1. 根目录:
2. net
3. ipv4
4. protocol.c

/*
 * INET		An implementation of the TCP/IP protocol suite for the LINUX
 *		operating system.  INET is implemented using the  BSD Socket
 *		interface as the means of communication with the user level.
 *
 *		INET protocol dispatch tables.
 *
 * Authors:	Ross Biro
 *		Fred N. van Kempen, <waltje@uWalt.NL.Mugnet.ORG>
 *
 * Fixes:
 *		Alan Cox	: Ahah! udp icmp errors don't work because
 *				  udp_err is never called!
 *		Alan Cox	: Added new fields for init and ready for
 *				  proper fragmentation (_NO_ 4K limits!)
 *		Richard Colella	: Hang on hash collision
 *		Vince Laviano	: Modified inet_del_protocol() to correctly
 *				  maintain copy bit.
 *
 *		This program is free software; you can redistribute it and/or
 *		modify it under the terms of the GNU General Public License
 *		as published by the Free Software Foundation; either version
 *		2 of the License, or (at your option) any later version.
 */
#include <linux/cache.h>
#include <linux/module.h>
#include <linux/netdevice.h>
#include <linux/spinlock.h>
#include <net/protocol.h>

const struct net_protocol __rcu *inet_protos[MAX_INET_PROTOS] __read_mostly;

/*
 *	Add a protocol handler to the hash tables
 */

int inet_add_protocol(const struct net_protocol *prot, unsigned char protocol)
{
	int hash = protocol & (MAX_INET_PROTOS - 1);

	return !cmpxchg((const struct net_protocol **)&inet_protos[hash],
			NULL, prot) ? 0 : -1;
}
EXPORT_SYMBOL(inet_add_protocol);

/*
 *	Remove a protocol from the hash tables.
 */

int inet_del_protocol(const struct net_protocol *prot, unsigned char protocol)
{
	int ret, hash = protocol & (MAX_INET_PROTOS - 1);

	ret = (cmpxchg((const struct net_protocol **)&inet_protos[hash],
		       prot, NULL) == prot) ? 0 : -1;

	synchronize_net();

	return ret;
}
EXPORT_SYMBOL(inet_del_protocol);