Currently in order to implement AlwaysRefCounted for gem objects, we use a
blanket implementation:
unsafe impl<T: IntoGEMObject> AlwaysRefCounted for T { … }
While this technically works, it comes with the rather unfortunate downside
that attempting to create a similar blanket implementation in any other
kernel crate will now fail in a rather confusing way.
Using an example from the (not yet upstream) rust DRM KMS bindings, if we
were to add:
unsafe impl<T: RcModeObject> AlwaysRefCounted for T { … }
Then the moment that both blanket implementations are present in the same
kernel tree, compilation fails with the following:
error[E0119]: conflicting implementations of trait `types::AlwaysRefCounted`
--> rust/kernel/drm/kms.rs:504:1
|
504 | unsafe impl<T: RcModeObject> AlwaysRefCounted for T {
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ conflicting implementation
|
::: rust/kernel/drm/gem/mod.rs:97:1
|
97 | unsafe impl<T: IntoGEMObject> AlwaysRefCounted for T {
| ---------------------------------------------------- first implementation here
So, revert these changes for now. The proper fix for this is to introduce a
macro for copy/pasting the same implementation of AlwaysRefCounted around.
This reverts commit 38cb08c3fc.
Signed-off-by: Lyude Paul <lyude@redhat.com>
Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Link: https://lore.kernel.org/r/20251016210955.2813186-2-lyude@redhat.com
5ae65bdcb8