Re: [PATCH v17 02/10] rust: types: Add Ownable/Owned types

[Alice Ryhl]

On Thu, Jun 04, 2026 at 10:11:14PM +0200, Andreas Hindborg wrote:
> From: Asahi Lina <lina+kernel@xxxxxxxxxxxxx>
> 
> By analogy to `AlwaysRefCounted` and `ARef`, an `Ownable` type is a
> (typically C FFI) type that *may* be owned by Rust, but need not be. Unlike
> `AlwaysRefCounted`, this mechanism expects the reference to be unique
> within Rust, and does not allow cloning.
> 
> Conceptually, this is similar to a `KBox<T>`, except that it delegates
> resource management to the `T` instead of using a generic allocator.
> 
> [ om:
>   - Split code into separate file and `pub use` it from types.rs.
>   - Make from_raw() and into_raw() public.
>   - Remove OwnableMut, and make DerefMut dependent on Unpin instead.
>   - Usage example/doctest for Ownable/Owned.
>   - Fixes to documentation and commit message.
> ]
> 
> Link: https://lore.kernel.org/all/20250202-rust-page-v1-1-e3170d7fe55e@xxxxxxxxxxxxx/
> Signed-off-by: Asahi Lina <lina+kernel@xxxxxxxxxxxxx>
> Co-developed-by: Oliver Mangold <oliver.mangold@xxxxx>
> Signed-off-by: Oliver Mangold <oliver.mangold@xxxxx>
> Reviewed-by: Boqun Feng <boqun.feng@xxxxxxxxx>
> Reviewed-by: Daniel Almeida <daniel.almeida@xxxxxxxxxxxxx>
> [ Andreas: Updated documentation, examples, and formatting. Change safety
>   requirements, safety comments. Use a reference for `release`. ]
> Reviewed-by: Gary Guo <gary@xxxxxxxxxxx>
> Co-developed-by: Andreas Hindborg <a.hindborg@xxxxxxxxxx>
> Signed-off-by: Andreas Hindborg <a.hindborg@xxxxxxxxxx>

Overall looks good to me, but two nits below. With them fixed:

Reviewed-by: Alice Ryhl <aliceryhl@xxxxxxxxxx>

> +pub trait Ownable {
> +    /// Tear down this `Ownable`.
> +    ///
> +    /// Implementers of `Ownable` can use this function to clean up the use of `Self`. This can
> +    /// include freeing the underlying object.
> +    ///
> +    /// # Safety
> +    ///
> +    /// Callers must ensure that the caller has exclusive ownership of `T`, and this ownership can
> +    /// be transferred to the `release` method.
> +    unsafe fn release(&mut self);

I'd make this take a raw pointer because the pointer can be freed during
the execution of release(), which references don't allow.

> diff --git a/rust/kernel/types.rs b/rust/kernel/types.rs
> index 4329d3c2c2e5..4aec7b699269 100644
> --- a/rust/kernel/types.rs
> +++ b/rust/kernel/types.rs
> @@ -11,6 +11,17 @@
>  };
>  use pin_init::{PinInit, Wrapper, Zeroable};
>  
> +pub use crate::{
> +    owned::{
> +        Ownable,
> +        Owned, //
> +    },
> +    sync::aref::{
> +        ARef,
> +        AlwaysRefCounted, //
> +    }, //
> +};

We removed the types::ARef re-export, so you shouldn't add it back.

Alice