One can use register_keyboard_notifier to get called back on keyboard
events (see kbd_keycode() function for details). The passed structure is
-keyboard_notifier_param:
+keyboard_notifier_param (see <linux/keyboard.h>):
- 'vc' always provide the VC for which the keyboard event applies;
- 'down' is 1 for a key press event, 0 for a key release;
- 'shift' is the current modifier state, mask bit indexes are KG_*;
+- 'ledstate' is the current LED state;
- 'value' depends on the type of event.
- KBD_KEYCODE events are always sent before other events, value is the keycode.