Understanding Linux Network Internals

Allocating net_device Structures

Network devices are defined with net_device structures. Because they are usually named dev in the kernel code, I use that name frequently in this chapter for a net_device. These data structures are allocated with alloc_netdev, defined in net/core/dev.c, which requires three input parameters:

Size of private data structure

We will see in the section "Organization of net_device Structures" that the net_device data structure can be extended by device drivers with a private data block to store the driver's parameters. This parameter specifies the size of the block.

Device name

This may be a partial name that the kernel will complete through some scheme that ensures unique device names.

Setup routine

This routine is used to initialize a portion of the net_device's fields. See the sections "Device Initialization" and "Device Type Initialization: xxx_setup Functions" for more details.

The return value is a pointer to the net_device structure allocated, or NULL in case of errors.

Every device is assigned a name that depends on the device type and that, to be unique, contains a number that is assigned sequentially as devices of the same type are registered. Ethernet devices, for instance, are called eth0, eth1, and so on. A single device may be called with different names depending on the order with which the devices are registered. For instance, if you had two cards handled by two different modules, the names of the devices would depend on the order in which ...