Re: [PATCH] rust: sync: extend module documentation of aref

[Daniel Sedlak]

Hi Benno,

On 7/22/25 2:14 PM, Benno Lossin wrote:
> Commit 07dad44aa9a9 ("rust: kernel: move ARef and AlwaysRefCounted to
> sync::aref") moved `ARef` and `AlwaysRefCounted` into their own module.
> In that process only a short, single line description of the module was
> added. Extend the description by explaining what is meant by "internal
> reference counting", the two items in the trait & the difference to
> `Arc`.
>
> Signed-off-by: Benno Lossin <lossin@xxxxxxxxxx>
> ---
>   rust/kernel/sync/aref.rs | 15 +++++++++++++++
>   1 file changed, 15 insertions(+)
>
> diff --git a/rust/kernel/sync/aref.rs b/rust/kernel/sync/aref.rs
> index dbd77bb68617..1c212238c0e5 100644
> --- a/rust/kernel/sync/aref.rs
> +++ b/rust/kernel/sync/aref.rs
> @@ -1,6 +1,21 @@
>   // SPDX-License-Identifier: GPL-2.0
>   
>   //! Internal reference counting support.
> +//!
> +//! Many C types already have their own reference counting mechanism (e.g. by storing a
> +//! `refcount_t`). This module provides support for directly using their internal reference count
> +//! from Rust; instead of making users have to use an additional Rust-reference count in the form of
> +//! [`Arc`].
> +//!
> +//! The smart pointer [`ARef<T>`] acts similarly to [`Arc<T>`] in that it holds a refcount on the
> +//! underlying object, but this refcount is internal to the object. It essentially is a Rust
> +//! implementation of the `get_` and `put_` pattern used in C for reference counting.
> +//!
> +//! To make use of [`ARef<MyType>`], `MyType` needs to implement [`AlwaysRefCounted`]. It is a trait
> +//! for accessing the internal reference count of an object of the `MyType` type.
> +//!
> +//! [`Arc`]: crate::sync::Arc
> +//! [`Arc<T>`]: crate::sync::Arc

It got me curios. Why is it required to declare the doc reference for 
Arc and Arc<T>, but not ARef<MyType> and ARef<T>?

Is it because ARef is in file scope but not the Arc?

If so, you could just add

	use crate::sync::Arc;

in the file imports and you wouldn't have to duplicate the

	//! [`Arc`]: crate::sync::Arc
	//! [`Arc<T>`]: crate::sync::Arc

And even cleanup it a bit by simplifying

	[`Arc`](crate::sync::Arc) to [`Arc`]

in the AlwaysRefCounted trait.

Thanks!
Daniel