- return fp->_IO_read_end - fp->_IO_read_ptr;
-#elif defined __sferror /* FreeBSD, NetBSD, OpenBSD, MacOS X, Cygwin */
- if ((fp->_flags & __SWR) != 0 || fp->_r < 0)
+ return (fp->_IO_read_end - fp->_IO_read_ptr)
+ + (fp->_flags & _IO_IN_BACKUP ? fp->_IO_save_end - fp->_IO_save_base :
+ 0);
+#elif defined __sferror || defined __DragonFly__ /* FreeBSD, NetBSD, OpenBSD, DragonFly, MacOS X, Cygwin */
+ if ((fp_->_flags & __SWR) != 0 || fp_->_r < 0)
+ return 0;
+ return fp_->_r
+ + (HASUB (fp) ? fp_->_ur : 0);
+#elif defined __EMX__ /* emx+gcc */
+ if ((fp->_flags & _IOWRT) != 0)