Understanding Linux Network Internals

Protocol Initialization and Cleanup

Each neighboring protocol has an initialization function that is executed at boot time if the protocol is included in the kernel, or at module load time if the protocol has been compiled as a module. As for other kernel subsystems, the initialization function allocates all of the resources that are needed by the subsystem to function properly. The four initialization functions of the four neighboring protocols implemented in the Linux kernel are listed in Table 27-1.

Table 27-1. Neighboring protocol init/cleanup functions

Protocol	Init function	Cleanup function	File
ARP	arp_init [*]	None	net/ipv4/arp.c
Neighbor Discovery (ND)	ndisc_init	ndisc_cleanup	net/ipv6/ndisc.c
DECnet	dn_neigh_init	dn_neigh_cleanup	net/decnet/dn_neigh.c
ARP over IP (clip)[*]	atm_clip_init	atm_clip_exit	net/atm/clip.c
[*] arp_init is described in the section "ARP Protocol Initialization" in Chapter 28. [*] clip represents a special case under ARP, not an independent protocol. Therefore, unlike the other three protocols, clip does not register with neigh_table_init, but accomplishes its initialization (such as memory pool allocation) by itself. Basically, it initializes its neigh_table structure and lets the ARP protocol (arp_bind_neighbour) take care of it.

Here are some of the common tasks accomplished by these functions:

• Initialize the neigh_table structure with neigh_table_init.

• Register a group of variables in the /proc filesystem ...