Re: ioctl SIOCGARP question

[Guillaume Morin <guillaume@morinfr.org>]

Dans un message du 20 jan à  3:28, Bernd Eckenfels écrivait :
>
> In article <20020119192045.GA25668@morinfr.org> you wrote:
> >        memset(&a,0,sizeof(a));
> >        strcpy(a.arp_dev,INTERFACE);
> >        sin = (struct sockaddr_in *) &(a.arp_pa);
> >        sin->sin_family = AF_INET;
> 
> You have to set the flags to ATF_PUB or ATF_DONTPUB.

I've modified this :
 
strcpy(a.arp_dev,INTERFACE);
sin = (struct sockaddr_in *) &(a.arp_pa);
sin->sin_family = AF_INET;
a.arp_flags = ATF_PUBL;

I still get EINVAL.

Your remark is weird, because in net/ipv4/arp.c arp_ioctl()

if (!(r.arp_flags & ATF_PUBL) &&
     (r.arp_flags & (ATF_NETMASK|ATF_DONTPUB)))
         return -EINVAL;

This condition should be false if arp_flags == 0

BTW, the other situation which returns EINVAL should not happen here: 

 if (!r.arp_ha.sa_family)
      r.arp_ha.sa_family = dev->type;
 err = -EINVAL;
 if ((r.arp_flags & ATF_COM) && r.arp_ha.sa_family != dev->type)
      goto out;

Indeed the memset sets arp_ha.sa_family to 0.

Any other ideas ? I am really puzzled ...

For reference, here is the complete 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;
	struct in_addr addr;
	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;
	a.arp_flags = ATF_PUBL;
	if (! inet_aton(IP,&addr)) {
		puts("Cannot convert " IP ".");
		return -1;
	}

	memcpy(&sin->sin_addr,&addr,sizeof(struct in_addr));
	if (ioctl(s,SIOCGARP,&a)) {
		perror("ioctl");
		return -1;
	}

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

/* EOF */

TIA.

-- 
Guillaume Morin <guillaume@morinfr.org>

    If it doesn't work, force it.  If it breaks, it needed replacing anyway.
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