#include <arpa/inet.h> #include <net/if.h> #include <netinet/in.h> #include <sys/types.h> #include <sys/ioctl.h> #include <sys/socket.h> #include <linux/netlink.h> #include <linux/rtnetlink.h> #include <stdio.h> #include <stdlib.h> #include <string.h> #include <unistd.h> #define BUFSIZE 2048 #define DEBUG struct route_info{ struct in_addr dstAddr; struct in_addr srcAddr; struct in_addr gateWay; char ifName[IF_NAMESIZE]; }; int readNlSock(int sockFd, char *bufPtr, int seqNum, int pId) { struct nlmsghdr *nlHdr; int readLen = 0, msgLen = 0; do { /* Recieve response from the kernel */ if((readLen = recv(sockFd, bufPtr, BUFSIZE - msgLen, 0)) < 0) { perror("SOCK READ: "); return -1; } nlHdr = (struct nlmsghdr *)bufPtr; /* Check if the header is valid */ if((NLMSG_OK(nlHdr, readLen) == 0) || (nlHdr->nlmsg_type == NLMSG_ERROR)) { perror("Error in recieved packet"); return -1; } /* Check if the its the last message */ if(nlHdr->nlmsg_type == NLMSG_DONE) { break; } else { /* Else move the pointer to buffer appropriately */ bufPtr += readLen; msgLen += readLen; } /* Check if its a multi part message */ if((nlHdr->nlmsg_flags & NLM_F_MULTI) == 0) { /* return if its not */ break; } } while((nlHdr->nlmsg_seq != seqNum) || (nlHdr->nlmsg_pid != pId)); return msgLen; } #ifdef DEBUG /* For printing the routes. */ void printRoute(struct route_info *rtInfo) { char tempBuf[512]; /* Print Destination address */ if(rtInfo->dstAddr.s_addr != 0) strcpy(tempBuf, inet_ntoa(rtInfo->dstAddr)); else sprintf(tempBuf,"*.*.*.*\t"); fprintf(stdout,"%s\t", tempBuf); /* Print Gateway address */ if(rtInfo->gateWay.s_addr != 0) strcpy(tempBuf, inet_ntoa(rtInfo->gateWay)); else sprintf(tempBuf,"*.*.*.*\t"); fprintf(stdout,"%s\t", tempBuf); /* Print Interface Name*/ fprintf(stdout,"%s\t\t", rtInfo->ifName); /* Print Source address */ if(rtInfo->srcAddr.s_addr != 0) strcpy(tempBuf, inet_ntoa(rtInfo->srcAddr)); else sprintf(tempBuf,"*.*.*.*\t"); fprintf(stdout,"%s\n", tempBuf); } #endif /* For parsing the route info returned */ void parseRoutes(struct nlmsghdr *nlHdr, struct route_info *rtInfo,char *gateway) { struct rtmsg *rtMsg; struct rtattr *rtAttr; int rtLen; char *tempBuf = NULL; tempBuf = (char *)malloc(100); rtMsg = (struct rtmsg *)NLMSG_DATA(nlHdr); /* If the route is not for AF_INET or does not belong to main routing table then return. */ if((rtMsg->rtm_family != AF_INET) || (rtMsg->rtm_table != RT_TABLE_MAIN)) return; /* get the rtattr field */ rtAttr = (struct rtattr *)RTM_RTA(rtMsg); rtLen = RTM_PAYLOAD(nlHdr); for(;RTA_OK(rtAttr,rtLen);rtAttr = RTA_NEXT(rtAttr,rtLen)) { switch(rtAttr->rta_type) { case RTA_OIF: if_indextoname(*(int *)RTA_DATA(rtAttr), rtInfo->ifName); break; case RTA_GATEWAY: rtInfo->gateWay.s_addr = *(u_int *)RTA_DATA(rtAttr); break; case RTA_PREFSRC: rtInfo->srcAddr.s_addr = *(u_int *)RTA_DATA(rtAttr); break; case RTA_DST: rtInfo->dstAddr.s_addr = *(u_int *)RTA_DATA(rtAttr); break; } } #ifdef DEBUG printRoute(rtInfo); #endif //printf("%s\n", inet_ntoa(rtInfo->dstAddr)); if(strstr(inet_ntoa(rtInfo->dstAddr), "0.0.0.0")) sprintf(gateway, "%s", inet_ntoa(rtInfo->gateWay)); free(tempBuf); return; } int get_gateway(char *gateway) { struct nlmsghdr *nlMsg; struct rtmsg *rtMsg; struct route_info *rtInfo; char msgBuf[BUFSIZE]; int sock, len, msgSeq = 0; /* Create Socket */ if((sock = socket(PF_NETLINK, SOCK_DGRAM, NETLINK_ROUTE)) < 0) { perror("Socket Creation: "); return -1; } /* Initialize the buffer */ memset(msgBuf, 0, BUFSIZE); /* point the header and the msg structure pointers into the buffer */ nlMsg = (struct nlmsghdr *)msgBuf; rtMsg = (struct rtmsg *)NLMSG_DATA(nlMsg); /* Fill in the nlmsg header*/ nlMsg->nlmsg_len = NLMSG_LENGTH(sizeof(struct rtmsg)); // Length of message. nlMsg->nlmsg_type = RTM_GETROUTE; // Get the routes from kernel routing table . nlMsg->nlmsg_flags = NLM_F_DUMP | NLM_F_REQUEST; // The message is a request for dump. nlMsg->nlmsg_seq = msgSeq++; // Sequence of the message packet. nlMsg->nlmsg_pid = getpid(); // PID of process sending the request. /* Send the request */ if(send(sock, nlMsg, nlMsg->nlmsg_len, 0) < 0) { printf("Write To Socket Failed...\n"); return -1; } /* Read the response */ if((len = readNlSock(sock, msgBuf, msgSeq, getpid())) < 0) { printf("Read From Socket Failed...\n"); return -1; } /* Parse and print the response */ rtInfo = (struct route_info *)malloc(sizeof(struct route_info)); // ADDED BY BOB /* THIS IS THE NETTSTAT -RL code I commented out the printing here and in parse routes */ #ifdef DEBUG fprintf(stdout, "Destination\tGateway\t\tInterface\tSource\n"); #endif for(; NLMSG_OK(nlMsg,len); nlMsg=NLMSG_NEXT(nlMsg,len)) { memset(rtInfo, 0, sizeof(struct route_info)); parseRoutes(nlMsg, rtInfo, gateway); } free(rtInfo); close(sock); return 0; } int main() { char gateway[255]={0}; get_gateway(gateway); printf("Gateway:%s\n", gateway); return 0; }

出處:http://blog.linuxmine.com/25219/viewspace-5465

創作者介紹

邱小新の工作筆記

台南小新 發表在 痞客邦 PIXNET 留言(0) 人氣()