linux-kernel - Re: [PATCH v3 6/6] Documentation: Add debugfs docs with run after boot

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Message-ID: <CABVgOS=JAn49ux6Cg2i1-V_2eNH4Utx_areqg4H1p5xwkT9FMA@mail.gmail.com>
Date:   Sat, 9 Dec 2023 15:57:59 +0800
From:   David Gow <davidgow@...gle.com>
To:     Rae Moar <rmoar@...gle.com>
Cc:     shuah@...nel.org, dlatypov@...gle.com, brendan.higgins@...ux.dev,
        sadiyakazi@...gle.com, keescook@...omium.org, arnd@...db.de,
        linux-kselftest@...r.kernel.org, linux-arch@...r.kernel.org,
        kunit-dev@...glegroups.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 6/6] Documentation: Add debugfs docs with run after boot

On Tue, 5 Dec 2023 at 06:19, Rae Moar <rmoar@...gle.com> wrote:
>
> Expand the documentation on the KUnit debugfs filesystem on the
> run_manual.rst page.
>
> Add section describing how to access results using debugfs.
>
> Add section describing how to run tests after boot using debugfs.
>
> Signed-off-by: Rae Moar <rmoar@...gle.com>
> ---

Looks good to me, some nitpicks below.

The other thing I'd really want to add is some documentation on
writing init-section suites, which covers the pitfalls better (as
mentioned in the previous emails). Though that could be a separate
patch if you want to keep this one debugfs-specific.

Otherwise,
Reviewed-by: David Gow <davidgow@...gle.com>

Cheers,
-- David

>
> Changes since v2:
> - Add info to documentation about cleaning up data, init tests, and
>   running tests concurrently
>
>  Documentation/dev-tools/kunit/run_manual.rst | 49 ++++++++++++++++++--
>  1 file changed, 45 insertions(+), 4 deletions(-)
>
> diff --git a/Documentation/dev-tools/kunit/run_manual.rst b/Documentation/dev-tools/kunit/run_manual.rst
> index e7b46421f247..aebb52ba9605 100644
> --- a/Documentation/dev-tools/kunit/run_manual.rst
> +++ b/Documentation/dev-tools/kunit/run_manual.rst
> @@ -49,9 +49,50 @@ loaded.
>
>  The results will appear in TAP format in ``dmesg``.
>
> +debugfs
> +=======
> +
> +``debugfs`` is a file system that enables user interaction with the files to
> +make kernel information available to user space (See more information at
> +Documentation/filesystems/debugfs.html)

Nit: reference debugfs.rst here, not debugfs.html -- sphinx ought to
update the link automatically.

Also, maybe we can make this introduction a _little_ bit more
KUnit-specific. I'd personally start by saying that KUnit can be
accessed from userspace via the debugfs filesystem (link), usually
mounted in /sys/kernel/debug/kunit, etc, if CONFIG_KUNIT_DEBUGFS is
enabled.

> +
> +By default, only the root user has access to the debugfs directory.
> +
> +If ``CONFIG_KUNIT_DEBUGFS`` is enabled, you can use KUnit debugfs
> +filesystem to perform the following actions.
> +
> +Retrieve Test Results
> +=====================
> +
> +You can use debugfs to retrieve KUnit test results. The test results are
> +accessible from the debugfs filesystem in the following read-only file:
> +
> +.. code-block :: bash
> +
> +       /sys/kernel/debug/kunit/<test_suite>/results
> +
> +The test results are available in KTAP format.

Do we want to note that this is a separate KTAP document, and so may
have different suite numbering from the dmesg log?

> +
> +Run Tests After Kernel Has Booted
> +=================================
> +
> +You can use the debugfs filesystem to trigger built-in tests to run after
> +boot. To run the test suite, you can use the following command to write to
> +the ``/sys/kernel/debug/kunit/<test_suite>/run`` file:
> +
> +.. code-block :: bash
> +
> +       echo "any string" > /sys/kernel/debugfs/kunit/<test_suite>/run
> +
> +As a result, the test suite runs and the results are printed to the kernel
> +log.
> +
> +However, this feature is not available with KUnit tests that use init data.

Let's expand this slightly, and mention that this is because the data
may have already been discarded, and that you can find such tests by
either looking for the kunit_test_init_section_suites() macro or the
is_init attribute.

> +
> +Also, you cannot use this feature to run tests concurrently as there is a
> +mutex lock around running KUnit tests at the same time.
> +

Instead of mentioning the mutex, which is an implementation detail,
just mention that tests will either wait for other tests to complete,
or fail having timed out.




>  .. note ::
>
> -       If ``CONFIG_KUNIT_DEBUGFS`` is enabled, KUnit test results will
> -       be accessible from the ``debugfs`` filesystem (if mounted).
> -       They will be in ``/sys/kernel/debug/kunit/<test_suite>/results``, in
> -       TAP format.
> +       For test authors, to use this feature, tests will need to correctly initialise
> +       and/or clean up any data, so the test runs correctly a second time.
> --
> 2.43.0.rc2.451.g8631bc7472-goog
>

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