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 <[e-mail]>
Cc: Andrew Morton <[e-mail]>
Cc: Jiri Olsa <[e-mail]>
Cc: Namhyung Kim <[e-mail]>
Link: http://lkml.kernel.org/r/[e-mail]
Signed-off-by: Arnaldo Carvalho de Melo <[e-mail]>

tools/lib/traceevent/kbuffer-parse.c

···
 
 	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;
+}

tools/lib/traceevent/kbuffer.h

···
 int kbuffer_subbuffer_size(struct kbuffer *kbuf);
 
 void kbuffer_set_old_format(struct kbuffer *kbuf);
+int kbuffer_start_of_data(struct kbuffer *kbuf);
 
 #endif /* _K_BUFFER_H */