sysdeps/unix/sysv/linux/gethostid.c

   1 /* Copyright (C) 1995,1996,1998,1999,2000,2001 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, write to the Free
  16    Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
  17    02111-1307 USA.  */
  18
  19 #include <alloca.h>
  20 #include <errno.h>
  21 #include <fcntl.h>
  22 #include <unistd.h>
  23 #include <netdb.h>
  24
  25 #define HOSTIDFILE "/etc/hostid"
  26 #define OLD_HOSTIDFILE "/etc/hostid"
  27
  28 #ifdef SET_PROCEDURE
  29 int
  30 sethostid (id)
  31      long int id;
  32 {
  33   int fd;
  34   ssize_t written;
  35
  36   /* Test for appropriate rights to set host ID.  */
  37   if (__libc_enable_secure)
  38     {
  39       __set_errno (EPERM);
  40       return -1;
  41     }
  42
  43   /* Open file for writing.  Everybody is allowed to read this file.  */
  44   fd = __open64 (HOSTIDFILE, O_CREAT|O_WRONLY|O_TRUNC, 0644);
  45   if (fd < 0)
  46     return -1;
  47
  48   written = __write (fd, &id, sizeof (id));
  49
  50   __close (fd);
  51
  52   return written != sizeof (id) ? -1 : 0;
  53 }
  54
  55 #else
  56 # include <string.h>
  57 # include <sys/param.h>
  58 # include <resolv/netdb.h>
  59 # include <netinet/in.h>
  60
  61 long int
  62 gethostid ()
  63 {
  64   char hostname[MAXHOSTNAMELEN + 1];
  65   size_t buflen;
  66   char *buffer;
  67   struct hostent hostbuf, *hp;
  68   unsigned long int id;
  69   struct in_addr in;
  70   int herr;
  71   int fd;
  72
  73   /* First try to get the ID from a former invocation of sethostid.  */
  74   fd = __open64 (HOSTIDFILE, O_RDONLY);
  75   if (fd < 0)
  76     fd = __open64 (OLD_HOSTIDFILE, O_RDONLY);
  77   if (fd >= 0)
  78     {
  79       ssize_t n = __read (fd, &id, sizeof (id));
  80
  81       __close (fd);
  82
  83       if (n == sizeof (id))
  84         return id;
  85     }
  86
  87   /* Getting from the file was not successful.  An intelligent guess for
  88      a unique number of a host is its IP address.  Return this.  */
  89   if (__gethostname (hostname, MAXHOSTNAMELEN) < 0 || hostname[0] == '\0')
  90     /* This also fails.  Return and arbitrary value.  */
  91     return 0;
  92
  93   buflen = 1024;
  94   buffer = __alloca (buflen);
  95
  96   /* To get the IP address we need to know the host name.  */
  97   while (__gethostbyname_r (hostname, &hostbuf, buffer, buflen, &hp, &herr)
  98          != 0
  99          || hp == NULL)
 100     if (herr != NETDB_INTERNAL || errno != ERANGE)
 101       return 0;
 102     else
 103       {
 104         /* Enlarge buffer.  */
 105         buflen *= 2;
 106         buffer = __alloca (buflen);
 107       }
 108
 109   in.s_addr = 0;
 110   memcpy (&in, hp->h_addr,
 111           (int) sizeof (in) < hp->h_length ? (int) sizeof (in) : hp->h_length);
 112
 113   /* For the return value to be not exactly the IP address we do some
 114      bit fiddling.  */
 115   return in.s_addr << 16 | in.s_addr >> 16;
 116 }
 117 #endif