QEMU virtio-fs shared file system daemon — QEMU 5.1.0 (v5.1.0-11824-g8699890d91-dirty) documentation

# 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`, or `debug`. The default is `info`.

  - 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