w.nextOffset += int64(n)
		if n != len(nextOut) {
			return 0, fmt.Errorf("expected write size %d but wrote %d bytes", len(nextOut), n)
		}
		if err != nil {
			return 0, err
		}
		goto again
	}

	return len(b), nil
}

func (f *sftpDriver) Filewrite(r *sftp.Request) (w io.WriterAt, err error) {
	stopFn := globalSftpMetrics.log(r, f.AccessKey())
	defer stopFn(err)