+/* ofproto_flow_mod() returns this value if the flow_mod could not be processed
+ * because it overlaps with an ongoing flow table operation that has not yet
+ * completed. The caller should retry the operation later.
+ *
+ * ofproto.c also uses this value internally for additional (similar) purposes.
+ *
+ * This particular value is a good choice because it is negative (so it won't
+ * collide with any errno value or any value returned by ofp_mkerr()) and large
+ * (so it won't accidentally collide with EOF or a negative errno value). */
+enum { OFPROTO_POSTPONE = -100000 };
+
+int ofproto_flow_mod(struct ofproto *, const struct ofputil_flow_mod *);