zebra: fix detection of interface renames

Restore the original logic in netlink_link_change() which works like this:
* once an interface event is detected, lookup the associated interface
  by its name;
* call the set_ifindex() function;
* set_ifindex() will lookup the interface again but now by its ifindex. If
  the lookups by name and ifindex yield to different results, then the
  interface was renamed and set_ifindex() will take care of that.

In the future, zns->if_table will be split into two different data
structures to allow faster lookups by both name and ifindex.

Fixes Issue #397.

Regression introduced by commit 12f6fb9.

Signed-off-by: Renato Westphal <renato@opensourcerouting.org>

zebra/if_netlink.c

@@ -746,7 +746,7 @@ netlink_link_change (struct sockaddr_nl *snl, struct nlmsghdr *h,
     }
 
   /* See if interface is present. */
-  ifp = if_lookup_by_index_per_ns (zns, ifi->ifi_index);
+  ifp = if_lookup_by_name_per_ns (zns, name);
 
   if (h->nlmsg_type == RTM_NEWLINK)
     {

zebra/interface.c

@@ -211,6 +211,23 @@ if_lookup_by_index_per_ns (struct zebra_ns *ns, u_int32_t ifindex)
   return ifp;
 }
 
+/* Look up an interface by name within a NS */
+struct interface *
+if_lookup_by_name_per_ns (struct zebra_ns *ns, const char *ifname)
+{
+  struct route_node *rn;
+  struct interface *ifp;
+
+  for (rn = route_top (ns->if_table); rn; rn = route_next (rn))
+    {
+      ifp = (struct interface *)rn->info;
+      if (ifp && strcmp (ifp->name, ifname) == 0)
+	return (ifp);
+    }
+
+  return NULL;
+}
+
 const char *
 ifindex2ifname_per_ns (struct zebra_ns *zns, unsigned int ifindex)
 {

zebra/interface.h

@@ -236,6 +236,7 @@ struct zebra_if
 
 
 extern struct interface *if_lookup_by_index_per_ns (struct zebra_ns *, u_int32_t);
+extern struct interface *if_lookup_by_name_per_ns (struct zebra_ns *, const char *);
 extern struct interface *if_link_per_ns (struct zebra_ns *, struct interface *);
 extern const char *ifindex2ifname_per_ns (struct zebra_ns *, unsigned int);