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, see
  17    <http://www.gnu.org/licenses/>.  */
  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
  28 #ifdef SET_PROCEDURE
  29 int
  30 sethostid (id)
  31      long int id;
  32 {
  33   int fd;
  34   ssize_t written;
  35   int32_t id32 = id;
  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   /* Make sure the ID is not too large.  Needed for bi-arch support.   */
  45   if (id32 != id)
  46     {
  47       __set_errno (EOVERFLOW);
  48       return -1;
  49     }
  50
  51   /* Open file for writing.  Everybody is allowed to read this file.  */
  52   fd = open_not_cancel (HOSTIDFILE, O_CREAT|O_WRONLY|O_TRUNC, 0644);
  53   if (fd < 0)
  54     return -1;
  55
  56   written = write_not_cancel (fd, &id32, sizeof (id32));
  57
  58   close_not_cancel_no_status (fd);
  59
  60   return written != sizeof (id32) ? -1 : 0;
  61 }
  62
  63 #else
  64 # include <string.h>
  65 # include <sys/param.h>
  66 # include <resolv/netdb.h>
  67 # include <netinet/in.h>
  68
  69 long int
  70 gethostid ()
  71 {
  72   char hostname[MAXHOSTNAMELEN + 1];
  73   size_t buflen;
  74   char *buffer;
  75   struct hostent hostbuf, *hp;
  76   int32_t id;
  77   struct in_addr in;
  78   int herr;
  79   int fd;
  80
  81   /* First try to get the ID from a former invocation of sethostid.  */
  82   fd = open_not_cancel (HOSTIDFILE, O_RDONLY|O_LARGEFILE, 0);
  83   if (fd >= 0)
  84     {
  85       ssize_t n = read_not_cancel (fd, &id, sizeof (id));
  86
  87       close_not_cancel_no_status (fd);
  88
  89       if (n == sizeof (id))
  90         return id;
  91     }
  92
  93   /* Getting from the file was not successful.  An intelligent guess for
  94      a unique number of a host is its IP address.  Return this.  */
  95   if (__gethostname (hostname, MAXHOSTNAMELEN) < 0 || hostname[0] == '\0')
  96     /* This also fails.  Return and arbitrary value.  */
  97     return 0;
  98
  99   buflen = 1024;
 100   buffer = __alloca (buflen);
 101
 102   /* To get the IP address we need to know the host name.  */
 103   while (__gethostbyname_r (hostname, &hostbuf, buffer, buflen, &hp, &herr)
 104          != 0
 105          || hp == NULL)
 106     if (herr != NETDB_INTERNAL || errno != ERANGE)
 107       return 0;
 108     else
 109       /* Enlarge buffer.  */
 110       buffer = extend_alloca (buffer, buflen, 2 * buflen);
 111
 112   in.s_addr = 0;
 113   memcpy (&in, hp->h_addr,
 114           (int) sizeof (in) < hp->h_length ? (int) sizeof (in) : hp->h_length);
 115
 116   /* For the return value to be not exactly the IP address we do some
 117      bit fiddling.  */
 118   return (int32_t) (in.s_addr << 16 | in.s_addr >> 16);
 119 }
 120 #endif