QEMU virtio-fs shared file system daemon¶
Synopsis¶
virtiofsd [OPTIONS]
Description¶
Share a host directory tree with a guest through a virtio-fs device. This program is a vhost-user backend that implements the virtio-fs device. Each virtio-fs device instance requires its own virtiofsd process.
This program is designed to work with QEMU’s --device vhost-user-fs-pci
but should work with any virtual machine monitor (VMM) that supports
vhost-user. See the Examples section below.
This program must be run as the root user. Upon startup the program will switch into a new file system namespace with the shared directory tree as its root. This prevents “file system escapes” due to symlinks and other file system objects that might lead to files outside the shared directory. The program also sandboxes itself using seccomp(2) to prevent ptrace(2) and other vectors that could allow an attacker to compromise the system after gaining control of the virtiofsd process.
Options¶
-
-h
,
--help
¶
Print help.
-
-V
,
--version
¶
Print version.
-
-d
¶
Enable debug output.
-
--syslog
¶
Print log messages to syslog instead of stderr.
-
-o
OPTION
¶ debug - Enable debug output.
flock|no_flock - Enable/disable flock. The default is
no_flock
.modcaps=CAPLIST Modify the list of capabilities allowed; CAPLIST is a colon separated list of capabilities, each preceded by either + or -, e.g. ‘’+sys_admin:-chown’’.
log_level=LEVEL - Print only log messages matching LEVEL or more severe. LEVEL is one of
err
,warn
,info
, ordebug
. The default isinfo
.norace - Disable racy fallback. The default is false.
posix_lock|no_posix_lock - Enable/disable remote POSIX locks. The default is
posix_lock
.readdirplus|no_readdirplus - Enable/disable readdirplus. The default is
readdirplus
.source=PATH - Share host directory tree located at PATH. This option is required.
timeout=TIMEOUT - I/O timeout in seconds. The default depends on cache= option.
writeback|no_writeback - Enable/disable writeback cache. The cache alows the FUSE client to buffer and merge write requests. The default is
no_writeback
.xattr|no_xattr - Enable/disable extended attributes (xattr) on files and directories. The default is
no_xattr
.
-
--socket-path
=PATH
¶ Listen on vhost-user UNIX domain socket at PATH.
-
--fd
=FDNUM
¶ Accept connections from vhost-user UNIX domain socket file descriptor FDNUM. The file descriptor must already be listening for connections.
-
--thread-pool-size
=NUM
¶ Restrict the number of worker threads per request queue to NUM. The default is 64.
-
--cache
=none|auto|always
¶ Select the desired trade-off between coherency and performance.
none
forbids the FUSE client from caching to achieve best coherency at the cost of performance.auto
acts similar to NFS with a 1 second metadata cache timeout.always
sets a long cache lifetime at the expense of coherency.
Examples¶
Export /var/lib/fs/vm001/
on vhost-user UNIX domain socket
/var/run/vm001-vhost-fs.sock
:
host# virtiofsd --socket-path=/var/run/vm001-vhost-fs.sock -o source=/var/lib/fs/vm001
host# qemu-system-x86_64 \
-chardev socket,id=char0,path=/var/run/vm001-vhost-fs.sock \
-device vhost-user-fs-pci,chardev=char0,tag=myfs \
-object memory-backend-memfd,id=mem,size=4G,share=on \
-numa node,memdev=mem \
...
guest# mount -t virtiofs myfs /mnt