sysdeps/unix/sysv/linux/gethostid.c

   1 /* Copyright (C) 1995,1996,1998-2001,2003 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 #include <not-cancel.h>
  25
  26 #define HOSTIDFILE "/etc/hostid"
  27 #define OLD_HOSTIDFILE "/etc/hostid"
  28
  29 #ifdef SET_PROCEDURE
  30 int
  31 sethostid (id)
  32      long int id;
  33 {
  34   int fd;
  35   ssize_t written;
  36
  37   /* Test for appropriate rights to set host ID.  */
  38   if (__libc_enable_secure)
  39     {
  40       __set_errno (EPERM);
  41       return -1;
  42     }
  43
  44   /* Open file for writing.  Everybody is allowed to read this file.  */
  45   fd = open_not_cancel (HOSTIDFILE, O_CREAT|O_WRONLY|O_TRUNC, 0644);
  46   if (fd < 0)
  47     return -1;
  48
  49   written = write_not_cancel (fd, &id, sizeof (id));
  50
  51   close_not_cancel_no_status (fd);
  52
  53   return written != sizeof (id) ? -1 : 0;
  54 }
  55
  56 #else
  57 # include <string.h>
  58 # include <sys/param.h>
  59 # include <resolv/netdb.h>
  60 # include <netinet/in.h>
  61
  62 long int
  63 gethostid ()
  64 {
  65   char hostname[MAXHOSTNAMELEN + 1];
  66   size_t buflen;
  67   char *buffer;
  68   struct hostent hostbuf, *hp;
  69   unsigned long int id;
  70   struct in_addr in;
  71   int herr;
  72   int fd;
  73
  74   /* First try to get the ID from a former invocation of sethostid.  */
  75   fd = open_not_cancel (HOSTIDFILE, O_RDONLY|O_LARGEFILE, 0);
  76   if (fd < 0)
  77     fd = open_not_cancel (OLD_HOSTIDFILE, O_RDONLY|O_LARGEFILE, 0);
  78   if (fd >= 0)
  79     {
  80       ssize_t n = read_not_cancel (fd, &id, sizeof (id));
  81
  82       close_not_cancel_no_status (fd);
  83
  84       if (n == sizeof (id))
  85         return id;
  86     }
  87
  88   /* Getting from the file was not successful.  An intelligent guess for
  89      a unique number of a host is its IP address.  Return this.  */
  90   if (__gethostname (hostname, MAXHOSTNAMELEN) < 0 || hostname[0] == '\0')
  91     /* This also fails.  Return and arbitrary value.  */
  92     return 0;
  93
  94   buflen = 1024;
  95   buffer = __alloca (buflen);
  96
  97   /* To get the IP address we need to know the host name.  */
  98   while (__gethostbyname_r (hostname, &hostbuf, buffer, buflen, &hp, &herr)
  99          != 0
 100          || hp == NULL)
 101     if (herr != NETDB_INTERNAL || errno != ERANGE)
 102       return 0;
 103     else
 104       /* Enlarge buffer.  */
 105       buffer = extend_alloca (buffer, buflen, 2 * buflen);
 106
 107   in.s_addr = 0;
 108   memcpy (&in, hp->h_addr,
 109           (int) sizeof (in) < hp->h_length ? (int) sizeof (in) : hp->h_length);
 110
 111   /* For the return value to be not exactly the IP address we do some
 112      bit fiddling.  */
 113   return in.s_addr << 16 | in.s_addr >> 16;
 114 }
 115 #endif