Unioning file systems: Architecture, features, and design choices

Actually, I strongly disagree. This is the way it would work anyway, in any implementation of union fs: "rm /c/f" removing /a/f but /b/f staying in its place for the next open() call (/b and /b/f are readonly, so you can't remove it again). That way, for instance, the readonly "bottom" fs can come with a default "/etc/resolv.conf" but it could be overwritten by user configuration on the readwrite "top" fs. If the user removes all configuration, the default config stays.

I actually think that "path in links" and "junction links" should be the default mounting mechanism instead of "/etc/fstab" because then it would be completely portable (you get a disk with n partitions, organize them with links to one another, disconnect it from one computer, connect it on another and voilá... everything is in its place.) And everything could be done lazily (you only actually mount a device once you access the link)