tracing: Add an 'overwrite' trace_option.

Add an "overwrite" trace_option for ftrace to control whether the buffer should
be overwritten on overflow or not. The default remains to overwrite old events
when the buffer is full. This patch adds the option to instead discard newest
events when the buffer is full. This is useful to get a snapshot of traces just
after enabling traces. Dropping the current event is also a simpler code path.

Signed-off-by: David Sharp <dhsharp@google.com>
LKML-Reference: <1291844807-15481-1-git-send-email-dhsharp@google.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

1 files changed, 2 insertions, 0 deletions

diff --git a/include/linux/ring_buffer.h b/include/linux/ring_buffer.h
index 8d3a2486544d..ab38ac80b0f9 100644
--- a/include/linux/ring_buffer.h
+++ b/include/linux/ring_buffer.h
@@ -100,6 +100,8 @@ void ring_buffer_free(struct ring_buffer *buffer);
 
 int ring_buffer_resize(struct ring_buffer *buffer, unsigned long size);
 
+void ring_buffer_change_overwrite(struct ring_buffer *buffer, int val);
+
 struct ring_buffer_event *ring_buffer_lock_reserve(struct ring_buffer *buffer,
                                                    unsigned long length);
 int ring_buffer_unlock_commit(struct ring_buffer *buffer,