libc/inet/hostid.c

   1 /* vi: set sw=4 ts=4: */
   2 /*
   3  * Copyright (C) 2000-2006 Erik Andersen <andersen@uclibc.org>
   4  *
   5  * Licensed under the LGPL v2.1, see the file COPYING.LIB in this tarball.
   6  */
   7
   8 #include <errno.h>
   9 #include <unistd.h>
  10 #include <sys/types.h>
  11 #include <fcntl.h>
  12 #include <stdlib.h>
  13 #include <string.h>
  14 #include <netdb.h>
  15 #include <not-cancel.h>
  16
  17 #define HOSTID "/etc/hostid"
  18
  19 #ifdef __USE_BSD
  20 int sethostid(long int new_id)
  21 {
  22         int fd;
  23         int ret;
  24
  25         if (geteuid() || getuid())
  26                 return __set_errno(EPERM);
  27         fd = open_not_cancel(HOSTID, O_CREAT|O_WRONLY, 0644);
  28         if (fd < 0)
  29                 return fd;
  30         ret = write_not_cancel(fd, &new_id, sizeof(new_id)) == sizeof(new_id) ? 0 : -1;
  31         close_not_cancel_no_status (fd);
  32         return ret;
  33 }
  34 #endif
  35
  36 #define _addr(a) (((struct sockaddr_in*)a->ai_addr)->sin_addr.s_addr)
  37 long int gethostid(void)
  38 {
  39         char host[HOST_NAME_MAX + 1];
  40         int fd, id = 0;
  41
  42         /* If hostid was already set then we can return that value.
  43          * It is not an error if we cannot read this file. It is not even an
  44          * error if we cannot read all the bytes, we just carry on trying...
  45          */
  46         fd = open_not_cancel_2(HOSTID, O_RDONLY);
  47         if (fd >= 0) {
  48                 int i = read_not_cancel(fd, &id, sizeof(id));
  49                 close_not_cancel_no_status(fd);
  50                 if (i > 0)
  51                         return id;
  52         }
  53         /* Try some methods of returning a unique 32 bit id. Clearly IP
  54          * numbers, if on the internet, will have a unique address. If they
  55          * are not on the internet then we can return 0 which means they should
  56          * really set this number via a sethostid() call. If their hostname
  57          * returns the loopback number (i.e. if they have put their hostname
  58          * in the /etc/hosts file with 127.0.0.1) then all such hosts will
  59          * have a non-unique hostid, but it doesn't matter anyway and
  60          * gethostid() will return a non zero number without the need for
  61          * setting one anyway.
  62          *                                              Mitch
  63          */
  64         if (gethostname(host, HOST_NAME_MAX) >= 0 && *host) {
  65                 struct addrinfo hints, *results, *addr;
  66                 memset(&hints, 0, sizeof(struct addrinfo));
  67                 if (!getaddrinfo(host, NULL, &hints, &results)) {
  68                         for (addr = results; addr; addr = results->ai_next) {
  69                                 /* Just so it doesn't look exactly like the
  70                                    IP addr */
  71                                 id = _addr(addr) << 16 | _addr(addr) >> 16;
  72                                 break;
  73                         }
  74                         freeaddrinfo(results);
  75                 }
  76         }
  77         return id;
  78 }