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Date:      Thu, 4 Jan 2001 18:48:28 +0100
From:      ecureuil <ecureuil@easynet.fr>
To:        hackers@FreeBSD.org
Subject:   getifaddrs
Message-ID:  <20010104184828.A12168@foret>
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[-- Attachment #1 --]
Hi

I'm trying to get interfaces' list and infos with getifaddrs().
The ifa_data struct should contain all needed information, but 
this is a NULL pointer for IPv4 interfaces. Why ?

a sample output for my ethernet card :

   ed0 (        6.3.6.0) : UP, AF_INET6 MTU=1500   (struct ifa_data)
   ed0 (       10.0.0.1) : UP MTU=1500   (struct ifa_data is a null pointer)


BTW, there is always 2 nodes for each interface, even if INET6 is not
enabled in the kernel. is it normal ?

thanks (see the source attached)

-- 
ecureuil <ecureuil@easynet.fr>

[-- Attachment #2 --]
/* ecureuil <ecureuil@easynet.fr>
   get interface information
 */

#include <stdio.h>
#include <string.h>
#include <sys/ioctl.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>	
#include <arpa/inet.h>
#include <net/if.h>
#include <unistd.h>
#include <ifaddrs.h>

int 
main(int argc, char **argv)
{
	struct ifaddrs 		*ifap, *ifa;
	struct sockaddr_in 	*sa;
	int             	fd;
	struct ifreq    	ifr;
	char			ifstraddr[16];
	sa_family_t		fam;

	if (getifaddrs(&ifap) < 0) {
		perror("getifaddrs");
		return -1;
	}

	for (ifa = ifap; ifa; ifa = ifa->ifa_next) {

		printf("%6s ", ifa->ifa_name);

                /* get if address */
                sa = (struct sockaddr_in *) ifa->ifa_addr;
                strncpy(ifstraddr, inet_ntoa(sa->sin_addr), 16);
                printf("(%15s) : ",ifstraddr);

		if (!(ifa->ifa_flags & IFF_UP)) printf("DOWN");
		else printf("UP");

		if (ifa->ifa_flags & IFF_PROMISC) printf(", PROMISCUOUS");

		if (ifa->ifa_addr->sa_family & AF_INET6) printf(", AF_INET6");

		/* get if mtu */
		fam = ifa->ifa_addr->sa_family == AF_LINK ? AF_INET : ifa->ifa_addr->sa_family;
		if ((fd = socket(AF_INET, SOCK_DGRAM, 0)) < 0 ) {
			perror("[get_if_name] socket(AF_INET, SOCK_DGRAM, 0)");
			return -1;
		}
		
		strncpy(ifr.ifr_name,ifa->ifa_name,IFNAMSIZ);		

		if (ioctl(fd, SIOCGIFMTU, &ifr) < 0 ) {
			perror("ioctl");
			return -1;
		} else {
			printf(" MTU=%d   ",ifr.ifr_mtu);
		}

		close(fd);
		
		if(ifa->ifa_data) printf("(struct ifa_data)\n");
		else printf("(struct ifa_data is a null pointer)\n");
		
	}		
		freeifaddrs(ifap);
		return 0;
}

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