Re: [RFC PATCH 3/4] hw/acpi: add VM generation counter field to VMClock

["Daniel P. Berrangé" <berrange@redhat.com>]

On Mon, Dec 01, 2025 at 02:29:57PM +0000, David Woodhouse wrote:
> On Mon, 2025-12-01 at 14:12 +0000, Daniel P. Berrangé wrote:
> > From QEMU's POV, live migration and snapshots
> > are indistiguishable operations, both using the same functionaility.
> > 
> > eg
> >   $ qemu-system-x86_64 -monitor stdio -device vmclock
> >   (qemu) migrate file:snapshot.img
> > 
> > and
> > 
> >   $ qemu-system-x86_64 -monitor stdio -device vmclock -incoming file:snapshot.img
> > 
> > 
> > and we can't check the QEMU migration target being "file:" and mgmt
> > apps can use the "fd:" protocol to pass in a pre-opened target which can
> > be a socket or pipe or file.
> 
> What triggers the vmgenid to actually get updated for a snapshot?
> That's the condition we're after, isn't it?

I don't quiet understand the sequences, but libvirt is involved in setting
guid=nnnn as an arg to -device vmgenid when it spawns QEMU. This means
libvirt has control over when it is changed or not.

With regards,
Daniel
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