docs/tools/virtiofsd.rst

   1 QEMU virtio-fs shared file system daemon
   2 ========================================
   3
   4 Synopsis
   5 --------
   6
   7 **virtiofsd** [*OPTIONS*]
   8
   9 Description
  10 -----------
  11
  12 Share a host directory tree with a guest through a virtio-fs device.  This
  13 program is a vhost-user backend that implements the virtio-fs device.  Each
  14 virtio-fs device instance requires its own virtiofsd process.
  15
  16 This program is designed to work with QEMU's ``--device vhost-user-fs-pci``
  17 but should work with any virtual machine monitor (VMM) that supports
  18 vhost-user.  See the Examples section below.
  19
  20 This program must be run as the root user.  Upon startup the program will
  21 switch into a new file system namespace with the shared directory tree as its
  22 root.  This prevents "file system escapes" due to symlinks and other file
  23 system objects that might lead to files outside the shared directory.  The
  24 program also sandboxes itself using seccomp(2) to prevent ptrace(2) and other
  25 vectors that could allow an attacker to compromise the system after gaining
  26 control of the virtiofsd process.
  27
  28 Options
  29 -------
  30
  31 .. program:: virtiofsd
  32
  33 .. option:: -h, --help
  34
  35   Print help.
  36
  37 .. option:: -V, --version
  38
  39   Print version.
  40
  41 .. option:: -d
  42
  43   Enable debug output.
  44
  45 .. option:: --syslog
  46
  47   Print log messages to syslog instead of stderr.
  48
  49 .. option:: -o OPTION
  50
  51   * debug -
  52     Enable debug output.
  53
  54   * flock|no_flock -
  55     Enable/disable flock.  The default is ``no_flock``.
  56
  57   * modcaps=CAPLIST
  58     Modify the list of capabilities allowed; CAPLIST is a colon separated
  59     list of capabilities, each preceded by either + or -, e.g.
  60     ''+sys_admin:-chown''.
  61
  62   * log_level=LEVEL -
  63     Print only log messages matching LEVEL or more severe.  LEVEL is one of
  64     ``err``, ``warn``, ``info``, or ``debug``.  The default is ``info``.
  65
  66   * norace -
  67     Disable racy fallback.  The default is false.
  68
  69   * posix_lock|no_posix_lock -
  70     Enable/disable remote POSIX locks.  The default is ``no_posix_lock``.
  71
  72   * readdirplus|no_readdirplus -
  73     Enable/disable readdirplus.  The default is ``readdirplus``.
  74
  75   * source=PATH -
  76     Share host directory tree located at PATH.  This option is required.
  77
  78   * timeout=TIMEOUT -
  79     I/O timeout in seconds.  The default depends on cache= option.
  80
  81   * writeback|no_writeback -
  82     Enable/disable writeback cache. The cache alows the FUSE client to buffer
  83     and merge write requests.  The default is ``no_writeback``.
  84
  85   * xattr|no_xattr -
  86     Enable/disable extended attributes (xattr) on files and directories.  The
  87     default is ``no_xattr``.
  88
  89 .. option:: --socket-path=PATH
  90
  91   Listen on vhost-user UNIX domain socket at PATH.
  92
  93 .. option:: --fd=FDNUM
  94
  95   Accept connections from vhost-user UNIX domain socket file descriptor FDNUM.
  96   The file descriptor must already be listening for connections.
  97
  98 .. option:: --thread-pool-size=NUM
  99
 100   Restrict the number of worker threads per request queue to NUM.  The default
 101   is 64.
 102
 103 .. option:: --cache=none|auto|always
 104
 105   Select the desired trade-off between coherency and performance.  ``none``
 106   forbids the FUSE client from caching to achieve best coherency at the cost of
 107   performance.  ``auto`` acts similar to NFS with a 1 second metadata cache
 108   timeout.  ``always`` sets a long cache lifetime at the expense of coherency.
 109
 110 Examples
 111 --------
 112
 113 Export ``/var/lib/fs/vm001/`` on vhost-user UNIX domain socket
 114 ``/var/run/vm001-vhost-fs.sock``:
 115
 116 ::
 117
 118   host# virtiofsd --socket-path=/var/run/vm001-vhost-fs.sock -o source=/var/lib/fs/vm001
 119   host# qemu-system-x86_64 \
 120       -chardev socket,id=char0,path=/var/run/vm001-vhost-fs.sock \
 121       -device vhost-user-fs-pci,chardev=char0,tag=myfs \
 122       -object memory-backend-memfd,id=mem,size=4G,share=on \
 123       -numa node,memdev=mem \
 124       ...
 125   guest# mount -t virtiofs myfs /mnt