/etc/initramfs-tools/scripts/overlay

overlay

# /etc/initramfs-tools/scripts/overlay
# default file generated by /usr/bin/raspi-config
# add highlighted lines to access lower and upper filesystems

# Local filesystem mounting			-*- shell-script -*-

#
# This script overrides local_mount_root() in /scripts/local
# and mounts root as a read-only filesystem with a temporary (rw)
# overlay filesystem.
#

. /scripts/local

local_mount_root()
{
	local_top
	local_device_setup "${ROOT}" "root file system"
	ROOT="${DEV}"

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

	local_premount

	# CHANGES TO THE ORIGINAL FUNCTION BEGIN HERE
	# N.B. this code still lacks error checking

	modprobe ${FSTYPE}
	checkfs ${ROOT} root "${FSTYPE}"

	# Create directories for root and the overlay
	mkdir /lower /upper

	# Mount read-only root to /lower
	if [ "${FSTYPE}" != "unknown" ]; then
		mount -r -t ${FSTYPE} ${ROOTFLAGS} ${ROOT} /lower
	else
		mount -r ${ROOTFLAGS} ${ROOT} /lower
	fi

	modprobe overlay || insmod "/lower/lib/modules/$(uname -r)/kernel/fs/overlayfs/overlay.ko"

	# Mount a tmpfs for the overlay in /upper
	mount -t tmpfs tmpfs /upper
	mkdir /upper/data /upper/work

	# Mount the final overlay-root in $rootmnt
	mount -t overlay \
	    -olowerdir=/lower,upperdir=/upper/data,workdir=/upper/work \
	    overlay ${rootmnt}

############ ADD THIS TO ACCESS OVERLAYS ###########
	mkdir ${rootmnt}/.ro
	mount --bind /lower ${rootmnt}/.ro
	mkdir ${rootmnt}/.rw
	mount --bind /upper ${rootmnt}/.rw
####################################################
}