On Thu, 11/02 12:02, Daniel P. Berrange wrote:
> One alternative approach to doing this would be to suggest that we should
> instead just spawn qemu-system-x86_64 with '--machine none' and use that
> as a replacement for qemu-nbd, since it already has a built-in NBD server
> which can do many exports at once and arbitrary block jobs.
Here is a crazy idea from KVM Forum discussions that may relate, so mention it
here: we could move the QEMU block layer to a separate program and guest can use
vhost-user-{blk,scsi} for I/O. It is something like this:
master-disk1.qcow2 (qemu-nbd)
^
| backing
|
cache-disk1.qcow2 (qemu-vhost) <-------------.
^ |
| backing | backing
| |
+- vm-a-disk1.qcow2 (qemu-vhost) +- vm-a-disk2.qcow2
(qemu-vhost)
^ ^
| vhost-user-blk |
vhost-user-blk
| |
+- VM-1 (qemu-system-XXX) +- VM-2
(qemu-system-XXX)
So on the compute node, there will be N qemu-system-XXX processes (where N is
the number of VMs) and 1 qemu-vhost process.
The hypothetical qemu-vhost program needs to support QMP as well and it runs the
COR/mirroring jobs from master disk to cache disk, just like what you propose to
do with the extended qemu-nbd. The only difference is replacing the local NBD
with vhost-user, which is more efficient.
Fam
