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

[Dr. David Alan Gilbert]

* Daniel P. Berrangé (berrange@redhat.com) wrote:
> On Wed, Feb 16, 2022 at 05:40:44PM +0000, Dr. David Alan Gilbert wrote:
> > * Thomas Huth (thuth@redhat.com) wrote:
> > > On 16/02/2022 12.01, 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?
> > > 
> > > I agree with Gerd. Getting rid of a default machine on x86 is likely 
> > > better
> > > than silently changing it to q35. But I'd maybe say that this should go
> > > through the deprecation process first?
> > 
> > So just adding something like the following under 'System emulator
> > machines':
> > 
> > x86 default machine type
> > ------------------------
> > 
> > x86 currently defaults to the very old ```pc``` machine type
> > which is based on the very old ```i440f``` chipset.  This default
> > will be removed and the user will be required to specify a machine
> > type explicitly using -M; users are encouraged to switch to the
> > not quite as old ```q35``` machine types.
> > 
> > 
> > (This option is going to take a lot more work switching all the
> > test cases over; in my world here I'd only changed the tests that broke
> > on q35, now everything is going to need to specify a type).
> 
> ....which is still nothing compared to how many users will be impacted
> and the docs all over the internet we'll never be able to change, which
> give illustrations using qemu command lines without '-M pc'

What's your prreference - it sounds like you'd prefer to leave the
default as 'pc' ?

aarch's message is:
qemu-system-aarch64: No machine specified, and there is no default
Use -machine help to list supported machines

We could add a:
'Use -machine pc for the old default behaviour'

Dave

> Regards,
> Daniel
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-- 
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK