device filtering support

[Xiaofan Chen]

On Sat, Feb 4, 2012 at 2:47 AM, Vitali Lovich <vlovich at gmail.com> wrote:
> I'm going to have to side with Travis - spawning a secondary
> process seems unnecessary & wasteful.

This is especially disturbing if it becomes compulsory for all
libusb applications.

> Maybe if libusb applications were likely to run simultaneously
> with a lot of other libusb applications it might make sense
> (& even then not so much).

The thing is those small amount of use cases should not
penalize the majority of the use cases.

> Is there really something wrong with caching the descriptors
> within the Windows backend, unless the driver already does it
> on our behalf (i.e. libusb0/libusbk)?  We can also throw away
> most of the cached information as soon as the device reference is
> released so there should be any significant long-term memory bloat.

Take note libusbK.dll supports libusb0.sys, libusbK.sys and
WinUSB.sys. Therefore using libusbK.dll covers most of the
driver used and only the HID is an exception.

However, Pete indicated that he would like to keep the
standalone WinUSB backend, so that will keep a lot of
duplicate codes inside the Windows backend.

Anyway, since Pete thinks that it will not cause performance
penalty and he seems to want to try out his ideas, let's
wait for his implementation. We may also prepare some
benchmarks to see how that is the case or not the case.

-- 
Xiaofan