Claude review: rust: add `Ownable` trait and `Owned` type

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Overall Series Review

Subject: rust: add `Ownable` trait and `Owned` type
Author: Andreas Hindborg <a.hindborg@kernel.org>
Patches: 15
Reviewed: 2026-02-23T06:08:49.862113

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This is v15 of a Rust kernel infrastructure series by Andreas Hindborg (with contributions from Asahi Lina and Oliver Mangold) that introduces the `Ownable` trait and `Owned<T>` smart pointer type. The series provides a way for C-allocated objects to be uniquely owned by Rust code with custom drop logic, analogous to how `AlwaysRefCounted`/`ARef` works for reference-counted objects. It also adds `OwnableRefCounted` for converting between `Owned` and `ARef`, converts `Page` to use the new infrastructure, implements `ForeignOwnable` for `Owned`, and adds `Page::from_raw()`.

The architecture is sound: splitting `AlwaysRefCounted` into `RefCounted` (the actual refcounting interface) and `AlwaysRefCounted` (a marker trait that permits `&T -> ARef<T>` conversions) is a correct way to prevent soundness issues when a type can be both uniquely owned and ref-counted. The `Owned<T>` type is well-designed as a pinned unique pointer with custom destruction.

I found one likely bug in the `ForeignOwnable` implementation for `Owned<T>` (`FOREIGN_ALIGN` is set incorrectly), a documentation link error, and a few documentation concerns. The mailing list feedback from Alice Ryhl and Miguel Ojeda is also incorporated below where relevant, as several of their comments identify real issues.

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