libio/freopen.c

   1 /* Copyright (C) 1993-2022 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 #include <shlib-compat.h>
  35
  36 FILE *
  37 freopen (const char *filename, const char *mode, FILE *fp)
  38 {
  39   FILE *result = NULL;
  40   struct fd_to_filename fdfilename;
  41
  42   CHECK_FILE (fp, NULL);
  43
  44   _IO_acquire_lock (fp);
  45   /* First flush the stream (failure should be ignored).  */
  46   _IO_SYNC (fp);
  47
  48   if (!(fp->_flags & _IO_IS_FILEBUF))
  49     goto end;
  50
  51   int fd = _IO_fileno (fp);
  52   const char *gfilename
  53     = filename != NULL ? filename : __fd_to_filename (fd, &fdfilename);
  54
  55   fp->_flags2 |= _IO_FLAGS2_NOCLOSE;
  56 #if SHLIB_COMPAT (libc, GLIBC_2_0, GLIBC_2_1)
  57   if (&_IO_stdin_used == NULL)
  58     {
  59       /* If the shared C library is used by the application binary which
  60          was linked against the older version of libio, we just use the
  61          older one even for internal use to avoid trouble since a pointer
  62          to the old libio may be passed into shared C library and wind
  63          up here. */
  64       _IO_old_file_close_it (fp);
  65       _IO_JUMPS_FUNC_UPDATE (fp, &_IO_old_file_jumps);
  66       result = _IO_old_file_fopen (fp, gfilename, mode);
  67     }
  68   else
  69 #endif
  70     {
  71       _IO_file_close_it (fp);
  72       _IO_JUMPS_FILE_plus (fp) = &_IO_file_jumps;
  73       if (_IO_vtable_offset (fp) == 0 && fp->_wide_data != NULL)
  74         fp->_wide_data->_wide_vtable = &_IO_wfile_jumps;
  75       result = _IO_file_fopen (fp, gfilename, mode, 1);
  76       if (result != NULL)
  77         result = __fopen_maybe_mmap (result);
  78     }
  79   fp->_flags2 &= ~_IO_FLAGS2_NOCLOSE;
  80   if (result != NULL)
  81     {
  82       /* unbound stream orientation */
  83       result->_mode = 0;
  84
  85       if (fd != -1 && _IO_fileno (result) != fd)
  86         {
  87           /* At this point we have both file descriptors already allocated,
  88              so __dup3 will not fail with EBADF, EINVAL, or EMFILE.  But
  89              we still need to check for EINVAL and, due Linux internal
  90              implementation, EBUSY.  It is because on how it internally opens
  91              the file by splitting the buffer allocation operation and VFS
  92              opening (a dup operation may run when a file is still pending
  93              'install' on VFS).  */
  94           if (__dup3 (_IO_fileno (result), fd,
  95                       (result->_flags2 & _IO_FLAGS2_CLOEXEC) != 0
  96                       ? O_CLOEXEC : 0) == -1)
  97             {
  98               _IO_file_close_it (result);
  99               result = NULL;
 100               goto end;
 101             }
 102           __close (_IO_fileno (result));
 103           _IO_fileno (result) = fd;
 104         }
 105     }
 106   else if (fd != -1)
 107     __close (fd);
 108
 109 end:
 110   _IO_release_lock (fp);
 111   return result;
 112 }