linux-kernel - [PATCH v4 1/3] rust: implement `Wrapper<T>` for `Opaque<T>`

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Message-Id: <20250530-b4-rust_miscdevice_registrationdata-v4-1-d313aafd7e59@gmail.com>
Date: Fri, 30 May 2025 22:46:27 +0200
From: Christian Schrefl <chrisi.schrefl@...il.com>
To: Miguel Ojeda <ojeda@...nel.org>, Danilo Krummrich <dakr@...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>, 
 Andreas Hindborg <a.hindborg@...nel.org>, Alice Ryhl <aliceryhl@...gle.com>, 
 Trevor Gross <tmgross@...ch.edu>, Arnd Bergmann <arnd@...db.de>, 
 Greg Kroah-Hartman <gregkh@...uxfoundation.org>, Lee Jones <lee@...nel.org>, 
 Daniel Almeida <daniel.almeida@...labora.com>, 
 Benno Lossin <lossin@...nel.org>, Benno Lossin <lossin@...nel.org>
Cc: Gerald Wisböck <gerald.wisboeck@...ther.ink>, 
 rust-for-linux@...r.kernel.org, linux-kernel@...r.kernel.org, 
 Christian Schrefl <chrisi.schrefl@...il.com>
Subject: [PATCH v4 1/3] 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.

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 86562e738eac85480a048041e979335b81c5e3c9..7ab70d5f76099c3442dce5b02c6b226fc74c851e 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.
 ///
@@ -345,17 +345,6 @@ 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
@@ -406,6 +395,18 @@ 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,
+            //   - `slot` is pinned in memory.
+            unsafe { PinInit::<T, E>::__pinned_init(slot, ptr) }
+        })
+    }
+}
 
 /// Types that are _always_ reference counted.
 ///

-- 
2.49.0