#!/bin/sh
#
# SPDX-License-Identifier:     GPL-3.0-or-later
#
# Copyright:
#	2012 Axel Heider
#	2015 Pascal Rosin
#	Sebastian P.
#	Nicholas A. Schembri State College PA USA
#
# Description:
#
#  Read-only Root-FS for Raspian
#
#  https://help.ubuntu.com/community/aufsRootFileSystemOnUsbFlash#Overlayfs
#
# Changelog:
#
# v1.0.0
#   - written by Axel Heider for Ubuntu 11.10
#
# v2.0.0
#   - Modified to work with overlayfs integrated in Linux Kernel (>= 3.18)
#   - introduce workdir needed for new overlayfs
#   - change `mount --move` to `mount -o move` to drop busybox requirement
#   - Tested with raspian-ua-netinst v1.0.7
#     (Linux 3.18.0-trunk-rpi, Debian 3.18.5) on a Raspberry Pi.
#     The aufs part is not tested!
#
# v0.3
#   - Add SPDX-License-Identifier: GPL3+
#   - Drop /etc/fstab manipulation
#   - Fix versioning scheme to a more simple one (new v0.3)
#
# Notes:
#   * no changes to the root fs are made by this script.
#   * if /home/[user] is on the RO root fs, files are in ram and not saved.
#
# Install:
#  put this file in /etc/initramfs-tools/scripts/init-bottom/root-ro
#  chmod 0755 /etc/initramfs-tools/scripts/init-bottom/root-ro
#  update-initramfs -u
#  add `root-ro-driver=overlay` to the line in /boot/cmdline.txt
#
# Disable read-only root fs
#   * option 1: kernel boot parameter "disable-root-ro=true"
#   * option 2: create file "/disable-root-ro"
#
# ROOT_RO_DRIVER variable controls which driver isused for the ro/rw layering
#   Supported drivers are: overlayfs, aufs
#  the kernel parameter "root-ro-driver=[driver]" can be used to initialize
#  the variable ROOT_RO_DRIVER. If nothing is given, overlayfs is used.
#

# no pre requirement
PREREQ=""

prereqs()
{
    echo "${PREREQ}"
}

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

# import /usr/share/initramfs-tools/scripts/functions
. /scripts/functions

MYTAG="root-ro"
DISABLE_MAGIC_FILE="/disable-root-ro"

# parse kernel boot command line 
ROOT_RO_DRIVER=
DISABLE_ROOT_RO=
for CMD_PARAM in $(cat /proc/cmdline); do
    case ${CMD_PARAM} in
        disable-root-ro=*)
            DISABLE_ROOT_RO=${CMD_PARAM#disable-root-ro=}
            ;;
        root-ro-driver=*)
            ROOT_RO_DRIVER=${CMD_PARAM#root-ro-driver=}
            ;;
    esac
done

# check if read-only root fs is disabled
if [ ! -z "${DISABLE_ROOT_RO}" ]; then
    log_warning_msg "${MYTAG}: disabled, found boot parameter disable-root-ro=${DISABLE_ROOT_RO}"
    exit 0
fi
if [ -e "${rootmnt}${DISABLE_MAGIC_FILE}" ]; then
    log_warning_msg "${MYTAG}: disabled, found file ${rootmnt}${DISABLE_MAGIC_FILE}"
    exit 0
fi

# generic settings
# ${ROOT} and ${rootmnt} are predefined by caller of this script. Note that
# the root fs ${rootmnt} it mounted readonly on the initrams, which fits nicely
# for our purposes.
ROOT_RO=/mnt/root-ro
ROOT_RW=/mnt/root-rw
ROOT_RW_UPPER=${ROOT_RW}/upper
ROOT_RW_WORK=${ROOT_RW}/work

# check if ${ROOT_RO_DRIVER} is defined, otherwise set default
if [ -z "${ROOT_RO_DRIVER}" ]; then
    ROOT_RO_DRIVER=overlay
fi
# settings based in ${ROOT_RO_DRIVER}, stop here if unsupported.
case ${ROOT_RO_DRIVER} in
    overlay)
        MOUNT_PARMS="-t overlay -o lowerdir=${ROOT_RO},upperdir=${ROOT_RW_UPPER},workdir=${ROOT_RW_WORK} overlay ${rootmnt}"
        ;;
    aufs)
        MOUNT_PARMS="-t aufs -o dirs=${ROOT_RW}:${ROOT_RO}=ro aufs-root ${rootmnt}"
        ;;
    *)
        panic "${MYTAG} ERROR 1: invalid ROOT_RO_DRIVER ${ROOT_RO_DRIVER}"
        ;;
esac


# check if kernel module exists
modprobe -qb ${ROOT_RO_DRIVER}
if [ $? -ne 0 ]; then
    log_failure_msg "${MYTAG} ERROR 2: missing kernel module ${ROOT_RO_DRIVER}"
    exit 0
fi

# make the mount point on the init root fs ${ROOT_RW}
[ -d ${ROOT_RW} ] || mkdir -p ${ROOT_RW}
if [ $? -ne 0 ]; then
    log_failure_msg "${MYTAG} ERROR 3: failed to create ${ROOT_RW}"
    exit 0
fi

# make the mount point on the init root fs ${ROOT_RO}
[ -d ${ROOT_RO} ] || mkdir -p ${ROOT_RO}
if [ $? -ne 0 ]; then
    log_failure_msg "${MYTAG} ERROR 4: failed to create ${ROOT_RO}"
    exit 0
fi

# make the mount point on the init root fs ${ROOT_WORKDIR}
[ -d ${ROOT_WORKDIR} ] || mkdir -p ${ROOT_WORKDIR}
if [ $? -ne 0 ]; then
    log_failure_msg "${MYTAG} ERROR 5: failed to create ${ROOT_WORKDIR}"
    exit 0
fi


# mount a tempfs using the device name tmpfs-root at ${ROOT_RW}
mount -t tmpfs tmpfs-root ${ROOT_RW}
if [ $? -ne 0 ]; then
    log_failure_msg "${MYTAG} ERROR 6: failed to create tmpfs"
    exit 0
fi

if [ "${ROOT_RO_DRIVER}" = "overlay" ]; then

    [ -d ${ROOT_RW_UPPER} ] || mkdir -p ${ROOT_RW_UPPER}
    if [ $? -ne 0 ]; then
        log_failure_msg "${MYTAG} ERROR 6.1: failed to create ${ROOT_RW_UPPER}"
        exit 0
    fi

    [ -d ${ROOT_RW_WORK} ] || mkdir -p ${ROOT_RW_WORK}
    if [ $? -ne 0 ]; then
        log_failure_msg "${MYTAG} ERROR 6.2: failed to create ${ROOT_RW_WORK}"
        exit 0
    fi

fi


# root is mounted on ${rootmnt}, move it to ${ROOT_RO}.
mount -o move ${rootmnt} ${ROOT_RO}
if [ $? -ne 0 ]; then
    log_failure_msg "${MYTAG} ERROR 7: failed to move root away from ${rootmnt} to ${ROOT_RO}"
    exit 0
fi

# there is nothing left at ${rootmnt} now. So for any error we get we should
# either do recovery to restore ${rootmnt} for drop to a initramfs shell using
# "panic". Otherwise the boot process is very likely to fail with even more
# errors and leave the system in a wired state.

# mount virtual fs ${rootmnt} with rw-fs ${ROOT_RW} on top or ro-fs ${ROOT_RO}.
mount ${MOUNT_PARMS}
if [ $? -ne 0 ]; then
    log_failure_msg "${MYTAG} ERROR 8: failed to create new ro/rw layerd ${rootmnt}"
    # do recovery and try resoring the mount for ${rootmnt}
    mount -o move ${ROOT_RO} ${rootmnt}
    if [ $? -ne 0 ]; then
       # thats bad, drop to shell to let the user try fixing this
       panic "${MYTAG} RECOVERY ERROR: failed to move ${ROOT_RO} back to ${rootmnt}"
    fi
    exit 0
fi

# now the real root fs is on ${ROOT_RO} of the init file system, our layered
# root fs is set up at ${rootmnt}. So we can write anywhere in {rootmnt} and the
# changes will end up in ${ROOT_RW} while ${ROOT_RO} it not touched. However
# ${ROOT_RO} and ${ROOT_RW} are on the initramfs root fs, which will be removed
# an replaced by ${rootmnt}. Thus we must move ${ROOT_RO} and ${ROOT_RW} to the
# rootfs visible later, ie. ${rootmnt}${ROOT_RO} and ${rootmnt}${ROOT_RO}.
# Since the layered ro/rw is already up, these changes also end up on
# ${ROOT_RW} while ${ROOT_RO} is not touched.

# move mount from ${ROOT_RO} to ${rootmnt}${ROOT_RO}
[ -d ${rootmnt}${ROOT_RO} ] || mkdir -p ${rootmnt}${ROOT_RO}
mount -o move ${ROOT_RO} ${rootmnt}${ROOT_RO}
if [ $? -ne 0 ]; then
    log_failure_msg "${MYTAG} ERROR 9: failed to move ${ROOT_RO} to ${rootmnt}${ROOT_RO}"
    exit 0
fi

# move mount from ${ROOT_RW} to ${rootmnt}${ROOT_RW}
[ -d ${rootmnt}${ROOT_RW} ] || mkdir -p ${rootmnt}${ROOT_RW}
mount -o move ${ROOT_RW} ${rootmnt}${ROOT_RW}
if [ $? -ne 0 ]; then
    log_failure_msg "${MYTAG}: ERROR 10: failed to move ${ROOT_RW} to ${rootmnt}${ROOT_RW}"
    exit 0
fi
