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

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Message-ID: <87ikmjz45e.fsf@kernel.org>
Date: Fri, 02 May 2025 12:41:01 +0200
From: Andreas Hindborg <a.hindborg@...nel.org>
To: "Oliver Mangold" <oliver.mangold@...me>
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

"Oliver Mangold" <oliver.mangold@...me> writes:

> SAFETY comment in rustdoc example was just 'TODO'. Fixed.
>
> Signed-off-by: Oliver Mangold <oliver.mangold@...me>
> ---
>  rust/kernel/types.rs | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
>
> 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`.
>> 

>      /// let data_ref: ARef<Empty> = unsafe { ARef::from_raw(ptr) };
>      /// let raw_ptr: NonNull<Empty> = ARef::into_raw(data_ref);
>      ///


Best regards,
Andreas Hindborg