-/* Returns the maximum size of transmitted (and received) packets on 'netdev',
- * in bytes, not including the hardware header; thus, this is typically 1500
- * bytes for Ethernet devices. */
+/* Retrieves the MTU of 'netdev'. The MTU is the maximum size of transmitted
+ * (and received) packets, in bytes, not including the hardware header; thus,
+ * this is typically 1500 bytes for Ethernet devices.
+ *
+ * If successful, returns 0 and stores the MTU size in '*mtup'. Stores INT_MAX
+ * in '*mtup' if 'netdev' does not have an MTU (as e.g. some tunnels do not).On
+ * failure, returns a positive errno value and stores ETH_PAYLOAD_MAX (1500) in
+ * '*mtup'. */
+int
+netdev_get_mtu(const struct netdev *netdev, int *mtup)
+{
+ int error = netdev_get_dev(netdev)->netdev_class->get_mtu(netdev, mtup);
+ if (error) {
+ VLOG_WARN_RL(&rl, "failed to retrieve MTU for network device %s: %s",
+ netdev_get_name(netdev), strerror(error));
+ *mtup = ETH_PAYLOAD_MAX;
+ }
+ return error;
+}
+
+/* Returns the ifindex of 'netdev', if successful, as a positive number. On
+ * failure, returns a negative errno value.
+ *
+ * The desired semantics of the ifindex value are a combination of those
+ * specified by POSIX for if_nametoindex() and by SNMP for ifIndex. An ifindex
+ * value should be unique within a host and remain stable at least until
+ * reboot. SNMP says an ifindex "ranges between 1 and the value of ifNumber"
+ * but many systems do not follow this rule anyhow.
+ *
+ * Some network devices may not implement support for this function. In such
+ * cases this function will always return -EOPNOTSUPP.
+ */