tracing: add ring_buffer_event_discard() to ring buffer

This patch overloads RINGBUF_TYPE_PADDING to provide a way to discard
events from the ring buffer, for the event-filtering mechanism
introduced in a subsequent patch.

I did the initial version but thanks to Steven Rostedt for adding
the parts that actually made it work. ;-)

Signed-off-by: Tom Zanussi <tzanussi@gmail.com>
Acked-by: Frederic Weisbecker <fweisbec@gmail.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 8 insertions, 3 deletions

diff --git a/include/linux/ring_buffer.h b/include/linux/ring_buffer.h
index 9e6052bd1a1c..e1b7b2173885 100644
--- a/include/linux/ring_buffer.h
+++ b/include/linux/ring_buffer.h
@@ -18,10 +18,13 @@ struct ring_buffer_event {
 /**
  * enum ring_buffer_type - internal ring buffer types
  *
- * @RINGBUF_TYPE_PADDING:       Left over page padding
- *                               array is ignored
- *                               size is variable depending on how much
+ * @RINGBUF_TYPE_PADDING:       Left over page padding or discarded event
+ *                               If time_delta is 0:
+ *                                array is ignored
+ *                                size is variable depending on how much
  *                                padding is needed
+ *                               If time_delta is non zero:
+ *                                everything else same as RINGBUF_TYPE_DATA
  *
  * @RINGBUF_TYPE_TIME_EXTEND:   Extend the time delta
  *                               array[0] = time delta (28 .. 59)
@@ -65,6 +68,8 @@ ring_buffer_event_time_delta(struct ring_buffer_event *event)
         return event->time_delta;
 }
 
+void ring_buffer_event_discard(struct ring_buffer_event *event);
+
 /*
  * size is in bytes for each per CPU buffer.
  */