1=================== 2QEMU Storage Daemon 3=================== 4 5Synopsis 6-------- 7 8**qemu-storage-daemon** [options] 9 10Description 11----------- 12 13``qemu-storage-daemon`` provides disk image functionality from QEMU, 14``qemu-img``, and ``qemu-nbd`` in a long-running process controlled via QMP 15commands without running a virtual machine. 16It can export disk images, run block job operations, and 17perform other disk-related operations. The daemon is controlled via a QMP 18monitor and initial configuration from the command-line. 19 20The daemon offers the following subset of QEMU features: 21 22* Block nodes 23* Block jobs 24* Block exports 25* Throttle groups 26* Character devices 27* Crypto and secrets 28* QMP 29* IOThreads 30 31Commands can be sent over a QEMU Monitor Protocol (QMP) connection. See the 32:manpage:`qemu-storage-daemon-qmp-ref(7)` manual page for a description of the 33commands. 34 35The daemon runs until it is stopped using the ``quit`` QMP command or 36SIGINT/SIGHUP/SIGTERM. 37 38**Warning:** Never modify images in use by a running virtual machine or any 39other process; this may destroy the image. Also, be aware that querying an 40image that is being modified by another process may encounter inconsistent 41state. 42 43Options 44------- 45 46.. program:: qemu-storage-daemon 47 48Standard options: 49 50.. option:: -h, --help 51 52 Display help and exit 53 54.. option:: -V, --version 55 56 Display version information and exit 57 58.. option:: -T, --trace [[enable=]PATTERN][,events=FILE][,file=FILE] 59 60 .. include:: ../qemu-option-trace.rst.inc 61 62.. option:: --blockdev BLOCKDEVDEF 63 64 is a block node definition. See the :manpage:`qemu(1)` manual page for a 65 description of block node properties and the :manpage:`qemu-block-drivers(7)` 66 manual page for a description of driver-specific parameters. 67 68.. option:: --chardev CHARDEVDEF 69 70 is a character device definition. See the :manpage:`qemu(1)` manual page for 71 a description of character device properties. A common character device 72 definition configures a UNIX domain socket:: 73 74 --chardev socket,id=char1,path=/var/run/qsd-qmp.sock,server=on,wait=off 75 76.. option:: --export [type=]nbd,id=<id>,node-name=<node-name>[,name=<export-name>][,writable=on|off][,bitmap=<name>] 77 --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>] 78 --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>] 79 --export [type=]fuse,id=<id>,node-name=<node-name>,mountpoint=<file>[,growable=on|off][,writable=on|off][,allow-other=on|off|auto] 80 81 is a block export definition. ``node-name`` is the block node that should be 82 exported. ``writable`` determines whether or not the export allows write 83 requests for modifying data (the default is off). 84 85 The ``nbd`` export type requires ``--nbd-server`` (see below). ``name`` is 86 the NBD export name (if not specified, it defaults to the given 87 ``node-name``). ``bitmap`` is the name of a dirty bitmap reachable from the 88 block node, so the NBD client can use NBD_OPT_SET_META_CONTEXT with the 89 metadata context name "qemu:dirty-bitmap:BITMAP" to inspect the bitmap. 90 91 The ``vhost-user-blk`` export type takes a vhost-user socket address on which 92 it accept incoming connections. Both 93 ``addr.type=unix,addr.path=<socket-path>`` for UNIX domain sockets and 94 ``addr.type=fd,addr.str=<fd>`` for file descriptor passing are supported. 95 ``logical-block-size`` sets the logical block size in bytes (the default is 96 512). ``num-queues`` sets the number of virtqueues (the default is 1). 97 98 The ``fuse`` export type takes a mount point, which must be a regular file, 99 on which to export the given block node. That file will not be changed, it 100 will just appear to have the block node's content while the export is active 101 (very much like mounting a filesystem on a directory does not change what the 102 directory contains, it only shows a different content while the filesystem is 103 mounted). Consequently, applications that have opened the given file before 104 the export became active will continue to see its original content. If 105 ``growable`` is set, writes after the end of the exported file will grow the 106 block node to fit. The ``allow-other`` option controls whether users other 107 than the user running the process will be allowed to access the export. Note 108 that enabling this option as a non-root user requires enabling the 109 user_allow_other option in the global fuse.conf configuration file. Setting 110 ``allow-other`` to auto (the default) will try enabling this option, and on 111 error fall back to disabling it. 112 113.. option:: --monitor MONITORDEF 114 115 is a QMP monitor definition. See the :manpage:`qemu(1)` manual page for 116 a description of QMP monitor properties. A common QMP monitor definition 117 configures a monitor on character device ``char1``:: 118 119 --monitor chardev=char1 120 121.. option:: --nbd-server addr.type=inet,addr.host=<host>,addr.port=<port>[,tls-creds=<id>][,tls-authz=<id>][,max-connections=<n>] 122 --nbd-server addr.type=unix,addr.path=<path>[,tls-creds=<id>][,tls-authz=<id>][,max-connections=<n>] 123 --nbd-server addr.type=fd,addr.str=<fd>[,tls-creds=<id>][,tls-authz=<id>][,max-connections=<n>] 124 125 is a server for NBD exports. Both TCP and UNIX domain sockets are supported. 126 A listen socket can be provided via file descriptor passing (see Examples 127 below). TLS encryption can be configured using ``--object`` tls-creds-* and 128 authz-* secrets (see below). 129 130 To configure an NBD server on UNIX domain socket path 131 ``/var/run/qsd-nbd.sock``:: 132 133 --nbd-server addr.type=unix,addr.path=/var/run/qsd-nbd.sock 134 135.. option:: --object help 136 --object <type>,help 137 --object <type>[,<property>=<value>...] 138 139 is a QEMU user creatable object definition. List object types with ``help``. 140 List object properties with ``<type>,help``. See the :manpage:`qemu(1)` 141 manual page for a description of the object properties. 142 143.. option:: --pidfile PATH 144 145 is the path to a file where the daemon writes its pid. This allows scripts to 146 stop the daemon by sending a signal:: 147 148 $ kill -SIGTERM $(<path/to/qsd.pid) 149 150 A file lock is applied to the file so only one instance of the daemon can run 151 with a given pid file path. The daemon unlinks its pid file when terminating. 152 153 The pid file is written after chardevs, exports, and NBD servers have been 154 created but before accepting connections. The daemon has started successfully 155 when the pid file is written and clients may begin connecting. 156 157.. option:: --daemonize 158 159 Daemonize the process. The parent process will exit once startup is complete 160 (i.e., after the pid file has been or would have been written) or failure 161 occurs. Its exit code reflects whether the child has started up successfully 162 or failed to do so. 163 164Examples 165-------- 166Launch the daemon with QMP monitor socket ``qmp.sock`` so clients can execute 167QMP commands:: 168 169 $ qemu-storage-daemon \ 170 --chardev socket,path=qmp.sock,server=on,wait=off,id=char1 \ 171 --monitor chardev=char1 172 173Launch the daemon from Python with a QMP monitor socket using file descriptor 174passing so there is no need to busy wait for the QMP monitor to become 175available:: 176 177 #!/usr/bin/env python3 178 import subprocess 179 import socket 180 181 sock_path = '/var/run/qmp.sock' 182 183 with socket.socket(socket.AF_UNIX, socket.SOCK_STREAM) as listen_sock: 184 listen_sock.bind(sock_path) 185 listen_sock.listen() 186 187 fd = listen_sock.fileno() 188 189 subprocess.Popen( 190 ['qemu-storage-daemon', 191 '--chardev', f'socket,fd={fd},server=on,id=char1', 192 '--monitor', 'chardev=char1'], 193 pass_fds=[fd], 194 ) 195 196 # listen_sock was automatically closed when leaving the 'with' statement 197 # body. If the daemon process terminated early then the following connect() 198 # will fail with "Connection refused" because no process has the listen 199 # socket open anymore. Launch errors can be detected this way. 200 201 qmp_sock = socket.socket(socket.AF_UNIX, socket.SOCK_STREAM) 202 qmp_sock.connect(sock_path) 203 ...QMP interaction... 204 205The same socket spawning approach also works with the ``--nbd-server 206addr.type=fd,addr.str=<fd>`` and ``--export 207type=vhost-user-blk,addr.type=fd,addr.str=<fd>`` options. 208 209Export raw image file ``disk.img`` over NBD UNIX domain socket ``nbd.sock``:: 210 211 $ qemu-storage-daemon \ 212 --blockdev driver=file,node-name=disk,filename=disk.img \ 213 --nbd-server addr.type=unix,addr.path=nbd.sock \ 214 --export type=nbd,id=export,node-name=disk,writable=on 215 216Export a qcow2 image file ``disk.qcow2`` as a vhost-user-blk device over UNIX 217domain socket ``vhost-user-blk.sock``:: 218 219 $ qemu-storage-daemon \ 220 --blockdev driver=file,node-name=file,filename=disk.qcow2 \ 221 --blockdev driver=qcow2,node-name=qcow2,file=file \ 222 --export type=vhost-user-blk,id=export,addr.type=unix,addr.path=vhost-user-blk.sock,node-name=qcow2 223 224Export a qcow2 image file ``disk.qcow2`` via FUSE on itself, so the disk image 225file will then appear as a raw image:: 226 227 $ qemu-storage-daemon \ 228 --blockdev driver=file,node-name=file,filename=disk.qcow2 \ 229 --blockdev driver=qcow2,node-name=qcow2,file=file \ 230 --export type=fuse,id=export,node-name=qcow2,mountpoint=disk.qcow2,writable=on 231 232See also 233-------- 234 235:manpage:`qemu(1)`, :manpage:`qemu-block-drivers(7)`, :manpage:`qemu-storage-daemon-qmp-ref(7)` 236