On Tue, May 29, 2018 at 10:43 PM Eric Blake <eblake@redhat.com> wrote:
On 05/28/2018 05:27 AM, Arik Hadas wrote:
> Few months ago people from the oVirt-storage team checked the qemu toolset
> and replied that this capability is not yet provided, therefore we
> implemented the workaround described above. Apparently, the desired ability
> can also be useful for the flow discussed in this thread so it worth asking
> for it again :)

You CAN get a logically collapsed view of storage (that is, what the
guest would see), by using an NBD export of volume V.  Reading from that
volume will then pull sectors from whichever portion of the chain you
need.  You can use either qemu-nbd (if no guest is writing to the
chain), or within a running qemu, you can use nbd-server-start and
nbd-server-add (over QMP) to get such an NBD server running.

NBD expose the guest data, but we want the qcow2 stream - without
creating a new image.