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Message-Id: <20221110164152.26136-29-ojeda@kernel.org>
Date: Thu, 10 Nov 2022 17:41:40 +0100
From: Miguel Ojeda <ojeda@...nel.org>
To: Miguel Ojeda <ojeda@...nel.org>,
Wedson Almeida Filho <wedsonaf@...il.com>,
Alex Gaynor <alex.gaynor@...il.com>,
Boqun Feng <boqun.feng@...il.com>, Gary Guo <gary@...yguo.net>,
Björn Roy Baron <bjorn3_gh@...tonmail.com>
Cc: rust-for-linux@...r.kernel.org, linux-kernel@...r.kernel.org,
patches@...ts.linux.dev
Subject: [PATCH v1 28/28] rust: types: add `Opaque` type
From: Wedson Almeida Filho <wedsonaf@...il.com>
Add the `Opaque` type, which is meant to be used with FFI objects
that are never interpreted by Rust code, e.g.:
struct Waiter {
completion: Opaque<bindings::completion>,
next: *mut Waiter,
}
It has the advantage that the objects don't have to be
zero-initialised before calling their init functions, making
the code performance closer to C.
Signed-off-by: Wedson Almeida Filho <wedsonaf@...il.com>
[Reworded, adapted for upstream and applied latest changes]
Signed-off-by: Miguel Ojeda <ojeda@...nel.org>
---
rust/kernel/types.rs | 25 +++++++++++++++++++++++++
1 file changed, 25 insertions(+)
diff --git a/rust/kernel/types.rs b/rust/kernel/types.rs
index 3b0c44769708..e84e51ec9716 100644
--- a/rust/kernel/types.rs
+++ b/rust/kernel/types.rs
@@ -2,6 +2,31 @@
//! Kernel types.
+use core::{cell::UnsafeCell, mem::MaybeUninit};
+
+/// Stores an opaque value.
+///
+/// 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>>);
+
+impl<T> Opaque<T> {
+ /// Creates a new opaque value.
+ pub const fn new(value: T) -> Self {
+ Self(MaybeUninit::new(UnsafeCell::new(value)))
+ }
+
+ /// Creates an uninitialised value.
+ pub const fn uninit() -> Self {
+ Self(MaybeUninit::uninit())
+ }
+
+ /// Returns a raw pointer to the opaque data.
+ pub fn get(&self) -> *mut T {
+ UnsafeCell::raw_get(self.0.as_ptr())
+ }
+}
+
/// A sum type that always holds either a value of type `L` or `R`.
pub enum Either<L, R> {
/// Constructs an instance of [`Either`] containing a value of type `L`.
--
2.38.1
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