Go で Windows のジャンクションを作ろうとしているけれども、なんかうまくいかないソース

junction_run.go

package main

import (
	"os"
	"unsafe"
	"errors"

	"golang.org/x/sys/windows"
	"golang.org/x/xerrors"
)

const (
	_MAXIMUM_REPARSE_DATA_BUFFER_SIZE = 16384
	_FSCTL_SET_REPARSE_POINT          = 589988
	_INVALID_HANDLE_VALUE = ^windows.Handle(0)
)

type _MountPointInfo struct {
	Tag                   uint32
	DataLength            uint16
	Reserved              uint16
	TargetOffset          uint16
	TargetByteLength      uint16
	DescriptionOffset     uint16
	DescriptionByteLength uint16
	Buffer                [(_MAXIMUM_REPARSE_DATA_BUFFER_SIZE - 4 - 2*6) / 2]uint16
}

func MountPointCreate(mountPointPath, target string) error {
	_mountPointPath, err := windows.UTF16FromString(mountPointPath)
	if err != nil {
		return xerrors.Errorf("UTF16FromString(%s): %v", mountPointPath, err)
	}
	_target, err := windows.UTF16FromString(target)
	if err != nil {
		return xerrors.Errorf("UTF16FromString(%s): %v", target, err)
	}
	var info _MountPointInfo

	info.Tag = windows.IO_REPARSE_TAG_MOUNT_POINT

	info.TargetOffset = 0
	info.TargetByteLength = uint16(len(_target) * 2 )
	for i := 0 ; i < len(_target) ; i++ {
		info.Buffer[i] = _target[i]
	}
	// copy(info.Buffer[:], _target)
	info.Buffer[len(_target)] = 0

	info.DescriptionOffset = uint16((len(_target)+1)  * 2)
	info.DescriptionByteLength = 0

	info.DataLength = uint16(8 + (len(_target)+1+1)*2)

	err = windows.CreateDirectory(&_mountPointPath[0], nil)
	if err != nil {
		return xerrors.Errorf("windows.CreateDirectory(%s): %v", mountPointPath, err)
	}

	handle, err := windows.CreateFile(&_mountPointPath[0],
		windows.GENERIC_WRITE,
		0,
		nil,
		windows.OPEN_EXISTING,
		windows.FILE_FLAG_BACKUP_SEMANTICS,
		0)
	if err != nil {
		return xerrors.Errorf("windows.CreateFile(%s): %v", mountPointPath, err)
	}
	if handle == _INVALID_HANDLE_VALUE {
		return errors.New("windows.CreateFile: invalid handle value")
	}
	defer windows.CloseHandle(handle)

	var size uint32

	err = windows.DeviceIoControl(
		handle,
		_FSCTL_SET_REPARSE_POINT,
		(*byte)(unsafe.Pointer(&info)),
		uint32(8+info.DataLength),
		nil,
		0,
		&size,
		nil)

	if err != nil {
		return xerrors.Errorf("windows.DeviceIoControl: %v", err)
	}
	return nil
}

func main() {
	if len(os.Args) < 3 {
		println("go run junction.go DST SRC")
		return
	}
	if err := MountPointCreate(os.Args[1], os.Args[2]); err != nil {
		println(err.Error())
		os.Exit(1)
	}
}