sysdeps/unix/getlogin.c

   1 /* Copyright (C) 1991, 1992, 1996 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 <errno.h>
  21 #include <unistd.h>
  22 #include <string.h>
  23 #include <stdio.h>
  24 #include <limits.h>
  25 #include <fcntl.h>
  26
  27 #include <utmp.h>
  28
  29 /* Return the login name of the user, or NULL if it can't be determined.
  30    The returned pointer, if not NULL, is good only until the next call.  */
  31
  32 char *
  33 DEFUN_VOID(getlogin)
  34 {
  35   char tty_pathname[2 + 2 * NAME_MAX];
  36   char *real_tty_path = tty_pathname;
  37   char *result = NULL;
  38   static struct utmp_data utmp_data;
  39   struct utmp *ut, line;
  40
  41   {
  42     int err = 0;
  43     int d = __open ("/dev/tty", 0);
  44     if (d < 0)
  45       return NULL;
  46
  47     if (ttyname_r (d, real_tty_path, sizeof (tty_pathname)) < 0)
  48       err = errno;
  49     (void) close (d);
  50
  51     if (errno != 0)
  52       {
  53         errno = err;
  54         return NULL;
  55       }
  56   }
  57
  58   real_tty_path += 5;           /* Remove "/dev/".  */
  59
  60   setutent_r (&utmp_data);
  61   strncpy (line.ut_line, real_tty_path, sizeof line.ut_line);
  62   if (getutline_r (&line, &ut, &utmp_data) < 0)
  63     {
  64       if (errno == ESRCH)
  65         /* The caller expects ENOENT if nothing is found.  */
  66         errno = ENOENT;
  67       result = NULL;
  68     }
  69   else
  70     result = ut->ut_line;
  71
  72   endutent_r (&utmp_data);
  73
  74   return result;
  75 }