n, sa, err = fd.pfd.ReadFrom(p)
	runtime.KeepAlive(fd)
	return n, sa, wrapSyscallError(readFromSyscallName, err)
}
func (fd *netFD) readFromInet4(p []byte, from *syscall.SockaddrInet4) (n int, err error) {
	n, err = fd.pfd.ReadFromInet4(p, from)
	runtime.KeepAlive(fd)
	return n, wrapSyscallError(readFromSyscallName, err)
}

}

func (c *UDPConn) readFrom(b []byte, addr *UDPAddr) (int, *UDPAddr, error) {
	var n int
	var err error
	switch c.fd.family {
	case syscall.AF_INET:
		var from syscall.SockaddrInet4
		n, err = c.fd.readFromInet4(b, &from)
		if err == nil {
			ip := from.Addr // copy from.Addr; ip escapes, so this line allocates 4 bytes
			*addr = UDPAddr{IP: ip[:], Port: from.Port}
		}
	case syscall.AF_INET6:
		var from syscall.SockaddrInet6

	return n, sa, err
}

func (ffd *fakeNetFD) readFromInet4(p []byte, sa *syscall.SockaddrInet4) (n int, err error) {
	n, _, err = ffd.queue.recvfrom(ffd.readDeadline.Load(), p, true, func(from sockaddr) error {
		fromSA, err := from.sockaddr(syscall.AF_INET)
		if err != nil {
			return err
		}
		if fromSA == nil {
			return os.NewSyscallError("readFromInet4", syscall.EINVAL)
		}

				if err = fd.pd.waitRead(fd.isFile); err == nil {
					continue
				}
			}
		}
		err = fd.eofError(n, err)
		return n, sa, err
	}
}

// ReadFromInet4 wraps the recvfrom network call for IPv4.
func (fd *FD) ReadFromInet4(p []byte, from *syscall.SockaddrInet4) (int, error) {
	if err := fd.readLock(); err != nil {
		return 0, err
	}
	defer fd.readUnlock()

	})
	err = fd.eofError(n, err)
	if err != nil {
		return n, nil, err
	}
	sa, _ := o.rsa.Sockaddr()
	return n, sa, nil
}

// ReadFromInet4 wraps the recvfrom network call for IPv4.
func (fd *FD) ReadFromInet4(buf []byte, sa4 *syscall.SockaddrInet4) (int, error) {
	if len(buf) == 0 {
		return 0, nil
	}
	if len(buf) > maxRW {
		buf = buf[:maxRW]
	}