linux 内核协议栈 邻居协议之 ARP 协议处理初始化

/* *	This structure defines an ethernet arp header. */ struct arphdr {	__be16		ar_hrd;		/* format of hardware address	*/	__be16		ar_pro;		/* format of protocol address	*/	unsigned char	ar_hln;		/* length of hardware address	*/	unsigned char	ar_pln;		/* length of protocol address	*/	__be16		ar_op;		/* ARP opcode (command)		*/ #if 0	 /*	  *	 Ethernet looks like this : This bit is variable sized however...	  */	unsigned char		ar_sha[ETH_ALEN];	/* sender hardware address	*/	unsigned char		ar_sip[4];		/* sender IP address		*/	unsigned char		ar_tha[ETH_ALEN];	/* target hardware address	*/	unsigned char		ar_tip[4];		/* target IP address		*/#endif };

/* ARP protocol opcodes. */#define	ARPOP_REQUEST	1		/* ARP request			*/#define	ARPOP_REPLY	2		/* ARP reply			*/#define	ARPOP_RREQUEST	3		/* RARP request			*/#define	ARPOP_RREPLY	4		/* RARP reply			*/#define	ARPOP_InREQUEST	8		/* InARP request		*/#define	ARPOP_InREPLY	9		/* InARP reply			*/#define	ARPOP_NAK	10		/* (ATM)ARP NAK			*/

/* *	Called once on startup. */ static struct packet_type arp_packet_type __read_mostly = {	.type =	cpu_to_be16(ETH_P_ARP),	.func =	arp_rcv,};  void __init arp_init(void){	neigh_table_init(&arp_tbl); 	dev_add_pack(&arp_packet_type);	arp_proc_init();#ifdef CONFIG_SYSCTL	neigh_sysctl_register(NULL, &arp_tbl.parms, "ipv4", NULL);#endif	register_netdevice_notifier(&arp_netdev_notifier);}

void neigh_table_init(struct neigh_table *tbl){	struct neigh_table *tmp; 	neigh_table_init_no_netlink(tbl);	write_lock(&neigh_tbl_lock);	for (tmp = neigh_tables; tmp; tmp = tmp->next) {		if (tmp->family == tbl->family)			break;	}	tbl->next	= neigh_tables;	neigh_tables	= tbl;	write_unlock(&neigh_tbl_lock); 	if (unlikely(tmp)) {		pr_err("Registering multiple tables for family %d\n",		       tbl->family);		dump_stack();	}}EXPORT_SYMBOL(neigh_table_init); 

static void neigh_table_init_no_netlink(struct neigh_table *tbl){	unsigned long now = jiffies;	unsigned long phsize; 	write_pnet(&tbl->Index of /, &init_net);	atomic_set(&tbl->parms.refcnt, 1);	tbl->parms.reachable_time =			  neigh_rand_reach_time(tbl->parms.base_reachable_time); 	tbl->stats = alloc_percpu(struct neigh_statistics);	if (!tbl->stats)		panic("cannot create neighbour cache statistics"); #ifdef CONFIG_PROC_FS	if (!proc_create_data(tbl->id, 0, init_net.proc_net_stat,			      &neigh_stat_seq_fops, tbl))		panic("cannot create neighbour proc dir entry");#endif 	RCU_INIT_POINTER(tbl->nht, neigh_hash_alloc(3)); 	phsize = (PNEIGH_HASHMASK + 1) * sizeof(struct pneigh_entry *);	tbl->phash_buckets = kzalloc(phsize, GFP_KERNEL); 	if (!tbl->nht || !tbl->phash_buckets)		panic("cannot allocate neighbour cache hashes"); 	if (!tbl->entry_size)		tbl->entry_size = ALIGN(offsetof(struct neighbour, primary_key) +					tbl->key_len, NEIGH_PRIV_ALIGN);	else		WARN_ON(tbl->entry_size % NEIGH_PRIV_ALIGN); 	rwlock_init(&tbl->lock);    /*创建带有延迟功能的工作队列，并将创建的工作添加      到工作队列keventd_wq中去，并开启一个定时器延迟tbl->parms.reachable_time      后，调用queue_work执行函数neigh_periodic_work          */	INIT_DEFERRABLE_WORK(&tbl->gc_work, neigh_periodic_work);	schedule_delayed_work(&tbl->gc_work, tbl->parms.reachable_time);	setup_timer(&tbl->proxy_timer, neigh_proxy_process, (unsigned long)tbl);	skb_queue_head_init_class(&tbl->proxy_queue,			&neigh_table_proxy_queue_class); 	tbl->last_flush = now;	tbl->last_rand	= now + tbl->parms.reachable_time * 20;}

struct neigh_table arp_tbl = {	.family		= AF_INET,	.key_len	= 4,//ipv4 地址长度	.hash		= arp_hash,//arp 协议的hash函数	.constructor	= arp_constructor,//邻居表现初始化函数，初始化neighbour项中与协议相关的成员	.proxy_redo	= parp_redo,	.id		= "arp_cache",	.parms		= {		.tbl			= &arp_tbl,		.base_reachable_time	= 30 * HZ,		.retrans_time		= 1 * HZ,		.gc_staletime		= 60 * HZ,		.reachable_time		= 30 * HZ,		.delay_probe_time	= 5 * HZ,		.queue_len_bytes	= 64*1024,		.ucast_probes		= 3,		.mcast_probes		= 3,		.anycast_delay		= 1 * HZ,		.proxy_delay		= (8 * HZ) / 10,		.proxy_qlen		= 64,		.locktime		= 1 * HZ,	},	.gc_interval	= 30 * HZ,	.gc_thresh1	= 128,	.gc_thresh2	= 512,	.gc_thresh3	= 1024,};EXPORT_SYMBOL(arp_tbl);

static int arp_constructor(struct neighbour *neigh){	__be32 addr = *(__be32 *)neigh->primary_key;	struct net_device *dev = neigh->dev;	struct in_device *in_dev;	struct neigh_parms *parms; 	rcu_read_lock();	in_dev = __in_dev_get_rcu(dev);	if (in_dev == NULL) {		rcu_read_unlock();		return -EINVAL;	} 	neigh->type = inet_addr_type(dev_net(dev), addr); 	parms = in_dev->arp_parms;	__neigh_parms_put(neigh->parms);	neigh->parms = neigh_parms_clone(parms);	rcu_read_unlock();		//对于以太网设备，其dev->header_ops为eth_header_ops	if (!dev->header_ops) {		neigh->nud_state = NUD_NOARP;		neigh->ops = &arp_direct_ops;		neigh->output = neigh_direct_output;	} else {		/* Good devices (checked by reading texts, but only Ethernet is		   tested)		   ARPHRD_ETHER: (ethernet, apfddi)		   ARPHRD_FDDI: (fddi)		   ARPHRD_IEEE802: (tr)		   ARPHRD_METRICOM: (strip)		   ARPHRD_ARCNET:		   etc. etc. etc.		   ARPHRD_IPDDP will also work, if author repairs it.		   I did not it, because this driver does not work even		   in old paradigm.		 */ #if 1		/* So... these "amateur" devices are hopeless.		   The only thing, that I can say now:		   It is very sad that we need to keep ugly obsolete		   code to make them happy.		   They should be moved to more reasonable state, now		   they use rebuild_header INSTEAD OF hard_start_xmit!!!		   Besides that, they are sort of out of date		   (a lot of redundant clones/copies, useless in 2.1),		   I wonder why people believe that they work.		 */		switch (dev->type) {		default:			break;		case ARPHRD_ROSE:#if IS_ENABLED(CONFIG_AX25)		case ARPHRD_AX25:#if IS_ENABLED(CONFIG_NETROM)		case ARPHRD_NETROM:#endif			neigh->ops = &arp_broken_ops;			neigh->output = neigh->ops->output;			return 0;#else			break;#endif		}#endif		/*		对于组播类型的 neighbour 项，则将该邻居项的状态设置为 NUD_NOARP		对于不需要 arp 的设备或者回环设备，将 nud_state 设置为 NUD_NOARP		对于广播类型或者点对点设备的邻居项，不需要 arp		*/		if (neigh->type == RTN_MULTICAST) {			neigh->nud_state = NUD_NOARP;			arp_mc_map(addr, neigh->ha, dev, 1);		} else if (dev->flags & (IFF_NOARP | IFF_LOOPBACK)) {			neigh->nud_state = NUD_NOARP;			memcpy(neigh->ha, dev->dev_addr, dev->addr_len);		} else if (neigh->type == RTN_BROADCAST ||			   (dev->flags & IFF_POINTOPOINT)) {			neigh->nud_state = NUD_NOARP;			memcpy(neigh->ha, dev->broadcast, dev->addr_len);		}		/*		如果设备的header_ops->cache存在，则将邻居项的ops设置为arp_hh_ops,		对于以太网设备，其header_ops->cache为eth_header_cache，所以对于以太网设备		其neighbour->ops为arp_hh_ops		*/		if (dev->header_ops->cache)			neigh->ops = &arp_hh_ops;		else			neigh->ops = &arp_generic_ops;				//对于邻居项状态为有效状态时，则将neigh->output设置为neigh->ops->connected_output		if (neigh->nud_state & NUD_VALID)			neigh->output = neigh->ops->connected_output;		else			neigh->output = neigh->ops->output;	}	return 0;}