tracing: Add missing forward declaration

Without this forward declaration compile may fail if this header is
included only for registering other probe event without struct
pool_workqueue.

Link: http://lkml.kernel.org/r/20180416023626.139915-1-cwahbong@google.com
Reviewed-by: Todd Poynor <toddpoynor@google.com>
Signed-off-by: Ahbong Chang <cwahbong@google.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>

diff --git a/include/trace/events/workqueue.h b/include/trace/events/workqueue.h
index 2f057a4..9a761bc 100644 (file)
--- a/include/trace/events/workqueue.h
+++ b/include/trace/events/workqueue.h
@@ -25,6 +25,8 @@ DECLARE_EVENT_CLASS(workqueue_work,
        TP_printk("work struct %p", __entry->work)
 );
 
+struct pool_workqueue;
+
 /**
  * workqueue_queue_work - called when a work gets queued
  * @req_cpu:   the requested cpu