More searching ... and I think running the mkimage.sh file in the sd-fuse_nanopi folder, after you apt-get install kpartx is the solution.
NanoPi-fuser-win32 requires a .img file. Could you explain how to generate a .img file from a rootfs or rootfs.tgz file?
I how found a utility called make_ext4fs but an usage example would be helpful, say for a 8G microSD card.
Thank you,
Dave