Re: [PATCH v4 04/20] rust: io: implement `Io` on reference types instead

["Alexandre Courbot" <acourbot@nvidia.com>]

On Fri Jun 12, 2026 at 1:28 AM JST, Gary Guo wrote:
> Currently, `Io` is implemented on owned I/O objects (e.g. `Bar`). This is
> going to change with I/O projections, as then `Io` need to work both for

nit: s/need/needs.

> owned objects and views of them. Views are themselves reference-like
> (however they obviously cannot be references, because they belong to a
> different address space).
>
> To faciliate the change, change `Io` to be implemented on reference types

typo: facilitate.

> for the owned I/O objects, and make methods take `self` instead of `&self`.
> When I/O views are implemented, we can then naturally implement `Io` for
> these objects.
>
> Signed-off-by: Gary Guo <gary@garyguo.net>
> ---
>  rust/kernel/io.rs     | 80 +++++++++++++++++++++++++--------------------------
>  rust/kernel/pci/io.rs | 12 ++++----
>  2 files changed, 46 insertions(+), 46 deletions(-)
>
> diff --git a/rust/kernel/io.rs b/rust/kernel/io.rs
> index 38281636b4da..3b478dcf10f9 100644
> --- a/rust/kernel/io.rs
> +++ b/rust/kernel/io.rs
> @@ -224,7 +224,7 @@ pub trait IoCapable<T> {
>      ///
>      /// - The range `[address..address + size_of::<T>()]` must be within the bounds of `Self`.
>      /// - `address` must be aligned.
> -    unsafe fn io_read(&self, address: usize) -> T;
> +    unsafe fn io_read(self, address: usize) -> T;
>  
>      /// Performs an I/O write of `value` at `address`.
>      ///
> @@ -232,7 +232,7 @@ pub trait IoCapable<T> {
>      ///
>      /// - The range `[address..address + size_of::<T>()]` must be within the bounds of `Self`.
>      /// - `address` must be aligned.
> -    unsafe fn io_write(&self, value: T, address: usize);
> +    unsafe fn io_write(self, value: T, address: usize);
>  }
>  
>  /// Describes a given I/O location: its offset, width, and type to convert the raw value from and
> @@ -299,21 +299,21 @@ fn offset(self) -> usize {
>  ///
>  /// For MMIO regions, all widths (u8, u16, u32, and u64 on 64-bit systems) are typically
>  /// supported. For PCI configuration space, u8, u16, and u32 are supported but u64 is not.
> -pub trait Io {
> +pub trait Io: Copy {

This requirement on `Copy` could seem a bit confusing without context -
maybe mention explicitly in `Io`'s doccomment that this type is expected
to be implemented on cheaply copyable handles like references and views?

Regardless,

Reviewed-by: Alexandre Courbot <acourbot@nvidia.com>