sysdeps/unix/ifreq.c

   1 /* Copyright (C) 1999-2024 Free Software Foundation, Inc.
   2    This file is part of the GNU C Library.
   3
   4    The GNU C Library is free software; you can redistribute it and/or
   5    modify it under the terms of the GNU Lesser General Public
   6    License as published by the Free Software Foundation; either
   7    version 2.1 of the License, or (at your option) any later version.
   8
   9    The GNU C Library is distributed in the hope that it will be useful,
  10    but WITHOUT ANY WARRANTY; without even the implied warranty of
  11    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  12    Lesser General Public License for more details.
  13
  14    You should have received a copy of the GNU Lesser General Public
  15    License along with the GNU C Library; if not, see
  16    <https://www.gnu.org/licenses/>.  */
  17
  18 #include "ifreq.h"
  19
  20
  21 void
  22 __ifreq (struct ifreq **ifreqs, int *num_ifs, int sockfd)
  23 {
  24   int fd = sockfd;
  25   struct ifconf ifc;
  26   int rq_len;
  27   int nifs;
  28 # define RQ_IFS 4
  29
  30   if (fd < 0)
  31     fd = __opensock ();
  32   if (fd < 0)
  33     {
  34       *num_ifs = 0;
  35       *ifreqs = NULL;
  36       return;
  37     }
  38
  39   ifc.ifc_buf = NULL;
  40   rq_len = RQ_IFS * sizeof (struct ifreq) / 2; /* Doubled in the loop.  */
  41   do
  42     {
  43       ifc.ifc_len = rq_len *= 2;
  44       void *newp = realloc (ifc.ifc_buf, ifc.ifc_len);
  45       if (newp == NULL || __ioctl (fd, SIOCGIFCONF, &ifc) < 0)
  46         {
  47           free (ifc.ifc_buf);
  48
  49           if (fd != sockfd)
  50             __close (fd);
  51           *num_ifs = 0;
  52           *ifreqs = NULL;
  53           return;
  54         }
  55       ifc.ifc_buf = newp;
  56     }
  57   while (rq_len < sizeof (struct ifreq) + ifc.ifc_len);
  58
  59   if (fd != sockfd)
  60     __close (fd);
  61
  62 #ifdef _HAVE_SA_LEN
  63   struct ifreq *ifr = *ifreqs;
  64   nifs = 0;
  65   while ((char *) ifr < ifc.ifc_buf + ifc.ifc_len)
  66     {
  67       ++nifs;
  68       ifr = __if_nextreq (ifr);
  69       if (ifr == NULL)
  70         break;
  71     }
  72 #else
  73   nifs = ifc.ifc_len / sizeof (struct ifreq);
  74 #endif
  75
  76   *num_ifs = nifs;
  77   *ifreqs = realloc (ifc.ifc_buf, nifs * sizeof (struct ifreq));
  78 }