[PATCH v4 2/5] rust: device: implement Device::parent()

Danilo Krummrich
2025-04-14T13:19:49Z

Device::parent() returns a reference to the device' parent device, if
any.

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

diff --git a/rust/kernel/device.rs b/rust/kernel/device.rs
index 585a3fcfeea3..911045e32c34 100644
--- a/rust/kernel/device.rs
+++ b/rust/kernel/device.rs
@@ -67,6 +67,25 @@ pub(crate) fn as_raw(&self) -> *mut bindings::device {
self.0.get()
}

+ /// Returns a reference to the parent device, if any.
+ #[expect(unused)]
+ pub(crate) fn parent(&self) -> Option<&Self> {
+ // SAFETY:
+ // - By the type invariant `self.as_raw()` is always valid.
+ // - The parent device is only ever set at device creation.
+ let parent = unsafe { (*self.as_raw()).parent };
+
+ if parent.is_null() {
+ None
+ } else {
+ // SAFETY:
+ // - Since `parent` is not NULL, it must be a valid pointer to a `struct device`.
+ // - `parent` is valid for the lifetime of `self`, since a `struct device` holds a
+ // reference count of its parent.
+ Some(unsafe { Self::as_ref(parent) })
+ }
+ }
+
/// Convert a raw C `struct device` pointer to a `&'a Device`.
///
/// # Safety
--
2.49.0