One more rtnetlink code

["Praveen Nair" <praveen.nair@patni.com>]

Hi all,
 i am including another piece of code which i have written to print the
routes
in the kernel routing table using rtnetlink. Please do let me know if there
is a better way of doing this.

#include <asm/types.h>
#include <netinet/ether.h>
#include <netinet/in.h>
#include <net/if.h>
#include <stdio.h>
#include <sys/socket.h>
#include <sys/ioctl.h>
#include <linux/netlink.h>
#include <linux/rtnetlink.h>
#include <sys/types.h>

#define BUFSIZE 8192

struct route_info{
	u_int	dstAddr;
	u_int	srcAddr;
	u_int	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;
}

/* For printing the routes. */
void printRoute(struct route_info *rtInfo)
{
	char tempBuf[512];

	/* Print Destination address */
	if(rtInfo->dstAddr != 0)
		strcpy(tempBuf, (char *)inet_ntoa(rtInfo->dstAddr));
	else
		sprintf(tempBuf,"*.*.*.*\t");
	fprintf(stdout,"%s\t", tempBuf);

	/* Print Gateway address */
	if(rtInfo->gateWay != 0)
		strcpy(tempBuf, (char *)inet_ntoa(rtInfo->gateWay));
	else
		sprintf(tempBuf,"*.*.*.*\t");
	fprintf(stdout,"%s\t", tempBuf);

	/* Print Interface Name*/
	fprintf(stdout,"%s\t", rtInfo->ifName);

	/* Print Source address */
	if(rtInfo->srcAddr != 0)
		strcpy(tempBuf, (char *)inet_ntoa(rtInfo->srcAddr));
	else
		sprintf(tempBuf,"*.*.*.*\t");
	fprintf(stdout,"%s\n", tempBuf);
}

/* For parsing the route info returned */
void parseRoutes(struct nlmsghdr *nlHdr, struct route_info *rtInfo)
{
	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 = *(u_int *)RTA_DATA(rtAttr);
			break;
		case RTA_PREFSRC:
			rtInfo->srcAddr = *(u_int *)RTA_DATA(rtAttr);
			break;
		case RTA_DST:
			rtInfo->dstAddr = *(u_int *)RTA_DATA(rtAttr);
			break;
		}
	}
	printRoute(rtInfo);
	free(tempBuf);
	return;
}

int main()
{
	struct nlmsghdr *nlMsg;
	struct rtmsg *rtMsg;
	struct route_info *rtInfo;
	char msgBuf[BUFSIZE];

	int sock, len, msgSeq = 0;
	char buff[1024];

	/* Create Socket */
	if((sock = socket(PF_NETLINK, SOCK_DGRAM, NETLINK_ROUTE)) < 0)
		perror("Socket Creation: ");

	/* 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 = readSock(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));
	fprintf(stdout, "Destination\tGateway\tInterface\tSource\n");
	for(;NLMSG_OK(nlMsg,len);nlMsg = NLMSG_NEXT(nlMsg,len)){
		memset(rtInfo, 0, sizeof(struct route_info));
		parseRoutes(nlMsg, rtInfo);
	}
	free(rtInfo);
	close(sock);
  	return 0;
}

Thanks & Regards,
Praveen M Nair.

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