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