The event_t typedef is declared in inet/generic/event.h:
typedef struct event
{
ev_func_t ev_func;
ev_arg_t ev_arg;
struct event *ev_next;
} event_t;
If an event needs to be scheduled, ev_enqueue() is called to place the event in the system-wide event queue whose head is ev_head. ev_process() is eventually called from the main loop in inet.c to process the events. ev_in_queue(ev) simply returns TRUE if the event ev, ev_in_queue()'s only parameter, has a non-null value for func (see below) and FALSE if func is null. In this way, ev_in_queue() determines whether the event has been configured.
ev_init(ev) simply zeroes out the ev_func and ev_next fields of the event ev, ev_init()'s only parameter.
ev_func: A function (e.g., ip_process_loopb()) that performs some task.
ev_arg:
typedef union ev_arg
{
int ev_int;
void *ev_ptr;
} ev_arg_t;
ev_arg is ev_func's argument. In the case of a packet destined for the loopback address (127.0.0.1), the argument will be the ip port associated with the ip file descriptor that is sending out the packet. In the case of a message from the ethernet task that caused a deadlock, ev_arg is a pointer to the message's destination ethernet port.
ev_next: The next event in the system-wide event queue.