[PATCH v0 0/2] virtio-blk and vhost-user-blk cross-device migration

[Denis Plotnikov]

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.

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(-)

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2.25.1