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From: Andreas Hindborg <a.hindborg@kernel.org>
To: "Oliver Mangold" <oliver.mangold@pm.me>
Cc: "Miguel Ojeda" <ojeda@kernel.org>,  "Alex Gaynor"
 <alex.gaynor@gmail.com>,  "Boqun Feng" <boqun.feng@gmail.com>,  "Gary Guo"
 <gary@garyguo.net>,  =?utf-8?Q?Bj=C3=B6rn?= Roy Baron
 <bjorn3_gh@protonmail.com>,  "Benno
 Lossin" <benno.lossin@proton.me>,  "Alice Ryhl" <aliceryhl@google.com>,
  "Trevor Gross" <tmgross@umich.edu>,  "Asahi Lina" <lina@asahilina.net>,
  <rust-for-linux@vger.kernel.org>,  <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v10 3/5] rust: Add missing SAFETY documentation for ARef
 example
In-Reply-To: <20250502-unique-ref-v10-3-25de64c0307f@pm.me> (Oliver Mangold's
	message of "Fri, 02 May 2025 09:02:46 +0000")
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	<20250502-unique-ref-v10-3-25de64c0307f@pm.me>
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Date: Fri, 02 May 2025 12:41:01 +0200
Message-ID: <87ikmjz45e.fsf@kernel.org>
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"Oliver Mangold" <oliver.mangold@pm.me> writes:

> SAFETY comment in rustdoc example was just 'TODO'. Fixed.
>
> Signed-off-by: Oliver Mangold <oliver.mangold@pm.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