There's OverlayFS. It does exactly what you want, although it was created for different use cases (Live CDs, layered images as used by Docker, etc.): https://

There's OverlayFS. It does exactly what you want, although it was created for different use cases (Live CDs, layered images as used by Docker, etc.): https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/Documentation/filesystems/overlayfs.txt https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux....