Commit 35cad617 authored by Alice Ryhl's avatar Alice Ryhl Committed by Miguel Ojeda
Browse files

rust: make `UnsafeCell` the outer type in `Opaque` 



When combining `UnsafeCell` with `MaybeUninit`, it is idiomatic to use
`UnsafeCell` as the outer type. Intuitively, this is because a
`MaybeUninit<T>` might not contain a `T`, but we always want the effect
of the `UnsafeCell`, even if the inner value is uninitialized.

Now, strictly speaking, this doesn't really make a difference. The
compiler will always apply the `UnsafeCell` effect even if the inner
value is uninitialized. But I think we should follow the convention
here.

Signed-off-by: default avatarAlice Ryhl <aliceryhl@google.com>
Reviewed-by: default avatarBenno Lossin <benno.lossin@proton.me>
Reviewed-by: default avatarGary Guo <gary@garyguo.net>
Reviewed-by: default avatarMartin Rodriguez Reboredo <yakoyoku@gmail.com>
Link: https://lore.kernel.org/r/20230614115328.2825961-1-aliceryhl@google.com


Signed-off-by: default avatarMiguel Ojeda <ojeda@kernel.org>
parent 0bb1c928

rust/kernel/types.rs

+5 −5
Original line number Diff line number Diff line
@@ -206,17 +206,17 @@ impl<T, F: FnOnce(T)> Drop for ScopeGuard<T, F> { 
///

/// This is meant to be used with FFI objects that are never interpreted by Rust code.

#[repr(transparent)]

pub struct Opaque<T>(MaybeUninit<UnsafeCell<T>>);

pub struct Opaque<T>(UnsafeCell<MaybeUninit<T>>);



impl<T> Opaque<T> {

    /// Creates a new opaque value.

    pub const fn new(value: T) -> Self {

        Self(MaybeUninit::new(UnsafeCell::new(value)))

        Self(UnsafeCell::new(MaybeUninit::new(value)))

    }



    /// Creates an uninitialised value.

    pub const fn uninit() -> Self {

        Self(MaybeUninit::uninit())

        Self(UnsafeCell::new(MaybeUninit::uninit()))

    }



    /// Creates a pin-initializer from the given initializer closure.
@@ -240,7 +240,7 @@ impl<T> Opaque<T> { 


    /// Returns a raw pointer to the opaque data.

    pub fn get(&self) -> *mut T {

        UnsafeCell::raw_get(self.0.as_ptr())

        UnsafeCell::get(&self.0).cast::<T>()

    }



    /// Gets the value behind `this`.
@@ -248,7 +248,7 @@ impl<T> Opaque<T> { 
    /// 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<T>>())

        UnsafeCell::raw_get(this.cast::<UnsafeCell<MaybeUninit<T>>>()).cast::<T>()

    }

}