sysdeps/unix/sysv/linux/ifreq.c

   1 /* Copyright (C) 1999, 2002, 2003, 2004 Free Software Foundation, Inc.
   2    This file is part of the GNU C Library.
   3    Contributed by Andreas Jaeger <aj@suse.de>.
   4
   5    The GNU C Library is free software; you can redistribute it and/or
   6    modify it under the terms of the GNU Lesser General Public
   7    License as published by the Free Software Foundation; either
   8    version 2.1 of the License, or (at your option) any later version.
   9
  10    The GNU C Library is distributed in the hope that it will be useful,
  11    but WITHOUT ANY WARRANTY; without even the implied warranty of
  12    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  13    Lesser General Public License for more details.
  14
  15    You should have received a copy of the GNU Lesser General Public
  16    License along with the GNU C Library; if not, write to the Free
  17    Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
  18    02111-1307 USA.  */
  19
  20 #include "ifreq.h"
  21
  22 /* Variable to signal whether SIOCGIFCONF is not available.  */
  23 #if __ASSUME_SIOCGIFNAME == 0 || 1
  24 static int old_siocgifconf;
  25 #else
  26 # define old_siocgifconf 0
  27 #endif
  28
  29
  30 void
  31 __ifreq (struct ifreq **ifreqs, int *num_ifs, int sockfd)
  32 {
  33   int fd = sockfd;
  34   struct ifconf ifc;
  35   int rq_len;
  36   int nifs;
  37 # define RQ_IFS 4
  38
  39   if (fd < 0)
  40     fd = __opensock ();
  41   if (fd < 0)
  42     {
  43       *num_ifs = 0;
  44       *ifreqs = NULL;
  45       return;
  46     }
  47
  48   ifc.ifc_buf = NULL;
  49
  50   /* We may be able to get the needed buffer size directly, rather than
  51      guessing.  */
  52   if (! old_siocgifconf)
  53     {
  54       ifc.ifc_buf = NULL;
  55       ifc.ifc_len = 0;
  56       if (__ioctl (fd, SIOCGIFCONF, &ifc) < 0 || ifc.ifc_len == 0)
  57         {
  58 # if __ASSUME_SIOCGIFNAME == 0
  59           old_siocgifconf = 1;
  60 # endif
  61           rq_len = RQ_IFS * sizeof (struct ifreq);
  62         }
  63       else
  64         rq_len = ifc.ifc_len;
  65     }
  66   else
  67     rq_len = RQ_IFS * sizeof (struct ifreq);
  68
  69   /* Read all the interfaces out of the kernel.  */
  70   while (1)
  71     {
  72       ifc.ifc_len = rq_len;
  73       void *newp = realloc (ifc.ifc_buf, ifc.ifc_len);
  74       if (newp == NULL
  75           || (ifc.ifc_buf = newp, __ioctl (fd, SIOCGIFCONF, &ifc)) < 0)
  76         {
  77           free (ifc.ifc_buf);
  78
  79           if (fd != sockfd)
  80             __close (fd);
  81
  82           *num_ifs = 0;
  83           *ifreqs = NULL;
  84           return;
  85         }
  86
  87       if (!old_siocgifconf || ifc.ifc_len < rq_len)
  88         break;
  89
  90       rq_len *= 2;
  91     }
  92
  93   nifs = ifc.ifc_len / sizeof (struct ifreq);
  94
  95   if (fd != sockfd)
  96     __close (fd);
  97
  98   *num_ifs = nifs;
  99   *ifreqs = realloc (ifc.ifc_buf, nifs * sizeof (struct ifreq));
 100 }