sysdeps/unix/sysv/linux/ttyname.c

   1 /* Copyright (C) 1991-2024 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 }