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

[Thomas Huth <thuth@redhat.com>]

On 20/01/2023 12.18, Philippe Mathieu-Daudé wrote:
> 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.

Sure, it's rather meant as a temporary solution until a proper QMP method is 
in place. We also have the advantage here that it is internal to the QEMU 
repository only - it's not like libvirt or some other upper layers are 
trying to parse the output here.

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

I agree, QMP should certainly be the final goal.

  Thomas