Understanding Linux Network Internals

Registering and Unregistering Devices

Network devices are registered and unregistered with the kernel with register_netdev and unregister_netdev, respectively. These are simple wrappers that take care of locking and then invoke the routines register_netdevice and unregister_netdevice, respectively. We already briefly introduced these functions in Figure 8-1. All of them are defined in net/core/dev.c.

Figure 8-4 shows the registration states a net_device can be set to, and shows where the aforementioned routines come into the picture. It also shows where other key routines are called. All of them will be described in later sections. In particular, note that:

• Changes of state may use intermediate states between NETREG_UNINITIALIZED and NETREG_REGISTERED. These progressions are handled by netdev_run_todo, described in the section "Split Operations: netdev_run_todo."

• The two net_device virtual functions init and uninit can be used by device drivers to initialize and clean up private data, respectively, when registering and unregistering a device. They are mainly used by virtual devices. See the section "Virtual Devices."

• The unregistration of a device cannot be completed until all references to the associated net_device data structure have been released: netdev_wait_allrefs does not return until that condition is met. See the section "Reference Counts."

• Both the registration and unregistration of a device are completed by netdev_run_todo. We will see in the section "Split Operations: netdev_run_todo ...