libc/inet/hostid.c

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