linux-kernel - Re: [PATCH 2/2] rust: arc: remove `ArcBorrow` in favour of `WithRef`

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Message-ID: <20230923081251.2f702cc7@gary-lowrisc-laptop>
Date:   Sat, 23 Sep 2023 08:12:51 +0800
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>,
        Benno Lossin <benno.lossin@...ton.me>,
        Andreas Hindborg <a.hindborg@...sung.com>,
        Alice Ryhl <aliceryhl@...gle.com>,
        linux-kernel@...r.kernel.org,
        Wedson Almeida Filho <walmeida@...rosoft.com>
Subject: Re: [PATCH 2/2] rust: arc: remove `ArcBorrow` in favour of
 `WithRef`

On Thu, 21 Sep 2023 18:34:40 -0300
Wedson Almeida Filho <wedsonaf@...il.com> wrote:

> From: Wedson Almeida Filho <walmeida@...rosoft.com>
> 
> With GATs, we don't need a separate type to represent a borrowed object
> with a refcount, we can just use Rust's regular shared borrowing. In
> this case, we use `&WithRef<T>` instead of `ArcBorrow<'_, T>`.
> 
> Co-developed-by: Boqun Feng <boqun.feng@...il.com>
> Signed-off-by: Boqun Feng <boqun.feng@...il.com>
> Signed-off-by: Wedson Almeida Filho <walmeida@...rosoft.com>

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

The implementation looks good to me, thanks Wedson.

A minor thing that worth considering is to implement `AlwaysRefCounted`
to `WithRef` and reimplement `Arc` with `ARef<TaskRef<T>>` or add
conversion functions between them.

It feels natural to have this this impl (because `WithRef` is indeed
always ref counted), but on the other hand I don't currently foresee
anyone to currently want to use this API :(

> ---
>  rust/kernel/sync.rs     |   2 +-
>  rust/kernel/sync/arc.rs | 180 ++++++++++++++--------------------------
>  2 files changed, 62 insertions(+), 120 deletions(-)