ipvs: preparations for using rcu in schedulers

Allow schedulers to use rcu_dereference when
returning destination on lookup. The RCU read-side critical
section will allow ip_vs_bind_dest to get dest refcnt as
preparation for the step where destinations will be
deleted without an IP_VS_WAIT_WHILE guard that holds the
packet processing during update.

	Add new optional scheduler methods add_dest,
del_dest and upd_dest. For now the methods are called
together with update_service but update_service will be
removed in a following change.

Signed-off-by: Julian Anastasov <ja@ssi.bg>
Signed-off-by: Simon Horman <horms@verge.net.au>
diff --git a/include/net/ip_vs.h b/include/net/ip_vs.h
index 43886bb..d91385c 100644
--- a/include/net/ip_vs.h
+++ b/include/net/ip_vs.h
@@ -805,6 +805,12 @@
 	int (*done_service)(struct ip_vs_service *svc);
 	/* scheduler updating service */
 	int (*update_service)(struct ip_vs_service *svc);
+	/* dest is linked */
+	int (*add_dest)(struct ip_vs_service *svc, struct ip_vs_dest *dest);
+	/* dest is unlinked */
+	int (*del_dest)(struct ip_vs_service *svc, struct ip_vs_dest *dest);
+	/* dest is updated */
+	int (*upd_dest)(struct ip_vs_service *svc, struct ip_vs_dest *dest);
 
 	/* selecting a server from the given service */
 	struct ip_vs_dest* (*schedule)(struct ip_vs_service *svc,