libio: Implement vtable verification [BZ #20191]

[thirdparty/glibc.git] / libio / oldfileops.c

/* Copyright (C) 1993-2016 Free Software Foundation, Inc.
   This file is part of the GNU C Library.
   Written by Per Bothner <bothner@cygnus.com>.

   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
   <http://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)

#ifndef _POSIX_SOURCE
# define _POSIX_SOURCE
#endif
#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>
#ifndef errno
extern int errno;
#endif
#ifndef __set_errno
# define __set_errno(Val) errno = (Val)
#endif


#ifdef _LIBC
# define open(Name, Flags, Prot) __open (Name, Flags, Prot)
# define close(FD) __close (FD)
# define lseek(FD, Offset, Whence) __lseek (FD, Offset, Whence)
# define read(FD, Buf, NBytes) __read (FD, Buf, NBytes)
# define write(FD, Buf, NBytes) __write (FD, Buf, NBytes)
#endif

/* 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._IO_file_flags |= CLOSED_FILEBUF_FLAGS;

  _IO_link_in (fp);
  fp->file._vtable_offset = ((int) sizeof (struct _IO_FILE)
			     - (int) sizeof (struct _IO_FILE_complete));
  fp->file._fileno = -1;

#if defined SHARED && defined _LIBC
  if (__builtin_expect (&_IO_stdin_used != NULL, 1)
      || (fp != (struct _IO_FILE_plus *) _IO_stdin
	  && fp != (struct _IO_FILE_plus *) _IO_stdout
	  && fp != (struct _IO_FILE_plus *) _IO_stderr))
    /* The object is dynamically allocated and large enough.  Initialize
       the _mode element as well.  */
    ((struct _IO_FILE_complete *) fp)->_mode = -1;
#endif
}

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 (_IO_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 (fp);

  close_status = ((fp->_flags2 & _IO_FLAGS2_NOCLOSE) == 0
		  ? _IO_SYSCLOSE (fp) : 0);

  /* Free buffer. */
  _IO_setb (fp, NULL, NULL, 0);
  _IO_setg (fp, NULL, NULL, NULL);
  _IO_setp (fp, NULL, NULL);

  _IO_un_link ((struct _IO_FILE_plus *) fp);
  fp->_flags = _IO_MAGIC|CLOSED_FILEBUF_FLAGS;
  fp->_fileno = -1;
  fp->_old_offset = _IO_pos_BAD;

  return close_status ? close_status : write_status;
}

void
attribute_compat_text_section
_IO_old_file_finish (_IO_FILE *fp, int dummy)
{
  if (_IO_file_is_open (fp))
    {
      _IO_old_do_flush (fp);
      if (!(fp->_flags & _IO_DELETE_DONT_CLOSE))
	_IO_SYSCLOSE (fp);
    }
  _IO_default_finish (fp, 0);
}

_IO_FILE *
attribute_compat_text_section
_IO_old_file_fopen (_IO_FILE *fp, const char *filename, const char *mode)
{
  int oflags = 0, omode;
  int read_write, fdesc;
  int oprot = 0666;
  if (_IO_file_is_open (fp))
    return 0;
  switch (*mode++)
    {
    case 'r':
      omode = O_RDONLY;
      read_write = _IO_NO_WRITES;
      break;
    case 'w':
      omode = O_WRONLY;
      oflags = O_CREAT|O_TRUNC;
      read_write = _IO_NO_READS;
      break;
    case 'a':
      omode = O_WRONLY;
      oflags = O_CREAT|O_APPEND;
      read_write = _IO_NO_READS|_IO_IS_APPENDING;
      break;
    default:
      __set_errno (EINVAL);
      return NULL;
    }
  if (mode[0] == '+' || (mode[0] == 'b' && mode[1] == '+'))
    {
      omode = O_RDWR;
      read_write &= _IO_IS_APPENDING;
    }
  fdesc = open (filename, omode|oflags, oprot);
  if (fdesc < 0)
    return NULL;
  fp->_fileno = fdesc;
  _IO_mask_flags (fp, read_write,_IO_NO_READS+_IO_NO_WRITES+_IO_IS_APPENDING);
  if (read_write & _IO_IS_APPENDING)
    if (_IO_SEEKOFF (fp, (_IO_off_t)0, _IO_seek_end, _IOS_INPUT|_IOS_OUTPUT)
	== _IO_pos_BAD && errno != ESPIPE)
      return NULL;
  _IO_link_in ((struct _IO_FILE_plus *) fp);
  return fp;
}

_IO_FILE *
attribute_compat_text_section
_IO_old_file_attach (_IO_FILE *fp, int fd)
{
  if (_IO_file_is_open (fp))
    return NULL;
  fp->_fileno = fd;
  fp->_flags &= ~(_IO_NO_READS+_IO_NO_WRITES);
  fp->_flags |= _IO_DELETE_DONT_CLOSE;
  /* Get the current position of the file. */
  /* We have to do that since that may be junk. */
  fp->_old_offset = _IO_pos_BAD;
  if (_IO_SEEKOFF (fp, (_IO_off_t)0, _IO_seek_cur, _IOS_INPUT|_IOS_OUTPUT)
      == _IO_pos_BAD && errno != ESPIPE)
    return NULL;
  return fp;
}

_IO_FILE *
attribute_compat_text_section
_IO_old_file_setbuf (_IO_FILE *fp, char *p, _IO_ssize_t len)
{
    if (_IO_default_setbuf (fp, p, len) == NULL)
      return NULL;

    fp->_IO_write_base = fp->_IO_write_ptr = fp->_IO_write_end
      = fp->_IO_buf_base;
    _IO_setg (fp, fp->_IO_buf_base, fp->_IO_buf_base, fp->_IO_buf_base);

    return fp;
}

static int old_do_write (_IO_FILE *, const char *, _IO_size_t);

/* Write TO_DO bytes from DATA to FP.
   Then mark FP as having empty buffers. */

int
attribute_compat_text_section
_IO_old_do_write (_IO_FILE *fp, const char *data, _IO_size_t to_do)
{
  return (to_do == 0 || (_IO_size_t) old_do_write (fp, data, to_do) == to_do)
	 ? 0 : EOF;
}

static int
attribute_compat_text_section
old_do_write (_IO_FILE *fp, const char *data, _IO_size_t to_do)
{
  _IO_size_t count;
  if (fp->_flags & _IO_IS_APPENDING)
    /* On a system without a proper O_APPEND implementation,
       you would need to sys_seek(0, SEEK_END) here, but is
       not needed nor desirable for Unix- or Posix-like systems.
       Instead, just indicate that offset (before and after) is
       unpredictable. */
    fp->_old_offset = _IO_pos_BAD;
  else if (fp->_IO_read_end != fp->_IO_write_base)
    {
      _IO_off_t new_pos
	= _IO_SYSSEEK (fp, fp->_IO_write_base - fp->_IO_read_end, 1);
      if (new_pos == _IO_pos_BAD)
	return 0;
      fp->_old_offset = new_pos;
    }
  count = _IO_SYSWRITE (fp, data, to_do);
  if (fp->_cur_column && count)
    fp->_cur_column = _IO_adjust_column (fp->_cur_column - 1, data, count) + 1;
  _IO_setg (fp, fp->_IO_buf_base, fp->_IO_buf_base, fp->_IO_buf_base);
  fp->_IO_write_base = fp->_IO_write_ptr = fp->_IO_buf_base;
  fp->_IO_write_end = ((fp->_flags & (_IO_LINE_BUF | _IO_UNBUFFERED))
		       ? fp->_IO_buf_base : fp->_IO_buf_end);
  return count;
}

int
attribute_compat_text_section
_IO_old_file_underflow (_IO_FILE *fp)
{
  _IO_ssize_t count;
#if 0
  /* SysV does not make this test; take it out for compatibility */
  if (fp->_flags & _IO_EOF_SEEN)
    return (EOF);
#endif

  if (fp->_flags & _IO_NO_READS)
    {
      fp->_flags |= _IO_ERR_SEEN;
      __set_errno (EBADF);
      return EOF;
    }
  if (fp->_IO_read_ptr < fp->_IO_read_end)
    return *(unsigned char *) fp->_IO_read_ptr;

  if (fp->_IO_buf_base == NULL)
    {
      /* Maybe we already have a push back pointer.  */
      if (fp->_IO_save_base != NULL)
	{
	  free (fp->_IO_save_base);
	  fp->_flags &= ~_IO_IN_BACKUP;
	}
      _IO_doallocbuf (fp);
    }

  /* Flush all line buffered files before reading. */
  /* FIXME This can/should be moved to genops ?? */
  if (fp->_flags & (_IO_LINE_BUF|_IO_UNBUFFERED))
    _IO_flush_all_linebuffered ();

  _IO_switch_to_get_mode (fp);

  /* This is very tricky. We have to adjust those
     pointers before we call _IO_SYSREAD () since
     we may longjump () out while waiting for
     input. Those pointers may be screwed up. H.J. */
  fp->_IO_read_base = fp->_IO_read_ptr = fp->_IO_buf_base;
  fp->_IO_read_end = fp->_IO_buf_base;
  fp->_IO_write_base = fp->_IO_write_ptr = fp->_IO_write_end
    = fp->_IO_buf_base;

  count = _IO_SYSREAD (fp, fp->_IO_buf_base,
		       fp->_IO_buf_end - fp->_IO_buf_base);
  if (count <= 0)
    {
      if (count == 0)
	fp->_flags |= _IO_EOF_SEEN;
      else
	fp->_flags |= _IO_ERR_SEEN, count = 0;
  }
  fp->_IO_read_end += count;
  if (count == 0)
    return EOF;
  if (fp->_old_offset != _IO_pos_BAD)
    _IO_pos_adjust (fp->_old_offset, count);
  return *(unsigned char *) fp->_IO_read_ptr;
}

int
attribute_compat_text_section
_IO_old_file_overflow (_IO_FILE *f, int ch)
{
  if (f->_flags & _IO_NO_WRITES) /* SET ERROR */
    {
      f->_flags |= _IO_ERR_SEEN;
      __set_errno (EBADF);
      return EOF;
    }
  /* If currently reading or no buffer allocated. */
  if ((f->_flags & _IO_CURRENTLY_PUTTING) == 0)
    {
      /* Allocate a buffer if needed. */
      if (f->_IO_write_base == 0)
	{
	  _IO_doallocbuf (f);
	  _IO_setg (f, f->_IO_buf_base, f->_IO_buf_base, f->_IO_buf_base);
	}
      /* Otherwise must be currently reading.
	 If _IO_read_ptr (and hence also _IO_read_end) is at the buffer end,
	 logically slide the buffer forwards one block (by setting the
	 read pointers to all point at the beginning of the block).  This
	 makes room for subsequent output.
	 Otherwise, set the read pointers to _IO_read_end (leaving that
	 alone, so it can continue to correspond to the external position). */
      if (f->_IO_read_ptr == f->_IO_buf_end)
	f->_IO_read_end = f->_IO_read_ptr = f->_IO_buf_base;
      f->_IO_write_ptr = f->_IO_read_ptr;
      f->_IO_write_base = f->_IO_write_ptr;
      f->_IO_write_end = f->_IO_buf_end;
      f->_IO_read_base = f->_IO_read_ptr = f->_IO_read_end;

      if (f->_flags & (_IO_LINE_BUF | _IO_UNBUFFERED))
	f->_IO_write_end = f->_IO_write_ptr;
      f->_flags |= _IO_CURRENTLY_PUTTING;
    }
  if (ch == EOF)
    return _IO_old_do_flush (f);
  if (f->_IO_write_ptr == f->_IO_buf_end ) /* Buffer is really full */
    if (_IO_old_do_flush (f) == EOF)
      return EOF;
  *f->_IO_write_ptr++ = ch;
  if ((f->_flags & _IO_UNBUFFERED)
      || ((f->_flags & _IO_LINE_BUF) && ch == '\n'))
    if (_IO_old_do_flush (f) == EOF)
      return EOF;
  return (unsigned char) ch;
}

int
attribute_compat_text_section
_IO_old_file_sync (_IO_FILE *fp)
{
  _IO_ssize_t delta;
  int retval = 0;

  /*    char* ptr = cur_ptr(); */
  if (fp->_IO_write_ptr > fp->_IO_write_base)
    if (_IO_old_do_flush(fp)) return EOF;
  delta = fp->_IO_read_ptr - fp->_IO_read_end;
  if (delta != 0)
    {
#ifdef TODO
      if (_IO_in_backup (fp))
	delta -= eGptr () - Gbase ();
#endif
      _IO_off_t new_pos = _IO_SYSSEEK (fp, delta, 1);
      if (new_pos != (_IO_off_t) EOF)
	fp->_IO_read_end = fp->_IO_read_ptr;
#ifdef ESPIPE
      else if (errno == ESPIPE)
	; /* Ignore error from unseekable devices. */
#endif
      else
	retval = EOF;
    }
  if (retval != EOF)
    fp->_old_offset = _IO_pos_BAD;
  /* FIXME: Cleanup - can this be shared? */
  /*    setg(base(), ptr, ptr); */
  return retval;
}

_IO_off64_t
attribute_compat_text_section
_IO_old_file_seekoff (_IO_FILE *fp, _IO_off64_t offset, int dir, int mode)
{
  _IO_off_t result;
  _IO_off64_t delta, new_offset;
  long count;
  /* POSIX.1 8.2.3.7 says that after a call the fflush() the file
     offset of the underlying file must be exact.  */
  int must_be_exact = (fp->_IO_read_base == fp->_IO_read_end
		       && fp->_IO_write_base == fp->_IO_write_ptr);

  if (mode == 0)
    dir = _IO_seek_cur, offset = 0; /* Don't move any pointers. */

  /* Flush unwritten characters.
     (This may do an unneeded write if we seek within the buffer.
     But to be able to switch to reading, we would need to set
     egptr to pptr.  That can't be done in the current design,
     which assumes file_ptr() is eGptr.  Anyway, since we probably
     end up flushing when we close(), it doesn't make much difference.)
     FIXME: simulate mem-mapped files. */

  if (fp->_IO_write_ptr > fp->_IO_write_base || _IO_in_put_mode (fp))
    if (_IO_switch_to_get_mode (fp))
      return EOF;

  if (fp->_IO_buf_base == NULL)
    {
      /* It could be that we already have a pushback buffer.  */
      if (fp->_IO_read_base != NULL)
	{
	  free (fp->_IO_read_base);
	  fp->_flags &= ~_IO_IN_BACKUP;
	}
      _IO_doallocbuf (fp);
      _IO_setp (fp, fp->_IO_buf_base, fp->_IO_buf_base);
      _IO_setg (fp, fp->_IO_buf_base, fp->_IO_buf_base, fp->_IO_buf_base);
    }

  switch (dir)
    {
    case _IO_seek_cur:
      /* Adjust for read-ahead (bytes is buffer). */
      offset -= fp->_IO_read_end - fp->_IO_read_ptr;
      if (fp->_old_offset == _IO_pos_BAD)
	goto dumb;
      /* Make offset absolute, assuming current pointer is file_ptr(). */
      offset += fp->_old_offset;

      dir = _IO_seek_set;
      break;
    case _IO_seek_set:
      break;
    case _IO_seek_end:
      {
	struct stat64 st;
	if (_IO_SYSSTAT (fp, &st) == 0 && S_ISREG (st.st_mode))
	  {
	    offset += st.st_size;
	    dir = _IO_seek_set;
	  }
	else
	  goto dumb;
      }
    }
  /* At this point, dir==_IO_seek_set. */

  /* If we are only interested in the current position we've found it now.  */
  if (mode == 0)
    return offset;

  /* If destination is within current buffer, optimize: */
  if (fp->_old_offset != _IO_pos_BAD && fp->_IO_read_base != NULL
      && !_IO_in_backup (fp))
    {
      /* Offset relative to start of main get area. */
      _IO_off_t rel_offset = (offset - fp->_old_offset
			      + (fp->_IO_read_end - fp->_IO_read_base));
      if (rel_offset >= 0)
	{
#if 0
	  if (_IO_in_backup (fp))
	    _IO_switch_to_main_get_area (fp);
#endif
	  if (rel_offset <= fp->_IO_read_end - fp->_IO_read_base)
	    {
	      _IO_setg (fp, fp->_IO_buf_base, fp->_IO_buf_base + rel_offset,
			fp->_IO_read_end);
	      _IO_setp (fp, fp->_IO_buf_base, fp->_IO_buf_base);
	      {
		_IO_mask_flags (fp, 0, _IO_EOF_SEEN);
		goto resync;
	      }
	    }
#ifdef TODO
	    /* If we have streammarkers, seek forward by reading ahead. */
	    if (_IO_have_markers (fp))
	      {
		int to_skip = rel_offset
		  - (fp->_IO_read_ptr - fp->_IO_read_base);
		if (ignore (to_skip) != to_skip)
		  goto dumb;
		_IO_mask_flags (fp, 0, _IO_EOF_SEEN);
		goto resync;
	      }
#endif
	}
#ifdef TODO
      if (rel_offset < 0 && rel_offset >= Bbase () - Bptr ())
	{
	  if (!_IO_in_backup (fp))
	    _IO_switch_to_backup_area (fp);
	  gbump (fp->_IO_read_end + rel_offset - fp->_IO_read_ptr);
	  _IO_mask_flags (fp, 0, _IO_EOF_SEEN);
	  goto resync;
	}
#endif
    }

#ifdef TODO
  _IO_unsave_markers (fp);
#endif

  if (fp->_flags & _IO_NO_READS)
    goto dumb;

  /* Try to seek to a block boundary, to improve kernel page management. */
  new_offset = offset & ~(fp->_IO_buf_end - fp->_IO_buf_base - 1);
  delta = offset - new_offset;
  if (delta > fp->_IO_buf_end - fp->_IO_buf_base)
    {
      new_offset = offset;
      delta = 0;
    }
  result = _IO_SYSSEEK (fp, new_offset, 0);
  if (result < 0)
    return EOF;
  if (delta == 0)
    count = 0;
  else
    {
      count = _IO_SYSREAD (fp, fp->_IO_buf_base,
			   (must_be_exact
			    ? delta : fp->_IO_buf_end - fp->_IO_buf_base));
      if (count < delta)
	{
	  /* We weren't allowed to read, but try to seek the remainder. */
	  offset = count == EOF ? delta : delta-count;
	  dir = _IO_seek_cur;
	  goto dumb;
	}
    }
  _IO_setg (fp, fp->_IO_buf_base, fp->_IO_buf_base + delta,
	    fp->_IO_buf_base + count);
  _IO_setp (fp, fp->_IO_buf_base, fp->_IO_buf_base);
  fp->_old_offset = result + count;
  _IO_mask_flags (fp, 0, _IO_EOF_SEEN);
  return offset;
 dumb:

  _IO_unsave_markers (fp);
  result = _IO_SYSSEEK (fp, offset, dir);
  if (result != EOF)
    {
      _IO_mask_flags (fp, 0, _IO_EOF_SEEN);
      fp->_old_offset = result;
      _IO_setg (fp, fp->_IO_buf_base, fp->_IO_buf_base, fp->_IO_buf_base);
      _IO_setp (fp, fp->_IO_buf_base, fp->_IO_buf_base);
    }
  return result;

resync:
  /* We need to do it since it is possible that the file offset in
     the kernel may be changed behind our back. It may happen when
     we fopen a file and then do a fork. One process may access the
     file and the kernel file offset will be changed. */
  if (fp->_old_offset >= 0)
    _IO_SYSSEEK (fp, fp->_old_offset, 0);

  return offset;
}

_IO_ssize_t
attribute_compat_text_section
_IO_old_file_write (_IO_FILE *f, const void *data, _IO_ssize_t n)
{
  _IO_ssize_t to_do = n;
  while (to_do > 0)
    {
      _IO_ssize_t count = write (f->_fileno, data, to_do);
      if (count == EOF)
	{
	  f->_flags |= _IO_ERR_SEEN;
	  break;
	}
      to_do -= count;
      data = (void *) ((char *) data + count);
    }
  n -= to_do;
  if (f->_old_offset >= 0)
    f->_old_offset += n;
  return n;
}

_IO_size_t
attribute_compat_text_section
_IO_old_file_xsputn (_IO_FILE *f, const void *data, _IO_size_t n)
{
  const char *s = (char *) data;
  _IO_size_t to_do = n;
  int must_flush = 0;
  _IO_size_t count = 0;

  if (n <= 0)
    return 0;
  /* This is an optimized implementation.
     If the amount to be written straddles a block boundary
     (or the filebuf is unbuffered), use sys_write directly. */

  /* First figure out how much space is available in the buffer. */
  if ((f->_flags & _IO_LINE_BUF) && (f->_flags & _IO_CURRENTLY_PUTTING))
    {
      count = f->_IO_buf_end - f->_IO_write_ptr;
      if (count >= n)
	{
	  const char *p;
	  for (p = s + n; p > s; )
	    {
	      if (*--p == '\n')
		{
		  count = p - s + 1;
		  must_flush = 1;
		  break;
		}
	    }
	}
    }
  else if (f->_IO_write_end > f->_IO_write_ptr)
    count = f->_IO_write_end - f->_IO_write_ptr; /* Space available. */

  /* Then fill the buffer. */
  if (count > 0)
    {
      if (count > to_do)
	count = to_do;
      if (count > 20)
	{
#ifdef _LIBC
	  f->_IO_write_ptr = __mempcpy (f->_IO_write_ptr, s, count);
#else
	  memcpy (f->_IO_write_ptr, s, count);
	  f->_IO_write_ptr += count;
#endif
	  s += count;
	}
      else
	{
	  char *p = f->_IO_write_ptr;
	  int i = (int) count;
	  while (--i >= 0)
	    *p++ = *s++;
	  f->_IO_write_ptr = p;
	}
      to_do -= count;
    }
  if (to_do + must_flush > 0)
    {
      _IO_size_t block_size, do_write;
      /* Next flush the (full) buffer. */
      if (__overflow (f, EOF) == EOF)
	return to_do == 0 ? EOF : n - to_do;

      /* Try to maintain alignment: write a whole number of blocks.
	 dont_write is what gets left over. */
      block_size = f->_IO_buf_end - f->_IO_buf_base;
      do_write = to_do - (block_size >= 128 ? to_do % block_size : 0);

      if (do_write)
	{
	  count = old_do_write (f, s, do_write);
	  to_do -= count;
	  if (count < do_write)
	    return n - to_do;
	}

      /* Now write out the remainder.  Normally, this will fit in the
	 buffer, but it's somewhat messier for line-buffered files,
	 so we let _IO_default_xsputn handle the general case. */
      if (to_do)
	to_do -= _IO_default_xsputn (f, s+do_write, to_do);
    }
  return n - to_do;
}


const struct _IO_jump_t _IO_old_file_jumps libio_vtable =
{
  JUMP_INIT_DUMMY,
  JUMP_INIT(finish, _IO_old_file_finish),
  JUMP_INIT(overflow, _IO_old_file_overflow),
  JUMP_INIT(underflow, _IO_old_file_underflow),
  JUMP_INIT(uflow, _IO_default_uflow),
  JUMP_INIT(pbackfail, _IO_default_pbackfail),
  JUMP_INIT(xsputn, _IO_old_file_xsputn),
  JUMP_INIT(xsgetn, _IO_default_xsgetn),
  JUMP_INIT(seekoff, _IO_old_file_seekoff),
  JUMP_INIT(seekpos, _IO_default_seekpos),
  JUMP_INIT(setbuf, _IO_old_file_setbuf),
  JUMP_INIT(sync, _IO_old_file_sync),
  JUMP_INIT(doallocate, _IO_file_doallocate),
  JUMP_INIT(read, _IO_file_read),
  JUMP_INIT(write, _IO_old_file_write),
  JUMP_INIT(seek, _IO_file_seek),
  JUMP_INIT(close, _IO_file_close),
  JUMP_INIT(stat, _IO_file_stat)
};

compat_symbol (libc, _IO_old_do_write, _IO_do_write, GLIBC_2_0);
compat_symbol (libc, _IO_old_file_attach, _IO_file_attach, GLIBC_2_0);
compat_symbol (libc, _IO_old_file_close_it, _IO_file_close_it, GLIBC_2_0);
compat_symbol (libc, _IO_old_file_finish, _IO_file_finish, GLIBC_2_0);
compat_symbol (libc, _IO_old_file_fopen, _IO_file_fopen, GLIBC_2_0);
compat_symbol (libc, _IO_old_file_init, _IO_file_init, GLIBC_2_0);
compat_symbol (libc, _IO_old_file_setbuf, _IO_file_setbuf, GLIBC_2_0);
compat_symbol (libc, _IO_old_file_sync, _IO_file_sync, GLIBC_2_0);
compat_symbol (libc, _IO_old_file_overflow, _IO_file_overflow, GLIBC_2_0);
compat_symbol (libc, _IO_old_file_seekoff, _IO_file_seekoff, GLIBC_2_0);
compat_symbol (libc, _IO_old_file_underflow, _IO_file_underflow, GLIBC_2_0);
compat_symbol (libc, _IO_old_file_write, _IO_file_write, GLIBC_2_0);
compat_symbol (libc, _IO_old_file_xsputn, _IO_file_xsputn, GLIBC_2_0);

#endif