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

[Philippe Mathieu-Daudé]

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."?

>> Having tests doing runtime checking allow to:
>>
>> - have easier reviews, having less #ifdef'ry
>> - build them once for all targets
>> - build them once for all ./configure options
>>   (thinking about CI, the a single job could build the tests, then
>>   we run them using the QEMU binaries from other jobs)
>> - use the same binaries to test the built binary and the distribution
>>   installed one
>> - remove the dependencies between tests and binaries
>>
>>>
>>>>      g_test_init(&argc, &argv, NULL);
>>>>  
>>>>      qmp_schema_init(&schema);
>>>
>