.. SPDX-License-Identifier: GPL-2.0
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=======================================
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v9fs: Plan 9 Resource Sharing for Linux
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=======================================
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About
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=====
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v9fs is a Unix implementation of the Plan 9 9p remote filesystem protocol.
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This software was originally developed by Ron Minnich <rminnich@sandia.gov>
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and Maya Gokhale. Additional development by Greg Watson
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<gwatson@lanl.gov> and most recently Eric Van Hensbergen
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<ericvh@gmail.com>, Latchesar Ionkov <lucho@ionkov.net> and Russ Cox
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<rsc@swtch.com>.
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The best detailed explanation of the Linux implementation and applications of
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the 9p client is available in the form of a USENIX paper:
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https://www.usenix.org/events/usenix05/tech/freenix/hensbergen.html
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Other applications are described in the following papers:
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* XCPU & Clustering
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http://xcpu.org/papers/xcpu-talk.pdf
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* KVMFS: control file system for KVM
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http://xcpu.org/papers/kvmfs.pdf
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* CellFS: A New Programming Model for the Cell BE
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http://xcpu.org/papers/cellfs-talk.pdf
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* PROSE I/O: Using 9p to enable Application Partitions
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http://plan9.escet.urjc.es/iwp9/cready/PROSE_iwp9_2006.pdf
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* VirtFS: A Virtualization Aware File System pass-through
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http://goo.gl/3WPDg
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Usage
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=====
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For remote file server::
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mount -t 9p 10.10.1.2 /mnt/9
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For Plan 9 From User Space applications (http://swtch.com/plan9)::
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mount -t 9p `namespace`/acme /mnt/9 -o trans=unix,uname=$USER
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For server running on QEMU host with virtio transport::
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mount -t 9p -o trans=virtio <mount_tag> /mnt/9
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where mount_tag is the tag associated by the server to each of the exported
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mount points. Each 9P export is seen by the client as a virtio device with an
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associated "mount_tag" property. Available mount tags can be
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seen by reading /sys/bus/virtio/drivers/9pnet_virtio/virtio<n>/mount_tag files.
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Options
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=======
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============= ===============================================================
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trans=name select an alternative transport. Valid options are
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currently:
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======== ============================================
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unix specifying a named pipe mount point
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tcp specifying a normal TCP/IP connection
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fd used passed file descriptors for connection
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(see rfdno and wfdno)
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virtio connect to the next virtio channel available
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(from QEMU with trans_virtio module)
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rdma connect to a specified RDMA channel
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======== ============================================
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uname=name user name to attempt mount as on the remote server. The
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server may override or ignore this value. Certain user
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names may require authentication.
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aname=name aname specifies the file tree to access when the server is
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offering several exported file systems.
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cache=mode specifies a caching policy. By default, no caches are used.
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none
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default no cache policy, metadata and data
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alike are synchronous.
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loose
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no attempts are made at consistency,
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intended for exclusive, read-only mounts
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fscache
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use FS-Cache for a persistent, read-only
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cache backend.
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mmap
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minimal cache that is only used for read-write
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mmap. Northing else is cached, like cache=none
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debug=n specifies debug level. The debug level is a bitmask.
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===== ================================
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0x01 display verbose error messages
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0x02 developer debug (DEBUG_CURRENT)
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0x04 display 9p trace
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0x08 display VFS trace
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0x10 display Marshalling debug
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0x20 display RPC debug
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0x40 display transport debug
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0x80 display allocation debug
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0x100 display protocol message debug
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0x200 display Fid debug
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0x400 display packet debug
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0x800 display fscache tracing debug
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===== ================================
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rfdno=n the file descriptor for reading with trans=fd
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wfdno=n the file descriptor for writing with trans=fd
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msize=n the number of bytes to use for 9p packet payload
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port=n port to connect to on the remote server
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noextend force legacy mode (no 9p2000.u or 9p2000.L semantics)
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version=name Select 9P protocol version. Valid options are:
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======== ==============================
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9p2000 Legacy mode (same as noextend)
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9p2000.u Use 9P2000.u protocol
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9p2000.L Use 9P2000.L protocol
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======== ==============================
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dfltuid attempt to mount as a particular uid
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dfltgid attempt to mount with a particular gid
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afid security channel - used by Plan 9 authentication protocols
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nodevmap do not map special files - represent them as normal files.
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This can be used to share devices/named pipes/sockets between
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hosts. This functionality will be expanded in later versions.
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access there are four access modes.
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user
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if a user tries to access a file on v9fs
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filesystem for the first time, v9fs sends an
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attach command (Tattach) for that user.
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This is the default mode.
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<uid>
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allows only user with uid=<uid> to access
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the files on the mounted filesystem
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any
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v9fs does single attach and performs all
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operations as one user
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clien
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ACL based access check on the 9p client
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side for access validation
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cachetag cache tag to use the specified persistent cache.
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cache tags for existing cache sessions can be listed at
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/sys/fs/9p/caches. (applies only to cache=fscache)
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============= ===============================================================
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Behavior
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========
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This section aims at describing 9p 'quirks' that can be different
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from a local filesystem behaviors.
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- Setting O_NONBLOCK on a file will make client reads return as early
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as the server returns some data instead of trying to fill the read
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buffer with the requested amount of bytes or end of file is reached.
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Resources
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=========
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Protocol specifications are maintained on github:
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http://ericvh.github.com/9p-rfc/
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9p client and server implementations are listed on
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http://9p.cat-v.org/implementations
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A 9p2000.L server is being developed by LLNL and can be found
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at http://code.google.com/p/diod/
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There are user and developer mailing lists available through the v9fs project
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on sourceforge (http://sourceforge.net/projects/v9fs).
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News and other information is maintained on a Wiki.
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(http://sf.net/apps/mediawiki/v9fs/index.php).
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Bug reports are best issued via the mailing list.
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For more information on the Plan 9 Operating System check out
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http://plan9.bell-labs.com/plan9
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For information on Plan 9 from User Space (Plan 9 applications and libraries
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ported to Linux/BSD/OSX/etc) check out https://9fans.github.io/plan9port/
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