rust: types: add Opaque::pin_init

Analogous to `Opaque::new` add `Opaque::pin_init`, which instead of a
value `T` takes a `PinInit<T>` and returns a `PinInit<Opaque<T>>`.

Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Suggested-by: Alice Ryhl <aliceryhl@google.com>
Signed-off-by: Danilo Krummrich <dakr@kernel.org>
Tested-by: Dirk Behme <dirk.behme@de.bosch.com>
Tested-by: Fabien Parent <fabien.parent@linaro.org>
Link: https://lore.kernel.org/r/20241219170425.12036-6-dakr@kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

rust/kernel/types.rs

@@ -281,6 +281,17 @@ 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 { init::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