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>

network: Restore fixed MTU functionality
a00fbab5 · Thomas Parrott · e0f80435 · a00fbab5
Commit a00fbab5 authored Jan 15, 2020 by Thomas Parrott
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Showing with 5 additions and 3 deletions

network.c src/lxc/network.c +5 -3

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--- 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;