sysdeps/posix/ttyname.c

   1 /* Copyright (C) 1991, 1992, 1993, 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 <errno.h>
  20 #include <limits.h>
  21 #include <stddef.h>
  22 #include <dirent.h>
  23 #include <sys/types.h>
  24 #include <sys/stat.h>
  25 #include <unistd.h>
  26 #include <string.h>
  27 #include <stdlib.h>
  28
  29 char *__ttyname = NULL;
  30
  31 /* Return the pathname of the terminal FD is open on, or NULL on errors.
  32    The returned storage is good only until the next call to this function.  */
  33 char *
  34 ttyname (fd)
  35      int fd;
  36 {
  37   static const char dev[] = "/dev";
  38   static char *name;
  39   static size_t namelen = 0;
  40   struct stat st;
  41   dev_t mydev;
  42   ino_t myino;
  43   DIR *dirstream;
  44   struct dirent *d;
  45   int save = errno;
  46
  47   if (!__isatty (fd))
  48     return NULL;
  49
  50   if (fstat (fd, &st) < 0)
  51     return NULL;
  52   mydev = st.st_dev;
  53   myino = st.st_ino;
  54
  55   dirstream = opendir (dev);
  56   if (dirstream == NULL)
  57     return NULL;
  58
  59   while ((d = readdir (dirstream)) != NULL)
  60     if ((ino_t) d->d_fileno == myino)
  61       {
  62         size_t dlen = _D_ALLOC_NAMLEN (d);
  63         if (sizeof (dev) + dlen > namelen)
  64           {
  65             free (name);
  66             namelen = 2 * (sizeof (dev) + dlen); /* Big enough.  */
  67             name = malloc (namelen);
  68             if (! name)
  69               return NULL;
  70             (void) memcpy (name, dev, sizeof (dev) - 1);
  71             name[sizeof (dev) - 1] = '/';
  72           }
  73         (void) memcpy (&name[sizeof (dev)], d->d_name, dlen);
  74         if (stat (name, &st) == 0 && st.st_dev == mydev)
  75           {
  76             (void) closedir (dirstream);
  77             __ttyname = name;
  78             __set_errno (save);
  79             return name;
  80           }
  81       }
  82
  83   (void) closedir (dirstream);
  84   __set_errno (save);
  85   return NULL;
  86 }