/etc/grub.d/10_linux_zfs doesn't add savedefault

[Deltik]

[Impact]
Ubuntu's ZFS boot support (`/etc/grub.d/10_linux_zfs`) does not add the `savedefault` command to non-recovery entries. This differs from the `/etc/grub.d/10_linux` (without ZFS) behavior, which adds `savedefault` to non-recovery entries.

[Test Case]
1. On a system that has a ZFS root (e.g. one installed with zsys), run `sudo update-grub`.

2. See that there are no mentions of `savedefault` in the relevant generated section:

    sed -n '/^### BEGIN \/etc\/grub\.d\/10_linux_zfs ###$/,/^### END \/etc\/grub\.d\/10_linux_zfs ###$/p;/^### END \/etc\/grub\.d\/10_linux_zfs ###$/q' /boot/grub/grub.cfg | grep savedefault

If this bug is fixed, the command above will return an output that has the string "savedefault".

[Regression Potential]
The patch makes the `/etc/grub.d/10_linux_zfs` logic for adding the `savedefault` command the same as that of `/etc/grub.d/10_linux`. It is a behavioral change but restores consistency with the non-ZFS Linux entry generator. The change should only affect those using the `GRUB_SAVEDEFAULT=true` and `GRUB_DEFAULT=saved` options in `/etc/default/grub`.

[Launchpad Janitor (janitor)]

This bug was fixed in the package grub2 - 2.04-1ubuntu14

---------------
grub2 (2.04-1ubuntu14) focal; urgency=medium

  * debian/patches/ubuntu-zfs-enhance-support.patch:
    - Handle the case where grub-probe returns several devices for a single
      pool (LP: #1848856). Thanks jpb for the report and the proposed patch.
    - Add savedefault to non-recovery entries (LP: #1850202). Thanks Deltik
      for the patch.
    - Do not crash on invalid fstab and report the invalid entry.
      (LP: #1849347) Thanks Deltik for the patch.
    - When a pool fails to import, catch and display the error message and
      continue with other pools. Import all the pools in readonly mode so we
      can import other pools with unsupported features (LP: #1848399) Thanks
      satmandu for the investigation and the proposed patch

 -- Jean-Baptiste Lallement <email address hidden> Mon, 18 Nov 2019 11:22:43 +0100

[Brian Murray (brian-murray)]

The Eoan Ermine has reached end of life, so this bug will not be fixed for that release