1.. _storage-daemon: 2 3=================== 4QEMU Storage Daemon 5=================== 6 7Synopsis 8-------- 9 10**qemu-storage-daemon** [options] 11 12Description 13----------- 14 15``qemu-storage-daemon`` provides disk image functionality from QEMU, 16``qemu-img``, and ``qemu-nbd`` in a long-running process controlled via QMP 17commands without running a virtual machine. 18It can export disk images, run block job operations, and 19perform other disk-related operations. The daemon is controlled via a QMP 20monitor and initial configuration from the command-line. 21 22The daemon offers the following subset of QEMU features: 23 24* Block nodes 25* Block jobs 26* Block exports 27* Throttle groups 28* Character devices 29* Crypto and secrets 30* QMP 31* IOThreads 32 33Commands can be sent over a QEMU Monitor Protocol (QMP) connection. See the 34:manpage:`qemu-storage-daemon-qmp-ref(7)` manual page for a description of the 35commands. 36 37The daemon runs until it is stopped using the ``quit`` QMP command or 38SIGINT/SIGHUP/SIGTERM. 39 40**Warning:** Never modify images in use by a running virtual machine or any 41other process; this may destroy the image. Also, be aware that querying an 42image that is being modified by another process may encounter inconsistent 43state. 44 45Options 46------- 47 48.. program:: qemu-storage-daemon 49 50Standard options: 51 52.. option:: -h, --help 53 54 Display help and exit 55 56.. option:: -V, --version 57 58 Display version information and exit 59 60.. option:: -T, --trace [[enable=]PATTERN][,events=FILE][,file=FILE] 61 62 .. include:: ../qemu-option-trace.rst.inc 63 64.. option:: --blockdev BLOCKDEVDEF 65 66 is a block node definition. See the :manpage:`qemu(1)` manual page for a 67 description of block node properties and the :manpage:`qemu-block-drivers(7)` 68 manual page for a description of driver-specific parameters. 69 70.. option:: --chardev CHARDEVDEF 71 72 is a character device definition. See the :manpage:`qemu(1)` manual page for 73 a description of character device properties. A common character device 74 definition configures a UNIX domain socket:: 75 76 --chardev socket,id=char1,path=/var/run/qsd-qmp.sock,server=on,wait=off 77 78.. option:: --export [type=]nbd,id=<id>,node-name=<node-name>[,name=<export-name>][,writable=on|off][,bitmap=<name>] 79 --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>] 80 --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>] 81 --export [type=]fuse,id=<id>,node-name=<node-name>,mountpoint=<file>[,growable=on|off][,writable=on|off][,allow-other=on|off|auto] 82 --export [type=]vduse-blk,id=<id>,node-name=<node-name>,name=<vduse-name>[,writable=on|off][,num-queues=<num-queues>][,queue-size=<queue-size>][,logical-block-size=<block-size>][,serial=<serial-number>] 83 84 is a block export definition. ``node-name`` is the block node that should be 85 exported. ``writable`` determines whether or not the export allows write 86 requests for modifying data (the default is off). 87 88 The ``nbd`` export type requires ``--nbd-server`` (see below). ``name`` is 89 the NBD export name (if not specified, it defaults to the given 90 ``node-name``). ``bitmap`` is the name of a dirty bitmap reachable from the 91 block node, so the NBD client can use NBD_OPT_SET_META_CONTEXT with the 92 metadata context name "qemu:dirty-bitmap:BITMAP" to inspect the bitmap. 93 94 The ``vhost-user-blk`` export type takes a vhost-user socket address on which 95 it accept incoming connections. Both 96 ``addr.type=unix,addr.path=<socket-path>`` for UNIX domain sockets and 97 ``addr.type=fd,addr.str=<fd>`` for file descriptor passing are supported. 98 ``logical-block-size`` sets the logical block size in bytes (the default is 99 512). ``num-queues`` sets the number of virtqueues (the default is 1). 100 101 The ``fuse`` export type takes a mount point, which must be a regular file, 102 on which to export the given block node. That file will not be changed, it 103 will just appear to have the block node's content while the export is active 104 (very much like mounting a filesystem on a directory does not change what the 105 directory contains, it only shows a different content while the filesystem is 106 mounted). Consequently, applications that have opened the given file before 107 the export became active will continue to see its original content. If 108 ``growable`` is set, writes after the end of the exported file will grow the 109 block node to fit. The ``allow-other`` option controls whether users other 110 than the user running the process will be allowed to access the export. Note 111 that enabling this option as a non-root user requires enabling the 112 user_allow_other option in the global fuse.conf configuration file. Setting 113 ``allow-other`` to auto (the default) will try enabling this option, and on 114 error fall back to disabling it. 115 116 The ``vduse-blk`` export type takes a ``name`` (must be unique across the host) 117 to create the VDUSE device. 118 ``num-queues`` sets the number of virtqueues (the default is 1). 119 ``queue-size`` sets the virtqueue descriptor table size (the default is 256). 120 121 The instantiated VDUSE device must then be added to the vDPA bus using the 122 vdpa(8) command from the iproute2 project:: 123 124 # vdpa dev add name <id> mgmtdev vduse 125 126 The device can be removed from the vDPA bus later as follows:: 127 128 # vdpa dev del <id> 129 130 For more information about attaching vDPA devices to the host with 131 virtio_vdpa.ko or attaching them to guests with vhost_vdpa.ko, see 132 https://vdpa-dev.gitlab.io/. 133 134 For more information about VDUSE, see 135 https://docs.kernel.org/userspace-api/vduse.html. 136 137.. option:: --monitor MONITORDEF 138 139 is a QMP monitor definition. See the :manpage:`qemu(1)` manual page for 140 a description of QMP monitor properties. A common QMP monitor definition 141 configures a monitor on character device ``char1``:: 142 143 --monitor chardev=char1 144 145.. option:: --nbd-server addr.type=inet,addr.host=<host>,addr.port=<port>[,tls-creds=<id>][,tls-authz=<id>][,max-connections=<n>] 146 --nbd-server addr.type=unix,addr.path=<path>[,tls-creds=<id>][,tls-authz=<id>][,max-connections=<n>] 147 --nbd-server addr.type=fd,addr.str=<fd>[,tls-creds=<id>][,tls-authz=<id>][,max-connections=<n>] 148 149 is a server for NBD exports. Both TCP and UNIX domain sockets are supported. 150 A listen socket can be provided via file descriptor passing (see Examples 151 below). TLS encryption can be configured using ``--object`` tls-creds-* and 152 authz-* secrets (see below). 153 154 To configure an NBD server on UNIX domain socket path 155 ``/var/run/qsd-nbd.sock``:: 156 157 --nbd-server addr.type=unix,addr.path=/var/run/qsd-nbd.sock 158 159.. option:: --object help 160 --object <type>,help 161 --object <type>[,<property>=<value>...] 162 163 is a QEMU user creatable object definition. List object types with ``help``. 164 List object properties with ``<type>,help``. See the :manpage:`qemu(1)` 165 manual page for a description of the object properties. 166 167.. option:: --pidfile PATH 168 169 is the path to a file where the daemon writes its pid. This allows scripts to 170 stop the daemon by sending a signal:: 171 172 $ kill -SIGTERM $(<path/to/qsd.pid) 173 174 A file lock is applied to the file so only one instance of the daemon can run 175 with a given pid file path. The daemon unlinks its pid file when terminating. 176 177 The pid file is written after chardevs, exports, and NBD servers have been 178 created but before accepting connections. The daemon has started successfully 179 when the pid file is written and clients may begin connecting. 180 181.. option:: --daemonize 182 183 Daemonize the process. The parent process will exit once startup is complete 184 (i.e., after the pid file has been or would have been written) or failure 185 occurs. Its exit code reflects whether the child has started up successfully 186 or failed to do so. 187 188Examples 189-------- 190Launch the daemon with QMP monitor socket ``qmp.sock`` so clients can execute 191QMP commands:: 192 193 $ qemu-storage-daemon \ 194 --chardev socket,path=qmp.sock,server=on,wait=off,id=char1 \ 195 --monitor chardev=char1 196 197Launch the daemon from Python with a QMP monitor socket using file descriptor 198passing so there is no need to busy wait for the QMP monitor to become 199available:: 200 201 #!/usr/bin/env python3 202 import subprocess 203 import socket 204 205 sock_path = '/var/run/qmp.sock' 206 207 with socket.socket(socket.AF_UNIX, socket.SOCK_STREAM) as listen_sock: 208 listen_sock.bind(sock_path) 209 listen_sock.listen() 210 211 fd = listen_sock.fileno() 212 213 subprocess.Popen( 214 ['qemu-storage-daemon', 215 '--chardev', f'socket,fd={fd},server=on,id=char1', 216 '--monitor', 'chardev=char1'], 217 pass_fds=[fd], 218 ) 219 220 # listen_sock was automatically closed when leaving the 'with' statement 221 # body. If the daemon process terminated early then the following connect() 222 # will fail with "Connection refused" because no process has the listen 223 # socket open anymore. Launch errors can be detected this way. 224 225 qmp_sock = socket.socket(socket.AF_UNIX, socket.SOCK_STREAM) 226 qmp_sock.connect(sock_path) 227 ...QMP interaction... 228 229The same socket spawning approach also works with the ``--nbd-server 230addr.type=fd,addr.str=<fd>`` and ``--export 231type=vhost-user-blk,addr.type=fd,addr.str=<fd>`` options. 232 233Export raw image file ``disk.img`` over NBD UNIX domain socket ``nbd.sock``:: 234 235 $ qemu-storage-daemon \ 236 --blockdev driver=file,node-name=disk,filename=disk.img \ 237 --nbd-server addr.type=unix,addr.path=nbd.sock \ 238 --export type=nbd,id=export,node-name=disk,writable=on 239 240Export a qcow2 image file ``disk.qcow2`` as a vhost-user-blk device over UNIX 241domain socket ``vhost-user-blk.sock``:: 242 243 $ qemu-storage-daemon \ 244 --blockdev driver=file,node-name=file,filename=disk.qcow2 \ 245 --blockdev driver=qcow2,node-name=qcow2,file=file \ 246 --export type=vhost-user-blk,id=export,addr.type=unix,addr.path=vhost-user-blk.sock,node-name=qcow2 247 248Export a qcow2 image file ``disk.qcow2`` via FUSE on itself, so the disk image 249file will then appear as a raw image:: 250 251 $ qemu-storage-daemon \ 252 --blockdev driver=file,node-name=file,filename=disk.qcow2 \ 253 --blockdev driver=qcow2,node-name=qcow2,file=file \ 254 --export type=fuse,id=export,node-name=qcow2,mountpoint=disk.qcow2,writable=on 255 256See also 257-------- 258 259:manpage:`qemu(1)`, :manpage:`qemu-block-drivers(7)`, :manpage:`qemu-storage-daemon-qmp-ref(7)` 260