libnetlink: introduce rta_nest and u8, u16, u64 helpers for nesting within rtattr

This patch introduces two new api's rta_nest and rta_nest_end to
nest attributes inside a rta attribute represented by 'struct rtattr'
as required to construct a nexthop. Also adds rta_addattr* variants
for u8, u16 and u64 as needed to support encapsulation.
Signed-off-by: Roopa Prabhu <roopa@cumulusnetworks.com>
Signed-off-by: Thomas Graf <tgraf@suug.ch>
Acked-by: Jiri Benc <jbenc@redhat.com>

include/libnetlink.h

@@ -86,7 +86,10 @@ int addattr_nest_end(struct nlmsghdr *n, struct rtattr *nest);
 struct rtattr *addattr_nest_compat(struct nlmsghdr *n, int maxlen, int type,
 				   const void *data, int len);
 int addattr_nest_compat_end(struct nlmsghdr *n, struct rtattr *nest);
+int rta_addattr8(struct rtattr *rta, int maxlen, int type, __u8 data);
+int rta_addattr16(struct rtattr *rta, int maxlen, int type, __u16 data);
 int rta_addattr32(struct rtattr *rta, int maxlen, int type, __u32 data);
+int rta_addattr64(struct rtattr *rta, int maxlen, int type, __u64 data);
 int rta_addattr_l(struct rtattr *rta, int maxlen, int type,
 		  const void *data, int alen);
 
@@ -98,6 +101,13 @@ int parse_rtattr_byindex(struct rtattr *tb[], int max,
 struct rtattr *parse_rtattr_one(int type, struct rtattr *rta, int len);
 int __parse_rtattr_nested_compat(struct rtattr *tb[], int max, struct rtattr *rta, int len);
 
+struct rtattr *rta_nest(struct rtattr *rta, int maxlen, int type);
+int rta_nest_end(struct rtattr *rta, struct rtattr *nest);
+
+#define RTA_TAIL(rta) \
+		((struct rtattr *) (((void *) (rta)) + \
+				    RTA_ALIGN((rta)->rta_len)))
+
 #define parse_rtattr_nested(tb, max, rta) \
 	(parse_rtattr((tb), (max), RTA_DATA(rta), RTA_PAYLOAD(rta)))
 

lib/libnetlink.c

@@ -721,6 +721,37 @@ int rta_addattr_l(struct rtattr *rta, int maxlen, int type,
 	return 0;
 }
 
+int rta_addattr8(struct rtattr *rta, int maxlen, int type, __u8 data)
+{
+	return rta_addattr_l(rta, maxlen, type, &data, sizeof(__u8));
+}
+
+int rta_addattr16(struct rtattr *rta, int maxlen, int type, __u16 data)
+{
+	return rta_addattr_l(rta, maxlen, type, &data, sizeof(__u16));
+}
+
+int rta_addattr64(struct rtattr *rta, int maxlen, int type, __u64 data)
+{
+	return rta_addattr_l(rta, maxlen, type, &data, sizeof(__u64));
+}
+
+struct rtattr *rta_nest(struct rtattr *rta, int maxlen, int type)
+{
+	struct rtattr *nest = RTA_TAIL(rta);
+
+	rta_addattr_l(rta, maxlen, type, NULL, 0);
+
+	return nest;
+}
+
+int rta_nest_end(struct rtattr *rta, struct rtattr *nest)
+{
+	nest->rta_len = (void *)RTA_TAIL(rta) - (void *)nest;
+
+	return rta->rta_len;
+}
+
 int parse_rtattr(struct rtattr *tb[], int max, struct rtattr *rta, int len)
 {
 	return parse_rtattr_flags(tb, max, rta, len, 0);