network: Restore fixed MTU functionality

If MTU setting is provided in network device config then always use it rather than inheriting from the link device.

Affected both bridge and router veth modes.

Signed-off-by: Thomas Parrott <thomas.parrott@canonical.com>

diff --git a/src/lxc/network.c b/src/lxc/network.c
index c8f44dd807a759551590109f54230f3bdf6948be..7b9ea1f25aed743eb6ec1ef2d5a7af2043460ba4 100644 (file)
--- a/src/lxc/network.c
+++ b/src/lxc/network.c
@@ -273,7 +273,7 @@ static int lxc_is_ip_forwarding_enabled(const char *ifname, int family)
 static int instantiate_veth(struct lxc_handler *handler, struct lxc_netdev *netdev)
 {
        int err;
-       unsigned int mtu;
+       unsigned int mtu = 1500;
        char *veth1, *veth2;
        char veth1buf[IFNAMSIZ], veth2buf[IFNAMSIZ];
 
@@ -302,8 +302,10 @@ static int instantiate_veth(struct lxc_handler *handler, struct lxc_netdev *netd
        if (!veth2)
                return -1;
 
-       if (netdev->mtu && lxc_safe_uint(netdev->mtu, &mtu)) {
-               return log_error_errno(-1, errno, "Failed to parse mtu");
+       /* if mtu is specified in config then use that, otherwise inherit from link device if provided. */
+       if (netdev->mtu) {
+               if (lxc_safe_uint(netdev->mtu, &mtu))
+                       return log_error_errno(-1, errno, "Failed to parse mtu");
        } else if (netdev->link[0] != '\0') {
                int ifindex_mtu;