KUnit integration for Rust doctests

Rust documentation tests are going to be build/run-tested with the KUnit integration added in a future patch, thus update them to make them compilable/testable so that we may start enforcing it.

Signed-off-by Miguel Ojeda <[email protected]>

Rust documentation tests are going to be build/run-tested with the KUnit integration added in a future patch, thus update them to make them compilable/testable so that we may start enforcing it.

Signed-off-by Miguel Ojeda <[email protected]>

Rust documentation tests are going to be build/run-tested with the KUnit integration added in a future patch, thus update them to make them compilable/testable so that we may start enforcing it.

Signed-off-by Miguel Ojeda <[email protected]>

Rust documentation tests are going to be build/run-tested with the KUnit integration added in a future patch, thus update them to make them compilable/testable so that we may start enforcing it.

Signed-off-by Miguel Ojeda <[email protected]>

Rust has documentation tests: these are typically examples of usage of any item (e.g. function, struct, module...).

They are very convenient because they are just written alongside the documentation. For instance:

    /// Sums two numbers.
    ///
    /// ```
    /// assert_eq!(mymod::f(10, 20), 30);
    /// ```
    pub fn f(a: i32, b: i32) -> i32 {
        a + b
    }

In userspace, the tests are collected and run via rustdoc. Using the tool as-is would be useful already, since it allows to compile-test most tests (thus enforcing they are kept in sync with the code they document) and run those that do not depend on in-kernel APIs.

However, by transforming the tests into a KUnit test suite, they can also be run inside the kernel. Moreover, the tests get to be compiled as other Rust kernel objects instead of targeting userspace.

On top of that, the integration with KUnit means the Rust support gets to reuse the existing testing facilities. For instance, the kernel log would look like:

KTAP version 1
1..1
KTAP version 1
# Subtest: rust_doctests_kernel
1..59
# Doctest from line 13
ok 1 rust_doctest_kernel_build_assert_rs_0 # Doctest from line 56
ok 2 rust_doctest_kernel_build_assert_rs_1 # Doctest from line 122
ok 3 rust_doctest_kernel_init_rs_0
...
# Doctest from line 150
ok 59 rust_doctest_kernel_types_rs_2
# rust_doctests_kernel: pass:59 fail:0 skip:0 total:59 # Totals: pass:59 fail:0 skip:0 total:59
ok 1 rust_doctests_kernel

Therefore, add support for running Rust documentation tests in KUnit. Some other notes about the current implementation and support follow.

The transformation is performed by a couple scripts written as Rust hostprogs.

Tests using the ? operator are also supported as usual, e.g.:

    /// ```
    /// # use kernel::{spawn_work_item, workqueue};
    /// spawn_work_item!(workqueue::system(), || pr_info!("x"))?;
    /// # Ok::<(), Error>(())
    /// ```

The tests are also compiled with Clippy under CLIPPY=1, just like normal code, thus also benefitting from extra linting.

The names of the tests are currently automatically generated. This allows to reduce the burden for documentation writers, while keeping them fairly stable for bisection. This is an improvement over the rustdoc-generated names, which include the line number; but ideally we would like to get rustdoc to provide the Rust item path and a number (for multiple examples in a single documented Rust item).

In order for developers to easily see from which original line a failed doctests came from, a KTAP diagnostic line is printed to the log. In the future, we may be able to use a proper KUnit facility to append this sort of information instead.

A notable difference from KUnit C tests is that the Rust tests appear to assert using the usual assert! and assert_eq! macros from the Rust standard library (core). We provide a custom version that forwards the call to KUnit instead. Importantly, these macros do not require passing context, unlike the KUnit C ones (i.e. struct kunit *). This makes them easier to use, and readers of the documentation do not need to care about which testing framework is used. In addition, it may allow us to test third-party code more easily in the future.

However, a current limitation is that KUnit does not support assertions in other tasks. Thus we presently simply print an error to the kernel log if an assertion actually failed. This should be revisited to properly fail the test, perhaps saving the context somewhere else, or letting KUnit handle it.

Signed-off-by Miguel Ojeda <[email protected]>

scripts/rustdoc_test_builder.rs new file +42 -0

+fn main() {
+    let mut stdin = std::io::stdin().lock();
+    let mut body = String::new();
+    stdin.read_to_string(&mut body).unwrap();
+
+    // Find the generated function name looking for the inner function inside `main()`.
+    //
+    // The line we are looking for looks like one of the following:
+    //
+    // ```
+    // fn main() { #[allow(non_snake_case)] fn _doctest_main_rust_kernel_file_rs_28_0() {
+    // fn main() { #[allow(non_snake_case)] fn _doctest_main_rust_kernel_file_rs_37_0() -> Result<(), impl core::fmt::Debug> {
+    // ```
+    //
+    // It should be unlikely that doctest code matches such lines (when code is formatted properly).
+    let rustdoc_function_name = body
+        .lines()
+        .find_map(|line| {
+            Some(
+                line.split_once("fn main() {")?
+                    .1
+                    .split_once("fn ")?
+                    .1
+                    .split_once("()")?
+                    .0,
+            )
+            .filter(|x| x.chars().all(|c| c.is_alphanumeric() || c == '_'))
+        })
+        .expect("No test function found in `rustdoc`'s output.");
+
+    // Qualify `Result` to avoid the collision with our own `Result` coming from the prelude.
+    let body = body.replace(
+        &format!("{rustdoc_function_name}() -> Result<(), impl core::fmt::Debug> {{"),
+        &format!("{rustdoc_function_name}() -> core::result::Result<(), impl core::fmt::Debug> {{"),
+    );
+
+    // For tests that get generated with `Result`, like above, `rustdoc` generates an `unwrap()` on
+    // the return value to check there were no returned errors. Instead, we use our assert macro
+    // since we want to just fail the test, not panic the kernel.
+    //
+    // We save the result in a variable so that the failed assertion message looks nicer.
+    let body = body.replace(

This could just be

std::fs::write(path, body.as_bytes());

+/// Prints a KUnit error.

Rust has documentation tests: these are typically examples of usage of any item (e.g. function, struct, module...).

They are very convenient because they are just written alongside the documentation. For instance:

    /// Sums two numbers.
    ///
    /// ```
    /// assert_eq!(mymod::f(10, 20), 30);
    /// ```
    pub fn f(a: i32, b: i32) -> i32 {
        a + b
    }

In userspace, the tests are collected and run via rustdoc. Using the tool as-is would be useful already, since it allows to compile-test most tests (thus enforcing they are kept in sync with the code they document) and run those that do not depend on in-kernel APIs.

However, by transforming the tests into a KUnit test suite, they can also be run inside the kernel. Moreover, the tests get to be compiled as other Rust kernel objects instead of targeting userspace.

On top of that, the integration with KUnit means the Rust support gets to reuse the existing testing facilities. For instance, the kernel log would look like:

KTAP version 1
1..1
KTAP version 1
# Subtest: rust_doctests_kernel
1..59
# Doctest from line 13
ok 1 rust_doctest_kernel_build_assert_rs_0 # Doctest from line 56
ok 2 rust_doctest_kernel_build_assert_rs_1 # Doctest from line 122
ok 3 rust_doctest_kernel_init_rs_0
...
# Doctest from line 150
ok 59 rust_doctest_kernel_types_rs_2
# rust_doctests_kernel: pass:59 fail:0 skip:0 total:59 # Totals: pass:59 fail:0 skip:0 total:59
ok 1 rust_doctests_kernel

Therefore, add support for running Rust documentation tests in KUnit. Some other notes about the current implementation and support follow.

The transformation is performed by a couple scripts written as Rust hostprogs.

Tests using the ? operator are also supported as usual, e.g.:

    /// ```
    /// # use kernel::{spawn_work_item, workqueue};
    /// spawn_work_item!(workqueue::system(), || pr_info!("x"))?;
    /// # Ok::<(), Error>(())
    /// ```

The tests are also compiled with Clippy under CLIPPY=1, just like normal code, thus also benefitting from extra linting.

The names of the tests are currently automatically generated. This allows to reduce the burden for documentation writers, while keeping them fairly stable for bisection. This is an improvement over the rustdoc-generated names, which include the line number; but ideally we would like to get rustdoc to provide the Rust item path and a number (for multiple examples in a single documented Rust item).

In order for developers to easily see from which original line a failed doctests came from, a KTAP diagnostic line is printed to the log. In the future, we may be able to use a proper KUnit facility to append this sort of information instead.

A notable difference from KUnit C tests is that the Rust tests appear to assert using the usual assert! and assert_eq! macros from the Rust standard library (core). We provide a custom version that forwards the call to KUnit instead. Importantly, these macros do not require passing context, unlike the KUnit C ones (i.e. struct kunit *). This makes them easier to use, and readers of the documentation do not need to care about which testing framework is used. In addition, it may allow us to test third-party code more easily in the future.

However, a current limitation is that KUnit does not support assertions in other tasks. Thus we presently simply print an error to the kernel log if an assertion actually failed. This should be revisited to properly fail the test, perhaps saving the context somewhere else, or letting KUnit handle it.

Signed-off-by Miguel Ojeda <[email protected]>

This is the initial KUnit integration for running Rust documentation tests within the kernel.

Thank you to the KUnit team for all the input and feedback on this over the months, as well as the Intel LKP 0-Day team!

This may be merged through either the KUnit or the Rust trees. If the KUnit team wants to merge it, then that would be great.

Please see the message in the main commit for the details.

Rust documentation tests are going to be build/run-tested with the KUnit integration added in a future patch, thus update them to make them compilable/testable so that we may start enforcing it.

Signed-off-by Miguel Ojeda <[email protected]>

---
[...]
//! # pub unsafe fn destroy_foo(_ptr: *mut foo) {}
//! # pub unsafe fn enable_foo(_ptr: *mut foo, _flags: u32) -> i32 { 0 }
//! # }

rust/kernel/init.rs +1 -0

+//! # trait FromErrno {

Rust documentation tests are going to be build/run-tested with the KUnit integration added in a future patch, thus update them to make them compilable/testable so that we may start enforcing it.

Signed-off-by Miguel Ojeda <[email protected]>

---
[...]

Rust documentation tests are going to be build/run-tested with the KUnit integration added in a future patch, thus update them to make them compilable/testable so that we may start enforcing it.

Signed-off-by Miguel Ojeda <[email protected]>

---
[...]

Rust documentation tests are going to be build/run-tested with the KUnit integration added in a future patch, thus update them to make them compilable/testable so that we may start enforcing it.

Signed-off-by Miguel Ojeda <[email protected]>

---
[...]

Rust has documentation tests: these are typically examples of usage of any item (e.g. function, struct, module...).

They are very convenient because they are just written alongside the documentation. For instance:

     /// Sums two numbers.
     ///
     /// ```
     /// assert_eq!(mymod::f(10, 20), 30);
     /// ```
     pub fn f(a: i32, b: i32) -> i32 {
         a + b
     }

In userspace, the tests are collected and run via rustdoc. Using the tool as-is would be useful already, since it allows to compile-test most tests (thus enforcing they are kept in sync with the code they document) and run those that do not depend on in-kernel APIs.

However, by transforming the tests into a KUnit test suite, they can also be run inside the kernel. Moreover, the tests get to be compiled as other Rust kernel objects instead of targeting userspace.

On top of that, the integration with KUnit means the Rust support gets to reuse the existing testing facilities. For instance, the kernel log would look like:

KTAP version 1
1..1
KTAP version 1
# Subtest: rust_doctests_kernel
1..59
# Doctest from line 13
ok 1 rust_doctest_kernel_build_assert_rs_0 # Doctest from line 56
ok 2 rust_doctest_kernel_build_assert_rs_1 # Doctest from line 122
ok 3 rust_doctest_kernel_init_rs_0
...
# Doctest from line 150
ok 59 rust_doctest_kernel_types_rs_2
# rust_doctests_kernel: pass:59 fail:0 skip:0 total:59 # Totals: pass:59 fail:0 skip:0 total:59
ok 1 rust_doctests_kernel

Therefore, add support for running Rust documentation tests in KUnit. Some other notes about the current implementation and support follow.

The transformation is performed by a couple scripts written as Rust hostprogs.

Tests using the ? operator are also supported as usual, e.g.:

     /// ```
     /// # use kernel::{spawn_work_item, workqueue};
     /// spawn_work_item!(workqueue::system(), || pr_info!("x"))?;
     /// # Ok::<(), Error>(())
     /// ```

The tests are also compiled with Clippy under CLIPPY=1, just like normal code, thus also benefitting from extra linting.

The names of the tests are currently automatically generated. This allows to reduce the burden for documentation writers, while keeping them fairly stable for bisection. This is an improvement over the rustdoc-generated names, which include the line number; but ideally we would like to get rustdoc to provide the Rust item path and a number (for multiple examples in a single documented Rust item).

In order for developers to easily see from which original line a failed doctests came from, a KTAP diagnostic line is printed to the log. In the future, we may be able to use a proper KUnit facility to append this sort of information instead.

A notable difference from KUnit C tests is that the Rust tests appear to assert using the usual assert! and assert_eq! macros from the Rust standard library (core). We provide a custom version that forwards the call to KUnit instead. Importantly, these macros do not require passing context, unlike the KUnit C ones (i.e. struct kunit *). This makes them easier to use, and readers of the documentation do not need to care about which testing framework is used. In addition, it may allow us to test third-party code more easily in the future.

However, a current limitation is that KUnit does not support assertions in other tasks. Thus we presently simply print an error to the kernel log if an assertion actually failed. This should be revisited to properly fail the test, perhaps saving the context somewhere else, or letting KUnit handle it.

Signed-off-by Miguel Ojeda <[email protected]>

---
[...]

scripts/rustdoc_test_builder.rs new file +0 -0

new file mode 100644
index 000000000000..e3b7138fb4f9

scripts/rustdoc_test_builder.rs new file +1 -0

+}

scripts/rustdoc_test_gen.rs new file +18 -0

new file mode 100644
index 000000000000..793885c32c0d
@@ -0,0 +1,162 @@
+// SPDX-License-Identifier: GPL-2.0
+
[...]
+
+use std::io::{BufWriter, Read, Write};
+use std::{fs, fs::File};
+
+fn main() {
+    let mut paths = fs::read_dir("rust/test/doctests/kernel")
+        .unwrap()
+        .map(|entry| entry.unwrap().path())
+        .collect::<Vec<_>>();
+
+    // Sort paths for clarity.
+    paths.sort();
+
+    let mut rust_tests = String::new();
+    let mut c_test_declarations = String::new();
+    let mut c_test_cases = String::new();

scripts/rustdoc_test_gen.rs new file +29 -0

+
[...]
+
+    write!(
+        BufWriter::new(File::create("rust/doctests_kernel_generated.rs").unwrap()),
+        r#"//! `kernel` crate documentation tests.
+
+const __LOG_PREFIX: &[u8] = b"rust_doctests_kernel\0";
+
+{rust_tests}
+"#
+    )
+    .unwrap();
+
+    write!(
+        BufWriter::new(File::create("rust/doctests_kernel_generated_kunit.c").unwrap()),
+        r#"/*
+ * `kernel` crate documentation tests.
+ */
+
+#include <kunit/test.h>
+
+{c_test_declarations}
+
+static struct kunit_case test_cases[] = {{
+    {c_test_cases}
+    {{ }}
+}};
+
+static struct kunit_suite test_suite = {{

+}

The KUnit maintainers would like to maintain these files on their side too (thanks!), so add them to their entry.

With this in place, scripts/get_maintainer.pl prints both sets of maintainers/reviewers (i.e. KUnit and Rust) for those files, which is the behavior we are looking for.

Signed-off-by Miguel Ojeda <[email protected]>

---
[...]

Great work! I've played this for a while, and it's really useful ;-)

The assertion warning only says line 35 but which file? Yes, the ".._sync_lock_spinlock_rs" name does provide the lead, however since we generate the test code, so we actually know the line # for each real test body, so I come up a way to give us the following:

[..] # rust_doctest_kernel_sync_lock_spinlock_rs_0: ASSERTION FAILED at rust/kernel/sync/lock/spinlock.rs:61 [..] Expected e.c == 11 to be true, but is false
[..] [FAILED] rust_doctest_kernel_sync_lock_spinlock_rs_0

Thoughts?

+ let src_file = format!("rust/kernel/{}", file.replace("_rs", ".rs").replace("_", "/"));

I can't remember that if this panic it will mention the path on it. Though if it does, then use something more explicit than .unwrap().

Please do not use unwrap here, one can easily create a path that it's not compliant under rust/test/doctests/kernel and get no clue about where this script has failed. Use .expect() or something else instead.

Little question, what's the purpose of FromErrno here?

Quoted 2 lines · Martin Rodriguez Reboredo

Little question, what's the purpose of FromErrno here?

It was because Error::from_errno is pub(crate) in the kernel crate. I should have added a comment -- my bad! :)

If we decided to make it pub eventually, then this FromErrno hack can be removed.

Cheers,
Miguel

Quoted 4 lines · Martin Rodriguez Reboredo

I can't remember that if this panic it will mention the path on it. Though if it does, then use something more explicit than .unwrap().

It doesn't print it, and I am happy to make things more explicit, but in which case(s) do you see it failing?

Quoted 4 lines

Please do not use unwrap here, one can easily create a path that it's not compliant under rust/test/doctests/kernel and get no clue about where this script has failed. Use .expect() or something else instead.

The folder is removed every time, so that should not happen I think. Yes, you can still hack things and call the script manually, but I wouldn't call that "easily".

Nevertheless, I am happy to change it if we think there is a risk, e.g. rustdoc changing the pattern (though we pin the version so far).

Thanks for taking a look Martin!

Cheers,
Miguel

The KUnit maintainers would like to maintain these files on their side too (thanks!), so add them to their entry.

With this in place, scripts/get_maintainer.pl prints both sets of maintainers/reviewers (i.e. KUnit and Rust) for those files, which is the behavior we are looking for.

Signed-off-by Miguel Ojeda <[email protected]>

Rust documentation tests are going to be build/run-tested with the KUnit integration added in a future patch, thus update them to make them compilable/testable so that we may start enforcing it.

Signed-off-by Miguel Ojeda <[email protected]>

---

Rust documentation tests are going to be build/run-tested with the KUnit integration added in a future patch, thus update them to make them compilable/testable so that we may start enforcing it.

Signed-off-by Miguel Ojeda <[email protected]>

---

Rust has documentation tests: these are typically examples of usage of any item (e.g. function, struct, module...).

They are very convenient because they are just written alongside the documentation. For instance:

    /// Sums two numbers.
    ///
    /// ```
    /// assert_eq!(mymod::f(10, 20), 30);
    /// ```
    pub fn f(a: i32, b: i32) -> i32 {
        a + b
    }

In userspace, the tests are collected and run via rustdoc. Using the tool as-is would be useful already, since it allows to compile-test most tests (thus enforcing they are kept in sync with the code they document) and run those that do not depend on in-kernel APIs.

However, by transforming the tests into a KUnit test suite, they can also be run inside the kernel. Moreover, the tests get to be compiled as other Rust kernel objects instead of targeting userspace.

On top of that, the integration with KUnit means the Rust support gets to reuse the existing testing facilities. For instance, the kernel log would look like:

KTAP version 1
1..1
KTAP version 1
# Subtest: rust_doctests_kernel
1..59
# Doctest from line 13
ok 1 rust_doctest_kernel_build_assert_rs_0 # Doctest from line 56
ok 2 rust_doctest_kernel_build_assert_rs_1 # Doctest from line 122
ok 3 rust_doctest_kernel_init_rs_0
...
# Doctest from line 150
ok 59 rust_doctest_kernel_types_rs_2
# rust_doctests_kernel: pass:59 fail:0 skip:0 total:59 # Totals: pass:59 fail:0 skip:0 total:59
ok 1 rust_doctests_kernel

Therefore, add support for running Rust documentation tests in KUnit. Some other notes about the current implementation and support follow.

The transformation is performed by a couple scripts written as Rust hostprogs.

Tests using the ? operator are also supported as usual, e.g.:

    /// ```
    /// # use kernel::{spawn_work_item, workqueue};
    /// spawn_work_item!(workqueue::system(), || pr_info!("x"))?;
    /// # Ok::<(), Error>(())
    /// ```

The tests are also compiled with Clippy under CLIPPY=1, just like normal code, thus also benefitting from extra linting.

The names of the tests are currently automatically generated. This allows to reduce the burden for documentation writers, while keeping them fairly stable for bisection. This is an improvement over the rustdoc-generated names, which include the line number; but ideally we would like to get rustdoc to provide the Rust item path and a number (for multiple examples in a single documented Rust item).

In order for developers to easily see from which original line a failed doctests came from, a KTAP diagnostic line is printed to the log. In the future, we may be able to use a proper KUnit facility to append this sort of information instead.

A notable difference from KUnit C tests is that the Rust tests appear to assert using the usual assert! and assert_eq! macros from the Rust standard library (core). We provide a custom version that forwards the call to KUnit instead. Importantly, these macros do not require passing context, unlike the KUnit C ones (i.e. struct kunit *). This makes them easier to use, and readers of the documentation do not need to care about which testing framework is used. In addition, it may allow us to test third-party code more easily in the future.

However, a current limitation is that KUnit does not support assertions in other tasks. Thus we presently simply print an error to the kernel log if an assertion actually failed. This should be revisited to properly fail the test, perhaps saving the context somewhere else, or letting KUnit handle it.

Signed-off-by Miguel Ojeda <[email protected]>

Quoted 2 lines · Boqun Feng

Great work! I've played this for a while, and it's really useful ;-)

Thanks!

Quoted 10 lines

The assertion warning only says line 35 but which file? Yes, the ".._sync_lock_spinlock_rs" name does provide the lead, however since we generate the test code, so we actually know the line # for each real test body, so I come up a way to give us the following:

[..] # rust_doctest_kernel_sync_lock_spinlock_rs_0: ASSERTION FAILED at rust/kernel/sync/lock/spinlock.rs:61 [..] Expected e.c == 11 to be true, but is false
[..] [FAILED] rust_doctest_kernel_sync_lock_spinlock_rs_0

Thoughts?

Sounds good to me. However, David/Philip, is this OK or do you really need/use the actual/compiled source file there? If you don't need it, does it need to exist / be a real file at least? If the latter answer is a "yes", which I guess it may be likely, then:

Quoted 2 lines

+ let src_file = format!("rust/kernel/{}", file.replace("_rs", ".rs").replace("_", "/"));

This would not work for files with a _ in their name, like locked_by.rs. I guess we could still find the real filename based on that information walking the dir, which is another hack I recall considering at some point.

Otherwise, if "fake" filenames in the line above are OK for David/Philip (I suspect they may want to open them for reporting?), then I guess the file one may be good enough and eventually we should get rustdoc to give us the proper metadata anyway.

This is the initial KUnit integration for running Rust documentation tests within the kernel.

Thank you to the KUnit team for all the input and feedback on this over the months, as well as the Intel LKP 0-Day team!

This may be merged through either the KUnit or the Rust trees. If the KUnit team wants to merge it, then that would be great.

Please see the message in the main commit for the details.

Miguel Ojeda (6):
rust: init: make doctests compilable/testable
rust: str: make doctests compilable/testable
rust: sync: make doctests compilable/testable
rust: types: make doctests compilable/testable
rust: support running Rust documentation tests as KUnit ones
MAINTAINERS: add Rust KUnit files to the KUnit entry

 MAINTAINERS                       |   2 +
 lib/Kconfig.debug                 |  13 +++
 rust/.gitignore                   |   2 +
 rust/Makefile                     |  29 ++++++
 rust/bindings/bindings_helper.h   |   1 +
 rust/helpers.c                    |   7 ++
 rust/kernel/init.rs               |  25 +++--
 rust/kernel/kunit.rs              | 156 ++++++++++++++++++++++++++++
 rust/kernel/lib.rs                |   2 +
 rust/kernel/str.rs                |   4 +-
 rust/kernel/sync/arc.rs           |   9 +-
 rust/kernel/sync/lock/mutex.rs    |   1 +
 rust/kernel/sync/lock/spinlock.rs |   1 +
 rust/kernel/types.rs              |   6 +-
 scripts/.gitignore                |   2 +
 scripts/Makefile                  |   4 +
 scripts/rustdoc_test_builder.rs   |  73 ++++++++++++++
 scripts/rustdoc_test_gen.rs       | 162 ++++++++++++++++++++++++++++++
 18 files changed, 484 insertions(+), 15 deletions(-)
 create mode 100644 rust/kernel/kunit.rs
 create mode 100644 scripts/rustdoc_test_builder.rs
 create mode 100644 scripts/rustdoc_test_gen.rs

base-commit: d2e3115d717197cb2bc020dd1f06b06538474ac3 --
2.41.0

Rust documentation tests are going to be build/run-tested with the KUnit integration added in a future patch, thus update them to make them compilable/testable so that we may start enforcing it.

Signed-off-by Miguel Ojeda <[email protected]>

---

Rust documentation tests are going to be build/run-tested with the KUnit integration added in a future patch, thus update them to make them compilable/testable so that we may start enforcing it.

Signed-off-by Miguel Ojeda <[email protected]>

---

Rust documentation tests are going to be build/run-tested with the KUnit integration added in a future patch, thus update them to make them compilable/testable so that we may start enforcing it.

Signed-off-by Miguel Ojeda <[email protected]>

---

Rust documentation tests are going to be build/run-tested with the KUnit integration added in a future patch, thus update them to make them compilable/testable so that we may start enforcing it.

Signed-off-by Miguel Ojeda <[email protected]>

---

Rust has documentation tests: these are typically examples of usage of any item (e.g. function, struct, module...).

They are very convenient because they are just written alongside the documentation. For instance:

    /// Sums two numbers.
    ///
    /// ```
    /// assert_eq!(mymod::f(10, 20), 30);
    /// ```
    pub fn f(a: i32, b: i32) -> i32 {
        a + b
    }

In userspace, the tests are collected and run via rustdoc. Using the tool as-is would be useful already, since it allows to compile-test most tests (thus enforcing they are kept in sync with the code they document) and run those that do not depend on in-kernel APIs.

However, by transforming the tests into a KUnit test suite, they can also be run inside the kernel. Moreover, the tests get to be compiled as other Rust kernel objects instead of targeting userspace.

On top of that, the integration with KUnit means the Rust support gets to reuse the existing testing facilities. For instance, the kernel log would look like:

KTAP version 1
1..1
KTAP version 1
# Subtest: rust_doctests_kernel
1..59
# Doctest from line 13
ok 1 rust_doctest_kernel_build_assert_rs_0 # Doctest from line 56
ok 2 rust_doctest_kernel_build_assert_rs_1 # Doctest from line 122
ok 3 rust_doctest_kernel_init_rs_0
...
# Doctest from line 150
ok 59 rust_doctest_kernel_types_rs_2
# rust_doctests_kernel: pass:59 fail:0 skip:0 total:59 # Totals: pass:59 fail:0 skip:0 total:59
ok 1 rust_doctests_kernel

Therefore, add support for running Rust documentation tests in KUnit. Some other notes about the current implementation and support follow.

The transformation is performed by a couple scripts written as Rust hostprogs.

Tests using the ? operator are also supported as usual, e.g.:

    /// ```
    /// # use kernel::{spawn_work_item, workqueue};
    /// spawn_work_item!(workqueue::system(), || pr_info!("x"))?;
    /// # Ok::<(), Error>(())
    /// ```

The tests are also compiled with Clippy under CLIPPY=1, just like normal code, thus also benefitting from extra linting.

The names of the tests are currently automatically generated. This allows to reduce the burden for documentation writers, while keeping them fairly stable for bisection. This is an improvement over the rustdoc-generated names, which include the line number; but ideally we would like to get rustdoc to provide the Rust item path and a number (for multiple examples in a single documented Rust item).

In order for developers to easily see from which original line a failed doctests came from, a KTAP diagnostic line is printed to the log. In the future, we may be able to use a proper KUnit facility to append this sort of information instead.

A notable difference from KUnit C tests is that the Rust tests appear to assert using the usual assert! and assert_eq! macros from the Rust standard library (core). We provide a custom version that forwards the call to KUnit instead. Importantly, these macros do not require passing context, unlike the KUnit C ones (i.e. struct kunit *). This makes them easier to use, and readers of the documentation do not need to care about which testing framework is used. In addition, it may allow us to test third-party code more easily in the future.

However, a current limitation is that KUnit does not support assertions in other tasks. Thus we presently simply print an error to the kernel log if an assertion actually failed. This should be revisited to properly fail the test, perhaps saving the context somewhere else, or letting KUnit handle it.

Signed-off-by Miguel Ojeda <[email protected]>

---

 lib/Kconfig.debug               |  13 +++
 rust/.gitignore                 |   2 +
 rust/Makefile                   |  29 ++++++
 rust/bindings/bindings_helper.h |   1 +
 rust/helpers.c                  |   7 ++
 rust/kernel/kunit.rs            | 156 ++++++++++++++++++++++++++++++
 rust/kernel/lib.rs              |   2 +
 scripts/.gitignore              |   2 +
 scripts/Makefile                |   4 +
 scripts/rustdoc_test_builder.rs |  73 ++++++++++++++
 scripts/rustdoc_test_gen.rs     | 162 ++++++++++++++++++++++++++++++++
 11 files changed, 451 insertions(+)
 create mode 100644 rust/kernel/kunit.rs
 create mode 100644 scripts/rustdoc_test_builder.rs
 create mode 100644 scripts/rustdoc_test_gen.rs

lib/Kconfig.debug +0 -0

index ce51d4dc6803..49f5e9c42200 100644

lib/Kconfig.debug +11 -0

+       depends on RUST && KUNIT=y
+       default KUNIT_ALL_TESTS
+       help
+         This builds the documentation tests of the `kernel` crate
+         as KUnit tests.
+
+         For more information on KUnit and unit tests in general,
+         please refer to the KUnit documentation in Documentation/dev-tools/kunit/.
+
+         If unsure, say N.
+
 endmenu # "Rust"
 
 endmenu # Kernel hacking

rust/.gitignore +2 -0

index 21552992b401..d3829ffab80b 100644
@@ -2,6 +2,8 @@
 
 bindings_generated.rs
 bindings_helpers_generated.rs
+doctests_kernel_generated.rs
+doctests_kernel_generated_kunit.c
 uapi_generated.rs
 exports_*_generated.h
 doc/

rust/Makefile +29 -0

index 7c9d9f11aec5..e4e8b83752e2 100644
@@ -27,6 +27,12 @@ endif
 
 obj-$(CONFIG_RUST) += exports.o
 
+always-$(CONFIG_RUST_KERNEL_KUNIT_TEST) += doctests_kernel_generated.rs
+always-$(CONFIG_RUST_KERNEL_KUNIT_TEST) += doctests_kernel_generated_kunit.c
+
+obj-$(CONFIG_RUST_KERNEL_KUNIT_TEST) += doctests_kernel_generated.o
+obj-$(CONFIG_RUST_KERNEL_KUNIT_TEST) += doctests_kernel_generated_kunit.o
+
 # Avoids running `$(RUSTC)` for the sysroot when it may not be available.
 ifdef CONFIG_RUST
 

@@ -39,9 +45,11 @@ ifeq ($(quiet),silent_)
 cargo_quiet=-q
 rust_test_quiet=-q
 rustdoc_test_quiet=--test-args -q
+rustdoc_test_kernel_quiet=>/dev/null
 else ifeq ($(quiet),quiet_)
 rust_test_quiet=-q
 rustdoc_test_quiet=--test-args -q
+rustdoc_test_kernel_quiet=>/dev/null
 else
 cargo_quiet=--verbose
 endif

@@ -157,6 +165,27 @@ quiet_cmd_rustdoc_test = RUSTDOC T $<
                -L$(objtree)/$(obj)/test --output $(objtree)/$(obj)/doc \
                --crate-name $(subst rusttest-,,$@) $<
 
+quiet_cmd_rustdoc_test_kernel = RUSTDOC TK $<
+      cmd_rustdoc_test_kernel = \
+       rm -rf $(objtree)/$(obj)/test/doctests/kernel; \
+       mkdir -p $(objtree)/$(obj)/test/doctests/kernel; \
+       OBJTREE=$(abspath $(objtree)) \
+       $(RUSTDOC) --test $(rust_flags) \
+               @$(objtree)/include/generated/rustc_cfg \
+               -L$(objtree)/$(obj) --extern alloc --extern kernel \
+               --extern build_error --extern macros \
+               --extern bindings --extern uapi \
+               --no-run --crate-name kernel -Zunstable-options \
+               --test-builder $(objtree)/scripts/rustdoc_test_builder \
+               $< $(rustdoc_test_kernel_quiet); \
+       $(objtree)/scripts/rustdoc_test_gen
+
+%/doctests_kernel_generated.rs %/doctests_kernel_generated_kunit.c: \
+    $(src)/kernel/lib.rs $(obj)/kernel.o \
+    $(objtree)/scripts/rustdoc_test_builder \
+    $(objtree)/scripts/rustdoc_test_gen FORCE
+       $(call if_changed,rustdoc_test_kernel)
+
 # We cannot use `-Zpanic-abort-tests` because some tests are dynamic,
 # so for the moment we skip `-Cpanic=abort`.
 quiet_cmd_rustc_test = RUSTC T  $<

rust/bindings/bindings_helper.h +1 -0

index 3e601ce2548d..0f8d37c31ac2 100644
@@ -6,6 +6,7 @@
  * Sorted alphabetically.
  */
 
+#include <kunit/test.h>
 #include <linux/errname.h>
 #include <linux/slab.h>
 #include <linux/refcount.h>

rust/helpers.c +7 -0

index bb594da56137..49a5e1a4f0ae 100644
@@ -18,6 +18,7 @@
  * accidentally exposed.
  */
 
+#include <kunit/test-bug.h>
 #include <linux/bug.h>
 #include <linux/build_bug.h>
 #include <linux/err.h>

@@ -135,6 +136,12 @@ void rust_helper_put_task_struct(struct task_struct *t)
 }
 EXPORT_SYMBOL_GPL(rust_helper_put_task_struct);
 
+struct kunit *rust_helper_kunit_get_current_test(void)
+{
+       return kunit_get_current_test();
+}
+EXPORT_SYMBOL_GPL(rust_helper_kunit_get_current_test);
+
 /*
  * We use `bindgen`'s `--size_t-is-usize` option to bind the C `size_t` type
  * as the Rust `usize` type, so we can use it in contexts where Rust

rust/kernel/kunit.rs new file +126 -0

new file mode 100644
index 000000000000..3c94efcd7f76
@@ -0,0 +1,156 @@
+// SPDX-License-Identifier: GPL-2.0
+
+//! KUnit-based macros for Rust unit tests.
+//!
+//! C header: [`include/kunit/test.h`](../../../../../include/kunit/test.h)
+//!
+//! Reference: <https://docs.kernel.org/dev-tools/kunit/index.html>
+
+use core::{ffi::c_void, fmt};
+
+/// Prints a KUnit error.
+///
+/// Public but hidden since it should only be used from KUnit generated code.
+#[doc(hidden)]
+pub fn err(args: fmt::Arguments<'_>) {
+    // SAFETY: The format string is null-terminated and the `%pA` specifier matches the argument we
+    // are passing.
+    #[cfg(CONFIG_PRINTK)]
+    unsafe {
+        bindings::_printk(
+            b"\x013%pA\0".as_ptr() as _,
+            &args as *const _ as *const c_void,
+        );
+    }
+}
+
+/// Prints a KUnit error.
+///
+/// Public but hidden since it should only be used from KUnit generated code.
+#[doc(hidden)]
+pub fn info(args: fmt::Arguments<'_>) {
+    // SAFETY: The format string is null-terminated and the `%pA` specifier matches the argument we
+    // are passing.
+    #[cfg(CONFIG_PRINTK)]
+    unsafe {
+        bindings::_printk(
+            b"\x016%pA\0".as_ptr() as _,
+            &args as *const _ as *const c_void,
+        );
+    }
+}
+
+/// Asserts that a boolean expression is `true` at runtime.
+///
+/// Public but hidden since it should only be used from generated tests.
+///
+/// Unlike the one in `core`, this one does not panic; instead, it is mapped to the KUnit
+/// facilities. See [`assert!`] for more details.
+#[doc(hidden)]
+#[macro_export]
+macro_rules! kunit_assert {
+    ($name:literal, $condition:expr $(,)?) => {
+        'out: {
+            // Do nothing if the condition is `true`.
+            if $condition {
+                break 'out;
+            }
+
+            static LINE: i32 = core::line!() as i32;
+            static FILE: &'static $crate::str::CStr = $crate::c_str!(core::file!());
+            static CONDITION: &'static $crate::str::CStr = $crate::c_str!(stringify!($condition));
+
+            // SAFETY: FFI call without safety requirements.
+            let kunit_test = unsafe { $crate::bindings::kunit_get_current_test() };
+            if kunit_test.is_null() {
+                // The assertion failed but this task is not running a KUnit test, so we cannot call
+                // KUnit, but at least print an error to the kernel log. This may happen if this
+                // macro is called from an spawned thread in a test (see
+                // `scripts/rustdoc_test_gen.rs`) or if some non-test code calls this macro by
+                // mistake (it is hidden to prevent that).
+                //
+                // This mimics KUnit's failed assertion format.
+                $crate::kunit::err(format_args!(
+                    "    # {}: ASSERTION FAILED at {FILE}:{LINE}\n",
+                    $name
+                ));
+                $crate::kunit::err(format_args!(
+                    "    Expected {CONDITION} to be true, but is false\n"
+                ));
+                $crate::kunit::err(format_args!(
+                    "    Failure not reported to KUnit since this is a non-KUnit task\n"
+                ));
+                break 'out;
+            }
+
+            #[repr(transparent)]
+            struct Location($crate::bindings::kunit_loc);
+
+            #[repr(transparent)]
+            struct UnaryAssert($crate::bindings::kunit_unary_assert);
+
+            // SAFETY: There is only a static instance and in that one the pointer field points to
+            // an immutable C string.
+            unsafe impl Sync for Location {}
+
+            // SAFETY: There is only a static instance and in that one the pointer field points to
+            // an immutable C string.
+            unsafe impl Sync for UnaryAssert {}
+
+            static LOCATION: Location = Location($crate::bindings::kunit_loc {
+                file: FILE.as_char_ptr(),
+                line: LINE,
+            });
+            static ASSERTION: UnaryAssert = UnaryAssert($crate::bindings::kunit_unary_assert {
+                assert: $crate::bindings::kunit_assert {},
+                condition: CONDITION.as_char_ptr(),
+                expected_true: true,
+            });
+
+            // SAFETY:
+            //   - FFI call.
+            //   - The `kunit_test` pointer is valid because we got it from
+            //     `kunit_get_current_test()` and it was not null. This means we are in a KUnit
+            //     test, and that the pointer can be passed to KUnit functions and assertions.
+            //   - The string pointers (`file` and `condition` above) point to null-terminated
+            //     strings since they are `CStr`s.
+            //   - The function pointer (`format`) points to the proper function.
+            //   - The pointers passed will remain valid since they point to `static`s.
+            //   - The format string is allowed to be null.
+            //   - There are, however, problems with this: first of all, this will end up stopping
+            //     the thread, without running destructors. While that is problematic in itself,
+            //     it is considered UB to have what is effectively a forced foreign unwind
+            //     with `extern "C"` ABI. One could observe the stack that is now gone from
+            //     another thread. We should avoid pinning stack variables to prevent library UB,
+            //     too. For the moment, given that test failures are reported immediately before the
+            //     next test runs, that test failures should be fixed and that KUnit is explicitly

rust/kernel/kunit.rs new file +20 -0

+            }
+        }
+    };
+}
+
+/// Asserts that two expressions are equal to each other (using [`PartialEq`]).
+///
+/// Public but hidden since it should only be used from generated tests.
+///
+/// Unlike the one in `core`, this one does not panic; instead, it is mapped to the KUnit
+/// facilities. See [`assert!`] for more details.
+#[doc(hidden)]
+#[macro_export]
+macro_rules! kunit_assert_eq {
+    ($name:literal, $left:expr, $right:expr $(,)?) => {{
+        // For the moment, we just forward to the expression assert because, for binary asserts,
+        // KUnit supports only a few types (e.g. integers).
+        $crate::kunit_assert!($name, $left == $right);
+    }};
+}

rust/kernel/lib.rs +2 -0

index 85b261209977..3642cadc34b1 100644
@@ -34,6 +34,8 @@
 pub mod error;
 pub mod init;
 pub mod ioctl;
+#[cfg(CONFIG_KUNIT)]
+pub mod kunit;
 pub mod prelude;
 pub mod print;
 mod static_assert;

scripts/.gitignore +2 -0

index 6e9ce6720a05..3dbb8bb2457b 100644
@@ -5,6 +5,8 @@
 /kallsyms
 /module.lds
 /recordmcount
+/rustdoc_test_builder
+/rustdoc_test_gen
 /sign-file
 /sorttable
 /target.json

scripts/Makefile +4 -0

index 32b6ba722728..d5a5382e753c 100644
@@ -9,6 +9,8 @@ hostprogs-always-$(CONFIG_BUILDTIME_TABLE_SORT)         += sorttable
 hostprogs-always-$(CONFIG_ASN1)                                += asn1_compiler
 hostprogs-always-$(CONFIG_MODULE_SIG_FORMAT)           += sign-file
 hostprogs-always-$(CONFIG_SYSTEM_EXTRA_CERTIFICATE)    += insert-sys-cert
+hostprogs-always-$(CONFIG_RUST_KERNEL_KUNIT_TEST)      += rustdoc_test_builder
+hostprogs-always-$(CONFIG_RUST_KERNEL_KUNIT_TEST)      += rustdoc_test_gen
 always-$(CONFIG_RUST)                                  += target.json
 
 filechk_rust_target = $< < include/config/auto.conf

@@ -18,6 +20,8 @@ $(obj)/target.json: scripts/generate_rust_target include/config/auto.conf FORCE
 
 hostprogs += generate_rust_target
 generate_rust_target-rust := y
+rustdoc_test_builder-rust := y
+rustdoc_test_gen-rust := y
 
 HOSTCFLAGS_sorttable.o = -I$(srctree)/tools/include
 HOSTLDLIBS_sorttable = -lpthread

scripts/rustdoc_test_builder.rs new file +73 -0

new file mode 100644
index 000000000000..e3b7138fb4f9
@@ -0,0 +1,73 @@
+// SPDX-License-Identifier: GPL-2.0
+
+//! Test builder for `rustdoc`-generated tests.
+//!
+//! This script is a hack to extract the test from `rustdoc`'s output. Ideally, `rustdoc` would
+//! have an option to generate this information instead, e.g. as JSON output.
+//!
+//! The `rustdoc`-generated test names look like `{file}_{line}_{number}`, e.g.
+//! `...path_rust_kernel_sync_arc_rs_42_0`. `number` is the "test number", needed in cases like
+//! a macro that expands into items with doctests is invoked several times within the same line.
+//!
+//! However, since these names are used for bisection in CI, the line number makes it not stable
+//! at all. In the future, we would like `rustdoc` to give us the Rust item path associated with
+//! the test, plus a "test number" (for cases with several examples per item) and generate a name
+//! from that. For the moment, we generate ourselves a new name, `{file}_{number}` instead, in
+//! the `gen` script (done there since we need to be aware of all the tests in a given file).
+
+use std::fs::File;
+use std::io::{BufWriter, Read, Write};
+
+fn main() {
+    let mut stdin = std::io::stdin().lock();
+    let mut body = String::new();
+    stdin.read_to_string(&mut body).unwrap();
+
+    // Find the generated function name looking for the inner function inside `main()`.
+    //
+    // The line we are looking for looks like one of the following:
+    //
+    // ```
+    // fn main() { #[allow(non_snake_case)] fn _doctest_main_rust_kernel_file_rs_28_0() {
+    // fn main() { #[allow(non_snake_case)] fn _doctest_main_rust_kernel_file_rs_37_0() -> Result<(), impl core::fmt::Debug> {
+    // ```
+    //
+    // It should be unlikely that doctest code matches such lines (when code is formatted properly).
+    let rustdoc_function_name = body
+        .lines()
+        .find_map(|line| {
+            Some(
+                line.split_once("fn main() {")?
+                    .1
+                    .split_once("fn ")?
+                    .1
+                    .split_once("()")?
+                    .0,
+            )
+            .filter(|x| x.chars().all(|c| c.is_alphanumeric() || c == '_'))
+        })
+        .expect("No test function found in `rustdoc`'s output.");
+
+    // Qualify `Result` to avoid the collision with our own `Result` coming from the prelude.
+    let body = body.replace(
+        &format!("{rustdoc_function_name}() -> Result<(), impl core::fmt::Debug> {{"),
+        &format!("{rustdoc_function_name}() -> core::result::Result<(), impl core::fmt::Debug> {{"),
+    );
+
+    // For tests that get generated with `Result`, like above, `rustdoc` generates an `unwrap()` on
+    // the return value to check there were no returned errors. Instead, we use our assert macro
+    // since we want to just fail the test, not panic the kernel.
+    //
+    // We save the result in a variable so that the failed assertion message looks nicer.
+    let body = body.replace(
+        &format!("}} {rustdoc_function_name}().unwrap() }}"),
+        &format!("}} let test_return_value = {rustdoc_function_name}(); assert!(test_return_value.is_ok()); }}"),
+    );
+
+    // Figure out a smaller test name based on the generated function name.
+    let name = rustdoc_function_name.split_once("_rust_kernel_").unwrap().1;
+
+    let path = format!("rust/test/doctests/kernel/{name}");
+
+    write!(BufWriter::new(File::create(path).unwrap()), "{body}").unwrap();
+}

scripts/rustdoc_test_gen.rs new file +12 -0

new file mode 100644
index 000000000000..793885c32c0d
@@ -0,0 +1,162 @@
+// SPDX-License-Identifier: GPL-2.0
+
+//! Generates KUnit tests from saved `rustdoc`-generated tests.
+//!
+//! KUnit passes a context (`struct kunit *`) to each test, which should be forwarded to the other
+//! KUnit functions and macros.
+//!
+//! However, we want to keep this as an implementation detail because:
+//!
+//!   - Test code should not care about the implementation.
+//!
+//!   - Documentation looks worse if it needs to carry extra details unrelated to the piece

scripts/rustdoc_test_gen.rs new file +73 -0

+//!
+//! Note that this means other threads/tasks potentially spawned by a given test, if failing, will
+//! report the failure in the kernel log but will not fail the actual test. Saving the pointer in
+//! e.g. a `static` per test does not fully solve the issue either, because currently KUnit does
+//! not support assertions (only expectations) from other tasks. Thus leave that feature for
+//! the future, which simplifies the code here too. We could also simply not allow `assert`s in
+//! other tasks, but that seems overly constraining, and we do want to support them, eventually.
+
+use std::io::{BufWriter, Read, Write};
+use std::{fs, fs::File};
+
+fn main() {
+    let mut paths = fs::read_dir("rust/test/doctests/kernel")
+        .unwrap()
+        .map(|entry| entry.unwrap().path())
+        .collect::<Vec<_>>();
+
+    // Sort paths for clarity.
+    paths.sort();
+
+    let mut rust_tests = String::new();
+    let mut c_test_declarations = String::new();
+    let mut c_test_cases = String::new();
+    let mut body = String::new();
+    let mut last_file = String::new();
+    let mut number = 0;
+    for path in paths {
+        // The `name` follows the `{file}_{line}_{number}` pattern (see description in
+        // `scripts/rustdoc_test_builder.rs`). Discard the `number`.
+        let name = path.file_name().unwrap().to_str().unwrap().to_string();
+
+        // Extract the `file` and the `line`, discarding the `number`.
+        let (file, line) = name.rsplit_once('_').unwrap().0.rsplit_once('_').unwrap();
+
+        // Generate an ID sequence ("test number") for each one in the file.
+        if file == last_file {
+            number += 1;
+        } else {
+            number = 0;
+            last_file = file.to_string();
+        }
+
+        // Generate a KUnit name (i.e. test name and C symbol) for this test.
+        //
+        // We avoid the line number, like `rustdoc` does, to make things slightly more stable for
+        // bisection purposes. However, to aid developers in mapping back what test failed, we will
+        // print a diagnostics line in the KTAP report.
+        let kunit_name = format!("rust_doctest_kernel_{file}_{number}");
+
+        // Read the test's text contents to dump it below.
+        body.clear();
+        File::open(path).unwrap().read_to_string(&mut body).unwrap();
+
+        let line = line.parse::<core::ffi::c_int>().unwrap();
+
+        use std::fmt::Write;
+        write!(
+            rust_tests,
+            r#"/// Generated `{name}` KUnit test case from a Rust documentation test.
+#[no_mangle]
+pub extern "C" fn {kunit_name}(__kunit_test: *mut kernel::bindings::kunit) {{
+    /// Overrides the usual [`assert!`] macro with one that calls KUnit instead.
+    #[allow(unused)]
+    macro_rules! assert {{
+        ($cond:expr $(,)?) => {{{{
+            kernel::kunit_assert!("{kunit_name}", $cond);
+        }}}}
+    }}
+
+    /// Overrides the usual [`assert_eq!`] macro with one that calls KUnit instead.
+    #[allow(unused)]
+    macro_rules! assert_eq {{
+        ($left:expr, $right:expr $(,)?) => {{{{

scripts/rustdoc_test_gen.rs new file +22 -0

+
+    {{
+        {body}
+        main();
+    }}
+}}
+
+"#
+        )
+        .unwrap();
+
+        write!(c_test_declarations, "void {kunit_name}(struct kunit *);\n").unwrap();
+        write!(c_test_cases, "    KUNIT_CASE({kunit_name}),\n").unwrap();
+    }
+
+    let rust_tests = rust_tests.trim();
+    let c_test_declarations = c_test_declarations.trim();
+    let c_test_cases = c_test_cases.trim();
+
+    write!(
+        BufWriter::new(File::create("rust/doctests_kernel_generated.rs").unwrap()),
+        r#"//! `kernel` crate documentation tests.

scripts/rustdoc_test_gen.rs new file +25 -1

+        r#"/*
+ * `kernel` crate documentation tests.
+ */
+
+#include <kunit/test.h>
+
+{c_test_declarations}
+
+static struct kunit_case test_cases[] = {{
+    {c_test_cases}
+    {{ }}
+}};
+
+static struct kunit_suite test_suite = {{
+    .name = "rust_doctests_kernel",
+    .test_cases = test_cases,
+}};
+
+kunit_test_suite(test_suite);
+
+MODULE_LICENSE("GPL");
+"#
+    )
+    .unwrap();
+}
--

2.41.0

The KUnit maintainers would like to maintain these files on their side too (thanks!), so add them to their entry.

With this in place, scripts/get_maintainer.pl prints both sets of maintainers/reviewers (i.e. KUnit and Rust) for those files, which is the behavior we are looking for.

Signed-off-by Miguel Ojeda <[email protected]>

---

 MAINTAINERS | 2 ++
 1 file changed, 2 insertions(+)

MAINTAINERS +2 -1

index 250518fc70ff..f4c9ce1b685f 100644
@@ -11323,6 +11323,8 @@ W:      https://google.github.io/kunit-docs/third_party/kernel/docs/
 F:     Documentation/dev-tools/kunit/
 F:     include/kunit/
 F:     lib/kunit/
+F:     rust/kernel/kunit.rs
+F:     scripts/rustdoc_test_*
 F:     tools/testing/kunit/
 
 KERNEL USERMODE HELPER
--

2.41.0

--
You received this message because you are subscribed to the Google Groups "KUnit Development" group.
To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To view this discussion on the web visit https://groups.google.com/d/msgid/kunit-dev/20230614180837.630180-7-ojeda%40kernel.org.

Rust documentation tests are going to be build/run-tested with the KUnit integration added in a future patch, thus update them to make them compilable/testable so that we may start enforcing it.

Signed-off-by Miguel Ojeda <[email protected]>

---
 rust/kernel/init.rs | 25 ++++++++++++++++---------
 1 file changed, 16 insertions(+), 9 deletions(-)

rust/kernel/init.rs +16 -9

index b4332a4ec1f4..1073515ed40e 100644
@@ -120,14 +120,23 @@
 //!   `slot` gets called.
 //!
 //! ```rust
-//! use kernel::{prelude::*, init};
+//! # #![allow(unreachable_pub, clippy::disallowed_names)]
+//! use kernel::{prelude::*, init, types::Opaque};
 //! use core::{ptr::addr_of_mut, marker::PhantomPinned, pin::Pin};
 //! # mod bindings {
+//! #     #![allow(non_camel_case_types)]
 //! #     pub struct foo;
 //! #     pub unsafe fn init_foo(_ptr: *mut foo) {}
 //! #     pub unsafe fn destroy_foo(_ptr: *mut foo) {}
 //! #     pub unsafe fn enable_foo(_ptr: *mut foo, _flags: u32) -> i32 { 0 }
 //! # }
+//! # trait FromErrno {
+//! #     fn from_errno(errno: core::ffi::c_int) -> Error {
+//! #         // Dummy error that can be constructed outside the `kernel` crate.
+//! #         Error::from(core::fmt::Error)
+//! #     }
+//! # }
+//! # impl FromErrno for Error {}
 //! /// # Invariants
 //! ///
 //! /// `foo` is always initialized

@@ -158,7 +167,7 @@
 //!                 if err != 0 {
 //!                     // Enabling has failed, first clean up the foo and then return the error.
 //!                     bindings::destroy_foo(Opaque::raw_get(foo));
-//!                     return Err(Error::from_kernel_errno(err));
+//!                     return Err(Error::from_errno(err));
 //!                 }
 //!
 //!                 // All fields of `RawFoo` have been initialized, since `_p` is a ZST.

@@ -226,8 +235,7 @@
 ///
 /// ```rust
 /// # #![allow(clippy::disallowed_names, clippy::new_ret_no_self)]
-/// # use kernel::{init, pin_init, stack_pin_init, init::*, sync::Mutex, new_mutex};
-/// # use macros::pin_data;
+/// # use kernel::{init, macros::pin_data, pin_init, stack_pin_init, init::*, sync::Mutex, new_mutex};
 /// # use core::pin::Pin;
 /// #[pin_data]
 /// struct Foo {

@@ -277,7 +285,7 @@ macro_rules! stack_pin_init {
 ///
 /// # Examples
 ///
-/// ```rust
+/// ```rust,ignore
 /// # #![allow(clippy::disallowed_names, clippy::new_ret_no_self)]
 /// # use kernel::{init, pin_init, stack_try_pin_init, init::*, sync::Mutex, new_mutex};
 /// # use macros::pin_data;

@@ -303,7 +311,7 @@ macro_rules! stack_pin_init {
 /// pr_info!("a: {}", &*foo.a.lock());
 /// ```
 ///
-/// ```rust
+/// ```rust,ignore
 /// # #![allow(clippy::disallowed_names, clippy::new_ret_no_self)]
 /// # use kernel::{init, pin_init, stack_try_pin_init, init::*, sync::Mutex, new_mutex};
 /// # use macros::pin_data;

@@ -513,8 +521,7 @@ macro_rules! stack_try_pin_init {
 /// For instance:
 ///
 /// ```rust
-/// # use kernel::pin_init;
-/// # use macros::pin_data;
+/// # use kernel::{macros::pin_data, pin_init};
 /// # use core::{ptr::addr_of_mut, marker::PhantomPinned};
 /// #[pin_data]
 /// struct Buf {

@@ -841,7 +848,7 @@ macro_rules! init {
 /// # Examples
 ///
 /// ```rust
-/// use kernel::{init::PinInit, error::Error, InPlaceInit};
+/// use kernel::{init::{PinInit, zeroed}, error::Error};
 /// struct BigBuf {
 ///     big: Box<[u8; 1024 * 1024 * 1024]>,
 ///     small: [u8; 1024 * 1024],

Signature · 1 line

2.41.0

Rust documentation tests are going to be build/run-tested with the KUnit integration added in a future patch, thus update them to make them compilable/testable so that we may start enforcing it.

Signed-off-by Miguel Ojeda <[email protected]>

---
 rust/kernel/str.rs | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

rust/kernel/str.rs +3 -1

index c9dd3bf59e34..c41607b2e4fe 100644
@@ -213,6 +213,7 @@ impl fmt::Display for CStr {
     ///
     /// ```
     /// # use kernel::c_str;
+    /// # use kernel::fmt;
     /// # use kernel::str::CStr;
     /// # use kernel::str::CString;
     /// let penguin = c_str!("🐧");

@@ -241,6 +242,7 @@ impl fmt::Debug for CStr {
     ///
     /// ```
     /// # use kernel::c_str;
+    /// # use kernel::fmt;
     /// # use kernel::str::CStr;
     /// # use kernel::str::CString;
     /// let penguin = c_str!("🐧");

@@ -529,7 +531,7 @@ fn write_str(&mut self, s: &str) -> fmt::Result {
 /// # Examples
 ///
 /// ```
-/// use kernel::str::CString;
+/// use kernel::{str::CString, fmt};
 ///
 /// let s = CString::try_from_fmt(fmt!("{}{}{}", "abc", 10, 20)).unwrap();
 /// assert_eq!(s.as_bytes_with_nul(), "abc1020\0".as_bytes());

Signature · 1 line

2.41.0

Rust documentation tests are going to be build/run-tested with the KUnit integration added in a future patch, thus update them to make them compilable/testable so that we may start enforcing it.

Signed-off-by Miguel Ojeda <[email protected]>

---
 rust/kernel/sync/arc.rs           | 9 +++++++--
 rust/kernel/sync/lock/mutex.rs    | 1 +
 rust/kernel/sync/lock/spinlock.rs | 1 +
 3 files changed, 9 insertions(+), 2 deletions(-)

rust/kernel/sync/arc.rs +7 -2

index a89843cacaad..1ecb2efab51e 100644
@@ -73,6 +73,7 @@
 /// assert_eq!(cloned.b, 20);
 ///
 /// // The refcount drops to zero when `cloned` goes out of scope, and the memory is freed.
+/// # Ok::<(), Error>(())
 /// ```
 ///
 /// Using `Arc<T>` as the type of `self`:

@@ -98,6 +99,7 @@
 /// let obj = Arc::try_new(Example { a: 10, b: 20 })?;
 /// obj.use_reference();
 /// obj.take_over();
+/// # Ok::<(), Error>(())
 /// ```
 ///
 /// Coercion from `Arc<Example>` to `Arc<dyn MyTrait>`:

@@ -121,6 +123,7 @@
 ///
 /// // `coerced` has type `Arc<dyn MyTrait>`.
 /// let coerced: Arc<dyn MyTrait> = obj;
+/// # Ok::<(), Error>(())
 /// ```
 pub struct Arc<T: ?Sized> {
     ptr: NonNull<ArcInner<T>>,

@@ -337,7 +340,7 @@ fn from(item: Pin<UniqueArc<T>>) -> Self {
 /// # Example
 ///
 /// ```
-/// use crate::sync::{Arc, ArcBorrow};
+/// use kernel::sync::{Arc, ArcBorrow};
 ///
 /// struct Example;
 ///

@@ -350,12 +353,13 @@ fn from(item: Pin<UniqueArc<T>>) -> Self {
 ///
 /// // Assert that both `obj` and `cloned` point to the same underlying object.
 /// assert!(core::ptr::eq(&*obj, &*cloned));
+/// # Ok::<(), Error>(())
 /// ```
 ///
 /// Using `ArcBorrow<T>` as the type of `self`:
 ///
 /// ```
-/// use crate::sync::{Arc, ArcBorrow};
+/// use kernel::sync::{Arc, ArcBorrow};
 ///
 /// struct Example {
 ///     a: u32,

@@ -370,6 +374,7 @@ fn from(item: Pin<UniqueArc<T>>) -> Self {
 ///
 /// let obj = Arc::try_new(Example { a: 10, b: 20 })?;
 /// obj.as_arc_borrow().use_reference();
+/// # Ok::<(), Error>(())
 /// ```
 pub struct ArcBorrow<'a, T: ?Sized + 'a> {
     inner: NonNull<ArcInner<T>>,

rust/kernel/sync/lock/mutex.rs +1 -0

index 923472f04af4..09276fedc091 100644
@@ -63,6 +63,7 @@ macro_rules! new_mutex {
 /// assert_eq!(e.c, 10);
 /// assert_eq!(e.d.lock().a, 20);
 /// assert_eq!(e.d.lock().b, 30);
+/// # Ok::<(), Error>(())
 /// ```
 ///
 /// The following example shows how to use interior mutability to modify the contents of a struct

rust/kernel/sync/lock/spinlock.rs +1 -0

index 979b56464a4e..91eb2c9e9123 100644
@@ -61,6 +61,7 @@ macro_rules! new_spinlock {
 /// assert_eq!(e.c, 10);
 /// assert_eq!(e.d.lock().a, 20);
 /// assert_eq!(e.d.lock().b, 30);
+/// # Ok::<(), Error>(())
 /// ```
 ///
 /// The following example shows how to use interior mutability to modify the contents of a struct

Signature · 1 line

2.41.0

Rust documentation tests are going to be build/run-tested with the KUnit integration added in a future patch, thus update them to make them compilable/testable so that we may start enforcing it.

Signed-off-by Miguel Ojeda <[email protected]>

---
 rust/kernel/types.rs | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

rust/kernel/types.rs +3 -3

index 1e5380b16ed5..696d6c5a3b9d 100644
@@ -109,7 +109,7 @@ unsafe fn from_foreign(_: *const core::ffi::c_void) -> Self {}
 /// In the example below, we have multiple exit paths and we want to log regardless of which one is
 /// taken:
 /// ```
-/// # use kernel::ScopeGuard;
+/// # use kernel::types::ScopeGuard;
 /// fn example1(arg: bool) {
 ///     let _log = ScopeGuard::new(|| pr_info!("example1 completed\n"));
 ///

@@ -127,7 +127,7 @@ unsafe fn from_foreign(_: *const core::ffi::c_void) -> Self {}
 /// In the example below, we want to log the same message on all early exits but a different one on
 /// the main exit path:
 /// ```
-/// # use kernel::ScopeGuard;
+/// # use kernel::types::ScopeGuard;
 /// fn example2(arg: bool) {
 ///     let log = ScopeGuard::new(|| pr_info!("example2 returned early\n"));
 ///

@@ -148,7 +148,7 @@ unsafe fn from_foreign(_: *const core::ffi::c_void) -> Self {}
 /// In the example below, we need a mutable object (the vector) to be accessible within the log
 /// function, so we wrap it in the [`ScopeGuard`]:
 /// ```
-/// # use kernel::ScopeGuard;
+/// # use kernel::types::ScopeGuard;
 /// fn example3(arg: bool) -> Result {
 ///     let mut vec =
 ///         ScopeGuard::new_with_data(Vec::new(), |v| pr_info!("vec had {} elements\n", v.len()));

Signature · 1 line

2.41.0

Rust has documentation tests: these are typically examples of usage of any item (e.g. function, struct, module...).

They are very convenient because they are just written alongside the documentation. For instance:

    /// Sums two numbers.
    ///
    /// ```
    /// assert_eq!(mymod::f(10, 20), 30);
    /// ```
    pub fn f(a: i32, b: i32) -> i32 {
        a + b
    }

In userspace, the tests are collected and run via rustdoc. Using the tool as-is would be useful already, since it allows to compile-test most tests (thus enforcing they are kept in sync with the code they document) and run those that do not depend on in-kernel APIs.

However, by transforming the tests into a KUnit test suite, they can also be run inside the kernel. Moreover, the tests get to be compiled as other Rust kernel objects instead of targeting userspace.

On top of that, the integration with KUnit means the Rust support gets to reuse the existing testing facilities. For instance, the kernel log would look like:

KTAP version 1
1..1
KTAP version 1
# Subtest: rust_doctests_kernel
1..59
# Doctest from line 13
ok 1 rust_doctest_kernel_build_assert_rs_0 # Doctest from line 56
ok 2 rust_doctest_kernel_build_assert_rs_1 # Doctest from line 122
ok 3 rust_doctest_kernel_init_rs_0
...
# Doctest from line 150
ok 59 rust_doctest_kernel_types_rs_2
# rust_doctests_kernel: pass:59 fail:0 skip:0 total:59 # Totals: pass:59 fail:0 skip:0 total:59
ok 1 rust_doctests_kernel

Therefore, add support for running Rust documentation tests in KUnit. Some other notes about the current implementation and support follow.

The transformation is performed by a couple scripts written as Rust hostprogs.

Tests using the ? operator are also supported as usual, e.g.:

    /// ```
    /// # use kernel::{spawn_work_item, workqueue};
    /// spawn_work_item!(workqueue::system(), || pr_info!("x"))?;
    /// # Ok::<(), Error>(())
    /// ```

The tests are also compiled with Clippy under CLIPPY=1, just like normal code, thus also benefitting from extra linting.

The names of the tests are currently automatically generated. This allows to reduce the burden for documentation writers, while keeping them fairly stable for bisection. This is an improvement over the rustdoc-generated names, which include the line number; but ideally we would like to get rustdoc to provide the Rust item path and a number (for multiple examples in a single documented Rust item).

In order for developers to easily see from which original line a failed doctests came from, a KTAP diagnostic line is printed to the log. In the future, we may be able to use a proper KUnit facility to append this sort of information instead.

A notable difference from KUnit C tests is that the Rust tests appear to assert using the usual assert! and assert_eq! macros from the Rust standard library (core). We provide a custom version that forwards the call to KUnit instead. Importantly, these macros do not require passing context, unlike the KUnit C ones (i.e. struct kunit *). This makes them easier to use, and readers of the documentation do not need to care about which testing framework is used. In addition, it may allow us to test third-party code more easily in the future.

However, a current limitation is that KUnit does not support assertions in other tasks. Thus we presently simply print an error to the kernel log if an assertion actually failed. This should be revisited to properly fail the test, perhaps saving the context somewhere else, or letting KUnit handle it.

Signed-off-by Miguel Ojeda <[email protected]>

---
 lib/Kconfig.debug               |  13 +++
 rust/.gitignore                 |   2 +
 rust/Makefile                   |  29 ++++++
 rust/bindings/bindings_helper.h |   1 +
 rust/helpers.c                  |   7 ++
 rust/kernel/kunit.rs            | 156 ++++++++++++++++++++++++++++++
 rust/kernel/lib.rs              |   2 +
 scripts/.gitignore              |   2 +
 scripts/Makefile                |   4 +
 scripts/rustdoc_test_builder.rs |  73 ++++++++++++++
 scripts/rustdoc_test_gen.rs     | 162 ++++++++++++++++++++++++++++++++
 11 files changed, 451 insertions(+)
 create mode 100644 rust/kernel/kunit.rs
 create mode 100644 scripts/rustdoc_test_builder.rs
 create mode 100644 scripts/rustdoc_test_gen.rs

lib/Kconfig.debug +13 -0

index ce51d4dc6803..49f5e9c42200 100644
@@ -2911,6 +2911,19 @@ config RUST_BUILD_ASSERT_ALLOW
 
          If unsure, say N.
 
+config RUST_KERNEL_KUNIT_TEST
+       bool "KUnit test for the `kernel` crate" if !KUNIT_ALL_TESTS
+       depends on RUST && KUNIT=y
+       default KUNIT_ALL_TESTS
+       help
+         This builds the documentation tests of the `kernel` crate
+         as KUnit tests.
+
+         For more information on KUnit and unit tests in general,
+         please refer to the KUnit documentation in Documentation/dev-tools/kunit/.
+
+         If unsure, say N.
+
 endmenu # "Rust"
 
 endmenu # Kernel hacking

rust/.gitignore +2 -0

index 21552992b401..d3829ffab80b 100644
@@ -2,6 +2,8 @@
 
 bindings_generated.rs
 bindings_helpers_generated.rs
+doctests_kernel_generated.rs
+doctests_kernel_generated_kunit.c
 uapi_generated.rs
 exports_*_generated.h
 doc/

rust/Makefile +29 -0

index 7c9d9f11aec5..e4e8b83752e2 100644
@@ -27,6 +27,12 @@ endif
 
 obj-$(CONFIG_RUST) += exports.o
 
+always-$(CONFIG_RUST_KERNEL_KUNIT_TEST) += doctests_kernel_generated.rs
+always-$(CONFIG_RUST_KERNEL_KUNIT_TEST) += doctests_kernel_generated_kunit.c
+
+obj-$(CONFIG_RUST_KERNEL_KUNIT_TEST) += doctests_kernel_generated.o
+obj-$(CONFIG_RUST_KERNEL_KUNIT_TEST) += doctests_kernel_generated_kunit.o
+
 # Avoids running `$(RUSTC)` for the sysroot when it may not be available.
 ifdef CONFIG_RUST
 

@@ -39,9 +45,11 @@ ifeq ($(quiet),silent_)
 cargo_quiet=-q
 rust_test_quiet=-q
 rustdoc_test_quiet=--test-args -q
+rustdoc_test_kernel_quiet=>/dev/null
 else ifeq ($(quiet),quiet_)
 rust_test_quiet=-q
 rustdoc_test_quiet=--test-args -q
+rustdoc_test_kernel_quiet=>/dev/null
 else
 cargo_quiet=--verbose
 endif

@@ -157,6 +165,27 @@ quiet_cmd_rustdoc_test = RUSTDOC T $<
                -L$(objtree)/$(obj)/test --output $(objtree)/$(obj)/doc \
                --crate-name $(subst rusttest-,,$@) $<
 
+quiet_cmd_rustdoc_test_kernel = RUSTDOC TK $<
+      cmd_rustdoc_test_kernel = \
+       rm -rf $(objtree)/$(obj)/test/doctests/kernel; \
+       mkdir -p $(objtree)/$(obj)/test/doctests/kernel; \
+       OBJTREE=$(abspath $(objtree)) \
+       $(RUSTDOC) --test $(rust_flags) \
+               @$(objtree)/include/generated/rustc_cfg \
+               -L$(objtree)/$(obj) --extern alloc --extern kernel \
+               --extern build_error --extern macros \
+               --extern bindings --extern uapi \
+               --no-run --crate-name kernel -Zunstable-options \
+               --test-builder $(objtree)/scripts/rustdoc_test_builder \
+               $< $(rustdoc_test_kernel_quiet); \
+       $(objtree)/scripts/rustdoc_test_gen
+
+%/doctests_kernel_generated.rs %/doctests_kernel_generated_kunit.c: \
+    $(src)/kernel/lib.rs $(obj)/kernel.o \
+    $(objtree)/scripts/rustdoc_test_builder \
+    $(objtree)/scripts/rustdoc_test_gen FORCE
+       $(call if_changed,rustdoc_test_kernel)
+
 # We cannot use `-Zpanic-abort-tests` because some tests are dynamic,
 # so for the moment we skip `-Cpanic=abort`.
 quiet_cmd_rustc_test = RUSTC T  $<

rust/bindings/bindings_helper.h +1 -0

index 3e601ce2548d..0f8d37c31ac2 100644
@@ -6,6 +6,7 @@
  * Sorted alphabetically.
  */
 
+#include <kunit/test.h>
 #include <linux/errname.h>
 #include <linux/slab.h>
 #include <linux/refcount.h>

rust/helpers.c +7 -0

index bb594da56137..49a5e1a4f0ae 100644
@@ -18,6 +18,7 @@
  * accidentally exposed.
  */
 
+#include <kunit/test-bug.h>
 #include <linux/bug.h>
 #include <linux/build_bug.h>
 #include <linux/err.h>

@@ -135,6 +136,12 @@ void rust_helper_put_task_struct(struct task_struct *t)
 }
 EXPORT_SYMBOL_GPL(rust_helper_put_task_struct);
 
+struct kunit *rust_helper_kunit_get_current_test(void)
+{
+       return kunit_get_current_test();
+}
+EXPORT_SYMBOL_GPL(rust_helper_kunit_get_current_test);
+
 /*
  * We use `bindgen`'s `--size_t-is-usize` option to bind the C `size_t` type
  * as the Rust `usize` type, so we can use it in contexts where Rust

rust/kernel/kunit.rs new file +156 -0

new file mode 100644
index 000000000000..3c94efcd7f76
@@ -0,0 +1,156 @@
+// SPDX-License-Identifier: GPL-2.0
+
+//! KUnit-based macros for Rust unit tests.
+//!
+//! C header: [`include/kunit/test.h`](../../../../../include/kunit/test.h)
+//!
+//! Reference: <https://docs.kernel.org/dev-tools/kunit/index.html>
+
+use core::{ffi::c_void, fmt};
+
+/// Prints a KUnit error.
+///
+/// Public but hidden since it should only be used from KUnit generated code.
+#[doc(hidden)]
+pub fn err(args: fmt::Arguments<'_>) {
+    // SAFETY: The format string is null-terminated and the `%pA` specifier matches the argument we
+    // are passing.
+    #[cfg(CONFIG_PRINTK)]
+    unsafe {
+        bindings::_printk(
+            b"\x013%pA\0".as_ptr() as _,
+            &args as *const _ as *const c_void,
+        );
+    }
+}
+
+/// Prints a KUnit error.
+///
+/// Public but hidden since it should only be used from KUnit generated code.
+#[doc(hidden)]
+pub fn info(args: fmt::Arguments<'_>) {
+    // SAFETY: The format string is null-terminated and the `%pA` specifier matches the argument we
+    // are passing.
+    #[cfg(CONFIG_PRINTK)]
+    unsafe {
+        bindings::_printk(
+            b"\x016%pA\0".as_ptr() as _,
+            &args as *const _ as *const c_void,
+        );
+    }
+}
+
+/// Asserts that a boolean expression is `true` at runtime.
+///
+/// Public but hidden since it should only be used from generated tests.
+///
+/// Unlike the one in `core`, this one does not panic; instead, it is mapped to the KUnit
+/// facilities. See [`assert!`] for more details.
+#[doc(hidden)]
+#[macro_export]
+macro_rules! kunit_assert {
+    ($name:literal, $condition:expr $(,)?) => {
+        'out: {
+            // Do nothing if the condition is `true`.
+            if $condition {
+                break 'out;
+            }
+
+            static LINE: i32 = core::line!() as i32;
+            static FILE: &'static $crate::str::CStr = $crate::c_str!(core::file!());
+            static CONDITION: &'static $crate::str::CStr = $crate::c_str!(stringify!($condition));
+
+            // SAFETY: FFI call without safety requirements.
+            let kunit_test = unsafe { $crate::bindings::kunit_get_current_test() };
+            if kunit_test.is_null() {
+                // The assertion failed but this task is not running a KUnit test, so we cannot call
+                // KUnit, but at least print an error to the kernel log. This may happen if this
+                // macro is called from an spawned thread in a test (see
+                // `scripts/rustdoc_test_gen.rs`) or if some non-test code calls this macro by
+                // mistake (it is hidden to prevent that).
+                //
+                // This mimics KUnit's failed assertion format.
+                $crate::kunit::err(format_args!(
+                    "    # {}: ASSERTION FAILED at {FILE}:{LINE}\n",
+                    $name
+                ));
+                $crate::kunit::err(format_args!(
+                    "    Expected {CONDITION} to be true, but is false\n"
+                ));
+                $crate::kunit::err(format_args!(
+                    "    Failure not reported to KUnit since this is a non-KUnit task\n"
+                ));
+                break 'out;
+            }
+
+            #[repr(transparent)]
+            struct Location($crate::bindings::kunit_loc);
+
+            #[repr(transparent)]
+            struct UnaryAssert($crate::bindings::kunit_unary_assert);
+
+            // SAFETY: There is only a static instance and in that one the pointer field points to
+            // an immutable C string.
+            unsafe impl Sync for Location {}
+
+            // SAFETY: There is only a static instance and in that one the pointer field points to
+            // an immutable C string.
+            unsafe impl Sync for UnaryAssert {}
+
+            static LOCATION: Location = Location($crate::bindings::kunit_loc {
+                file: FILE.as_char_ptr(),
+                line: LINE,
+            });
+            static ASSERTION: UnaryAssert = UnaryAssert($crate::bindings::kunit_unary_assert {
+                assert: $crate::bindings::kunit_assert {},
+                condition: CONDITION.as_char_ptr(),
+                expected_true: true,
+            });
+
+            // SAFETY:
+            //   - FFI call.
+            //   - The `kunit_test` pointer is valid because we got it from
+            //     `kunit_get_current_test()` and it was not null. This means we are in a KUnit
+            //     test, and that the pointer can be passed to KUnit functions and assertions.
+            //   - The string pointers (`file` and `condition` above) point to null-terminated
+            //     strings since they are `CStr`s.
+            //   - The function pointer (`format`) points to the proper function.
+            //   - The pointers passed will remain valid since they point to `static`s.
+            //   - The format string is allowed to be null.
+            //   - There are, however, problems with this: first of all, this will end up stopping
+            //     the thread, without running destructors. While that is problematic in itself,
+            //     it is considered UB to have what is effectively a forced foreign unwind
+            //     with `extern "C"` ABI. One could observe the stack that is now gone from
+            //     another thread. We should avoid pinning stack variables to prevent library UB,
+            //     too. For the moment, given that test failures are reported immediately before the
+            //     next test runs, that test failures should be fixed and that KUnit is explicitly
+            //     documented as not suitable for production environments, we feel it is reasonable.
+            unsafe {
+                $crate::bindings::kunit_do_failed_assertion(
+                    kunit_test,
+                    core::ptr::addr_of!(LOCATION.0),
+                    $crate::bindings::kunit_assert_type_KUNIT_ASSERTION,
+                    core::ptr::addr_of!(ASSERTION.0.assert),
+                    Some($crate::bindings::kunit_unary_assert_format),
+                    core::ptr::null(),
+                );
+            }
+        }
+    };
+}
+
+/// Asserts that two expressions are equal to each other (using [`PartialEq`]).
+///
+/// Public but hidden since it should only be used from generated tests.
+///
+/// Unlike the one in `core`, this one does not panic; instead, it is mapped to the KUnit
+/// facilities. See [`assert!`] for more details.
+#[doc(hidden)]
+#[macro_export]
+macro_rules! kunit_assert_eq {
+    ($name:literal, $left:expr, $right:expr $(,)?) => {{
+        // For the moment, we just forward to the expression assert because, for binary asserts,
+        // KUnit supports only a few types (e.g. integers).
+        $crate::kunit_assert!($name, $left == $right);
+    }};
+}

rust/kernel/lib.rs +2 -0

index 85b261209977..3642cadc34b1 100644
@@ -34,6 +34,8 @@
 pub mod error;
 pub mod init;
 pub mod ioctl;
+#[cfg(CONFIG_KUNIT)]
+pub mod kunit;
 pub mod prelude;
 pub mod print;
 mod static_assert;

scripts/.gitignore +2 -0

index 6e9ce6720a05..3dbb8bb2457b 100644
@@ -5,6 +5,8 @@
 /kallsyms
 /module.lds
 /recordmcount
+/rustdoc_test_builder
+/rustdoc_test_gen
 /sign-file
 /sorttable
 /target.json

scripts/Makefile +4 -0

index 32b6ba722728..d5a5382e753c 100644
@@ -9,6 +9,8 @@ hostprogs-always-$(CONFIG_BUILDTIME_TABLE_SORT)         += sorttable
 hostprogs-always-$(CONFIG_ASN1)                                += asn1_compiler
 hostprogs-always-$(CONFIG_MODULE_SIG_FORMAT)           += sign-file
 hostprogs-always-$(CONFIG_SYSTEM_EXTRA_CERTIFICATE)    += insert-sys-cert
+hostprogs-always-$(CONFIG_RUST_KERNEL_KUNIT_TEST)      += rustdoc_test_builder
+hostprogs-always-$(CONFIG_RUST_KERNEL_KUNIT_TEST)      += rustdoc_test_gen
 always-$(CONFIG_RUST)                                  += target.json
 
 filechk_rust_target = $< < include/config/auto.conf

@@ -18,6 +20,8 @@ $(obj)/target.json: scripts/generate_rust_target include/config/auto.conf FORCE
 
 hostprogs += generate_rust_target
 generate_rust_target-rust := y
+rustdoc_test_builder-rust := y
+rustdoc_test_gen-rust := y
 
 HOSTCFLAGS_sorttable.o = -I$(srctree)/tools/include
 HOSTLDLIBS_sorttable = -lpthread

scripts/rustdoc_test_builder.rs new file +73 -0

new file mode 100644
index 000000000000..e3b7138fb4f9
@@ -0,0 +1,73 @@
+// SPDX-License-Identifier: GPL-2.0
+
+//! Test builder for `rustdoc`-generated tests.
+//!
+//! This script is a hack to extract the test from `rustdoc`'s output. Ideally, `rustdoc` would
+//! have an option to generate this information instead, e.g. as JSON output.
+//!
+//! The `rustdoc`-generated test names look like `{file}_{line}_{number}`, e.g.
+//! `...path_rust_kernel_sync_arc_rs_42_0`. `number` is the "test number", needed in cases like
+//! a macro that expands into items with doctests is invoked several times within the same line.
+//!
+//! However, since these names are used for bisection in CI, the line number makes it not stable
+//! at all. In the future, we would like `rustdoc` to give us the Rust item path associated with
+//! the test, plus a "test number" (for cases with several examples per item) and generate a name
+//! from that. For the moment, we generate ourselves a new name, `{file}_{number}` instead, in
+//! the `gen` script (done there since we need to be aware of all the tests in a given file).
+
+use std::fs::File;
+use std::io::{BufWriter, Read, Write};
+
+fn main() {
+    let mut stdin = std::io::stdin().lock();
+    let mut body = String::new();
+    stdin.read_to_string(&mut body).unwrap();
+
+    // Find the generated function name looking for the inner function inside `main()`.
+    //
+    // The line we are looking for looks like one of the following:
+    //
+    // ```
+    // fn main() { #[allow(non_snake_case)] fn _doctest_main_rust_kernel_file_rs_28_0() {
+    // fn main() { #[allow(non_snake_case)] fn _doctest_main_rust_kernel_file_rs_37_0() -> Result<(), impl core::fmt::Debug> {
+    // ```
+    //
+    // It should be unlikely that doctest code matches such lines (when code is formatted properly).
+    let rustdoc_function_name = body
+        .lines()
+        .find_map(|line| {
+            Some(
+                line.split_once("fn main() {")?Tested-by: Sergio González Collado <[email protected]>
+                    .1
+                    .split_once("fn ")?
+                    .1
+                    .split_once("()")?
+                    .0,
+            )
+            .filter(|x| x.chars().all(|c| c.is_alphanumeric() || c == '_'))
+        })
+        .expect("No test function found in `rustdoc`'s output.");
+
+    // Qualify `Result` to avoid the collision with our own `Result` coming from the prelude.
+    let body = body.replace(
+        &format!("{rustdoc_function_name}() -> Result<(), impl core::fmt::Debug> {{"),
+        &format!("{rustdoc_function_name}() -> core::result::Result<(), impl core::fmt::Debug> {{"),
+    );
+
+    // For tests that get generated with `Result`, like above, `rustdoc` generates an `unwrap()` on
+    // the return value to check there were no returned errors. Instead, we use our assert macro
+    // since we want to just fail the test, not panic the kernel.
+    //
+    // We save the result in a variable so that the failed assertion message looks nicer.
+    let body = body.replace(
+        &format!("}} {rustdoc_function_name}().unwrap() }}"),
+        &format!("}} let test_return_value = {rustdoc_function_name}(); assert!(test_return_value.is_ok()); }}"),
+    );
+
+    // Figure out a smaller test name based on the generated function name.
+    let name = rustdoc_function_name.split_once("_rust_kernel_").unwrap().1;
+
+    let path = format!("rust/test/doctests/kernel/{name}");
+
+    write!(BufWriter::new(File::create(path).unwrap()), "{body}").unwrap();
+}

scripts/rustdoc_test_gen.rs new file +162 -1

new file mode 100644
index 000000000000..793885c32c0d
@@ -0,0 +1,162 @@
+// SPDX-License-Identifier: GPL-2.0
+
+//! Generates KUnit tests from saved `rustdoc`-generated tests.
+//!
+//! KUnit passes a context (`struct kunit *`) to each test, which should be forwarded to the other
+//! KUnit functions and macros.
+//!
+//! However, we want to keep this as an implementation detail because:
+//!
+//!   - Test code should not care about the implementation.
+//!
+//!   - Documentation looks worse if it needs to carry extra details unrelated to the piece
+//!     being described.
+//!
+//!   - Test code should be able to define functions and call them, without having to carry
+//!     the context.
+//!
+//!   - Later on, we may want to be able to test non-kernel code (e.g. `core`, `alloc` or
+//!     third-party crates) which likely use the standard library `assert*!` macros.
+//!
+//! For this reason, instead of the passed context, `kunit_get_current_test()` is used instead
+//! (i.e. `current->kunit_test`).
+//!
+//! Note that this means other threads/tasks potentially spawned by a given test, if failing, will
+//! report the failure in the kernel log but will not fail the actual test. Saving the pointer in
+//! e.g. a `static` per test does not fully solve the issue either, because currently KUnit does
+//! not support assertions (only expectations) from other tasks. Thus leave that feature for
+//! the future, which simplifies the code here too. We could also simply not allow `assert`s in
+//! other tasks, but that seems overly constraining, and we do want to support them, eventually.
+
+use std::io::{BufWriter, Read, Write};
+use std::{fs, fs::File};
+
+fn main() {
+    let mut paths = fs::read_dir("rust/test/doctests/kernel")
+        .unwrap()
+        .map(|entry| entry.unwrap().path())
+        .collect::<Vec<_>>();
+
+    // Sort paths for clarity.
+    paths.sort();
+
+    let mut rust_tests = String::new();
+    let mut c_test_declarations = String::new();
+    let mut c_test_cases = String::new();
+    let mut body = String::new();
+    let mut last_file = String::new();
+    let mut number = 0;
+    for path in paths {
+        // The `name` follows the `{file}_{line}_{number}` pattern (see description in
+        // `scripts/rustdoc_test_builder.rs`). Discard the `number`.
+        let name = path.file_name().unwrap().to_str().unwrap().to_string();
+
+        // Extract the `file` and the `line`, discarding the `number`.
+        let (file, line) = name.rsplit_once('_').unwrap().0.rsplit_once('_').unwrap();
+
+        // Generate an ID sequence ("test number") for each one in the file.
+        if file == last_file {
+            number += 1;
+        } else {
+            number = 0;
+            last_file = file.to_string();
+        }
+
+        // Generate a KUnit name (i.e. test name and C symbol) for this test.
+        //
+        // We avoid the line number, like `rustdoc` does, to make things slightly more stable for
+        // bisection purposes. However, to aid developers in mapping back what test failed, we will
+        // print a diagnostics line in the KTAP report.
+        let kunit_name = format!("rust_doctest_kernel_{file}_{number}");
+
+        // Read the test's text contents to dump it below.
+        body.clear();
+        File::open(path).unwrap().read_to_string(&mut body).unwrap();
+
+        let line = line.parse::<core::ffi::c_int>().unwrap();
+
+        use std::fmt::Write;
+        write!(
+            rust_tests,
+            r#"/// Generated `{name}` KUnit test case from a Rust documentation test.
+#[no_mangle]
+pub extern "C" fn {kunit_name}(__kunit_test: *mut kernel::bindings::kunit) {{
+    /// Overrides the usual [`assert!`] macro with one that calls KUnit instead.
+    #[allow(unused)]
+    macro_rules! assert {{
+        ($cond:expr $(,)?) => {{{{
+            kernel::kunit_assert!("{kunit_name}", $cond);
+        }}}}
+    }}
+
+    /// Overrides the usual [`assert_eq!`] macro with one that calls KUnit instead.
+    #[allow(unused)]
+    macro_rules! assert_eq {{
+        ($left:expr, $right:expr $(,)?) => {{{{
+            kernel::kunit_assert_eq!("{kunit_name}", $left, $right);
+        }}}}
+    }}
+
+    // Many tests need the prelude, so provide it by default.
+    #[allow(unused)]
+    use kernel::prelude::*;
+
+    // Display line number so that developers can map the test easily to the source code.
+    kernel::kunit::info(format_args!("    # Doctest from line {line}\n"));
+
+    {{
+        {body}
+        main();
+    }}
+}}
+
+"#
+        )
+        .unwrap();
+
+        write!(c_test_declarations, "void {kunit_name}(struct kunit *);\n").unwrap();
+        write!(c_test_cases, "    KUNIT_CASE({kunit_name}),\n").unwrap();
+    }
+
+    let rust_tests = rust_tests.trim();
+    let c_test_declarations = c_test_declarations.trim();
+    let c_test_cases = c_test_cases.trim();
+
+    write!(
+        BufWriter::new(File::create("rust/doctests_kernel_generated.rs").unwrap()),
+        r#"//! `kernel` crate documentation tests.
+
+const __LOG_PREFIX: &[u8] = b"rust_doctests_kernel\0";
+
+{rust_tests}
+"#
+    )
+    .unwrap();
+
+    write!(
+        BufWriter::new(File::create("rust/doctests_kernel_generated_kunit.c").unwrap()),
+        r#"/*
+ * `kernel` crate documentation tests.
+ */
+
+#include <kunit/test.h>
+
+{c_test_declarations}
+
+static struct kunit_case test_cases[] = {{
+    {c_test_cases}
+    {{ }}
+}};
+
+static struct kunit_suite test_suite = {{
+    .name = "rust_doctests_kernel",
+    .test_cases = test_cases,
+}};
+
+kunit_test_suite(test_suite);
+
+MODULE_LICENSE("GPL");
+"#
+    )
+    .unwrap();
+}
--

2.41.0

Rust documentation tests are going to be build/run-tested with the KUnit integration added in a future patch, thus update them to make them compilable/testable so that we may start enforcing it.

Signed-off-by Miguel Ojeda <[email protected]>

---
  rust/kernel/init.rs | 25 ++++++++++++++++---------
  1 file changed, 16 insertions(+), 9 deletions(-)

rust/kernel/init.rs +16 -10

index b4332a4ec1f4..1073515ed40e 100644
@@ -120,14 +120,23 @@
  //!   `slot` gets called.
  //!
  //! ```rust
-//! use kernel::{prelude::*, init};
+//! # #![allow(unreachable_pub, clippy::disallowed_names)]
+//! use kernel::{prelude::*, init, types::Opaque};
  //! use core::{ptr::addr_of_mut, marker::PhantomPinned, pin::Pin};
  //! # mod bindings {
+//! #     #![allow(non_camel_case_types)]
  //! #     pub struct foo;
  //! #     pub unsafe fn init_foo(_ptr: *mut foo) {}
  //! #     pub unsafe fn destroy_foo(_ptr: *mut foo) {}
  //! #     pub unsafe fn enable_foo(_ptr: *mut foo, _flags: u32) -> i32 { 0 }
  //! # }
+//! # trait FromErrno {
+//! #     fn from_errno(errno: core::ffi::c_int) -> Error {
+//! #         // Dummy error that can be constructed outside the `kernel` crate.
+//! #         Error::from(core::fmt::Error)
+//! #     }
+//! # }
+//! # impl FromErrno for Error {}
  //! /// # Invariants
  //! ///
  //! /// `foo` is always initialized

@@ -158,7 +167,7 @@
  //!                 if err != 0 {
  //!                     // Enabling has failed, first clean up the foo and then return the error.
  //!                     bindings::destroy_foo(Opaque::raw_get(foo));
-//!                     return Err(Error::from_kernel_errno(err));
+//!                     return Err(Error::from_errno(err));
  //!                 }
  //!
  //!                 // All fields of `RawFoo` have been initialized, since `_p` is a ZST.

@@ -226,8 +235,7 @@
  ///
  /// ```rust
  /// # #![allow(clippy::disallowed_names, clippy::new_ret_no_self)]
-/// # use kernel::{init, pin_init, stack_pin_init, init::*, sync::Mutex, new_mutex};
-/// # use macros::pin_data;
+/// # use kernel::{init, macros::pin_data, pin_init, stack_pin_init, init::*, sync::Mutex, new_mutex};
  /// # use core::pin::Pin;
  /// #[pin_data]
  /// struct Foo {

@@ -277,7 +285,7 @@ macro_rules! stack_pin_init {
  ///
  /// # Examples
  ///
-/// ```rust
+/// ```rust,ignore
  /// # #![allow(clippy::disallowed_names, clippy::new_ret_no_self)]
  /// # use kernel::{init, pin_init, stack_try_pin_init, init::*, sync::Mutex, new_mutex};
  /// # use macros::pin_data;

@@ -303,7 +311,7 @@ macro_rules! stack_pin_init {
  /// pr_info!("a: {}", &*foo.a.lock());
  /// ```
  ///
-/// ```rust
+/// ```rust,ignore
  /// # #![allow(clippy::disallowed_names, clippy::new_ret_no_self)]
  /// # use kernel::{init, pin_init, stack_try_pin_init, init::*, sync::Mutex, new_mutex};
  /// # use macros::pin_data;

@@ -513,8 +521,7 @@ macro_rules! stack_try_pin_init {
  /// For instance:
  ///
  /// ```rust
-/// # use kernel::pin_init;
-/// # use macros::pin_data;
+/// # use kernel::{macros::pin_data, pin_init};
  /// # use core::{ptr::addr_of_mut, marker::PhantomPinned};
  /// #[pin_data]
  /// struct Buf {

@@ -841,7 +848,7 @@ macro_rules! init {
  /// # Examples
  ///
  /// ```rust
-/// use kernel::{init::PinInit, error::Error, InPlaceInit};
+/// use kernel::{init::{PinInit, zeroed}, error::Error};
  /// struct BigBuf {
  ///     big: Box<[u8; 1024 * 1024 * 1024]>,
  ///     small: [u8; 1024 * 1024],
--

2.41.0

rust/helpers.c +6 -0

 #include <linux/bug.h>
 #include <linux/build_bug.h>
 #include <linux/err.h>

@@ -135,6 +136,12 @@ void rust_helper_put_task_struct(struct task_struct *t)
 }
 EXPORT_SYMBOL_GPL(rust_helper_put_task_struct);
 
+struct kunit *rust_helper_kunit_get_current_test(void)
+{
+	return kunit_get_current_test();
+}
+EXPORT_SYMBOL_GPL(rust_helper_kunit_get_current_test);
+
 /*
  * We use `bindgen`'s `--size_t-is-usize` option to bind the C `size_t` type
  * as the Rust `usize` type, so we can use it in contexts where Rust