Some files from my Netbooting Pi series. See this introduction post for the entire series: https://blog.mei-home.net/posts/rpi-netboot/intro/

eeprom-boot-mount-dep.conf

# The eeprom update check service needs to have access to the files
# on the firmware partition.

[Unit]
RequiresMountsFor=/boot/firmware

rbd-boot-script.sh

# this file has been taken from https://github.com/ltsp/ltsp/pull/50
# This file is part of LTSP, https://ltsp.github.io
# Originally written by Paul Emmerich, emmericp@net.in.tum.de
# Extended and adapted for LTSP by Markus Kienast, mark@trickkiste.at
# Based on the initramfs-tools nfs script.
# SPDX-License-Identifier: GPL-3.0-or-later

# Inject LTSP code under initramfs-tools

# RBD root mounting			-*- shell-script -*-


rbd_top()
{
	if [ "${rbd_top_used}" != "yes" ]; then
		[ "$quiet" != "y" ] && log_begin_msg "Running /scripts/rbd-top"
		run_scripts /scripts/rbd-top
		[ "$quiet" != "y" ] && log_end_msg
	fi
	rbd_top_used=yes
}

rbd_premount()
{
	if [ "${rbd_premount_used}" != "yes" ]; then
		[ "$quiet" != "y" ] && log_begin_msg "Running /scripts/rbd-premount"
		run_scripts /scripts/rbd-premount
		[ "$quiet" != "y" ] && log_end_msg
	fi
	rbd_premount_used=yes
}

rbd_bottom()
{
	if [ "${rbd_premount_used}" = "yes" ] || [ "${rbd_top_used}" = "yes" ]; then
		[ "$quiet" != "y" ] && log_begin_msg "Running /scripts/rbd-bottom"
		run_scripts /scripts/rbd-bottom
		[ "$quiet" != "y" ] && log_end_msg
	fi
	rbd_premount_used=no
	rbd_top_used=no
}

# parse rbd bootargs and mount rbd
rbd_map_root_impl()
{
	configure_networking

	# get rbd root from dhcp
	if [ "x${RBDROOT}" = "xauto" ]; then
		RBDROOT=${ROOTPATH}
	fi

	local mons user key pool image snap partition

	# rbdroot=<mons>:<user>:<key>:<pool>:<image>[@<snapshot>]:[<partition>]:[<mountopts>]
	if [ -n "${RBDROOT}" ]; then
		local i=1
		local OLD_IFS=${IFS}
		IFS=":"
		for arg in ${RBDROOT} ; do
			case ${i} in
				1)
					mons=$(echo ${arg} | tr ";" ":")
					;;
				2)
					user=${arg}
					;;
				3)
					key=${arg}
					;;
				4)
					pool=${arg}
					;;
				5)
					# image contains an @, i.e. a snapshot
					if [ ${arg#*@*} != ${arg} ] ; then
						image=${arg%%@*}
						snap=${arg##*@}
					else
						image=${arg}
						snap=""
					fi
					;;
				6)
					partition=${arg}
					;;
				7)
				  mountopts=${arg}
					;;
			esac
			i=$((${i} + 1))
		done
		IFS=${OLD_IFS}
	fi

	# the kernel will reject writes to add if add_single_major exists
	local rbd_bus
	if [ -e /sys/bus/rbd/add_single_major ]; then
		rbd_bus=/sys/bus/rbd/add_single_major
	elif [ -e /sys/bus/rbd/add ]; then
		rbd_bus=/sys/bus/rbd/add
	else
		echo "ERROR: /sys/bus/rbd/add does not exist"
		return 1
	fi

  ### FIXME: this must not repeat if successful but mount fails for some reason

	# tell the kernel rbd client to map the block device
	echo "${mons} name=${user},secret=${key} ${pool} ${image} ${snap}" > ${rbd_bus}
	# figure out where the block device appeared
	dev=$(ls /dev/rbd* | grep '/dev/rbd[0-9]*$' | tail -n 1)
	# add partition if set
	if [ ${partition} ]; then
		dev=${dev}p${partition}
	fi
}

rbd_mount_root_impl()
{
	if [ ${readonly} = y ]; then
		roflag="-r"
	else
		roflag="-w"
	fi

	if [[ ! -z "$mountopts" ]] ; then
		mountopts="-o $mountopts"
	fi

	# get the root filesystem type if not set
	if [ -z "${ROOTFSTYPE}" ]; then
		FSTYPE=$(get_fstype "${dev}")
	else
		FSTYPE=${ROOTFSTYPE}
	fi

	rbd_premount

	# mount the fs
	modprobe ${FSTYPE}
	echo "EXECUTING: \"mount -t ${FSTYPE} ${roflag},${mountopts} $dev ${rootmnt}\""
	mount -t ${FSTYPE} ${roflag} ${mountopts} $dev ${rootmnt}

}


# RBD root mounting
rbd_mount_root()
{

	export RBDROOT=

	# Parse command line options for rbdroot option
	for x in $(cat /proc/cmdline); do
		case $x in
		rbdroot=*)
			RBDROOT="${x#rbdroot=}"
			;;
		esac
	done

	rbd_top

	modprobe rbd
	# For DHCP
	modprobe af_packet

	wait_for_udev 10

	# Default delay is around 180s
	delay=${ROOTDELAY:-120}

	# loop until rbd mount succeeds
	rbd_map_root_impl
	rbd_map_retry_count=0
	while [ ${rbd_map_retry_count} -lt ${delay} ] \
		&& [[ -z "$dev" ]] ; do
		[ "$quiet" != "y" ] && log_begin_msg "Retrying rbd map"
		/bin/sleep 1
		rbd_map_root_impl
		rbd_map_retry_count=$(( ${rbd_map_retry_count} + 1 ))
		[ "$quiet" != "y" ] && log_end_msg
	done

  if [ -z "$dev" ] ; then
		echo "ERROR: RBD could not be mapped"
		return 1
	fi

	# loop until rbd mount succeeds
	rbd_mount_root_impl
	rbd_mount_retry_count=0
	while [ ${rbd_mount_retry_count} -lt ${delay} ] \
		&& ! chroot "${rootmnt}" test -x "${init}" ; do
		[ "$quiet" != "y" ] && log_begin_msg "Retrying rbd mount"
		/bin/sleep 1
		rbd_mount_root_impl
		rbd_mount_retry_count=$(( ${rbd_mount_retry_count} + 1 ))
		[ "$quiet" != "y" ] && log_end_msg
	done
}

mountroot()
{
	rbd_mount_root
}

mount_top()
{
	# Note, also called directly in case it's overridden.
	rbd_top
}

mount_premount()
{
	# Note, also called directly in case it's overridden.
	rbd_premount
}

mount_bottom()
{
	# Note, also called directly in case it's overridden.
	rbd_bottom
}

rbd-gen-hook.sh

#!/bin/sh
# this file has been taken from https://github.com/ltsp/ltsp/pull/50

# This file is part of LTSP, https://ltsp.github.io
# Copyright 2019 the LTSP team, see AUTHORS
# SPDX-License-Identifier: GPL-3.0-or-later

# Inject LTSP code under initramfs-tools

# Hook scripts (from man initramfs-tools(8))
# These  are  used  when an initramfs image is created and not included in the
# image itself. They can however cause files to be included in the image.  Hook
# scripts are executed under errexit.  Thus  a hook script can abort the
# mkinitramfs build on possible errors (exitcode != 0).

# Notes:
# Use functions and local variables, to avoid namespace pollution

# Initramfs hook for ltsp

PREREQ=""

prereqs()
{
  echo "$PREREQ"
}

case "$1" in
  prereqs)
    prereqs
    exit 0
    ;;
esac

. /usr/share/initramfs-tools/hook-functions

modules="rbd aes cbc"
manual_add_modules $modules

zzz-chmod-kernel-image

#!/bin/sh
# This is needed because something makes the kernel image under
# /boot/firmware readonly by root.
# With that, tftp/dnsmasq can't read the kernel image when it
# is requested during netboot by the Pis.

echo "Changing permissions for /boot/firmware"

set -e
version="$1"
if [ -z "$version" ]; then
  exit 0
fi
exec dpkg-statoverride --force-statoverride-add --update --add root root 0644 "/boot/vmlinuz-${version}"