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Date:   Wed, 5 Apr 2023 21:21:54 +0100
From:   Gary Guo <gary@garyguo.net>
To:     Wedson Almeida Filho <wedsonaf@gmail.com>
Cc:     rust-for-linux@vger.kernel.org, Miguel Ojeda <ojeda@kernel.org>,
        Alex Gaynor <alex.gaynor@gmail.com>,
        Boqun Feng <boqun.feng@gmail.com>,
        =?UTF-8?B?QmrDtnJu?= Roy Baron <bjorn3_gh@protonmail.com>,
        linux-kernel@vger.kernel.org,
        Wedson Almeida Filho <walmeida@microsoft.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Ingo Molnar <mingo@redhat.com>, Will Deacon <will@kernel.org>,
        Waiman Long <longman@redhat.com>
Subject: Re: [PATCH v2 01/13] rust: sync: introduce `LockClassKey`
Message-ID: <20230405212154.79a9fb72.gary@garyguo.net>
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On Wed,  5 Apr 2023 14:50:59 -0300
Wedson Almeida Filho <wedsonaf@gmail.com> wrote:

> From: Wedson Almeida Filho <walmeida@microsoft.com>
> 
> It is a wrapper around C's `lock_class_key`, which is used by the
> synchronisation primitives that are checked with lockdep. This is in
> preparation for introducing Rust abstractions for these primitives.
> 
> Cc: Peter Zijlstra <peterz@infradead.org>
> Cc: Ingo Molnar <mingo@redhat.com>
> Cc: Will Deacon <will@kernel.org>
> Cc: Waiman Long <longman@redhat.com>
> Co-developed-by: Boqun Feng <boqun.feng@gmail.com>
> Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
> Signed-off-by: Wedson Almeida Filho <walmeida@microsoft.com>
> ---
> v1 -> v2: Fixed a typo in comment
> 
>  rust/kernel/sync.rs | 45 +++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 45 insertions(+)
> 
> diff --git a/rust/kernel/sync.rs b/rust/kernel/sync.rs
> index 33da23e3076d..84a4b560828c 100644
> --- a/rust/kernel/sync.rs
> +++ b/rust/kernel/sync.rs
> @@ -5,6 +5,51 @@
>  //! This module contains the kernel APIs related to synchronisation that have been ported or
>  //! wrapped for usage by Rust code in the kernel.
>  
> +use crate::types::Opaque;
> +
>  mod arc;
>  
>  pub use arc::{Arc, ArcBorrow, UniqueArc};
> +
> +/// Represents a lockdep class. It's a wrapper around C's `lock_class_key`.
> +#[repr(transparent)]
> +pub struct LockClassKey(Opaque<bindings::lock_class_key>);
> +
> +// SAFETY: `bindings::lock_class_key` is designed to be used concurrently from multiple threads and
> +// provides its own synchronization.
> +unsafe impl Sync for LockClassKey {}
> +
> +impl LockClassKey {
> +    /// Creates a new lock class key.
> +    pub const fn new() -> Self {
> +        Self(Opaque::uninit())
> +    }
> +
> +    #[allow(dead_code)]
> +    pub(crate) fn as_ptr(&self) -> *mut bindings::lock_class_key {
> +        self.0.get()
> +    }
> +}
> +
> +/// Defines a new static lock class and returns a pointer to it.
> +#[doc(hidden)]
> +#[macro_export]
> +macro_rules! static_lock_class {
> +    () => {{
> +        static CLASS: $crate::sync::LockClassKey = $crate::sync::LockClassKey::new();
> +        &CLASS
> +    }};
> +}
> +
> +/// Returns the given string, if one is provided, otherwise generates one based on the source code
> +/// location.
> +#[doc(hidden)]
> +#[macro_export]
> +macro_rules! optional_name {
> +    () => {
> +        $crate::c_str!(core::concat!(core::file!(), ":", core::line!()))

nit: prefer `::core` to `core` in macro.

> +    };
> +    ($name:literal) => {
> +        $crate::c_str!($name)
> +    };
> +}