networkd: sit-tunnel add support for pmtudisc

This patch adds path of mtu discovery for sit tunnel.
To enable/disable DiscoverPathMTU is introduced.

Example configuration

file: sit.netdev
[NetDev]
Name=sit-tun
Kind=sit
MTUBytes=1480

[Tunnel]
DiscoverPathMTU=1
Local=X.X.X.X
Remote=X.X.X.X

By default pmtudisc is turned on , if DiscoverPathMTU
is missing from the config. To turn it off
DiscoverPathMTU=0 needs to be set.

1 files changed, 8 insertions, 0 deletions

diff --git a/src/network/networkd-tunnel.c b/src/network/networkd-tunnel.c
index 9b4cb4f959..1a06a17c7b 100644
--- a/src/network/networkd-tunnel.c
+++ b/src/network/networkd-tunnel.c
@@ -207,6 +207,14 @@ static int netdev_fill_sit_rtnl_message(Link *link, sd_rtnl_message *m) {
                 return r;
         }
 
+        r = sd_rtnl_message_append_u8(m, IFLA_IPTUN_PMTUDISC, netdev->tunnel_pmtudisc);
+        if (r < 0) {
+                log_error_netdev(netdev,
+                                 "Could not append IFLA_IPTUN_PMTUDISC attribute: %s",
+                                 strerror(-r));
+                return r;
+        }
+
         r = sd_rtnl_message_close_container(m);
         if (r < 0) {
                 log_error_netdev(netdev,