sysdeps/unix/sysv/linux/gethostid.c

   1 /* Copyright (C) 1995, 1996 Free Software Foundation, Inc.
   2
   3 The GNU C Library is free software; you can redistribute it and/or
   4 modify it under the terms of the GNU Library General Public License as
   5 published by the Free Software Foundation; either version 2 of the
   6 License, or (at your option) any later version.
   7
   8 The GNU C Library is distributed in the hope that it will be useful,
   9 but WITHOUT ANY WARRANTY; without even the implied warranty of
  10 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  11 Library General Public License for more details.
  12
  13 You should have received a copy of the GNU Library General Public
  14 License along with the GNU C Library; see the file COPYING.LIB.  If
  15 not, write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
  16 Boston, MA 02111-1307, USA.  */
  17
  18 #include <errno.h>
  19 #include <fcntl.h>
  20 #include <unistd.h>
  21
  22 #define HOSTIDFILE "/var/adm/hostid"
  23
  24 #ifdef SET_PROCEDURE
  25 int
  26 sethostid (id)
  27      long int id;
  28 {
  29   int fd;
  30   ssize_t written;
  31
  32   /* Test for appropriate rights to set host ID.  */
  33   if (geteuid () || getuid ())
  34     {
  35       errno = EPERM;
  36       return -1;
  37     }
  38
  39   /* Open file for writing.  Everybody is allowed to read this file.  */
  40   fd = __open (HOSTIDFILE, O_CREAT|O_WRONLY, 0644);
  41   if (fd < 0)
  42     return -1;
  43
  44   written = __write (fd, &id, sizeof (id));
  45
  46   __close (fd);
  47
  48   return written != sizeof (id) ? -1 : 0;
  49 }
  50
  51 #else
  52 # include <string.h>
  53 # include <sys/param.h>
  54 # include <resolv/netdb.h>
  55 # include <netinet/in.h>
  56
  57 long int
  58 gethostid ()
  59 {
  60   char hostname[MAXHOSTNAMELEN + 1];
  61   struct hostent *hp;
  62   unsigned long id;
  63   struct in_addr in;
  64   int fd;
  65
  66   /* First try to get the ID from a former invocation of sethostid.  */
  67   fd = __open (HOSTIDFILE, O_RDONLY);
  68   if (fd >= 0)
  69     {
  70       ssize_t n = __read (fd, &id, sizeof (id));
  71
  72       __close (fd);
  73
  74       if (n == sizeof (id))
  75         return id;
  76     }
  77
  78   /* Getting from the file was not succesful.  An intelligent guess for
  79      a unique number of a host is its IP address.  Return this.  */
  80   if (gethostname (hostname, MAXHOSTNAMELEN) < 0 || hostname[0] == '\0')
  81     /* This also fails.  Return and arbitrary value.  */
  82     return 0;
  83
  84   /* To get the IP address we need to know the host name.  */
  85   hp = gethostbyname (hostname);
  86   if (hp == NULL)
  87     return 0;
  88
  89   in.s_addr = 0;
  90   memcpy (&in, hp->h_addr,
  91           (int) sizeof (in) < hp->h_length ? sizeof (in) : hp->h_length);
  92
  93   /* For the return value to be not exactly the IP address we do some
  94      bit fiddling.  */
  95   return in.s_addr << 16 | in.s_addr >> 16;
  96 }
  97 #endif