[PATCH 3/7] drm/rust: add File::device() helper

[Deborah Brouwer <deborah.brouwer@collabora.com>]

Add a helper to retrieve the DRM device associated with an open
`drm::file::File<T>`.

This wraps the common pattern of traversing `drm_file.minor->dev` and
returning the corresponding `drm::Device<T::Driver>`.

This is useful for DRM file operation callbacks that need access to the
owning DRM device from a `File<T>` reference, avoiding repeated open-coded
raw pointer traversal in drivers.

Signed-off-by: Deborah Brouwer <deborah.brouwer@collabora.com>
---
 rust/kernel/drm/file.rs | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/rust/kernel/drm/file.rs b/rust/kernel/drm/file.rs
index 10160601ce5a..5af28a9558e9 100644
--- a/rust/kernel/drm/file.rs
+++ b/rust/kernel/drm/file.rs
@@ -45,6 +45,18 @@ pub(super) fn as_raw(&self) -> *mut bindings::drm_file {
         self.0.get()
     }
 
+    /// Returns the DRM device associated with this open file.
+    pub fn device(&self) -> &drm::Device<T::Driver> {
+        // SAFETY: By the type invariant, `self.as_raw()` points to a valid open
+        // `struct drm_file`. DRM initializes `minor` for open DRM files, and
+        // `minor->dev` points to the registered DRM device associated with this
+        // file.
+        unsafe {
+            let minor = (*self.as_raw()).minor;
+            drm::Device::from_raw((*minor).dev)
+        }
+    }
+
     fn driver_priv(&self) -> *mut T {
         // SAFETY: By the type invariants of `Self`, `self.as_raw()` is always valid.
         unsafe { (*self.as_raw()).driver_priv }.cast()

-- 
2.53.0