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Subject[PATCH 7/7] rust: sync: add support for dispatching on Arc and ArcBorrow.
Date
Trait objects (`dyn T`) require trait `T` to be "object safe". One of
the requirements for "object safety" is that the receiver have one of
the allowed types. This commit adds `Arc<T>` and `ArcBorrow<'_, T>` to
the list of allowed types.

Signed-off-by: Wedson Almeida Filho <wedsonaf@gmail.com>
---
rust/kernel/lib.rs | 1 +
rust/kernel/sync/arc.rs | 20 ++++++++++++++++++--
2 files changed, 19 insertions(+), 2 deletions(-)

diff --git a/rust/kernel/lib.rs b/rust/kernel/lib.rs
index 4bde65e7b06b..e0b0e953907d 100644
--- a/rust/kernel/lib.rs
+++ b/rust/kernel/lib.rs
@@ -15,6 +15,7 @@
#![feature(allocator_api)]
#![feature(coerce_unsized)]
#![feature(core_ffi_c)]
+#![feature(dispatch_from_dyn)]
#![feature(receiver_trait)]
#![feature(unsize)]

diff --git a/rust/kernel/sync/arc.rs b/rust/kernel/sync/arc.rs
index 832bafc74a90..ff73f9240ca1 100644
--- a/rust/kernel/sync/arc.rs
+++ b/rust/kernel/sync/arc.rs
@@ -92,9 +92,15 @@ use core::{
/// Coercion from `Arc<Example>` to `Arc<dyn MyTrait>`:
///
/// ```
-/// use kernel::sync::Arc;
+/// use kernel::sync::{Arc, ArcBorrow};
+///
+/// trait MyTrait {
+/// // Trait has a function whose `self` type is `Arc<Self>`.
+/// fn example1(self: Arc<Self>) {}
///
-/// trait MyTrait {}
+/// // Trait has a function whose `self` type is `ArcBorrow<'_, Self>`.
+/// fn example2(self: ArcBorrow<'_, Self>) {}
+/// }
///
/// struct Example;
/// impl MyTrait for Example {}
@@ -123,6 +129,9 @@ impl<T: ?Sized> core::ops::Receiver for Arc<T> {}
// dynamically-sized type (DST) `U`.
impl<T: ?Sized + Unsize<U>, U: ?Sized> core::ops::CoerceUnsized<Arc<U>> for Arc<T> {}

+// This is to allow `Arc<U>` to be dispatched on when `Arc<T>` can be coerced into `Arc<U>`.
+impl<T: ?Sized + Unsize<U>, U: ?Sized> core::ops::DispatchFromDyn<Arc<U>> for Arc<T> {}
+
// SAFETY: It is safe to send `Arc<T>` to another thread when the underlying `T` is `Sync` because
// it effectively means sharing `&T` (which is safe because `T` is `Sync`); additionally, it needs
// `T` to be `Send` because any thread that has an `Arc<T>` may ultimately access `T` directly, for
@@ -297,6 +306,13 @@ pub struct ArcBorrow<'a, T: ?Sized + 'a> {
// This is to allow [`ArcBorrow`] (and variants) to be used as the type of `self`.
impl<T: ?Sized> core::ops::Receiver for ArcBorrow<'_, T> {}

+// This is to allow `ArcBorrow<U>` to be dispatched on when `ArcBorrow<T>` can be coerced into
+// `ArcBorrow<U>`.
+impl<T: ?Sized + Unsize<U>, U: ?Sized> core::ops::DispatchFromDyn<ArcBorrow<'_, U>>
+ for ArcBorrow<'_, T>
+{
+}
+
impl<T: ?Sized> Clone for ArcBorrow<'_, T> {
fn clone(&self) -> Self {
*self
--
2.34.1
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