Re: [Qemu-devel] migrating instances from qemu-kvm to qemu

["Serge E. Hallyn" <serge@hallyn.com>]

Quoting Dr. David Alan Gilbert (dgilbert@redhat.com):
> * Serge E. Hallyn (serge@hallyn.com) wrote:
> 
> > Although, some people are using newer qemu with '-M pc-1.0'.  So we'd be
> > stopping thing from migrating to support the people coming from qemu-kvm.
> > Hmm.
> 
> What sometimes happens is that you create a VM (lets say with virt-manager)
> on an old installation, and it has the XML file for that VM which I think
> includes the machine type.   You upgrade your host or copy your VMs over
> and so you still use the old machine definition, and hence still have the
> -M pc-1.0

Right, but so long as it is a shutdown vm image, it shouldn't matter to
this case whether qemu 1.7 uses the old qemu-kvm cirrus vga ram size, or
the qemu ram size, right?

> Some people have snapshots rather than just disk images taken with particular
> versions and they expect those to be reloadable into newer versions.

Disk snapshots should be fine right?  Live snapshots no, but then
I didn't they were actually very well supported anyway.  In any case,
they point would remain that if x% of people have snapshots from qemu-kvm,
and the rest have snapshots created using qemu but older machine types,
then whether or not we change the values, either way the other x% or
100-x % will not be able to restore...

So still it seems the only sure way to handle this would be for qemu
to say "old vram size != new vram size;  so let me resize the vram".

-serge