sysdeps/unix/sysv/linux/ifreq.c

   1 /* Copyright (C) 1999-2014 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, see
  17    <http://www.gnu.org/licenses/>.  */
  18
  19 #include "ifreq.h"
  20 #include <kernel-features.h>
  21
  22
  23 void
  24 __ifreq (struct ifreq **ifreqs, int *num_ifs, int sockfd)
  25 {
  26   int fd = sockfd;
  27   struct ifconf ifc;
  28   int rq_len;
  29   int nifs;
  30 # define RQ_IFS 4
  31
  32   if (fd < 0)
  33     fd = __opensock ();
  34   if (fd < 0)
  35     {
  36       *num_ifs = 0;
  37       *ifreqs = NULL;
  38       return;
  39     }
  40
  41   ifc.ifc_buf = NULL;
  42
  43   /* We may be able to get the needed buffer size directly, rather than
  44      guessing.  */
  45   ifc.ifc_buf = NULL;
  46   ifc.ifc_len = 0;
  47   if (__ioctl (fd, SIOCGIFCONF, &ifc) < 0 || ifc.ifc_len == 0)
  48     rq_len = RQ_IFS * sizeof (struct ifreq);
  49   else
  50     rq_len = ifc.ifc_len;
  51
  52   /* Read all the interfaces out of the kernel.  */
  53   ifc.ifc_len = rq_len;
  54   void *newp = realloc (ifc.ifc_buf, ifc.ifc_len);
  55   if (newp == NULL
  56       || (ifc.ifc_buf = newp, __ioctl (fd, SIOCGIFCONF, &ifc)) < 0)
  57     {
  58       free (ifc.ifc_buf);
  59
  60       if (fd != sockfd)
  61         __close (fd);
  62
  63       *num_ifs = 0;
  64       *ifreqs = NULL;
  65       return;
  66     }
  67
  68   nifs = ifc.ifc_len / sizeof (struct ifreq);
  69
  70   if (fd != sockfd)
  71     __close (fd);
  72
  73   *num_ifs = nifs;
  74   *ifreqs = realloc (ifc.ifc_buf, nifs * sizeof (struct ifreq));
  75 }