QEMU Monitor Protocol

The QEMU Monitor Protocol (QMP) is a JSON-based protocol which allows applications to communicate with QEMU's Monitor.

QMP's main features are:

Lightweight, text-based, easy to parse data format
Asynchronous messages support (ie. events)
Capabilities Negotiation
Stability (starting QEMU version 0.13)

The README file has a simple introduction and the full specification is recommended for application writers.

General Status

A preview version of QMP is available in QEMU version 0.12. This means that QMP is still under development and there will be incompatible changes between QEMU 0.12 and QEMU 0.13.

For more information about converted handlers, please check #Conversion Status.

Examples

In the following examples, 'C' stands for 'Client' and 'S' stands for 'Server'.

Server Greeting

S: { "QMP": { "version": { "qemu": "0.12.50", "package": "" }, "capabilities": [] } }

Query version

C: { "execute": "query-version" }
S: { "return": { "qemu": "0.12.50", "package": ""} }

Eject a device

C: { "execute": "eject", "arguments": { "device": "ide1-cd0" } }
S: {"return": {}}

Development

Primary contact is Luiz Capitulino, but all QMP-related discussions happen on the qemu-devel mailing list.

Next features, hot fixes and other patches are stored in the QMP unstable repository:

http://repo.or.cz/w/qemu/qmp-unstable.git

NOTE: all branches in this repository are constantly rebased (master inclusive).

TODO

Convert all remaining commands
High-level protocol documentation
High-level internal documentation
Improve internal API, currently it's too low-level
Better QObjects and QMP debug support
Array-based Monitor's command table
Libqmp

Conversion Status

UPDATED: 2009-12-16

	Command	Info
Handlers	62	36
Converted	19	15
Percentage	30%	41%

The following tables have a per-function status. There is one table for command handlers and another one for info handlers.

Status can be:

merged: already merged upstream
partial: merged, but error handling is incomplete

NOTE: Handlers used by Libvirt are marked with yellow.

Command handlers

Handler name	Status	Version	Comments
do_acl_add()
do_acl_policy()
do_acl_remove()
do_acl_reset()
do_acl_show()
do_balloon()	merged	0.12
do_block_set_passwd()	merged	0.12
do_boot_set()
do_change()	merged	0.12
do_closefd()	merged	0.12
do_commit()
do_cont()	merged	0.12
do_cpu_set()	merged	0.12.50
do_delvm()
do_device_add()	merged	0.12.50
do_device_del()
do_eject()	merged	0.12
do_gdbserver()
do_getfd()	merged	0.12
do_help_cmd()
do_info()	merged	0.12	as 'query-' commands
do_inject_mce()
do_inject_nmi()
do_ioport_read()
do_ioport_write()
do_loadvm()
do_log()
do_logfile()
do_memory_dump()
do_memory_save()	merged	0.12.50
do_migrate()	partial	0.12
do_migrate_cancel()	merged	0.12
do_migrate_set_downtime()	merged	0.12.50
do_migrate_set_speed()	merged	0.12.50
do_mouse_button()
do_mouse_move()
do_mouse_set()
do_pci_device_hot_remove()	partial	0.12	legacy, use device_del instead
do_physical_memory_dump()
do_physical_memory_save()	merged	0.12.50
do_print()
do_quit()	merged	0.12
do_savevm()
do_screen_dump()
do_sendkey()
do_set_link()
do_singlestep()
do_stop()	merged	0.12
do_stop_capture()
do_sum()
do_system_powerdown()	merged	0.12
do_system_reset()	merged	0.12
do_usb_add()			legacy, use device_add instead
do_usb_del()			legacy, use device_del instead
do_watchdog_action()
do_wav_capture()
drive_hot_add()
net_host_device_add()			consider do_netdev_add() instead
net_host_device_remove()			consider do_netdev_del() instead
net_slirp_hostfwd_add()
net_slirp_hostfwd_remove()
pci_device_hot_add()	partial	0.12	legacy, use device_add instead
do_chardev_add()			to be created
do_chardev_del()			to be created
do_blockdev_add()			to be created
do_blockdev_del()			to be created
do_netdev_add()			to be created
do_netdev_del()			to be created

Info handlers

Handler name	Status	Version	Comments
bdrv_info()	merged	0.12
bdrv_info_stats()	merged	0.12
do_info_balloon()	merged	0.12
do_info_capture()
do_info_cpus()	merged	0.12
do_info_cpu_stats()
do_info_history()
do_info_hpet()	merged	0.12
do_info_jit()
do_info_kvm()	merged	0.12
do_info_mice()	merged	0.12
do_info_migrate()	merged	0.12
do_info_name()	merged	0.12
do_info_network()
do_info_numa()
do_info_profile()
do_info_qdm()
do_info_qtree()
do_info_registers()
do_info_roms()
do_info_snapshots()
do_info_status()	merged	0.12
do_info_usernet()
do_info_uuid()	merged	0.12
do_info_version()	merged	0.12
do_info_vnc()	merged	0.12
irq_info()
mem_info()
pci_info()
pcmcia_info()
pic_info()
qemu_chr_info()	merged	0.12
tlb_info()
usb_host_info()
usb_info()

Testing

Unfortunately, there is no automated tool to test QMP correctness yet. Probably, the right thing to do is to integrate with kvm-autotest but we still have to think how this should be done.

Meanwhile, QMP testing is a low-level procedure which requires knowledge about the protocol and its implementation, so the first thing to do is to read the README and spec files.

This section describes two ways of testing QMP:

By hand (difficult, only worth it if you're chasing a specific bug)
Using qmp-shell script (automates part of the job)

Libvirt

1. Install yajl-devel before running 'autogen.sh'. Make sure the final summary of autogen.sh tells you that it found the yajl library. If you`re running Fedora 12(or above) just yum install yajl-devel.

2. From a fresh checkout of GIT master run the following:

./autogen.sh --system --enable-compile-warnings=error

NOTE: The '--system' flag is a shortcut for compiling with the --prefix and other directories matching a system RPM build.

3. Run 'make' to build. There is no need to 'make install' anything especially since that would overwrite your RPM based install

4. As root simply stop the current daemon & start the one you built

/etc/init.d/libvirtd stop
$HOME/your/git/checkout/of/libvirt/daemon/libvirtd

5. As root you can use the newly built virsh too

cd $HOME/your/git/checkout/of/libvirt/src
./virsh <BLAH>

6. To enable QMP support, before you build edit src/qemu/qemu_conf.c and find:

#if 0
   if (version >= 13000)
       flags |= QEMUD_CMD_FLAG_MONITOR_JSON;
#endif

NOTE: If enabled libvirt will use QMP as default monitor.

7. Change that to an '#if 1', and change the version to 12000 so it detects your GIT build of QEMU

By hand

1. Start QMP on a TCP socket, so that telnet can be used

qemu [...] -qmp tcp:localhost:4444,server

2. Now, run telnet

telnet localhost 4444

3. You should see the following prompt

{"QMP": {"capabilities": []}}

4. Now you can issue commands. To get a list of QMP supported commands, run query-commands

{ "execute": "query-commands" }

NOTE: all "info" commands are available under QMP as "query-", for example "info vnc" is "query-vnc".

The output of query-commands is a JSON array of objects, each with a 'name' key, which has the name of the supported command. QMP doesn't have user documentation yet, this means that, to find out which arguments a command accepts or what's its output, you will have to either check the qemu-monitor.hx file and/or the function which implements the command.

Yes, it's that low-level.

qmp-shell script

This script is available under the QMP directory in QEMU's source-tree. It automates a bit the testing work, as it can construct commands.

1. Start QMP on a unix socket, like:

qemu [...] -qmp unix:./qmp-sock,server

2. Run the script

qmp-shell ./qmp-sock

3. You should get the following prompt

(QEMU)

4. Now you can run commands. For example, let's change the VNC password:

(QEMU) change device=vnc target=password arg='1234'

So, it's needed to name the arguments and the script is not very smart. Again, to find out what arguments a command accepts, you have to either check the qemu-monitor.hx file and/or the function which implements the command.

Have fun!

History

This was the fourth proposal for a Monitor protocol, past discussions can be found in the following links:

MonitorProtocol

Contents