eth_arrive() is called when either the ethernet task receives an ethernet packet, when an ethernet multicast/broadcast packet is sent out of an ethernet port, or when an ethernet packet is destined for a local ethernet port. For a given packet, eth_arrive() finds the ethernet file descriptors that are interested in the packet. eth_arrive() then hands the packet off to the ip layer by calling either packet2user() or ip_eth_arrived() for these ethernet file descriptors.