sysdeps/unix/sysv/linux/gethostid.c

   1 /* Copyright (C) 1995, 1996, 1998, 1999 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 not,
  15    write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
  16    Boston, MA 02111-1307, USA.  */
  17
  18 #include <alloca.h>
  19 #include <errno.h>
  20 #include <fcntl.h>
  21 #include <unistd.h>
  22 #include <netdb.h>
  23
  24 #define HOSTIDFILE "/var/adm/hostid"
  25
  26 #ifdef SET_PROCEDURE
  27 int
  28 sethostid (id)
  29      long int id;
  30 {
  31   int fd;
  32   ssize_t written;
  33
  34   /* Test for appropriate rights to set host ID.  */
  35   if (__libc_enable_secure)
  36     {
  37       __set_errno (EPERM);
  38       return -1;
  39     }
  40
  41   /* Open file for writing.  Everybody is allowed to read this file.  */
  42   fd = __open (HOSTIDFILE, O_CREAT|O_WRONLY, 0644);
  43   if (fd < 0)
  44     return -1;
  45
  46   written = __write (fd, &id, sizeof (id));
  47
  48   __close (fd);
  49
  50   return written != sizeof (id) ? -1 : 0;
  51 }
  52
  53 #else
  54 # include <string.h>
  55 # include <sys/param.h>
  56 # include <resolv/netdb.h>
  57 # include <netinet/in.h>
  58
  59 long int
  60 gethostid ()
  61 {
  62   char hostname[MAXHOSTNAMELEN + 1];
  63   size_t buflen;
  64   char *buffer;
  65   struct hostent hostbuf, *hp;
  66   unsigned long int id;
  67   struct in_addr in;
  68   int herr;
  69   int fd;
  70
  71   /* First try to get the ID from a former invocation of sethostid.  */
  72   fd = __open (HOSTIDFILE, O_RDONLY);
  73   if (fd >= 0)
  74     {
  75       ssize_t n = __read (fd, &id, sizeof (id));
  76
  77       __close (fd);
  78
  79       if (n == sizeof (id))
  80         return id;
  81     }
  82
  83   /* Getting from the file was not successful.  An intelligent guess for
  84      a unique number of a host is its IP address.  Return this.  */
  85   if (__gethostname (hostname, MAXHOSTNAMELEN) < 0 || hostname[0] == '\0')
  86     /* This also fails.  Return and arbitrary value.  */
  87     return 0;
  88
  89   buflen = 1024;
  90   buffer = __alloca (buflen);
  91
  92   /* To get the IP address we need to know the host name.  */
  93   while (__gethostbyname_r (hostname, &hostbuf, buffer, buflen, &hp, &herr)
  94          != 0
  95          || hp == NULL)
  96     if (herr != NETDB_INTERNAL || errno != ERANGE)
  97       return 0;
  98     else
  99       {
 100         /* Enlarge buffer.  */
 101         buflen *= 2;
 102         buffer = __alloca (buflen);
 103       }
 104
 105   in.s_addr = 0;
 106   memcpy (&in, hp->h_addr,
 107           (int) sizeof (in) < hp->h_length ? sizeof (in) : hp->h_length);
 108
 109   /* For the return value to be not exactly the IP address we do some
 110      bit fiddling.  */
 111   return in.s_addr << 16 | in.s_addr >> 16;
 112 }
 113 #endif