lib: Show tunnel egress interface in ovsdb

This commit parses rtnetlink address notifications from the
kernel in order to display the egress interface of tunnels in the
database.

Bug #4103.

Author: ejj

lib/automake.mk

@@ -191,7 +191,9 @@ lib_libopenvswitch_a_SOURCES += \
 	lib/rtnetlink.c \
 	lib/rtnetlink.h \
 	lib/rtnetlink-link.c \
-	lib/rtnetlink-link.h
+	lib/rtnetlink-link.h \
+	lib/rtnetlink-route.c \
+	lib/rtnetlink-route.h
 endif
 
 if HAVE_OPENSSL

lib/netdev-dummy.c

@@ -320,6 +320,7 @@ static const struct netdev_class dummy_class = {
     NULL,                       /* get_in6 */
     NULL,                       /* add_router */
     NULL,                       /* get_next_hop */
+    NULL,                       /* get_tnl_iface */
     NULL,                       /* arp_lookup */
 
     netdev_dummy_update_flags,

lib/netdev-linux.c

@@ -2176,6 +2176,7 @@ netdev_linux_poll_remove(struct netdev_notifier *notifier_)
     netdev_linux_get_in6,                                       \
     netdev_linux_add_router,                                    \
     netdev_linux_get_next_hop,                                  \
+    NULL,                       /* get_tnl_iface */             \
     netdev_linux_arp_lookup,                                    \
                                                                 \
     netdev_linux_update_flags,                                  \

lib/netdev-provider.h

@@ -518,6 +518,17 @@ struct netdev_class {
     int (*get_next_hop)(const struct in_addr *host, struct in_addr *next_hop,
                         char **netdev_name);
 
+    /* Looks up the name of the interface out of which traffic will egress if
+     * 'netdev' is a tunnel.  If unsuccessful, or 'netdev' is not a tunnel,
+     * will return null.  This function does not necessarily return the
+     * physical interface out which traffic will egress.  Instead it returns
+     * the interface which is assigned 'netdev's remote_ip.  This may be an
+     * internal interface such as a bridge port.
+     *
+     * This function may be set to null if 'netdev' is not a tunnel or it is
+     * not supported. */
+    const char *(*get_tnl_iface)(const struct netdev *netdev);
+
     /* Looks up the ARP table entry for 'ip' on 'netdev' and stores the
      * corresponding MAC address in 'mac'.  A return value of ENXIO, in
      * particular, indicates that there is no ARP table entry for 'ip' on