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Input: add keyboard notifier documentation

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Document the keyboard notifier.

Signed-off-by: Samuel Thibault <samuel.thibault@ens-lyon.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>
SIgned-off-by: Dmitry Torokhov <dtor@mail.ru>
This commit is contained in:
Samuel Thibault 2008-03-10 03:08:45 -07:00 committed by Dmitry Torokhov
parent 05be5fc4c7
commit e32f7ee876
1 changed files with 52 additions and 0 deletions
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52
Documentation/input/notifier.txt Normal file
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Keyboard notifier
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:
- '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_*;
- 'value' depends on the type of event.
- KBD_KEYCODE events are always sent before other events, value is the keycode.
- KBD_UNBOUND_KEYCODE events are sent if the keycode is not bound to a keysym.
value is the keycode.
- KBD_UNICODE events are sent if the keycode -> keysym translation produced a
unicode character. value is the unicode value.
- KBD_KEYSYM events are sent if the keycode -> keysym translation produced a
non-unicode character. value is the keysym.
- KBD_POST_KEYSYM events are sent after the treatment of non-unicode keysyms.
That permits one to inspect the resulting LEDs for instance.
For each kind of event but the last, the callback may return NOTIFY_STOP in
order to "eat" the event: the notify loop is stopped and the keyboard event is
dropped.
In a rough C snippet, we have:
kbd_keycode(keycode) {
...
params.value = keycode;
if (notifier_call_chain(KBD_KEYCODE,&params) == NOTIFY_STOP)
|| !bound) {
notifier_call_chain(KBD_UNBOUND_KEYCODE,&params);
return;
}
if (unicode) {
param.value = unicode;
if (notifier_call_chain(KBD_UNICODE,&params) == NOTIFY_STOP)
return;
emit unicode;
return;
}
params.value = keysym;
if (notifier_call_chain(KBD_KEYSYM,&params) == NOTIFY_STOP)
return;
apply keysym;
notifier_call_chain(KBD_POST_KEYSYM,&params);
}
NOTE: This notifier is usually called from interrupt context.