[PATCH v4 02/12] ip: Introduce for_each_addr() macro for address iteration

[Jon Maloy <jmaloy@redhat.com>]

Add the for_each_addr() macro to iterate over addresses in the unified
array. The macro supports an address family filter parameter (AF_INET,
AF_INET6, or 0 for all) using a _next_addr_idx() helper function to
skip non-matching entries.

Signed-off-by: Jon Maloy <jmaloy@redhat.com>

---
v1: - Broke out as separate commit
    - I kept the third argument, despite David's comment, since I still
      find it practical. If we want to iterate the list without filter
      we can just use AF_UNSPEC (== 0)
---
 passt.h | 34 ++++++++++++++++++++++++++++++++++
 1 file changed, 34 insertions(+)

diff --git a/passt.h b/passt.h
index 2a78ff5..15d6596 100644
--- a/passt.h
+++ b/passt.h
@@ -342,6 +342,40 @@ static inline int inany_prefix4(const struct inany_addr_entry *e)
 	return e->prefix_len - 96;
 }
 
+/**
+ * _next_addr_idx() - Find next address index matching family filter
+ * @c:		Pointer to struct ctx
+ * @i:		Starting index
+ * @af:		Address family filter: AF_INET, AF_INET6, or 0 for all
+ *
+ * Return: next matching index, or addr_count if none found
+ */
+static inline int _next_addr_idx(const struct ctx *c, int i, sa_family_t af)
+{
+	for (; i < c->addr_count; i++) {
+		sa_family_t entry_af;
+
+		entry_af = inany_v4(&c->addrs[i].addr) ? AF_INET : AF_INET6;
+
+		if (!af || af == entry_af)
+			return i;
+	}
+	return i;
+}
+
+/**
+ * for_each_addr() - Iterate over addresses in unified array
+ * @e:		Pointer variable for current entry (struct inany_addr_entry *)
+ * @c:		Pointer to struct ctx
+ * @af:		Address family filter: AF_INET, AF_INET6, or 0 for all
+ *
+ * Note: @_i is the internal loop counter, uses _next_addr_idx() helper
+ */
+#define for_each_addr(e, c, af)						\
+	for (int _i = _next_addr_idx((c), 0, (af));			\
+	     _i < (c)->addr_count && ((e) = &(c)->addrs[_i], true);	\
+	     _i = _next_addr_idx((c), _i + 1, (af)))
+
 void proto_update_l2_buf(const unsigned char *eth_d);
 
 #endif /* PASST_H */
-- 
2.52.0