v9fs: Plan 9 Resource Sharing for Linux

About

v9fs is a Unix implementation of the Plan 9 9p remote filesystem protocol.

This software was originally developed by Ron Minnich <rminnich@sandia.gov> and Maya Gokhale. Additional development by Greg Watson <gwatson@lanl.gov> and most recently Eric Van Hensbergen <ericvh@gmail.com>, Latchesar Ionkov <lucho@ionkov.net> and Russ Cox <rsc@swtch.com>.

The best detailed explanation of the Linux implementation and applications of the 9p client is available in the form of a USENIX paper:

Other applications are described in the following papers:

Usage

For remote file server:

mount -t 9p 10.10.1.2 /mnt/9

For Plan 9 From User Space applications (http://swtch.com/plan9):

mount -t 9p `namespace`/acme /mnt/9 -o trans=unix,uname=$USER

For server running on QEMU host with virtio transport:

mount -t 9p -o trans=virtio <mount_tag> /mnt/9

where mount_tag is the tag associated by the server to each of the exported mount points. Each 9P export is seen by the client as a virtio device with an associated “mount_tag” property. Available mount tags can be seen by reading /sys/bus/virtio/drivers/9pnet_virtio/virtio<n>/mount_tag files.

Options

trans=name

select an alternative transport. Valid options are currently:

unix

specifying a named pipe mount point

tcp

specifying a normal TCP/IP connection

fd

used passed file descriptors for connection (see rfdno and wfdno)

virtio

connect to the next virtio channel available (from QEMU with trans_virtio module)

rdma

connect to a specified RDMA channel

uname=name

user name to attempt mount as on the remote server. The server may override or ignore this value. Certain user names may require authentication.

aname=name

aname specifies the file tree to access when the server is offering several exported file systems.

cache=mode

specifies a caching policy. By default, no caches are used.

none

default no cache policy, metadata and data alike are synchronous.

loose

no attempts are made at consistency, intended for exclusive, read-only mounts

fscache

use FS-Cache for a persistent, read-only cache backend.

mmap

minimal cache that is only used for read-write mmap. Northing else is cached, like cache=none

debug=n

specifies debug level. The debug level is a bitmask.

0x01

display verbose error messages

0x02

developer debug (DEBUG_CURRENT)

0x04

display 9p trace

0x08

display VFS trace

0x10

display Marshalling debug

0x20

display RPC debug

0x40

display transport debug

0x80

display allocation debug

0x100

display protocol message debug

0x200

display Fid debug

0x400

display packet debug

0x800

display fscache tracing debug

rfdno=n

the file descriptor for reading with trans=fd

wfdno=n

the file descriptor for writing with trans=fd

msize=n

the number of bytes to use for 9p packet payload

port=n

port to connect to on the remote server

noextend

force legacy mode (no 9p2000.u or 9p2000.L semantics)

version=name

Select 9P protocol version. Valid options are:

9p2000

Legacy mode (same as noextend)

9p2000.u

Use 9P2000.u protocol

9p2000.L

Use 9P2000.L protocol

dfltuid

attempt to mount as a particular uid

dfltgid

attempt to mount with a particular gid

afid

security channel - used by Plan 9 authentication protocols

nodevmap

do not map special files - represent them as normal files. This can be used to share devices/named pipes/sockets between hosts. This functionality will be expanded in later versions.

access
there are four access modes.
user

if a user tries to access a file on v9fs filesystem for the first time, v9fs sends an attach command (Tattach) for that user. This is the default mode.

<uid>

allows only user with uid=<uid> to access the files on the mounted filesystem

any

v9fs does single attach and performs all operations as one user

clien

ACL based access check on the 9p client side for access validation

cachetag

cache tag to use the specified persistent cache. cache tags for existing cache sessions can be listed at /sys/fs/9p/caches. (applies only to cache=fscache)

Behavior

This section aims at describing 9p ‘quirks’ that can be different from a local filesystem behaviors.

  • Setting O_NONBLOCK on a file will make client reads return as early as the server returns some data instead of trying to fill the read buffer with the requested amount of bytes or end of file is reached.

Resources

Protocol specifications are maintained on github: http://ericvh.github.com/9p-rfc/

9p client and server implementations are listed on http://9p.cat-v.org/implementations

A 9p2000.L server is being developed by LLNL and can be found at http://code.google.com/p/diod/

There are user and developer mailing lists available through the v9fs project on sourceforge (http://sourceforge.net/projects/v9fs).

News and other information is maintained on a Wiki. (http://sf.net/apps/mediawiki/v9fs/index.php).

Bug reports are best issued via the mailing list.

For more information on the Plan 9 Operating System check out http://plan9.bell-labs.com/plan9

For information on Plan 9 from User Space (Plan 9 applications and libraries ported to Linux/BSD/OSX/etc) check out http://swtch.com/plan9