#!/bin/bash
# Brian K. White - b.kenyon.w@gmail.com
# Update xfs.mod and grub.cfg on the EFI partition.
# Run at shutdown to ensure the EFI partition will be bootable.
# Work-around for https://bugs.launchpad.net/ubuntu/+source/grub2/+bug/1652822
# Copies xfs.mod to the ESP (efi system partition) and prepends "insmod xfs" to grub.cfg

# Also generates 3 other versions of grub.cfg: emergency.cfg, old.cfg, static.cfg

# * grub.cfg - is automatically generated any time grub2 is installed or updated,
#   This script takes the grub.cfg that was automatically generated, and prepends "insmod /path/to/xfs.mod" to that.
# * emergency.cfg - is a copy of the latest grub.cfg
# * old.cfg - is a copy of the most recent emergency.cfg before the current one
# * static.cfg - is an ultimate emergency backup, totally static hardcoded version of grub.cfg that doesn't derive from the package manager auto-generated grub.cfg at all, and doesn't use the search for uuid method to find the root fs.

# TO USE
# When booting fails, you will normally be left at a "grub>" prompt.
# At the grub> prompt type this:
#
#   configfile $cmdpath/emergency.cfg
#
# if that doesn't work, try either old.cfg or static.cfg
#
#   configfile $cmdpath/old.cfg
# or
#   configfile $cmdpath/static.cfga
#
# Then after booting, run this script, which will fix the normal grub.cfg, and booting will be normal again until the next time a grub package update breaks it again.

set -f

ESP_DIR=/boot/efi/EFI/ubuntu
XFS_MOD=/boot/grub/x86_64-efi/xfs.mod

pr () { echo "$@" >&2 ; }
abrt () { echo "$0: $@" >&2 ; exit 1 ; }

pr "Checking for broken grub + efi + xfs config..."
pr
pr "EFI System Partition ESP_DIR=${ESP_DIR}"
ls -l ${ESP_DIR} >&2
pr
pr "Grub-* package's xfs.mod XFS_MOD=${XFS_MOD}"
ls -l ${XFS_MOD} >&2
pr

# If it doesn't already exist, generate a fully static config file just as an
# extra alternative emergency backup.
# It's commented-out because this must be manually customized for your actual
# disk layout.
# This is the actual correct example for my particular laptop, which still has
# the original factory partitions including uefi boot and Win10. To install
# Linux I only defragged and resized the Win10 C: partition, and created a new
# partition in the freed space. The uefi partition is original. Win10 was not
# wiped or reinstalled. In order for grub to be able to boot the xfs root fs,
# all it really needs is xfs.mod, and since there already is a FAT filesystem
# for UEFI, you can place a copy of xfs.mod on the EFI filesystem, and tell
# the initial grub.cfg where to find it, and then grub can get everything else
# from /boot on "/", without needing /boot to be a separate ext2 filesystem.
#[[ -s ${ESP_DIR}/static.cfg ]] || cat >${ESP_DIR}/static.cfg <<-"%%EOF"
#	insmod (hd0,gpt1)/EFI/ubuntu/xfs.mod
#	root=hd0,gpt5
#	prefix=($root)/boot/grub
#	configfile $prefix/grub.cfg
#%%EOF

# If the copy of xfs.mod on the root fs is newer than the one on the esp
# then update the copy on the esp.
# This single line does the same thing but no messages
#[[ ! -s xfs.mod ]] || [[ ${XFS_MOD} -nt xfs.mod ]] && cp -f ${XFS_MOD} xfs.mod
pr "Checking xfs.mod ..."
UPDATE_XFS_MOD=false
[[ -s ${ESP_DIR}/xfs.mod ]] && {
	pr "${ESP_DIR}/xfs.mod is present"
	[[ ${XFS_MOD} -nt ${ESP_DIR}/xfs.mod ]] && {
		ls -l ${XFS_MOD} >&2
		ls -l ${ESP_DIR}/xfs.mod >&2
		pr "${ESP_DIR}/xfs.mod is older than ${XFS_MOD}"
		UPDATE_XFS_MOD=true
	} || {
		pr "${ESP_DIR}/xfs.mod is up to date"
	}
} || {
	pr "${ESP_DIR}/xfs.mod is missing"
	UPDATE_XFS_MOD=true
}
${UPDATE_XFS_MOD} && {
	pr "Updating ${ESP_DIR}/xfs.mod"
	cp -vf ${XFS_MOD} ${ESP_DIR}/xfs.mod >&2
	:
} || {
	pr "No update needed for ${ESP_DIR}/xfs.mod"
}
pr

# If the efi partition's grub.cfg doesn't have some form of "insmod xfs",
# (sample possible values: "insmod xfs", "insmod $cmdpath/xfs.mod")
pr "Checking ${ESP_DIR}/grub.cfg ..."
grep '^insmod .*xfs.*' ${ESP_DIR}/grub.cfg >&2 && {
	pr "${ESP_DIR}/grub.cfg contains insmod xfs"
	pr "No update needed for ${ESP_DIR}/grub.cfg"
} || {
	pr "${ESP_DIR}/grub.cfg does not contain insmod xfs"
	pr "(A grub-* package update has generated a new ${ESP_DIR}/grub.cfg incorrectly)"
	# Copy the current existing emergency.cfg to old.cfg
	[[ -s ${ESP_DIR}/emergency.cfg ]] && {
		pr "emergency.cfg exists"
		pr "Copying current emergency.cfg to old.cfg"
		cp -vf ${ESP_DIR}/emergency.cfg ${ESP_DIR}/old.cfg >&2
	}
	# Generate a new emergency.cfg by writing the insmod line followed by the new grub.cfg
	pr "Generating a new emergency.cfg by prepending insmod xfs to the new grub.cfg"
	echo 'insmod $cmdpath/xfs.mod' > ${ESP_DIR}/emergency.cfg
	cat ${ESP_DIR}/grub.cfg >> ${ESP_DIR}/emergency.cfg
	# Copy the new emergency.cfg over grub.cfg
	pr
	pr "Summary:"
	pr "${ESP_DIR}/grub.cfg before apt upgrade:"
	cat ${ESP_DIR}/old.cfg >&2
	pr
	pr "${ESP_DIR}/grub.cfg after apt upgrade:"
	cat ${ESP_DIR}/grub.cfg >&2
	pr
	pr "${ESP_DIR}/emergency.cfg we just generated:"
	cat ${ESP_DIR}/emergency.cfg >&2
	pr
	pr "Copying new emergency.cfg over grub.cfg"
	cp -vf ${ESP_DIR}/emergency.cfg ${ESP_DIR}/grub.cfg >&2
}

pr
pr "Finished"
pr
pr "This is the ${ESP_DIR}/grub.cfg currently in effect for the next boot:"
pr "---"
cat ${ESP_DIR}/grub.cfg >&2
pr "---"