tools lib traceevent: Add way to find sub buffer boundary

For debugging purposes, it may be helpful for the kbuffer library to flag
when crossing a sub buffer.

Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Link: http://lkml.kernel.org/r/20150324135923.650983637@goodmis.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/lib/traceevent/kbuffer-parse.c

@@ -729,3 +729,14 @@ void kbuffer_set_old_format(struct kbuffer *kbuf)
 
 	kbuf->next_event = __old_next_event;
 }
+
+/**
+ * kbuffer_start_of_data - return offset of where data starts on subbuffer
+ * @kbuf:	The kbuffer
+ *
+ * Returns the location on the subbuffer where the data starts.
+ */
+int kbuffer_start_of_data(struct kbuffer *kbuf)
+{
+	return kbuf->start;
+}