[Qemu-devel] Getting VM state from outside QEMU?

[Qemu-devel] Getting VM state from outside QEMU?

[Erik Rull]

Hi all,

I need a pretty simple way to get the current state of the VM running in QEMU -
I only need the VM state (e.g. running, paused,...). Since my environment does
not have any perl, python or other high level scripting capabilities, a simple
way e.g. via a shell script would be nice. QEMU is running daemonized, so
interacting with the qemu console is not possible.
Are there any usable entries in /proc, /dev or /sys that could be used?

Thanks.

Best regards,

Erik

Re: [Qemu-devel] Getting VM state from outside QEMU?

[Paulo Ricardo Paz Vital]

On Tue, 2015-04-07 at 15:31 +0200, Erik Rull wrote:
> Hi all,
> 
> I need a pretty simple way to get the current state of the VM running in QEMU -
> I only need the VM state (e.g. running, paused,...). Since my environment does
> not have any perl, python or other high level scripting capabilities, a simple
> way e.g. via a shell script would be nice. QEMU is running daemonized, so
> interacting with the qemu console is not possible.
> Are there any usable entries in /proc, /dev or /sys that could be used?
> 

Hello Erik,

My suggestion is to create a script that sends the QMP command
"query-status" an then parse the result. The syntax and output is:

-> { "execute": "query-status" }
<- { "return": { "running": true, "singlestep": false, "status":
"running" } }


> Thanks.
> 
> Best regards,
> 
> Erik
> 

-- 
Paulo Ricardo Paz Vital <paulo.vital@profitbricks.com>
ProfitBricks GmbH

Re: [Qemu-devel] Getting VM state from outside QEMU?

[Erik Rull]

Hello Paulo,

> On April 7, 2015 at 3:42 PM Paulo Ricardo Paz Vital
> <paulo.vital@profitbricks.com> wrote:
> 
> 
> On Tue, 2015-04-07 at 15:31 +0200, Erik Rull wrote:
> > Hi all,
> > 
> > I need a pretty simple way to get the current state of the VM running in
> > QEMU -
> > I only need the VM state (e.g. running, paused,...). Since my environment
> > does
> > not have any perl, python or other high level scripting capabilities, a
> > simple
> > way e.g. via a shell script would be nice. QEMU is running daemonized, so
> > interacting with the qemu console is not possible.
> > Are there any usable entries in /proc, /dev or /sys that could be used?
> > 
> 
> Hello Erik,
> 
> My suggestion is to create a script that sends the QMP command
> "query-status" an then parse the result. The syntax and output is:
> 
> -> { "execute": "query-status" }
> <- { "return": { "running": true, "singlestep": false, "status":
> "running" } }
> 

Sounds good - I tried that - but all attempts return that the command has not
been found. I added the following command line snippet and the results are:
[...] -qmp tcp:localhost:4444,server,nowait [...]

172.17.48.45 ~ # telnet 127.0.0.1 4444
{"QMP": {"version": {"qemu": {"micro": 0, "minor": 1, "major": 2}, "package":
""}, "capabilities": []}}

{ "execute": "query-status" }
{"error": {"class": "CommandNotFound", "desc": "The command query-status has not
been found"}}
{ "execute": "info status" }
{"error": {"class": "CommandNotFound", "desc": "The command info status has not
been found"}}
{ "execute": "info", "arguments": { "status": "" } }
{"error": {"class": "CommandNotFound", "desc": "The command info has not been
found"}}
{ "execute": "query-kvm" }
{"error": {"class": "CommandNotFound", "desc": "The command query-kvm has not
been found"}}

Any ideas what's wrong here?

Thanks.

Best regards,

Erik

Re: [Qemu-devel] Getting VM state from outside QEMU?

[Eric Blake]

On 04/08/2015 10:10 AM, Erik Rull wrote:
>>
>> My suggestion is to create a script that sends the QMP command
>> "query-status" an then parse the result. The syntax and output is:
>>
>> -> { "execute": "query-status" }
>> <- { "return": { "running": true, "singlestep": false, "status":
>> "running" } }
>>
> 
> Sounds good - I tried that - but all attempts return that the command has not
> been found. I added the following command line snippet and the results are:
> [...] -qmp tcp:localhost:4444,server,nowait [...]
> 
> 172.17.48.45 ~ # telnet 127.0.0.1 4444
> {"QMP": {"version": {"qemu": {"micro": 0, "minor": 1, "major": 2}, "package":
> ""}, "capabilities": []}}

You HAVE to use {"execute":"qmp_capabilities"} (possibly with an
"id":...) as your first command on the monitor, before you can issue any
other command.  I really wish we could improve the error message:

> 
> { "execute": "query-status" }
> {"error": {"class": "CommandNotFound", "desc": "The command query-status has not
> been found"}}

it would be a LOT nicer if we reported 'still in negotiation phase;
"qmp_capabilities" expected' than a bland "CommandNotFound".  Of course,
patches are welcome to improve the experience there!

Similarly, once you are NOT in capabilities negotiation, any subsequent
use of "qmp_capabilities" fails.  That's also something where the error
message could be improved.

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

Re: [Qemu-devel] Getting VM state from outside QEMU?

[Erik Rull]

Hi Eric,

> On April 8, 2015 at 6:16 PM Eric Blake <eblake@redhat.com> wrote:
> 
> 
> On 04/08/2015 10:10 AM, Erik Rull wrote:
> >>
> >> My suggestion is to create a script that sends the QMP command
> >> "query-status" an then parse the result. The syntax and output is:
> >>
> >> -> { "execute": "query-status" }
> >> <- { "return": { "running": true, "singlestep": false, "status":
> >> "running" } }
> >>
> > 
> > Sounds good - I tried that - but all attempts return that the command has
> > not
> > been found. I added the following command line snippet and the results are:
> > [...] -qmp tcp:localhost:4444,server,nowait [...]
> > 
> > 172.17.48.45 ~ # telnet 127.0.0.1 4444
> > {"QMP": {"version": {"qemu": {"micro": 0, "minor": 1, "major": 2},
> > "package":
> > ""}, "capabilities": []}}
> 
> You HAVE to use {"execute":"qmp_capabilities"} (possibly with an
> "id":...) as your first command on the monitor, before you can issue any
> other command.  I really wish we could improve the error message:
> 
> > 
> > { "execute": "query-status" }
> > {"error": {"class": "CommandNotFound", "desc": "The command query-status has
> > not
> > been found"}}
> 
> it would be a LOT nicer if we reported 'still in negotiation phase;
> "qmp_capabilities" expected' than a bland "CommandNotFound".  Of course,
> patches are welcome to improve the experience there!
> 
> Similarly, once you are NOT in capabilities negotiation, any subsequent
> use of "qmp_capabilities" fails.  That's also something where the error
> message could be improved.
> 
> -- 
> Eric Blake   eblake redhat com    +1-919-301-3266
> Libvirt virtualization library http://libvirt.org

Thanks! That fixed it - even if I don't know why this was actually necessary :-)

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

Best regards,

Erik

Re: [Qemu-devel] Getting VM state from outside QEMU?

[Eric Blake]

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On 04/08/2015 10:21 AM, Erik Rull wrote:

>>> 172.17.48.45 ~ # telnet 127.0.0.1 4444
>>> {"QMP": {"version": {"qemu": {"micro": 0, "minor": 1, "major": 2},
>>> "package":
>>> ""}, "capabilities": []}}
>>
>> You HAVE to use {"execute":"qmp_capabilities"} (possibly with an
>> "id":...) as your first command on the monitor, before you can issue any
>> other command.  I really wish we could improve the error message:

> Thanks! That fixed it - even if I don't know why this was actually necessary :-)

docs/qmp/qmp-spec.txt

It's part of the protocol, to allow us to make non-backwards-compatible
changes to how QMP is parsed while still keeping sane interactions
between mismatches in server vs. client (to date, we have wisely not
needed to add any capabilities).

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org


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Re: [Qemu-devel] Getting VM state from outside QEMU?

[Paulo Ricardo Paz Vital]

Sorry guys only checked the emails this morning :-D

On Wed, 2015-04-08 at 10:16 -0600, Eric Blake wrote:
> On 04/08/2015 10:10 AM, Erik Rull wrote:
> >>
> >> My suggestion is to create a script that sends the QMP command
> >> "query-status" an then parse the result. The syntax and output is:
> >>
> >> -> { "execute": "query-status" }
> >> <- { "return": { "running": true, "singlestep": false, "status":
> >> "running" } }
> >>
> > 
> > Sounds good - I tried that - but all attempts return that the command has not
> > been found. I added the following command line snippet and the results are:
> > [...] -qmp tcp:localhost:4444,server,nowait [...]
> > 
> > 172.17.48.45 ~ # telnet 127.0.0.1 4444
> > {"QMP": {"version": {"qemu": {"micro": 0, "minor": 1, "major": 2}, "package":
> > ""}, "capabilities": []}}
> 
> You HAVE to use {"execute":"qmp_capabilities"} (possibly with an
> "id":...) as your first command on the monitor, before you can issue any
> other command.  I really wish we could improve the error message:
> 
> > 
> > { "execute": "query-status" }
> > {"error": {"class": "CommandNotFound", "desc": "The command query-status has not
> > been found"}}
> 
> it would be a LOT nicer if we reported 'still in negotiation phase;
> "qmp_capabilities" expected' than a bland "CommandNotFound".  Of course,
> patches are welcome to improve the experience there!

That's an interesting point to see. I'm going to take a look on this and
submit a patch until next week, probably good to 2.4 release.

> 
> Similarly, once you are NOT in capabilities negotiation, any subsequent
> use of "qmp_capabilities" fails.  That's also something where the error
> message could be improved.
> 

-- 
Paulo Ricardo Paz Vital <paulo.vital@profitbricks.com>
ProfitBricks GmbH

Re: [Qemu-devel] Getting VM state from outside QEMU?

[John Snow]

On 04/07/2015 09:31 AM, Erik Rull wrote:
> Hi all,
>
> I need a pretty simple way to get the current state of the VM running in QEMU -
> I only need the VM state (e.g. running, paused,...). Since my environment does
> not have any perl, python or other high level scripting capabilities, a simple
> way e.g. via a shell script would be nice. QEMU is running daemonized, so
> interacting with the qemu console is not possible.
> Are there any usable entries in /proc, /dev or /sys that could be used?
>
> Thanks.
>
> Best regards,
>
> Erik
>

Assuming this is some sort of embedded system under which python is not 
an option:

You'll need to use the monitor interface (-monitor), and set it to a 
pipe. you can echo commands into the pipe ("info status") and read lines 
out of it.

try:

mkfifo monitor.out
mkfifo monitor.in
./qemu-system-blah -monitor pipe:monitor &
echo "info status" > monitor.in
read $line < monitor.out # 'info status'
read $line < monitor.out # 'VM status: running'

And now you've got e.g. "VM status: running" in $line. Use whichever 
shell tricks to distill this down as needed.

Warning: this is using the human monitor protocol, which as the name 
implies, is not meant for you to be scraping it with tools. It could 
change arbitrarily in the future and shouldn't be used in production.

Really recommend the QMP interface and something capable of 
sending/reading JSON for programmatic scripting of QEMU. Check out 
scripts/qmp.py for a nice library for sending/receiving these sorts of 
things.

Alternatively you can use a similar fifo trick for -qmp and try to parse 
the answers you get with sed/awk/bash regex etc.