ipmr, ip6mr: add RTNH_F_UNRESOLVED flag to unresolved cache entries

While working with ipmr, we noticed that it is impossible to determine
if an entry is actually unresolved or its IIF interface has disappeared
(e.g. virtual interface got deleted). These entries look almost
identical to user-space when dumping or receiving notifications. So in
order to recognize them add a new RTNH_F_UNRESOLVED flag which is set when
sending an unresolved cache entry to user-space.

Suggested-by: Roopa Prabhu <roopa@cumulusnetworks.com>
Signed-off-by: Nikolay Aleksandrov <nikolay@cumulusnetworks.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/uapi/linux/rtnetlink.h

@@ -350,6 +350,7 @@ struct rtnexthop {
 #define RTNH_F_ONLINK		4	/* Gateway is forced on link	*/
 #define RTNH_F_OFFLOAD		8	/* offloaded route */
 #define RTNH_F_LINKDOWN		16	/* carrier-down on nexthop */
+#define RTNH_F_UNRESOLVED	32	/* The entry is unresolved (ipmr) */
 
 #define RTNH_COMPARE_MASK	(RTNH_F_DEAD | RTNH_F_LINKDOWN | RTNH_F_OFFLOAD)
 

net/ipv4/ipmr.c

@@ -2091,8 +2091,10 @@ static int __ipmr_fill_mroute(struct mr_table *mrt, struct sk_buff *skb,
 	int ct;
 
 	/* If cache is unresolved, don't try to parse IIF and OIF */
-	if (c->mfc_parent >= MAXVIFS)
+	if (c->mfc_parent >= MAXVIFS) {
+		rtm->rtm_flags |= RTNH_F_UNRESOLVED;
 		return -ENOENT;
+	}
 
 	if (VIF_EXISTS(mrt, c->mfc_parent) &&
 	    nla_put_u32(skb, RTA_IIF, mrt->vif_table[c->mfc_parent].dev->ifindex) < 0)

net/ipv6/ip6mr.c

@@ -2243,8 +2243,10 @@ static int __ip6mr_fill_mroute(struct mr6_table *mrt, struct sk_buff *skb,
 	int ct;
 
 	/* If cache is unresolved, don't try to parse IIF and OIF */
-	if (c->mf6c_parent >= MAXMIFS)
+	if (c->mf6c_parent >= MAXMIFS) {
+		rtm->rtm_flags |= RTNH_F_UNRESOLVED;
 		return -ENOENT;
+	}
 
 	if (MIF_EXISTS(mrt, c->mf6c_parent) &&
 	    nla_put_u32(skb, RTA_IIF, mrt->vif6_table[c->mf6c_parent].dev->ifindex) < 0)