libio/freopen.c

   1 /* Copyright (C) 1993-2017 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    <http://www.gnu.org/licenses/>.
  17
  18    As a special exception, if you link the code in this file with
  19    files compiled with a GNU compiler to produce an executable,
  20    that does not cause the resulting executable to be covered by
  21    the GNU Lesser General Public License.  This exception does not
  22    however invalidate any other reasons why the executable file
  23    might be covered by the GNU Lesser General Public License.
  24    This exception applies to code released by its copyright holders
  25    in files containing the exception.  */
  26
  27 #include "libioP.h"
  28 #include "stdio.h"
  29 #include <fcntl.h>
  30 #include <stdlib.h>
  31 #include <unistd.h>
  32
  33 #include <shlib-compat.h>
  34 #include <fd_to_filename.h>
  35
  36 #include <kernel-features.h>
  37
  38 FILE *
  39 freopen (const char *filename, const char *mode, FILE *fp)
  40 {
  41   FILE *result;
  42   CHECK_FILE (fp, NULL);
  43   if (!(fp->_flags & _IO_IS_FILEBUF))
  44     return NULL;
  45   _IO_acquire_lock (fp);
  46   int fd = _IO_fileno (fp);
  47   const char *gfilename = (filename == NULL && fd >= 0
  48                            ? fd_to_filename (fd) : filename);
  49   fp->_flags2 |= _IO_FLAGS2_NOCLOSE;
  50 #if SHLIB_COMPAT (libc, GLIBC_2_0, GLIBC_2_1)
  51   if (&_IO_stdin_used == NULL)
  52     {
  53       /* If the shared C library is used by the application binary which
  54          was linked against the older version of libio, we just use the
  55          older one even for internal use to avoid trouble since a pointer
  56          to the old libio may be passed into shared C library and wind
  57          up here. */
  58       _IO_old_file_close_it (fp);
  59       _IO_JUMPS_FILE_plus (fp) = &_IO_old_file_jumps;
  60       result = _IO_old_file_fopen (fp, gfilename, mode);
  61     }
  62   else
  63 #endif
  64     {
  65       _IO_file_close_it (fp);
  66       _IO_JUMPS_FILE_plus (fp) = &_IO_file_jumps;
  67       if (_IO_vtable_offset (fp) == 0 && fp->_wide_data != NULL)
  68         fp->_wide_data->_wide_vtable = &_IO_wfile_jumps;
  69       result = _IO_file_fopen (fp, gfilename, mode, 1);
  70       if (result != NULL)
  71         result = __fopen_maybe_mmap (result);
  72     }
  73   fp->_flags2 &= ~_IO_FLAGS2_NOCLOSE;
  74   if (result != NULL)
  75     {
  76       /* unbound stream orientation */
  77       result->_mode = 0;
  78
  79       if (fd != -1 && _IO_fileno (result) != fd)
  80         {
  81           /* At this point we have both file descriptors already allocated,
  82              so __dup3 will not fail with EBADF, EINVAL, or EMFILE.  But
  83              we still need to check for EINVAL and, due Linux internal
  84              implementation, EBUSY.  It is because on how it internally opens
  85              the file by splitting the buffer allocation operation and VFS
  86              opening (a dup operation may run when a file is still pending
  87              'install' on VFS).  */
  88           if (__dup3 (_IO_fileno (result), fd,
  89                       (result->_flags2 & _IO_FLAGS2_CLOEXEC) != 0
  90                       ? O_CLOEXEC : 0) == -1)
  91             {
  92               _IO_file_close_it (result);
  93               result = NULL;
  94               goto end;
  95             }
  96           __close (_IO_fileno (result));
  97           _IO_fileno (result) = fd;
  98         }
  99     }
 100   else if (fd != -1)
 101     __close (fd);
 102
 103 end:
 104   if (filename == NULL)
 105     free ((char *) gfilename);
 106
 107   _IO_release_lock (fp);
 108   return result;
 109 }