glibc/sysdeps/unix/getlogin_r.c

/* Reentrant function to return the current login name.  Unix version.
   Copyright (C) 1991, 1992, 1996, 1997, 1998 Free Software Foundation, Inc.
   This file is part of the GNU C Library.

   The GNU C Library is free software; you can redistribute it and/or
   modify it under the terms of the GNU Library General Public License as
   published by the Free Software Foundation; either version 2 of the
   License, or (at your option) any later version.

   The GNU C Library is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
   Library General Public License for more details.

   You should have received a copy of the GNU Library General Public
   License along with the GNU C Library; see the file COPYING.LIB.  If not,
   write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
   Boston, MA 02111-1307, USA.  */

#include <errno.h>
#include <unistd.h>
#include <string.h>
#include <stdio.h>
#include <limits.h>
#include <fcntl.h>

#include <utmp.h>

/* Return at most NAME_LEN characters of the login name of the user in NAME.
   If it cannot be determined or some other error occurred, return the error
   code.  Otherwise return 0.  */

int
getlogin_r (name, name_len)
     char *name;
     size_t name_len;
{
  char tty_pathname[2 + 2 * NAME_MAX];
  char *real_tty_path = tty_pathname;
  int result = 0;
  struct utmp *ut, line, buffer;

  {
    int d = __open ("/dev/tty", 0);
    if (d < 0)
      return errno;

    result = __ttyname_r (d, real_tty_path, sizeof (tty_pathname));
    (void) __close (d);

    if (result != 0)
      {
	__set_errno (result);
	return result;
      }
  }

  real_tty_path += 5;		/* Remove "/dev/".  */

  __setutent ();
  strncpy (line.ut_line, real_tty_path, sizeof line.ut_line);
  if (__getutline_r (&line, &buffer, &ut) < 0)
    {
      if (errno == ESRCH)
	/* The caller expects ENOENT if nothing is found.  */
	result = ENOENT;
      else
	result = errno;
    }
  else
    {
      size_t needed = strlen (ut->ut_line) + 1;

      if (needed < name_len)
	{
	  __set_errno (ERANGE);
	  result = ERANGE;
	}
      else
	{
	  memcpy (name, ut->ut_line, needed);
	  result = 0;
	}
    }
  __endutent ();

  return result;
}