wdiff draft-ietf-nfsv4-rfc5667bis-03.txt draft-ietf-nfsv4-rfc5667bis-04.txt

Network File System Version 4 C. Lever, Ed.
Internet-Draft Oracle
Obsoletes: 5667 (if approved) September 28, 2016 January 20, 2017
Intended status: Standards Track
Expires: April 1, July 24, 2017

Network File System (NFS) Upper Layer Binding To RPC-Over-RDMA
draft-ietf-nfsv4-rfc5667bis-03
draft-ietf-nfsv4-rfc5667bis-04

Abstract

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

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Conveying NFS Operations On RPC-Over-RDMA Transports . . . . . . . . . . 3
3. Upper Layer Binding For NFS Versions 2 And 3 Upper Layer Binding . . . . . . . . . . 4 5
4. NFS Version 4 Upper Layer Binding For NFS Version 4 . . . . . . . . . . . . . . 6 7
5. Extending NFS Upper Layer Bindings . . . . . . . . . . . . . 13
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 13 14
7. Security Considerations . . . . . . . . . . . . . . . . . . . 13 14
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 14 15
Appendix A. Changes Since RFC 5667 . . . . . . . . . . . . . . . 15 16
Appendix B. Acknowledgments . . . . . . . . . . . . . . . . . . 16 17
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 17 18

1. Introduction

An RPC-over-RDMA transport, such as the one defined in
[I-D.ietf-nfsv4-rfc5666bis], may employ direct data placement to
convey data payloads associated with RPC transactions. Each 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 enable
successful interoperation, RPC client and server implementations must
agree in advance on what as to which XDR data items in which what particular 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] [RFC7862]

Upper Layer Bindings specified in this document apply to all versions
of RPC-over-RDMA.

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
principles are applied to in the specifics context of the conveying NFS protocol. procedures on
RPC-over-RDMA. Some issues common to all NFS protocol versions are
introduced.

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
procedure, are can be referenced by the Read list. The NFS server pulls
such payloads from the client and places them directly into its own
memory.

Exactly which XDR unmarshaling code on the NFS server identifies the correspondence
between Read chunks and particular NFS arguments via the chunk
Position value encoded data items may be conveyed in each Read segment. this fashion is
detailed later in this document.

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, such as the payload of an NFS version 3 READ
procedure, are can be referenced by the Write list. The NFS server
pushes such payloads to the client, placing them directly into 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.

2.2.1. Empty Write Chunks

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

An NFS client might wish an NFS server to return a DDP-eligible
result inline. If there is only one DDP-eligible result item in the
reply, the NFS client simply specifies an empty Write list to 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

Exactly which XDR data item that it wishes to items may 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 conveyed in that position this fashion is
detailed later in
the Write list. this document.

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
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 in the form of a Long Call. The entire NFS request is
sent in a special Read chunk called a Position-Zero Position Zero Read chunk.

If an NFS client predicts determines that the maximum size of an NFS reply
could be too large to be conveyed 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 places the entire NFS
reply in the Reply chunk.

When the RPC authentication flavor requires that DDP-eligible data
items are never removed from RPC messages, an NFS client can provide
both a Position Zero Read chunk and a Reply chunk for the same RPC.

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

2.4. Scatter-Gather Considerations

A chunk comprises typically corresponds to 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 convey 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.

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 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 READ or READLINK reply,
or if the client has not provided

2.5. DDP Eligibility Violations

To report a large enough Reply chunk to
convey DDP-eligibity violation, 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

Subsequent sections of this document describe further considerations
particular to specific NFS protocols or procedures.

2.6. Reply Size Estimation

During the construction of each RPC Call message, an NFS client is
responsible for allocating appropriate resources for receiving the
matching Reply message. A Reply buffer overrun can result in
corruption of the Reply message or termination of the transport
connection. Therefore reliable reply size estimation is necessary to
ensure successful interoperation.

In many cases the Upper Layer Protocol's XDR definition provides
enough information to enable the client to make a reliable prediction
of the maximum size of the expected Reply message. If there are
variable-size data items in the result, the maximum size of the RPC
Reply message can be reliably estimated in most cases:

o The client requests only a specific portion of an object (for
example, using the "count" and "offset" fields in an NFS READ).

o The client has already cached the size of the whole object it is
about to request (say, via a previous NFS GETATTR request).

It is occasionally not give any indication possible to determine the maximum Reply
message size based solely on the above criteria. NFS client
implementers can choose to provide the largest possible Reply buffer
in those cases, based on, for instance, the largest possible NFS READ
or WRITE payload (which is negotiated at mount time).

In rare cases, a client may encounter a reply for which no a priori
determination of reply size bound is possible. The client SHOULD
expect a transport error to indicate that it must either terminate
that RPC transaction, or retry it with a larger Reply chunk.

The use of NFS COMPOUND operations raises the possibility of non-
idempotent requests that combine a non-idempotent operation with an
operation whose reply size is uncertain. This causes potential
difficulties with retrying the transaction. Note however that many
operations normally considered non-idempotent (e.g WRITE, SETATTR)
are actually idempotent. Truly non-idempotent operations are quite
unusual in COMPOUNDs that include operations with uncertain reply
sizes.

3. Upper Layer Binding For NFS Versions 2 And 3

This Upper Layer Binding specification applies to NFS Version 2
[RFC1094] and NFS Version 3 [RFC1813]. For brevity, in this section
a "legacy NFS client" refers to an NFS client using NFS version 2 or
NFS version 3 clients of whether to communicate with an NFS server. Likewise, a "legacy
NFS server" is an NFS server communicating with clients using NFS
version 2 or NFS version 3.

The following XDR data items in NFS versions 2 and 3 are DDP-
eligible:

o The opaque file data argument in the NFS WRITE procedure

o The pathname argument in the NFS SYMLINK procedure

o The opaque file data result in the NFS READ procedure

o The pathname result in the NFS READLINK procedure

All other argument or result data items in NFS versions 2 and 3 are
not DDP-eligible.

A legacy server's response to a DDP-eligibility violation (described
in Section 2.5) does not give an indication to legacy clients of
whether the server has processed the arguments of the RPC Call, or
whether the NFS version 2 or 3 server has accessed NFS or modified client memory associated
with that RPC.

A legacy NFS version 2 or version 3 clients already successfully estimate client determines the maximum reply size of for each
operation using the basic criteria outlined in order to Section 2.6. Such
clients 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 size,
exclusive of any data items represented by Write chunks, 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, sometimes referred to as "auxiliary" protocols. "NFS auxiliary protocols." These
are separate RPC protcols which handle operations programs that define procedures which are not part
of the main NFS protocol. version 2 or version 3 RPC programs. These include the include:

o The MOUNT and NLM protocols, introduced in an appendix of [RFC1813]; the
[RFC1813]

o The NSM protocol, described in Chapter 11 of [NSM]; and the [NSM]

o The NFSACL protocol, which does not have a public
definition. However NFSACL definition
(NFSACL here is treated as a de facto standard and as there are
several interoperating implementations. implementations).

RPC-over-RDMA considers these programs as individual distinct Upper Layer
Protocols [I-D.ietf-nfsv4-rfc5666bis]. Therefore to operate To enable the use of these
ULPs on an RPC-over-
RDMA RPC-over-RDMA transport, an Upper Layer Binding must be
specification is provided here for each of
these. each.

3.1.1. MOUNT, NLM, And NSM Protocols

Typically MOUNT, NLM, and NSM are conveyed via TCP rather than RPC-
over-RDMA. Note that only metadata is conveyed TCP, even in
deployments where NFS operations on RPC-over-RDMA. When a legacy
server supports these protocols,
thus direct programs on RPC-over-RDMA, it advertises the
port address via the usual rpcbind service [RFC1833].

No operation in these protocols conveys a significant data placement is never necessary, payload,
and the size of RPC messages in these protocols is uniformly small.
Therefore, no XDR data items in these protocols are DDP-eligible.
The maximum size of replies largest variable-length XDR data item is easily
determined by examining an xdr_netobj. In most
implementations this data item is not larger than 1024 bytes, making
reliable reply size estimation straightforward using the XDR definitions of these protocols.

Implementations criteria
outlined in Section 2.6.

3.1.2. NFSACL Protocol

Legacy clients and servers that support the NFSACL protocol RPC program
typically send convey NFSACL procedures on the same connection as the main NFS protocol.
RPC program. This obviates the need for separate rpcbind queries to
discover server support for this RPC program.

ACLs are typically small, but even large ACLs must be encoded and
decoded to some degree. Thus NFSACL does require an Upper Layer Binding.

No no data item in this protocol Upper Layer
Protocol is DDP-eligible.

For procedures whose replies do not include an ACL object, the size
of a reply is determined directly from the NFSACL program's XDR
definition.

There is no protocol protocol-wide size limit for NFS version 3 ACL objects. The ACLs, and
there is no mechanism in either the NFSACL or NFS programs for a
legacy client can have some
difficulty ascertaining to ascertain the largest ACL a legacy server can store.
Legacy client implementations should choose a maximum size of ACLs to be read from servers.
Practically speaking, for ACLs are not large (less than 4KB in most
cases), but
based on their own internal limits. A recommended lower bound for
this maximum is 32,768 bytes, though a large larger Reply chunk may be provided when the client is in
doubt. The usual rules apply (up to the use of Long Messages when the
size of an NFSACL RPC exceeds a connection's inline thresholds.
negotiated rsize setting) can be provided.

4. Upper Layer Binding For NFS Version 4

This Upper Layer Binding

This specification applies to all protocols
defined in 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 defined in the same documents. [RFC7862].

4.1. DDP-Eligibility

For each WRITE operation in an NFS version 4 COMPOUND procedure, an
NFS version 4 client MAY provide a single Read chunk to supply the
opaque file data argument. For each CREATE(NF4LNK) operation in an
NFS version 4 COMPOUND procedure, An NFS version 4 client MAY provide
a single Read chunk to supply the pathname argument.

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

Only the pathname argument.

An NFS version 4 client MUST NOT provide a Read or Write chunk that
corresponds with any other following 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.

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 items in a Read
list to match the size COMPOUND procedure of a DDP-eligible NFS argument data item, or
if an all
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: minor versions are DDP-eligible:

o An RPC-over-RDMA message of type RDMA_ERROR, with the rdma_xid The opaque data field set to the XID of the matching NFS Call, and in the rdma_error
field set to ERR_CHUNK; or WRITE4args structure

o An RPC message (via an RDMA_MSG message) with the xid field set to
the XID of the matching NFS Call, the stat field set to
MSG_ACCEPTED, and the accept_stat The linkdata 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, NF4LNK arm 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. createtype4 union

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 opaque data 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 NFS version 4 data items whose size cannot be
estimated by clients reliably, however, because there is no protocol-
specified size limit on these structures. These include but are not
limited to opaque types, such as: the READ4resok structure

o The attrlist4 linkdata field

o Fields containing ACLs such as fattr4_acl, fattr4_dacl,
fattr4_sacl

o Fields in the fs_locations4 and fs_locations_info4 data structures READLINK4resok structure

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, In NFS minor version 4.1 2 and later minor versions, newer, the csa_fore_chan_attrs
argument of the CREATE_SESSION operation contains a
ca_maxresponsesize field. The value in this rpc_data 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 estimate a reply size upper bound precisely. In
practice, objects such as ACLs, named attributes, layout 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 the
read_plus_content union (further restrictions on their own
architectural limits to keep reply buffer sizes reasonable. For
instance, although the NFS version 4 protocol is capable use 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 this
data item follow below).

4.1.1. READ_PLUS Replies

The NFS version 4.2 READ_PLUS operation returns a complex data type
[I-D.ietf-nfsv4-minorversion2].
[RFC7862]. 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.

4.2. NFS Version 4 COMPOUND Requests

A single Reply Size Estimation

An NFS version 4 COMPOUND procedure supplies arguments for client provides a
sequence of operations, Reply chunk when the maximum
possible reply size is larger than the client's responder inline
threshold.

There are certain NFS version 4 data items whose size cannot be
estimated by clients reliably, however, because there is no protocol-
specified size limit on these structures. These include:

o The attrlist4 field

o Fields containing ACLs such as fattr4_acl, fattr4_dacl,
fattr4_sacl

o Fields in the fs_locations4 and returns results from fs_locations_info4 data 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,

4.2.1. Reply Size Estimation For Minor Version 0

The items enumerated above in Section 4.2 make it difficult to
predict the maximum size of GETATTR replies that sequence, all interrogate
variable-length attributes. As discussed in Section 2.6, client
implementations can rely on their own internal architectural limits
to bound the reply size, but such limits are not guaranteed to be
reliable.

If a client implementation is equipped to recognize that a transport
error could mean that it provisioned an inadequately sized Reply
chunk, it can retry the operation with a larger Reply chunk.
Otherwise, the client must terminate the RPC transaction.

It is best to avoid issuing single round-trip [RFC7530]. An COMPOUNDs that contain both non-
idempotent operations and operations where the maximum reply size
cannot be reliably predicted.

4.2.2. Reply Size Estimation For Minor Version 1 And Newer

In NFS version 4.1 and newer 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 client MAY
construct an server.

This value can be used in cases where it is not possible to estimate
a reply size upper bound precisely. In practice, objects such as
ACLs, named attributes, layout bodies, and security labels are much
smaller than this maximum.

4.3. NFS Version 4 COMPOUND Requests

The NFS version 4 COMPOUND procedure that provides allows the transmission of more
than one chunk in the Read list or Write list as long as it observes the
restrictions in Section 4.1. DDP-eligible data item per Call and Reply message. An NFS
version 4 client provides XDR Position values in each Read chunk to
disambiguate which chunk is associated with which 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 4.3.2 of
[I-D.ietf-nfsv4-rfc5666bis]) is applied here, with some additional
restrictions.
restrictions that appear below. In the following list, an "NFS Read"
operation refers to any NFS Version 4 operation which has a DDP-eligible 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 NFS
Read READ
operation in an NFS version 4 COMPOUND procedure. The next Write
chunk is used by the next NFS Read READ operation, and so on.

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

o If an NFS version 4 client has provided an empty matching Write
chunk, then the corresponding NFS Read READ operation MUST return all of
its result data items inline.

o If an NFS Read 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 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 and 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 via RDMA, it provides an empty Write chunk for buffer B to
indicate that the READLINK result must be returned inline.

4.4. NFS Version 4 Callback

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

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 Upper Layer
Binding for

No operation in the NFS version 4.0 callback RPC program conveys a
significant data payload. Therefore, no XDR data items in this RPC
program is provided DDP-eligible.

A CB_RECALL reply is small and fixed in size. The CB_GETATTR reply
contains a variable-length fattr4 data item. See Section 4.2.1 for a
discussion of reply size prediction for this
document. data item.

An NFS version 4.0 client advertises netids and ad hoc port addresses
for contacting its NFS version 4.0 callback service using the
SETCLIENTID operation.

4.4.2. NFS Version 4.1 Callback

In NFS version 4.1 and later newer minor versions, callback operations may
appear on the same connection as 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 procedures defined
in NFS version 4.1 or NFS version 4.2. However, some callback
requests,
operations, such as messages that convey device ID information, may can
be large, in which case a Long Call or Reply may might be appropriate. required.

When
the an NFS version 4 4.1 client reports a backchannel ca_maxresponsesize
ca_maxrequestsize 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). Calls.
Otherwise an NFS version 4 server MUST use Short messages to convey
backchannel operations.

See Section 4.1 for a discussion

4.5. Session-Related Considerations

Typically the presence of how an NFS version 4 server
handles situations where 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 version 4 client has 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
inadequate RDMA resources or the one provided is of
insufficient length.

These two situations, which arise due to convey incorrect implementations or
underestimation of reply size, 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 backchannel reply.

4.5. reply indicates that some or all of the operations
were executed.

In both instances, the client SHOULD NOT retry the operation without
addressing reply resource inadequacy. Such a retry can 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.

4.6. 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.

Some RDMA transports (such as Reliable Connections on InfiniBand)
have no keep-alive mechanism. Without a disconnect or new RPC
traffic, RDMA transport such 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 2, or separately published extensions to an existing NFS
version 4 extensions that are
documented separately from a new minor version. version, as described in [I-D.ietf-nfsv4-versioning].

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 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 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

RPC-over-RDMA supports all RPC security models, including RPCSEC_GSS
security and transport-level security [RFC2203]. The choice of RDMA
Read and RDMA Write to convey RPC argument and results does not
affect this, since it 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.

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 draft-ietf-nfsv4-rfc5666bis-09 (work in progress),
May 2016.
January 2017.

[I-D.ietf-nfsv4-rpcrdma-bidirection]
Lever, C., "Bi-directional Remote Procedure Call On RPC-
over-RDMA Transports", draft-ietf-nfsv4-rpcrdma-
bidirection-05
bidirection-06 (work in progress), June 2016. January 2017.

[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>.

[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>.

[RFC7862] Haynes, T., "Network File System (NFS) Version 4 Minor
Version 2 Protocol", RFC 7862, DOI 10.17487/RFC7862,
November 2016, <http://www.rfc-editor.org/info/rfc7862>.

8.2. Informative References

[I-D.ietf-nfsv4-versioning]
Noveck, D., "Rules for NFSv4 Extensions and Minor
Versions", draft-ietf-nfsv4-versioning-09 (work in
progress), December 2016.

[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.

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.

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.

Requirements to ignore extra Read or Write chunks have been removed
from the NFS version 2 and 3 Upper Layer Binding, as they conflict
with [I-D.ietf-nfsv4-rfc5666bis].

A complete discussion of reply size estimation has been introduced
for all protocols covered by the Upper Layer Bindings in this
document.

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

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. Dave also contributed the text of Section 4.1.1. 4.5

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 248 816 6463
Email: chuck.lever@oracle.com