linux-kernel - [PATCH 2/2] rust: device: implement Device::as

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Message-ID: <20250713182737.64448-2-dakr@kernel.org>
Date: Sun, 13 Jul 2025 20:26:54 +0200
From: Danilo Krummrich <dakr@...nel.org>
To: gregkh@...uxfoundation.org,
	rafael@...nel.org,
	ojeda@...nel.org,
	alex.gaynor@...il.com,
	boqun.feng@...il.com,
	gary@...yguo.net,
	bjorn3_gh@...tonmail.com,
	lossin@...nel.org,
	a.hindborg@...nel.org,
	aliceryhl@...gle.com,
	tmgross@...ch.edu,
	daniel.almeida@...labora.com,
	m.wilczynski@...sung.com
Cc: rust-for-linux@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Danilo Krummrich <dakr@...nel.org>
Subject: [PATCH 2/2] rust: device: implement Device::as_bound()

Provide an unsafe functions for abstractions to convert a regular
&Device to a &Device<Bound>.

This is useful for registrations that provide certain guarantees for the
scope of their callbacks, such as IRQs or certain class device
registrations (e.g. PWM, miscdevice).

Signed-off-by: Danilo Krummrich <dakr@...nel.org>
---
 rust/kernel/device.rs | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

diff --git a/rust/kernel/device.rs b/rust/kernel/device.rs
index d527ceef829e..4d9b052afe92 100644
--- a/rust/kernel/device.rs
+++ b/rust/kernel/device.rs
@@ -60,6 +60,25 @@ pub unsafe fn get_device(ptr: *mut bindings::device) -> ARef<Self> {
         // SAFETY: By the safety requirements ptr is valid
         unsafe { Self::as_ref(ptr) }.into()
     }
+
+    /// Convert a [`&Device`](Device) into a [`&Device<Bound>`](Device<Bound>).
+    ///
+    /// # Safety
+    ///
+    /// The caller is responsible to ensure that the returned [`&Device<Bound>`](Device<Bound>)
+    /// only lives as long as it can be guaranteed that the [`Device`] is actually bound.
+    pub unsafe fn as_bound(&self) -> &Device<Bound> {
+        let ptr = core::ptr::from_ref(self);
+
+        // CAST: By the safety requirements the caller is responsible to guarantee that the
+        // returned reference only lives as long as the device is actually bound.
+        let ptr = ptr.cast::<Device<Bound>>();
+
+        // SAFETY:
+        // - `ptr` comes from `from_ref(self)` above, hence it's guaranteed to be valid.
+        // - Any valid `Device` pointer is also a valid pointer for `Device<Bound>`.
+        unsafe { &*ptr.cast() }
+    }
 }
 
 impl Device<CoreInternal> {
-- 
2.50.0