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

Tamir Duberstein
2025-03-12T15:14:17Z

On Wed, Mar 12, 2025 at 10:22 AM Benno Lossin <benno.lossin@proton.me> wrote:
>
> 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

Thanks for doing that! Yeah, I think moving to that syntax would be
good but as you say requires enabling the feature and/or bumping the
rust version, so it can't be done here directly.