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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: Alice Ryhl <aliceryhl@google.com>
Reviewed-by: Benno Lossin <benno.lossin@proton.me>
Reviewed-by: Gary Guo <gary@garyguo.net>
Reviewed-by: Martin Rodriguez Reboredo <yakoyoku@gmail.com>
Link: https://lore.kernel.org/r/20230614115328.2825961-1-aliceryhl@google.com
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>
This commit is contained in:
Alice Ryhl 2023-06-14 11:53:28 +00:00 committed by Miguel Ojeda
parent 0bb1c9282e
commit 35cad617df
1 changed files with 5 additions and 5 deletions
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10
rust/kernel/types.rs
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@ -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. /// This is meant to be used with FFI objects that are never interpreted by Rust code.
#[repr(transparent)] #[repr(transparent)]
pub struct Opaque<T>(MaybeUninit<UnsafeCell<T>>); pub struct Opaque<T>(UnsafeCell<MaybeUninit<T>>);
impl<T> Opaque<T> { impl<T> Opaque<T> {
/// Creates a new opaque value. /// Creates a new opaque value.
pub const fn new(value: T) -> Self { pub const fn new(value: T) -> Self {
Self(MaybeUninit::new(UnsafeCell::new(value))) Self(UnsafeCell::new(MaybeUninit::new(value)))
} }
/// Creates an uninitialised value. /// Creates an uninitialised value.
pub const fn uninit() -> Self { pub const fn uninit() -> Self {
Self(MaybeUninit::uninit()) Self(UnsafeCell::new(MaybeUninit::uninit()))
} }
/// Creates a pin-initializer from the given initializer closure. /// 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. /// Returns a raw pointer to the opaque data.
pub fn get(&self) -> *mut T { pub fn get(&self) -> *mut T {
UnsafeCell::raw_get(self.0.as_ptr()) UnsafeCell::get(&self.0).cast::<T>()
} }
/// Gets the value behind `this`. /// 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 /// This function is useful to get access to the value without creating intermediate
/// references. /// references.
pub const fn raw_get(this: *const Self) -> *mut T { 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>()
} }
} }