device filtering support

[Xiaofan Chen]

On Wed, Feb 1, 2012 at 4:46 PM, Xiaofan Chen <xiaofanc at gmail.com> wrote:
> Take note we are talking about filtering during enumeration
> (getting the device list), not after the enumeration. You can
> filter many things after getting the device list.
>
> Currently libusb-1.0 implementations enumerate all USB
> device on all platforms which is quite an expensive operation,
> especially under Windows. So this makes filtering during
> enumeration process a desirable feature.
>
> libusb-win32/libusbK use different mechanisms which makes
> the enumeration faster since we mainly deal with specific
> devices and only enumerate the device with supported drivers.
>

Looking at Vitali's patch, I am not so sure if this will make
the enumeration issues under Windows much better or not.

There is a fundamental problem here as Tim Roberts mentioned
here.
http://libusb.6.n5.nabble.com/libusb-windows-devices-only-detected-in-late-pass-ignoring-tp4463538p4521855.html

+++++++++++++++++++++++++++++++++++++++++++++
However, the bigger problem is that we are trying to shove a square peg
into a round hole.  Libusb undeniably has a Linux heritage, and its
philosophy is strongly oriented towards the Linux way of doing things,
which are very different from the world of Windows devices.  The concept
of "show me every device in the system so I can find mine," which is
found in the driver stack for virtually every Linux bus type, is foreign
to Windows.  It does not scale well.  It requires each
driver/application to have knowledge of the internal workings of its bus
-- information that it should not need to have.  Windows abstracts all
that, so that a driver merely says "this is my device", and it's up to
PnP and the Device Manager to do the searching and the matching, and the
hotplug management.  We are battling that abstraction.

I'm not saying I have an answer.  There is an impedance mismatch here
that is, in large part, unresolvable.  As long as libusb tries to
pretend that it is offers the Linux philosophy on Windows, there will be
ugliness underneath, and it's not going to get better.
+++++++++++++++++++++++++++++++++++++++++

I am hoping that the filter mechanism will help to minimize the
impact on the bus for the current libusb-1.0 Windows device
list enumeration implementation. But it might be not that easy.

The whole thread is quite long and there are quite some
questions unanswered in that thread. Maybe it is a good
time to discuss this issue again but I understand to bring
up the issue may well open a new can of worm...
http://libusb.6.n5.nabble.com/libusb-windows-devices-only-detected-in-late-pass-ignoring-td4463538.html


-- 
Xiaofan