1 QEMU virtio-fs shared file system daemon
2 ========================================
7 **virtiofsd** [*OPTIONS*]
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.
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.
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.
31 .. program:: virtiofsd
33 .. option:: -h, --help
37 .. option:: -V, --version
47 Print log messages to syslog instead of stderr.
55 Enable/disable flock. The default is ``no_flock``.
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''.
63 Print only log messages matching LEVEL or more severe. LEVEL is one of
64 ``err``, ``warn``, ``info``, or ``debug``. The default is ``info``.
67 Disable racy fallback. The default is false.
69 * posix_lock|no_posix_lock -
70 Enable/disable remote POSIX locks. The default is ``posix_lock``.
72 * readdirplus|no_readdirplus -
73 Enable/disable readdirplus. The default is ``readdirplus``.
76 Share host directory tree located at PATH. This option is required.
79 I/O timeout in seconds. The default depends on cache= option.
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``.
86 Enable/disable extended attributes (xattr) on files and directories. The
87 default is ``no_xattr``.
89 .. option:: --socket-path=PATH
91 Listen on vhost-user UNIX domain socket at PATH.
93 .. option:: --fd=FDNUM
95 Accept connections from vhost-user UNIX domain socket file descriptor FDNUM.
96 The file descriptor must already be listening for connections.
98 .. option:: --thread-pool-size=NUM
100 Restrict the number of worker threads per request queue to NUM. The default
103 .. option:: --cache=none|auto|always
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.
113 Export ``/var/lib/fs/vm001/`` on vhost-user UNIX domain socket
114 ``/var/run/vm001-vhost-fs.sock``:
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 \
125 guest# mount -t virtiofs myfs /mnt