virsh snapshot-revert win7 before_patches
qemu-img create -f qcow2 -o preallocation=metadata windows7.qcow2 40G windows 7qcow2
Eventually, you must migrate. Use your qcow2 image as a source: virsh snapshot-revert win7 before_patches
Windows 7 is an older operating system. If you are running it on modern hardware via QEMU/KVM, you may encounter issues with drivers: qemu-img create -f qcow2 -o preallocation=metadata windows7