v9fs: Plan 9 Resource Sharing for Linux


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:


For remote file server:

mount -t 9p /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.



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.

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

default no cache policy, metadata and data alike are synchronous.
no attempts are made at consistency, intended for exclusive, read-only mounts
use FS-Cache for a persistent, read-only cache backend.
minimal cache that is only used for read-write mmap. Northing else is cached, like cache=none

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)

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.
there are four access modes.
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.
allows only user with uid=<uid> to access the files on the mounted filesystem
v9fs does single attach and performs all operations as one user
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)


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.


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 https://9fans.github.io/plan9port/