linux-kernel - Re: [PATCH 1/2] kunit: Expose 'static stub' API to redirect functions

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Date:   Sat, 17 Dec 2022 00:09:38 -0500
From:   Brendan Higgins <brendanhiggins@...gle.com>
To:     David Gow <davidgow@...gle.com>
Cc:     Brendan Higgins <brendan.higgins@...ux.dev>,
        Shuah Khan <skhan@...uxfoundation.org>,
        Daniel Latypov <dlatypov@...gle.com>,
        Kees Cook <keescook@...omium.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Joe Fradley <joefradley@...gle.com>,
        Steve Muckle <smuckle@...gle.com>,
        Jonathan Corbet <corbet@....net>,
        linux-kselftest@...r.kernel.org, kunit-dev@...glegroups.com,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] kunit: Expose 'static stub' API to redirect functions

On Thu, Dec 8, 2022 at 1:18 AM 'David Gow' via KUnit Development
<kunit-dev@...glegroups.com> wrote:
>
> Add a simple way of redirecting calls to functions by including a
> special prologue in the "real" function which checks to see if the
> replacement function should be called (and, if so, calls it).
>
> To redirect calls to a function, make the first (non-declaration) line
> of the function:
>
>         KUNIT_STATIC_STUB_REDIRECT(function_name, [function arguments]);
>
> (This will compile away to nothing if KUnit is not enabled, otherwise it
> will check if a redirection is active, call the replacement function,
> and return. This check is protected by a static branch, so has very
> little overhead when there are no KUnit tests running.)
>
> Calls to the real function can be redirected to a replacement using:
>
>         kunit_activate_static_stub(test, real_fn, replacement_fn);
>
> The redirection will only affect calls made from within the kthread of
> the current test, and will be automatically disabled when the test
> completes. It can also be manually disabled with
> kunit_deactivate_static_stub().
>
> The 'example' KUnit test suite has a more complete example.
>
> Co-developed-by: Daniel Latypov <dlatypov@...gle.com>
> Signed-off-by: Daniel Latypov <dlatypov@...gle.com>
> Signed-off-by: David Gow <davidgow@...gle.com>

Reviewed-by: Brendan Higgins <brendanhiggins@...gle.com>