Re: [PATCH v17 03/10] rust: implement `ForeignOwnable` for `Owned`

[Andreas Hindborg <a.hindborg@kernel.org>]

"Gary Guo" <gary@garyguo.net> writes:

> On Thu Jun 4, 2026 at 9:11 PM BST, Andreas Hindborg wrote:
>> Implement `ForeignOwnable` for `Owned<T>`. This allows use of `Owned<T>` in
>> places such as the `XArray`.
>>
>> Note that `T` does not need to implement `ForeignOwnable` for `Owned<T>` to
>> implement `ForeignOwnable`.
>>
>> Signed-off-by: Andreas Hindborg <a.hindborg@kernel.org>
>> ---
>>  rust/kernel/owned.rs | 46 ++++++++++++++++++++++++++++++++++++++++++++++
>>  1 file changed, 46 insertions(+)
>>
>> diff --git a/rust/kernel/owned.rs b/rust/kernel/owned.rs
>> index 456e239e906e..5eacdf327d12 100644
>> --- a/rust/kernel/owned.rs
>> +++ b/rust/kernel/owned.rs
>> @@ -15,6 +15,8 @@
>>      ptr::NonNull, //
>>  };
>>  
>> +use kernel::types::ForeignOwnable;
>> +
>>  /// Types that specify their own way of performing allocation and destruction. Typically, this trait
>>  /// is implemented on types from the C side.
>>  ///
>> @@ -108,6 +110,7 @@ pub trait Ownable {
>>  ///
>>  /// - Until `T::release` is called, this `Owned<T>` exclusively owns the underlying `T`.
>>  /// - The `T` value is pinned.
>> +#[repr(transparent)]
>
> AFAIT this `#[repr(transparent)]` isn't actually needed.

I'll drop it.

>
>>  pub struct Owned<T: Ownable> {
>>      ptr: NonNull<T>,
>>  }
>> @@ -185,3 +188,46 @@ fn drop(&mut self) {
>>          unsafe { T::release(self.ptr.as_mut()) };
>>      }
>>  }
>> +
>> +// SAFETY: We derive the pointer to `T` from a valid `T`, so the returned
>> +// pointer satisfy alignment requirements of `T`.
>> +unsafe impl<T: Ownable + 'static> ForeignOwnable for Owned<T> {
>
> You should drop the `'static` bound and put where bound on the GAT below
> instead. See how `Box` is doing it.

I will take a look.


Best regards,
Andreas Hindborg