linux-kernel - Re: [PATCH] rust: sync: create the `get

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Message-Id: <20250131160235.305557-1-trintaeoitogc@gmail.com>
Date: Fri, 31 Jan 2025 13:02:35 -0300
From: Guilherme Giacomo Simoes <trintaeoitogc@...il.com>
To: boqun.feng@...il.com
Cc: a.hindborg@...nel.org,
	alex.gaynor@...il.com,
	aliceryhl@...gle.com,
	benno.lossin@...ton.me,
	bjorn3_gh@...tonmail.com,
	gary@...yguo.net,
	linux-kernel@...r.kernel.org,
	longman@...hat.com,
	mingo@...hat.com,
	ojeda@...nel.org,
	peterz@...radead.org,
	rust-for-linux@...r.kernel.org,
	tmgross@...ch.edu,
	trintaeoitogc@...il.com,
	will@...nel.org
Subject: Re: [PATCH] rust: sync: create the `get_mut()` function

Boqun Feng <boqun.feng@...il.com> wrotes:
> Hi Guilherme,
> 
> Thanks for the patch. First I would prefer the title being:
> 
> 	rust: sync: lock: Add Lock::get_mut()
> 
> "create" is not a good word to use here, and the parentheses after
> "get_mut" already says it's a function.
> 
> On Thu, Jan 30, 2025 at 03:51:38PM -0300, Guilherme Giacomo Simoes wrote:
> > Create a `get_mut()` function that receive a mutable instance of Lock,
> > and return a mutable reference to data because if the instance is
> > mutable, the rust compiler guarantee the access control.
> > 
> 
> This commit log doesn't include "why we need this", so please add the
> reason or the usage of this function, maybe you or someone need it
> because of some initialization/setup code after creating a lock
> protected object? Moreover...
> 
> > Suggested-by: Björn Roy Baron <bjorn3_gh@...tonmail.com>
> > Signed-off-by: Guilherme Giacomo Simoes <trintaeoitogc@...il.com>
> > ---
> >  rust/kernel/sync/lock.rs | 6 ++++++
> >  1 file changed, 6 insertions(+)
> > 
> > diff --git a/rust/kernel/sync/lock.rs b/rust/kernel/sync/lock.rs
> > index eb80048e0110..3f9d78bcb37c 100644
> > --- a/rust/kernel/sync/lock.rs
> > +++ b/rust/kernel/sync/lock.rs
> > @@ -140,6 +140,12 @@ pub fn new(t: T, name: &'static CStr, key: &'static LockClassKey) -> impl PinIni
> >              }),
> >          })
> >      }
> > +
> > +    /// Get a mutable reference to data
> 
> ... please provide an example of the usage in the doc.
> 
> > +    pub fn get_mut(&mut self) -> &mut T {
> > +        // SAFETY: the caller must guarantee that the instance is only used in one place
> 
> SAFETY comments should explain why it's safe, here it's phrased like a
> requirement, maybe something like:
> 
>     // SAFETY: `&mut self` guarantees the exclusive access to the
>     // underlying data, therefore it's safe to reborrow the inner data.
> 
> Regards,
> Boqun

Ok, I make this changes and sent a new patch:

https://lore.kernel.org/all/20250131155940.305403-1-trintaeoitogc@gmail.com

Thanks,
Guilherme