where is _IO_cookie_file used?

[Greg McGary]

... if anywhere.

libio.h defines the type:

struct _IO_cookie_file
{
  struct _IO_FILE __file;
  const void *__vtable;
  void *__cookie;
  _IO_cookie_io_functions_t __io_functions;
};

As much as possible, I'd like to get rid of these ad-hoc vtable decls
and have everyone use _IO_FILE_plus, but _IO_FILE_plus is defined
in libioP.h, so in order to do this I must either move _IO_FILE_plus
to libio.h (I prefer *not* to do that), or move _IO_cookie_file to
libioP.h (I prefer this, but fear there might be user code that
needs this struct)

Please advise.