libio/freopen64.c

   1 /* Copyright (C) 1993-2024 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    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 <stdio.h>
  28 #include <fcntl.h>
  29 #include <stdlib.h>
  30 #include <unistd.h>
  31
  32 #include <libioP.h>
  33 #include <fd_to_filename.h>
  34
  35 FILE *
  36 freopen64 (const char *filename, const char *mode, FILE *fp)
  37 {
  38   FILE *result = NULL;
  39   struct fd_to_filename fdfilename;
  40
  41   CHECK_FILE (fp, NULL);
  42
  43   _IO_acquire_lock (fp);
  44   /* First flush the stream (failure should be ignored).  */
  45   _IO_SYNC (fp);
  46
  47   if (!(fp->_flags & _IO_IS_FILEBUF))
  48     goto end;
  49
  50   int fd = _IO_fileno (fp);
  51   const char *gfilename
  52     = filename != NULL ? filename : __fd_to_filename (fd, &fdfilename);
  53
  54   fp->_flags2 |= _IO_FLAGS2_NOCLOSE;
  55   _IO_file_close_it (fp);
  56   _IO_JUMPS_FILE_plus (fp) = &_IO_file_jumps;
  57   if (_IO_vtable_offset (fp) == 0 && fp->_wide_data != NULL)
  58     fp->_wide_data->_wide_vtable = &_IO_wfile_jumps;
  59   result = _IO_file_fopen (fp, gfilename, mode, 0);
  60   fp->_flags2 &= ~_IO_FLAGS2_NOCLOSE;
  61   if (result != NULL)
  62     result = __fopen_maybe_mmap (result);
  63   if (result != NULL)
  64     {
  65       /* unbound stream orientation */
  66       result->_mode = 0;
  67
  68       if (fd != -1 && _IO_fileno (result) != fd)
  69         {
  70           /* At this point we have both file descriptors already allocated,
  71              so __dup3 will not fail with EBADF, EINVAL, or EMFILE.  But
  72              we still need to check for EINVAL and, due Linux internal
  73              implementation, EBUSY.  It is because on how it internally opens
  74              the file by splitting the buffer allocation operation and VFS
  75              opening (a dup operation may run when a file is still pending
  76              'install' on VFS).  */
  77           if (__dup3 (_IO_fileno (result), fd,
  78                       (result->_flags2 & _IO_FLAGS2_CLOEXEC) != 0
  79                       ? O_CLOEXEC : 0) == -1)
  80             {
  81               _IO_file_close_it (result);
  82               result = NULL;
  83               goto end;
  84             }
  85           __close (_IO_fileno (result));
  86           _IO_fileno (result) = fd;
  87         }
  88     }
  89   else if (fd != -1)
  90     __close (fd);
  91
  92 end:
  93   _IO_release_lock (fp);
  94   return result;
  95 }