linux-kernel - [PATCH v3 13/13] rust: sync: add functions for initializing `UniqueArc<MaybeUninit<T>>`

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Message-ID: <20230329223239.138757-14-y86-dev@protonmail.com>
Date:   Wed, 29 Mar 2023 22:33:53 +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
Subject: [PATCH v3 13/13] rust: sync: add functions for initializing `UniqueArc<MaybeUninit<T>>`

From: Benno Lossin <y86-dev@...tonmail.com>

Add two functions `init_with` and `pin_init_with` to
`UniqueArc<MaybeUninit<T>>` to initialize the memory of already allocated
`UniqueArc`s. This is useful when you want to allocate memory check some
condition inside of a context where allocation is forbidden and then
conditionally initialize an object.

Signed-off-by: Benno Lossin <y86-dev@...tonmail.com>
---
 rust/kernel/sync/arc.rs | 24 ++++++++++++++++++++++++
 1 file changed, 24 insertions(+)

diff --git a/rust/kernel/sync/arc.rs b/rust/kernel/sync/arc.rs
index 4ed6329a5e5f..64b0e9d67025 100644
--- a/rust/kernel/sync/arc.rs
+++ b/rust/kernel/sync/arc.rs
@@ -540,6 +540,30 @@ impl<T> UniqueArc<MaybeUninit<T>> {
             inner: unsafe { Arc::from_inner(inner.cast()) },
         }
     }
+
+    /// Initialize `self` using the given initializer.
+    pub fn init_with<E>(mut self, init: impl Init<T, E>) -> core::result::Result<UniqueArc<T>, E> {
+        // SAFETY: The supplied pointer is valid for initialization.
+        match unsafe { init.__init(self.as_mut_ptr()) } {
+            // SAFETY: Initialization completed successfully.
+            Ok(()) => Ok(unsafe { self.assume_init() }),
+            Err(err) => Err(err),
+        }
+    }
+
+    /// Pin-initialize `self` using the given pin-initializer.
+    pub fn pin_init_with<E>(
+        mut self,
+        init: impl PinInit<T, E>,
+    ) -> core::result::Result<Pin<UniqueArc<T>>, E> {
+        // SAFETY: The supplied pointer is valid for initialization and we will later pin the value
+        // to ensure it does not move.
+        match unsafe { init.__pinned_init(self.as_mut_ptr()) } {
+            // SAFETY: Initialization completed successfully.
+            Ok(()) => Ok(unsafe { self.assume_init() }.into()),
+            Err(err) => Err(err),
+        }
+    }
 }

 impl<T: ?Sized> From<UniqueArc<T>> for Pin<UniqueArc<T>> {
--
2.39.2