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

[Danilo Krummrich]

On 7/28/25 5:39 AM, Alexandre Courbot wrote:
> On Sun Jul 27, 2025 at 9:39 PM JST, Benno Lossin wrote:
> > 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@xxxxxxxxxx> 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?
>
> Given where we are in the merge cycle, it seems like we have a couple of
> months until that code gets merged anyway, so I don't see any reason to
> not send a v4 with Alice's suggestion? The only drawback I see is that I
> would have to reset the Reviewed-by tags.

I'd make it a series and add as_bytes_mut() as a separate patch.