碼為uip_arpc中的void uip_arp_arpin(void)函數(shù)

1、.ARP應答部分代碼為uip_arp.c中的void uip_arp_arpin(void)函數(shù).這個函數(shù)是在設備接收到ARP包時,由驅(qū)動程序調(diào)用的.如果收到是ARP包是一個對本地主機上次發(fā)送的ARP請求的應答,那么就從包中取得自己想要的主機的MAC地址,加入自己的ARP緩存表中.如果收到是一個ARP請求,那就把自己的MAC地址打包成一個ARP應答,發(fā)送給請求的主機.看代碼uip_arp.c的254行:1. /*-*/2. /*3. * ARP processing for incoming ARP packets.4. *對傳入的ARP包的處理.5. * This function shou

2、ld be called by the device driver when an ARP6. * packet has been received. The function will act differently7. * depending on the ARP packet type: if it is a reply for a request8. * that we previously sent out, the ARP cache will be filled in with9. * the values from the ARP reply. If the incoming

3、ARP packet is an ARP10. * request for our IP address, an ARP reply packet is created and put11. * into the uip_buf buffer.12. *此函數(shù)在收到ARP包時由設備驅(qū)動調(diào)用,函數(shù)行為會因包類型而有不同.如果收到的是一個對前先發(fā)送的請求的應答13. *則根據(jù)應答的值填充緩存.如果傳入的包是對我們的IP的請求,則創(chuàng)建一個ARP應答,并放入uip_buf中.14. * When the function returns, the value of the global variabl

4、e uip_len15. * indicates whether the device driver should send out a packet or16. * not. If uip_len is zero, no packet should be sent. If uip_len is17. * non-zero, it contains the length of the outbound packet that is18. * present in the uip_buf buffer.19. *函數(shù)返回時,全局變量uip_len的值指明了設備驅(qū)動要不要發(fā)送包.若uip_len為

5、0,則不需發(fā)送,若uip_len不是0,20. * 則其值是uip_buf中包含的要傳出的包的大小.21. * This function expects an ARP packet with a prepended Ethernet22. * header in the uip_buf buffer, and the length of the packet in the23. * global variable uip_len.此函數(shù)預期中的uip_buf中有一個帶以太網(wǎng)頭的ARP包.其長度存為uip_len中.24. */25. /*-*/26. void27. uip_arp_arpi

6、n(void)28. 29.30. if(uip_len < sizeof(struct arp_hdr) 31. uip_len = 0;32. return;33. 34. uip_len = 0;35.36. switch(BUF->opcode) 37. case HTONS(ARP_REQUEST):38. /* ARP request. If it asked for our address, we send out a39. reply. 如果是一個ARP請求,則發(fā)送應答.*/40. if(uip_ipaddr_cmp(BUF->dipaddr, uip_hos

7、taddr) 41. /* First, we register the one who made the request in our ARP42. table, since it is likely that we will do more communication43. with this host in the future.首先,我們將發(fā)送請求的主機注冊到ARP緩存表中,因為我們很可能要跟它要有更多的交流 */44. uip_arp_update(BUF->sipaddr, &BUF->shwaddr);45.46. /* The reply opcode is

8、 2. 應答的操作碼為2*/47. BUF->opcode = HTONS(2);48.49. memcpy(BUF->dhwaddr.addr, BUF->shwaddr.addr, 6);50. memcpy(BUF->shwaddr.addr, uip_ethaddr.addr, 6);51. memcpy(BUF->ethhdr.src.addr, uip_ethaddr.addr, 6);52. memcpy(BUF->ethhdr.dest.addr, BUF->dhwaddr.addr, 6);53.54. BUF->dipaddr

9、0 = BUF->sipaddr0;55. BUF->dipaddr1 = BUF->sipaddr1;56. BUF->sipaddr0 = uip_hostaddr0;57. BUF->sipaddr1 = uip_hostaddr1;58.59. BUF->ethhdr.type = HTONS(UIP_ETHTYPE_ARP);60. uip_len = sizeof(struct arp_hdr);61. 62. break;63. case HTONS(ARP_REPLY):64. /* ARP reply. We insert or updat

10、e the ARP table if it was meant65. for us. 如果收到的是一個ARP應答,而且也是我們所要的應答的話,就插件并更新ARP緩存表*/66. if(uip_ipaddr_cmp(BUF->dipaddr, uip_hostaddr) 67. uip_arp_update(BUF->sipaddr, &BUF->shwaddr);68. 69. break;70. 71.72. return;73. 復制代碼這里有一件事是很有意思的,就是說如果某個主機請求得到我們的MAC的地址,我們先把它的MAC地址加入到自己的表中.就好比社交網(wǎng)絡中

11、,別人請求加我們?yōu)楹糜?如果我們接收的話,也自動加對方為好友一樣.既然對方找上我們了,肯定是要做進一步的交流,互加MAC地址也很自然的.有了上一篇文章,這里似乎不必做過多的解釋了.但還是說一下吧,看看我們怎么做應答的.如果收到了一個請求,我們要做應答:1. /* The reply opcode is 2. */2. BUF->opcode = HTONS(2);3.4. memcpy(BUF->dhwaddr.addr, BUF->shwaddr.addr, 6);5. memcpy(BUF->shwaddr.addr, uip_ethaddr.addr, 6);6.

12、 memcpy(BUF->ethhdr.src.addr, uip_ethaddr.addr, 6);7. memcpy(BUF->ethhdr.dest.addr, BUF->dhwaddr.addr, 6);8.9. BUF->dipaddr0 = BUF->sipaddr0;10. BUF->dipaddr1 = BUF->sipaddr1;11. BUF->sipaddr0 = uip_hostaddr0;12. BUF->sipaddr1 = uip_hostaddr1;13.14. BUF->ethhdr.type = H

13、TONS(UIP_ETHTYPE_ARP);15. uip_len = sizeof(struct arp_hdr);復制代碼由于請求和應答包很多地方是相同的,如上文中的綠色部分.我們只需將收到的請求稍加修改就可以發(fā)送回去了.首先,要改一下MAC地址,四個地方.然后要將目標主機IP設為設為請求包的源主機IP,目的主機IP設為我們的IP.就可以了.另外說下對ARP緩存表的設置:1. 這個函數(shù)是集插入,更新一體的,有兩個參數(shù),IP地址,MAC地址.2. static void3. uip_arp_update(u16_t *ipaddr, struct uip_eth_addr *ethaddr)

14、4. 5. register struct arp_entry *tabptr;6. /* Walk through the ARP mapping table and try to find an entry to7. update. If none is found, the IP -> MAC address mapping is8. inserted in the ARP table. 遍歷ARP映射表,看看有沒有需要更新的表項,如果沒有,就將新的表項插入.*/9. for(i = 0; i < UIP_ARPTAB_SIZE; +i) 10.11. tabptr = &a

15、mp;arp_tablei;12. /* Only check those entries that are actually in use. 所謂更新就是傳入?yún)?shù)IP在表中己經(jīng)存在了,這時不需要新建表項,而是要修改己存表項.只查使用中的表項,如果有些表項IP是0,那么就不是使用中的*/13. if(tabptr->ipaddr0 != 0 &&14. tabptr->ipaddr1 != 0) 15.16. /* Check if the source IP address of the incoming packet matches17. the IP addr

16、ess in this ARP table entry. 看看傳入的IP有沒有匹配項.*/18. if(ipaddr0 = tabptr->ipaddr0 &&19. ipaddr1 = tabptr->ipaddr1) 20.21. /* An old entry found, update this and return. 如果有己存的匹配項,修改該項的MAC地址和更新時間.*/22. memcpy(tabptr->ethaddr.addr, ethaddr->addr, 6);23. tabptr->time = arptime;24.25.

17、 return;26. 27. 28. 29.30. /* If we get here, no existing ARP table entry was found, so we31. create one. 如果運行到這里,說明沒有己存的表項,則創(chuàng)建一個.*/32.33. /* First, we try to find an unused entry in the ARP table. 先看看有沒有空表項可用.*/34. for(i = 0; i < UIP_ARPTAB_SIZE; +i) 35. tabptr = &arp_tablei;36. if(tabptr-&g

18、t;ipaddr0 = 0 &&37. tabptr->ipaddr1 = 0) 38. break;39. 40. 41.42. /* If no unused entry is found, we try to find the oldest entry and43. throw it away. 如果沒空表項,就找到一個最舊的表項,扔掉它,換成我們的.*/44. if(i = UIP_ARPTAB_SIZE) 45. tmpage = 0;46. c = 0;47. for(i = 0; i < UIP_ARPTAB_SIZE; +i) 48. tabptr

19、= &arp_tablei;49. if(arptime - tabptr->time > tmpage) 50. tmpage = arptime - tabptr->time;51. c = i;52. 53. 54. i = c;55. tabptr = &arp_tablei;56. 57.   /* Now, i is the ARP table entry which we will fill with the new58.      information. 現(xiàn)在i就是我們最終得到的表項

20、,我們把新的信息插入到這里.*/59.   memcpy(tabptr->ipaddr, ipaddr, 4);60.   memcpy(tabptr->ethaddr.addr, ethaddr->addr, 6);61.   tabptr->time = arptime;復制代碼OK,uip_arp.c中還有兩個函數(shù),樓下繼續(xù).1.看代碼:1. /*-*/2. /*3. * Periodic ARP processing function.4. *ARP周期性處理函數(shù).5. * This function

21、performs periodic timer processing in the ARP module6. * and should be called at regular intervals. The recommended interval7. * is 10 seconds between the calls.8. *此函數(shù)在ARP模塊中施行周期性處理,它應該每隔一段時間就調(diào)用一次.推薦為10秒.9. */10. /*-*/11. void12. uip_arp_timer(void)13. 14.   struct arp_entry *tabptr;15.   16.   +arptime;17.   for(i = 0; i &l