Understanding Linux Network Internals

Initializing the Device Handling Layer: net_dev_init

An important part of initialization for the networking code, including Traffic Control and per-CPU ingress queues, is performed at boot time by net_dev_init, defined in net/core/dev.c:

static int _ _init net_dev_init(void)
{
    ...
}
subsys_initcall(net_dev_init);

See Chapter 7 for how the subsys_initcall macros ensure that net_dev_init runs before any NIC device drivers register themselves, and why this is important. You also will see why net_dev_init is tagged with the _ _init macro.

Let's walk through the main parts of net_dev_init:

• The per-CPU data structures used by the two networking software interrupts (softirqs) are initialized. In Chapter 9, we will see what a softirq is and go into detail on how the networking code uses softirqs.

• When the kernel is compiled with support for the /proc filesystem (which is the default configuration), a few files are added to /proc with dev_proc_init and dev_mcast_init. See the later section "Tuning via /proc Filesystem" for more details.

• netdev_sysfs_init registers the net class with sysfs. This creates the directory /sys/class/net, under which you will find a subdirectory for each registered network device. These directories include lots of files, some of which used to be in /proc.

• net_random_init initializes a per-CPU vector of seeds that will be used when generating random numbers with the net_random routine. net_random is used in different contexts, described later in this section.

• The protocol-independent ...