perf: Allow for custom overflow handlers

in-kernel perf users might wish to have custom actions on the
sample interrupt.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Paul Mackerras <paulus@samba.org>
LKML-Reference: <20091120212508.222339539@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

kernel/perf_event.c

@@ -3710,7 +3710,11 @@ static int __perf_event_overflow(struct perf_event *event, int nmi,
 			perf_event_disable(event);
 	}
 
-	perf_event_output(event, nmi, data, regs);
+	if (event->overflow_handler)
+		event->overflow_handler(event, nmi, data, regs);
+	else
+		perf_event_output(event, nmi, data, regs);
+
 	return ret;
 }
 
@@ -4836,6 +4840,8 @@ inherit_event(struct perf_event *parent_event,
 	if (parent_event->attr.freq)
 		child_event->hw.sample_period = parent_event->hw.sample_period;
 
+	child_event->overflow_handler = parent_event->overflow_handler;
+
 	/*
 	 * Link it up in the child's context:
 	 */