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NFSv4 T. Haynes
Internet-Draft Editor
Intended status: Standards Track April 18, 2011
Expires: October 20, 2011
NFS Version 4 Minor Version 2
draft-ietf-nfsv4-minorversion2-00.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 to IETF in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as Internet-
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and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
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The list of current Internet-Drafts can be accessed at
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This Internet-Draft will expire on October 20, 2011.
Copyright Notice
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Copyright (c) 2011 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
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Contributions published or made publicly available before November
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Without obtaining an adequate license from the person(s) controlling
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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.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1. The NFS Version 4 Minor Version 2 Protocol . . . . . . . . 4
1.2. Scope of This Document . . . . . . . . . . . . . . . . . . 4
1.3. NFSv4.2 Goals . . . . . . . . . . . . . . . . . . . . . . 4
1.4. Overview of NFSv4.2 Features . . . . . . . . . . . . . . . 4
1.5. Differences from NFSv4.1 . . . . . . . . . . . . . . . . . 4
2. pNFS Access Permissions Check . . . . . . . . . . . . . . . . 4
2.1. Introduction . . . . . . . . . . . . . . . . . . . . . . . 4
2.2. Changes to Operation 51: LAYOUTRETURN (RFC 5661) . . . . . 6
2.2.1. ARGUMENT (18.44.1) . . . . . . . . . . . . . . . . . . 7
2.2.2. RESULT (18.44.2) . . . . . . . . . . . . . . . . . . . 8
2.2.3. DESCRIPTION (18.44.3) . . . . . . . . . . . . . . . . 8
2.2.4. IMPLEMENTATION (18.44.4) . . . . . . . . . . . . . . . 9
2.3. Change to NFS4ERR_NXIO Usage . . . . . . . . . . . . . . . 11
2.4. Security Considerations . . . . . . . . . . . . . . . . . 11
2.5. IANA Considerations . . . . . . . . . . . . . . . . . . . 11
3. Sharing change attribute implementation details with NFSv4
clients . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
3.1. Abstract . . . . . . . . . . . . . . . . . . . . . . . . . 11
3.2. Introduction . . . . . . . . . . . . . . . . . . . . . . . 12
3.3. Definition of the 'change_attr_type' per-file system
attribute . . . . . . . . . . . . . . . . . . . . . . . . 12
4. NFS Server-side Copy . . . . . . . . . . . . . . . . . . . . . 13
4.1. Introduction . . . . . . . . . . . . . . . . . . . . . . . 14
4.2. Protocol Overview . . . . . . . . . . . . . . . . . . . . 14
4.2.1. Intra-Server Copy . . . . . . . . . . . . . . . . . . 16
4.2.2. Inter-Server Copy . . . . . . . . . . . . . . . . . . 17
4.2.3. Server-to-Server Copy Protocol . . . . . . . . . . . . 20
4.3. Operations . . . . . . . . . . . . . . . . . . . . . . . . 22
4.3.1. netloc4 - Network Locations . . . . . . . . . . . . . 22
4.3.2. Operation 61: COPY_NOTIFY - Notify a source server
of a future copy . . . . . . . . . . . . . . . . . . . 23
4.3.3. Operation 62: COPY_REVOKE - Revoke a destination
server's copy privileges . . . . . . . . . . . . . . . 25
4.3.4. Operation 59: COPY - Initiate a server-side copy . . . 26
4.3.5. Operation 60: COPY_ABORT - Cancel a server-side
copy . . . . . . . . . . . . . . . . . . . . . . . . . 34
4.3.6. Operation 63: COPY_STATUS - Poll for status of a
server-side copy . . . . . . . . . . . . . . . . . . . 35
4.3.7. Operation 15: CB_COPY - Report results of a
server-side copy . . . . . . . . . . . . . . . . . . . 36
4.3.8. Copy Offload Stateids . . . . . . . . . . . . . . . . 37
4.4. Security Considerations . . . . . . . . . . . . . . . . . 38
4.4.1. Inter-Server Copy Security . . . . . . . . . . . . . . 38
4.5. IANA Considerations . . . . . . . . . . . . . . . . . . . 46
5. Space Reservation . . . . . . . . . . . . . . . . . . . . . . 46
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5.1. Introduction . . . . . . . . . . . . . . . . . . . . . . . 46
5.2. Use Cases . . . . . . . . . . . . . . . . . . . . . . . . 47
5.2.1. Space Reservation . . . . . . . . . . . . . . . . . . 47
5.2.2. Space freed on deletes . . . . . . . . . . . . . . . . 48
5.2.3. Operations and attributes . . . . . . . . . . . . . . 49
5.2.4. Attribute 77: space_reserve . . . . . . . . . . . . . 49
5.2.5. Attribute 78: space_freed . . . . . . . . . . . . . . 49
5.2.6. Attribute 79: max_hole_punch . . . . . . . . . . . . . 49
5.2.7. Operation 64: HOLE_PUNCH - Zero and deallocate
blocks backing the file in the specified range. . . . 50
5.3. Security Considerations . . . . . . . . . . . . . . . . . 51
5.4. IANA Considerations . . . . . . . . . . . . . . . . . . . 51
6. Simple and Efficient Read Support for Sparse Files . . . . . . 51
6.1. Introduction . . . . . . . . . . . . . . . . . . . . . . . 51
6.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 52
6.3. Applications and Sparse Files . . . . . . . . . . . . . . 52
6.4. Overview of Sparse Files and NFSv4 . . . . . . . . . . . . 53
6.5. Operation 65: READPLUS . . . . . . . . . . . . . . . . . . 54
6.5.1. ARGUMENT . . . . . . . . . . . . . . . . . . . . . . . 55
6.5.2. RESULT . . . . . . . . . . . . . . . . . . . . . . . . 55
6.5.3. DESCRIPTION . . . . . . . . . . . . . . . . . . . . . 55
6.5.4. IMPLEMENTATION . . . . . . . . . . . . . . . . . . . . 57
6.5.5. READPLUS with Sparse Files Example . . . . . . . . . . 58
6.6. Related Work . . . . . . . . . . . . . . . . . . . . . . . 59
6.7. Security Considerations . . . . . . . . . . . . . . . . . 59
6.8. IANA Considerations . . . . . . . . . . . . . . . . . . . 59
7. Security Considerations . . . . . . . . . . . . . . . . . . . 60
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 60
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 60
9.1. Normative References . . . . . . . . . . . . . . . . . . . 60
9.2. Informative References . . . . . . . . . . . . . . . . . . 60
Appendix A. Acknowledgments . . . . . . . . . . . . . . . . . . . 62
Appendix B. RFC Editor Notes . . . . . . . . . . . . . . . . . . 62
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 62
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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 [10] 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 RFC 3530bis.
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.
1.3. NFSv4.2 Goals
1.4. Overview of NFSv4.2 Features
1.5. Differences from NFSv4.1
2. pNFS Access Permissions Check
2.1. Introduction
Figure 1 shows the overall architecture of a Parallel NFS (pNFS)
system:
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+-----------+
|+-----------+ +-----------+
||+-----------+ | |
||| | NFSv4.1 + pNFS | |
+|| Clients |<------------------------------>| MDS |
+| | | |
+-----------+ | |
||| +-----------+
||| |
||| |
||| Storage +-----------+ |
||| Protocol |+-----------+ |
||+----------------||+-----------+ Control |
|+-----------------||| | Protocol |
+------------------+|| Storage |------------+
+| Devices |
+-----------+
Figure 1: pNFS Architecture
In this document, "storage device" is used as a general term for a
data server and/or storage server for the file, block, or object pNFS
layouts.
The current pNFS protocol [2] assumes that a client can access every
storage device (SD) included in a valid layout sent by the MDS
server, and provides no means to communicate client access failures
to the MDS. Access failures can impair pNFS performance scaling and
allow significant errors to go unreported. If the MDS can access all
the storage devices involved, but the client doesn't have sufficient
access rights to some storage devices, the client may choose to fall
back to accessing the file system using NFSV4.1 without pNFS support;
there are environments in which this behavior is undesirable,
especially if it occurs silently. An important example is addition
of a new storage device to which a large population of pNFS clients
(e.g., 1000s) lacks access permission. Layouts granted that use this
new device, result in client errors, requiring that all I/Os to that
new storage device be served by the MDS server. This creates a
performance and scalability bottleneck that may be difficult to
detect based on I/O behavior because the other storage devices are
functioning correctly.
The preferable approach to this scenario is to report the access
failures before any client attempts to issue any I/Os that can only
be serviced by the MDS server. This makes the problem explicit,
rather than forcing the MDS, or a system administrator, to diagnose
the performance problem caused by client I/O using NFS instead of
pNFS. There are limits to this approach because complex mount
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structures may prevent a client from detecting this situation at
mount time, but at a minimum, access problems involving the root of
the mount structure can be detected.
The most suitable time for the client to report inability to access a
storage device is at mount time, but this is not always possible. If
the application uses a special tag or a switch to the mount command
(e.g., -pnfs) and syscall to declare its intention to use pNFS, at
the client, the client can check for both pNFS support and device
accessibility.
This document introduces an error reporting mechanism that is an
extension to the return of a pNFS layout; a pNFS client MAY use this
mechanism to inform the MDS that the layout is being returned because
one or more data servers are not accessible to the client. Error
reporting at I/O time is not affected because the result of an
inaccessible data server may not be an I/O error if a subsequent
retry of the operation via the MDS is successful.
There is a related problem scenario involving an MDS that cannot
access some storage devices and hence cannot perform I/Os on behalf
of a client. In the case of the block layout [3] if the MDS lacks
access to a storage device (e.g., LUN), MDS implementations generally
do not export any filesystem using that storage device. In contrast
to the block layout, MDSs for the file [2] and object [4] layouts may
be unable to access the storage devices that store data for an
exported filesystem. This enables a file or object layout MDS to
provide layouts that contain client-inaccessible devices. For the
specific case of adding a new storage device to a filesystem, MDS
issuance of test I/Os to the newly added device before using it in
layouts avoids this problem scenario, but does not cover loss of
access to existing storage devices at a later time.
In addition, [2] states that a client can write through or read from
the MDS, even if it has a layout; this assumes that the MDS can
access all the storage devices. This document makes that assumed
access an explicit requirement.
2.2. Changes to Operation 51: LAYOUTRETURN (RFC 5661)
The existing LAYOUTRETURN operation is extended by introducing three
new layout return types that correspond to the existing types:
o LAYOUT4_RET_REC_FILE_NO_ACCESS at file scope;
o LAYOUT4_RET_REC_FSID_NO_ACCESS at fsid scope; and
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o LAYOUT4_RET_REC_ALL_NO_ACCESS at client scope.
The first return type returns the layout for an individual file and
informs the server that the reason for the return is a storage device
connectivity problem. The second return type performs that function
for all layouts held by the client for the filesystem that
corresponds to the current filehandle used for the LAYOUTRETURN
operation. The third return type performs that function for all
layouts held by the client; it is intended for situations in which a
device is shared across all or most of the filesystems from a server
for which the client has layouts.
2.2.1. ARGUMENT (18.44.1)
The ARGUMENT specification of the LAYOUTRETURN operation in section
18.44.1 of [2] is replaced by the following XDR code [11]:
/* Constants used for new LAYOUTRETURN and CB_LAYOUTRECALL */
const LAYOUT4_RET_REC_FILE = 1;
const LAYOUT4_RET_REC_FSID = 2;
const LAYOUT4_RET_REC_ALL = 3;
const LAYOUT4_RET_REC_FILE_NO_ACCESS = 4;
const LAYOUT4_RET_REC_FSID_NO_ACESSS = 5;
const LAYOUT4_RET_REC_ALL_NO_ACCESS = 6;
enum layoutreturn_type4 {
LAYOUTRETURN4_FILE = LAYOUT4_RET_REC_FILE,
LAYOUTRETURN4_FSID = LAYOUT4_RET_REC_FSID,
LAYOUTRETURN4_ALL = LAYOUT4_RET_REC_ALL,
LAYOUTRETURN4_FILE_NO_ACCESS = LAYOUT4_RET_REC_FILE_NO_ACCESS,
LAYOUTRETURN4_FSID_NO_ACCESS = LAYOUT4_RET_REC_FSID_NO_ACCESS,
LAYOUTRETURN4_ALL_NO_ACCESS = LAYOUT4_RET_REC_ALL_NO_ACCESS
};
struct layoutreturn_file4 {
offset4 lrf_offset;
length4 lrf_length;
stateid4 lrf_stateid;
/* layouttype4 specific data */
opaque lrf_body<>;
};
struct layoutreturn_device_no_access4 {
deviceid4 lrdna_deviceid;
nfsstat4 lrdna_status;
};
struct layoutreturn_file_no_access4 {
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offset4 lrfna_offset;
length4 lrfna_length;
stateid4 lrfna_stateid;
deviceid4 lrfna_deviceid;
nfsstat4 lrfna_status;
/* layouttype4 specific data */
opaque lrfna_body<>;
};
union layoutreturn4 switch(layoutreturn_type4 lr_returntype) {
case LAYOUTRETURN4_FILE:
layoutreturn_file4 lr_layout;
case LAYOUTRETURN4_FILE_NO_ACCESS:
layoutreturn_file_no_access4 lr_layout_na;
case LAYOUTRETURN4_FSID_NO_ACCESS:
case LAYOUTRETURN4_ALL_NO_ACCESS:
layoutreturn_device_no_access4 lr_device<>;
default:
void;
};
2.2.2. RESULT (18.44.2)
The RESULT of the LAYOUTRETURN operation is unchanged; see section
18.44.2 of [2]
2.2.3. DESCRIPTION (18.44.3)
The following text is added to the end of the LAYOUTRETURN operation
DESCRIPTION in section 18.44.3 of [2]
There are three NO_ACCESS layoutreturn_type4 values that indicate a
persistent lack of client ability to access storage device(s),
LAYOUT4_RET_REC_FILE_NO_ACCESS, LAYOUT4_RET_REC_FSID_NO_ACCESS and
LAYOUT4_RET_REC_ALL_NO_ACCESS. A client uses these return types to
return a layout (or portion thereof) for a file, return all layouts
for an FSID or all layouts from that server held by the client, and
in all cases to inform the server that the reason for the return is
the client's inability to access one or more storage devices. The
same stateid may be used or the client MAY force use of a new stateid
in order to report a new error.
An NFS error value (nfsstat4) is included for each device for these
three NO_ACCESS return types to provide additional information on the
cause. The allowed NFS errors are those that are valid for an NFS
READ or WRITE operation, and NFS4ERR_NXIO is also allowed to report
an inaccessible device. The server SHOULD log the received NFS error
value, but that error value does not affect server processing of the
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LAYOUTRETURN operation. All uses of the NO_ACCESS layout return
types that report NFS errors SHOULD be logged by the client.
The client MAY use the new LAYOUT4_RET_REC_FILE_NO_ACCESS when only
one file, or a small number of files are affected. If the access
problem affects multiple devices, the client may use multiple file
layout return operations; each return operation SHOULD return a
layout extent obtained from the device for which an error is being
reported. In contrast, both LAYOUT4_RET_REC_FSID_NO_ACCESS and
LAYOUT4_RET_REC_ALL_NO_ACCESS include an array of <device, status>
pairs to enable a single operation to report errors for multiple
devices in a single operation.
2.2.4. IMPLEMENTATION (18.44.4)
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 NO_ACCESS layout return types 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
server under appropriate conditions.
When an I/O fails because a storage device is inaccessible, 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
inaccessible portion thereof, and SHOULD indicate which storage
device or devices was or were inaccessible. If the client does not
do this, the MDS may issue a layout recall callback in order to
perform the retried I/O.
Backwards compatibility may require a client to perform two layout
return operations to deal with servers that don't implement the
NO_ACCESS layoutreturn_type4 values and hence respond to them with
NFS4ERR_INVAL. In this situation, the client SHOULD perform an
ordinary layout return operation and remember that the new layout
NO_ACCESS return types are not to be used with that server.
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The metadata server (MDS) SHOULD NOT use storage devices in pNFS
layouts that are not accessible to the MDS. At a minimum, the server
SHOULD check its own storage device accessibility before exporting a
filesystem that supports pNFS and when the device configuration for
such an exported filesystem is changed (e.g., to add a storage
device).
If an MDS is aware that a storage device is inaccessible to a client,
the MDS SHOULD NOT include that storage device in any pNFS layouts
sent to that client. An MDS SHOULD react to a client return of
inaccessible layouts by not using the inaccessible storage devices in
layouts for that client, but the MDS is not required to indefinitely
retain per-client storage device inaccessibility information. An MDS
is also not required to automatically reinstate use of a previously
inaccessible 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.
2.2.4.1. Storage Device Error Mapping (18.44.4.1, new)
The following text is added as new subsection 18.44.4.1 of [2]
An NFS error value is sent for each device that the client reports as
inaccessible via a NO_ACCESS layout return type. In general:
o If the client is unable to access the storage device, NFS4ERR_NXIO
SHOULD be used.
o If the client is able to access the storage device, but permission
is denied, NFS4ERR_ACCESS SHOULD be used.
Beyond these two rules, error code usage is layout-type specific:
o For the pNFS file layout, an indicative NFS error from a failed
read or write operation on the inaccessible device SHOULD be used.
o For the pNFS block layout, other errors from the Storage Protocol
SHOULD be mapped to NFS4ERR_IO. In addition, the client SHOULD
log information about the actual storage protocol error (e.g.,
SCSI status and sense data), but that information is not sent to
the pNFS server.
o For the pNFS object layout, occurrences of the object error types
specified in [4] SHOULD be mapped to the following NFS errors for
use in LAYOUTRETURN:
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* PNFS_OSD_ERR_EIO -> NFS4ERR_IO
* PNFS_OSD_ERR_NOT_FOUND -> NFS4ERR_STALE
* PNFS_OSD_ERR_NO_SPACE -> NFS4ERR_NOSPC
* PNFS_OSD_ERR_BAD_CRED -> NFS4ERR_INVAL
* PNFS_OSD_ERR_NO_ACCESS -> NFS4ERR_ACCESS
* PNFS_OSD_ERR_UNREACHABLE -> NFS4ERR_NXIO
* PNFS_OSD_ERR_RESOURCE -> NFS4ERR_SERVERFAULT
The LAYOUTRETURN NO_ACCESS return types are used for persistent
device errors; they do not replace other error reporting mechanisms
that also apply to transient errors (e.g., as specified for the
object layout in [4]).
2.3. Change to NFS4ERR_NXIO Usage
This document specifies that the NFS4ERR_NXIO error SHOULD be used to
report an inaccessible storage device. To enable that usage, this
document updates [2] to allow use of the currently obsolete
NFS4ERR_NXIO error in the ARGUMENT of LAYOUTRETURN; NFS4ERR_NXIO
remains obsolete for all other uses of NFS errors.
2.4. Security Considerations
This section adds a small extension to the NFSv4 LAYOUTRETURN
operation. The NFS and pNFS security considerations in [2], [3], and
[4] apply to the extended LAYOUTRETURN operation.
2.5. IANA Considerations
There are no additional IANA considerations in this section beyond
the IANA Considerations covered in [2]
3. Sharing change attribute implementation details with NFSv4 clients
3.1. Abstract
This document describes an extension to the NFSv4 protocol that
allows the server to share information about the implementation of
its change attribute with the client. The aim is to improve the
client's ability to determine the order in which parallel updates to
the same file were processed.
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3.2. Introduction
Although both the NFSv4 [10] 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 the spec
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
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.
In order to avoid this kind of inefficiency, we propose a method to
allow 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.
3.3. 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 proposed solution is to enable 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. To do
so, we define a new recommended attribute, 'change_attr_type', which
may take values from enum change_attr_typeinfo as follows:
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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
writes.
NFS4_CHANGE_TYPE_IS_TIME_METADATA: The change attribute is
implemented as suggested in the NFSv4 spec [10] 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.
4. NFS Server-side Copy
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4.1. Introduction
This document 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.
4.2. 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
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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
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.
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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 4.3. This
section provides an overview of how these operations are used to
perform server-side copies.
4.2.1. 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 2. 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.
Client Server
+ +
| |
|--- COPY ---------------------------->| Client requests
|<------------------------------------/| a file copy
| |
| |
Figure 2: A synchronous intra-server copy.
An asynchronous intra-server copy is shown in Figure 3. 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.
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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 3: An asynchronous intra-server copy.
4.2.2. 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 4, 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
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.
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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 4: 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 5. 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 6. In this case, the
destination server chooses to respond to the client's COPY request
immediately and then perform the copy asynchronously.
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Client Source Destination
+ + +
| | |
|--- COPY_NOTIFY --->| |
|<------------------/| |
| | |
| | |
|--- COPY ---------------------------->|
| | |
| | |
| |<----- read -----|
| |\--------------->|
| | |
| | . | Multiple reads may
| | . | be necessary
| | . |
| | |
| | |
|<------------------------------------/| Destination replies
| | | to COPY
Figure 5: A synchronous inter-server copy.
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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 6: An asynchronous inter-server copy.
4.2.3. 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.
4.2.3.1. 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
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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.
4.2.3.2. 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 4.4.1.2.4 and Section 4.4.1.4.
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4.3. 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.
4.3.1. 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 [5]
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 4, their values may be evaluated on the source server,
destination server, and client. The network environment in which
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these systems operate should be configured so that the netloc4 values
are interpreted as intended on each system.
4.3.2. Operation 61: COPY_NOTIFY - Notify a source server of a future
copy
4.3.2.1. ARGUMENT
struct COPY_NOTIFY4args {
/* CURRENT_FH: source file */
netloc4 cna_destination_server;
};
4.3.2.2. RESULT
union COPY_NOTIFY4res switch (nfsstat4 cnr_status) {
case NFS4_OK:
nfstime4 cnr_lease_time;
netloc4 cnr_source_server<>;
default:
void;
};
4.3.2.3. 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.
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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
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
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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.
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.
4.3.3. Operation 62: COPY_REVOKE - Revoke a destination server's copy
privileges
4.3.3.1. ARGUMENT
struct COPY_REVOKE4args {
/* CURRENT_FH: source file */
netloc4 cra_destination_server;
};
4.3.3.2. RESULT
struct COPY_REVOKE4res {
nfsstat4 crr_status;
};
4.3.3.3. DESCRIPTION
This operation is used for an inter-server copy. A client sends this
operation in a COMPOUND request to the source server to 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
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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.
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.
4.3.4. Operation 59: COPY - Initiate a server-side copy
4.3.4.1. 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<>;
};
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4.3.4.2. RESULT
union COPY4res switch (nfsstat4 cr_status) {
/* CURRENT_FH: destination file */
case NFS4_OK:
stateid4 cr_callback_id<1>;
default:
length4 cr_bytes_copied;
};
4.3.4.3. DESCRIPTION
The COPY operation is used for both intra- 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
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.
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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
(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
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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 4.2.3 and Section 4.4.1.
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).
[NOTE: Earlier versions of this document defined a
COPY4_SPACE_RESERVED flag for controlling space reservations on the
destination file. This flag has been removed with the expectation
that the space_reserve attribute defined in XXX_TDH_XXX will be
adopted.]
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.
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.
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+--------------------+----+---------------------------+
| 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 |
| fs_locations_info | 67 | no |
| fs_status | 61 | no |
| hidden | 25 | MUST |
| homogeneous | 26 | no |
| layout_alignment | 66 | no |
| layout_blksize | 65 | no |
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| 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_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 |
+--------------------+----+---------------------------+
Table 2
[NOTE: The space_reserve attribute XXX_TDH_XXX will be in the MUST
set.]
[NOTE: The source file's attribute values will take precedence over
any attribute values inherited by the destination file.]
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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
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.
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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_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.
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.
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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.
4.3.5. Operation 60: COPY_ABORT - Cancel a server-side copy
4.3.5.1. ARGUMENT
struct COPY_ABORT4args {
/* CURRENT_FH: desination file */
stateid4 caa_stateid;
};
4.3.5.2. RESULT
struct COPY_ABORT4res {
nfsstat4 car_status;
};
4.3.5.3. 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
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.
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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.
4.3.6. Operation 63: COPY_STATUS - Poll for status of a server-side
copy
4.3.6.1. ARGUMENT
struct COPY_STATUS4args {
/* CURRENT_FH: destination file */
stateid4 csa_stateid;
};
4.3.6.2. RESULT
union COPY_STATUS4res switch (nfsstat4 csr_status) {
case NFS4_OK:
length4 csr_bytes_copied;
nfsstat4 csr_complete<1>;
default:
void;
};
4.3.6.3. 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
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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.
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 4.3.8
below).
NFS4ERR_EXPIRED: The stateid has expired (see Copy Offload Stateid
section below).
4.3.7. Operation 15: CB_COPY - Report results of a server-side copy
4.3.7.1. 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;
};
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4.3.7.2. RESULT
struct CB_COPY4res {
nfsstat4 ccr_status;
};
4.3.7.3. 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):
NFS4ERR_NOTSUPP: The copy offload operation is not supported by the
NFS client receiving this request.
4.3.8. 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
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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.
4.4. Security Considerations
The security considerations pertaining to NFSv4 [10] apply to this
document.
The standard security mechanisms provide by NFSv4 [10] 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 [6],
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 [6] to secure server-side copy operations.
4.4.1. Inter-Server Copy Security
4.4.1.1. Requirements for Secure Inter-Server Copy
Inter-server copy is driven by several requirements:
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
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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.
4.4.1.2. 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
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 [6] 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
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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.
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),
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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;
};
4.4.1.2.1. 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,
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
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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
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:
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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.
4.4.1.2.2. 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.
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.
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4.4.1.2.3. 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:
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.
4.4.1.2.4. 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
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[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].
4.4.1.3. 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 triple:
<source fh, user ID, destination address Y>. If the destination uses
one of these target netlocs to contact 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.
For example, suppose the network topology is as shown in Figure 4.
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/10.11.78.56/_FH/0x12345
nfs://192.168.33.18//_COPY/10.11.78.56/_FH/0x12345
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:
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COMPOUND { PUTROOTFH, LOOKUP "_COPY" ; LOOKUP "10.11.78.56"; LOOKUP
"_FH" ; OPEN "0x12345" ; GETFH }
The source server will therefore know that these NFSv4.1 operations
are being issued by the destination server identified in the
COPY_NOTIFY.
4.4.1.4. Inter-Server Copy without ONC RPC and RPCSEC_GSSv3
The same techniques as Section 4.4.1.3, using unique URLs for each
destination server, can be used for other protocols (e.g. HTTP [14]
and FTP [15]) as well.
4.5. IANA Considerations
This section has no actions for IANA.
5. Space Reservation
5.1. 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.
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:
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
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filesystems that support block sharing. 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.
We propose the following operations and attributes for the
aforementioned use cases:
space_reserve 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.
max_hole_punch This attribute specifies the maximum sized hole that
can be punched on the filesystem.
HOLE_PUNCH This operation zeroes and/or deallocates the blocks
backing a region of the file.
5.2. Use Cases
5.2.1. Space Reservation
Some applications require that once a file of a certain size is
created, writes to that file never fail with an out of space
condition. One such example is that of a hypervisor writing to a
virtual disk. An out of space condition while writing to virtual
disks would mean that the virtual machine would need to be frozen.
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.
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5.2.2. Space freed on deletes
Currently, files in NFS have two size attributes:
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.
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 *
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.
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5.2.3. Operations and attributes
In the sections that follow, one operation and three attributes are
defined that together provide the space management facilities
outlined earlier in the document. The operation is intended to be
OPTIONAL and the attributes RECOMMENDED as defined in section 17 of
[2].
5.2.4. Attribute 77: space_reserve
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
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.
5.2.5. 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.
5.2.6. Attribute 79: max_hole_punch
max_hole_punch specifies the maximum size of a hole that the
HOLE_PUNCH operation can handle. This attribute is read only and of
type length4. It is a per filesystem attribute. This attribute MUST
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be implemented if HOLE_PUNCH is implemented.
5.2.7. Operation 64: HOLE_PUNCH - Zero and deallocate blocks backing
the file in the specified range.
5.2.7.1. ARGUMENT
struct HOLE_PUNCH4args {
/* CURRENT_FH: file */
offset4 hpa_offset;
length4 hpa_count;
};
5.2.7.2. RESULT
struct HOLEPUNCH4res {
nfsstat4 hpr_status;
};
5.2.7.3. DESCRIPTION
Whenever a client wishes to deallocate the blocks backing a
particular region in the file, it calls the HOLE_PUNCH 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
zeros until overwritten. The filehandle specified must be that of a
regular file.
Situations may arise where hpa_offset and/or hpa_offset + hpa_count
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 HOLE_PUNCH 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, HOLE_PUNCH 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.
HOLE_PUNCH will result in the space_used attribute being decreased by
the number of bytes that were deallocated. The space_freed attribute
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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 HOLE_PUNCH 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 HOLE_PUNCH 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.
5.3. Security Considerations
There are no security considerations for this section.
5.4. IANA Considerations
This section has no actions for IANA.
6. Simple and Efficient Read Support for Sparse Files
6.1. Introduction
NFS is now used in many data centers as the sole or primary method of
data access. Consequently, more types of applications are using NFS
than ever before, each with their own requirements and generated
workloads. As part of this, sparse files are increasing in number
while NFS continues to lack any specific knowledge of a sparse file's
layout. This document puts forth a proposal for the NFSv4.2 protocol
to support efficient reading of sparse files.
A sparse file is a common way of representing a large file without
having to reserve 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
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UNIX file systems and NTFS, but notably not Apple's HFS+. Common
examples of sparse files include 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
returns 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. Once the zeroes arrive, they then
steal memory or cache space from real data. To make matters worse,
if an application then proceeds to write data to another file system,
the zeros are written into the file, expanding the sparse file into a
full sized regular file. Beyond wasting disk space, this can
actually prevent large sparse files from ever being copied to another
storage location due to space limitations.
This document adds a new READPLUS operation to efficiently read from
sparse files by avoiding the transfer of all zero regions from the
server to the client. READPLUS supports all the features of READ but
includes a minimal extension to support sparse files. In addition,
the return value of READPLUS is now compatible with NFSv4.1 minor
versioning rules and could support other future extensions without
requiring yet another operation. READPLUS is guaranteed to perform
no worse than READ, and can dramatically improve performance with
sparse files. READPLUS does not depend on pNFS protocol features,
but can be used by pNFS to support sparse files.
6.2. Terminology
Regular file Regular file: An object of file type NF4REG or
NF4NAMEDATTR.
Sparse file Sparse File. A Regular file that contains one or more
Holes.
Hole 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.
6.3. Applications and Sparse Files
Applications may cause an NFS client to read holes in a file for
several reasons. This section describes three different application
workloads that cause the NFS client to transfer data unnecessarily.
These workloads are simply examples, and there are probably many more
workloads that are negatively impacted by sparse files.
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The first workload that can cause holes to be read is sequential
reads within a sparse file. When this happens, the NFS client may
perform read requests ("readahead") into sections of the file not
explicitly requested by the application. Since the NFS client cannot
differentiate between holes and non-holes, the NFS client may
prefetch empty sections of the file.
This workload is exemplified by Virtual Machines and their associated
file system images, e.g., VMware .vmdk files, which are large sparse
files encapsulating an entire operating system. If a VM reads files
within the file system image, this will translate to sequential NFS
read requests into the much larger file system image file. Since NFS
does not understand the internals of the file system image, it ends
up performing readahead file holes.
The second workload is generated by copying a file from a directory
in NFS to either the same NFS server, to another file system, e.g.,
another NFS or Samba server, to a local ext3 file system, or even a
network socket. In this case, bandwidth and server resources are
wasted as the entire file is transferred from the NFS server to the
NFS client. Once a byte range of the file has been transferred to
the client, it is up to the client application, e.g., rsync, cp, scp,
on how it writes the data to the target location. For example, cp
supports sparse files and will not write all zero regions, whereas
scp does not support sparse files and will transfer every byte of the
file.
The third workload is generated by applications that do not utilize
the NFS client cache, but instead use direct I/O and manage cached
data independently, e.g., databases. These applications may perform
whole file caching with sparse files, which would mean that even the
holes will be transferred to the clients and cached.
6.4. Overview of Sparse Files and NFSv4
This proposal seeks to provide sparse file support to the largest
number of NFS client and server implementations, and as such proposes
to add a new return code to the mandatory NFSv4.1 READPLUS operation
instead of proposing additions or extensions of new or existing
optional features (such as pNFS).
As well, this document seeks to ensure that the proposed extensions
are simple and do not transfer data between the client and server
unnecessarily. For example, one possible way to implement sparse
file read support would be to have the client, on the first hole
encountered or at OPEN time, request a Data Region Map from the
server. A Data Region Map would specify all zero and non-zero
regions in a file. While this option seems simple, it is less useful
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and can become inefficient and cumbersome for several reasons:
o Data Region Maps can be large, and transferring them can reduce
overall read performance. For example, VMware's .vmdk files can
have a file size of over 100 GBs and have a map well over several
MBs.
o Data Region Maps can change frequently, and become invalidated on
every write to the file. This can result the map being
transferred multiple times with each update to the file. For
example, a VM that updates a config file in its file system image
would invalidate the Data Region Map not only for itself, but for
all other clients accessing the same file system image.
o Data Region Maps do not handle all zero-filled sections of the
file, reducing the effectiveness of the solution. While it may be
possible to modify the maps to handle zero-filled sections (at
possibly great effort to the server), it is almost impossible with
pNFS. With pNFS, the owner of the Data Region Map is the metadata
server, which is not in the data path and has no knowledge of the
contents of a data region.
Another way to handle holes is compression, but this not ideal since
it requires all implementations to agree on a single compression
algorithm and requires a fair amount of computational overhead.
Note that supporting writing to a sparse file does not require
changes to the protocol. Applications and/or NFS implementations can
choose to ignore WRITE requests of all zeroes to the NFS server
without consequence.
6.5. Operation 65: READPLUS
The section introduces a new read operation, named READPLUS, which
allows NFS clients to avoid reading holes in a sparse file. READPLUS
is guaranteed to perform no worse than READ, and can dramatically
improve performance with sparse files.
READPLUS 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 all zeroes from a file hole, wasting computational and
network resources and reducing performance. READPLUS 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.
Returning the hole's byte-range, and only upon request, avoids
transferring large Data Region Maps that may be soon invalidated and
contain information about a file that may not even be read in its
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entirely.
A new read operation is required due to NFSv4.1 minor versioning
rules that do not allow modification of existing operation's
arguments or results. READPLUS is designed in such a way to allow
future extensions to the result structure. The same approach could
be taken to extend the argument structure, but a good use case is
first required to make such a change.
6.5.1. ARGUMENT
struct COPY_NOTIFY4args {
/* CURRENT_FH: source file */
netloc4 cna_destination_server;
};
6.5.2. RESULT
union COPY_NOTIFY4res switch (nfsstat4 cnr_status) {
case NFS4_OK:
nfstime4 cnr_lease_time;
netloc4 cnr_source_server<>;
default:
void;
};
6.5.3. DESCRIPTION
The READPLUS 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 an offset of where the READPLUS is to start and a
count of how many bytes are to be read. An offset of zero means to
read data starting at the beginning of the file. If offset is
greater than or equal to the size of the file, the status NFS4_OK is
returned with nfs_readplusrestype4 set to READ_OK, data length set to
zero, and eof set to TRUE. The READPLUS is subject to access
permissions checking.
If the client specifies a count value of zero, the READPLUS 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.
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If the client specifies an offset and count value that is entirely
contained within a hole of the file, the status NFS4_OK is returned
with nfs_readplusresok4 set to READ_HOLE, and if information is
available regarding the hole, a nfs_readplusreshole structure
containing the offset and range of the entire hole. The
nfs_readplusreshole structure is considered valid until the file is
changed (detected via the change attribute). The server MUST provide
the same semantics for nfs_readplusreshole 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 offset and count value that begins in a
non-hole of the file but extends into hole the server should return a
short read with status NFS4_OK, nfs_readplusresok4 set to READ_OK,
and data length set to the number of bytes returned. The client will
then issue another READPLUS for the remaining bytes, which the server
will respond with information about the hole in the file.
If the server knows that the requested byte range is into a hole of
the file, but has no further information regarding the hole, it
returns a nfs_readplusreshole structure with holeres4 set to
HOLE_NOINFO.
If hole information is available on the server and can be returned to
the client, the server returns a nfs_readplusreshole structure with
the value of holeres4 to HOLE_INFO. The values of hole_offset and
hole_length define the byte-range for the current hole in the file.
These values represent the information known to the server and may
describe a byte-range smaller than the true size of the hole.
Except when special stateids are used, the stateid value for a
READPLUS 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
READPLUS operation, if offset + count is equal to the size of the
file), or the READPLUS operation extends beyond the size of the file
(if offset + count is greater than the size of the file), eof is
returned as TRUE; otherwise, it is FALSE. A successful READPLUS 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
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returned. In all other cases, NFS4ERR_WRONG_TYPE is returned.
For a READPLUS with a stateid value of all bits equal to zero, the
server MAY allow the READPLUS to be serviced subject to mandatory
byte-range locks or the current share deny modes for the file. For a
READPLUS with a stateid value of all bits equal to one, the server
MAY allow READPLUS operations to bypass locking checks at the server.
On success, the current filehandle retains its value.
6.5.4. IMPLEMENTATION
If the server returns a "short read" (i.e., fewer data than requested
and eof is set to FALSE), the client should send another READPLUS 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 reduce 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 READPLUS. When the READPLUS completes, the client
should release the byte-range lock via LOCKU.
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 READPLUS
operation since the recall will occur as a result of an earlier OPEN.
However, since it is possible for a READPLUS 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.
6.5.4.1. Additional pNFS Implementation Information
With pNFS, the semantics of using READPLUS remains the same. Any
data server MAY return a READ_HOLE result for a READPLUS request that
it receives.
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When a data server chooses to return a READ_HOLE result, it has a
certain level of flexibility in how it fills out the
nfs_readplusreshole structure.
1. For a data server that cannot determine any hole information, the
data server SHOULD return HOLE_NOINFO.
2. For a data server that can only 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.
3. For a data server that can obtain hole information for the entire
file without severe performance impact, it MAY return HOLE_INFO
nd the byte range of the entire file hole.
In general, a data server should do its best to return as much
information about a hole as is feasible. In general, pNFS server
implementers should try ensure that data servers do not overload the
metadata server with requests for information. Therefore, if
supplying global sparse information for a file to data servers can
overwhelm a metadata server, then data servers should use option 1 or
2 above.
When a pNFS client receives a READ_HOLE result and a non-empty
nfs_readplusreshole structure, it MAY use this information in
conjunction with a valid layout for the file to determine the next
data server for the next region of data that is not in a hole.
6.5.5. READPLUS with Sparse Files Example
To see how the return value READ_HOLE will work, the following table
describes a sparse file. For each byte range, the file contains
either non-zero data or a hole.
+-------------+----------+
| Byte-Range | Contents |
+-------------+----------+
| 0-31999 | 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
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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 and
acquired a valid stateid and just needs to issue READPLUS requests.
1. READPLUS(s, 0, 64K) --> NFS_OK, readplusrestype4 = READ_OK, eof =
false, data<>[32K]. Return a short read, as the last half of the
equest was all zeroes.
2. READPLUS(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. READPLUS(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. READPLUS(s, 288K, 64K) --> NFS_OK, readplusrestype4 = READ_HOLE,
nfs_readplusreshole(HOLE_INFO)(288K, 66K).
5. READPLUS(s, 354K, 64K) --> NFS_OK, readplusrestype4 = READ_OK,
eof = true, data<>[64K].
6.6. Related Work
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.
XFS supports the XFS_IOC_GETBMAP extended attribute, which returns
the Data Region Map for a file. Clients can then use this
information to avoid reading holes in a file.
NTFS and CIFS support the FSCTL_SET_SPARSE attribute, which allows
applications to control whether empty regions of the file are
preallocated and filled in with zeros or simply left unallocated.
6.7. Security Considerations
The additions to the NFS protocol for supporting sparse file reads
does not alter the security considerations of the NFSv4.1 protocol
[2].
6.8. IANA Considerations
There are no IANA considerations in this section.
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7. Security Considerations
8. IANA Considerations
This section uses terms that are defined in [17].
9. References
9.1. 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] Black, D., Glasgow, J., and S. Fridella, "Parallel NFS (pNFS)
Block/Volume Layout", RFC 5663, January 2010.
[4] Halevy, B., Welch, B., and J. Zelenka, "Object-Based Parallel
NFS (pNFS) Operations", RFC 5664, January 2010.
[5] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
Resource Identifier (URI): Generic Syntax", STD 66, RFC 3986,
January 2005.
[6] Williams, N., "Remote Procedure Call (RPC) Security Version 3",
draft-williams-rpcsecgssv3 (work in progress), 2008.
[7] 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.
[8] Haynes, T., "Network File System (NFS) Version 4 Minor Version
2 External Data Representation Standard (XDR) Description",
April 2011.
[9] Eisler, M., Chiu, A., and L. Ling, "RPCSEC_GSS Protocol
Specification", RFC 2203, September 1997.
9.2. Informative References
[10] Haynes, T. and D. Noveck, "Network File System (NFS) version 4
Protocol", draft-ietf-nfsv4-rfc3530bis-09 (Work In Progress),
April 2011.
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[11] Eisler, M., "XDR: External Data Representation Standard",
RFC 4506, May 2006.
[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] Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA
Considerations Section in RFCs", BCP 26, RFC 5226, May 2008.
[18] Nowicki, B., "NFS: Network File System Protocol specification",
RFC 1094, March 1989.
[19] Callaghan, B., Pawlowski, B., and P. Staubach, "NFS Version 3
Protocol Specification", RFC 1813, June 1995.
[20] Srinivasan, R., "Binding Protocols for ONC RPC Version 2",
RFC 1833, August 1995.
[21] 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.
[22] Callaghan, B., "NFS URL Scheme", RFC 2224, October 1997.
[23] Shepler, S., "NFS Version 4 Design Considerations", RFC 2624,
June 1999.
[24] Reynolds, J., "Assigned Numbers: RFC 1700 is Replaced by an On-
line Database", RFC 3232, January 2002.
[25] Linn, J., "The Kerberos Version 5 GSS-API Mechanism", RFC 1964,
June 1996.
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[26] 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.
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. 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.
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]
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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
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