Understanding Linux Network Internals

Notification Chains for the Networking Subsystems

The kernel defines at least 10 different notification chains. Here we are interested in the ones that are used to signal events of particular importance to the networking code. The main ones are:

inetaddr_chain

Sends notifications about the insertion, removal, and change of an Internet Protocol Version 4 (IPv4) address on a local interface. Chapter 23 describes when such notifications are generated. Internet Protocol Version 6 (IPv6) uses a similar chain (inet6addr_chain ).

netdev_chain

Sends notifications about the registration status of network devices. Chapter 8 describes when such notifications are generated.

For these chains, and others used by the networking subsystems, their purposes and uses are described in the chapter about the relevant notifier subsystem.

The networking code can register to notifications generated by other kernel components, too. For example, some NIC device drivers register with the reboot_notifier_list chain, which is a chain that warns when the system is about to reboot.

Wrappers

Most notification chains come with a set of wrappers used to register to them and unregister from them. For example, this is the wrapper used to register to netdev_chain:

int register_netdevice_notifier(struct notifier_block *nb)
{
        return notifier_chain_register(&netdev_chain, nb);
}

Common names for wrappers include [un]register_ xxx _notifier, xxx _[un]register_notifier, and xxx _[un]register.

Examples

Registrations to notification ...