Understanding Linux Network Internals

Device Registration and Initialization

For a network device to be usable, it must be recognized by the kernel and associated with the correct driver. The driver stores, in private data structures, all the information needed to drive the device and interact with other kernel components that require the device. The registration and initialization tasks are taken care of partially by the core kernel and partially by the device driver. Let's go over the initialization phases:

Hardware initialization

This is done by the device driver in cooperation with the generic bus layer (e.g., PCI or USB). The driver, sometimes alone and sometimes with the help of user-supplied parameters, configures such features of each device as the IRQ and I/O address so that they can interact with the kernel. Because this activity is closer to the device drivers than to the higher-layer protocols and features, we will not spend much time on it. We will see one example for the PCI layer.

Software initialization

Before the device can be used, depending on what network protocols are enabled and configured, the user may need to provide some other configuration parameters, such as IP addresses. This task is addressed in other chapters.

Feature initialization

The Linux kernel comes with lots of networking options. Because some of them need per-device configuration, the device initialization boot sequence must take care of them. One example is Traffic Control, the subsystem that implements Quality of Service (QoS) ...