rust: implement `Wrapper<T>` for `Opaque<T>`

Moves the implementation for `pin-init` from an associated function
to the trait function of the `Wrapper` trait and extends the
implementation to support pin-initializers with error types.

Adds a use for the `Wrapper` trait in `revocable.rs`, to use the new
`pin-init` function. This is currently the only usage in the kernel.

Reviewed-by: Gerald Wisböck <gerald.wisboeck@feather.ink>
Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Reviewed-by: Benno Lossin <lossin@kernel.org>
Acked-by: Miguel Ojeda <ojeda@kernel.org>
Signed-off-by: Christian Schrefl <chrisi.schrefl@gmail.com>
Link: https://lore.kernel.org/r/20250610-b4-rust_miscdevice_registrationdata-v6-1-b03f5dfce998@gmail.com
Signed-off-by: Danilo Krummrich <dakr@kernel.org>

2 files changed, 16 insertions, 12 deletions

diff --git a/rust/kernel/revocable.rs b/rust/kernel/revocable.rs
index 06a3cdfce344..fa1fd70efa27 100644
--- a/rust/kernel/revocable.rs
+++ b/rust/kernel/revocable.rs
@@ -5,6 +5,8 @@
 //! The [`Revocable`] type wraps other types and allows access to them to be revoked. The existence
 //! of a [`RevocableGuard`] ensures that objects remain valid.
 
+use pin_init::Wrapper;
+
 use crate::{bindings, prelude::*, sync::rcu, types::Opaque};
 use core::{
     marker::PhantomData,
diff --git a/rust/kernel/types.rs b/rust/kernel/types.rs
index 22985b6f6982..3958a5f44d56 100644
--- a/rust/kernel/types.rs
+++ b/rust/kernel/types.rs
@@ -9,7 +9,7 @@ use core::{
     ops::{Deref, DerefMut},
     ptr::NonNull,
 };
-use pin_init::{PinInit, Zeroable};
+use pin_init::{PinInit, Wrapper, Zeroable};
 
 /// Used to transfer ownership to and from foreign (non-Rust) languages.
 ///
@@ -353,17 +353,6 @@ impl<T> Opaque<T> {
         }
     }
 
-    /// Create an opaque pin-initializer from the given pin-initializer.
-    pub fn pin_init(slot: impl PinInit<T>) -> impl PinInit<Self> {
-        Self::ffi_init(|ptr: *mut T| {
-            // SAFETY:
-            //   - `ptr` is a valid pointer to uninitialized memory,
-            //   - `slot` is not accessed on error; the call is infallible,
-            //   - `slot` is pinned in memory.
-            let _ = unsafe { PinInit::<T>::__pinned_init(slot, ptr) };
-        })
-    }
-
     /// Creates a pin-initializer from the given initializer closure.
     ///
     /// The returned initializer calls the given closure with the pointer to the inner `T` of this
@@ -415,6 +404,19 @@ impl<T> Opaque<T> {
     }
 }
 
+impl<T> Wrapper<T> for Opaque<T> {
+    /// Create an opaque pin-initializer from the given pin-initializer.
+    fn pin_init<E>(slot: impl PinInit<T, E>) -> impl PinInit<Self, E> {
+        Self::try_ffi_init(|ptr: *mut T| {
+            // SAFETY:
+            //   - `ptr` is a valid pointer to uninitialized memory,
+            //   - `slot` is not accessed on error,
+            //   - `slot` is pinned in memory.
+            unsafe { PinInit::<T, E>::__pinned_init(slot, ptr) }
+        })
+    }
+}
+
 /// Types that are _always_ reference counted.
 ///
 /// It allows such types to define their own custom ref increment and decrement functions.