Re: VM id in KVM?

["Daniel P. Berrange" <berrange-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>]

On Mon, Jul 23, 2007 at 02:19:41PM +0300, Avi Kivity wrote:
> Avi Kivity wrote:
> > Carsten Otte wrote:
> >> Avi Kivity wrote:
> >>>  From a Linux point of view, the pid identifies the VM.  A 
> >>> management application can, however, use its own VM identifiers as 
> >>> it sees fit, and map the (possibly persistent, gloablly unique, and 
> >>> ridiculously long) VMID to the pid.
> >> It might be preferable to have something that is persistent over 
> >> guest migration. Makes life easier for the management application as 
> >> far as I see.
> >
> > It may make sense to add a vmid to qemu (or to keep it in the 
> > management application entirely).  Certainly the kernel doesn't need 
> > to know about it.
> >
> 
> I take it back.  The only entity that can enforce uniqueness is the 
> management application, therefore that should be the entity that knows 
> about them.

When managing QEMU & KVM guests, libvirt provides 3 identifiers with
varying levels of uniqueness

 - ID - a integer unique amongst all active guests on a host
 - Name - a string uninque amongst all active & inactive guests on a host
 - UUID - 32 byte hex string unique globally

We don't expose the PID directly of the QEMU binary directly. Name and UUID
are both stable across migration - the ID changes upon migration. As Avi 
says I dont't see how a individual QEMU process could provide any meaningful
identifier itself aside from its PID whose uniqueness is guarenteed by the
OS on its behalf.

Regards,
Dan.
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