Re: [PATCH] rust: drm: Drop the use of Opaque for ioctl arguments

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

On Thu Jun 19, 2025 at 12:55 PM CEST, Danilo Krummrich wrote:
> On Thu, Jun 19, 2025 at 12:21:02PM +0200, Beata Michalska wrote:
>> diff --git a/rust/kernel/drm/ioctl.rs b/rust/kernel/drm/ioctl.rs
>> index 445639404fb7..12b296131672 100644
>> --- a/rust/kernel/drm/ioctl.rs
>> +++ b/rust/kernel/drm/ioctl.rs
>> @@ -139,7 +139,7 @@ pub mod internal {
>>                              // asserted above matches the size of this type, and all bit patterns of
>>                              // UAPI structs must be valid.
>>                              let data = unsafe {
>> -                                &*(raw_data as *const $crate::types::Opaque<$crate::uapi::$struct>)
>> +                                &mut *(raw_data as *mut $crate::uapi::$struct)
>
> I think we have to document the guarantees we rely on to create this mutable
> reference.

If the C side is using pointers to read/write the value concurrently,
this is wrong, it needs to be wrapped in Opaque.

---
Cheers,
Benno