I have two image A and B, and A is the backing file of B I write data in address addr in A. Then create B and set A as backing file of B. Then I discard the same addr in B. So the entry of addr in l2 table should be 1( also is QCOW2_CLUSTER_ZERO_PLAIN) , right?
But the addr cluster in A will fill with zero after I execute `qemu-img commit B` I thought it will truncate or decrease the ref count of the cluster corresponding the addr, but it looks like just fill zero. Is that the default behavior?
