SLAX Modules and union file systems

[jmansion]

Does FreeBSD have a working union-type file system? And also compressed readonly filesystem?

I'm asking because I've been looking at SLAX, and my understanding is that SLAX modules are essentially files containing a compressed filesystem (squashfs in that case) that are then union-ed into root.

And I'm thinking - that achieves what PBIs try to achieve, doesn't it? You mount all the compressed packages readonly unioned together, and at the top of the union is a read-write layer that does copyup on demand and lets you modify things where a package needs a central config in its installation.

Addition and removal of a package then becomes somewhat straightforward. And its pretty space efficient. And the modules can be enabled or disabled pretty easily for different boot configurations.

It would appear that it even has the facility to provide overrides of libraries in lower union levels and provide some means to address replacement of individual components by replacing them with soft links to an external writable filesystem (or even a 'latest' package).

Seems neat to me. I had in mind that FreeBSD has some of the necessary facilities, but I've seen aspersions cast on, I think, one of the Dragonlfly lists. Can't remember.

Anyone got any thoughts on this?

I confess I haven't tried SLAX yet - but I'm surely going to.

James