Input: simplify event handling logic

Streamline event handling code by providing batch implementations for
filtering and event processing and using them in place of the main
event handler, as needed, instead of having complex branching logic
in the middle of the event processing code.

Reviewed-by: Jeff LaBundy <jeff@labundy.com>
Reviewed-by: Benjamin Tissoires <bentiss@kernel.org>
Link: https://lore.kernel.org/r/20240703213756.3375978-5-dmitry.torokhov@gmail.com
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>

drivers/input/input.c

@@ -99,45 +99,13 @@ static void input_stop_autorepeat(struct input_dev *dev)
 	del_timer(&dev->timer);
 }
 
-/*
- * Pass event first through all filters and then, if event has not been
- * filtered out, through all open handles. This function is called with
- * dev->event_lock held and interrupts disabled.
- */
-static unsigned int input_to_handler(struct input_handle *handle,
-			struct input_value *vals, unsigned int count)
-{
-	struct input_handler *handler = handle->handler;
-	struct input_value *end = vals;
-	struct input_value *v;
-
-	if (handler->filter) {
-		for (v = vals; v != vals + count; v++) {
-			if (handler->filter(handle, v->type, v->code, v->value))
-				continue;
-			if (end != v)
-				*end = *v;
-			end++;
-		}
-		count = end - vals;
-	}
-
-	if (!count)
-		return 0;
-
-	if (handler->events)
-		handler->events(handle, vals, count);
-	else if (handler->event)
-		for (v = vals; v != vals + count; v++)
-			handler->event(handle, v->type, v->code, v->value);
-
-	return count;
-}
-
 /*
  * Pass values first through all filters and then, if event has not been
- * filtered out, through all open handles. This function is called with
+ * filtered out, through all open handles. This order is achieved by placing
- * dev->event_lock held and interrupts disabled.
+ * filters at the head of the list of handles attached to the device, and
+ * placing regular handles at the tail of the list.
+ *
+ * This function is called with dev->event_lock held and interrupts disabled.
  */
 static void input_pass_values(struct input_dev *dev,
 			      struct input_value *vals, unsigned int count)
@@ -154,11 +122,12 @@ static void input_pass_values(struct input_dev *dev,
 
 	handle = rcu_dereference(dev->grab);
 	if (handle) {
-		count = input_to_handler(handle, vals, count);
+		count = handle->handler->events(handle, vals, count);
 	} else {
 		list_for_each_entry_rcu(handle, &dev->h_list, d_node)
 			if (handle->open) {
-				count = input_to_handler(handle, vals, count);
+				count = handle->handler->events(handle, vals,
+								count);
 				if (!count)
 					break;
 			}
@@ -2537,6 +2506,57 @@ static int input_handler_check_methods(const struct input_handler *handler)
 	return 0;
 }
 
+/*
+ * An implementation of input_handler's events() method that simply
+ * invokes handler->event() method for each event one by one.
+ */
+static unsigned int input_handler_events_default(struct input_handle *handle,
+						 struct input_value *vals,
+						 unsigned int count)
+{
+	struct input_handler *handler = handle->handler;
+	struct input_value *v;
+
+	for (v = vals; v != vals + count; v++)
+		handler->event(handle, v->type, v->code, v->value);
+
+	return count;
+}
+
+/*
+ * An implementation of input_handler's events() method that invokes
+ * handler->filter() method for each event one by one and removes events
+ * that were filtered out from the "vals" array.
+ */
+static unsigned int input_handler_events_filter(struct input_handle *handle,
+						struct input_value *vals,
+						unsigned int count)
+{
+	struct input_handler *handler = handle->handler;
+	struct input_value *end = vals;
+	struct input_value *v;
+
+	for (v = vals; v != vals + count; v++) {
+		if (handler->filter(handle, v->type, v->code, v->value))
+			continue;
+		if (end != v)
+			*end = *v;
+		end++;
+	}
+
+	return end - vals;
+}
+
+/*
+ * An implementation of input_handler's events() method that does nothing.
+ */
+static unsigned int input_handler_events_null(struct input_handle *handle,
+					      struct input_value *vals,
+					      unsigned int count)
+{
+	return count;
+}
+
 /**
  * input_register_handler - register a new input handler
  * @handler: handler to be registered
@@ -2554,12 +2574,19 @@ int input_register_handler(struct input_handler *handler)
 	if (error)
 		return error;
 
+	INIT_LIST_HEAD(&handler->h_list);
+
+	if (handler->filter)
+		handler->events = input_handler_events_filter;
+	else if (handler->event)
+		handler->events = input_handler_events_default;
+	else if (!handler->events)
+		handler->events = input_handler_events_null;
+
 	error = mutex_lock_interruptible(&input_mutex);
 	if (error)
 		return error;
 
-	INIT_LIST_HEAD(&handler->h_list);
-
 	list_add_tail(&handler->node, &input_handler_list);
 
 	list_for_each_entry(dev, &input_dev_list, node)