Messages in this thread |  | | Date | Mon, 20 Jan 2025 09:24:30 -0800 | | From | Boqun Feng <> | | Subject | Re: [PATCH 1/3] rust: add Aliased type |
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Hi Christian,
[Cc Daniel and Danilo]
Thanks for the patch!
On Sun, Jan 19, 2025 at 11:11:13PM +0100, Christian Schrefl wrote: > This type is useful for cases where a value might be shared with C code > but not interpreted by it. > In partiquarly this is added to for data that is shared between a Driver > and a MiscDevice implementation. > > Similar to Opaque but guarantees that the value is initialized and the > inner value is dropped when Aliased is dropped. > > This was origianally proposed for the IRQ abstractions [0], but also > useful for other cases where Data may be aliased, but is always valid > and automatic drop is desired. > > Link: https://lore.kernel.org/rust-for-linux/CAH5fLgiOASgjoYKFz6kWwzLaH07DqP2ph+3YyCDh2+gYqGpABA@mail.gmail.com [0] > Suggested-by: Alice Ryhl <aliceryhl@google.com> > Signed-off-by: Christian Schrefl <chrisi.schrefl@gmail.com> > --- > rust/kernel/types.rs | 40 ++++++++++++++++++++++++++++++++++++++++ > 1 file changed, 40 insertions(+) > > diff --git a/rust/kernel/types.rs b/rust/kernel/types.rs > index 3aea6af9a0bca70ee42b4bad2fe31a99750cbf11..5640128c9a9055476a0040033946ba6caa6e7076 100644 > --- a/rust/kernel/types.rs > +++ b/rust/kernel/types.rs > @@ -528,3 +528,43 @@ pub enum Either<L, R> { > /// [`NotThreadSafe`]: type@NotThreadSafe > #[allow(non_upper_case_globals)] > pub const NotThreadSafe: NotThreadSafe = PhantomData; > + > +/// Stores a value that may be aliased. > +/// > +/// This is similar to `Opaque<T>` but is guaranteed to contain valid data and will > +/// Call the Drop implementation of T when dropped. > +#[repr(transparent)] > +pub struct Aliased<T> {
As I already mentioned [1], the name `Aliased` is more reflecting the fact that this wrapper will avoid generating the "noalias" attribute(?) on the reference/pointer to the type rather than an intuitive idea about "why or when do I need this". Moreover, I think the argument about the naming of the counterpart in unstable Rust (UnsafePinned) makes sense to me [2]: this type alone won't prevent `&mut Aliased` getting `swap`, and it has to be used with `Pin`.
Therefore, I think we should use a different name, perhaps `(Always)Shared`, or just use `UnsafePinned`, or, as always, looking fowards to a better name from anybody ;-)
[1]: https://lore.kernel.org/rust-for-linux/Z407egxOy7oNLpq8@boqun-archlinux/ [2]: https://rust-lang.github.io/rfcs/3467-unsafe-pinned.html#naming
Regards, Boqun
> + value: UnsafeCell<T>, > + _pin: PhantomPinned, > +} > + > +impl<T> Aliased<T> { > + /// Creates a new `Aliased` value. > + pub const fn new(value: T) -> Self { > + Self { > + value: UnsafeCell::new(value), > + _pin: PhantomPinned, > + } > + } > + /// Create an `Aliased` pin-initializer from the given pin-initializer. > + pub fn try_pin_init<E>(value: impl PinInit<T, E>) -> impl PinInit<Self, E> { > + // SAFETY: > + // In case of an error in value the error is returned, otherwise the slot is fully initialized, > + // since value is initialized and _pin is a Zero sized type. > + // The pin invariants of value are upheld, since no moving occurs. > + unsafe { init::pin_init_from_closure(move |slot| value.__pinned_init(Self::raw_get(slot))) } > + } > + /// Returns a raw pointer to the opaque data. > + pub const fn get(&self) -> *mut T { > + UnsafeCell::get(&self.value).cast::<T>() > + } > + > + /// Gets the value behind `this`. > + /// > + /// This function is useful to get access to the value without creating intermediate > + /// references. > + pub const fn raw_get(this: *const Self) -> *mut T { > + UnsafeCell::raw_get(this.cast::<UnsafeCell<MaybeUninit<T>>>()).cast::<T>() > + } > +} > > -- > 2.48.1 >
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