linux-kernel - Re: [PATCH v10 3/5] rust: Add missing SAFETY documentation for ARef example

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Message-ID: <aBSofsTTbt4pgsDU@mango>
Date: Fri, 02 May 2025 11:12:05 +0000
From: Oliver Mangold <oliver.mangold@...me>
To: Andreas Hindborg <a.hindborg@...nel.org>
Cc: 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>, Benno Lossin <benno.lossin@...ton.me>, Alice Ryhl <aliceryhl@...gle.com>, Trevor Gross <tmgross@...ch.edu>, Asahi Lina <lina@...hilina.net>, rust-for-linux@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v10 3/5] rust: Add missing SAFETY documentation for ARef example

On 250502 1241, Andreas Hindborg wrote:
> >
> > diff --git a/rust/kernel/types.rs b/rust/kernel/types.rs
> > index d7fa8934c545f46a646ca900ab8957a04b0ad34d..33d2b4e4a87b991c6d934f4e8d2c6c71a15b1bcb 100644
> > --- a/rust/kernel/types.rs
> > +++ b/rust/kernel/types.rs
> > @@ -498,7 +498,9 @@ pub unsafe fn from_raw(ptr: NonNull<T>) -> Self {
> >      ///
> >      /// struct Empty {}
> >      ///
> > -    /// # // SAFETY: TODO.
> > +    /// // SAFETY: The `RefCounted` implementation for `Empty` does not count references
> > +    /// // and never frees the underlying object. Thus we can act as having a
> > +    /// // refcount on the object that we pass to the newly created `ARef`.
> >      /// unsafe impl RefCounted for Empty {
> >      ///     fn inc_ref(&self) {}
> >      ///     unsafe fn dec_ref(_obj: NonNull<Self>) {}
> > @@ -506,7 +508,7 @@ pub unsafe fn from_raw(ptr: NonNull<T>) -> Self {
> >      ///
> >      /// let mut data = Empty {};
> >      /// let ptr = NonNull::<Empty>::new(&mut data).unwrap();
> > -    /// # // SAFETY: TODO.
> > +    /// // SAFETY: We keep `data` around longer than the `ARef`.
> 
> I still think this applies:
> 
> >> How about:
> >>
> >>   The `RefCounted` implementation for `Empty` does not count references
> >>   and never frees the underlying object. Thus we can act as having a
> >>   refcount on the object that we pass to the newly created `ARef`.
> >>

Hi Andreas,

I agree. Sorry, I just messed up the fix. Your wording landed in the
previous to-be-fixed unsafe comment, as you can see.

Happens when you are too much in a hurry and didn't touch the patch for
too long :/

I will fix it in the next version.

Best,

Oliver