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Re: [Qemu-devel] [PATCH 1/2] acpi_piix4: fix migration of gpe fields

From: Philipp Hahn
Subject: Re: [Qemu-devel] [PATCH 1/2] acpi_piix4: fix migration of gpe fields
Date: Tue, 21 Mar 2017 10:03:53 +0100
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Icedove/45.6.0

Hello Marcelo,

Am 21.03.2017 um 00:20 schrieb Marcelo Tosatti:
> On Mon, Mar 20, 2017 at 01:02:10PM +0100, Philipp Hahn wrote:
>> Hello Marcelo, cc:qemu,
>> Sorry for re-using this old thread, but I have a problem loading some
>> saved state from qemu-kvm-1.1.2, which fails for piix4_pm.
>> You following patch was committed as
>> <http://git.qemu-project.org/?p=qemu.git;a=commitdiff;h=b0b873a07872f7ab7f66f259c73fb9dd42aa66a9>:
>> Am 15.11.2012 um 01:11 schrieb Marcelo Tosatti:
>>> Migrate 16 bytes for en/sts fields (which is the correct size),
>>> increase version to 3, and document how to support incoming
>>> migration from qemu-kvm 1.2.
>> I my case qemu-kvm-1.1.2/hw/acpi_piix4.c:284
>> | VMSTATE_STRUCT(ar.gpe, PIIX4PMState, 2, vmstate_gpe, ACPIGPE),
>> only saves 4 bytes, not 16 bytes.
> IIRC qemu-1.1.2 saved 16 bytes, which is the correct size, not 4 bytes.

I found 23910d3f669d46073b403876e30a7314599633af in qemu, which changed
"gpe" to be an array[4] instead of single "struct gpe_regs" without
changing the version number. So the incompatibility was introduced there.

> So while merging from qemu-kvm -> qemu, it was decided to maintain
> backwards compability with qemu, and not qemu-kvm.
> Is there any way to differentiate between the two (qemu vs qemu-kvm, 
> perhaps via some other field not in the VMState of ACPI PIIX4), so
> your patch can be integrated upstream?

I had a look and haven't found any reliable indicator to distinguish
between "qemu" and "qemu-kvm" yet. I'll have another look if my time
permits, but as I know "qemu-kvm" was used in my case, I will hard code
that knowledge for now in my private build.

Thank you four sharing your knowledge.


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