On Sun, Feb 2, 2025 at 2:06 PM Asahi Lina <lina@xxxxxxxxxxxxx> wrote:
>
> By analogy to AlwaysRefCounted and ARef, an Ownable type is a (typically
> C FFI) type that *may* be owned by Rust, but need not be. Unlike
> AlwaysRefCounted, this mechanism expects the reference to be unique
> within Rust, and does not allow cloning.
>
> Conceptually, this is similar to a KBox<T>, except that it delegates
> resource management to the T instead of using a generic allocator.
>
> Signed-off-by: Asahi Lina <lina@xxxxxxxxxxxxx>
Overall LGTM.
> +/// A subtrait of Ownable that asserts that an `Owned<T>` Rust reference is not only unique
> +/// within Rust and keeps the `T` alive, but also guarantees that the C code follows the
> +/// usual mutable reference requirements. That is, the kernel will never mutate the
> +/// `T` (excluding internal mutability that follows the usual rules) while Rust owns it.
> +///
> +/// When this type is implemented for an [`Ownable`] type, it allows `Owned<T>` to be
> +/// dereferenced into a &mut T.
> +///
> +/// # Safety
> +///
> +/// Implementers must ensure that the kernel never mutates the underlying type while
> +/// Rust owns it.
> +pub unsafe trait OwnableMut: Ownable {}
Giving out mutable references allows users to call core::mem::swap on
the object. We must require that this is allowed.
> +impl<T: Ownable> Owned<T> {
> + /// Creates a new instance of [`Owned`].
> + ///
> + /// It takes over ownership of the underlying object.
> + ///
> + /// # Safety
> + ///
> + /// Callers must ensure that the underlying object is acquired and can be considered owned by
> + /// Rust.
> + pub(crate) unsafe fn from_raw(ptr: NonNull<T>) -> Self {
> + // INVARIANT: The safety requirements guarantee that the new instance now owns the
> + // reference.
> + Self {
> + ptr,
> + _p: PhantomData,
> + }
> + }
> +
> + /// Consumes the `Owned`, returning a raw pointer.
> + ///
> + /// This function does not actually relinquish ownership of the object.
> + /// After calling this function, the caller is responsible for ownership previously managed
> + /// by the `Owned`.
> + #[allow(dead_code)]
> + pub(crate) fn into_raw(me: Self) -> NonNull<T> {
I would just make these methods public, like the ARef ones. Then you
can drop the #[allow(dead_code)] annotation.
Alice
