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

Brendan Higgins
2019-05-14T06:40:03Z

On Sat, May 11, 2019 at 08:17:47AM +0200, Knut Omang wrote:
> On Fri, 2019-05-10 at 15:18 -0700, Frank Rowand wrote:
> > On 5/10/19 1:54 PM, Brendan Higgins wrote:
> > > On Fri, May 10, 2019 at 5:13 AM Knut Omang <knut.omang@oracle.com> 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@oracle.com> 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.
> >
> > This would not be the first time that a patch submitter has been
> > told "do B instead of A" for version 1, then told "do C instead of
> > B" for version 2, then told "do A instead of C" for the final version.
> >
> > It sucks, but it happens.

Sure, I have been there before, but I thought those original opinions
were based on a pretty well established convention. Also, I don't think
those original opinions have changed. If they have, please chime in and
correct me.

> Sorry, I must have overlooked the B instead of A instance - otherwise
> I would have objected against it - in addition to the recognizability
> and portability issue I think it is important that these primitives are
> not unnecessary long since they will be written a *lot* of times if things go
> our way.

I get that. That is why I thought I might have been worthy of an
exception. It is definitely easier to write EXPECT_EQ(...) than
KUNIT_EXPECT_EQ(...) or TEST_EXPECT_EQ(...), but no one else seemed to
agree in the past.

Even now, it is only you (and maybe Frank?) telling me to change it; I
would like to maybe hear Shuah, Kees, or Greg chime in on this before I
go about actually chaning it back, as I distinctly remember each of them
telling me that I should go with KUNIT_*.

> And the reason for using unique names elsewhere is to be able to co-exist with
> other components with the same needs. In the case of tests, I believe they are

That's the policy I was talking about.

> in a different category, they are not supposed to be part of production kernels,
> and we want them to be used all over, that should warrant having the ASSERT_ and EXPECT_
> prefixes "reserved" for the purpose, so I would urge some pragmatism here!

I don't disagree. Again, this is what I initially proposed, but no one
agreed with me on this point.

I am not saying no. Nevertheless, this is a pretty consistently applied
pattern for new stuff, and I would really prefer not to make waves on
something that really doesn't matter all that much.

So like I said, if we can get some more discussion on this and it seems
like broad consensus says we can reserve ASSERT_* and EXPECT_*, then I
will go along with it.

> > As an aside, can you point to where the "clear policy in place" is
> > documented, and what the policy is?

Global namespacing policy that Knut mentioned above.

> >
> > -Frank
> >
> >
> > >> 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.
>
> Using a similar syntax is a good thing, since it makes it easier for people
> who write tests in user land frameworks to contribute to the kernel tests.
> And if, lets say, someone later comes up with a way to run the KUnit tests in "real"
> user land within Googletest ;-) then less editing would be needed..
>
> > >> 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.
>
> I was thinking of moves between KUnit tests and KTF tests, kernel code only.
> Some test functions may easily be usable both in a "pure" mocking environment
> and in an integrated setting with hardware/driver/userspace dependencies.

Speaking for KUnit, you are right. I got KUnit working on other
architectures a couple revisions ago (apparently I didn't advertise that
well enough).

> > >>
> > >> 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?
>
> I think the importance of a well thought through
> test API definition is not to be underestimated

I agree. That is why I am saying that I think we are in good shape if we
are only arguing about the name.

> - the sooner we can unify and establish a common base, the better,
> I think.

Again, I agree. That is what I am trying to do here.

>
> My other concern is, as mentioned earlier, whether UML is really that
> different from just running in a VM wrt debugging support, and that
> there exists a better approach based on automatically generating
> an environment where the test code and the source under test
> can be compiled in a normal user land program. But it seems
> there are enough clients of the UML approach to justify it
> as a lightweight entry. We want to make it easy and inexcusable
> not to test the code, having a low bar of entry is certainly good.

Yep.

> Other than that, I really would need to spend some more time with
> the details on KUnit to verify my so far fairly
> shallow observations!

Are we arguing about anything other than naming schemes here? If that's
it, we can refactor the under the hood stuff later; if we even need to
at all.

Cheers!