Re: [PATCH v2 1/5] rust: retain pointer mut-ness in `container_of!`

Benno Lossin
2025-03-12T14:22:48Z

On Sun Mar 9, 2025 at 5:00 PM CET, Tamir Duberstein wrote:
> Avoid casting the input pointer to `*const _`, allowing the output
> pointer to be `*mut` if the input is `*mut`. This allows a number of
> `*const` to `*mut` conversions to be removed at the cost of slightly
> worse ergonomics when the macro is used with a reference rather than a
> pointer; the only example of this was in the macro's own doctest.
>
> Signed-off-by: Tamir Duberstein <tamird@gmail.com>

One tiny nit below, but even without that:

Reviewed-by: Benno Lossin <benno.lossin@proton.me>

> ---
> rust/kernel/lib.rs | 5 ++---
> rust/kernel/pci.rs | 2 +-
> rust/kernel/platform.rs | 2 +-
> rust/kernel/rbtree.rs | 23 ++++++++++-------------
> 4 files changed, 14 insertions(+), 18 deletions(-)
>
> diff --git a/rust/kernel/lib.rs b/rust/kernel/lib.rs
> index 7697c60b2d1a..9cd6b6864739 100644
> --- a/rust/kernel/lib.rs
> +++ b/rust/kernel/lib.rs
> @@ -187,7 +187,7 @@ fn panic(info: &core::panic::PanicInfo<'_>) -> ! {
> /// }
> ///
> /// let test = Test { a: 10, b: 20 };
> -/// let b_ptr = &test.b;
> +/// let b_ptr: *const _ = &test.b;

You could also use `&raw test.b` to get a pointer instead of relying on
the pointer coercion. That syntax is stable since 1.82.0, so older
compilers would need to enable the `raw_ref_op` feature.

I created an orthogonal good-first-issue for changing uses of
`addr_of[_mut]!` to `&raw [mut]`, so maybe that can also be done there:

https://github.com/Rust-for-Linux/linux/issues/1148

---
Cheers,
Benno