Still consider following piece of code, I see there is a change in
this part of code,here showed the same part of code but came from
different kernel version,one is sampled from kernel 2.6.10,while
another is sampled from kernel 2.6.21.
inside hub_events() sampled from drivers/usb/core/hub.c, 2.6.10:
2594 /* deal with port status changes */
2595 for (i = 0; i < hub->descriptor->bNbrPorts; i++) {
2596 connect_change = test_bit(i, hub->change_bits);
2597 if (!test_and_clear_bit(i+1,
hub->event_bits) &&
2598 !connect_change)
2599 continue;
This is the same part of code but just picked up from 2.6.21.
2682 /* deal with port status changes */
2683 for (i = 1; i <= hub->descriptor->bNbrPorts; i++) {
2684 if (test_bit(i, hub->busy_bits))
2685 continue;
2686 connect_change = test_bit(i, hub->change_bits);
2687 if (!test_and_clear_bit(i, hub->event_bits) &&
2688 !connect_change &&
!hub->activating)
2689 continue;
an interesting thing is, in the former one,we call
test_and_clear_bit(i+1, **), while in the latter one, we call
test_and_clear_bit(i, **),this change is somehow strange,is one of
them wrong?
additionally,I am wondering the reason, for the change_bits map, we
just test, for the event_bits,besides test,we also need to clear the
bit, why?
Thanks
Jason
>
> event_bits records which ports have their bits set in the hub's
> interrupt URB. change_bits records the ports for which we want to
> force a disable and re-enumeration.
>
> Sometimes the core needs to act as though a device has disconnected
> even when it really hasn't. That's what change_bits is for.
> event_bits, on the other hand, tells us about real connect and
> disconnect events. So the driver has to check both bit-vectors.
>
> Alan Stern
>
>
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