Re: [PATCH v2 00/17] kunit: introduce KUnit, the Linux kernel unit testing framework

Frank Rowand
2019-05-10T05:18:30Z

On 5/9/19 4:40 PM, Logan Gunthorpe wrote:
>
>
> On 2019-05-09 5:30 p.m., Theodore Ts'o wrote:
>> On Thu, May 09, 2019 at 04:20:05PM -0600, Logan Gunthorpe wrote:
>>>
>>> The second item, arguably, does have significant overlap with kselftest.
>>> Whether you are running short tests in a light weight UML environment or
>>> higher level tests in an heavier VM the two could be using the same
>>> framework for writing or defining in-kernel tests. It *may* also be valuable
>>> for some people to be able to run all the UML tests in the heavy VM
>>> environment along side other higher level tests.
>>>
>>> Looking at the selftests tree in the repo, we already have similar items to
>>> what Kunit is adding as I described in point (2) above. kselftest_harness.h
>>> contains macros like EXPECT_* and ASSERT_* with very similar intentions to
>>> the new KUNIT_EXECPT_* and KUNIT_ASSERT_* macros.
>>>
>>> However, the number of users of this harness appears to be quite small. Most
>>> of the code in the selftests tree seems to be a random mismash of scripts
>>> and userspace code so it's not hard to see it as something completely
>>> different from the new Kunit:
>>>
>>> $ git grep --files-with-matches kselftest_harness.h *
>>
>> To the extent that we can unify how tests are written, I agree that
>> this would be a good thing.  However, you should note that
>> kselftest_harness.h is currently assums that it will be included in
>> userspace programs.  This is most obviously seen if you look closely
>> at the functions defined in the header files which makes calls to
>> fork(), abort() and fprintf().
>
> Ah, yes. I obviously did not dig deep enough. Using kunit for
> in-kernel tests and kselftest_harness for userspace tests seems like
> a sensible line to draw to me. Trying to unify kernel and userspace
> here sounds like it could be difficult so it's probably not worth
> forcing the issue unless someone wants to do some really fancy work
> to get it done.
>
> Based on some of the other commenters, I was under the impression
> that kselftests had in-kernel tests but I'm not sure where or if they
> exist.

YES, kselftest has in-kernel tests. (Excuse the shouting...)

Here is a likely list of them in the kernel source tree:

$ grep module_init lib/test_*.c
lib/test_bitfield.c:module_init(test_bitfields)
lib/test_bitmap.c:module_init(test_bitmap_init);
lib/test_bpf.c:module_init(test_bpf_init);
lib/test_debug_virtual.c:module_init(test_debug_virtual_init);
lib/test_firmware.c:module_init(test_firmware_init);
lib/test_hash.c:module_init(test_hash_init); /* Does everything */
lib/test_hexdump.c:module_init(test_hexdump_init);
lib/test_ida.c:module_init(ida_checks);
lib/test_kasan.c:module_init(kmalloc_tests_init);
lib/test_list_sort.c:module_init(list_sort_test);
lib/test_memcat_p.c:module_init(test_memcat_p_init);
lib/test_module.c:static int __init test_module_init(void)
lib/test_module.c:module_init(test_module_init);
lib/test_objagg.c:module_init(test_objagg_init);
lib/test_overflow.c:static int __init test_module_init(void)
lib/test_overflow.c:module_init(test_module_init);
lib/test_parman.c:module_init(test_parman_init);
lib/test_printf.c:module_init(test_printf_init);
lib/test_rhashtable.c:module_init(test_rht_init);
lib/test_siphash.c:module_init(siphash_test_init);
lib/test_sort.c:module_init(test_sort_init);
lib/test_stackinit.c:module_init(test_stackinit_init);
lib/test_static_key_base.c:module_init(test_static_key_base_init);
lib/test_static_keys.c:module_init(test_static_key_init);
lib/test_string.c:module_init(string_selftest_init);
lib/test_ubsan.c:module_init(test_ubsan_init);
lib/test_user_copy.c:module_init(test_user_copy_init);
lib/test_uuid.c:module_init(test_uuid_init);
lib/test_vmalloc.c:module_init(vmalloc_test_init)
lib/test_xarray.c:module_init(xarray_checks);

> If they do exists, it seems like it would make sense to
> convert those to kunit and have Kunit tests run-able in a VM or
> baremetal instance.

They already run in a VM.

They already run on bare metal.

They already run in UML.

This is not to say that KUnit does not make sense. But I'm still trying
to get a better description of the KUnit features (and there are
some).

-Frank