linux-kernel - Re: [PATCH v4 3/3] rust: kunit: allow to know if we are in a test

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Message-ID: <ZyVIQxTf1qkts1d_@Boquns-Mac-mini.local>
Date: Fri, 1 Nov 2024 14:29:39 -0700
From: Boqun Feng <boqun.feng@...il.com>
To: David Gow <davidgow@...gle.com>
Cc: Miguel Ojeda <ojeda@...nel.org>,
	José Expósito <jose.exposito89@...il.com>,
	Brendan Higgins <brendan.higgins@...ux.dev>,
	Rae Moar <rmoar@...gle.com>, Alex Gaynor <alex.gaynor@...il.com>,
	Gary Guo <gary@...yguo.net>, Benno Lossin <benno.lossin@...ton.me>,
	Björn Roy Baron <bjorn3_gh@...tonmail.com>,
	Alice Ryhl <aliceryhl@...gle.com>,
	Matt Gilbride <mattgilbride@...gle.com>, kunit-dev@...glegroups.com,
	linux-kselftest@...r.kernel.org, rust-for-linux@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 3/3] rust: kunit: allow to know if we are in a test

On Fri, Nov 01, 2024 at 02:45:02PM +0800, David Gow wrote:
[...]
> +/// ```
> +/// // Import our mock naming it as the real module.
> +/// #[cfg(CONFIG_KUNIT)]
> +/// use bindings_mock_example as bindings;
> +///
> +/// // This module mocks `bindings`.
> +/// mod bindings_mock_example {
> +///     use kernel::kunit::in_kunit_test;
> +///     use kernel::bindings::u64_;
> +///
> +///     // Make the other binding functions available.
> +///     pub(crate) use kernel::bindings::*;
> +///
> +///     // Mock `ktime_get_boot_fast_ns` to return a well-known value when running a KUnit test.
> +///     pub(crate) unsafe fn ktime_get_boot_fast_ns() -> u64_ {

Clippy complains this `unsafe` pub function doesn't have a "# Safety"
section. Actually this function is not necessarily to be `unsafe`.

> +///         if in_kunit_test() {
> +///             1234
> +///         } else {
> +///             unsafe { kernel::bindings::ktime_get_boot_fast_ns() }

Need safety comments here,

> +///         }
> +///     }
> +/// }
> +///
> +/// // This is the function we want to test. Since `bindings` has been mocked, we can use its
> +/// // functions seamlessly.
> +/// fn get_boot_ns() -> u64 {
> +///     unsafe { bindings::ktime_get_boot_fast_ns() }

and here. If you make ktime_get_boot_fast_ns() safe, then no unsafe
block is needed here.

Regards,
Boqun

> +/// }
> +///
> +/// let time = get_boot_ns();
> +/// assert_eq!(time, 1234);
> +/// ```
> +pub fn in_kunit_test() -> bool {
> +    // SAFETY: kunit_get_current_test() is always safe to call from C (it has fallbacks for
> +    // when KUnit is not enabled), and we're only comparing the result to NULL.
> +    unsafe { !bindings::kunit_get_current_test().is_null() }
> +}
> +
>  #[kunit_tests(rust_kernel_kunit)]
>  mod tests {
> +    use super::*;
> +
>      #[test]
>      fn rust_test_kunit_example_test() {
>          assert_eq!(1 + 1, 2);
>      }
> +
> +    #[test]
> +    fn rust_test_kunit_in_kunit_test() {
> +        let in_kunit = in_kunit_test();
> +        assert!(in_kunit);
> +    }
>  }
> -- 
> 2.47.0.199.ga7371fff76-goog
>