ioctl SIOCGARP question

[Guillaume Morin <guillaume@morinfr.org>]

Hi,

I am trying to play with SIOCGARP. Here is the program


#include <sys/socket.h>
#include <netinet/in.h>
#include <net/if_arp.h>
#include <stdio.h>
#include <errno.h>
#include <sys/ioctl.h>
#include <arpa/inet.h>
#include <string.h>

#define IP "62.4.22.236"
#define INTERFACE "eth1"

int main(int argc, char ** argv) {
	int s;
	struct arpreq a;
	struct sockaddr_in * sin;
	
	if ((s = socket(AF_INET,SOCK_DGRAM,0) == -1)) {
		perror("socket");
		return -1;
	}
	memset(&a,0,sizeof(a));
	strcpy(a.arp_dev,INTERFACE);
	sin = (struct sockaddr_in *) &(a.arp_pa);
	sin->sin_family = AF_INET;
	if (! inet_aton(IP,&sin->sin_addr)) {
		puts("Cannot convert " IP ".");
		return -1;
	}

	if (ioctl(s,SIOCGARP,&a)) {
		perror("ioctl");
		return -1;
	}

	printf("HWADDR: %x\n",*a.arp_ha.sa_data);
	return 0;
}

ioctl always returns EINVAL. I've looked at net/ipv4/arp.c, I don't see
how this is possible.

Could anyone tell me what I am missing ?

TIA.

-- 
Guillaume Morin <guillaume@morinfr.org>

                             La vie est facétieuse
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