ospf6d: add an iterator for LSA descriptors

Adds iterator macros for the descriptors in an LSA, to replace the
number of repeated open coded pointer casts and pointer arithmetic.

Signed-off-by: Andrew Cooks <acooks.at.bda@gmail.com>

ospf6d/ospf6_lsa.h

@@ -116,6 +116,19 @@ inline uint16_t ospf6_lsa_size(struct ospf6_lsa_header *header)
 #define OSPF6_LSA_IS_CHANGED(L1, L2) ospf6_lsa_is_changed (L1, L2)
 #define OSPF6_LSA_IS_SEQWRAP(L) ((L)->header->seqnum == htonl(OSPF_MAX_SEQUENCE_NUMBER + 1))
 
+#define lsa_from_container(type, container)                                    \
+	((struct type *)((char *)container->header +                           \
+			 sizeof(struct ospf6_lsa_header)))
+
+#define lsdesc_start(lsdesc_type, lsa)                                         \
+	((struct lsdesc_type *)((char *)lsa + sizeof(*lsa)))
+
+#define for_each_lsdesc(current, lsa_type, lsdesc_type, lsa_container)          \
+	for (current =                                                          \
+		     lsdesc_start(lsdesc_type,                                  \
+				  lsa_from_container(lsa_type, lsa_container)); \
+	     (char *)(current + 1) <= ospf6_lsa_end(lsa_container->header);     \
+	     current++)
 
 struct ospf6_lsa {
 	char name[64]; /* dump string */