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

["Philippe Mathieu-Daudé" <philmd@linaro.org>]

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.