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|
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. The program drops privileges where
possible during startup although it must be able to create and access files
with any uid/gid:
* The ability to invoke syscalls is limited using seccomp(2).
* Linux capabilities(7) are dropped.
In "namespace" sandbox mode the program switches into a new file system
namespace and invokes pivot_root(2) to make the shared directory tree its root.
A new pid and net namespace is also created to isolate the process.
In "chroot" sandbox mode the program invokes chroot(2) to make the shared
directory tree its root. This mode is intended for container environments where
the container runtime has already set up the namespaces and the program does
not have permission to create namespaces itself.
Both sandbox modes prevent "file system escapes" due to symlinks and other file
system objects that might lead to files outside the shared directory.
Options
-------
.. program:: virtiofsd
.. option:: -h, --help
Print help.
.. option:: -V, --version
Print version.
.. option:: -d
Enable debug output.
.. option:: --syslog
Print log messages to syslog instead of stderr.
.. option:: -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``.
* posix_lock|no_posix_lock -
Enable/disable remote POSIX locks. The default is ``no_posix_lock``.
* readdirplus|no_readdirplus -
Enable/disable readdirplus. The default is ``readdirplus``.
* sandbox=namespace|chroot -
Sandbox mode:
- namespace: Create mount, pid, and net namespaces and pivot_root(2) into
the shared directory.
- chroot: chroot(2) into shared directory (use in containers).
The default is "namespace".
* 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 allows 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``.
.. option:: --socket-path=PATH
Listen on vhost-user UNIX domain socket at PATH.
.. option:: --socket-group=GROUP
Set the vhost-user UNIX domain socket gid to GROUP.
.. option:: --fd=FDNUM
Accept connections from vhost-user UNIX domain socket file descriptor FDNUM.
The file descriptor must already be listening for connections.
.. option:: --thread-pool-size=NUM
Restrict the number of worker threads per request queue to NUM. The default
is 64.
.. option:: --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.
The default is ``auto``.
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
|
