Upcall is a direct communication tool between VMM and guest developed
upon vsock. The server side of the upcall is a driver in guest kernel
(kernel patches are needed for this feature) and it'll start to serve
the requests after the kernel starts. And the client side is in
Dragonball VMM , it'll be a thread that communicates with vsock through
uds.
We want to keep the lightweight of the VM through the implementation of
the upcall, through which we could achieve vCPU hotplug, virtio-mmio
hotplug without implementing complex and heavy virtualization features
such as ACPI virtualization.
fixes: #5642
Signed-off-by: Chao Wu <chaowu@linux.alibaba.com>
