[PATCH 1/4] rust: device: implement Device::parent()

[Danilo Krummrich <dakr@kernel.org>]

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

Signed-off-by: Danilo Krummrich <dakr@kernel.org>
---
 rust/kernel/device.rs | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/rust/kernel/device.rs b/rust/kernel/device.rs
index 21b343a1dc4d..76b341441f3f 100644
--- a/rust/kernel/device.rs
+++ b/rust/kernel/device.rs
@@ -65,6 +65,19 @@ pub(crate) fn as_raw(&self) -> *mut bindings::device {
         self.0.get()
     }
 
+    /// Returns a reference to the parent device, if any.
+    pub fn parent<'a>(&self) -> Option<&'a Self> {
+        // SAFETY: By the type invariant `self.as_raw()` is always valid.
+        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`.
+            Some(unsafe { Self::as_ref(parent) })
+        }
+    }
+
     /// Convert a raw C `struct device` pointer to a `&'a Device`.
     ///
     /// # Safety
-- 
2.48.1