[bug #59614] grub-mkconfig on ZFS root result has invalid root=ZFS= value

[Todd Markley]

URL:
  <https://savannah.gnu.org/bugs/?59614>

                 Summary: grub-mkconfig on ZFS root result has invalid
root=ZFS= value
                 Project: GNU GRUB
            Submitted by: csleuth7
            Submitted on: Thu 03 Dec 2020 08:55:13 PM UTC
                Category: Configuration
                Severity: Major
                Priority: 5 - Normal
              Item Group: Software Error
                  Status: None
                 Privacy: Public
             Assigned to: None
         Originator Name: Todd
        Originator Email: code@compusleuth.com
             Open/Closed: Open
                 Release: 
                 Release: other
         Discussion Lock: Any
         Reproducibility: Every Time
         Planned Release: None

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Details:

This problem was identified using Ubuntu 20.04.1 and selecting the ZFS root
option during installation. The grub version is 2.04-1ubuntu26.7

Installation will boot, but after any install or upgrade that requires
touching the grub configuration the resulting grub.cfg has an invalid
root=ZFS=/ROOT/ubuntu_xxxxxx value which is missing the zpool name, the
correct value should look like this:
root=ZFS=rpool/ROOT/ubuntu_xxxxxx



The root cause seems to be in these two files:
/etc/grub.d/10_linux           (line 137)
/etc/grub.d/20_linux_xen       (line 88)

Which contain a line that sets the value of ${rpool} like this:

rpool=`${grub_probe} --device ${GRUB_DEVICE} --target=fs_label 2>/dev/null ||
true`


This is setting ${rpool} to NULL since the grub-probe fails:
root@stream:/etc/grub.d# /usr/sbin/grub-probe --device /dev/nvme0n1p4
--target=fs_label
/usr/sbin/grub-probe: error: unknown filesystem.

Since this rpool= line should only be run when the root filesystem is ZFS, I
would expect this will always fail on every system with a ZFS root.

This is my hack test fix, (applied to both files):

------------------------------
        rpool=`${grub_probe} --device ${GRUB_DEVICE} --target=fs_label
2>/dev/null || true`
        if [ "${rpool}" = "" ]; then
           rpool=`/usr/sbin/zfs list | awk '{if( $5 == "/" ) { print $1; }}' |
sed "s:/.*::" | head -1`
        fi
        bootfs="`make_system_path_relative_to_its_root / | sed -e "s,@$,,"`"
        LINUX_ROOT_DEVICE="ZFS=${rpool}${bootfs%/}"

------------------------------

This test resolved the problem and worked on my three test systems:
Ubuntu 20.04 ZFS root
Ubuntu 20.04 ZFS root with Xen installed
Ubuntu 20.04 xfs root

Although this worked, I expect a better fix would just change the rpool=``
line with a command that works. My example fix assumed Ubuntu 20.04 was
installed with ZFS, and I did not consider any other configurations. I don't
expect details about my hardware would affect this issue, but two used
ASRock+AMD and the 3rd was an old Lenovo laptop.











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File Attachments:


-------------------------------------------------------
Date: Thu 03 Dec 2020 08:55:13 PM UTC  Name: grub-mkconfig.log  Size: 17KiB  
By: csleuth7
Example grub-mkconfig log
<http://savannah.gnu.org/bugs/download.php?file_id=50393>

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