Linux Kernel Networking: Implementation and Theory

CHAPTER 2

Netlink Sockets

Chapter 1 discusses the roles of the Linux kernel networking subsystem and the three layers in which it operates. The netlink socket interface appeared first in the 2.2 Linux kernel as AF_NETLINK socket. It was created as a more flexible alternative to the awkward IOCTL communication method between userspace processes and the kernel. The IOCTL handlers cannot send asynchronous messages to userspace from the kernel, whereas netlink sockets can. In order to use IOCTL, there is another level of complexity: you need to define IOCTL numbers. The operation model of netlink is quite simple: you open and register a netlink socket ...