Ubuntu: Go back to bpool/grub

For a mirror or raidz topology, /boot/grub is on a separate dataset.
This was originally bpool/grub, then changed on 2020-05-30 to
bpool/BOOT/ubuntu_UUID/grub to work-around zsys setting canmount=off
which would result in /boot/grub not mounting.  This work-around lead
to issues with snapshot restores. The underlying zsys issue
ubuntu/zsys#164 was fixed and backported to 20.04, so it is now back to
being bpool/grub.

This reverts commit b6fd009edd.  It
conceptually reverts the errata notes from commit
04d3c1cee4, but includes new steps for
people in the pre-2020-05-30 state.

Signed-off-by: Richard Laager <rlaager@wiktel.com>
Fixes #55

docs/Getting Started/Ubuntu/Ubuntu 20.04 Root on ZFS.rst

@@ -15,45 +15,29 @@ applicable:
 /boot/grub Not Mounted
 ~~~~~~~~~~~~~~~~~~~~~~
 
-| **Severity:** Grave
-| **Fixed:** 2020-05-30
+| **Severity:** Normal (previously Grave)
+| **Fixed:** 2020-12-05 (previously 2020-05-30)
 
 For a mirror or raidz topology, ``/boot/grub`` is on a separate dataset. This
-is now ``bpool/BOOT/ubuntu_UUID/grub``, but was previously ``bpool/grub``.
-Unfortunately, zsys sets ``canmount=off`` on ``bpool/grub``, so it is not
-mounted. As a result, updates the GRUB configuration will be written to the
-``/boot`` filesystem and not used by GRUB (because it is still looking in
-``bpool/grub``). Check for ``bpool/grub``::
+was originally ``bpool/grub``, then changed on 2020-05-30 to
+``bpool/BOOT/ubuntu_UUID/grub`` to work-around zsys setting ``canmount=off``
+which would result in ``/boot/grub`` not mounting.  This work-around lead to
+`issues with snapshot restores
+<https://github.com/openzfs/openzfs-docs/issues/55>`__.  The underlying `zsys
+issue <https://github.com/ubuntu/zsys/issues/164>`__ was fixed and backported
+to 20.04, so it is now back to being ``bpool/grub``.
 
-  zfs list bpool/grub
+* If you never applied the 2020-05-30 errata fix, then ``/boot/grub`` is
+  probably not mounting.  Check that::
 
-If this says “dataset does not exist”, you are good. If it exists, fix it.
+    mount | grep /boot/grub
 
-Once you start this process, the system will be unbootable until you have
-completed it. Do not reboot until you have completed all of the steps.
-
-#. Rename the dataset::
-
-     umount /boot/grub
-     # Ignore any error about it not being mounted.
-
-     rm -rf /boot/grub
-
-     zfs list -r bpool
-     # Replace UUID below:
-     zfs rename bpool/grub bpool/BOOT/ubuntu_UUID/grub
-     zfs inherit com.ubuntu.zsys:bootfs bpool/BOOT/ubuntu_UUID/grub
-     zfs set canmount=on bpool/BOOT/ubuntu_UUID/grub
-     zfs mount bpool/BOOT/ubuntu_UUID/grub
-
-#. Ensure that zed updated the cache to use ``bpool/BOOT/ubuntu_UUID/grub``::
-
-     grep grub /etc/zfs/zfs-list.cache/bpool
-
-#. Rebuild the initrd and reinstall GRUB::
+  If it is mounted, everything is fine. Stop. Otherwise::
 
+    zfs set canmount=on bpool/boot/grub
     update-initramfs -c -k all
     update-grub
+
     grub-install --target=x86_64-efi --efi-directory=/boot/efi \
         --bootloader-id=ubuntu --recheck --no-floppy
 
@@ -70,15 +54,13 @@ completed it. Do not reboot until you have completed all of the steps.
         /boot/efi/EFI/ubuntu/grub.cfg \
         /boot/efi2/EFI/ubuntu-2/grub.cfg
 
-#. If using encryption, patch a dependency loop::
+* If you applied the 2020-05-30 errata fix, then you should revert the dataset
+  rename::
 
-     sudo apt install --yes curl patch
-     curl https://launchpadlibrarian.net/478315221/2150-fix-systemd-dependency-loops.patch | \
-         sed "s|/etc|/lib|;s|\.in$||" | (cd / ; patch -p1)
-
-#. Disable grub-initrd-fallback.service::
-
-     systemctl mask grub-initrd-fallback.service
+    umount /boot/grub
+    zfs rename bpool/BOOT/ubuntu_UUID/grub bpool/grub
+    zfs set com.ubuntu.zsys:bootfs=no bpool/grub
+    zfs mount bpool/grub
 
 AccountsService Not Mounted
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~
@@ -629,7 +611,7 @@ Step 3: System Installation
 
    For a mirror or raidz topology, create a dataset for ``/boot/grub``::
 
-     zfs create bpool/BOOT/ubuntu_$UUID/grub
+     zfs create -o com.ubuntu.zsys:bootfs=no bpool/grub
 
    A tmpfs is recommended later, but if you want a separate dataset for
    ``/tmp``::