[ewg] Link available/unavailable notification

[Hefty, Sean]

> I initially thought that with the use of ib_register_event_handler() I can
> achieve this. But after reading a little bit more (IB spec chapter 11 and
> chapter 7) it looks like only one such handler can be registered with the
> device. So if my module has to co-exist with any other kernel module using the
> IB device for such events, this approach may not work. Any comments on this? I
> am simply interested in getting to know the change in port status as soon as it
> is done (event based approach preferred than polling for it).

ib_register_event_handler supports multiple users.  The device 'invokes' a handler, which is responsible for reporting the event to all registered clients.