openwrt/package/base-files/files/lib/firstboot/40_copy_ramoverlay

#!/bin/sh

# Copyright (C) 2006-2010 OpenWrt.org
# Copyright (C) 2010 Vertical Communications

copy_ramoverlay() {
    # try to avoid fs changing while copying
    mount -o remount,ro none / 2>&-
    # copy ramoverlay to jffs2
    echo -n "copying files ... "
    cp -a /tmp/root/* /rom/overlay 2>&-
    echo "done"
}

boot_hook_add switch2jffs copy_ramoverlay