Re: [Linux-kernel-mentees] [RFC 0/3] kunit: add support to use modules

[David Gow via Linux-kernel-mentees <linux-kernel-mentees@lists.linuxfoundation.org>]

On Wed, Jul 15, 2020 at 11:11 AM Vitor Massaru Iha <vitor@massaru.org> wrote:
>
> Currently, KUnit does not allow the use of tests as a module.
> This prevents the implementation of tests that require userspace.

If this is what I think it is, thanks! I'll hopefully get a chance to
play with it over the next few days.

Can we clarify what this means: the current description is a little
misleading, as KUnit tests can already be built and run as modules,
and "tests that require userspace" is a bit broad.

As I understand it, this patchset does three things:
- Let kunit_tool install modules to a root filesystem and boot UML
with that filesystem.
- Have tests inherit the mm of the process that started them, which
(if the test is in a module), provides a user-space memory context so
that copy_{from,to}_user() works.
- Port the test_user_copy.c tests to KUnit, using this new feature.

A few comments from my quick glance over it:
- The rootfs support is useful: I'm curious how it'll interact with
non-UML architectures in [1]. It'd be nice for this to be extensible
and to not explicitly state UML where possible.
- The inheriting of the mm stuff still means that
copy_{from,to}_user() will only work if loaded as a module. This
really needs to be documented. (Ideally, we'd find a way of having
this work even for built-in tests, but I don't have any real ideas as
to how that could be done).
- It'd be nice to split the test_user_copy.c test port into a separate
commit. In fact, it may make sense to also split the kunit_tool
changes and the mm changes into separate series, as they're both quite
useful independently.

Cheers,
-- David

> This patchset makes this possible by introducing the use of
> the root filesystem in KUnit. And it allows the use of tests
> that can be compiled as a module
>
> Vitor Massaru Iha (3):
>   kunit: tool: Add support root filesystem in kunit-tool
>   lib: Allows to borrow mm in userspace on KUnit
>   lib: Convert test_user_copy to KUnit test
>
>  include/kunit/test.h                        |   1 +
>  lib/Kconfig.debug                           |  17 ++
>  lib/Makefile                                |   2 +-
>  lib/kunit/try-catch.c                       |  15 +-
>  lib/{test_user_copy.c => user_copy_kunit.c} | 196 +++++++++-----------
>  tools/testing/kunit/kunit.py                |  37 +++-
>  tools/testing/kunit/kunit_kernel.py         | 105 +++++++++--
>  7 files changed, 238 insertions(+), 135 deletions(-)
>  rename lib/{test_user_copy.c => user_copy_kunit.c} (55%)
>
>
> base-commit: 725aca9585956676687c4cb803e88f770b0df2b2
> prerequisite-patch-id: 582b6d9d28ce4b71628890ec832df6522ca68de0
> --
> 2.26.2
>
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