Re: [Qemu-devel] [PATCH 10/10] qdev: fix create in place obj's life cycle problem

[Jan Kiszka]

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.

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.

Jan

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