施乐复印机提示e7(Linux内核-arp协议)

Posted 2023-05-28

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施乐复印机提示e7(Linux内核-arp协议)

从ip_finish_output2到dev_queue_xmit路径：

arping命令：

http://www.bluestep.cc/linux%e5%91%bd%e4%bb%a4arping-%e7%bd%91%e7%bb%9c%e7%ae%a1%e7%90%86-%e9%80%9a%e8%bf%87%e5%8f%91%e9%80%81arp%e5%8d%8f%e8%ae%ae%e6%8a%a5%e6%96%87%e6%b5%8b%e8%af%95%e7%bd%91%e7%bb%9c/

arp协议：

arp报文结构：

(1).硬件类型：

硬件地址类型，该字段值一般为ARPHRD_ETHER，表示以太网。

F:\\company\\Linux\\linux-4.1.45\\linux-4.1.45\\include\\uapi\\linux\\if_arp.h/* ARP protocol HARDWARE identifiers. */#define ARPHRD_NETROM	0		/* from KA9Q: NET/ROM pseudo	*/#define ARPHRD_ETHER 	1		/* Ethernet 10Mbps		*/#define	ARPHRD_EETHER	2		/* Experimental Ethernet	*/#define	ARPHRD_AX25	3		/* AX.25 Level 2		*/#define	ARPHRD_PRONET	4		/* PROnet token ring		*/#define	ARPHRD_CHAOS	5		/* Chaosnet			*/#define	ARPHRD_IEEE802	6		/* IEEE 802.2 Ethernet/TR/TB	*/#define	ARPHRD_ARCNET	7		/* ARCnet			*/#define	ARPHRD_APPLETLK	8		/* APPLEtalk			*/#define ARPHRD_DLCI	15		/* Frame Relay DLCI		*/#define ARPHRD_ATM	19		/* ATM 				*/...

(2).协议类型：

表示三层地址使用的协议，该字段值一般为ETH_P_IP，表示IP协议

F:\\company\\Linux\\linux-4.1.45\\linux-4.1.45\\include\\uapi\\linux\\if_ether.h#define ETH_P_LOOP	0x0060		/* Ethernet Loopback packet	*/#define ETH_P_PUP	0x0200		/* Xerox PUP packet		*/#define ETH_P_PUPAT	0x0201		/* Xerox PUP Addr Trans packet	*/#define ETH_P_IP	0x0800		/* Internet Protocol packet	*/#define ETH_P_X25	0x0805		/* CCITT X.25			*/#define ETH_P_ARP	0x0806		/* Address Resolution packet	*/...

(3)硬件地址长度，以太网MAC地址就是6；

(4)协议地址长度，IP地址就是4；

(5)操作码

常见的有四种，arp请求，arp相应，rarp请求，rarp相应。

F:\\company\\Linux\\linux-4.1.45\\linux-4.1.45\\include\\uapi\\linux\\if_arp.h/* 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			*/

(6)发送方硬件地址与IP地址，(7)目标硬件地址与目标IP地址。

arp头数据结构：

F:\\company\\Linux\\linux-4.1.45\\linux-4.1.45\\include\\uapi\\linux\\if_arp.h/* *	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;

1. arp_init()

arp模块的初始化函数为arp_init()，这个函数在ipv4协议栈的初始化函数inet_init()中被调用。
1.初始化arp表arp_tbl;
2.注册arp协议类型；
3.建立arp相关proc文件，/proc/net/arp；
4.注册通知事件

F:\\company\\Linux\\linux-4.1.45\\linux-4.1.45\\net\\ipv4\\arp.cvoid __init arp_init(void)	neigh_table_init(NEIGH_ARP_TABLE, &arp_tbl);//初始化arp协议的邻居表	dev_add_pack(&arp_packet_type);//在协议栈中注册arp协议	arp_proc_init();//建立proc对象#ifdef CONFIG_SYSCTL	neigh_sysctl_register(NULL, &arp_tbl.parms, NULL);#endif	register_netdevice_notifier(&arp_netdev_notifier);//注册通知事件

arp邻居项函数指针表：

F:\\company\\Linux\\linux-4.1.45\\linux-4.1.45\\net\\ipv4\\arp.cstatic const struct neigh_ops arp_generic_ops = 	.family =		AF_INET,	.solicit =		arp_solicit,	.error_report =		arp_error_report,	.output =		neigh_resolve_output,	.connected_output =	neigh_connected_output,;static const struct neigh_ops arp_hh_ops = 	.family =		AF_INET,	.solicit =		arp_solicit,	.error_report =		arp_error_report,	.output =		neigh_resolve_output,	.connected_output =	neigh_resolve_output,;static const struct neigh_ops arp_direct_ops = 	.family =		AF_INET,	.output =		neigh_direct_output,	.connected_output =	neigh_direct_output,;

neigh_table:

一个neigh_table对应一种邻居协议，IPv4就是arp协议。用来存储于邻居协议相关的参数、功能函数、邻居项散列表等。

struct neigh_table 	int			family;/*地址族，arp为AF_INET*/	/*邻居项结构大小：sizeof(neighbour+4),因为neighbour结构最后一个成员0长数组，用于存储4字节长IP地址。*/	int			entry_size;	/*hash函数所使用的键值长度，就是IP地址长度，为4*/	int			key_len;	/*ETH_P_IP*/	__be16			protocol;	/*hash函数，arp_hash*/	__u32			(*hash)(const void *pkey,					const struct net_device *dev,					__u32 *hash_rnd);	bool			(*key_eq)(const struct neighbour *, const void *pkey);	/*邻居表项初始化函数，用于初始化neighbour结构实例，即arp_constructor，在neigh_create中被调用*/	int			(*constructor)(struct neighbour *);	/*创建和释放一个代理项时被调用，代理先不管*/	int			(*pconstructor)(struct pneigh_entry *);	void			(*pdestructor)(struct pneigh_entry *);	/*用来处理在proxy_queue缓存队列中的代理arp报文*/	void			(*proxy_redo)(struct sk_buff *skb);	/*用来分配neighbour结构实例的缓存区名，即arp_cache。*/	char			*id;	/*存储一些与协议相关的可调节参数，如超时重传时间，proxy_queue队列长度等*/	struct neigh_parms	parms;	struct list_head	parms_list;	int			gc_interval;	int			gc_thresh1;	int			gc_thresh2;	int			gc_thresh3;	unsigned long		last_flush;	struct delayed_work	gc_work;	/*处理proxy_queue的定时器*/	struct timer_list 	proxy_timer;	/*对于接收到的需要进行代理的arp报文，先缓存到proxy_queue,在定时器处理函数中再对其进行处理。*/	struct sk_buff_head	proxy_queue;	/*邻居项条目数，在neigh_alloc()、neigh_destroy()中更新*/	atomic_t		entries;	rwlock_t		lock;	unsigned long		last_rand;	/*记录邻居表中有关邻居项的各类统计数据*/	struct neigh_statistics	__percpu *stats;	/*存储邻居项的散列表：hash表，用来存储邻居项*/	struct neigh_hash_table __rcu *nht;	/*存储arp代理三层协议地址的散列表*/	struct pneigh_entry	**phash_buckets;;

neighbour

一个neighbour对应一个邻居项，就是一个arp条目

struct neighbour 	struct neighbour __rcu	*next;	struct neigh_table	*tbl;/*指向arp_tbl*/	struct neigh_parms	*parms;	unsigned long		confirmed;	unsigned long		updated;	rwlock_t		lock;	atomic_t		refcnt;/*引用计数*/	struct sk_buff_head	arp_queue;/*用来缓存待发送的报文*/	unsigned int		arp_queue_len_bytes;	struct timer_list	timer;/*定时器*/	unsigned long		used;	atomic_t		probes;	__u8			flags;	__u8			nud_state;/*邻居项状态*/	__u8			type;/*邻居地址类型，例如单播、组播、广播等*/	/*生存标志，为1时，表示该邻居项正在被删除，最终通过垃圾回收将其删除*/	__u8			dead;	seqlock_t		ha_lock;	/*邻居项MAC地址*/	unsigned char		ha[ALIGN(MAX_ADDR_LEN, sizeof(unsigned long))];	/*缓存二层报头，包括目的MAC地址*/	struct hh_cache		hh;	/*输出函数，用来将报文输出到该邻居*/	int			(*output)(struct neighbour *, struct sk_buff *);	/*邻居项函数指针*/	const struct neigh_ops	*ops;	struct rcu_head		rcu;	struct net_device	*dev;/*通过该设备访问邻居项*/	u8			primary_key[0];/*存储IP地址*/;

邻居项函数指针表，实现三层和二层的dev_queue_xmit()之间的跳转。

struct neigh_ops 	int			family;//AF_INET	/*发送arp报文*/	void			(*solicit)(struct neighbour *, struct sk_buff *);	/*向三层报告错误*/	void			(*error_report)(struct neighbour *, struct sk_buff *);	/*通用的输出函数，实现了完整的输出过程，存在较多的操作。*/	int			(*output)(struct neighbour *, struct sk_buff *);	/*确定邻居可达，即状态为NUD_CONNETCTE时的输出函数，由于所有输出所需要的信息都已具备，	该函数只是简单地添加二层首部，发送*/	int			(*connected_output)(struct neighbour *, struct sk_buff *);;

neigh_statistics

用来存储统计信息，一个结构实例对应一个网络设备上的一种邻居协议。

struct neigh_statistics 	unsigned long allocs;		/* number of allocated neighs */	unsigned long destroys;		/* number of destroyed neighs */	unsigned long hash_grows;	/* number of hash resizes */	unsigned long res_failed;	/* number of failed resolutions */	unsigned long lookups;		/* number of lookups */	unsigned long hits;		/* number of hits (among lookups) */	unsigned long rcv_probes_mcast;	/* number of received mcast ipv6 */	unsigned long rcv_probes_ucast; /* number of received ucast ipv6 */	unsigned long periodic_gc_runs;	/* number of periodic GC runs */	unsigned long forced_gc_runs;	/* number of forced GC runs */	unsigned long unres_discards;	/* number of unresolved drops */;

arp表结构：arp_tbl

F:\\company\\Linux\\linux-4.1.45\\linux-4.1.45\\net\\ipv4\\arp.cstruct neigh_table arp_tbl = 	.family		= AF_INET,	.key_len	= 4,	.protocol	= cpu_to_be16(ETH_P_IP),	.hash		= arp_hash,	.key_eq		= arp_key_eq,	.constructor	= arp_constructor,	.proxy_redo	= parp_redo,	.id		= "arp_cache",	.parms		= 		.tbl			= &arp_tbl,		.reachable_time		= 30 * HZ,		.data	= 			[NEIGH_VAR_MCAST_PROBES] = 3,			[NEIGH_VAR_UCAST_PROBES] = 3,			[NEIGH_VAR_RETRANS_TIME] = 1 * HZ,			[NEIGH_VAR_BASE_REACHABLE_TIME] = 30 * HZ,			[NEIGH_VAR_DELAY_PROBE_TIME] = 5 * HZ,			[NEIGH_VAR_GC_STALETIME] = 60 * HZ,			[NEIGH_VAR_QUEUE_LEN_BYTES] = 64 * 1024,			[NEIGH_VAR_PROXY_QLEN] = 64,			[NEIGH_VAR_ANYCAST_DELAY] = 1 * HZ,			[NEIGH_VAR_PROXY_DELAY]	= (8 * HZ) / 10,			[NEIGH_VAR_LOCKTIME] = 1 * HZ,		,	,	.gc_interval	= 30 * HZ,	.gc_thresh1	= 128,	.gc_thresh2	= 512,	.gc_thresh3	= 1024,;

dev_add_pack()

注册arp报文类型：dev_add_pack(&arp_packet_type);

就是把arp_packet_type添加到ptype_base哈希表中。

void dev_add_pack(struct packet_type *pt)	struct list_head *head = ptype_head(pt);	spin_lock(&ptype_lock);	list_add_rcu(&pt->list, head);	spin_unlock(&ptype_lock);static inline struct list_head *ptype_head(const struct packet_type *pt)	if (pt->type == htons(ETH_P_ALL))		return pt->dev ? &pt->dev->ptype_all : &ptype_all;	else		return pt->dev ? &pt->dev->ptype_specific :				 &ptype_base[ntohs(pt->type) & PTYPE_HASH_MASK];struct list_head ptype_base[PTYPE_HASH_SIZE] __read_mostly;static struct packet_type arp_packet_type __read_mostly = 	.type =	cpu_to_be16(ETH_P_ARP),	.func =	arp_rcv,;struct packet_type 	__be16			type;	/* This is really htons(ether_type). */	struct net_device	*dev;	/* NULL is wildcarded here	     */	int			(*func) (struct sk_buff *,					 struct net_device *,					 struct packet_type *,					 struct net_device *);	bool			(*id_match)(struct packet_type *ptype,					    struct sock *sk);	void			*af_packet_priv;	struct list_head	list;;

register_netdevice_notifier

注册新通知事件的时候，在已经注册和UP的设备上，会调用一次这个通知事件。

/** *	register_netdevice_notifier - register a network notifier block *	@nb: notifier * *	Register a notifier to be called when network device events occur. *	The notifier passed is linked into the kernel structures and must *	not be reused until it has been unregistered. A negative errno code *	is returned on a failure. * * 	When registered all registration and up events are replayed *	to the new notifier to allow device to have a race free *	view of the network device list. */int register_netdevice_notifier(struct notifier_block *nb)	struct net_device *dev;	struct net_device *last;	struct net *net;	int err;	rtnl_lock();	/*新事件注册到netdev_chain通知链上*/	err = raw_notifier_chain_register(&netdev_chain, nb);	if (err)		goto unlock;	if (dev_boot_phase)		goto unlock;	for_each_net(net) 		for_each_netdev(net, dev) 			/*在已经注册的设备上调用该事件*/			err = call_netdevice_notifier(nb, NETDEV_REGISTER, dev);			err = notifier_to_errno(err);			if (err)				goto rollback;			if (!(dev->flags & IFF_UP))				continue;			/*在UP的设备上调用该事件*/			call_netdevice_notifier(nb, NETDEV_UP, dev);			unlock:	rtnl_unlock();	return err;rollback:	last = dev;	for_each_net(net) 		for_each_netdev(net, dev) 			if (dev == last)				goto outroll;			if (dev->flags & IFF_UP) 				call_netdevice_notifier(nb, NETDEV_GOING_DOWN,							dev);				call_netdevice_notifier(nb, NETDEV_DOWN, dev);						call_netdevice_notifier(nb, NETDEV_UNREGISTER, dev);			outroll:	raw_notifier_chain_unregister(&netdev_chain, nb);	goto unlock;

static RAW_NOTIFIER_HEAD(netdev_chain);#define RAW_NOTIFIER_HEAD(name)					\\	struct raw_notifier_head name =				\\		RAW_NOTIFIER_INIT(name)		struct raw_notifier_head 	struct notifier_block __rcu *head;;		搞了半天就是：struct raw_notifier_head netdev_chain = .head = NULL

设备事件类型：

/* netdevice notifier chain. Please remember to update the rtnetlink * notification exclusion list in rtnetlink_event() when adding new * types. */#define NETDEV_UP	0x0001	/* For now you can't veto a device up/down */#define NETDEV_DOWN	0x0002#define NETDEV_REBOOT	0x0003	/* Tell a protocol stack a network interface				   detected a hardware crash and restarted				   - we can use this eg to kick tcp sessions				   once done */#define NETDEV_CHANGE	0x0004	/* Notify device state change */#define NETDEV_REGISTER 0x0005#define NETDEV_UNREGISTER	0x0006#define NETDEV_CHANGEMTU	0x0007 /* notify after mtu change happened */#define NETDEV_CHANGEADDR	0x0008#define NETDEV_GOING_DOWN	0x0009#define NETDEV_CHANGENAME	0x000A#define NETDEV_FEAT_CHANGE	0x000B#define NETDEV_BONDING_FAILOVER 0x000C#define NETDEV_PRE_UP		0x000D#define NETDEV_PRE_TYPE_CHANGE	0x000E#define NETDEV_POST_TYPE_CHANGE	0x000F#define NETDEV_POST_INIT	0x0010#define NETDEV_UNREGISTER_FINAL 0x0011#define NETDEV_RELEASE		0x0012#define NETDEV_NOTIFY_PEERS	0x0013#define NETDEV_JOIN		0x0014#define NETDEV_CHANGEUPPER	0x0015#define NETDEV_RESEND_IGMP	0x0016#define NETDEV_PRECHANGEMTU	0x0017 /* notify before mtu change happened */#define NETDEV_CHANGEINFODATA	0x0018#define NETDEV_BONDING_INFO	0x0019

__neigh_create：

创建一个邻居项，并将其添加到散列表上，返回指向该邻居项的指针。
tbl:待创建的邻居项所属的邻居表，即arp_tbl；
pkey：三层协议地址(IP地址)
dev：输出设备
want_ref：？？

struct neighbour *__neigh_create(struct neigh_table *tbl, const void *pkey,				 struct net_device *dev, bool want_ref)	u32 hash_val;	int key_len = tbl->key_len;	int error;	/*调用neigh_alloc创建邻居项*/	struct neighbour *n1, *rc, *n = neigh_alloc(tbl, dev);	struct neigh_hash_table *nht;	if (!n) 		rc = ERR_PTR(-ENOBUFS);		goto out;		/*设置邻居项的三层协议地址、输出设备*/	memcpy(n->primary_key, pkey, key_len);	n->dev = dev;		/*增加设备引用计数*/	dev_hold(dev);	/* Protocol specific setup. */	/*执行邻居表的邻居项初始化函数，arp为arp_constructor完成*/	if (tbl->constructor &&	(error = tbl->constructor(n)) < 0) 		rc = ERR_PTR(error);		goto out_neigh_release;		/*指向设备的邻居项初始化函数*/	if (dev->netdev_ops->ndo_neigh_construct) 		error = dev->netdev_ops->ndo_neigh_construct(n);		if (error < 0) 			rc = ERR_PTR(error);			goto out_neigh_release;				/* Device specific setup. */	/*以太网设备neigh_setup为NULL*/	if (n->parms->neigh_setup &&	    (error = n->parms->neigh_setup(n)) < 0) 		rc = ERR_PTR(error);		goto out_neigh_release;		/*初始化邻居项的确认时间*/	n->confirmed = jiffies - (NEIGH_VAR(n->parms, BASE_REACHABLE_TIME) << 1);	write_lock_bh(&tbl->lock);	nht = rcu_dereference_protected(tbl->nht,					lockdep_is_held(&tbl->lock));	/*hash扩容*/	if (atomic_read(&tbl->entries) > (1 << nht->hash_shift))		nht = neigh_hash_grow(tbl, nht->hash_shift + 1);	/*计算hash值*/	hash_val = tbl->hash(pkey, dev, nht->hash_rnd) >> (32 - nht->hash_shift);	/*邻居项正在被删除*/	if (n->parms->dead) 		rc = ERR_PTR(-EINVAL);		goto out_tbl_unlock;		/*邻居项已经存在，递增其引用计数，释放新创建的邻居项*/	for (n1 = rcu_dereference_protected(nht->hash_buckets[hash_val],					    lockdep_is_held(&tbl->lock));	     n1 != NULL;	     n1 = rcu_dereference_protected(n1->next,			lockdep_is_held(&tbl->lock))) 		if (dev == n1->dev && !memcmp(n1->primary_key, pkey, key_len)) 			if (want_ref)				/*增加引用计数，#define neigh_hold(n)	atomic_inc(&(n)->refcnt)*/				neigh_hold(n1); 			rc = n1;			goto out_tbl_unlock;				n->dead = 0;	if (want_ref)		neigh_hold(n);	/*不存在，添加邻居项到hash表中*/	rcu_assign_pointer(n->next,			   rcu_dereference_protected(nht->hash_buckets[hash_val],						     lockdep_is_held(&tbl->lock)));	rcu_assign_pointer(nht->hash_buckets[hash_val], n);	write_unlock_bh(&tbl->lock);	neigh_dbg(2, "neigh %p is created\\n", n);	rc = n;out:	return rc;out_tbl_unlock:	write_unlock_bh(&tbl->lock);out_neigh_release:	neigh_release(n);	goto out;

neigh_alloc

创建邻居项

static struct neighbour *neigh_alloc(struct neigh_table *tbl, struct net_device *dev)	struct neighbour *n = NULL;	unsigned long now = jiffies;	int entries;	/*递增邻居表中邻居项的条目，然后返回当前条目(递增前)*/	entries = atomic_inc_return(&tbl->entries) - 1;	/*数目>=gc_thresh3,或者 >=gc_thresh2并且已超过5s未刷新，则必须立即刷新并强制垃圾回收*/	if (entries >= tbl->gc_thresh3 ||	    (entries >= tbl->gc_thresh2 &&	     time_after(now, tbl->last_flush + 5 * HZ))) 		/*如果垃圾回收失败，并且数目>=gc_thresh3，则不分配邻居项*/		if (!neigh_forced_gc(tbl) &&		    entries >= tbl->gc_thresh3)			goto out_entries;		/*分配邻居项*/	n = kzalloc(tbl->entry_size + dev->neigh_priv_len, GFP_ATOMIC);	if (!n)		goto out_entries;	/*初始化neighbour成员*/	__skb_queue_head_init(&n->arp_queue);	rwlock_init(&n->lock);	seqlock_init(&n->ha_lock);	n->updated	  = n->used = now;	n->nud_state	  = NUD_NONE;	n->output	  = neigh_blackhole;	seqlock_init(&n->hh.hh_lock);	/*parms初始化为tbl->parms*/	n->parms	  = neigh_parms_clone(&tbl->parms);	/*设置定时器*/	setup_timer(&n->timer, neigh_timer_handler, (unsigned long)n);	NEIGH_CACHE_STAT_INC(tbl, allocs);	n->tbl		  = tbl;	atomic_set(&n->refcnt, 1);	n->dead		  = 1;/*刚创建neighbour时，n->dead为1，在__neigh_create中被设置为0*/out:	return n;out_entries:	atomic_dec(&tbl->entries);	goto out;

arp_constructor

1.设置邻居项的类型
2.设置邻居项的ops指针
3.设置邻居项的output函数指针

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();	/*获取IP配置块*/	in_dev = __in_dev_get_rcu(dev);	if (!in_dev) 		rcu_read_unlock();		return -EINVAL;		/*获取邻居项的类型*/	neigh->type = inet_addr_type(dev_net(dev), addr);	/*neigh->parms在neigh_alloc函数中初始化为tbl->parms，在这里初始化为in_dev->arp_parms*/	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 (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);				/*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;

dst_neigh_output

static inline int dst_neigh_output(struct dst_entry *dst, struct neighbour *n,				   struct sk_buff *skb)	const struct hh_cache *hh;	if (dst->pending_confirm) 		unsigned long now = jiffies;		dst->pending_confirm = 0;		/* avoid dirtying neighbour */		if (n->confirmed != now)			n->confirmed = now;		hh = &n->hh;	if ((n->nud_state & NUD_CONNECTED) && hh->hh_len)		return neigh_hh_output(hh, skb);	else		return n->output(n, skb);

neigh_resolve_output

/* Slow and careful. */int neigh_resolve_output(struct neighbour *neigh, struct sk_buff *skb)	int rc = 0;	if (!neigh_event_send(neigh, skb)) 		int err;		struct net_device *dev = neigh->dev;		unsigned int seq;		if (dev->header_ops->cache && !neigh->hh.hh_len)			neigh_hh_init(neigh);		do 			__skb_pull(skb, skb_network_offset(skb));			seq = read_seqbegin(&neigh->ha_lock);			/*sbk添加二层头*/			err = dev_hard_header(skb, dev, ntohs(skb->protocol),					      neigh->ha, NULL, skb->len);		 while (read_seqretry(&neigh->ha_lock, seq));		if (err >= 0)			/*发送skb*/			rc = dev_queue_xmit(skb);		else			goto out_kfree_skb;	out:	return rc;out_kfree_skb:	rc = -EINVAL;	kfree_skb(skb);	goto out;

neigh_event_send

static inline int neigh_event_send(struct neighbour *neigh, struct sk_buff *skb)	unsigned long now = jiffies;		/*更新最近一次使用时间*/	if (neigh->used != now)		neigh->used = now;	/*此时状态为NUD_NONE*/	if (!(neigh->nud_state&(NUD_CONNECTED|NUD_DELAY|NUD_PROBE)))		return __neigh_event_send(neigh, skb);	return 0;

__neigh_event_send

int __neigh_event_send(struct neighbour *neigh, struct sk_buff *skb)	int rc;	bool immediate_probe = false;	write_lock_bh(&neigh->lock);	rc = 0;	if (neigh->nud_state & (NUD_CONNECTED | NUD_DELAY | NUD_PROBE))		goto out_unlock_bh;	if (neigh->dead)		goto out_dead;	if (!(neigh->nud_state & (NUD_STALE | NUD_INCOMPLETE))) 		if (NEIGH_VAR(neigh->parms, MCAST_PROBES) +		    NEIGH_VAR(neigh->parms, APP_PROBES)) 			unsigned long next, now = jiffies;			atomic_set(&neigh->probes,				   NEIGH_VAR(neigh->parms, UCAST_PROBES));			/*设置邻居状态为NUD_INCOMPLETE*/			neigh->nud_state     = NUD_INCOMPLETE;			neigh->updated = now;			next = now + max(NEIGH_VAR(neigh->parms, RETRANS_TIME),					 HZ/2);			/*添加定时器*/			neigh_add_timer(neigh, next);			immediate_probe = true;		 else 			neigh->nud_state = NUD_FAILED;			neigh->updated = jiffies;			write_unlock_bh(&neigh->lock);			kfree_skb(skb);			return 1;			 else if (neigh->nud_state & NUD_STALE) 		neigh_dbg(2, "neigh %p is delayed\\n", neigh);		neigh->nud_state = NUD_DELAY;		neigh->updated = jiffies;		neigh_add_timer(neigh, jiffies +				NEIGH_VAR(neigh->parms, DELAY_PROBE_TIME));		/*如果队列满了，把arp队列中前面几个skb删除*/	if (neigh->nud_state == NUD_INCOMPLETE) 		if (skb) 			while (neigh->arp_queue_len_bytes + skb->truesize >			       NEIGH_VAR(neigh->parms, QUEUE_LEN_BYTES)) 				struct sk_buff *buff;				buff = __skb_dequeue(&neigh->arp_queue);				if (!buff)					break;				neigh->arp_queue_len_bytes -= buff->truesize;				kfree_skb(buff);				NEIGH_CACHE_STAT_INC(neigh->tbl, unres_discards);						skb_dst_force(skb);			/*队列添加到arp队列*/			__skb_queue_tail(&neigh->arp_queue, skb);			neigh->arp_queue_len_bytes += skb->truesize;				rc = 1;	out_unlock_bh:	if (immediate_probe)		neigh_probe(neigh);	else		write_unlock(&neigh->lock);	local_bh_enable();	return rc;out_dead:	if (neigh->nud_state & NUD_STALE)		goto out_unlock_bh;	write_unlock_bh(&neigh->lock);	kfree_skb(skb);	return 1;

neigh_timer_handler

/* Called when a timer expires for a neighbour entry. */static void neigh_timer_handler(unsigned long arg)	unsigned long now, next;	struct neighbour *neigh = (struct neighbour *)arg;	unsigned int state;	int notify = 0;	write_lock(&neigh->lock);	state = neigh->nud_state;	now = jiffies;	next = now + HZ;	if (!(state & NUD_IN_TIMER))		goto out;	if (state & NUD_REACHABLE) 		if (time_before_eq(now,				   neigh->confirmed + neigh->parms->reachable_time)) 			neigh_dbg(2, "neigh %p is still alive\\n", neigh);			next = neigh->confirmed + neigh->parms->reachable_time;		 else if (time_before_eq(now,					  neigh->used +					  NEIGH_VAR(neigh->parms, DELAY_PROBE_TIME))) 			neigh_dbg(2, "neigh %p is delayed\\n", neigh);			neigh->nud_state = NUD_DELAY;			neigh->updated = jiffies;			neigh_suspect(neigh);			next = now + NEIGH_VAR(neigh->parms, DELAY_PROBE_TIME);		 else 			neigh_dbg(2, "neigh %p is suspected\\n", neigh);			neigh->nud_state = NUD_STALE;			neigh->updated = jiffies;			neigh_suspect(neigh);			notify = 1;			 else if (state & NUD_DELAY) 		if (time_before_eq(now,				   neigh->confirmed +				   NEIGH_VAR(neigh->parms, DELAY_PROBE_TIME))) 			neigh_dbg(2, "neigh %p is now reachable\\n", neigh);			neigh->nud_state = NUD_REACHABLE;			neigh->updated = jiffies;			neigh_connect(neigh);			notify = 1;			next = neigh->confirmed + neigh->parms->reachable_time;		 else 			neigh_dbg(2, "neigh %p is probed\\n", neigh);			neigh->nud_state = NUD_PROBE;			neigh->updated = jiffies;			atomic_set(&neigh->probes, 0);			next = now + NEIGH_VAR(neigh->parms, RETRANS_TIME);			 else 		/* NUD_PROBE|NUD_INCOMPLETE */		next = now + NEIGH_VAR(neigh->parms, RETRANS_TIME);		/*发送报文请求次数大于上限*/	if ((neigh->nud_state & (NUD_INCOMPLETE | NUD_PROBE)) &&	    atomic_read(&neigh->probes) >= neigh_max_probes(neigh)) 		neigh->nud_state = NUD_FAILED;		notify = 1;		neigh_invalidate(neigh);		goto out;		if (neigh->nud_state & NUD_IN_TIMER) 		if (time_before(next, jiffies + HZ/2))			next = jiffies + HZ/2;		if (!mod_timer(&neigh->timer, next))			neigh_hold(neigh);		/*发送arp请求报文*/	if (neigh->nud_state & (NUD_INCOMPLETE | NUD_PROBE)) 		neigh_probe(neigh);	 else out:		write_unlock(&neigh->lock);		if (notify)		neigh_update_notify(neigh);	neigh_release(neigh);

neigh_probe

static void neigh_probe(struct neighbour *neigh)	__releases(neigh->lock)	struct sk_buff *skb = skb_peek_tail(&neigh->arp_queue);	/* keep skb alive even if arp_queue overflows */	if (skb)		skb = skb_copy(skb, GFP_ATOMIC);	write_unlock(&neigh->lock);	/*调用arp_solicit发送arp请求报文*/	if (neigh->ops->solicit)		neigh->ops->solicit(neigh, skb);	atomic_inc(&neigh->probes);	kfree_skb(skb);

arp_error_report()

调用dst_link_failure()函数向三层报告错误，当邻居项缓存中还有未发送的报文，而该邻居却无法访问时被调用。不懂。

static void arp_error_report(struct neighbour *neigh, struct sk_buff *skb)	dst_link_failure(skb);	kfree_skb(skb);

arp_solicit()

用来发送arp请求，在邻居项状态定时器处理函数中被调用。

neigh：arp请求的目的邻居项

skb：缓存在该邻居项中的待发送报文，用来获取该skb的源ip地址。

static void arp_solicit(struct neighbour *neigh, struct sk_buff *skb)	__be32 saddr = 0;	u8 dst_ha[MAX_ADDR_LEN], *dst_hw = NULL;	struct net_device *dev = neigh->dev;	__be32 target = *(__be32 *)neigh->primary_key;	int probes = atomic_read(&neigh->probes);	struct in_device *in_dev;	rcu_read_lock();	in_dev = __in_dev_get_rcu(dev);	if (!in_dev) 		rcu_read_unlock();		return;		switch (IN_DEV_ARP_ANNOUNCE(in_dev)) 	default:	case 0:		/* By default announce any local IP */		if (skb && inet_addr_type(dev_net(dev),					  ip_hdr(skb)->saddr) == RTN_LOCAL)			saddr = ip_hdr(skb)->saddr;		break;	case 1:		/* Restrict announcements of saddr in same subnet */		if (!skb)			break;		saddr = ip_hdr(skb)->saddr;		if (inet_addr_type(dev_net(dev), saddr) == RTN_LOCAL) 			/* saddr should be known to target */			if (inet_addr_onlink(in_dev, target, saddr))				break;				saddr = 0;		break;	case 2:		/* Avoid secondary IPs, get a primary/preferred one */		break;		rcu_read_unlock();	if (!saddr)		saddr = inet_select_addr(dev, target, RT_SCOPE_LINK);	probes -= NEIGH_VAR(neigh->parms, UCAST_PROBES);	if (probes < 0) 		if (!(neigh->nud_state & NUD_VALID))			pr_debug("trying to ucast probe in NUD_INVALID\\n");		neigh_ha_snapshot(dst_ha, neigh, dev);		dst_hw = dst_ha;	 else 		probes -= NEIGH_VAR(neigh->parms, APP_PROBES);		if (probes < 0) 			neigh_app_ns(neigh);			return;				arp_send(ARPOP_REQUEST, ETH_P_ARP, target, dev, saddr,		 dst_hw, dev->dev_addr, NULL);

将得到的硬件源、目的地址，IP源、目的地址等作为参数，调用arp_send()函数创建一个arp报文并将其输出。

arp_send()

创建及发送arp报文

/* *	Create and send an arp packet. */void arp_send(int type, int ptype, __be32 dest_ip,	      struct net_device *dev, __be32 src_ip,	      const unsigned char *dest_hw, const unsigned char *src_hw,	      const unsigned char *target_hw)	struct sk_buff *skb;	/*	 *	No arp on this interface.	 */	if (dev->flags&IFF_NOARP)		return;	skb = arp_create(type, ptype, dest_ip, dev, src_ip,			 dest_hw, src_hw, target_hw);	if (!skb)		return;	arp_xmit(skb);

arp_create()

创建arp报文，填充字段。

/* *	Interface to link layer: send routine and receive handler. *//* *	Create an arp packet. If dest_hw is not set, we create a broadcast *	message. */struct sk_buff *arp_create(int type, int ptype, __be32 dest_ip,			   struct net_device *dev, __be32 src_ip,			   const unsigned char *dest_hw,			   const unsigned char *src_hw,			   const unsigned char *target_hw)	struct sk_buff *skb;	struct arphdr *arp;	unsigned char *arp_ptr;	int hlen = LL_RESERVED_SPACE(dev);	int tlen = dev->needed_tailroom;	/*	 *	Allocate a buffer	 */	skb = alloc_skb(arp_hdr_len(dev) + hlen + tlen, GFP_ATOMIC);	if (!skb)		return NULL;	skb_reserve(skb, hlen);	skb_reset_network_header(skb);	arp = (struct arphdr *) skb_put(skb, arp_hdr_len(dev));	skb->dev = dev;	skb->protocol = htons(ETH_P_ARP);	if (!src_hw)		src_hw = dev->dev_addr;        /*目的MAC未知时，置1*/	if (!dest_hw)		dest_hw = dev->broadcast;	/*	 *	Fill the device header for the ARP frame	 */	if (dev_hard_header(skb, dev, ptype, dest_hw, src_hw, skb->len) < 0)		goto out;	/*	 * Fill out the arp protocol part.	 *	 * The arp hardware type should match the device type, except for FDDI,	 * which (according to RFC 1390) should always equal 1 (Ethernet).	 */	/*	 *	Exceptions everywhere. AX.25 uses the AX.25 PID value not the	 *	DIX code for the protocol. Make these device structure fields.	 */	switch (dev->type) 	default:		arp->ar_hrd = htons(dev->type);		arp->ar_pro = htons(ETH_P_IP);		break;#if IS_ENABLED(CONFIG_AX25)	case ARPHRD_AX25:		arp->ar_hrd = htons(ARPHRD_AX25);		arp->ar_pro = htons(AX25_P_IP);		break;#if IS_ENABLED(CONFIG_NETROM)	case ARPHRD_NETROM:		arp->ar_hrd = htons(ARPHRD_NETROM);		arp->ar_pro = htons(AX25_P_IP);		break;#endif#endif#if IS_ENABLED(CONFIG_FDDI)	case ARPHRD_FDDI:		arp->ar_hrd = htons(ARPHRD_ETHER);		arp->ar_pro = htons(ETH_P_IP);		break;#endif		arp->ar_hln = dev->addr_len;	arp->ar_pln = 4;	arp->ar_op = htons(type);	arp_ptr = (unsigned char *)(arp + 1);	memcpy(arp_ptr, src_hw, dev->addr_len);	arp_ptr += dev->addr_len;	memcpy(arp_ptr, &src_ip, 4);	arp_ptr += 4;	switch (dev->type) #if IS_ENABLED(CONFIG_FIREWIRE_NET)	case ARPHRD_IEEE1394:		break;#endif	default:		if (target_hw)			memcpy(arp_ptr, target_hw, dev->addr_len);		else			memset(arp_ptr, 0, dev->addr_len);		arp_ptr += dev->addr_len;		memcpy(arp_ptr, &dest_ip, 4);	return skb;out:	kfree_skb(skb);	return NULL;

arp_xmit()

发送arp报文

/* *	Send an arp packet. */void arp_xmit(struct sk_buff *skb)	/* Send it off, maybe filter it using firewalling first.  */	NF_HOOK(NFPROTO_ARP, NF_ARP_OUT, NULL, skb,		NULL, skb->dev, dev_queue_xmit_sk);

arp报文的输入：

arp_rcv()

用来从二层接收并处理一个arp报文。这个函数中就是做了一些参数检查，然后调用arp_process()函数。

/* *	Receive an arp request from the device layer. */static int arp_rcv(struct sk_buff *skb, struct net_device *dev,		   struct packet_type *pt, struct net_device *orig_dev)	const struct arphdr *arp;	/* do not tweak dropwatch on an ARP we will ignore */	if (dev->flags & IFF_NOARP || //网络设备知否支持arp协议	    skb->pkt_type == PACKET_OTHERHOST || //arp报文是否是转发的包，表示这个包不应该由自己接收	    skb->pkt_type == PACKET_LOOPBACK) //arp报文来自回环接口		goto consumeskb;	skb = skb_share_check(skb, GFP_ATOMIC);//如果skb是共享的，就复制一份	if (!skb)		goto out_of_mem;	/* ARP header, plus 2 device addresses, plus 2 IP addresses.  */        /*检测arp报文的完整性，其长度是否等于一个arp头部长度+两个硬件地址长度+两个IP地址长度*/	if (!pskb_may_pull(skb, arp_hdr_len(dev)))		goto freeskb;	arp = arp_hdr(skb);        /*arp报文的硬件地址长度与网络设备的硬件地址长度是否匹配，arp报文的协议地址长度是否为4*/	if (arp->ar_hln != dev->addr_len || arp->ar_pln != 4)		goto freeskb;	memset(NEIGH_CB(skb), 0, sizeof(struct neighbour_cb)); //#define NEIGH_CB(skb)	((struct neighbour_cb *)(skb)->cb)cb[]数组中存放的是每一协议层都可以自由使用的一段空间，一般用来存放控制指令和控制数据       	return NF_HOOK(NFPROTO_ARP, NF_ARP_IN, NULL, skb, //netfilter arp hook函数		       dev, NULL, arp_process);consumeskb:	consume_skb(skb);	return 0;freeskb:	kfree_skb(skb);out_of_mem:	return 0;

arp_process()

/* *	Process an arp request. */static int arp_process(struct sock *sk, struct sk_buff *skb)	struct net_device *dev = skb->dev;	struct in_device *in_dev = __in_dev_get_rcu(dev);	struct arphdr *arp;	unsigned char *arp_ptr;	struct rtable *rt;	unsigned char *sha;	__be32 sip, tip;	u16 dev_type = dev->type;	int addr_type;	struct neighbour *n;	struct net *net = dev_net(dev);	bool is_garp = false;	/* arp_rcv below verifies the ARP header and verifies the device	 * is ARP'able.	 */	if (!in_dev)//输入网络设备的IP配置块		goto out;	arp = arp_hdr(skb);                //根据网络设备类型，检测arp报文中硬件类型与协议类型的有效性	switch (dev_type) 	default:		if (arp->ar_pro != htons(ETH_P_IP) ||		    htons(dev_type) != arp->ar_hrd)			goto out;		break;	case ARPHRD_ETHER:	case ARPHRD_FDDI:	case ARPHRD_IEEE802:		/*		 * ETHERNET, and Fibre Channel (which are IEEE 802		 * devices, according to RFC 2625) devices will accept ARP		 * hardware types of either 1 (Ethernet) or 6 (IEEE 802.2).		 * This is the case also of FDDI, where the RFC 1390 says that		 * FDDI devices should accept ARP hardware of (1) Ethernet,		 * however, to be more robust, we'll accept both 1 (Ethernet)		 * or 6 (IEEE 802.2)		 */		if ((arp->ar_hrd != htons(ARPHRD_ETHER) &&		     arp->ar_hrd != htons(ARPHRD_IEEE802)) ||		    arp->ar_pro != htons(ETH_P_IP))			goto out;		break;	case ARPHRD_AX25:		if (arp->ar_pro != htons(AX25_P_IP) ||		    arp->ar_hrd != htons(ARPHRD_AX25))			goto out;		break;	case ARPHRD_NETROM:		if (arp->ar_pro != htons(AX25_P_IP) ||		    arp->ar_hrd != htons(ARPHRD_NETROM))			goto out;		break;		/* Understand only these message types */	if (arp->ar_op != htons(ARPOP_REPLY) &&	    arp->ar_op != htons(ARPOP_REQUEST))		goto out;/* *	Extract fields */     //从arp报文中解析发送方MAC,IP，目的target IP。	arp_ptr = (unsigned char *)(arp + 1);	sha	= arp_ptr;//发送方硬件地址	arp_ptr += dev->addr_len;	memcpy(&sip, arp_ptr, 4);//解析源IP	arp_ptr += 4;	switch (dev_type) #if IS_ENABLED(CONFIG_FIREWIRE_NET)	case ARPHRD_IEEE1394:		break;#endif	default:		arp_ptr += dev->addr_len;		memcpy(&tip, arp_ptr, 4);//解析目的IP/* *	Check for bad requests for 127.x.x.x and requests for multicast *	addresses.  If this is one such, delete it. */        //丢弃ip地址为组播或互换地址的arp报文	if (ipv4_is_multicast(tip) ||	    (!IN_DEV_ROUTE_LOCALNET(in_dev) && ipv4_is_loopback(tip)))		goto out;/* *     Special case: We must set Frame Relay source Q.922 address */    //如果硬件类型为Q.922，则arp应答报文中目的硬件地址设置为网路设备的广播地址	if (dev_type == ARPHRD_DLCI)		sha = dev->broadcast;/* *  Process entry.  The idea here is we want to send a reply if it is a *  request for us or if it is a request for someone else that we hold *  a proxy for.  We want to add an entry to our cache if it is a reply *  to us or if it is a request for our address. *  (The assumption for this last is that if someone is requesting our *  address, they are probably intending to talk to us, so it saves time *  if we cache their address.  Their address is also probably not in *  our cache, since ours is not in their cache.) * *  Putting this another way, we only care about replies if they are to *  us, in which case we add them to the cache.  For requests, we care *  about those for us and those for our proxies.  We reply to both, *  and in the case of requests for us we add the requester to the arp *  cache. */	/* Special case: IPv4 duplicate address detection packet (RFC2131) */        //如果请求报文的源ip为0，则该arp报文是用来检测ipv4地址冲突的，因此在确定请求报文的目的IP为本地IP地址后，以该IP地址为源地址及目的地址发送arp响应报文。	if (sip == 0) 		if (arp->ar_op == htons(ARPOP_REQUEST) &&		    inet_addr_type(net, tip) == RTN_LOCAL &&		    !arp_ignore(in_dev, sip, tip))			arp_send(ARPOP_REPLY, ETH_P_ARP, sip, dev, tip, sha,				 dev->dev_addr, sha);		goto out;		if (arp->ar_op == htons(ARPOP_REQUEST) &&	    ip_route_input_noref(skb, tip, sip, 0, dev) == 0)  //找目的IP对应的路由		rt = skb_rtable(skb);		addr_type = rt->rt_type;            /*如果arp报文是发送给本机的，调用neigh_event_ns更新对应的邻居项，然后根据系统设置来决定是否过滤和丢弃arp报文，最后发送arp响应报文。*/		if (addr_type == RTN_LOCAL) 			int dont_send;			dont_send = arp_ignore(in_dev, sip, tip);			if (!dont_send && IN_DEV_ARPFILTER(in_dev))				dont_send = arp_filter(sip, tip, dev);			if (!dont_send) 				n = neigh_event_ns(&arp_tbl, sha, &sip, dev);				if (n) 					arp_send(ARPOP_REPLY, ETH_P_ARP, sip,						 dev, tip, sha, dev->dev_addr,						 sha);					neigh_release(n);										goto out;		         /*对于不是发送给本机的arp请求报文，根据系统参数确定是否进行arp代理。*/                else if (IN_DEV_FORWARD(in_dev)) 			if (addr_type == RTN_UNICAST  &&			    (arp_fwd_proxy(in_dev, dev, rt) ||			     arp_fwd_pvlan(in_dev, dev, rt, sip, tip) ||			     (rt->dst.dev != dev &&			      pneigh_lookup(&arp_tbl, net, &tip, dev, 0)))) 				n = neigh_event_ns(&arp_tbl, sha, &sip, dev);				if (n)					neigh_release(n);				if (NEIGH_CB(skb)->flags & LOCALLY_ENQUEUED ||				    skb->pkt_type == PACKET_HOST ||				    NEIGH_VAR(in_dev->arp_parms, PROXY_DELAY) == 0) 					arp_send(ARPOP_REPLY, ETH_P_ARP, sip,						 dev, tip, sha, dev->dev_addr,						 sha);				 else 					pneigh_enqueue(&arp_tbl,						       in_dev->arp_parms, skb);					return 0;								goto out;							/* Update our ARP tables */        /*对于arp应答消息，或未处理的代理请求，则需要更新邻居表，因此现在邻居表中根据sip找到对应的邻居项*/	n = __neigh_lookup(&arp_tbl, &sip, dev, 0);        /*对于那些并非由arp请求而接收到的arp应答，在系统允许接收的情况下，创建相应的邻居项*/	if (IN_DEV_ARP_ACCEPT(in_dev)) 		/* Unsolicited ARP is not accepted by default.		   It is possible, that this option should be enabled for some		   devices (strip is candidate)		 */		is_garp = arp->ar_op == htons(ARPOP_REQUEST) && tip == sip &&			  inet_addr_type(net, sip) == RTN_UNICAST;		if (!n &&		    ((arp->ar_op == htons(ARPOP_REPLY)  &&		      inet_addr_type(net, sip) == RTN_UNICAST) || is_garp))			n = __neigh_lookup(&arp_tbl, &sip, dev, 1);	/*更新或创建新的邻居项，首先确定邻居项的新状态，如果是发送给本机的arp应答报文，则对应邻居项状态应转变为NUD_REACHABLE，否则转到NUD_STALE。然后调用neigh_update更新邻居项，如果其更新时间已超过locktime,则用覆盖的方式进行更新。*/	if (n) 		int state = NUD_REACHABLE;		int override;		/* If several different ARP replies follows back-to-back,		   use the FIRST one. It is possible, if several proxy		   agents are active. Taking the first reply prevents		   arp trashing and chooses the fastest router.		 */		override = time_after(jiffies,				      n->updated +				      NEIGH_VAR(n->parms, LOCKTIME)) ||			   is_garp;		/* Broadcast replies and request packets		   do not assert neighbour reachability.		 */		if (arp->ar_op != htons(ARPOP_REPLY) ||		    skb->pkt_type != PACKET_HOST)			state = NUD_STALE;		neigh_update(n, sha, state,			     override ? NEIGH_UPDATE_F_OVERRIDE : 0);		neigh_release(n);	out:	consume_skb(skb);	return 0;

neigh_event_ns

struct neighbour *neigh_event_ns(struct neigh_table *tbl,				 u8 *lladdr, void *saddr,				 struct net_device *dev)	/*创建neighbour*/	struct neighbour *neigh = __neigh_lookup(tbl, saddr, dev,						 lladdr || !dev->addr_len);	if (neigh)		neigh_update(neigh, lladdr, NUD_STALE,			     NEIGH_UPDATE_F_OVERRIDE);	return neigh;

neigh_update

这个函数的作用就是更新邻居项硬件地址和状态。分支比较多。

/* Generic update routine.   -- lladdr is new lladdr or NULL, if it is not supplied.   -- new    is new state.   -- flags	NEIGH_UPDATE_F_OVERRIDE allows to override existing lladdr,				if it is different.	NEIGH_UPDATE_F_WEAK_OVERRIDE will suspect existing "connected"				lladdr instead of overriding it				if it is different.				It also allows to retain current state				if lladdr is unchanged.	NEIGH_UPDATE_F_ADMIN	means that the change is administrative.	NEIGH_UPDATE_F_OVERRIDE_ISROUTER allows to override existing				NTF_ROUTER flag.	NEIGH_UPDATE_F_ISROUTER	indicates if the neighbour is known as				a router.   Caller MUST hold reference count on the entry. *//*new：邻居项新状态，lladdr：邻居项新硬件地址*/int neigh_update(struct neighbour *neigh, const u8 *lladdr, u8 new,		 u32 flags)	u8 old;//邻居项老的状态	int err;	int notify = 0;//是否通知该事件	struct net_device *dev;	int update_isrouter = 0;//邻居项是否为路由器	write_lock_bh(&neigh->lock);	dev    = neigh->dev;	old    = neigh->nud_state;	err    = -EPERM;	/*case1:邻居项原先状态为NUD_NOARP或者NUD_PERMANENT时，标志位必须包含NEIGH_UPDATE_F_ADMIN	才允许更新，表示是管理员进行的操作，否则不允许更新。*/	if (!(flags & NEIGH_UPDATE_F_ADMIN) &&	    (old & (NUD_NOARP | NUD_PERMANENT)))		goto out;	if (neigh->dead)		goto out;	/*case2:新状态为无效状态，删除其定时器。如果原先状态为NUD_CONNECTED状态，调用neigh_suspect	更新其输出函数；如果老状态为NUD_INCOMPLETE或者NUD_PROBE，新状态为NUD_FAILED，执行neigh_invalidate操作。*/	if (!(new & NUD_VALID)) 		neigh_del_timer(neigh);		if (old & NUD_CONNECTED)			neigh_suspect(neigh);		neigh->nud_state = new;		err = 0;		notify = old & NUD_VALID;		if ((old & (NUD_INCOMPLETE | NUD_PROBE)) &&		    (new & NUD_FAILED)) 			neigh_invalidate(neigh);			notify = 1;				goto out;		/* Compare new lladdr with cached one */	if (!dev->addr_len) 		/* First case: device needs no address. */		lladdr = neigh->ha;	 else if (lladdr) 		/* The second case: if something is already cached		   and a new address is proposed:		   - compare new & old		   - if they are different, check override flag		 */		if ((old & NUD_VALID) &&		    !memcmp(lladdr, neigh->ha, dev->addr_len))			lladdr = neigh->ha;	 else 		/* No address is supplied; if we know something,		   use it, otherwise discard the request.		 */		err = -EINVAL;		if (!(old & NUD_VALID))			goto out;		lladdr = neigh->ha;		if (new & NUD_CONNECTED)		neigh->confirmed = jiffies;	neigh->updated = jiffies;	/* If entry was valid and address is not changed,	   do not change entry state, if new one is STALE.	 */	err = 0;	update_isrouter = flags & NEIGH_UPDATE_F_OVERRIDE_ISROUTER;	if (old & NUD_VALID) 		/*前后地址不相同，并且没有NEIGH_UPDATE_F_OVERRIDE标志*/		if (lladdr != neigh->ha && !(flags & NEIGH_UPDATE_F_OVERRIDE)) 			update_isrouter = 0;			/*带有NEIGH_UPDATE_F_WEAK_OVERRIDE标志，并且老状态为NUD_CONNECTED*/			if ((flags & NEIGH_UPDATE_F_WEAK_OVERRIDE) &&			    (old & NUD_CONNECTED)) 				lladdr = neigh->ha;				new = NUD_STALE;			 else				goto out;		 else 			if (lladdr == neigh->ha && new == NUD_STALE &&			    ((flags & NEIGH_UPDATE_F_WEAK_OVERRIDE) ||			     (old & NUD_CONNECTED))			    )				new = old;				if (new != old) 		neigh_del_timer(neigh);		if (new & NUD_IN_TIMER)			neigh_add_timer(neigh, (jiffies +						((new & NUD_REACHABLE) ?						 neigh->parms->reachable_time :						 0)));		neigh->nud_state = new;		notify = 1;		/*前后地址不相同，更新地址*/	if (lladdr != neigh->ha) 		write_seqlock(&neigh->ha_lock);		memcpy(&neigh->ha, lladdr, dev->addr_len);		write_sequnlock(&neigh->ha_lock);		neigh_update_hhs(neigh);		if (!(new & NUD_CONNECTED))			neigh->confirmed = jiffies -				      (NEIGH_VAR(neigh->parms, BASE_REACHABLE_TIME) << 1);		notify = 1;		if (new == old)		goto out;	if (new & NUD_CONNECTED)		neigh_connect(neigh);//更新output函数	else		neigh_suspect(neigh);//更新output函数	/*如果邻居项是无效状态变为有效状态，则便利arp_queue,将缓存在队列中的报文逐个发出。*/	if (!(old & NUD_VALID)) 		struct sk_buff *skb;		/* Again: avoid dead loop if something went wrong */		while (neigh->nud_state & NUD_VALID &&		       (skb = __skb_dequeue(&neigh->arp_queue)) != NULL) 			struct dst_entry *dst = skb_dst(skb);			struct neighbour *n2, *n1 = neigh;			write_unlock_bh(&neigh->lock);			rcu_read_lock();			/* Why not just use 'neigh' as-is?  The problem is that			 * things such as shaper, eql, and sch_teql can end up			 * using alternative, different, neigh objects to output			 * the packet in the output path.  So what we need to do			 * here is re-lookup the top-level neigh in the path so			 * we can reinject the packet there.			 */			n2 = NULL;			if (dst) 				n2 = dst_neigh_lookup_skb(dst, skb);				if (n2)					n1 = n2;						n1->output(n1, skb);			if (n2)				neigh_release(n2);			rcu_read_unlock();			write_lock_bh(&neigh->lock);				__skb_queue_purge(&neigh->arp_queue);		neigh->arp_queue_len_bytes = 0;	out:	if (update_isrouter) 		neigh->flags = (flags & NEIGH_UPDATE_F_ISROUTER) ?			(neigh->flags | NTF_ROUTER) :			(neigh->flags & ~NTF_ROUTER);		write_unlock_bh(&neigh->lock);	/*发送通知事件*/	if (notify)		neigh_update_notify(neigh);	return err;

neigh_update_notify

static void neigh_update_notify(struct neighbour *neigh)	call_netevent_notifiers(NETEVENT_NEIGH_UPDATE, neigh);	__neigh_notify(neigh, RTM_NEWNEIGH, 0);

arp_ignore()

static int arp_ignore(struct in_device *in_dev, __be32 sip, __be32 tip)	struct net *net = dev_net(in_dev->dev);	int scope;	switch (IN_DEV_ARP_IGNORE(in_dev)) 	case 0:	/* Reply, the tip is already validated */		return 0;	case 1:	/* Reply only if tip is configured on the incoming interface */		sip = 0;		scope = RT_SCOPE_HOST;		break;	case 2:	/*		 * Reply only if tip is configured on the incoming interface		 * and is in same subnet as sip		 */		scope = RT_SCOPE_HOST;		break;	case 3:	/* Do not reply for scope host addresses */		sip = 0;		scope = RT_SCOPE_LINK;		in_dev = NULL;		break;	case 4:	/* Reserved */	case 5:	case 6:	case 7:		return 0;	case 8:	/* Do not reply */		return 1;	default:		return 0;		return !inet_confirm_addr(net, in_dev, sip, tip, scope);

arp_filter

static int arp_filter(__be32 sip, __be32 tip, struct net_device *dev)	struct rtable *rt;	int flag = 0;	/*unsigned long now; */	struct net *net = dev_net(dev);	rt = ip_route_output(net, sip, tip, 0, 0);	if (IS_ERR(rt))		return 1;	if (rt->dst.dev != dev) 		NET_INC_STATS_BH(net, LINUX_MIB_ARPFILTER);		flag = 1;		ip_rt_put(rt);	return flag;

arp代理

代理arp（proxy arp），通常像路由器这样的设备才使用，用来代替处于另一个网段的主机回答本网段主机的arp请求。

感觉代码ARP好像没啥用呀。

网络主机发包的一般过程：

1.当目的IP和自己在同一网段时，直接arp请求该目的IP的MAC。

2.当目的IP和自己不再同一网段时，arp请求默认网关的MAC。

https://www.cnblogs.com/taitai139/p/12336554.html

https://www.cnblogs.com/Widesky/p/10489514.html

当主机没有默认网关的时候，arp请求别的网段的报文，到达路由器后，本来路由器是要隔离广播的，把这个arp请求报文给丢弃，这样就没法通信了。当路由器开启arp proxy后，路由器发现请求的目的IP在其他网段，就自己给主机回复一个arp响应报文，这样源主机就把路由器的MAC当成目的IP主机对应的MAC，可以通信了。这样可能会造成主机arp表中，多个IP地址都对应于路由器的同一个MAC地址。

可以使用arping命令发送指定IP的arp请求报文。

写完了发现这个老妹写的arp代理文章蛮好的，不过她好像是转载的。