linux-kernel - Re: [PATCH 01/13] rust: sync: introduce `LockClassKey`

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Message-ID: <CANeycqq0ORMD2ybFoysnFVYcpnkVpr10GKyqsFuq8kehKveyTg@mail.gmail.com>
Date:   Wed, 5 Apr 2023 14:42:17 -0300
From:   Wedson Almeida Filho <wedsonaf@...il.com>
To:     Alice Ryhl <alice@...l.io>
Cc:     rust-for-linux@...r.kernel.org, Miguel Ojeda <ojeda@...nel.org>,
        Alex Gaynor <alex.gaynor@...il.com>,
        Boqun Feng <boqun.feng@...il.com>, Gary Guo <gary@...yguo.net>,
        Björn Roy Baron <bjorn3_gh@...tonmail.com>,
        linux-kernel@...r.kernel.org,
        Wedson Almeida Filho <walmeida@...rosoft.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>, Will Deacon <will@...nel.org>,
        Waiman Long <longman@...hat.com>
Subject: Re: [PATCH 01/13] rust: sync: introduce `LockClassKey`

On Fri, 31 Mar 2023 at 04:28, Alice Ryhl <alice@...l.io> wrote:
>
> On 3/30/23 06:39, Wedson Almeida Filho wrote:
> > From: Wedson Almeida Filho <walmeida@...rosoft.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@...radead.org>
> > Cc: Ingo Molnar <mingo@...hat.com>
> > Cc: Will Deacon <will@...nel.org>
> > Cc: Waiman Long <longman@...hat.com>
> > 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>
> > ---
> > +// SAFETY: `bindings::lock_class_key` is designed to be used concurrently from multiple threads and
> > +// provides its own synchronization.
> > +unsafe impl Sync for LockClassKey {}
>
> No Send?

We haven't needed it. We can add it when needed.

> > +
> > +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()
> > +    }
>
> I would just make this pub and drop the `#[allow(dead_code)]`. I think
> it is often useful to have methods like this available publicly.

The `allow(dead_code)` is removed on the next patch, it's here just to
make this patch compile when applied alone.

This isn't public because the return type refers to a type from
`bindings`, which we intend to eventually hide from drivers, making it
public now would like our lives harder in the future.