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

[Danilo Krummrich <dakr@kernel.org>]

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;
+}
+
 /// A pointer to a page that owns the page allocation.
 ///
 /// # Invariants
-- 
2.50.1