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]
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.
107
108.. option:: --monitor MONITORDEF
109
110  is a QMP monitor definition. See the :manpage:`qemu(1)` manual page for
111  a description of QMP monitor properties. A common QMP monitor definition
112  configures a monitor on character device ``char1``::
113
114  --monitor chardev=char1
115
116.. option:: --nbd-server addr.type=inet,addr.host=<host>,addr.port=<port>[,tls-creds=<id>][,tls-authz=<id>][,max-connections=<n>]
117  --nbd-server addr.type=unix,addr.path=<path>[,tls-creds=<id>][,tls-authz=<id>][,max-connections=<n>]
118  --nbd-server addr.type=fd,addr.str=<fd>[,tls-creds=<id>][,tls-authz=<id>][,max-connections=<n>]
119
120  is a server for NBD exports. Both TCP and UNIX domain sockets are supported.
121  A listen socket can be provided via file descriptor passing (see Examples
122  below). TLS encryption can be configured using ``--object`` tls-creds-* and
123  authz-* secrets (see below).
124
125  To configure an NBD server on UNIX domain socket path
126  ``/var/run/qsd-nbd.sock``::
127
128  --nbd-server addr.type=unix,addr.path=/var/run/qsd-nbd.sock
129
130.. option:: --object help
131  --object <type>,help
132  --object <type>[,<property>=<value>...]
133
134  is a QEMU user creatable object definition. List object types with ``help``.
135  List object properties with ``<type>,help``. See the :manpage:`qemu(1)`
136  manual page for a description of the object properties.
137
138.. option:: --pidfile PATH
139
140  is the path to a file where the daemon writes its pid. This allows scripts to
141  stop the daemon by sending a signal::
142
143    $ kill -SIGTERM $(<path/to/qsd.pid)
144
145  A file lock is applied to the file so only one instance of the daemon can run
146  with a given pid file path. The daemon unlinks its pid file when terminating.
147
148  The pid file is written after chardevs, exports, and NBD servers have been
149  created but before accepting connections. The daemon has started successfully
150  when the pid file is written and clients may begin connecting.
151
152Examples
153--------
154Launch the daemon with QMP monitor socket ``qmp.sock`` so clients can execute
155QMP commands::
156
157  $ qemu-storage-daemon \
158      --chardev socket,path=qmp.sock,server=on,wait=off,id=char1 \
159      --monitor chardev=char1
160
161Launch the daemon from Python with a QMP monitor socket using file descriptor
162passing so there is no need to busy wait for the QMP monitor to become
163available::
164
165  #!/usr/bin/env python3
166  import subprocess
167  import socket
168
169  sock_path = '/var/run/qmp.sock'
170
171  with socket.socket(socket.AF_UNIX, socket.SOCK_STREAM) as listen_sock:
172      listen_sock.bind(sock_path)
173      listen_sock.listen()
174
175      fd = listen_sock.fileno()
176
177      subprocess.Popen(
178          ['qemu-storage-daemon',
179           '--chardev', f'socket,fd={fd},server=on,id=char1',
180           '--monitor', 'chardev=char1'],
181          pass_fds=[fd],
182      )
183
184  # listen_sock was automatically closed when leaving the 'with' statement
185  # body. If the daemon process terminated early then the following connect()
186  # will fail with "Connection refused" because no process has the listen
187  # socket open anymore. Launch errors can be detected this way.
188
189  qmp_sock = socket.socket(socket.AF_UNIX, socket.SOCK_STREAM)
190  qmp_sock.connect(sock_path)
191  ...QMP interaction...
192
193The same socket spawning approach also works with the ``--nbd-server
194addr.type=fd,addr.str=<fd>`` and ``--export
195type=vhost-user-blk,addr.type=fd,addr.str=<fd>`` options.
196
197Export raw image file ``disk.img`` over NBD UNIX domain socket ``nbd.sock``::
198
199  $ qemu-storage-daemon \
200      --blockdev driver=file,node-name=disk,filename=disk.img \
201      --nbd-server addr.type=unix,addr.path=nbd.sock \
202      --export type=nbd,id=export,node-name=disk,writable=on
203
204Export a qcow2 image file ``disk.qcow2`` as a vhosts-user-blk device over UNIX
205domain socket ``vhost-user-blk.sock``::
206
207  $ qemu-storage-daemon \
208      --blockdev driver=file,node-name=file,filename=disk.qcow2 \
209      --blockdev driver=qcow2,node-name=qcow2,file=file \
210      --export type=vhost-user-blk,id=export,addr.type=unix,addr.path=vhost-user-blk.sock,node-name=qcow2
211
212Export a qcow2 image file ``disk.qcow2`` via FUSE on itself, so the disk image
213file will then appear as a raw image::
214
215  $ qemu-storage-daemon \
216      --blockdev driver=file,node-name=file,filename=disk.qcow2 \
217      --blockdev driver=qcow2,node-name=qcow2,file=file \
218      --export type=fuse,id=export,node-name=qcow2,mountpoint=disk.qcow2,writable=on
219
220See also
221--------
222
223:manpage:`qemu(1)`, :manpage:`qemu-block-drivers(7)`, :manpage:`qemu-storage-daemon-qmp-ref(7)`
224