[Docs] [txt|pdf] [Tracker] [WG] [Email] [Diff1] [Diff2] [Nits]
Versions: (draft-haynes-nfsv4-minorversion2)
00 01 02 03 04 05 06 07 08 09 10 11
12 13 14 15 16 17 19 20 21 22 23 24
25 26 27 28 29 30 31 32 33 34 35 36
37 38 39 40 41 RFC 7862
NFSv4 T. Haynes
Internet-Draft Editor
Intended status: Standards Track January 04, 2012
Expires: July 7, 2012
NFS Version 4 Minor Version 2
draft-ietf-nfsv4-minorversion2-07.txt
Abstract
This Internet-Draft describes NFS version 4 minor version two,
focusing mainly on the protocol extensions made from NFS version 4
minor version 0 and NFS version 4 minor version 1. Major extensions
introduced in NFS version 4 minor version two include: Server-side
Copy, Space Reservations, and Support for Sparse Files.
Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [1].
Status of this Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on July 7, 2012.
Copyright Notice
Copyright (c) 2012 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
Haynes Expires July 7, 2012 [Page 1]
Internet-Draft NFSv4.2 January 2012
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
This document may contain material from IETF Documents or IETF
Contributions published or made publicly available before November
10, 2008. The person(s) controlling the copyright in some of this
material may not have granted the IETF Trust the right to allow
modifications of such material outside the IETF Standards Process.
Without obtaining an adequate license from the person(s) controlling
the copyright in such materials, this document may not be modified
outside the IETF Standards Process, and derivative works of it may
not be created outside the IETF Standards Process, except to format
it for publication as an RFC or to translate it into languages other
than English.
Haynes Expires July 7, 2012 [Page 2]
Internet-Draft NFSv4.2 January 2012
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 5
1.1. The NFS Version 4 Minor Version 2 Protocol . . . . . . . 5
1.2. Scope of This Document . . . . . . . . . . . . . . . . . 5
1.3. NFSv4.2 Goals . . . . . . . . . . . . . . . . . . . . . . 5
1.4. Overview of NFSv4.2 Features . . . . . . . . . . . . . . 5
1.4.1. Sparse Files . . . . . . . . . . . . . . . . . . . . . 5
1.4.2. Application I/O Advise . . . . . . . . . . . . . . . . 6
1.5. Differences from NFSv4.1 . . . . . . . . . . . . . . . . 6
2. NFS Server-side Copy . . . . . . . . . . . . . . . . . . . . . 6
2.1. Introduction . . . . . . . . . . . . . . . . . . . . . . 6
2.2. Protocol Overview . . . . . . . . . . . . . . . . . . . . 7
2.2.1. Intra-Server Copy . . . . . . . . . . . . . . . . . . 8
2.2.2. Inter-Server Copy . . . . . . . . . . . . . . . . . . 9
2.2.3. Server-to-Server Copy Protocol . . . . . . . . . . . . 12
2.3. Operations . . . . . . . . . . . . . . . . . . . . . . . 14
2.3.1. netloc4 - Network Locations . . . . . . . . . . . . . 14
2.3.2. Copy Offload Stateids . . . . . . . . . . . . . . . . 15
2.4. Security Considerations . . . . . . . . . . . . . . . . . 15
2.4.1. Inter-Server Copy Security . . . . . . . . . . . . . . 15
3. Sparse Files . . . . . . . . . . . . . . . . . . . . . . . . . 24
3.1. Introduction . . . . . . . . . . . . . . . . . . . . . . 24
3.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 24
3.3. Determining the next hole/data . . . . . . . . . . . . . 25
4. Space Reservation . . . . . . . . . . . . . . . . . . . . . . 25
4.1. Introduction . . . . . . . . . . . . . . . . . . . . . . 25
5. Support for Application IO Hints . . . . . . . . . . . . . . . 27
5.1. Introduction . . . . . . . . . . . . . . . . . . . . . . 27
5.2. POSIX Requirements . . . . . . . . . . . . . . . . . . . 28
5.3. Additional Requirements . . . . . . . . . . . . . . . . . 29
5.4. Security Considerations . . . . . . . . . . . . . . . . . 30
5.5. IANA Considerations . . . . . . . . . . . . . . . . . . . 30
6. Application Data Block Support . . . . . . . . . . . . . . . . 30
6.1. Generic Framework . . . . . . . . . . . . . . . . . . . . 31
6.1.1. Data Block Representation . . . . . . . . . . . . . . 31
6.1.2. Data Content . . . . . . . . . . . . . . . . . . . . . 32
6.2. pNFS Considerations . . . . . . . . . . . . . . . . . . . 32
6.3. An Example of Detecting Corruption . . . . . . . . . . . 33
6.4. Example of READ_PLUS . . . . . . . . . . . . . . . . . . 34
6.5. Zero Filled Holes . . . . . . . . . . . . . . . . . . . . 35
7. Labeled NFS . . . . . . . . . . . . . . . . . . . . . . . . . 35
7.1. Introduction . . . . . . . . . . . . . . . . . . . . . . 35
7.2. Definitions . . . . . . . . . . . . . . . . . . . . . . . 36
7.3. MAC Security Attribute . . . . . . . . . . . . . . . . . 37
7.3.1. Interpreting FATTR4_SEC_LABEL . . . . . . . . . . . . 37
7.3.2. Delegations . . . . . . . . . . . . . . . . . . . . . 38
7.3.3. Permission Checking . . . . . . . . . . . . . . . . . 38
Haynes Expires July 7, 2012 [Page 3]
Internet-Draft NFSv4.2 January 2012
7.3.4. Object Creation . . . . . . . . . . . . . . . . . . . 39
7.3.5. Existing Objects . . . . . . . . . . . . . . . . . . . 39
7.3.6. Label Changes . . . . . . . . . . . . . . . . . . . . 39
7.4. pNFS Considerations . . . . . . . . . . . . . . . . . . . 40
7.5. Discovery of Server LNFS Support . . . . . . . . . . . . 40
7.6. MAC Security NFS Modes of Operation . . . . . . . . . . . 41
7.6.1. Full Mode . . . . . . . . . . . . . . . . . . . . . . 41
7.6.2. Smart Client Mode . . . . . . . . . . . . . . . . . . 42
7.6.3. Smart Server Mode . . . . . . . . . . . . . . . . . . 43
7.7. Security Considerations . . . . . . . . . . . . . . . . . 44
8. Sharing change attribute implementation details with NFSv4
clients . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
8.1. Introduction . . . . . . . . . . . . . . . . . . . . . . 44
8.2. Definition of the 'change_attr_type' per-file system
attribute . . . . . . . . . . . . . . . . . . . . . . . . 45
9. Security Considerations . . . . . . . . . . . . . . . . . . . 46
10. File Attributes . . . . . . . . . . . . . . . . . . . . . . . 46
10.1. Attribute Definitions . . . . . . . . . . . . . . . . . . 46
11. Operations: REQUIRED, RECOMMENDED, or OPTIONAL . . . . . . . . 47
12. NFSv4.2 Operations . . . . . . . . . . . . . . . . . . . . . . 50
12.1. Operation 59: COPY - Initiate a server-side copy . . . . 50
12.2. Operation 60: COPY_ABORT - Cancel a server-side copy . . 58
12.3. Operation 61: COPY_NOTIFY - Notify a source server of
a future copy . . . . . . . . . . . . . . . . . . . . . . 59
12.4. Operation 62: COPY_REVOKE - Revoke a destination
server's copy privileges . . . . . . . . . . . . . . . . 62
12.5. Operation 63: COPY_STATUS - Poll for status of a
server-side copy . . . . . . . . . . . . . . . . . . . . 63
12.6. Modification to Operation 42: EXCHANGE_ID -
Instantiate Client ID . . . . . . . . . . . . . . . . . . 64
12.7. Operation 64: INITIALIZE . . . . . . . . . . . . . . . . 65
12.8. Operation 67: IO_ADVISE - Application I/O access
pattern hints . . . . . . . . . . . . . . . . . . . . . . 69
12.9. Changes to Operation 51: LAYOUTRETURN . . . . . . . . . . 75
12.10. Operation 65: READ_PLUS . . . . . . . . . . . . . . . . . 78
12.11. Operation 66: SEEK . . . . . . . . . . . . . . . . . . . 84
13. NFSv4.2 Callback Operations . . . . . . . . . . . . . . . . . 86
13.1. Procedure 16: CB_ATTR_CHANGED - Notify Client that
the File's Attributes Changed . . . . . . . . . . . . . . 86
13.2. Operation 15: CB_COPY - Report results of a
server-side copy . . . . . . . . . . . . . . . . . . . . 86
14. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 88
15. References . . . . . . . . . . . . . . . . . . . . . . . . . . 88
15.1. Normative References . . . . . . . . . . . . . . . . . . 88
15.2. Informative References . . . . . . . . . . . . . . . . . 89
Appendix A. Acknowledgments . . . . . . . . . . . . . . . . . . . 91
Appendix B. RFC Editor Notes . . . . . . . . . . . . . . . . . . 91
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 91
Haynes Expires July 7, 2012 [Page 4]
Internet-Draft NFSv4.2 January 2012
1. Introduction
1.1. The NFS Version 4 Minor Version 2 Protocol
The NFS version 4 minor version 2 (NFSv4.2) protocol is the third
minor version of the NFS version 4 (NFSv4) protocol. The first minor
version, NFSv4.0, is described in [11] and the second minor version,
NFSv4.1, is described in [2]. It follows the guidelines for minor
versioning that are listed in Section 11 of [11].
As a minor version, NFSv4.2 is consistent with the overall goals for
NFSv4, but extends the protocol so as to better meet those goals,
based on experiences with NFSv4.1. In addition, NFSv4.2 has adopted
some additional goals, which motivate some of the major extensions in
NFSv4.2.
1.2. Scope of This Document
This document describes the NFSv4.2 protocol. With respect to
NFSv4.0 and NFSv4.1, this document does not:
o describe the NFSv4.0 or NFSv4.1 protocols, except where needed to
contrast with NFSv4.2.
o modify the specification of the NFSv4.0 or NFSv4.1 protocols.
o clarify the NFSv4.0 or NFSv4.1 protocols. I.e., any
clarifications made here apply to NFSv4.2 and neither of the prior
protocols.
The full XDR for NFSv4.2 is presented in [3].
1.3. NFSv4.2 Goals
[[Comment.1: This needs fleshing out! --TH]]
1.4. Overview of NFSv4.2 Features
[[Comment.2: This needs fleshing out! --TH]]
1.4.1. Sparse Files
Two new operations are defined to support the reading of sparse files
(READ_PLUS) and the punching of holes to remove backing storage
(INITIALIZE).
Haynes Expires July 7, 2012 [Page 5]
Internet-Draft NFSv4.2 January 2012
1.4.2. Application I/O Advise
We propose a new IO_ADVISE operation for NFSv4.2 that clients can use
to communicate expected I/O behavior to the server. By communicating
future I/O behavior such as whether a file will be accessed
sequentially or randomly, and whether a file will or will not be
accessed in the near future, servers can optimize future I/O requests
for a file by, for example, prefetching or evicting data. This
operation can be used to support the posix_fadvise function as well
as other applications such as databases and video editors.
1.5. Differences from NFSv4.1
[[Comment.3: This needs fleshing out! --TH]]
2. NFS Server-side Copy
2.1. Introduction
This section describes a server-side copy feature for the NFS
protocol.
The server-side copy feature provides a mechanism for the NFS client
to perform a file copy on the server without the data being
transmitted back and forth over the network.
Without this feature, an NFS client copies data from one location to
another by reading the data from the server over the network, and
then writing the data back over the network to the server. Using
this server-side copy operation, the client is able to instruct the
server to copy the data locally without the data being sent back and
forth over the network unnecessarily.
In general, this feature is useful whenever data is copied from one
location to another on the server. It is particularly useful when
copying the contents of a file from a backup. Backup-versions of a
file are copied for a number of reasons, including restoring and
cloning data.
If the source object and destination object are on different file
servers, the file servers will communicate with one another to
perform the copy operation. The server-to-server protocol by which
this is accomplished is not defined in this document.
Haynes Expires July 7, 2012 [Page 6]
Internet-Draft NFSv4.2 January 2012
2.2. Protocol Overview
The server-side copy offload operations support both intra-server and
inter-server file copies. An intra-server copy is a copy in which
the source file and destination file reside on the same server. In
an inter-server copy, the source file and destination file are on
different servers. In both cases, the copy may be performed
synchronously or asynchronously.
Throughout the rest of this document, we refer to the NFS server
containing the source file as the "source server" and the NFS server
to which the file is transferred as the "destination server". In the
case of an intra-server copy, the source server and destination
server are the same server. Therefore in the context of an intra-
server copy, the terms source server and destination server refer to
the single server performing the copy.
The operations described below are designed to copy files. Other
file system objects can be copied by building on these operations or
using other techniques. For example if the user wishes to copy a
directory, the client can synthesize a directory copy by first
creating the destination directory and then copying the source
directory's files to the new destination directory. If the user
wishes to copy a namespace junction [12] [13], the client can use the
ONC RPC Federated Filesystem protocol [13] to perform the copy.
Specifically the client can determine the source junction's
attributes using the FEDFS_LOOKUP_FSN procedure and create a
duplicate junction using the FEDFS_CREATE_JUNCTION procedure.
For the inter-server copy protocol, the operations are defined to be
compatible with a server-to-server copy protocol in which the
destination server reads the file data from the source server. This
model in which the file data is pulled from the source by the
destination has a number of advantages over a model in which the
source pushes the file data to the destination. The advantages of
the pull model include:
o The pull model only requires a remote server (i.e., the
destination server) to be granted read access. A push model
requires a remote server (i.e., the source server) to be granted
write access, which is more privileged.
o The pull model allows the destination server to stop reading if it
has run out of space. In a push model, the destination server
must flow control the source server in this situation.
o The pull model allows the destination server to easily flow
control the data stream by adjusting the size of its read
Haynes Expires July 7, 2012 [Page 7]
Internet-Draft NFSv4.2 January 2012
operations. In a push model, the destination server does not have
this ability. The source server in a push model is capable of
writing chunks larger than the destination server has requested in
attributes and session parameters. In theory, the destination
server could perform a "short" write in this situation, but this
approach is known to behave poorly in practice.
The following operations are provided to support server-side copy:
COPY_NOTIFY: For inter-server copies, the client sends this
operation to the source server to notify it of a future file copy
from a given destination server for the given user.
COPY_REVOKE: Also for inter-server copies, the client sends this
operation to the source server to revoke permission to copy a file
for the given user.
COPY: Used by the client to request a file copy.
COPY_ABORT: Used by the client to abort an asynchronous file copy.
COPY_STATUS: Used by the client to poll the status of an
asynchronous file copy.
CB_COPY: Used by the destination server to report the results of an
asynchronous file copy to the client.
These operations are described in detail in Section 2.3. This
section provides an overview of how these operations are used to
perform server-side copies.
2.2.1. Intra-Server Copy
To copy a file on a single server, the client uses a COPY operation.
The server may respond to the copy operation with the final results
of the copy or it may perform the copy asynchronously and deliver the
results using a CB_COPY operation callback. If the copy is performed
asynchronously, the client may poll the status of the copy using
COPY_STATUS or cancel the copy using COPY_ABORT.
A synchronous intra-server copy is shown in Figure 1. In this
example, the NFS server chooses to perform the copy synchronously.
The copy operation is completed, either successfully or
unsuccessfully, before the server replies to the client's request.
The server's reply contains the final result of the operation.
Haynes Expires July 7, 2012 [Page 8]
Internet-Draft NFSv4.2 January 2012
Client Server
+ +
| |
|--- COPY ---------------------------->| Client requests
|<------------------------------------/| a file copy
| |
| |
Figure 1: A synchronous intra-server copy.
An asynchronous intra-server copy is shown in Figure 2. In this
example, the NFS server performs the copy asynchronously. The
server's reply to the copy request indicates that the copy operation
was initiated and the final result will be delivered at a later time.
The server's reply also contains a copy stateid. The client may use
this copy stateid to poll for status information (as shown) or to
cancel the copy using a COPY_ABORT. When the server completes the
copy, the server performs a callback to the client and reports the
results.
Client Server
+ +
| |
|--- COPY ---------------------------->| Client requests
|<------------------------------------/| a file copy
| |
| |
|--- COPY_STATUS --------------------->| Client may poll
|<------------------------------------/| for status
| |
| . | Multiple COPY_STATUS
| . | operations may be sent.
| . |
| |
|<-- CB_COPY --------------------------| Server reports results
|\------------------------------------>|
| |
Figure 2: An asynchronous intra-server copy.
2.2.2. Inter-Server Copy
A copy may also be performed between two servers. The copy protocol
is designed to accommodate a variety of network topologies. As shown
in Figure 3, the client and servers may be connected by multiple
networks. In particular, the servers may be connected by a
specialized, high speed network (network 192.168.33.0/24 in the
diagram) that does not include the client. The protocol allows the
Haynes Expires July 7, 2012 [Page 9]
Internet-Draft NFSv4.2 January 2012
client to setup the copy between the servers (over network
10.11.78.0/24 in the diagram) and for the servers to communicate on
the high speed network if they choose to do so.
192.168.33.0/24
+-------------------------------------+
| |
| |
| 192.168.33.18 | 192.168.33.56
+-------+------+ +------+------+
| Source | | Destination |
+-------+------+ +------+------+
| 10.11.78.18 | 10.11.78.56
| |
| |
| 10.11.78.0/24 |
+------------------+------------------+
|
|
| 10.11.78.243
+-----+-----+
| Client |
+-----------+
Figure 3: An example inter-server network topology.
For an inter-server copy, the client notifies the source server that
a file will be copied by the destination server using a COPY_NOTIFY
operation. The client then initiates the copy by sending the COPY
operation to the destination server. The destination server may
perform the copy synchronously or asynchronously.
A synchronous inter-server copy is shown in Figure 4. In this case,
the destination server chooses to perform the copy before responding
to the client's COPY request.
An asynchronous copy is shown in Figure 5. In this case, the
destination server chooses to respond to the client's COPY request
immediately and then perform the copy asynchronously.
Haynes Expires July 7, 2012 [Page 10]
Internet-Draft NFSv4.2 January 2012
Client Source Destination
+ + +
| | |
|--- COPY_NOTIFY --->| |
|<------------------/| |
| | |
| | |
|--- COPY ---------------------------->|
| | |
| | |
| |<----- read -----|
| |\--------------->|
| | |
| | . | Multiple reads may
| | . | be necessary
| | . |
| | |
| | |
|<------------------------------------/| Destination replies
| | | to COPY
Figure 4: A synchronous inter-server copy.
Haynes Expires July 7, 2012 [Page 11]
Internet-Draft NFSv4.2 January 2012
Client Source Destination
+ + +
| | |
|--- COPY_NOTIFY --->| |
|<------------------/| |
| | |
| | |
|--- COPY ---------------------------->|
|<------------------------------------/|
| | |
| | |
| |<----- read -----|
| |\--------------->|
| | |
| | . | Multiple reads may
| | . | be necessary
| | . |
| | |
| | |
|--- COPY_STATUS --------------------->| Client may poll
|<------------------------------------/| for status
| | |
| | . | Multiple COPY_STATUS
| | . | operations may be sent
| | . |
| | |
| | |
| | |
|<-- CB_COPY --------------------------| Destination reports
|\------------------------------------>| results
| | |
Figure 5: An asynchronous inter-server copy.
2.2.3. Server-to-Server Copy Protocol
During an inter-server copy, the destination server reads the file
data from the source server. The source server and destination
server are not required to use a specific protocol to transfer the
file data. The choice of what protocol to use is ultimately the
destination server's decision.
2.2.3.1. Using NFSv4.x as a Server-to-Server Copy Protocol
The destination server MAY use standard NFSv4.x (where x >= 1) to
read the data from the source server. If NFSv4.x is used for the
server-to-server copy protocol, the destination server can use the
filehandle contained in the COPY request with standard NFSv4.x
Haynes Expires July 7, 2012 [Page 12]
Internet-Draft NFSv4.2 January 2012
operations to read data from the source server. Specifically, the
destination server may use the NFSv4.x OPEN operation's CLAIM_FH
facility to open the file being copied and obtain an open stateid.
Using the stateid, the destination server may then use NFSv4.x READ
operations to read the file.
2.2.3.2. Using an alternative Server-to-Server Copy Protocol
In a homogeneous environment, the source and destination servers
might be able to perform the file copy extremely efficiently using
specialized protocols. For example the source and destination
servers might be two nodes sharing a common file system format for
the source and destination file systems. Thus the source and
destination are in an ideal position to efficiently render the image
of the source file to the destination file by replicating the file
system formats at the block level. Another possibility is that the
source and destination might be two nodes sharing a common storage
area network, and thus there is no need to copy any data at all, and
instead ownership of the file and its contents might simply be re-
assigned to the destination. To allow for these possibilities, the
destination server is allowed to use a server-to-server copy protocol
of its choice.
In a heterogeneous environment, using a protocol other than NFSv4.x
(e.g,. HTTP [14] or FTP [15]) presents some challenges. In
particular, the destination server is presented with the challenge of
accessing the source file given only an NFSv4.x filehandle.
One option for protocols that identify source files with path names
is to use an ASCII hexadecimal representation of the source
filehandle as the file name.
Another option for the source server is to use URLs to direct the
destination server to a specialized service. For example, the
response to COPY_NOTIFY could include the URL
ftp://s1.example.com:9999/_FH/0x12345, where 0x12345 is the ASCII
hexadecimal representation of the source filehandle. When the
destination server receives the source server's URL, it would use
"_FH/0x12345" as the file name to pass to the FTP server listening on
port 9999 of s1.example.com. On port 9999 there would be a special
instance of the FTP service that understands how to convert NFS
filehandles to an open file descriptor (in many operating systems,
this would require a new system call, one which is the inverse of the
makefh() function that the pre-NFSv4 MOUNT service needs).
Authenticating and identifying the destination server to the source
server is also a challenge. Recommendations for how to accomplish
this are given in Section 2.4.1.2.4 and Section 2.4.1.4.
Haynes Expires July 7, 2012 [Page 13]
Internet-Draft NFSv4.2 January 2012
2.3. Operations
In the sections that follow, several operations are defined that
together provide the server-side copy feature. These operations are
intended to be OPTIONAL operations as defined in section 17 of [2].
The COPY_NOTIFY, COPY_REVOKE, COPY, COPY_ABORT, and COPY_STATUS
operations are designed to be sent within an NFSv4 COMPOUND
procedure. The CB_COPY operation is designed to be sent within an
NFSv4 CB_COMPOUND procedure.
Each operation is performed in the context of the user identified by
the ONC RPC credential of its containing COMPOUND or CB_COMPOUND
request. For example, a COPY_ABORT operation issued by a given user
indicates that a specified COPY operation initiated by the same user
be canceled. Therefore a COPY_ABORT MUST NOT interfere with a copy
of the same file initiated by another user.
An NFS server MAY allow an administrative user to monitor or cancel
copy operations using an implementation specific interface.
2.3.1. netloc4 - Network Locations
The server-side copy operations specify network locations using the
netloc4 data type shown below:
enum netloc_type4 {
NL4_NAME = 0,
NL4_URL = 1,
NL4_NETADDR = 2
};
union netloc4 switch (netloc_type4 nl_type) {
case NL4_NAME: utf8str_cis nl_name;
case NL4_URL: utf8str_cis nl_url;
case NL4_NETADDR: netaddr4 nl_addr;
};
If the netloc4 is of type NL4_NAME, the nl_name field MUST be
specified as a UTF-8 string. The nl_name is expected to be resolved
to a network address via DNS, LDAP, NIS, /etc/hosts, or some other
means. If the netloc4 is of type NL4_URL, a server URL [4]
appropriate for the server-to-server copy operation is specified as a
UTF-8 string. If the netloc4 is of type NL4_NETADDR, the nl_addr
field MUST contain a valid netaddr4 as defined in Section 3.3.9 of
[2].
When netloc4 values are used for an inter-server copy as shown in
Figure 3, their values may be evaluated on the source server,
destination server, and client. The network environment in which
Haynes Expires July 7, 2012 [Page 14]
Internet-Draft NFSv4.2 January 2012
these systems operate should be configured so that the netloc4 values
are interpreted as intended on each system.
2.3.2. Copy Offload Stateids
A server may perform a copy offload operation asynchronously. An
asynchronous copy is tracked using a copy offload stateid. Copy
offload stateids are included in the COPY, COPY_ABORT, COPY_STATUS,
and CB_COPY operations.
Section 8.2.4 of [2] specifies that stateids are valid until either
(A) the client or server restart or (B) the client returns the
resource.
A copy offload stateid will be valid until either (A) the client or
server restart or (B) the client returns the resource by issuing a
COPY_ABORT operation or the client replies to a CB_COPY operation.
A copy offload stateid's seqid MUST NOT be 0 (zero). In the context
of a copy offload operation, it is ambiguous to indicate the most
recent copy offload operation using a stateid with seqid of 0 (zero).
Therefore a copy offload stateid with seqid of 0 (zero) MUST be
considered invalid.
2.4. Security Considerations
The security considerations pertaining to NFSv4 [11] apply to this
document.
The standard security mechanisms provide by NFSv4 [11] may be used to
secure the protocol described in this document.
NFSv4 clients and servers supporting the the inter-server copy
operations described in this document are REQUIRED to implement [5],
including the RPCSEC_GSSv3 privileges copy_from_auth and
copy_to_auth. If the server-to-server copy protocol is ONC RPC
based, the servers are also REQUIRED to implement the RPCSEC_GSSv3
privilege copy_confirm_auth. These requirements to implement are not
requirements to use. NFSv4 clients and servers are RECOMMENDED to
use [5] to secure server-side copy operations.
2.4.1. Inter-Server Copy Security
2.4.1.1. Requirements for Secure Inter-Server Copy
Inter-server copy is driven by several requirements:
Haynes Expires July 7, 2012 [Page 15]
Internet-Draft NFSv4.2 January 2012
o The specification MUST NOT mandate an inter-server copy protocol.
There are many ways to copy data. Some will be more optimal than
others depending on the identities of the source server and
destination server. For example the source and destination
servers might be two nodes sharing a common file system format for
the source and destination file systems. Thus the source and
destination are in an ideal position to efficiently render the
image of the source file to the destination file by replicating
the file system formats at the block level. In other cases, the
source and destination might be two nodes sharing a common storage
area network, and thus there is no need to copy any data at all,
and instead ownership of the file and its contents simply gets re-
assigned to the destination.
o The specification MUST provide guidance for using NFSv4.x as a
copy protocol. For those source and destination servers willing
to use NFSv4.x there are specific security considerations that
this specification can and does address.
o The specification MUST NOT mandate pre-configuration between the
source and destination server. Requiring that the source and
destination first have a "copying relationship" increases the
administrative burden. However the specification MUST NOT
preclude implementations that require pre-configuration.
o The specification MUST NOT mandate a trust relationship between
the source and destination server. The NFSv4 security model
requires mutual authentication between a principal on an NFS
client and a principal on an NFS server. This model MUST continue
with the introduction of COPY.
2.4.1.2. Inter-Server Copy with RPCSEC_GSSv3
When the client sends a COPY_NOTIFY to the source server to expect
the destination to attempt to copy data from the source server, it is
expected that this copy is being done on behalf of the principal
(called the "user principal") that sent the RPC request that encloses
the COMPOUND procedure that contains the COPY_NOTIFY operation. The
user principal is identified by the RPC credentials. A mechanism
that allows the user principal to authorize the destination server to
perform the copy in a manner that lets the source server properly
authenticate the destination's copy, and without allowing the
destination to exceed its authorization is necessary.
An approach that sends delegated credentials of the client's user
principal to the destination server is not used for the following
reasons. If the client's user delegated its credentials, the
destination would authenticate as the user principal. If the
Haynes Expires July 7, 2012 [Page 16]
Internet-Draft NFSv4.2 January 2012
destination were using the NFSv4 protocol to perform the copy, then
the source server would authenticate the destination server as the
user principal, and the file copy would securely proceed. However,
this approach would allow the destination server to copy other files.
The user principal would have to trust the destination server to not
do so. This is counter to the requirements, and therefore is not
considered. Instead an approach using RPCSEC_GSSv3 [5] privileges is
proposed.
One of the stated applications of the proposed RPCSEC_GSSv3 protocol
is compound client host and user authentication [+ privilege
assertion]. For inter-server file copy, we require compound NFS
server host and user authentication [+ privilege assertion]. The
distinction between the two is one without meaning.
RPCSEC_GSSv3 introduces the notion of privileges. We define three
privileges:
copy_from_auth: A user principal is authorizing a source principal
("nfs@<source>") to allow a destination principal ("nfs@
<destination>") to copy a file from the source to the destination.
This privilege is established on the source server before the user
principal sends a COPY_NOTIFY operation to the source server.
struct copy_from_auth_priv {
secret4 cfap_shared_secret;
netloc4 cfap_destination;
/* the NFSv4 user name that the user principal maps to */
utf8str_mixed cfap_username;
/* equal to seq_num of rpc_gss_cred_vers_3_t */
unsigned int cfap_seq_num;
};
cap_shared_secret is a secret value the user principal generates.
copy_to_auth: A user principal is authorizing a destination
principal ("nfs@<destination>") to allow it to copy a file from
the source to the destination. This privilege is established on
the destination server before the user principal sends a COPY
operation to the destination server.
Haynes Expires July 7, 2012 [Page 17]
Internet-Draft NFSv4.2 January 2012
struct copy_to_auth_priv {
/* equal to cfap_shared_secret */
secret4 ctap_shared_secret;
netloc4 ctap_source;
/* the NFSv4 user name that the user principal maps to */
utf8str_mixed ctap_username;
/* equal to seq_num of rpc_gss_cred_vers_3_t */
unsigned int ctap_seq_num;
};
ctap_shared_secret is a secret value the user principal generated
and was used to establish the copy_from_auth privilege with the
source principal.
copy_confirm_auth: A destination principal is confirming with the
source principal that it is authorized to copy data from the
source on behalf of the user principal. When the inter-server
copy protocol is NFSv4, or for that matter, any protocol capable
of being secured via RPCSEC_GSSv3 (i.e., any ONC RPC protocol),
this privilege is established before the file is copied from the
source to the destination.
struct copy_confirm_auth_priv {
/* equal to GSS_GetMIC() of cfap_shared_secret */
opaque ccap_shared_secret_mic<>;
/* the NFSv4 user name that the user principal maps to */
utf8str_mixed ccap_username;
/* equal to seq_num of rpc_gss_cred_vers_3_t */
unsigned int ccap_seq_num;
};
2.4.1.2.1. Establishing a Security Context
When the user principal wants to COPY a file between two servers, if
it has not established copy_from_auth and copy_to_auth privileges on
the servers, it establishes them:
o The user principal generates a secret it will share with the two
servers. This shared secret will be placed in the
cfap_shared_secret and ctap_shared_secret fields of the
appropriate privilege data types, copy_from_auth_priv and
copy_to_auth_priv.
o An instance of copy_from_auth_priv is filled in with the shared
secret, the destination server, and the NFSv4 user id of the user
principal. It will be sent with an RPCSEC_GSS3_CREATE procedure,
Haynes Expires July 7, 2012 [Page 18]
Internet-Draft NFSv4.2 January 2012
and so cfap_seq_num is set to the seq_num of the credential of the
RPCSEC_GSS3_CREATE procedure. Because cfap_shared_secret is a
secret, after XDR encoding copy_from_auth_priv, GSS_Wrap() (with
privacy) is invoked on copy_from_auth_priv. The
RPCSEC_GSS3_CREATE procedure's arguments are:
struct {
rpc_gss3_gss_binding *compound_binding;
rpc_gss3_chan_binding *chan_binding_mic;
rpc_gss3_assertion assertions<>;
rpc_gss3_extension extensions<>;
} rpc_gss3_create_args;
The string "copy_from_auth" is placed in assertions[0].privs. The
output of GSS_Wrap() is placed in extensions[0].data. The field
extensions[0].critical is set to TRUE. The source server calls
GSS_Unwrap() on the privilege, and verifies that the seq_num
matches the credential. It then verifies that the NFSv4 user id
being asserted matches the source server's mapping of the user
principal. If it does, the privilege is established on the source
server as: <"copy_from_auth", user id, destination>. The
successful reply to RPCSEC_GSS3_CREATE has:
struct {
opaque handle<>;
rpc_gss3_chan_binding *chan_binding_mic;
rpc_gss3_assertion granted_assertions<>;
rpc_gss3_assertion server_assertions<>;
rpc_gss3_extension extensions<>;
} rpc_gss3_create_res;
The field "handle" is the RPCSEC_GSSv3 handle that the client will
use on COPY_NOTIFY requests involving the source and destination
server. granted_assertions[0].privs will be equal to
"copy_from_auth". The server will return a GSS_Wrap() of
copy_to_auth_priv.
o An instance of copy_to_auth_priv is filled in with the shared
secret, the source server, and the NFSv4 user id. It will be sent
with an RPCSEC_GSS3_CREATE procedure, and so ctap_seq_num is set
to the seq_num of the credential of the RPCSEC_GSS3_CREATE
procedure. Because ctap_shared_secret is a secret, after XDR
encoding copy_to_auth_priv, GSS_Wrap() is invoked on
copy_to_auth_priv. The RPCSEC_GSS3_CREATE procedure's arguments
Haynes Expires July 7, 2012 [Page 19]
Internet-Draft NFSv4.2 January 2012
are:
struct {
rpc_gss3_gss_binding *compound_binding;
rpc_gss3_chan_binding *chan_binding_mic;
rpc_gss3_assertion assertions<>;
rpc_gss3_extension extensions<>;
} rpc_gss3_create_args;
The string "copy_to_auth" is placed in assertions[0].privs. The
output of GSS_Wrap() is placed in extensions[0].data. The field
extensions[0].critical is set to TRUE. After unwrapping,
verifying the seq_num, and the user principal to NFSv4 user ID
mapping, the destination establishes a privilege of
<"copy_to_auth", user id, source>. The successful reply to
RPCSEC_GSS3_CREATE has:
struct {
opaque handle<>;
rpc_gss3_chan_binding *chan_binding_mic;
rpc_gss3_assertion granted_assertions<>;
rpc_gss3_assertion server_assertions<>;
rpc_gss3_extension extensions<>;
} rpc_gss3_create_res;
The field "handle" is the RPCSEC_GSSv3 handle that the client will
use on COPY requests involving the source and destination server.
The field granted_assertions[0].privs will be equal to
"copy_to_auth". The server will return a GSS_Wrap() of
copy_to_auth_priv.
2.4.1.2.2. Starting a Secure Inter-Server Copy
When the client sends a COPY_NOTIFY request to the source server, it
uses the privileged "copy_from_auth" RPCSEC_GSSv3 handle.
cna_destination_server in COPY_NOTIFY MUST be the same as the name of
the destination server specified in copy_from_auth_priv. Otherwise,
COPY_NOTIFY will fail with NFS4ERR_ACCESS. The source server
verifies that the privilege <"copy_from_auth", user id, destination>
exists, and annotates it with the source filehandle, if the user
principal has read access to the source file, and if administrative
policies give the user principal and the NFS client read access to
the source file (i.e., if the ACCESS operation would grant read
access). Otherwise, COPY_NOTIFY will fail with NFS4ERR_ACCESS.
Haynes Expires July 7, 2012 [Page 20]
Internet-Draft NFSv4.2 January 2012
When the client sends a COPY request to the destination server, it
uses the privileged "copy_to_auth" RPCSEC_GSSv3 handle.
ca_source_server in COPY MUST be the same as the name of the source
server specified in copy_to_auth_priv. Otherwise, COPY will fail
with NFS4ERR_ACCESS. The destination server verifies that the
privilege <"copy_to_auth", user id, source> exists, and annotates it
with the source and destination filehandles. If the client has
failed to establish the "copy_to_auth" policy it will reject the
request with NFS4ERR_PARTNER_NO_AUTH.
If the client sends a COPY_REVOKE to the source server to rescind the
destination server's copy privilege, it uses the privileged
"copy_from_auth" RPCSEC_GSSv3 handle and the cra_destination_server
in COPY_REVOKE MUST be the same as the name of the destination server
specified in copy_from_auth_priv. The source server will then delete
the <"copy_from_auth", user id, destination> privilege and fail any
subsequent copy requests sent under the auspices of this privilege
from the destination server.
2.4.1.2.3. Securing ONC RPC Server-to-Server Copy Protocols
After a destination server has a "copy_to_auth" privilege established
on it, and it receives a COPY request, if it knows it will use an ONC
RPC protocol to copy data, it will establish a "copy_confirm_auth"
privilege on the source server, using nfs@<destination> as the
initiator principal, and nfs@<source> as the target principal.
The value of the field ccap_shared_secret_mic is a GSS_VerifyMIC() of
the shared secret passed in the copy_to_auth privilege. The field
ccap_username is the mapping of the user principal to an NFSv4 user
name ("user"@"domain" form), and MUST be the same as ctap_username
and cfap_username. The field ccap_seq_num is the seq_num of the
RPCSEC_GSSv3 credential used for the RPCSEC_GSS3_CREATE procedure the
destination will send to the source server to establish the
privilege.
The source server verifies the privilege, and establishes a
<"copy_confirm_auth", user id, destination> privilege. If the source
server fails to verify the privilege, the COPY operation will be
rejected with NFS4ERR_PARTNER_NO_AUTH. All subsequent ONC RPC
requests sent from the destination to copy data from the source to
the destination will use the RPCSEC_GSSv3 handle returned by the
source's RPCSEC_GSS3_CREATE response.
Note that the use of the "copy_confirm_auth" privilege accomplishes
the following:
Haynes Expires July 7, 2012 [Page 21]
Internet-Draft NFSv4.2 January 2012
o if a protocol like NFS is being used, with export policies, export
policies can be overridden in case the destination server as-an-
NFS-client is not authorized
o manual configuration to allow a copy relationship between the
source and destination is not needed.
If the attempt to establish a "copy_confirm_auth" privilege fails,
then when the user principal sends a COPY request to destination, the
destination server will reject it with NFS4ERR_PARTNER_NO_AUTH.
2.4.1.2.4. Securing Non ONC RPC Server-to-Server Copy Protocols
If the destination won't be using ONC RPC to copy the data, then the
source and destination are using an unspecified copy protocol. The
destination could use the shared secret and the NFSv4 user id to
prove to the source server that the user principal has authorized the
copy.
For protocols that authenticate user names with passwords (e.g., HTTP
[14] and FTP [15]), the nfsv4 user id could be used as the user name,
and an ASCII hexadecimal representation of the RPCSEC_GSSv3 shared
secret could be used as the user password or as input into non-
password authentication methods like CHAP [16].
2.4.1.3. Inter-Server Copy via ONC RPC but without RPCSEC_GSSv3
ONC RPC security flavors other than RPCSEC_GSSv3 MAY be used with the
server-side copy offload operations described in this document. In
particular, host-based ONC RPC security flavors such as AUTH_NONE and
AUTH_SYS MAY be used. If a host-based security flavor is used, a
minimal level of protection for the server-to-server copy protocol is
possible.
In the absence of strong security mechanisms such as RPCSEC_GSSv3,
the challenge is how the source server and destination server
identify themselves to each other, especially in the presence of
multi-homed source and destination servers. In a multi-homed
environment, the destination server might not contact the source
server from the same network address specified by the client in the
COPY_NOTIFY. This can be overcome using the procedure described
below.
When the client sends the source server the COPY_NOTIFY operation,
the source server may reply to the client with a list of target
addresses, names, and/or URLs and assign them to the unique
quadruple: <random number, source fh, user ID, destination address
Y>. If the destination uses one of these target netlocs to contact
Haynes Expires July 7, 2012 [Page 22]
Internet-Draft NFSv4.2 January 2012
the source server, the source server will be able to uniquely
identify the destination server, even if the destination server does
not connect from the address specified by the client in COPY_NOTIFY.
The level of assurance in this identification depends on the
unpredictability, strength and secrecy of the random number.
For example, suppose the network topology is as shown in Figure 3.
If the source filehandle is 0x12345, the source server may respond to
a COPY_NOTIFY for destination 10.11.78.56 with the URLs:
nfs://10.11.78.18//_COPY/FvhH1OKbu8VrxvV1erdjvR7N/10.11.78.56/_FH/
0x12345
nfs://192.168.33.18//_COPY/FvhH1OKbu8VrxvV1erdjvR7N/10.11.78.56/
_FH/0x12345
The name component after _COPY is 24 characters of base 64, more than
enough to encode a 128 bit random number.
The client will then send these URLs to the destination server in the
COPY operation. Suppose that the 192.168.33.0/24 network is a high
speed network and the destination server decides to transfer the file
over this network. If the destination contacts the source server
from 192.168.33.56 over this network using NFSv4.1, it does the
following:
COMPOUND { PUTROOTFH, LOOKUP "_COPY" ; LOOKUP
"FvhH1OKbu8VrxvV1erdjvR7N" ; LOOKUP "10.11.78.56"; LOOKUP "_FH" ;
OPEN "0x12345" ; GETFH }
Provided that the random number is unpredictable and has been kept
secret by the parties involved, the source server will therefore know
that these NFSv4.x operations are being issued by the destination
server identified in the COPY_NOTIFY. This random number technique
only provides initial authentication of the destination server, and
cannot defend against man-in-the-middle attacks after authentication
or an eavesdropper that observes the random number on the wire.
Other secure communication techniques (e.g., IPsec) are necessary to
block these attacks.
2.4.1.4. Inter-Server Copy without ONC RPC and RPCSEC_GSSv3
The same techniques as Section 2.4.1.3, using unique URLs for each
destination server, can be used for other protocols (e.g., HTTP [14]
and FTP [15]) as well.
Haynes Expires July 7, 2012 [Page 23]
Internet-Draft NFSv4.2 January 2012
3. Sparse Files
3.1. Introduction
A sparse file is a common way of representing a large file without
having to utilize all of the disk space for it. Consequently, a
sparse file uses less physical space than its size indicates. This
means the file contains 'holes', byte ranges within the file that
contain no data. Most modern file systems support sparse files,
including most UNIX file systems and NTFS, but notably not Apple's
HFS+. Common examples of sparse files include Virtual Machine (VM)
OS/disk images, database files, log files, and even checkpoint
recovery files most commonly used by the HPC community.
If an application reads a hole in a sparse file, the file system must
return all zeros to the application. For local data access there is
little penalty, but with NFS these zeroes must be transferred back to
the client. If an application uses the NFS client to read data into
memory, this wastes time and bandwidth as the application waits for
the zeroes to be transferred.
A sparse file is typically created by initializing the file to be all
zeros - nothing is written to the data in the file, instead the hole
is recorded in the metadata for the file. So a 8G disk image might
be represented initially by a couple hundred bits in the inode and
nothing on the disk. If the VM then writes 100M to a file in the
middle of the image, there would now be two holes represented in the
metadata and 100M in the data.
This section introduces a new operation READ_PLUS (Section 12.10)
which supports all the features of READ but includes an extension to
support sparse pattern files. READ_PLUS is guaranteed to perform no
worse than READ, and can dramatically improve performance with sparse
files. READ_PLUS does not depend on pNFS protocol features, but can
be used by pNFS to support sparse files.
3.2. Terminology
Regular file: An object of file type NF4REG or NF4NAMEDATTR.
Sparse file: A Regular file that contains one or more Holes.
Hole: A byte range within a Sparse file that contains regions of all
zeroes. For block-based file systems, this could also be an
unallocated region of the file.
Haynes Expires July 7, 2012 [Page 24]
Internet-Draft NFSv4.2 January 2012
Hole Threshold: The minimum length of a Hole as determined by the
server. If a server chooses to define a Hole Threshold, then it
would not return hole information about holes with a length
shorter than the Hole Threshold.
3.3. Determining the next hole/data
Solaris and ZFS support an extension to lseek(2) that allows
applications to discover holes in a file. The values, SEEK_HOLE and
SEEK_DATA, allow clients to seek to the next hole or beginning of
data, respectively.
4. Space Reservation
4.1. Introduction
This section describes a set of operations that allow applications
such as hypervisors to reserve space for a file, report the amount of
actual disk space a file occupies and freeup the backing space of a
file when it is not required. In virtualized environments, virtual
disk files are often stored on NFS mounted volumes. Since virtual
disk files represent the hard disks of virtual machines, hypervisors
often have to guarantee certain properties for the file.
One such example is space reservation. When a hypervisor creates a
virtual disk file, it often tries to preallocate the space for the
file so that there are no future allocation related errors during the
operation of the virtual machine. Such errors prevent a virtual
machine from continuing execution and result in downtime.
Currently, in order to achieve such a guarantee, applications zero
the entire file. The initial zeroing allocates the backing blocks
and all subsequent writes are overwrites of already allocated blocks.
This approach is not only inefficient in terms of the amount of I/O
done, it is also not guaranteed to work on filesystems that are log
structured or deduplicated. An efficient way of guaranteeing space
reservation would be beneficial to such applications.
If the space_reserved attribute is set on a file, it is guaranteed
that writes that do not grow the file will not fail with
NFSERR_NOSPC.
Another useful feature would be the ability to report the number of
blocks that would be freed when a file is deleted. Currently, NFS
reports two size attributes:
Haynes Expires July 7, 2012 [Page 25]
Internet-Draft NFSv4.2 January 2012
size The logical file size of the file.
space_used The size in bytes that the file occupies on disk
While these attributes are sufficient for space accounting in
traditional filesystems, they prove to be inadequate in modern
filesystems that support block sharing. In such filesystems,
multiple inodes can point to a single block with a block reference
count to guard against premature freeing. Having a way to tell the
number of blocks that would be freed if the file was deleted would be
useful to applications that wish to migrate files when a volume is
low on space.
Since virtual disks represent a hard drive in a virtual machine, a
virtual disk can be viewed as a filesystem within a file. Since not
all blocks within a filesystem are in use, there is an opportunity to
reclaim blocks that are no longer in use. A call to deallocate
blocks could result in better space efficiency. Lesser space MAY be
consumed for backups after block deallocation.
The following operations and attributes can be used to resolve this
issues:
space_reserved This attribute specifies whether the blocks backing
the file have been preallocated.
space_freed This attribute specifies the space freed when a file is
deleted, taking block sharing into consideration.
INITIALIZED This operation zeroes and/or deallocates the blocks
backing a region of the file.
If space_used of a file is interpreted to mean the size in bytes of
all disk blocks pointed to by the inode of the file, then shared
blocks get double counted, over-reporting the space utilization.
This also has the adverse effect that the deletion of a file with
shared blocks frees up less than space_used bytes.
On the other hand, if space_used is interpreted to mean the size in
bytes of those disk blocks unique to the inode of the file, then
shared blocks are not counted in any file, resulting in under-
reporting of the space utilization.
For example, two files A and B have 10 blocks each. Let 6 of these
blocks be shared between them. Thus, the combined space utilized by
the two files is 14 * BLOCK_SIZE bytes. In the former case, the
combined space utilization of the two files would be reported as 20 *
BLOCK_SIZE. However, deleting either would only result in 4 *
Haynes Expires July 7, 2012 [Page 26]
Internet-Draft NFSv4.2 January 2012
BLOCK_SIZE being freed. Conversely, the latter interpretation would
report that the space utilization is only 8 * BLOCK_SIZE.
Adding another size attribute, space_freed, is helpful in solving
this problem. space_freed is the number of blocks that are allocated
to the given file that would be freed on its deletion. In the
example, both A and B would report space_freed as 4 * BLOCK_SIZE and
space_used as 10 * BLOCK_SIZE. If A is deleted, B will report
space_freed as 10 * BLOCK_SIZE as the deletion of B would result in
the deallocation of all 10 blocks.
The addition of this problem doesn't solve the problem of space being
over-reported. However, over-reporting is better than under-
reporting.
5. Support for Application IO Hints
5.1. Introduction
Applications currently have several options for communicating I/O
access patterns to the NFS client. While this can help the NFS
client optimize I/O and caching for a file, it does not allow the NFS
server and its exported file system to do likewise. Therefore, here
we put forth a proposal for the NFSv4.2 protocol to allow
applications to communicate their expected behavior to the server.
By communicating expected access pattern, e.g., sequential or random,
and data re-use behavior, e.g., data range will be read multiple
times and should be cached, the server will be able to better
understand what optimizations it should implement for access to a
file. For example, if a application indicates it will never read the
data more than once, then the file system can avoid polluting the
data cache and not cache the data.
The first application that can issue client I/O hints is the
posix_fadvise operation. For example, on Linux, when an application
uses posix_fadvise to specify a file will be read sequentially, Linux
doubles the readahead buffer size.
Another instance where applications provide an indication of their
desired I/O behavior is the use of direct I/O. By specifying direct
I/O, clients will no longer cache data, but this information is not
passed to the server, which will continue caching data.
Application specific NFS clients such as those used by hypervisors
and databases can also leverage application hints to communicate
their specialized requirements.
Haynes Expires July 7, 2012 [Page 27]
Internet-Draft NFSv4.2 January 2012
This section adds a new IO_ADVISE operation to communicate the client
file access patterns to the NFS server. The NFS server upon
receiving a IO_ADVISE operation MAY choose to alter its I/O and
caching behavior, but is under no obligation to do so.
5.2. POSIX Requirements
The first key requirement of the IO_ADVISE operation is to support
the posix_fadvise function [6], which is supported in Linux and many
other operating systems. Examples and guidance on how to use
posix_fadvise to improve performance can be found here [17].
posix_fadvise is defined as follows,
int posix_fadvise(int fd, off_t offset, off_t len, int advice);
The posix_fadvise() function shall advise the implementation on the
expected behavior of the application with respect to the data in the
file associated with the open file descriptor, fd, starting at offset
and continuing for len bytes. The specified range need not currently
exist in the file. If len is zero, all data following offset is
specified. The implementation may use this information to optimize
handling of the specified data. The posix_fadvise() function shall
have no effect on the semantics of other operations on the specified
data, although it may affect the performance of other operations.
The advice to be applied to the data is specified by the advice
parameter and may be one of the following values:
POSIX_FADV_NORMAL - Specifies that the application has no advice to
give on its behavior with respect to the specified data. It is
the default characteristic if no advice is given for an open file.
POSIX_FADV_SEQUENTIAL - Specifies that the application expects to
access the specified data sequentially from lower offsets to
higher offsets.
POSIX_FADV_RANDOM - Specifies that the application expects to access
the specified data in a random order.
POSIX_FADV_WILLNEED - Specifies that the application expects to
access the specified data in the near future.
POSIX_FADV_DONTNEED - Specifies that the application expects that it
will not access the specified data in the near future.
Haynes Expires July 7, 2012 [Page 28]
Internet-Draft NFSv4.2 January 2012
POSIX_FADV_NOREUSE - Specifies that the application expects to
access the specified data once and then not reuse it thereafter.
Upon successful completion, posix_fadvise() shall return zero;
otherwise, an error number shall be returned to indicate the error.
5.3. Additional Requirements
Many use cases exist for sending application I/O hints to the server
that cannot utilize the POSIX supported interface. This is because
some applications may benefit from additional hints not specified by
posix_fadvise, and some applications may not use POSIX altogether.
One use case is "Opportunistic Prefetch", which allows a stateid
holder to tell the server that it is possible that it will access the
specified data in the near future. This is similar to
POSIX_FADV_WILLNEED, but the client is unsure it will in fact read
the specified data, so the server should only prefetch the data if it
can be done at a marginal cost. For example, when a server receives
this hint, it could prefetch only the indirect blocks for a file
instead of all the data. This would still improve performance if the
client does read the data, but with less pressure on server memory.
An example use case for this hint is a database that reads in a
single record that points to additional records in either other areas
of the same file or different files located on the same or different
server. While it is likely that the application may access the
additional records, it is far from guaranteed. Therefore, the
database may issue an opportunistic prefetch (instead of
POSIX_FADV_WILLNEED) for the data in the other files pointed to by
the record.
Another use case is "Direct I/O", which allows a stated holder to
inform the server that it does not wish to cache data. Today, for
applications that only intend to read data once, the use of direct
I/O disables client caching, but does not affect server caching. By
caching data that will not be re-read, the server is polluting its
cache and possibly causing useful cached data to be evicted. By
informing the server of its expected I/O access, this situation can
be avoid. Direct I/O can be used in Linux and AIX via the open()
O_DIRECT parameter, in Solaris via the directio() function, and in
Windows via the CreateFile() FILE_FLAG_NO_BUFFERING flag.
Another use case is "Backward Sequential Read", which allows a stated
holder to inform the server that it intends to read the specified
data backwards, i.e., back the end to the beginning. This is
different than POSIX_FADV_SEQUENTIAL, whose implied intention was
that data will be read from beginning to end. This hint allows
Haynes Expires July 7, 2012 [Page 29]
Internet-Draft NFSv4.2 January 2012
servers to prefetch data at the end of the range first, and then
prefetch data sequentially in a backwards manner to the start of the
data range. One example of an application that can make use of this
hint is video editing.
5.4. Security Considerations
None.
5.5. IANA Considerations
The IO_ADVISE_type4 will be extended through an IANA registry.
6. Application Data Block Support
At the OS level, files are contained on disk blocks. Applications
are also free to impose structure on the data contained in a file and
we can define an Application Data Block (ADB) to be such a structure.
From the application's viewpoint, it only wants to handle ADBs and
not raw bytes (see [18]). An ADB is typically comprised of two
sections: a header and data. The header describes the
characteristics of the block and can provide a means to detect
corruption in the data payload. The data section is typically
initialized to all zeros.
The format of the header is application specific, but there are two
main components typically encountered:
1. An ADB Number (ADBN), which allows the application to determine
which data block is being referenced. The ADBN is a logical
block number and is useful when the client is not storing the
blocks in contiguous memory.
2. Fields to describe the state of the ADB and a means to detect
block corruption. For both pieces of data, a useful property is
that allowed values be unique in that if passed across the
network, corruption due to translation between big and little
endian architectures are detectable. For example, 0xF0DEDEF0 has
the same bit pattern in both architectures.
Applications already impose structures on files [18] and detect
corruption in data blocks [19]. What they are not able to do is
efficiently transfer and store ADBs. To initialize a file with ADBs,
the client must send the full ADB to the server and that must be
stored on the server. When the application is initializing a file to
have the ADB structure, it could compress the ADBs to just the
information to necessary to later reconstruct the header portion of
Haynes Expires July 7, 2012 [Page 30]
Internet-Draft NFSv4.2 January 2012
the ADB when the contents are read back. Using sparse file
techniques, the disk blocks described by would not be allocated.
Unlike sparse file techniques, there would be a small cost to store
the compressed header data.
In this section, we are going to define a generic framework for an
ADB, present one approach to detecting corruption in a given ADB
implementation, and describe the model for how the client and server
can support efficient initialization of ADBs, reading of ADB holes,
punching holes in ADBs, and space reservation. Further, we need to
be able to extend this model to applications which do not support
ADBs, but wish to be able to handle sparse files, hole punching, and
space reservation.
6.1. Generic Framework
We want the representation of the ADB to be flexible enough to
support many different applications. The most basic approach is no
imposition of a block at all, which means we are working with the raw
bytes. Such an approach would be useful for storing holes, punching
holes, etc. In more complex deployments, a server might be
supporting multiple applications, each with their own definition of
the ADB. One might store the ADBN at the start of the block and then
have a guard pattern to detect corruption [Section 11.4.3, Detecting Memory Corruption of Solaris Internals"">20]. The next might store
the ADBN at an offset of 100 bytes within the block and have no guard
pattern at all. The point is that existing applications might
already have well defined formats for their data blocks.
The guard pattern can be used to represent the state of the block, to
protect against corruption, or both. Again, it needs to be able to
be placed anywhere within the ADB.
We need to be able to represent the starting offset of the block and
the size of the block. Note that nothing prevents the application
from defining different sized blocks in a file.
6.1.1. Data Block Representation
struct app_data_block4 {
offset4 adb_offset;
length4 adb_block_size;
length4 adb_block_count;
length4 adb_reloff_blocknum;
count4 adb_block_num;
length4 adb_reloff_pattern;
opaque adb_pattern<>;
};
Haynes Expires July 7, 2012 [Page 31]
Internet-Draft NFSv4.2 January 2012
The app_data_block4 structure captures the abstraction presented for
the ADB. The additional fields present are to allow the transmission
of adb_block_count ADBs at one time. We also use adb_block_num to
convey the ADBN of the first block in the sequence. Each ADB will
contain the same adb_pattern string.
As both adb_block_num and adb_pattern are optional, if either
adb_reloff_pattern or adb_reloff_blocknum is set to NFS4_UINT64_MAX,
then the corresponding field is not set in any of the ADB.
6.1.2. Data Content
/*
* Use an enum such that we can extend new types.
*/
enum data_content4 {
NFS4_CONTENT_DATA = 0,
NFS4_CONTENT_APP_BLOCK = 1,
NFS4_CONTENT_HOLE = 2
};
New operations might need to differentiate between wanting to access
data versus an ADB. Also, future minor versions might want to
introduce new data formats. This enumeration allows that to occur.
6.2. pNFS Considerations
While this document does not mandate how sparse ADBs are recorded on
the server, it does make the assumption that such information is not
in the file. I.e., the information is metadata. As such, the
INITIALIZE operation is defined to be not supported by the DS - it
must be issued to the MDS. But since the client must not assume a
priori whether a read is sparse or not, the READ_PLUS operation MUST
be supported by both the DS and the MDS. I.e., the client might
impose on the MDS to asynchronously read the data from the DS.
Furthermore, each DS MUST not report to a client either a sparse ADB
or data which belongs to another DS. One implication of this
requirement is that the app_data_block4's adb_block_size MUST be
either be the stripe width or the stripe width must be an even
multiple of it.
The second implication here is that the DS must be able to use the
Control Protocol to determine from the MDS where the sparse ADBs
occur. [[Comment.4: Need to discuss what happens if after the file
is being written to and an INITIALIZE occurs? --TH]] Perhaps instead
of the DS pulling from the MDS, the MDS pushes to the DS? Thus an
INITIALIZE causes a new push? [[Comment.5: Still need to consider
Haynes Expires July 7, 2012 [Page 32]
Internet-Draft NFSv4.2 January 2012
race cases of the DS getting a WRITE and the MDS getting an
INITIALIZE. --TH]]
6.3. An Example of Detecting Corruption
In this section, we define an ADB format in which corruption can be
detected. Note that this is just one possible format and means to
detect corruption.
Consider a very basic implementation of an operating system's disk
blocks. A block is either data or it is an indirect block which
allows for files to be larger than one block. It is desired to be
able to initialize a block. Lastly, to quickly unlink a file, a
block can be marked invalid. The contents remain intact - which
would enable this OS application to undelete a file.
The application defines 4k sized data blocks, with an 8 byte block
counter occurring at offset 0 in the block, and with the guard
pattern occurring at offset 8 inside the block. Furthermore, the
guard pattern can take one of four states:
0xfeedface - This is the FREE state and indicates that the ADB
format has been applied.
0xcafedead - This is the DATA state and indicates that real data
has been written to this block.
0xe4e5c001 - This is the INDIRECT state and indicates that the
block contains block counter numbers that are chained off of this
block.
0xba1ed4a3 - This is the INVALID state and indicates that the block
contains data whose contents are garbage.
Finally, it also defines an 8 byte checksum [21] starting at byte 16
which applies to the remaining contents of the block. If the state
is FREE, then that checksum is trivially zero. As such, the
application has no need to transfer the checksum implicitly inside
the ADB - it need not make the transfer layer aware of the fact that
there is a checksum (see [19] for an example of checksums used to
detect corruption in application data blocks).
Corruption in each ADB can be detected thusly:
o If the guard pattern is anything other than one of the allowed
values, including all zeros.
Haynes Expires July 7, 2012 [Page 33]
Internet-Draft NFSv4.2 January 2012
o If the guard pattern is FREE and any other byte in the remainder
of the ADB is anything other than zero.
o If the guard pattern is anything other than FREE, then if the
stored checksum does not match the computed checksum.
o If the guard pattern is INDIRECT and one of the stored indirect
block numbers has a value greater than the number of ADBs in the
file.
o If the guard pattern is INDIRECT and one of the stored indirect
block numbers is a duplicate of another stored indirect block
number.
As can be seen, the application can detect errors based on the
combination of the guard pattern state and the checksum. But also,
the application can detect corruption based on the state and the
contents of the ADB. This last point is important in validating the
minimum amount of data we incorporated into our generic framework.
I.e., the guard pattern is sufficient in allowing applications to
design their own corruption detection.
Finally, it is important to note that none of these corruption checks
occur in the transport layer. The server and client components are
totally unaware of the file format and might report everything as
being transferred correctly even in the case the application detects
corruption.
6.4. Example of READ_PLUS
The hypothetical application presented in Section 6.3 can be used to
illustrate how READ_PLUS would return an array of results. A file is
created and initialized with 100 4k ADBs in the FREE state:
INITIALIZE {0, 4k, 100, 0, 0, 8, 0xfeedface}
Further, assume the application writes a single ADB at 16k, changing
the guard pattern to 0xcafedead, we would then have in memory:
0 -> (16k - 1) : 4k, 4, 0, 0, 8, 0xfeedface
16k -> (20k - 1) : 00 00 00 05 ca fe de ad XX XX ... XX XX
20k -> 400k : 4k, 95, 0, 6, 0xfeedface
And when the client did a READ_PLUS of 64k at the start of the file,
it would get back a result of an ADB, some data, and a final ADB:
ADB {0, 4, 0, 0, 8, 0xfeedface}
data 4k
Haynes Expires July 7, 2012 [Page 34]
Internet-Draft NFSv4.2 January 2012
ADB {20k, 4k, 59, 0, 6, 0xfeedface}
6.5. Zero Filled Holes
As applications are free to define the structure of an ADB, it is
trivial to define an ADB which supports zero filled holes. Such a
case would encompass the traditional definitions of a sparse file and
hole punching. For example, to punch a 64k hole, starting at 100M,
into an existing file which has no ADB structure:
INITIALIZE {100M, 64k, 1, NFS4_UINT64_MAX,
0, NFS4_UINT64_MAX, 0x0}
7. Labeled NFS
7.1. Introduction
Access control models such as Unix permissions or Access Control
Lists are commonly referred to as Discretionary Access Control (DAC)
models. These systems base their access decisions on user identity
and resource ownership. In contrast Mandatory Access Control (MAC)
models base their access control decisions on the label on the
subject (usually a process) and the object it wishes to access.
These labels may contain user identity information but usually
contain additional information. In DAC systems users are free to
specify the access rules for resources that they own. MAC models
base their security decisions on a system wide policy established by
an administrator or organization which the users do not have the
ability to override. In this section, we add a MAC model to NFSv4.
The first change necessary is to devise a method for transporting and
storing security label data on NFSv4 file objects. Security labels
have several semantics that are met by NFSv4 recommended attributes
such as the ability to set the label value upon object creation.
Access control on these attributes are done through a combination of
two mechanisms. As with other recommended attributes on file objects
the usual DAC checks (ACLs and permission bits) will be performed to
ensure that proper file ownership is enforced. In addition a MAC
system MAY be employed on the client, server, or both to enforce
additional policy on what subjects may modify security label
information.
The second change is to provide a method for the server to notify the
client that the attribute changed on an open file on the server. If
the file is closed, then during the open attempt, the client will
gather the new attribute value. The server MUST not communicate the
new value of the attribute, the client MUST query it. This
Haynes Expires July 7, 2012 [Page 35]
Internet-Draft NFSv4.2 January 2012
requirement stems from the need for the client to provide sufficient
access rights to the attribute.
The final change necessary is a modification to the RPC layer used in
NFSv4 in the form of a new version of the RPCSEC_GSS [7] framework.
In order for an NFSv4 server to apply MAC checks it must obtain
additional information from the client. Several methods were
explored for performing this and it was decided that the best
approach was to incorporate the ability to make security attribute
assertions through the RPC mechanism. RPCSECGSSv3 [5] outlines a
method to assert additional security information such as security
labels on gss context creation and have that data bound to all RPC
requests that make use of that context.
7.2. Definitions
Label Format Specifier (LFS): is an identifier used by the client to
establish the syntactic format of the security label and the
semantic meaning of its components. These specifiers exist in a
registry associated with documents describing the format and
semantics of the label.
Label Format Registry: is the IANA registry containing all
registered LFS along with references to the documents that
describe the syntactic format and semantics of the security label.
Policy Identifier (PI): is an optional part of the definition of a
Label Format Specifier which allows for clients and server to
identify specific security policies.
Domain of Interpretation (DOI): represents an administrative
security boundary, where all systems within the DOI have
semantically coherent labeling. That is, a security attribute
must always mean exactly the same thing anywhere within the DOI.
Object: is a passive resource within the system that we wish to be
protected. Objects can be entities such as files, directories,
pipes, sockets, and many other system resources relevant to the
protection of the system state.
Subject: A subject is an active entity usually a process which is
requesting access to an object.
Multi-Level Security (MLS): is a traditional model where objects are
given a sensitivity level (Unclassified, Secret, Top Secret, etc)
and a category set [Section 46.6. Multi-Level Security (MLS) of Deployment Guide: Deployment, configuration and administration of Red Hat Enterprise Linux 5, Edition 6"">22].
Haynes Expires July 7, 2012 [Page 36]
Internet-Draft NFSv4.2 January 2012
7.3. MAC Security Attribute
MAC models base access decisions on security attributes bound to
subjects and objects. This information can range from a user
identity for an identity based MAC model, sensitivity levels for
Multi-level security, or a type for Type Enforcement. These models
base their decisions on different criteria but the semantics of the
security attribute remain the same. The semantics required by the
security attributes are listed below:
o Must provide flexibility with respect to MAC model.
o Must provide the ability to atomically set security information
upon object creation
o Must provide the ability to enforce access control decisions both
on the client and the server
o Must not expose an object to either the client or server name
space before its security information has been bound to it.
NFSv4 implements the security attribute as a recommended attribute.
These attributes have a fixed format and semantics, which conflicts
with the flexible nature of the security attribute. To resolve this
the security attribute consists of two components. The first
component is a LFS as defined in [23] to allow for interoperability
between MAC mechanisms. The second component is an opaque field
which is the actual security attribute data. To allow for various
MAC models NFSv4 should be used solely as a transport mechanism for
the security attribute. It is the responsibility of the endpoints to
consume the security attribute and make access decisions based on
their respective models. In addition, creation of objects through
OPEN and CREATE allows for the security attribute to be specified
upon creation. By providing an atomic create and set operation for
the security attribute it is possible to enforce the second and
fourth requirements. The recommended attribute FATTR4_SEC_LABEL will
be used to satisfy this requirement.
7.3.1. Interpreting FATTR4_SEC_LABEL
The XDR [24] necessary to implement Labeled NFSv4 is presented below:
const FATTR4_SEC_LABEL = 81;
typedef uint32_t policy4;
Figure 6
Haynes Expires July 7, 2012 [Page 37]
Internet-Draft NFSv4.2 January 2012
struct labelformat_spec4 {
policy4 lfs_lfs;
policy4 lfs_pi;
};
struct sec_label_attr_info {
labelformat_spec4 slai_lfs;
opaque slai_data<>;
};
The FATTR4_SEC_LABEL contains an array of two components with the
first component being an LFS. It serves to provide the receiving end
with the information necessary to translate the security attribute
into a form that is usable by the endpoint. Label Formats assigned
an LFS may optionally choose to include a Policy Identifier field to
allow for complex policy deployments. The LFS and Label Format
Registry are described in detail in [23]. The translation used to
interpret the security attribute is not specified as part of the
protocol as it may depend on various factors. The second component
is an opaque section which contains the data of the attribute. This
component is dependent on the MAC model to interpret and enforce.
In particular, it is the responsibility of the LFS specification to
define a maximum size for the opaque section, slai_data<>. When
creating or modifying a label for an object, the client needs to be
guaranteed that the server will accept a label that is sized
correctly. By both client and server being part of a specific MAC
model, the client will be aware of the size.
7.3.2. Delegations
In the event that a security attribute is changed on the server while
a client holds a delegation on the file, the client should follow the
existing protocol with respect to attribute changes. It should flush
all changes back to the server and relinquish the delegation.
7.3.3. Permission Checking
It is not feasible to enumerate all possible MAC models and even
levels of protection within a subset of these models. This means
that the NFSv4 client and servers cannot be expected to directly make
access control decisions based on the security attribute. Instead
NFSv4 should defer permission checking on this attribute to the host
system. These checks are performed in addition to existing DAC and
ACL checks outlined in the NFSv4 protocol. Section 7.6 gives a
specific example of how the security attribute is handled under a
particular MAC model.
Haynes Expires July 7, 2012 [Page 38]
Internet-Draft NFSv4.2 January 2012
7.3.4. Object Creation
When creating files in NFSv4 the OPEN and CREATE operations are used.
One of the parameters to these operations is an fattr4 structure
containing the attributes the file is to be created with. This
allows NFSv4 to atomically set the security attribute of files upon
creation. When a client is MAC aware it must always provide the
initial security attribute upon file creation. In the event that the
server is the only MAC aware entity in the system it should ignore
the security attribute specified by the client and instead make the
determination itself. A more in depth explanation can be found in
Section 7.6.
7.3.5. Existing Objects
Note that under the MAC model, all objects must have labels.
Therefore, if an existing server is upgraded to include LNFS support,
then it is the responsibility of the security system to define the
behavior for existing objects. For example, if the security system
is LFS 0, which means the server just stores and returns labels, then
existing files should return labels which are set to an empty value.
7.3.6. Label Changes
As per the requirements, when a file's security label is modified,
the server must notify all clients which have the file opened of the
change in label. It does so with CB_ATTR_CHANGED. There are
preconditions to making an attribute change imposed by NFSv4 and the
security system might want to impose others. In the process of
meeting these preconditions, the server may chose to either serve the
request in whole or return NFS4ERR_DELAY to the SETATTR operation.
If there are open delegations on the file belonging to client other
than the one making the label change, then the process described in
Section 7.3.2 must be followed.
As the server is always presented with the subject label from the
client, it does not necessarily need to communicate the fact that the
label has changed to the client. In the cases where the change
outright denies the client access, the client will be able to quickly
determine that there is a new label in effect. It is in cases where
the client may share the same object between multiple subjects or a
security system which is not strictly hierarchical that the
CB_ATTR_CHANGED callback is very useful. It allows the server to
inform the clients that the cached security attribute is now stale.
Consider a system in which the clients enforce MAC checks and and the
server has a very simple security system which just stores the
Haynes Expires July 7, 2012 [Page 39]
Internet-Draft NFSv4.2 January 2012
labels. In this system, the MAC label check always allows access,
regardless of the subject label.
The way in which MAC labels are enforced is by the smart client. So
if client A changes a security label on a file, then the server MUST
inform all clients that have the file opened that the label has
changed via CB_ATTR_CHANGED. Then the clients MUST retrieve the new
label and MUST enforce access via the new attribute values.
[[Comment.6: Describe a LFS of 0, which will be the means to indicate
such a deployment. In the current LFR, 0 is marked as reserved. If
we use it, then we define the default LFS to be used by a LNFS aware
server. I.e., it lets smart clients work together in the face of a
dumb server. Note that will supporting this system is optional, it
will make for a very good debugging mode during development. I.e.,
even if a server does not deploy with another security system, this
mode gets your foot in the door. --TH]]
7.4. pNFS Considerations
This section examines the issues in deploying LNFS in a pNFS
community of servers.
7.4.1. MAC Label Checks
The new FATTR4_SEC_LABEL attribute is metadata information and as
such the DS is not aware of the value contained on the MDS.
Fortunately, the NFSv4.1 protocol [2] already has provisions for
doing access level checks from the DS to the MDS. In order for the
DS to validate the subject label presented by the client, it SHOULD
utilize this mechanism.
If a file's FATTR4_SEC_LABEL is changed, then the MDS should utilize
CB_ATTR_CHANGED to inform the client of that fact. If the MDS is
maintaining
7.5. Discovery of Server LNFS Support
The server can easily determine that a client supports LNFS when it
queries for the FATTR4_SEC_LABEL label for an object. Note that it
cannot assume that the presence of RPCSEC_GSSv3 indicates LNFS
support. The client might need to discover which LFS the server
supports.
A server which supports LNFS MUST allow a client with any subject
label to retrieve the FATTR4_SEC_LABEL attribute for the root
filehandle, ROOTFH. The following compound must always succeed as
far as a MAC label check is concerned:
Haynes Expires July 7, 2012 [Page 40]
Internet-Draft NFSv4.2 January 2012
PUTROOTFH, GETATTR {FATTR4_SEC_LABEL}
Note that the server might have imposed a security flavor on the root
that precludes such access. I.e., if the server requires kerberized
access and the client presents a compound with AUTH_SYS, then the
server is allowed to return NFS4ERR_WRONGSEC in this case. But if
the client presents a correct security flavor, then the server MUST
return the FATTR4_SEC_LABEL attribute with the supported LFS filled
in.
7.6. MAC Security NFS Modes of Operation
A system using Labeled NFS may operate in three modes. The first
mode provides the most protection and is called "full mode". In this
mode both the client and server implement a MAC model allowing each
end to make an access control decision. The remaining two modes are
variations on each other and are called "smart client" and "smart
server" modes. In these modes one end of the connection is not
implementing a MAC model and because of this these operating modes
offer less protection than full mode.
7.6.1. Full Mode
Full mode environments consist of MAC aware NFSv4 servers and clients
and may be composed of mixed MAC models and policies. The system
requires that both the client and server have an opportunity to
perform an access control check based on all relevant information
within the network. The file object security attribute is provided
using the mechanism described in Section 7.3. The security attribute
of the subject making the request is transported at the RPC layer
using the mechanism described in RPCSECGSSv3 [5].
7.6.1.1. Initial Labeling and Translation
The ability to create a file is an action that a MAC model may wish
to mediate. The client is given the responsibility to determine the
initial security attribute to be placed on a file. This allows the
client to make a decision as to the acceptable security attributes to
create a file with before sending the request to the server. Once
the server receives the creation request from the client it may
choose to evaluate if the security attribute is acceptable.
Security attributes on the client and server may vary based on MAC
model and policy. To handle this the security attribute field has an
LFS component. This component is a mechanism for the host to
identify the format and meaning of the opaque portion of the security
attribute. A full mode environment may contain hosts operating in
several different LFSs and DOIs. In this case a mechanism for
Haynes Expires July 7, 2012 [Page 41]
Internet-Draft NFSv4.2 January 2012
translating the opaque portion of the security attribute is needed.
The actual translation function will vary based on MAC model and
policy and is out of the scope of this document. If a translation is
unavailable for a given LFS and DOI then the request SHOULD be
denied. Another recourse is to allow the host to provide a fallback
mapping for unknown security attributes.
7.6.1.2. Policy Enforcement
In full mode access control decisions are made by both the clients
and servers. When a client makes a request it takes the security
attribute from the requesting process and makes an access control
decision based on that attribute and the security attribute of the
object it is trying to access. If the client denies that access an
RPC call to the server is never made. If however the access is
allowed the client will make a call to the NFS server.
When the server receives the request from the client it extracts the
security attribute conveyed in the RPC request. The server then uses
this security attribute and the attribute of the object the client is
trying to access to make an access control decision. If the server's
policy allows this access it will fulfill the client's request,
otherwise it will return NFS4ERR_ACCESS.
Implementations MAY validate security attributes supplied over the
network to ensure that they are within a set of attributes permitted
from a specific peer, and if not, reject them. Note that a system
may permit a different set of attributes to be accepted from each
peer.
7.6.2. Smart Client Mode
Smart client environments consist of NFSv4 servers that are not MAC
aware but NFSv4 clients that are. Clients in this environment are
may consist of groups implementing different MAC models policies.
The system requires that all clients in the environment be
responsible for access control checks. Due to the amount of trust
placed in the clients this mode is only to be used in a trusted
environment.
7.6.2.1. Initial Labeling and Translation
Just like in full mode the client is responsible for determining the
initial label upon object creation. The server in smart client mode
does not implement a MAC model, however, it may provide the ability
to restrict the creation and labeling of object with certain labels
based on different criteria as described in Section 7.6.1.2.
Haynes Expires July 7, 2012 [Page 42]
Internet-Draft NFSv4.2 January 2012
In a smart client environment a group of clients operate in a single
DOI. This removes the need for the clients to maintain a set of DOI
translations. Servers should provide a method to allow different
groups of clients to access the server at the same time. However it
should not let two groups of clients operating in different DOIs to
access the same files.
7.6.2.2. Policy Enforcement
In smart client mode access control decisions are made by the
clients. When a client accesses an object it obtains the security
attribute of the object from the server and combines it with the
security attribute of the process making the request to make an
access control decision. This check is in addition to the DAC checks
provided by NFSv4 so this may fail based on the DAC criteria even if
the MAC policy grants access. As the policy check is located on the
client an access control denial should take the form that is native
to the platform.
7.6.3. Smart Server Mode
Smart server environments consist of NFSv4 servers that are MAC aware
and one or more MAC unaware clients. The server is the only entity
enforcing policy, and may selectively provide standard NFS services
to clients based on their authentication credentials and/or
associated network attributes (e.g., IP address, network interface).
The level of trust and access extended to a client in this mode is
configuration-specific.
7.6.3.1. Initial Labeling and Translation
In smart server mode all labeling and access control decisions are
performed by the NFSv4 server. In this environment the NFSv4 clients
are not MAC aware so they cannot provide input into the access
control decision. This requires the server to determine the initial
labeling of objects. Normally the subject to use in this calculation
would originate from the client. Instead the NFSv4 server may choose
to assign the subject security attribute based on their
authentication credentials and/or associated network attributes
(e.g., IP address, network interface).
In smart server mode security attributes are contained solely within
the NFSv4 server. This means that all security attributes used in
the system remain within a single LFS and DOI. Since security
attributes will not cross DOIs or change format there is no need to
provide any translation functionality above that which is needed
internally by the MAC model.
Haynes Expires July 7, 2012 [Page 43]
Internet-Draft NFSv4.2 January 2012
7.6.3.2. Policy Enforcement
All access control decisions in smart server mode are made by the
server. The server will assign the subject a security attribute
based on some criteria (e.g., IP address, network interface). Using
the newly calculated security attribute and the security attribute of
the object being requested the MAC model makes the access control
check and returns NFS4ERR_ACCESS on a denial and NFS4_OK on success.
This check is done transparently to the client so if the MAC
permission check fails the client may be unaware of the reason for
the permission failure. When operating in this mode administrators
attempting to debug permission failures should be aware to check the
MAC policy running on the server in addition to the DAC settings.
7.7. Security Considerations
This entire document deals with security issues.
Depending on the level of protection the MAC system offers there may
be a requirement to tightly bind the security attribute to the data.
When only one of the client or server enforces labels, it is
important to realize that the other side is not enforcing MAC
protections. Alternate methods might be in use to handle the lack of
MAC support and care should be taken to identify and mitigate threats
from possible tampering outside of these methods.
An example of this is that a server that modifies READDIR or LOOKUP
results based on the client's subject label might want to always
construct the same subject label for a client which does not present
one. This will prevent a non-LNFS client from mixing entries in the
directory cache.
8. Sharing change attribute implementation details with NFSv4 clients
8.1. Introduction
Although both the NFSv4 [11] and NFSv4.1 protocol [2], define the
change attribute as being mandatory to implement, there is little in
the way of guidance. The only feature that is mandated by them is
that the value must change whenever the file data or metadata change.
While this allows for a wide range of implementations, it also leaves
the client with a conundrum: how does it determine which is the most
recent value for the change attribute in a case where several RPC
calls have been issued in parallel? In other words if two COMPOUNDs,
both containing WRITE and GETATTR requests for the same file, have
Haynes Expires July 7, 2012 [Page 44]
Internet-Draft NFSv4.2 January 2012
been issued in parallel, how does the client determine which of the
two change attribute values returned in the replies to the GETATTR
requests corresponds to the most recent state of the file? In some
cases, the only recourse may be to send another COMPOUND containing a
third GETATTR that is fully serialised with the first two.
NFSv4.2 avoids this kind of inefficiency by allowing the server to
share details about how the change attribute is expected to evolve,
so that the client may immediately determine which, out of the
several change attribute values returned by the server, is the most
recent.
8.2. Definition of the 'change_attr_type' per-file system attribute
enum change_attr_typeinfo {
NFS4_CHANGE_TYPE_IS_MONOTONIC_INCR = 0,
NFS4_CHANGE_TYPE_IS_VERSION_COUNTER = 1,
NFS4_CHANGE_TYPE_IS_VERSION_COUNTER_NOPNFS = 2,
NFS4_CHANGE_TYPE_IS_TIME_METADATA = 3,
NFS4_CHANGE_TYPE_IS_UNDEFINED = 4
};
+------------------+----+---------------------------+-----+
| Name | Id | Data Type | Acc |
+------------------+----+---------------------------+-----+
| change_attr_type | XX | enum change_attr_typeinfo | R |
+------------------+----+---------------------------+-----+
The solution enables the NFS server to provide additional information
about how it expects the change attribute value to evolve after the
file data or metadata has changed. 'change_attr_type' is defined as a
new recommended attribute, and takes values from enum
change_attr_typeinfo as follows:
NFS4_CHANGE_TYPE_IS_MONOTONIC_INCR: The change attribute value MUST
monotonically increase for every atomic change to the file
attributes, data or directory contents.
NFS4_CHANGE_TYPE_IS_VERSION_COUNTER: The change attribute value MUST
be incremented by one unit for every atomic change to the file
attributes, data or directory contents. This property is
preserved when writing to pNFS data servers.
NFS4_CHANGE_TYPE_IS_VERSION_COUNTER_NOPNFS: The change attribute
value MUST be incremented by one unit for every atomic change to
the file attributes, data or directory contents. In the case
where the client is writing to pNFS data servers, the number of
increments is not guaranteed to exactly match the number of
Haynes Expires July 7, 2012 [Page 45]
Internet-Draft NFSv4.2 January 2012
writes.
NFS4_CHANGE_TYPE_IS_TIME_METADATA: The change attribute is
implemented as suggested in the NFSv4 spec [11] in terms of the
time_metadata attribute.
NFS4_CHANGE_TYPE_IS_UNDEFINED: The change attribute does not take
values that fit into any of these categories.
If either NFS4_CHANGE_TYPE_IS_MONOTONIC_INCR,
NFS4_CHANGE_TYPE_IS_VERSION_COUNTER, or
NFS4_CHANGE_TYPE_IS_TIME_METADATA are set, then the client knows at
the very least that the change attribute is monotonically increasing,
which is sufficient to resolve the question of which value is the
most recent.
If the client sees the value NFS4_CHANGE_TYPE_IS_TIME_METADATA, then
by inspecting the value of the 'time_delta' attribute it additionally
has the option of detecting rogue server implementations that use
time_metadata in violation of the spec.
Finally, if the client sees NFS4_CHANGE_TYPE_IS_VERSION_COUNTER, it
has the ability to predict what the resulting change attribute value
should be after a COMPOUND containing a SETATTR, WRITE, or CREATE.
This again allows it to detect changes made in parallel by another
client. The value NFS4_CHANGE_TYPE_IS_VERSION_COUNTER_NOPNFS permits
the same, but only if the client is not doing pNFS WRITEs.
9. Security Considerations
10. File Attributes
10.1. Attribute Definitions
10.1.1. Attribute 77: space_reserved
The space_reserve attribute is a read/write attribute of type
boolean. It is a per file attribute. When the space_reserved
attribute is set via SETATTR, the server must ensure that there is
disk space to accommodate every byte in the file before it can return
success. If the server cannot guarantee this, it must return
NFS4ERR_NOSPC.
If the client tries to grow a file which has the space_reserved
attribute set, the server must guarantee that there is disk space to
accommodate every byte in the file with the new size before it can
Haynes Expires July 7, 2012 [Page 46]
Internet-Draft NFSv4.2 January 2012
return success. If the server cannot guarantee this, it must return
NFS4ERR_NOSPC.
It is not required that the server allocate the space to the file
before returning success. The allocation can be deferred, however,
it must be guaranteed that it will not fail for lack of space.
The value of space_reserved can be obtained at any time through
GETATTR.
In order to avoid ambiguity, the space_reserve bit cannot be set
along with the size bit in SETATTR. Increasing the size of a file
with space_reserve set will fail if space reservation cannot be
guaranteed for the new size. If the file size is decreased, space
reservation is only guaranteed for the new size and the extra blocks
backing the file can be released.
10.1.2. Attribute 78: space_freed
space_freed gives the number of bytes freed if the file is deleted.
This attribute is read only and is of type length4. It is a per file
attribute.
11. Operations: REQUIRED, RECOMMENDED, or OPTIONAL
The following tables summarize the operations of the NFSv4.2 protocol
and the corresponding designation of REQUIRED, RECOMMENDED, and
OPTIONAL to implement or MUST NOT implement. The designation of MUST
NOT implement is reserved for those operations that were defined in
either NFSv4.0 or NFSV4.1 and MUST NOT be implemented in NFSv4.2.
For the most part, the REQUIRED, RECOMMENDED, or OPTIONAL designation
for operations sent by the client is for the server implementation.
The client is generally required to implement the operations needed
for the operating environment for which it serves. For example, a
read-only NFSv4.2 client would have no need to implement the WRITE
operation and is not required to do so.
The REQUIRED or OPTIONAL designation for callback operations sent by
the server is for both the client and server. Generally, the client
has the option of creating the backchannel and sending the operations
on the fore channel that will be a catalyst for the server sending
callback operations. A partial exception is CB_RECALL_SLOT; the only
way the client can avoid supporting this operation is by not creating
a backchannel.
Since this is a summary of the operations and their designation,
Haynes Expires July 7, 2012 [Page 47]
Internet-Draft NFSv4.2 January 2012
there are subtleties that are not presented here. Therefore, if
there is a question of the requirements of implementation, the
operation descriptions themselves must be consulted along with other
relevant explanatory text within this either specification or that of
NFSv4.1 [2]..
The abbreviations used in the second and third columns of the table
are defined as follows.
REQ REQUIRED to implement
REC RECOMMEND to implement
OPT OPTIONAL to implement
MNI MUST NOT implement
For the NFSv4.2 features that are OPTIONAL, the operations that
support those features are OPTIONAL, and the server would return
NFS4ERR_NOTSUPP in response to the client's use of those operations.
If an OPTIONAL feature is supported, it is possible that a set of
operations related to the feature become REQUIRED to implement. The
third column of the table designates the feature(s) and if the
operation is REQUIRED or OPTIONAL in the presence of support for the
feature.
The OPTIONAL features identified and their abbreviations are as
follows:
pNFS Parallel NFS
FDELG File Delegations
DDELG Directory Delegations
COPY Server Side Copy
ADB Application Data Blocks
Operations
+----------------------+--------------------+-----------------------+
| Operation | REQ, REC, OPT, or | Feature (REQ, REC, or |
| | MNI | OPT) |
+----------------------+--------------------+-----------------------+
| ACCESS | REQ | |
| BACKCHANNEL_CTL | REQ | |
| BIND_CONN_TO_SESSION | REQ | |
Haynes Expires July 7, 2012 [Page 48]
Internet-Draft NFSv4.2 January 2012
| CLOSE | REQ | |
| COMMIT | REQ | |
| COPY | OPT | COPY (REQ) |
| COPY_ABORT | OPT | COPY (REQ) |
| COPY_NOTIFY | OPT | COPY (REQ) |
| COPY_REVOKE | OPT | COPY (REQ) |
| COPY_STATUS | OPT | COPY (REQ) |
| CREATE | REQ | |
| CREATE_SESSION | REQ | |
| DELEGPURGE | OPT | FDELG (REQ) |
| DELEGRETURN | OPT | FDELG, DDELG, pNFS |
| | | (REQ) |
| DESTROY_CLIENTID | REQ | |
| DESTROY_SESSION | REQ | |
| EXCHANGE_ID | REQ | |
| FREE_STATEID | REQ | |
| GETATTR | REQ | |
| GETDEVICEINFO | OPT | pNFS (REQ) |
| GETDEVICELIST | OPT | pNFS (OPT) |
| GETFH | REQ | |
| INITIALIZE | OPT | ADB (REQ) |
| GET_DIR_DELEGATION | OPT | DDELG (REQ) |
| LAYOUTCOMMIT | OPT | pNFS (REQ) |
| LAYOUTGET | OPT | pNFS (REQ) |
| LAYOUTRETURN | OPT | pNFS (REQ) |
| LINK | OPT | |
| LOCK | REQ | |
| LOCKT | REQ | |
| LOCKU | REQ | |
| LOOKUP | REQ | |
| LOOKUPP | REQ | |
| NVERIFY | REQ | |
| OPEN | REQ | |
| OPENATTR | OPT | |
| OPEN_CONFIRM | MNI | |
| OPEN_DOWNGRADE | REQ | |
| PUTFH | REQ | |
| PUTPUBFH | REQ | |
| PUTROOTFH | REQ | |
| READ | OPT | |
| READDIR | REQ | |
| READLINK | OPT | |
| READ_PLUS | OPT | ADB (REQ) |
| RECLAIM_COMPLETE | REQ | |
| RELEASE_LOCKOWNER | MNI | |
| REMOVE | REQ | |
| RENAME | REQ | |
| RENEW | MNI | |
Haynes Expires July 7, 2012 [Page 49]
Internet-Draft NFSv4.2 January 2012
| RESTOREFH | REQ | |
| SAVEFH | REQ | |
| SECINFO | REQ | |
| SECINFO_NO_NAME | REC | pNFS file layout |
| | | (REQ) |
| SEQUENCE | REQ | |
| SETATTR | REQ | |
| SETCLIENTID | MNI | |
| SETCLIENTID_CONFIRM | MNI | |
| SET_SSV | REQ | |
| TEST_STATEID | REQ | |
| VERIFY | REQ | |
| WANT_DELEGATION | OPT | FDELG (OPT) |
| WRITE | REQ | |
+----------------------+--------------------+-----------------------+
Callback Operations
+-------------------------+-------------------+---------------------+
| Operation | REQ, REC, OPT, or | Feature (REQ, REC, |
| | MNI | or OPT) |
+-------------------------+-------------------+---------------------+
| CB_COPY | OPT | COPY (REQ) |
| CB_GETATTR | OPT | FDELG (REQ) |
| CB_LAYOUTRECALL | OPT | pNFS (REQ) |
| CB_NOTIFY | OPT | DDELG (REQ) |
| CB_NOTIFY_DEVICEID | OPT | pNFS (OPT) |
| CB_NOTIFY_LOCK | OPT | |
| CB_PUSH_DELEG | OPT | FDELG (OPT) |
| CB_RECALL | OPT | FDELG, DDELG, pNFS |
| | | (REQ) |
| CB_RECALL_ANY | OPT | FDELG, DDELG, pNFS |
| | | (REQ) |
| CB_RECALL_SLOT | REQ | |
| CB_RECALLABLE_OBJ_AVAIL | OPT | DDELG, pNFS (REQ) |
| CB_SEQUENCE | OPT | FDELG, DDELG, pNFS |
| | | (REQ) |
| CB_WANTS_CANCELLED | OPT | FDELG, DDELG, pNFS |
| | | (REQ) |
+-------------------------+-------------------+---------------------+
12. NFSv4.2 Operations
12.1. Operation 59: COPY - Initiate a server-side copy
Haynes Expires July 7, 2012 [Page 50]
Internet-Draft NFSv4.2 January 2012
12.1.1. ARGUMENT
const COPY4_GUARDED = 0x00000001;
const COPY4_METADATA = 0x00000002;
struct COPY4args {
/* SAVED_FH: source file */
/* CURRENT_FH: destination file or */
/* directory */
offset4 ca_src_offset;
offset4 ca_dst_offset;
length4 ca_count;
uint32_t ca_flags;
component4 ca_destination;
netloc4 ca_source_server<>;
};
12.1.2. RESULT
union COPY4res switch (nfsstat4 cr_status) {
case NFS4_OK:
stateid4 cr_callback_id<1>;
default:
length4 cr_bytes_copied;
};
12.1.3. DESCRIPTION
The COPY operation is used for both intra-server and inter-server
copies. In both cases, the COPY is always sent from the client to
the destination server of the file copy. The COPY operation requests
that a file be copied from the location specified by the SAVED_FH
value to the location specified by the combination of CURRENT_FH and
ca_destination.
The SAVED_FH must be a regular file. If SAVED_FH is not a regular
file, the operation MUST fail and return NFS4ERR_WRONG_TYPE.
In order to set SAVED_FH to the source file handle, the compound
procedure requesting the COPY will include a sub-sequence of
operations such as
PUTFH source-fh
SAVEFH
Haynes Expires July 7, 2012 [Page 51]
Internet-Draft NFSv4.2 January 2012
If the request is for a server-to-server copy, the source-fh is a
filehandle from the source server and the compound procedure is being
executed on the destination server. In this case, the source-fh is a
foreign filehandle on the server receiving the COPY request. If
either PUTFH or SAVEFH checked the validity of the filehandle, the
operation would likely fail and return NFS4ERR_STALE.
In order to avoid this problem, the minor version incorporating the
COPY operations will need to make a few small changes in the handling
of existing operations. If a server supports the server-to-server
COPY feature, a PUTFH followed by a SAVEFH MUST NOT return
NFS4ERR_STALE for either operation. These restrictions do not pose
substantial difficulties for servers. The CURRENT_FH and SAVED_FH
may be validated in the context of the operation referencing them and
an NFS4ERR_STALE error returned for an invalid file handle at that
point.
The CURRENT_FH and ca_destination together specify the destination of
the copy operation. If ca_destination is of 0 (zero) length, then
CURRENT_FH specifies the target file. In this case, CURRENT_FH MUST
be a regular file and not a directory. If ca_destination is not of 0
(zero) length, the ca_destination argument specifies the file name to
which the data will be copied within the directory identified by
CURRENT_FH. In this case, CURRENT_FH MUST be a directory and not a
regular file.
If the file named by ca_destination does not exist and the operation
completes successfully, the file will be visible in the file system
namespace. If the file does not exist and the operation fails, the
file MAY be visible in the file system namespace depending on when
the failure occurs and on the implementation of the NFS server
receiving the COPY operation. If the ca_destination name cannot be
created in the destination file system (due to file name
restrictions, such as case or length), the operation MUST fail.
The ca_src_offset is the offset within the source file from which the
data will be read, the ca_dst_offset is the offset within the
destination file to which the data will be written, and the ca_count
is the number of bytes that will be copied. An offset of 0 (zero)
specifies the start of the file. A count of 0 (zero) requests that
all bytes from ca_src_offset through EOF be copied to the
destination. If concurrent modifications to the source file overlap
with the source file region being copied, the data copied may include
all, some, or none of the modifications. The client can use standard
NFS operations (e.g., OPEN with OPEN4_SHARE_DENY_WRITE or mandatory
byte range locks) to protect against concurrent modifications if the
client is concerned about this. If the source file's end of file is
being modified in parallel with a copy that specifies a count of 0
Haynes Expires July 7, 2012 [Page 52]
Internet-Draft NFSv4.2 January 2012
(zero) bytes, the amount of data copied is implementation dependent
(clients may guard against this case by specifying a non-zero count
value or preventing modification of the source file as mentioned
above).
If the source offset or the source offset plus count is greater than
or equal to the size of the source file, the operation will fail with
NFS4ERR_INVAL. The destination offset or destination offset plus
count may be greater than the size of the destination file. This
allows for the client to issue parallel copies to implement
operations such as "cat file1 file2 file3 file4 > dest".
If the destination file is created as a result of this command, the
destination file's size will be equal to the number of bytes
successfully copied. If the destination file already existed, the
destination file's size may increase as a result of this operation
(e.g. if ca_dst_offset plus ca_count is greater than the
destination's initial size).
If the ca_source_server list is specified, then this is an inter-
server copy operation and the source file is on a remote server. The
client is expected to have previously issued a successful COPY_NOTIFY
request to the remote source server. The ca_source_server list
SHOULD be the same as the COPY_NOTIFY response's cnr_source_server
list. If the client includes the entries from the COPY_NOTIFY
response's cnr_source_server list in the ca_source_server list, the
source server can indicate a specific copy protocol for the
destination server to use by returning a URL, which specifies both a
protocol service and server name. Server-to-server copy protocol
considerations are described in Section 2.2.3 and Section 2.4.1.
The ca_flags argument allows the copy operation to be customized in
the following ways using the guarded flag (COPY4_GUARDED) and the
metadata flag (COPY4_METADATA).
If the guarded flag is set and the destination exists on the server,
this operation will fail with NFS4ERR_EXIST.
If the guarded flag is not set and the destination exists on the
server, the behavior is implementation dependent.
If the metadata flag is set and the client is requesting a whole file
copy (i.e., ca_count is 0 (zero)), a subset of the destination file's
attributes MUST be the same as the source file's corresponding
attributes and a subset of the destination file's attributes SHOULD
be the same as the source file's corresponding attributes. The
attributes in the MUST and SHOULD copy subsets will be defined for
each NFS version.
Haynes Expires July 7, 2012 [Page 53]
Internet-Draft NFSv4.2 January 2012
For NFSv4.1, Table 1 and Table 2 list the REQUIRED and RECOMMENDED
attributes respectively. A "MUST" in the "Copy to destination file?"
column indicates that the attribute is part of the MUST copy set. A
"SHOULD" in the "Copy to destination file?" column indicates that the
attribute is part of the SHOULD copy set.
+--------------------+----+---------------------------+
| Name | Id | Copy to destination file? |
+--------------------+----+---------------------------+
| supported_attrs | 0 | no |
| type | 1 | MUST |
| fh_expire_type | 2 | no |
| change | 3 | SHOULD |
| size | 4 | MUST |
| link_support | 5 | no |
| symlink_support | 6 | no |
| named_attr | 7 | no |
| fsid | 8 | no |
| unique_handles | 9 | no |
| lease_time | 10 | no |
| rdattr_error | 11 | no |
| filehandle | 19 | no |
| suppattr_exclcreat | 75 | no |
+--------------------+----+---------------------------+
Table 1
+--------------------+----+---------------------------+
| Name | Id | Copy to destination file? |
+--------------------+----+---------------------------+
| acl | 12 | MUST |
| aclsupport | 13 | no |
| archive | 14 | no |
| cansettime | 15 | no |
| case_insensitive | 16 | no |
| case_preserving | 17 | no |
| change_policy | 60 | no |
| chown_restricted | 18 | MUST |
| dacl | 58 | MUST |
| dir_notif_delay | 56 | no |
| dirent_notif_delay | 57 | no |
| fileid | 20 | no |
| files_avail | 21 | no |
| files_free | 22 | no |
| files_total | 23 | no |
| fs_charset_cap | 76 | no |
| fs_layout_type | 62 | no |
| fs_locations | 24 | no |
Haynes Expires July 7, 2012 [Page 54]
Internet-Draft NFSv4.2 January 2012
| fs_locations_info | 67 | no |
| fs_status | 61 | no |
| hidden | 25 | MUST |
| homogeneous | 26 | no |
| layout_alignment | 66 | no |
| layout_blksize | 65 | no |
| layout_hint | 63 | no |
| layout_type | 64 | no |
| maxfilesize | 27 | no |
| maxlink | 28 | no |
| maxname | 29 | no |
| maxread | 30 | no |
| maxwrite | 31 | no |
| mdsthreshold | 68 | no |
| mimetype | 32 | MUST |
| mode | 33 | MUST |
| mode_set_masked | 74 | no |
| mounted_on_fileid | 55 | no |
| no_trunc | 34 | no |
| numlinks | 35 | no |
| owner | 36 | MUST |
| owner_group | 37 | MUST |
| quota_avail_hard | 38 | no |
| quota_avail_soft | 39 | no |
| quota_used | 40 | no |
| rawdev | 41 | no |
| retentevt_get | 71 | MUST |
| retentevt_set | 72 | no |
| retention_get | 69 | MUST |
| retention_hold | 73 | MUST |
| retention_set | 70 | no |
| sacl | 59 | MUST |
| space_avail | 42 | no |
| space_free | 43 | no |
| space_freed | 78 | no |
| space_reserved | 77 | MUST |
| space_total | 44 | no |
| space_used | 45 | no |
| system | 46 | MUST |
| time_access | 47 | MUST |
| time_access_set | 48 | no |
| time_backup | 49 | no |
| time_create | 50 | MUST |
| time_delta | 51 | no |
| time_metadata | 52 | SHOULD |
| time_modify | 53 | MUST |
| time_modify_set | 54 | no |
+--------------------+----+---------------------------+
Haynes Expires July 7, 2012 [Page 55]
Internet-Draft NFSv4.2 January 2012
Table 2
[NOTE: The source file's attribute values will take precedence over
any attribute values inherited by the destination file.]
In the case of an inter-server copy or an intra-server copy between
file systems, the attributes supported for the source file and
destination file could be different. By definition,the REQUIRED
attributes will be supported in all cases. If the metadata flag is
set and the source file has a RECOMMENDED attribute that is not
supported for the destination file, the copy MUST fail with
NFS4ERR_ATTRNOTSUPP.
Any attribute supported by the destination server that is not set on
the source file SHOULD be left unset.
Metadata attributes not exposed via the NFS protocol SHOULD be copied
to the destination file where appropriate.
The destination file's named attributes are not duplicated from the
source file. After the copy process completes, the client MAY
attempt to duplicate named attributes using standard NFSv4
operations. However, the destination file's named attribute
capabilities MAY be different from the source file's named attribute
capabilities.
If the metadata flag is not set and the client is requesting a whole
file copy (i.e., ca_count is 0 (zero)), the destination file's
metadata is implementation dependent.
If the client is requesting a partial file copy (i.e., ca_count is
not 0 (zero)), the client SHOULD NOT set the metadata flag and the
server MUST ignore the metadata flag.
If the operation does not result in an immediate failure, the server
will return NFS4_OK, and the CURRENT_FH will remain the destination's
filehandle.
If an immediate failure does occur, cr_bytes_copied will be set to
the number of bytes copied to the destination file before the error
occurred. The cr_bytes_copied value indicates the number of bytes
copied but not which specific bytes have been copied.
A return of NFS4_OK indicates that either the operation is complete
or the operation was initiated and a callback will be used to deliver
the final status of the operation.
If the cr_callback_id is returned, this indicates that the operation
Haynes Expires July 7, 2012 [Page 56]
Internet-Draft NFSv4.2 January 2012
was initiated and a CB_COPY callback will deliver the final results
of the operation. The cr_callback_id stateid is termed a copy
stateid in this context. The server is given the option of returning
the results in a callback because the data may require a relatively
long period of time to copy.
If no cr_callback_id is returned, the operation completed
synchronously and no callback will be issued by the server. The
completion status of the operation is indicated by cr_status.
If the copy completes successfully, either synchronously or
asynchronously, the data copied from the source file to the
destination file MUST appear identical to the NFS client. However,
the NFS server's on disk representation of the data in the source
file and destination file MAY differ. For example, the NFS server
might encrypt, compress, deduplicate, or otherwise represent the on
disk data in the source and destination file differently.
In the event of a failure the state of the destination file is
implementation dependent. The COPY operation may fail for the
following reasons (this is a partial list).
NFS4ERR_MOVED: The file system which contains the source file, or
the destination file or directory is not present. The client can
determine the correct location and reissue the operation with the
correct location.
NFS4ERR_NOTSUPP: The copy offload operation is not supported by the
NFS server receiving this request.
NFS4ERR_PARTNER_NOTSUPP: The remote server does not support the
server-to-server copy offload protocol.
NFS4ERR_OFFLOAD_DENIED: The copy offload operation is supported by
both the source and the destination, but the destination is not
allowing it for this file. If the client sees this error, it
should fall back to the normal copy semantics.
NFS4ERR_PARTNER_NO_AUTH: The remote server does not authorize a
server-to-server copy offload operation. This may be due to the
client's failure to send the COPY_NOTIFY operation to the remote
server, the remote server receiving a server-to-server copy
offload request after the copy lease time expired, or for some
other permission problem.
Haynes Expires July 7, 2012 [Page 57]
Internet-Draft NFSv4.2 January 2012
NFS4ERR_FBIG: The copy operation would have caused the file to grow
beyond the server's limit.
NFS4ERR_NOTDIR: The CURRENT_FH is a file and ca_destination has non-
zero length.
NFS4ERR_WRONG_TYPE: The SAVED_FH is not a regular file.
NFS4ERR_ISDIR: The CURRENT_FH is a directory and ca_destination has
zero length.
NFS4ERR_INVAL: The source offset or offset plus count are greater
than or equal to the size of the source file.
NFS4ERR_DELAY: The server does not have the resources to perform the
copy operation at the current time. The client should retry the
operation sometime in the future.
NFS4ERR_METADATA_NOTSUPP: The destination file cannot support the
same metadata as the source file.
NFS4ERR_WRONGSEC: The security mechanism being used by the client
does not match the server's security policy.
12.2. Operation 60: COPY_ABORT - Cancel a server-side copy
12.2.1. ARGUMENT
struct COPY_ABORT4args {
/* CURRENT_FH: desination file */
stateid4 caa_stateid;
};
12.2.2. RESULT
struct COPY_ABORT4res {
nfsstat4 car_status;
};
12.2.3. DESCRIPTION
COPY_ABORT is used for both intra- and inter-server asynchronous
copies. The COPY_ABORT operation allows the client to cancel a
server-side copy operation that it initiated. This operation is sent
in a COMPOUND request from the client to the destination server.
This operation may be used to cancel a copy when the application that
requested the copy exits before the operation is completed or for
Haynes Expires July 7, 2012 [Page 58]
Internet-Draft NFSv4.2 January 2012
some other reason.
The request contains the filehandle and copy stateid cookies that act
as the context for the previously initiated copy operation.
The result's car_status field indicates whether the cancel was
successful or not. A value of NFS4_OK indicates that the copy
operation was canceled and no callback will be issued by the server.
A copy operation that is successfully canceled may result in none,
some, or all of the data copied.
If the server supports asynchronous copies, the server is REQUIRED to
support the COPY_ABORT operation.
The COPY_ABORT operation may fail for the following reasons (this is
a partial list):
NFS4ERR_NOTSUPP: The abort operation is not supported by the NFS
server receiving this request.
NFS4ERR_RETRY: The abort failed, but a retry at some time in the
future MAY succeed.
NFS4ERR_COMPLETE_ALREADY: The abort failed, and a callback will
deliver the results of the copy operation.
NFS4ERR_SERVERFAULT: An error occurred on the server that does not
map to a specific error code.
12.3. Operation 61: COPY_NOTIFY - Notify a source server of a future
copy
12.3.1. ARGUMENT
struct COPY_NOTIFY4args {
/* CURRENT_FH: source file */
netloc4 cna_destination_server;
};
Haynes Expires July 7, 2012 [Page 59]
Internet-Draft NFSv4.2 January 2012
12.3.2. RESULT
struct COPY_NOTIFY4resok {
nfstime4 cnr_lease_time;
netloc4 cnr_source_server<>;
};
union COPY_NOTIFY4res switch (nfsstat4 cnr_status) {
case NFS4_OK:
COPY_NOTIFY4resok resok4;
default:
void;
};
12.3.3. DESCRIPTION
This operation is used for an inter-server copy. A client sends this
operation in a COMPOUND request to the source server to authorize a
destination server identified by cna_destination_server to read the
file specified by CURRENT_FH on behalf of the given user.
The cna_destination_server MUST be specified using the netloc4
network location format. The server is not required to resolve the
cna_destination_server address before completing this operation.
If this operation succeeds, the source server will allow the
cna_destination_server to copy the specified file on behalf of the
given user. If COPY_NOTIFY succeeds, the destination server is
granted permission to read the file as long as both of the following
conditions are met:
o The destination server begins reading the source file before the
cnr_lease_time expires. If the cnr_lease_time expires while the
destination server is still reading the source file, the
destination server is allowed to finish reading the file.
o The client has not issued a COPY_REVOKE for the same combination
of user, filehandle, and destination server.
The cnr_lease_time is chosen by the source server. A cnr_lease_time
of 0 (zero) indicates an infinite lease. To renew the copy lease
time the client should resend the same copy notification request to
the source server.
To avoid the need for synchronized clocks, copy lease times are
granted by the server as a time delta. However, there is a
requirement that the client and server clocks do not drift
Haynes Expires July 7, 2012 [Page 60]
Internet-Draft NFSv4.2 January 2012
excessively over the duration of the lease. There is also the issue
of propagation delay across the network which could easily be several
hundred milliseconds as well as the possibility that requests will be
lost and need to be retransmitted.
To take propagation delay into account, the client should subtract it
from copy lease times (e.g., if the client estimates the one-way
propagation delay as 200 milliseconds, then it can assume that the
lease is already 200 milliseconds old when it gets it). In addition,
it will take another 200 milliseconds to get a response back to the
server. So the client must send a lease renewal or send the copy
offload request to the cna_destination_server at least 400
milliseconds before the copy lease would expire. If the propagation
delay varies over the life of the lease (e.g., the client is on a
mobile host), the client will need to continuously subtract the
increase in propagation delay from the copy lease times.
The server's copy lease period configuration should take into account
the network distance of the clients that will be accessing the
server's resources. It is expected that the lease period will take
into account the network propagation delays and other network delay
factors for the client population. Since the protocol does not allow
for an automatic method to determine an appropriate copy lease
period, the server's administrator may have to tune the copy lease
period.
A successful response will also contain a list of names, addresses,
and URLs called cnr_source_server, on which the source is willing to
accept connections from the destination. These might not be
reachable from the client and might be located on networks to which
the client has no connection.
If the client wishes to perform an inter-server copy, the client MUST
send a COPY_NOTIFY to the source server. Therefore, the source
server MUST support COPY_NOTIFY.
For a copy only involving one server (the source and destination are
on the same server), this operation is unnecessary.
The COPY_NOTIFY operation may fail for the following reasons (this is
a partial list):
NFS4ERR_MOVED: The file system which contains the source file is not
present on the source server. The client can determine the
correct location and reissue the operation with the correct
location.
Haynes Expires July 7, 2012 [Page 61]
Internet-Draft NFSv4.2 January 2012
NFS4ERR_NOTSUPP: The copy offload operation is not supported by the
NFS server receiving this request.
NFS4ERR_WRONGSEC: The security mechanism being used by the client
does not match the server's security policy.
12.4. Operation 62: COPY_REVOKE - Revoke a destination server's copy
privileges
12.4.1. ARGUMENT
struct COPY_REVOKE4args {
/* CURRENT_FH: source file */
netloc4 cra_destination_server;
};
12.4.2. RESULT
struct COPY_REVOKE4res {
nfsstat4 crr_status;
};
12.4.3. DESCRIPTION
This operation is used for an inter-server copy. A client sends this
operation in a COMPOUND request to the source server to revoke the
authorization of a destination server identified by
cra_destination_server from reading the file specified by CURRENT_FH
on behalf of given user. If the cra_destination_server has already
begun copying the file, a successful return from this operation
indicates that further access will be prevented.
The cra_destination_server MUST be specified using the netloc4
network location format. The server is not required to resolve the
cra_destination_server address before completing this operation.
The COPY_REVOKE operation is useful in situations in which the source
server granted a very long or infinite lease on the destination
server's ability to read the source file and all copy operations on
the source file have been completed.
For a copy only involving one server (the source and destination are
on the same server), this operation is unnecessary.
If the server supports COPY_NOTIFY, the server is REQUIRED to support
the COPY_REVOKE operation.
Haynes Expires July 7, 2012 [Page 62]
Internet-Draft NFSv4.2 January 2012
The COPY_REVOKE operation may fail for the following reasons (this is
a partial list):
NFS4ERR_MOVED: The file system which contains the source file is not
present on the source server. The client can determine the
correct location and reissue the operation with the correct
location.
NFS4ERR_NOTSUPP: The copy offload operation is not supported by the
NFS server receiving this request.
12.5. Operation 63: COPY_STATUS - Poll for status of a server-side copy
12.5.1. ARGUMENT
struct COPY_STATUS4args {
/* CURRENT_FH: destination file */
stateid4 csa_stateid;
};
12.5.2. RESULT
struct COPY_STATUS4resok {
length4 csr_bytes_copied;
nfsstat4 csr_complete<1>;
};
union COPY_STATUS4res switch (nfsstat4 csr_status) {
case NFS4_OK:
COPY_STATUS4resok resok4;
default:
void;
};
12.5.3. DESCRIPTION
COPY_STATUS is used for both intra- and inter-server asynchronous
copies. The COPY_STATUS operation allows the client to poll the
server to determine the status of an asynchronous copy operation.
This operation is sent by the client to the destination server.
If this operation is successful, the number of bytes copied are
returned to the client in the csr_bytes_copied field. The
csr_bytes_copied value indicates the number of bytes copied but not
which specific bytes have been copied.
Haynes Expires July 7, 2012 [Page 63]
Internet-Draft NFSv4.2 January 2012
If the optional csr_complete field is present, the copy has
completed. In this case the status value indicates the result of the
asynchronous copy operation. In all cases, the server will also
deliver the final results of the asynchronous copy in a CB_COPY
operation.
The failure of this operation does not indicate the result of the
asynchronous copy in any way.
If the server supports asynchronous copies, the server is REQUIRED to
support the COPY_STATUS operation.
The COPY_STATUS operation may fail for the following reasons (this is
a partial list):
NFS4ERR_NOTSUPP: The copy status operation is not supported by the
NFS server receiving this request.
NFS4ERR_BAD_STATEID: The stateid is not valid (see Section 2.3.2
below).
NFS4ERR_EXPIRED: The stateid has expired (see Copy Offload Stateid
section below).
12.6. Modification to Operation 42: EXCHANGE_ID - Instantiate Client ID
12.6.1. ARGUMENT
/* new */
const EXCHGID4_FLAG_SUPP_FENCE_OPS = 0x00000004;
12.6.2. RESULT
Unchanged
12.6.3. MOTIVATION
Enterprise applications require guarantees that an operation has
either aborted or completed. NFSv4.1 provides this guarantee as long
as the session is alive: simply send a SEQUENCE operation on the same
slot with a new sequence number, and the successful return of
SEQUENCE indicates the previous operation has completed. However, if
the session is lost, there is no way to know when any in progress
operations have aborted or completed. In hindsight, the NFSv4.1
specification should have mandated that DESTROY_SESSION abort/
complete all outstanding operations.
Haynes Expires July 7, 2012 [Page 64]
Internet-Draft NFSv4.2 January 2012
12.6.4. DESCRIPTION
A client SHOULD request the EXCHGID4_FLAG_SUPP_FENCE_OPS capability
when it sends an EXCHANGE_ID operation. The server SHOULD set this
capability in the EXCHANGE_ID reply whether the client requests it or
not. If the client ID is created with this capability then the
following will occur:
o The server will not reply to DESTROY_SESSION until all operations
in progress are completed or aborted.
o The server will not reply to subsequent EXCHANGE_ID invoked on the
same Client Owner with a new verifier until all operations in
progress on the Client ID's session are completed or aborted.
o When DESTROY_CLIENTID is invoked, if there are sessions (both idle
and non-idle), opens, locks, delegations, layouts, and/or wants
(Section 18.49) associated with the client ID are removed.
Pending operations will be completed or aborted before the
sessions, opens, locks, delegations, layouts, and/or wants are
deleted.
o The NFS server SHOULD support client ID trunking, and if it does
and the EXCHGID4_FLAG_SUPP_FENCE_OPS capability is enabled, then a
session ID created on one node of the storage cluster MUST be
destroyable via DESTROY_SESSION. In addition, DESTROY_CLIENTID
and an EXCHANGE_ID with a new verifier affects all sessions
regardless what node the sessions were created on.
12.7. Operation 64: INITIALIZE
This operation can be used to initialize the structure imposed by an
application onto a file and to punch a hole into a file.
The server has no concept of the structure imposed by the
application. It is only when the application writes to a section of
the file does order get imposed. In order to detect corruption even
before the application utilizes the file, the application will want
to initialize a range of ADBs. It uses the INITIALIZE operation to
do so.
Haynes Expires July 7, 2012 [Page 65]
Internet-Draft NFSv4.2 January 2012
12.7.1. ARGUMENT
/*
* We use data_content4 in case we wish to
* extend new types later. Note that we
* are explicitly disallowing data.
*/
union initialize_arg4 switch (data_content4 content) {
case NFS4_CONTENT_APP_BLOCK:
app_data_block4 ia_adb;
case NFS4_CONTENT_HOLE:
data_info4 ia_hole;
default:
void;
};
struct INITIALIZE4args {
/* CURRENT_FH: file */
stateid4 ia_stateid;
stable_how4 ia_stable;
initialize_arg4 ia_data<>;
};
12.7.2. RESULT
struct INITIALIZE4resok {
count4 ir_count;
stable_how4 ir_committed;
verifier4 ir_writeverf;
data_content4 ir_sparse;
};
union INITIALIZE4res switch (nfsstat4 status) {
case NFS4_OK:
INITIALIZE4resok resok4;
default:
void;
};
12.7.3. DESCRIPTION
When the client invokes the INITIALIZE operation, it has two desired
results:
Haynes Expires July 7, 2012 [Page 66]
Internet-Draft NFSv4.2 January 2012
1. The structure described by the app_data_block4 be imposed on the
file.
2. The contents described by the app_data_block4 be sparse.
If the server supports the INITIALIZE operation, it still might not
support sparse files. So if it receives the INITIALIZE operation,
then it MUST populate the contents of the file with the initialized
ADBs. In other words, if the server supports INITIALIZE, then it
supports the concept of ADBs. [[Comment.7: Do we want to support an
asynchronous INITIALIZE? Do we have to? --TH]] [[Comment.8: Need to
document union arm error code. --TH]]
If the data was already initialized, There are two interesting
scenarios:
1. The data blocks are allocated.
2. Initializing in the middle of an existing ADB.
If the data blocks were already allocated, then the INITIALIZE is a
hole punch operation. If INITIALIZE supports sparse files, then the
data blocks are to be deallocated. If not, then the data blocks are
to be rewritten in the indicated ADB format. [[Comment.9: Need to
document interaction between space reservation and hole punching?
--TH]]
Since the server has no knowledge of ADBs, it should not report
misaligned creation of ADBs. Even while it can detect them, it
cannot disallow them, as the application might be in the process of
changing the size of the ADBs. Thus the server must be prepared to
handle an INITIALIZE into an existing ADB.
This document does not mandate the manner in which the server stores
ADBs sparsely for a file. It does assume that if ADBs are stored
sparsely, then the server can detect when an INITIALIZE arrives that
will force a new ADB to start inside an existing ADB. For example,
assume that ADBi has a adb_block_size of 4k and that an INITIALIZE
starts 1k inside ADBi. The server should [[Comment.10: Need to flesh
this out. --TH]]
12.7.3.1. Hole punching
Whenever a client wishes to deallocate the blocks backing a
particular region in the file, it calls the INITIALIZE operation with
the current filehandle set to the filehandle of the file in question,
start offset and length in bytes of the region set in hpa_offset and
hpa_count respectively. All further reads to this region MUST return
Haynes Expires July 7, 2012 [Page 67]
Internet-Draft NFSv4.2 January 2012
zeros until overwritten. The filehandle specified must be that of a
regular file.
Situations may arise where ia_hole.hi_offset and/or ia_hole.hi_offset
+ ia_hole.hi_length will not be aligned to a boundary that the server
does allocations/ deallocations in. For most filesystems, this is
the block size of the file system. In such a case, the server can
deallocate as many bytes as it can in the region. The blocks that
cannot be deallocated MUST be zeroed. Except for the block
deallocation and maximum hole punching capability, a INITIALIZE
operation is to be treated similar to a write of zeroes.
The server is not required to complete deallocating the blocks
specified in the operation before returning. It is acceptable to
have the deallocation be deferred. In fact, INITIALIZE is merely a
hint; it is valid for a server to return success without ever doing
anything towards deallocating the blocks backing the region
specified. However, any future reads to the region MUST return
zeroes.
If used to hole punch, INITIALIZE will result in the space_used
attribute being decreased by the number of bytes that were
deallocated. The space_freed attribute may or may not decrease,
depending on the support and whether the blocks backing the specified
range were shared or not. The size attribute will remain unchanged.
The INITIALIZE operation MUST NOT change the space reservation
guarantee of the file. While the server can deallocate the blocks
specified by hpa_offset and hpa_count, future writes to this region
MUST NOT fail with NFSERR_NOSPC.
The INITIALIZE operation may fail for the following reasons (this is
a partial list):
NFS4ERR_NOTSUPP The Hole punch operations are not supported by the
NFS server receiving this request.
NFS4ERR_DIR The current filehandle is of type NF4DIR.
NFS4ERR_SYMLINK The current filehandle is of type NF4LNK.
NFS4ERR_WRONG_TYPE The current filehandle does not designate an
ordinary file.
Haynes Expires July 7, 2012 [Page 68]
Internet-Draft NFSv4.2 January 2012
12.8. Operation 67: IO_ADVISE - Application I/O access pattern hints
This section introduces a new operation, named IO_ADVISE, which
allows NFS clients to communicate application I/O access pattern
hints to the NFS server. This new operation will allow hints to be
sent to the server when applications use posix_fadvise, direct I/O,
or at any other point at which the client finds useful.
12.8.1. ARGUMENT
enum IO_ADVISE_type4 {
IO_ADVISE4_NORMAL = 0,
IO_ADVISE4_SEQUENTIAL = 1,
IO_ADVISE4_SEQUENTIAL_BACKWARDS = 2,
IO_ADVISE4_RANDOM = 3,
IO_ADVISE4_WILLNEED = 4,
IO_ADVISE4_WILLNEED_OPPORTUNISTIC = 5,
IO_ADVISE4_DONTNEED = 6,
IO_ADVISE4_NOREUSE = 7,
IO_ADVISE4_READ = 8,
IO_ADVISE4_WRITE = 9
};
struct IO_ADVISE4args {
/* CURRENT_FH: file */
stateid4 iar_stateid;
offset4 iar_offset;
length4 iar_count;
bitmap4 iar_hints;
};
12.8.2. RESULT
struct IO_ADVISE4resok {
bitmap4 ior_hints;
};
union IO_ADVISE4res switch (nfsstat4 _status) {
case NFS4_OK:
IO_ADVISE4resok resok4;
default:
void;
};
Haynes Expires July 7, 2012 [Page 69]
Internet-Draft NFSv4.2 January 2012
12.8.3. DESCRIPTION
The IO_ADVISE operation sends an I/O access pattern hint to the
server for the owner of stated for a given byte range specified by
iar_offset and iar_count. The byte range specified by iar_offset and
iar_count need not currently exist in the file, but the iar_hints
will apply to the byte range when it does exist. If iar_count is 0,
all data following iar_offset is specified. The server MAY ignore
the advice.
The following are the possible hints:
IO_ADVISE4_NORMAL Specifies that the application has no advice to
give on its behavior with respect to the specified data. It is
the default characteristic if no advice is given.
IO_ADVISE4_SEQUENTIAL Specifies that the stated holder expects to
access the specified data sequentially from lower offsets to
higher offsets.
IO_ADVISE4_SEQUENTIAL BACKWARDS Specifies that the stated holder
expects to access the specified data sequentially from higher
offsets to lower offsets.
IO_ADVISE4_RANDOM Specifies that the stated holder expects to access
the specified data in a random order.
IO_ADVISE4_WILLNEED Specifies that the stated holder expects to
access the specified data in the near future.
IO_ADVISE4_WILLNEED_OPPORTUNISTIC Specifies that the stated holder
expects to possibly access the data in the near future. This is a
speculative hint, and therefore the server should prefetch data or
indirect blocks only if it can be done at a marginal cost.
IO_ADVISE_DONTNEED Specifies that the stated holder expects that it
will not access the specified data in the near future.
IO_ADVISE_NOREUSE Specifies that the stated holder expects to access
the specified data once and then not reuse it thereafter.
IO_ADVISE4_READ Specifies that the stated holder expects to read the
specified data in the near future.
IO_ADVISE4_WRITE Specifies that the stated holder expects to write
the specified data in the near future.
The server will return success if the operation is properly formed,
Haynes Expires July 7, 2012 [Page 70]
Internet-Draft NFSv4.2 January 2012
otherwise the server will return an error. The server MUST NOT
return an error if it does not recognize or does not support the
requested advice. This is also true even if the client sends
contradictory hints to the server, e.g., IO_ADVISE4_SEQUENTIAL and
IO_ADVISE4_RANDOM in a single IO_ADVISE operation. In this case, the
server MUST return success and a ior_hints value that indicates the
hint it intends to optimize. For contradictory hints, this may mean
simply returning IO_ADVISE4_NORMAL for example.
The ior_hints returned by the server is primarily for debugging
purposes since the server is under no obligation to carry out the
hints that it describes in the ior_hints result. In addition, while
the server may have intended to implement the hints returned in
ior_hints, as time progresses, the server may need to change its
handling of a given file due to several reasons including, but not
limited to, memory pressure, additional IO_ADVISE hints sent by other
clients, and heuristically detected file access patterns.
The server MAY return different advice than what the client
requested. If it does, then this might be due to one of several
conditions, including, but not limited to another client advising of
a different I/O access pattern; a different I/O access pattern from
another client that that the server has heuristically detected; or
the server is not able to support the requested I/O access pattern,
perhaps due to a temporary resource limitation.
Each issuance of the IO_ADVISE operation overrides all previous
issuances of IO_ADVISE for a given byte range. This effectively
follows a strategy of last hint wins for a given stated and byte
range.
Clients should assume that hints included in an IO_ADVISE operation
will be forgotten once the file is closed.
12.8.4. IMPLEMENTATION
The NFS client may choose to issue and IO_ADVISE operation to the
server in several different instances.
The most obvious is in direct response to an applications execution
of posix_fadvise. In this case, IO_ADVISE4_WRITE and IO_ADVISE4_READ
may be set based upon the type of file access specified when the file
was opened.
Another useful point would be when an application indicates it is
using direct I/O. Direct I/O may be specified at file open, in which
case a IO_ADVISE may be included in the same compound as the OPEN
operation with the IO_ADVISE4_NOREUSE flag set. Direct I/O may also
Haynes Expires July 7, 2012 [Page 71]
Internet-Draft NFSv4.2 January 2012
be specified separately, in which case a IO_ADVISE operation can be
sent to the server separately. As above, IO_ADVISE4_WRITE and
IO_ADVISE4_READ may be set based upon the type of file access
specified when the file was opened.
12.8.5. pNFS File Layout Data Type Considerations
The IO_ADVISE considerations for pNFS are very similar to the COMMIT
considerations for pNFS. That is, as with COMMIT, some NFS server
implementations prefer IO_ADVISE be done on the DS, and some prefer
it be done on the MDS.
So for the file's layout type, it is proposed that NFSv4.2 include an
additional hint NFL42_CARE_IO_ADVISE_THRU_MDS which is valid only on
NFSv4.2 or higher. Any file's layout obtained with NFSv4.1 MUST NOT
have NFL42_UFLG_IO_ADVISE_THRU_MDS set. Any file's layout obtained
with NFSv4.2 MAY have NFL42_UFLG_IO_ADVISE_THRU_MDS set. If the
client does not implement IO_ADVISE, then it MUST ignore
NFL42_UFLG_IO_ADVISE_THRU_MDS.
If NFL42_UFLG_IO_ADVISE_THRU_MDS is set, then if the client
implements IO_ADVISE, then if it wants the DS to honor IO_ADVISE, the
client MUST send the operation to the MDS, and the server will
communicate the advice back each DS. If the client sends IO_ADVISE
to the DS, then the server MAY return NFS4ERR_NOTSUPP.
If NFL42_UFLG_IO_ADVISE_THRU_MDS is not set, then this indicates to
client that if wants to inform the server via IO_ADVISE of the
client's intended use of the file, then the client SHOULD send an
IO_ADVISE to each DS. While the client MAY always send IO_ADVISE to
the MDS, if the server has not set NFL42_UFLG_IO_ADVISE_THRU_MDS, the
client should expect that such an IO_ADVISE is futile. Note that a
client SHOULD use the same set of arguments on each IO_ADVISE sent to
a DS for the same open file reference.
The server is not required to support different advice for different
DS's with the same open file reference.
12.8.5.1. Dense and Sparse Packing Considerations
The IO_ADVISE operation MUST use the iar_offset and byte range as
dictated by the presence or absence of NFL4_UFLG_DENSE.
E.g., if NFL4_UFLG_DENSE is present, and a READ or WRITE to the DS
for iar_offset 0 really means iar_offset 10000 in the logical file,
then an IO_ADVISE for iar_offset 0 means iar_offset 10000.
E.g., if NFL4_UFLG_DENSE is absent, then a READ or WRITE to the DS
Haynes Expires July 7, 2012 [Page 72]
Internet-Draft NFSv4.2 January 2012
for iar_offset 0 really means iar_offset 0 in the logical file, then
an IO_ADVISE for iar_offset 0 means iar_offset 0 in the logical file.
E.g., if NFL4_UFLG_DENSE is present, the stripe unit is 1000 bytes
and the stripe count is 10, and the dense DS file is serving
iar_offset 0. A READ or WRITE to the DS for iar_offsets 0, 1000,
2000, and 3000, really mean iar_offsets 10000, 20000, 30000, and
40000 (implying a stripe count of 10 and a stripe unit of 1000), then
an IO_ADVISE sent to the same DS with an iar_offset of 500, and a
iar_count of 3000 means that the IO_ADVISE applies to these byte
ranges of the dense DS file:
- 500 to 999
- 1000 to 1999
- 2000 to 2999
- 3000 to 3499
I.e., the contiguous range 500 to 3499 as specified in IO_ADVISE.
It also applies to these byte ranges of the logical file:
- 10500 to 10999 (500 bytes)
- 20000 to 20999 (1000 bytes)
- 30000 to 30999 (1000 bytes)
- 40000 to 40499 (500 bytes)
(total 3000 bytes)
E.g., if NFL4_UFLG_DENSE is absent, the stripe unit is 250 bytes, the
stripe count is 4, and the sparse DS file is serving iar_offset 0.
Then a READ or WRITE to the DS for iar_offsets 0, 1000, 2000, and
3000, really mean iar_offsets 0, 1000, 2000, and 3000 in the logical
file, keeping in mind that on the DS file,. byte ranges 250 to 999,
1250 to 1999, 2250 to 2999, and 3250 to 3999 are not accessible.
Then an IO_ADVISE sent to the same DS with an iar_offset of 500, and
a iar_count of 3000 means that the IO_ADVISE applies to these byte
ranges of the logical file and the sparse DS file:
- 500 to 999 (500 bytes) - no effect
- 1000 to 1249 (250 bytes) - effective
- 1250 to 1999 (750 bytes) - no effect
- 2000 to 2249 (250 bytes) - effective
- 2250 to 2999 (750 bytes) - no effect
- 3000 to 3249 (250 bytes) - effective
- 3250 to 3499 (250 bytes) - no effect
(subtotal 2250 bytes) - no effect
(subtotal 750 bytes) - effective
(grand total 3000 bytes) - no effect + effective
Haynes Expires July 7, 2012 [Page 73]
Internet-Draft NFSv4.2 January 2012
If neither of the flags NFL42_UFLG_IO_ADVISE_THRU_MDS and
NFL4_UFLG_DENSE are set in the layout, then any IO_ADVISE request
sent to the data server with a byte range that overlaps stripe unit
that the data server does not serve MUST NOT result in the status
NFS4ERR_PNFS_IO_HOLE. Instead, the response SHOULD be successful and
if the server applies IO_ADVISE hints on any stripe units that
overlap with the specified range, those hints SHOULD be indicated in
the response.
12.8.6. Number of Supported File Segments
In theory IO_ADVISE allows a client and server to support multiple
file segments, meaning that different, possibly overlapping, byte
ranges of the same open file reference will support different hints.
This is not practical, and in general the server will support just
one set of hints, and these will apply to the entire file. However,
there are some hints that very ephemeral, and are essentially amount
to one time instructions to the NFS server, which will be forgotten
momentarily after IO_ADVISE is executed.
The following hints will always apply to the entire file, regardless
of the specified byte range:
o IO_ADVISE4_NORMAL
o IO_ADVISE4_SEQUENTIAL
o IO_ADVISE4_SEQUENTIAL_BACKWARDS
o IO_ADVISE4_RANDOM
The following hints will always apply to specified byte range, and
will treated as one time instructions:
o IO_ADVISE4_WILLNEED
o IO_ADVISE4_WILLNEED_OPPORTUNISTIC
o IO_ADVISE4_DONTNEED
o IO_ADVISE4_NOREUSE
The following hints are modifiers to all other hints, and will apply
to the entire file and/or to a one time instruction on the specified
byte range:
Haynes Expires July 7, 2012 [Page 74]
Internet-Draft NFSv4.2 January 2012
o IO_ADVISE4_READ
o IO_ADVISE4_WRITE
12.8.7. Possible Additional Hint - IO_ADVISE4_RECENTLY_USED
IO_ADVISE4_RECENTLY_USED The client has recently accessed the byte
range in its own cache. This informs the server that the data in
the byte range remains important to the client. When the server
reaches resource exhaustion, knowing which data is more important
allows the server to make better choices about which data to, for
example purge from a cache, or move to secondary storage. It also
informs the server which delegations are more important, since if
delegations are working correctly, once delegated to a client, a
server might never receive another I/O request for the file.
A use case for this hint is that of the NFS client or application
restart. In the event of restart, the app's/client's cache will be
cold and it will need to fill it from the server. If the server is
maintaining a list (LRU most likely) of byte ranges tagged with
IO_ADVISE4_RECENTLY_USED, then the server could have stored the data
in these ranges into a storage medium that is less expensive than
DRAM, and faster than random access magnetic or optical media, such
as flash. This allows the end to end application to storage system
to co-operate to meet a service level agreement/objective contracted
to the end user by the IT provider.
On the other side, this is effectively a hint regarding multi-level
caching, and it may be more useful to specify a more formal multi-
level caching system. In addition, the action to be taken by the
server file system with this hint, and hence its usefulness, is
unclear. For example, as most clients already cache data that they
know is important, having this data cached twice may be unnecessary.
In fact, substantial performance improvements have been demonstrated
by making caches more exclusive between each other [25], not the
other way around. This means that there is a strong argument to be
made that servers should immediately purge the described cached data
upon receiving this hint. Other work showed that even infinite sized
secondary caches can be largely ineffective [26], but this of course
is subject to the workload.
12.9. Changes to Operation 51: LAYOUTRETURN
12.9.1. Introduction
In the pNFS description provided in [2], the client is not enabled to
relay an error code from the DS to the MDS. In the specification of
the Objects-Based Layout protocol [8], use is made of the opaque
Haynes Expires July 7, 2012 [Page 75]
Internet-Draft NFSv4.2 January 2012
lrf_body field of the LAYOUTRETURN argument to do such a relaying of
error codes. In this section, we define a new data structure to
enable the passing of error codes back to the MDS and provide some
guidelines on what both the client and MDS should expect in such
circumstances.
There are two broad classes of errors, transient and persistent. The
client SHOULD strive to only use this new mechanism to report
persistent errors. It MUST be able to deal with transient issues by
itself. Also, while the client might consider an issue to be
persistent, it MUST be prepared for the MDS to consider such issues
to be persistent. A prime example of this is if the MDS fences off a
client from either a stateid or a filehandle. The client will get an
error from the DS and might relay either NFS4ERR_ACCESS or
NFS4ERR_STALE_STATEID back to the MDS, with the belief that this is a
hard error. The MDS on the other hand, is waiting for the client to
report such an error. For it, the mission is accomplished in that
the client has returned a layout that the MDS had most likley
recalled.
The existing LAYOUTRETURN operation is extended by introducing a new
data structure to report errors, layoutreturn_device_error4. Also,
layoutreturn_device_error4 is introduced to enable an array of errors
to be reported.
12.9.2. ARGUMENT
The ARGUMENT specification of the LAYOUTRETURN operation in section
18.44.1 of [2] is augmented by the following XDR code [24]:
struct layoutreturn_device_error4 {
deviceid4 lrde_deviceid;
nfsstat4 lrde_status;
nfs_opnum4 lrde_opnum;
};
struct layoutreturn_error_report4 {
layoutreturn_device_error4 lrer_errors<>;
};
12.9.3. RESULT
The RESULT of the LAYOUTRETURN operation is unchanged; see section
18.44.2 of [2].
Haynes Expires July 7, 2012 [Page 76]
Internet-Draft NFSv4.2 January 2012
12.9.4. DESCRIPTION
The following text is added to the end of the LAYOUTRETURN operation
DESCRIPTION in section 18.44.3 of [2].
When a client used LAYOUTRETURN with a type of LAYOUTRETURN4_FILE,
then if the lrf_body field is NULL, it indicates to the MDS that the
client experienced no errors. If lrf_body is non-NULL, then the
field references error information which is layout type specific.
I.e., the Objects-Based Layout protocol can continue to utilize
lrf_body as specified in [8]. For both Files-Based Layouts, the
field references a layoutreturn_device_error4, which contains an
array of layoutreturn_device_error4.
Each individual layoutreturn_device_error4 descibes a single error
associated with a DS, which is identfied via lrde_deviceid. The
operation which returned the error is identified via lrde_opnum.
Finally the NFS error value (nfsstat4) encountered is provided via
lrde_status and may consist of the following error codes:
NFS4_OKAY: No issues were found for this device.
NFS4ERR_NXIO: The client was unable to establish any communication
with the DS.
NFS4ERR_*: The client was able to establish communication with the
DS and is returning one of the allowed error codes for the
operation denoted by lrde_opnum.
12.9.5. IMPLEMENTATION
The following text is added to the end of the LAYOUTRETURN operation
IMPLEMENTATION in section 18.4.4 of [2].
A client that expects to use pNFS for a mounted filesystem SHOULD
check for pNFS support at mount time. This check SHOULD be performed
by sending a GETDEVICELIST operation, followed by layout-type-
specific checks for accessibility of each storage device returned by
GETDEVICELIST. If the NFS server does not support pNFS, the
GETDEVICELIST operation will be rejected with an NFS4ERR_NOTSUPP
error; in this situation it is up to the client to determine whether
it is acceptable to proceed with NFS-only access.
Clients are expected to tolerate transient storage device errors, and
hence clients SHOULD NOT use the LAYOUTRETURN error handling for
device access problems that may be transient. The methods by which a
client decides whether an access problem is transient vs. persistent
are implementation-specific, but may include retrying I/Os to a data
Haynes Expires July 7, 2012 [Page 77]
Internet-Draft NFSv4.2 January 2012
server under appropriate conditions.
When an I/O fails to a storage device, the client SHOULD retry the
failed I/O via the MDS. In this situation, before retrying the I/O,
the client SHOULD return the layout, or the affected portion thereof,
and SHOULD indicate which storage device or devices was problematic.
If the client does not do this, the MDS may issue a layout recall
callback in order to perform the retried I/O.
The client needs to be cognizant that since this error handling is
optional in the MDS, the MDS may silently ignore this functionality.
Also, as the MDS may consider some issues the client reports to be
expected (see Section 12.9.1), the client might find it difficult to
detect a MDS which has not implemented error handling via
LAYOUTRETURN.
If an MDS is aware that a storage device is proving problematic to a
client, the MDS SHOULD NOT include that storage device in any pNFS
layouts sent to that client. If the MDS is aware that a storage
device is affecting many clients, then the MDS SHOULD NOT include
that storage device in any pNFS layouts sent out. Clients must still
be aware that the MDS might not have any choice in using the storage
device, i.e., there might only be one possible layout for the system.
Another interesting complication is that for existing files, the MDS
might have no choice in which storage devices to hand out to clients.
The MDS might try to restripe a file across a different storage
device, but clients need to be aware that not all implementations
have restriping support.
An MDS SHOULD react to a client return of layouts with errors by not
using the problematic storage devices in layouts for that client, but
the MDS is not required to indefinitely retain per-client storage
device error information. An MDS is also not required to
automatically reinstate use of a previously problematic storage
device; administrative intervention may be required instead.
A client MAY perform I/O via the MDS even when the client holds a
layout that covers the I/O; servers MUST support this client
behavior, and MAY recall layouts as needed to complete I/Os.
12.10. Operation 65: READ_PLUS
READ_PLUS is a new read operation which allows NFS clients to avoid
reading holes in a sparse file and to efficiently transfer ADBs.
READ_PLUS is guaranteed to perform no worse than READ, and can
dramatically improve performance with sparse files.
Haynes Expires July 7, 2012 [Page 78]
Internet-Draft NFSv4.2 January 2012
READ_PLUS supports all the features of the existing NFSv4.1 READ
operation [2] and adds a simple yet significant extension to the
format of its response. The change allows the client to avoid
returning data for portions of the file which are either initialized
and contain no backing store or if the result would appear to be so.
I.e., if the result was a data block composed entirely of zeros, then
it is easier to return a hole. Returning data blocks of unitialized
data wastes computational and network resources, thus reducing
performance. READ_PLUS uses a new result structure that tells the
client that the result is all zeroes AND the byte-range of the hole
in which the request was made.
If the client sends a READ operation, it is explicitly stating that
it is neither supporting sparse files or ADBs. So if a READ occurs
on a sparse ADB or file, then the server must expand such data to be
raw bytes. If a READ occurs in the middle of a hole or ADB, the
server can only send back bytes starting from that offset.
Such an operation is inefficient for transfer of sparse sections of
the file. As such, READ is marked as OBSOLETE in NFSv4.2. Instead,
a client should issue READ_PLUS. Note that as the client has no a
priori knowledge of whether an ADB is present or not, it should
always use READ_PLUS.
12.10.1. ARGUMENT
struct READ_PLUS4args {
/* CURRENT_FH: file */
stateid4 rpa_stateid;
offset4 rpa_offset;
count4 rpa_count;
};
Haynes Expires July 7, 2012 [Page 79]
Internet-Draft NFSv4.2 January 2012
12.10.2. RESULT
union read_plus_content switch (data_content4 content) {
case NFS4_CONTENT_DATA:
opaque rpc_data<>;
case NFS4_CONTENT_APP_BLOCK:
app_data_block4 rpc_block;
case NFS4_CONTENT_HOLE:
data_info4 rpc_hole;
default:
void;
};
/*
* Allow a return of an array of contents.
*/
struct read_plus_res4 {
bool rpr_eof;
read_plus_content rpr_contents<>;
};
union READ_PLUS4res switch (nfsstat4 status) {
case NFS4_OK:
read_plus_res4 resok4;
default:
void;
};
12.10.3. DESCRIPTION
The READ_PLUS operation is based upon the NFSv4.1 READ operation [2],
and similarly reads data from the regular file identified by the
current filehandle.
The client provides a rpa_offset of where the READ_PLUS is to start
and a rpa_count of how many bytes are to be read. A rpa_offset of
zero means to read data starting at the beginning of the file. If
rpa_offset is greater than or equal to the size of the file, the
status NFS4_OK is returned with di_length (the data length) set to
zero and eof set to TRUE. READ_PLUS is subject to access permissions
checking.
The READ_PLUS result is comprised of an array of rpr_contents, each
of which describe a data_content4 type of data. For NFSv4.2, the
allowed values are data, ADB, and hole. A server is required to
support the data type, but not ADB nor hole. Both an ADB and a hole
Haynes Expires July 7, 2012 [Page 80]
Internet-Draft NFSv4.2 January 2012
must be returned in its entirety - clients must be prepared to get
more information than they requested.
If the data to be returned is comprised entirely of zeros, then the
server may elect to return that data as a hole. The server
differentiates this to the client by setting di_allocated to TRUE in
this case. Note that in such a scenario, the server is not required
to determine the full extent of the "hole" - it does not need to
determine where the zeros start and end.
The server may elect to return adjacent elements of the same type.
For example, the guard pattern or block size of an ADB might change,
which would require adjacent elements of type ADB. Likewise if the
server has a range of data comprised entirely of zeros and then a
hole, it might want to return two adjacent holes to the client.
If the client specifies a rpa_count value of zero, the READ_PLUS
succeeds and returns zero bytes of data, again subject to access
permissions checking. In all situations, the server may choose to
return fewer bytes than specified by the client. The client needs to
check for this condition and handle the condition appropriately.
If the client specifies an rpa_offset and rpa_count value that is
entirely contained within a hole of the file, then the di_offset and
di_length returned must be for the entire hole. This result is
considered valid until the file is changed (detected via the change
attribute). The server MUST provide the same semantics for the hole
as if the client read the region and received zeroes; the implied
holes contents lifetime MUST be exactly the same as any other read
data.
If the client specifies an rpa_offset and rpa_count value that begins
in a non-hole of the file but extends into hole the server should
return an array comprised of both data and a hole. The client MUST
be prepared for the server to reurn a short read describing just the
data. The client will then issue another READ_PLUS for the remaining
bytes, which the server will respond with information about the hole
in the file.
Except when special stateids are used, the stateid value for a
READ_PLUS request represents a value returned from a previous byte-
range lock or share reservation request or the stateid associated
with a delegation. The stateid identifies the associated owners if
any and is used by the server to verify that the associated locks are
still valid (e.g., have not been revoked).
If the read ended at the end-of-file (formally, in a correctly formed
READ_PLUS operation, if rpa_offset + rpa_count is equal to the size
Haynes Expires July 7, 2012 [Page 81]
Internet-Draft NFSv4.2 January 2012
of the file), or the READ_PLUS operation extends beyond the size of
the file (if rpa_offset + rpa_count is greater than the size of the
file), eof is returned as TRUE; otherwise, it is FALSE. A successful
READ_PLUS of an empty file will always return eof as TRUE.
If the current filehandle is not an ordinary file, an error will be
returned to the client. In the case that the current filehandle
represents an object of type NF4DIR, NFS4ERR_ISDIR is returned. If
the current filehandle designates a symbolic link, NFS4ERR_SYMLINK is
returned. In all other cases, NFS4ERR_WRONG_TYPE is returned.
For a READ_PLUS with a stateid value of all bits equal to zero, the
server MAY allow the READ_PLUS to be serviced subject to mandatory
byte-range locks or the current share deny modes for the file. For a
READ_PLUS with a stateid value of all bits equal to one, the server
MAY allow READ_PLUS operations to bypass locking checks at the
server.
On success, the current filehandle retains its value.
12.10.4. IMPLEMENTATION
If the server returns a short read, then the client should send
another READ_PLUS to get the remaining data. A server may return
less data than requested under several circumstances. The file may
have been truncated by another client or perhaps on the server
itself, changing the file size from what the requesting client
believes to be the case. This would reduce the actual amount of data
available to the client. It is possible that the server reduced the
transfer size and so return a short read result. Server resource
exhaustion may also occur in a short read.
If mandatory byte-range locking is in effect for the file, and if the
byte-range corresponding to the data to be read from the file is
WRITE_LT locked by an owner not associated with the stateid, the
server will return the NFS4ERR_LOCKED error. The client should try
to get the appropriate READ_LT via the LOCK operation before re-
attempting the READ_PLUS. When the READ_PLUS completes, the client
should release the byte-range lock via LOCKU. In addition, the
server MUST return an array of rpr_contents with values of that are
within the owner's locked byte range.
If another client has an OPEN_DELEGATE_WRITE delegation for the file
being read, the delegation must be recalled, and the operation cannot
proceed until that delegation is returned or revoked. Except where
this happens very quickly, one or more NFS4ERR_DELAY errors will be
returned to requests made while the delegation remains outstanding.
Normally, delegations will not be recalled as a result of a READ_PLUS
Haynes Expires July 7, 2012 [Page 82]
Internet-Draft NFSv4.2 January 2012
operation since the recall will occur as a result of an earlier OPEN.
However, since it is possible for a READ_PLUS to be done with a
special stateid, the server needs to check for this case even though
the client should have done an OPEN previously.
12.10.4.1. Additional pNFS Implementation Information
[[Comment.11: We need to go over this section. --TH]] With pNFS, the
semantics of using READ_PLUS remains the same. Any data server MAY
return a READ_HOLE result for a READ_PLUS request that it receives.
When a data server chooses to return a READ_HOLE result, it has the
option of returning hole information for the data stored on that data
server (as defined by the data layout), but it MUST not return a
nfs_readplusreshole structure with a byte range that includes data
managed by another data server.
1. Data servers that cannot determine hole information SHOULD return
HOLE_NOINFO.
2. Data servers that can obtain hole information for the parts of
the file stored on that data server, the data server SHOULD
return HOLE_INFO and the byte range of the hole stored on that
data server.
A data server should do its best to return as much information about
a hole as is feasible without having to contact the metadata server.
If communication with the metadata server is required, then every
attempt should be taken to minimize the number of requests.
If mandatory locking is enforced, then the data server must also
ensure that to return only information for a Hole that is within the
owner's locked byte range.
12.10.5. READ_PLUS with Sparse Files Example
The following table describes a sparse file. For each byte range,
the file contains either non-zero data or a hole. In addition, the
server in this example uses a Hole Threshold of 32K.
Haynes Expires July 7, 2012 [Page 83]
Internet-Draft NFSv4.2 January 2012
+-------------+----------+
| Byte-Range | Contents |
+-------------+----------+
| 0-15999 | Hole |
| 16K-31999 | Non-Zero |
| 32K-255999 | Hole |
| 256K-287999 | Non-Zero |
| 288K-353999 | Hole |
| 354K-417999 | Non-Zero |
+-------------+----------+
Table 3
Under the given circumstances, if a client was to read the file from
beginning to end with a max read size of 64K, the following will be
the result. This assumes the client has already opened the file,
acquired a valid stateid ('s' in the example), and just needs to
issue READ_PLUS requests. [[Comment.12: Change the results to match
array results. --TH]]
1. READ_PLUS(s, 0, 64K) --> NFS_OK, eof = false, data<>[32K].
Return a short read, as the last half of the request was all
zeroes. Note that the first hole is read back as all zeros as it
is below the Hole Threshhold.
2. READ_PLUS(s, 32K, 64K) --> NFS_OK, readplusrestype4 = READ_HOLE,
nfs_readplusreshole(HOLE_INFO)(32K, 224K). The requested range
was all zeros, and the current hole begins at offset 32K and is
224K in length.
3. READ_PLUS(s, 256K, 64K) --> NFS_OK, readplusrestype4 = READ_OK,
eof = false, data<>[32K]. Return a short read, as the last half
of the request was all zeroes.
4. READ_PLUS(s, 288K, 64K) --> NFS_OK, readplusrestype4 = READ_HOLE,
nfs_readplusreshole(HOLE_INFO)(288K, 66K).
5. READ_PLUS(s, 354K, 64K) --> NFS_OK, readplusrestype4 = READ_OK,
eof = true, data<>[64K].
12.11. Operation 66: SEEK
SEEK is an operation that allows a client to determine the location
of the next data_content4 in a file.
Haynes Expires July 7, 2012 [Page 84]
Internet-Draft NFSv4.2 January 2012
12.11.1. ARGUMENT
struct SEEK4args {
/* CURRENT_FH: file */
stateid4 sa_stateid;
offset4 sa_offset;
data_content4 sa_what;
};
12.11.2. RESULT
union seek_content switch (data_content4 content) {
case NFS4_CONTENT_DATA:
data_info4 sc_data;
case NFS4_CONTENT_APP_BLOCK:
app_data_block4 sc_block;
case NFS4_CONTENT_HOLE:
data_info4 sc_hole;
default:
void;
};
struct seek_res4 {
bool sr_eof;
seek_content sr_contents;
};
union SEEK4res switch (nfsstat4 status) {
case NFS4_OK:
seek_res4 resok4;
default:
void;
};
12.11.3. DESCRIPTION
From the given sa_offset, find the next data_content4 of type sa_what
in the file. For either a hole or ADB, this must return the
data_content4 in its entirety. For data, it must not return the
actual data.
SEEK must follow the same rules for stateids as READ_PLUS
(Section 12.10.3).
If the server could not find a corresponding sa_what, then the status
would still be NFS4_OK, but sr_eof would be TRUE. The sr_contents
would contain a zero-ed out content of the appropriate type.
Haynes Expires July 7, 2012 [Page 85]
Internet-Draft NFSv4.2 January 2012
13. NFSv4.2 Callback Operations
13.1. Procedure 16: CB_ATTR_CHANGED - Notify Client that the File's
Attributes Changed
13.1.1. ARGUMENTS
struct CB_ATTR_CHANGED4args {
nfs_fh4 acca_fh;
bitmap4 acca_critical;
bitmap4 acca_info;
};
13.1.2. RESULTS
struct CB_ATTR_CHANGED4res {
nfsstat4 accr_status;
};
13.1.3. DESCRIPTION
The CB_ATTR_CHANGED callback operation is used by the server to
indicate to the client that the file's attributes have been modified
on the server. The server does not convey how the attributes have
changed, just that they have been modified. The server can inform
the client about both critical and informational attribute changes in
the bitmask arguments. The client SHOULD query the server about all
attributes set in acca_critical. For all changes reflected in
acca_info, the client can decide whether or not it wants to poll the
server.
The CB_ATTR_CHANGED callback operation with the FATTR4_SEC_LABEL set
in acca_critical is the method used by the server to indicate that
the MAC label for the file referenced by acca_fh has changed. In
many ways, the server does not care about the result returned by the
client.
13.2. Operation 15: CB_COPY - Report results of a server-side copy
Haynes Expires July 7, 2012 [Page 86]
Internet-Draft NFSv4.2 January 2012
13.2.1. ARGUMENT
union copy_info4 switch (nfsstat4 cca_status) {
case NFS4_OK:
void;
default:
length4 cca_bytes_copied;
};
struct CB_COPY4args {
nfs_fh4 cca_fh;
stateid4 cca_stateid;
copy_info4 cca_copy_info;
};
13.2.2. RESULT
struct CB_COPY4res {
nfsstat4 ccr_status;
};
13.2.3. DESCRIPTION
CB_COPY is used for both intra- and inter-server asynchronous copies.
The CB_COPY callback informs the client of the result of an
asynchronous server-side copy. This operation is sent by the
destination server to the client in a CB_COMPOUND request. The copy
is identified by the filehandle and stateid arguments. The result is
indicated by the status field. If the copy failed, cca_bytes_copied
contains the number of bytes copied before the failure occurred. The
cca_bytes_copied value indicates the number of bytes copied but not
which specific bytes have been copied.
In the absence of an established backchannel, the server cannot
signal the completion of the COPY via a CB_COPY callback. The loss
of a callback channel would be indicated by the server setting the
SEQ4_STATUS_CB_PATH_DOWN flag in the sr_status_flags field of the
SEQUENCE operation. The client must re-establish the callback
channel to receive the status of the COPY operation. Prolonged loss
of the callback channel could result in the server dropping the COPY
operation state and invalidating the copy stateid.
If the client supports the COPY operation, the client is REQUIRED to
support the CB_COPY operation.
The CB_COPY operation may fail for the following reasons (this is a
partial list):
Haynes Expires July 7, 2012 [Page 87]
Internet-Draft NFSv4.2 January 2012
NFS4ERR_NOTSUPP: The copy offload operation is not supported by the
NFS client receiving this request.
14. IANA Considerations
This section uses terms that are defined in [27].
15. References
15.1. Normative References
[1] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", March 1997.
[2] Shepler, S., Eisler, M., and D. Noveck, "Network File System
(NFS) Version 4 Minor Version 1 Protocol", RFC 5661,
January 2010.
[3] Haynes, T., "Network File System (NFS) Version 4 Minor Version
2 External Data Representation Standard (XDR) Description",
March 2011.
[4] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
Resource Identifier (URI): Generic Syntax", STD 66, RFC 3986,
January 2005.
[5] Haynes, T. and N. Williams, "Remote Procedure Call (RPC)
Security Version 3", draft-williams-rpcsecgssv3 (work in
progress), 2011.
[6] The Open Group, "Section 'posix_fadvise()' of System Interfaces
of The Open Group Base Specifications Issue 6, IEEE Std 1003.1,
2004 Edition", 2004.
[7] Eisler, M., Chiu, A., and L. Ling, "RPCSEC_GSS Protocol
Specification", RFC 2203, September 1997.
[8] Halevy, B., Welch, B., and J. Zelenka, "Object-Based Parallel
NFS (pNFS) Operations", RFC 5664, January 2010.
[9] Shepler, S., Eisler, M., and D. Noveck, "Network File System
(NFS) Version 4 Minor Version 1 External Data Representation
Standard (XDR) Description", RFC 5662, January 2010.
[10] Black, D., Glasgow, J., and S. Fridella, "Parallel NFS (pNFS)
Block/Volume Layout", RFC 5663, January 2010.
Haynes Expires July 7, 2012 [Page 88]
Internet-Draft NFSv4.2 January 2012
15.2. Informative References
[11] Haynes, T. and D. Noveck, "Network File System (NFS) version 4
Protocol", draft-ietf-nfsv4-rfc3530bis-09 (Work In Progress),
March 2011.
[12] Lentini, J., Everhart, C., Ellard, D., Tewari, R., and M. Naik,
"NSDB Protocol for Federated Filesystems",
draft-ietf-nfsv4-federated-fs-protocol (Work In Progress),
2010.
[13] Lentini, J., Everhart, C., Ellard, D., Tewari, R., and M. Naik,
"Administration Protocol for Federated Filesystems",
draft-ietf-nfsv4-federated-fs-admin (Work In Progress), 2010.
[14] Fielding, R., Gettys, J., Mogul, J., Frystyk, H., Masinter, L.,
Leach, P., and T. Berners-Lee, "Hypertext Transfer Protocol --
HTTP/1.1", RFC 2616, June 1999.
[15] Postel, J. and J. Reynolds, "File Transfer Protocol", STD 9,
RFC 959, October 1985.
[16] Simpson, W., "PPP Challenge Handshake Authentication Protocol
(CHAP)", RFC 1994, August 1996.
[17] VanDeBogart, S., Frost, C., and E. Kohler, "Reducing Seek
Overhead with Application-Directed Prefetching", Proceedings of
USENIX Annual Technical Conference , June 2009.
[18] Strohm, R., "Chapter 2, Data Blocks, Extents, and Segments, of
Oracle Database Concepts 11g Release 1 (11.1)", January 2011.
[19] Ashdown, L., "Chapter 15, Validating Database Files and
Backups, of Oracle Database Backup and Recovery User's Guide
11g Release 1 (11.1)", August 2008.
[20] McDougall, R. and J. Mauro, "Section 11.4.3, Detecting Memory
Corruption of Solaris Internals", 2007.
[21] Bairavasundaram, L., Goodson, G., Schroeder, B., Arpaci-
Dusseau, A., and R. Arpaci-Dusseau, "An Analysis of Data
Corruption in the Storage Stack", Proceedings of the 6th USENIX
Symposium on File and Storage Technologies (FAST '08) , 2008.
[22] "Section 46.6. Multi-Level Security (MLS) of Deployment Guide:
Deployment, configuration and administration of Red Hat
Enterprise Linux 5, Edition 6", 2011.
Haynes Expires July 7, 2012 [Page 89]
Internet-Draft NFSv4.2 January 2012
[23] Quigley, D. and J. Lu, "Registry Specification for MAC Security
Label Formats", draft-quigley-label-format-registry (work in
progress), 2011.
[24] Eisler, M., "XDR: External Data Representation Standard",
RFC 4506, May 2006.
[25] Wong, T. and J. Wilkes, "My cache or yours? Making storage more
exclusive", Proceedings of the USENIX Annual Technical
Conference , 2002.
[26] Muntz, D. and P. Honeyman, "Multi-level Caching in Distributed
File Systems", Proceedings of USENIX Annual Technical
Conference , 1992.
[27] Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA
Considerations Section in RFCs", BCP 26, RFC 5226, May 2008.
[28] Nowicki, B., "NFS: Network File System Protocol specification",
RFC 1094, March 1989.
[29] Callaghan, B., Pawlowski, B., and P. Staubach, "NFS Version 3
Protocol Specification", RFC 1813, June 1995.
[30] Srinivasan, R., "Binding Protocols for ONC RPC Version 2",
RFC 1833, August 1995.
[31] Eisler, M., "NFS Version 2 and Version 3 Security Issues and
the NFS Protocol's Use of RPCSEC_GSS and Kerberos V5",
RFC 2623, June 1999.
[32] Callaghan, B., "NFS URL Scheme", RFC 2224, October 1997.
[33] Shepler, S., "NFS Version 4 Design Considerations", RFC 2624,
June 1999.
[34] Reynolds, J., "Assigned Numbers: RFC 1700 is Replaced by an On-
line Database", RFC 3232, January 2002.
[35] Linn, J., "The Kerberos Version 5 GSS-API Mechanism", RFC 1964,
June 1996.
[36] Shepler, S., Callaghan, B., Robinson, D., Thurlow, R., Beame,
C., Eisler, M., and D. Noveck, "Network File System (NFS)
version 4 Protocol", RFC 3530, April 2003.
Haynes Expires July 7, 2012 [Page 90]
Internet-Draft NFSv4.2 January 2012
Appendix A. Acknowledgments
For the pNFS Access Permissions Check, the original draft was by
Sorin Faibish, David Black, Mike Eisler, and Jason Glasgow. The work
was influenced by discussions with Benny Halevy and Bruce Fields. A
review was done by Tom Haynes.
For the Sharing change attribute implementation details with NFSv4
clients, the original draft was by Trond Myklebust.
For the NFS Server-side Copy, the original draft was by James
Lentini, Mike Eisler, Deepak Kenchammana, Anshul Madan, and Rahul
Iyer. Tom Talpey co-authored an unpublished version of that
document. It was also was reviewed by a number of individuals:
Pranoop Erasani, Tom Haynes, Arthur Lent, Trond Myklebust, Dave
Noveck, Theresa Lingutla-Raj, Manjunath Shankararao, Satyam Vaghani,
and Nico Williams.
For the NFS space reservation operations, the original draft was by
Mike Eisler, James Lentini, Manjunath Shankararao, and Rahul Iyer.
For the sparse file support, the original draft was by Dean
Hildebrand and Marc Eshel. Valuable input and advice was received
from Sorin Faibish, Bruce Fields, Benny Halevy, Trond Myklebust, and
Richard Scheffenegger.
For the Application IO Hints, the original draft was by Dean
Hildebrand, Mike Eisler, Trond Myklebust, and Sam Falkner. Some
early reviwers included Benny Halevy and Pranoop Erasani.
For Labeled NFS, the original draft was by David Quigley, James
Morris, Jarret Lu, and Tom Haynes. Peter Staubach, Trond Myklebust,
Sorrin Faibish, Nico Williams, and David Black also contributed in
the final push to get this accepted.
Appendix B. RFC Editor Notes
[RFC Editor: please remove this section prior to publishing this
document as an RFC]
[RFC Editor: prior to publishing this document as an RFC, please
replace all occurrences of RFCTBD10 with RFCxxxx where xxxx is the
RFC number of this document]
Haynes Expires July 7, 2012 [Page 91]
Internet-Draft NFSv4.2 January 2012
Author's Address
Thomas Haynes
NetApp
9110 E 66th St
Tulsa, OK 74133
USA
Phone: +1 918 307 1415
Email: thomas@netapp.com
URI: http://www.tulsalabs.com
Haynes Expires July 7, 2012 [Page 92]
Html markup produced by rfcmarkup 1.129d, available from
https://tools.ietf.org/tools/rfcmarkup/