Network Management API¶

The Network Management APIs allow applications, as well as network layer code itself, to call defined network routines at any level in the IP stack, or receive notifications on relevant network events. For example, by using these APIs, code can request a scan be done on a WiFi- or Bluetooth-based network interface, or request notification if a network interface IP address changes.

The Network Management API implementation is designed to save memory by eliminating code at build time for management routines that are not used. Distinct and statically defined APIs for network management procedures are not used. Instead, defined procedure handlers are registered by using a NET_MGMT_REGISTER_REQUEST_HANDLER macro. Procedure requests are done through a single net_mgmt() API that invokes the registered handler for the corresponding request.

The current implementation is experimental and may change and improve in future releases.

Requesting a defined procedure¶

All network management requests are of the form net_mgmt(mgmt_request, ...). The mgmt_request parameter is a bit mask that tells which stack layer is targeted, if a net_if object is implied, and the specific management procedure being requested. The available procedure requests depend on what has been implemented in the stack.

To avoid extra cost, all net_mgmt() calls are direct. Though this may change in a future release, it will not affect the users of this function.

Listening to network events¶

You can receive notifications on network events by registering a callback function and specifying a set of events used to filter when your callback is invoked.

Two functions are available, net_mgmt_add_event_callback() for registering the callback function, and net_mgmt_del_event_callback() for unregistering a callback. A helper function, net_mgmt_init_event_callback(), can be used to ease the initialization of the callback structure.

When an event occurs that matches a callback’s event set, the associated callback function is invoked with the actual event code. This makes it possible for different events to be handled by the same callback function, if desired.

Warning

Event set filtering allows false positives for events that have the same layer and layer code. A callback handler function must check the event code (passed as an argument) against the specific network events it will handle, regardless of how many events were in the set passed to net_mgmt_init_event_callback().

(False positives can occur for events which have the same layer and layer code.)

An example follows.

/*
 * Set of events to handle.
 * See e.g. include/net/net_event.h for some NET_EVENT_xxx values.
 */
#define EVENT_SET (NET_EVENT_xxx | NET_EVENT_yyy)

struct net_mgmt_event_callback callback;

void callback_handler(struct net_mgmt_event_callback *cb, u32_t mgmt_event,
                      struct net_if *iface)
{
        if (mgmt_event == NET_EVENT_xxx) {
                /* Handle NET_EVENT_xxx */
        } else if (mgmt_event == NET_EVENT_yyy) {
                /* Handle NET_EVENT_yyy */
        } else {
                /* Spurious (false positive) invocation. */
        }
}

void register_cb(void)
{
        net_mgmt_init_event_callback(&callback, callback_handler, EVENT_SET);
        netmgmt_add_event_callback(&callback);
}

Defining a network management procedure¶

You can provide additional management procedures specific to your stack implementation by defining a handler and registering it with an associated mgmt_request code.

Management request code are defined in relevant places depending on the targeted layer or eventually, if l2 is the layer, on the technology as well. For instance, all IP layer management request code will be found in the include/net/net_mgmt.h header file. But in case of an L2 technology, let’s say Ethernet, these would be found in include/net/ethernet.h

You define your handler modeled with this signature:

static int your_handler(u32_t mgmt_event, struct net_if *iface,
                        void *data, size_t len);

and then register it with an associated mgmt_request code:

NET_MGMT_REGISTER_REQUEST_HANDLER(<mgmt_request code>, your_handler);

This new management procedure could then be called by using:

net_mgmt(<mgmt_request code>, ...);

Signaling a network event¶

You can signal a specific network event using the net_mgmt_notify() function and provide the network event code. See include/net/net_mgmt.h for details. As for the management request code, event code can be also found on specific L2 technology mgmt headers, for example include/net/ieee802154_mgmt.h would be the right place if 802.15.4 L2 is the technology one wants to listen to events.