udhcp源碼詳解(四) 之租賃IP的管理
Author : hui <[email protected]>
From : <http://blog.csdn.net/hui_love2046>
Created : 2010-10-4
Server端對於租賃出去的IP的管理是基於結構體dhcpOfferedAddr的,該結構體的定義是在leases.c文件裏:(結構體的成員介紹說明見詳解之數據結構)
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- struct dhcpOfferedAddr {
- uint8_t chaddr[16];
- uint32_t yiaddr; /* network order */
- uint32_t expires; /* host order */
- };
在dhcpd.c文件裏用該結構體定義指向該結構數組的指針leases;
/* dhcpd.c */
#include <leases.h>
struct dhcpOfferedAddr *leases;
在讀取完配置信息server_config後,就可以依據配置信息的內存爲該結構數組申請內存空間了:
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- /*
- * strut dhcpOfferedAddr {
- * uint8_t chaddr[16];
- * uint32_t yiaddr; //network order
- * uint32_t expires; //host order
- * };
- *
- * 該結構數組leases是記錄租賃出去的IP, yiaddr
- * 租賃IP客戶機的MAC, charddr
- * 租賃的到期時間,expires(從1970年1月1日00:00:00到租賃到期的總共的秒數)
- *
- * dhcp server啓動後(可能是異常重啓)
- * 所以要充server_config.file裏讀取上次爲哪些客戶機分配了IP
- * 並把讀取到的內容添加到leases數組裏
- */
- leases = xzalloc(server_config.max_leases * sizeof(struct dhcpOfferedAddr));
- read_leases(server_config.lease_file);
- //server_config.lease_file = "/var/lib/misc/udhcpd.leases"
2). 查找租賃最早到期的租約:
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- /*
- * add a lease into the table, clearing out any old ones
- * add_lease是把MAC:chaddr, IP : yiaddr, expires: lease
- * 租賃信息添加到leases數組裏
- * 函數首先調用clear_lease把數組裏舊的刪除掉(與chaddr or yiaddr相同的)
- * 從leases數組裏找到最早到期的,再添加
- *
- * 返回oldest (NULL 表示未添加成功)
- */
- struct dhcpOfferedAddr *add_lease(uint8_t *chaddr, uint32_t yiaddr, unsigned long lease)
- {
- struct dhcpOfferedAddr *oldest;
- /* clean out any old ones */
- clear_lease(chaddr, yiaddr);
- /* 從leases數組裏找到一個最早到期的oldest,以便添加新的 */
- oldest = oldest_expired_lease();
- if (oldest) //oldest != NULL ,Found...
- {
- memcpy(oldest->chaddr, chaddr, 16);
- oldest->yiaddr = yiaddr;
- /*
- * 函數的第三個參數,即lease,表示的是租賃的剩餘時間
- * 在動態租賃數組leases裏記錄的租賃到期時間
- *
- * 所以 oldest->expires = time(0) + lease;
- */
- oldest->expires = time(0) + lease;
- }
- return oldest;
- }
3). 通過MAC或IP查找租約:
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- /* Find the first lease that matches chaddr, NULL if no match */
- struct dhcpOfferedAddr *find_lease_by_chaddr(uint8_t *chaddr)
- {
- unsigned int i;
- for (i = 0; i < server_config.max_leases; i++)
- if (!memcmp(leases[i].chaddr, chaddr, 16)) return &(leases[i]);
- return NULL;
- }
- /* Find the first lease that matches yiaddr, NULL is no match */
- struct dhcpOfferedAddr *find_lease_by_yiaddr(uint32_t yiaddr)
- {
- unsigned int i;
- for (i = 0; i < server_config.max_leases; i++)
- if (leases[i].yiaddr == yiaddr) return &(leases[i]);
- return NULL;
- }
4). 檢查IP addr是否被網絡中主機所使用,若被使用的話添加到leases數組裏:
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- /*
- * check is an IP is taken, if it is, add it to the lease table
- *
- * 檢查addr is a free IP(網絡中是否有主機使用addr)
- * if addr is a used IP, 把addr添加到租賃數組裏
- *
- * 1. 返回0 表示addr 是a free IP
- * 2. 返回1表示addr已被網絡中的某臺主機使用了
- * 並且把使用addr的主機添加到leases數組裏
- * 其中MAC: blank_chaddr, IP: addr, expires: server_config.confict_time(def: 3600sec)
- *
- */
- static int check_ip(uint32_t addr)
- {
- struct in_addr temp;
- /* arpping()返回0表示addr used */
- if (arpping(addr, server_config.server, server_config.arp, server_config.interface) == 0) {
- temp.s_addr = addr;
- LOG(LOG_INFO, "%s belongs to someone, reserving it for %ld seconds",
- inet_ntoa(temp), server_config.conflict_time);
- /*
- * 因爲剛在未在leases數組裏找到這個已被used 的IP
- * 所以要把這個used IP添加到leases數組裏
- * 租賃客戶機MAC 爲blank_chaddr(黑戶)
- * 租賃的IP即used IP(addr)
- * 租賃時間:server_config.conflict_time
- */
- add_lease(blank_chaddr, addr, server_config.conflict_time);
- return 1;
- } else return 0;
- }
5) 從可用IP地址池裏找到一個可用的IP(a Free IP)
uint32_t find_address(int check_expire);
該函數的調用是在,server端接收到DHCPDISOCVER的報文的時候,會爲client提供一個IP地址:
a) server首先利用client的MAC地址在leases數組裏查找該client以前是否在這裏租賃過IP,租賃過的話,把以前的IP提供給client
b) 第一種情況不滿足的話,server會檢查DHCPDISCOVER報文的選項字段,client是否有請求的IP(該選項信息的CODE :DHCP_REQUESTED_IP),有的話檢查該IP是否爲Free,可以的話把Request IP提供給client。
c) 上面兩種情況都不滿足的話,就調用find_address這個函數了。
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- /*
- * find an assignable address, it check_expired is true,
- * we check all the expired leases as well.
- * Maybe this should try expired leases by age...
- *
- * 找到一個可分配的IP,如果check_expired is true,
- * 會檢查所有到期租約
- * find_address()函數找到free IP 返回IP的值(network order)
- * 未找到返回0
- *
- */
- uint32_t find_address(int check_expired)
- {
- uint32_t addr, ret;
- struct dhcpOfferedAddr *lease = NULL;
- /*
- * 在端上進行計算比較的時候使用 host order
- * 一般存儲的時候採用 network order
- *
- * 遍歷整個可分配地址server_config.start -- server_config.end
- */
- /* addr is in host order here */
- addr = ntohl(server_config.start);
- for (;addr <= ntohl(server_config.end); addr++)
- {
- /* ie, 192.168.55.0 */
- if (!(addr & 0xFF)) continue;
- /* ie, 192.168.55.255 */
- if ((addr & 0xFF) == 0xFF) continue;
- /*
- * Only do if it isn't
- * an assigned as a static lease
- * rexervedIP()檢查addr是否在靜態租賃鏈表裏
- * addr在靜態鏈表的話,函數返回1,反之返回0
- */
- if(!reservedIp(server_config.static_leases, htonl(addr)))
- {
- /* lease is not taken */
- ret = htonl(addr);
- /* !(lease = find_lease_by_yiaddr(ret)) 地址addr是否已被租賃出去了 */
- if ((!(lease = find_lease_by_yiaddr(ret)) ||
- /*
- * or it expired and we are checking for expired leases
- * or 租賃出去的話,
- * addr是否是a free IP還取決與
- * lease_expired(lease)是否已到期和check_expired
- *
- */
- (check_expired && lease_expired(lease))) &&
- /*
- * and it isn't on the network
- * 如果addr滿足上面兩個條件的其中一個
- * 1.!(lease = find_lease_by_yiaddr(ret)) 沒有被租賃出去 * 2.(check_expired && lease_expired(lease)) 已被租賃出去了,
- * 但租賃過期了(check_expired == ture)
- *
- * addr 滿足上面條件之一,還要檢查addr是否被網絡上其他主機使用
- *
- * check_ip() 發送arp Request包確認addr是否被使用
- * 返回0, addr is a free IP
- */
- !check_ip(ret))
- {
- return ret;
- break;
- }
- }
- }
- return 0;
- }