[PATCH v4 15/15] rust: sync: add functions for initializing `UniqueArc<MaybeUninit<T>>`

[y86-dev@protonmail.com]

From: Benno Lossin <y86-dev@protonmail.com>

Add two functions `init_with` and `pin_init_with` to
`UniqueArc<MaybeUninit<T>>` to initialize the memory of already allocated
`UniqueArc`s. This is useful when you want to allocate memory check some
condition inside of a context where allocation is forbidden and then
conditionally initialize an object.

Signed-off-by: Benno Lossin <y86-dev@protonmail.com>
Reviewed-by: Gary Guo <gary@garyguo.net>
Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Reviewed-by: Andreas Hindborg <a.hindborg@samsung.com>
---
 rust/kernel/sync/arc.rs | 24 ++++++++++++++++++++++++
 1 file changed, 24 insertions(+)

diff --git a/rust/kernel/sync/arc.rs b/rust/kernel/sync/arc.rs
index 5f64affd8f33..fddb7a2b1890 100644
--- a/rust/kernel/sync/arc.rs
+++ b/rust/kernel/sync/arc.rs
@@ -540,6 +540,30 @@ impl<T> UniqueArc<MaybeUninit<T>> {
             inner: unsafe { Arc::from_inner(inner.cast()) },
         }
     }
+
+    /// Initialize `self` using the given initializer.
+    pub fn init_with<E>(mut self, init: impl Init<T, E>) -> core::result::Result<UniqueArc<T>, E> {
+        // SAFETY: The supplied pointer is valid for initialization.
+        match unsafe { init.__init(self.as_mut_ptr()) } {
+            // SAFETY: Initialization completed successfully.
+            Ok(()) => Ok(unsafe { self.assume_init() }),
+            Err(err) => Err(err),
+        }
+    }
+
+    /// Pin-initialize `self` using the given pin-initializer.
+    pub fn pin_init_with<E>(
+        mut self,
+        init: impl PinInit<T, E>,
+    ) -> core::result::Result<Pin<UniqueArc<T>>, E> {
+        // SAFETY: The supplied pointer is valid for initialization and we will later pin the value
+        // to ensure it does not move.
+        match unsafe { init.__pinned_init(self.as_mut_ptr()) } {
+            // SAFETY: Initialization completed successfully.
+            Ok(()) => Ok(unsafe { self.assume_init() }.into()),
+            Err(err) => Err(err),
+        }
+    }
 }

 impl<T: ?Sized> From<UniqueArc<T>> for Pin<UniqueArc<T>> {
--
2.39.2