sysdeps/unix/sysv/linux/ifreq.c

   1 /* Copyright (C) 1999,2002,2003,2004,2005,2006 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 #include <kernel-features.h>
  22
  23 /* Variable to signal whether SIOCGIFCONF is not available.  */
  24 #if __ASSUME_SIOCGIFNAME == 0 || 1
  25 static int old_siocgifconf;
  26 #else
  27 # define old_siocgifconf 0
  28 #endif
  29
  30
  31 void
  32 __ifreq (struct ifreq **ifreqs, int *num_ifs, int sockfd)
  33 {
  34   int fd = sockfd;
  35   struct ifconf ifc;
  36   int rq_len;
  37   int nifs;
  38 # define RQ_IFS 4
  39
  40   if (fd < 0)
  41     fd = __opensock ();
  42   if (fd < 0)
  43     {
  44       *num_ifs = 0;
  45       *ifreqs = NULL;
  46       return;
  47     }
  48
  49   ifc.ifc_buf = NULL;
  50
  51   /* We may be able to get the needed buffer size directly, rather than
  52      guessing.  */
  53   if (! old_siocgifconf)
  54     {
  55       ifc.ifc_buf = NULL;
  56       ifc.ifc_len = 0;
  57       if (__ioctl (fd, SIOCGIFCONF, &ifc) < 0 || ifc.ifc_len == 0)
  58         {
  59 # if __ASSUME_SIOCGIFNAME == 0
  60           old_siocgifconf = 1;
  61 # endif
  62           rq_len = RQ_IFS * sizeof (struct ifreq);
  63         }
  64       else
  65         rq_len = ifc.ifc_len;
  66     }
  67   else
  68     rq_len = RQ_IFS * sizeof (struct ifreq);
  69
  70   /* Read all the interfaces out of the kernel.  */
  71   while (1)
  72     {
  73       ifc.ifc_len = rq_len;
  74       void *newp = realloc (ifc.ifc_buf, ifc.ifc_len);
  75       if (newp == NULL
  76           || (ifc.ifc_buf = newp, __ioctl (fd, SIOCGIFCONF, &ifc)) < 0)
  77         {
  78           free (ifc.ifc_buf);
  79
  80           if (fd != sockfd)
  81             __close (fd);
  82
  83           *num_ifs = 0;
  84           *ifreqs = NULL;
  85           return;
  86         }
  87
  88       if (!old_siocgifconf || ifc.ifc_len < rq_len)
  89         break;
  90
  91       rq_len *= 2;
  92     }
  93
  94   nifs = ifc.ifc_len / sizeof (struct ifreq);
  95
  96   if (fd != sockfd)
  97     __close (fd);
  98
  99   *num_ifs = nifs;
 100   *ifreqs = realloc (ifc.ifc_buf, nifs * sizeof (struct ifreq));
 101 }