[Bug 1899372] Re: update-grub 10_linux_zfs fails when /usr is a separate filesystem

[Tessa]

I think it's an important use case to support, since it's more than
likely going to be needed once Ubuntu supports ZFS on server installs.
the zfs tools and scripts should definitely be bulletproof'd to handle
any zfs fs configuration, especially around something like this where it
should be easy to fix.

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https://bugs.launchpad.net/bugs/1899372

Title:
  update-grub 10_linux_zfs fails when /usr is a separate filesystem

Status in grub2 package in Ubuntu:
  Incomplete
Status in grubzfs-testsuite package in Ubuntu:
  Confirmed

Bug description:
  Description:    Ubuntu 20.04.1 LTS
  Release:        20.04
  grub-common: 2.04-1ubuntu26.4

  I expect grub-update to create grub.cfg with Linux entries for ZFS.
  Instead I am left with an empty list and an unbootable OS.

  The output from update-grub:
  Sourcing file `/etc/default/grub'
  Sourcing file `/etc/default/grub.d/init-select.cfg'
  Sourcing file `/etc/default/grub.d/kdump-tools.cfg'
  Generating grub configuration file ...
  /etc/grub.d/10_linux_zfs: 404: .: Can't open /tmp/zfsmnt.stGSQC/etc/os-release
  Found memtest86+ image: /memtest86+.elf
  Found memtest86+ image: /memtest86+.bin
  done

  This is failing because I have a separate ZFS filesystem for /usr.
  The 10_linux_zfs script is gathering information from /etc/os-release
  which is a symlink to ../usr/lib/os-release.

  The first issue I see in 10_linux_zfs is under function get_dataset_info() at line 382:
  mount -o noatime,zfsutil -t zfs "${base_dataset}" "${mntdir}"

  Since /usr is under a separate filesystem, the symlink would be broken
  and the script fails.  This should mount /usr as well if it is a
  separate filesystem.

  The next issue I see is when the script iterates the zsys snapshots at line 514:
  for snapshot_dataset in $(zfs list -H -o name -t snapshot "${dataset}"); do
      boot_list="${boot_list}$(get_dataset_info ${snapshot_dataset} ${mntdir})\n"
  done

  You would get a similar error message about os-release.
  /etc/grub.d/10_linux_zfs: 410: .: Can't open /.zfs/snapshot/autozsys_oiimb5/etc/os-release

  Again, the script should consider reading the /usr snapshot as well if
  it is a separate filesystem.

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