NFSv4 J. Lentini
Internet-Draft M. Eisler
Intended status: Standards Track R. Iyer
Expires: October 8, 2009 D. Kenchammana
A. Madan
NetApp
April 6, 2009
NFS Server-side Copy
draft-lentini-nfsv4-server-side-copy-01.txt
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Abstract
This document describes a set of NFS operations for offloading a file
copy to a file server or between two file servers.
Table of Contents
1. Requirements notation . . . . . . . . . . . . . . . . . . . . 3
2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Protocol Overview . . . . . . . . . . . . . . . . . . . . . . 3
3.1. Intra-Server Copy . . . . . . . . . . . . . . . . . . . . 5
3.2. Inter-Server Copy . . . . . . . . . . . . . . . . . . . . 5
3.3. Server-to-Server Copy Protocol . . . . . . . . . . . . . . 6
4. Operations . . . . . . . . . . . . . . . . . . . . . . . . . . 7
4.1. netloc4 - Network Locations . . . . . . . . . . . . . . . 8
4.2. Operation T: COPY_NOTIFY - Notify a server of a future
copy . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
4.3. Operation U: COPY_REVOKE - Revoke a server's copy
privileges . . . . . . . . . . . . . . . . . . . . . . . . 10
4.4. Operation V: COPY - Copy a file on the server . . . . . . 11
4.5. Operation X: COPY_ABORT - Cancel a server-side copy . . . 16
4.6. Operation Y: COPY_STATUS - Report results of a
server-side copy . . . . . . . . . . . . . . . . . . . . . 17
4.7. Operation Z: CB_COPY - Report results of a server-side
copy . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
4.8. Copy Offload Stateids . . . . . . . . . . . . . . . . . . 19
5. Security Considerations . . . . . . . . . . . . . . . . . . . 19
5.1. Inter-Server Copy Security Issues . . . . . . . . . . . . 20
5.1.1. Requirements for Secure Inter-Server Copy . . . . . . 20
5.1.2. Using RPCSEC_GSSv3 for Inter-Server File Copy . . . . 20
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 26
7. Normative References . . . . . . . . . . . . . . . . . . . . . 26
Appendix A. Acknowledgments . . . . . . . . . . . . . . . . . . . 26
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 27
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1. Requirements notation
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
2. 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 snapshot. Snapshot-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.
3. Protocol Overview
The server-side copy offload operations support both intra-server and
inter-server file copies. In both cases, the server may choose to
perform the copy operation 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.
For the inter-server copy protocol, the operations are defined to be
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compatible with a server-to-server copy protocol in which the
destination server reads the file data from the source server. A
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 A remote server only needs to be granted read access. A push
model requires a remote 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.
COPY_REVOKE: Also for inter-server copies, the client sends this
operation to the source server to revoke permission to copy a
file.
COPY: Used by the client to request a file copy.
COPY_ABORT: Used by the client to abort an asynchronous file copy.
COPY_STATUS: Used by the client to poll the status of an
asynchronous file copy.
CB_COPY: Used by the server to report the results of an asynchronous
file copy to the client.
These operations are described in detail in Section 4. This section
provides an overview of how these operations are used to perform
server-side copies.
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3.1. 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. This is show in the figure below:
Client Server
+ +
| |
|--- COPY ---------------------------->| Client requests
|<------------------------------------/| a file copy
| |
| |
If the server performs an asynchronous copy
| |
| |
|--- COPY_STATUS --------------------->| Client may poll
|<------------------------------------/| for status
| |
| . | Multiple COPY_STATUS
| . | operations may be sent.
| . |
| |
|<-- CB_COPY --------------------------| Server reports results
|\------------------------------------>|
| |
3.2. Inter-Server Copy
A copy may also be performed between two servers. In this case, the
client notifies the source server that a file will be copied by the
destination server using COPY_NOTIFY. 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. An asynchronous copy is shown below:
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Client Source Destination
+ + +
| | |
| --- COPY_NOTIFY -->| |
| <-- 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 --------------------------| Server reports results
|\------------------------------------>|
| | |
3.3. 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.
The destination server MAY use standard NFSv4.x 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 operations to read data from
the source server.
If NFSv4.x is not used in a heterogeneous environment, the
destination server is presented with the challenge of accessing the
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source file given only an NFSv4.x filehandle. Authenticating the
destination server to the source server is also a challenge.
Possible methods of addressing these issues include:
o for protocols that authenticate user names with passwords, (e.g.
HTTP and FTP) the nfsv4 user id could be used as the user name,
and an ASCII hexadecimal representation of the RPCSEC_GSS shared
secret could be used as the user password.
o for protocols that identify source files with path names, an ASCII
hexadecimal representation of the source filehandle could be used
as the file name.
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.
4. 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
[NFSv4.1]. 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. 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.
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4.1. 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
via DNS, LDAP, NIS, /etc/hosts, or some other means to a network
address. If the netloc4 is of type NL4_URL, the URL [RFC3986] of
server appropriate for the server-to-server copy operation is
specified at a UTF-8 string. If the netloc4 is of type NL4_NETADDR,
the nl_addr field MUST contain a valid netaddr4.
4.2. Operation T: COPY_NOTIFY - Notify a server of a future copy
ARGUMENTS
struct COPY_NOTIFY4args {
/* CURRENT_FH: source file */
netloc4 cna_destination_server;
};
RESULTS
union COPY_NOTIFY4res switch (nfsstat4 cnr_status) {
case NFS4_OK:
nfstime4 cnr_lease_time;
netloc4 cnr_source_server<>;
default:
void;
};
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
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destination server identified by cna_destination_server to read the
file specified by CURRENT_FH.
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 recipient will allow the
cna_destination_server to copy the specified file exactly once before
the copy lease time cnr_lease_time expires. The cnr_lease_time is
chosen by the 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 addresses, called
cnr_source_server, on which the source is willing to accept
connections from the destination. These addresses might not be
reachable from the client and might be located on networks to which
the client has no connection.
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For a copy only involving one server (the source and destination are
on the same server), this operation is unnecessary.
The COPY_NOTIFY operation may fail for the following reasons (this is
a partial list):
NFS4ERR_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. Operation U: COPY_REVOKE - Revoke a server's copy privileges
ARGUMENTS
struct COPY_REVOKE4args {
/* CURRENT_FH: source file */
netloc4 cra_destination_server;
};
RESULTS
struct COPY_REVOKE4res {
nfsstat4 crr_status;
};
DESCRIPTION
This operation is used for an inter-server copy. A client sends this
operation in a COMPOUND request to the source server to prevent a
destination server identified by cra_destination_server from reading
the file specified by CURRENT_FH. 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 involving an
asynchronous server-to-server copy. For example, suppose an NFS
client initiates a copy of file X from NFS server A to NFS server B.
If NFS server B decides to perform an asynchronous copy and a network
partition prevents communication between the NFS client and NFS
server B (without disrupting communication between the NFS client and
NFS server A or between NFS server A and NFS server B), the NFS
client may like to write new information to file X. In this
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situation, the client may treat the copy as a failure and start
writing to file X regardless of the ultimate status (if the network
partition is removed and the copy operation does succeeded, the
contents of the copied file would be uncertain). However, if the
client wishes to write sensitive information to file X that NFS
server B is not intended to see, the client MUST use a COPY_REVOKE
operation to ensure NFS server B is prevented access to the updates
to file X.
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_NOTSUPP: The copy offload operation is not supported by the
NFS server receiving this request.
4.4. Operation V: COPY - Copy a file on the server
ARGUMENTS
#define COPY4_GUARDED = 0x00000001;
#define COPY4_METADATA = 0x00000002;
#define COPY4_SPACE_RESERVED = 0x00000004;
struct COPY4args {
/* SAVED_FH: source file */
/* CURRENT_FH: destination directory */
offset4 ca_src_offset;
offset4 ca_dst_offset;
length4 ca_count;
uint32_t ca_flags;
component4 ca_destination;
netloc4 ca_source_server<>;
};
RESULTS
union COPY4res switch (nfsstat4 cr_status) {
/* CURRENT_FH: destination file */
case NFS4_OK:
stateid4 cr_callback_id<1>;
default:
length4 cr_bytes_copied;
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};
DESCRIPTION
The COPY operation request 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 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 (which is the same as the source server for an intra-server
copy).
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.
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 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
file.
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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 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. 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).
If the source offset or the source offset plus count is greater than
or equal to the size of the source file, the operation will fail with
NFS4ERR_INVAL. The destination offset or destination offset plus
count may be greater than the size of the destination file. This
allows for the client to issue parallel copies to implement
operations such as "cat file1 file2 file3 file4 > dest".
If the destination file is created as a result of this command, the
destination file's size will be equal to the number of bytes
successfully copied. If the destination file already existed, the
destination file's size may increase as a result of this operation
(e.g. if ca_dst_offset plus ca_count is greater than the
destination's initial size).
If the ca_source_server list is specified, the source of the copy
operation 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. The server-to-server
protocol used to copy the data is not prescribed by this document.
However, if the destination has an NFSv4.x client, NFSv4.x would be a
reasonable server-to-server copy protocol. The Security
Considerations discuss specifics around security if NFSv4.x or any
other ONC RPC protocol is used to copy the file. In addition,
because an element of the cnr_source_server_list can contain a URL,
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and because URLs specify both protocol services and server names, the
source server, indirectly via the response from COPY_NOTIFY and then
argument to COPY, can indicate to the destination a specific copy
protocol to use.
The fact that the destination only knows the source file by NFS
filehandle is not a barrier to using non-NFS protocols, because a URL
not only indicates a server name or address and service, but also a
port. For example, the response to COPY_NOTICE could include
ftp://s1.example.com:9999/. When the destination server receives the
source server's URL, it could convert the source filehandle to ASCII
hexadecimal, and use that as the file name to pass to ftp server
listening on port 9999 of s1.example.com. On port 9999 there would
be 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() system that the pre-NFSv4 MOUNT service
needs). Furthermore, the shared secret discussed in the Security
Considerations for RPCSEC_GSSv3 could be used as the secret for
authenticating the the destination's ftp client to the source's ftp
server, such as by converting the secret to an ASCII hexadecimal
string for use as a password, or as input into non-password
authentication methods like CHAP.
The ca_flags argument allows the copy operation to be customized in
the following ways using the guarded flag (COPY4_GUARDED), the
metadata flag (COPY4_METADATA), and the space reserved flag
(COPY4_SPACE_RESERVED).
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, the destination's metadata MUST match
the source's metadata. In particular, all of the REQUIRED,
RECOMMENDED, and named attributes of the destination file MUST be the
same as the source file. To preserve namespace junctions, if access
to the source file generates an NFS4ERR_MOVED error, access to the
destination file MUST also generate an NFS4ERR_MOVED error. If these
requirements cannot be met, the server MUST return
NFS4ERR_ATTRNOTSUPP.
If the metadata flag is not set, the destination's metadata is
implementation dependent.
If the space reserved flag is set, the operation will only succeed if
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the file server can guarantee that all writes to the copied file will
not fail due to insufficient space.
If space_reserved is not set, the space reservation state of the new
file is implementation dependent.
If the operation does not result in an immediate failure, the server
will return NFS4_OK, and the CURRENT_FH will be set to 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.
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.
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.
The 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 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.
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NFS4ERR_NOTDIR: The CURRENT_FH is a file and ca_destination has non-
zero length.
NFS4ERR_WRONG_TYPE: The SAVED_FH is not a regular file.
NFS4ERR_ISDIR: The CURRENT_FH is a directory and ca_destination has
zero length.
NFS4ERR_INVAL: The source offset or offset plus count are greater
than or equal to the size of the source file.
NFS4ERR_DELAY: The server does not have the resources to perform the
copy operation at the current time. The client should retry the
operation sometime in the future.
NFS4ERR_METADATA_NOTSUPP: The destination file cannot support the
same metadata as the source file.
NFS4ERR_WRONGSEC: The security mechanism being used by the client
does not match the server's security policy.
4.5. Operation X: COPY_ABORT - Cancel a server-side copy
ARGUMENTS
struct COPY_ABORT4args {
/* CURRENT_FH: destination file */
stateid4 caa_stateid;
};
RESULTS
struct COPY_ABORT4res {
nfsstat4 car_status;
};
DESCRIPTION
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 (which is
also the source server for an intra-server copy). 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.
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The result's car_status field indicates whether the cancel was
successful or not. A value of NFS4_OK indicates that the copy
operation was canceled and no callback will be issued by the server.
A copy operation that is successfully canceled may result in none,
some, or all of the data copied.
If the server supports asynchronous copies, the server is REQUIRED to
support the COPY_ABORT operation.
The COPY_ABORT operation may fail for the following reasons (this is
a partial list):
NFS4ERR_NOTSUPP: The abort operation is not supported by the NFS
server receiving this request.
NFS4ERR_RETRY: The abort failed, but a retry at some time in the
future MAY succeed.
NFS4ERR_COMPLETE_ALREADY: The abort failed, and a callback will
deliver the results of the copy operation.
NFS4ERR_SERVERFAULT: An error occurred on the server that does not
map to a specific error code.
4.6. Operation Y: COPY_STATUS - Report results of a server-side copy
ARGUMENTS
struct COPY_STATUS4args {
/* CURRENT_FH: destination file */
stateid4 csa_stateid;
};
RESULTS
union COPY_STATUS4res switch (nfsstat4 cr_status) {
case NFS4_OK:
length4 csr_bytes_copied;
default:
void;
};
DESCRIPTION
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 (which is
also the source server for an intra-server copy). If this operation
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is successful, the number of bytes copied are returned to the client.
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 4.8
below).
NFS4ERR_EXPIRED: The stateid has expired (see Copy Offload Stateid
section below).
4.7. Operation Z: CB_COPY - Report results of a server-side copy
ARGUMENTS
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;
};
RESULTS
struct CB_COPY4res {
nfsstat4 ccr_status;
};
DESCRIPTION
The CB_COPY callback informs the client of the result of a server-
side copy operation. This operation is sent by the destination
server (which is also the source server for an intra-server copy) to
the client in a CB_COMPOUND request. The copy operation is
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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.
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.
4.8. 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 include in the COPY, COPY_ABORT, COPY_STATUS,
and CB_COPY operations.
Section 8.2.4 of [NFSv4.1] specifies that stateids are valid until
either (A) the client or server restart or (B) the client returns the
resource. Case (A) applies to a copy offload stateid, but case (B)
does not (there is no way for the client to "return the resources").
A copy offload stateid will be valid until either (A) the client or
server restart or (C) 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.
5. Security Considerations
The security considerations pertaining to NFSv4 [RFC3530] apply to
this document.
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The standard security mechanisms provide by NFSv4 [RFC3530] may be
used to secure the protocol described in this document.
5.1. Inter-Server Copy Security Issues
5.1.1. Requirements for Secure Inter-Server Copy
The authors believe that 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 situation that exists between a source 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. For example, the
source and destination might be two nodes sharing a common storage
area network, and thus there is no need to copy any data at all,
and instead ownership of the file and its contents simply gets re-
assigned to the destination.
o The specification MUST provide guidance for using NFSv4.x as a
copy protocol. For those source and destination servers willing
to use NFSv4.x there are specific security considerations that
this specification can and does address.
o The specification MUST NOT mandate pre-configuration between the
source and destination server. Requiring that the source and
destination first have a "copying relationship" increases the
administrative burden. However the specification MUST NOT
preclude implementations that require pre-configuration.
o The specification MUST NOT mandate a trust relationship between
the source and destination server. The NFSv4 security model
requires mutual authentication between a principal on an NFS
client and a principal on an NFS server. This model MUST continue
with the introduction of COPY.
5.1.2. Using RPCSEC_GSSv3 for Inter-Server File Copy
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 operations. The
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user principal is identified by the credentials. The problem is how
can the user principal provide an authorization that directs the
source to allow the destination to perform the copy in a manner that
lets the source properly authenticate the destination's copy, and
without allowing the destination to exceed its authorization?
One way would be to send delegated credentials of the user principal
of the client to the destination server. The destination would then
be authenticated as the user principal. If the destination were
using the NFSv4 protocol to perform the copy, then the source would
authenticate the destination as the user principal, and the file copy
could securely proceed. However, the destination would also be
allowed to copy other files. The user principal would have to trust
the destination to not do so. This is counter to the requirements,
and so is not presented here. Instead an approach using RPCSEC_GSSv3
[RPCSEC_GSSv3] privileges is proposed.
One of the stated applications of the proposed RPCSEC_GSSv3 protocol
is:
b. compound client host & user authentication [+ privilege
assertion];
For inter-server file copy, the application needed is very similar,
and
compound NFS server host & user authentication [+ privilege
assertion];
is a distinction without meaning.
RPCSEC_GSSv3 introduces the notion of privileges. We define three
privileges:
copy_from_auth
A user principal is authorizing a source principal ("nfs@
<source>") to allow a destination principal ("nfs@
<destination>") to copy a file from the source to the
destination. This privilege is established on the source
server before the user principal sends a COPY_NOTIFY operation
to the source server.
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struct copy_from_auth_priv {
opaque 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;
};
cfap_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 */
opaque 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;
};
copy_confirm_auth
A destination principal is confirming with the source principal
that it is authorized to copy data from the source on behalf of
the user principal. When the inter-server copy protocol is
NFSv4, or for that matter, any protocol capable of being
secured via RPCSEC_GSSv3 (i.e. any ONC RPC protocol), this
privilege is established before the file is copied from the
source to the destination.
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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;
};
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 server, it establishes them:
o 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 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 it set to the seq_num of the credential of the
RPCSEC_GSS3_CREATE procedure. Because cfap_shared_secret is a
secret, after XDR encoding copy_from_auth_priv, GSS_Wrap() (with
privacy) is invoked on copy_from_auth_priv. The
RPCSEC_GSS3_CREATE procedure's arguments are:
struct {
rpc_gss3_gss_binding *compound_binding;
rpc_gss3_chan_binding *chan_binding_mic;
rpc_gss3_assertion assertions<>;
rpc_gss3_extension extensions<>;
} rpc_gss3_create_args;
The string "copy_from_auth" is placed in assertions[0].privs. The
output of GSS_Wrap() is placed in extensions[0].data. The field
extensions[0].critical is set to TRUE. The source server calls
GSS_Unwrap() on the privilege, and verifies that the seq_num
matches the credential. It then verifies that the NFSv4 user id
being asserted matches the source server's mapping of the user
principal. If it does, the privilege is established on the source
server as: <"copy_from_auth", user id, destination>. The
successful reply to RPCSEC_GSS3_CREATE has:
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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_GSS 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 it 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:
struct {
opaque handle<>;
rpc_gss3_chan_binding *chan_binding_mic;
rpc_gss3_assertion granted_assertions<>;
rpc_gss3_assertion server_assertions<>;
rpc_gss3_extension extensions<>;
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} rpc_gss3_create_res;
The field "handle" is the RPCSEC_GSS 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.
When the client sends a COPY_NOTIFY request to the source server, it
uses the privileged "copy_from_auth" RPCSEC_GSS handle. 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_GSS handle. 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.
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_N_AUTH. All subsequent ONC RPC
requests send from the destination to copy data from the source to
the destination will use the RPCSEC_GSS handle returned by the
source's RPCSEC_GSS3_CREATE response. Note that the use of the
"copy_confirm_auth" privilege accomplishes the following:
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o if a protocol like NFS is being used, with export policies, export
policies can be over ridden 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.
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 uses the shared secret and the NFSv4 user id to prove to
the source server that the user principal has authorized the copy.
6. IANA Considerations
This document has no actions for IANA.
7. Normative References
[NFSv4.1] Shepler, S., et al., "NFS Version 4 Minor Version 1 (Work
In Progress)", draft-ietf-nfsv4-minorversion1 , 2008.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3530] 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.
[RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
Resource Identifier (URI): Generic Syntax", STD 66,
RFC 3986, January 2005.
[RPCSEC_GSSv3]
Williams, N., "Remote Procedure Call (RPC) Security
Version 3 (Work In Progress)",
draft-williams-rpcsecgssv3 , 2008.
Appendix A. Acknowledgments
Tom Talpey co-authored an unpublished version of this document. We
thank Tom for his contributions, especially with regards to the
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asynchronous completion callback mechanism.
This document was reviewed by a number of individuals. We would like
to thank Pranoop Erasani, Tom Haynes, Arthur Lent, Trond Myklebust,
Dave Noveck, and Nico Williams for their input and advice.
Authors' Addresses
James Lentini
NetApp
1601 Trapelo Rd, Suite 16
Waltham, MA 02451
USA
Phone: +1 781-768-5359
Email: jlentini@netapp.com
Mike Eisler
NetApp
5765 Chase Point Circle
Colorado Springs, CO 80919
USA
Phone: +1 719-599-9026
Email: mike@eisler.com
URI: http://www.eisler.com
Rahul Iyer
NetApp
475 East Java Drive
Sunnyvale, CA 94089
USA
Phone: +1 408-822-3980
Email: iyer@netapp.com
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Deepak Kenchammana
NetApp
475 East Java Drive
Sunnyvale, CA 94089
USA
Phone: +1 408-822-4765
Email: kencham@netapp.com
Anshul Madan
NetApp
3rd Floor, Fair Winds Block EGL Software Park
Bangalore, Karnataka 560 071
India
Phone: +91 80-41843349
Email: anshul@netapp.com
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