Re: [Qemu-devel] [PULL 42/43] piix4: add acpi pci hotplug support

[Paolo Bonzini]

Il 15/10/2013 16:35, Michael S. Tsirkin ha scritto:
> On Tue, Oct 15, 2013 at 04:31:31PM +0200, Paolo Bonzini wrote:
>> Il 14/10/2013 17:01, Michael S. Tsirkin ha scritto:
>>> -        VMSTATE_STRUCT(pci0_status, PIIX4PMState, 2, vmstate_pci_status,
>>> -                       struct pci_status),
>>> +        VMSTATE_STRUCT_TEST(pci0_status, PIIX4PMState,
>>> +                            vmstate_test_no_use_acpi_pci_hotplug,
>>> +                            2, vmstate_pci_status,
>>> +                            struct pci_status),
>>
>> There's no reason to remove this from the stream when a new machine type
>> is in use.  You'll just send out zeroes.
> 
> Seemed cleaner not to.

It certainly would be if we had a self-descriptive migration stream format.

However, what we have is "send bytes, parse them on the destination,
hope the format matches".  Hence, anything that makes the format less
declarative adds to the complication and complicates debugging.  This is
the same reason why I prefer a subsection for the new hotplug stuff---it
makes the format more declarative and self-descriptive.

Paolo

>>> +        VMSTATE_PCI_HOTPLUG(acpi_pci_hotplug, PIIX4PMState,
>>> +                            vmstate_test_use_acpi_pci_hotplug),
>>
>> This works, but it is a bit different from other cases that are already
>> present, which use a subsection.  It is a bit ugly because it looks like
>> a version-1 field, but in fact it is not version 1.
>>
>> I'll let other people decide whether it's acceptable or not, but I'm
>> leaning towards asking you to use a subsection.
>>
>> Paolo