1 /* Copyright (C) 1999-2021 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
__ifreq(struct ifreq ** ifreqs,int * num_ifs,int sockfd)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 }
74