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

[Brendan Higgins]

On Fri, May 10, 2019 at 5:13 AM Knut Omang <knut.omang@xxxxxxxxxx> wrote:
> On Fri, 2019-05-10 at 03:23 -0700, Brendan Higgins wrote:
> > > On Fri, May 10, 2019 at 7:49 AM Knut Omang <knut.omang@xxxxxxxxxx> wrote:
> > > >
> > > > On Thu, 2019-05-09 at 22:18 -0700, Frank Rowand wrote:
> > > > > 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).
> > > >
> > > > FYI, I have a master student who looks at converting some of these to KTF, such as
> > for
> > > > instance the XArray tests, which lended themselves quite good to a semi-automated
> > > > conversion.
> > > >
> > > > The result is also a somewhat more compact code as well as the flexibility
> > > > provided by the Googletest executor and the KTF frameworks, such as running selected
> > > > tests, output formatting, debugging features etc.
> > >
> > > So is KTF already in upstream? Or is the plan to unify the KTF and
> >
> > I am not certain about KTF's upstream plans, but I assume that Knut
> > would have CC'ed me on the thread if he had started working on it.
>
> You are on the Github watcher list for KTF?

Yep! I have been since LPC in 2017.

> Quite a few of the commits there are preparatory for a forthcoming kernel patch set.
> I'll of course CC: you on the patch set when we send it to the list.

Awesome! I appreciate it.

>
> > > Kunit in-kernel test harnesses? Because there's tons of these
> >
> > No, no plan. Knut and I talked about this a good while ago and it
> > seemed that we had pretty fundamentally different approaches both in
> > terms of implementation and end goal. Combining them seemed pretty
> > infeasible, at least from a technical perspective. Anyway, I am sure
> > Knut would like to give him perspective on the matter and I don't want
> > to say too much without first giving him a chance to chime in on the
> > matter.
>
> I need more time to study KUnit details to say, but from a 10k feet perspective:
> I think at least there's a potential for some API unification, in using the same macro
> names. How about removing the KUNIT_ prefix to the test macros ;-) ?

Heh, heh. That's actually the way I had it in the earliest versions of
KUnit! But that was pretty much the very first thing everyone
complained about. I think I went from no prefix (like you are
suggesting) to TEST_* before the first version of the RFC at the
request of several people I was kicking the idea around with, and then
I think I was asked to go from TEST_* to KUNIT_* in the very first
revision of the RFC.

In short, I am sympathetic to your suggestion, but I think that is
non-negotiable at this point. The community has a clear policy in
place on the matter, and at this point I would really prefer not to
change all the symbol names again.

> That would make the names shorter, saving typing when writing tests, and storage ;-)
> and also make the names more similar to KTF's, and those of user land unit test

You mean the Googletest/Googlemock expectations/assertions?

It's a great library (with not so great a name), but unfortunately it
is written in C++, which I think pretty much counts it out here.

> frameworks? Also it will make it possible to have functions compiling both with KTF and
> KUnit, facilitating moving code between the two.

I think that would be cool, but again, I don't think this will be
possible with Googletest/Googlemock.

>
> Also the string stream facilities of KUnit looks interesting to share.

I am glad you think so!

If your biggest concern on my side is test macro names (which I think
is a no-go as I mentioned above), I think we should be in pretty good
shape once you are ready to move forward. Besides, I have a lot more
KUnit patches coming after this: landing this patchset is just the
beginning. So how about we keep moving forward on this patchset?