rust: add try-ffi-init

IMPORTANT: This work is by Wedson A.F.! This patch will not be send to
the lists. If patches are send to the list, they will be based on a
tree that contains these patches.

Author: Valentin Obst

rust/kernel/types.rs

@@ -250,6 +250,18 @@ impl<T> Opaque<T> {
         }
     }
 
+    /// Similar to [`Self::ffi_init`], except that the closure can fail.
+    ///
+    /// To avoid leaks on failure, the closure must drop any fields it has initialised before the
+    /// failure.
+    pub fn try_ffi_init<E>(
+        init_func: impl FnOnce(*mut T) -> Result<(), E>,
+    ) -> impl PinInit<Self, E> {
+        // SAFETY: We contain a `MaybeUninit`, so it is OK for the `init_func` to not fully
+        // initialize the `T`.
+        unsafe { init::pin_init_from_closure(|slot| init_func(Self::raw_get(slot))) }
+    }
+
     /// Returns a raw pointer to the opaque data.
     pub fn get(&self) -> *mut T {
         UnsafeCell::get(&self.value).cast::<T>()