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Subject: Re: [PATCH v2 00/17] kunit: introduce KUnit, the Linux kernel unit
 testing framework
From:   Knut Omang <knut.omang@oracle.com>
To:     Frank Rowand <frowand.list@gmail.com>,
        Logan Gunthorpe <logang@deltatee.com>,
        "Theodore Ts'o" <tytso@mit.edu>, Tim.Bird@sony.com,
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        linux-um@lists.infradead.org, Alexander.Levin@microsoft.com,
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        mpe@ellerman.id.au, pmladek@suse.com, richard@nod.at,
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Date:   Fri, 10 May 2019 07:48:35 +0200
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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.

Knut

> -Frank