zebra: add iterator for walking all tables in RIB

* lib/zebra.h

    Add macro ZEBRA_NUM_OF, which returns the number of elements in a
    static array.

  * zebra/rib.h

    Add the rib_tables_iter_t structure and associated functions,
    which allow one to walk all tables in the rib.

  * zebra/zebra_rib.c

    - Add vrf_id_get_next() to retrieve the first VRF id (if any) that
      is greater than a given VRF id.

    - Add rib_tables_iter_next().

Signed-off-by: Avneesh Sachdev <avneesh@opensourcerouting.org>
Signed-off-by: David Lamparter <equinox@opensourcerouting.org>
diff --git a/zebra/rib.h b/zebra/rib.h
index c98d99a..4f99d71 100644
--- a/zebra/rib.h
+++ b/zebra/rib.h
@@ -286,6 +286,25 @@
 
 } rib_table_info_t;
 
+typedef enum
+{
+  RIB_TABLES_ITER_S_INIT,
+  RIB_TABLES_ITER_S_ITERATING,
+  RIB_TABLES_ITER_S_DONE
+} rib_tables_iter_state_t;
+
+/*
+ * Structure that holds state for iterating over all tables in the
+ * Routing Information Base.
+ */
+typedef struct rib_tables_iter_t_
+{
+  uint32_t vrf_id;
+  int afi_safi_ix;
+
+  rib_tables_iter_state_t state;
+} rib_tables_iter_t;
+
 extern struct nexthop *nexthop_ifindex_add (struct rib *, unsigned int);
 extern struct nexthop *nexthop_ifname_add (struct rib *, char *);
 extern struct nexthop *nexthop_blackhole_add (struct rib *);
@@ -374,6 +393,7 @@
 #endif /* HAVE_IPV6 */
 
 extern int rib_gc_dest (struct route_node *rn);
+extern struct route_table *rib_tables_iter_next (rib_tables_iter_t *iter);
 
 /*
  * Inline functions.
@@ -453,4 +473,36 @@
   return rib_table_info (rib_dest_table (dest))->vrf;
 }
 
+/*
+ * rib_tables_iter_init
+ */
+static inline void
+rib_tables_iter_init (rib_tables_iter_t *iter)
+
+{
+  memset (iter, 0, sizeof (*iter));
+  iter->state = RIB_TABLES_ITER_S_INIT;
+}
+
+/*
+ * rib_tables_iter_started
+ *
+ * Returns TRUE if this iterator has started iterating over the set of
+ * tables.
+ */
+static inline int
+rib_tables_iter_started (rib_tables_iter_t *iter)
+{
+  return iter->state != RIB_TABLES_ITER_S_INIT;
+}
+
+/*
+ * rib_tables_iter_cleanup
+ */
+static inline void
+rib_tables_iter_cleanup (rib_tables_iter_t *iter)
+{
+  iter->state = RIB_TABLES_ITER_S_DONE;
+}
+
 #endif /*_ZEBRA_RIB_H */