[Bug 1965983] Re: ZFS snapshots without etc directory causes grub.cfg build failure

[Mate Kukri]

The fix for this apparently doesn't fix the issue at all, and more
investigation needs to be done.

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Title:
  ZFS snapshots without etc directory causes grub.cfg build failure

Status in grub2 package in Ubuntu:
  Triaged
Status in grub2 source package in Focal:
  Triaged
Status in grub2 source package in Jammy:
  Triaged

Bug description:
  In /etc/grub.d/10_linux_zfs (built during install from util/grub.d/10_linux_zfs.in), get_dataset_info() tries to unmount mount locations starting with the logic
  ```
  case "${etc_dir}" in /.zfs/snapshot/*/etc)
  ```

  This process occasionally and silently fails while building /boot/grub/grub.cfg when running in FIPS mode (with FIPS kernels), which leaves the generated /boot/grub/grub.cfg without any kernel (linux ...) lines.
  It appears that not all ZFS snapsshots that match the switch statement actually have an .../etc directory.

  As ZFS is only an option in the Focal Desktop installer, this issue
  was only tested with Focal running Canonical's FIPS packages.

  In order to reproduce this issue in FIPS mode, the ubuntu-fips and
  fips-initramfs-generic packages both need to implement a couple of
  patches that haven't released yet. Without these two patches and
  without manual intervention, the FIPS kernel will be unable to boot
  with a ZFS /boot device. I can provide these additional patches --
  please feel free to reach out to me!

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