Comment 11 for bug 1838525

The values for:

default_bootdev=/dev/vda1
bootfs=/dev/mapper/vgubuntu-root
disk=/dev/mapper

in that code part. Which means, disk is wrong:

disk=$(device_to_disk "$bootfs")

coming from:

# This should probably be rewritten using udevadm or similar.
device_to_disk () {
    echo "$1" | \
        sed 's:\(/dev/\(cciss\|ida\|rs\)/c[0-9]d[0-9][0-9]*\|/dev/mmcblk[0-9]\|/dev/nvme[0-9][0-9]*n[0-9][0-9]*\|/dev/\(ad\|ada\|da\|vtbd\|x bd\)[0-9]\+\|/dev/[hms]d[0-9]\+\|/dev/[a-z]\+\).*:\1:'
}

I'll brb to fix this.