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 https://kernel.org/doc/ols/2010/ols2010-pages-109-120.pdf 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 generated 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 56USBG Usage 57========== 58 59To mount a 9p FS on a USB Host accessible via the gadget at runtime:: 60 61 mount -t 9p -o trans=usbg,aname=/path/to/fs <device> /mnt/9 62 63To mount a 9p FS on a USB Host accessible via the gadget as root filesystem:: 64 65 root=<device> rootfstype=9p rootflags=trans=usbg,cache=loose,uname=root,access=0,dfltuid=0,dfltgid=0,aname=/path/to/rootfs 66 67where <device> is the tag associated by the usb gadget transport. 68It is defined by the configfs instance name. 69 70USBG Example 71============ 72 73The USB host exports a filesystem, while the gadget on the USB device 74side makes it mountable. 75 76Diod (9pfs server) and the forwarder are on the development host, where 77the root filesystem is actually stored. The gadget is initialized during 78boot (or later) on the embedded board. Then the forwarder will find it 79on the USB bus and start forwarding requests. 80 81In this case the 9p requests come from the device and are handled by the 82host. The reason is that USB device ports are normally not available on 83PCs, so a connection in the other direction would not work. 84 85When using the usbg transport, for now there is no native usb host 86service capable to handle the requests from the gadget driver. For 87this we have to use the extra python tool p9_fwd.py from tools/usb. 88 89Just start the 9pfs capable network server like diod/nfs-ganesha e.g.:: 90 91 $ diod -f -n -d 0 -S -l 0.0.0.0:9999 -e $PWD 92 93Optionaly scan your bus if there are more then one usbg gadgets to find their path:: 94 95 $ python $kernel_dir/tools/usb/p9_fwd.py list 96 97 Bus | Addr | Manufacturer | Product | ID | Path 98 --- | ---- | ---------------- | ---------------- | --------- | ---- 99 2 | 67 | unknown | unknown | 1d6b:0109 | 2-1.1.2 100 2 | 68 | unknown | unknown | 1d6b:0109 | 2-1.1.3 101 102Then start the python transport:: 103 104 $ python $kernel_dir/tools/usb/p9_fwd.py --path 2-1.1.2 connect -p 9999 105 106After that the gadget driver can be used as described above. 107 108One use-case is to use it as an alternative to NFS root booting during 109the development of embedded Linux devices. 110 111Options 112======= 113 114 ============= =============================================================== 115 trans=name select an alternative transport. Valid options are 116 currently: 117 118 ======== ============================================ 119 unix specifying a named pipe mount point 120 tcp specifying a normal TCP/IP connection 121 fd used passed file descriptors for connection 122 (see rfdno and wfdno) 123 virtio connect to the next virtio channel available 124 (from QEMU with trans_virtio module) 125 rdma connect to a specified RDMA channel 126 usbg connect to a specified usb gadget channel 127 ======== ============================================ 128 129 uname=name user name to attempt mount as on the remote server. The 130 server may override or ignore this value. Certain user 131 names may require authentication. 132 133 aname=name aname specifies the file tree to access when the server is 134 offering several exported file systems. 135 136 cache=mode specifies a caching policy. By default, no caches are used. 137 The mode can be specified as a bitmask or by using one of the 138 preexisting common 'shortcuts'. 139 The bitmask is described below: (unspecified bits are reserved) 140 141 ========== ==================================================== 142 0b00000000 all caches disabled, mmap disabled 143 0b00000001 file caches enabled 144 0b00000010 meta-data caches enabled 145 0b00000100 writeback behavior (as opposed to writethrough) 146 0b00001000 loose caches (no explicit consistency with server) 147 0b10000000 fscache enabled for persistent caching 148 ========== ==================================================== 149 150 The current shortcuts and their associated bitmask are: 151 152 ========= ==================================================== 153 none 0b00000000 (no caching) 154 readahead 0b00000001 (only read-ahead file caching) 155 mmap 0b00000101 (read-ahead + writeback file cache) 156 loose 0b00001111 (non-coherent file and meta-data caches) 157 fscache 0b10001111 (persistent loose cache) 158 ========= ==================================================== 159 160 NOTE: only these shortcuts are tested modes of operation at the 161 moment, so using other combinations of bit-patterns is not 162 known to work. Work on better cache support is in progress. 163 164 IMPORTANT: loose caches (and by extension at the moment fscache) 165 do not necessarily validate cached values on the server. In other 166 words changes on the server are not guaranteed to be reflected 167 on the client system. Only use this mode of operation if you 168 have an exclusive mount and the server will modify the filesystem 169 underneath you. 170 171 debug=n specifies debug level. The debug level is a bitmask. 172 173 ===== ================================ 174 0x01 display verbose error messages 175 0x02 developer debug (DEBUG_CURRENT) 176 0x04 display 9p trace 177 0x08 display VFS trace 178 0x10 display Marshalling debug 179 0x20 display RPC debug 180 0x40 display transport debug 181 0x80 display allocation debug 182 0x100 display protocol message debug 183 0x200 display Fid debug 184 0x400 display packet debug 185 0x800 display fscache tracing debug 186 ===== ================================ 187 188 rfdno=n the file descriptor for reading with trans=fd 189 190 wfdno=n the file descriptor for writing with trans=fd 191 192 msize=n the number of bytes to use for 9p packet payload 193 194 port=n port to connect to on the remote server 195 196 noextend force legacy mode (no 9p2000.u or 9p2000.L semantics) 197 198 version=name Select 9P protocol version. Valid options are: 199 200 ======== ============================== 201 9p2000 Legacy mode (same as noextend) 202 9p2000.u Use 9P2000.u protocol 203 9p2000.L Use 9P2000.L protocol 204 ======== ============================== 205 206 dfltuid attempt to mount as a particular uid 207 208 dfltgid attempt to mount with a particular gid 209 210 afid security channel - used by Plan 9 authentication protocols 211 212 nodevmap do not map special files - represent them as normal files. 213 This can be used to share devices/named pipes/sockets between 214 hosts. This functionality will be expanded in later versions. 215 216 directio bypass page cache on all read/write operations 217 218 ignoreqv ignore qid.version==0 as a marker to ignore cache 219 220 noxattr do not offer xattr functions on this mount. 221 222 access there are four access modes. 223 user 224 if a user tries to access a file on v9fs 225 filesystem for the first time, v9fs sends an 226 attach command (Tattach) for that user. 227 This is the default mode. 228 <uid> 229 allows only user with uid=<uid> to access 230 the files on the mounted filesystem 231 any 232 v9fs does single attach and performs all 233 operations as one user 234 clien 235 ACL based access check on the 9p client 236 side for access validation 237 238 cachetag cache tag to use the specified persistent cache. 239 cache tags for existing cache sessions can be listed at 240 /sys/fs/9p/caches. (applies only to cache=fscache) 241 ============= =============================================================== 242 243Behavior 244======== 245 246This section aims at describing 9p 'quirks' that can be different 247from a local filesystem behaviors. 248 249 - Setting O_NONBLOCK on a file will make client reads return as early 250 as the server returns some data instead of trying to fill the read 251 buffer with the requested amount of bytes or end of file is reached. 252 253Resources 254========= 255 256Protocol specifications are maintained on github: 257http://ericvh.github.com/9p-rfc/ 258 2599p client and server implementations are listed on 260http://9p.cat-v.org/implementations 261 262A 9p2000.L server is being developed by LLNL and can be found 263at http://code.google.com/p/diod/ 264 265There are user and developer mailing lists available through the v9fs project 266on sourceforge (http://sourceforge.net/projects/v9fs). 267 268News and other information is maintained on a Wiki. 269(http://sf.net/apps/mediawiki/v9fs/index.php). 270 271Bug reports are best issued via the mailing list. 272 273For more information on the Plan 9 Operating System check out 274http://plan9.bell-labs.com/plan9 275 276For information on Plan 9 from User Space (Plan 9 applications and libraries 277ported to Linux/BSD/OSX/etc) check out https://9fans.github.io/plan9port/ 278