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(1) manual page 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(1) manual page for a description of character device properties. A common character device definition configures a UNIX domain socket:

--chardev socket,id=char1,path=/tmp/qmp.sock,server,nowait
--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>]

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. 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).

--monitor MONITORDEF

is a QMP monitor definition. See the qemu(1) manual page 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>]

is a server for NBD exports. Both TCP and UNIX domain sockets are supported. TLS encryption can be configured using --object tls-creds-* and authz-* secrets (see below).

To configure an NBD server on UNIX domain socket path /tmp/nbd.sock:

--nbd-server addr.type=unix,addr.path=/tmp/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.

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,nowait,id=char1 \
    --monitor chardev=char1

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 vhosts-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

See also

qemu(1), qemu-block-drivers(7), qemu-storage-daemon-qmp-ref(7)