From: José Expósito jose.exposito89@gmail.com

Add a couple of Rust const functions and macros to allow to develop KUnit tests without relying on generated C code:

- The `kunit_unsafe_test_suite!` Rust macro is similar to the `kunit_test_suite` C macro. It requires a NULL-terminated array of test cases (see below). - The `kunit_case` Rust function is similar to the `KUNIT_CASE` C macro. It generates as case from the name and function. - The `kunit_case_null` Rust function generates a NULL test case, which is to be used as delimiter in `kunit_test_suite!`.

While these functions and macros can be used on their own, a future patch will introduce another macro to create KUnit tests using a user-space like syntax.

Signed-off-by: José Expósito jose.exposito89@gmail.com Co-developed-by: Matt Gilbride mattgilbride@google.com Signed-off-by: Matt Gilbride mattgilbride@google.com Co-developed-by: Miguel Ojeda ojeda@kernel.org Signed-off-by: Miguel Ojeda ojeda@kernel.org Co-developed-by: David Gow davidgow@google.com Signed-off-by: David Gow davidgow@google.com ---

Changes since v6: https://lore.kernel.org/rust-for-linux/20250214074051.1619256-2-davidgow@goo... - Fixed an [allow(unused_unsafe)] which ended up in patch 2 instead of patch 1. (Thanks, Tamir!) - Doc comments now have several useful links. (Thanks, Tamir!) - Fix a potential compile error under macos. (Thanks, Tamir!) - Several small tidy-ups to limit unsafe usage. (Thanks, Tamir!)

Changes since v5: https://lore.kernel.org/all/20241213081035.2069066-2-davidgow@google.com/ - Rebased against 6.14-rc1 - Several documentation touch-ups, including noting that the example test function need not be unsafe. (Thanks, Miguel) - Remove the need for static_mut_refs, by using core::addr_of_mut!() combined with a cast. (Thanks, Miguel) - While this should also avoid the need for const_mut_refs, it seems to have been enabled for other users anyway. - Use ::kernel::ffi::c_char for C strings, rather than i8 directly. (Thanks, Miguel)

Changes since v4: https://lore.kernel.org/linux-kselftest/20241101064505.3820737-2-davidgow@go... - Rebased against 6.13-rc1 - Allowed an unused_unsafe warning after the behaviour of addr_of_mut!() changed in Rust 1.82. (Thanks Boqun, Miguel) - Fix a couple of minor rustfmt issues which were triggering checkpatch warnings.

Changes since v3: https://lore.kernel.org/linux-kselftest/20241030045719.3085147-4-davidgow@go... - The kunit_unsafe_test_suite!() macro now panic!s if the suite name is too long, triggering a compile error. (Thanks, Alice!)

Changes since v2: https://lore.kernel.org/linux-kselftest/20241029092422.2884505-2-davidgow@go... - The kunit_unsafe_test_suite!() macro will truncate the name of the suite if it is too long. (Thanks Alice!) - We no longer needlessly use UnsafeCell<> in kunit_unsafe_test_suite!(). (Thanks Alice!)

Changes since v1: https://lore.kernel.org/lkml/20230720-rustbind-v1-1-c80db349e3b5@google.com/ - Rebase on top of rust-next - As a result, KUnit attributes are new set. These are hardcoded to the defaults of "normal" speed and no module name. - Split the kunit_case!() macro into two const functions, kunit_case() and kunit_case_null() (for the NULL terminator).

--- rust/kernel/kunit.rs | 122 +++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 122 insertions(+)

diff --git a/rust/kernel/kunit.rs b/rust/kernel/kunit.rs index 824da0e9738a..ffb3606f748c 100644 --- a/rust/kernel/kunit.rs +++ b/rust/kernel/kunit.rs @@ -161,3 +161,125 @@ macro_rules! kunit_assert_eq { $crate::kunit_assert!($name, $file, $diff, $left == $right); }}; } + +/// Represents an individual test case. +/// +/// The [`kunit_unsafe_test_suite!`] macro expects a NULL-terminated list of valid test cases. +/// Use [`kunit_case_null`] to generate such a delimiter. +#[doc(hidden)] +pub const fn kunit_case( + name: &'static kernel::str::CStr, + run_case: unsafe extern "C" fn(*mut kernel::bindings::kunit), +) -> kernel::bindings::kunit_case { + kernel::bindings::kunit_case { + run_case: Some(run_case), + name: name.as_char_ptr(), + attr: kernel::bindings::kunit_attributes { + speed: kernel::bindings::kunit_speed_KUNIT_SPEED_NORMAL, + }, + generate_params: None, + status: kernel::bindings::kunit_status_KUNIT_SUCCESS, + module_name: core::ptr::null_mut(), + log: core::ptr::null_mut(), + } +} + +/// Represents the NULL test case delimiter. +/// +/// The [`kunit_unsafe_test_suite!`] macro expects a NULL-terminated list of test cases. This +/// function returns such a delimiter. +#[doc(hidden)] +pub const fn kunit_case_null() -> kernel::bindings::kunit_case { + kernel::bindings::kunit_case { + run_case: None, + name: core::ptr::null_mut(), + generate_params: None, + attr: kernel::bindings::kunit_attributes { + speed: kernel::bindings::kunit_speed_KUNIT_SPEED_NORMAL, + }, + status: kernel::bindings::kunit_status_KUNIT_SUCCESS, + module_name: core::ptr::null_mut(), + log: core::ptr::null_mut(), + } +} + +/// Registers a KUnit test suite. +/// +/// # Safety +/// +/// `test_cases` must be a NULL terminated array of valid test cases. +/// +/// # Examples +/// +/// ```ignore +/// extern "C" fn test_fn(_test: *mut kernel::bindings::kunit) { +/// let actual = 1 + 1; +/// let expected = 2; +/// assert_eq!(actual, expected); +/// } +/// +/// static mut KUNIT_TEST_CASES: [kernel::bindings::kunit_case; 2] = [ +/// kernel::kunit::kunit_case(kernel::c_str!("name"), test_fn), +/// kernel::kunit::kunit_case_null(), +/// ]; +/// kernel::kunit_unsafe_test_suite!(suite_name, KUNIT_TEST_CASES); +/// ``` +#[doc(hidden)] +#[macro_export] +macro_rules! kunit_unsafe_test_suite { + ($name:ident, $test_cases:ident) => { + const _: () = { + const KUNIT_TEST_SUITE_NAME: [::kernel::ffi::c_char; 256] = { + let name_u8 = ::core::stringify!($name).as_bytes(); + let mut ret = [0; 256]; + + if name_u8.len() > 255 { + panic!(concat!( + "The test suite name `", + ::core::stringify!($name), + "` exceeds the maximum length of 255 bytes." + )); + } + + let mut i = 0; + while i < name_u8.len() { + ret[i] = name_u8[i] as ::kernel::ffi::c_char; + i += 1; + } + + ret + }; + + static mut KUNIT_TEST_SUITE: ::kernel::bindings::kunit_suite = + ::kernel::bindings::kunit_suite { + name: KUNIT_TEST_SUITE_NAME, + #[allow(unused_unsafe)] + // SAFETY: User is expected to pass a correct `test_cases`, given the safety + // precondition; hence this macro named `unsafe`. + test_cases: unsafe { + ::core::ptr::addr_of_mut!($test_cases) + .cast::<::kernel::bindings::kunit_case>() + }, + suite_init: None, + suite_exit: None, + init: None, + exit: None, + attr: ::kernel::bindings::kunit_attributes { + speed: ::kernel::bindings::kunit_speed_KUNIT_SPEED_NORMAL, + }, + status_comment: [0; 256usize], + debugfs: ::core::ptr::null_mut(), + log: ::core::ptr::null_mut(), + suite_init_err: 0, + is_init: false, + }; + + #[used] + #[allow(unused_unsafe)] + #[cfg_attr(not(target_os = "macos"), link_section = ".kunit_test_suites")] + static mut KUNIT_TEST_SUITE_ENTRY: *const ::kernel::bindings::kunit_suite = + // SAFETY: `KUNIT_TEST_SUITE` is static. + unsafe { ::core::ptr::addr_of_mut!(KUNIT_TEST_SUITE) }; + }; + }; +}

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: Miguel Ojeda ojeda@kernel.org Signed-off-by: Miguel Ojeda ojeda@kernel.org Co-developed-by: David Gow davidgow@google.com Signed-off-by: David Gow davidgow@google.com ---

Changes since v6: https://lore.kernel.org/rust-for-linux/20250214074051.1619256-4-davidgow@goo... - Doc comments now have a useful link. (Thanks, Tamir!) - A small tidy-up to limit unsafe usage. (Thanks, Tamir!)

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 2131443a5f1e..91aa49da0265 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: +/// +/// ``` +/// // 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); +/// ``` +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() +} + #[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()); + } }