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

["Emilio López" <emilio.lopez@collabora.co.uk>]

Hi,

El 28/03/16 a las 10:48, Emil Velikov escribió:
>>>> 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@collabora.co.uk>
>>>> Signed-off-by: Emilio López <emilio.lopez@collabora.co.uk>
>>>> ---
>>>>
>>>
>>>>    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?

Thanks,
Emilio

[0] 
https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/tools/testing/selftests/memfd/memfd_test.c#n2