rust: device_id: add macro for alias generation

For modpost to work, we need the device id table to be named as follow:
	__mod_{type}__{name}_device_table

In C, this is done by calling MODULE_DEVICE_TABLE(type, name), which declares
a new symbol that aliases to `name`.

As far as I know it is not possible to create such aliases in Rust, so
here we instead create a new static variable which contains a copy of the
device_id tables, but without the extra `id_infos` used on the Rust
side.

Signed-off-by: Fabien Parent <[email protected]>

Author: Fabo

rust/kernel/device_id.rs

@@ -40,11 +40,25 @@ pub unsafe trait RawDeviceId {
     const DRIVER_DATA_OFFSET: usize;
 }
 
-/// A zero-terminated device id array, followed by context data.
+/// A zero-terminated device id array.
 #[repr(C)]
-pub struct IdArray<T: RawDeviceId, U, const N: usize> {
+pub struct RawIdArray<T: RawDeviceId, const N: usize> {
     ids: [T::RawType; N],
     sentinel: MaybeUninit<T::RawType>,
+}
+
+impl<T: RawDeviceId, const N: usize> RawIdArray<T, N> {
+    #[doc(hidden)]
+    pub const fn len(&self) -> usize {
+        (N + 1) * core::mem::size_of::<T>()
+    }
+}
+
+/// A zero-terminated device id array, followed by context data.
+#[repr(C)]
+pub struct IdArray<T: RawDeviceId, U, const N: usize> {
+    #[doc(hidden)]
+    pub raw_ids: RawIdArray<T, N>,
     id_infos: [U; N],
 }
 
@@ -83,8 +97,10 @@ impl<T: RawDeviceId, U, const N: usize> IdArray<T, U, N> {
             // SAFETY: this is effectively `array_assume_init`, which is unstable, so we use
             // `transmute_copy` instead. We have initialized all elements of `raw_ids` so this
             // `array_assume_init` is safe.
-            ids: unsafe { core::mem::transmute_copy(&raw_ids) },
-            sentinel: MaybeUninit::zeroed(),
+            raw_ids: RawIdArray {
+                ids: unsafe { core::mem::transmute_copy(&raw_ids) },
+                sentinel: MaybeUninit::zeroed(),
+            },
             // SAFETY: We have initialized all elements of `infos` so this `array_assume_init` is
             // safe.
             id_infos: unsafe { core::mem::transmute_copy(&infos) },
@@ -117,10 +133,20 @@ impl<T: RawDeviceId, U, const N: usize> IdTable<T, U> for IdArray<T, U, N> {
     }
 
     fn id(&self, index: usize) -> &T::RawType {
-        &self.ids[index]
+        &self.raw_ids.ids[index]
     }
 
     fn info(&self, index: usize) -> &U {
         &self.id_infos[index]
     }
 }
+
+/// Create device table alias for modpost.
+#[macro_export]
+macro_rules! module_device_table {
+    ($table_type: literal, $module_table_name:ident, $table_name:ident) => {
+        #[export_name = concat!("__mod_", $table_type, "__", stringify!($table_name), "_device_table")]
+        static $module_table_name: [u8; $table_name.raw_ids.len()] =
+            unsafe { core::mem::transmute_copy(&$table_name.raw_ids) };
+    };
+}