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

[Thomas Huth]

On 16/02/2022 18.40, 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

I'd scrath the "very old" above since you repeat it below...

> 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.

... but otherwise this sounds good to me.

> (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).

We've got a bunch of targets now already that do not have a default machine 
type yet (aarch64/arm, avr, rx, tricore), and some where the default machine 
type does not make too much sense for testing anyway (e.g. m68k) ... so it 
would maybe be good to have a global qtest_get_default_machine() function in 
the qtest framework anyway instead of re-encoding this in each and every 
test case.

Anyway, if we agree that the default machine type of x86 should go through 
the deprecation process, we've got plenty of time to fix this up in the 
tests, no need to rush this now before 7.0.

Other heretic question: Should we maybe get rid of the default machine type 
for *all* targets? ... so that we do not continue to run into this issue 
again and again and again...

 Thomas