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Date:   Wed, 29 Mar 2023 22:32:58 +0000
To:     Miguel Ojeda <ojeda@kernel.org>,
        Alex Gaynor <alex.gaynor@gmail.com>,
        Wedson Almeida Filho <wedsonaf@gmail.com>,
        Boqun Feng <boqun.feng@gmail.com>, Gary Guo <gary@garyguo.net>,
        =?utf-8?Q?Bj=C3=B6rn_Roy_Baron?= <bjorn3_gh@protonmail.com>,
        Alice Ryhl <alice@ryhl.io>
From:   y86-dev@protonmail.com
Cc:     rust-for-linux@vger.kernel.org, linux-kernel@vger.kernel.org,
        patches@lists.linux.dev
Subject: [PATCH v3 02/13] rust: sync: add `assume_init` to `UniqueArc`
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From: Benno Lossin <y86-dev@protonmail.com>

Adds the `assume_init` function to `UniqueArc<MaybeUninit<T>>` that
unsafely assumes the value to be initialized and yields a value of type
`UniqueArc<T>`. This function is used when manually initializing the
pointee of an `UniqueArc`.

Signed-off-by: Benno Lossin <y86-dev@protonmail.com>
---
 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 f2f1c83d72ba..16ec174637b2 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 wr=
iting a value into it.
     pub fn write(mut self, value: T) -> UniqueArc<T> {
         self.deref_mut().write(value);
+        // SAFETY: We just wrote the value to be initialized.
+        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 =3D ManuallyDrop::new(self).inner.ptr;
         UniqueArc {
             // SAFETY: The new `Arc` is taking over `ptr` from `self.inner=
` (which won't be
--
2.39.2