[PATCH 6/7] pasta: Disable neighbour solicitations on device up to prevent DAD

[Stefano Brivio <sbrivio@redhat.com>]

As soon as we the kernel notifier for IPv6 address configuration
(addrconf_notify()) sees that we bring the target interface up
(NETDEV_UP), it will schedule duplicate address detection, so, by
itself, setting the nodad flag later is useless, because that won't
stop a detection that's already in progress.

However, if we disable neighbour solicitations with IFF_NOARP (which
is a misnomer for IPv6 interfaces, but there's no possibility of
mixing things up), the notifier will not trigger DAD, because it can't
be done, of course, without neighbour solicitations.

Set IFF_NOARP as we bring up the device, and drop it after we had a
chance to set the nodad attribute on the link.

Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
---
 pasta.c | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/pasta.c b/pasta.c
index cebf54f..babbfd5 100644
--- a/pasta.c
+++ b/pasta.c
@@ -303,10 +303,15 @@ void pasta_ns_conf(struct ctx *c)
 		    strerror(-rc));
 
 	if (c->pasta_conf_ns) {
+		unsigned int flags = IFF_UP;
+
 		if (c->mtu != -1)
 			nl_link_set_mtu(nl_sock_ns, c->pasta_ifi, c->mtu);
 
-		nl_link_set_flags(nl_sock_ns, c->pasta_ifi, IFF_UP, IFF_UP);
+		if (c->ifi6) /* Avoid duplicate address detection on link up */
+			flags |= IFF_NOARP;
+
+		nl_link_set_flags(nl_sock_ns, c->pasta_ifi, flags, flags);
 
 		if (c->ifi4) {
 			if (c->ip4.no_copy_addrs) {
@@ -353,6 +358,10 @@ void pasta_ns_conf(struct ctx *c)
 				    strerror(-rc));
 			}
 
+			/* We dodged DAD: re-enable neighbour solicitations */
+			nl_link_set_flags(nl_sock_ns, c->pasta_ifi,
+					  0, IFF_NOARP);
+
 			if (c->ip6.no_copy_addrs) {
 				rc = nl_addr_set(nl_sock_ns, c->pasta_ifi,
 						 AF_INET6, &c->ip6.addr, 64);
-- 
@@ -303,10 +303,15 @@ void pasta_ns_conf(struct ctx *c)
 		    strerror(-rc));
 
 	if (c->pasta_conf_ns) {
+		unsigned int flags = IFF_UP;
+
 		if (c->mtu != -1)
 			nl_link_set_mtu(nl_sock_ns, c->pasta_ifi, c->mtu);
 
-		nl_link_set_flags(nl_sock_ns, c->pasta_ifi, IFF_UP, IFF_UP);
+		if (c->ifi6) /* Avoid duplicate address detection on link up */
+			flags |= IFF_NOARP;
+
+		nl_link_set_flags(nl_sock_ns, c->pasta_ifi, flags, flags);
 
 		if (c->ifi4) {
 			if (c->ip4.no_copy_addrs) {
@@ -353,6 +358,10 @@ void pasta_ns_conf(struct ctx *c)
 				    strerror(-rc));
 			}
 
+			/* We dodged DAD: re-enable neighbour solicitations */
+			nl_link_set_flags(nl_sock_ns, c->pasta_ifi,
+					  0, IFF_NOARP);
+
 			if (c->ip6.no_copy_addrs) {
 				rc = nl_addr_set(nl_sock_ns, c->pasta_ifi,
 						 AF_INET6, &c->ip6.addr, 64);
-- 
2.43.0