tracing: expand the ring buffers when an event is activated

To save memory, the tracer ring buffers are set to a minimum.
The activating of a trace expands the ring buffer size. This patch
adds this expanding, when an event is activated.

Signed-off-by: Steven Rostedt <srostedt@redhat.com>
diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
index c5e1d88..336324d 100644
--- a/kernel/trace/trace.h
+++ b/kernel/trace/trace.h
@@ -737,6 +737,9 @@
 }
 #endif /* CONFIG_BRANCH_TRACER */
 
+/* set ring buffers to default size if not already done so */
+int tracing_update_buffers(void);
+
 /* trace event type bit fields, not numeric */
 enum {
 	TRACE_EVENT_TYPE_PRINTF		= 1,