sysdeps/unix/sysv/linux/gethostid.c

   1 /* Copyright (C) 1995,1996,1998-2001,2003,2004,2006
   2    Free Software Foundation, Inc.
   3    This file is part of the GNU C Library.
   4
   5    The GNU C Library is free software; you can redistribute it and/or
   6    modify it under the terms of the GNU Lesser General Public
   7    License as published by the Free Software Foundation; either
   8    version 2.1 of the License, or (at your option) any later version.
   9
  10    The GNU C Library is distributed in the hope that it will be useful,
  11    but WITHOUT ANY WARRANTY; without even the implied warranty of
  12    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  13    Lesser General Public License for more details.
  14
  15    You should have received a copy of the GNU Lesser General Public
  16    License along with the GNU C Library; if not, write to the Free
  17    Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
  18    02111-1307 USA.  */
  19
  20 #include <alloca.h>
  21 #include <errno.h>
  22 #include <fcntl.h>
  23 #include <unistd.h>
  24 #include <netdb.h>
  25 #include <not-cancel.h>
  26
  27 #define 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   int32_t id32 = id;
  37
  38   /* Test for appropriate rights to set host ID.  */
  39   if (__libc_enable_secure)
  40     {
  41       __set_errno (EPERM);
  42       return -1;
  43     }
  44
  45   /* Make sure the ID is not too large.  Needed for bi-arch support.   */
  46   if (id32 != id)
  47     {
  48       __set_errno (EOVERFLOW);
  49       return -1;
  50     }
  51
  52   /* Open file for writing.  Everybody is allowed to read this file.  */
  53   fd = open_not_cancel (HOSTIDFILE, O_CREAT|O_WRONLY|O_TRUNC, 0644);
  54   if (fd < 0)
  55     return -1;
  56
  57   written = write_not_cancel (fd, &id32, sizeof (id32));
  58
  59   close_not_cancel_no_status (fd);
  60
  61   return written != sizeof (id32) ? -1 : 0;
  62 }
  63
  64 #else
  65 # include <string.h>
  66 # include <sys/param.h>
  67 # include <resolv/netdb.h>
  68 # include <netinet/in.h>
  69
  70 long int
  71 gethostid ()
  72 {
  73   char hostname[MAXHOSTNAMELEN + 1];
  74   size_t buflen;
  75   char *buffer;
  76   struct hostent hostbuf, *hp;
  77   int32_t id;
  78   struct in_addr in;
  79   int herr;
  80   int fd;
  81
  82   /* First try to get the ID from a former invocation of sethostid.  */
  83   fd = open_not_cancel (HOSTIDFILE, O_RDONLY|O_LARGEFILE, 0);
  84   if (fd >= 0)
  85     {
  86       ssize_t n = read_not_cancel (fd, &id, sizeof (id));
  87
  88       close_not_cancel_no_status (fd);
  89
  90       if (n == sizeof (id))
  91         return id;
  92     }
  93
  94   /* Getting from the file was not successful.  An intelligent guess for
  95      a unique number of a host is its IP address.  Return this.  */
  96   if (__gethostname (hostname, MAXHOSTNAMELEN) < 0 || hostname[0] == '\0')
  97     /* This also fails.  Return and arbitrary value.  */
  98     return 0;
  99
 100   buflen = 1024;
 101   buffer = __alloca (buflen);
 102
 103   /* To get the IP address we need to know the host name.  */
 104   while (__gethostbyname_r (hostname, &hostbuf, buffer, buflen, &hp, &herr)
 105          != 0
 106          || hp == NULL)
 107     if (herr != NETDB_INTERNAL || errno != ERANGE)
 108       return 0;
 109     else
 110       /* Enlarge buffer.  */
 111       buffer = extend_alloca (buffer, buflen, 2 * buflen);
 112
 113   in.s_addr = 0;
 114   memcpy (&in, hp->h_addr,
 115           (int) sizeof (in) < hp->h_length ? (int) sizeof (in) : hp->h_length);
 116
 117   /* For the return value to be not exactly the IP address we do some
 118      bit fiddling.  */
 119   return (int32_t) (in.s_addr << 16 | in.s_addr >> 16);
 120 }
 121 #endif