Internet DRAFT - draft-ietf-nfsv4-sess
draft-ietf-nfsv4-sess
INTERNET-DRAFT Tom Talpey
Expires: December 2005 Network Appliance, Inc.
Spencer Shepler
Sun Microsystems, Inc.
Jon Bauman
University of Michigan
July, 2005
NFSv4 Session Extensions
draft-ietf-nfsv4-sess-02
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Copyright (C) The Internet Society (2005). All Rights Reserved.
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Abstract
Extensions are proposed to NFS version 4 which enable it to support
long-lived sessions, endpoint management, and operation atop a
variety of RPC transports, including TCP and RDMA. These
extensions enable support for reliably implemented client response
caching by NFSv4 servers, enhanced security, multipathing and
trunking of transport connections. These extensions provide
identical benefits over both TCP and RDMA connection types.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Motivation . . . . . . . . . . . . . . . . . . . . . . . 4
1.2. Problem Statement . . . . . . . . . . . . . . . . . . . 5
1.3. NFSv4 Session Extension Characteristics . . . . . . . . 7
2. Transport Issues . . . . . . . . . . . . . . . . . . . . . 7
2.1. Session Model . . . . . . . . . . . . . . . . . . . . . 7
2.1.1. Connection State . . . . . . . . . . . . . . . . . . . 9
2.1.2. NFSv4 Channels, Sessions and Connections . . . . . . . 9
2.1.3. Reconnection, Trunking and Failover . . . . . . . . . 11
2.1.4. Server Duplicate Request Cache . . . . . . . . . . . . 12
2.2. Session Initialization and Transfer Models . . . . . . . 13
2.2.1. Session Negotiation . . . . . . . . . . . . . . . . . 13
2.2.2. RDMA Requirements . . . . . . . . . . . . . . . . . . 15
2.2.3. RDMA Connection Resources . . . . . . . . . . . . . . 15
2.2.4. TCP and RDMA Inline Transfer Model . . . . . . . . . . 16
2.2.5. RDMA Direct Transfer Model . . . . . . . . . . . . . . 19
2.3. Connection Models . . . . . . . . . . . . . . . . . . . 22
2.3.1. TCP Connection Model . . . . . . . . . . . . . . . . . 23
2.3.2. Negotiated RDMA Connection Model . . . . . . . . . . . 24
2.3.3. Automatic RDMA Connection Model . . . . . . . . . . . 24
2.4. Buffer Management, Transfer, Flow Control . . . . . . . 25
2.5. Retry and Replay . . . . . . . . . . . . . . . . . . . . 28
2.6. The Back Channel . . . . . . . . . . . . . . . . . . . . 28
2.7. COMPOUND Sizing Issues . . . . . . . . . . . . . . . . . 30
2.8. Data Alignment . . . . . . . . . . . . . . . . . . . . . 30
3. NFSv4 Integration . . . . . . . . . . . . . . . . . . . . 31
3.1. Minor Versioning . . . . . . . . . . . . . . . . . . . . 32
3.2. Slot Identifiers and Server Duplicate Request Cache . . 32
3.3. COMPOUND and CB_COMPOUND . . . . . . . . . . . . . . . . 36
3.4. eXternal Data Representation Efficiency . . . . . . . . 37
3.5. Effect of Sessions on Existing Operations . . . . . . . 37
3.6. Authentication Efficiencies . . . . . . . . . . . . . . 38
4. Security Considerations . . . . . . . . . . . . . . . . . 39
4.1. Authentication . . . . . . . . . . . . . . . . . . . . . 40
5. IANA Considerations . . . . . . . . . . . . . . . . . . . 41
6. NFSv4 Protocol Extensions . . . . . . . . . . . . . . . . 42
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6.1. Operation: CREATECLIENTID . . . . . . . . . . . . . . . 42
6.2. Operation: CREATESESSION . . . . . . . . . . . . . . . . 47
6.3. Operation: BIND_BACKCHANNEL . . . . . . . . . . . . . . 52
6.4. Operation: DESTROYSESSION . . . . . . . . . . . . . . . 54
6.5. Operation: SEQUENCE . . . . . . . . . . . . . . . . . . 55
6.6. Callback operation: CB_RECALLCREDIT . . . . . . . . . . 57
6.7. Callback operation: CB_SEQUENCE . . . . . . . . . . . . 57
7. NFSv4 Session Protocol Description . . . . . . . . . . . . 59
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . 65
9. References . . . . . . . . . . . . . . . . . . . . . . . . 65
9.1. Normative References . . . . . . . . . . . . . . . . . . 65
9.2. Informative References . . . . . . . . . . . . . . . . . 66
10. Authors' Addresses . . . . . . . . . . . . . . . . . . . . 68
11. Full Copyright Statement . . . . . . . . . . . . . . . . . 69
1. Introduction
This draft proposes extensions to NFS version 4 [RFC3530] enabling
it to support sessions and endpoint management, and to support
operation atop RDMA-capable RPC over transports such as iWARP.
[RDMAP, DDP] These extensions enable support for exactly-once
semantics by NFSv4 servers, multipathing and trunking of transport
connections, and enhanced security. The ability to operate over
RDMA enables greatly enhanced performance. Operation over existing
TCP is enhanced as well.
While discussed here with respect to IETF-chartered transports, the
proposed protocol is intended to function over other standards,
such as Infiniband. [IB]
The following are the major aspects of this proposal:
o Changes are proposed within the framework of NFSv4 minor
versioning. RPC, XDR, and the NFSv4 procedures and operations
are preserved. The proposed extension functions equally well
over existing transports and RDMA, and interoperates
transparently with existing implementations, both at the local
programmatic interface and over the wire.
o An explicit session is introduced to NFSv4, and new operations
are added to support it. The session allows for enhanced
trunking, failover and recovery, and authentication
efficiency, along with necessary support for RDMA. The
session is implemented as operations within NFSv4 COMPOUND and
does not impact layering or interoperability with existing
NFSv4 implementations. The NFSv4 callback channel is
dynamically associated and is connected by the client and not
the server, enhancing security and operation through
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firewalls. In fact, the callback channel will be enabled to
share the same connection as the operations channel.
o An enhanced RPC layer enables NFSv4 operation atop RDMA. The
session assists RDMA-mode connection, and additional
facilities are provided for managing RDMA resources at both
NFSv4 server and client. Existing NFSv4 operations continue
to function as before, though certain size limits are
negotiated. A companion draft to this document, "RDMA
Transport for ONC RPC" [RPCRDMA] is to be referenced for
details of RPC RDMA support.
o Support for exactly-once semantics ("EOS") is enabled by the
new session facilities, by providing to the server a way to
bound the size of the duplicate request cache for a single
client, and to manage its persistent storage.
Block Diagram
+-----------------+-------------------------------------+
| NFSv4 | NFSv4 + session extensions |
+-----------------+------+----------------+-------------+
| Operations | Session | |
+------------------------+----------------+ |
| RPC/XDR | |
+-------------------------------+---------+ |
| Stream Transport | RDMA Transport |
+-------------------------------+-----------------------+
1.1. Motivation
NFS version 4 [RFC3530] has been granted "Proposed Standard"
status. The NFSv4 protocol was developed along several design
points, important among them: effective operation over wide-area
networks, including the Internet itself; strong security
integrated into the protocol; extensive cross-platform
interoperability including integrated locking semantics compatible
with multiple operating systems; and protocol extensibility.
The NFS version 4 protocol, however, does not provide support for
certain important transport aspects. For example, the protocol
does not address response caching, which is required to provide
correctness for retried client requests across a network partition,
nor does it provide an interoperable way to support trunking and
multipathing of connections. This leads to inefficiencies,
especially where trunking and multipathing are concerned, and
presents additional difficulties in supporting RDMA fabrics, in
which endpoints may require dedicated or specialized resources.
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Sessions can be employed to unify NFS-level constructs such as the
clientid, with transport-level constructs such as transport
endpoints. Each transport endpoint draws on resources via its
membership in a session. Resource management can be more strictly
maintained, leading to greater server efficiency in implementing
the protocol. The enhanced operation over a session affords an
opportunity to the server to implement a highly reliable duplicate
request cache, and thereby export exactly-once semantics.
NFSv4 advances the state of high-performance local sharing, by
virtue of its integrated security, locking, and delegation, and its
excellent coverage of the sharing semantics of multiple operating
systems. It is precisely this environment where exactly-once
semantics become a fundamental requirement.
Additionally, efforts to standardize a set of protocols for Remote
Direct Memory Access, RDMA, over the Internet Protocol Suite have
made significant progress. RDMA is a general solution to the
problem of CPU overhead incurred due to data copies, primarily at
the receiver. Substantial research has addressed this and has
borne out the efficacy of the approach. An overview of this is the
RDDP Problem Statement document, [RDDPPS].
Numerous upper layer protocols achieve extremely high bandwidth and
low overhead through the use of RDMA. Products from a wide variety
of vendors employ RDMA to advantage, and prototypes have
demonstrated the effectiveness of many more. Here, we are
concerned specifically with NFS and NFS-style upper layer
protocols; examples from Network Appliance [DAFS, DCK+03], Fujitsu
Prime Software Technologies [FJNFS, FJDAFS] and Harvard University
[KM02] are all relevant.
By layering a session binding for NFS version 4 directly atop a
standard RDMA transport, a greatly enhanced level of performance
and transparency can be supported on a wide variety of operating
system platforms. These combined capabilities alter the landscape
between local filesystems and network attached storage, enable a
new level of performance, and lead new classes of application to
take advantage of NFS.
1.2. Problem Statement
Two issues drive the current proposal: correctness, and
performance. Both are instances of "raising the bar" for NFS,
whereby the desire to use NFS in new classes applications can be
accommodated by providing the basic features to make such use
feasible. Such applications include tightly coupled sharing
environments such as cluster computing, high performance computing
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(HPC) and information processing such as databases. These trends
are explored in depth in [NFSPS].
The first issue, correctness, exemplified among the attributes of
local filesystems, is support for exactly-once semantics. Such
semantics have not been reliably available with NFS. Server-based
duplicate request caches [CJ89] help, but do not reliably provide
strict correctness. For the type of application which is expected
to make extensive use of the high-performance RDMA-enabled
environment, the reliable provision of such semantics is a
fundamental requirement.
Introduction of a session to NFSv4 will address these issues. With
higher performance and enhanced semantics comes the problem of
enabling advanced endpoint management, for example high-speed
trunking, multipathing and failover. These characteristics enable
availability and performance. RFC3530 presents some issues in
permitting a single clientid to access a server over multiple
connections.
A second issue encountered in common by NFS implementations is the
CPU overhead required to implement the protocol. Primary among the
sources of this overhead is the movement of data from NFS protocol
messages to its eventual destination in user buffers or aligned
kernel buffers. The data copies consume system bus bandwidth and
CPU time, reducing the available system capacity for applications.
[RDDPPS] Achieving zero-copy with NFS has to date required
sophisticated, "header cracking" hardware and/or extensive
platform-specific virtual memory mapping tricks.
Combined in this way, NFSv4, RDMA and the emerging high-speed
network fabrics will enable delivery of performance which matches
that of the fastest local filesystems, preserving the key existing
local filesystem semantics, while enhancing them by providing
network filesystem sharing semantics.
RDMA implementations generally have other interesting properties,
such as hardware assisted protocol access, and support for user
space access to I/O. RDMA is compelling here for another reason;
hardware offloaded networking support in itself does not avoid data
copies, without resorting to implementing part of the NFS protocol
in the NIC. Support of RDMA by NFS enables the highest performance
at the architecture level rather than by implementation; this
enables ubiquitous and interoperable solutions.
By providing file access performance equivalent to that of local
file systems, NFSv4 over RDMA will enable applications running on a
set of client machines to interact through an NFSv4 file system,
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just as applications running on a single machine might interact
through a local file system.
This raises the issue of whether additional protocol enhancements
to enable such interaction would be desirable and what such
enhancements would be. This is a complicated issue which the
working group needs to address and will not be further discussed in
this document.
1.3. NFSv4 Session Extension Characteristics
This draft will present a solution based upon minor versioning of
NFSv4. It will introduce a session to collect transport endpoints
and resources such as reply caching, which in turn enables
enhancements such as trunking, failover and recovery. It will
describe use of RDMA by employing support within an underlying RPC
layer [RPCRDMA]. Most importantly, it will focus on making the
best possible use of an RDMA transport.
These extensions are proposed as elements of a new minor revision
of NFS version 4. In this draft, NFS version 4 will be referred to
generically as "NFSv4", when describing properties common to all
minor versions. When referring specifically to properties of the
original, minor version 0 protocol, "NFSv4.0" will be used, and
changes proposed here for minor version 1 will be referred to as
"NFSv4.1".
This draft proposes only changes which are strictly upward-
compatible with existing RPC and NFS Application Programming
Interfaces (APIs).
2. Transport Issues
The Transport Issues section of the document explores the details
of utilizing the various supported transports.
2.1. Session Model
The first and most evident issue in supporting diverse transports
is how to provide for their differences. This draft proposes
introducing an explicit session.
A session introduces minimal protocol requirements, and provides
for a highly useful and convenient way to manage numerous endpoint-
related issues. The session is a local construct; it represents a
named, higher-layer object to which connections can refer, and
encapsulates properties important to each associated client.
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A session is a dynamically created, long-lived server object
created by a client, used over time from one or more transport
connections. Its function is to maintain the server's state
relative to the connection(s) belonging to a client instance. This
state is entirely independent of the connection itself. The
session in effect becomes the object representing an active client
on a connection or set of connections.
Clients may create multiple sessions for a single clientid, and may
wish to do so for optimization of transport resources, buffers, or
server behavior. A session could be created by the client to
represent a single mount point, for separate read and write
"channels", or for any number of other client-selected parameters.
The session enables several things immediately. Clients may
disconnect and reconnect (voluntarily or not) without loss of
context at the server. (Of course, locks, delegations and related
associations require special handling, and generally expire in the
extended absence of an open connection.) Clients may connect
multiple transport endpoints to this common state. The endpoints
may have all the same attributes, for instance when trunked on
multiple physical network links for bandwidth aggregation or path
failover. Or, the endpoints can have specific, special purpose
attributes such as callback channels.
The NFSv4 specification does not provide for any form of flow
control; instead it relies on the windowing provided by TCP to
throttle requests. This unfortunately does not work with RDMA,
which in general provides no operation flow control and will
terminate a connection in error when limits are exceeded. Limits
are therefore exchanged when a session is created; These limits
then provide maxima within which each session's connections must
operate, they are managed within these limits as described in
[RPCRDMA]. The limits may also be modified dynamically at the
server's choosing by manipulating certain parameters present in
each NFSv4.1 request.
The presence of a maximum request limit on the session bounds the
requirements of the duplicate request cache. This can be used to
advantage by a server, which can accurately determine any storage
needs and enable it to maintain duplicate request cache persistence
and to provide reliable exactly-once semantics.
Finally, given adequate connection-oriented transport security
semantics, authentication and authorization may be cached on a per-
session basis, enabling greater efficiency in the issuing and
processing of requests on both client and server. A proposal for
transparent, server-driven implementation of this in NFSv4 has been
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made. [CCM] The existence of the session greatly facilitates the
implementation of this approach. This is discussed in detail in
the Authentication Efficiencies section later in this draft.
2.1.1. Connection State
In RFC3530, the combination of a connected transport endpoint and a
clientid forms the basis of connection state. While has been made
to be workable with certain limitations, there are difficulties in
correct and robust implementation. The NFSv4.0 protocol must
provide a server-initiated connection for the callback channel, and
must carefully specify the persistence of client state at the
server in the face of transport interruptions. The server has only
the client's transport address binding (the IP 4-tuple) to identify
the client RPC transaction stream and to use as a lookup tag on the
duplicate request cache. (A useful overview of this is in [RW96].)
If the server listens on multiple adddresses, and the client
connects to more than one, it must employ different clientid's on
each, negating its ability to aggregate bandwidth and redundancy.
In effect, each transport connection is used as the server's
representation of client state. But, transport connections are
potentially fragile and transitory.
In this proposal, a session identifier is assigned by the server
upon initial session negotiation on each connection. This
identifier is used to associate additional connections, to
renegotiate after a reconnect, to provide an abstraction for the
various session properties, and to address the duplicate request
cache. No transport-specific information is used in the duplicate
request cache implementation of an NFSv4.1 server, nor in fact the
RPC XID itself. The session identifier is unique within the
server's scope and may be subject to certain server policies such
as being bounded in time.
It is envisioned that the primary transport model will be
connection oriented. Connection orientation brings with it certain
potential optimizations, such as caching of per-connection
properties, which are easily leveraged through the generality of
the session. However, it is possible that in future, other
transport models could be accommodated below the session
abstraction.
2.1.2. NFSv4 Channels, Sessions and Connections
There are at least two types of NFSv4 channels: the "operations"
channel used for ordinary requests from client to server, and the
"back" channel, used for callback requests from server to client.
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As mentioned above, different NFSv4 operations on these channels
can lead to different resource needs. For example, server callback
operations (CB_RECALL) are specific, small messages which flow from
server to client at arbitrary times, while data transfers such as
read and write have very different sizes and asymmetric behaviors.
It is sometimes impractical for the RDMA peers (NFSv4 client and
NFSv4 server) to post buffers for these various operations on a
single connection. Commingling of requests with responses at the
client receive queue is particularly troublesome, due both to the
need to manage both solicited and unsolicited completions, and to
provision buffers for both purposes. Due to the lack of any
ordering of callback requests versus response arrivals, without any
other mechanisms, the client would be forced to allocate all
buffers sized to the worst case.
The callback requests are likely to be handled by a different task
context from that handling the responses. Significant
demultiplexing and thread management may be required if both are
received on the same queue. However, if callbacks are relatively
rare (perhaps due to client access patterns), many of these
difficulties can be minimized.
Also, the client may wish to perform trunking of operations channel
requests for performance reasons, or multipathing for availability.
This proposal permits both, as well as many other session and
connection possibilities, by permitting each operation to carry
session membership information and to share session (and clientid)
state in order to draw upon the appropriate resources. For
example, reads and writes may be assigned to specific, optimized
connections, or sorted and separated by any or all of size,
idempotency, etc.
To address the problems described above, this proposal allows
multiple sessions to share a clientid, as well as for multiple
connections to share a session.
Single Connection model:
NFSv4.1 Session
/ \
Operations_Channel [Back_Channel]
\ /
Connection
|
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Multi-connection trunked model (2 operations channels shown):
NFSv4.1 Session
/ \
Operations_Channels [Back_Channel]
| | |
Connection Connection [Connection]
| | |
Multi-connection split-use model (2 mounts shown):
NFSv4.1 Session
/ \
(/home) (/usr/local - readonly)
/ \ |
Operations_Channel [Back_Channel] |
| | Operations_Channel
Connection [Connection] |
| | Connection
|
In this way, implementation as well as resource management may be
optimized. Each session will have its own response caching and
buffering, and each connection or channel will have its own
transport resources, as appropriate. Clients which do not require
certain behaviors may optimize such resources away completely, by
using specific sessions and not even creating the additional
channels and connections.
2.1.3. Reconnection, Trunking and Failover
Reconnection after failure references stored state on the server
associated with lease recovery during the grace period. The
session provides a convenient handle for storing and managing
information regarding the client's previous state on a per-
connection basis, e.g. to be used upon reconnection. Reconnection
to a previously existing session, and its stored resources, are
covered in the "Connection Models" section below.
One important aspect of reconnection is that of RPC library
support. Traditionally, an Upper Layer RPC-based Protocol such as
NFS leaves all transport knowledge to the RPC layer implementation
below it. This allows NFS to operate over a wide variety of
transports and has proven to be a highly successful approach. The
session, however, introduces an abstraction which is, in a way,
"between" RPC and NFSv4.1. It is important that the session
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abstraction not have ramifications within the RPC layer.
One such issue arises within the reconnection logic of RPC.
Previously, an explicit session binding operation, which
established session context for each new connection, was explored.
This however required that the session binding also be performed
during reconnect, which in turn required an RPC request. This
additional request requires new RPC semantics, both in
implementation and the fact that a new request is inserted into the
RPC stream. Also, the binding of a connection to a session
required the upper layer to become "aware" of connections,
something the RPC layer abstraction architecturally abstracts away.
Therefore the session binding is not handled in connection scope
but instead explicitly carried in each request.
For Reliability Availability and Serviceability (RAS) issues such
as bandwidth aggregation and multipathing, clients frequently seek
to make multiple connections through multiple logical or physical
channels. The session is a convenient point to aggregate and
manage these resources.
2.1.4. Server Duplicate Request Cache
Server duplicate request caches, while not a part of an NFS
protocol, have become a standard, even required, part of any NFS
implementation. First described in [CJ89], the duplicate request
cache was initially found to reduce work at the server by avoiding
duplicate processing for retransmitted requests. A second, and in
the long run more important benefit, was improved correctness, as
the cache avoided certain destructive non-idempotent requests from
being reinvoked.
However, such caches do not provide correctness guarantees; they
cannot be managed in a reliable, persistent fashion. The reason is
understandable - their storage requirement is unbounded due to the
lack of any such bound in the NFS protocol, and they are dependent
on transport addresses for request matching.
As proposed in this draft, the presence of maximum request count
limits and negotiated maximum sizes allows the size and duration of
the cache to be bounded, and coupled with a long-lived session
identifier, enables its persistent storage on a per-session basis.
This provides a single unified mechanism which provides the
following guarantees required in the NFSv4 specification, while
extending them to all requests, rather than limiting them only to a
subset of state-related requests:
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"It is critical the server maintain the last response sent to
the client to provide a more reliable cache of duplicate non-
idempotent requests than that of the traditional cache
described in [CJ89]..." [RFC3530]
The maximum request count limit is the count of active operations,
which bounds the number of entries in the cache. Constraining the
size of operations additionally serves to limit the required
storage to the product of the current maximum request count and the
maximum response size. This storage requirement enables server-
side efficiencies.
Session negotiation allows the server to maintain other state. An
NFSv4.1 client invoking the session destroy operation will cause
the server to denegotiate (close) the session, allowing the server
to deallocate cache entries. Clients can potentially specify that
such caches not be kept for appropriate types of sessions (for
example, read-only sessions). This can enable more efficient
server operation resulting in improved response times, and more
efficient sizing of buffers and response caches.
Similarly, it is important for the client to explicitly learn
whether the server is able to implement reliable semantics.
Knowledge of whether these semantics are in force is critical for a
highly reliable client, one which must provide transactional
integrity guarantees. When clients request that the semantics be
enabled for a given session, the session reply must inform the
client if the mode is in fact enabled. In this way the client can
confidently proceed with operations without having to implement
consistency facilities of its own.
2.2. Session Initialization and Transfer Models
Session initialization issues, and data transfer models relevant to
both TCP and RDMA are discussed in this section.
2.2.1. Session Negotiation
The following parameters are exchanged between client and server at
session creation time. Their values allow the server to properly
size resources allocated in order to service the client's requests,
and to provide the server with a way to communicate limits to the
client for proper and optimal operation. They are exchanged prior
to all session-related activity, over any transport type.
Discussion of their use is found in their descriptions as well as
throughout this section.
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Maximum Requests
The client's desired maximum number of concurrent requests is
passed, in order to allow the server to size its reply cache
storage. The server may modify the client's requested limit
downward (or upward) to match its local policy and/or
resources. Over RDMA-capable RPC transports, the per-request
management of low-level transport message credits is handled
within the RPC layer. [RPCRDMA]
Maximum Request/Response Sizes
The maximum request and response sizes are exchanged in order
to permit allocation of appropriately sized buffers and
request cache entries. The size must allow for certain
protocol minima, allowing the receipt of maximally sized
operations (e.g. RENAME requests which contains two name
strings). Note the maximum request/response sizes cover the
entire request/response message and not simply the data
payload as traditional NFS maximum read or write size. Also
note the server implementation may not, in fact probably does
not, require the reply cache entries to be sized as large as
the maximum response. The server may reduce the client's
requested sizes.
Inline Padding/Alignment
The server can inform the client of any padding which can be
used to deliver NFSv4 inline WRITE payloads into aligned
buffers. Such alignment can be used to avoid data copy
operations at the server for both TCP and inline RDMA
transfers. For RDMA, the client informs the server in each
operation when padding has been applied. [RPCRDMA]
Transport Attributes
A placeholder for transport-specific attributes is provided,
with a format to be determined. Possible examples of
information to be passed in this parameter include transport
security attributes to be used on the connection, RDMA-
specific attributes, legacy "private data" as used on existing
RDMA fabrics, transport Quality of Service attributes, etc.
This information is to be passed to the peer's transport layer
by local means which is currently outside the scope of this
draft, however one attribute is provided in the RDMA case:
RDMA Read Resources
RDMA implementations must explicitly provision resources
to support RDMA Read requests from connected peers.
These values must be explicitly specified, to provide
adequate resources for matching the peer's expected needs
and the connection's delay-bandwidth parameters. The
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client provides its chosen value to the server in the
initial session creation, the value must be provided in
each client RDMA endpoint. The values are asymmetric and
should be set to zero at the server in order to conserve
RDMA resources, since clients do not issue RDMA Read
operations in this proposal. The result is communicated
in the session response, to permit matching of values
across the connection. The value may not be changed in
the duration of the session, although a new value may be
requested as part of a new session.
2.2.2. RDMA Requirements
A complete discussion of the operation of RPC-based protocols atop
RDMA transports is in [RPCRDMA]. Where RDMA is considered, this
proposal assumes the use of such a layering; it addresses only the
upper layer issues relevant to making best use of RPC/RDMA.
A connection oriented (reliable sequenced) RDMA transport will be
required. There are several reasons for this. First, this model
most closely reflects the general NFSv4 requirement of long-lived
and congestion-controlled transports. Second, to operate correctly
over either an unreliable or unsequenced RDMA transport, or both,
would require significant complexity in the implementation and
protocol not appropriate for a strict minor version. For example,
retransmission on connected endpoints is explicitly disallowed in
the current NFSv4 draft; it would again be required with these
alternate transport characteristics. Third, the proposal assumes a
specific RDMA ordering semantic, which presents the same set of
ordering and reliability issues to the RDMA layer over such
transports.
The RDMA implementation provides for making connections to other
RDMA-capable peers. In the case of the current proposals before
the RDDP working group, these RDMA connections are preceded by a
"streaming" phase, where ordinary TCP (or NFS) traffic might flow.
However, this is not assumed here and sizes and other parameters
are explicitly exchanged upon a session entering RDMA mode.
2.2.3. RDMA Connection Resources
On transport endpoints which support automatic RDMA mode, that is,
endpoints which are created in the RDMA-enabled state, a single,
preposted buffer must initially be provided by both peers, and the
client session negotiation must be the first exchange.
On transport endpoints supporting dynamic negotiation, a more
sophisticated negotiation is possible, but is not discussed in the
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current draft.
RDMA imposes several requirements on upper layer consumers.
Registration of memory and the need to post buffers of a specific
size and number for receive operations are a primary consideration.
Registration of memory can be a relatively high-overhead operation,
since it requires pinning of buffers, assignment of attributes
(e.g. readable/writable), and initialization of hardware
translation. Preregistration is desirable to reduce overhead.
These registrations are specific to hardware interfaces and even to
RDMA connection endpoints, therefore negotiation of their limits is
desirable to manage resources effectively.
Following the basic registration, these buffers must be posted by
the RPC layer to handle receives. These buffers remain in use by
the RPC/NFSv4 implementation; the size and number of them must be
known to the remote peer in order to avoid RDMA errors which would
cause a fatal error on the RDMA connection.
The session provides a natural way for the server to manage
resource allocation to each client rather than to each transport
connection itself. This enables considerable flexibility in the
administration of transport endpoints.
2.2.4. TCP and RDMA Inline Transfer Model
The basic transfer model for both TCP and RDMA is referred to as
"inline". For TCP, this is the only transfer model supported,
since TCP carries both the RPC header and data together in the data
stream.
For RDMA, the RDMA Send transfer model is used for all NFS requests
and replies, but data is optionally carried by RDMA Writes or RDMA
Reads. Use of Sends is required to ensure consistency of data and
to deliver completion notifications. The pure-Send method is
typically used where the data payload is small, or where for
whatever reason target memory for RDMA is not available.
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Inline message exchange
Client Server
: Request :
Send : ------------------------------> : untagged
: : buffer
: Response :
untagged : <------------------------------ : Send
buffer : :
Client Server
: Read request :
Send : ------------------------------> : untagged
: : buffer
: Read response with data :
untagged : <------------------------------ : Send
buffer : :
Client Server
: Write request with data :
Send : ------------------------------> : untagged
: : buffer
: Write response :
untagged : <------------------------------ : Send
buffer : :
Responses must be sent to the client on the same connection that
the request was sent. It is important that the server does not
assume any specific client implementation, in particular whether
connections within a session share any state at the client. This
is also important to preserve ordering of RDMA operations, and
especially RMDA consistency. Additionally, it ensures that the RPC
RDMA layer makes no requirement of the RDMA provider to open its
memory registration handles (Steering Tags) beyond the scope of a
single RDMA connection. This is an important security
consideration.
Two values must be known to each peer prior to issuing Sends: the
maximum number of sends which may be posted, and their maximum
size. These values are referred to, respectively, as the message
credits and the maximum message size. While the message credits
might vary dynamically over the duration of the session, the
maximum message size does not. The server must commit to
preserving this number of duplicate request cache entires, and
preparing a number of receive buffers equal to or greater than its
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currently advertised credit value, each of the advertised size.
These ensure that transport resources are allocated sufficient to
receive the full advertised limits.
Note that the server must post the maximum number of session
requests to each client operations channel. The client is not
required to spread its requests in any particular fashion across
connections within a session. If the client wishes, it may create
multiple sessions, each with a single or small number of operations
channels to provide the server with this resource advantage. Or,
over RDMA the server may employ a "shared receive queue". The
server can in any case protect its resources by restricting the
client's request credits.
While tempting to consider, it is not possible to use the TCP
window as an RDMA operation flow control mechanism. First, to do
so would violate layering, requiring both senders to be aware of
the existing TCP outbound window at all times. Second, since
requests are of variable size, the TCP window can hold a widely
variable number of them, and since it cannot be reduced without
actually receiving data, the receiver cannot limit the sender.
Third, any middlebox interposing on the connection would wreck any
possible scheme. [MIDTAX] In this proposal, maximum request count
limits are exchanged at the session level to allow correct
provisioning of receive buffers by transports.
When operating over TCP or other similar transport, request limits
and sizes are still employed in NFSv4.1, but instead of being
required for correctness, they provide the basis for efficient
server implementation of the duplicate request cache. The limits
are chosen based upon the expected needs and capabilities of the
client and server, and are in fact arbitrary. Sizes may be
specified by the client as zero (requesting the server's preferred
or optimal value), and request limits may be chosen in proportion
to the client's capabilities. For example, a limit of 1000 allows
1000 requests to be in progress, which may generally be far more
than adequate to keep local networks and servers fully utilized.
Both client and server have independent sizes and buffering, but
over RDMA fabrics client credits are easily managed by posting a
receive buffer prior to sending each request. Each such buffer may
not be completed with the corresponding reply, since responses from
NFSv4 servers arrive in arbitrary order. When an operations
channel is also used for callbacks, the client must account for
callback requests by posting additional buffers. Note that
implementation-specific facilities such as a shared receive queue
may also allow optimization of these allocations.
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When a session is created, the client requests a preferred buffer
size, and the server provides its answer. The server posts all
buffers of at least this size. The client must comply by not
sending requests greater than this size. It is recommended that
server implementations do all they can to accommodate a useful
range of possible client requests. There is a provision in
[RPCRDMA] to allow the sending of client requests which exceed the
server's receive buffer size, but it requires the server to "pull"
the client's request as a "read chunk" via RDMA Read. This
introduces at least one additional network roundtrip, plus other
overhead such as registering memory for RDMA Read at the client and
additional RDMA operations at the server, and is to be avoided.
An issue therefore arises when considering the NFSv4 COMPOUND
procedures. Since an arbitrary number (total size) of operations
can be specified in a single COMPOUND procedure, its size is
effectively unbounded. This cannot be supported by RDMA Sends, and
therefore this size negotiation places a restriction on the
construction and maximum size of both COMPOUND requests and
responses. If a COMPOUND results in a reply at the server that is
larger than can be sent in an RDMA Send to the client, then the
COMPOUND must terminate and the operation which causes the overflow
will provide a TOOSMALL error status result.
2.2.5. RDMA Direct Transfer Model
Placement of data by explicitly tagged RDMA operations is referred
to as "direct" transfer. This method is typically used where the
data payload is relatively large, that is, when RDMA setup has been
performed prior to the operation, or when any overhead for setting
up and performing the transfer is regained by avoiding the overhead
of processing an ordinary receive.
The client advertises RDMA buffers in this proposed model, and not
the server. This means the "XDR Decoding with Read Chunks"
described in [RPCRDMA] is not employed by NFSv4.1 replies, and
instead all results transferred via RDMA to the client employ "XDR
Decoding with Write Chunks". There are several reasons for this.
First, it allows for a correct and secure mode of transfer. The
client may advertise specific memory buffers only during specific
times, and may revoke access when it pleases. The server is not
required to expose copies of local file buffers for individual
clients, or to lock or copy them for each client access.
Second, client credits based on fixed-size request buffers are
easily managed on the server, but for the server additional
management of buffers for client RDMA Reads is not well-bounded.
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For example, the client may not perform these RDMA Read operations
in a timely fashion, therefore the server would have to protect
itself against denial-of-service on these resources.
Third, it reduces network traffic, since buffer exposure outside
the scope and duration of a single request/response exchange
necessitates additional memory management exchanges.
There are costs associated with this decision. Primary among them
is the need for the server to employ RDMA Read for operations such
as large WRITE. The RDMA Read operation is a two-way exchange at
the RDMA layer, which incurs additional overhead relative to RDMA
Write. Additionally, RDMA Read requires resources at the data
source (the client in this proposal) to maintain state and to
generate replies. These costs are overcome through use of
pipelining with credits, with sufficient RDMA Read resources
negotiated at session initiation, and appropriate use of RDMA for
writes by the client - for example only for transfers above a
certain size.
A description of which NFSv4 operation results are eligible for
data transfer via RDMA Write is in [NFSDDP]. There are only two
such operations: READ and READLINK. When XDR encoding these
requests on an RDMA transport, the NFSv4.1 client must insert the
appropriate xdr_write_list entries to indicate to the server
whether the results should be transferred via RDMA or inline with a
Send. As described in [NFSDDP], a zero-length write chunk is used
to indicate an inline result. In this way, it is unnecessary to
create new operations for RDMA-mode versions of READ and READLINK.
Another tool to avoid creation of new, RDMA-mode operations is the
Reply Chunk [RPCRDMA], which is used by RPC in RDMA mode to return
large replies via RDMA as if they were inline. Reply chunks are
used for operations such as READDIR, which returns large amounts of
information, but in many small XDR segments. Reply chunks are
offered by the client and the server can use them in preference to
inline. Reply chunks are transparent to upper layers such as
NFSv4.
In any very rare cases where another NFSv4.1 operation requires
larger buffers than were negotiated when the session was created
(for example extraordinarily large RENAMEs), the underlying RPC
layer may support the use of "Message as an RDMA Read Chunk" and
"RDMA Write of Long Replies" as described in [RPCRDMA]. No
additional support is required in the NFSv4.1 client for this. The
client should be certain that its requested buffer sizes are not so
small as to make this a frequent occurrence, however.
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All operations are initiated by a Send, and are completed with a
Send. This is exactly as in conventional NFSv4, but under RDMA has
a significant purpose: RDMA operations are not complete, that is,
guaranteed consistent, at the data sink until followed by a
successful Send completion (i.e. a receive). These events provide
a natural opportunity for the initiator (client) to enable and
later disable RDMA access to the memory which is the target of each
operation, in order to provide for consistent and secure operation.
The RDMAP Send with Invalidate operation may be worth employing in
this respect, as it relieves the client of certain overhead in this
case.
A "onetime" boolean advisory to each RDMA region might become a
hint to the server that the client will use the three-tuple for
only one NFSv4 operation. For a transport such as iWARP, the
server can assist the client in invalidating the three-tuple by
performing a Send with Solicited Event and Invalidate. The server
may ignore this hint, in which case the client must perform a local
invalidate after receiving the indication from the server that the
NFSv4 operation is complete. This may be considered in a future
version of this draft and [NFSDDP].
In a trusted environment, it may be desirable for the client to
persistently enable RDMA access by the server. Such a model is
desirable for the highest level of efficiency and lowest overhead.
RDMA message exchanges
Client Server
: Direct Read Request :
Send : ------------------------------> : untagged
: : buffer
: Segment :
tagged : <------------------------------ : RDMA Write
buffer : : :
: [Segment] :
tagged : <------------------------------ : [RDMA Write]
buffer : :
: Direct Read Response :
untagged : <------------------------------ : Send (w/Inv.)
buffer : :
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Client Server
: Direct Write Request :
Send : ------------------------------> : untagged
: : buffer
: Segment :
tagged : v------------------------------ : RDMA Read
buffer : +-----------------------------> :
: : :
: [Segment] :
tagged : v------------------------------ : [RDMA Read]
buffer : +-----------------------------> :
: :
: Direct Write Response :
untagged : <------------------------------ : Send (w/Inv.)
buffer : :
2.3. Connection Models
There are three scenarios in which to discuss the connection model.
Each will be discussed individually, after describing the common
case encountered at initial connection establishment.
After a successful connection, the first request proceeds, in the
case of a new client association, to initial session creation, and
then optionally to session callback channel binding, prior to
regular operation.
Commonly, each new client "mount" will be the action which drives
creation of a new session. However there are any number of other
approaches. Clients may choose to share a single connection and
session among all their mount points. Or, clients may support
trunking, where additional connections are created but all within a
single session. Alternatively, the client may choose to create
multiple sessions, each tuned to the buffering and reliability
needs of the mount point. For example, a readonly mount can
sharply reduce its write buffering and also makes no requirement
for the server to support reliable duplicate request caching.
Similarly, the client can choose among several strategies for
clientid usage. Sessions can share a single clientid, or create
new clientids as the client deems appropriate. For kernel-based
clients which service multiple authenticated users, a single
clientid shared across all mount points is generally the most
appropriate and flexible approach. For example, all the client's
file operations may wish to share locking state and the local
client kernel takes the responsibility for arbitrating access
locally. For clients choosing to support other authentication
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models, perhaps example userspace implementations, a new clientid
is indicated. Through use of session create options, both models
are supported at the client's choice.
Since the session is explicitly created and destroyed by the
client, and each client is uniquely identified, the server may be
specifically instructed to discard unneeded presistent state. For
this reason, it is possible that a server will retain any previous
state indefinitely, and place its destruction under administrative
control. Or, a server may choose to retain state for some
configurable period, provided that the period meets other NFSv4
requirements such as lease reclamation time, etc. However, since
discarding this state at the server may affect the correctness of
the server as seen by the client across network partitioning, such
discarding of state should be done only in a conservative manner.
Each client request to the server carries a new SEQUENCE operation
within each COMPOUND, which provides the session context. This
session context then governs the request control, duplicate request
caching, and other persistent parameters managed by the server for
a session.
2.3.1. TCP Connection Model
The following is a schematic diagram of the NFSv4.1 protocol
exchanges leading up to normal operation on a TCP stream.
Client Server
TCPmode : Create Clientid(nfs_client_id4) : TCPmode
: ------------------------------> :
: :
: Clientid reply(clientid, ...) :
: <------------------------------ :
: :
: Create Session(clientid, size S, :
: maxreq N, STREAM, ...) :
: ------------------------------> :
: :
: Session reply(sessionid, size S', :
: maxreq N') :
: <------------------------------ :
: :
: <normal operation> :
: ------------------------------> :
: <------------------------------ :
: : :
No net additional exchange is added to the initial negotiation by
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this proposal. In the NFSv4.1 exchange, the CREATECLIENTID
replaces SETCLIENTID (eliding the callback "clientaddr4"
addressing) and CREATESESSION subsumes the function of
SETCLIENTID_CONFIRM, as described elsewhere in this document.
Callback channel binding is optional, as in NFSv4.0. Note that the
STREAM transport type is shown above, but since the transport mode
remains unchanged and transport attributes are not necessarily
exchanged, DEFAULT could also be passed.
2.3.2. Negotiated RDMA Connection Model
One possible design which has been considered is to have a
"negotiated" RDMA connection model, supported via use of a session
bind operation as a required first step. However due to issues
mentioned earlier, this proved problematic. This section remains
as a reminder of that fact, and it is possible such a mode can be
supported.
It is not considered critical that this be supported for two
reasons. One, the session persistence provides a way for the
server to remember important session parameters, such as sizes and
maximum request counts. These values can be used to restore the
endpoint prior to making the first reply. Two, there are currently
no critical RDMA parameters to set in the endpoint at the server
side of the connection. RDMA Read resources, which are in general
not settable after entering RDMA mode, are set only at the client -
the originator of the connection. Therefore as long as the RDMA
provider supports an automatic RDMA connection mode, no further
support is required from the NFSv4.1 protocol for reconnection.
Note, the client must provide at least as many RDMA Read resources
to its local queue for the benefit of the server when reconnecting,
as it used when negotiating the session. If this value is no
longer appropriate, the client should resynchronize its session
state, destroy the existing session, and start over with the more
appropriate values.
2.3.3. Automatic RDMA Connection Model
The following is a schematic diagram of the NFSv4.1 protocol
exchanges performed on an RDMA connection.
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Client Server
RDMAmode : : : RDMAmode
: : :
Prepost : : : Prepost
receive : : : receive
: :
: Create Clientid(nfs_client_id4) :
: ------------------------------> :
: : Prepost
: Clientid reply(clientid, ...) : receive
: <------------------------------ :
Prepost : :
receive : Create Session(clientid, size S, :
: maxreq N, RDMA ...) :
: ------------------------------> :
: : Prepost <=N'
: Session reply(sessionid, size S', : receives of
: maxreq N') : size S'
: <------------------------------ :
: :
: <normal operation> :
: ------------------------------> :
: <------------------------------ :
: : :
2.4. Buffer Management, Transfer, Flow Control
Inline operations in NFSv4.1 behave effectively the same as TCP
sends. Procedure results are passed in a single message, and its
completion at the client signal the receiving process to inspect
the message.
RDMA operations are performed solely by the server in this
proposal, as described in the previous "RDMA Direct Model" section.
Since server RDMA operations do not result in a completion at the
client, and due to ordering rules in RDMA transports, after all
required RDMA operations are complete, a Send (Send with Solicited
Event for iWARP) containing the procedure results is performed from
server to client. This Send operation will result in a completion
which will signal the client to inspect the message.
In the case of client read-type NFSv4 operations, the server will
have issued RDMA Writes to transfer the resulting data into client-
advertised buffers. The subsequent Send operation performs two
necessary functions: finalizing any active or pending DMA at the
client, and signaling the client to inspect the message.
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In the case of client write-type NFSv4 operations, the server will
have issued RDMA Reads to fetch the data from the client-advertised
buffers. No data consistency issues arise at the client, but the
completion of the transfer must be acknowledged, again by a Send
from server to client.
In either case, the client advertises buffers for direct (RDMA
style) operations. The client may desire certain advertisement
limits, and may wish the server to perform remote invalidation on
its behalf when the server has completed its RDMA. This may be
considered in a future version of this draft.
In the absence of remote invalidation, the client may perform its
own, local invalidation after the operation completes. This
invalidation should occur prior to any RPCSEC GSS integrity
checking, since a validly remotely accessible buffer can possibly
be modified by the peer. However, after invalidation and the
contents integrity checked, the contents are locally secure.
Credit updates over RDMA transports are supported at the RPC layer
as described in [RPCRDMA]. In each request, the client requests a
desired number of credits to be made available to the connection on
which it sends the request. The client must not send more requests
than the number which the server has previously advertised, or in
the case of the first request, only one. If the client exceeds its
credit limit, the connection may close with a fatal RDMA error.
The server then executes the request, and replies with an updated
credit count accompanying its results. Since replies are sequenced
by their RDMA Send order, the most recent results always reflect
the server's limit. In this way the client will always know the
maximum number of requests it may safely post.
Because the client requests an arbitrary credit count in each
request, it is relatively easy for the client to request more, or
fewer, credits to match its expected need. A client that
discovered itself frequently queuing outgoing requests due to lack
of server credits might increase its requested credits
proportionately in response. Or, a client might have a simple,
configurable number. The protocol also provides a per-operation
"maxslot" exchange to assist in dynamic adjustment at the session
level, described in a later section.
Occasionally, a server may wish to reduce the total number of
credits it offers a certain client on a connection. This could be
encountered if a client were found to be consuming its credits
slowly, or not at all. A client might notice this itself, and
reduce its requested credits in advance, for instance requesting
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only the count of operations it currently has queued, plus a few as
a base for starting up again. Such mechanisms can, however, be
potentially complicated and are implementation-defined. The
protocol does not require them.
Because of the way in which RDMA fabrics function, it is not
possible for the server (or client back channel) to cancel
outstanding receive operations. Therefore, effectively only one
credit can be withdrawn per receive completion. The server (or
client back channel) would simply not replenish a receive operation
when replying. The server can still reduce the available credit
advertisement in its replies to the target value it desires, as a
hint to the client that its credit target is lower and it should
expect it to be reduced accordingly. Of course, even if the server
could cancel outstanding receives, it cannot do so, since the
client may have already sent requests in expectation of the
previous limit.
This brings out an interesting scenario similar to the client
reconnect discussed earlier in "Connection Models". How does the
server reduce the credits of an inactive client?
One approach is for the server to simply close such a connection
and require the client to reconnect at a new credit limit. This is
acceptable, if inefficient, when the connection setup time is short
and where the server supports persistent session semantics.
A better approach is to provide a back channel request to return
the operations channel credits. The server may request the client
to return some number of credits, the client must comply by
performing operations on the operations channel, provided of course
that the request does not drop the client's credit count to zero
(in which case the connection would deadlock). If the client finds
that it has no requests with which to consume the credits it was
previously granted, it must send zero-length Send RDMA operations,
or NULL NFSv4 operations in order to return the resources to the
server. If the client fails to comply in a timely fashion, the
server can recover the resources by breaking the connection.
While in principle, the back channel credits could be subject to a
similar resource adjustment, in practice this is not an issue,
since the back channel is used purely for control and is expected
to be statically provisioned.
It is important to note that in addition to maximum request counts,
the sizes of buffers are negotiated per-session. This permits the
most efficient allocation of resources on both peers. There is an
important requirement on reconnection: the sizes posted by the
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server at reconnect must be at least as large as previously used,
to allow recovery. Any replies that are replayed from the server's
duplicate request cache must be able to be received into client
buffers. In the case where a client has received replies to all
its retried requests (and therefore received all its expected
responses), then the client may disconnect and reconnect with
different buffers at will, since no cache replay will be required.
2.5. Retry and Replay
NFSv4.0 forbids retransmission on active connections over reliable
transports; this includes connected-mode RDMA. This restriction
must be maintained in NFSv4.1.
If one peer were to retransmit a request (or reply), it would
consume an additional credit on the other. If the server
retransmitted a reply, it would certainly result in an RDMA
connection loss, since the client would typically only post a
single receive buffer for each request. If the client
retransmitted a request, the additional credit consumed on the
server might lead to RDMA connection failure unless the client
accounted for it and decreased its available credit, leading to
wasted resources.
RDMA credits present a new issue to the duplicate request cache in
NFSv4.1. The request cache may be used when a connection within a
session is lost, such as after the client reconnects. Credit
information is a dynamic property of the connection, and stale
values must not be replayed from the cache. This implies that the
request cache contents must not be blindly used when replies are
issued from it, and credit information appropriate to the channel
must be refreshed by the RPC layer.
Finally, RDMA fabrics do not guarantee that the memory handles
(Steering Tags) within each rdma three-tuple are valid on a scope
outside that of a single connection. Therefore, handles used by
the direct operations become invalid after connection loss. The
server must ensure that any RDMA operations which must be replayed
from the request cache use the newly provided handle(s) from the
most recent request.
2.6. The Back Channel
The NFSv4 callback operations present a significant resource
problem for the RDMA enabled client. Clearly, callbacks must be
negotiated in the way credits are for the ordinary operations
channel for requests flowing from client to server. But, for
callbacks to arrive on the same RDMA endpoint as operation replies
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would require dedicating additional resources, and specialized
demultiplexing and event handling. Or, callbacks may not require
RDMA sevice at all (they do not normally carry substantial data
payloads). It is highly desirable to streamline this critical path
via a second communications channel.
The session callback channel binding facility is designed for
exactly such a situation, by dynamically associating a new
connected endpoint with the session, and separately negotiating
sizes and counts for active callback channel operations. The
binding operation is firewall-friendly since it does not require
the server to initiate the connection.
This same method serves as well for ordinary TCP connection mode.
It is expected that all NFSv4.1 clients may make use of the session
facility to streamline their design.
The back channel functions exactly the same as the operations
channel except that no RDMA operations are required to perform
transfers, instead the sizes are required to be sufficiently large
to carry all data inline, and of course the client and server
reverse their roles with respect to which is in control of credit
management. The same rules apply for all transfers, with the
server being required to flow control its callback requests.
The back channel is optional. If not bound on a given session, the
server must not issue callback operations to the client. This in
turn implies that such a client must never put itself in the
situation where the server will need to do so, lest the client lose
its connection by force, or its operation be incorrect. For the
same reason, if a back channel is bound, the client is subject to
revocation of its delegations if the back channel is lost. Any
connection loss should be corrected by the client as soon as
possible.
This can be convenient for the NFSv4.1 client; if the client
expects to make no use of back channel facilities such as
delegations, then there is no need to create it. This may save
significant resources and complexity at the client.
For these reasons, if the client wishes to use the back channel,
that channel must be bound first, before using the operations
channel. In this way, the server will not find itself in a
position where it will send callbacks on the operations channel
when the client is not prepared for them.
There is one special case, that where the back channel is bound in
fact to the operations channel's connection. This configuration
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would be used normally over a TCP stream connection to exactly
implement the NFSv4.0 behavior, but over RDMA would require complex
resource and event management at both sides of the connection. The
server is not required to accept such a bind request on an RDMA
connection for this reason, though it is recommended.
2.7. COMPOUND Sizing Issues
Very large responses may pose duplicate request cache issues.
Since servers will want to bound the storage required for such a
cache, the unlimited size of response data in COMPOUND may be
troublesome. If COMPOUND is used in all its generality, then the
inclusion of certain non-idempotent operations within a single
COMPOUND request may render the entire request non-idempotent.
(For example, a single COMPOUND request which read a file or
symbolic link, then removed it, would be obliged to cache the data
in order to allow identical replay). Therefore, many requests
might include operations that return any amount of data.
It is not satisfactory for the server to reject COMPOUNDs at will
with NFS4ERR_RESOURCE when they pose such difficulties for the
server, as this results in serious interoperability problems.
Instead, any such limits must be explicitly exposed as attributes
of the session, ensuring that the server can explicitly support any
duplicate request cache needs at all times.
2.8. Data Alignment
A negotiated data alignment enables certain scatter/gather
optimizations. A facility for this is supported by [RPCRDMA].
Where NFS file data is the payload, specific optimizations become
highly attractive.
Header padding is requested by each peer at session initiation, and
may be zero (no padding). Padding leverages the useful property
that RDMA receives preserve alignment of data, even when they are
placed into anonymous (untagged) buffers. If requested, client
inline writes will insert appropriate pad bytes within the request
header to align the data payload on the specified boundary. The
client is encouraged to be optimistic and simply pad all WRITEs
within the RPC layer to the negotiated size, in the expectation
that the server can use them efficiently.
It is highly recommended that clients offer to pad headers to an
appropriate size. Most servers can make good use of such padding,
which allows them to chain receive buffers in such a way that any
data carried by client requests will be placed into appropriate
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buffers at the server, ready for filesystem processing. The
receiver's RPC layer encounters no overhead from skipping over pad
bytes, and the RDMA layer's high performance makes the insertion
and transmission of padding on the sender a significant
optimization. In this way, the need for servers to perform RDMA
Read to satisfy all but the largest client writes is obviated. An
added benefit is the reduction of message roundtrips on the network
- a potentially good trade, where latency is present.
The value to choose for padding is subject to a number of criteria.
A primary source of variable-length data in the RPC header is the
authentication information, the form of which is client-determined,
possibly in response to server specification. The contents of
COMPOUNDs, sizes of strings such as those passed to RENAME, etc.
all go into the determination of a maximal NFSv4 request size and
therefore minimal buffer size. The client must select its offered
value carefully, so as not to overburden the server, and vice-
versa. The payoff of an appropriate padding value is higher
performance.
Sender gather:
|RPC Request|Pad bytes|Length| -> |User data...|
\------+---------------------/ \
\ \
\ Receiver scatter: \-----------+- ...
/-----+----------------\ \ \
|RPC Request|Pad|Length| -> |FS buffer|->|FS buffer|->...
In the above case, the server may recycle unused buffers to the
next posted receive if unused by the actual received request, or
may pass the now-complete buffers by reference for normal write
processing. For a server which can make use of it, this removes
any need for data copies of incoming data, without resorting to
complicated end-to-end buffer advertisement and management. This
includes most kernel-based and integrated server designs, among
many others. The client may perform similar optimizations, if
desired.
Padding is negotiated by the session creation operation, and
subsequently used by the RPC RDMA layer, as described in [RPCRDMA].
3. NFSv4 Integration
The following section discusses the integration of the proposed
RDMA extensions with NFSv4.0.
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3.1. Minor Versioning
Minor versioning is the existing facility to extend the NFSv4
protocol, and this proposal takes that approach.
Minor versioning of NFSv4 is relatively restrictive, and allows for
tightly limited changes only. In particular, it does not permit
adding new "procedures" (it permits adding only new "operations").
Interoperability concerns make it impossible to consider additional
layering to be a minor revision. This somewhat limits the changes
that can be proposed when considering extensions.
To support the duplicate request cache integrated with sessions and
request control, it is desirable to tag each request with an
identifier to be called a Slotid. This identifier must be passed
by NFSv4 when running atop any transport, including traditional
TCP. Therefore it is not desirable to add the Slotid to a new RPC
transport, even though such a transport is indicated for support of
RDMA. This draft and [RPCRDMA] do not propose such an approach.
Instead, this proposal conforms to the requirements of NFSv4 minor
versioning, through the use of a new operation within NFSv4
COMPOUND procedures as detailed below.
If sessions are in use for a given clientid, this same clientid
cannot be used for non-session NFSv4 operation, including NFSv4.0.
Because the server will have allocated session-specific state to
the active clientid, it would be an unnecessary burden on the
server implementor to support and account for additional, non-
session traffic, in addition to being of no benefit. Therefore
this proposal prohibits a single clientid from doing this.
Nevertheless, employing a new clientid for such traffic is
supported.
3.2. Slot Identifiers and Server Duplicate Request Cache
The presence of deterministic maximum request limits on a session
enables in-progress requests to be assigned unique values with
useful properties.
The RPC layer provides a transaction ID (xid), which, while
required to be unique, is not especially convenient for tracking
requests. The transaction ID is only meaningful to the issuer
(client), it cannot be interpreted at the server except to test for
equality with previously issued requests. Because RPC operations
may be completed by the server in any order, many transaction IDs
may be outstanding at any time. The client may therefore perform a
computationally expensive lookup operation in the process of
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demultiplexing each reply.
In the proposal, there is a limit to the number of active requests.
This immediately enables a convenient, computationally efficient
index for each request which is designated as a Slot Identifier, or
slotid.
When the client issues a new request, it selects a slotid in the
range 0..N-1, where N is the server's current "totalrequests" limit
granted the client on the session over which the request is to be
issued. The slotid must be unused by any of the requests which the
client has already active on the session. "Unused" here means the
client has no outstanding request for that slotid. Because the
slot id is always an integer in the range 0..N-1, client
implementations can use the slotid from a server response to
efficiently match responses with outstanding requests, such as, for
example, by using the slotid to index into a outstanding request
array. This can be used to avoid expensive hashing and lookup
functions in the performace-critical receive path.
The sequenceid, which accompanies the slotid in each request, is
important for a second, important check at the server: it must be
able to be determined efficiently whether a request using a certain
slotid is a retransmit or a new, never-before-seen request. It is
not feasible for the client to assert that it is retransmitting to
implement this, because for any given request the client cannot
know the server has seen it unless the server actually replies. Of
course, if the client has seen the server's reply, the client would
not retransmit!
The sequenceid must increase monotonically for each new transmit of
a given slotid, and must remain unchanged for any retransmission.
The server must in turn compare each newly received request's
sequenceid with the last one previously received for that slotid,
to see if the new request is:
o A new request, in which the sequenceid is greater than that
previously seen in the slot (accounting for sequence
wraparound). The server proceeds to execute the new request.
o A retransmitted request, in which the sequenceid is equal to
that last seen in the slot. Note that this request may be
either complete, or in progress. The server performs replay
processing in these cases.
o A misordered duplicate, in which the sequenceid is less than
that previously seen in the slot. The server must drop the
incoming request, which may imply dropping the connection if
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the transport is reliable, as dictated by section 3.1.1 of
[RFC3530].
This last condition is possible on any connection, not just
unreliable, unordered transports. Delayed behavior on abandoned
TCP connections which are not yet closed at the server, or
pathological client implementations can cause it, among other
causes. Therefore, the server may wish to harden itself against
certain repeated occurrences of this, as it would for
retransmissions in [RFC3530].
It is recommended, though not necessary for protocol correctness,
that the client simply increment the sequenceid by one for each new
request on each slotid. This reduces the wraparound window to a
minimum, and is useful for tracing and avoidance of possible
implementation errors.
The client may however, for implementation-specific reasons, choose
a different algorithm. For example it might maintain a single
sequence space for all slots in the session - e.g. employing the
RPC XID itself. The sequenceid, in any case, is never interpreted
by the server for anything but to test by comparison with
previously seen values.
The server may thereby use the slotid, in conjunction with the
sessionid and sequenceid, within the SEQUENCE portion of the
request to maintain its duplicate request cache (DRC) for the
session, as opposed to the traditional approach of ONC RPC
applications that use the XID along with certain transport
information [RW96].
Unlike the XID, the slotid is always within a specific range; this
has two implications. The first implication is that for a given
session, the server need only cache the results of a limited number
of COMPOUND requests. The second implication derives from the
first, which is unlike XID-indexed DRCs, the slotid DRC by its
nature cannot be overflowed. Through use of the sequenceid to
identify retransmitted requests, it is notable that the server does
not need to actually cache the request itself, reducing the storage
requirements of the DRC further. These new facilities makes it
practical to maintain all the required entries for an effective
DRC.
The slotid and sequenceid therefore take over the traditional role
of the port number in the server DRC implementation, and the
session replaces the IP address. This approach is considerably
more portable and completely robust - it is not subject to the
frequent reassignment of ports as clients reconnect over IP
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networks. In addition, the RPC XID is not used in the reply cache,
enhancing robustness of the cache in the face of any rapid reuse of
XIDs by the client.
It is required to encode the slotid information into each request
in a way that does not violate the minor versioning rules of the
NFSv4.0 specification. This is accomplished here by encoding it in
a control operation within each NFSv4.1 COMPOUND and CB_COMPOUND
procedure. The operation easily piggybacks within existing
messages. The implementation section of this document describes
the specific proposal.
In general, the receipt of a new sequenced request arriving on any
valid slot is an indication that the previous DRC contents of that
slot may be discarded. In order to further assist the server in
slot management, the client is required to use the lowest available
slot when issuing a new request. In this way, the server may be
able to retire additional entries.
However, in the case where the server is actively adjusting its
granted maximum request count to the client, it may not be able to
use receipt of the slotid to retire cache entries. The slotid used
in an incoming request may not reflect the server's current idea of
the client's session limit, because the request may have been sent
from the client before the update was received. Therefore, in the
downward adjustment case, the server may have to retain a number of
duplicate request cache entries at least as large as the old value,
until operation sequencing rules allow it to infer that the client
has seen its reply.
The SEQUENCE (and CB_SEQUENCE) operation also carries a "maxslot"
value which carries additional client slot usage information. The
client must always provide its highest-numbered outstanding slot
value in the maxslot argument, and the server may reply with a new
recognized value. The client should in all cases provide the most
conservative value possible, although it can be increased somewhat
above the actual instantaneous usage to maintain some minimum or
optimal level. This provides a way for the client to yield unused
request slots back to the server, which in turn can use the
information to reallocate resources. Obviously, maxslot can never
be zero, or the session would deadlock.
The server also provides a target maxslot value to the client,
which is an indication to the client of the maxslot the server
wishes the client to be using. This permits the server to withdraw
(or add) resources from a client that has been found to not be
using them, in order to more fairly share resources among a varying
level of demand from other clients. The client must always comply
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with the server's value updates, since they indicate newly
established hard limits on the client's access to session
resources. However, because of request pipelining, the client may
have active requests in flight reflecting prior values, therefore
the server must not immediately require the client to comply.
It is worthwhile to note that Sprite RPC [BW87] defined a "channel"
which in some ways is similar to the slotid proposed here. Sprite
RPC used channels to implement parallel request processing and
request/response cache retirement.
3.3. COMPOUND and CB_COMPOUND
Support for per-operation control can be piggybacked onto NFSv4
COMPOUNDs with full transparency, by placing such facilities into
their own, new operation, and placing this operation first in each
COMPOUND under the new NFSv4 minor protocol revision. The contents
of the operation would then apply to the entire COMPOUND.
Recall that the NFSv4 minor revision is contained within the
COMPOUND header, encoded prior to the COMPOUNDed operations. By
simply requiring that the new operation always be contained in
NFSv4 minor COMPOUNDs, the control protocol can piggyback perfectly
with each request and response.
In this way, the NFSv4 RDMA Extensions may stay in compliance with
the minor versioning requirements specified in section 10 of
[RFC3530].
Referring to section 13.1 of the same document, the proposed
session-enabled COMPOUND and CB_COMPOUND have the form:
+-----+--------------+-----------+------------+-----------+----
| tag | minorversion | numops | control op | op + args | ...
| | (== 1) | (limited) | + args | |
+-----+--------------+-----------+------------+-----------+----
and the reply's structure is:
+------------+-----+--------+-------------------------------+--//
|last status | tag | numres | status + control op + results | //
+------------+-----+--------+-------------------------------+--//
//-----------------------+----
// status + op + results | ...
//-----------------------+----
The single control operation within each NFSv4.1 COMPOUND defines
the context and operational session parameters which govern that
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COMPOUND request and reply. Placing it first in the COMPOUND
encoding is required in order to allow its processing before other
operations in the COMPOUND.
3.4. eXternal Data Representation Efficiency
RDMA is a copy avoidance technology, and it is important to
maintain this efficiency when decoding received messages.
Traditional XDR implementations frequently use generated
unmarshaling code to convert objects to local form, incurring a
data copy in the process (in addition to subjecting the caller to
recursive calls, etc). Often, such conversions are carried out
even when no size or byte order conversion is necessary.
It is recommended that implementations pay close attention to the
details of memory referencing in such code. It is far more
efficient to inspect data in place, using native facilities to deal
with word size and byte order conversion into registers or local
variables, rather than formally (and blindly) performing the
operation via fetch, reallocate and store.
Of particular concern is the result of the READDIR operation, in
which such encoding abounds.
3.5. Effect of Sessions on Existing Operations
The use of a session replaces the use of the SETCLIENTID and
SETCLIENTID_CONFIRM operations, and allows certain simplification
of the RENEW and callback addressing mechanisms in the base
protocol.
The cb_program and cb_location which are obtained by the server in
SETCLIENTID_CONFIRM must not be used by the server, because the
NFSv4.1 client performs callback channel designation with
BIND_BACKCHANNEL. Therefore the SETCLIENTID and
SETCLIENTID_CONFIRM operations becomes obsolete when sessions are
in use, and a server should return an error to NFSv4.1 clients
which might issue either operation.
Another favorable result of the session is that the server is able
to avoid requiring the client to perform OPEN_CONFIRM operations.
The existence of a reliable and effective DRC means that the server
will be able to determine whether an OPEN request carrying a
previously known open_owner from a client is or is not a
retransmission. Because of this, the server no longer requires
OPEN_CONFIRM to verify whether the client is retransmitting an open
request. This in turn eliminates the server's reason for
requesting OPEN_CONFIRM - the server can simply replace any
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previous information on this open_owner. Client OPEN operations
are therefore streamlined, reducing overhead and latency through
avoiding the additional OPEN_CONFIRM exchange.
Since the session carries the client liveness indication with it
implicitly, any request on a session associated with a given client
will renew that client's leases. Therefore the RENEW operation is
made unnecessary when a session is present, as any request
(including a SEQUENCE operation with or without additional NFSv4
operations) performs its function. It is possible (though this
proposal does not make any recommendation) that the RENEW operation
could be made obsolete.
An interesting issue arises however if an error occurs on such a
SEQUENCE operation. If the SEQUENCE operation fails, perhaps due
to an invalid slotid or other non-renewal-based issue, the server
may or may not have performed the RENEW. In this case, the state
of any renewal is undefined, and the client should make no
assumption that it has been performed. In practice, this should
not occur but even if it did, it is expected the client would
perform some sort of recovery which would result in a new,
successful, SEQUENCE operation being run and the client assured
that the renewal took place.
3.6. Authentication Efficiencies
NFSv4 requires the use of the RPCSEC_GSS ONC RPC security flavor
[RFC2203] to provide authentication, integrity, and privacy via
cryptography. The server dictates to the client the use of
RPCSEC_GSS, the service (authentication, integrity, or privacy),
and the specific GSS-API security mechanism that each remote
procedure call and result will use.
If the connection's integrity is protected by an additional means
than RPCSEC_GSS, such as via IPsec, then the use of RPCSEC_GSS's
integrity service is nearly redundant (See the Security
Considerations section for more explanation of why it is "nearly"
and not completely redundant). Likewise, if the connection's
privacy is protected by additional means, then the use of both
RPCSEC_GSS's integrity and privacy services is nearly redundant.
Connection protection schemes, such as IPsec, are more likely to be
implemented in hardware than upper layer protocols like RPCSEC_GSS.
Hardware-based cryptography at the IPsec layer will be more
efficient than software-based cryptography at the RPCSEC_GSS layer.
When transport integrity can be obtained, it is possible for server
and client to downgrade their per-operation authentication, after
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an appropriate exchange. This downgrade can in fact be as complete
as to establish security mechanisms that have zero cryptographic
overhead, effectively using the underlying integrity and privacy
services provided by transport.
Based on the above observations, a new GSS-API mechanism, called
the Channel Conjunction Mechanism [CCM], is being defined. The CCM
works by creating a GSS-API security context using as input a
cookie that the initiator and target have previously agreed to be a
handle for GSS-API context created previously over another GSS-API
mechanism.
NFSv4.1 clients and servers should support CCM and they must use as
the cookie the handle from a successful RPCSEC_GSS context creation
over a non-CCM mechanism (such as Kerberos V5). The value of the
cookie will be equal to the handle field of the rpc_gss_init_res
structure from the RPCSEC_GSS specification.
The [CCM] Draft provides further discussion and examples.
4. Security Considerations
The NFSv4 minor version 1 retains all of existing NFSv4 security;
all security considerations present in NFSv4.0 apply to it equally.
Security considerations of any underlying RDMA transport are
additionally important, all the more so due to the emerging nature
of such transports. Examining these issues is outside the scope of
this draft.
When protecting a connection with RPCSEC_GSS, all data in each
request and response (whether transferred inline or via RDMA)
continues to receive this protection over RDMA fabrics [RPCRDMA].
However when performing data transfers via RDMA, RPCSEC_GSS
protection of the data transfer portion works against the
efficiency which RDMA is typically employed to achieve. This is
because such data is normally managed solely by the RDMA fabric,
and intentionally is not touched by software. Therefore when
employing RPCSEC_GSS under CCM, and where integrity protection has
been "downgraded", the cooperation of the RDMA transport provider
is critical to maintain any integrity and privacy otherwise in
place for the session. The means by which the local RPCSEC_GSS
implementation is integrated with the RDMA data protection
facilities are outside the scope of this draft.
It is logical to use the same GSS context on a session's callback
channel as that used on its operations channel(s), particularly
when the connection is shared by both. The client must indicate to
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the server:
- what security flavor(s) to use in the call back. A special
callback flavor might be defined for this.
- if the flavor is RPCSEC_GSS, then the client must have previously
created an RPCSEC_GSS session with the server. The client offers to
the server the the opaque handle<> value from the rpc_gss_init_res
structure, the window size of RPCSEC_GSS sequence numbers, and an
opaque gss_cb_handle.
This exchange can be performed as part of session and clientid
creation, and the issue warrants careful analysis before being
specified.
If the NFS client wishes to maintain full control over RPCSEC_GSS
protection, it may still perform its transfer operations using
either the inline or RDMA transfer model, or of course employ
traditional TCP stream operation. In the RDMA inline case, header
padding is recommended to optimize behavior at the server. At the
client, close attention should be paid to the implementation of
RPCSEC_GSS processing to minimize memory referencing and especially
copying. These are well-advised in any case!
The proposed session callback channel binding improves security
over that provided by NFSv4 for the callback channel. The
connection is client-initiated, and subject to the same firewall
and routing checks as the operations channel. The connection
cannot be hijacked by an attacker who connects to the client port
prior to the intended server. The connection is set up by the
client with its desired attributes, such as optionally securing
with IPsec or similar. The binding is fully authenticated before
being activated.
4.1. Authentication
Proper authentication of the principal which issues any session and
clientid in the proposed NFSv4.1 operations exactly follows the
similar requirement on client identifiers in NFSv4.0. It must not
be possible for a client to impersonate another by guessing its
session identifiers for NFSv4.1 operations, nor to bind a callback
channel to an existing session. To protect against this, NFSv4.0
requires appropriate authentication and matching of the principal
used. This is discussed in Section 16, Security Considerations of
[RFC3530]. The same requirement when using a session identifier
applies to NFSv4.1 here.
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Going beyond NFSv4.0, the presence of a session associated with any
clientid may also be used to enhance NFSv4.1 security with respect
to client impersonation. In NFSv4.0, there are many operations
which carry no clientid, including in particular those which employ
a stateid argument. A rogue client which wished to carry out a
denial of service attack on another client could perform CLOSE,
DELEGRETURN, etc operations with that client's current filehandle,
sequenceid and stateid, after having obtained them from
eavesdropping or other approach. Locking and open downgrade
operations could be similarly attacked.
When an NFSv4.1 session is in place for any clientid,
countermeasures are easily applied through use of authentication by
the server. Because the clientid and sessionid must be present in
each request within a session, the server may verify that the
clientid is in fact originating from a principal with the
appropriate authenticated credentials, that the sessionid belongs
to the clientid, and that the stateid is valid in these contexts.
This is in general not possible with the affected operations in
NFSv4.0 due to the fact that the clientid is not present in the
requests.
In the event that authentication information is not available in
the incoming request, for example after a reconnection when the
security was previously downgraded using CCM, the server must
require the client re-establish the authentication in order that
the server may validate the other client-provided context, prior to
executing any operation. The sessionid, present in the newly
retransmitted request, combined with the retransmission detection
enabled by the NFSv4.1 duplicate request cache, are a convenient
and reliable context for the server to use for this contingency.
The server should take care to protect itself against denial of
service attacks in the creation of sessions and clientids. Clients
who connect and create sessions, only to disconnect and never use
them may leave significant state behind. (The same issue applies
to NFSv4.0 with clients who may perform SETCLIENTID, then never
perform SETCLIENTID_CONFIRM.) Careful authentication coupled with
resource checks is highly recommended.
5. IANA Considerations
As a proposal based on minor protocol revision, any new minor
number might be registered and reserved with the agreed-upon
specification. Assigned operation numbers and any RPC constants
might undergo the same process.
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There are no issues stemming from RDMA use itself regarding port
number assignments not already specified by [RFC3530]. Initial
connection is via ordinary TCP stream services, operating on the
same ports and under the same set of naming services.
In the Automatic RDMA connection model described above, it is
possible that a new well-known port, or a new transport type
assignment (netid) as described in [RFC3530], may be desirable.
6. NFSv4 Protocol Extensions
This section specifies details of the extensions to NFSv4 proposed
by this document. Existing NFSv4 operations (under minor version
0) continue to be fully supported, unmodified.
6.1. Operation: CREATECLIENTID - Instantiate Clientid
SYNOPSIS
client -> clientid
ARGUMENT
struct CREATECLIENTID4args {
nfs_client_id4 clientdesc;
};
RESULT
struct CREATECLIENTID4resok {
clientid4 clientid;
verifier4 clientid_confirm;
};
union SETCLIENTID4res switch (nfsstat4 status) {
case NFS4_OK:
CREATECLIENTID4resok resok4;
case NFS4ERR_CLID_INUSE:
void;
default:
void;
};
DESCRIPTION
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The client uses the CREATECLIENTID operation to register a
particular client identifier with the server. The clientid
returned from this operation will be necessary for requests that
create state on the server and will serve as a parent object to
sessions created by the client. In order to verify the clientid it
must first be used as an argument to CREATESESSION.
IMPLEMENTATION
A server's client record is a 5-tuple:
1. clientdesc.id:
The long form client identifier, sent via the client.id
subfield of the CREATECLIENTID4args structure
2. clientdesc.verifier:
A client-specific value used to indicate reboots, sent via the
clientdesc.verifier subfield of the CREATECLIENTID4args
structure
3. principal:
The RPCSEC_GSS principal sent via the RPC headers
4. clientid:
The shorthand client identifier, generated by the server and
returned via the clientid field in the CREATECLIENTID4resok
structure
5. confirmed:
A private field on the server indicating whether or not a
client record has been confirmed. A client record is
confirmed if there has been a successful CREATESESSION
operation to confirm it. Otherwise it is unconfirmed. An
unconfirmed record is established by a CREATECLIENTID call.
Any unconfirmed record that is not confirmed within a lease
period may be removed.
The following identifiers represent special values for the fields
in the records.
id_arg:
The value of the clientdesc.id subfield of the
CREATECLIENTID4args structure of the current request.
verifier_arg:
The value of the clientdesc.verifier subfield of the
CREATECLIENTID4args structure of the current request.
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old_verifier_arg:
A value of the clientdesc.verifier field of a client record
received in a previous request; this is distinct from
verifier_arg.
principal_arg:
The value of the RPCSEC_GSS principal for the current request.
old_principal_arg:
A value of the RPCSEC_GSS principal received for a previous
request. This is distinct from principal_arg.
clientid_ret:
The value of the clientid field the server will return in the
CREATECLIENTID4resok structure for the current request.
old_clientid_ret:
The value of the clientid field the server returned in the
CREATECLIENTID4resok structure for a previous request. This
is distinct from clientid_ret.
Since CREATECLIENTID is a non-idempotent operation, we must
consider the possibility that replays may occur as a result of a
client reboot, network partition, malfunctioning router, etc.
Replays are identified by the value of the client field of
CREATECLIENTID4args and the method for dealing with them is
outlined in the scenarios below.
The scenarios are described in terms of what client records whose
clientdesc.id subfield have value equal to id_arg exist in the
server's set of client records. Any cases in which there is more
than one record with identical values for id_arg represent a server
implementation error. Operation in the potential valid cases is
summarized as follows.
1) Common case
If no client records with clientdesc.id matching id_arg exist,
a new shorthand client identifier clientid_ret is generated,
and the following unconfirmed record is added to the server's
state.
{ id_arg, verifier_arg, principal_arg, clientid_ret, FALSE }
Subsequently, the server returns clientid_ret.
2) Router Replay
If the server has the following confirmed record, then this
request is likely the result of a replayed request due to a
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faulty router or lost connection.
{ id_arg, verifier_arg, principal_arg, clientid_ret, TRUE }
Since the record has been confirmed, the client must have
received the server's reply from the initial CREATECLIENTID
request. Since this is simply a spurious request, there is no
modification to the server's state, and the server makes no
reply to the client.
3) Client Collision
If the server has the following confirmed record, then this
request is likely the result of a chance collision between the
values of the clientdesc.id subfield of CREATECLIENTID4args
for two different clients.
{ id_arg, *, old_principal_arg, clientid_ret, TRUE }
Since the value of the clientdesc.id subfield of each client
record must be unique, there is no modification of the
server's state, and NFS4ERR_CLID_INUSE is returned to indicate
the client should retry with a different value for the
clientdesc.id subfield of CREATECLIENTID4args.
This scenario may also represent a malicious attempt to
destroy a client's state on the server. For security reasons,
the server MUST NOT remove the client's state when there is a
principal mismatch.
4) Replay
If the server has the following unconfirmed record then this
request is likely the result of a client replay due to a
network partition or some other connection failure.
{ id_arg, verifier_arg, principal_arg, clientid_ret, FALSE }
Since the response to the CREATECLIENTID request that created
this record may have been lost, it is not acceptable to drop
this duplicate request. However, rather than processing it
normally, the existing record is left unchanged and
clientid_ret, which was generated for the previous request, is
returned.
5) Change of Principal
If the server has the following unconfirmed record then this
request is likely the result of a client which has for
whatever reasons changed principals (possibly to change
security flavor) after calling CREATECLIENTID, but before
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calling CREATESESSION.
{ id_arg, verifier_arg, old_principal_arg, clientid_ret, FALSE}
Since the client has not changed, the principal field of the
unconfirmed record is updated to principal_arg and
clientid_ret is again returned. There is a small possibility
that this is merely a collision on the client field of
CREATECLIENTID4args between unrelated clients, but since that
is unlikely, and an unconfirmed record does not generally have
any filesystem pertinent state, we can assume it is the same
client without risking loss of any important state.
After processing, the following record will exist on the
server.
{ id_arg, verifier_arg, principal_arg, clientid_ret, FALSE}
6) Client Reboot
If the server has the following confirmed client record, then
this request is likely from a previously confirmed client
which has rebooted.
{ id_arg, old_verifier_arg, principal_arg, clientid_ret, TRUE }
Since the previous incarnation of the same client will no
longer be making requests, lock and share reservations should
be released immediately rather than forcing the new
incarnation to wait for the lease time on the previous
incarnation to expire. Furthermore, session state should be
removed since if the client had maintained that information
across reboot, this request would not have been issued. If
the server does not support the CLAIM_DELEGATE_PREV claim
type, associated delegations should be purged as well;
otherwise, delegations are retained and recovery proceeds
according to RFC3530. The client record is updated with the
new verifier and its status is changed to unconfirmed.
After processing, clientid_ret is returned to the client and
the following record will exist on the server.
{ id_arg, verifier_arg, principal_arg, clientid_ret, FALSE }
7) Reboot before confirmation
If the server has the following unconfirmed record, then this
request is likely from a client which rebooted before sending
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a CREATESESSION request.
{ id_arg, old_verifier_arg, *, clientid_ret, FALSE }
Since this is believed to be a request from a new incarnation
of the original client, the server updates the value of
clientdesc.verifier and returns the original clientid_ret.
After processing, the following state exists on the server.
{ id_arg, verifier_arg, *, clientid_ret, FALSE }
ERRORS
NFS4ERR_BADXDR
NFS4ERR_CLID_INUSE
NFS4ERR_INVAL
NFS4ERR_RESOURCE
NFS4ERR_SERVERFAULT
6.2. Operation: CREATESESSION - Create New Session and Confirm Clientid
SYNOPSIS
clientid, session_args -> sessionid, session_args
ARGUMENT
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struct CREATESESSION4args {
clientid4 clientid;
bool persist;
count4 maxrequestsize;
count4 maxresponsesize;
count4 maxrequests;
count4 headerpadsize;
switch (bool clientid_confirm) {
case TRUE:
verifier4 setclientid_confirm;
case FALSE:
void;
}
switch (channelmode4 mode) {
case DEFAULT:
void;
case STREAM:
streamchannelattrs4 streamchanattrs;
case RDMA:
rdmachannelattrs4 rdmachanattrs;
};
};
RESULT
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typedef opaque sessionid4[16];
struct CREATESESSION4resok {
sessionid4 sessionid;
bool persist;
count4 maxrequestsize;
count4 maxresponsesize;
count4 maxrequests;
count4 headerpadsize;
switch (channelmode4 mode) {
case DEFAULT:
void;
case STREAM:
streamchannelattrs4 streamchanattrs;
case RDMA:
rdmachannelattrs4 rdmachanattrs;
};
};
union CREATESESSION4res switch (nfsstat4 status) {
case NFS4_OK:
CREATESESSION4resok resok4;
default:
void;
};
DESCRIPTION
This operation is used by the client to create new session objects
on the server. Additionally the first session created with a new
shorthand client identifier serves to confirm the creation of that
client's state on the server. The server returns the parameter
values for the new session.
IMPLEMENTATION
To describe the implementation, the same notation for client
records introduced in the description of CREATECLIENTID is used
with the following addition.
clientid_arg:
The value of the clientid field of the CREATESESSION4args
structure of the current request.
Since CREATESESSION is a non-idempotent operation, we must consider
the possibility that replays may occur as a result of a client
reboot, network partition, malfunctioning router, etc. Replays are
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identified by the value of the clientid and sessionid fields of
CREATESESSION4args and the method for dealing with them is outlined
in the scenarios below.
The processing of this operation is divided into two phases:
clientid confirmation and session creation. In case the state for
the provided clientid has not been verified, it is confirmed before
the session is created. Otherwise the clientid confirmation phase
is skipped and only the session creation phase occurs. Note that
since only confirmed clients may create sessions, the clientid
confirmation stage does not depend upon sessionid_arg.
CLIENTID CONFIRMATION
The operational cases are described in terms of what client records
whose clientid field have value equal to clientid_arg exist in the
server's set of client records. Any cases in which there is more
than one record with identical values for clientid represent a
server implementation error. Operation in the potential valid
cases is summarized as follows.
1) Common Case
If the server has the following unconfirmed record, then this
is the expected confirmation of an unconfirmed record.
{ *, *, principal_arg, clientid_arg, FALSE }
The confirmed field of the record is set to TRUE and
processing of the operation continues normally.
2) Stale Clientid
If the server contains no records with clientid equal to
clientid_arg, then most likely the client's state has been
purged during a period of inactivity, possibly due to a loss
of connectivity. NFS4ERR_STALE_CLIENTID is returned, and no
changes are made to any client records on the server.
3) Principal Change or Collision
If the server has the following record, then the client has
changed principals after the previous CREATECLIENTID request,
or there has been a chance collision between shortand client
identifiers.
{ *, *, old_principal_arg, clientid_arg, * }
Neither of these cases are permissible. Processing stops and
NFS4ERR_CLID_INUSE is returned to the client. No changes are
made to any client records on the server.
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SESSION CREATION
To determine whether this request is a replay, the server examines
the sessionid argument provided by the client. If the sessionid
matches the identifier of a previously created session, then this
request must be interpreted as a replay. No new state is created
and a reply with the parameters of the existing session is returned
to the client. If a session corresponding to the sessionid does
not already exist, then the request is not a replay and is
processed as follows.
NOTE: It is the responsibility of the client to generate
appropriate values for sessionid. Since the ordering of messages
sent on different transport connections is not guaranteed,
immediately reusing the sessionid of a previously destroyed session
may yield unpredictable results. Client implementations should
avoid recently used sessionids to ensure correct behavior.
The server examines the persist, maxrequestsize, maxresponsesize,
maxrequests and headerpadsize arguments. For each argument, if the
value is acceptable to the server, it is recommended that the
server use the provided value to create the new session. If it is
not acceptable, the server may use a different value, but must
return the value used to the client. These parameters have the
following interpretation.
persist:
True if the client desires server support for "reliable"
semantics. For sessions in which only idempotent operations
will be used (e.g. a read-only session), clients should set
this value to false. If the server does not or cannot provide
"reliable" semantics this value must be set to false on
return.
maxrequestsize:
The maximum size of a COMPOUND request that will be sent by
the client including RPC headers.
maxresponsesize:
The maximum size of a COMPOUND reply that the client will
accept from the server including RPC headers. The server must
not increase the value of this parameter. If a client sends a
COMPOUND request for which the size of the reply would exceed
this value, the server will return NFS4ERR_RESOURCE.
maxrequests:
The maximum number of concurrent COMPOUND requests that the
client will issue on the session. Subsequent COMPOUND
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requests will each be assigned a slot identifier by the client
on the range 0 to maxrequests - 1 inclusive. A slot id cannot
be reused until the previous request on that slot has
completed.
headerpadsize:
The maximum amount of padding the client is willing to apply
to ensure that write payloads are aligned on some boundary at
the server. The server should reply with its preferred value,
or zero if padding is not in use. The server may decrease
this value but must not increase it.
The server creates the session by recording the parameter values
used and if the persist parameter is true and has been accepted by
the server, allocating space for the duplicate request cache (DRC).
If the session state is created successfully, the server associates
it with the session identifier provided by the client. This
identifier must be unique among the client's active sessions but
there is no need for it to be globally unique. Finally, the server
returns the negotiated values used to create the session to the
client.
ERRORS
NFS4ERR_BADXDR
NFS4ERR_CLID_INUSE
NFS4ERR_RESOURCE
NFS4ERR_SERVERFAULT
NFS4ERR_STALE_CLIENTID
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6.3. Operation: BIND_BACKCHANNEL - Create a callback channel binding
SYNOPSIS
Establish a callback channel on the connection.
ARGUMENTS
struct BIND_BACKCHANNEL4args {
clientid4 clientid;
uint32_t callback_program;
uint32_t callback_ident;
count4 maxrequestsize;
count4 maxresponsesize;
count4 maxrequests;
switch (channelmode4 mode) {
case DEFAULT:
void;
case STREAM:
streamchannelattrs4 streamchanattrs;
case RDMA:
rdmachannelattrs4 rdmachanattrs;
};
};
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RESULTS
struct BIND_BACKCHANNEL4resok {
count4 maxrequestsize;
count4 maxresponsesize;
count4 maxrequests;
switch (channelmode4 mode) {
case DEFAULT:
void;
case STREAM:
streamchannelattrs4 streamchanattrs;
case RDMA:
rdmachannelattrs4 rdmachanattrs;
};
};
union BIND_BACKCHANNEL4res switch (nfsstat4 status) {
case NFS4_OK:
BIND_BACKCHANNEL4resok resok4;
default:
void;
};
DESCRIPTION
The BIND_BACKCHANNEL operation serves to establish the current
connection as a designated callback channel for the specified
session. Normally, only one callback channel is bound, however if
more than one are established, they are used at the server's
prerogative, no affinity or preference is specified by the client.
The arguments and results of the BIND_BACKCHANNEL call are a subset
of the session parameters, and used identically to those values on
the callback channel only. However, not all session operation
channel parameters are relevant to the callback channel, for
example header padding (since writes of bulk data are not performed
in callbacks).
ERRORS
...
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6.4. Operation: DESTROYSESSION - Destroy existing session
SYNOPSIS
void -> status
ARGUMENT
struct DESTROYSESSION4args {
sessionid4 sessionid; };
RESULT
struct SESSION_DESTROYres {
nfsstat status;
};
DESCRIPTION
The SESSION_DESTROY operation closes the session and discards any
active state such as locks, leases, and server duplicate request
cache entries. Any remaining connections bound to the session are
immediately unbound and may additionally be closed by the server.
This operation must be the final, or only operation in any request.
Because the operation results in destruction of the session, any
duplicate request caching for this request, as well as previously
completed requests, will be lost. For this reason, it is advisable
to not place this operation in a request with other state-modifying
operations. In addition, a SEQUENCE operation is not required in
the request.
Note that because the operation will never be replayed by the
server, a client that retransmits the request may receive an error
in response, even though the session may have been successfully
destroyed.
...
ERRORS
<tbd>
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6.5. Operation: SEQUENCE - Supply per-procedure sequencing and control
SYNOPSIS
control -> control
ARGUMENT
typedef uint32_t sequenceid4;
typedef uint32_t slotid4;
struct SEQUENCE4args {
clientid4 clientid;
sessionid4 sessionid;
sequenceid4 sequenceid;
slotid4 slotid;
slotid4 maxslot;
};
RESULT
struct SEQUENCE4resok {
clientid4 clientid;
sessionid4 sessionid;
sequenceid4 sequenceid;
slotid4 slotid;
slotid4 maxslot;
slotid4 target_maxslot;
};
union SEQUENCE4res switch (nfsstat4 status) {
case NFS4_OK:
SEQUENCE4resok resok4;
default:
void;
};
DESCRIPTION
The SEQUENCE operation is used to manage operational accounting for
the session on which the operation is sent. The contents include
the client and session to which this request belongs, slotid and
sequenceid, used by the server to implement session request control
and the duplicate reply cache semantics, and exchanged slot counts
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which are used to adjust these values. This operation must appear
once as the first operation in each COMPOUND sent after the channel
is successfully bound, or a protocol error must result.
...
ERRORS
NFS4ERR_BADSESSION
NFS4ERR_BADSLOT
6.6. Callback operation: CB_RECALLCREDIT - change flow control limits
SYNOPSIS
targetcount -> status
ARGUMENTS
struct CB_RECALLCREDIT4args {
sessionid4 sessionid;
uint32_t target;
};
RESULT
struct CB_RECALLCREDIT4res {
nfsstat4 status;
};
DESCRIPTION
The CB_RECALLCREDIT operation requests the client to return session
and transport credits to the server, by zero-length RDMA Sends or
NULL NFSv4 operations.
...
ERRORS
<none>
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6.7. Callback operation: CB_SEQUENCE - Supply callback channel
sequencing and control
SYNOPSIS
control -> control
ARGUMENT
typedef uint32_t sequenceid4;
typedef uint32_t slotid4;
struct CB_SEQUENCE4args {
clientid4 clientid;
sessionid4 sessionid;
sequenceid4 sequenceid;
slotid4 slotid;
slotid4 maxslot;
};
RESULT
struct CB_SEQUENCE4resok {
clientid4 clientid;
sessionid4 sessionid;
sequenceid4 sequenceid;
slotid4 slotid;
slotid4 maxslot;
slotid4 target_maxslot;
};
union CB_SEQUENCE4res switch (nfsstat4 status) {
case NFS4_OK:
CB_SEQUENCE4resok resok4;
default:
void;
};
DESCRIPTION
The CB_SEQUENCE operation is used to manage operational accounting
for the callback channel of the session on which the operation is
sent. The contents include the client and session to which this
request belongs, slotid and sequenceid, used by the server to
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implement session request control and the duplicate reply cache
semantics, and exchanged slot counts which are used to adjust these
values. This operation must appear once as the first operation in
each CB_COMPOUND sent after the callback channel is successfully
bound, or a protocol error must result.
...
ERRORS
NFS4ERR_BADSESSION
NFS4ERR_BADSLOT
7. NFSv4 Session Protocol Description
This section contains the proposed protocol changes in RPC
description language. The constants named in this section are
illustrative. When the working group decides on the full content
of the NFSv4.1 minor revision, they may change in order to avoid
conflict.
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NFS4ERR_BADSESSION = 10049,/* invalid session */
NFS4ERR_BADSLOT = 10050 /* invalid slotid */
/*
* CREATECLIENTID: v4.1 setclientid for session use
*/
struct CREATECLIENTID4args {
nfs_client_id4 clientdesc;
};
struct CREATECLIENTID4resok {
clientid4 clientid;
verifier4 clientid_confirm;
};
union CREATECLIENTID4res switch (nfsstat4 status) {
case NFS4_OK:
CREATECLIENTID4resok resok4;
default:
void;
};
/*
* Channel attributes - TBD.
*/
enum channelmode4 {
DEFAULT = 0, /* don't change */
STREAM = 1, /* TCP stream */
RDMA = 2 /* upshift to RDMA */
};
struct streamchannelattrs4 {
opaque nothing[0]; /* TBD */
};
struct rdmachannelattrs4 {
count4 maxrdmareads;
/* plus TBD */
};
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/*
* CREATESESSION: v4.1 session creation and optional
* clientid confirm
*/
typedef opaque sessionid4[16];
union optverifier4 switch (bool clientid_confirm) {
case TRUE:
verifier4 setclientid_confirm;
case FALSE:
void;
};
union transportattrs4 switch (channelmode4 mode) {
case DEFAULT:
void;
case STREAM:
streamchannelattrs4 streamchanattrs;
case RDMA:
rdmachannelattrs4 rdmachanattrs;
};
struct CREATESESSION4args {
clientid4 clientid;
bool persist;
count4 maxrequestsize;
count4 maxresponsesize;
count4 maxrequests;
count4 headerpadsize;
optverifier4 verifier;
transportattrs4 transportattrs;
};
struct CREATESESSION4resok {
sessionid4 sessionid;
bool persist;
count4 maxrequestsize;
count4 maxresponsesize;
count4 maxrequests;
count4 headerpadsize;
transportattrs4 transportattrs;
};
union CREATESESSION4res switch (nfsstat4 status) {
case NFS4_OK:
CREATESESSION4resok resok4;
default:
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void;
};
/*
* BIND_BACKCHANNEL: v4.1 callback binding
*/
struct BIND_BACKCHANNEL4args {
clientid4 clientid;
uint32_t callback_program;
uint32_t callback_ident;
count4 maxrequestsize;
count4 maxresponsesize;
count4 maxrequests;
transportattrs4 transportattrs;
};
struct BIND_BACKCHANNEL4resok {
count4 maxrequestsize;
count4 maxresponsesize;
count4 maxrequests;
transportattrs4 transportattrs;
};
union BIND_BACKCHANNEL4res switch (nfsstat4 status) {
case NFS4_OK:
BIND_BACKCHANNEL4resok resok4;
default:
void;
};
/*
* DESTROYSESSION: v4.1 session destruction
*/
struct DESTROYSESSION4args {
sessionid4 sessionid;
};
struct DESTROYSESSION4res {
nfsstat4 status;
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};
/*
* SEQUENCE: v4.1 operation sequence control
*/
typedef uint32_t sequenceid4;
typedef uint32_t slotid4;
struct SEQUENCE4args {
clientid4 clientid;
sessionid4 sessionid;
sequenceid4 sequenceid;
slotid4 slotid;
slotid4 maxslot;
};
struct SEQUENCE4resok {
clientid4 clientid;
sessionid4 sessionid;
sequenceid4 sequenceid;
slotid4 slotid;
slotid4 maxslot;
slotid4 target_maxslot;
};
union SEQUENCE4res switch (nfsstat4 status) {
case NFS4_OK:
struct SEQUENCE4resok resok4;
default:
void;
};
/* Operation values */
OP_CREATECLIENTID = 40,
OP_CREATESESSION = 41,
OP_BIND_BACKCHANNEL= 42,
OP_DESTROYSESSION = 43,
OP_SEQUENCE = 44,
/* Operation arguments */
case OP_CREATECLIENTID:
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CREATECLIENTID4args opcreateclientid;
case OP_CREATESESSION:
CREATESESSION4args opcreatesession;
case OP_BIND_BACKCHANNEL:
BIND_BACKCHANNEL4args opbind_backchannel;
case OP_DESTROYSESSION:
DESTROYSESSION4args opdestroysession;
case OP_SEQUENCE:
SEQUENCE4args opsequence;
/* Operation results */
case OP_CREATECLIENTID:
CREATECLIENTID4res opcreateclientid;
case OP_CREATESESSION:
CREATESESSION4res opcreatesession;
case OP_BIND_BACKCHANNEL:
BIND_BACKCHANNEL4res opbind_backchannel;
case OP_DESTROYSESSION:
DESTROYSESSION4res opdestroysession;
case OP_SEQUENCE:
SEQUENCE4res opsequence;
/*
* CB_RECALLCREDIT: Recall session credits from
* operations channel(s)
*/
struct CB_RECALLCREDIT4args {
sessionid4 sessionid;
uint32_t target;
};
struct CB_RECALLCREDIT4res {
nfsstat4 status;
};
/*
* CB_SEQUENCE: v4.1 operation sequence control
*/
struct CB_SEQUENCE4args {
clientid4 clientid;
sessionid4 sessionid;
sequenceid4 sequenceid;
slotid4 slotid;
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slotid4 maxslot;
};
struct CB_SEQUENCE4resok {
clientid4 clientid;
sessionid4 sessionid;
sequenceid4 sequenceid;
slotid4 slotid;
slotid4 maxslot;
slotid4 target_maxslot;
};
union CB_SEQUENCE4res switch (nfsstat4 status) {
case NFS4_OK:
struct CB_SEQUENCE4resok resok4;
default:
void;
};
/* Operation values */
OP_CB_RECALL_CREDIT = 5,
OP_CB_SEQUENCE = 6
/* Operation arguments */
case OP_CB_RECALLCREDIT:
CB_RECALLCREDIT4args opcbrecallcredit;
case OP_CB_SEQUENCE:
CB_SEQUENCE4args opcbsequence;
/* Operation results */
case OP_CB_RECALLCREDIT:
CB_RECALLCREDIT4res opcbrecallcredit;
case OP_CB_SEQUENCE:
CB_SEQUENCE4res opcbsequence;
8. Acknowledgements
The authors wish to acknowledge the valuable contributions and
review of Charles Antonelli, Brent Callaghan, Mike Eisler, John
Howard, Chet Juszczak, Trond Myklebust, Dave Noveck, John Scott,
Mike Stolarchuk and Mark Wittle.
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9. References
9.1. Normative References
[RFC3530]
S. Shepler, et al., "NFS Version 4 Protocol", Standards Track
RFC, http://www.ietf.org/rfc/rfc3530
9.2. Informative References
[BW87]
B. Welch, "The Sprite Remote Procedure Call System",
University of California Berkeley Technical Report CSD-87-302,
ftp://sunsite.berkeley.edu/pub/techreps/CSD-87-302.html
[CCM]
M. Eisler, N. Williams, "The Channel Conjunction Mechanism
(CCM) for GSS", Internet-Draft Work in Progress,
http://www.ietf.org/internet-drafts/draft-ietf-nfsv4-ccm
[CJ89]
C. Juszczak, "Improving the Performance and Correctness of an
NFS Server," Winter 1989 USENIX Conference Proceedings, USENIX
Association, Berkeley, CA, Februry 1989, pages 53-63.
[DAFS]
Direct Access File System, available from
http://www.dafscollaborative.org
[DCK+03]
M. DeBergalis, P. Corbett, S. Kleiman, A. Lent, D. Noveck, T.
Talpey, M. Wittle, "The Direct Access File System", in
Proceedings of 2nd USENIX Conference on File and Storage
Technologies (FAST '03), San Francisco, CA, March 31 - April
2, 2003
[DDP]
H. Shah, J. Pinkerton, R. Recio, P. Culley, "Direct Data
Placement over Reliable Transports", Internet-Draft Work in
Progress, http://www.ietf.org/internet-drafts/draft-ietf-rddp-
ddp
[FJDAFS]
Fujitsu Prime Software Technologies, "Meet the DAFS
Performance with DAFS/VI Kernel Implementation using cLAN",
http://www.pst.fujitsu.com/english/dafsdemo/index.html
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[FJNFS]
Fujitsu Prime Software Technologies, "An Adaptation of VIA to
NFS on Linux",
http://www.pst.fujitsu.com/english/nfs/index.html
[IB] InfiniBand Architecture Specification, Volume 1, Release 1.1.
available from http://www.infinibandta.org
[KM02]
K. Magoutis, "Design and Implementation of a Direct Access
File System (DAFS) Kernel Server for FreeBSD", in Proceedings
of USENIX BSDCon 2002 Conference, San Francisco, CA, February
11-14, 2002.
[MAF+02]
K. Magoutis, S. Addetia, A. Fedorova, M. Seltzer, J. Chase, D.
Gallatin, R. Kisley, R. Wickremesinghe, E. Gabber, "Structure
and Performance of the Direct Access File System (DAFS)", in
Proceedings of 2002 USENIX Annual Technical Conference,
Monterey, CA, June 9-14, 2002.
[MIDTAX]
B. Carpenter, S. Brim, "Middleboxes: Taxonomy and Issues",
Informational RFC, http://www.ietf.org/rfc/rfc3234
[NFSDDP]
B. Callaghan, T. Talpey, "NFS Direct Data Placement",
Internet-Draft Work in Progress, http://www.ietf.org/internet-
drafts/draft-ietf-nfsv4-nfsdirect
[NFSPS]
T. Talpey, C. Juszczak, "NFS RDMA Problem Statement",
Internet-Draft Work in Progress, http://www.ietf.org/internet-
drafts/draft-ietf-nfsv4-nfs-rdma-problem-statement
[RDDP]
Remote Direct Data Placement Working Group charter,
http://www.ietf.org/html.charters/rddp-charter.html
[RDDPPS]
A. Romanow, J. Mogul, T. Talpey, S. Bailey, Remote Direct Data
Placement Working Group Problem Statement, Standards Track
Informational RFC, http://www.ietf.org/internet-drafts/draft-
ietf-rddp-problem-statement
[RDMAP]
R. Recio, P. Culley, D. Garcia, J. Hilland, "An RDMA Protocol
Specification", Internet-Draft Work in Progress,
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http://www.ietf.org/internet-drafts/draft-ietf-rddp-rdmap
[RPCRDMA]
B. Callaghan, T. Talpey, "RDMA Transport for ONC RPC"
Internet-Draft Work in Progress, http://www.ietf.org/internet-
drafts/draft-ietf-nfsv4-rpcrdma
[RFC2203]
M. Eisler, A. Chiu, L. Ling, "RPCSEC_GSS Protocol
Specification", Standards Track RFC,
http://www.ietf.org/rfc/rfc2203
[RW96]
R. Werme, "RPC XID Issues", Connectathon 1996, San Jose, CA,
http://www.cthon.org/talks96/werme1.pdf
10. Authors' Addresses
Comments on this draft may be sent to the NFSv4 Working Group
(nfsv4@ietf.org) and/or the authors.
Tom Talpey
Network Appliance, Inc.
375 Totten Pond Road
Waltham, MA 02451 USA
Phone: +1 781 768 5329
EMail: thomas.talpey@netapp.com
Spencer Shepler
Sun Microsystems, Inc.
7808 Moonflower Drive
Austin, TX 78750 USA
Phone: +1 512 349 9376
EMail: spencer.shepler@sun.com
Jon Bauman
University of Michigan
Center for Information Technology Integration
535 W. William St. Suite 3100
Ann Arbor, MI 48103 USA
Phone: +1 734 615-4782
Email: baumanj@umich.edu
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11. Full Copyright Statement
Copyright (C) The Internet Society (2005). This document is
subject to the rights, licenses and restrictions contained in BCP
78, and except as set forth therein, the authors retain all their
rights.
This document and the information contained herein are provided on
an "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE
REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND
THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES,
EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT
THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR
ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A
PARTICULAR PURPOSE.
Intellectual Property
The IETF takes no position regarding the validity or scope of any
Intellectual Property Rights or other rights that might be claimed
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Copies of IPR disclosures made to the IETF Secretariat and any
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Acknowledgement
Funding for the RFC Editor function is currently provided by the
Internet Society.
Talpey et al. Expires December 2005 [Page 69]
