[Scaevolus]

Not purely in-memory, but something like https://github.com/jrwwallis/qcow2fuse maybe? It's clunky compared to OSX's DMGs, but if you squint it achieves similar ends.

Otherwise you could achieve this with a tmpfs wrapped to serialize to a tarball (preserving symlinks) when unmounted.

[ranger_danger]

Oh nice, I didn't even know that existed. I've been using qemu-nbd and parted by hand and it gets cumbersome, so this might help a lot. Thanks!