On Sun, Jun 24, 2012 at 03:59:27PM -0600, Alex Williamson wrote: > On Sun, 2012-06-24 at 18:49 +0300, Michael S. Tsirkin wrote: > > On Sun, Jun 24, 2012 at 09:18:38AM -0600, Alex Williamson wrote: > > > > > @@ -242,7 +299,8 @@ kvm_irqfd_assign(struct kvm *kvm, struct kvm_irqfd *args) > > > > > > > > > > ret = 0; > > > > > list_for_each_entry(tmp, &kvm->irqfds.items, list) { > > > > > - if (irqfd->eventfd != tmp->eventfd) > > > > > + if (irqfd->eventfd != tmp->eventfd && > > > > > + irqfd->eventfd != tmp->eoi_eventfd) > > > > > continue; > > > > > > > > So we allow duplicate irqfd with differing eoifd (or edge-triggered and > > > > level-triggered irqfd on the same context). > > > > > > > > (why the check in the first place? just so we can have a reliable > > > > deassign or is it avoiding a deeper problem?) > > > > > > I really wasn't sure to what extent we wanted to prevent duplicates. My > > > guess was that we don't want to have an irqfd trigger more than one > > > thing. That seems to be what the current code does. I don't see any > > > problems with multiple irqfds triggering the same eventfd though. I > > > only added a test that a new irqfd can't be triggered by an existing > > > eoi_eventfd as that could make a nasty loop. > > > > How would that make a loop? You can have the same thing > > with e.g. ioeventfd - why isn't it a problem there? > > eoi_eventfd1 -> irqfd2 [eoi] eoi_eventfd2 -> irqfd1 [eoi] eoi_eventfd1 ->... Sorry I don't understand. What does this [eoi] mean? How is eoi eventfd different from ioeventfd? > > Yes, in reality we'd need to search fds from all the interfaces and come > up with some grossly complicated truth table of what's allowed and > what's not. The original code didn't go to that kind of extreme, so I > just added something that seemed like a reasonable case > we'd want to prevent. Thanks, > > Alex -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html