You can set any property for virtio-blk-pci now. You can set the pci
address via addr=. You can switch the device into 0.10 compat mode
using class=0x0180. As this is per device you can have one 0.10 and one
0.11 virtio block device in a single virtual machine.
Old syntax continues to work. Internally it does the same as the two
lines above though. One side effect this has is a different
initialization order, which might result in a different pci address
being assigned by default.
Long term plan here is to have this working for all block devices, i.e.
once all scsi is properly qdev-ified you will be able to do something
like this: