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lft_ifname.c

/*

  This file is part of LFT.

  The LFT software provided in this Distribution is
  Copyright 2002 MainNerve, Inc.
 
  The full text of our legal notices is contained in the file called
  COPYING, included with this Distribution.

  ifname.c : ljd
  $Id: lft_ifname.c,v 1.5 2003/04/23 18:28:44 nils Exp $
*/

#include <stdio.h>
#include <sys/types.h>
#include <sys/ioctl.h>
#include <sys/socket.h>
#if !defined(linux) && !defined(__CYGWIN__)
#include <sys/sockio.h>
#endif
#include <netinet/in.h>
#include <arpa/inet.h>
#include <net/if.h>
#include <string.h>
#include <unistd.h>

#include "lft_ifname.h"
#include "acconfig.h"

static int        sock = -1;

u_long
lft_getifaddr (const char *ifname)
{
      struct ifreq            ifr;

      /* Only do this once of course */
      if (sock < 0) {
            if ((sock = socket (AF_INET, SOCK_DGRAM, 0)) < 0) {
                  perror ("socket");
                  return -1;
            }
      }

      STRNCPY(ifr.ifr_name, (char*)ifname, IFNAMSIZ);

      if (ioctl(sock, SIOCGIFADDR, &ifr) < 0) {
            perror("ioctl");
            return -1;
      }

      return ((struct sockaddr_in *)(&(ifr.ifr_addr)))->sin_addr.s_addr;
}

char *
lft_getifname (struct in_addr addr)
{
      struct ifconf           ifc;
      char buffer[2048];
      int i, skip;

      /* Only do this once of course */
      if (sock < 0) {
            if ((sock = socket (AF_INET, SOCK_DGRAM, 0)) < 0) {
                  perror ("socket");
                  return NULL;
            }
      }
      
      ifc.ifc_len = sizeof(buffer);
      ifc.ifc_buf = buffer;

      if (ioctl(sock, SIOCGIFCONF, &ifc) < 0) {
            perror("ioctl");
            return NULL;
      }

      for (i = 0; i < ifc.ifc_len; i += skip) {
            struct ifreq ifr;
            struct in_addr thisaddr;

            memcpy(&ifr, ifc.ifc_buf + i, sizeof(struct ifreq));

            skip = sizeof(struct ifreq);
#ifdef HAVE_SOCKADDR_SA_LEN
            if (ifr.ifr_addr.sa_len > sizeof(struct sockaddr)) {
              skip = ifr.ifr_addr.sa_len + IFNAMSIZ;
            }
#endif

            if (ifr.ifr_addr.sa_family != AF_INET) continue;

            thisaddr = ((struct sockaddr_in *)&ifr.ifr_addr)->sin_addr;

            if (thisaddr.s_addr == addr.s_addr)
              return strdup(ifr.ifr_name);
      }

      /* not found */
      return NULL;
}



#ifdef      LFT_IFADDR_TESTING
extern int
main (int argc, char *argv[])
{
      struct in_addr          in;
      char              *addr;

      if (argc > 1)
            addr = strdup (argv[1]);
      else
            addr = strdup ("eth0");

      in.s_addr = lft_getifaddr (addr);
      if (in.s_addr == -1) {
            fprintf (stderr, "%s: Error reading ifname\n", addr);
            fflush (stderr);
            free(addr);
            exit (-1);
      }

      fprintf (stdout, "%s: %s\n", addr,
            inet_ntoa (in));
      fflush (stdout);
      free (addr);
      exit (0);
}

#endif /*LFT_IFNAME_TESTING*/

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