neighbour: support for NTF_EXT_LEARNED flag

This patch extends NTF_EXT_LEARNED support to the neighbour system.
Example use-case: An Ethernet VPN implementation (eg in FRR routing suite)
can use this flag to add dynamic reachable external neigh entires
learned via control plane. The use of neigh NTF_EXT_LEARNED in this
patch is consistent with its use with bridge and vxlan fdb entries.

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

include/net/neighbour.h

@@ -246,6 +246,7 @@ static inline void *neighbour_priv(const struct neighbour *n)
 #define NEIGH_UPDATE_F_OVERRIDE			0x00000001
 #define NEIGH_UPDATE_F_WEAK_OVERRIDE		0x00000002
 #define NEIGH_UPDATE_F_OVERRIDE_ISROUTER	0x00000004
+#define NEIGH_UPDATE_F_EXT_LEARNED		0x20000000
 #define NEIGH_UPDATE_F_ISROUTER			0x40000000
 #define NEIGH_UPDATE_F_ADMIN			0x80000000
 
@@ -526,5 +527,21 @@ static inline void neigh_ha_snapshot(char *dst, const struct neighbour *n,
 	} while (read_seqretry(&n->ha_lock, seq));
 }
 
+static inline void neigh_update_ext_learned(struct neighbour *neigh, u32 flags,
+					    int *notify)
+{
+	u8 ndm_flags = 0;
 
+	if (!(flags & NEIGH_UPDATE_F_ADMIN))
+		return;
+
+	ndm_flags |= (flags & NEIGH_UPDATE_F_EXT_LEARNED) ? NTF_EXT_LEARNED : 0;
+	if ((neigh->flags ^ ndm_flags) & NTF_EXT_LEARNED) {
+		if (ndm_flags & NTF_EXT_LEARNED)
+			neigh->flags |= NTF_EXT_LEARNED;
+		else
+			neigh->flags &= ~NTF_EXT_LEARNED;
+		*notify = 1;
+	}
+}
 #endif

net/core/neighbour.c

@@ -820,7 +820,8 @@ static void neigh_periodic_work(struct work_struct *work)
 			write_lock(&n->lock);
 
 			state = n->nud_state;
-			if (state & (NUD_PERMANENT | NUD_IN_TIMER)) {
+			if ((state & (NUD_PERMANENT | NUD_IN_TIMER)) ||
+			    (n->flags & NTF_EXT_LEARNED)) {
 				write_unlock(&n->lock);
 				goto next_elt;
 			}
@@ -1136,6 +1137,8 @@ int neigh_update(struct neighbour *neigh, const u8 *lladdr, u8 new,
 	if (neigh->dead)
 		goto out;
 
+	neigh_update_ext_learned(neigh, flags, &notify);
+
 	if (!(new & NUD_VALID)) {
 		neigh_del_timer(neigh);
 		if (old & NUD_CONNECTED)
@@ -1781,6 +1784,9 @@ static int neigh_add(struct sk_buff *skb, struct nlmsghdr *nlh,
 			flags &= ~NEIGH_UPDATE_F_OVERRIDE;
 	}
 
+	if (ndm->ndm_flags & NTF_EXT_LEARNED)
+		flags |= NEIGH_UPDATE_F_EXT_LEARNED;
+
 	if (ndm->ndm_flags & NTF_USE) {
 		neigh_event_send(neigh, NULL);
 		err = 0;