rust: drm: gem: Add DriverFile type alias

Just to reduce the clutter with the File<…> types in gem.rs.

Signed-off-by: Lyude Paul <lyude@redhat.com>
Reviewed-by: Daniel Almeida <daniel.almeida@collabora.com>
Acked-by: Danilo Krummrich <dakr@kernel.org>
Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Link: https://lore.kernel.org/r/20250908185239.135849-3-lyude@redhat.com
Signed-off-by: Alice Ryhl <aliceryhl@google.com>

Author: Lyude

rust/kernel/drm/gem/mod.rs

@@ -14,6 +14,13 @@ use crate::{
 };
 use core::{mem, ops::Deref, ptr::NonNull};
 
+/// A type alias for retrieving a [`Driver`]s [`DriverFile`] implementation from its
+/// [`DriverObject`] implementation.
+///
+/// [`Driver`]: drm::Driver
+/// [`DriverFile`]: drm::file::DriverFile
+pub type DriverFile<T> = drm::File<<<T as DriverObject>::Driver as drm::Driver>::File>;
+
 /// GEM object functions, which must be implemented by drivers.
 pub trait DriverObject: Sync + Send + Sized {
     /// Parent `Driver` for this object.
@@ -23,19 +30,12 @@ pub trait DriverObject: Sync + Send + Sized {
     fn new(dev: &drm::Device<Self::Driver>, size: usize) -> impl PinInit<Self, Error>;
 
     /// Open a new handle to an existing object, associated with a File.
-    fn open(
-        _obj: &<Self::Driver as drm::Driver>::Object,
-        _file: &drm::File<<Self::Driver as drm::Driver>::File>,
-    ) -> Result {
+    fn open(_obj: &<Self::Driver as drm::Driver>::Object, _file: &DriverFile<Self>) -> Result {
         Ok(())
     }
 
     /// Close a handle to an existing object, associated with a File.
-    fn close(
-        _obj: &<Self::Driver as drm::Driver>::Object,
-        _file: &drm::File<<Self::Driver as drm::Driver>::File>,
-    ) {
-    }
+    fn close(_obj: &<Self::Driver as drm::Driver>::Object, _file: &DriverFile<Self>) {}
 }
 
 /// Trait that represents a GEM object subtype
@@ -79,7 +79,8 @@ extern "C" fn open_callback<T: DriverObject>(
     raw_file: *mut bindings::drm_file,
 ) -> core::ffi::c_int {
     // SAFETY: `open_callback` is only ever called with a valid pointer to a `struct drm_file`.
-    let file = unsafe { drm::File::<<T::Driver as drm::Driver>::File>::from_raw(raw_file) };
+    let file = unsafe { DriverFile::<T>::from_raw(raw_file) };
+
     // SAFETY: `open_callback` is specified in the AllocOps structure for `DriverObject<T>`,
     // ensuring that `raw_obj` is contained within a `DriverObject<T>`
     let obj = unsafe { <<T::Driver as drm::Driver>::Object as IntoGEMObject>::from_raw(raw_obj) };
@@ -95,7 +96,7 @@ extern "C" fn close_callback<T: DriverObject>(
     raw_file: *mut bindings::drm_file,
 ) {
     // SAFETY: `open_callback` is only ever called with a valid pointer to a `struct drm_file`.
-    let file = unsafe { drm::File::<<T::Driver as drm::Driver>::File>::from_raw(raw_file) };
+    let file = unsafe { DriverFile::<T>::from_raw(raw_file) };
 
     // SAFETY: `close_callback` is specified in the AllocOps structure for `Object<T>`, ensuring
     // that `raw_obj` is indeed contained within a `Object<T>`.