[RFC PATCH 09/11] RUST: implement `ForeignOwnable` for `Pin`

[Andreas Hindborg <nmi@metaspace.dk>]

From: Andreas Hindborg <a.hindborg@samsung.com>

Implement `ForeignOwnable for Pin<T> where T: ForeignOwnable + Deref`.

Imported from rust tree [1]

[1] https://github.com/Rust-for-Linux/linux/tree/bc22545f38d74473cfef3e9fd65432733435b79f

Cc: Wedson Almeida Filho <wedsonaf@gmail.com>
---
 rust/kernel/types.rs | 24 ++++++++++++++++++++++++
 1 file changed, 24 insertions(+)

diff --git a/rust/kernel/types.rs b/rust/kernel/types.rs
index 29db59d6119a..98e71e96a7fc 100644
--- a/rust/kernel/types.rs
+++ b/rust/kernel/types.rs
@@ -9,6 +9,7 @@ use core::{
     marker::PhantomData,
     mem::MaybeUninit,
     ops::{Deref, DerefMut},
+    pin::Pin,
     ptr::NonNull,
 };
 
@@ -100,6 +101,29 @@ impl ForeignOwnable for () {
     unsafe fn from_foreign(_: *const core::ffi::c_void) -> Self {}
 }
 
+impl<T: ForeignOwnable + Deref> ForeignOwnable for Pin<T> {
+    type Borrowed<'a> = T::Borrowed<'a>;
+
+    fn into_foreign(self) -> *const core::ffi::c_void {
+        // SAFETY: We continue to treat the pointer as pinned by returning just a pointer to it to
+        // the caller.
+        let inner = unsafe { Pin::into_inner_unchecked(self) };
+        inner.into_foreign()
+    }
+
+    unsafe fn borrow<'a>(ptr: *const core::ffi::c_void) -> Self::Borrowed<'a> {
+        // SAFETY: The safety requirements for this function are the same as the ones for
+        // `T::borrow`.
+        unsafe { T::borrow(ptr) }
+    }
+
+    unsafe fn from_foreign(p: *const core::ffi::c_void) -> Self {
+        // SAFETY: The object was originally pinned.
+        // The passed pointer comes from a previous call to `T::into_foreign`.
+        unsafe { Pin::new_unchecked(T::from_foreign(p)) }
+    }
+}
+
 /// Runs a cleanup function/closure when dropped.
 ///
 /// The [`ScopeGuard::dismiss`] function prevents the cleanup function from running.
-- 
2.40.0