网站怎么申请备案手机网站建设案例
参见linux内核网络栈源代码情景分析一书
arp协议是围着一个数组链表的数据结构进行的，包括对节点的增删改查，一些回调函数的设置。
相关数据结构：
arp协议流程图：
// 维护ip和mac地址映射的数组链表
struct arp_table
{struct arp_table *next; /* Linked entry list */// 该条数据上一次使用的时间，用来判断该数据是否已经过期unsigned long last_used; /* For expiry */// 该条数据的一些设置，比如是否是永久性的，如果是则不会过期，也就是会一直存在该数组链表中unsigned int flags; /* Control status */unsigned long ip; /* ip address of entry */unsigned long mask; /* netmask - used for generalised proxy arps (tridge) */unsigned char ha[MAX_ADDR_LEN]; /* Hardware address */unsigned char hlen; /* Length of hardware address */unsigned short htype; /* Type of hardware in use */struct device *dev; /* Device the entry is tied to *//** The following entries are only used for unresolved hw addresses.*/// 定时器struct timer_list timer; /* expire timer */// 重试的次数int retries; /* remaining retries */// 因为还没有完成ip和mac映射而导致无法发送的数据包，完成映射会进行处理这些数据包struct sk_buff_head skb; /* list of queued packets */
};/** Configurable Parameters (don't touch unless you know what you are doing*//** If an arp request is send, ARP_RES_TIME is the timeout value until the* next request is send.*/
// 如果第一个查询的包发出去后，ARP_RES_TIME长的时间还没有收到回复，就重新发一个
#define ARP_RES_TIME (250*(HZ/10))/** The number of times an arp request is send, until the host is* considered unreachable.*/// 最多重发ARP_MAX_TRIES次查询包
#define ARP_MAX_TRIES 3/** After that time, an unused entry is deleted from the arp table.*/
// arp_table数组链表中的数据最多存活的时长
#define ARP_TIMEOUT (600*HZ)/** How often is the function 'arp_check_retries' called.* An entry is invalidated in the time between ARP_TIMEOUT and* (ARP_TIMEOUT+ARP_CHECK_INTERVAL).*/
// 隔ARP_CHECK_INTERVAL秒查一次arp_table数组链表中的数据，看是否有过期的数据
#define ARP_CHECK_INTERVAL (60 * HZ)enum proxy {PROXY_EXACT=0,PROXY_ANY,PROXY_NONE,
};/* Forward declarations. */
static void arp_check_expire (unsigned long);
static struct arp_table *arp_lookup(unsigned long paddr, enum proxy proxy);static struct timer_list arp_timer ={ NULL, NULL, ARP_CHECK_INTERVAL, 0L, &arp_check_expire };/** The default arp netmask is just 255.255.255.255 which means it's* a single machine entry. Only proxy entries can have other netmasks*
*/
// 默认掩码是全1
#define DEF_ARP_NETMASK (~0)/** The size of the hash table. Must be a power of two.* Maybe we should remove hashing in the future for arp and concentrate* on Patrick Schaaf's Host-Cache-Lookup...*///arp_table数组的大小，不包括代理的的
#define ARP_TABLE_SIZE 16/* The ugly +1 here is to cater for proxy entries. They are put in their own list for efficiency of lookup. If you don't want to find a proxyentry then don't look in the last entry, otherwise do
*/
// 整个arp_table数组的大小，包括代理的
#define FULL_ARP_TABLE_SIZE (ARP_TABLE_SIZE+1)
// 初始化arp_table数组链表
struct arp_table *arp_tables[FULL_ARP_TABLE_SIZE] =
{NULL,
};/** The last bits in the IP address are used for the cache lookup.* A special entry is used for proxy arp entries*/
// arp_table中的数组是通过hash的方式存储到相应的位置的，这里是hash算法的实现
#define HASH(paddr) (htonl(paddr) & (ARP_TABLE_SIZE - 1))
// 代理的位置索引
#define PROXY_HASH ARP_TABLE_SIZE/** Check if there are too old entries and remove them. If the ATF_PERM* flag is set, they are always left in the arp cache (permanent entry).* Note: Only fully resolved entries, which don't have any packets in* the queue, can be deleted, since ARP_TIMEOUT is much greater than* ARP_MAX_TRIES*ARP_RES_TIME.*/
// 隔一段时间检查arp_table中的数组，看是否有需要删除的
static void arp_check_expire(unsigned long dummy)
{int i;// 当前时间unsigned long now = jiffies;unsigned long flags;save_flags(flags);cli();for (i = 0; i < FULL_ARP_TABLE_SIZE; i++){struct arp_table *entry;// 指向整个arp_table数组链表struct arp_table **pentry = &arp_tables[i];while ((entry = *pentry) != NULL){ // 如果上一次使用的时间离现在超过了ARP_TIMEOUT的大小，并且该数组没有设置永久存储标记，则删除该数据if ((now - entry->last_used) > ARP_TIMEOUT && !(entry->flags & ATF_PERM)){*pentry = entry->next; /* remove from list */// 清除定时器del_timer(&entry->timer); /* Paranoia */// 释放该数据对应的结构体kfree_s(entry, sizeof(struct arp_table));}elsepentry = &entry->next; /* go to next entry */}}restore_flags(flags);/** Set the timer again.*/// 删除旧的定时器，增加新的定时器（重置定时器），add_timer函数会自动加上当前时间jiffies，所以只需要设置时间间隔ARP_CHECK_INTERVAL就行del_timer(&arp_timer);arp_timer.expires = ARP_CHECK_INTERVAL;add_timer(&arp_timer);
}/** Release all linked skb's and the memory for this entry.*/
/* 释放某条arp缓存相关的内存，包括：1.挂在arp缓存结构体的sk_buff队列2.定时器3.arp缓存项对应的结构体
*/
static void arp_release_entry(struct arp_table *entry)
{struct sk_buff *skb;unsigned long flags;save_flags(flags);cli();// 释放该数据对应的sk_buff，也就是因为没有完成映射导致还没有发送出去的数据包/* Release the list of `skb' pointers. */while ((skb = skb_dequeue(&entry->skb)) != NULL){skb_device_lock(skb);restore_flags(flags);dev_kfree_skb(skb, FREE_WRITE);}restore_flags(flags);// 释放定时器del_timer(&entry->timer);// 释放该数据本身的结构体kfree_s(entry, sizeof(struct arp_table));return;
}/** Purge a device from the ARP queue*/
// 硬件有问题时释放该硬件对应的arp数据
int arp_device_event(unsigned long event, void *ptr)
{struct device *dev=ptr;int i;unsigned long flags;if(event!=NETDEV_DOWN)return NOTIFY_DONE;/** This is a bit OTT - maybe we need some arp semaphores instead.*/save_flags(flags);cli();// 遍历arp缓存数组链表for (i = 0; i < FULL_ARP_TABLE_SIZE; i++){struct arp_table *entry;struct arp_table **pentry = &arp_tables[i];while ((entry = *pentry) != NULL){ // 找到和该设备相关的arp缓存项if(entry->dev==dev){*pentry = entry->next; /* remove from list */del_timer(&entry->timer); /* Paranoia */kfree_s(entry, sizeof(struct arp_table));}elsepentry = &entry->next; /* go to next entry */}}restore_flags(flags);return NOTIFY_DONE;
}/** Create and send an arp packet. If (dest_hw == NULL), we create a broadcast* message.*/
// 发送arp包
void arp_send(int type, int ptype, unsigned long dest_ip, struct device *dev, unsigned long src_ip, unsigned char *dest_hw, unsigned char *src_hw){struct sk_buff *skb;struct arphdr *arp;unsigned char *arp_ptr;/** No arp on this interface.*/if(dev->flags&IFF_NOARP)return;/** Allocate a buffer*/// 申请一个sk_buff和设置包的内容skb = alloc_skb(sizeof(struct arphdr)+ 2*(dev->addr_len+4)+ dev->hard_header_len, GFP_ATOMIC);if (skb == NULL){printk("ARP: no memory to send an arp packet\n");return;}// len为有效数据的长度，此时为arp头(sizeof(struct arphdr))+两个ip和硬件地址(2*(dev->addr_len+4))+mac头长度(dev->hard_header_len)skb->len = sizeof(struct arphdr) + dev->hard_header_len + 2*(dev->addr_len+4);skb->arp = 1;skb->dev = dev;skb->free = 1;/** Fill the device header for the ARP frame*/// 设置mac头部dev->hard_header(skb->data,dev,ptype,dest_hw?dest_hw:dev->broadcast,src_hw?src_hw:NULL,skb->len,skb);/* Fill out the arp protocol part. */arp = (struct arphdr *) (skb->data + dev->hard_header_len);arp->ar_hrd = htons(dev->type);// 设置arp的上层协议
#ifdef CONFIG_AX25arp->ar_pro = (dev->type != ARPHRD_AX25)? htons(ETH_P_IP) : htons(AX25_P_IP);
#elsearp->ar_pro = htons(ETH_P_IP);
#endifarp->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;if (dest_hw != NULL)memcpy(arp_ptr, dest_hw, dev->addr_len);elsememset(arp_ptr, 0, dev->addr_len);arp_ptr+=dev->addr_len;memcpy(arp_ptr, &dest_ip, 4);// 传给链路层进行处理dev_queue_xmit(skb, dev, 0);
}/** This function is called, if an entry is not resolved in ARP_RES_TIME.* Either resend a request, or give it up and free the entry.*/
// arp解析请求超时重发
static void arp_expire_request (unsigned long arg)
{struct arp_table *entry = (struct arp_table *) arg;struct arp_table **pentry;unsigned long hash;unsigned long flags;save_flags(flags);cli();/** Since all timeouts are handled with interrupts enabled, there is a* small chance, that this entry has just been resolved by an incoming* packet. This is the only race condition, but it is handled...*/// 说明该数据已经完成了映射if (entry->flags & ATF_COM){restore_flags(flags);return;}// 如果重传次数还大于0,if (--entry->retries > 0){unsigned long ip = entry->ip;struct device *dev = entry->dev;// 重试定时器，如果ARP_RES_TIME秒后还没有回复，可能需要继续发送/* Set new timer. */del_timer(&entry->timer);entry->timer.expires = ARP_RES_TIME;add_timer(&entry->timer);restore_flags(flags);// 发送arp包arp_send(ARPOP_REQUEST, ETH_P_ARP, ip, dev, dev->pa_addr, NULL, dev->dev_addr);return;}/** Arp request timed out. Delete entry and all waiting packets.* If we give each entry a pointer to itself, we don't have to* loop through everything again. Maybe hash is good enough, but* I will look at it later.*/// 找到该数据对应的ip在arp_table里的位置hash = HASH(entry->ip);/* proxy entries shouldn't really time out so this is reallyonly here for completeness*/if (entry->flags & ATF_PUBL)pentry = &arp_tables[PROXY_HASH];elsepentry = &arp_tables[hash];// 删除解析失败的arp数据while (*pentry != NULL){if (*pentry == entry){*pentry = entry->next; /* delete from linked list */del_timer(&entry->timer);restore_flags(flags);arp_release_entry(entry);return;}pentry = &(*pentry)->next;}restore_flags(flags);printk("Possible ARP queue corruption.\n");/** We should never arrive here.*/
}/** This will try to retransmit everything on the queue.*/
// 完成某条数据的arp解析后，需要处理该数据对应的sk_buff链表
static void arp_send_q(struct arp_table *entry, unsigned char *hw_dest)
{struct sk_buff *skb;unsigned long flags;/** Empty the entire queue, building its data up ready to send*/// 该数据没有完成解析，则不能发送对应的数据包if(!(entry->flags&ATF_COM)){printk("arp_send_q: incomplete entry for %s\n",in_ntoa(entry->ip));return;}save_flags(flags);cli();// 处理该条数据对应的sk_buff链表while((skb = skb_dequeue(&entry->skb)) != NULL){IS_SKB(skb);skb_device_lock(skb);restore_flags(flags);// 系统发送数据包时，如果没有找到需要的ip和马刺地址的映射，则不会创建mac头，这里需要加上if(!skb->dev->rebuild_header(skb->data,skb->dev,skb->raddr,skb)){ // 标记已经完成arp解析skb->arp = 1;// 传给链路层处理if(skb->sk==NULL)dev_queue_xmit(skb, skb->dev, 0);elsedev_queue_xmit(skb,skb->dev,skb->sk->priority);}else{/* This routine is only ever called when 'entry' iscomplete. Thus this can't fail. */printk("arp_send_q: The impossible occurred. Please notify Alan.\n");printk("arp_send_q: active entity %s\n",in_ntoa(entry->ip));printk("arp_send_q: failed to find %s\n",in_ntoa(skb->raddr));}}restore_flags(flags);
}/** Delete an ARP mapping entry in the cache.*/
// 删除某个ip对应的arp缓存
void arp_destroy(unsigned long ip_addr, int force)
{int checked_proxies = 0;struct arp_table *entry;struct arp_table **pentry;// 找到该ip对应的位置索引unsigned long hash = HASH(ip_addr);ugly:cli();pentry = &arp_tables[hash];// 如果没找到，继续找arp代理的if (! *pentry) /* also check proxy entries */pentry = &arp_tables[PROXY_HASH];while ((entry = *pentry) != NULL){ // 遍历链表，找到和该ip相等的数据if (entry->ip == ip_addr){ // 判断是否是持久性的数据，如果是则根据force来判断是否强制删除if ((entry->flags & ATF_PERM) && !force)return;*pentry = entry->next;del_timer(&entry->timer);sti();arp_release_entry(entry);/* this would have to be cleaned up */goto ugly;/* perhaps like this ?cli();entry = *pentry;*/}pentry = &entry->next;// 检查完一般的arp缓存后，还需要检查arp代理链表if (!checked_proxies && ! *pentry){ /* ugly. we have to make sure we check proxyentries as well */checked_proxies = 1;pentry = &arp_tables[PROXY_HASH];}}sti();
}/** Receive an arp request by the device layer. Maybe I rewrite it, to* use the incoming packet for the reply. The time for the current* "overhead" isn't that high...*/
// 处理从链路层上报的数据包
int arp_rcv(struct sk_buff *skb, struct device *dev, struct packet_type *pt)
{
/** We shouldn't use this type conversion. Check later.*/struct arphdr *arp = (struct arphdr *)skb->h.raw;unsigned char *arp_ptr= (unsigned char *)(arp+1);struct arp_table *entry;struct arp_table *proxy_entry;int addr_hint,hlen,htype;unsigned long hash;unsigned char ha[MAX_ADDR_LEN]; /* So we can enable ints again. */long sip,tip;unsigned char *sha,*tha;/** The hardware length of the packet should match the hardware length* of the device. Similarly, the hardware types should match. The* device should be ARP-able. Also, if pln is not 4, then the lookup* is not from an IP number. We can't currently handle this, so toss* it. */ // 硬件地址长度和类型是否相等，协议长度是否等于4，即ip协议，目前只支持这种if (arp->ar_hln != dev->addr_len || dev->type != ntohs(arp->ar_hrd) || dev->flags & IFF_NOARP ||arp->ar_pln != 4){kfree_skb(skb, FREE_READ);return 0;}/** Another test.* The logic here is that the protocol being looked up by arp should * match the protocol the device speaks. If it doesn't, there is a* problem, so toss the packet.*/switch(dev->type){
#ifdef CONFIG_AX25case ARPHRD_AX25:if(arp->ar_pro != htons(AX25_P_IP)){kfree_skb(skb, FREE_READ);return 0;}break;
#endifcase ARPHRD_ETHER:case ARPHRD_ARCNET:if(arp->ar_pro != htons(ETH_P_IP)){kfree_skb(skb, FREE_READ);return 0;}break;default:printk("ARP: dev->type mangled!\n");kfree_skb(skb, FREE_READ);return 0;}/** Extract fields*/// 硬件长度和类型hlen = dev->addr_len;htype = dev->type;// arp层数据// arp_ptr指向数据首地址，sha等于发送者的硬件地址sha=arp_ptr;// 移动硬件长度hlen个字节arp_ptr+=hlen;// sip等于发送者ipmemcpy(&sip,arp_ptr,4);// 继续移动4个字节，即移动ip长度个字节arp_ptr+=4;// 接收者的硬件地址tha=arp_ptr;// 继续移动arp_ptr+=hlen;// 接收者ipmemcpy(&tip,arp_ptr,4);/* * Check for bad requests for 127.0.0.1. If this is one such, delete it.*/// 该包是自己发的if(tip == INADDR_LOOPBACK){kfree_skb(skb, FREE_READ);return 0;}/** 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.*/// 检测接收者ip类型addr_hint = ip_chk_addr(tip);// 如果该包是一个回复包if(arp->ar_op == htons(ARPOP_REPLY)){ // 但是接收地址不是本机地址，则丢弃if(addr_hint!=IS_MYADDR){
/* * Replies to other machines get tossed. */kfree_skb(skb, FREE_READ);return 0;}
/** Fall through to code below that adds sender to cache. */}// 是一个请求包else{
/* * It is now an arp request */
/** Only reply for the real device address or when it's in our proxy tables*/ // 接收者地址不是本机，这时候需要判断本机代理的arp缓存中是否有接收者的数据if(tip!=dev->pa_addr){
/** To get in here, it is a request for someone else. We need to* check if that someone else is one of our proxies. If it isn't,* we can toss it.*/cli();for(proxy_entry=arp_tables[PROXY_HASH];proxy_entry;proxy_entry = proxy_entry->next){/* we will respond to a proxy arp requestif the masked arp table ip matches the maskedtip. This allows a single proxy arp tableentry to be used on a gateway machine to handleall requests for a whole network, rather thanhaving to use a huge number of proxy arp entriesand having to keep them uptodate.*/if (proxy_entry->dev != dev && proxy_entry->htype == htype &&!((proxy_entry->ip^tip)&proxy_entry->mask))break;}// 找到了发送回复包if (proxy_entry){memcpy(ha, proxy_entry->ha, hlen);sti();arp_send(ARPOP_REPLY,ETH_P_ARP,sip,dev,tip,sha,ha);kfree_skb(skb, FREE_READ);return 0;}// 找不到则丢弃包else{sti();kfree_skb(skb, FREE_READ);return 0;}}// 接收者是本机的包，则发送回复包else{
/** To get here, it must be an arp request for us. We need to reply.*/arp_send(ARPOP_REPLY,ETH_P_ARP,sip,dev,tip,sha,dev->dev_addr);}}/** Now all replies are handled. Next, anything that falls through to here* needs to be added to the arp cache, or have its entry updated if it is * there.*/// 更新arp缓存的数据hash = HASH(sip);cli();for(entry=arp_tables[hash];entry;entry=entry->next)if(entry->ip==sip && entry->htype==htype)break;// 如果本来就有发送者ip的缓存项，则更新数据if(entry){
/** Entry found; update it.*/memcpy(entry->ha, sha, hlen);entry->hlen = hlen;entry->last_used = jiffies;// 判断该ip对应的arp项是否处于已经完成解析状态，不是的话，把他置为解析完成并且发送缓存在sk_buff中的包if (!(entry->flags & ATF_COM)){
/** This entry was incomplete. Delete the retransmit timer* and switch to complete status.*/ // 删除定时器del_timer(&entry->timer);// 修改该数据的状态为解析完成entry->flags |= ATF_COM;sti();
/* * Send out waiting packets. We might have problems, if someone is * manually removing entries right now -- entry might become invalid * underneath us.*/ // 发送滞留的包arp_send_q(entry, sha);}else{sti();}}// 没有找到发送者ip对应的数据，则插入一条新的arp缓存项else{
/** No entry found. Need to add a new entry to the arp table.*/entry = (struct arp_table *)kmalloc(sizeof(struct arp_table),GFP_ATOMIC);if(entry == NULL){sti();printk("ARP: no memory for new arp entry\n");kfree_skb(skb, FREE_READ);return 0;}entry->mask = DEF_ARP_NETMASK;entry->ip = sip;entry->hlen = hlen;entry->htype = htype;entry->flags = ATF_COM;init_timer(&entry->timer);memcpy(entry->ha, sha, hlen);entry->last_used = jiffies;entry->dev = skb->dev;skb_queue_head_init(&entry->skb);// 头插法entry->next = arp_tables[hash];arp_tables[hash] = entry;sti();}/** Replies have been sent, and entries have been added. All done.*/kfree_skb(skb, FREE_READ);return 0;
}/** Find an arp mapping in the cache. If not found, post a request.*/
// 在根据ip在arp缓存表里找相关的数据，找不到则发送arp请求去找
int arp_find(unsigned char *haddr, unsigned long paddr, struct device *dev,unsigned long saddr, struct sk_buff *skb)
{struct arp_table *entry;unsigned long hash;
#ifdef CONFIG_IP_MULTICASTunsigned long taddr;
#endif switch (ip_chk_addr(paddr)){ // 如果找的是本机ip和mac地址的映射，则返回本机的硬件地址，并设置完成解析标记case IS_MYADDR:printk("ARP: arp called for own IP address\n");memcpy(haddr, dev->dev_addr, dev->addr_len);skb->arp = 1;return 0;
#ifdef CONFIG_IP_MULTICAST// 如果多播地址，则组装对应的mac地址case IS_MULTICAST:if(dev->type==ARPHRD_ETHER || dev->type==ARPHRD_IEEE802){ // ip多播地址和mac多播地址的关系是ip多播地址的后23位直接映射到mac多播地址，而mac多播地址的前25位是固定的// 前面25位是固定的haddr[0]=0x01;haddr[1]=0x00;haddr[2]=0x5e;taddr=ntohl(paddr);// 取后8位进行赋值haddr[5]=taddr&0xff;// 剩下的值往右挪8位taddr=taddr>>8;// 再取8位进行赋值haddr[4]=taddr&0xff;// 剩下的值往右挪8位taddr=taddr>>8;// 取7位进行赋值即可haddr[3]=taddr&0x7f;return 0;}/** If a device does not support multicast broadcast the stuff (eg AX.25 for now)*/
#endif// 广播地址，则取mac广播地址进行赋值case IS_BROADCAST:memcpy(haddr, dev->broadcast, dev->addr_len);skb->arp = 1;return 0;}hash = HASH(paddr);cli();/** Find an entry*/// 通过ip找对应的arp缓存，并设置不从代理里找entry = arp_lookup(paddr, PROXY_NONE);// 找到if (entry != NULL) /* It exists */{ // 缓存中有对应的数据但没有完成解析，先把数据包挂到该条数据的sk_buff队列中if (!(entry->flags & ATF_COM)){/** A request was already send, but no reply yet. Thus* queue the packet with the previous attempt*/if (skb != NULL){skb_queue_tail(&entry->skb, skb);skb_device_unlock(skb);}sti();return 1;}// 缓存中有对应的数据并且已经解析完成/** Update the record*/// 更新缓存中该条数据的信息entry->last_used = jiffies;// 把找到的arp缓存项的mac地址赋值给haddrmemcpy(haddr, entry->ha, dev->addr_len);// 设置arp解析完成标记位if (skb)skb->arp = 1;sti();return 0;}/** Create a new unresolved entry.*/// 没有找到该ip对应的数据，则新增一条数据entry = (struct arp_table *) kmalloc(sizeof(struct arp_table),GFP_ATOMIC);if (entry != NULL){ // 初始化新增数据的内容entry->mask = DEF_ARP_NETMASK;entry->ip = paddr;entry->hlen = dev->addr_len;entry->htype = dev->type;entry->flags = 0;memset(entry->ha, 0, dev->addr_len);entry->dev = dev;entry->last_used = jiffies;init_timer(&entry->timer);entry->timer.function = arp_expire_request;entry->timer.data = (unsigned long)entry;entry->timer.expires = ARP_RES_TIME;entry->next = arp_tables[hash];arp_tables[hash] = entry;add_timer(&entry->timer);entry->retries = ARP_MAX_TRIES;skb_queue_head_init(&entry->skb);if (skb != NULL){skb_queue_tail(&entry->skb, skb);skb_device_unlock(skb);}}else{if (skb != NULL && skb->free)kfree_skb(skb, FREE_WRITE);}sti();/** If we didn't find an entry, we will try to send an ARP packet.*/// 加完新增的数据后，发送arp进行ip和mac地址的解析arp_send(ARPOP_REQUEST, ETH_P_ARP, paddr, dev, saddr, NULL, dev->dev_addr);return 1;
}/** Write the contents of the ARP cache to a PROCfs file.*/#define HBUFFERLEN 30int arp_get_info(char *buffer, char **start, off_t offset, int length)
{int len=0;off_t begin=0;off_t pos=0;int size;struct arp_table *entry;char hbuffer[HBUFFERLEN];int i,j,k;const char hexbuf[] = "0123456789ABCDEF";size = sprintf(buffer,"IP address HW type Flags HW address Mask\n");pos+=size;len+=size;cli();for(i=0; i<FULL_ARP_TABLE_SIZE; i++){for(entry=arp_tables[i]; entry!=NULL; entry=entry->next){
/** Convert hardware address to XX:XX:XX:XX ... form.*/
#ifdef CONFIG_AX25if(entry->htype==ARPHRD_AX25)strcpy(hbuffer,ax2asc((ax25_address *)entry->ha));else {
#endiffor(k=0,j=0;k<HBUFFERLEN-3 && j<entry->hlen;j++){hbuffer[k++]=hexbuf[ (entry->ha[j]>>4)&15 ];hbuffer[k++]=hexbuf[ entry->ha[j]&15 ];hbuffer[k++]=':';}hbuffer[--k]=0;#ifdef CONFIG_AX25}
#endifsize = sprintf(buffer+len,"%-17s0x%-10x0x%-10x%s",in_ntoa(entry->ip),(unsigned int)entry->htype,entry->flags,hbuffer);size += sprintf(buffer+len+size," %-17s\n",entry->mask==DEF_ARP_NETMASK?"*":in_ntoa(entry->mask));len+=size;pos=begin+len;if(pos<offset){len=0;begin=pos;}if(pos>offset+length)break;}}sti();*start=buffer+(offset-begin); /* Start of wanted data */len-=(offset-begin); /* Start slop */if(len>length)len=length; /* Ending slop */return len;
}/** This will find an entry in the ARP table by looking at the IP address.* If proxy is PROXY_EXACT then only exact IP matches will be allowed* for proxy entries, otherwise the netmask will be used*/
// 根据ip到arp缓存里找arp项，找不到就返回空
static struct arp_table *arp_lookup(unsigned long paddr, enum proxy proxy)
{struct arp_table *entry;unsigned long hash = HASH(paddr);for (entry = arp_tables[hash]; entry != NULL; entry = entry->next)if (entry->ip == paddr) break;/* it's possibly a proxy entry (with a netmask) */// 如果找不到并且没有设置不需要从代理里找，则到代理中找if (!entry && proxy != PROXY_NONE){for (entry=arp_tables[PROXY_HASH]; entry != NULL; entry = entry->next){/* 代理匹配两种方式，一种是精确匹配(PROXY_EXACT)，一直是网络号匹配即可(PROXY_ANY)(entry->ip^paddr)&entry->mask)逻辑为，异或是不相等的话结果是1，否则为0，比如0^1等于1，所以entry->ip^paddr比较好，前n位如果相等则结果的前n位都是0，而entry->mask是前n位是网络号且全为1，后面为全0，如果(entry->ip^paddr)&entry->mask)结果为0，所说明entry->ip^paddr的结果中，前n位等于0的个数大于等于mask中前面的1，说明网络号是一样的。*/if ((proxy==PROXY_EXACT) ? (entry->ip==paddr) : !((entry->ip^paddr)&entry->mask)) break;}}return entry;
}/** Set (create) an ARP cache entry.*/
// 修改或新增arp缓存项
static int arp_req_set(struct arpreq *req)
{struct arpreq r;struct arp_table *entry;struct sockaddr_in *si;int htype, hlen;unsigned long ip;struct rtable *rt;memcpy_fromfs(&r, req, sizeof(r));/* We only understand about IP addresses... */if (r.arp_pa.sa_family != AF_INET)return -EPFNOSUPPORT;/** Find out about the hardware type.* We have to be compatible with BSD UNIX, so we have to* assume that a "not set" value (i.e. 0) means Ethernet.*/switch (r.arp_ha.sa_family) {case ARPHRD_ETHER:htype = ARPHRD_ETHER;hlen = ETH_ALEN;break;case ARPHRD_ARCNET:htype = ARPHRD_ARCNET;hlen = 1; /* length of arcnet addresses */break;#ifdef CONFIG_AX25case ARPHRD_AX25:htype = ARPHRD_AX25;hlen = 7;break;
#endifdefault:return -EPFNOSUPPORT;}si = (struct sockaddr_in *) &r.arp_pa;ip = si->sin_addr.s_addr;if (ip == 0){printk("ARP: SETARP: requested PA is 0.0.0.0 !\n");return -EINVAL;}/** Is it reachable directly ?*/// ip是否可达，不可达的ip不允许更新rt = ip_rt_route(ip, NULL, NULL);if (rt == NULL)return -ENETUNREACH;/** Is there an existing entry for this address?*/cli();/** Find the entry*/// 如果已经存在该ip对应的arp缓存项，使用精确匹配entry = arp_lookup(ip, PROXY_EXACT);// 新的缓存项和原来的标记位不一样，则先删除再新增if (entry && (entry->flags & ATF_PUBL) != (r.arp_flags & ATF_PUBL)){sti();arp_destroy(ip,1);cli();entry = NULL;}/** Do we need to create a new entry*/// entry为NULL可能是找不到该ip对应的缓存项，或者找到了，但是标记位不一样，被删除了，这里需要新增if (entry == NULL){ // 先预先得到一个位置索引unsigned long hash = HASH(ip);// 如果设置了ATF_PUBL标记位，说明该arp项应该挂到arp代理的链表中if (r.arp_flags & ATF_PUBL)hash = PROXY_HASH;entry = (struct arp_table *) kmalloc(sizeof(struct arp_table),GFP_ATOMIC);if (entry == NULL){sti();return -ENOMEM;}entry->ip = ip;entry->hlen = hlen;entry->htype = htype;init_timer(&entry->timer);// 头插法entry->next = arp_tables[hash];arp_tables[hash] = entry;skb_queue_head_init(&entry->skb);}/** We now have a pointer to an ARP entry. Update it!*/// 此处的entry代表的可能是一个新生成的arp项，也可能是arp缓存链表里原本就存在的项memcpy(&entry->ha, &r.arp_ha.sa_data, hlen);entry->last_used = jiffies;/* 在原有的标记位上，追加设置该arp缓存项已经解析完成标记位或者逻辑为：如果arp_flags是0，证明没有任何标记位，与运算后arp_flags等于ATF_COM的值如果arp_flags是等于ATF_COM的值，证明之前已经设置了该标记位，与运算后，值不变如果arp_flags为其他的标记位，则标记位累加。具体可见下面的标记位，他们都有自己的位，不会冲突。#define ATF_COM 0x02 #define ATF_PERM 0x04 #define ATF_PUBL 0x08 #define ATF_USETRAILERS 0x10 #define ATF_NETMASK 0x20 */entry->flags = r.arp_flags | ATF_COM;// 设置了这个两个位说明是一个代理项，则对掩码进行赋值，否则使用DEF_ARP_NETMASK作为掩码if ((entry->flags & ATF_PUBL) && (entry->flags & ATF_NETMASK)){si = (struct sockaddr_in *) &r.arp_netmask;entry->mask = si->sin_addr.s_addr;}elseentry->mask = DEF_ARP_NETMASK;entry->dev = rt->rt_dev;sti();return 0;
}/** Get an ARP cache entry.*/
// 获取arp缓存项
static int arp_req_get(struct arpreq *req)
{struct arpreq r;struct arp_table *entry;struct sockaddr_in *si;/** We only understand about IP addresses...*/memcpy_fromfs(&r, req, sizeof(r));// 只支持AF_INET协议簇if (r.arp_pa.sa_family != AF_INET)return -EPFNOSUPPORT;/** Is there an existing entry for this address?*/si = (struct sockaddr_in *) &r.arp_pa;cli();// 通过ip找arp缓存项entry = arp_lookup(si->sin_addr.s_addr,PROXY_ANY);if (entry == NULL){sti();return -ENXIO;}/** We found it; copy into structure.*/// 赋值硬件信息memcpy(r.arp_ha.sa_data, &entry->ha, entry->hlen);r.arp_ha.sa_family = entry->htype;// arp缓存项标记位赋值r.arp_flags = entry->flags;sti();/** Copy the information back*/memcpy_tofs(req, &r, sizeof(r));return 0;
}/** Handle an ARP layer I/O control request.*/
// 操作arp_table里的数据，从而管理arp缓存
int arp_ioctl(unsigned int cmd, void *arg)
{struct arpreq r;struct sockaddr_in *si;int err;switch(cmd){case SIOCDARP:// 权限校验if (!suser())return -EPERM;err = verify_area(VERIFY_READ, arg, sizeof(struct arpreq));if(err)return err;memcpy_fromfs(&r, arg, sizeof(r));if (r.arp_pa.sa_family != AF_INET)return -EPFNOSUPPORT;si = (struct sockaddr_in *) &r.arp_pa;// 删除arp_destroy(si->sin_addr.s_addr, 1);return 0;case SIOCGARP:err = verify_area(VERIFY_WRITE, arg, sizeof(struct arpreq));if(err)return err;// 查询return arp_req_get((struct arpreq *)arg);case SIOCSARP:if (!suser())return -EPERM;err = verify_area(VERIFY_READ, arg, sizeof(struct arpreq));if(err)return err;// 修改、增加return arp_req_set((struct arpreq *)arg);default:return -EINVAL;}/*NOTREACHED*/return 0;
}/** Called once on startup.*/
// 挂到链路层packet_type链表的节点，链路层收到arp包会调用arp_rcv函数进行处理
static struct packet_type arp_packet_type =
{0, /* Should be: __constant_htons(ETH_P_ARP) - but this _doesn't_ come out constant! */NULL, /* All devices */arp_rcv,NULL,NULL
};
// 硬件设备状态变更会调用arp_device_event处理
static struct notifier_block arp_dev_notifier={arp_device_event,NULL,0
};
// 初始化arp协议
void arp_init (void)
{/* Register the packet type */// 注册arp协议到链路层，链路层收到包后会根据packet_type链表判断上层协议，然后上报数据包arp_packet_type.type=htons(ETH_P_ARP);dev_add_pack(&arp_packet_type);/* Start with the regular checks for expired arp entries. */// 系统启动时就开始隔段时间检查arp缓存的数据add_timer(&arp_timer);/* Register for device down reports */// 注册回调事件，arp的数据和具体硬件设备有关，所以设备状态发生变化时，需要通知arp协议进行处理register_netdevice_notifier(&arp_dev_notifier);
}