Re: [PATCH v2 2/6] rust: page: define PageOwner trait

[Alice Ryhl <aliceryhl@google.com>]

On Wed, Aug 06, 2025 at 10:50:11PM +0200, Danilo Krummrich wrote:
> Introduce the PageOwner trait, which can be implemented by any entity
> that potentially owns one or multiple pages and allow users to borrow
> them.
> 
> For instance, this is useful to access and borrow the backing pages of
> allocation primitives, such as Box and Vec, backing a scatterlist.
> 
> Signed-off-by: Danilo Krummrich <dakr@kernel.org>
> ---
>  rust/kernel/page.rs | 12 ++++++++++++
>  1 file changed, 12 insertions(+)
> 
> diff --git a/rust/kernel/page.rs b/rust/kernel/page.rs
> index 631718a6ad7d..93ce4956f782 100644
> --- a/rust/kernel/page.rs
> +++ b/rust/kernel/page.rs
> @@ -103,6 +103,18 @@ fn deref(&self) -> &Self::Target {
>      }
>  }
>  
> +/// Represents a potential owner of one or multiple [`Page`]s.
> +///
> +/// This trait may be implemented by types that potentially hold ownership of memory pages. It
> +/// allows users to iterate over those pages and borrow them as [`BorrowedPage`].
> +pub trait PageOwner {
> +    /// Returns an [`Iterator`] of [`BorrowedPage`] items over all pages owned by `self`.
> +    fn page_iter<'a>(&'a mut self) -> impl Iterator<Item = BorrowedPage<'a>>;
> +
> +    /// Returns the number of pages currently owned by `self`.
> +    fn page_count(&self) -> usize;
> +}

Honestly, I don't entirely love this trait on its own merits. But I'd
need to know more about how it will be used to give a clearer opinion.

Either way, I think the implementation of VBox and VVec could be merged
to some shared VmallocPageIter that iterates a region of pages.

Alice