src/common/tuklib_open_stdxxx.c

   1 // SPDX-License-Identifier: 0BSD
   2
   3 ///////////////////////////////////////////////////////////////////////////////
   4 //
   5 /// \file       tuklib_open_stdxxx.c
   6 /// \brief      Make sure that file descriptors 0, 1, and 2 are open
   7 //
   8 //  Author:     Lasse Collin
   9 //
  10 ///////////////////////////////////////////////////////////////////////////////
  11
  12 #include "tuklib_open_stdxxx.h"
  13
  14 #ifndef TUKLIB_DOSLIKE
  15 #       include <stdlib.h>
  16 #       include <errno.h>
  17 #       include <fcntl.h>
  18 #       include <unistd.h>
  19 #endif
  20
  21
  22 extern void
  23 tuklib_open_stdxxx(int err_status)
  24 {
  25 #ifdef TUKLIB_DOSLIKE
  26         // Do nothing, just silence warnings.
  27         (void)err_status;
  28
  29 #else
  30         for (int i = 0; i <= 2; ++i) {
  31                 // We use fcntl() to check if the file descriptor is open.
  32                 if (fcntl(i, F_GETFD) == -1 && errno == EBADF) {
  33                         // With stdin, we could use /dev/full so that
  34                         // writing to stdin would fail. However, /dev/full
  35                         // is Linux specific, and if the program tries to
  36                         // write to stdin, there's already a problem anyway.
  37                         const int fd = open("/dev/null", O_NOCTTY
  38                                         | (i == 0 ? O_WRONLY : O_RDONLY));
  39
  40                         if (fd != i) {
  41                                 if (fd != -1)
  42                                         (void)close(fd);
  43
  44                                 // Something went wrong. Exit with the
  45                                 // exit status we were given. Don't try
  46                                 // to print an error message, since stderr
  47                                 // may very well be non-existent. This
  48                                 // error should be extremely rare.
  49                                 exit(err_status);
  50                         }
  51                 }
  52         }
  53 #endif
  54
  55         return;
  56 }