=================
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 (see <linux/keyboard.h>):

- '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_*;
- 'ledstate' is the current LED state;
- '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.
'linux-2.6.26.y'>linux-2.6.26.y</option>
<option value='linux-2.6.27.y'>linux-2.6.27.y</option>
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<tr><td class='sub'>Hosts the 0x221E linux distro kernel.</td><td class='sub right'>Ubuntu</td></tr></table>
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<div class='path'>path: <a href='/distro/kernel/log/?id=b7ee79abcc1bd549eadf5a9852657058e6ecca47'>root</a>/<a href='/distro/kernel/log/tools?id=b7ee79abcc1bd549eadf5a9852657058e6ecca47'>tools</a>/<a href='/distro/kernel/log/tools/perf?id=b7ee79abcc1bd549eadf5a9852657058e6ecca47'>perf</a>/<a href='/distro/kernel/log/tools/perf/scripts?id=b7ee79abcc1bd549eadf5a9852657058e6ecca47'>scripts</a>/<a href='/distro/kernel/log/tools/perf/scripts/python?id=b7ee79abcc1bd549eadf5a9852657058e6ecca47'>python</a>/<a href='/distro/kernel/log/tools/perf/scripts/python/check-perf-trace.py?id=b7ee79abcc1bd549eadf5a9852657058e6ecca47'>check-perf-trace.py</a></div><div class='content'><table class='list nowrap'><tr class='nohover'><th class='left'>Age</th><th class='left'>Commit message (<a href='/distro/kernel/log/tools/perf/scripts/python/check-perf-trace.py?id=b7ee79abcc1bd549eadf5a9852657058e6ecca47&amp;showmsg=1'>Expand</a>)</th><th class='left'>Author</th></tr>
<tr><td><span title='2010-12-25 11:29:02 -0200'>2010-12-25</span></td><td><a href='/distro/kernel/commit/tools/perf/scripts/python/check-perf-trace.py?id=765532c8aaac624b5f8687af6d319c6a1138a257'>perf script: Finish the rename from trace to script</a></td><td>Arnaldo Carvalho de Melo</td></tr>
<tr><td><span title='2010-06-01 06:12:35 -0300'>2010-06-01</span></td><td><a href='/distro/kernel/commit/tools/perf/scripts/python/check-perf-trace.py?id=c02514850d67be8db6b2b6658cbc23ac1fbf8bc7'>perf scripts python: Give field dict to unhandled callback</a></td><td>Pierre Tardy</td></tr>
<tr><td><span title='2010-02-25 04:07:48 +0100'>2010-02-25</span></td><td><a href='/distro/kernel/commit/tools/perf/scripts/python/check-perf-trace.py?id=4d161f0360d00d46a89827b3fd6da395f00c5d90'>perf/scripts: Add syscall tracing scripts</a></td><td>Tom Zanussi</td></tr>