QEMU-STORAGE-DAEMON(1) QEMU QEMU-STORAGE-DAEMON(1)
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 SIG-
INT/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 incon-
sistent 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 con-
tain 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(1) manual page for a
description of block node properties and the qemu-block-driv-
ers(7) manual page for a description of driver-specific parame-
ters.
--chardev CHARDEVDEF
is a character device definition. See the qemu(1) manual page
for a description of character device properties. A common char-
acter 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=<ex-
port-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][,log-
ical-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][,log-
ical-block-size=<block-size>][,num-queues=<num-queues>]
--export [type=]fuse,id=<id>,node-name=<node-name>,mount-
point=<file>[,growable=on|off][,writable=on|off][,al-
low-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>][,log-
ical-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 ex-
port 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_CON-
TEXT 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 regu-
lar 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 mount-
ing a filesystem on a directory does not change what the direc-
tory 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 con-
tinue 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 ex-
port. Note that enabling this option as a non-root user re-
quires 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 num-
ber 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(1) manual page for a
description of QMP monitor properties. A common QMP monitor def-
inition 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-au-
thz=<id>][,max-connections=<n>]
--nbd-server addr.type=unix,addr.path=<path>[,tls-creds=<id>][,tls-au-
thz=<id>][,max-connections=<n>]
--nbd-server addr.type=fd,addr.str=<fd>[,tls-creds=<id>][,tls-au-
thz=<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 de-
scriptor 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 al-
lows 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 exe-
cute 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 de-
scriptor 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
7.2.11 May 09, 2024 QEMU-STORAGE-DAEMON(1)
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