server: Allow async i/o operations to send completion messages.
diff --git a/server/protocol.def b/server/protocol.def
index 90e943b..93e4887 100644
--- a/server/protocol.def
+++ b/server/protocol.def
@@ -179,6 +179,7 @@
     void           *arg;           /* opaque user data to pass to callback */
     void           *apc;           /* user apc to call */
     obj_handle_t    event;         /* event to signal when done */
+    unsigned long   cvalue;        /* completion value to use for completion events */
 } async_data_t;
 
 /* structures for extra message data */