Re: [PATCH 06/11] rust/block: Add I/O buffer traits

[Paolo Bonzini <pbonzini@redhat.com>]

On 2/11/25 22:43, Kevin Wolf wrote:
> +/// Implementing `SizedIoBuffer` provides an implementation for [`IoBuffer`] without having to
> +/// implement any functions manually.
> +///
> +/// # Safety
> +///
> +/// Types implementing `SizedIoBuffer` guarantee that the whole object can be accessed as an I/O
> +/// buffer that is safe to contain any byte patterns.
> +pub unsafe trait SizedIoBuffer: Sized {

This is similar to the ByteValued trait in rust-vmm.  Can you name it 
the same so that we can later consider replacing it?

> +    fn from_byte_slice(buf: &[u8]) -> Option<&Self> {
> +        if buf.len() < std::mem::size_of::<Self>() {
> +            return None;
> +        }
> +
> +        let ptr = buf.as_ptr() as *const Self;
> +
> +        // TODO Use ptr.is_aligned() when MSRV is updated to at least 1.79.0
> +        if (ptr as usize) % std::mem::align_of::<Self>() != 0 {
> +            return None;
> +        }
> +
> +        // SAFETY: This function checked that the byte slice is large enough and aligned.
> +        // Implementing SizedIoBuffer promises that any byte pattern is valid for the type.
> +        Some(unsafe { &*ptr })

If you want, the function can be written also

     // SAFETY: implementing SizedIoBuffer promises that any byte pattern
     // is valid for the type
     match unsafe { buf.align_to::<Self>() } {
         ([], mid, _) => mid.get(0),
         _ => None
     }

(trick stolen from rust-vmm, in fact).

Paolo