The way I see block filter currently implemented is as a special block device
with `is_filter` set to true.
Is this a correct characterization of the current incarnation?
If so, I was wondering if it is possible to "insert" a block filter layer on top
of an existing block device once QEMU is executing (via QMP commands)?
It seems possible to add block filter managed block devices, but I don't think
I see a way of adding a block filter to an existing block device.
--
Wolf