1QEMU Storage Daemon 2=================== 3 4Synopsis 5-------- 6 7**qemu-storage-daemon** [options] 8 9Description 10----------- 11 12qemu-storage-daemon provides disk image functionality from QEMU, qemu-img, and 13qemu-nbd in a long-running process controlled via QMP commands without running 14a virtual machine. It can export disk images, run block job operations, and 15perform other disk-related operations. The daemon is controlled via a QMP 16monitor and initial configuration from the command-line. 17 18The daemon offers the following subset of QEMU features: 19 20* Block nodes 21* Block jobs 22* Block exports 23* Throttle groups 24* Character devices 25* Crypto and secrets 26* QMP 27* IOThreads 28 29Commands can be sent over a QEMU Monitor Protocol (QMP) connection. See the 30:manpage:`qemu-storage-daemon-qmp-ref(7)` manual page for a description of the 31commands. 32 33The daemon runs until it is stopped using the ``quit`` QMP command or 34SIGINT/SIGHUP/SIGTERM. 35 36**Warning:** Never modify images in use by a running virtual machine or any 37other process; this may destroy the image. Also, be aware that querying an 38image that is being modified by another process may encounter inconsistent 39state. 40 41Options 42------- 43 44.. program:: qemu-storage-daemon 45 46Standard options: 47 48.. option:: -h, --help 49 50 Display help and exit 51 52.. option:: -V, --version 53 54 Display version information and exit 55 56.. option:: -T, --trace [[enable=]PATTERN][,events=FILE][,file=FILE] 57 58 .. include:: ../qemu-option-trace.rst.inc 59 60.. option:: --blockdev BLOCKDEVDEF 61 62 is a block node definition. See the :manpage:`qemu(1)` manual page for a 63 description of block node properties and the :manpage:`qemu-block-drivers(7)` 64 manual page for a description of driver-specific parameters. 65 66.. option:: --chardev CHARDEVDEF 67 68 is a character device definition. See the :manpage:`qemu(1)` manual page for 69 a description of character device properties. A common character device 70 definition configures a UNIX domain socket:: 71 72 --chardev socket,id=char1,path=/var/run/qsd-qmp.sock,server=on,wait=off 73 74.. option:: --export [type=]nbd,id=<id>,node-name=<node-name>[,name=<export-name>][,writable=on|off][,bitmap=<name>] 75 --export [type=]vhost-user-blk,id=<id>,node-name=<node-name>,addr.type=unix,addr.path=<socket-path>[,writable=on|off][,logical-block-size=<block-size>][,num-queues=<num-queues>] 76 --export [type=]vhost-user-blk,id=<id>,node-name=<node-name>,addr.type=fd,addr.str=<fd>[,writable=on|off][,logical-block-size=<block-size>][,num-queues=<num-queues>] 77 --export [type=]fuse,id=<id>,node-name=<node-name>,mountpoint=<file>[,growable=on|off][,writable=on|off] 78 79 is a block export definition. ``node-name`` is the block node that should be 80 exported. ``writable`` determines whether or not the export allows write 81 requests for modifying data (the default is off). 82 83 The ``nbd`` export type requires ``--nbd-server`` (see below). ``name`` is 84 the NBD export name (if not specified, it defaults to the given 85 ``node-name``). ``bitmap`` is the name of a dirty bitmap reachable from the 86 block node, so the NBD client can use NBD_OPT_SET_META_CONTEXT with the 87 metadata context name "qemu:dirty-bitmap:BITMAP" to inspect the bitmap. 88 89 The ``vhost-user-blk`` export type takes a vhost-user socket address on which 90 it accept incoming connections. Both 91 ``addr.type=unix,addr.path=<socket-path>`` for UNIX domain sockets and 92 ``addr.type=fd,addr.str=<fd>`` for file descriptor passing are supported. 93 ``logical-block-size`` sets the logical block size in bytes (the default is 94 512). ``num-queues`` sets the number of virtqueues (the default is 1). 95 96 The ``fuse`` export type takes a mount point, which must be a regular file, 97 on which to export the given block node. That file will not be changed, it 98 will just appear to have the block node's content while the export is active 99 (very much like mounting a filesystem on a directory does not change what the 100 directory contains, it only shows a different content while the filesystem is 101 mounted). Consequently, applications that have opened the given file before 102 the export became active will continue to see its original content. If 103 ``growable`` is set, writes after the end of the exported file will grow the 104 block node to fit. 105 106.. option:: --monitor MONITORDEF 107 108 is a QMP monitor definition. See the :manpage:`qemu(1)` manual page for 109 a description of QMP monitor properties. A common QMP monitor definition 110 configures a monitor on character device ``char1``:: 111 112 --monitor chardev=char1 113 114.. option:: --nbd-server addr.type=inet,addr.host=<host>,addr.port=<port>[,tls-creds=<id>][,tls-authz=<id>][,max-connections=<n>] 115 --nbd-server addr.type=unix,addr.path=<path>[,tls-creds=<id>][,tls-authz=<id>][,max-connections=<n>] 116 --nbd-server addr.type=fd,addr.str=<fd>[,tls-creds=<id>][,tls-authz=<id>][,max-connections=<n>] 117 118 is a server for NBD exports. Both TCP and UNIX domain sockets are supported. 119 A listen socket can be provided via file descriptor passing (see Examples 120 below). TLS encryption can be configured using ``--object`` tls-creds-* and 121 authz-* secrets (see below). 122 123 To configure an NBD server on UNIX domain socket path 124 ``/var/run/qsd-nbd.sock``:: 125 126 --nbd-server addr.type=unix,addr.path=/var/run/qsd-nbd.sock 127 128.. option:: --object help 129 --object <type>,help 130 --object <type>[,<property>=<value>...] 131 132 is a QEMU user creatable object definition. List object types with ``help``. 133 List object properties with ``<type>,help``. See the :manpage:`qemu(1)` 134 manual page for a description of the object properties. 135 136.. option:: --pidfile PATH 137 138 is the path to a file where the daemon writes its pid. This allows scripts to 139 stop the daemon by sending a signal:: 140 141 $ kill -SIGTERM $(<path/to/qsd.pid) 142 143 A file lock is applied to the file so only one instance of the daemon can run 144 with a given pid file path. The daemon unlinks its pid file when terminating. 145 146 The pid file is written after chardevs, exports, and NBD servers have been 147 created but before accepting connections. The daemon has started successfully 148 when the pid file is written and clients may begin connecting. 149 150Examples 151-------- 152Launch the daemon with QMP monitor socket ``qmp.sock`` so clients can execute 153QMP commands:: 154 155 $ qemu-storage-daemon \ 156 --chardev socket,path=qmp.sock,server=on,wait=off,id=char1 \ 157 --monitor chardev=char1 158 159Launch the daemon from Python with a QMP monitor socket using file descriptor 160passing so there is no need to busy wait for the QMP monitor to become 161available:: 162 163 #!/usr/bin/env python3 164 import subprocess 165 import socket 166 167 sock_path = '/var/run/qmp.sock' 168 169 with socket.socket(socket.AF_UNIX, socket.SOCK_STREAM) as listen_sock: 170 listen_sock.bind(sock_path) 171 listen_sock.listen() 172 173 fd = listen_sock.fileno() 174 175 subprocess.Popen( 176 ['qemu-storage-daemon', 177 '--chardev', f'socket,fd={fd},server=on,id=char1', 178 '--monitor', 'chardev=char1'], 179 pass_fds=[fd], 180 ) 181 182 # listen_sock was automatically closed when leaving the 'with' statement 183 # body. If the daemon process terminated early then the following connect() 184 # will fail with "Connection refused" because no process has the listen 185 # socket open anymore. Launch errors can be detected this way. 186 187 qmp_sock = socket.socket(socket.AF_UNIX, socket.SOCK_STREAM) 188 qmp_sock.connect(sock_path) 189 ...QMP interaction... 190 191The same socket spawning approach also works with the ``--nbd-server 192addr.type=fd,addr.str=<fd>`` and ``--export 193type=vhost-user-blk,addr.type=fd,addr.str=<fd>`` options. 194 195Export raw image file ``disk.img`` over NBD UNIX domain socket ``nbd.sock``:: 196 197 $ qemu-storage-daemon \ 198 --blockdev driver=file,node-name=disk,filename=disk.img \ 199 --nbd-server addr.type=unix,addr.path=nbd.sock \ 200 --export type=nbd,id=export,node-name=disk,writable=on 201 202Export a qcow2 image file ``disk.qcow2`` as a vhosts-user-blk device over UNIX 203domain socket ``vhost-user-blk.sock``:: 204 205 $ qemu-storage-daemon \ 206 --blockdev driver=file,node-name=file,filename=disk.qcow2 \ 207 --blockdev driver=qcow2,node-name=qcow2,file=file \ 208 --export type=vhost-user-blk,id=export,addr.type=unix,addr.path=vhost-user-blk.sock,node-name=qcow2 209 210Export a qcow2 image file ``disk.qcow2`` via FUSE on itself, so the disk image 211file will then appear as a raw image:: 212 213 $ qemu-storage-daemon \ 214 --blockdev driver=file,node-name=file,filename=disk.qcow2 \ 215 --blockdev driver=qcow2,node-name=qcow2,file=file \ 216 --export type=fuse,id=export,node-name=qcow2,mountpoint=disk.qcow2,writable=on 217 218See also 219-------- 220 221:manpage:`qemu(1)`, :manpage:`qemu-block-drivers(7)`, :manpage:`qemu-storage-daemon-qmp-ref(7)` 222