rust: kunit: Support KUnit tests with a user-space like syntax

From: José Expósito <[email protected]>

Add a couple of Rust 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.
- The kunit_case! Rust macro is similar to the KUNIT_CASE C macro. It can be used with parameters to generate a test case or without parameters to be used as delimiter in kunit_test_suite!.

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

Co-developed-by David Gow <[email protected]>

Signed-off-by David Gow <[email protected]>

Signed-off-by José Expósito <[email protected]>

---
 rust/kernel/kunit.rs | 92 ++++++++++++++++++++++++++++++++++++++++++++++++++++
 rust/kernel/lib.rs   |  1 +
 2 files changed, 93 insertions(+)

rust/kernel/kunit.rs +0 -0

index 722655b2d62d..4cffc71e463b 100644
@@ -161,3 +161,95 @@ macro_rules! kunit_assert_eq {
         $crate::kunit_assert!($name, $file, $diff, $left == $right);
     }};
 }

rust/kernel/kunit.rs +82 -0

+    () => {
+        $crate::bindings::kunit_case {
+            run_case: None,
+            name: core::ptr::null_mut(),
+            generate_params: None,
+            status: $crate::bindings::kunit_status_KUNIT_SUCCESS,
+            log: core::ptr::null_mut(),
+        }
+    };
+    ($name:ident, $run_case:ident) => {
+        $crate::bindings::kunit_case {
+            run_case: Some($run_case),
+            name: $crate::c_str!(core::stringify!($name)).as_char_ptr(),
+            generate_params: None,
+            status: $crate::bindings::kunit_status_KUNIT_SUCCESS,
+            log: core::ptr::null_mut(),
+        }
+    };
+}
+
+/// Registers a KUnit test suite.
+///
+/// # Safety
+///
+/// `test_cases` must be a NULL terminated array of test cases.
+///
+/// # Examples
+///
+/// ```ignore
+/// unsafe extern "C" fn test_fn(_test: *mut crate::bindings::kunit) {
+///     let actual = 1 + 1;
+///     let expected = 2;
+///     assert_eq!(actual, expected);
+/// }
+///
+/// static mut KUNIT_TEST_CASE: crate::bindings::kunit_case = crate::kunit_case!(name, test_fn);
+/// static mut KUNIT_NULL_CASE: crate::bindings::kunit_case = crate::kunit_case!();
+/// static mut KUNIT_TEST_CASES: &mut[crate::bindings::kunit_case] = unsafe {
+///     &mut[KUNIT_TEST_CASE, KUNIT_NULL_CASE]
+/// };
+/// crate::kunit_unsafe_test_suite!(suite_name, KUNIT_TEST_CASES);
+/// ```
+#[macro_export]
+macro_rules! kunit_unsafe_test_suite {
+    ($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];
+
+                let mut i = 0;
+                while i < name_u8.len() {
+                    ret[i] = name_u8[i] as i8;
+                    i += 1;
+                }
+
+                ret
+            };
+
+            // SAFETY: `test_cases` is valid as it should be static.
+            static mut KUNIT_TEST_SUITE: core::cell::UnsafeCell<$crate::bindings::kunit_suite> =
+                core::cell::UnsafeCell::new($crate::bindings::kunit_suite {
+                    name: KUNIT_TEST_SUITE_NAME,
+                    test_cases: unsafe { $test_cases.as_mut_ptr() },
+                    suite_init: None,
+                    suite_exit: None,
+                    init: None,
+                    exit: None,
+                    status_comment: [0; 256usize],
+                    debugfs: core::ptr::null_mut(),
+                    log: core::ptr::null_mut(),
+                    suite_init_err: 0,
+                });
+
+            // SAFETY: `KUNIT_TEST_SUITE` is static.
+            #[used]
+            #[link_section = ".kunit_test_suites"]
+            static mut KUNIT_TEST_SUITE_ENTRY: *const $crate::bindings::kunit_suite =
+                unsafe { KUNIT_TEST_SUITE.get() };
+        };
+    };
+}

rust/kernel/lib.rs +1 -0

index 3642cadc34b1..ec81fd28d71a 100644
@@ -18,6 +18,7 @@
 #![feature(new_uninit)]
 #![feature(receiver_trait)]
 #![feature(unsize)]
+#![feature(const_mut_refs)]
 
 // Ensure conditional compilation based on the kernel configuration works;
 // otherwise we may silently break things like initcall handling.

Signature · 2 lines

-- 
2.41.0.255.g8b1d071c50-goog

From: José Expósito <[email protected]>

Add a new procedural macro (#[kunit_tests(kunit_test_suit_name)]) to run KUnit tests using a user-space like syntax.

The macro, that should be used on modules, transforms every #[test] in a kunit_case! and adds a kunit_unsafe_test_suite! registering all of them.

The only difference with user-space tests is that instead of using #[cfg(test)], #[kunit_tests(kunit_test_suit_name)] is used.

Note that #[cfg(CONFIG_KUNIT)] is added so the test module is not compiled when CONFIG_KUNIT is set to n.

Reviewed-by David Gow <[email protected]>

Signed-off-by José Expósito <[email protected]>

---
 MAINTAINERS          |   1 +
 rust/kernel/kunit.rs |  11 ++++
 rust/macros/kunit.rs | 149 +++++++++++++++++++++++++++++++++++++++++++++++++++
 rust/macros/lib.rs   |  29 ++++++++++
 4 files changed, 190 insertions(+)

MAINTAINERS +1 -0

index 2a942fe59144..c32ba6b29a96 100644
@@ -11373,6 +11373,7 @@ F:	Documentation/dev-tools/kunit/
 F:	include/kunit/
 F:	lib/kunit/
 F:	rust/kernel/kunit.rs
+F:	rust/macros/kunit.rs
 F:	scripts/rustdoc_test_*
 F:	tools/testing/kunit/
 

rust/kernel/kunit.rs +11 -0

index 4cffc71e463b..44ea67028316 100644
@@ -40,6 +40,8 @@ pub fn info(args: fmt::Arguments<'_>) {
     }
 }
 
+use macros::kunit_tests;
+
 /// Asserts that a boolean expression is `true` at runtime.
 ///
 /// Public but hidden since it should only be used from generated tests.

@@ -253,3 +255,12 @@ macro_rules! kunit_unsafe_test_suite {
         };
     };
 }
+
+#[kunit_tests(rust_kernel_kunit)]
+mod tests {
+    #[test]
+    fn rust_test_kunit_kunit_tests() {
+        let running = true;
+        assert_eq!(running, true);
+    }
+}

rust/macros/kunit.rs new file +132 -0

new file mode 100644
index 000000000000..69dac253232f
@@ -0,0 +1,149 @@
+// SPDX-License-Identifier: GPL-2.0
+
+//! Procedural macro to run KUnit tests using a user-space like syntax.
+//!
+//! Copyright (c) 2023 José Expósito <[email protected]>
+
+use proc_macro::{Delimiter, Group, TokenStream, TokenTree};
+use std::fmt::Write;
+
+pub(crate) fn kunit_tests(attr: TokenStream, ts: TokenStream) -> TokenStream {
+    if attr.to_string().is_empty() {
+        panic!("Missing test name in #[kunit_tests(test_name)] macro")
+    }
+
+    let mut tokens: Vec<_> = ts.into_iter().collect();
+
+    // Scan for the "mod" keyword.
+    tokens
+        .iter()
+        .find_map(|token| match token {
+            TokenTree::Ident(ident) => match ident.to_string().as_str() {
+                "mod" => Some(true),
+                _ => None,
+            },
+            _ => None,
+        })
+        .expect("#[kunit_tests(test_name)] attribute should only be applied to modules");
+
+    // Retrieve the main body. The main body should be the last token tree.
+    let body = match tokens.pop() {
+        Some(TokenTree::Group(group)) if group.delimiter() == Delimiter::Brace => group,
+        _ => panic!("cannot locate main body of module"),
+    };
+
+    // Get the functions set as tests. Search for `[test]` -> `fn`.
+    let mut body_it = body.stream().into_iter();
+    let mut tests = Vec::new();
+    while let Some(token) = body_it.next() {
+        match token {
+            TokenTree::Group(ident) if ident.to_string() == "[test]" => match body_it.next() {
+                Some(TokenTree::Ident(ident)) if ident.to_string() == "fn" => {
+                    let test_name = match body_it.next() {
+                        Some(TokenTree::Ident(ident)) => ident.to_string(),
+                        _ => continue,
+                    };
+                    tests.push(test_name);
+                }
+                _ => continue,
+            },
+            _ => (),
+        }
+    }
+
+    // Add `#[cfg(CONFIG_KUNIT)]` before the module declaration.
+    let config_kunit = "#[cfg(CONFIG_KUNIT)]".to_owned().parse().unwrap();
+    tokens.insert(
+        0,
+        TokenTree::Group(Group::new(Delimiter::None, config_kunit)),
+    );
+
+    // Generate the test KUnit test suite and a test case for each `#[test]`.
+    // The code generated for the following test module:
+    //
+    // ```
+    // #[kunit_tests(kunit_test_suit_name)]
+    // mod tests {
+    //     #[test]
+    //     fn foo() {
+    //         assert_eq!(1, 1);
+    //     }
+    //
+    //     #[test]
+    //     fn bar() {
+    //         assert_eq!(2, 2);
+    //     }
+    // ```
+    //
+    // Looks like:
+    //
+    // ```
+    // unsafe extern "C" fn kunit_rust_wrapper_foo(_test: *mut kernel::bindings::kunit) {
+    //     foo();
+    // }
+    // static mut KUNIT_CASE_FOO: kernel::bindings::kunit_case =
+    //     kernel::kunit_case!(foo, kunit_rust_wrapper_foo);
+    //
+    // unsafe extern "C" fn kunit_rust_wrapper_bar(_test: * mut kernel::bindings::kunit) {
+    //     bar();
+    // }
+    // static mut KUNIT_CASE_BAR: kernel::bindings::kunit_case =
+    //     kernel::kunit_case!(bar, kunit_rust_wrapper_bar);
+    //
+    // static mut KUNIT_CASE_NULL: kernel::bindings::kunit_case = kernel::kunit_case!();
+    //
+    // static mut TEST_CASES : &mut[kernel::bindings::kunit_case] = unsafe {
+    //     &mut [KUNIT_CASE_FOO, KUNIT_CASE_BAR, KUNIT_CASE_NULL]
+    // };
+    //
+    // kernel::kunit_unsafe_test_suite!(kunit_test_suit_name, TEST_CASES);
+    // ```
+    let mut kunit_macros = "".to_owned();
+    let mut test_cases = "".to_owned();
+    for test in tests {
+        let kunit_wrapper_fn_name = format!("kunit_rust_wrapper_{}", test);
+        let kunit_case_name = format!("KUNIT_CASE_{}", test.to_uppercase());
+        let kunit_wrapper = format!(
+            "unsafe extern \"C\" fn {}(_test: *mut kernel::bindings::kunit) {{ {}(); }}",
+            kunit_wrapper_fn_name, test
+        );
+        let kunit_case = format!(
+            "static mut {}: kernel::bindings::kunit_case = kernel::kunit_case!({}, {});",
+            kunit_case_name, test, kunit_wrapper_fn_name
+        );
+        writeln!(kunit_macros, "{kunit_wrapper}").unwrap();
+        writeln!(kunit_macros, "{kunit_case}").unwrap();
+        writeln!(test_cases, "{kunit_case_name},").unwrap();
+    }
+
+    writeln!(
+        kunit_macros,
+        "static mut KUNIT_CASE_NULL: kernel::bindings::kunit_case = kernel::kunit_case!();"
+    )
+    .unwrap();
+
+    writeln!(
+        kunit_macros,
+        "static mut TEST_CASES : &mut[kernel::bindings::kunit_case] = unsafe {{ &mut[{test_cases} KUNIT_CASE_NULL] }};"
+    )
+    .unwrap();
+
+    writeln!(
+        kunit_macros,

rust/macros/kunit.rs new file +7 -0

+    tokens.push(TokenTree::Group(Group::new(
+        Delimiter::Brace,
+        new_body.parse().unwrap(),
+    )));
+
+    tokens.into_iter().collect()
+}

rust/macros/lib.rs +29 -0

index 3fc74cb4ea19..cd0b720514ff 100644
@@ -6,6 +6,7 @@
 mod quote;
 mod concat_idents;
 mod helpers;
+mod kunit;
 mod module;
 mod pin_data;
 mod pinned_drop;

@@ -246,3 +247,31 @@ pub fn pin_data(inner: TokenStream, item: TokenStream) -> TokenStream {
 pub fn pinned_drop(args: TokenStream, input: TokenStream) -> TokenStream {
     pinned_drop::pinned_drop(args, input)
 }
+
+/// Registers a KUnit test suite and its test cases using a user-space like syntax.
+///
+/// This macro should be used on modules. If `CONFIG_KUNIT` (in `.config`) is `n`, the target module
+/// is ignored.
+///
+/// # Examples
+///
+/// ```ignore
+/// # use macros::kunit_tests;
+///
+/// #[kunit_tests(kunit_test_suit_name)]
+/// mod tests {
+///     #[test]
+///     fn foo() {
+///         assert_eq!(1, 1);
+///     }
+///
+///     #[test]
+///     fn bar() {
+///         assert_eq!(2, 2);
+///     }
+/// }
+/// ```
+#[proc_macro_attribute]
+pub fn kunit_tests(attr: TokenStream, ts: TokenStream) -> TokenStream {
+    kunit::kunit_tests(attr, ts)
+}

Signature · 2 lines

-- 
2.41.0.255.g8b1d071c50-goog

The only difference with user-space tests is that instead of using #[cfg(test)], #[kunit_tests(kunit_test_suit_name)] is used.

From: José Expósito <[email protected]>

In some cases, you 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 some distros compile KUnit in production kernels, so checking at runtime that current->kunit_test != NULL is required.

Note that the C function kunit_get_current_test() can not be used because it is not present in the current Rust tree yet. Once it is available we might want to change our Rust wrapper to use it.

This patch adds a function to know whether we are in a KUnit test or not and examples showing how to mock a function and a module.

Reviewed-by David Gow <[email protected]>

Signed-off-by José Expósito <[email protected]>

---
 rust/kernel/kunit.rs | 78 ++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 78 insertions(+)

rust/kernel/kunit.rs +54 -0

index 44ea67028316..dcaac19bb108 100644
@@ -40,6 +40,8 @@ pub fn info(args: fmt::Arguments<'_>) {
     }
 }
 
+use crate::task::Task;
+use core::ops::Deref;
 use macros::kunit_tests;
 
 /// Asserts that a boolean expression is `true` at runtime.

@@ -256,11 +258,87 @@ 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) unsafe fn ktime_get_boot_fast_ns() -> u64_ {
+///         if in_kunit_test() {
+///             1234
+///         } else {
+///             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 {

rust/kernel/kunit.rs +14 -0

+        !test.is_null()
+    } else {
+        false
+    }
+}
+
 #[kunit_tests(rust_kernel_kunit)]
 mod tests {
+    use super::*;
+
     #[test]
     fn rust_test_kunit_kunit_tests() {
         let running = true;
         assert_eq!(running, true);
     }
+
+    #[test]
+    fn rust_test_kunit_in_kunit_test() {
+        let in_kunit = in_kunit_test();
+        assert_eq!(in_kunit, true);
+    }
 }

Signature · 2 lines

-- 
2.41.0.255.g8b1d071c50-goog