Re: [PATCH] rust: sync: add `UniqueArc::as_ptr`

["Benno Lossin" <lossin@kernel.org>]

On Mon Feb 16, 2026 at 8:13 AM CET, Andreas Hindborg wrote:
> "Benno Lossin" <lossin@kernel.org> writes:
>
>> On Sun Feb 15, 2026 at 9:38 PM CET, Andreas Hindborg wrote:
>>> Add a method to `UniqueArc` for getting a raw pointer. The implementation
>>> defers to the `Arc` implementation of the same method.
>>>
>>> Signed-off-by: Andreas Hindborg <a.hindborg@kernel.org>
>>> ---
>>>  rust/kernel/sync/arc.rs | 5 +++++
>>>  1 file changed, 5 insertions(+)
>>>
>>> diff --git a/rust/kernel/sync/arc.rs b/rust/kernel/sync/arc.rs
>>> index 289f77abf415a..9c70fdd39bd2f 100644
>>> --- a/rust/kernel/sync/arc.rs
>>> +++ b/rust/kernel/sync/arc.rs
>>> @@ -770,6 +770,11 @@ pub fn new_uninit(flags: Flags) -> Result<UniqueArc<MaybeUninit<T>>, AllocError>
>>>              inner: unsafe { Arc::from_inner(KBox::leak(inner).into()) },
>>>          })
>>>      }
>>> +
>>> +    /// Return a raw pointer to the data in this unique arc.
>>> +    pub fn as_ptr(&self) -> *const T {
>>
>> This should be an associated function instead of an inherent method.
>
> I think this is so that we always call the function on the intended
> object rather than going through Deref. Could you please clarify if this
> is correct?

If you declare an inherent method on a type that is `Deref` (or
`Receiver`), then you can never call a method with the same name on the
object it derefs to:

    struct MyThing;

    impl MyThing {
        fn as_ptr(&self) -> *const () { /* ... */ }
    }

    let my_thing = UniqueArc::new(MyThing);
    let _: *const MyThing = my_thing.as_ptr(); // this is the method from `UniqueArc`
    // to call the other one, we have to write:
    let _: *const () = MyThing::my_thing(&*my_thing);

Especially a function with the name `as_ptr` should be associated, since
both very likely return a pointer; this increases the likelihood of
accidentally calling the wrong one.

Cheers,
Benno