[libusb] windows support for LIBUSB_REQUEST_TYPE_VENDOR

[Peter H. <ph...@gm...>]

Hi,

I see that LIBUSB_REQUEST_TYPE_VENDOR is not supported on windows (but 
it is well supported on linux). This is well visible on line 4115 of 
windows_usb.c (function hid_submit_control_transfer).

I'm playing with a keyboard firmware and the keyboard is supposed to be 
configurable using an application running on a PC. The application 
should be portable to both linux and windows.

It may look like vendor specific extensions over a control endpoint 
would be a good choice. Well, at least I do not need one more endpoint 
on the device (since the control endpoint is already there). And this 
works fine on linux. But the support is missing on windows.

Now my two questions:

1) Why is the support on windows missing? Is it because the windows API 
does not allow to use vendor extensions on the control endpoint? Or is 
it only because nobody needed this yet and therefore it was not implemented?

2) As a workaround, I'm considering to add one more endpoint to the 
keyboard: a Virtual COM Port. Would both linux and windows ports of 
libusb support sending and receiving data over the COM Port endpoint?

Thanks,
   Peter.