[Bug 1884933] Re: Backport casper changes from groovy to support interactive network boot on focal, and improved interractive boot UX on server

[Michael Hudson-Doyle]

I fixed the typo Frank mentioned in the git repo, it doesn't seem worth
a new upload.

I made myself an amd64 ISO with an initrd built with casper from
proposed and tested a few boot scenarios. They all worked and I observed
the desired UX improvements. I also tested the interactive netboot and
that worked, although as expected there is a significant delay on amd64
and lots of messages about failing to mount /dev/sr0. We can worry about
those in the future!

Together with Frank's testing, I'm going to mark this verification done.

** Tags removed: verification-needed verification-needed-focal
** Tags added: verification-done-focal

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https://bugs.launchpad.net/bugs/1884933

Title:
  Backport casper changes from groovy to support interactive network
  boot on focal, and improved interractive boot UX on server

Status in Ubuntu on IBM z Systems:
  In Progress
Status in casper package in Ubuntu:
  Fix Released
Status in casper source package in Focal:
  Fix Committed

Bug description:
  [Impact]

   * With legacy-server iso in focal it is possible to network boot and interactively setup networking configuration.
   * This feature lacks in the initrd used by subiquity, and thus is not available on the live-server.
   * This feature is now implemented in groovy and has been tested to work on multiple architectures, including s390x specific hardware (zdev code path)
   * Backport this feature to focal for 20.04.1

  [Test Case - interractive boot]

   * Build live-server iso with proposed pocket enabled

   * Download just the kernel & initrd artefacts

   * Boot kerenl & initrd and specify ignore_uuid kernel cmdline
  parameter, but nothing about ip= or url= and _without_ any subiquity
  iso attached.

   * Wait for boot to offer to perform network boot, configure
  networking, and accept default url, await to be booted to subiquity
  welcome screen

  [Test case - improved UX]

   * During live server boot, there is no plymouth running, and thus
  some messages displayed during boot are ugly warnings, which are
  harmless and actually should not be there or improved:

    - Newline added between progress '.....' and the check result message
    - Warning "Connection to playmouth" is dropped, as server normally boots without plymouth, thus this warning should not be printed.
    - Failure to mount /cow -> the code to expose /cow in the root never worked, and always printed error, stop doing that.

   * Ideally, booting kernel+initrd with "quiet" should result in crisp
  experience without a single warning message printed, until one is
  informed that local installation media was not found and remote
  network boot is offered.

   * Test case is to check that fsck progress dots look nice, there is
  no inline mixed '....' with text, and that there is no "Connection to
  plymouth" error message, or an error message about /cow.

  
  [Regression Potential]

   * Previously when booting kernel/initrd without iso attached to the
  machine, the boot would fail and drop to emergency shell. Now
  interactive network setup is offered, and if that fails, then drop to
  emergency shell. So whilst there is added interactivity, eventually
  dropping to emergency shell is still there.

  [Other Info]

   * There are many other bug reports requesting this feature, all of
  which will be closed once this update lands on the daily isos.

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