Re: [PATCH v4 4/5] rust: types: ForeignOwnable: Add type Target

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

On Fri Jun 27, 2025 at 1:21 AM CEST, Boqun Feng wrote:
> On Thu, Jun 26, 2025, at 4:17 PM, Benno Lossin wrote:
>> On Thu Jun 26, 2025 at 10:20 PM CEST, Boqun Feng wrote:
>>> On Thu, Jun 26, 2025 at 10:00:42PM +0200, Danilo Krummrich wrote:
>>>> diff --git a/rust/kernel/types.rs b/rust/kernel/types.rs
>>>> index 3958a5f44d56..74c787b352a9 100644
>>>> --- a/rust/kernel/types.rs
>>>> +++ b/rust/kernel/types.rs
>>>> @@ -27,6 +27,9 @@
>>>>  /// [`into_foreign`]: Self::into_foreign
>>>>  /// [`PointedTo`]: Self::PointedTo
>>>>  pub unsafe trait ForeignOwnable: Sized {
>>>> +    /// The payload type of the foreign-owned value.
>>>> +    type Target;
>>>
>>> I think `ForeignOwnable` also implies a `T` maybe get dropped via a
>>> pointer from `into_foreign()`. Not sure it's worth mentioning though.
>>
>> What? How would that happen?
>
> The owner of the pointer can do from_foreign() and eventually drop
> the ForeignOwnable, hence dropping T.

I'm confused, you said `into_foreign` above. I don't think any sensible
ForeignOwnable implementation will drop a T in any of its functions.

---
Cheers,
Benno