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 78 is a block export definition. ``node-name`` is the block node that should be 79 exported. ``writable`` determines whether or not the export allows write 80 requests for modifying data (the default is off). 81 82 The ``nbd`` export type requires ``--nbd-server`` (see below). ``name`` is 83 the NBD export name. ``bitmap`` is the name of a dirty bitmap reachable from 84 the block node, so the NBD client can use NBD_OPT_SET_META_CONTEXT with the 85 metadata context name "qemu:dirty-bitmap:BITMAP" to inspect the bitmap. 86 87 The ``vhost-user-blk`` export type takes a vhost-user socket address on which 88 it accept incoming connections. Both 89 ``addr.type=unix,addr.path=<socket-path>`` for UNIX domain sockets and 90 ``addr.type=fd,addr.str=<fd>`` for file descriptor passing are supported. 91 ``logical-block-size`` sets the logical block size in bytes (the default is 92 512). ``num-queues`` sets the number of virtqueues (the default is 1). 93 94.. option:: --monitor MONITORDEF 95 96 is a QMP monitor definition. See the :manpage:`qemu(1)` manual page for 97 a description of QMP monitor properties. A common QMP monitor definition 98 configures a monitor on character device ``char1``:: 99 100 --monitor chardev=char1 101 102.. option:: --nbd-server addr.type=inet,addr.host=<host>,addr.port=<port>[,tls-creds=<id>][,tls-authz=<id>][,max-connections=<n>] 103 --nbd-server addr.type=unix,addr.path=<path>[,tls-creds=<id>][,tls-authz=<id>][,max-connections=<n>] 104 --nbd-server addr.type=fd,addr.str=<fd>[,tls-creds=<id>][,tls-authz=<id>][,max-connections=<n>] 105 106 is a server for NBD exports. Both TCP and UNIX domain sockets are supported. 107 A listen socket can be provided via file descriptor passing (see Examples 108 below). TLS encryption can be configured using ``--object`` tls-creds-* and 109 authz-* secrets (see below). 110 111 To configure an NBD server on UNIX domain socket path 112 ``/var/run/qsd-nbd.sock``:: 113 114 --nbd-server addr.type=unix,addr.path=/var/run/qsd-nbd.sock 115 116.. option:: --object help 117 --object <type>,help 118 --object <type>[,<property>=<value>...] 119 120 is a QEMU user creatable object definition. List object types with ``help``. 121 List object properties with ``<type>,help``. See the :manpage:`qemu(1)` 122 manual page for a description of the object properties. 123 124.. option:: --pidfile PATH 125 126 is the path to a file where the daemon writes its pid. This allows scripts to 127 stop the daemon by sending a signal:: 128 129 $ kill -SIGTERM $(<path/to/qsd.pid) 130 131 A file lock is applied to the file so only one instance of the daemon can run 132 with a given pid file path. The daemon unlinks its pid file when terminating. 133 134 The pid file is written after chardevs, exports, and NBD servers have been 135 created but before accepting connections. The daemon has started successfully 136 when the pid file is written and clients may begin connecting. 137 138Examples 139-------- 140Launch the daemon with QMP monitor socket ``qmp.sock`` so clients can execute 141QMP commands:: 142 143 $ qemu-storage-daemon \ 144 --chardev socket,path=qmp.sock,server=on,wait=off,id=char1 \ 145 --monitor chardev=char1 146 147Launch the daemon from Python with a QMP monitor socket using file descriptor 148passing so there is no need to busy wait for the QMP monitor to become 149available:: 150 151 #!/usr/bin/env python3 152 import subprocess 153 import socket 154 155 sock_path = '/var/run/qmp.sock' 156 157 with socket.socket(socket.AF_UNIX, socket.SOCK_STREAM) as listen_sock: 158 listen_sock.bind(sock_path) 159 listen_sock.listen() 160 161 fd = listen_sock.fileno() 162 163 subprocess.Popen( 164 ['qemu-storage-daemon', 165 '--chardev', f'socket,fd={fd},server=on,id=char1', 166 '--monitor', 'chardev=char1'], 167 pass_fds=[fd], 168 ) 169 170 # listen_sock was automatically closed when leaving the 'with' statement 171 # body. If the daemon process terminated early then the following connect() 172 # will fail with "Connection refused" because no process has the listen 173 # socket open anymore. Launch errors can be detected this way. 174 175 qmp_sock = socket.socket(socket.AF_UNIX, socket.SOCK_STREAM) 176 qmp_sock.connect(sock_path) 177 ...QMP interaction... 178 179The same socket spawning approach also works with the ``--nbd-server 180addr.type=fd,addr.str=<fd>`` and ``--export 181type=vhost-user-blk,addr.type=fd,addr.str=<fd>`` options. 182 183Export raw image file ``disk.img`` over NBD UNIX domain socket ``nbd.sock``:: 184 185 $ qemu-storage-daemon \ 186 --blockdev driver=file,node-name=disk,filename=disk.img \ 187 --nbd-server addr.type=unix,addr.path=nbd.sock \ 188 --export type=nbd,id=export,node-name=disk,writable=on 189 190Export a qcow2 image file ``disk.qcow2`` as a vhosts-user-blk device over UNIX 191domain socket ``vhost-user-blk.sock``:: 192 193 $ qemu-storage-daemon \ 194 --blockdev driver=file,node-name=file,filename=disk.qcow2 \ 195 --blockdev driver=qcow2,node-name=qcow2,file=file \ 196 --export type=vhost-user-blk,id=export,addr.type=unix,addr.path=vhost-user-blk.sock,node-name=qcow2 197 198See also 199-------- 200 201:manpage:`qemu(1)`, :manpage:`qemu-block-drivers(7)`, :manpage:`qemu-storage-daemon-qmp-ref(7)` 202