Re: [PATCH v3] rust: transmute: add `as_bytes` method for `AsBytes` trait

["Benno Lossin" <lossin@kernel.org>]

On Sun Jul 27, 2025 at 12:23 PM CEST, Alice Ryhl wrote:
> On Sun, Jul 27, 2025 at 08:52:00AM +0200, Alice Ryhl wrote:
>> On Sat, Jul 26, 2025 at 4:47 AM Alexandre Courbot <acourbot@nvidia.com> wrote:
>> > diff --git a/rust/kernel/transmute.rs b/rust/kernel/transmute.rs
>> > index 1c7d43771a37b90150de86699f114a2ffb84db91..69c46c19a89191d8a2abc5801564cacda232218c 100644
>> > --- a/rust/kernel/transmute.rs
>> > +++ b/rust/kernel/transmute.rs
>> > @@ -47,7 +47,16 @@ macro_rules! impl_frombytes {
>> >  ///
>> >  /// Values of this type may not contain any uninitialized bytes. This type must not have interior
>> >  /// mutability.
>> > -pub unsafe trait AsBytes {}
>> > +pub unsafe trait AsBytes {
>> > +    /// Returns `self` as a slice of bytes.
>> > +    fn as_bytes(&self) -> &[u8] {
>> > +        let data = core::ptr::from_ref(self).cast::<u8>();
>> > +        let len = size_of_val(self);
>> > +
>> > +        // SAFETY: `data` is non-null and valid for `len * sizeof::<u8>()` bytes.
>> > +        unsafe { core::slice::from_raw_parts(data, len) }
>> > +    }
>> > +}
>> 
>> Let's also have an as_bytes_mut() method. I would require the type to
>> also implement FromBytes as it lets you replace the value with another
>> set of bytes.
>
> s/I would/It would/
>
> FromBytes is needed only for as_bytes_mut(), not for the existing
> method.

I agree with your suggestion, but it can be an independent patch and
doesn't need to go in via this one, right?

---
Cheers,
Benno