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