sysdeps/posix/ttyname.c

   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 <stddef.h>
  21 #include <dirent.h>
  22 #include <sys/types.h>
  23 #include <sys/stat.h>
  24 #include <unistd.h>
  25 #include <string.h>
  26 #include <stdlib.h>
  27
  28 char *__ttyname;
  29
  30 static char *getttyname (int fd, dev_t mydev, ino_t myino,
  31                          int save, int *dostat);
  32
  33
  34 libc_freeres_ptr (static char *getttyname_name);
  35
  36 static char *
  37 getttyname (int fd, dev_t mydev, ino_t myino, int save, int *dostat)
  38 {
  39   static const char dev[] = "/dev";
  40   static size_t namelen;
  41   struct stat st;
  42   DIR *dirstream;
  43   struct dirent *d;
  44
  45   dirstream = __opendir (dev);
  46   if (dirstream == NULL)
  47     {
  48       *dostat = -1;
  49       return NULL;
  50     }
  51
  52   while ((d = __readdir (dirstream)) != NULL)
  53     if (((ino_t) d->d_fileno == myino || *dostat)
  54         && strcmp (d->d_name, "stdin")
  55         && strcmp (d->d_name, "stdout")
  56         && strcmp (d->d_name, "stderr"))
  57       {
  58         size_t dlen = _D_ALLOC_NAMLEN (d);
  59         if (sizeof (dev) + dlen > namelen)
  60           {
  61             free (getttyname_name);
  62             namelen = 2 * (sizeof (dev) + dlen); /* Big enough.  */
  63             getttyname_name = malloc (namelen);
  64             if (! getttyname_name)
  65               {
  66                 *dostat = -1;
  67                 /* Perhaps it helps to free the directory stream buffer.  */
  68                 (void) __closedir (dirstream);
  69                 return NULL;
  70               }
  71             *((char *) __mempcpy (getttyname_name, dev, sizeof (dev) - 1))
  72               = '/';
  73           }
  74         (void) __mempcpy (&getttyname_name[sizeof (dev)], d->d_name, dlen);
  75         if (stat (getttyname_name, &st) == 0
  76 #ifdef _STATBUF_ST_RDEV
  77             && S_ISCHR (st.st_mode) && st.st_rdev == mydev
  78 #else
  79             && (ino_t) d->d_fileno == myino && st.st_dev == mydev
  80 #endif
  81            )
  82           {
  83             (void) __closedir (dirstream);
  84             __ttyname = getttyname_name;
  85             __set_errno (save);
  86             return getttyname_name;
  87           }
  88       }
  89
  90   (void) __closedir (dirstream);
  91   __set_errno (save);
  92   return NULL;
  93 }
  94
  95 /* Return the pathname of the terminal FD is open on, or NULL on errors.
  96    The returned storage is good only until the next call to this function.  */
  97 char *
  98 ttyname (int fd)
  99 {
 100   struct stat st;
 101   int dostat = 0;
 102   char *name;
 103   int save = errno;
 104
 105   if (!__isatty (fd))
 106     return NULL;
 107
 108   if (fstat (fd, &st) < 0)
 109     return NULL;
 110
 111 #ifdef _STATBUF_ST_RDEV
 112   name = getttyname (fd, st.st_rdev, st.st_ino, save, &dostat);
 113 #else
 114   name = getttyname (fd, st.st_dev, st.st_ino, save, &dostat);
 115 #endif
 116
 117   if (!name && dostat != -1)
 118     {
 119       dostat = 1;
 120 #ifdef _STATBUF_ST_RDEV
 121       name = getttyname (fd, st.st_rdev, st.st_ino, save, &dostat);
 122 #else
 123       name = getttyname (fd, st.st_dev, st.st_ino, save, &dostat);
 124 #endif
 125     }
 126
 127   return name;
 128 }