Re: [RFC PATCH 1/2] rust: add initial scatterlist bindings

[Danilo Krummrich <dakr@kernel.org>]

On Mon, May 12, 2025 at 08:39:36AM -0300, Daniel Almeida wrote:
> > On 12 May 2025, at 06:53, Abdiel Janulgue <abdiel.janulgue@gmail.com> wrote:
> > +impl SGEntry {
> > +    /// Convert a raw `struct scatterlist *` to a `&'a SGEntry`.
> > +    ///
> > +    /// # Safety
> > +    ///
> > +    /// Callers must ensure that the `struct scatterlist` pointed to by `ptr` is valid for the lifetime
> > +    /// of the returned reference.
> > +    pub unsafe fn as_ref<'a>(ptr: *mut bindings::scatterlist) -> &'a Self {
> > +        // SAFETY: The pointer is valid and guaranteed by the safety requirements of the function.
> > +        unsafe { &*ptr.cast() }
> > +    }
> 
> Hmm, this name is not good. When people see as_ref() they will think of the
> standard library where it is used to convert from &T to &U. This is not what is
> happening here. Same in other places where as_ref() is used in this patch.

as_ref() is fine, we use this exact way commonly in the kernel, e.g. for Device,
GlobalLockedBy, Cpumask and for various DRM types.

Rust std does the same, e.g. in [1].

I think I also asked for this in your Resource patch for consistency, where you
call this from_ptr() instead.

[1] https://doc.rust-lang.org/std/ptr/struct.NonNull.html#method.as_ref