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SubjectRe: [RFC PATCH 0/2] kunit: Support redirecting function calls
+Steve Muckle - since I think this might affect things he is working on.

On Thu, Mar 17, 2022 at 10:13 PM David Gow <davidgow@google.com> wrote:
>
> When writing tests, it'd often be very useful to be able to intercept
> calls to a function in the code being tested and replace it with a
> test-specific stub. This has always been an obviously missing piece of
> KUnit, and the solutions always involve some tradeoffs with cleanliness,
> performance, or impact on non-test code. See the folowing document for
> some of the challenges:
> https://kunit.dev/mocking.html
>
> This series consists of two prototype patches which add support for this
> sort of redirection to KUnit tests:
>
> 1: static_stub: Any function which might want to be intercepted adds a
> call to a macro which checks if a test has redirected calls to it, and
> calls the corresponding replacement.
>
> 2: ftrace_stub: Functions are intercepted using ftrace and livepatch.
> This doesn't require adding a new prologue to each function being
> replaced, but does have more dependencies (which restricts it to a small
> number of architectures, not including UML), and doesn't work well with
> inline functions.
>
> The API for both implementations is very similar, so it should be easy
> to migrate from one to the other if necessary. Both of these
> implementations restrict the redirection to the test context: it is
> automatically undone after the KUnit test completes, and does not affect
> calls in other threads. If CONFIG_KUNIT is not enabled, there should be
> no overhead in either implementation.
>
> Does either (or both) of these features sound useful, and is this
> sort-of API the right model? (Personally, I think there's a reasonable
> scope for both.) Is anything obviously missing or wrong? Do the names,
> descriptions etc. make any sense?
>
> Note that these patches are definitely still at the "prototype" level,
> and things like error-handling, documentation, and testing are still
> pretty sparse. There is also quite a bit of room for optimisation.
> These'll all be improved for v1 if the concept seems good.
>
> Cheers,
> -- David
>
> Daniel Latypov (1):
> kunit: expose ftrace-based API for stubbing out functions during tests
>
> David Gow (1):
> kunit: Expose 'static stub' API to redirect functions
>
> include/kunit/ftrace_stub.h | 84 +++++++++++++++++
> include/kunit/static_stub.h | 106 +++++++++++++++++++++
> lib/kunit/Kconfig | 11 +++
> lib/kunit/Makefile | 5 +
> lib/kunit/ftrace_stub.c | 138 ++++++++++++++++++++++++++++
> lib/kunit/kunit-example-test.c | 64 +++++++++++++
> lib/kunit/static_stub.c | 125 +++++++++++++++++++++++++
> lib/kunit/stubs_example.kunitconfig | 11 +++
> 8 files changed, 544 insertions(+)
> create mode 100644 include/kunit/ftrace_stub.h
> create mode 100644 include/kunit/static_stub.h
> create mode 100644 lib/kunit/ftrace_stub.c
> create mode 100644 lib/kunit/static_stub.c
> create mode 100644 lib/kunit/stubs_example.kunitconfig
>
> --
> 2.35.1.894.gb6a874cedc-goog
>

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