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

[liu ping fan]

On Mon, Aug 27, 2012 at 3:47 PM, Jan Kiszka <address@hidden> 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

Hi Jan, thanks for reminder, but could you explain it more detail?
mmio dispatch table holds 1 ref for device, before releasing this
ref,( When unplugging, we detach all the device's mr from memory, then
drop the ref. So I think that no leak will be exposed by mr  and it is
safe to use device as 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
Yes, it is right. Device can pass away only after mr removed from
dispatching tables

Thanx pingfan
> 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
>
>