ipv4: Refactor nexthop attributes in fib_dump_info

Similar to ipv6, move addition of nexthop attributes to dump
message into helpers that are called for both single path and
multipath routes. Align the new helpers to the IPv6 variant
which most notably means computing the flags argument based on
settings in nh_flags.

The RTA_FLOW argument is unique to IPv4, so it is appended after
the new fib_nexthop_info helper. The intent of a later patch is to
make both fib_nexthop_info and fib_add_nexthop usable for both IPv4
and IPv6. This patch is stepping stone in that direction.
Signed-off-by: David Ahern <dsahern@gmail.com>
Acked-by: Martin KaFai Lau <kafai@fb.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv4/fib_semantics.c

@@ -1317,6 +1317,103 @@ struct fib_info *fib_create_info(struct fib_config *cfg,
 	return ERR_PTR(err);
 }
 
+static int fib_nexthop_info(struct sk_buff *skb, const struct fib_nh *nh,
+			    unsigned int *flags, bool skip_oif)
+{
+	if (nh->fib_nh_flags & RTNH_F_DEAD)
+		*flags |= RTNH_F_DEAD;
+
+	if (nh->fib_nh_flags & RTNH_F_LINKDOWN) {
+		*flags |= RTNH_F_LINKDOWN;
+
+		rcu_read_lock();
+		if (ip_ignore_linkdown(nh->fib_nh_dev))
+			*flags |= RTNH_F_DEAD;
+		rcu_read_unlock();
+	}
+
+	if (nh->fib_nh_gw4 &&
+	    nla_put_in_addr(skb, RTA_GATEWAY, nh->fib_nh_gw4))
+		goto nla_put_failure;
+
+	*flags |= (nh->fib_nh_flags & RTNH_F_ONLINK);
+	if (nh->fib_nh_flags & RTNH_F_OFFLOAD)
+		*flags |= RTNH_F_OFFLOAD;
+
+	if (!skip_oif && nh->fib_nh_dev &&
+	    nla_put_u32(skb, RTA_OIF, nh->fib_nh_dev->ifindex))
+		goto nla_put_failure;
+
+	if (nh->fib_nh_lws &&
+	    lwtunnel_fill_encap(skb, nh->fib_nh_lws) < 0)
+		goto nla_put_failure;
+
+	return 0;
+
+nla_put_failure:
+	return -EMSGSIZE;
+}
+
+#ifdef CONFIG_IP_ROUTE_MULTIPATH
+static int fib_add_nexthop(struct sk_buff *skb, const struct fib_nh *nh)
+{
+	const struct net_device *dev = nh->fib_nh_dev;
+	struct rtnexthop *rtnh;
+	unsigned int flags = 0;
+
+	rtnh = nla_reserve_nohdr(skb, sizeof(*rtnh));
+	if (!rtnh)
+		goto nla_put_failure;
+
+	rtnh->rtnh_hops = nh->fib_nh_weight - 1;
+	rtnh->rtnh_ifindex = dev ? dev->ifindex : 0;
+
+	if (fib_nexthop_info(skb, nh, &flags, true) < 0)
+		goto nla_put_failure;
+
+	rtnh->rtnh_flags = flags;
+
+	/* length of rtnetlink header + attributes */
+	rtnh->rtnh_len = nlmsg_get_pos(skb) - (void *)rtnh;
+
+	return 0;
+
+nla_put_failure:
+	return -EMSGSIZE;
+}
+
+static int fib_add_multipath(struct sk_buff *skb, struct fib_info *fi)
+{
+	struct nlattr *mp;
+
+	mp = nla_nest_start(skb, RTA_MULTIPATH);
+	if (!mp)
+		goto nla_put_failure;
+
+	for_nexthops(fi) {
+		if (fib_add_nexthop(skb, nh) < 0)
+			goto nla_put_failure;
+#ifdef CONFIG_IP_ROUTE_CLASSID
+		if (nh->nh_tclassid &&
+		    nla_put_u32(skb, RTA_FLOW, nh->nh_tclassid))
+			goto nla_put_failure;
+#endif
+	} endfor_nexthops(fi);
+
+	nla_nest_end(skb, mp);
+
+	return 0;
+
+nla_put_failure:
+	return -EMSGSIZE;
+}
+#else
+static int fib_add_multipath(struct sk_buff *skb, struct fib_info *fi)
+{
+	return 0;
+}
+#endif
+
 int fib_dump_info(struct sk_buff *skb, u32 portid, u32 seq, int event,
 		  u32 tb_id, u8 type, __be32 dst, int dst_len, u8 tos,
 		  struct fib_info *fi, unsigned int flags)
@@ -1357,72 +1454,23 @@ int fib_dump_info(struct sk_buff *skb, u32 portid, u32 seq, int event,
 	    nla_put_in_addr(skb, RTA_PREFSRC, fi->fib_prefsrc))
 		goto nla_put_failure;
 	if (fi->fib_nhs == 1) {
-		if (fi->fib_nh->fib_nh_gw4 &&
-		    nla_put_in_addr(skb, RTA_GATEWAY, fi->fib_nh->fib_nh_gw4))
-			goto nla_put_failure;
-		if (fi->fib_nh->fib_nh_oif &&
-		    nla_put_u32(skb, RTA_OIF, fi->fib_nh->fib_nh_oif))
+		struct fib_nh *nh = &fi->fib_nh[0];
+		unsigned int flags = 0;
+
+		if (fib_nexthop_info(skb, nh, &flags, false) < 0)
 			goto nla_put_failure;
-		if (fi->fib_nh->fib_nh_flags & RTNH_F_LINKDOWN) {
-			rcu_read_lock();
-			if (ip_ignore_linkdown(fi->fib_nh->fib_nh_dev))
-				rtm->rtm_flags |= RTNH_F_DEAD;
-			rcu_read_unlock();
-		}
-		if (fi->fib_nh->fib_nh_flags & RTNH_F_OFFLOAD)
-			rtm->rtm_flags |= RTNH_F_OFFLOAD;
+
+		rtm->rtm_flags = flags;
 #ifdef CONFIG_IP_ROUTE_CLASSID
-		if (fi->fib_nh[0].nh_tclassid &&
-		    nla_put_u32(skb, RTA_FLOW, fi->fib_nh[0].nh_tclassid))
+		if (nh->nh_tclassid &&
+		    nla_put_u32(skb, RTA_FLOW, nh->nh_tclassid))
 			goto nla_put_failure;
 #endif
-		if (fi->fib_nh->fib_nh_lws &&
-		    lwtunnel_fill_encap(skb, fi->fib_nh->fib_nh_lws) < 0)
+	} else {
+		if (fib_add_multipath(skb, fi) < 0)
 			goto nla_put_failure;
 	}
-#ifdef CONFIG_IP_ROUTE_MULTIPATH
-	if (fi->fib_nhs > 1) {
-		struct rtnexthop *rtnh;
-		struct nlattr *mp;
-
-		mp = nla_nest_start(skb, RTA_MULTIPATH);
-		if (!mp)
-			goto nla_put_failure;
 
-		for_nexthops(fi) {
-			rtnh = nla_reserve_nohdr(skb, sizeof(*rtnh));
-			if (!rtnh)
-				goto nla_put_failure;
-
-			rtnh->rtnh_flags = nh->fib_nh_flags & 0xFF;
-			if (nh->fib_nh_flags & RTNH_F_LINKDOWN) {
-				rcu_read_lock();
-				if (ip_ignore_linkdown(nh->fib_nh_dev))
-					rtnh->rtnh_flags |= RTNH_F_DEAD;
-				rcu_read_unlock();
-			}
-			rtnh->rtnh_hops = nh->fib_nh_weight - 1;
-			rtnh->rtnh_ifindex = nh->fib_nh_oif;
-
-			if (nh->fib_nh_gw4 &&
-			    nla_put_in_addr(skb, RTA_GATEWAY, nh->fib_nh_gw4))
-				goto nla_put_failure;
-#ifdef CONFIG_IP_ROUTE_CLASSID
-			if (nh->nh_tclassid &&
-			    nla_put_u32(skb, RTA_FLOW, nh->nh_tclassid))
-				goto nla_put_failure;
-#endif
-			if (nh->fib_nh_lws &&
-			    lwtunnel_fill_encap(skb, nh->fib_nh_lws) < 0)
-				goto nla_put_failure;
-
-			/* length of rtnetlink header + attributes */
-			rtnh->rtnh_len = nlmsg_get_pos(skb) - (void *) rtnh;
-		} endfor_nexthops(fi);
-
-		nla_nest_end(skb, mp);
-	}
-#endif
 	nlmsg_end(skb, nlh);
 	return 0;