rust: init/sync: add `InPlaceInit` trait to pin-initialize smart pointers

The `InPlaceInit` trait that provides two functions, for initializing
using `PinInit<T, E>` and `Init<T>`. It is implemented by `Arc<T>`,
`UniqueArc<T>` and `Box<T>`.

Signed-off-by: Benno Lossin <benno.lossin@proton.me>
Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Reviewed-by: Gary Guo <gary@garyguo.net>
Reviewed-by: Andreas Hindborg <a.hindborg@samsung.com>
Link: https://lore.kernel.org/r/20230408122429.1103522-9-y86-dev@protonmail.com
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

1 files changed, 24 insertions, 0 deletions

diff --git a/rust/kernel/sync/arc.rs b/rust/kernel/sync/arc.rs
index 34d0e7cbe62e..b45769a29541 100644
--- a/rust/kernel/sync/arc.rs
+++ b/rust/kernel/sync/arc.rs
@@ -17,6 +17,8 @@
 
 use crate::{
     bindings,
+    error::{self, Error},
+    init::{InPlaceInit, Init, PinInit},
     types::{ForeignOwnable, Opaque},
 };
 use alloc::boxed::Box;
@@ -166,6 +168,28 @@ impl<T> Arc<T> {
         // `Arc` object.
         Ok(unsafe { Self::from_inner(Box::leak(inner).into()) })
     }
+
+    /// Use the given initializer to in-place initialize a `T`.
+    ///
+    /// If `T: !Unpin` it will not be able to move afterwards.
+    #[inline]
+    pub fn pin_init<E>(init: impl PinInit<T, E>) -> error::Result<Self>
+    where
+        Error: From<E>,
+    {
+        UniqueArc::pin_init(init).map(|u| u.into())
+    }
+
+    /// Use the given initializer to in-place initialize a `T`.
+    ///
+    /// This is equivalent to [`pin_init`], since an [`Arc`] is always pinned.
+    #[inline]
+    pub fn init<E>(init: impl Init<T, E>) -> error::Result<Self>
+    where
+        Error: From<E>,
+    {
+        UniqueArc::init(init).map(|u| u.into())
+    }
 }
 
 impl<T: ?Sized> Arc<T> {