[Merge] ~jibel/livecd-rootfs/+git/add_multi_layered_squashfses_support:ubuntu/master into livecd-rootfs:ubuntu/master

[Michael Hudson-Doyle]

> I think rewriting live-build is outside of the scope of this MP.

Yes. Obviously.

> We try to
> ensure that the multi-layer and mono-layer builds are as close from each other
> as possible to avoid unexpected side-effects (unseen diverging behaviours).

I think that's a fine goal but we've already experienced divergent behaviour with hooks that turn out not to be idempotent so...

> A rewrite would rather include all pieces used to build an ISO, meaning
> livecd-rootfs, live-build, debian-cd and ubuntu-cdimage, which are all
> intertwined, require a local archive on disk and such. 

Well no, I really just mean replacing the parts of live-build we use with something else. Part of the reason we use so little of it is that we use debian-cd (in particular) to do what large parts of live-build do.

> So, a way bigger scope than this MP.

That's true but also not what I was trying to suggest. What I meant was writing lb_chroot_layered more directly, without using live-build style obfuscations. But well it's done now so the suggestion is probably too late to be useful.
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https://code.launchpad.net/~jibel/livecd-rootfs/+git/add_multi_layered_squashfses_support/+merge/360878
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