On Fri, 14 Feb 2025 at 22:41, Tamir Duberstein <[email protected]> wrote: > > On Fri, Feb 14, 2025 at 2:42 AM David Gow <[email protected]> wrote: > > > > From: José Expósito <[email protected]> > > > > In some cases, we need to call test-only code from outside the test > > case, for example, to mock a function or a module. > > > > In order to check whether we are in a test or not, we need to test if > > `CONFIG_KUNIT` is set. > > Unfortunately, we cannot rely only on this condition because: > > - a test could be running in another thread, > > - some distros compile KUnit in production kernels, so checking at runtime > > that `current->kunit_test != NULL` is required. > > > > Forturately, KUnit provides an optimised check in > > `kunit_get_current_test()`, which checks CONFIG_KUNIT, a global static > > key, and then the current thread's running KUnit test. > > > > Add a safe wrapper function around this to know whether or not we are in > > a KUnit test and examples showing how to mock a function and a module. > > > > Signed-off-by: José Expósito <[email protected]> > > Co-developed-by: David Gow <[email protected]> > > Signed-off-by: David Gow <[email protected]> > > Co-developed-by: Miguel Ojeda <[email protected]> > > Signed-off-by: Miguel Ojeda <[email protected]> > > --- > > > > Changes since v5: > > https://lore.kernel.org/all/[email protected]/ > > - Greatly improved documentation, which is both clearer and better > > matches the rustdoc norm. (Thanks, Miguel) > > - The examples and safety comments are also both more idiomatic an > > cleaner. (Thanks, Miguel) > > - More things sit appropriately behind CONFIG_KUNIT (Thanks, Miguel) > > > > Changes since v4: > > https://lore.kernel.org/linux-kselftest/[email protected]/ > > - Rebased against 6.13-rc1 > > - Fix some missing safety comments, and remove some unneeded 'unsafe' > > blocks. (Thanks Boqun) > > > > Changes since v3: > > https://lore.kernel.org/linux-kselftest/[email protected]/ > > - The example test has been updated to no longer use assert_eq!() with > > a constant bool argument (fixes a clippy warning). > > > > No changes since v2: > > https://lore.kernel.org/linux-kselftest/[email protected]/ > > > > Changes since v1: > > https://lore.kernel.org/lkml/[email protected]/ > > - Rebased on top of rust-next. > > - Use the `kunit_get_current_test()` C function, which wasn't previously > > available, instead of rolling our own. > > - (Thanks also to Boqun for suggesting a nicer way of implementing this, > > which I tried, but the `kunit_get_current_test()` version obsoleted.) > > --- > > rust/kernel/kunit.rs | 66 ++++++++++++++++++++++++++++++++++++++++++++ > > 1 file changed, 66 insertions(+) > > > > diff --git a/rust/kernel/kunit.rs b/rust/kernel/kunit.rs > > index 9e27b74a605b..3aad7a281b6d 100644 > > --- a/rust/kernel/kunit.rs > > +++ b/rust/kernel/kunit.rs > > @@ -286,11 +286,77 @@ macro_rules! kunit_unsafe_test_suite { > > }; > > } > > > > +/// Returns whether we are currently running a KUnit test. > > +/// > > +/// In some cases, you need to call test-only code from outside the test > > case, for example, to > > +/// create a function mock. This function allows to change behavior > > depending on whether we are > > +/// currently running a KUnit test or not. > > +/// > > +/// # Examples > > +/// > > +/// This example shows how a function can be mocked to return a well-known > > value while testing: > > +/// > > +/// ``` > > +/// # use kernel::kunit::in_kunit_test; > > +/// fn fn_mock_example(n: i32) -> i32 { > > +/// if in_kunit_test() { > > +/// return 100; > > +/// } > > +/// > > +/// n + 1 > > +/// } > > +/// > > +/// let mock_res = fn_mock_example(5); > > +/// assert_eq!(mock_res, 100); > > +/// ``` > > +/// > > +/// Sometimes, you don't control the code that needs to be mocked. This > > example shows how the > > +/// `bindings` module can be mocked: > > [`bindings`] here, please. There are two more instances below but > those aren't doc comments, so I don't think bracketing them will do > anything. >
Done in v7. Alas, I'll have to keep getting used to the differences
between kerneldoc and rustdoc...
> > +///
> > +/// ```
> > +/// // Import our mock naming it as the real module.
> > +/// #[cfg(CONFIG_KUNIT)]
> > +/// use bindings_mock_example as bindings;
> > +/// #[cfg(not(CONFIG_KUNIT))]
> > +/// use kernel::bindings;
> > +///
> > +/// // This module mocks `bindings`.
> > +/// #[cfg(CONFIG_KUNIT)]
> > +/// mod bindings_mock_example {
> > +/// /// Mock `ktime_get_boot_fast_ns` to return a well-known value
> > when running a KUnit test.
> > +/// pub(crate) fn ktime_get_boot_fast_ns() -> u64 {
> > +/// 1234
> > +/// }
> > +/// }
> > +///
> > +/// // This is the function we want to test. Since `bindings` has been
> > mocked, we can use its
> > +/// // functions seamlessly.
> > +/// fn get_boot_ns() -> u64 {
> > +/// // SAFETY: `ktime_get_boot_fast_ns()` is always safe to call.
> > +/// unsafe { bindings::ktime_get_boot_fast_ns() }
> > +/// }
> > +///
> > +/// let time = get_boot_ns();
> > +/// assert_eq!(time, 1234);
> > +/// ```
>
> Isn't this swapping out the bindings module at compile time, and for
> the whole build? In other words cfg(CONFIG_KUNIT) will apply to all
> code, both test and non-test.
>
I believe so, so this is probably something best done only in test files.
Ideally, we'd have support for something like the KUnit function
mocking features here, but that's horribly C-specific at the moment.
> > +pub fn in_kunit_test() -> bool {
> > + // SAFETY: `kunit_get_current_test()` is always safe to call (it has
> > fallbacks for
> > + // when KUnit is not enabled).
> > + unsafe { !bindings::kunit_get_current_test().is_null() }
>
> Nit if you care about reducing unsafe blocks:
>
> !unsafe { bindings::kunit_get_current_test() }.is_null()
>
>
Huh, I thought this wouldn't work, but it's working fine for me here,
so I've made the change.
Thanks!
> > +}
> > +
> > #[kunit_tests(rust_kernel_kunit)]
> > mod tests {
> > + use super::*;
> > +
> > #[test]
> > fn rust_test_kunit_example_test() {
> > #![expect(clippy::eq_op)]
> > assert_eq!(1 + 1, 2);
> > }
> > +
> > + #[test]
> > + fn rust_test_kunit_in_kunit_test() {
> > + assert!(in_kunit_test());
> > + }
> > }
> > --
> > 2.48.1.601.g30ceb7b040-goog
> >
> >
Thanks a lot, these should be fixed in v7.
Cheers,
-- David
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