Re: [Qemu-devel] [PATCH 1/8] virtio-blk-x: fix configuration synchronization.

["KONRAD Frédéric" <fred.konrad@greensocs.com>]

On 05/04/2013 21:24, Anthony Liguori wrote:
> Peter Maydell <peter.maydell@linaro.org> writes:
>
>> On 5 April 2013 17:47, Anthony Liguori <anthony@codemonkey.ws> wrote:
>>> Kevin Wolf <kwolf@redhat.com> writes:
>>>
>>>> From: KONRAD Frederic <fred.konrad@greensocs.com>
>>>>
>>>> The virtio-blk-x configuration is not in sync with virtio-blk configuration.
>>>> So this patch remove the virtio-blk-x configuration field, and use virtio-blk
>>>> one for setting the properties.
>>>>
>>>> This also remove a useless configuration copy in virtio_blk_device_init.
>>>>
>>>> Signed-off-by: KONRAD Frederic <fred.konrad@greensocs.com>
>>>> Tested-by: Cornelia Huck <cornelia.huck@de.ibm.com>
>>>> Signed-off-by: Kevin Wolf <kwolf@redhat.com>
>>> This breaks -M pc-1.0 as it breaks global properties.
>> The first level analysis of why this happens:
>>
>>   (1) global values are set as part of DeviceState's instance_init function
>>       [and we set the config_wce field to 0 here]
>>   (2) virtio_blk_pci_instance_init is a subclass instance_init so runs second
>>   (3) it calls object_initialize on its embedded virtio-blk object
>>   (4) the DeviceState instance_init for that child object sets the
>>       properties to their init values [thus resetting config_wce to 1]
>>
>> The effect is that at the moment you can't have a property on
>> a parent object whose value is stored in the child object
>> (unless you do something hacky like read the default before
>> calling object_initialize and restore it afterwards].
>>
>> It seems to me that the underlying problem here is that we
>> set global values too early -- they should be set after a
>> device is completely instance_init'd, not halfway through init.
> Here is an in-progress series that forwards properties from the
> virtio-blk-pci to virtio-blk.
>
> I think it's the best solution.  The approach needs some polishing but I
> wanted to share early.
>
> https://github.com/aliguori/qemu/commits/qom-forward.1
>
> Regards,
>
> Anthony Liguori
>
>> -- PMM
Seems, it's what we need here.

I think it is the same think for all other backends?

Fred