As with libvirt 11.10 a new flag for backup operation has been inroduced: VIR_DOMAIN_BACKUP_BEGIN_PRESERVE_SHUTDOWN_DOMAIN.

According to the documentation “It instructs libvirt to avoid termination of the VM if the guest OS shuts down while the backup is still running. The VM is in that scenario reset and paused instead of terminated allowing the backup to finish. Once the backup finishes the VM process is terminated.”

Added support for this in virtnbdbackup 2.40.