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
21void
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 (ptr: ifc.ifc_buf, size: ifc.ifc_len);
45 if (newp == NULL || __ioctl (fd, SIOCGIFCONF, &ifc) < 0)
46 {
47 free (ptr: 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 (ptr: ifc.ifc_buf, size: nifs * sizeof (struct ifreq));
78}
79

source code of glibc/sysdeps/unix/ifreq.c