device filtering support

[Travis]

On 2/7/2012 4:42 PM, Segher Boessenkool wrote:
>> 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...
>

At this point I don't know if we are talking about class GUIDs or device 
interface GUIDs but getting the class guid given a VID:PID is certainly 
possible.  Getting the list of device interface guids given a VID:PID is 
also possible.

> 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?

Yes, but not in the form of descriptors.  However, you could nearly 
re-create the device descriptor with the information in the registry.

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

Yes.  ..as a bonus, windows also caches the serial number. ;)

Regards,
Travis

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