init-bottom-overlay

#!/bin/sh

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

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

. /scripts/functions

if grep -q -E '(^|\s)skipoverlay(\s|$)' /proc/cmdline; then
	log_begin_msg "Skipping overlay, found 'skipoverlay' in cmdline"
	log_end_msg
	exit 0
fi

log_begin_msg "Starting overlay"
log_end_msg

# default is for the activity light to blink on sd card access
# but with tmpfs overlay there's not as much activity
echo cpu0 > /sys/class/leds/led0/trigger

mkdir -p /overlay

# if we have a filesystem label of overlaytmp
# use that as the overlay, otherwise use tmpfs.
# overlaytmp is semi permanent, it can get wiped though.
# also, overlaytmp on usb doesn't get unmounted.
# i don't have a head to watch shutdown messages
# so I don't know why. which means if you put
# overlaytmp on usb, it's probably going to get
# formated every boot, which will slow boot speed
OLDEV=`blkid -L overlaytmp`
if [ -z "${OLDEV}" ]; then
	mount -t tmpfs tmpfs /overlay
else
	_checkfs_once ${OLDEV} /overlay >> /log.txt 2>&1 ||  \
	mke2fs -FL overlaytmp -t ext4 -E lazy_itable_init,lazy_journal_init ${OLDEV}
	mount ${OLDEV} /overlay
fi

# if you sudo touch /overlay/reformatoverlay
# next reboot will give you a fresh /overlay
if [ -f /overlay/reformatoverlay ]; then
	umount /overlay
	mke2fs -FL overlaytmp -t ext4 -E lazy_itable_init,lazy_journal_init ${OLDEV}
	mount ${OLDEV} /overlay
fi

mkdir -p /overlay/upper
mkdir -p /overlay/work
mkdir -p /overlay/lower

# make the readonly root available
mount -n -o move ${rootmnt} /overlay/lower
mount -t overlay overlay -olowerdir=/overlay/lower,upperdir=/overlay/upper,workdir=/overlay/work ${rootmnt}

mkdir -p ${rootmnt}/overlay
mount -n -o rbind /overlay ${rootmnt}/overlay

# fix up fstab
cp ${rootmnt}/etc/fstab ${rootmnt}/etc/fstab.orig
awk '$2 != "/" {print $0}' ${rootmnt}/etc/fstab.orig > ${rootmnt}/etc/fstab
awk '$2 == "'${rootmnt}'" { $2 = "/" ; print $0}' /etc/mtab >> ${rootmnt}/etc/fstab

exit 0