Multi-Layer Support Coming To OverlayFS In Linux 3.19
OverlayFS, which is mostly used as a union file-system by Live DVD/USB Linux distributions, with Linux 3.19 adds support for multiple read-only layers to OverlayFS. Beyond having support for multiple ready-only layers, the upper layer can be optionally made writable.
That's the only main change for OverlayFS in Linux 3.19. The pull request by Miklos Szeredi that does the few hundred lines of changes can be found via the Indiana kernel mailing list.