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 * KVMFS: control file system for KVM 27 * CellFS: A New Programming Model for the Cell BE 28 * PROSE I/O: Using 9p to enable Application Partitions 29 http://web.archive.org/web/20110101152020/http://plan9.escet.urjc.es/iwp9/cready/PROSE_iwp9_2006.pdf 30 * VirtFS: A Virtualization Aware File System pass-through 31 https://kernel.org/doc/ols/2010/ols2010-pages-109-120.pdf 32 33Usage 34===== 35 36For remote file server:: 37 38 mount -t 9p 10.10.1.2 /mnt/9 39 40For Plan 9 From User Space applications (https://9fans.github.io/plan9port/):: 41 42 mount -t 9p `namespace`/acme /mnt/9 -o trans=unix,uname=$USER 43 44For server running on QEMU host with virtio transport:: 45 46 mount -t 9p -o trans=virtio <mount_tag> /mnt/9 47 48where mount_tag is the tag generated by the server to each of the exported 49mount points. Each 9P export is seen by the client as a virtio device with an 50associated "mount_tag" property. Available mount tags can be 51seen by reading /sys/bus/virtio/drivers/9pnet_virtio/virtio<n>/mount_tag files. 52 53USBG Usage 54========== 55 56To mount a 9p FS on a USB Host accessible via the gadget at runtime:: 57 58 mount -t 9p -o trans=usbg,aname=/path/to/fs <device> /mnt/9 59 60To mount a 9p FS on a USB Host accessible via the gadget as root filesystem:: 61 62 root=<device> rootfstype=9p rootflags=trans=usbg,cache=loose,uname=root,access=0,dfltuid=0,dfltgid=0,aname=/path/to/rootfs 63 64where <device> is the tag associated by the usb gadget transport. 65It is defined by the configfs instance name. 66 67USBG Example 68============ 69 70The USB host exports a filesystem, while the gadget on the USB device 71side makes it mountable. 72 73Diod (9pfs server) and the forwarder are on the development host, where 74the root filesystem is actually stored. The gadget is initialized during 75boot (or later) on the embedded board. Then the forwarder will find it 76on the USB bus and start forwarding requests. 77 78In this case the 9p requests come from the device and are handled by the 79host. The reason is that USB device ports are normally not available on 80PCs, so a connection in the other direction would not work. 81 82When using the usbg transport, for now there is no native usb host 83service capable to handle the requests from the gadget driver. For 84this we have to use the extra python tool p9_fwd.py from tools/usb. 85 86Just start the 9pfs capable network server like diod/nfs-ganesha e.g.:: 87 88 $ diod -f -n -d 0 -S -l 0.0.0.0:9999 -e $PWD 89 90Optionally scan your bus if there are more then one usbg gadgets to find their path:: 91 92 $ python $kernel_dir/tools/usb/p9_fwd.py list 93 94 Bus | Addr | Manufacturer | Product | ID | Path 95 --- | ---- | ---------------- | ---------------- | --------- | ---- 96 2 | 67 | unknown | unknown | 1d6b:0109 | 2-1.1.2 97 2 | 68 | unknown | unknown | 1d6b:0109 | 2-1.1.3 98 99Then start the python transport:: 100 101 $ python $kernel_dir/tools/usb/p9_fwd.py --path 2-1.1.2 connect -p 9999 102 103After that the gadget driver can be used as described above. 104 105One use-case is to use it as an alternative to NFS root booting during 106the development of embedded Linux devices. 107 108Options 109======= 110 111 ============= =============================================================== 112 trans=name select an alternative transport. Valid options are 113 currently: 114 115 ======== ============================================ 116 unix specifying a named pipe mount point 117 tcp specifying a normal TCP/IP connection 118 fd used passed file descriptors for connection 119 (see rfdno and wfdno) 120 virtio connect to the next virtio channel available 121 (from QEMU with trans_virtio module) 122 rdma connect to a specified RDMA channel 123 usbg connect to a specified usb gadget channel 124 ======== ============================================ 125 126 uname=name user name to attempt mount as on the remote server. The 127 server may override or ignore this value. Certain user 128 names may require authentication. 129 130 aname=name aname specifies the file tree to access when the server is 131 offering several exported file systems. 132 133 cache=mode specifies a caching policy. By default, no caches are used. 134 The mode can be specified as a bitmask or by using one of the 135 preexisting common 'shortcuts'. 136 The bitmask is described below: (unspecified bits are reserved) 137 138 ========== ==================================================== 139 0b00000000 all caches disabled, mmap disabled 140 0b00000001 file caches enabled 141 0b00000010 meta-data caches enabled 142 0b00000100 writeback behavior (as opposed to writethrough) 143 0b00001000 loose caches (no explicit consistency with server) 144 0b10000000 fscache enabled for persistent caching 145 ========== ==================================================== 146 147 The current shortcuts and their associated bitmask are: 148 149 ========= ==================================================== 150 none 0b00000000 (no caching) 151 readahead 0b00000001 (only read-ahead file caching) 152 mmap 0b00000101 (read-ahead + writeback file cache) 153 loose 0b00001111 (non-coherent file and meta-data caches) 154 fscache 0b10001111 (persistent loose cache) 155 ========= ==================================================== 156 157 NOTE: only these shortcuts are tested modes of operation at the 158 moment, so using other combinations of bit-patterns is not 159 known to work. Work on better cache support is in progress. 160 161 IMPORTANT: loose caches (and by extension at the moment fscache) 162 do not necessarily validate cached values on the server. In other 163 words changes on the server are not guaranteed to be reflected 164 on the client system. Only use this mode of operation if you 165 have an exclusive mount and the server will not modify the 166 filesystem underneath you. 167 168 debug=n specifies debug level. The debug level is a bitmask. 169 170 ===== ================================ 171 0x01 display verbose error messages 172 0x02 developer debug (DEBUG_CURRENT) 173 0x04 display 9p trace 174 0x08 display VFS trace 175 0x10 display Marshalling debug 176 0x20 display RPC debug 177 0x40 display transport debug 178 0x80 display allocation debug 179 0x100 display protocol message debug 180 0x200 display Fid debug 181 0x400 display packet debug 182 0x800 display fscache tracing debug 183 ===== ================================ 184 185 rfdno=n the file descriptor for reading with trans=fd 186 187 wfdno=n the file descriptor for writing with trans=fd 188 189 msize=n the number of bytes to use for 9p packet payload 190 191 port=n port to connect to on the remote server 192 193 noextend force legacy mode (no 9p2000.u or 9p2000.L semantics) 194 195 version=name Select 9P protocol version. Valid options are: 196 197 ======== ============================== 198 9p2000 Legacy mode (same as noextend) 199 9p2000.u Use 9P2000.u protocol 200 9p2000.L Use 9P2000.L protocol 201 ======== ============================== 202 203 dfltuid attempt to mount as a particular uid 204 205 dfltgid attempt to mount with a particular gid 206 207 afid security channel - used by Plan 9 authentication protocols 208 209 nodevmap do not map special files - represent them as normal files. 210 This can be used to share devices/named pipes/sockets between 211 hosts. This functionality will be expanded in later versions. 212 213 directio bypass page cache on all read/write operations 214 215 ignoreqv ignore qid.version==0 as a marker to ignore cache 216 217 noxattr do not offer xattr functions on this mount. 218 219 access there are four access modes. 220 user 221 if a user tries to access a file on v9fs 222 filesystem for the first time, v9fs sends an 223 attach command (Tattach) for that user. 224 This is the default mode. 225 <uid> 226 allows only user with uid=<uid> to access 227 the files on the mounted filesystem 228 any 229 v9fs does single attach and performs all 230 operations as one user 231 clien 232 ACL based access check on the 9p client 233 side for access validation 234 235 cachetag cache tag to use the specified persistent cache. 236 cache tags for existing cache sessions can be listed at 237 /sys/fs/9p/caches. (applies only to cache=fscache) 238 239 negtimeout the duration (in milliseconds) that negative dentries (paths 240 that do not actually exist) are retained in the cache. If 241 set to a negative value, those entries are kept indefinitely 242 until evicted by the buffer cache management system 243 ============= =============================================================== 244 245Behavior 246======== 247 248This section aims at describing 9p 'quirks' that can be different 249from a local filesystem behaviors. 250 251 - Setting O_NONBLOCK on a file will make client reads return as early 252 as the server returns some data instead of trying to fill the read 253 buffer with the requested amount of bytes or end of file is reached. 254 255Resources 256========= 257 258Protocol specifications are maintained on github: 259http://ericvh.github.com/9p-rfc/ 260 2619p client and server implementations are listed on 262http://9p.cat-v.org/implementations 263 264A 9p2000.L server is being developed by LLNL and can be found 265at http://code.google.com/p/diod/ 266 267There are user and developer mailing lists available through the v9fs project 268on sourceforge (http://sourceforge.net/projects/v9fs). 269 270News and other information is maintained on a Wiki. 271(http://sf.net/apps/mediawiki/v9fs/index.php). 272 273Bug reports are best issued via the mailing list. 274 275For more information on the Plan 9 Operating System check out 276http://plan9.bell-labs.com/plan9 277 278For information on Plan 9 from User Space (Plan 9 applications and libraries 279ported to Linux/BSD/OSX/etc) check out https://9fans.github.io/plan9port/ 280