Description of problem:
Add a new qcow2 disk image to VM fedora-rawhide use virt-manager,find the disk size is exactly the same as the virtual size.
[root@bogon libvirttestapi]# qemu-img info /var/lib/libvirt/images/fedora-rawhide-1.qcow2
image: /var/lib/libvirt/images/fedora-rawhide-1.qcow2
file format: qcow2
virtual size: 20 GiB (21474836480 bytes)
disk size: 20 GiB
cluster_size: 65536
Format specific information:
    compat: 1.1
    lazy refcounts: true
    refcount bits: 16
    corrupt: false


Version-Release number of selected component (if applicable):
virt-manager-2.2.1-2.fc31.noarch
libvirt-5.6.0-5.fc31.x86_64


How reproducible:
always 

Steps to Reproduce:
1.
2.
3.

Actual results:


Expected results:
The disk size of the "new" created qcow2 image should be way smaller than the virtual size

Additional info: