Messages in this thread Patch in this message | | | Date | Wed, 14 Jun 2023 19:42:55 +0100 | From | Gary Guo <> | Subject | Re: [PATCH] rust: make `UnsafeCell` the outer type in `Opaque` |
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On Wed, 14 Jun 2023 11:53:28 +0000 Alice Ryhl <aliceryhl@google.com> wrote:
> 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: Gary Guo <gary@garyguo.net>
> --- > rust/kernel/types.rs | 10 +++++----- > 1 file changed, 5 insertions(+), 5 deletions(-) > > diff --git a/rust/kernel/types.rs b/rust/kernel/types.rs > index 1e5380b16ed5..fb41635f1e1f 100644 > --- a/rust/kernel/types.rs > +++ b/rust/kernel/types.rs > @@ -224,17 +224,17 @@ fn drop(&mut self) { > /// > /// 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. > @@ -258,7 +258,7 @@ pub fn ffi_init(init_func: impl FnOnce(*mut T)) -> impl PinInit<Self> { > > /// 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`. > @@ -266,7 +266,7 @@ pub fn get(&self) -> *mut 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>()
This can just be `this.cast_mut().cast()` since all types involved are transparent.
> } > } > > > base-commit: d2e3115d717197cb2bc020dd1f06b06538474ac3
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