[Bug 1481117] Re: casper 1.340.1 breaks previous persistency

[Andy Whitcroft]

Ok tested with the bits in the package in -proposed.  Tested create
persistence from .2 and then boot against .2, invalid format specifier,
and a clean create from the -proposed bits.  Seems to work as expected.

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Title:
  casper 1.340.1 breaks previous persistency

Status in casper package in Ubuntu:
  In Progress
Status in casper source package in Trusty:
  Fix Committed
Status in casper source package in Vivid:
  New
Status in casper source package in Wily:
  In Progress

Bug description:
  Likely scenario (unless I missed a crucial piece of information):

  - User has a working persistency file (or partition), with an Ubuntu 14.04.2 ISO
  - User upgrades to an Ubuntu 14.04.3 ISO, and boots it with the same persistency settings

  Likely result:

  - It appears to the user that the persistent data is lost

  Cause:

  - In casper 1.340, persistency data is stored in the root of the persistency partition
  - In casper 1.340.1, persistency data is stored in the /upper directory of the persistency partition

  Actual issue I faced:

  - I maintain a personal, custom Kubuntu ISO. Nothing too fancy: it is just the regular Kubuntu ISO, with many additional packages (digikam, darktable, etc.; all from the official Ubuntu repository). I regularly update my ISO by chrooting in the uncompressed squashfs and running aptitude there. I have a script to rebuild the ISO afterwards.
  - Today's update brought me casper 1.340.1, which broke my persistency as described above
  - Additionally, since I'm still running Linux 3.16, casper.log also featured a magnificent red herring:

  > mount: mounting /cow on /root failed: Invalid argument

  It took me a while to understand that the mount was actually
  successful (the first mount with the workdir option fails and emits
  the message, the second mount succeeds silently).

  My solution was quite simply:

  - Boot without persistency
  - Mount the persistent partition
  - Empty the /upper directory that had been created when I first booted with casper 1.340.1
  - Move data from the root of the persistent partition to the /upper directory
  - Reboot with persistency

  I'm not sure all users of the persistency feature will be as adept at
  fixing their persistency partition. It is surprising to see such an
  incompatible change introduced in a minor update of an LTS version.

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