Chapter 2. Critical Data Structures

A few key data structures are referenced throughout the Linux networking code. Both when reading this book and when studying the source code directly, you'll need to understand the fields in these data structures. To be sure, going over data structures field by field is less fun than unraveling functions, but it's an important foundation to have. "Show me your data," said the legendary software engineer, Frederick P. Brooks.

This chapter introduces the following data structures, and mentions some of the functions and macros that manipulate them:

struct sk_buff

This is where a packet is stored. The structure is used by all the network layers to store their headers, information about the user data (the payload), and other information needed internally for coordinating their work.

struct net_device

Each network device is represented in the Linux kernel by this data structure, which contains information about both its hardware and its software configuration. See Chapter 8 for details on when and how net_device data structures are allocated.

Another critical data structure for Linux networking is struct sock, which stores the networking information for sockets. Because this book does not cover sockets, I have not included sock in this chapter.