[PATCH v2 3/5] rust: types: implement `ForeignOwnable` for `Box`

Wedson Almeida Filho
2023-01-30T06:44:48Z

This allows us to hand ownership of Rust dynamically allocated
objects to the C side of the kernel.

Signed-off-by: Wedson Almeida Filho <wedsonaf@gmail.com>
Reviewed-by: Gary Guo <gary@garyguo.net>
Reviewed-by: Vincenzo Palazzo <vincenzopalazzodev@gmail.com>
Reviewed-by: Alice Ferrazzi <alice.ferrazzi@miraclelinux.com>
---
v1 -> v2: Add `use alloc::boxed::Box`, which wasn't needed before

rust/kernel/types.rs | 23 +++++++++++++++++++++++
1 file changed, 23 insertions(+)

diff --git a/rust/kernel/types.rs b/rust/kernel/types.rs
index 72710b7442a3..411655eca3e9 100644
--- a/rust/kernel/types.rs
+++ b/rust/kernel/types.rs
@@ -2,6 +2,7 @@

//! Kernel types.

+use alloc::boxed::Box;
use core::{
cell::UnsafeCell,
mem::MaybeUninit,
@@ -62,6 +63,28 @@ pub trait ForeignOwnable: Sized {
unsafe fn from_foreign(ptr: *const core::ffi::c_void) -> Self;
}

+impl<T: 'static> ForeignOwnable for Box<T> {
+ type Borrowed<'a> = &'a T;
+
+ fn into_foreign(self) -> *const core::ffi::c_void {
+ Box::into_raw(self) as _
+ }
+
+ unsafe fn borrow<'a>(ptr: *const core::ffi::c_void) -> &'a T {
+ // SAFETY: The safety requirements for this function ensure that the object is still alive,
+ // so it is safe to dereference the raw pointer.
+ // The safety requirements of `from_foreign` also ensure that the object remains alive for
+ // the lifetime of the returned value.
+ unsafe { &*ptr.cast() }
+ }
+
+ unsafe fn from_foreign(ptr: *const core::ffi::c_void) -> Self {
+ // SAFETY: The safety requirements of this function ensure that `ptr` comes from a previous
+ // call to `Self::into_foreign`.
+ unsafe { Box::from_raw(ptr as _) }
+ }
+}
+
/// Runs a cleanup function/closure when dropped.
///
/// The [`ScopeGuard::dismiss`] function prevents the cleanup function from running.
--
2.34.1