On 08/27/2012 12:47 AM, Jan Kiszka wrote: > On 2012-08-27 09:01, Paolo Bonzini wrote: > > Il 25/08/2012 09:42, liu ping fan ha scritto: > >>>> > >>>> I don't see why MMIO dispatch should hold the IDEBus ref rather than the > >>>> PCIIDEState. > >>>> > >> When transfer memory_region_init_io() 3rd para from void* opaque to > >> Object* obj, the obj : opaque is not neccessary 1:1 map. For such > >> situation, in order to let MemoryRegionOps tell between them, we > >> should pass PCIIDEState->bus[0], bus[1] separately. > > > > The rule should be that the obj is the object that you want referenced, > > and that should be the PCIIDEState. > > > > But this is anyway moot because it only applies to objects that are > > converted to use unlocked dispatch. This likely will not be the case > > for IDE. > > BTW, I'm pretty sure - after implementing the basics for BQL-free PIO > dispatching - that device objects are the wrong target for reference > counting. We keep memory regions in our dispatching tables (PIO > dispatching needs some refactoring for this), and those regions need > protection for BQL-free use. Devices can't pass away as long as the have > referenced regions, memory region deregistration services will have to > take care of this. > > I'm currently not using reference counting at all, I'm enforcing that > only BQL-protected regions can be deregistered.
That's a pretty harsh constraint. > Also note that there seems to be another misconception in the > discussions: deregistration is not only bound to device unplug. It also > happens on device reconfiguration, e.g. PCI BAR (re-)mapping. Another > strong indicator that we should worry about individual memory regions, > not devices. > > Deregistration is fine, the problem is destruction. -- I have a truly marvellous patch that fixes the bug which this signature is too narrow to contain.