Messages in this thread | | | Date | Mon, 3 Apr 2023 16:26:09 +0100 | From | Gary Guo <> | Subject | Re: [PATCH v2 2/2] rust: sync: arc: Add UniqueArc<MaybeUninit<T>::assume_init() |
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On Mon, 03 Apr 2023 19:01:12 +0900 Asahi Lina <lina@asahilina.net> wrote:
> We can already create `UniqueArc<MaybeUninit<T>>` instances with > `UniqueArc::try_new_uninit()` and write to them with `write()`. Add > the missing unsafe `assume_init()` function to promote it to > `UniqueArc<T>`, so users can do piece-wise initialization of the > contents instead of doing it all at once as long as they keep the > invariants (the same requirements as `MaybeUninit::assume_init()`). > > This mirrors the std `Arc::assume_init()` function. In the kernel, > since we have `UniqueArc`, arguably this only belongs there since most > use cases will initialize it immediately after creating it, before > demoting it to `Arc` to share it. > > Co-authored-by: Benno Lossin <y86-dev@protonmail.com> > Signed-off-by: Benno Lossin <y86-dev@protonmail.com> > Signed-off-by: Asahi Lina <lina@asahilina.net>
Reviewed-by: Gary Guo <gary@garyguo.net>
> --- > rust/kernel/sync/arc.rs | 11 +++++++++++ > 1 file changed, 11 insertions(+) > > diff --git a/rust/kernel/sync/arc.rs b/rust/kernel/sync/arc.rs > index b904ed898d3a..b664b41e473d 100644 > --- a/rust/kernel/sync/arc.rs > +++ b/rust/kernel/sync/arc.rs > @@ -489,6 +489,17 @@ impl<T> UniqueArc<MaybeUninit<T>> { > /// Converts a `UniqueArc<MaybeUninit<T>>` into a `UniqueArc<T>` by writing a value into it. > pub fn write(mut self, value: T) -> UniqueArc<T> { > self.deref_mut().write(value); > + // SAFETY: We have just written the contents fully. > + unsafe { self.assume_init() } > + } > + > + /// Unsafely assume that `self` is initialized. > + /// > + /// # Safety > + /// > + /// The caller guarantees that the value behind this pointer has been initialized. It is > + /// *immediate* UB to call this when the value is not initialized. > + pub unsafe fn assume_init(self) -> UniqueArc<T> { > let inner = ManuallyDrop::new(self).inner.ptr; > UniqueArc { > // SAFETY: The new `Arc` is taking over `ptr` from `self.inner` (which won't be >
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