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= QEMU Monitor Protocol =
= QEMU Machine Protocol =


The QEMU Monitor Protocol (QMP) is a [http://www.json.org/ JSON]-based protocol which allows applications to communicate with QEMU's Monitor the right way.
The QEMU Machine Protocol (QMP) is a [http://www.json.org/ JSON]-based protocol which allows applications to control a QEMU instance.


QMP's main features are:
Features:


* Lightweight, text-based, easy to parse data format
* Lightweight, text-based, easy to parse data format
* Asynchronous messages support (ie. events)
* Asynchronous messages support (events)
* Capabilities negotiation
* Capabilities negotiation
* API/ABI stability guarantees
* API/ABI stability guarantees


Please, check the [http://git.savannah.gnu.org/cgit/qemu.git/tree/QMP/README README] file for more information.
Please, also check the [http://git.qemu.org/?p=qemu.git;a=blob_plain;f=docs/interop/qmp-intro.txt;hb=HEAD QMP intro] file for more information.


== General Status ==
== Examples ==


A supported version of QMP is available since QEMU 0.13 (and a "feature preview" version in QEMU 0.12), however several commands in the current API have badly defined semantics.
The first example explains some important details about QMP. The others are simpler and run on top of the first one.


This means that we will be introducing a deprecation policy soon. Users should always check QMP documentation as soon as a new release of QEMU is out, so that they don't run in the risk of using a deprecated command which may be removed in a future release.
In all examples "C" stands for "Client" and "S" stands for "Server".


== Examples ==
=== Capabilities Negotiation ===


In the following examples, 'C' stands for 'Client' and 'S' stands for 'Server'.
When a new QMP connection is established, QMP sends its greeting message and enters ''capabilities negotiation'' mode. In this mode, only the qmp_capabilities command works. To exit ''capabilities negotiation'' mode and enter ''command mode'', the qmp_capabilities command must be issued:


=== Server Greeting ===
  S: {
        "QMP": {
            "version": {
                "qemu": {
                    "micro": 0,
                    "minor": 6,
                    "major": 1
                },
                "package": ""
            },
            "capabilities": [
            ]
        }
    }
C: { "execute": "qmp_capabilities" }
S: { "return": {}}


S: { "QMP": { "version": { "qemu": { "micro": 50, "minor": 13, "major": 0 }, "package": "" }, "capabilities": []}}
The ''{ "return": {} }'' response is QMP's success response. An error response will contain the "error" keyword instead of "return".


=== Query version ===
=== Eject a medium ===


  C: { "execute": "query-status" }
  C: { "execute": "eject", "arguments": { "device": "ide1-cd0" } }
  S: { "return": { "singlestep": false, "running": true } }
  S: { "return": {}}


=== Eject a medium ===
=== Query VM status ===


  C: { "execute": "eject", "arguments": { "device": "ide1-cd0" } }
  C: { "execute": "query-status" }
S: {"return": {}}
S: {
        "return": {
            "status": "running",
            "singlestep": false,
            "running": true
        }
    }


=== Asynchronous message ===
=== Asynchronous message ===
Line 44: Line 65:
       "timestamp": { "seconds": 1265044230, "microseconds": 450486 } }
       "timestamp": { "seconds": 1265044230, "microseconds": 450486 } }


== Development ==
QMP being a core part of QEMU, all discussions happen on the [http://lists.nongnu.org/mailman/listinfo/qemu-devel qemu-devel] mailing list.
== Trying it ==
=== By hand ===
1. Start QMP on a TCP socket, so that telnet can be used
# qemu [...] -qmp tcp:localhost:4444,server,wait=off
2. Run telnet
$ telnet localhost 4444
3. You should see QMP's greeting banner
{"QMP": {"version": {"qemu": {"micro": 0, "minor": 6, "major": 1}, "package": ""}, "capabilities": []}}
4. Issue the ''qmp_capabilities'' command, so that QMP enters command mode
{ "execute": "qmp_capabilities" }
5. You can now issue commands. For example, to get a list of QMP supported commands, issue ''query-commands''
{ "execute": "query-commands" }
There's an optimization to this procedure in case you plan to use it often:
1. Install programs ''socat'' and ''rlwrap''. If you're running Fedora, you can do
# yum install socat rlwrap
2. Add the following sections to your QEMU config file (or create a ''qemu-qmp.conf'' one):
[chardev "qmp"]
  backend = "socket"
  path = "path to the QMP unix socket"
  server = "on"
  wait = "off"
[mon "qmp"]
  mode = "control"
  chardev = "qmp"
  pretty = "on"
3. Run QEMU


== Development ==
# qemu [...] -readconfig qemu-qmp.conf
 
4. Run rlwrap
 
# rlwrap -C qmp socat STDIO UNIX:path-to-the-QMP-unix-socket
 
You can now issue commands, rlwrap will give you readline support (including persistent history).
 
=== qmp-shell script ===
 
This script is available under the [http://git.qemu.org/?p=qemu.git;a=tree;f=scripts/qmp;hb=HEAD scripts/qmp/] directory in QEMU's source-tree. It automates a bit the testing work, as it can construct commands objects for you.
 
1. Start QMP on a unix socket
 
# qemu [...] -qmp unix:./qmp-sock,server,wait=off


Main developers are [mailto:lcapitulino@redhat.com Luiz Capitulino] and [mailto:armbru@redhat.com Markus Armbruster], but all QMP-related discussions happen on the [http://lists.nongnu.org/mailman/listinfo/qemu-devel qemu-devel] mailing list.
2. Run the script


Next features, hot fixes and other patches are stored in the QMP unstable repository:
# qmp-shell ./qmp-sock


http://repo.or.cz/w/qemu/qmp-unstable.git
3. You should get the following prompt


'''IMPORTANT''': all branches in this repository are constantly ''rebased'' (master inclusive).
(QEMU)


== TODO ==
4. You can now issue commands. For example, let's add a new device


=== short term ===
(QEMU) device_add driver=e1000 id=net1


* Decouple HMP and QMP
== Historic information ==
* Re-work the error infrastructure
* HMP passthrough via QMP
* Improve QMP testing (unit-tests, kvm-autoest and libvirt-TCK)


=== medium/long term ===
* Luiz's QMP talk on KVM Forum 2010 can be found [http://www.linux-kvm.org/images/1/17/2010-forum-qmp-status-talk.pp.pdf here]
* Old QMP page can be accessed [http://www.linux-kvm.org/index.php?title=MonitorProtocol&oldid=3100 here]


* Self-description & improved user documentation
[[Category:User documentation]]
* Begin adding sane commands
* Asynchronous commands support

Latest revision as of 12:35, 22 March 2022

QEMU Machine Protocol

The QEMU Machine Protocol (QMP) is a JSON-based protocol which allows applications to control a QEMU instance.

Features:

  • Lightweight, text-based, easy to parse data format
  • Asynchronous messages support (events)
  • Capabilities negotiation
  • API/ABI stability guarantees

Please, also check the QMP intro file for more information.

Examples

The first example explains some important details about QMP. The others are simpler and run on top of the first one.

In all examples "C" stands for "Client" and "S" stands for "Server".

Capabilities Negotiation

When a new QMP connection is established, QMP sends its greeting message and enters capabilities negotiation mode. In this mode, only the qmp_capabilities command works. To exit capabilities negotiation mode and enter command mode, the qmp_capabilities command must be issued:

 S: {
        "QMP": {
            "version": {
                "qemu": {
                    "micro": 0,
                    "minor": 6,
                    "major": 1
                },
                "package": ""
            },
            "capabilities": [
            ]
        }
    }
C: { "execute": "qmp_capabilities" }
S: { "return": {}}

The { "return": {} } response is QMP's success response. An error response will contain the "error" keyword instead of "return".

Eject a medium

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

Query VM status

C: { "execute": "query-status" }
S: {
       "return": {
           "status": "running",
           "singlestep": false,
           "running": true
       }
   }

Asynchronous message

S: { "event": "BLOCK_IO_ERROR",
     "data": { "device": "ide0-hd1",
               "operation": "write",
               "action": "stop" },
     "timestamp": { "seconds": 1265044230, "microseconds": 450486 } }

Development

QMP being a core part of QEMU, all discussions happen on the qemu-devel mailing list.

Trying it

By hand

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

# qemu [...] -qmp tcp:localhost:4444,server,wait=off

2. Run telnet

$ telnet localhost 4444

3. You should see QMP's greeting banner

{"QMP": {"version": {"qemu": {"micro": 0, "minor": 6, "major": 1}, "package": ""}, "capabilities": []}}

4. Issue the qmp_capabilities command, so that QMP enters command mode

{ "execute": "qmp_capabilities" }

5. You can now issue commands. For example, to get a list of QMP supported commands, issue query-commands

{ "execute": "query-commands" }

There's an optimization to this procedure in case you plan to use it often:

1. Install programs socat and rlwrap. If you're running Fedora, you can do

# yum install socat rlwrap

2. Add the following sections to your QEMU config file (or create a qemu-qmp.conf one):

[chardev "qmp"]
  backend = "socket"
  path = "path to the QMP unix socket"
  server = "on"
  wait = "off"
[mon "qmp"]
  mode = "control"
  chardev = "qmp"
  pretty = "on"

3. Run QEMU

# qemu [...] -readconfig qemu-qmp.conf

4. Run rlwrap

# rlwrap -C qmp socat STDIO UNIX:path-to-the-QMP-unix-socket

You can now issue commands, rlwrap will give you readline support (including persistent history).

qmp-shell script

This script is available under the scripts/qmp/ directory in QEMU's source-tree. It automates a bit the testing work, as it can construct commands objects for you.

1. Start QMP on a unix socket

# qemu [...] -qmp unix:./qmp-sock,server,wait=off

2. Run the script

# qmp-shell ./qmp-sock

3. You should get the following prompt

(QEMU)

4. You can now issue commands. For example, let's add a new device

(QEMU) device_add driver=e1000 id=net1

Historic information

  • Luiz's QMP talk on KVM Forum 2010 can be found here
  • Old QMP page can be accessed here