N2. Packet TX path 1 : Basic

This page contains the basic code flow while transmitting a packet. It begins with the userspace sendmsg, enters the UDP and IP stacks, finds a route, enters core networking and finally being handed over to the driver which pushes it out. TX, unlike RX, can happen without a softirq being raised. The processing happens completely in the application context. In this page I describe packet transmission without a softirq being raised. I'll cover how qdiscs are used in a separate page, after which NET_TX with qdiscs will be described.

UDP & IP stack processing and routing will be described in detail in a separate page, this is just a basic overview. We will end the discussion by handling over the packet to the driver. How the driver actually transmits the packet will be described in later pages.