sysdeps/unix/sysv/linux/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
  41   /* We may be able to get the needed buffer size directly, rather than
  42      guessing.  */
  43   ifc.ifc_buf = NULL;
  44   ifc.ifc_len = 0;
  45   if (__ioctl (fd, SIOCGIFCONF, &ifc) < 0 || ifc.ifc_len == 0)
  46     rq_len = RQ_IFS * sizeof (struct ifreq);
  47   else
  48     rq_len = ifc.ifc_len;
  49
  50   /* Read all the interfaces out of the kernel.  */
  51   ifc.ifc_len = rq_len;
  52   void *newp = realloc (ifc.ifc_buf, ifc.ifc_len);
  53   if (newp == NULL
  54       || (ifc.ifc_buf = newp, __ioctl (fd, SIOCGIFCONF, &ifc)) < 0)
  55     {
  56       free (ifc.ifc_buf);
  57
  58       if (fd != sockfd)
  59         __close (fd);
  60
  61       *num_ifs = 0;
  62       *ifreqs = NULL;
  63       return;
  64     }
  65
  66   nifs = ifc.ifc_len / sizeof (struct ifreq);
  67
  68   if (fd != sockfd)
  69     __close (fd);
  70
  71   *num_ifs = nifs;
  72   *ifreqs = realloc (ifc.ifc_buf, nifs * sizeof (struct ifreq));
  73 }