1.. SPDX-License-Identifier: GPL-2.0
2
3=======================================
4v9fs: Plan 9 Resource Sharing for Linux
5=======================================
6
7About
8=====
9
10v9fs is a Unix implementation of the Plan 9 9p remote filesystem protocol.
11
12This software was originally developed by Ron Minnich <rminnich@sandia.gov>
13and Maya Gokhale.  Additional development by Greg Watson
14<gwatson@lanl.gov> and most recently Eric Van Hensbergen
15<ericvh@gmail.com>, Latchesar Ionkov <lucho@ionkov.net> and Russ Cox
16<rsc@swtch.com>.
17
18The best detailed explanation of the Linux implementation and applications of
19the 9p client is available in the form of a USENIX paper:
20
21   https://www.usenix.org/events/usenix05/tech/freenix/hensbergen.html
22
23Other applications are described in the following papers:
24
25	* XCPU & Clustering
26	  http://xcpu.org/papers/xcpu-talk.pdf
27	* KVMFS: control file system for KVM
28	  http://xcpu.org/papers/kvmfs.pdf
29	* CellFS: A New Programming Model for the Cell BE
30	  http://xcpu.org/papers/cellfs-talk.pdf
31	* PROSE I/O: Using 9p to enable Application Partitions
32	  http://plan9.escet.urjc.es/iwp9/cready/PROSE_iwp9_2006.pdf
33	* VirtFS: A Virtualization Aware File System pass-through
34	  http://goo.gl/3WPDg
35
36Usage
37=====
38
39For remote file server::
40
41	mount -t 9p 10.10.1.2 /mnt/9
42
43For Plan 9 From User Space applications (http://swtch.com/plan9)::
44
45	mount -t 9p `namespace`/acme /mnt/9 -o trans=unix,uname=$USER
46
47For server running on QEMU host with virtio transport::
48
49	mount -t 9p -o trans=virtio <mount_tag> /mnt/9
50
51where mount_tag is the tag associated by the server to each of the exported
52mount points. Each 9P export is seen by the client as a virtio device with an
53associated "mount_tag" property. Available mount tags can be
54seen by reading /sys/bus/virtio/drivers/9pnet_virtio/virtio<n>/mount_tag files.
55
56Options
57=======
58
59  ============= ===============================================================
60  trans=name	select an alternative transport.  Valid options are
61  		currently:
62
63			========  ============================================
64			unix 	  specifying a named pipe mount point
65			tcp	  specifying a normal TCP/IP connection
66			fd   	  used passed file descriptors for connection
67                                  (see rfdno and wfdno)
68			virtio	  connect to the next virtio channel available
69				  (from QEMU with trans_virtio module)
70			rdma	  connect to a specified RDMA channel
71			========  ============================================
72
73  uname=name	user name to attempt mount as on the remote server.  The
74  		server may override or ignore this value.  Certain user
75		names may require authentication.
76
77  aname=name	aname specifies the file tree to access when the server is
78  		offering several exported file systems.
79
80  cache=mode	specifies a caching policy.  By default, no caches are used.
81		The mode can be specified as a bitmask or by using one of the
82		preexisting common 'shortcuts'.
83		The bitmask is described below: (unspecified bits are reserved)
84
85			==========  ====================================================
86			0b00000000  all caches disabled, mmap disabled
87			0b00000001  file caches enabled
88			0b00000010  meta-data caches enabled
89			0b00000100  writeback behavior (as opposed to writethrough)
90			0b00001000  loose caches (no explicit consistency with server)
91			0b10000000  fscache enabled for persistent caching
92			==========  ====================================================
93
94		The current shortcuts and their associated bitmask are:
95
96			=========   ====================================================
97			none        0b00000000 (no caching)
98			readahead   0b00000001 (only read-ahead file caching)
99			mmap        0b00000101 (read-ahead + writeback file cache)
100			loose       0b00001111 (non-coherent file and meta-data caches)
101			fscache     0b10001111 (persistent loose cache)
102			=========   ====================================================
103
104		NOTE: only these shortcuts are tested modes of operation at the
105		moment, so using other combinations of bit-patterns is not
106		known to work.  Work on better cache support is in progress.
107
108		IMPORTANT: loose caches (and by extension at the moment fscache)
109		do not necessarily validate cached values on the server.  In other
110		words changes on the server are not guaranteed to be reflected
111		on the client system.  Only use this mode of operation if you
112		have an exclusive mount and the server will modify the filesystem
113		underneath you.
114
115  debug=n	specifies debug level.  The debug level is a bitmask.
116
117			=====   ================================
118			0x01    display verbose error messages
119			0x02    developer debug (DEBUG_CURRENT)
120			0x04    display 9p trace
121			0x08    display VFS trace
122			0x10    display Marshalling debug
123			0x20    display RPC debug
124			0x40    display transport debug
125			0x80    display allocation debug
126			0x100   display protocol message debug
127			0x200   display Fid debug
128			0x400   display packet debug
129			0x800   display fscache tracing debug
130			=====   ================================
131
132  rfdno=n	the file descriptor for reading with trans=fd
133
134  wfdno=n	the file descriptor for writing with trans=fd
135
136  msize=n	the number of bytes to use for 9p packet payload
137
138  port=n	port to connect to on the remote server
139
140  noextend	force legacy mode (no 9p2000.u or 9p2000.L semantics)
141
142  version=name	Select 9P protocol version. Valid options are:
143
144			========        ==============================
145			9p2000          Legacy mode (same as noextend)
146			9p2000.u        Use 9P2000.u protocol
147			9p2000.L        Use 9P2000.L protocol
148			========        ==============================
149
150  dfltuid	attempt to mount as a particular uid
151
152  dfltgid	attempt to mount with a particular gid
153
154  afid		security channel - used by Plan 9 authentication protocols
155
156  nodevmap	do not map special files - represent them as normal files.
157  		This can be used to share devices/named pipes/sockets between
158		hosts.  This functionality will be expanded in later versions.
159
160  directio	bypass page cache on all read/write operations
161
162  ignoreqv	ignore qid.version==0 as a marker to ignore cache
163
164  noxattr	do not offer xattr functions on this mount.
165
166  access	there are four access modes.
167			user
168				if a user tries to access a file on v9fs
169			        filesystem for the first time, v9fs sends an
170			        attach command (Tattach) for that user.
171				This is the default mode.
172			<uid>
173				allows only user with uid=<uid> to access
174				the files on the mounted filesystem
175			any
176				v9fs does single attach and performs all
177				operations as one user
178			clien
179				 ACL based access check on the 9p client
180			         side for access validation
181
182  cachetag	cache tag to use the specified persistent cache.
183		cache tags for existing cache sessions can be listed at
184		/sys/fs/9p/caches. (applies only to cache=fscache)
185  ============= ===============================================================
186
187Behavior
188========
189
190This section aims at describing 9p 'quirks' that can be different
191from a local filesystem behaviors.
192
193 - Setting O_NONBLOCK on a file will make client reads return as early
194   as the server returns some data instead of trying to fill the read
195   buffer with the requested amount of bytes or end of file is reached.
196
197Resources
198=========
199
200Protocol specifications are maintained on github:
201http://ericvh.github.com/9p-rfc/
202
2039p client and server implementations are listed on
204http://9p.cat-v.org/implementations
205
206A 9p2000.L server is being developed by LLNL and can be found
207at http://code.google.com/p/diod/
208
209There are user and developer mailing lists available through the v9fs project
210on sourceforge (http://sourceforge.net/projects/v9fs).
211
212News and other information is maintained on a Wiki.
213(http://sf.net/apps/mediawiki/v9fs/index.php).
214
215Bug reports are best issued via the mailing list.
216
217For more information on the Plan 9 Operating System check out
218http://plan9.bell-labs.com/plan9
219
220For information on Plan 9 from User Space (Plan 9 applications and libraries
221ported to Linux/BSD/OSX/etc) check out https://9fans.github.io/plan9port/
222