[Bug 1561606] Re: Re-enable multi-layer squashfs support

[Richard Nelson]

Greetings,

Humble appreciation that you are addressing this bug! I submitted the
patch because I believed it to solve the issue and, imo, my patch is
very clean, less intrusive, and does not introduce new variables. Please
test the patch and confirm for yourself with not just one extra partial
squashfs update (I call them PSU files), test with several and test
stacking order.

To make the PSU files I just ripped the iso and made PSU files, several
times, using live-partial-squashfs-updates , I believe it is should be
in live-tools package, but here is git

https://github.com/unixabg/live-medium-install-tools/blob/master/scripts
/live-partial-squashfs-updates

Then composed iso again with the PSU files and tested that it did stack
on Live. As I recall the PSU files do not get installed during
installation, which I how it should be imo.

Thank you for the dialog and your consideration of my patch.

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https://bugs.launchpad.net/bugs/1561606

Title:
  Re-enable multi-layer squashfs support

Status in casper package in Ubuntu:
  In Progress

Bug description:
  AFAIK, Casper supports booting when there is more than one squashfs
  file in the casper directory. At least, this _was_ supported under
  Ubuntu trusty which used aufs as union file system. Then there came
  utopic, wily, vivid which switched to overlayfs. This file system
  didn't support layering more than one ro sources in its early versions
  so that this feature didn't work anymore. The code in the casper
  script looks like a work-around about this by stacked mounting
  multiple overlayfs. Unfortunately, I've never seen a version of
  overlayfs which supported another overlayfs as source.

  Since kernel 3.19, overlayfs officially supports multiple layers
  (http://www.phoronix.com/scan.php?page=news_item&px=MTg1Nzg), so it's
  time to rewrite this piece of code in the casper script.

  Fully-working patch attached.

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