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    SubjectRe: [PATCH 5/5] rust: types: implement `ForeignOwnable` for `Arc<T>`
    From
    On Thu Jan 19, 2023 at 6:40 PM CET, Wedson Almeida Filho wrote:
    > This allows us to hand ownership of Rust ref-counted objects to
    > the C side of the kernel.
    >
    > Signed-off-by: Wedson Almeida Filho <wedsonaf@gmail.com>
    > ---
    Reviewed-by: Vincenzo Palazzo <vincenzopalazzodev@gmail.com>

    > rust/kernel/sync/arc.rs | 32 +++++++++++++++++++++++++++++++-
    > 1 file changed, 31 insertions(+), 1 deletion(-)
    >
    > diff --git a/rust/kernel/sync/arc.rs b/rust/kernel/sync/arc.rs
    > index ff73f9240ca1..519a6ec43644 100644
    > --- a/rust/kernel/sync/arc.rs
    > +++ b/rust/kernel/sync/arc.rs
    > @@ -15,7 +15,11 @@
    > //!
    > //! [`Arc`]: https://doc.rust-lang.org/std/sync/struct.Arc.html
    >
    > -use crate::{bindings, error::Result, types::Opaque};
    > +use crate::{
    > + bindings,
    > + error::Result,
    > + types::{ForeignOwnable, Opaque},
    > +};
    > use alloc::boxed::Box;
    > use core::{
    > marker::{PhantomData, Unsize},
    > @@ -189,6 +193,32 @@ impl<T: ?Sized> Arc<T> {
    > }
    > }
    >
    > +impl<T: 'static> ForeignOwnable for Arc<T> {
    > + type Borrowed<'a> = ArcBorrow<'a, T>;
    > +
    > + fn into_foreign(self) -> *const core::ffi::c_void {
    > + ManuallyDrop::new(self).ptr.as_ptr() as _
    > + }
    > +
    > + unsafe fn borrow<'a>(ptr: *const core::ffi::c_void) -> ArcBorrow<'a, T> {
    > + // SAFETY: By the safety requirement of this function, we know that `ptr` came from
    > + // a previous call to `Arc::into_foreign`.
    > + let inner = NonNull::new(ptr as *mut ArcInner<T>).unwrap();
    > +
    > + // SAFETY: The safety requirements of `from_foreign` ensure that the object remains alive
    > + // for the lifetime of the returned value. Additionally, the safety requirements of
    > + // `ForeignOwnable::borrow_mut` ensure that no new mutable references are created.
    > + unsafe { ArcBorrow::new(inner) }
    > + }
    > +
    > + unsafe fn from_foreign(ptr: *const core::ffi::c_void) -> Self {
    > + // SAFETY: By the safety requirement of this function, we know that `ptr` came from
    > + // a previous call to `Arc::into_foreign`, which owned guarantees that `ptr` is valid and
    > + // owns a reference.
    > + unsafe { Self::from_inner(NonNull::new(ptr as _).unwrap()) }
    > + }
    > +}
    > +
    > impl<T: ?Sized> Deref for Arc<T> {
    > type Target = T;
    >
    > --
    > 2.34.1

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