device filtering support

[Segher Boessenkool]

> GUID -> VID:PID is easy, since the Windows API works with GUID.
> VID:PID -> GUID is a bit more complex [ ... ]

I have no idea about the actual interfaces you have to use,
but...

libusbx has to figure out what devices are there (it simply is
part of our API, and it makes sense).  You can get a list of
the USB devices on your system pretty cheaply I would think
(in whatever format)?  Certainly without causing traffic on the
USB?

And you can ask what is the VID/PID of any device you found,
again without causing traffic, and cheaply?

That is all you need for filtering on VID/PID.


Segher