if err := fd.writeLock(); err != nil {
		return 0, 0, err
	}
	defer fd.writeUnlock()
	if err := fd.pd.prepareWrite(fd.isFile); err != nil {
		return 0, 0, err
	}
	for {
		n, err := unix.SendmsgNInet6(fd.Sysfd, p, oob, sa, 0)
		if err == syscall.EINTR {
			continue
		}
		if err == syscall.EAGAIN && fd.pd.pollable() {
			if err = fd.pd.waitWrite(fd.isFile); err == nil {
				continue
			}
		}