Function GetDiskFreeSpaceExW 

pub unsafe extern "system" fn GetDiskFreeSpaceExW(
    lpdirectoryname: PCWSTR,
    lpfreebytesavailabletocaller: *mut u64,
    lptotalnumberofbytes: *mut u64,
    lptotalnumberoffreebytes: *mut u64,
) -> BOOL