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

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Message-ID: <20250414131934.28418-3-dakr@kernel.org>
Date: Mon, 14 Apr 2025 15:18:05 +0200
From: Danilo Krummrich <dakr@...nel.org>
To: gregkh@...uxfoundation.org,
	rafael@...nel.org,
	david.m.ertman@...el.com,
	ira.weiny@...el.com,
	ojeda@...nel.org,
	alex.gaynor@...il.com,
	boqun.feng@...il.com,
	gary@...yguo.net,
	bjorn3_gh@...tonmail.com,
	benno.lossin@...ton.me,
	a.hindborg@...nel.org,
	aliceryhl@...gle.com,
	tmgross@...ch.edu,
	airlied@...il.com,
	acourbot@...dia.com,
	jhubbard@...dia.com
Cc: linux-kernel@...r.kernel.org,
	rust-for-linux@...r.kernel.org,
	Danilo Krummrich <dakr@...nel.org>
Subject: [PATCH v4 2/5] rust: device: implement Device::parent()

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

Reviewed-by: Alice Ryhl <aliceryhl@...gle.com>
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 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