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SubjectRe: [PATCH 3/5] rust: types: implement `ForeignOwnable` for `Box<T>`
On Thu, 19 Jan 2023 14:40:34 -0300
Wedson Almeida Filho <wedsonaf@gmail.com> wrote:

> 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>

> ---
> rust/kernel/types.rs | 22 ++++++++++++++++++++++
> 1 file changed, 22 insertions(+)
>
> diff --git a/rust/kernel/types.rs b/rust/kernel/types.rs
> index 5475f6163002..e037c262f23e 100644
> --- a/rust/kernel/types.rs
> +++ b/rust/kernel/types.rs
> @@ -63,6 +63,28 @@ pub trait ForeignOwnable {
> 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.

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