The VJOYD_OpenConfigKey_Service macro is used by joystick drivers to open a configuration key. This should mirror the IDirectInputJoyConfig8::OpenConfigKey method.
eax = ID of key to open
ecx = address of a DWORD in which to store the key
eax = same as _RegOpenKey except that ERROR_CANTOPEN is returned if VJoyD has not yet established the current configuration key.