networkd: VXLAN add support to configure IP Don't fragment.

Allow users to set the IPv4 DF bit in outgoing packets, or to inherit its
value from the IPv4 inner header. If the encapsulated protocol is IPv6 and
DF is configured to be inherited, always set it.

src/network/netdev/vxlan.c

@@ -7,6 +7,7 @@
 #include "conf-parser.h"
 #include "alloc-util.h"
 #include "extract-word.h"
+#include "string-table.h"
 #include "string-util.h"
 #include "strv.h"
 #include "parse-util.h"
@@ -15,6 +16,15 @@
 #include "networkd-link.h"
 #include "netdev/vxlan.h"
 
+static const char* const df_table[_NETDEV_VXLAN_DF_MAX] = {
+        [NETDEV_VXLAN_DF_NO] = "no",
+        [NETDEV_VXLAN_DF_YES] = "yes",
+        [NETDEV_VXLAN_DF_INHERIT] = "inherit",
+};
+
+DEFINE_STRING_TABLE_LOOKUP_WITH_BOOLEAN(df, VxLanDF, NETDEV_VXLAN_DF_YES);
+DEFINE_CONFIG_PARSE_ENUM(config_parse_df, df, VxLanDF, "Failed to parse VXLAN IPDoNotFragment= setting");
+
 static int netdev_vxlan_fill_message_create(NetDev *netdev, Link *link, sd_netlink_message *m) {
         VxLan *v;
         int r;
@@ -150,6 +160,12 @@ static int netdev_vxlan_fill_message_create(NetDev *netdev, Link *link, sd_netli
                         return log_netdev_error_errno(netdev, r, "Could not append IFLA_VXLAN_GPE attribute: %m");
         }
 
+        if (v->df != _NETDEV_VXLAN_DF_INVALID) {
+                r = sd_netlink_message_append_u8(m, IFLA_VXLAN_DF, v->df);
+                if (r < 0)
+                        return log_netdev_error_errno(netdev, r, "Could not append IFLA_VXLAN_DF attribute: %m");
+        }
+
         return r;
 }
 
@@ -305,6 +321,7 @@ static void vxlan_init(NetDev *netdev) {
         assert(v);
 
         v->vni = VXLAN_VID_MAX + 1;
+        v->df = _NETDEV_VXLAN_DF_INVALID;
         v->learning = true;
         v->udpcsum = false;
         v->udp6zerocsumtx = false;