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

[Fam Zheng]

On Fri, 05/16 11:22, Andreas Färber wrote:
> 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.
> 

FWIW, I just realized that "broken" may be loaded from device status bit in the
future, so we don't need to migrate the field separately:

https://tools.oasis-open.org/issues/browse/VIRTIO-98

Fam