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Re: [PATCH v0 0/2] virtio-blk and vhost-user-blk cross-device migration
From: |
Michael S. Tsirkin |
Subject: |
Re: [PATCH v0 0/2] virtio-blk and vhost-user-blk cross-device migration |
Date: |
Mon, 4 Oct 2021 11:11:00 -0400 |
On Mon, Oct 04, 2021 at 06:07:29PM +0300, Denis Plotnikov wrote:
> It might be useful for the cases when a slow block layer should be replaced
> with a more performant one on running VM without stopping, i.e. with very low
> downtime comparable with the one on migration.
>
> It's possible to achive that for two reasons:
>
> 1.The VMStates of "virtio-blk" and "vhost-user-blk" are almost the same.
> They consist of the identical VMSTATE_VIRTIO_DEVICE and differs from
> each other in the values of migration service fields only.
> 2.The device driver used in the guest is the same: virtio-blk
>
> In the series cross-migration is achieved by adding a new type.
> The new type uses virtio-blk VMState instead of vhost-user-blk specific
> VMstate, also it implements migration save/load callbacks to be compatible
> with migration stream produced by "virtio-blk" device.
>
> Adding the new type instead of modifying the existing one is convenent.
> It ease to differ the new virtio-blk-compatible vhost-user-blk
> device from the existing non-compatible one using qemu machinery without any
> other modifiactions. That gives all the variety of qemu device related
> constraints out of box.
Hmm I'm not sure I understand. What is the advantage for the user?
What if vhost-user-blk became an alias for vhost-user-virtio-blk?
We could add some hacks to make it compatible for old machine types.
> 0001: adds new type "vhost-user-virtio-blk"
> 0002: add new type "vhost-user-virtio-blk-pci"
>
> Denis Plotnikov (2):
> vhost-user-blk: add a new vhost-user-virtio-blk type
> vhost-user-blk-pci: add new pci device type to support
> vhost-user-virtio-blk
>
> hw/block/vhost-user-blk.c | 63 ++++++++++++++++++++++++++++++
> hw/virtio/vhost-user-blk-pci.c | 43 ++++++++++++++++++--
> include/hw/virtio/vhost-user-blk.h | 2 +
> 3 files changed, 105 insertions(+), 3 deletions(-)
>
> --
> 2.25.1
- [PATCH v0 0/2] virtio-blk and vhost-user-blk cross-device migration, Denis Plotnikov, 2021/10/04
- [PATCH v0 1/2] vhost-user-blk: add a new vhost-user-virtio-blk type, Denis Plotnikov, 2021/10/04
- [PATCH v0 2/2] vhost-user-blk-pci: add new pci device type to support vhost-user-virtio-blk, Denis Plotnikov, 2021/10/04
- Re: [PATCH v0 0/2] virtio-blk and vhost-user-blk cross-device migration,
Michael S. Tsirkin <=
- Re: [PATCH v0 0/2] virtio-blk and vhost-user-blk cross-device migration, Roman Kagan, 2021/10/04
- Re: [PATCH v0 0/2] virtio-blk and vhost-user-blk cross-device migration, Michael S. Tsirkin, 2021/10/05
- Re: [PATCH v0 0/2] virtio-blk and vhost-user-blk cross-device migration, Dr. David Alan Gilbert, 2021/10/05
- Re: [PATCH v0 0/2] virtio-blk and vhost-user-blk cross-device migration, Eduardo Habkost, 2021/10/05
- Re: [PATCH v0 0/2] virtio-blk and vhost-user-blk cross-device migration, Michael S. Tsirkin, 2021/10/05
- Re: [PATCH v0 0/2] virtio-blk and vhost-user-blk cross-device migration, Dr. David Alan Gilbert, 2021/10/06
- Re: [PATCH v0 0/2] virtio-blk and vhost-user-blk cross-device migration, Michael S. Tsirkin, 2021/10/06
- Re: [PATCH v0 0/2] virtio-blk and vhost-user-blk cross-device migration, Dr. David Alan Gilbert, 2021/10/06
- Re: [PATCH v0 0/2] virtio-blk and vhost-user-blk cross-device migration, Michael S. Tsirkin, 2021/10/06
- Re: [PATCH v0 0/2] virtio-blk and vhost-user-blk cross-device migration, Dr. David Alan Gilbert, 2021/10/06