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