sysdeps/unix/getlogin.c

   1 /* Copyright (C) 1991, 1992 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 Library General Public License as
   6 published by the Free Software Foundation; either version 2 of the
   7 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 Library General Public License for more details.
  13
  14 You should have received a copy of the GNU Library General Public
  15 License along with the GNU C Library; see the file COPYING.LIB.  If
  16 not, write to the Free Software Foundation, Inc., 675 Mass Ave,
  17 Cambridge, MA 02139, USA.  */
  18
  19 #include <ansidecl.h>
  20 #include <stddef.h>
  21 #include <errno.h>
  22 #include <unistd.h>
  23 #include <string.h>
  24 #include <stdio.h>
  25 #include <limits.h>
  26 #include <fcntl.h>
  27
  28 #include <utmp.h>
  29
  30 /* Defined in ttyname.c.  */
  31 extern char *__ttyname;
  32
  33 /* Return the login name of the user, or NULL if it can't be determined.
  34    The returned pointer, if not NULL, is good only until the next call.  */
  35
  36 char *
  37 DEFUN_VOID(getlogin)
  38 {
  39   char save_tty_pathname[2 + 2 * NAME_MAX];
  40   char *save_ttyname;
  41   char *real_tty_path;
  42   char *result = NULL;
  43   FILE *f;
  44   static struct utmp ut;
  45
  46   if (__ttyname == NULL)
  47     save_ttyname = NULL;
  48   else
  49     save_ttyname = strcpy (save_tty_pathname, __ttyname);
  50
  51   {
  52     int err;
  53     int d = __open ("/dev/tty", 0);
  54     if (d < 0)
  55       return NULL;
  56
  57     real_tty_path = ttyname (d);
  58     err = errno;
  59     (void) close (d);
  60
  61     if (real_tty_path == NULL)
  62       {
  63         errno = err;
  64         return NULL;
  65       }
  66   }
  67
  68   real_tty_path += 5;           /* Remove "/dev/".  */
  69
  70   f = fopen ("/etc/utmp", "r");
  71   if (f != NULL)
  72     {
  73       while (fread ((PTR) &ut, sizeof(ut), 1, f) == 1)
  74         if (!strncmp (ut.ut_line, real_tty_path, sizeof (ut.ut_line)))
  75           {
  76             result = ut.ut_name;
  77             /* The name is not null-terminated if
  78                it is as long as sizeof (ut.ut_name).  */
  79             result[sizeof (ut.ut_name)] = '\0';
  80             break;
  81           }
  82       (void) fclose (f);
  83     }
  84
  85   if (save_ttyname != NULL)
  86     strcpy (__ttyname, save_ttyname);
  87   if (result == NULL)
  88     errno = ENOENT;
  89   return result;
  90 }