Provided by: qemu-utils_8.0.4+dfsg-1ubuntu3.23.10.5_amd64 
NAME
qemu-storage-daemon - QEMU storage daemon
SYNOPSIS
qemu-storage-daemon [options]
DESCRIPTION
qemu-storage-daemon provides disk image functionality from QEMU, qemu-img, and qemu-nbd in
a long-running process controlled via QMP commands without running a virtual machine. It
can export disk images, run block job operations, and perform other disk-related
operations. The daemon is controlled via a QMP monitor and initial configuration from the
command-line.
The daemon offers the following subset of QEMU features:
• Block nodes
• Block jobs
• Block exports
• Throttle groups
• Character devices
• Crypto and secrets
• QMP
• IOThreads
Commands can be sent over a QEMU Monitor Protocol (QMP) connection. See the
qemu-storage-daemon-qmp-ref(7) manual page for a description of the commands.
The daemon runs until it is stopped using the quit QMP command or SIGINT/SIGHUP/SIGTERM.
Warning: Never modify images in use by a running virtual machine or any other process;
this may destroy the image. Also, be aware that querying an image that is being modified
by another process may encounter inconsistent state.
OPTIONS
Standard options:
-h, --help
Display help and exit
-V, --version
Display version information and exit
-T, --trace [[enable=]PATTERN][,events=FILE][,file=FILE]
Specify tracing options.
[enable=]PATTERN
Immediately enable events matching PATTERN (either event name or a globbing
pattern). This option is only available if QEMU has been compiled with the
simple, log or ftrace tracing backend. To specify multiple events or patterns,
specify the -trace option multiple times.
Use -trace help to print a list of names of trace points.
events=FILE
Immediately enable events listed in FILE. The file must contain one event name
(as listed in the trace-events-all file) per line; globbing patterns are
accepted too. This option is only available if QEMU has been compiled with the
simple, log or ftrace tracing backend.
file=FILE
Log output traces to FILE. This option is only available if QEMU has been
compiled with the simple tracing backend.
--blockdev BLOCKDEVDEF
is a block node definition. See the qemu-system(1) manual page (in qemu-system-
common package) for a description of block node properties and the
qemu-block-drivers(7) manual page for a description of driver-specific parameters.
--chardev CHARDEVDEF
is a character device definition. See the qemu-system(1) manual page (in qemu-
system-common package) for a description of character device properties. A common
character device definition configures a UNIX domain socket:
--chardev socket,id=char1,path=/var/run/qsd-qmp.sock,server=on,wait=off
--export
[type=]nbd,id=<id>,node-name=<node-name>[,name=<export-name>][,writable=on|off][,bitmap=<name>]
--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>]
--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>]
--export
[type=]fuse,id=<id>,node-name=<node-name>,mountpoint=<file>[,growable=on|off][,writable=on|off][,allow-other=on|off|auto]
--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>]
is a block export definition. node-name is the block node that should be exported.
writable determines whether or not the export allows write requests for modifying
data (the default is off).
The nbd export type requires --nbd-server (see below). name is the NBD export name
(if not specified, it defaults to the given node-name). bitmap is the name of a
dirty bitmap reachable from the block node, so the NBD client can use
NBD_OPT_SET_META_CONTEXT with the metadata context name "qemu:dirty-bitmap:BITMAP"
to inspect the bitmap.
The vhost-user-blk export type takes a vhost-user socket address on which it accept
incoming connections. Both addr.type=unix,addr.path=<socket-path> for UNIX domain
sockets and addr.type=fd,addr.str=<fd> for file descriptor passing are supported.
logical-block-size sets the logical block size in bytes (the default is 512).
num-queues sets the number of virtqueues (the default is 1).
The fuse export type takes a mount point, which must be a regular file, on which to
export the given block node. That file will not be changed, it will just appear to
have the block node's content while the export is active (very much like mounting a
filesystem on a directory does not change what the directory contains, it only
shows a different content while the filesystem is mounted). Consequently,
applications that have opened the given file before the export became active will
continue to see its original content. If growable is set, writes after the end of
the exported file will grow the block node to fit. The allow-other option controls
whether users other than the user running the process will be allowed to access the
export. Note that enabling this option as a non-root user requires enabling the
user_allow_other option in the global fuse.conf configuration file. Setting
allow-other to auto (the default) will try enabling this option, and on error fall
back to disabling it.
The vduse-blk export type takes a name (must be unique across the host) to create
the VDUSE device. num-queues sets the number of virtqueues (the default is 1).
queue-size sets the virtqueue descriptor table size (the default is 256).
The instantiated VDUSE device must then be added to the vDPA bus using the vdpa(8)
command from the iproute2 project:
# vdpa dev add name <id> mgmtdev vduse
The device can be removed from the vDPA bus later as follows:
# vdpa dev del <id>
For more information about attaching vDPA devices to the host with virtio_vdpa.ko
or attaching them to guests with vhost_vdpa.ko, see https://vdpa-dev.gitlab.io/.
For more information about VDUSE, see
https://docs.kernel.org/userspace-api/vduse.html.
--monitor MONITORDEF
is a QMP monitor definition. See the qemu-system(1) manual page (in qemu-system-
common package) for a description of QMP monitor properties. A common QMP monitor
definition configures a monitor on character device char1:
--monitor chardev=char1
--nbd-server
addr.type=inet,addr.host=<host>,addr.port=<port>[,tls-creds=<id>][,tls-authz=<id>][,max-connections=<n>]
--nbd-server
addr.type=unix,addr.path=<path>[,tls-creds=<id>][,tls-authz=<id>][,max-connections=<n>]
--nbd-server
addr.type=fd,addr.str=<fd>[,tls-creds=<id>][,tls-authz=<id>][,max-connections=<n>]
is a server for NBD exports. Both TCP and UNIX domain sockets are supported. A
listen socket can be provided via file descriptor passing (see Examples below). TLS
encryption can be configured using --object tls-creds-* and authz-* secrets (see
below).
To configure an NBD server on UNIX domain socket path /var/run/qsd-nbd.sock:
--nbd-server addr.type=unix,addr.path=/var/run/qsd-nbd.sock
--object help
--object <type>,help
--object <type>[,<property>=<value>...]
is a QEMU user creatable object definition. List object types with help. List
object properties with <type>,help. See the qemu(1) manual page for a description
of the object properties.
--pidfile PATH
is the path to a file where the daemon writes its pid. This allows scripts to stop
the daemon by sending a signal:
$ kill -SIGTERM $(<path/to/qsd.pid)
A file lock is applied to the file so only one instance of the daemon can run with
a given pid file path. The daemon unlinks its pid file when terminating.
The pid file is written after chardevs, exports, and NBD servers have been created
but before accepting connections. The daemon has started successfully when the pid
file is written and clients may begin connecting.
--daemonize
Daemonize the process. The parent process will exit once startup is complete (i.e.,
after the pid file has been or would have been written) or failure occurs. Its exit
code reflects whether the child has started up successfully or failed to do so.
EXAMPLES
Launch the daemon with QMP monitor socket qmp.sock so clients can execute QMP commands:
$ qemu-storage-daemon \
--chardev socket,path=qmp.sock,server=on,wait=off,id=char1 \
--monitor chardev=char1
Launch the daemon from Python with a QMP monitor socket using file descriptor passing so
there is no need to busy wait for the QMP monitor to become available:
#!/usr/bin/env python3
import subprocess
import socket
sock_path = '/var/run/qmp.sock'
with socket.socket(socket.AF_UNIX, socket.SOCK_STREAM) as listen_sock:
listen_sock.bind(sock_path)
listen_sock.listen()
fd = listen_sock.fileno()
subprocess.Popen(
['qemu-storage-daemon',
'--chardev', f'socket,fd={fd},server=on,id=char1',
'--monitor', 'chardev=char1'],
pass_fds=[fd],
)
# listen_sock was automatically closed when leaving the 'with' statement
# body. If the daemon process terminated early then the following connect()
# will fail with "Connection refused" because no process has the listen
# socket open anymore. Launch errors can be detected this way.
qmp_sock = socket.socket(socket.AF_UNIX, socket.SOCK_STREAM)
qmp_sock.connect(sock_path)
...QMP interaction...
The same socket spawning approach also works with the --nbd-server
addr.type=fd,addr.str=<fd> and --export type=vhost-user-blk,addr.type=fd,addr.str=<fd>
options.
Export raw image file disk.img over NBD UNIX domain socket nbd.sock:
$ qemu-storage-daemon \
--blockdev driver=file,node-name=disk,filename=disk.img \
--nbd-server addr.type=unix,addr.path=nbd.sock \
--export type=nbd,id=export,node-name=disk,writable=on
Export a qcow2 image file disk.qcow2 as a vhost-user-blk device over UNIX domain socket
vhost-user-blk.sock:
$ qemu-storage-daemon \
--blockdev driver=file,node-name=file,filename=disk.qcow2 \
--blockdev driver=qcow2,node-name=qcow2,file=file \
--export type=vhost-user-blk,id=export,addr.type=unix,addr.path=vhost-user-blk.sock,node-name=qcow2
Export a qcow2 image file disk.qcow2 via FUSE on itself, so the disk image file will then
appear as a raw image:
$ qemu-storage-daemon \
--blockdev driver=file,node-name=file,filename=disk.qcow2 \
--blockdev driver=qcow2,node-name=qcow2,file=file \
--export type=fuse,id=export,node-name=qcow2,mountpoint=disk.qcow2,writable=on
SEE ALSO
qemu(1), qemu-block-drivers(7), qemu-storage-daemon-qmp-ref(7)
COPYRIGHT
2024, The QEMU Project Developers