src/common/tuklib_open_stdxxx.c

   1 ///////////////////////////////////////////////////////////////////////////////
   2 //
   3 /// \file       tuklib_open_stdxxx.c
   4 /// \brief      Make sure that file descriptors 0, 1, and 2 are open
   5 //
   6 //  Author:     Lasse Collin
   7 //
   8 //  This file has been put into the public domain.
   9 //  You can do whatever you want with this file.
  10 //
  11 ///////////////////////////////////////////////////////////////////////////////
  12
  13 #include "tuklib_open_stdxxx.h"
  14
  15 #ifndef TUKLIB_DOSLIKE
  16 #       include <stdlib.h>
  17 #       include <errno.h>
  18 #       include <fcntl.h>
  19 #       include <unistd.h>
  20 #endif
  21
  22
  23 extern void
  24 tuklib_open_stdxxx(int err_status)
  25 {
  26 #ifndef TUKLIB_DOSLIKE
  27         for (int i = 0; i <= 2; ++i) {
  28                 // We use fcntl() to check if the file descriptor is open.
  29                 if (fcntl(i, F_GETFD) == -1 && errno == EBADF) {
  30                         // With stdin, we could use /dev/full so that
  31                         // writing to stdin would fail. However, /dev/full
  32                         // is Linux specific, and if the program tries to
  33                         // write to stdin, there's already a problem anyway.
  34                         const int fd = open("/dev/null", O_NOCTTY
  35                                         | (i == 0 ? O_WRONLY : O_RDONLY));
  36
  37                         if (fd != i) {
  38                                 // Something went wrong. Exit with the
  39                                 // exit status we were given. Don't try
  40                                 // to print an error message, since stderr
  41                                 // may very well be non-existent. This
  42                                 // error should be extremely rare.
  43                                 (void)close(fd);
  44                                 exit(err_status);
  45                         }
  46                 }
  47         }
  48 #endif
  49
  50         return;
  51 }