[v2,5/5] rust: types: implement `ForeignOwnable` for `Arc<T>`
Commit Message
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: Gary Guo <gary@garyguo.net>
Reviewed-by: Vincenzo Palazzo <vincenzopalazzodev@gmail.com>
Reviewed-by: Alice Ferrazzi <alice.ferrazzi@miraclelinux.com>
---
v1 -> v2: Unmodified
rust/kernel/sync/arc.rs | 32 +++++++++++++++++++++++++++++++-
1 file changed, 31 insertions(+), 1 deletion(-)
Comments
Wedson Almeida Filho <wedsonaf@gmail.com> writes:
> 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: Gary Guo <gary@garyguo.net>
> Reviewed-by: Vincenzo Palazzo <vincenzopalazzodev@gmail.com>
> Reviewed-by: Alice Ferrazzi <alice.ferrazzi@miraclelinux.com>
> ---
> v1 -> v2: Unmodified
>
> 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.
The last part of the sentence does not read clearly to me. Would this
make sense instead:
// SAFETY: By the safety requirement of this function, we know that `ptr` came from
// a previous call to `Arc::into_foreign`, which guarantees that `ptr` is valid and
// holds a reference count increment that is transferrable to us.
> + unsafe { Self::from_inner(NonNull::new(ptr as _).unwrap()) }
> + }
> +}
> +
> impl<T: ?Sized> Deref for Arc<T> {
> type Target = T;
Cheers,
Andreas
On Wed, Feb 1, 2023 at 11:35 AM Andreas Hindborg <nmi@metaspace.dk> wrote:
>
> The last part of the sentence does not read clearly to me. Would this
> make sense instead:
>
> // SAFETY: By the safety requirement of this function, we know that `ptr` came from
> // a previous call to `Arc::into_foreign`, which guarantees that `ptr` is valid and
> // holds a reference count increment that is transferrable to us.
In a private chat with Wedson he agreed the "owned" was a typo and he
is fine with this change. Thus I rebased to apply this and avoid a v3
given it is trivial and almost at the top of the stack. If you want
the `Reviewed-by`, please let me know!
Cheers,
Miguel
Miguel Ojeda <miguel.ojeda.sandonis@gmail.com> writes:
> On Wed, Feb 1, 2023 at 11:35 AM Andreas Hindborg <nmi@metaspace.dk> wrote:
>>
>> The last part of the sentence does not read clearly to me. Would this
>> make sense instead:
>>
>> // SAFETY: By the safety requirement of this function, we know that `ptr` came from
>> // a previous call to `Arc::into_foreign`, which guarantees that `ptr` is valid and
>> // holds a reference count increment that is transferrable to us.
>
> In a private chat with Wedson he agreed the "owned" was a typo and he
> is fine with this change. Thus I rebased to apply this and avoid a v3
> given it is trivial and almost at the top of the stack. If you want
> the `Reviewed-by`, please let me know!
Sure, if it's no trouble, add my the tag :)
- Andreas
On Tue, Feb 7, 2023 at 10:34 AM Andreas Hindborg <nmi@metaspace.dk> wrote:
>
> Sure, if it's no trouble, add my the tag :)
Done!
Cheers,
Miguel
@@ -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;