/**
     * @return
     * @throws SmbException
     */
    synchronized SmbFileHandleImpl ensureOpen () throws CIFSException {
        // ensure file is open
        if ( this.handle == null || !this.handle.isValid() ) {
            // one extra acquire to keep this open till the stream is released
            this.handle = this.file.openUnshared(this.openFlags, this.access, this.sharing, SmbConstants.ATTR_NORMAL, this.options).acquire();