linux-kernel - Re: [PATCH 1/3] rust: implement `kernel::sync::Refcount`

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Message-ID: <55e1fdeb-97f8-40e4-b3a8-bc7ce8271b9a@gmail.com>
Date: Fri, 4 Oct 2024 18:34:51 +0200
From: Dirk Behme <dirk.behme@...il.com>
To: Gary Guo <gary@...yguo.net>, 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@...nel.org>, Alice Ryhl <aliceryhl@...gle.com>,
 Trevor Gross <tmgross@...ch.edu>,
 Martin Rodriguez Reboredo <yakoyoku@...il.com>
Cc: Will Deacon <will@...nel.org>, Peter Zijlstra <peterz@...radead.org>,
 Mark Rutland <mark.rutland@....com>, Dirk Behme <dirk.behme@...bosch.com>,
 linux-kernel@...r.kernel.org, rust-for-linux@...r.kernel.org
Subject: Re: [PATCH 1/3] rust: implement `kernel::sync::Refcount`

Am 04.10.24 um 17:52 schrieb Gary Guo:
> This is a wrapping layer of `include/linux/refcount.h`. Currently only
> the most basic operations (read/set/inc/dec/dec_and_test) are implemented,
> additional methods can be implemented when they are needed.
> 
> Currently the kernel refcount has already been used in `Arc`, however it
> calls into FFI directly.
> 
> Cc: Will Deacon <will@...nel.org>
> Cc: Peter Zijlstra <peterz@...radead.org>
> Cc: Boqun Feng <boqun.feng@...il.com>
> Cc: Mark Rutland <mark.rutland@....com>
> Signed-off-by: Gary Guo <gary@...yguo.net>
> ---
>   rust/helpers/refcount.c      | 15 ++++++
...
> diff --git a/rust/kernel/sync.rs b/rust/kernel/sync.rs
> index 0ab20975a3b5..534f098a44eb 100644
> --- a/rust/kernel/sync.rs
> +++ b/rust/kernel/sync.rs
> @@ -11,12 +11,14 @@
>   mod condvar;
>   pub mod lock;
>   mod locked_by;
> +mod refcount;
>   
>   pub use arc::{Arc, ArcBorrow, UniqueArc};
>   pub use condvar::{new_condvar, CondVar, CondVarTimeoutResult};
>   pub use lock::mutex::{new_mutex, Mutex};
>   pub use lock::spinlock::{new_spinlock, SpinLock};
>   pub use locked_by::LockedBy;
> +pub use refcount::Refcount;
>   
>   /// Represents a lockdep class. It's a wrapper around C's `lock_class_key`.
>   #[repr(transparent)]
> diff --git a/rust/kernel/sync/refcount.rs b/rust/kernel/sync/refcount.rs
> new file mode 100644
> index 000000000000..4a5b815adc05
> --- /dev/null
> +++ b/rust/kernel/sync/refcount.rs
> @@ -0,0 +1,94 @@
> +// SPDX-License-Identifier: GPL-2.0
> +
> +//! Atomic reference counting.
> +//!
> +//! C header: [`include/linux/refcount.h`](srctree/include/linux/refcount.h)
> +
> +use crate::types::Opaque;
> +use core::sync::atomic::AtomicI32;
> +
> +/// Atomic reference counter.
> +///
> +/// This type is conceptually an atomic integer, but provides a saturation semantics compared to

"a ... samantics": Do you like to check that? Either "a ... semantic" 
(without 's')? Or if it shall be plural drop the 'a'?

...
> +    /// Increment a refcount.
> +    ///
> +    /// It will saturate if overflows and `WARN`. It will also `WARN` is the refcount is 0, as this

WARN if ? Not "is" ?

Best regards

Dirk