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Date: Tue, 27 Oct 2015 17:02:23 +0000
From: Stefan Hajnoczi <stefanha@redhat.com>
Message-ID: <20151027170223.GC9986@stefanha-x1.localdomain>
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Subject: Re: [Qemu-devel] [PATCH 1/1] virtio: sync the dataplane vring state
 to the virtqueue before virtio_save
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To: "Denis V. Lunev" <den@openvz.org>
Cc: Kevin Wolf <kwolf@redhat.com>, Paolo Bonzini <pbonzini@redhat.com>, "Michael S. Tsirkin" <mst@redhat.com>, qemu-devel@nongnu.org, Pavel Butsykin <pbutsykin@virtuozzo.com>

On Mon, Oct 26, 2015 at 02:42:57PM +0300, Denis V. Lunev wrote:
> From: Pavel Butsykin <pbutsykin@virtuozzo.com>
> 
> When creating snapshot with the dataplane enabled, the snapshot file gets
> not the actual state of virtqueue, because the current state is stored in
> VirtIOBlockDataPlane. Therefore, before saving snapshot need to sync
> the dataplane vring state to the virtqueue. The dataplane will resume its
> work at the next notify virtqueue.
> 
> When snapshot loads with loadvm we get a message:
> VQ 0 size 0x80 Guest index 0x15f5 inconsistent with Host index 0x0:
>     delta 0x15f5
> error while loading state for instance 0x0 of device
>     '0000:00:08.0/virtio-blk'
> Error -1 while loading VM state
> 
> to reproduce the error I used the following hmp commands:
> savevm snap1
> loadvm snap1
> 
> qemu parameters:
> --enable-kvm -smp 4 -m 1024 -drive file=/var/lib/libvirt/images/centos6.4.qcow2,if=none,id=drive-virtio-disk0,format=qcow2,cache=none,aio=native -device virtio-blk-pci,scsi=off,bus=pci.0,addr=0x8,drive=drive-virtio-disk0,id=virtio-disk0 -set device.virtio-disk0.x-data-plane=on
> 
> Signed-off-by: Pavel Butsykin <pbutsykin@virtuozzo.com>
> Signed-off-by: Denis V. Lunev <den@openvz.org>
> CC: Stefan Hajnoczi <stefanha@redhat.com>
> CC: "Michael S. Tsirkin" <mst@redhat.com>
> CC: Kevin Wolf <kwolf@redhat.com>
> CC: Paolo Bonzini <pbonzini@redhat.com>
> ---
>  hw/block/virtio-blk.c | 5 +++++
>  hw/scsi/virtio-scsi.c | 5 +++++
>  2 files changed, 10 insertions(+)

Thanks, applied to my block tree:
https://github.com/stefanha/qemu/commits/block

Stefan