linux-kernel - [PATCH v2 4/5] rust: types: implement `ForeignOwnable` for the unit type

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Message-Id: <20230130064404.744600-4-wedsonaf@gmail.com>
Date:   Mon, 30 Jan 2023 03:44:03 -0300
From:   Wedson Almeida Filho <wedsonaf@...il.com>
To:     rust-for-linux@...r.kernel.org
Cc:     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>,
        linux-kernel@...r.kernel.org,
        Wedson Almeida Filho <wedsonaf@...il.com>,
        Vincenzo Palazzo <vincenzopalazzodev@...il.com>
Subject: [PATCH v2 4/5] rust: types: implement `ForeignOwnable` for the unit type

This allows us to use the unit type `()` when we have no object whose
ownership must be managed but one implementing the `ForeignOwnable`
trait is needed.

Signed-off-by: Wedson Almeida Filho <wedsonaf@...il.com>
Reviewed-by: Vincenzo Palazzo <vincenzopalazzodev@...il.com>
---
v1 -> v2: use `NonNull::dangling` to generate pointer

 rust/kernel/types.rs | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/rust/kernel/types.rs b/rust/kernel/types.rs
index 411655eca3e9..9d0fdbc55843 100644
--- a/rust/kernel/types.rs
+++ b/rust/kernel/types.rs
@@ -85,6 +85,18 @@ impl<T: 'static> ForeignOwnable for Box<T> {
     }
 }
 
+impl ForeignOwnable for () {
+    type Borrowed<'a> = ();
+
+    fn into_foreign(self) -> *const core::ffi::c_void {
+        core::ptr::NonNull::dangling().as_ptr()
+    }
+
+    unsafe fn borrow<'a>(_: *const core::ffi::c_void) -> Self::Borrowed<'a> {}
+
+    unsafe fn from_foreign(_: *const core::ffi::c_void) -> Self {}
+}
+
 /// Runs a cleanup function/closure when dropped.
 ///
 /// The [`ScopeGuard::dismiss`] function prevents the cleanup function from running.
-- 
2.34.1