Documentation/QMP: Difference between revisions

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* API/ABI stability guarantees
* API/ABI stability guarantees


Please, also check the [http://git.qemu.org/?p=qemu.git;a=blob_plain;f=QMP/README;hb=HEAD 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.


== Examples ==
== Examples ==
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The first example explains some important details about QMP. The others are simpler and run on top of the first one.
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'.
In all examples "C" stands for "Client" and "S" stands for "Server".


=== Capabilities Negotiation ===
=== Capabilities Negotiation ===
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== Development ==
== Development ==


Main developer in charge is [mailto:lcapitulino@redhat.com Luiz Capitulino]. All QMP-related discussions happen on the [http://lists.nongnu.org/mailman/listinfo/qemu-devel qemu-devel] mailing list.
QMP being a core part of QEMU, all discussions happen on the [http://lists.nongnu.org/mailman/listinfo/qemu-devel qemu-devel] mailing list.
 
Luiz's QMP queue can be found at:
 
http://repo.or.cz/w/qemu/qmp-unstable.git/shortlog/refs/heads/queue/qmp
 
'''IMPORTANT''': This branch is constantly rebased!
 
=== TODO ===
 
In order of importance.
 
==== Drop the qmp-commands.hx file ====
 
The qmp-commands.hx file is basically a command table. Today, with the advent of the QAPI, the qapi-schema.json file serves the same purpose. We should drop qmp-commands.hx in favor of qapi-schema.json.
 
This is more or less what it takes to do that:
 
# Convert do_device_add() and do_qmp_capabilities() to propagate errors (ie, fill an Error ** object instead of doing qerror_report() calls)
# Do something about qmp_netdev_add(), qmp_qom_get() and qmp_qom_set() (drop them or add QAPI wrappers?)
# Change QMP code in monitor.c to use the QAPI to do command parameter validation and command dispatching (just like qemu-ga does)
# Move QMP examples from qmp-commands.hx to qapi-schema.json
# Drop qmp-commands.hx
 
==== Add full introspection support ====
 
This is about adding a command which returns all QMP types, commands (input and output parameters) and events.
 
Amos Kong is working on this:
 
http://marc.info/?l=qemu-devel&m=137059998004419&w=2
 
==== Add events support to the QAPI ====
 
Today events are exclusively part of the text protocol. This means that they are open coded, QEMU subsystems can't make use of them and they are not listed in qapi-schema.json.
 
We would solve all those problems by adding event support to the QAPI.
 
==== QMP testing ====
 
There should be a QMP test-suite. Either in QEMU itself or externally, like in kvm-autotest (which seems to be the best option).
 
==== HMP command conversion to the QAPI ====
 
Our long term plan is to make HMP, the human monitor, independent of QEMU. This means that HMP code shouldn't call QEMU code other than the monitor.
 
To achieve this we have to split existing HMP-only commands (eg. do_wav_capture() or do_ioport_read()) into a QMP part and an HMP part. Just like new QMP commands.


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


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


2. Run telnet
2. Run telnet
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=== qmp-shell script ===
=== qmp-shell script ===


This script is available under the [http://git.savannah.gnu.org/cgit/qemu.git/tree/QMP QMP] directory in QEMU's source-tree. It automates a bit the testing work, as it can construct commands objects for you.
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
1. Start QMP on a unix socket


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


2. Run the script
2. Run the script
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  (QEMU) device_add driver=e1000 id=net1
  (QEMU) device_add driver=e1000 id=net1


== Other information ==
== Historic information ==
 
* 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]


* Luiz's QMP talk on KVM Forum 2010 can be found [http://www.cpu.eti.br/talks/qmp-talk-kvm-forum-2010.pdf here]
[[Category:User documentation]]
* Old QMP page can be accessed [http://www.linux-kvm.org/wiki/index.php?title=MonitorProtocol&direction=prev&oldid=3232 here]

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