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Input: add keyboard notifier documentation
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>
authored by
Samuel Thibault
and committed by
Dmitry Torokhov
e32f7ee8
05be5fc4
+52
+52
Documentation/input/notifier.txt
+52
Documentation/input/notifier.txt
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Keyboard notifier
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One can use register_keyboard_notifier to get called back on keyboard
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events (see kbd_keycode() function for details). The passed structure is
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keyboard_notifier_param:
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- 'vc' always provide the VC for which the keyboard event applies;
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- 'down' is 1 for a key press event, 0 for a key release;
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- 'shift' is the current modifier state, mask bit indexes are KG_*;
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- 'value' depends on the type of event.
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- KBD_KEYCODE events are always sent before other events, value is the keycode.
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- KBD_UNBOUND_KEYCODE events are sent if the keycode is not bound to a keysym.
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value is the keycode.
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- KBD_UNICODE events are sent if the keycode -> keysym translation produced a
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unicode character. value is the unicode value.
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- KBD_KEYSYM events are sent if the keycode -> keysym translation produced a
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non-unicode character. value is the keysym.
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- KBD_POST_KEYSYM events are sent after the treatment of non-unicode keysyms.
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That permits one to inspect the resulting LEDs for instance.
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For each kind of event but the last, the callback may return NOTIFY_STOP in
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order to "eat" the event: the notify loop is stopped and the keyboard event is
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dropped.
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In a rough C snippet, we have:
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kbd_keycode(keycode) {
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...
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params.value = keycode;
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if (notifier_call_chain(KBD_KEYCODE,¶ms) == NOTIFY_STOP)
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|| !bound) {
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notifier_call_chain(KBD_UNBOUND_KEYCODE,¶ms);
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return;
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}
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if (unicode) {
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param.value = unicode;
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if (notifier_call_chain(KBD_UNICODE,¶ms) == NOTIFY_STOP)
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return;
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emit unicode;
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return;
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}
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params.value = keysym;
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if (notifier_call_chain(KBD_KEYSYM,¶ms) == NOTIFY_STOP)
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return;
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apply keysym;
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notifier_call_chain(KBD_POST_KEYSYM,¶ms);
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}
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NOTE: This notifier is usually called from interrupt context.