registered Memory
Registered memory is a segment of memory that is assigned a
steering tag that temporarily permits access by the RDMA provider
to perform data transfer operations. The RPC-over-RDMA Version
One protocol assumes that each segment of registered memory MUST
be identified with a steering tag of no more than 32 bits and
memory addresses of up to 64 bits in length.

RDMA Send
The RDMA provider supports an RDMA Send operation, with completion
signaled on the receiving peer after data has been placed in a
pre-posted memory segment. Sends complete at the receiver in the
order they were issued at the sender. The amount of data
transferred by an RDMA Send operation is limited by the size of
the remote pre-posted memory segment.

RDMA Receive
The RDMA provider supports an RDMA Receive operation to receive
data conveyed by incoming RDMA Send operations. To reduce the
amount of memory that must remain pinned awaiting incoming Sends,
the amount of pre-posted memory is limited. Flow-control to
prevent overrunning receiver resources is provided by the RDMA
consumer (in this case, the RPC-over-RDMA Version One protocol).

RDMA Write
The RDMA provider supports an RDMA Write operation to directly
place data in remote memory. The local host initiates an RDMA
Write, and completion is signaled there. No completion is
signaled on the remote. The local host provides a steering tag,
memory address, and length of the remote's memory segment.

RDMA Writes are not necessarily ordered with respect to one
another, but are ordered with respect to RDMA Sends. A subsequent
RDMA Send completion obtained at the write initiator guarantees
that prior RDMA Write data has been successfully placed in the
remote peer's memory.

RDMA Read
The RDMA provider supports an RDMA Read operation to directly
place peer source data in the read initiator's memory. The local
host initiates an RDMA Read, and completion is signaled there; no
completion is signaled on the remote. The local host provides
steering tags, memory addresses, and a length for the remote
source and local destination memory segments.

The remote peer receives no notification of RDMA Read completion.
The local host signals completion as part of an a subsequent RDMA
Send message so that the remote peer can release steering tags and
subsequently free associated source memory segments.

The RPC-over-RDMA Version One protocol is designed to be carried over
RDMA transports that support the above abstract operations. This
protocol conveys to the RPC peer information sufficient for that RPC
peer to direct an RDMA layer to perform transfers containing RPC data
and to communicate their result(s). For example, it is readily
carried over RDMA transports such as Internet Wide Area RDMA Protocol
(iWARP) [RFC5040] [RFC5041].

4. RPC-Over-RDMA Protocol Framework

4.1. Transfer Models

A "transfer model" designates which endpoint is responsible for
performing RDMA Read and Write operations. To enable these
operations, the peer endpoint first exposes segments of its memory to
the endpoint performing the RDMA Read and Write operations.

Read-Read
Requesters expose their memory to the responder, and the responder
exposes its memory to requesters. The responder employs RDMA Read
operations to pull RPC arguments or whole RPC calls from the
requester. Requesters employ RDMA Read operations to pull RPC
results or whole RPC relies from the responder.

Write-Write
Requesters expose their memory to the responder, and the responder
exposes its memory to requesters. Requesters employ RDMA Write
operations to push RPC arguments or whole RPC calls to the
responder. The responder employs RDMA Write operations to push
RPC results or whole RPC relies to the requester.

Read-Write
Requesters expose their memory to the responder, but the responder
does not expose its memory. The responder employs RDMA Read
operations to pull RPC arguments or whole RPC calls from the
requester. The responder employs RDMA Write operations to push
RPC results or whole RPC relies to the requester.

Write-Read
The responder exposes its memory to requesters, but requesters do
not expose their memory. Requesters employ RDMA Write operations
to push RPC arguments or whole RPC calls to the responder.
Requesters employ RDMA Read operations to pull RPC results or
whole RPC relies from the responder.

[RFC5666] specifies the use of both the Read-Read and the Read-Write
Transfer Model. All current RPC-over-RDMA Version One
implementations use only the Read-Write Transfer Model. Use Therefore
the use of the Read-
Read Read-Read Transfer Model by RPC-over-RDMA Version One
implementations is no longer supported. Other Transfer Models may be
used by a future version of RPC-over-RDMA.

4.2. RPC Message Framing

On an RPC-over-RDMA transport, each RPC message is encapsulated by an
RPC-over-RDMA message. An RPC-over-RDMA message consists of two XDR
streams.

Transport-Specific

RPC Payload Stream
The "transport-specific XDR stream," or "Transport stream," "Payload stream" contains an RPC-over-RDMA header that describes the encapsulated RPC message being
transferred by this RPC-over-RDMA message. This stream always
begins with the XID field of the encapsulated RPC message.

Transport-Specific Stream
The "Transport stream" contains a header that describes and
controls the transfer of the Payload stream in this RPC-over-RDMA
message. This header is analogous to the record marking used for
RPC over TCP but is more extensive, since RDMA transports support
several modes of data transfer.

RPC Payload XDR Stream
The "RPC payload stream," or "Payload stream", contains the
encapsulated RPC message being transferred by this RPC-over-RDMA
message.

In its simplest form, an RPC-over-RDMA message consists of a
Transport stream followed immediately by a Payload stream conveyed
together in a single RDMA Send. To transmit large RPC messages, a
combination of one RDMA Send operation and one or more RDMA Read or
Write operations is employed.

RPC-over-RDMA framing replaces all other RPC framing (such as TCP
record marking) when used atop an RPC-over-RDMA association, even
when the underlying RDMA protocol may itself be layered atop a
transport with a defined RPC framing (such as TCP).

It is however possible for RPC-over-RDMA to be dynamically enabled in
the course of negotiating the use of RDMA via an Upper Layer Protocol
exchange. Because RPC framing delimits an entire RPC request or
reply, the resulting shift in framing must occur between distinct RPC
messages, and in concert with the underlying transport.

4.3. Flow Control Managing Receiver Resources

It is critical to provide RDMA Send flow control for an RDMA
connection. RDMA If no pre-posted receive operations can fail if buffer is large enough to
accept an incoming RDMA Send, the RDMA Send operation fails. If a
pre-posted receive buffer is not available to accept an incoming RDMA
Send, and repeated the RDMA Send operation can fail. Repeated occurrences of such
errors can be fatal to the connection. This is a departure from
conventional TCP/IP networking where buffers are allocated
dynamically as part of receiving messages.

The longevity of an RDMA connection requires that sending endpoints
respect the resource limits of peer receivers. To ensure messages
can be sent and received reliably, there are two operational
parameters for each connection.

4.3.1. Credit Limit

The number of pre-posted RDMA Receive operations is sometimes
referred to as a peer's "credit limit." Flow control for RDMA Send
operations directed to the responder is implemented as a simple
request/grant protocol in the RPC-over-RDMA header associated with
each RPC message (Section message. Section 5.2.3 has details). further detail.

o The RPC-over-RDMA header for RPC call Call messages contains a
requested credit value for the responder. This is the maximum
number of RPC replies the requester can handle at once,
independent of how many RPCs are in flight at that moment. The
requester MAY dynamically adjust the requested credit value to
match its expected needs.

o The RPC-over-RDMA header for RPC reply Reply messages provides the
granted result. This is the maximum number of RPC calls the
responder can handle at once, without regard to how many RPCs are
in flight at that moment. The granted value MUST NOT be zero,
since such a value would result in deadlock. The responder MAY
dynamically adjust the granted credit value to match its needs or
policies (e.g. to accommodate the available resources in a shared
receive queue).

The requester MUST NOT send unacknowledged requests in excess of this
granted responder credit limit. If the limit is exceeded, the RDMA
layer may signal an error, possibly terminating the connection. Even
if If
an RDMA layer error does not occur, the responder MAY handle excess
requests or return an RPC layer error to the requester.

While RPC calls complete in any order, the current flow control limit
at the responder is known to the requester from the Send ordering
properties. It is always the lower of the requested and granted
credit values, minus the number of requests in flight. Advertised
credit values are not altered when individual RPCs are started or
completed.

On occasion a requester or responder may need to adjust the amount of
resources available to a connection. When this happens, the
responder needs to ensure that a credit increase is effected (i.e.
receives
RDMA Receives are posted) before the next reply is sent.

Certain RDMA implementations may impose additional flow control
restrictions, such as limits on RDMA Read operations in progress at
the responder. Accommodation of such restrictions is considered the
responsibility of each RPC-over-RDMA Version One implementation.

4.3.1. Initial Connection State

There are two operational parameters for each connection:

Credit Limit
As described above, the total number of responder receive buffers
is sometimes referred to as a connection's credit limit. The
credit limit is advertised in the RPC-over-RDMA header in each RPC
message, and can change during the lifetime of a connection.

4.3.2. Inline Threshold

A receiver's "inline threshold" value is the largest message size (in bytes)
octets) that the receiver can be conveyed accept via an RDMA Send/Receive
combination. Receive operation.
Each connection has two inline threshold values, one for each peer
receiver.

Unlike the connection's credit limit, limits, inline threshold values are not advertised to
peers via the RPC-over-RDMA Version One protocol, and there is no
provision for the inline threshold value to change during the
lifetime of an RPC-over-RDMA Version One connection.

The longevity of a transport connection requires that sending
endpoints respect the resource limits of peer receivers. However,
when

4.3.3. Initial Connection State

When a connection is first established, peers cannot might not know how many
receive buffers the other has, nor how large the these buffers are.

As a basis for an initial exchange of RPC requests, each RPC-over-
RDMA Version One connection provides the ability to exchange at least
one RPC message at a time that is 1024 bytes in size. A responder
MAY exceed this basic level of configuration, but a requester MUST
NOT assume more than one credit is available, and MUST receive a
valid reply from the responder carrying the actual number of
available credits, prior to sending its next request.

Receiver implementations MUST support an inline threshold of 1024
bytes, but MAY support larger inline thresholds values. A mechanism
for discovering a peer's inline threshold value before a connection
is established may be used to optimize the use of RDMA Send
operations. In the absense of such a mechanism, senders MUST assume
a receiver's inline threshold is 1024 bytes.

4.4. XDR Encoding With Chunks

When RDMA is available, during XDR data items in an RPC message are encoded as a contiguous sequence
of bytes for network transmission. This sequence of bytes is known
as an XDR stream. In the case of an RDMA transport, during XDR
encoding it can be determined that encoding it can be determined that
an XDR data item is large enough that it might be more efficient if
the transport placed the content of the data item directly in the
receiver's memory.

4.4.1. Reducing An XDR Stream

RPC-over-RDMA Version One provides a mechanism for moving part of an
RPC message via a data transfer separate from an RDMA Send/Receive.
The sender removes one or more XDR data items from the Payload
stream. They are conveyed via one or more RDMA Read or Write
operations. The receiver inserts the data items into the Payload
stream before passing it to the Upper Layer.

A contiguous piece of a Payload stream that is split out and moved
via separate RDMA operations is known as a "chunk." A Payload stream
after chunks have been removed is referred to as a "reduced" Payload
stream.

4.4.2. DDP-Eligibility

Only an XDR data item that might benefit from Direct Data Placement
may be reduced. The eligibility of particular XDR data items to be
reduced is not specified by this document.

To maintain interoperability on an RPC-over-RDMA transport, a
determination must be made of which XDR data items in each Upper
Layer Protocol are allowed to use Direct Data Placement. Therefore
an additional specification is needed that describes how an Upper
Layer Protocol enables Direct Data Placement. The set of
requirements for an Upper Layer Protocol to use an RPC-over-RDMA
transport is known as an "Upper Layer Binding specification," or ULB.

An Upper Layer Binding specification states which specific individual
XDR data items in an Upper Layer Protocol MAY be transferred via
Direct Data Placement. This document will refer to XDR data items
that are permitted to be reduced as "DDP-eligible". All other XDR
data items MUST NOT be reduced. RPC-over-RDMA Version One uses RDMA
Read and Write operations to transfer DDP-eligible data that has been
reduced.

Detailed requirements for Upper Layer Bindings are discussed in full
in Section 8.

4.4.3. RDMA Segments

When encoding a Payload stream that contains a DDP-eligible data
item, a sender may choose to reduce that data item. It does not
place the item into the Payload stream. Instead, the sender records
in the RPC-over-RDMA header the actual address and size of the memory
region containing that data item.

The requester provides location information for DDP-eligible data
items in both RPC calls Calls and replies. Replies. The responder uses this
information to initiate RDMA Read and Write operations to retrieve or
update the content specified region of the requester's memory.

An "RDMA segment", or just "segment", a "plain segment", is an RPC-over-RDMA header
data object that contains the precise co-ordinates of a contiguous
memory region that is to be conveyed via one or more RDMA Read or
RDMA Write operations. The following fields are contained in each segment:
segment.

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Handle |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ Offset +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Handle
Steering tag (STag) or handle obtained when the segment's memory
is registered for RDMA. Sometimes Also known as an R_key. R_key, this value is
generated by registering this memory with the RDMA provider.

Length
The length of the segment memory segment, in bytes. octets.

Offset
The offset or beginning memory address of the segment.

See [RFC5040] for further discussion of the meaning of these fields.

4.4.4. Chunks

In RPC-over-RDMA Version One, a "chunk" refers to a portion of the
Payload stream that is moved via RDMA Read or Write operations.
Chunk data is removed from the sender's Payload stream, transferred
by separate RDMA operations, and then re-inserted into the receiver's
Payload stream.

Each chunk consists of one or more RDMA segments. Each segment
represents a single contiguous piece of that chunk. Segments MAY
divide a chunk on any boundary that is convenient to the requester.

Except in special cases, a chunk contains exactly one XDR data item.
This makes it straightforward to remove chunks from an XDR stream
without affecting XDR alignment. Not every RPC-over-RDMA message has
chunks associated with it.

4.4.4.1. Counted Arrays

If a chunk contains a counted array data type, the count of array
elements MUST remain in the Payload stream, while the array elements
MUST be moved to the chunk. For example, when encoding an opaque
byte array as a chunk, the count of bytes stays in the Payload
stream, while the bytes in the array are removed from the Payload
stream and transferred within the chunk.

Any byte count left in the Payload stream MUST match the sum of the
lengths of the segments making up the chunk. If they do not agree,
an RPC protocol encoding error results.

Individual array elements appear in a chunk in their entirety. For
example, when encoding an array of arrays as a chunk, the count of
items in the enclosing array stays in the Payload stream, but each
enclosed array, including its item count, is transferred as part of
the chunk.

4.4.4.2. Optional-data

If a chunk contains an optional-data data type, the "is present"
field MUST remain in the Payload stream, while the data, if present,
MUST be moved to the chunk.

4.4.4.3. XDR Unions

A union data type should never be made DDP-eligible, but one or more
of its arms may be DDP-eligible.

4.4.5. Read Chunks

A "Read chunk" represents an XDR data item that is to be pulled from
the requester to the responder using RDMA Read operations.

A Read chunk is a list of one or more RDMA segments. Each RDMA
segment in a Read chunk is a plain segment which has an additional
Position field.

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Position |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Handle |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ Offset +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Position
The byte offset in the Payload stream where the receiver re-
inserts the data item conveyed in a chunk. The Position value
MUST be computed from the beginning of the Payload stream, which
begins at Position zero. All RDMA segments belonging to the same
Read chunk have the same value in their Position field.

While constructing an RPC-over-RDMA Call message, a requester
registers memory segments containing data in Read chunks. It
advertises these chunks in the RPC-over-RDMA header of the RPC call. Call.

After receiving an RPC call Call sent via an RDMA Send operation, a
responder transfers the chunk data from the requester using RDMA Read
operations. The responder reconstructs the transferred chunk data by
concatenating the contents of each segment, in list order, into the
received Payload stream at the Position value recorded in the
segment.

Put another way, a receiver inserts the first segment in a Read chunk
into the Payload stream at the byte offset indicated by its Position
field. Segments whose Position field value match this offset are
concatenated afterwards, until there are no more segments at that
Position value. The next XDR data item in the Payload stream
follows.

4.4.5.1. Read Chunk Round-up

XDR requires each encoded data item to start on four-byte alignment.
When an odd-length data item is marshaled, encoded, its length is encoded
literally, while the data is padded so the next data item in the XDR
stream can start on a four-byte boundary. Receivers ignore the
content of the pad bytes.

After an XDR data item has been reduced, all data items remaining in
the Payload stream must continue to adhere to these padding
requirements. Thus when an XDR data item is moved from the Payload
stream into a Read chunk, the requester MUST remove XDR padding for
that data item from the Payload stream as well.

The length of a Read chunk is the sum of the lengths of the read
segments that comprise it. If this sum is not a multiple of four,
the requester MAY choose to send a Read chunk without any XDR
padding.
The If the requester provides no actual round-up in a Read
chunk, the responder MUST be prepared to provide appropriate round-up
in the reconstructed call XDR stream if the requester provides no actual
round-up in a Read chunk.

The Position field in a read segments segment indicates where the containing
Read chunk starts in the RPC message XDR Payload stream. The value in this field
MUST be a multiple of four. Moreover, all segments in the same Read
chunk share the same Position value, even if one or more of the
segments have a non-four-byte aligned length.

4.4.5.2. Decoding Read Chunks

When

While decoding an RPC-over-RDMA message, the responder first decodes
the chunk lists from the RPC-over-RDMA header, then proceeds to
decode the a received Payload stream. Whenever stream, whenever the XDR offset in
the Payload stream matches that of a Read chunk, the transport
initiates an RDMA Read to bring over pull the chunk chunk's data content into locally
registered memory for on the destination buffer. responder.

The responder acknowledges its completion of use of Read chunk source
buffers when it replies sends an RPC Reply to the requester. The requester
may then release Read chunks advertised in the request.

4.4.6. Write Chunks

A "Write chunk" represents an XDR data item that is to be pushed from
a responder to a requester using RDMA Write operations.

A Write chunk is an array of one or more plain RDMA segments. Segments in
a Write chunk do not have a Position field because Write
chunks are provided by a requester long before the responder has
prepared the reply Payload stream. Therefore RDMA segments in a
Write chunk do not have a Position field.

While constructing an RPC call Call message, a requester also prepares
memory regions to catch DDP-eligible reply data items. A requester
does not know the actual length of the result data item to be
returned, thus it MUST register a Write chunk long enough to
accommodate the maximum possible size of the returned data item.

A responder copies the requester-provided Write chunk segments into
the RPC-over-RDMA header that it returns with the reply. The
responder MUST NOT change the number of segments in the Write chunk.

The responder fills the segments in array order until the data item
has been completely written. The responder updates the segment
length fields to reflect the actual amount of data that is being
returned in the Write chunk. The
updated length of each segment. If a Write chunk segment MAY be zero if the segment
was is not filled by
the responder. However the responder MUST NOT
change responder, the number updated length of segments in the Write chunk. segment SHOULD be zero.

The responder then sends the RPC reply Reply via an RDMA Send operation.
After receiving the RPC reply, Reply, the requester reconstructs the
transferred data by concatenating the contents of each segment, in
array order, into RPC reply Reply XDR stream.

4.4.6.1. Unused Write Chunks

There are occasions when a requester provides a Write chunk but the
responder does not use it. For example, an Upper Layer Protocol may
define a union result where some arms of the union contain a DDP-
eligible data item, and other arms do not. To return an unused Write
chunk, the responder MUST set the length of all segments in the chunk
to zero.

Unused write chunks, or unused bytes in write chunk segments, are not
returned as results and their memory is returned to the Upper Layer
as part of RPC completion. However, the RPC layer MUST NOT assume
that the buffers have not been modified.

4.4.6.2. Write Chunk Round-up

After a data item is reduced, data items remaining in the Payload
stream must continue to adhere to these padding requirements. Thus
when an XDR data item is moved from a reply Payload stream into a
Write chunk, the responder MUST remove XDR padding for that data item
from the reply Payload stream as well.

A requester SHOULD NOT provide extra length in a Write chunk to
accommodate XDR pad bytes. A responder MUST NOT write XDR pad bytes
for a Write chunk.

4.5. Message Size

A receiver of RDMA Send operations is required by RDMA to have
previously posted one or more adequately sized buffers. Memory
savings can be achieved on both requesters and responders by leaving
the inline threshold small.

4.5.1. Short Messages

RPC messages

4.4.6.2. Unused Write Chunks

There are frequently smaller than typical inline thresholds. occasions when a requester provides a Write chunk but the
responder does not use it.

For example, the NFS version 3 GETATTR request is only 56 bytes: 20
bytes an Upper Layer Protocol may define a union result where
some arms of RPC header, plus the union contain a 32-byte file handle argument and 4 bytes
for its length. DDP-eligible data item while other
arms do not. The reply requester is required to provide a Write chunk in
this common request is about 100 bytes.

Since all RPC messages conveyed via RPC-over-RDMA require an RDMA case, but if the responder returns a result that uses an arm of
the union that has no DDP-eligible data item, the Write chunk remains
unused.

When forming an RPC-over-RDMA Reply message with an unused Write
chunk, the responder MUST set the length of all segments in the chunk
to zero.

Unused write chunks, or unused bytes in write chunk segments, are not
returned as results. Their memory is returned to the Upper Layer as
part of RPC completion. However, the RPC layer MUST NOT assume that
the buffers have not been modified.

4.5. Message Size

4.5.1. Short Messages

RPC messages are frequently smaller than typical inline thresholds.
For example, the NFS version 3 GETATTR request is only 56 bytes: 20
bytes of RPC header, plus a 32-byte file handle argument and 4 bytes
for its length. The reply to this common request is about 100 bytes.

Since all RPC messages conveyed via RPC-over-RDMA require an RDMA
Send operation, the most efficient way to send an RPC message that is
smaller than the receiver's inline threshold is to append the Payload
stream directly to the Transport stream. An RPC-over-RDMA header
with a small RPC call Call or reply Reply message immediately following is
transferred using a single RDMA Send operation. No RDMA Read or
Write operations are needed.

4.5.2. Chunked Messages

If DDP-eligible data items are present in a Payload stream, a sender
MAY reduce the Payload stream and use RDMA Read or Write operations
to move the reduced data items. The Transport stream with the
reduced Payload stream immediately following is transferred using a
single RDMA Send operation.

After receiving the Transport and Payload streams of a Chunked RPC-
over-RDMA Call message, the responder uses RDMA Read operations to
move reduced data items in Read chunks. Before sending the Transport
and Payload streams of a Chunked RPC-over-RDMA Reply message, the
responder uses RDMA Write operations to move reduced data items in
Write and Reply chunks.

4.5.3. Long Messages

When a Payload stream is larger than the receiver's inline threshold,
the Payload stream is reduced by removing DDP-eligible data items and
placing them in chunks to be moved separately. If there are no DDP-
eligible data items in the Payload stream, or the Payload stream is
still too large after it has been reduced, the RDMA transport MUST
use RDMA Read or Write operations to convey the Payload stream
itself. This mechanism is referred to as a "Long Message."

To transmit a Long Message, the sender conveys only the Transport
stream with an RDMA Send operation. The Payload stream is not
included in the Send buffer in this instance. Instead, the requester
provides chunks that the responder uses to move the Payload stream.

Long RPC call Call
To send a Long RPC-over-RDMA Call message, the requester provides
a special Read chunk that contains the RPC call's Call's Payload stream.
Every segment in this Read chunk MUST contain zero in its Position
field. Thus this chunk is known as a "Position Zero Read chunk."

Long RPC reply Reply
To send a Long RPC-over-RDMA Reply message, the requester provides
a single special Write chunk in advance, known as the "Reply
chunk", that will contain the RPC reply's Reply's Payload stream. The
requester sizes the Reply chunk to accommodate the maximum
expected reply size for that Upper Layer operation.

Though the purpose of a Long Message is to handle large RPC messages,
requesters MAY use a Long Message at any time to convey an RPC call. Call.
Responders MUST send a Long reply whenever a Reply chunk has been
provided by a requester.

Because these special chunks contain a whole RPC message, any XDR
data item MAY appear in one of these special chunks without regard to
its DDP-eligibility. DDP-eligible data items MAY be removed from
these special chunks and conveyed via normal chunks, but non-eligible
data items MUST NOT appear in normal chunks.

5. RPC-Over-RDMA In Operation

Every RPC-over-RDMA Version One message has a header that includes a
copy of the message's transaction ID, data for managing RDMA flow
control credits, and lists of RDMA segments used for RDMA Read and
Write operations. All RPC-over-RDMA header content is contained in
the Transport stream, and thus MUST be XDR encoded.

RPC message layout is unchanged from that described in [RFC5531]
except for the possible reduction of data items that are moved by
RDMA Read or Write operations.

5.1. XDR Protocol Definition

Code components extracted from this document must include the
following license boilerplate.

/*
* Copyright (c) 2010, 2015 IETF Trust and the persons
* identified as authors of the code. All rights reserved.
*
* The authors of the code are:
* B. Callaghan, T. Talpey, and C. Lever.
*
* 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.
*/

struct rpcrdma1_segment {
uint32 rdma_handle;
uint32 rdma_length;
uint64 rdma_offset;
};

struct rpcrdma1_read_segment {
uint32 rdma_position;
struct rpcrdma1_segment rdma_target;
};

struct rpcrdma1_read_list {
struct rpcrdma1_read_segment rdma_entry;
struct rpcrdma1_read_list *rdma_next;
};

struct rpcrdma1_write_chunk {
struct rpcrdma1_segment rdma_target<>;
};

struct rpcrdma1_write_list {
struct rpcrdma1_write_chunk rdma_entry;
struct rpcrdma1_write_list *rdma_next;
};

struct rpcrdma1_header {
uint32 rdma_xid;
uint32 rdma_vers;
uint32 rdma_credit;
rpcrdma1_body rdma_body;
};

enum rpcrdma1_proc {
RDMA_MSG = 0,
RDMA_NOMSG = 1,
RDMA_MSGP = 2, /* Reserved */
RDMA_DONE = 3, /* Reserved */
RDMA_ERROR = 4
};

struct rpcrdma1_chunks {
struct rpcrdma1_read_list *rdma_reads;
struct rpcrdma1_write_list *rdma_writes;
struct rpcrdma1_write_chunk *rdma_reply;
};

enum rpcrdma1_errcode {
RDMA_ERR_VERS = 1,
RDMA_ERR_CHUNK = 2
};

union rpcrdma1_error switch (rpcrdma1_errcode rdma_err) {
case RDMA_ERR_VERS:
uint32 rdma_vers_low;
uint32 rdma_vers_high;
case RDMA_ERR_CHUNK:
void;
};

union rdma_body rpcrdma1_body switch (rpcrdma1_proc rdma_proc) {
case RDMA_MSG:
case RDMA_NOMSG:
rpcrdma1_chunks rdma_chunks;
case RDMA_MSGP:
uint32 rdma_align;
uint32 rdma_thresh;
rpcrdma1_chunks rdma_achunks;
case RDMA_DONE:
void;
case RDMA_ERROR:
rpcrdma1_error rdma_error;
};

5.2. Fixed Header Fields

The RPC-over-RDMA header begins with four fixed 32-bit fields that
MUST be present and that
control the RDMA interaction including RDMA-
specific flow control. interaction. These four fields are: fields, which must remain
with the same meanings and in the same positions in all subsequent
versions of the RPC-over-RDMA protocol, are described below.

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| XID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Version Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Credit Value |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Procedure Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

5.2.1. Transaction ID (XID)

The XID generated for the RPC Call and Reply. Having the XID at a
fixed location in the header makes it easy for the receiver to
establish context as soon as the each RPC-over-RDMA message arrives.
This XID MUST be the same as the XID in the RPC message. The
receiver MAY perform its processing based solely on the XID in the
RPC-over-RDMA header, and thereby ignore the XID in the RPC message,
if it so chooses.

5.2.2. Version number Number

For RPC-over-RDMA Version One, this field MUST contain the value 1
(one). Further discussion of one
(1). Rules regarding changes to this transport protocol extensibility version
number can be found in Section 9. 9.2.

5.2.3. Flow control credit value Credit Value

When sent in an RPC Call message, the requested credit value is
provided. When sent in an RPC Reply message, the granted credit
value is returned. RPC Calls SHOULD NOT be sent in excess of the
currently granted limit. Further discussion of flow control how the credit value
is determined can be found in Section 4.3.

5.2.4. Message type Procedure number

o RDMA_MSG = 0 indicates that chunk lists and an RPC message a Payload stream
follow. The format of the chunk lists is discussed below.

o RDMA_NOMSG = 1 indicates that after the chunk lists there is no
RPC message.
Payload stream. In this case, the chunk lists provide information
to allow the responder to transfer the RPC message Payload stream using RDMA
Read or Write operations.

o RDMA_MSGP = 2 is reserved.

o RDMA_DONE = 3 is reserved.

o RDMA_ERROR = 4 is used to signal an encoding error in RDMA chunk encoding. the RPC-
over-RDMA header.

An RDMA_MSG type message procedure conveys the Transport stream and the Payload
stream via an RDMA Send operation. The Transport stream contains the
four fixed fields, followed by the Read and Write lists and the Reply
chunk, though any or all three MAY be marked as not present. The
Payload stream then follows, beginning with its XID field. If a Read
or Write chunk list is present, a portion of the Payload stream has
been excised and is conveyed separately via RDMA Read or Write
operations.

An RDMA_NOMSG type message procedure conveys the Transport stream via an RDMA Send
operation. The Transport stream contains the four fixed fields,
followed by the Read and Write chunk lists and the Reply chunk.
Though any of these MAY be marked as not present, one MUST be present
and MUST hold the Payload stream for this RPC-over-RDMA message, beginning
with its XID field. message. If
a Read or Write chunk list is present, a portion of the Payload
stream has been excised and is conveyed separately via RDMA Read or
Write operations.

An RDMA_ERROR type message procedure conveys the Transport stream via an RDMA Send
operation. The Transport stream contains the four fixed fields,
followed by formatted error information. No Payload stream is
conveyed in this type of RPC-over-RDMA message.

A gather operation on each RDMA Send operation can be used to marshal combine
the Transport and Payload streams separately. streams, which might have been constructed
in separate buffers. However, the total length of the gathered send
buffers MUST NOT exceed the peer receiver's inline threshold.

5.3. Chunk Lists

The chunk lists in an RPC-over-RDMA Version One header are three XDR
optional-data fields that MUST follow the fixed header fields in RDMA_MSG
and RDMA_NOMSG type messages. procedures. Read Section 4.19 of [RFC4506] carefully
to understand how optional-data fields work. Examples of XDR encoded
chunk lists are provided in Section 5.7 as an aid to understanding.

5.3.1. Read List

Each RDMA_MSG or RDMA_NOMSG type message procedure has one "Read list." The Read
list is a list of zero or more Read segments, provided by the
requester, that are grouped by their Position fields into Read
chunks. Each Read chunk advertises the location of argument data the
responder is to retrieve via RDMA Read operations. The requester has
removed the data in these chunks from the call's Payload stream.

Via a Position Zero Read Chunk, a requester may provide an RPC Call
message as a chunk in the Read list.

The Read list is empty if

If the RPC Call has no argument data that is
DDP-eligible, DDP-eligible and the
Position Zero Read Chunk is not being used. used, the requester leaves the
Read list empty.

5.3.2. Write List

Each RDMA_MSG or RDMA_NOMSG type message procedure has one "Write list." The
Write list is a list of zero or more Write chunks, provided by the
requester. Each Write chunk is an array of RDMA segments, thus the
Write list is a list of counted arrays. Each Write chunk advertises
receptacles for DDP-eligible data to be pushed by the responder via
RDMA Write operations. If the RPC Reply has no possible DDP-eligible
result data items, the requester leaves the Write list empty.

*** This section needs to specify when a requester must provide Write
chunks, and how many chunks must be provided. ***

When a Write list is provided for the results of an RPC Call, the
responder MUST provide any data corresponding to DDP-eligible XDR data
items via RDMA Write operations to the memory referenced in the chunk's segments. The Write list is empty
if
list. The responder removes the RPC operation has no DDP-eligible result data. data in these chunks from the
reply's Payload stream.

When multiple Write chunks are present, the responder fills in each
Write chunk with a DDP-eligible result until either there are no more
results or no more Write chunks. The requester may not be able to
predict which DDP-eligible data item goes in which chunk. Thus the
requester is responsible for allocating and registering Write chunks
large enough to accommodate the largest XDR data item that might be
associated with each chunk in the list.

The RPC reply Reply conveys the size of result data items by returning the each
Write
list chunk to the requester with the segment lengths rewritten to
match the actual
transfer. data transferred. Decoding the reply therefore
performs no local data
transfer copying but merely returns the length obtained
from the reply.

Each decoded result consumes one entry in the Write list, which in
turn consists of an array of RDMA segments. The length of a Write
chunk is therefore the sum of all returned lengths in all segments
comprising the corresponding list entry. As each Write chunk is
decoded, the entire Write list entry is consumed.

5.3.3. Reply Chunk

Each RDMA_MSG or RDMA_NOMSG type message has one "Reply chunk." The
Reply chunk is a Write

A requester constructs the Write list for an RPC transaction before
the responder has formulated its reply. When there is only one DDP-
eligible result data item, the requester inserts only a single Write
chunk in the Write list. If the responder populates that chunk with
data, the requester knows with certainty which result data item is
contained in it.

However, Upper Layer Protocol procedures may allow replies where more
than one result data item is DDP-eligible. For example, an NFSv4
COMPOUND procedure is composed of individual NFSv4 operations, more
than one of which may have a reply containing a DDP-eligible result.

As stated above, when multiple Write chunks are present, the
responder reduces DDP-eligible result until either there are no more
results or no more Write chunks. Then, as the requester decodes the
reply Payload stream, it is clear from the contents of the reply
which Write chunk contains which data item.

5.3.3. Reply Chunk

Each RDMA_MSG or RDMA_NOMSG procedure has one "Reply chunk." The
Reply chunk is a Write chunk, provided by the requester. The Reply
chunk is a single counted array of RDMA segments.

A requester MUST provide a Reply chunk whenever the maximum possible
size of the reply is larger than its own inline threshold. The Reply
chunk MUST be large enough to contain a Payload stream (RPC message)
of this maximum size.

When a Reply chunk is provided, a responder MUST convey If the RPC actual reply Payload stream is smaller
than the requester's inline threshold, the responder MAY return it as
a Short message in this rather than using the Reply chunk.

5.4. Memory Registration

RDMA requires that data is transferred between only registered memory
segments at the source and destination. All protocol headers as well
as separately transferred data chunks must reside in registered
memory.

Since the cost of registering and de-registering memory can be a
significant proportion of the RDMA transaction cost, it is important
to minimize registration activity. This can be achieved within RPC-
controlled For memory that is targeted by allocating chunk list data
RDMA Send and RPC headers Receive operations, a local-only registration is
sufficient and can be left in place during the life of a
reusable way from pre-registered pools. connection
without any risk of data exposure.

5.4.1. Registration Longevity

Data chunks transferred via RDMA Read and Write MAY can reside in a memory
allocation that persists outside not in the bounds control of the RPC
transaction. Hence, the default behavior of an RPC-over-RDMA
transport is to register transport. These
memory allocations can persist outside the bounds of an RPC
transaction. They are registered and invalidate these chunks on every invalidated as needed, as part
of each RPC transaction.

The requester endpoint must ensure that these memory segments associated
with each RPC transaction are properly fenced from the responder responders before
allowing Upper Layer access to the data contained in them. The data in such segments Moreover,
the requester must be at
rest not access these memory segments while a the
responder has access to that memory. them.

This includes segments that are associated with canceled RPCs. A
responder cannot know that the requester is no longer waiting for a
reply, and might proceed to read or even update memory that the
requester has might have released for other use.

5.4.2. Communicating DDP-Eligibility

The interface by which an Upper Layer Protocol implementation
communicates the eligibility of a data item locally to its local RPC-
over-RDMA endpoint is not described by this specification.

Depending on the implementation and constraints imposed by Upper
Layer Bindings, it is possible to implement reduction transparently
to upper layers. Such implementations may lead to inefficiencies,
either because they require the RPC layer to perform expensive
registration and de-registration of memory "on the fly", or they may
require using RDMA chunks in reply messages, along with the resulting
additional handshaking with the RPC-over-RDMA peer.

However, these issues are internal and generally confined to the
local interface between RPC and its upper layers, one in which
implementations are free to innovate. The only requirement is that
the resulting RPC-over-RDMA protocol sent to the peer is valid for
the upper layer.

5.4.3. Registration Strategies

The choice of which memory registration strategies to employ is left
to requester and responder implementers. To support the widest array
of RDMA implementations, as well as the most general steering tag
scheme, an Offset field is included in each segment.

While zero-based offset schemes are available in many RDMA
implementations, their use by RPC requires individual registration of
each segment. For such implementations, this can be a significant
overhead. By providing an offset in each chunk, many pre-
registration or region-based registrations can be readily supported.
By using a single, universal chunk representation, the RPC-over-RDMA
protocol implementation is simplified to its most general form.

5.5. Error Handling

A receiver performs basic validity checks on the RPC-over-RDMA header
and chunk contents before it passes the RPC message to the RPC
consumer. If errors are detected in an RPC-over-RDMA header, an
RDMA_ERROR type message procedure MUST be generated. Because the transport layer
may not be aware of the direction of a problematic RPC message, an
RDMA_ERROR type message procedure MAY be generated by either a requester or a
responder.

To form an RDMA_ERROR type message: procedure: The rdma_xid field MUST contain the
same XID that was in the rdma_xid field in the failing request; The
rdma_vers field MUST contain the same version that was in the
rdma_vers field in the failing request; The rdma_proc field MUST
contain the value RDMA_ERROR; The rdma_err field contains a value
that reflects the type of error that occurred, as described below.

An RDMA_ERROR type message procedure indicates a permanent error. When receiving
an RDMA_ERROR type message, procedure, a requester should attempt to terminate the
RPC transaction if it recognizes the XID in the reply's rdma_xid
field, and return an error to the application to prevent retrying the
failed RPC transaction.

To avoid an infinite loop, a receiver should drop an RDMA_ERROR type
message
procedure that is malformed.

5.5.1. Header Version Mismatch

When a receiver detects an RPC-over-RDMA header version that it does
not support (currently this document defines only Version One), it
MUST reply with an RDMA_ERROR procedure and set the rdma_err value of ERR_VERS, to
RDMA_ERR_VERS, also providing the low and high inclusive version
numbers it does, in fact, support.

5.5.2. XDR Errors

A receiver might encounter an XDR parsing error that prevents it from
processing the incoming Transport stream. Examples of such errors
include an invalid value in the rdma_proc field, an RDMA_NOMSG
message that has no chunk lists, or the contents of the rdma_xid
field might not match the contents of the XID field in the
accompanying RPC message. In such cases, If the rdma_vers field contains a
recognized value, but an XDR parsing error occurs, the responder MUST
reply with an RDMA_ERROR procedure and set the rdma_err value of ERR_CHUNK. to
RDMA_ERR_CHUNK.

When a responder receives a valid RPC-over-RDMA header but the
responder's Upper Layer Protocol implementation cannot parse the RPC
arguments in the RPC Call message, the responder SHOULD return a
RPC_GARBAGEARGS reply, using an RDMA_MSG type message. procedure. This type of
parsing failure might be due to mismatches between chunk sizes or
offsets and the contents of the Payload stream, for example. A
responder MAY also report the presence of a non-DDP-eligible data
item in a Read or Write chunk using RPC_GARBAGEARGS.

5.5.3. Responder Operational Errors

Problems can arise as a responder attempts to use requester-provided
resources for RDMA Read or Write operations. For example:

o Chunks can be validated only by using their contents to form RDMA
Read or Write operations. If chunk contents are invalid (say, a
segment is no longer registered, or a chunk length is too long), a
Remote Access error occurs.

o If a requester's receive buffer is too small, the responder's Send
operation completes with a Local Length Error.

o If the requester-provided Reply chunk is too small to accommodate
a large RPC reply, Reply, a Remote Access error occurs. A responder can
detect this problem before attempting to write past the end of the
Reply chunk.

Operational errors are typically fatal to the connection. To avoid a
retransmission loop and repeated connection loss that deadlocks the
connection, once the requester has re-established a connection, the
responder should send an RDMA_ERROR reply with an rdma_err value of
ERR_CHUNK
RDMA_ERR_CHUNK to indicate that no RPC-level reply is possible for
that XID.

5.5.4. RDMA Transport Errors

The RDMA connection and physical link provide some degree of error
detection and retransmission. iWARP's Marker PDU Aligned (MPA) layer
(when used over TCP), Stream Control Transmission Protocol (SCTP), as
well as the InfiniBand link layer all provide Cyclic Redundancy Check
(CRC) protection of the RDMA payload, and CRC-class protection is a
general attribute of such transports.

Additionally, the RPC layer itself can accept errors from the link
level and recover via retransmission. RPC recovery can handle
complete loss and re-establishment of the link.

The details of reporting and recovery from RDMA link layer errors are
outside the scope of this protocol specification. See Section 10 for
further discussion of the use of RPC-level integrity schemes to
detect errors.

5.6. Protocol Elements No Longer Supported

The following protocol elements are no longer supported in RPC-over-
RDMA Version One. Related enum values and structure definitions
remain in the RPC-over-RDMA Version One protocol for backwards
compatibility.

5.6.1. RDMA_MSGP

The specification of RDMA_MSGP in Section 3.9 of [RFC5666] is
incomplete. To fully specify RDMA_MSGP would require:

o Updating the definition of DDP-eligibility to include data items
that may be transferred, with padding, via RDMA_MSGP type messages procedures

o Adding full operational descriptions of the alignment and
threshold fields

o Discussing how alignment preferences are communicated between two
peers without using CCP

o Describing the treatment of RDMA_MSGP type messages procedures that convey Read
or Write chunks

The RDMA_MSGP message type is beneficial only when the padded data
payload is at the end of an RPC message's argument or result list.
This is not typical for NFSv4 COMPOUND RPCs, which often include a
GETATTR operation as the final element of the compound operation
array.

Without a full specification of RDMA_MSGP, there has been no fully
implemented prototype of it. Without a complete prototype of
RDMA_MSGP support, it is difficult to assess whether this protocol
element has benefit, or can even be made to work interoperably.

Therefore, senders MUST NOT send RDMA_MSGP type messages. procedures. When
receiving an RDMA_MSGP type message, procedure, receivers SHOULD reply with an
RDMA_ERROR type message, procedure, setting the rdma_err field to ERR_CHUNK. RDMA_ERR_CHUNK.

5.6.2. RDMA_DONE

Because no implementation of RPC-over-RDMA Version One uses the Read-
Read transfer model, there is never a need to send an RDMA_DONE type
message.
procedure.

Therefore, senders MUST NOT send RDMA_DONE messages. When receiving
an RDMA_DONE type message, procedure, receivers SHOULD reply with an RDMA_ERROR
type message,
procedure, setting the rdma_err field to ERR_CHUNK. RDMA_ERR_CHUNK.

5.7. XDR Examples

RPC-over-RDMA chunk lists are complex data types. In this appendix,
illustrations are provided to help readers grasp how chunk lists are
represented inside an RPC-over-RDMA header.

An RDMA segment is the simplest component, being made up of a 32-bit
handle (H), a 32-bit length (L), and 64-bits of offset (OO). Once
flattened into an XDR stream, RDMA segments appear as

HLOO

A Read segment has an additional 32-bit position field. Read
segments appear as

PHLOO

A Read chunk is a list of Read segments. Each segment is preceded by
a 32-bit word containing a one if there is a segment, or a zero if
there are no more segments (optional-data). In XDR form, this would
look like

1 PHLOO 1 PHLOO 1 PHLOO 0

where P would hold the same value for each segment belonging to the
same Read chunk.

The Read List is also a list of Read segments. In XDR form, this
would look like a Read chunk, except that the P values could vary
across the list. An empty Read List is encoded as a single 32-bit
zero.

One Write chunk is a counted array of segments. In XDR form, the
count would appear as the first 32-bit word, followed by an HLOO for
each element of the array. For instance, a Write chunk with three
elements would look like
3 HLOO HLOO HLOO

The Write List is a list of counted arrays. In XDR form, this is a
combination of optional-data and counted arrays. To represent a
Write List containing a Write chunk with three segments and a Write
chunk with two segments, XDR would encode

1 3 HLOO HLOO HLOO 1 2 HLOO HLOO 0

An empty Write List is encoded as a single 32-bit zero.

The Reply chunk is a Write chunk. Since it is an optional-data
field, however, there is a 32-bit field in front of it that contains
a one if the Reply chunk is present, or a zero if it is not. After
encoding, a Reply chunk with 2 segments would look like

1 2 HLOO HLOO

Frequently a requester does not provide any chunks. In that case,
after the four fixed fields in the RPC-over-RDMA header, there are
simply three 32-bit fields that contain zero.

6. RPC Bind Parameters

In setting up a new RDMA connection, the first action by a requester
is to obtain a transport address for the responder. The mechanism
used to obtain this address, and to open an RDMA connection is
dependent on the type of RDMA transport, and is the responsibility of
each RPC protocol binding and its local implementation.

RPC services normally register with a portmap or rpcbind [RFC1833]
service, which associates an RPC Program number with a service
address. (In the case of UDP or TCP, the service address for NFS is
normally port 2049.) This policy is no different with RDMA
transports, although it may require the allocation of port numbers
appropriate to each Upper Layer Protocol that uses the RPC framing
defined here.

When mapped atop the iWARP transport [RFC5040] [RFC5041], which uses
IP port addressing due to its layering on TCP and/or SCTP, port
mapping is trivial and consists merely of issuing the port in the
connection process. The NFS/RDMA protocol service address has been
assigned port 20049 by IANA, for both iWARP/TCP and iWARP/SCTP.

When mapped atop InfiniBand [IB], which uses a Group Identifier
(GID)-based service endpoint naming scheme, a translation MUST be
employed. One such translation is defined in the InfiniBand Port
Addressing Annex [IBPORT], which is appropriate for translating IP
port addressing to the InfiniBand network. Therefore, in this case,
IP port addressing may be readily employed by the upper layer.

When a mapping standard or convention exists for IP ports on an RDMA
interconnect, there are several possibilities for each upper layer to
consider:

o One possibility is to have responder register its mapped IP port
with the rpcbind service, under the netid (or netid's) defined
here. An RPC-over-RDMA-aware requester can then resolve its
desired service to a mappable port, and proceed to connect. This
is the most flexible and compatible approach, for those upper
layers that are defined to use the rpcbind service.

o A second possibility is to have the responder's portmapper
register itself on the RDMA interconnect at a "well known" service
address (on UDP or TCP, this corresponds to port 111). A
requester could connect to this service address and use the
portmap protocol to obtain a service address in response to a
program number, e.g., an iWARP port number, or an InfiniBand GID.

o Alternatively, the requester could simply connect to the mapped
well-known port for the service itself, if it is appropriately
defined. By convention, the NFS/RDMA service, when operating atop
such an InfiniBand fabric, will use the same 20049 assignment as
for iWARP.

Historically, different RPC protocols have taken different approaches
to their port assignment; therefore, the specific method is left to
each RPC-over-RDMA-enabled Upper Layer binding, and not addressed
here.

In Section 11, this specification defines two new "netid" values, to
be used for registration of upper layers atop iWARP [RFC5040]
[RFC5041] and (when a suitable port translation service is available)
InfiniBand [IB]. Additional RDMA-capable networks MAY define their
own netids, or if they provide a port translation, MAY share the one
defined here.

7. Bi-Directional RPC-Over-RDMA
7.1. RPC Direction

7.1.1. Forward Direction

A traditional ONC RPC client is always a requester. A traditional
ONC RPC service is always a responder. This traditional form of ONC
RPC message passing is referred to as operation in the "forward
direction."

During forward direction operation, the ONC RPC client is responsible
for establishing transport connections.

7.1.2. Backward Direction

The ONC RPC standard does not forbid passing messages in the other
direction. An ONC RPC service endpoint can act as a requester, in
which case an ONC RPC client endpoint acts as a responder. This form
of message passing is referred to as operation in the "backward
direction."

During backward direction operation, the ONC RPC client is
responsible for establishing transport connections, even though ONC
RPC Calls come from the ONC RPC server.

7.1.3. Bi-direction

A pair of endpoints may choose to use only forward or only backward
direction operations on a particular transport. Or, the endpoints
may send operations in both directions concurrently on the same
transport.

Bi-directional operation occurs when both transport endpoints act as
a requester and a responder at the same time. As above, the ONC RPC
client is responsible for establishing transport connections.

7.1.4. XIDs with Bi-direction

During bi-directional operation, the forward and backward directions
use independent xid spaces.

In other words, a forward direction requester MAY use the same xid
value at the same time as a backward direction requester on the same
transport connection, but such concurrent requests represent distinct
ONC RPC transactions.

7.2. Backward Direction Flow Control

7.2.1. Backward RPC-over-RDMA Credits

Credits work the same way in the backward direction as they do in the
forward direction. However, forward direction credits and backward
direction credits are accounted separately.

In other words, the forward direction credit value is the same
whether or not there are backward direction resources associated with
an RPC-over-RDMA transport connection. The backward direction credit
value MAY be different than the forward direction credit value. The
rdma_credit field in a backward direction RPC-over-RDMA message MUST
NOT contain the value zero.

A backward direction requester (an RPC-over-RDMA service endpoint)
requests credits from the responder (an RPC-over-RDMA client
endpoint). The responder reports how many credits it can grant.
This is the number of backward direction Calls the responder is
prepared to handle at once.

When an RPC-over-RDMA server endpoint is operating correctly, it
sends no more outstanding requests at a time than the client
endpoint's advertised backward direction credit value.

7.2.2. Receive Buffer Management

An RPC-over-RDMA transport endpoint must pre-post receive buffers
before it can receive and process incoming RPC-over-RDMA messages.
If a sender transmits a message for a receiver which has no posted
receive buffer, the RDMA provider MAY drop the RDMA connection.

7.2.2.1. Client Receive Buffers

Typically an RPC-over-RDMA caller posts only as many receive buffers
as there are outstanding RPC Calls. A client endpoint without
backward direction support might therefore at times have no pre-
posted receive buffers.

To receive incoming backward direction Calls, an RPC-over-RDMA client
endpoint must pre-post enough additional receive buffers to match its
advertised backward direction credit value. Each outstanding forward
direction RPC requires an additional receive buffer above this
minimum.

When an RDMA transport connection is lost, all active receive buffers
are flushed and are no longer available to receive incoming messages.
When a fresh transport connection is established, a client endpoint
must re-post a receive buffer to handle the Reply for each
retransmitted forward direction Call, and a full set of receive
buffers to handle backward direction Calls.

7.2.2.2. Server Receive Buffers

A forward direction RPC-over-RDMA service endpoint posts as many
receive buffers as it expects incoming forward direction Calls. That
is, it posts no fewer buffers than the number of RPC-over-RDMA
credits it advertises in the rdma_credit field of forward direction
RPC replies.

To receive incoming backward direction replies, an RPC-over-RDMA
server endpoint must pre-post a receive buffer for each backward
direction Call it sends.

When the existing transport connection is lost, all active receive
buffers are flushed and are no longer available to receive incoming
messages. When a fresh transport connection is established, a server
endpoint must re-post a receive buffer to handle the Reply for each
retransmitted backward direction Call, and a full set of receive
buffers for receiving forward direction Calls.

7.3. Conventions For Backward Operation

7.3.1. In the Absense of Backward Direction Support

An RPC-over-RDMA transport endpoint might not support backward
direction operation. There might be no mechanism in the transport
implementation to do so, or the Upper Layer Protocol consumer might
not yet have configured the transport to handle backward direction
traffic.

A loss of the RDMA connection may result if the receiver is not
prepared to receive an incoming message. Thus a denial-of-service
could result if a sender continues to send backchannel messages after
every transport reconnect to an endpoint that is not prepared to
receive them.

For RPC-over-RDMA Version One transports, the Upper Layer Protocol is
responsible for informing its peer when it has established a backward
direction capability. Otherwise even a simple backward direction
NULL probe from a peer would result in a lost connection.

An Upper Layer Protocol consumer MUST NOT perform backward direction
ONC RPC operations unless the peer consumer has indicated it is
prepared to handle them. A description of Upper Layer Protocol
mechanisms used for this indication is outside the scope of this
document.

7.3.2. Backward Direction Retransmission

In rare cases, an ONC RPC transaction cannot be completed within a
certain time. This can be because the transport connection was lost,
the Call or Reply message was dropped, or because the Upper Layer
consumer delayed or dropped the ONC RPC request. Typically, the
requester sends the transaction again, reusing the same RPC XID.
This is known as an "RPC retransmission".

In the forward direction, the Caller is the ONC RPC client. The
client is always responsible for establishing a transport connection
before sending again.

In the backward direction, the Caller is the ONC RPC server. Because
an ONC RPC server does not establish transport connections with
clients, it cannot send a retransmission if there is no transport
connection. It must wait for the ONC RPC client to re-establish the
transport connection before it can retransmit ONC RPC transactions in
the backward direction.

If an ONC RPC client has no work to do, it may be some time before it
re-establishes a transport connection. Backward direction Callers
must be prepared to wait indefinitely before a connection is
established before a pending backward direction ONC RPC Call can be
retransmitted.

7.3.3. Backward Direction Message Size

RPC-over-RDMA backward direction messages are transmitted and
received using the same buffers as messages in the forward direction.
Therefore they are constrained to be no larger than receive buffers
posted for forward messages.

It is expected that the Upper Layer Protocol consumer establishes an
appropriate payload size limit for backward direction operations,
either by advertising that size limit to its peers, or by convention.
If that is done, backward direction messages do not exceed the size
of receive buffers at either endpoint.

If a sender transmits a backward direction message that is larger
than the receiver is prepared for, the RDMA provider drops the
message and the RDMA connection.

7.3.4. Sending A Backward Direction Call

To form a backward direction RPC-over-RDMA Call message on an RPC-
over-RDMA Version One transport, an ONC RPC service endpoint
constructs an RPC-over-RDMA header containing a fresh RPC XID in the
rdma_xid field.

The rdma_vers field MUST contain the value one. The number of
requested credits is placed in the rdma_credit field.

The rdma_proc field in the RPC-over-RDMA header MUST contain the
value RDMA_MSG. All three chunk lists MUST be empty.

The ONC RPC Call header MUST follow immediately, starting with the
same XID value that is present in the RPC-over-RDMA header. The Call
header's msg_type field MUST contain the value CALL.

7.3.5. Sending A Backward Direction Reply

To form a backward direction RPC-over-RDMA Reply message on an RPC-
over-RDMA Version One transport, an ONC RPC client endpoint
constructs an RPC-over-RDMA header containing a copy of the matching
ONC RPC Call's RPC XID in the rdma_xid field.

The rdma_vers field MUST contain the value one. The number of
granted credits is placed in the rdma_credit field.

The rdma_proc field in the RPC-over-RDMA header MUST contain the
value RDMA_MSG. All three chunk lists MUST be empty.

The ONC RPC Reply header MUST follow immediately, starting with the
same XID value that is present in the RPC-over-RDMA header. The
Reply header's msg_type field MUST contain the value REPLY.

7.4. Backward Direction Upper Layer Binding

RPC programs that operate on RPC-over-RDMA Version One only in the
backward direction do not require an Upper Layer Binding
specification. Because RPC-over-RDMA Version One operation in the
backward direction does not allow reduction, there can be no DDP-
eligible data items in such a program. Backward direction operation
occurs on an already-established connection, thus there is no need to
specify RPC bind parameters.

8. Upper Layer Binding Specifications

Each RPC program and version tuple that operates on an RDMA transport
MUST have an Upper Layer Binding (ULB) specification. An Upper Layer
Binding specification can be part of another protocol specification
document, or it might be a stand-alone document, similar to
[RFC5667].

An Upper Layer Protocol is typically defined independently of a any
particular RPC transport. An Upper Layer Binding specification (ULB)
provides guidance that helps the Upper Layer Protocol interoperate
correctly and efficiently over a particular transport, such as RPC-
over-RDMA transport. For RPC-over-
RDMA Version One. In particular, it One, a ULB provides:

o A taxonomy of XDR data items that are eligible for Direct Data
Placement

o Clarifications on how to compute A method for determining the maximum reply size of the reply Payload
stream for
operations all procedures in the Upper Layer Protocol

o An rpcbind port assignment for operation of the RPC Program and
Version on an RPC-over-RDMA transport

8.1. DDP-Eligibility

To optimize the use of an RDMA transport,

Each RPC Program and Version tuple that utilizes RPC-over-RDMA
Version One needs to have an Upper Layer Binding
designates some XDR data items as eligible specification.
Requesters MUST NOT send RPC-over-RDMA messages for Direct Data Placement.
A data item is Upper Layer
Protocols that do not have a candidate Upper Layer Binding. Responders MUST
NOT reply to RPC-over-RDMA messages for eligibility Upper Layer Protocols that do
not have a Upper Layer Binding.

8.1. DDP-Eligibility

An Upper Layer Binding designates some XDR data items as eligible for
Direct Data Placement. As an RPC-over-RDMA message is formed, DDP-
eligible data items can be removed from the Payload stream and placed
directly in the receiver's memory (reduced).

An XDR data item should be considered for DDP-eligibility if there is
a clear benefit for to moving the contents of the item directly from the
sender's memory into to the receiver's memory. Criteria for DDP-
eligibility include:

o The size of the XDR data item is frequently sent or received, and its size is
often much larger than the typical inline threshold.

2. thresholds.

o Transport-level processing of the XDR data item is not needed.
For example, the data item is an opaque byte array, which requires
no XDR encoding and decoding of its content.

o The content of the XDR data item is sensitive to address
alignment. For example, pullup would be required on the receiver
before the content of the item can be used.

As RPC-over-RDMA messages are formed, DDP-eligible data items are
treated specially. A DDP-eligible

o The XDR data item is one that MAY be
conveyed by itself in a separate chunk. The Upper Layer Protocol
implementation or the RDMA transport implementation decides when to
move a does not contain DDP-eligible data item into a chunk instead of leaving the
item in the RPC message's XDR stream.

All other XDR items.

Senders MUST NOT reduce data items that are considered non-DDP-eligible, and MUST
NOT be moved in a separate chunk. They not DDP-eligible. Such
data items MAY, however, be moved as part of a Position Zero Read
Chunk or a Reply chunk.

The interface by which an Upper Layer implementation indicates the
DDP-eligibility of a data item to the RPC transport is not described
by this specification. The only requirements are that the receiver
can re-assemble the transmitted RPC-over-RDMA message into a valid
XDR stream, and that DDP-eligibility rules specified by the Upper
Layer Binding are respected.

There is no provision to express DDP-eligibility within the XDR
language. The only definitive specification of DDP-eligibility is
the Upper Layer Binding itself.

It is the responsibility of the protocol's Upper Layer Binding to
specify DDP-eligibity rules so that if

8.1.1. DDP-Eligibility Violation

A DDP-eligibility violation occurs when a requester forms a Call
message with a non-DDP-eligible data item in a Read chunk. A
violation occurs when a responder forms a Reply message without
reducing a DDP-eligible XDR data item when there is embedded within another, only one of these two objects is to be
represented by a chunk. This ensures that Write list provided
by the mapping from XDR
position to requester.

In the XDR object represented is unambiguous. Note however first case, a responder MUST NOT process the Call message.

In the second case, as a requester parses a Reply message, it must
assume that such complex the responder has correctly reduced a DDP-eligible result
data item. If the responder has not done so, it is likely that the
requester cannot finish parsing the Payload stream and that an XDR
error would result.

Both types are unlikely to of violations MUST be good candidates reported as described in
Section 5.5.2.

8.2. Maximum Reply Size

A requester provides resources for
Direct Data Placement.

8.1.1. Write List Ordering Ambiguity both a Call message and its
matching Reply message. A requester constructs forms the Call message itself,
thus can compute the exact resources needed for it.

A requester must allocate resources for the Reply message (an RPC-
over-RDMA credit, a Receive buffer, and possibly a Write list for an RPC transaction and
Reply chunk) before the responder has formulated its formed the actual reply. When there is only one
result data item that is DDP-eligible, To
accommodate all possible replies for the requester appends only procedure in the Call
message, a
single Write chunk to that Write list. If requester must allocate reply resources based on the responder populates
that chunk with data,
maximum possible size of the requester knows with certainty which result
is contained expected Reply message.

If there are procedures in it.

However, the Upper Layer Protocol procedures may allow replies where more
than one result data item is DDP-eligible. For example, an NFSv4
COMPOUND is composed of individual NFSv4 operations, more than one of for which may have a there
is no clear reply containing size maximum, the Upper Layer Binding needs to
specify a DDP-eligible result. As stated
in Section 5.3.2, when multiple Write chunks are present, dependable means for determining the
responder fills maximum.

8.3. Additional Considerations

There may be other details provided in each Write chunk with a DDP-eligible result until
either there are no more results or no more Write chunks.

Ambiguities can arise when replies contain XDR unions an Upper Layer Binding.

o An Upper Layer Binding may recommend an inline threshold value or arrays of
complex data types which allow
other transport-related parameters for RPC-over-RDMA Version One
connections bearing that Upper Layer Protocol.

o An Upper Layer Protocol may provide a responder options about whether means to communicate these
transport-related parameters between peers. Note that RPC-over-
RDMA Version One does not specify any mechanism for changing any
transport-related parameter after a
DDP-eligible data item is included or not. It is connection has been
established.

o Multiple Upper Layer Protocols may share a single RPC-over-RDMA
Version One connection when their Upper Layer Bindings allow the responsibility
use of RPC-over-RDMA Version One and the rpcbind port assignments
for the Protocols allow connection sharing. In this case, the
same transport parameters (such as inline threshold) apply to all
Protocols using that connection.

Given the above, Upper Layer Binding Bindings and Upper Layer Protocols must
be designed to avoid situations where interoperate correctly no matter what connection
parameters are in effect on a connection.

8.4. Upper Layer Protocol Extensions

An RPC Program and Version tuple may be extensible. For instance,
there may be a minor versioning scheme that is
ambiguity about which result is in which chunk not reflected in the Write list. If
an ambiguity is unavoidable,
RPC version number. Or, the Upper Layer Binding MUST specify how
Write list entries are mapped to DDP-eligible results.

8.1.2. DDP-Eligibility Violation

A DDP-eligibility violation occurs when a requester forms a Call
message with a non-DDP-eligible data item in a Read chunk, or
provides a Write list when there are no DDP-eligible items allowed in
the operation's reply. A violation occurs when a responder forms a
Reply message without reducing a DDP-eligible data item when there is
a Write list provided by the requester.

In the first case, a responder might attempt to parse and process the
Call message anyway. If the responder cannot process the Call, it
MUST report this either via an RDMA_ERROR type message with the
rdma_err field set to ERR_CHUNK, or via an RPC-level RPC_GARBAGEARGS
message.

In the second case, the responder is in a bind: when a Write chunk is
provided, it MUST use it, but the ULB specification does not say what
result is expected in that chunk. This is considered a transport-
level error, and MUST be reported to the requester via an RDMA_ERROR
type message with the rdma_err field set to ERR_CHUNK.

In the third case, a requester might attempt to parse and process the
Reply message anyway. If the requester cannot process the Reply, it
MUST report this via an RDMA_ERROR type message with the rdma_err
field set to ERR_CHUNK.

8.2. Maximum Reply Size

A requester provides resources for both a Call message and its
matching Reply message. A requester forms the Call message itself,
thus can compute the exact resources needed for it.

A requester must allocate resources for the Reply message (an RPC-
over-RDMA credit, a Receive buffer, and possibly a Write list and
Reply chunk) before the responder has formed the actual reply. To
accommodate all possible replies for the operation in the Call
message, a requester must allocate reply resources based on the
maximum possible size of the expected reply.

If there are operations in Protocol may allow
additional features to be specified after the original RPC program
specification was ratified.

Upper Layer Protocol Bindings are provided for which there
is no clear payload maximum, an interoperable RPC Programs and
Versions by extending existing Upper Layer Binding MUST provide a
mechanism a requester implementation can use Bindings to determine reflect the
resources needed for these operations.

8.3. Additional Considerations

There may be
changes made necessary by each addition to the existing XDR.

9. Extensibility Guidelines

The RPC-over-RDMA header format is specified using XDR, unlike other details provided in an Upper Layer Binding.

o An Upper Layer Binding may recommend an inline threshold value
RPC transport protocols such as TCP or
other transport-related parameters UDP. This creates
opportunities for addressing minor issues with the transport protocol
and for introducing optional features, all without having to
increment the RPC-over-RDMA Version One
connections bearing that Upper Layer Protocol.

o An Upper Layer Protocol may provide protocol version number. When more
invasive changes to the protocol are needed, a means protocol version
number change is required. In either case, no changes to communicate these
transport-related parameters between peers. Note that the RPC-
over-RDMA protocol can be made without Working Group discussion and
approval by the IESG.

Unlike the rest of this document, which defines the base of RPC-over-
RDMA Version One does not specify any mechanism for changing any
transport-related parameter after a connection has been
established.

o Multiple Upper Layer Protocols One, Section 9 applies to all versions of RPC-over-RDMA.
New versions of RPC-over-RDMA may share a single be published as separate protocols
without updating this document, but any change to the extensibility
model defined here requires updating this document.

9.1. Extending RPC-over-RDMA
Version One connection when their Upper Layer Bindings allow Header XDR

The first four fields in the
use of RPC-over-RDMA Version One and the rpcbind port assignments
for the Protocols allow connection sharing. In this case, header must remain aligned
at the same transport parameters (such as inline threshold) apply to fixed offsets for all
Protocols using that connection.

Given versions of the above, Upper Layer Bindings and Upper Layer Protocols RPC-over-RDMA
protocol. The version number must be designed to interoperate correctly no matter what connection
parameters are in effect on a connection.

8.4. Upper Layer Protocol Extensions

An RPC Program and Version tuple may fixed place in order for
version mismatches to be extensible. detected. For instance,
there may version mismatches to be
reported in a minor versioning scheme fashion that is not reflected in the
RPC all future version number. Or, implementations can
reliably decode, the Upper Layer Protocol may allow
additional features to rdma_proc field must be specified after in a fixed place, the original RPC program
specification was ratified. Upper Layer Bindings are provided for
interoperable programs
value of RDMA_ERR_VERS must always remain the same, and versions by extending existing Upper Layer
Bindings to reflect the changes made necessary by each addition to field
placement of the existing XDR.

9. Transport Protocol Extensibility

Upper Layer RPC Protocols are defined solely by their XDR
definitions. They are independent RDMA_ERR_VERS arm of the transport mechanism used rpcrdma1_error union must
always remain the same.

Given these constraints, one way to
convey base RPC messages. Protocols defined by XDR often have
signifcant extensibility restrictions placed on them.

Not all extensibility restrictions on RPC-based Upper Layer Protocols extend RPC-over-RDMA is to add
new values to the rdma_proc enumerated type and new components (arms)
to the rpcrdma1_body union. New argument and result types may be
introduced for each new procedure defined this way. These extensions
would be specified by new Internet Drafts with appropriate for an RPC transport protocol. TCP [RFC0793], for
example, is an RPC transport protocol that has been extended many
times independently of the RPC Working
Group and IESG review to ensure continued interoperation with
existing implementations.

XDR standards.

RPC-over-RDMA might be considered as extensions may introduce only optional features to an extension of the RPC existing
RPC-over-RDMA protocol
rather than version. To detect when an optional rdma_proc
value is supported by a separate transport, however.

o The mechanisms that TCP uses to move data are opaque receiver, it is desirable to have a specific
value of the RPC
implementation and RPC programs using it. Upper Layer Protocols
are often aware that RPC-over-RDMA is present, as they identify
data items rdma_err field, say, RDMA_ERR_PROC, that can be moved via direct data placement.

o RPC-over-RDMA is used only for moving RPC messages, and indicates when
the receiver does not ever
for generic data transfer.

o recognize an rdma_proc value.

In RPC-over-RDMA relies on Version One, a more sophisticated receiver can indicate that it does
not recognize an rdma_proc enum value only by returning an RDMA_ERROR
procedure with the rdma_err field set of base transport
operations than traditional socket-based transports.
Interoperability depends on RPC-over-RDMA implementations using
these operations in to RDMA_ERR_CHUNK (see
Section 5.5.2). This is indistinguishable from a predictable way.

o The RPC-over-RDMA header situation where the
receiver does indeed support the procedure, but the XDR is specified using XDR, unlike other RPC
transport protocols.

9.1. malformed.

To resolve this problem, an RPC-over-RDMA Version Numbering

Because One sender uses the version number is encoded as part of
following convention. If the RPC-over-RDMA
header first time the sender uses an optional
rdma_proc value the receiver returns an RDMA_ERROR procedure with
RDMA_ERR_CHUNK in the rdma_err field, the sender simply marks that
feature as unsupported and does not send it again on the RDMA_ERROR message type is used current
connection instance. Subsequent to indicate errors,
these first four fields and the start an initial successful result,
receiving RDMA_ERR_CHUNK retains its more relaxed meaning of "generic
XDR parsing error."

To ensure backwards compatibility when such an extension mechanism is
in place, the chunk lists MUST always value of RDMA_ERR_CHUNK must remain aligned at the same fixed offsets for all
versions of the RPC-
over-RDMA header. RPC-over-RDMA protocol.

9.2. RPC-over-RDMA Version Numbering

Before becoming REQUIRED, features created by XDR extension will
often need a significant period of optional general use to ensure
they are mature. This is especially true for infrastructural
features that others will build upon. When optional features become
REQUIRED, that would be an occasion to bump the RPC-over-RDMA
protocol version.

9.2.1. Incrementing The Version Number

The value of the RPC-over-RDMA header's version field MUST has to be changed

o Whenever the on-the-wire format of
updated when the RPC-over-RDMA header protocol is
changed altered in a way that prevents
interoperability with current
implementations implementations. Two examples of such
changes include:

o Whenever the set of abstract RDMA operations that may be used RPC-over-RDMA header XDR definition is changed to add
a REQUIRED protocol element, or whenever a REQUIRED protocol
element is removed

o Whenever the set use of allowable transfer models a new abstract RDMA operation is altered specified as
REQUIRED, or the use of an existing REQUIRED abstract RDMA
operation is removed

When a version number bump is forced (e.g. a REQUIRED feature is to
be introduced), the Working Group can:

o Document the whole protocol as amended

o Normatively reference all features added since the previous
version

o Include all REQUIRED functionality, and normatively reference
optional functionality

The Working Group retains all these options but the last is typically
preferred.

10. Security Considerations

10.1. Memory Protection

A primary consideration is the protection of the integrity and
privacy of local memory by an RPC-over-RDMA transport. The use of
RPC-over-RDMA MUST NOT introduce any vulnerabilities to system memory
contents, nor to memory owned by user processes.

It is REQUIRED that any RDMA provider used for RPC transport be
conformant to the requirements of [RFC5042] in order to satisfy these
protections. These protections are provided by the RDMA layer
specifications, and specifically in particular, their security models.

10.1.1. Protection Domains

The use of Protection Domains to limit the exposure of memory
segments to a single connection is critical. Any attempt by a host an
endpoint not participating in that connection to re-use memory
handles will should result in
a connection failure. immediate failure of that connection.
Because Upper Layer Protocol security mechanisms rely on this aspect
of Reliable Connection behavior, strong authentication of the remote
endpoints is recommended.

10.1.2. Handle Predictability

Unpredictable memory handles should be used for any operation
requiring advertised memory segments. Advertising a continuously
registered memory region allows a remote host to read or write to
that region even when an RPC involving that memory is not under way.
Therefore implementations should avoid advertising persistently
registered memory.

10.1.3. Memory Fencing

Advertised memory segments should be invalidated as soon as related
RPC operations are complete. Invalidation and DMA unmapping of
segments should be complete before an RPC application the Upper Layer is allowed to
continue execution and use or alter the contents of a memory region.

10.2. Using GSS With RPC-Over-RDMA

ONC RPC provides its own security via the RPCSEC_GSS framework
[RFC2203]. RPCSEC_GSS can provide message authentication, integrity
checking, and privacy. This security mechanism is unaffected by the
RDMA transport. However, there is much host data movement associated
with the computation and verification of integrity and with
encryption/decryption, so performance advantages can be lost.

For efficiency, a more appropriate security mechanism for RDMA links
may be link-level protection, such as certain configurations of
IPsec, which may be co-located in the RDMA hardware. The use of
link-level protection MAY be negotiated through the use of the
RPCSEC_GSS mechanism defined in [RFC5403] in conjunction with the
Channel Binding mechanism [RFC5056] and IPsec Channel Connection
Latching [RFC5660]. Use of such mechanisms is REQUIRED where
integrity and/or privacy is desired, and where efficiency is
required.

Once delivered securely by the RDMA provider, any RDMA-exposed memory
will contain only RPC payloads in the chunk lists, transferred under
the protection of RPCSEC_GSS integrity and privacy. By these means,
the data will be protected end-to-end, as required by the RPC layer
security model.

11. IANA Considerations

Three new assignments are specified by this document:

o A new set of RPC "netids" for resolving RPC-over-RDMA services

o Optional service port assignments for Upper Layer Bindings

o An RPC program number assignment for the configuration protocol

These assignments have been established, as below.

The new RPC transport has been assigned an RPC "netid", which is an
rpcbind [RFC1833] string used to describe the underlying protocol in
order for RPC to select the appropriate transport framing, as well as
the format of the service addresses and ports.

The following "Netid" registry strings are defined for this purpose:

NC_RDMA "rdma"
NC_RDMA6 "rdma6"

These netids MAY be used for any RDMA network satisfying the
requirements of Section 2, and able to identify service endpoints
using IP port addressing, possibly through use of a translation
service as described above in Section 6. The "rdma" netid is to be
used when IPv4 addressing is employed by the underlying transport,
and "rdma6" for IPv6 addressing.

The netid assignment policy and registry are defined in [RFC5665].

As a new RPC transport, this protocol has no effect on RPC Program
numbers or existing registered port numbers. However, new port
numbers MAY be registered for use by RPC-over-RDMA-enabled services,
as appropriate to the new networks over which the services will
operate.

For example, the NFS/RDMA service defined in [RFC5667] has been
assigned the port 20049, in the IANA registry:

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

The RPC program number assignment policy and registry are defined in
[RFC5531].

12. Acknowledgments

The editor gratefully acknowledges the work of Brent Callaghan and
Tom Talpey on the original RPC-over-RDMA Version One specification
[RFC5666].

Dave Noveck provided excellent review, constructive suggestions, and
consistent navigational guidance throughout the process of drafting
this document. Dave also contributed much of the organization and
content of Section 9.

The comments and contributions of Karen Deitke, Dai Ngo, Chunli
Zhang, Dominique Martinet, and Mahesh Siddheshwar are accepted with
many and
great thanks. The editor also wishes to thank Bill Baker for his
unwavering support of this work.

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

13. References

13.1. Normative References

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

[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>.

[RFC2203] Eisler, M., Chiu, A., and L. Ling, "RPCSEC_GSS Protocol
Specification", RFC 2203, DOI 10.17487/RFC2203, September
1997, <http://www.rfc-editor.org/info/rfc2203>.

[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>.

[RFC5042] Pinkerton, J. and E. Deleganes, "Direct Data Placement
Protocol (DDP) / Remote Direct Memory Access Protocol
(RDMAP) Security", RFC 5042, DOI 10.17487/RFC5042, October
2007, <http://www.rfc-editor.org/info/rfc5042>.

[RFC5056] Williams, N., "On the Use of Channel Bindings to Secure
Channels", RFC 5056, DOI 10.17487/RFC5056, November 2007,
<http://www.rfc-editor.org/info/rfc5056>.

[RFC5403] Eisler, M., "RPCSEC_GSS Version 2", RFC 5403, DOI
10.17487/RFC5403, February 2009,
<http://www.rfc-editor.org/info/rfc5403>.

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

[RFC5660] Williams, N., "IPsec Channels: Connection Latching", RFC
5660, DOI 10.17487/RFC5660, October 2009,
<http://www.rfc-editor.org/info/rfc5660>.

[RFC5665] Eisler, M., "IANA Considerations for Remote Procedure Call
(RPC) Network Identifiers and Universal Address Formats",
RFC 5665, DOI 10.17487/RFC5665, January 2010,
<http://www.rfc-editor.org/info/rfc5665>.

13.2. Informative References

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

[IBPORT] InfiniBand Trade Association, "IP Addressing Annex",
<http://www.infinibandta.org>.

[RFC0768] Postel, J., "User Datagram Protocol", STD 6, RFC 768, DOI
10.17487/RFC0768, August 1980,
<http://www.rfc-editor.org/info/rfc768>.

[RFC0793] Postel, J., "Transmission Control Protocol", STD 7, RFC
793, DOI 10.17487/RFC0793, September 1981,
<http://www.rfc-editor.org/info/rfc793>.

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

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

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

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

[RFC5532] Talpey, T. and C. Juszczak, "Network File System (NFS)
Remote Direct Memory Access (RDMA) Problem Statement", RFC
5532, DOI 10.17487/RFC5532, May 2009,
<http://www.rfc-editor.org/info/rfc5532>.

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

[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>.

[RFC5667] Talpey, T. and B. Callaghan, "Network File System (NFS)
Direct Data Placement", RFC 5667, DOI 10.17487/RFC5667,
January 2010, <http://www.rfc-editor.org/info/rfc5667>.

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

Authors' Addresses

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

Phone: +1 734 274 2396
Email: chuck.lever@oracle.com

William Allen Simpson
DayDreamer
1384 Fontaine
Madison Heights, MI 48071
USA

Email: william.allen.simpson@gmail.com

Tom Talpey
Microsoft Corp.
One Microsoft Way
Redmond, WA 98052
USA

Phone: +1 425 704-9945
Email: ttalpey@microsoft.com