#!/bin/sh

# Get the value of the root env variable found in /proc/cmdline
get_root() {
    local root="$(cat /proc/cmdline)"
    root="${root##* root=PARTLABEL=}"
    root="${root%% *}"
    [ "${root}" != "" ] && echo "${root}"
}

fslist="proc sys dev run"
rodir=/mnt/rofs
cd /
mkdir -p $fslist
mount dev dev -tdevtmpfs
mount sys sys -tsysfs
mount proc proc -tproc
mount tmpfs run -t tmpfs -o mode=755,nodev

# Move the secondary GPT to the end of the device if needed. Look for the GPT
# header signature "EFI PART" located 512 bytes from the end of the device.
magic=$(tail -c 512 /dev/mmcblk0 | hexdump -C -n 8 | grep "EFI PART")
if test -z "${magic}"; then
    sgdisk -e /dev/mmcblk0
    partprobe
fi

# There eMMC GPT labels for the rootfs are rofs-a and rofs-b, and the label for
# the read-write partition is rwfs. Run udev to make the partition labels show 
# up. Mounting by label allows for partition numbers to change if needed.
udevd --daemon
udevadm trigger --type=devices --action=add
udevadm settle --timeout=10

mkdir -p $rodir
if ! mount /dev/disk/by-partlabel/"$(get_root)" $rodir -t ext4 -o ro; then
    /bin/sh
fi
if ! mount /dev/disk/by-partlabel/rwfs $rodir/var -t ext4 -o rw; then
    /bin/sh
fi

rm -rf $rodir/var/persist/etc-work/
mkdir -p $rodir/var/persist/etc $rodir/var/persist/etc-work $rodir/var/persist/home/root
mount overlay $rodir/etc -t overlay -o lowerdir=$rodir/etc,upperdir=$rodir/var/persist/etc,workdir=$rodir/var/persist/etc-work

for f in $fslist; do
    mount --move $f $rodir/$f
done

exec chroot $rodir /sbin/init