rtnetlink code

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

Hi all,
 i am including a piece of code i have written to get the network interfaces
and their IP addresses 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 NL_BUFSIZE 8192

int readSock(int sockFd, char *bufPtr, int seqNum, int pId)
{
	struct nlmsghdr *nlHdr;
	int readLen = 0, flag = 0, msgLen = 0;

	do{
		/* Recieve response from kernel */
		if((readLen = recv(sockFd, bufPtr, NL_BUFSIZE - msgLen, 0)) < 0){
			perror("SOCK READ: ");
			return -1;
		}
		nlHdr = (struct nlmsghdr *)bufPtr;

		/* Check if header is valid */
		if((NLMSG_OK(nlHdr, readLen) == 0) || (nlHdr->nlmsg_type == NLMSG_ERROR)){
			perror("Error in recieved packet");
			return -1;
		}

		/* Check if its the last message */
		if(nlHdr->nlmsg_type == NLMSG_DONE)	{
			flag = 1;
			break;
		}
		else{
			/* Move the buffer pointer appropriately */
			bufPtr += readLen;
			msgLen += readLen;
		}
		if((nlHdr->nlmsg_flags & NLM_F_MULTI) == 0){
			flag = 1;
			break;
		}
	} while((nlHdr->nlmsg_seq != seqNum) || (nlHdr->nlmsg_pid != pId) || (flag
== 0));
	return msgLen;
}

void parseIfAddr(struct nlmsghdr *nlHdr)
{
	struct ifaddrmsg *ifAddrs;
	struct rtattr *rtAttr;
	int rtLen;
	char *tempBuf = NULL;

	tempBuf = (char *)malloc(100);
	ifAddrs = (struct ifaddrmsg *)NLMSG_DATA(nlHdr);

	rtAttr = (struct rtattr *)IFA_RTA(ifAddrs);
	rtLen = IFA_PAYLOAD(nlHdr);
	for(;RTA_OK(rtAttr,rtLen);rtAttr = RTA_NEXT(rtAttr,rtLen)){
		switch(rtAttr->rta_type)	{
		case IFA_ADDRESS:
			inet_ntop(AF_INET, RTA_DATA(rtAttr), tempBuf);
			fprintf(stdout, "Interface Address : %s\n",tempBuf);
			break;
		case IFA_LABEL:
			fprintf(stdout, "Interface Name : %s\n",RTA_DATA(rtAttr));
			break;
		}
	}
	free(tempBuf);
	return;
}

int main()
{
	struct nlmsghdr *nlMsg;
	struct ifaddrmsg *addrMsg;
	char msgBuf[NL_BUFSIZE];
	int sock, len, msgSeq = 0;
	char buff[1024];

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

	memset(msgBuf, 0, NL_BUFSIZE);

	nlMsg = (struct nlmsghdr *)msgBuf;
	addrMsg = (struct ifaddrmsg *)NLMSG_DATA(nlMsg);

	/* For getting interface addresses */
	nlMsg->nlmsg_len = NLMSG_LENGTH(sizeof(struct ifaddrmsg));
	nlMsg->nlmsg_type = RTM_GETADDR;
	nlMsg->nlmsg_flags = NLM_F_DUMP | NLM_F_REQUEST;
	nlMsg->nlmsg_seq = msgSeq++;
	nlMsg->nlmsg_pid = getpid();

	if(write(sock, nlMsg, nlMsg->nlmsg_len) < 0){
		printf("Write To Socket Failed...\n");
		return -1;
	}

	if((len = readSock(sock, msgBuf, msgSeq, getpid())) < 0){
		printf("Read From Socket Failed...\n");
		return -1;
	}

	for(;NLMSG_OK(nlMsg,len);nlMsg = NLMSG_NEXT(nlMsg,len)){
		/* For getting interface addresses */
		parseIfAddr(nlMsg);

	}
	close(sock);
    	return 0;
}

Thanks & Regards,
Praveen M Nair.

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