Re: [RFC PATCH v1 1/9] selftest: sync: basic tests for sw_sync framework

[Emil Velikov]

On 4 April 2016 at 05:12, Emilio LÃpez <emilio.lopez@xxxxxxxxxxxxxxx> wrote:
> Hi,
>
> El 28/03/16 a las 10:48, Emil Velikov escribiÃ:
>
>>>>> These tests are based on the libsync test suite from Android.
>>>>> This commit lays the ground for future tests, as well as includes
>>>>> tests for a variety of basic allocation commands.
>>>>>
>>>>> Signed-off-by: Gustavo Padovan <gustavo.padovan@xxxxxxxxxxxxxxx>
>>>>> Signed-off-by: Emilio LÃpez <emilio.lopez@xxxxxxxxxxxxxxx>
>>>>> ---
>>>>>
>>>>
>>>>>    tools/testing/selftests/sync/sync.h       | 119 ++++++++++++++++++
>>>>
>>>>
>>>> Admittedly I know nothing about the kernel selftests although copying
>>>> the UAPI header, seems to defeat the purpose of this exercise.
>>>> Shouldn't one reuse the existing header ? It would even cause issues
>>>> as the interface gets updated (iirc Gustavo changed the ioctl numbers
>>>> and/or header name with latter series).
>>>
>>>
>>>
>>> The problem is that one cannot use the system header without having built
>>> and installed the kernel first, which is rather problematic for eg.
>>> crosscompiling or virtualization. I discussed this with Gustavo and we
>>> agreed that the best way forward would be to copy the interfaces, as
>>> suggested by kernelnewbies' wiki[0]:
>>>
>> In the case of using a system header one can just `make
>> headers_install' without building the kernel, as mentioned in the very
>> same page ;-) Although I wasn't thinking that one should be using the
>> header already available in tree. After all this series is not
>> supposed to land before Gustavo's work, is it ?
>>
>>  From a quick skim though the selftests, I cannot see cases where UAPI
>> headers are copied/duplicated.
>>
>>> """
>>> The correct way to address this problem is to isolate the specific
>>> interfaces that you need, e.g. a single header file that is patched in a
>>> new
>>> kernel providing the ioctl numbers for a character device used by your
>>> program. In your own program, add a copy of that source file, with a
>>> notice
>>> that it should be kept in sync with new kernel versions.
>>> """
>>
>> My understanding of the article is that it refers to building user
>> space programs that do _not_ live in the same tree as the kernel. Am I
>> missing something ?
>
>
> When I tried using the header directly from the kernel tree, the compiler
> told me not to do that and pointed me to that kernelnewbies page; I could
> try overriding the check like I see memfd does[0] but I don't know if that's
> the way to go. Shuah, what's your thoughts on this?
>
Afaics the warning comes up, as the uapi header gets picked up prior
to the normal one (in include/).

Thus by reordering the includes things should work. One could even do
a similar thing for memfd and drop the hack(?). Then again, not sure
what's the policy on any of this is. I'm thinking that it should be
documented somewhere, but I could not find anything :-\

Regards,
Emil