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1=================2Keyboard notifier3=================4 5One can use register_keyboard_notifier to get called back on keyboard6events (see kbd_keycode() function for details). The passed structure is7keyboard_notifier_param (see <linux/keyboard.h>):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- 'ledstate' is the current LED state;13- 'value' depends on the type of event.14 15- KBD_KEYCODE events are always sent before other events, value is the keycode.16- KBD_UNBOUND_KEYCODE events are sent if the keycode is not bound to a keysym.17 value is the keycode.18- KBD_UNICODE events are sent if the keycode -> keysym translation produced a19 unicode character. value is the unicode value.20- KBD_KEYSYM events are sent if the keycode -> keysym translation produced a21 non-unicode character. value is the keysym.22- KBD_POST_KEYSYM events are sent after the treatment of non-unicode keysyms.23 That permits one to inspect the resulting LEDs for instance.24 25For each kind of event but the last, the callback may return NOTIFY_STOP in26order to "eat" the event: the notify loop is stopped and the keyboard event is27dropped.28 29In a rough C snippet, we have::30 31 kbd_keycode(keycode) {32 ...33 params.value = keycode;34 if (notifier_call_chain(KBD_KEYCODE,¶ms) == NOTIFY_STOP)35 || !bound) {36 notifier_call_chain(KBD_UNBOUND_KEYCODE,¶ms);37 return;38 }39 40 if (unicode) {41 param.value = unicode;42 if (notifier_call_chain(KBD_UNICODE,¶ms) == NOTIFY_STOP)43 return;44 emit unicode;45 return;46 }47 48 params.value = keysym;49 if (notifier_call_chain(KBD_KEYSYM,¶ms) == NOTIFY_STOP)50 return;51 apply keysym;52 notifier_call_chain(KBD_POST_KEYSYM,¶ms);53 }54 55.. note:: This notifier is usually called from interrupt context.56