[Bug 1688424] Re: grub-mkrelpath returns invalid zfs dataset -> initramfs: mount /root fails

[Jens Elkner]

** Patch added: "grub-cfg.patch"
   https://bugs.launchpad.net/ubuntu/+source/grub2/+bug/1688424/+attachment/4872219/+files/grub-cfg.patch

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Title:
  grub-mkrelpath returns invalid zfs dataset -> initramfs: mount /root
  fails

Status in grub2 package in Ubuntu:
  New

Bug description:
  If zfs is used for boot, boot will fail because of bogus information returned by
  /usr/bin/grub-mkrelpath.  E.g. if the zfs dataset for / is rpool/ROOT/linux:

  # /usr/bin/grub-mkrelpath /
  /ROOT/linux@

  
  This leads to a bogus /boot/grub/grub.cfg because /etc/grub.d/10_linux generates a boot entry like this:
  linux   /ROOT/linux@/boot/vmlinuz-4.4.0-77-generic root=ZFS=/ROOT/linux ro crashkernel=384M-2G:64M,2G-:128M bootdegraded=true debug=y console=ttyS1,115200  crashkernel=384M-:128M

  This in turn causes that initramfs to fail on boot:
  ...
  + wait_for_udev
  + command -v udevadm
  + udevadm settle
  + modprobe zfs zfs_autoimport_disable=1
  + ZFS_BOOTFS=/ROOT/linux
  + echo /ROOT/linux
  + sed -e s,/.*,,
  + ZFS_RPOOL=
  + delay=0
  + [ 0 -gt 0 ]
  + unset delay
  + zpool import -N 
  [   10.922149] SPL: The /etc/hostid file is not found.
  [   10.927031] SPL: using hostid 0x00000000
  + ZFS_STDERR=cannot import '': no such pool available
  + ZFS_ERROR=1
  + [ 1 -ne 0 ]
  + panic Command: zpool import -N 
  Message: cannot import '': no such pool available
  Error: 1

  Manually import the root pool at the command prompt and then exit.
  Hint: Try:  zpool import -f -R / -N 

  
  Wrong hint BTW, but at least a hint: "zpool import; zpool import ${poolID}|rpool" fixes it.
  Anyway, when continuing after an 'exit' it fails with:

  ...
  + zpool status -L 
  + [ n != y ]
  + log_begin_msg Setting mountpoint=/ on ZFS filesystem /ROOT/linux
  + _log_msg Begin: Setting mountpoint=/ on ZFS filesystem /ROOT/linux ... 
  + [ n = y ]
  + printf Begin: Setting mountpoint=/ on ZFS filesystem /ROOT/linux ... 
  Begin: Setting mountpoint=/ on ZFS filesystem /ROOT/linux ... + zfs set mountpoint=/ /ROOT/linux
  + ZFS_STDERR=cannot open '/ROOT/linux': invalid dataset name
  + [ n != y ]
  + log_end_msg
  + _log_msg done.\n
  + [ n = y ]
  + printf done.\n
  done.
  + [ n != y ]
  + log_begin_msg Mounting ZFS filesystem /ROOT/linux
  + _log_msg Begin: Mounting ZFS filesystem /ROOT/linux ... 
  + [ n = y ]
  + printf Begin: Mounting ZFS filesystem /ROOT/linux ... 
  Begin: Mounting ZFS filesystem /ROOT/linux ... + mount -t zfs -o zfsutil /ROOT/linux /root
  + ZFS_STDERR=filesystem 'ROOT/linux' cannot be mounted, unable to open the dataset
  mount: mounting /ROOT/linux on /root failed: No such file or directory
  + ZFS_ERROR=1
  + [ n != y ]
  + log_end_msg
  + _log_msg done.\n
  + [ n = y ]
  + printf done.\n
  done.
  + [ 1 -ne 0 ]
  + panic Command: mount -t zfs -o zfsutil /ROOT/linux /root
  Message: filesystem 'ROOT/linux' cannot be mounted, unable to open the dataset
  mount: mounting /ROOT/linux on /root failed: No such file or directory
  Error: 1

  Manually mount the root filesystem on /root and then exit.

  
  A 'mount -t zfs -o zfsutil rpool/ROOT/linux /root' fixis it and after an 'exit' the system finally starts.

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