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 ofthe 9p client is available in the form of a USENIX paper:
Other applications are described in the following papers:
XCPU & Clusteringhttp://xcpu.org/papers/xcpu-talk.pdf
KVMFS: control file system for KVMhttp://xcpu.org/papers/kvmfs.pdf
CellFS: A New Programming Model for the Cell BEhttp://xcpu.org/papers/cellfs-talk.pdf
PROSE I/O: Using 9p to enable Application Partitionshttp://plan9.escet.urjc.es/iwp9/cready/PROSE_iwp9_2006.pdf
VirtFS: A Virtualization Aware File System pass-throughhttp://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 exportedmount points. Each 9P export is seen by the client as a virtio device with anassociated “mount_tag” property. Available mount tags can beseen by reading /sys/bus/virtio/drivers/9pnet_virtio/virtio<n>/mount_tag files.
Options¶
trans=name
select an alternative transport. Valid options arecurrently:
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. Theserver may override or ignore this value. Certain usernames may require authentication.
aname=name
aname specifies the file tree to access when the server isoffering several exported file systems.
cache=mode
specifies a caching policy. By default, no caches are used.The mode can be specified as a bitmask or by using one of thepreexisting common ‘shortcuts’.The bitmask is described below: (unspecified bits are reserved)
0b00000000
all caches disabled, mmap disabled
0b00000001
file caches enabled
0b00000010
meta-data caches enabled
0b00000100
writeback behavior (as opposed to writethrough)
0b00001000
loose caches (no explicit consistency with server)
0b10000000
fscache enabled for persistent caching
The current shortcuts and their associated bitmask are:
none
0b00000000 (no caching)
readahead
0b00000001 (only read-ahead file caching)
mmap
0b00000101 (read-ahead + writeback file cache)
loose
0b00001111 (non-coherent file and meta-data caches)
fscache
0b10001111 (persistent loose cache)
NOTE: only these shortcuts are tested modes of operation at themoment, so using other combinations of bit-patterns is notknown to work. Work on better cache support is in progress.
IMPORTANT: loose caches (and by extension at the moment fscache)do not necessarily validate cached values on the server. In otherwords changes on the server are not guaranteed to be reflectedon the client system. Only use this mode of operation if youhave an exclusive mount and the server will modify the filesystemunderneath you.
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 betweenhosts. This functionality will be expanded in later versions.
directio
bypass page cache on all read/write operations
ignoreqv
ignore qid.version==0 as a marker to ignore cache
noxattr
do not offer xattr functions on this mount.
access
- there are four access modes.
- user
if a user tries to access a file on v9fsfilesystem for the first time, v9fs sends anattach command (Tattach) for that user.This is the default mode.
- <uid>
allows only user with uid=<uid> to accessthe files on the mounted filesystem
- any
v9fs does single attach and performs alloperations as one user
- clien
ACL based access check on the 9p clientside 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 differentfrom a local filesystem behaviors.
Setting O_NONBLOCK on a file will make client reads return as earlyas the server returns some data instead of trying to fill the readbuffer 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 onhttp://9p.cat-v.org/implementations
A 9p2000.L server is being developed by LLNL and can be foundat http://code.google.com/p/diod/
There are user and developer mailing lists available through the v9fs projecton 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 outhttp://plan9.bell-labs.com/plan9
For information on Plan 9 from User Space (Plan 9 applications and librariesported to Linux/BSD/OSX/etc) check out https://9fans.github.io/plan9port/
