Re: [PATCH] ext: EXT4_KUNIT_TESTS should depend on EXT4_FS instead of selecting it

[Brendan Higgins]

On Wed, Oct 21, 2020 at 3:36 PM Theodore Y. Ts'o <tytso@xxxxxxx> wrote:
>
> On Wed, Oct 21, 2020 at 02:16:56PM -0700, Randy Dunlap wrote:
> > On 10/21/20 2:15 PM, Brendan Higgins wrote:
> > > On Tue, Oct 20, 2020 at 12:37 AM Geert Uytterhoeven
> > > <geert@xxxxxxxxxxxxxx> wrote:
> > >>
> > >> EXT4_KUNIT_TESTS selects EXT4_FS, thus enabling an optional feature the
> > >> user may not want to enable.  Fix this by making the test depend on
> > >> EXT4_FS instead.
> > >>
> > >> Fixes: 1cbeab1b242d16fd ("ext4: add kunit test for decoding extended timestamps")
> > >> Signed-off-by: Geert Uytterhoeven <geert@xxxxxxxxxxxxxx>
> > >
> > > If I remember correctly, having EXT4_KUNIT_TESTS select EXT4_FS was
> > > something that Ted specifically requested, but I don't have any strong
> > > feelings on it either way.
> >
> > omg, please No. depends on is the right fix here.
>
> So my requirement which led to that particular request is to keep what
> needs to be placed in .kunitconfig to a small and reasonable set.
>
> Per Documentation/dev-tools/kunit, we start by:
>
>     cd $PATH_TO_LINUX_REPO
>     cp arch/um/configs/kunit_defconfig .kunitconfig
>
> we're then supposed to add whatever Kunit tests we want to enable, to wit:
>
> CONFIG_EXT4_KUNIT_TESTS=y
>
> so that .kunitconfig would look like this:
>
> CONFIG_KUNIT=y
> CONFIG_KUNIT_TEST=y
> CONFIG_KUNIT_EXAMPLE_TEST=y
> CONFIG_EXT4_KUNIT_TESTS=y
>
> ... and then you should be able to run:
>
> ./tools/testing/kunit/kunit.py run
>
> ... and have the kunit tests run.  I would *not* like to have to put a
> huge long list of CONFIG_* dependencies into the .kunitconfig file.
>
> I'm don't particularly care how this gets achieved, but please think
> about how to make it easy for a kernel developer to run a specific set
> of subsystem unit tests.  (In fact, being able to do something like
> "kunit.py run fs/ext4 fs/jbd2" or maybe "kunit.py run fs/..." would be
> *great*.  No need to fuss with hand editing the .kunitconfig file at
> all would be **wonderful**.

So you, me, Luis, David, and a whole bunch of other people have been
thinking about this problem for a while. What if we just put
kunitconfig fragments in directories along side the test files they
enable?

For example, we could add a file to fs/ext4/kunitconfig which contains:

CONFIG_EXT4_FS=y
CONFIG_EXT4_KUNIT_TESTS=y

We could do something similar in fs/jdb2, etc.

Obviously some logically separate KUnit tests (different maintainers,
different Kconfig symbols, etc) reside in the same directory, for
these we could name the kunitconfig file something like
lib/list-test.kunitconfig (not a great example because lists are
always built into Linux), but you get the idea.

Then like Ted suggested, if you call kunit.py run foo/bar, then

if bar is a directory, then kunit.py will look for foo/bar/kunitconfig

if bar is a file ending with .kunitconfig like foo/bar.kunitconfig,
then it will use that kunitconfig

if bar is '...' (foo/...) then kunit.py will look for all kunitconfigs
underneath foo.

Once all the kunitconfigs have been resolved, they will be merged into
the .kunitconfig. If they can be successfully merged together, the new
.kunitconfig will then continue to function as it currently does.

What do people think about this?