Re: [PATCH v4 10/12] qtest/qmp-cmd-test: Make test build-independent from accelerator

[Markus Armbruster <armbru@redhat.com>]

Philippe Mathieu-Daudé <philmd@redhat.com> writes:

> On 4/29/21 3:22 PM, Markus Armbruster wrote:
>> Philippe Mathieu-Daudé <philmd@redhat.com> writes:
>>>>> Now than we can probe if the TCG accelerator is available
>>>>> at runtime with a QMP command, do it once at the beginning
>>>>> and only register the tests we can run.
>>>>> We can then replace the #ifdef'ry by a runtime check.
>>>>>
>>>>> Suggested-by: Paolo Bonzini <pbonzini@redhat.com>
>>>>> Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
>>>>
>>>> Please read the last remark first.  The other ones are detail; feel free
>>>> to skip them until we're done with the last one.
>>>>
>>>>> ---
>>>>>  tests/qtest/qmp-cmd-test.c | 18 ++++++++++++++----
>>>>>  1 file changed, 14 insertions(+), 4 deletions(-)
>>>
>>>>> +    tcg_accel_available = qtest_has_accel("tcg");
>>>>> +
>>>>
>>>> When does tcg_accel_available differ from defined(CONFIG_TCG)?
>>>
>>> qtest_has_accel("tcg") is a runtime check, while defined(CONFIG_TCG)
>>> is build-time.
>> 
>> Let me rephrase my question: under what conditions can the values of
>> qtest_has_accel("tcg") and defined(CONFIG_TCG) differ?
>
> They are currently the same, so this patch is a no-op. *But* it
> allows us to remove the global dependence on CONFIG_TCG in the
> Meson machinery (see the last commit in this series).
>
> Is that missing part of the commit description?
>
> "This will allow us to remove the global CONFIG_TCG dependency
> in our Meson machinery in a pair of commits."?

Do you mean "in the next two commits"?

Please also note that the probing at run-time always gives the same
result as the compile-time check it replaces.

I don't understand what exactly the conversion to probing enables and
how, but I believe I don't have to.

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