wdiff draft-ietf-nfsv4-rfc5667bis-02.txt draft-ietf-nfsv4-rfc5667bis-03.txt

Network File System Version 4 C. Lever, Ed.
Internet-Draft Oracle
Obsoletes: 5667 (if approved) August 25, September 28, 2016
Intended status: Standards Track
Expires: February 26, April 1, 2017

Network File System (NFS) Upper Layer Binding To RPC-Over-RDMA
draft-ietf-nfsv4-rfc5667bis-02
draft-ietf-nfsv4-rfc5667bis-03

Abstract

This document specifies Upper Layer Bindings of Network File System
(NFS) protocol versions to RPC-over-RDMA transports. These bindings
are required to enable RPC-based protocols such as NFS to use direct
data placement on RPC-over-RDMA transports. This document obsoletes
RFC 5667.

Requirements Language

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].

Status of This Memo

This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.

Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
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time. It is inappropriate to use Internet-Drafts as reference
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This Internet-Draft will expire on February 26, April 1, 2017.

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Table of Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Changes Since RFC 5667 . . . . . . . . . . . . . . . . . 3
1.2. Extending This Upper Layer Binding . . . . . . . . . . . 4
1.3. Requirements Language . . . . . . . . . . . . . . . . . . 4
2. Conveying NFS Operations On RPC-Over-RDMA Transports . . . . 4
2.1. Use Of The Read List . . . . . . . . . . . . . . . . . . 4
2.2. Use Of The Write List . . . . . . . . . . . . . . . . . . 4
2.3. Construction Of Individual Chunks . . . . . . . . . . . . 5
2.4. Use Of Long Calls And Replies . . . . . . . . . . . . . . 5 3
3. NFS Versions 2 And 3 Upper Layer Binding . . . . . . . . . . 5 4
4. NFS Version 4 Upper Layer Binding . . . . . . . . . . . . . . 6
4.1. DDP-Eligibility . . . . . . . . . . . . . . . . . . . . . 6
4.2. Reply Size Estimation . . . . . . . . . . . . . . . . . . 7
4.3. NFS Version 4 COMPOUND Considerations . . . . . . . . . . 7
4.4.
5. Extending NFS Version 4 Callback . . . . Upper Layer Bindings . . . . . . . . . . . . . 9
5. 13
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9
6. 13
7. Security Considerations . . . . . . . . . . . . . . . . . . . 10
7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 10 13
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 10
8.1. Normative References . . 14
Appendix A. Changes Since RFC 5667 . . . . . . . . . . . . . . . 15
Appendix B. Acknowledgments . 10
8.2. Informative References . . . . . . . . . . . . . . . . . 11 16
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 12 17

1. Introduction

An RPC-over-RDMA transport, such as defined in
[I-D.ietf-nfsv4-rfc5666bis], may employ direct data placement to
transmit large
convey data payloads associated with RPC transactions. Each
RPC-over-RDMA RPC-
over-RDMA transport header conveys lists of memory locations
corresponding to XDR data items defined in an Upper Layer Protocol
(such as NFS).

To facilitate interoperation, RPC client and server implementations
must agree in advance on what XDR data items in which RPC procedures
are eligible for direct data placement (DDP). This document contains
material required of Upper Layer Bindings, as specified in
[I-D.ietf-nfsv4-rfc5666bis], for the following NFS protocol versions:

o NFS Version 2 [RFC1094]

o NFS Version 3 [RFC1813]

o NFS Version 4.0 [RFC7530]

o NFS Version 4.1 [RFC5661]

o NFS Version 4.2 [I-D.ietf-nfsv4-minorversion2]

1.1. Changes Since RFC 5667

Corrections and updates made necessary by new language in
[I-D.ietf-nfsv4-rfc5666bis] have been introduced. For example,
references to deprecated features of RPC-over-RDMA Version One, such
as RDMA_MSGP, and the use of the Read list for handling RPC replies,
has been removed. The term "mapping" has been replaced with the term
"binding" or "Upper Layer Binding" throughout the document. Material
that duplicates what is in [I-D.ietf-nfsv4-rfc5666bis] has been
deleted.

Material required by [I-D.ietf-nfsv4-rfc5666bis] for Upper Layer
Bindings that was not present in [RFC5667] has been added, including
discussion of how each NFS version properly estimates the maximum
size of RPC replies.

The following changes have been made, relative to [RFC5667]:

o Ambiguous or erroneous uses of RFC2119 terms have been corrected.

o References to specific data movement mechanisms have been made
generic or removed.

o References to obsolete RFCs have been replaced.

o Technical corrections have been made. For example, the mention of
12KB and 36KB inline thresholds have been removed. The reference
to a non-existant NFS version 4 SYMLINK operation has been
replaced with NFS version 4 CREATE(NF4LNK). The discussion of NFS
version 4 COMPOUND handling has been completed.

o An IANA Considerations Section has replaced the "Port Usage
Considerations" Section.

o Code excerpts have been removed, and figures have been modernized.

o Language inconsistent with or contradictory to
[I-D.ietf-nfsv4-rfc5666bis] has been removed from Sections 2 and
3, and both Sections have been combined into Section 2 in the
present document.

o An explicit discussion of NFSv4.0 and NFSv4.1 backchannel
operation will replace the previous treatment of callback
operations. No NFSv4.x callback operation is DDP-eligible.

o The binding for NFSv4.1 has been completed. No DDP-eligible
operations exist in NFSv4.1 that did not exist in NFSv4.0.

o A binding for NFSv4.2 has been added that includes discussion of
new data-bearing operations like READ_PLUS.

1.2. Extending This Upper Layer Binding

As stated earlier, RPC programs such as NFS are required to have an
Upper Layer Binding specification to interoperate on RPC-over-RDMA
transports [I-D.ietf-nfsv4-rfc5666bis]. The Upper Layer Binding
specified in this document can be extended to cover versions of the
NFS version 4 protocol specified after NFS version 4 minor version 2
via standards action. This includes NFSv4 extensions that are
documented separately from a new minor version.

1.3. 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].

2. Conveying NFS Operations On RPC-Over-RDMA Transports

Definitions of terminology and a general discussion of how RPC-over-
RDMA is used to convey RPC transactions can be found in
[I-D.ietf-nfsv4-rfc5666bis]. In this section, these general
principals are applied to the specifics of the NFS protocol.

2.1. Use Of The Read List

The Read list in each RPC-over-RDMA transport header represents a set
of memory regions containing DDP-eligible NFS argument data. Large
data items, such as the data payload of an NFS version 3 WRITE request,
procedure, are referenced by the Read list. The NFS server pulls
such payloads from the client and places these them directly into its own
memory.

XDR unmarshaling code on the NFS server identifies the correspondence
between Read chunks and particular NFS arguments via the chunk
Position value encoded in each Read chunk. segment.

2.2. Use Of The Write List

The Write list in each RPC-over-RDMA transport header represents a
set of memory regions that can receive DDP-eligible NFS result data.
Large data items items, such as the payload of an NFS version 3 READ request
procedure, are referenced by the Write list. The NFS server places these pushes
such payloads to the client, placing them directly into
client the client's
memory.

Each Write chunk corresponds to a specific XDR data item in an NFS
reply. This document specifies how NFS client and server
implementations identify the correspondence between Write chunks and
XDR results.

2.3. Construction Of Individual

2.2.1. Empty Write Chunks

Each Read

Section 4.4.6.2 of [I-D.ietf-nfsv4-rfc5666bis] defines the concept of
unused Write chunks. An unused Write chunk is represented as a list of Write chunk with
either zero segments at or where all segments in the same XDR
Position, and each Write chunk is represented have
zero length. In this document these are referred to as an array "empty" Write
chunks. A "non-empty" Write chunk has at least one segment of
segments. non-
zero length.

An NFS client thus has the flexibility might wish an NFS server to advertise return a set
of discontiguous memory regions DDP-eligible
result inline. If there is only one DDP-eligible result item in which the
reply, the NFS client simply specifies an empty Write list to send or receive a single force
the NFS server to return that result inline. If there are multiple
DDP-eligible results, the NFS client specifies empty Write chunks for
each DDP-eligible data item.

2.4. item that it wishes to be returned inline.

An NFS server might encounter an XDR union result where there are
arms that have a DDP-eligible result, and arms that do not. If the
NFS client has provided a non-empty Write chunk that matches with a
DDP-eligible result, but the response does not contain that result,
the NFS server MUST return an empty Write chunk in that position in
the Write list.

2.3. Use Of Long Calls And Replies

Small RPC messages are conveyed using RDMA Send operations which are
of limited size. If an NFS request is too large to be conveyed via
an RDMA Send,
within the NFS server's responder inline threshold, and there are no
DDP-eligible data items that can be removed, an NFS client must send
the request using a Long Call. The entire NFS request is sent in a
special Read chunk called a Position-
Zero Position-Zero Read chunk.

If a an NFS client predicts that the maximum size of an NFS reply is could
be too large to be conveyed via an RDMA Send, within it's own responder inline
threshold, it provides a Reply chunk in the RPC-over-RDMA transport
header conveying the NFS request. The server can place places the entire NFS
reply in the Reply chunk.

These special chunks are described in more detail in
[I-D.ietf-nfsv4-rfc5666bis].

2.4. Scatter-Gather Considerations

A chunk comprises exactly one XDR data item. Each Read chunk is
represented as a list of segments at the same XDR Position. Each
Write chunk is represented as an array of segments. An NFS client
thus has the flexibility to advertise a set of discontiguous memory
regions in which to send or receive a single DDP-eligible XDR data
item.

3. NFS Versions 2 And 3 Upper Layer Binding

An NFS version 2 or version 3 client MAY send a single Read chunk to
supply the opaque file data for an NFS WRITE procedure, or the
pathname for an NFS SYMLINK procedure. For these procedures, NFS
version 2 or 3 servers MUST ignore Read chunks beyond the first in
the Read list. For all other NFS procedures, NFS version 2 or 3
servers MUST ignore Read chunks that have a non-zero value in their
Position fields, and
Read chunks beyond the first in the Read list. fields.

Similarly, an NFS version 2 or version 3 client MAY provide a single
Write chunk to receive either the opaque file data from an NFS READ
procedure, or the pathname from an NFS READLINK procedure. For these
procedures, NFS version 2 or 3 servers MUST ignore the Write
list for any other NFS procedure, and any Write chunks
beyond the first in the Write list. For all other NFS procedures,
NFS version 2 or 3 servers MUST ignore the Write list.

There are no NFS version 2 or 3 procedures that have DDP-eligible
data items in both their Call and Reply. However, when an NFS
version 2 or version 3 client sends a Long Call or Reply, it MAY
provide a combination of a Read list, a Write list, and/or a Reply
chunk in the same RPC-over-RDMA header.

If an NFS version 2 or version 3 client has not provided enough bytes
in a Read list to match the size of a DDP-eligible NFS argument data
item, or if an NFS version 2 or version 3 client has not provided
enough Write list resources to handle an NFS
WRITE READ or READLINK reply,
or if the client has not provided a large enough Reply chunk to
convey an NFS reply, the server MUST return one of:

o An RPC-over-RDMA message of type RDMA_ERROR, with the rdma_xid
field set to the XID of the matching NFS Call, and the rdma_error
field set to ERR_CHUNK; or

o An RPC message (via an RDMA_MSG message) with the xid field set to
the XID of the matching NFS Call, the mtype field set to REPLY,
the stat field set to MSG_ACCEPTED, and the accept_stat field set
to GARBAGE_ARGS.

These replies do not give any indication to NFS version 2 or version
3 clients of whether an NFS version 2 or 3 server has processed the
arguments of the RPC Call, or whether the NFS version 2 or 3 server
has accessed NFS client memory associated with that RPC.

NFS version 2 or version 3 clients already successfully estimate the
maximum reply size of each operation in order to provide an adequate
set of buffers to receive each NFS reply. An NFS version 2 or
version 3 client provides a Reply chunk when the maximum possible
reply size is larger than the client's responder inline threshold.

3.1. Auxiliary Protocols

NFS versions 2 and 3 are typically deployed with several other
protocols, referred to as "auxiliary" protocols. These are separate
RPC protcols which handle operations that are not part of the main
NFS protocol. These include the MOUNT and NLM protocols, introduced
in an appendix of [RFC1813]; the NSM protocol, described in Chapter
11 of [NSM]; and the NFSACL protocol, which does not have a public
definition. However NFSACL is treated as a de facto standard and
there are several interoperating implementations.

RPC-over-RDMA considers these as individual Upper Layer Protocols
[I-D.ietf-nfsv4-rfc5666bis]. Therefore to operate on an RPC-over-
RDMA transport, an Upper Layer Binding must be provided for each of
these.

Typically MOUNT, NLM, and NSM are conveyed via TCP rather than RPC-
over-RDMA. Note that only metadata is conveyed in these protocols,
thus direct data placement is never necessary, and the size of RPC
messages is uniformly small. The maximum size of replies is easily
determined by examining the XDR definitions of these protocols.

Implementations that support the NFSACL protocol typically send
NFSACL procedures on the same connection as the main NFS protocol.
Thus NFSACL does require an Upper Layer Binding.

No data item in this protocol is DDP-eligible. There is no protocol
size limit for NFS version 3 ACL objects. The client can have some
difficulty ascertaining the size of ACLs to be read from servers.
Practically speaking, ACLs are not large (less than 4KB in most
cases), but a large Reply chunk may be provided when the client is in
doubt. The usual rules apply to the use of Long Messages when the
size of an NFSACL RPC exceeds a connection's inline thresholds.

4. NFS Version 4 Upper Layer Binding

This specification applies to NFS Version 4.0 [RFC7530], NFS Version
4.1 [RFC5661], and NFS Version 4.2 [I-D.ietf-nfsv4-minorversion2].
It also applies to the callback protocols associated with each of
these minor versions. versions defined in the same documents.

4.1. DDP-Eligibility

For each WRITE operation in an NFS version 4 COMPOUND procedure, an
NFS version 4 client MAY send provide a single Read chunk to supply the
opaque file data for a
WRITE operation or the pathname for a argument. For each CREATE(NF4LNK) operation in an
NFS version 4 COMPOUND procedure. procedure, An NFS version 4 client MUST NOT send MAY provide
a single Read chunk that corresponds with any other XDR data item in any other NFS
version 4 to supply the pathname argument.

Similarly, for each READ operation in an NFS version 4 COMPOUND
procedure, or in an NFS version 4 NULL procedure.

Similarly, an NFS client MAY provide a single Write chunk
to receive either the opaque file data from a READ operation, NFS4_CONTENT_DATA from a argument. For each READ_PLUS operation, or the pathname from
operation in an NFS version 4 COMPOUND procedure, an NFS version 4
client MAY provide a single Write chunk to receive NFS4_CONTENT_DATA.
For each READLINK operation in an NFS version 4 COMPOUND procedure. procedure,
an NFS version 4 client MAY provide a single Write chunk to receive
the pathname argument.

An NFS version 4 client MUST NOT provide a Read or Write chunk that
corresponds with any other XDR data item in any other NFS version 4
operation in an NFS version 4 COMPOUND procedure, or in an NFS
version 4 NULL procedure.

There is no prohibition against an NFS version 4 COMPOUND procedure
constructed with both a READ and WRITE operation, say. Thus it

It is possible for NFS version 4 COMPOUND procedures to use both the
Read list and Write list simultaneously. An NFS version 4 client MAY
provide a Read list and a Write list in the same transaction if it is
sending a Long Call or Reply.

If an NFS version 4 client has not provided enough bytes in a Read
list to match the size of a DDP-eligible NFS argument data item, or
if an NFS version 4 client has not provided enough Write list
resources to handle a WRITE or READLINK operation, or if the client
has not provided a large enough Reply chunk to convey an NFS reply,
the server MUST return one of:

o An RPC-over-RDMA message of type RDMA_ERROR, with the rdma_xid
field set to the XID of the matching NFS Call, and the rdma_error
field set to ERR_CHUNK; or

o An RPC message (via an RDMA_MSG message) with the mtype xid field set to REPLY,
the XID of the matching NFS Call, the stat field set to
MSG_ACCEPTED, and the accept_stat field set to GARBAGE_ARGS.

Such error replies are permanent errors, and constitute both
completion of the RPC transaction, and a valid server response. It
is not necessary for an NFS version 4 server to drop the transport
connection in this case.

4.1.1. Session-Related Considerations

In most cases, the presence of an NFS session [RFC5661] has no effect
on the operation of RPC-over-RDMA. None of the operations introduced
to support NFS sessions contain DDP-eligible data items. There is no
need to match the number of session slots with the number of
available RPC-over-RDMA credits.

However, there are some rare error conditions which require special
handling when an NFS session is operating on an RPC-over-RDMA
transport. For example, a requester might receive, in response to an
RPC request, an RDMA_ERROR message with an rdma_err value of
ERR_CHUNK, or an RDMA_MSG containing an RPC_GARBAGEARGS reply.
Within RPC-over-RDMA Version One, this class of error can be
generated for two different reasons:

o There was an XDR error detected parsing the RPC-over-RDMA headers.

o There was an error sending the response, because, for example, a
necessary reply chunk was not provided or the one provided is of
insufficient length.

These two situations, which arise only due to incorrect
implementations, have different implications with regard to Exactly-
Once Semantics. An XDR error in decoding the request precludes the
execution of the request on the responder, but failure to send a
reply indicates that some or all of the operations were executed.

In both instances, the client SHOULD NOT retry the operation. A
retry is liable to result in the same sort of error seen previously.
Instead, it is best to consider the operation as completed
unsuccessfully and report an error to the consumer who requested the
RPC.

In addition, within the error response, the requester does not have
the result of the execution of the SEQUENCE operation, which
identifies the session, slot, and sequence id for the request which
has failed. The xid associated with the request, obtained from the
rdma_xid field of the RDMA_ERROR or RDMA_MSG message, must be used to
determine the session and slot for the request which failed, and the
slot must be properly retired. If this is not done, the slot could
be rendered permanently unavailable.

4.2. Reply Size Estimation

An NFS version 4 client provides a Reply chunk when the maximum
possible reply size is larger than the client's responder inline
threshold. NFS version 4 clients already successfully estimate the
maximum reply size of most operations in order to provide an adequate
set of buffers to receive each NFS reply.

There are certain NFSv4 NFS version 4 data items whose size cannot be reliably
estimated by clients, clients reliably, however, because there is no protocol-specified protocol-
specified size limit on these structures. These include but are not
limited to opaque types types, such as the as:

o The attrlist4 field; fields field

o Fields containing ACLs such as fattr4_acl, fattr4_dacl, fattr4_sacl; fields
fattr4_sacl

o Fields in the fs_locations4 and fs_locations_info4 data structures; and opaque structures
o Opaque fields which pertain to pNFS layout metadata, such as
loc_body, loh_body, da_addr_body, lou_body, lrf_body,
fattr_layout_types and fs_layout_types, which pertain

In NFS version 4.1 and later minor versions, the csa_fore_chan_attrs
argument of the CREATE_SESSION operation contains a
ca_maxresponsesize field. The value in this field can be taken as
the absolute maximum size of replies generated by a replying NFS
version 4 server. This value can be used in cases where it is not
possible to pNFS estimate a reply size upper bound precisely. In
practice, objects such as ACLs, named attributes, layout metadata. bodies, and
security labels are much smaller than this maximum.

With regard to NFS version 4.0, things are more troublesome.
Typically NFS version 4.0 client implementations rely on their own
architectural limits to keep reply buffer sizes reasonable. For
instance, although the NFS version 4 protocol is capable of conveying
a megabyte-sized ACL, nearly all known physical filesystems store
ACLs in on-disk containers which are small in size.

4.2.1. Managing READ_PLUS Replies

The NFS version 4.2 READ_PLUS operation returns a complex data type
[I-D.ietf-nfsv4-minorversion2]. The rpr_contents field in the result
of this operation is an array of read_plus_content unions, one arm of
which contains an opaque byte stream (d_data).

The size of d_data is limited to the value of the rpa_count field,
but the protocol does not bound the number of elements which can be
returned in the rpr_contents array. In order to make the size of
READ_PLUS replies predictable by NFS version 4.2 clients, the
following restrictions are placed on the use of the READ_PLUS
operation on RPC-over-RDMA transports:

o An NFS version 4.2 client MUST NOT provide more than one Write
chunk for any READ_PLUS operation. When providing a Write chunk
for a READ_PLUS operation, an NFS version 4.2 client MUST provide
a Write chunk that is either empty (which forces all result data
items for this operation to be returned inline) or large enough to
receive rpa_count bytes in a single element of the rpr_contents
array.

o If the Write chunk provided for a READ_PLUS operation by an NFS
version 4.2 client is not empty, an NFS version 4.2 server MUST
use that chunk for the first element of the rpr_contents array
that has an rpc_data arm.

o An NFS version 4.2 server MUST NOT return more than two elements
in the rpr_contents array of any READ_PLUS operation. It returns
as much of the requested byte range as it can fit within these two
elements. If the NFS version 4.2 server has not asserted rpr_eof
in the reply, the NFS version 4.2 client SHOULD send additional
READ_PLUS requests for any remaining bytes.

4.3. NFS Version 4 COMPOUND Considerations

An Requests

A single NFS version 4 COMPOUND procedure supplies arguments for a
sequence of operations, and returns results from that sequence. A sequence, all
in a single round-trip [RFC7530]. An NFS version 4 client MAY
construct an NFS version 4 COMPOUND procedure that uses provides more than
one chunk in either the Read list or Write list. The list as long as it observes the
restrictions in Section 4.1.

An NFS version 4 client provides XDR Position values in each Read
chunk to disambiguate which chunk is associated with which XDR argument
data item. However NFS version 4 server and client implementations
must agree in advance on how to pair Write chunks with returned
result data items.

The mechanism specified in Section 5.3.2 of
[I-D.ietf-nfsv4-rfc5666bis]) is applied here: here, with some additional
restrictions. In the following list, an "NFS Read" operation refers
to any NFS Version 4 operation which has a DDP-eligible result data
item (i.e., either a READ, READ_PLUS, or READLINK operation).

o If an NFS version 4 client wishes all DDP-eligible items in an NFS
reply to be conveyed inline, it leaves the Write list empty.

o The first chunk in the Write list MUST be used by the first READ
or READLINK NFS
Read operation in an NFS version 4 COMPOUND procedure. The next
Write chunk is used by the next READ or READLINK, NFS Read operation, and so on.

o If there are more READ or READLINK operations than Write chunks,
then any remaining operations MUST return their results inline.

o If an NFS version 4 client presents has provided a matching non-empty Write
chunk, then the corresponding
READ or READLINK NFS Read operation MUST return its
DDP-eligible data by placing data
into item using that chunk.

o If the Write chunk an NFS version 4 client has zero RDMA segments, or if the total size of
the segments is zero, provided an empty matching Write
chunk, then the corresponding READ or READLINK NFS Read operation MUST return all
of its result data items inline.

o If an NFS Read operation returns a union arm which does not
contain a DDP-eligible result, and the NFS version 4 client has
provided a matching non-empty Write chunk, an NFS version 4 server
MUST return an empty Write chunk in that Write list position.

o If there are more NFS Read operations than Write chunks, then
remaining NFS Read operations in an NFS version 4 COMPOUND that
have no matching Write chunk MUST return their results inline.

4.3.1. NFS Version 4 COMPOUND Example

The following example shows a Write list with three Write chunks, A,
B, and C. The NFS version 4 server consumes the provided Write
chunks by writing the results of the designated operations in the
compound request,
READ request (READ and READLINK, READLINK) back to each chunk.

Write list:

A --> B --> C

NFS version 4 COMPOUND request:

PUTFH LOOKUP READ PUTFH LOOKUP READLINK PUTFH LOOKUP READ
| | |
v v v
A B C

If the NFS version 4 client does not want to have the READLINK result
returned
directly, via RDMA, it provides a zero-length array of segment triplets for
buffer B or sets the values in the segment triplet an empty Write chunk for buffer B to
zeros to
indicate that the READLINK result must be returned inline.

Unlike NFS versions 2 and 3, the maximum size of an NFS version 4
COMPOUND is not bounded. However, typical NFS version 4 clients
rarely issue such problematic requests. In practice, NFS version 4
clients behave in much more predictable ways. Rsize and wsize apply
to COMPOUND operations by capping the total amount of data payload
allowed in each COMPOUND. An extension to NFS version 4 supporting a
comprehensive exchange of upper-layer message size parameters is part
of [RFC5661].

4.4. NFS Version 4 Callback

The NFS version 4 protocols support server-initiated callbacks to
notify clients of events such as recalled delegations. There are

4.4.1. NFS Version 4.0 Callback

NFS version 4.0 implementations typically employ a separate TCP
connection to handle callback operations, even when the forward
channel uses a RPC-over-RDMA transport. Therefore no
DDP-eligible data items in Upper Layer
Binding for the NFS version 4.0 callback protocols associated with
NFSv4.0, NFSv4.1, or NFSv4.2. program is provided in this
document.

4.4.2. NFS Version 4.1 Callback

In NFS version 4.1 and 4.2, later minor versions, callback operations may
appear on the same connection as one is used for NFS version 4 forward
channel client requests. NFS version 4 clients and servers MUST use
the mechanism described in [I-D.ietf-nfsv4-rpcrdma-bidirection] when
backchannel operations are conveyed on RPC-over-RDMA transports.

The csa_back_chan_attrs argument of the CREATE_SESSION operation
contains a ca_maxresponsesize field. The value in this field can be
taken as the absolute maximum size of backchannel replies generated
by a replying NFS version 4 client.

There are no DDP-eligible data items in callback protocols associated
with NFS version 4.1 or NFS version 4.2. However, some callback
requests, such as messages that convey device ID information, may be
large, in which case a Long Call or Reply may be appropriate. When
the NFS version 4 client reports a backchannel ca_maxresponsesize
that is larger than the connection's inline thresholds, the NFS
version 4 client can support Long messages (i.e., Read chunks and
Reply chunks). Otherwise an NFS version 4 server MUST use Short
messages to convey backchannel operations.

See Section 4.1 for a discussion of how an NFS version 4 server
handles situations where an NFS version 4 client has provided
inadequate RDMA resources to convey a backchannel reply.

4.5. Connection Keep-Alive

NFS version 4 client implementations often rely on a transport-layer
keep-alive mechanism to detect when an NFS version 4 server has
become unresponsive. When an NFS server is no longer responsive,
client-side keep-alive terminates the connection, which in turn
triggers reconnection and RPC retransmission.

RDMA transports have no keep-alive mechanism. Without a disconnect
or new RPC traffic, RDMA transport connections can remain alive long
after an NFS server has become unresponsive. Once an NFS client has
consumed all available RPC-over-RDMA credits on that transport
connection, it will forever await a reply before sending another RPC
request.

NFS version 4 clients SHOULD reserve one RPC-over-RDMA credit to use
for periodic server or connection health assessment. This credit can
be used to drive an RPC request on an otherwise idle connection,
triggering either a quick affirmative server response or immediate
connection termination.

To prevent lease expiry, NFS version 4 clients should use a lease-
extending operation such as RENEW or SEQUENCE, rather than a NULL
request, when performing a periodic health assessment.

5. Extending NFS Upper Layer Bindings

RPC programs such as NFS are required to have an Upper Layer Binding
specification to interoperate on RPC-over-RDMA transports
[I-D.ietf-nfsv4-rfc5666bis]. Via standards action, the Upper Layer
Binding specified in this document can be extended to cover versions
of the NFS version 4 protocol specified after NFS version 4 minor
version 2. This includes NFS version 4 extensions that are
documented separately from a new minor version.

6. IANA Considerations

NFS use of direct data placement introduces a need for an additional
NFS port number assignment for networks that share traditional UDP
and TCP port spaces with RDMA services. The iWARP [RFC5041]
[RFC5040] protocol is such an example (InfiniBand is not).

NFS servers for versions 2 and 3 [RFC1094] [RFC1813] traditionally
listen for clients on UDP and TCP port 2049, and additionally, they
register these with the portmapper and/or rpcbind [RFC1833] service.
However, [RFC7530] requires NFS servers for version 4 servers to listen on TCP
port 2049, and they are not required to register.

An NFS version 2 or version 3 server supporting RPC-over-RDMA on such
a network and registering itself with the RPC portmapper MAY choose
an arbitrary port, or MAY use the alternative well-known port number
for its RPC-over-RDMA service. The chosen port MAY be registered
with the RPC portmapper under the netid assigned by the requirement
in [I-D.ietf-nfsv4-rfc5666bis].

An NFS version 4 server supporting RPC-over-RDMA on such a network
MUST use the alternative well-known port number for its RPC-over-RDMA
service. Clients SHOULD connect to this well-known port without
consulting the RPC portmapper (as for NFSv4/TCP). NFS version 4 on TCP
transports).

The port number assigned to an NFS service over an RPC-over-RDMA
transport is available from the IANA port registry [RFC3232].

7. Security Considerations

The RDMA transport for RPC [I-D.ietf-nfsv4-rfc5666bis]

RPC-over-RDMA supports all RPC [RFC5531] security models, including RPCSEC_GSS [RFC2203]
security and transport-level security. security [RFC2203]. The choice of RDMA
Read and RDMA Write to convey RPC argument and results does not
affect this, since it only changes only the method of data transfer.
Specifically, the requirements of [I-D.ietf-nfsv4-rfc5666bis] ensure
that this choice does not introduce new vulnerabilities.

Because this document defines only the binding of the NFS protocols
atop [I-D.ietf-nfsv4-rfc5666bis], all relevant security
considerations are therefore to be described at that layer.

7. Acknowledgments

The author gratefully acknowledges the work of Brent Callaghan and
Tom Talpey on the original NFS Direct Data Placement specification
[RFC5667]. The author also wishes to thank Bill Baker and Greg
Marsden for their support of this work.

Dave Noveck provided excellent review, constructive suggestions, and
consistent navigational guidance throughout the process of drafting
this document.

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

8. References

8.1. Normative References

[I-D.ietf-nfsv4-minorversion2]
Haynes, T., "NFS Version 4 Minor Version 2", draft-ietf-
nfsv4-minorversion2-41 (work in progress), January 2016.

[I-D.ietf-nfsv4-rfc5666bis]
Lever, C., Simpson, W., and T. Talpey, "Remote Direct
Memory Access Transport for Remote Procedure Call, Version
One", draft-ietf-nfsv4-rfc5666bis-07 (work in progress),
May 2016.

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

[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>.

[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>.

[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>.

[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>.

8.2. Informative References

[NSM] The Open Group, "Protocols for Interworking: XNFS, Version
3W", February 1998.

[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>.

[RFC3232] Reynolds, J., Ed., "Assigned Numbers: RFC 1700 is Replaced
by an On-line Database", RFC 3232, DOI 10.17487/RFC3232,
January 2002, <http://www.rfc-editor.org/info/rfc3232>.

[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>.

[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>.

Appendix A. Changes Since RFC 5667

Corrections and updates made necessary by new language in
[I-D.ietf-nfsv4-rfc5666bis] have been introduced. For example,
references to deprecated features of RPC-over-RDMA Version One, such
as RDMA_MSGP, and the use of the Read list for handling RPC replies,
have been removed. The term "mapping" has been replaced with the
term "binding" or "Upper Layer Binding" throughout the document.
Some material that duplicates what is in [I-D.ietf-nfsv4-rfc5666bis]
has been deleted.

Technical corrections have been made. For example, the mention of
12KB and 36KB inline thresholds have been removed. The reference to
a non-existant NFS version 4 SYMLINK operation has been replaced with
NFS version 4 CREATE(NF4LNK).

The discussion of NFS version 4 COMPOUND handling has been completed.
Some changes were made to the algorithm for matching DDP-eligible
results to Write chunks.

The following additional improvements have been made, relative to
[RFC5667]:

o An explicit discussion of NFS version 4.0 and NFS version 4.1
backchannel operation has replaced the previous treatment of
callback operations.

o A binding for NFS version 4.2 has been added that includes
discussion of new data-bearing operations like READ_PLUS.

o A section suggesting a mechanism for periodically assessing
connection health has been introduced.

o Language inconsistent with or contradictory to
[I-D.ietf-nfsv4-rfc5666bis] has been removed from Sections 2 and
3, and both Sections have been combined into Section 2 in the
present document.

o Ambiguous or erroneous uses of RFC2119 terms have been corrected.

o References to obsolete RFCs have been updated.

o An IANA Considerations Section has replaced the "Port Usage
Considerations" Section.

o Code excerpts have been removed, and figures have been modernized.

Appendix B. Acknowledgments

Dave Noveck provided excellent review, constructive suggestions, and
consistent navigational guidance throughout the process of drafting
this document. Dave also contributed the text of Section 4.1.1.

Thanks to Karen Deitke for her sharp observations about idempotency,
and the clarity of the discussion of NFS COMPOUNDs.

Special thanks go to Transport Area Director Spencer Dawkins, nfsv4
Working Group Chair Spencer Shepler, and nfsv4 Working Group
Secretary Thomas Haynes for their support.

Author's Address

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

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