Network File System (NFS) Upper-Layer Binding To RPC-Over-RDMA Version 2
draft-ietf-nfsv4-nfs-ulb-v2-07
| Document | Type | Active Internet-Draft (nfsv4 WG) | |
|---|---|---|---|
| Author | Chuck Lever | ||
| Last updated | 2022-05-13 | ||
| Stream | Internet Engineering Task Force (IETF) | ||
| Intended RFC status | (None) | ||
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draft-ietf-nfsv4-nfs-ulb-v2-07
Network File System Version 4 C. Lever
Internet-Draft Oracle
Intended status: Standards Track 13 May 2022
Expires: 14 November 2022
Network File System (NFS) Upper-Layer Binding To RPC-Over-RDMA Version 2
draft-ietf-nfsv4-nfs-ulb-v2-07
Abstract
This document specifies Upper-Layer Bindings of Network File System
(NFS) protocol versions to RPC-over-RDMA version 2.
Note
Discussion of this draft takes place on the NFSv4 working group
mailing list (nfsv4@ietf.org), archived at
https://mailarchive.ietf.org/arch/browse/nfsv4/. Working Group
information is available at https://datatracker.ietf.org/wg/nfsv4/
about/.
Submit suggestions and changes as pull requests at
https://github.com/chucklever/i-d-nfs-ulb-v2. Instructions are on
that page.
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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Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on 14 November 2022.
Copyright Notice
Copyright (c) 2022 IETF Trust and the persons identified as the
document authors. All rights reserved.
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This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents (https://trustee.ietf.org/
license-info) in effect on the date of publication of this document.
Please review these documents carefully, as they describe your rights
and restrictions with respect to this document. Code Components
extracted from this document must include Revised BSD License text as
described in Section 4.e of the Trust Legal Provisions and are
provided without warranty as described in the Revised BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Requirements Language . . . . . . . . . . . . . . . . . . . . 3
3. Upper-Layer Binding for NFS Versions 2 and 3 . . . . . . . . 4
3.1. DDP-Eligibility . . . . . . . . . . . . . . . . . . . . . 4
3.2. Reply Size Estimation . . . . . . . . . . . . . . . . . . 5
3.3. RPC Binding Considerations . . . . . . . . . . . . . . . 5
3.4. Transport Considerations . . . . . . . . . . . . . . . . 5
3.4.1. Keep-Alive . . . . . . . . . . . . . . . . . . . . . 6
3.4.2. Replay Detection . . . . . . . . . . . . . . . . . . 6
4. Upper-Layer Bindings for NFS Version 2 and 3 Auxiliary
Protocols . . . . . . . . . . . . . . . . . . . . . . . . 7
4.1. MOUNT, NLM, and NSM Protocols . . . . . . . . . . . . . . 7
4.2. NFSACL Protocol . . . . . . . . . . . . . . . . . . . . . 7
5. Upper-Layer Binding For NFS Version 4 . . . . . . . . . . . . 8
5.1. DDP-Eligibility . . . . . . . . . . . . . . . . . . . . . 8
5.1.1. The NFSv4.2 READ_PLUS operation . . . . . . . . . . . 8
5.1.2. NFS Version 4 COMPOUND Requests . . . . . . . . . . . 9
5.2. Reply Size Estimation . . . . . . . . . . . . . . . . . . 11
5.2.1. Reply Size Estimation for Minor Version 0 . . . . . . 11
5.2.2. Reply Size Estimation for Minor Version 1 and
Newer . . . . . . . . . . . . . . . . . . . . . . . . 12
5.3. RPC Binding Considerations . . . . . . . . . . . . . . . 12
5.4. Transport Considerations . . . . . . . . . . . . . . . . 12
5.4.1. Congestion Avoidance . . . . . . . . . . . . . . . . 12
5.4.2. Retransmission and Keep-alive . . . . . . . . . . . . 13
5.5. Session-Related Considerations . . . . . . . . . . . . . 13
6. Upper-Layer Binding For NFS Version 4 Callbacks . . . . . . . 14
6.1. NFS Version 4.0 Callback . . . . . . . . . . . . . . . . 14
6.2. NFS Version 4.1 Callback . . . . . . . . . . . . . . . . 15
7. Extending NFS Upper-Layer Bindings . . . . . . . . . . . . . 15
8. Security Considerations . . . . . . . . . . . . . . . . . . . 15
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 16
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 16
10.1. Normative References . . . . . . . . . . . . . . . . . . 16
10.2. Informative References . . . . . . . . . . . . . . . . . 17
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 18
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 18
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1. Introduction
The RPC-over-RDMA version 2 transport can employ direct data
placement to convey data payloads associated with RPC transactions,
as described in [I-D.ietf-nfsv4-rpcrdma-version-two]. As mandated by
that document, RPC client and server implementations using RPC-over-
RDMA version 2 MUST agree in advance which XDR data items and RPC
procedures are eligible for direct data placement (DDP).
An Upper-Layer Binding specifies this agreement for one or more
versions of one RPC program. Other operational details, such as RPC
binding assignments, pairing Write chunks with result data items, and
reply size estimation, are also specified by such a Binding.
This document contains material required of Upper-Layer Bindings, as
specified in Appendix A of [I-D.ietf-nfsv4-rpcrdma-version-two], for
the following NFS protocol versions:
* NFS version 2 [RFC1094]
* NFS version 3 [RFC1813]
* NFS version 4.0 [RFC7530]
* NFS version 4.1 [RFC8881]
* NFS version 4.2 [RFC7862]
The current document also provides Upper-Layer Bindings for auxiliary
protocols used with NFS versions 2 and 3 (see Section 4).
This document assumes the reader is already familiar with concepts
and terminology defined throughout
[I-D.ietf-nfsv4-rpcrdma-version-two] and the documents it references.
2. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in
BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
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3. Upper-Layer Binding for NFS Versions 2 and 3
The Upper-Layer Binding specification in this section applies to NFS
version 2 [RFC1094] and NFS version 3 [RFC1813]. For brevity, in
this document, a "Legacy NFS client" refers to an NFS client using
version 2 or version 3 of the NFS RPC program (100003) 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.
3.1. DDP-Eligibility
Generally, storage protocols based on RDMA divide both read and write
operations into two steps. This division enables the payload
receiver to allocate the sink buffer for each I/O operation in
advance of the network payload transfer. By allocating the sink
buffer tactically, a good quality receiver implementation reduces the
amount of data movement it must perform during and after the I/O
operation.
During an NFS WRITE that involves explicit RDMA, first the NFS client
sends a request that indicates where the NFS server can find the
payload buffer, then the NFS server pulls the WRITE payload from that
buffer. Likewise, during an NFS READ that involves explicit RDMA,
the NFS client provides the location of the destination buffer, then
the NFS server pushes the READ payload to that buffer.
Therefore, the following XDR data items in NFS versions 2 and 3 are
DDP-eligible:
* The opaque file data argument in the NFS WRITE procedure
* The pathname argument in the NFS SYMLINK procedure
* The opaque file data result in the NFS READ procedure
* 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.
Regardless of whether an NFS operation is considered non-idempotent,
a transport error might not indicate whether the server has processed
the arguments of the RPC Call or whether the server has accessed or
modified client memory associated with that RPC.
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3.2. Reply Size Estimation
During the construction of each RPC Call message, a Requester is
responsible for allocating appropriate RDMA resources to receive the
corresponding Reply message. These resources must be capable of
holding the entire Reply. Therefore the Requester needs to estimate
the maximum possible size of the expected Reply message.
* Often, the expected Reply can fit in a limited number of RDMA Send
messages. The Requester need not provision any RDMA resources for
the Reply, relying instead on message continuation to handle the
entire Reply message.
* In cases where the Upper Layer Binding permits direct data
placement of the results (DDP), a Requester can provision Write
chunks to receive those results. The Requester MUST reliably
estimate the maximum size of each result receive via a Write
chunk.
* A Requester that expects a large Reply message can provision a
Reply chunk. The Requester MUST reliably estimate the maximum
size of the payload received via the Reply chunk.
* If RDMA resources are not available to send a Reply, a Responder
falls back to message continuation.
A correctly implemented Legacy NFS client thus avoids retransmission
of non-idempotent NFS requests due to improperly estimated Reply
resources.
3.3. RPC Binding Considerations
Legacy NFS servers typically listen for clients on UDP and TCP port
2049. Additionally, they register these ports with a local
portmapper service [RFC1833].
A Legacy NFS server supporting RPC-over-RDMA version 2 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 (see Section 9). The chosen port MAY be registered
with the RPC portmapper using the netids assigned in Section 12 of
[I-D.ietf-nfsv4-rpcrdma-version-two].
3.4. Transport Considerations
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3.4.1. Keep-Alive
Legacy NFS client implementations can rely on connection keep-alive
to detect when a Legacy NFS server has become unresponsive. When an
NFS server is no longer responsive, client-side keep-alive terminates
the connection, triggering reconnection and retransmission of
outstanding RPC transactions.
Some RDMA transports (such as the Reliable Connected QP type on
InfiniBand) have no keep-alive mechanism. Without a disconnect or
new RPC traffic, such connections can remain alive long after an NFS
server has become unresponsive or unreachable. Once an NFS client
has consumed all available RPC-over-RDMA version 2 credits on that
transport connection, it awaits a reply indefinitely before sending
another RPC request.
Legacy NFS clients SHOULD reserve one RPC-over-RDMA version 2 credit
to use for periodic server or connection health assessment. Either
peer can use this credit to drive an RPC request on an otherwise idle
connection, triggering either an affirmative server response or a
connection termination.
3.4.2. Replay Detection
Like NFSv4.0, Legacy NFS servers typically employ request replay
detection to reduce the risk of data and file namespace corruption
that could result when an NFS client retransmits a non-idempotent NFS
request. A Legacy NFS server can send a cached response when a
replay is detected, rather than executing the request again. Replay
detection is not perfect, but it is usually adequate.
For Legacy NFS servers, replay detection commonly utilizes heuristic
indicators such as the IP address of the NFS client, the source port
of the connection, the transaction ID of the request, and the
contents of the request's RPC and upper-layer protocol headers. A
Legacy NFS client is careful to re-use the same source port when
reconnecting so that Legacy NFS servers can better detect RPC
retransmission.
However, a Legacy NFS client operating over an RDMA transport has no
control over connection source ports. It is almost certain that an
RPC request retransmitted on a new connection can never be detected
as a replay if the receiving Legacy NFS server includes the
connection source port in its replay detection heuristics.
Therefore a Legacy NFS server using an RDMA transport should never
use a connection's source port as part of its NFS request replay
detection mechanism.
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4. Upper-Layer Bindings for NFS Version 2 and 3 Auxiliary Protocols
Storage administrators typically deploy NFS versions 2 and 3 with
several other protocols, sometimes called the "NFS auxiliary
protocols." These are distinct RPC programs that define procedures
not part of the NFS RPC program (100003). The Upper-Layer Bindings
in this section apply to:
* Versions 2 and 3 of the MOUNT RPC program (100005) [RFC1813]
* Versions 1, 3, and 4 of the NLM RPC program (100021) [RFC1813]
* Version 1 of the NSM RPC program (100024), described in Chapter 11
of [XNFS]
* Versions 2 and 3 of the NFSACL RPC program (100227). The NFSACL
program does not have a public definition. This document treats
the NFSACL program as a de facto standard, as there are several
interoperating implementations.
4.1. MOUNT, NLM, and NSM Protocols
Historically, NFS/RDMA implementations have conveyed the MOUNT, NLM,
and NSM protocols via TCP. A Legacy NFS server implementation MUST
provide support for these auxiliary protocols via TCP.
Moreover, there is little benefit from transporting these protocols
via RDMA. Thus this document does not provide an Upper-Layer binding
for them.
4.2. NFSACL Protocol
Legacy NFS clients and servers convey NFSACL procedures on the same
transport connection and port as the NFS RPC program (100003).
Utilizing the same port obviates the need for a separate rpcbind
query to discover server support for this RPC program.
ACLs are typically small, but even large ACLs must be encoded and
decoded to some degree before being being stored in local
filesystems. Thus no data item in this Upper-Layer Protocol is DDP-
eligible.
For procedures whose replies do not include an ACL object, the size
of each Reply is determined directly from the NFSACL RPC program's
XDR definition.
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The NFSACL protocol does not provide a mechanism to determine the
size of a received ACL in advance. When preparing for responses that
include ACLs, Legacy NFS clients estimate a maximum reply size based
on limits within their local file systems. If that estimation is
inadequate, a Responder falls back to message continuation.
5. Upper-Layer Binding For NFS Version 4
The Upper-Layer Binding specification in this section applies to
versions of the NFS RPC program defined in NFS version 4.0 [RFC7530],
NFS version 4.1 [RFC8881], and NFS version 4.2 [RFC7862].
5.1. DDP-Eligibility
Only the following XDR data items in the COMPOUND procedure of all
NFS version 4 minor versions are DDP-eligible:
* The opaque data field in the WRITE4args structure
* The linkdata field of the NF4LNK arm in the createtype4 union
* The opaque data field in the READ4resok structure
* The linkdata field in the READLINK4resok structure
5.1.1. The NFSv4.2 READ_PLUS operation
NFS version 4.2 introduces an enhanced READ operation called
READ_PLUS [RFC7862]. READ_PLUS enables an NFS server to compact
returned READ data payloads. No part of a READ_PLUS Reply is DDP-
eligible.
In a READ_PLUS result, returned file content appears as a list of one
or more of the following items:
* Regular data content, the same as the result of a traditional READ
operation
* Unallocated space in a file, where no data has been written, or
previously-written data has been removed via a hole-punch
operation
* A counted pattern
Upon receipt of a READ_PLUS result, an NFSv4.2 client expands the
returned list into its preferred representation of the original file
content.
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Before receiving that result, an NFSv4.2 client is unaware of how the
NFS server has organized the file content. Thus it is not possible
to predict the size or structure of a READ_PLUS Reply in advance.
The use of direct data placement is therefore challenging. Moreover,
the usual benefits of hardware-assisted data placement are entirely
lost if the client must parse the result of each READ I/O.
Therefore this Upper Layer Binding does not make elements of an
NFSv4.2 READ_PLUS Reply DDP-eligible. Further, this Upper Layer
Binding recommends that NFS client implemenations avoid using the
READ_PLUS operation on NFS/RDMA mount points.
5.1.2. NFS Version 4 COMPOUND Requests
5.1.2.1. Multiple DDP-eligible Data Items
An NFS version 4 COMPOUND procedure can contain more than one
operation that carries a DDP-eligible data item. An NFS version 4
client provides XDR Position values in each Read chunk to determine
which chunk is associated with which argument data item. However,
NFS version 4 server and client implementations must agree on how to
pair Write chunks with returned result data items.
A "READ operation" refers to any NFS version 4 operation with a DDP-
eligible result data item in the following lists. An NFS version 4
client applies the mechanism specified in Section 4.3.2 of
[I-D.ietf-nfsv4-rpcrdma-version-two] to this class of operations as
follows:
* 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.
An NFS version 4 server acts as follows:
* The first READ operation MUST use the first chunk in the Write
list in an NFS version 4 COMPOUND procedure. The next READ
operation uses the next Write chunk, and so on.
* If an NFS version 4 client has provided a matching non-empty Write
chunk, then the corresponding READ operation MUST return its DDP-
eligible data item using that chunk.
* If an NFS version 4 client has provided an empty matching Write
chunk, then the corresponding READ operation MUST return all of
its result data items inline.
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* If a 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.
* If there are more 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.
5.1.2.2. Chunk List Complexity
By default, the RPC-over-RDMA version 2 protocol limits the number of
chunks or segments that may appear in Read or Write lists (see
Section 5.2 of [I-D.ietf-nfsv4-rpcrdma-version-two]).
These implementation limits are significant when Kerberos integrity
or privacy is in use [RFC7861]. GSS services increase the size of
credential material in RPC headers, potentially requiring the more
frequent use of less efficient Special Payload or Continued Payload
messages.
NFS version 4 clients follow the prescriptions listed below when
constructing RPC-over-RDMA version 2 messages in the absence of an
explicit transport property exchange that alters these limits. NFS
version 4 servers MUST accept and process all such requests.
* The Read list can contain either a Call chunk, no more than one
Read chunk, or both a Call chunk and one Read chunk.
* The Write list can contain no more than one Write chunk.
NFS version 4 clients wishing to send more complex chunk lists can
use transport properties to bound the complexity of NFS version 4
COMPOUNDs, limit the number of elements in scatter-gather operations,
and avoid other sources of chunk overruns at the receiving peer.
5.1.2.3. 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.
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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 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.
5.2. Reply Size Estimation
Within NFS version 4, there are certain variable-length result data
items whose maximum size cannot be estimated by clients reliably
because there is no protocol-specified size limit on these result
arrays. These include:
* The attrlist4 field
* Fields containing ACLs such as fattr4_acl, fattr4_dacl, and
fattr4_sacl
* Fields in the fs_locations4 and fs_locations_info4 data structures
* 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
5.2.1. Reply Size Estimation for Minor Version 0
The NFS version 4.0 protocol itself does not impose any bound on the
size of NFS Calls or Replies.
Variable-length fattr4 attributes make it particularly difficult for
clients to predict the maximum size of some NFS version 4.0 Replies.
Client implementations might rely upon internal architectural limits
to constrain the reply size, but such limits are not always reliable.
When an NFS version 4.0 client cannot predict the size of a Reply, it
can rely on message continuation to enable a Reply under any
circumstances.
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5.2.2. 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 is the absolute
maximum size of replies generated by an NFS version 4.1 server.
An NFS version 4 client can use this value when it is impossible 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.
5.3. RPC Binding Considerations
NFS version 4 servers are required to listen on TCP port 2049 and are
not required to register with an rpcbind service [RFC7530].
Therefore, an NFS version 4 server supporting RPC-over-RDMA version 2
MUST use the alternative well-known port number for its RPC-over-RDMA
service defined in Section 9.
5.4. Transport Considerations
5.4.1. Congestion Avoidance
Section 3.1 of [RFC7530] states:
Where an NFS version 4 implementation supports operation over the
IP network protocol, the supported transport layer between NFS and
IP MUST be an IETF standardized transport protocol that is
specified to avoid network congestion; such transports include TCP
and the Stream Control Transmission Protocol (SCTP).
Section 2.9.1 of [RFC8881] further states:
Even if NFS version 4.1 is used over a non-IP network protocol, it
is RECOMMENDED that the transport support congestion control.
It is permissible for a connectionless transport to be used under
NFS version 4.1; however, reliable and in-order delivery of data
combined with congestion control by the connectionless transport
is REQUIRED. As a consequence, UDP by itself MUST NOT be used as
an NFS version 4.1 transport.
RPC-over-RDMA version 2 utilizes only reliable, connection-oriented
transports that guarantee in-order delivery, meeting all the above
requirements for NFS version 4.0 and 4.1. See Section 4.2.1 of
[I-D.ietf-nfsv4-rpcrdma-version-two] for more details.
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5.4.2. Retransmission and Keep-alive
NFS version 4 client implementations often rely on a transport-layer
connection 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,
triggering reconnection and RPC retransmission.
Some RDMA transports (such as the Reliable Connected QP type on
InfiniBand) have no keep-alive mechanism. Without a disconnect or
new RPC traffic, such connections can remain alive long after an NFS
server has become unresponsive. Once an NFS client has consumed all
available RPC-over-RDMA version 2 credits on that transport
connection, it indefinitely awaits a reply before sending another RPC
request.
NFS version 4 peers SHOULD reserve one RPC-over-RDMA version 2 credit
for periodic server or connection health assessment. Either peer can
use this credit to drive an RPC request on an otherwise idle
connection, triggering either a quick affirmative server response or
immediate connection termination.
In addition to network partition and request loss scenarios, RPC-
over-RDMA version 2 peers can terminate a connection when a Transport
header is malformed or when too many RPC-over-RDMA messages are sent
without a credit update. In such cases:
* If a transport error occurs (e.g., an RDMA2_ERROR type message is
received) just before the disconnect or instead of a disconnect,
the Requester MUST respond to that error as prescribed by the
specification of the RPC transport. Then the NFS version 4 rules
for handling retransmission apply.
* If there is a transport disconnect and the Responder has provided
no other response for a request, then only the NFS version 4 rules
for handling retransmission apply.
5.5. Session-Related Considerations
The presence of an NFS version 4 session (as defined in [RFC8881])
does not affect the operation of RPC-over-RDMA version 2. None of
the operations introduced to support NFS sessions (e.g., the SEQUENCE
operation) contain DDP-eligible data items. There is no need to
match the number of session slots with the available RPC-over-RDMA
version 2 credits.
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However, there are a few new cases where an RPC transaction can fail.
For example, a Requester might receive, in response to an RPC
request, an RDMA2_ERROR message with a rdma_err value of
RDMA2_ERR_BADXDR. These situations are not different from existing
RPC errors, which an NFS session implementation can already handle
for other transport types. Moreover, there might be no SEQUENCE
result available to the Requester to distinguish whether failure
occurred before or after the Responder executed the requested
operations.
When a transport error occurs (e.g., an RDMA2_ERROR type message is
received), the Requester proceeds, as usual, to match the incoming
XID value to a waiting RPC Call. The Requester terminates the RPC
transaction and reports the result status to the RPC consumer. The
Requester's session implementation then determines the session ID and
slot for the failed request and performs slot recovery to make that
slot usable again. Otherwise, that slot is rendered permanently
unavailable.
When an NFS session is not present (for example, when NFS version 4.0
is in use), a transport error does not indicate whether the server
has processed the arguments of the RPC Call, or whether the server
has accessed or modified client memory associated with that RPC.
6. Upper-Layer Binding For NFS Version 4 Callbacks
The NFS version 4 family of protocols supports server-initiated
callbacks to notify NFS version 4 clients of events such as recalled
delegations.
6.1. NFS Version 4.0 Callback
An NFS version 4.0 client uses the SETCLIENTID operation for
advertising the IP address, port, and netid of its NFS version 4.0
callback service. When an NFS version 4.0 server provides a
backchannel service to an NFS version 4.0 client that uses RPC-over-
RDMA version 2 for its forward channel, the server MUST advertise the
backchannel service using either the "tcp" or "tcp6" netid.
Because the NFSv4.0 backchannel does not operate on RPC-over-RDMA,
this document does not specify an Upper-Layer binding for the NFSv4.0
backchannel RPC program.
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6.2. NFS Version 4.1 Callback
In NFS version 4.1 and newer minor versions, callback operations may
appear on the same connection that is in use for NFS version 4
forward channel client requests. NFS version 4 clients and servers
MUST use the mechanisms described in Section 4.5 of
[I-D.ietf-nfsv4-rpcrdma-version-two] to convey backchannel operations
on an RPC-over-RDMA version 2 transport.
The csa_back_chan_attrs argument of the CREATE_SESSION operation
contains a ca_maxresponsesize field. The value in this field is the
absolute maximum size of backchannel replies generated by a replying
NFS version 4 client.
There are no DDP-eligible data items in callback procedures defined
in NFS version 4.1 or NFS version 4.2. However, some callback
operations, such as messages that convey device ID information, can
be sizeable. A sender can use Message Continuation or a Special
Payload message in this situation.
When an NFS version 4.1 client can support Special Payload Calls in
its backchannel, it reports a backchannel ca_maxrequestsize that is
larger than the connection's inline thresholds. Otherwise, an NFS
version 4 server MUST use only Simple Payload or Continued Payload
messages to convey backchannel operations.
7. Extending NFS Upper-Layer Bindings
RPC programs such as NFS must have an Upper-Layer Binding
specification to operate on an RPC-over-RDMA version 2 transport
[I-D.ietf-nfsv4-rpcrdma-version-two]. 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, or to cover separately published
extensions to an existing NFS version 4 minor version, as described
in [RFC8178].
8. Security Considerations
RPC-over-RDMA version 2 supports all RPC security models, including
RPCSEC_GSS security and transport-level security [RFC7861]. The
choice of what Direct Data Placement mechanism to convey RPC argument
and results does not affect this since it changes only the method of
data transfer. Because the current document defines only the binding
of the NFS protocols atop RPC-over-RDMA version 2
[I-D.ietf-nfsv4-rpcrdma-version-two], all relevant security
considerations are, therefore, described at that layer.
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9. IANA Considerations
The use of direct data placement in NFS introduces a need for an
additional port number assignment for networks that share traditional
UDP and TCP port spaces with RDMA services. The DDP protocol is such
an example [RFC5041].
For this purpose, the current document lists a set of port number
assignments that IANA has already assigned for NFS/RDMA in the IANA
port registry, according to the guidelines described in [RFC6335].
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 author requests that IANA add the current document as a reference
for the existing nfsrdma port assignments. This document does not
alter these assignments.
10. References
10.1. Normative References
[I-D.ietf-nfsv4-rpcrdma-version-two]
Lever, C. and D. Noveck, "RPC-over-RDMA Version 2
Protocol", Work in Progress, Internet-Draft, draft-ietf-
nfsv4-rpcrdma-version-two-06, 2 January 2022,
<https://datatracker.ietf.org/doc/html/draft-ietf-nfsv4-
rpcrdma-version-two-06>.
[RFC1833] Srinivasan, R., "Binding Protocols for ONC RPC Version 2",
RFC 1833, DOI 10.17487/RFC1833, August 1995,
<https://www.rfc-editor.org/rfc/rfc1833>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/rfc/rfc2119>.
[RFC6335] Cotton, M., Eggert, L., Touch, J., Westerlund, M., and S.
Cheshire, "Internet Assigned Numbers Authority (IANA)
Procedures for the Management of the Service Name and
Transport Protocol Port Number Registry", BCP 165,
RFC 6335, DOI 10.17487/RFC6335, August 2011,
<https://www.rfc-editor.org/rfc/rfc6335>.
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[RFC7530] Haynes, T., Ed. and D. Noveck, Ed., "Network File System
(NFS) Version 4 Protocol", RFC 7530, DOI 10.17487/RFC7530,
March 2015, <https://www.rfc-editor.org/rfc/rfc7530>.
[RFC7861] Adamson, A. and N. Williams, "Remote Procedure Call (RPC)
Security Version 3", RFC 7861, DOI 10.17487/RFC7861,
November 2016, <https://www.rfc-editor.org/rfc/rfc7861>.
[RFC7862] Haynes, T., "Network File System (NFS) Version 4 Minor
Version 2 Protocol", RFC 7862, DOI 10.17487/RFC7862,
November 2016, <https://www.rfc-editor.org/rfc/rfc7862>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/rfc/rfc8174>.
[RFC8881] Noveck, D., Ed. and C. Lever, "Network File System (NFS)
Version 4 Minor Version 1 Protocol", RFC 8881,
DOI 10.17487/RFC8881, August 2020,
<https://www.rfc-editor.org/rfc/rfc8881>.
10.2. Informative References
[RFC1094] Nowicki, B., "NFS: Network File System Protocol
specification", RFC 1094, DOI 10.17487/RFC1094, March
1989, <https://www.rfc-editor.org/rfc/rfc1094>.
[RFC1813] Callaghan, B., Pawlowski, B., and P. Staubach, "NFS
Version 3 Protocol Specification", RFC 1813,
DOI 10.17487/RFC1813, June 1995,
<https://www.rfc-editor.org/rfc/rfc1813>.
[RFC5041] Shah, H., Pinkerton, J., Recio, R., and P. Culley, "Direct
Data Placement over Reliable Transports", RFC 5041,
DOI 10.17487/RFC5041, October 2007,
<https://www.rfc-editor.org/rfc/rfc5041>.
[RFC8178] Noveck, D., "Rules for NFSv4 Extensions and Minor
Versions", RFC 8178, DOI 10.17487/RFC8178, July 2017,
<https://www.rfc-editor.org/rfc/rfc8178>.
[XNFS] The Open Group, "Protocols for Interworking: XNFS, Version
3W", January 1998.
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Acknowledgments
Thanks to Tom Talpey, who contributed the text of Section 5.1.2.2.
David Noveck contributed the text of Section 5.5 and Section 7. The
author also wishes to thank Bill Baker and Greg Marsden for their
support of this work.
Special thanks go to Transport Area Directors Zaheduzzaman Sarker,
NFSV4 Working Group Chairs Brian Pawlowski, and David Noveck, and
NFSV4 Working Group Secretary Thomas Haynes for their support.
Author's Address
Charles Lever
Oracle Corporation
United States of America
Email: chuck.lever@oracle.com
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