[PATCH v5 1/3] rust: kunit: add KUnit case and suite macros

[David Gow]

From: José Expósito <jose.exposito89@xxxxxxxxx>

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@xxxxxxxxx>
Co-developed-by: Matt Gilbride <mattgilbride@xxxxxxxxxx>
Signed-off-by: Matt Gilbride <mattgilbride@xxxxxxxxxx>
Co-developed-by: David Gow <davidgow@xxxxxxxxxx>
Signed-off-by: David Gow <davidgow@xxxxxxxxxx>
---

Changes since v4:
https://lore.kernel.org/linux-kselftest/20241101064505.3820737-2-davidgow@xxxxxxxxxx/
- 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@xxxxxxxxxx/
- 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@xxxxxxxxxx/
- 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@xxxxxxxxxx/
- 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 | 118 +++++++++++++++++++++++++++++++++++++++++++
 rust/kernel/lib.rs   |   1 +
 2 files changed, 119 insertions(+)

diff --git a/rust/kernel/kunit.rs b/rust/kernel/kunit.rs
index 824da0e9738a..5003282cb4c4 100644
--- a/rust/kernel/kunit.rs
+++ b/rust/kernel/kunit.rs
@@ -161,3 +161,121 @@ macro_rules! kunit_assert_eq {
         $crate::kunit_assert!($name, $file, $diff, $left == $right);
     }};
 }
+
+/// Represents an individual test case.
+///
+/// The test case should have the signature
+/// `unsafe extern "C" fn test_case(test: *mut crate::bindings::kunit)`.
+///
+/// The `kunit_unsafe_test_suite!` macro expects a NULL-terminated list of test cases.
+/// Use `kunit_case_null` to generate such a delimeter.
+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 retuns such a delimiter.
+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 test cases.
+///
+/// # Examples
+///
+/// ```ignore
+/// unsafe extern "C" fn test_fn(_test: *mut crate::bindings::kunit) {
+///     let actual = 1 + 1;
+///     let expected = 2;
+///     assert_eq!(actual, expected);
+/// }
+///
+/// static mut KUNIT_TEST_CASE: crate::bindings::kunit_case = crate::kunit_case(name, test_fn);
+/// static mut KUNIT_NULL_CASE: crate::bindings::kunit_case = crate::kunit_case_null();
+/// static mut KUNIT_TEST_CASES: &mut[crate::bindings::kunit_case] = unsafe {
+///     &mut[KUNIT_TEST_CASE, KUNIT_NULL_CASE]
+/// };
+/// crate::kunit_unsafe_test_suite!(suite_name, KUNIT_TEST_CASES);
+/// ```
+#[macro_export]
+macro_rules! kunit_unsafe_test_suite {
+    ($name:ident, $test_cases:ident) => {
+        const _: () = {
+            static KUNIT_TEST_SUITE_NAME: [i8; 256] = {
+                let name_u8 = core::stringify!($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 i8;
+                    i += 1;
+                }
+
+                ret
+            };
+
+            static mut KUNIT_TEST_SUITE: $crate::bindings::kunit_suite =
+                $crate::bindings::kunit_suite {
+                    name: KUNIT_TEST_SUITE_NAME,
+                    // SAFETY: User is expected to pass a correct `test_cases`, hence this macro
+                    // named 'unsafe'.
+                    test_cases: unsafe { $test_cases.as_mut_ptr() },
+                    suite_init: None,
+                    suite_exit: None,
+                    init: None,
+                    exit: None,
+                    attr: $crate::bindings::kunit_attributes {
+                        speed: $crate::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]
+            #[link_section = ".kunit_test_suites"]
+            static mut KUNIT_TEST_SUITE_ENTRY: *const $crate::bindings::kunit_suite =
+                // SAFETY: `KUNIT_TEST_SUITE` is static.
+                unsafe { core::ptr::addr_of_mut!(KUNIT_TEST_SUITE) };
+        };
+    };
+}
diff --git a/rust/kernel/lib.rs b/rust/kernel/lib.rs
index e1065a7551a3..02a70c5ad8ee 100644
--- a/rust/kernel/lib.rs
+++ b/rust/kernel/lib.rs
@@ -18,6 +18,7 @@
 #![feature(inline_const)]
 #![feature(lint_reasons)]
 #![feature(unsize)]
+#![feature(const_mut_refs)]
 
 // Ensure conditional compilation based on the kernel configuration works;
 // otherwise we may silently break things like initcall handling.
-- 
2.47.1.613.gc27f4b7a9f-goog