On Fri, Feb 14, 2025 at 2:42 AM David Gow <davidgow@xxxxxxxxxx> wrote: > > From: José Expósito <jose.exposito89@xxxxxxxxx> > > 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 <jose.exposito89@xxxxxxxxx> > Co-developed-by: David Gow <davidgow@xxxxxxxxxx> > Signed-off-by: David Gow <davidgow@xxxxxxxxxx> > Co-developed-by: Miguel Ojeda <ojeda@xxxxxxxxxx> > Signed-off-by: Miguel Ojeda <ojeda@xxxxxxxxxx> > --- > > Changes since v5: > https://lore.kernel.org/all/20241213081035.2069066-4-davidgow@xxxxxxxxxx/ > - 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/20241101064505.3820737-4-davidgow@xxxxxxxxxx/ > - 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/20241030045719.3085147-8-davidgow@xxxxxxxxxx/ > - 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/20241029092422.2884505-4-davidgow@xxxxxxxxxx/ > > Changes since v1: > https://lore.kernel.org/lkml/20230720-rustbind-v1-3-c80db349e3b5@xxxxxxxxxx/ > - 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. > +/// > +/// ``` > +/// // 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. > +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() > +} > + > #[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 > >
