sysdeps/unix/sysv/linux/gethostid.c

   1 /* Copyright (C) 1995-2017 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 (long int id)
  30 {
  31   int fd;
  32   ssize_t written;
  33   int32_t id32 = id;
  34
  35   /* Test for appropriate rights to set host ID.  */
  36   if (__libc_enable_secure)
  37     {
  38       __set_errno (EPERM);
  39       return -1;
  40     }
  41
  42   /* Make sure the ID is not too large.  Needed for bi-arch support.   */
  43   if (id32 != id)
  44     {
  45       __set_errno (EOVERFLOW);
  46       return -1;
  47     }
  48
  49   /* Open file for writing.  Everybody is allowed to read this file.  */
  50   fd = open_not_cancel (HOSTIDFILE, O_CREAT|O_WRONLY|O_TRUNC, 0644);
  51   if (fd < 0)
  52     return -1;
  53
  54   written = write_not_cancel (fd, &id32, sizeof (id32));
  55
  56   close_not_cancel_no_status (fd);
  57
  58   return written != sizeof (id32) ? -1 : 0;
  59 }
  60
  61 #else
  62 # include <string.h>
  63 # include <sys/param.h>
  64 # include <resolv/netdb.h>
  65 # include <netinet/in.h>
  66
  67 long int
  68 gethostid (void)
  69 {
  70   char hostname[MAXHOSTNAMELEN + 1];
  71   size_t buflen;
  72   char *buffer;
  73   struct hostent hostbuf, *hp;
  74   int32_t id;
  75   struct in_addr in;
  76   int herr;
  77   int fd;
  78
  79   /* First try to get the ID from a former invocation of sethostid.  */
  80   fd = open_not_cancel (HOSTIDFILE, O_RDONLY|O_LARGEFILE, 0);
  81   if (fd >= 0)
  82     {
  83       ssize_t n = read_not_cancel (fd, &id, sizeof (id));
  84
  85       close_not_cancel_no_status (fd);
  86
  87       if (n == sizeof (id))
  88         return id;
  89     }
  90
  91   /* Getting from the file was not successful.  An intelligent guess for
  92      a unique number of a host is its IP address.  Return this.  */
  93   if (__gethostname (hostname, MAXHOSTNAMELEN) < 0 || hostname[0] == '\0')
  94     /* This also fails.  Return and arbitrary value.  */
  95     return 0;
  96
  97   buflen = 1024;
  98   buffer = __alloca (buflen);
  99
 100   /* To get the IP address we need to know the host name.  */
 101   while (__gethostbyname_r (hostname, &hostbuf, buffer, buflen, &hp, &herr)
 102          != 0
 103          || hp == NULL)
 104     if (herr != NETDB_INTERNAL || errno != ERANGE)
 105       return 0;
 106     else
 107       /* Enlarge buffer.  */
 108       buffer = extend_alloca (buffer, buflen, 2 * buflen);
 109
 110   in.s_addr = 0;
 111   memcpy (&in, hp->h_addr,
 112           (int) sizeof (in) < hp->h_length ? (int) sizeof (in) : hp->h_length);
 113
 114   /* For the return value to be not exactly the IP address we do some
 115      bit fiddling.  */
 116   return (int32_t) (in.s_addr << 16 | in.s_addr >> 16);
 117 }
 118 #endif