inet/ether_ntoh.c

   1 /* Copyright (C) 1996-2020 Free Software Foundation, Inc.
   2    This file is part of the GNU C Library.
   3    Contributed by Ulrich Drepper <drepper@cygnus.com>, 1996.
   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, see
  17    <https://www.gnu.org/licenses/>.  */
  18
  19 #include <errno.h>
  20 #include <netinet/ether.h>
  21 #include <netinet/if_ether.h>
  22 #include <string.h>
  23
  24 #include <nss/nsswitch.h>
  25
  26
  27 /* Type of the lookup function we need here.  */
  28 typedef int (*lookup_function) (const struct ether_addr *, struct etherent *,
  29                                 char *, size_t, int *);
  30
  31 int
  32 ether_ntohost (char *hostname, const struct ether_addr *addr)
  33 {
  34   static service_user *startp;
  35   static lookup_function start_fct;
  36   service_user *nip;
  37   union
  38   {
  39     lookup_function f;
  40     void *ptr;
  41   } fct;
  42   int no_more;
  43   enum nss_status status = NSS_STATUS_UNAVAIL;
  44   struct etherent etherent;
  45
  46   if (startp == NULL)
  47     {
  48       no_more = __nss_ethers_lookup2 (&nip, "getntohost_r", NULL, &fct.ptr);
  49       if (no_more)
  50         startp = (service_user *) -1;
  51       else
  52         {
  53           startp = nip;
  54           start_fct = fct.f;
  55         }
  56     }
  57   else
  58     {
  59       fct.f = start_fct;
  60       no_more = (nip = startp) == (service_user *) -1;
  61     }
  62
  63   while (no_more == 0)
  64     {
  65       char buffer[1024];
  66
  67       status = (*fct.f) (addr, &etherent, buffer, sizeof buffer, &errno);
  68
  69       no_more = __nss_next2 (&nip, "getntohost_r", NULL, &fct.ptr, status, 0);
  70     }
  71
  72   if (status == NSS_STATUS_SUCCESS)
  73     /* XXX This is a potential cause of trouble because the size of
  74        the HOSTNAME buffer is not known but the interface does not
  75        provide this information.  */
  76     strcpy (hostname, etherent.e_name);
  77
  78   return status == NSS_STATUS_SUCCESS ? 0 : -1;
  79 }