Documentation/input/notifier.rst

   1 =================
   2 Keyboard notifier
   3 =================
   4
   5 One can use register_keyboard_notifier to get called back on keyboard
   6 events (see kbd_keycode() function for details).  The passed structure is
   7 keyboard_notifier_param:
   8
   9 - 'vc' always provide the VC for which the keyboard event applies;
  10 - 'down' is 1 for a key press event, 0 for a key release;
  11 - 'shift' is the current modifier state, mask bit indexes are KG_*;
  12 - 'value' depends on the type of event.
  13
  14 - KBD_KEYCODE events are always sent before other events, value is the keycode.
  15 - KBD_UNBOUND_KEYCODE events are sent if the keycode is not bound to a keysym.
  16   value is the keycode.
  17 - KBD_UNICODE events are sent if the keycode -> keysym translation produced a
  18   unicode character. value is the unicode value.
  19 - KBD_KEYSYM events are sent if the keycode -> keysym translation produced a
  20   non-unicode character. value is the keysym.
  21 - KBD_POST_KEYSYM events are sent after the treatment of non-unicode keysyms.
  22   That permits one to inspect the resulting LEDs for instance.
  23
  24 For each kind of event but the last, the callback may return NOTIFY_STOP in
  25 order to "eat" the event: the notify loop is stopped and the keyboard event is
  26 dropped.
  27
  28 In a rough C snippet, we have::
  29
  30     kbd_keycode(keycode) {
  31         ...
  32         params.value = keycode;
  33         if (notifier_call_chain(KBD_KEYCODE,&params) == NOTIFY_STOP)
  34             || !bound) {
  35                 notifier_call_chain(KBD_UNBOUND_KEYCODE,&params);
  36                 return;
  37         }
  38
  39         if (unicode) {
  40                 param.value = unicode;
  41                 if (notifier_call_chain(KBD_UNICODE,&params) == NOTIFY_STOP)
  42                         return;
  43                 emit unicode;
  44                 return;
  45         }
  46
  47         params.value = keysym;
  48         if (notifier_call_chain(KBD_KEYSYM,&params) == NOTIFY_STOP)
  49                 return;
  50         apply keysym;
  51         notifier_call_chain(KBD_POST_KEYSYM,&params);
  52     }
  53
  54 .. note:: This notifier is usually called from interrupt context.