linux-kernel - [PATCH v3 2/3] rust: implement `Wrapper<T>` for `Opaque<T>`

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Message-Id: <20250510-rust_unsafe_pinned-v3-2-57ce151123f9@gmail.com>
Date: Sat, 10 May 2025 11:32:27 +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>, 
 Nathan Chancellor <nathan@...nel.org>, 
 Nick Desaulniers <nick.desaulniers+lkml@...il.com>, 
 Bill Wendling <morbo@...gle.com>, Justin Stitt <justinstitt@...gle.com>
Cc: linux-kernel@...r.kernel.org, rust-for-linux@...r.kernel.org, 
 llvm@...ts.linux.dev, Christian Schrefl <chrisi.schrefl@...il.com>, 
 Benno Lossin <lossin@...nel.org>
Subject: [PATCH v3 2/3] rust: implement `Wrapper<T>` for `Opaque<T>`

Moves the implementation for `pin-init` from an associated function
to the trait function of the `Wrapper` trait and extends the
implementation to support pin-initializers with error types.

This allows to declare functions that are generic over `Wrapper`
types.

Adds a use for the `Wrapper` trait in `revocable.rs`, to use the new
`pin-init` function. This is currently the only usage in the kernel.

Reviewed-by: Gerald Wisböck <gerald.wisboeck@...ther.ink>
Reviewed-by: Alice Ryhl <aliceryhl@...gle.com>
Reviewed-by: Benno Lossin <lossin@...nel.org>
Signed-off-by: Christian Schrefl <chrisi.schrefl@...il.com>
---
 rust/kernel/revocable.rs |  2 ++
 rust/kernel/types.rs     | 25 +++++++++++++------------
 2 files changed, 15 insertions(+), 12 deletions(-)

diff --git a/rust/kernel/revocable.rs b/rust/kernel/revocable.rs
index 1e5a9d25c21b279b01f90b02997492aa4880d84f..4db68ea2207ebafcc09d082fdc1e281f31846a38 100644
--- a/rust/kernel/revocable.rs
+++ b/rust/kernel/revocable.rs
@@ -5,6 +5,8 @@
 //! The [`Revocable`] type wraps other types and allows access to them to be revoked. The existence
 //! of a [`RevocableGuard`] ensures that objects remain valid.
 
+use pin_init::Wrapper;
+
 use crate::{bindings, prelude::*, sync::rcu, types::Opaque};
 use core::{
     marker::PhantomData,
diff --git a/rust/kernel/types.rs b/rust/kernel/types.rs
index 705f420fdfbc4a576de1c4546578f2f04cdf615e..f06e8720e012102e5c41e79fd97b0607e927d71c 100644
--- a/rust/kernel/types.rs
+++ b/rust/kernel/types.rs
@@ -9,7 +9,7 @@
     ops::{Deref, DerefMut},
     ptr::NonNull,
 };
-use pin_init::{PinInit, Zeroable};
+use pin_init::{PinInit, Wrapper, Zeroable};
 
 /// Used to transfer ownership to and from foreign (non-Rust) languages.
 ///
@@ -332,17 +332,6 @@ pub const fn uninit() -> Self {
         }
     }
 
-    /// Create an opaque pin-initializer from the given pin-initializer.
-    pub fn pin_init(slot: impl PinInit<T>) -> impl PinInit<Self> {
-        Self::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.
-            let _ = unsafe { PinInit::<T>::__pinned_init(slot, ptr) };
-        })
-    }
-
     /// Creates a pin-initializer from the given initializer closure.
     ///
     /// The returned initializer calls the given closure with the pointer to the inner `T` of this
@@ -393,6 +382,18 @@ pub const fn raw_get(this: *const Self) -> *mut T {
         UnsafeCell::raw_get(this.cast::<UnsafeCell<MaybeUninit<T>>>()).cast::<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) }
+        })
+    }
+}
 
 /// Types that are _always_ reference counted.
 ///

-- 
2.49.0