Message-ID: <CAGS_qxp9fjKyw4z3sE2TDRrXB3=mMCcomcRq=CszOFLzsw6yNA@mail.gmail.com>
Date:   Sat, 2 Oct 2021 11:11:15 -0700
From:   Daniel Latypov <dlatypov@...gle.com>
To:     Marcelo Schmitt <marcelo.schmitt1@...il.com>
Cc:     brendanhiggins@...gle.com, andy.li@...soc.com,
        andersonreisrosa@...il.com, linux-kernel@...r.kernel.org,
        kunit-dev@...glegroups.com
Subject: Re: [PATCH] kunit: mock: add support for function mocks with no parameters

On Sat, Oct 2, 2021 at 11:09 AM Daniel Latypov <dlatypov@...gle.com> wrote:
>
> On Mon, Sep 27, 2021 at 9:44 AM Daniel Latypov <dlatypov@...gle.com> wrote:
> >
> > [2]
> > On Sat, Sep 25, 2021 at 12:30 PM Marcelo Schmitt
> > <marcelo.schmitt1@...il.com> wrote:
> > >
> > > Hi Daniel,
> > >
> > > Thanks for your review.
> > >
> > > On 09/21, Daniel Latypov wrote:
> > > > On Sat, Sep 18, 2021 at 12:44 PM Marcelo Schmitt
> > > > <marcelo.schmitt1@...il.com> wrote:
> > > > >
> > > > > Function mocks defined with DEFINE_FUNCTION_MOCK(...) do not support
> > > > > empty parameters list due to strict function prototypes enforcement
> > > > > (-Werror=strict-prototypes). Add support for function mocks with no
> > > > > parameters by adding checks to declare strict function prototypes when
> > > > > an empty param list is provided.
> > > > > Further, add an expectation to test that the generated code works.
> > > > >
> > > > > Co-developed-by: Anderson Reis Rosa <andersonreisrosa@...il.com>
> > > > > Signed-off-by: Anderson Reis Rosa <andersonreisrosa@...il.com>
> > > > > Signed-off-by: Marcelo Schmitt <marcelo.schmitt1@...il.com>
> > > >
> > > > Meta: kunit/alpha/master isn't really maintained anymore.
> > > > I think David and myself having some commits from this year might give
> > > > the wrong impression.
> > > > But all of my patches in 2021 were to make it easier to get people to
> > > > *move away* from kunit/alpha/master ;)
> > >
> > > We can't submit it upstream because the mock stuff isn't there yet.
> > > By the way, as nothing from mocking is upstream and kunit/alpha/master is
> > > being frozen somewhat, what tree/branch should we base our work on if we
> > > decide to develop more on the mocking framework?
> > > I recall the branch with the POC for mocking was at
> > > https://kunit-review.googlesource.com/c/linux/+/1114
> > > Should we use this branch to base future work on mocking?
> > > Or will the mocking framework be discontinued?
> >
> > All the mocking stuff is in limbo at the moment.
> > The v2 of the class mocking RFC was sent out Oct 2020,
> > https://lore.kernel.org/linux-kselftest/20201012222050.999431-1-dlatypov@google.com/
> >
> > Until we have user interest in mocking support, that RFC will likely
> > just sit there.
> > Or maybe we scrap it and just introduce the functionality piece by piece.
> >
> > There's https://kunit.dev/mocking.html which talks about how one can
> > implement mocking on their own, or (better yet) write fakes while
> > leveraging KUnit.
> > If we start seeing adoption of that, we can start factoring out
> > functionality into shared code as needed, e.g. support for saying a
> > mock should be called N times, then maybe gradually the parameter
> > matchers and return values, etc.
> >
> > I missed it, but I know David and Brendan talked a bit about this in
> > their recent LPC talk, https://youtu.be/Y_minEhZNm8?t=15905
> >
> > >
> > > Sorry for asking so many questions. We just want to help to enhance KUnit.
> >
> > No worries, and we really appreciate it.
> >
> > > We can work on something else besides mocking if it makes more sense to the
> > > project.
> >
> > Mocking doesn't feel like an area where we can expect to see progress right now.
> > In terms of other KUnit features we know would be useful now, I think
> > it's mostly just [1] and [2], which hopefully will land in 5.16.
>
> To be clear, if anyone thinks up a useful feature, that'd be great.
> I personally am just out of ideas at the moment, and I think so are
> Brendan and David.
>
> We'd want to prioritize features that can improve existing tests or
> unblock known new tests.
> Mocking in the alpha version of KUnit is a case where a feature
> sounded really good on paper and had a bunch of bells and whistles
> (e.g. strict/nice/naggy mocks support, etc.) but was perhaps
> overengineered and thus failed to find a home upstream.
>
> But I just thought of a few more things we could do in the kunit.py script.
> I think we have more room for improvement there than in the in-kernel
> part of KUnit right now, but I assume it's the more boring part for
> most people.
>
> One thing I'd really like to see is getting code coverage to work in
> kunit.py while using QEMU.
> We have a process for doing so under UML here:
> https://lore.kernel.org/linux-kselftest/20210901190623.315736-1-rmoar@google.com/

wrong copy-paste, meant
https://www.kernel.org/doc/html/latest/dev-tools/kunit/running_tips.html#generating-code-coverage-reports-under-uml

> UML actually uses a different coverage implementation than normal, so
> there's a few things that would need to change.
>
> We can build and run against "normal" coverage kernels pretty easily:
>
> $ cat >qemu_coverage_kunitconfig <<EOF
> CONFIG_KUNIT=y
> CONFIG_KUNIT_EXAMPLE_TEST=y
> CONFIG_GCOV_KERNEL=y
> CONFIG_DEBUG_FS=y
> CONFIG_GCOV_PROFILE_ALL=y
> EOF
> $ ./tools/testing/kunit/kunit.py run --arch=x86_64
> --kunitconfig=qemu_coverage_kunitconfig
>
> The problem is we'd need to copy the coverage data off the VM instead
> of just letting it shutdown when tests are done.
> If we had a userspace running, we'd basically do something like
> $ scp -r user@vm:/sys/kernel/debug/gcov .
> <some stuff to get these files in the right spot under .kunit/>
> <then we'd run lcov and genhtml, just like we do for UML>
>
> Normal KUnit tests definitely don't want to have to have the overhead
> of running a userspace, so the implementation might look like a
> "--qemu_coverage" flag, or maybe a set of generic flags that would
> give a user enough control over the VM to do this.
> Or maybe the right answer is to not involve kunit.py at all.
>
> Not sure if that sounds interesting to you or anyone.
>
> >
> > I think right now we probably need more tests written to have a better
> > idea of what else we could/should do.
> > Partly because of that, David is trying to get the ball rolling on
> > testing ext4. We're also hopeful that it'll be easier to add tests if
> > adjacent code is already tested (sharing fakes, conventions, ability
> > to copy-paste, etc.).
> >
> > [1] https://git.kernel.org/pub/scm/linux/kernel/git/shuah/linux-kselftest.git/commit/?h=kunit&id=3b29021ddd10cfb6b2565c623595bd3b02036f33
> > [2] https://lore.kernel.org/linux-kselftest/20210909001037.2842954-1-dlatypov@google.com/
> >
> >

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