linux-kernel - Re: [PATCH 2/7] rust: sync: allow type of `self` to be `Arc<T>` or variants

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Message-ID: <20221231193720.4428eb7d.gary@garyguo.net>
Date:   Sat, 31 Dec 2022 19:37:20 +0000
From:   Gary Guo <gary@...yguo.net>
To:     Wedson Almeida Filho <wedsonaf@...il.com>
Cc:     rust-for-linux@...r.kernel.org, Miguel Ojeda <ojeda@...nel.org>,
        Alex Gaynor <alex.gaynor@...il.com>,
        Boqun Feng <boqun.feng@...il.com>,
        Björn Roy Baron <bjorn3_gh@...tonmail.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/7] rust: sync: allow type of `self` to be `Arc<T>` or
 variants

On Wed, 28 Dec 2022 06:03:41 +0000
Wedson Almeida Filho <wedsonaf@...il.com> wrote:

> This allows associated functions whose `self` argument has `Arc<T>` or
> variants as their type. This, in turn, allows callers to use the dot
> syntax to make calls.
> 
> Signed-off-by: Wedson Almeida Filho <wedsonaf@...il.com>

Reviewed-by: Gary Guo <gary@...yguo.net>

> ---
>  rust/kernel/lib.rs      |  1 +
>  rust/kernel/sync/arc.rs | 28 ++++++++++++++++++++++++++++
>  2 files changed, 29 insertions(+)
> 
> diff --git a/rust/kernel/lib.rs b/rust/kernel/lib.rs
> index ace064a3702a..1a10f7c0ddd9 100644
> --- a/rust/kernel/lib.rs
> +++ b/rust/kernel/lib.rs
> @@ -14,6 +14,7 @@
>  #![no_std]
>  #![feature(allocator_api)]
>  #![feature(core_ffi_c)]
> +#![feature(receiver_trait)]
>  
>  // Ensure conditional compilation based on the kernel configuration works;
>  // otherwise we may silently break things like initcall handling.
> diff --git a/rust/kernel/sync/arc.rs b/rust/kernel/sync/arc.rs
> index 22290eb5ab9b..e2eb0e67d483 100644
> --- a/rust/kernel/sync/arc.rs
> +++ b/rust/kernel/sync/arc.rs
> @@ -57,6 +57,31 @@ use core::{marker::PhantomData, ops::Deref, ptr::NonNull};
>  ///
>  /// // The refcount drops to zero when `cloned` goes out of scope, and the memory is freed.
>  /// ```
> +///
> +/// Using `Arc<T>` as the type of `self`:
> +///
> +/// ```
> +/// use kernel::sync::Arc;
> +///
> +/// struct Example {
> +///     a: u32,
> +///     b: u32,
> +/// }
> +///
> +/// impl Example {
> +///     fn take_over(self: Arc<Self>) {
> +///         // ...
> +///     }
> +///
> +///     fn use_reference(self: &Arc<Self>) {
> +///         // ...
> +///     }
> +/// }
> +///
> +/// let obj = Arc::try_new(Example { a: 10, b: 20 })?;
> +/// obj.use_reference();
> +/// obj.take_over();
> +/// ```
>  pub struct Arc<T: ?Sized> {
>      ptr: NonNull<ArcInner<T>>,
>      _p: PhantomData<ArcInner<T>>,
> @@ -68,6 +93,9 @@ struct ArcInner<T: ?Sized> {
>      data: T,
>  }
>  
> +// This is to allow [`Arc`] (and variants) to be used as the type of `self`.
> +impl<T: ?Sized> core::ops::Receiver for Arc<T> {}
> +
>  // SAFETY: It is safe to send `Arc<T>` to another thread when the underlying `T` is `Sync` because
>  // it effectively means sharing `&T` (which is safe because `T` is `Sync`); additionally, it needs
>  // `T` to be `Send` because any thread that has an `Arc<T>` may ultimately access `T` directly, for