After a SYN_DROPPED, drop all events in the queue

Ideally, we could sync by pre-pending all the sync events and then pretend
nothing happened but our queue is too small and likely too full for any
extra events. So drop all events, then add the sync events to the queue.

Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>

1 files changed, 18 insertions, 1 deletions

diff --git a/libevdev/libevdev.c b/libevdev/libevdev.c
index 561d0c5..2c5742e 100644
--- a/libevdev/libevdev.c
+++ b/libevdev/libevdev.c
@@ -381,13 +381,30 @@ out:
 static int
 sync_state(struct libevdev *dev)
 {
+	int i;
 	int rc = 0;
 	struct input_event *ev;
 
 	/* FIXME: if we have events in the queue after the SYN_DROPPED (which was
-	   queue[0]) we need to shift this backwards somehow.
+	   queue[0]) we need to shift this backwards. Except that chances are that the
+	   queue may be either full or too full to prepend all the events needed for
+	   syncing.
+
+	   so we search for the last sync event in the queue and drop everything before
+	   including that event and rely on the kernel to tell us the right value for that
+	   bitfield during the sync process.
 	 */
 
+	for (i = queue_num_elements(dev) - 1; i >= 0; i--) {
+		struct input_event e;
+		queue_peek(dev, i, &e);
+		if (e.type == EV_SYN)
+			break;
+	}
+
+	if (i > 0)
+		queue_shift_multiple(dev, i + 1, NULL);
+
 	if (libevdev_has_event_type(dev, EV_KEY))
 		rc = sync_key_state(dev);
 	if (rc == 0 && libevdev_has_event_type(dev, EV_ABS))