Re: [RFC PATCH 6/8] tests/qtest/libqtest: Allow checking for HVF accelerator

[Philippe Mathieu-Daudé]

On 20/1/23 11:26, Thomas Huth wrote:
> On 19/01/2023 13.05, Thomas Huth wrote:
> > On 19/01/2023 12.30, Philippe Mathieu-Daudé wrote:
> > > On 19/1/23 12:24, Thomas Huth wrote:
> > > > On 19/01/2023 11.05, Philippe Mathieu-Daudé wrote:
> > > > > Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
> > > > > ---
> > > > > RFC: CONFIG_HVF is poisoned.
> > > > >
> > > > > We could pass host config definitions to qtest using:
> > > > >
> > > > >    diff --git a/meson.build b/meson.build
> > > > >    @@ -2547,6 +2547,7 @@ foreach target : target_dirs
> > > > >
> > > > >       accel_kconfig = []
> > > > >       foreach sym: accelerators
> > > > >    +    config_host_data.set(sym + '_QTEST', '')
> > > > >         if sym == 'CONFIG_TCG' or target in 
> > > > > accelerator_targets.get(sym, [])
> > > > >           config_target += { sym: 'y' }
> > > > >           config_all += { sym: 'y' }
> > > > >
> > > > > Then test for CONFIG_HVF_QTEST ...
> > > >
> > > > I don't think that would really work well. The qtests are build once 
> > > > for all targets, and HVF is only available in the target that 
> > > > matches the host architecture. It's poisoned on purpose.
> > > >
> > > > The TCG accelerator is special, since we have it in either none or 
> > > > in all targets, that's why we can use CONFIG_TCG there.
> > > >
> > > > The kvm part is also rather a hack... we should maybe rather 
> > > > additionally use the "query-kvm" QAPI command to check whether it is 
> > > > really available...?
> > > >
> > > > To fix this properly for HVF, I think you'd need a way to query the 
> > > > available accelerators via QMP, too... Hmmm, weren't there some 
> > > > patches for something like that in the past ... can't remember right 
> > > > now ...
> > >
> > > https://lore.kernel.org/qemu-devel/20210505125806.1263441-3-philmd@redhat.com/ 
> > > :(
> >
> > Ah, right, and we ended up with the competing patch from Igor since we 
> > could not quite settle on the QAPI extensions?
> >
> > Hmm, what happens if you execute "query-qmp-schema" on a HVF-enabled 
> > host these days? Is there a "hvf"-related entry somewhere in the 
> > response?
>
> Alternative idea: execute QEMU once with "-accel help" via 
> g_spawn_command_line_sync() or g_spawn_sync() once and look for the 
> accelerator in the standard output.

There is no stability guaranty with the help output.

QMP is a stable API, we should really rely on it here IMO.