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.. SPDX-License-Identifier: GPL-2.0
=======================================
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:
https://www.usenix.org/events/usenix05/tech/freenix/hensbergen.html
Other applications are described in the following papers:
* XCPU & Clustering
http://xcpu.org/papers/xcpu-talk.pdf
* KVMFS: control file system for KVM
http://xcpu.org/papers/kvmfs.pdf
* CellFS: A New Programming Model for the Cell BE
http://xcpu.org/papers/cellfs-talk.pdf
* PROSE I/O: Using 9p to enable Application Partitions
http://plan9.escet.urjc.es/iwp9/cready/PROSE_iwp9_2006.pdf
* VirtFS: A Virtualization Aware File System pass-through
http://goo.gl/3WPDg
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 https://9fans.github.io/plan9port/
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