Re: [PATCH v4 2/3] rust: miscdevice: add additional data to MiscDeviceRegistration

[Christian Schrefl <chrisi.schrefl@gmail.com>]

On 04.06.25 11:40 AM, Alice Ryhl wrote:
> On Mon, Jun 02, 2025 at 11:16:33PM +0200, Christian Schrefl wrote:
>> On 31.05.25 2:23 PM, Benno Lossin wrote:
>>> On Fri May 30, 2025 at 10:46 PM CEST, Christian Schrefl wrote:
>>>> +        unsafe { core::ptr::drop_in_place(self.data.get()) };
>>>>      }
>>>>  }
>>>>  
>>>> @@ -109,6 +135,13 @@ pub trait MiscDevice: Sized {
>>>>      /// What kind of pointer should `Self` be wrapped in.
>>>>      type Ptr: ForeignOwnable + Send + Sync;
>>>>  
>>>> +    /// The additional data carried by the [`MiscDeviceRegistration`] for this [`MiscDevice`].
>>>> +    /// If no additional data is required than the unit type `()` should be used.
>>>> +    ///
>>>> +    /// This data can be accessed in [`MiscDevice::open()`] using
>>>> +    /// [`MiscDeviceRegistration::data()`].
>>>> +    type RegistrationData: Sync;
>>>
>>> Why do we require `Sync` here?
>>
>> Needed for `MiscDeviceRegistration` to be `Send`, see response above.
> 
> Even if `MiscDeviceRegistration` is non-Send, the registration data must
> still be Sync. The f_ops->open callback can *always* be called from any
> thread no matter what we do here, so the data it gives you access must
> always be Sync no matter what.

Right I meant to write `Sync` sorry.

Cheers
Christian