Re: [PATCH v5 12/20] rust: io: move `Io` methods to extension trait

On Fri Jun 26, 2026 at 11:45 PM JST, Gary Guo wrote:
> `Io` trait now has a single required methods with many more provided

nit: s/methods/method

> methods. Provided methods may want to rely on their implementations to not
> be arbitrarily overridden by implementers for correctness or soundness.
>
> Thus, extract these methods to a new trait and provide a blanket
> implementation. This pattern is used extensively in userspace Rust
> libraries e.g. `tokio` where `AsyncRead` has minimum methods and
> `AsyncReadExt` is what users mostly interact with.
>
> To avoid changing all user imports, the base trait is renamed to `IoBase`
> and the newly added trait takes the existing `Io` name.
>
> A `size` method is added as an example of methods that users should not
> override.

WDYM by "an example"? There are already all the I/O accessors that we
wish not to override; this looks more like a new method is just added.

Besides, it is not used until patch 19, so how about introducing it
there?

<...>
> @@ -326,6 +323,21 @@ pub trait Io<'a>: Copy {
>  
>      /// Return a view that covers the full region.
>      fn as_view(self) -> <Self::Backend as IoBackend>::View<'a, Self::Target>;
> +}
> +
> +/// Extension trait to provide I/O operation methods to types that implement [`IoBase`].
> +///
> +/// This trait provides:
> +/// - Helper methods for offset validation and address calculation
> +/// - Fallible (runtime checked) accessors for different data widths
> +///
> +/// Which I/O methods are available depends on the associated [`IoBackend`] implementation.
> +pub trait Io<'a>: IoBase<'a> {
> +    /// Returns the size of this I/O region.
> +    #[inline]
> +    fn size(self) -> usize {
> +        KnownSize::size(Self::Backend::as_ptr(self.as_view()))

nit: the documentation for `as_ptr` says that the pointer "should be
used for projection only". Technically we are not projecting here; maybe
the documentation should be updated to say the pointer must not be
dereferenced instead.

In any case,

Reviewed-by: Alexandre Courbot <[email protected]>