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> --- 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 | 75 ++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 75 insertions(+) diff --git a/rust/kernel/kunit.rs b/rust/kernel/kunit.rs index a92f12da77d5..2196e35e5d75 100644 --- a/rust/kernel/kunit.rs +++ b/rust/kernel/kunit.rs @@ -285,11 +285,86 @@ macro_rules! kunit_unsafe_test_suite { }; } +/// In some cases, you need to call test-only code from outside the test case, for example, to +/// create a function mock. This function can be invoked to know 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() { +/// 100 +/// } else { +/// 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: +/// +/// ``` +/// // Import our mock naming it as the real module. +/// #[cfg(CONFIG_KUNIT)] +/// use bindings_mock_example as bindings; +/// +/// // This module mocks `bindings`. +/// mod bindings_mock_example { +/// use kernel::kunit::in_kunit_test; +/// use kernel::bindings::u64_; +/// +/// // Make the other binding functions available. +/// pub(crate) use kernel::bindings::*; +/// +/// /// 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_ { +/// if in_kunit_test() { +/// 1234 +/// } else { +/// // SAFETY: ktime_get_boot_fast_ns() is safe to call, and just returns a u64. +/// // Additionally, this is never actually called in this example, as we're in a test +/// // and it's mocked out. +/// unsafe { kernel::bindings::ktime_get_boot_fast_ns() } +/// } +/// } +/// } +/// +/// // This is the function we want to test. Since `bindings` has been mocked, we can use its +/// // functions seamlessly. +/// fn get_boot_ns() -> u64 { +/// bindings::ktime_get_boot_fast_ns() +/// } +/// +/// let time = get_boot_ns(); +/// assert_eq!(time, 1234); +/// ``` +pub fn in_kunit_test() -> bool { + // SAFETY: kunit_get_current_test() is always safe to call from C (it has fallbacks for + // when KUnit is not enabled), and we're only comparing the result to NULL. + 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() { + let in_kunit = in_kunit_test(); + assert!(in_kunit); + } } -- 2.47.1.613.gc27f4b7a9f-goog
