Re: [PATCH 3/3] x86: Switch to q35 as the default machine type

[Daniel P . Berrangé]

On Wed, Feb 16, 2022 at 11:01:24AM +0000, Dr. David Alan Gilbert wrote:
> * Gerd Hoffmann (kraxel@redhat.com) wrote:
> >   Hi,
> >  
> > > Given the semantic differences from 'i440fx', changing the default
> > > machine type has effects that are equivalent to breaking command
> > > line syntax compatibility, which is something we've always tried
> > > to avoid.
> > 
> > And if we are fine breaking backward compatibility I'd rather *not* pick
> > a default, effectively making -M $something mandatory, similar to arm.
> 
> Oh, that's probably easy to do;  what are other peoples thoughts on
> that?

On the libvirt side it won't matter & will have no effect. Libvirt ignores
QEMU defaults an explicitly sets 'pc' as the default, so that our users
are protected against QEMU changes in defaults that could break app usage.

We would of course suggest that all apps using libvirt explicitly pick
a machine type they want, but if they dont, we'll set it for them and
guarantee that default won't change as long as the machine type exists
in QEMU.

IOW, whether QEMU selects 'q35' or <nothing at all>  as the default
machine, libvirt will continue to set 'pc' as the default in absence
of a mgmt app explicit choice.

Regards,
Daniel
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