On Sat, May 7, 2022 at 1:25 PM Miguel Ojeda ojeda@kernel.org wrote:
Rust support
<...>
Support running documentation tests in-kernel, based on KUnit.
Rust documentation tests 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, e.g.:
/// Sums two numbers. /// /// # Examples /// /// ``` /// assert_eq!(mymod::f(10, 20), 30); /// ``` pub fn f(a: i32, b: i32) -> i32 { a + b }So far, we were compiling and running them in the host as any other Rust documentation test. However, that meant we could not run tests that used kernel APIs (though we were compile-testing them, which was already useful to keep the documentation in sync with the code).
Now, the documentation tests for the `kernel` crate are transformed into a KUnit test suite during compilation and run within the kernel at boot time, if enabled. This means now we can run the tests that use kernel APIs.
They look like this (their name is generated by `rustdoc`, based on the file and line):
[ 0.581961] TAP version 14 [ 0.582092] 1..1 [ 0.582267] # Subtest: rust_kernel_doctests [ 0.582358] 1..70 [ 0.583626] ok 1 - rust_kernel_doctest_build_assert_rs_12_0 [ 0.584579] ok 2 - rust_kernel_doctest_build_assert_rs_55_0 [ 0.587357] ok 3 - rust_kernel_doctest_device_rs_361_0 [ 0.588037] ok 4 - rust_kernel_doctest_device_rs_386_0 ... [ 0.659249] ok 69 - rust_kernel_doctest_types_rs_445_0 [ 0.660451] ok 70 - rust_kernel_doctest_types_rs_509_0 [ 0.660680] # rust_kernel_doctests: pass:70 fail:0 skip:0 total:70 [ 0.660894] # Totals: pass:70 fail:0 skip:0 total:70 [ 0.661135] ok 1 - rust_kernel_doctestsThere are other benefits from this, such as being able to remove unneeded wrapper functions (that were used to avoid running some tests) as well as ensuring test code would actually compile within the kernel (e.g. `alloc` used different `cfg`s).
It's great to see some KUnit support here!
It's also possible to run these tests using the KUnit wrapper tool with: $ ./tools/testing/kunit/kunit.py run --kconfig_add CONFIG_RUST=y --make_options LLVM=1 --arch x86_64 'rust_kernel_doctests'
That also nicely formats the results.
(It obviously doesn't run under UML yet, though I did get it to work after indiscriminately hacking out everything that wasn't supported. Assuming we can hide the irq and iomem stuff behind the appropriate config options, and rework some of the architecture detection to either support SUBARCH or check for X86_64 instead of X86, it should be pretty easy to get going.)
That all being said, I can't say I'm thrilled with the test names here: none of them are particularly descriptive, and they'll probably not be static (which would make it difficult to track results / regressions / etc between kernel versions). Neither of those are necessarily deal breakers, though it might make sense to hide them behind a kernel option (like all other KUnit tests) so that they can easily be excluded where they would otherwise clutter up results. (And if there's a way to properly name them, or maybe even split them into per-file or per-module suites, that would make them a bit easier to deal.) Additionally, there are some plans to taint the kernel[1] when KUnit tests run, so having a way to turn them off would be very useful.
Regardless, this is very neat, and I'm looking forward to taking a closer look at it.
Cheers, -- David
[1]: https://lore.kernel.org/linux-kselftest/20220429043913.626647-1-davidgow@goo...