sysdeps/unix/sysv/linux/gethostid.c

   1 /* Copyright (C) 1995-2014 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, see
  16    <http://www.gnu.org/licenses/>.  */
  17
  18 #include <alloca.h>
  19 #include <errno.h>
  20 #include <fcntl.h>
  21 #include <unistd.h>
  22 #include <netdb.h>
  23 #include <not-cancel.h>
  24
  25 #define HOSTIDFILE "/etc/hostid"
  26
  27 #ifdef SET_PROCEDURE
  28 int
  29 sethostid (id)
  30      long int id;
  31 {
  32   int fd;
  33   ssize_t written;
  34   int32_t id32 = id;
  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   /* Make sure the ID is not too large.  Needed for bi-arch support.   */
  44   if (id32 != id)
  45     {
  46       __set_errno (EOVERFLOW);
  47       return -1;
  48     }
  49
  50   /* Open file for writing.  Everybody is allowed to read this file.  */
  51   fd = open_not_cancel (HOSTIDFILE, O_CREAT|O_WRONLY|O_TRUNC, 0644);
  52   if (fd < 0)
  53     return -1;
  54
  55   written = write_not_cancel (fd, &id32, sizeof (id32));
  56
  57   close_not_cancel_no_status (fd);
  58
  59   return written != sizeof (id32) ? -1 : 0;
  60 }
  61
  62 #else
  63 # include <string.h>
  64 # include <sys/param.h>
  65 # include <resolv/netdb.h>
  66 # include <netinet/in.h>
  67
  68 long int
  69 gethostid (void)
  70 {
  71   char hostname[MAXHOSTNAMELEN + 1];
  72   size_t buflen;
  73   char *buffer;
  74   struct hostent hostbuf, *hp;
  75   int32_t id;
  76   struct in_addr in;
  77   int herr;
  78   int fd;
  79
  80   /* First try to get the ID from a former invocation of sethostid.  */
  81   fd = open_not_cancel (HOSTIDFILE, O_RDONLY|O_LARGEFILE, 0);
  82   if (fd >= 0)
  83     {
  84       ssize_t n = read_not_cancel (fd, &id, sizeof (id));
  85
  86       close_not_cancel_no_status (fd);
  87
  88       if (n == sizeof (id))
  89         return id;
  90     }
  91
  92   /* Getting from the file was not successful.  An intelligent guess for
  93      a unique number of a host is its IP address.  Return this.  */
  94   if (__gethostname (hostname, MAXHOSTNAMELEN) < 0 || hostname[0] == '\0')
  95     /* This also fails.  Return and arbitrary value.  */
  96     return 0;
  97
  98   buflen = 1024;
  99   buffer = __alloca (buflen);
 100
 101   /* To get the IP address we need to know the host name.  */
 102   while (__gethostbyname_r (hostname, &hostbuf, buffer, buflen, &hp, &herr)
 103          != 0
 104          || hp == NULL)
 105     if (herr != NETDB_INTERNAL || errno != ERANGE)
 106       return 0;
 107     else
 108       /* Enlarge buffer.  */
 109       buffer = extend_alloca (buffer, buflen, 2 * buflen);
 110
 111   in.s_addr = 0;
 112   memcpy (&in, hp->h_addr,
 113           (int) sizeof (in) < hp->h_length ? (int) sizeof (in) : hp->h_length);
 114
 115   /* For the return value to be not exactly the IP address we do some
 116      bit fiddling.  */
 117   return (int32_t) (in.s_addr << 16 | in.s_addr >> 16);
 118 }
 119 #endif