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

[Knut Omang <knut.omang-QHcLZuEGTsvQT0dZR+AlfA@public.gmane.org>]

On Fri, 2019-05-10 at 10:12 +0200, Daniel Vetter wrote:
> On Fri, May 10, 2019 at 7:49 AM Knut Omang <knut.omang-QHcLZuEGTsvQT0dZR+AlfA@public.gmane.org> 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? 

No..

> Or is the plan to unify the KTF and
> Kunit in-kernel test harnesses? 

Since KTF delegates reporting and test running to user space - reporting is based on
netlink communication with the user land frontend (Googletest based, but can in principle
be ported to any user land framework if need be) - little specific test harness features
are needed for KTF, so there's little if no direct overlap with the infrastructure in
kselftests (as far as I understand, I'd like to spend more time on the details there..)

> Because there's tons of these
> in-kernel unit tests already, and every merge we get more (Frank's
> list didn't even look into drivers or anywhere else, e.g. it's missing
> the locking self tests I worked on in the past), and a more structured
> approach would really be good.

That's been my thinking too. Having a unified way to gradually move to would benefit
anyone who needs to relate to these tests in that there will be less to learn.
But that would be a long term evolutionary goal of course.

Also I think each of these test suites/sets would benefit from being more available for
running even in kernels not made specifically for testing, and I think using the module
structure and a lean, common module (ktf.ko) as a library for the tests, but no
"polluting" of the "production" kernel code with anything else, is a kind of a policy that
comes implicitly with KTF that can make it easier to maintain a sort of standard
"language" for writing kernel tests. 

Wrt KTF, we're working on making a suitable patch set for the kernel,
but also have projects running internally that uses KTF as a standalone git repository,
and that inspires new features and other changes, as well as a growing set of tests. 
I want to make sure we find a good candidate kernel integration that can coexist nicely
with the separate git repo version without becoming too much of a back/forward porting
challenge.

Knut

> -Daniel