path: root/libio/oldfileops.c

/* Copyright (C) 1993-2025 Free Software Foundation, Inc.
   Copyright The GNU Toolchain Authors.
   This file is part of the GNU C Library.

   The GNU C Library is free software; you can redistribute it and/or
   modify it under the terms of the GNU Lesser General Public
   License as published by the Free Software Foundation; either
   version 2.1 of the License, or (at your option) any later version.

   The GNU C Library is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
   Lesser General Public License for more details.

   You should have received a copy of the GNU Lesser General Public
   License along with the GNU C Library; if not, see
   <https://www.gnu.org/licenses/>.

   As a special exception, if you link the code in this file with
   files compiled with a GNU compiler to produce an executable,
   that does not cause the resulting executable to be covered by
   the GNU Lesser General Public License.  This exception does not
   however invalidate any other reasons why the executable file
   might be covered by the GNU Lesser General Public License.
   This exception applies to code released by its copyright holders
   in files containing the exception.  */

/* This is a compatibility file.  If we don't build the libc with
   versioning don't compile this file.  */
#include <shlib-compat.h>
#if SHLIB_COMPAT (libc, GLIBC_2_0, GLIBC_2_1)

#define _IO_USE_OLD_IO_FILE
#include "libioP.h"
#include <fcntl.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <string.h>
#include <errno.h>
#include <stdlib.h>
#include <unistd.h>

/* An fstream can be in at most one of put mode, get mode, or putback mode.
   Putback mode is a variant of get mode.

   In a filebuf, there is only one current position, instead of two
   separate get and put pointers.  In get mode, the current position
   is that of gptr(); in put mode that of pptr().

   The position in the buffer that corresponds to the position
   in external file system is normally _IO_read_end, except in putback
   mode, when it is _IO_save_end.
   If the field _fb._offset is >= 0, it gives the offset in
   the file as a whole corresponding to eGptr(). (?)

   PUT MODE:
   If a filebuf is in put mode, then all of _IO_read_ptr, _IO_read_end,
   and _IO_read_base are equal to each other.  These are usually equal
   to _IO_buf_base, though not necessarily if we have switched from
   get mode to put mode.  (The reason is to maintain the invariant
   that _IO_read_end corresponds to the external file position.)
   _IO_write_base is non-NULL and usually equal to _IO_buf_base.
   We also have _IO_write_end == _IO_buf_end, but only in fully buffered mode.
   The un-flushed character are those between _IO_write_base and _IO_write_ptr.

   GET MODE:
   If a filebuf is in get or putback mode, eback() != egptr().
   In get mode, the unread characters are between gptr() and egptr().
   The OS file position corresponds to that of egptr().

   PUTBACK MODE:
   Putback mode is used to remember "excess" characters that have
   been sputbackc'd in a separate putback buffer.
   In putback mode, the get buffer points to the special putback buffer.
   The unread characters are the characters between gptr() and egptr()
   in the putback buffer, as well as the area between save_gptr()
   and save_egptr(), which point into the original reserve buffer.
   (The pointers save_gptr() and save_egptr() are the values
   of gptr() and egptr() at the time putback mode was entered.)
   The OS position corresponds to that of save_egptr().

   LINE BUFFERED OUTPUT:
   During line buffered output, _IO_write_base==base() && epptr()==base().
   However, ptr() may be anywhere between base() and ebuf().
   This forces a call to filebuf::overflow(int C) on every put.
   If there is more space in the buffer, and C is not a '\n',
   then C is inserted, and pptr() incremented.

   UNBUFFERED STREAMS:
   If a filebuf is unbuffered(), the _shortbuf[1] is used as the buffer.
*/

#define CLOSED_FILEBUF_FLAGS \
  (_IO_IS_FILEBUF+_IO_NO_READS+_IO_NO_WRITES+_IO_TIED_PUT_GET)


void
attribute_compat_text_section
_IO_old_file_init_internal (struct _IO_FILE_plus *fp)
{
  /* POSIX.1 allows another file handle to be used to change the position
     of our file descriptor.  Hence we actually don't know the actual
     position before we do the first fseek (and until a following fflush). */
  fp->file._old_offset = _IO_pos_BAD;
  fp->file._flags |= CLOSED_FILEBUF_FLAGS;

  /* NB: _vtable_offset must be set before calling _IO_link_in since
     _IO_vtable_offset is used to detect the old binaries.  */
  fp->file._vtable_offset = ((int) sizeof (struct _IO_FILE)
			     - (int) sizeof (struct _IO_FILE_complete));
  _IO_link_in (fp);
  fp->file._fileno = -1;

  if (&_IO_stdin_used != NULL || !_IO_legacy_file ((FILE *) fp))
    /* The object is dynamically allocated and large enough.  Initialize
       the _mode element as well.  */
    ((struct _IO_FILE_complete *) fp)->_mode = -1;
}

void
attribute_compat_text_section
_IO_old_file_init (struct _IO_FILE_plus *fp)
{
  IO_set_accept_foreign_vtables (&_IO_vtable_check);
  _IO_old_file_init_internal (fp);
}

int
attribute_compat_text_section
_IO_old_file_close_it (FILE *fp)
{
  int write_status, close_status;
  if (!_IO_file_is_open (fp))
    return EOF;

  write_status = _IO_old_do_flush (fp);

  _IO_unsave_markers (f