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From:   Wedson Almeida Filho <wedsonaf@gmail.com>
To:     rust-for-linux@vger.kernel.org
Cc:     Miguel Ojeda <ojeda@kernel.org>,
        Alex Gaynor <alex.gaynor@gmail.com>,
        Boqun Feng <boqun.feng@gmail.com>, Gary Guo <gary@garyguo.net>,
        =?UTF-8?q?Bj=C3=B6rn=20Roy=20Baron?= <bjorn3_gh@protonmail.com>,
        linux-kernel@vger.kernel.org,
        Wedson Almeida Filho <wedsonaf@gmail.com>
Subject: [PATCH 4/5] rust: types: implement `ForeignOwnable` for the unit type
Date:   Thu, 19 Jan 2023 14:40:35 -0300
Message-Id: <20230119174036.64046-4-wedsonaf@gmail.com>
In-Reply-To: <20230119174036.64046-1-wedsonaf@gmail.com>
References: <20230119174036.64046-1-wedsonaf@gmail.com>
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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@gmail.com>
---
 rust/kernel/types.rs | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/rust/kernel/types.rs b/rust/kernel/types.rs
index e037c262f23e..8f80cffbff59 100644
--- a/rust/kernel/types.rs
+++ b/rust/kernel/types.rs
@@ -85,6 +85,19 @@ impl<T: 'static> ForeignOwnable for Box<T> {
     }
 }
 
+impl ForeignOwnable for () {
+    type Borrowed<'a> = ();
+
+    fn into_foreign(self) -> *const core::ffi::c_void {
+        // We use 1 to be different from a null pointer.
+        1usize as _
+    }
+
+    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