Documentation/input/notifier.txt

   1 Keyboard notifier
   2
   3 One can use register_keyboard_notifier to get called back on keyboard
   4 events (see kbd_keycode() function for details).  The passed structure is
   5 keyboard_notifier_param:
   6
   7 - 'vc' always provide the VC for which the keyboard event applies;
   8 - 'down' is 1 for a key press event, 0 for a key release;
   9 - 'shift' is the current modifier state, mask bit indexes are KG_*;
  10 - 'value' depends on the type of event.
  11
  12 - KBD_KEYCODE events are always sent before other events, value is the keycode.
  13 - KBD_UNBOUND_KEYCODE events are sent if the keycode is not bound to a keysym.
  14   value is the keycode.
  15 - KBD_UNICODE events are sent if the keycode -> keysym translation produced a
  16   unicode character. value is the unicode value.
  17 - KBD_KEYSYM events are sent if the keycode -> keysym translation produced a
  18   non-unicode character. value is the keysym.
  19 - KBD_POST_KEYSYM events are sent after the treatment of non-unicode keysyms.
  20   That permits one to inspect the resulting LEDs for instance.
  21
  22 For each kind of event but the last, the callback may return NOTIFY_STOP in
  23 order to "eat" the event: the notify loop is stopped and the keyboard event is
  24 dropped.
  25
  26 In a rough C snippet, we have:
  27
  28 kbd_keycode(keycode) {
  29         ...
  30         params.value = keycode;
  31         if (notifier_call_chain(KBD_KEYCODE,&params) == NOTIFY_STOP)
  32             || !bound) {
  33                 notifier_call_chain(KBD_UNBOUND_KEYCODE,&params);
  34                 return;
  35         }
  36
  37         if (unicode) {
  38                 param.value = unicode;
  39                 if (notifier_call_chain(KBD_UNICODE,&params) == NOTIFY_STOP)
  40                         return;
  41                 emit unicode;
  42                 return;
  43         }
  44
  45         params.value = keysym;
  46         if (notifier_call_chain(KBD_KEYSYM,&params) == NOTIFY_STOP)
  47                 return;
  48         apply keysym;
  49         notifier_call_chain(KBD_POST_KEYSYM,&params);
  50 }
  51
  52 NOTE: This notifier is usually called from interrupt context.