openwrt: revive 4MB flash devices! updated for 22.03

openwrt-revive-small-flash-default-ram-mount-with-etc-persistence.sh

mkdir -p openwrt-rootfs/lib/preinit
[ ! -f openwrt-rootfs/lib/preinit/80_mount_root ] && cat <<'EOF' > openwrt-rootfs/lib/preinit/80_mount_root
# Copyright (C) 2006 OpenWrt.org
# Copyright (C) 2010 Vertical Communications

ram_mount_root() {
	echo "- ram overlay -"
	rdev=$(find_mtd_part rootfs_data)
	if [ -z "$rdev" ]; then
		echo "- bad rdev -"
		return
	fi
	mount $rdev /overlay -o noatime -t jffs2 || {
		echo "- overlay failed, please try jffs2reset -"
		return
	}
	[ -f /overlay/sysupgrade.tgz ] && ln -s /overlay/sysupgrade.tgz /sysupgrade.tgz
	mkdir -p /overlay/upper/etc
	# note: custom init script in /etc/rc.local only
	rm -rf /overlay/upper/etc/init.d 2>/dev/null
	mkdir -p /overlay/work
	mkdir -p /tmp/etc-init.d/upper
	mkdir -p /tmp/etc-init.d/work
	/bin/mount -o noatime,lowerdir=/rom/etc,upperdir=/overlay/upper/etc,workdir=/overlay/work -t overlay "overlayfs:/etc" /etc
	/bin/mount -o noatime,lowerdir=/rom/etc/init.d,upperdir=/tmp/etc-init.d/upper,workdir=/tmp/etc-init.d/work -t overlay "overlayfs:/etc/init.d" /etc/init.d
}

missing_lines() {
	local file1 file2 line
	file1="$1"
	file2="$2"
	oIFS="$IFS"
	IFS=":"
	while read line; do
		set -- $line
		grep -q "^$1:" "$file2" || echo "$*"
	done < "$file1"
	IFS="$oIFS"
}

do_mount_root() {
	mount_root ram
	ram_mount_root || true
	boot_run_hook preinit_mount_root
	[ -f /sysupgrade.tgz -o -f /tmp/sysupgrade.tar ] && {
		echo "- config restore -"
		cp /etc/passwd /etc/group /etc/shadow /tmp
		cd /
		[ -f /sysupgrade.tgz ] && tar xzf /sysupgrade.tgz
		[ -f /tmp/sysupgrade.tar ] && tar xf /tmp/sysupgrade.tar
		missing_lines /tmp/passwd /etc/passwd >> /etc/passwd
		missing_lines /tmp/group /etc/group >> /etc/group
		missing_lines /tmp/shadow /etc/shadow >> /etc/shadow
		rm /tmp/passwd /tmp/group /tmp/shadow
		# Prevent configuration corruption on a power loss
		sync
	}
}

[ "$INITRAMFS" = "1" ] || boot_hook_add preinit_main do_mount_root
EOF
mkdir -p openwrt-rootfs/etc/init.d
[ ! -f openwrt-rootfs/etc/init.d/done ] && cat <<'EOF' > openwrt-rootfs/etc/init.d/done
#!/bin/sh /etc/rc.common
# Copyright (C) 2006 OpenWrt.org

START=95
boot() {
        mount_root done
        rm -f /sysupgrade.tgz
        rm -f /overlay/sysupgrade.tgz

        # process user commands
        [ -f /etc/rc.local ] && {
                sh /etc/rc.local
        }

        # set leds to normal state
        . /etc/diag.sh
        set_state done
}
EOF
chmod +x openwrt-rootfs/etc/init.d/done

example usage:

make image FILES="path/to/openwrt-rootfs" PROFILE="tplink_tl-wr703n" PACKAGES="base-files -ca-bundle dropbear fstools libc libgcc -libustream-wolfssl logd mtd netifd opkg uci -uclient-fetch urandom-seed urngd busybox procd procd-seccomp kmod-gpio-button-hotplug swconfig -kmod-ath9k uboot-envtools -wpad-basic-wolfssl dnsmasq firewall4 nftables kmod-nft-offload odhcp6c -odhcpd-ipv6only -ppp -ppp-mod-pppoe -kmod-usb-chipidea2"