FreeBSD Device Drivers

Chapter 17. Network Drivers, Part 2: Packet Reception and Transmission

This chapter examines the packet reception and transmission components of em(4). Predictably, em(4) uses both mbufs and MSI for packet reception and transmission.

Packet Reception

When an interface receives a packet, it sends an interrupt. Naturally, this causes its interrupt handler to execute. For example, here is what executes in em(4):

static void
em_msix_rx(void *arg)
{
        struct rx_ring *rxr = arg;
        struct adapter *adapter = rxr->adapter;
        bool more;

        ++rxr->rx_irq;

        more = em_rxeof(rxr, ...