linux-kernel - [PATCH v4 04/15] rust: sync: add `assume

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Message-ID: <20230331215053.585759-5-y86-dev@protonmail.com>
Date:   Fri, 31 Mar 2023 21:52:27 +0000
From:   y86-dev@...tonmail.com
To:     Miguel Ojeda <ojeda@...nel.org>,
        Alex Gaynor <alex.gaynor@...il.com>,
        Wedson Almeida Filho <wedsonaf@...il.com>,
        Boqun Feng <boqun.feng@...il.com>, Gary Guo <gary@...yguo.net>,
        Björn Roy Baron <bjorn3_gh@...tonmail.com>,
        Alice Ryhl <alice@...l.io>
Cc:     rust-for-linux@...r.kernel.org, linux-kernel@...r.kernel.org,
        patches@...ts.linux.dev, Benno Lossin <y86-dev@...tonmail.com>,
        Wedson Almeida Filho <walmeida@...rosoft.com>,
        Andreas Hindborg <a.hindborg@...sung.com>,
        Alice Ryhl <aliceryhl@...gle.com>
Subject: [PATCH v4 04/15] rust: sync: add `assume_init` to `UniqueArc`

From: Benno Lossin <y86-dev@...tonmail.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@...tonmail.com>
Reviewed-by: Wedson Almeida Filho <walmeida@...rosoft.com>
Reviewed-by: Andreas Hindborg <a.hindborg@...sung.com>
Reviewed-by: Alice Ryhl <aliceryhl@...gle.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 aa7135f0f238..eee7008e5e3e 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 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 = ManuallyDrop::new(self).inner.ptr;
         UniqueArc {
             // SAFETY: The new `Arc` is taking over `ptr` from `self.inner` (which won't be
--
2.39.2