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Message-Id: <20250430-rust_unsafe_pinned-v2-3-fc8617a74024@gmail.com>
Date: Wed, 30 Apr 2025 10:36:13 +0200
From: Christian Schrefl <chrisi.schrefl@...il.com>
To: Sky <sky@...9.dev>, Miguel Ojeda <ojeda@...nel.org>,
Alex Gaynor <alex.gaynor@...il.com>, Boqun Feng <boqun.feng@...il.com>,
Gary Guo <gary@...yguo.net>,
Björn Roy Baron <bjorn3_gh@...tonmail.com>,
Benno Lossin <benno.lossin@...ton.me>,
Andreas Hindborg <a.hindborg@...nel.org>, Alice Ryhl <aliceryhl@...gle.com>,
Trevor Gross <tmgross@...ch.edu>, Danilo Krummrich <dakr@...nel.org>,
Gerald Wisböck <gerald.wisboeck@...ther.ink>
Cc: linux-kernel@...r.kernel.org, rust-for-linux@...r.kernel.org,
Christian Schrefl <chrisi.schrefl@...il.com>
Subject: [PATCH v2 3/3] rust: use `UnsafePinned` in the implementation of
`Opaque`
This change makes the semantics of the `Opaque` implementation
clearer and prepares for the switch to the upstream rust UnsafePinned`
type in the future.
`Opaque` still uses `UnsafeCell` even though the kernel implementation
of `UnsafePinned` already includes it, since the current upstream
version does not.
Reviewed-by: Gerald Wisböck <gerald.wisboeck@...ther.ink>
Signed-off-by: Christian Schrefl <chrisi.schrefl@...il.com>
---
rust/kernel/types.rs | 29 ++++++++++++-----------------
1 file changed, 12 insertions(+), 17 deletions(-)
diff --git a/rust/kernel/types.rs b/rust/kernel/types.rs
index f06e8720e012102e5c41e79fd97b0607e927d71c..44d96423a8a6c358bb7ebf12c24fad98e5c2cb61 100644
--- a/rust/kernel/types.rs
+++ b/rust/kernel/types.rs
@@ -4,12 +4,12 @@
use core::{
cell::UnsafeCell,
- marker::{PhantomData, PhantomPinned},
+ marker::PhantomData,
mem::{ManuallyDrop, MaybeUninit},
ops::{Deref, DerefMut},
ptr::NonNull,
};
-use pin_init::{PinInit, Wrapper, Zeroable};
+use pin_init::{cast_pin_init, PinInit, Wrapper, Zeroable};
/// Used to transfer ownership to and from foreign (non-Rust) languages.
///
@@ -308,8 +308,7 @@ fn drop(&mut self) {
/// ```
#[repr(transparent)]
pub struct Opaque<T> {
- value: UnsafeCell<MaybeUninit<T>>,
- _pin: PhantomPinned,
+ value: UnsafePinned<UnsafeCell<MaybeUninit<T>>>,
}
// SAFETY: `Opaque<T>` allows the inner value to be any bit pattern, including all zeros.
@@ -319,16 +318,14 @@ impl<T> Opaque<T> {
/// Creates a new opaque value.
pub const fn new(value: T) -> Self {
Self {
- value: UnsafeCell::new(MaybeUninit::new(value)),
- _pin: PhantomPinned,
+ value: UnsafePinned::new(UnsafeCell::new(MaybeUninit::new(value))),
}
}
/// Creates an uninitialised value.
pub const fn uninit() -> Self {
Self {
- value: UnsafeCell::new(MaybeUninit::uninit()),
- _pin: PhantomPinned,
+ value: UnsafePinned::new(UnsafeCell::new(MaybeUninit::uninit())),
}
}
@@ -371,7 +368,7 @@ pub fn try_ffi_init<E>(
/// Returns a raw pointer to the opaque data.
pub const fn get(&self) -> *mut T {
- UnsafeCell::get(&self.value).cast::<T>()
+ UnsafeCell::raw_get(self.value.get()).cast::<T>()
}
/// Gets the value behind `this`.
@@ -384,14 +381,12 @@ pub const fn raw_get(this: *const Self) -> *mut T {
}
impl<T> Wrapper<T> for Opaque<T> {
/// Create an opaque pin-initializer from the given pin-initializer.
- fn pin_init<E>(slot: impl PinInit<T, E>) -> impl PinInit<Self, E> {
- Self::try_ffi_init(|ptr: *mut T| {
- // SAFETY:
- // - `ptr` is a valid pointer to uninitialized memory,
- // - `slot` is not accessed on error; the call is infallible,
- // - `slot` is pinned in memory.
- unsafe { PinInit::<T, E>::__pinned_init(slot, ptr) }
- })
+ fn pin_init<E>(value_init: impl PinInit<T, E>) -> impl PinInit<Self, E> {
+ let value_init =
+ UnsafePinned::pin_init(UnsafeCell::pin_init(MaybeUninit::pin_init(value_init)));
+ // SAFETY: `Opaque<T>` is a `repr(transparent)` wrapper around
+ // `UnsafePinned<UnsafeCell<MabeUninit<T>>>` so the memory representation is compatible.
+ unsafe { cast_pin_init(value_init) }
}
}
--
2.49.0
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