1  /* Copyright (C) 1991-2023 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 Lesser General Public
       6     License as published by the Free Software Foundation; either
       7     version 2.1 of the 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     Lesser General Public License for more details.
      13  
      14     You should have received a copy of the GNU Lesser General Public
      15     License along with the GNU C Library; if not, see
      16     <https://www.gnu.org/licenses/>.  */
      17  
      18  #include <errno.h>
      19  #include <limits.h>
      20  #include <termios.h>
      21  #include <stdlib.h>
      22  #include <set-freeres.h>
      23  #include "ttyname.h"
      24  
      25  static char *ttyname_buf = NULL;
      26  weak_alias (ttyname_buf, __ttyname_freemem_ptr)
      27  
      28  /* Return the pathname of the terminal FD is open on, or NULL on errors.
      29     The returned storage is good only until the next call to this function.  */
      30  char *
      31  ttyname (int fd)
      32  {
      33    /* isatty check, tcgetattr is used because it sets the correct
      34       errno (EBADF resp. ENOTTY) on error.  Fast error path to avoid the
      35       allocation  */
      36    struct termios term;
      37    if (__glibc_unlikely (__tcgetattr (fd, &term) < 0))
      38      return NULL;
      39  
      40    if (ttyname_buf == NULL)
      41      {
      42        ttyname_buf = malloc (PATH_MAX);
      43        if (ttyname_buf == NULL)
      44  	return NULL;
      45      }
      46  
      47    int result = __ttyname_r (fd, ttyname_buf, PATH_MAX);
      48    if (result != 0)
      49      {
      50        __set_errno (result);
      51        return NULL;
      52      }
      53    return ttyname_buf;
      54  }