inet/ether_ntoh.c

   1 /* Copyright (C) 1996-2021 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 <errno.h>
  19 #include <netinet/ether.h>
  20 #include <netinet/if_ether.h>
  21 #include <string.h>
  22
  23 #include <nss/nsswitch.h>
  24
  25
  26 /* Type of the lookup function we need here.  */
  27 typedef int (*lookup_function) (const struct ether_addr *, struct etherent *,
  28                                 char *, size_t, int *);
  29
  30 int
  31 ether_ntohost (char *hostname, const struct ether_addr *addr)
  32 {
  33   nss_action_list nip;
  34   union
  35   {
  36     lookup_function f;
  37     void *ptr;
  38   } fct;
  39   int no_more;
  40   enum nss_status status = NSS_STATUS_UNAVAIL;
  41   struct etherent etherent;
  42
  43   no_more = __nss_ethers_lookup2 (&nip, "getntohost_r", NULL, &fct.ptr);
  44
  45   while (no_more == 0)
  46     {
  47       char buffer[1024];
  48
  49       status = (*fct.f) (addr, &etherent, buffer, sizeof buffer, &errno);
  50
  51       no_more = __nss_next2 (&nip, "getntohost_r", NULL, &fct.ptr, status, 0);
  52     }
  53
  54   if (status == NSS_STATUS_SUCCESS)
  55     /* XXX This is a potential cause of trouble because the size of
  56        the HOSTNAME buffer is not known but the interface does not
  57        provide this information.  */
  58     strcpy (hostname, etherent.e_name);
  59
  60   return status == NSS_STATUS_SUCCESS ? 0 : -1;
  61 }