| .. 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 |
| https://kernel.org/doc/ols/2010/ols2010-pages-109-120.pdf |
| |
| Usage |
| ===== |
| |
| For remote file server:: |
| |
| mount -t 9p 10.10.1.2 /mnt/9 |
| |
| For Plan 9 From User Space applications (https://9fans.github.io/plan9port/):: |
| |
| 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 generated 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. |
| |
| USBG Usage |
| ========== |
| |
| To mount a 9p FS on a USB Host accessible via the gadget at runtime:: |
| |
| mount -t 9p -o trans=usbg,aname=/path/to/fs <device> /mnt/9 |
| |
| To mount a 9p FS on a USB Host accessible via the gadget as root filesystem:: |
| |
| root=<device> rootfstype=9p rootflags=trans=usbg,cache=loose,uname=root,access=0,dfltuid=0,dfltgid=0,aname=/path/to/rootfs |
| |
| where <device> is the tag associated by the usb gadget transport. |
| It is defined by the configfs instance name. |
| |
| USBG Example |
| ============ |
| |
| The USB host exports a filesystem, while the gadget on the USB device |
| side makes it mountable. |
| |
| Diod (9pfs server) and the forwarder are on the development host, where |
| the root filesystem is actually stored. The gadget is initialized during |
| boot (or later) on the embedded board. Then the forwarder will find it |
| on the USB bus and start forwarding requests. |
| |
| In this case the 9p requests come from the device and are handled by the |
| host. The reason is that USB device ports are normally not available on |
| PCs, so a connection in the other direction would not work. |
| |
| When using the usbg transport, for now there is no native usb host |
| service capable to handle the requests from the gadget driver. For |
| this we have to use the extra python tool p9_fwd.py from tools/usb. |
| |
| Just start the 9pfs capable network server like diod/nfs-ganesha e.g.:: |
| |
| $ diod -f -n -d 0 -S -l 0.0.0.0:9999 -e $PWD |
| |
| Optionally scan your bus if there are more then one usbg gadgets to find their path:: |
| |
| $ python $kernel_dir/tools/usb/p9_fwd.py list |
| |
| Bus | Addr | Manufacturer | Product | ID | Path |
| --- | ---- | ---------------- | ---------------- | --------- | ---- |
| 2 | 67 | unknown | unknown | 1d6b:0109 | 2-1.1.2 |
| 2 | 68 | unknown | unknown | 1d6b:0109 | 2-1.1.3 |
| |
| Then start the python transport:: |
| |
| $ python $kernel_dir/tools/usb/p9_fwd.py --path 2-1.1.2 connect -p 9999 |
| |
| After that the gadget driver can be used as described above. |
| |
| One use-case is to use it as an alternative to NFS root booting during |
| the development of embedded Linux devices. |
| |
| 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 |
| usbg connect to a specified usb gadget 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. |
| The mode can be specified as a bitmask or by using one of the |
| preexisting 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 the |
| moment, so using other combinations of bit-patterns is not |
| known 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 other |
| words changes on the server are not guaranteed to be reflected |
| on the client system. Only use this mode of operation if you |
| have an exclusive mount and the server will not modify the |
| filesystem underneath 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 between |
| hosts. 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 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/ |
