[libvirt-users] Get PID of a domain's QEMU instance from its domain ID

[Peter Krempa]

On Tue, Mar 21, 2017 at 12:06:25 +0100, Martin Kletzander wrote:
> On Mon, Mar 20, 2017 at 02:11:21PM +0100, Thibaut SAUTEREAU wrote:
> > Hello,
> > 
> > I cannot find a way to retrieve PIDs of QEMU instances from libvirt domains'
> > IDs (I'm using libvirt C API). I recognize it sounds like a bad idea doing so
> > (and I know PIDs are explicitly made not available, as I gathered from the
> > source code and on your IRC channel) but I need that to use the perf_event_open
> > syscall in order to gather statistics on my QEMU/KVM guests. I also know
> > libvirt now supports some perf events but only a few and I need more. I could
> > submit patches to add them and I will definitely consider that but in the
> > meantime...

Looks like you are looking for:
http://libvirt.org/formatdomain.html#elementsPerf

and 

http://libvirt.org/html/libvirt-libvirt-domain.html#virDomainGetPerfEvents

> > 
> > What would be the best way to get those PIDs? I tried using the XML file but
> > PID is hidden in there too. I took a look at QEMU Machine Protocol. Now I'm
> > going to walk /proc and match on guests names but it is not that elegant.
> > Any ideas?

Just to re-iterate. We hide it because users should not fiddle with the
VMs behind our backs.

> > 
> 
> `ps aux | grep $UUID | grep -v grep` ??

This will obviously work, but we won't give you an elegant way since we
don't want you to know the pid.
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