On Sat, Feb 15, 2025 at 4:03 AM David Gow davidgow@google.com wrote:
On Fri, 14 Feb 2025 at 22:41, Tamir Duberstein tamird@gmail.com wrote:
On Fri, Feb 14, 2025 at 2:42 AM David Gow davidgow@google.com wrote:
From: José Expósito jose.exposito89@gmail.com
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@gmail.com Co-developed-by: David Gow davidgow@google.com Signed-off-by: David Gow davidgow@google.com Co-developed-by: Miguel Ojeda ojeda@kernel.org Signed-off-by: Miguel Ojeda ojeda@kernel.org
Changes since v5: https://lore.kernel.org/all/20241213081035.2069066-4-davidgow@google.com/
- 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@go...
- 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@go...
- 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@go...
Changes since v1: https://lore.kernel.org/lkml/20230720-rustbind-v1-3-c80db349e3b5@google.com/
- 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.
Why would you need conditional compilation of this kind in test files?
What I was getting at with this comment is that this example might mislead a user to think that this is how they should imbue their code with test-specific behavior, which is not what this will do. Instead this would break kernels built with CONFIG_KUNIT, which I think is not where we want to be going. Right?
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