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Re: [Qemu-devel] [PATCH RFC 1/8] virtio: add subsections to the migratio

From: Andreas Färber
Subject: Re: [Qemu-devel] [PATCH RFC 1/8] virtio: add subsections to the migration stream
Date: Fri, 16 May 2014 11:22:28 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:24.0) Gecko/20100101 Thunderbird/24.5.0

Am 16.05.2014 11:14, schrieb Fam Zheng:
> On Thu, 05/15 12:08, Greg Kurz wrote:
>>>> The main problem I see is that virtio sucks: as you see in patch 8, we have
>>>> to be careful not to call vring or virtqueue stuff before the device knows
>>>> its endianness or it breaks... I need to study how the virtio-bus gets
>>>> migrated to ensure the endian section is streamed before the devices.
>>> There is no ordering guarantee. The state needs to be migrated in the
>>> device or bus where it sits, if post-load processing is required; i.e.,
>>> if it's in VirtIODevice then something like this series, if it were on
>>> VirtioBus exclusively (device asking bus for its endianness each time
>>> and does not do post-load stuff) then endianness could be migrated as a
>>> new bus section. Not sure if that would help the "broken" state though?
>> IIRW the "broken" state was proposed as a per-device property...
> Yes.

Sure, and that makes sense, but we do have a 1:1 relation of bus/device,
or does virtio-mmio support more? If device doesn't work for some
reason, we could (mis)use the bus as fallback then.


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