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 (if not specified, it defaults to the given
84  ``node-name``). ``bitmap`` is the name of a dirty bitmap reachable from the
85  block node, so the NBD client can use NBD_OPT_SET_META_CONTEXT with the
86  metadata context name "qemu:dirty-bitmap:BITMAP" to inspect the bitmap.
87
88  The ``vhost-user-blk`` export type takes a vhost-user socket address on which
89  it accept incoming connections. Both
90  ``addr.type=unix,addr.path=<socket-path>`` for UNIX domain sockets and
91  ``addr.type=fd,addr.str=<fd>`` for file descriptor passing are supported.
92  ``logical-block-size`` sets the logical block size in bytes (the default is
93  512). ``num-queues`` sets the number of virtqueues (the default is 1).
94
95.. option:: --monitor MONITORDEF
96
97  is a QMP monitor definition. See the :manpage:`qemu(1)` manual page for
98  a description of QMP monitor properties. A common QMP monitor definition
99  configures a monitor on character device ``char1``::
100
101  --monitor chardev=char1
102
103.. option:: --nbd-server addr.type=inet,addr.host=<host>,addr.port=<port>[,tls-creds=<id>][,tls-authz=<id>][,max-connections=<n>]
104  --nbd-server addr.type=unix,addr.path=<path>[,tls-creds=<id>][,tls-authz=<id>][,max-connections=<n>]
105  --nbd-server addr.type=fd,addr.str=<fd>[,tls-creds=<id>][,tls-authz=<id>][,max-connections=<n>]
106
107  is a server for NBD exports. Both TCP and UNIX domain sockets are supported.
108  A listen socket can be provided via file descriptor passing (see Examples
109  below). TLS encryption can be configured using ``--object`` tls-creds-* and
110  authz-* secrets (see below).
111
112  To configure an NBD server on UNIX domain socket path
113  ``/var/run/qsd-nbd.sock``::
114
115  --nbd-server addr.type=unix,addr.path=/var/run/qsd-nbd.sock
116
117.. option:: --object help
118  --object <type>,help
119  --object <type>[,<property>=<value>...]
120
121  is a QEMU user creatable object definition. List object types with ``help``.
122  List object properties with ``<type>,help``. See the :manpage:`qemu(1)`
123  manual page for a description of the object properties.
124
125.. option:: --pidfile PATH
126
127  is the path to a file where the daemon writes its pid. This allows scripts to
128  stop the daemon by sending a signal::
129
130    $ kill -SIGTERM $(<path/to/qsd.pid)
131
132  A file lock is applied to the file so only one instance of the daemon can run
133  with a given pid file path. The daemon unlinks its pid file when terminating.
134
135  The pid file is written after chardevs, exports, and NBD servers have been
136  created but before accepting connections. The daemon has started successfully
137  when the pid file is written and clients may begin connecting.
138
139Examples
140--------
141Launch the daemon with QMP monitor socket ``qmp.sock`` so clients can execute
142QMP commands::
143
144  $ qemu-storage-daemon \
145      --chardev socket,path=qmp.sock,server=on,wait=off,id=char1 \
146      --monitor chardev=char1
147
148Launch the daemon from Python with a QMP monitor socket using file descriptor
149passing so there is no need to busy wait for the QMP monitor to become
150available::
151
152  #!/usr/bin/env python3
153  import subprocess
154  import socket
155
156  sock_path = '/var/run/qmp.sock'
157
158  with socket.socket(socket.AF_UNIX, socket.SOCK_STREAM) as listen_sock:
159      listen_sock.bind(sock_path)
160      listen_sock.listen()
161
162      fd = listen_sock.fileno()
163
164      subprocess.Popen(
165          ['qemu-storage-daemon',
166           '--chardev', f'socket,fd={fd},server=on,id=char1',
167           '--monitor', 'chardev=char1'],
168          pass_fds=[fd],
169      )
170
171  # listen_sock was automatically closed when leaving the 'with' statement
172  # body. If the daemon process terminated early then the following connect()
173  # will fail with "Connection refused" because no process has the listen
174  # socket open anymore. Launch errors can be detected this way.
175
176  qmp_sock = socket.socket(socket.AF_UNIX, socket.SOCK_STREAM)
177  qmp_sock.connect(sock_path)
178  ...QMP interaction...
179
180The same socket spawning approach also works with the ``--nbd-server
181addr.type=fd,addr.str=<fd>`` and ``--export
182type=vhost-user-blk,addr.type=fd,addr.str=<fd>`` options.
183
184Export raw image file ``disk.img`` over NBD UNIX domain socket ``nbd.sock``::
185
186  $ qemu-storage-daemon \
187      --blockdev driver=file,node-name=disk,filename=disk.img \
188      --nbd-server addr.type=unix,addr.path=nbd.sock \
189      --export type=nbd,id=export,node-name=disk,writable=on
190
191Export a qcow2 image file ``disk.qcow2`` as a vhosts-user-blk device over UNIX
192domain socket ``vhost-user-blk.sock``::
193
194  $ qemu-storage-daemon \
195      --blockdev driver=file,node-name=file,filename=disk.qcow2 \
196      --blockdev driver=qcow2,node-name=qcow2,file=file \
197      --export type=vhost-user-blk,id=export,addr.type=unix,addr.path=vhost-user-blk.sock,node-name=qcow2
198
199See also
200--------
201
202:manpage:`qemu(1)`, :manpage:`qemu-block-drivers(7)`, :manpage:`qemu-storage-daemon-qmp-ref(7)`
203