FriendlyElec NanoPi Duo2 make SD card readonly with temporary ramdisk overlay, in order to avoid filesystem corruption

rootfs.cpio.scripts.local.patch

--- a/scripts/local	2019-10-17 07:29:20.000000000 +0200
+++ b/scripts/local	2021-05-12 20:30:38.000000000 +0200
@@ -198,56 +198,10 @@
 
 local_mount_overlay()
 {
-	# Test (mmc) block device
-	[ -b "${USERDATA%p*}" ] && \
-	   [ -b "${USERDATA}" ] || return
-
-	local_device_setup "${USERDATA}" "userdata file system"
-	DATA="${DEV}"
-	RESIZE_STAT=${datamnt}/.ext4.resized
-
-	if [ -z "${ROOTFSTYPE}" ]; then
-		FSTYPE=$(get_fstype "${DATA}")
-	else
-		FSTYPE=${ROOTFSTYPE}
-	fi
-
-	if [ "$wipedata" = "y" ]; then
-		roflag=-w
-		remountopts=
-
-		true ${FSTYPE:="ext4"}
-		mkfs.${FSTYPE} -F -L userdata ${DATA}
-		[ $? -eq 0 ] && :> ${RESIZE_STAT} && sync
-	else
-		roflag=-r
-		remountopts="-o remount,rw"
-
-		checkfs ${DATA} userdata "${FSTYPE}"
-	fi
-
-	mount ${roflag} ${FSTYPE:+-t ${FSTYPE} }${ROOTFLAGS} ${DATA} ${datamnt}
+	RW_SIZE=256m
+	mount -t tmpfs -o "size=${RW_SIZE}" overlay-rw ${datamnt}
 	mountoverlay_status="$?"
 
-	# Resize userdata filesystem
-	if [ -n "${remountopts}" ]; then
-		if [ -f ${RESIZE_STAT} ]; then
-			mount ${remountopts} ${datamnt}
-			mountoverlay_status="$?"
-
-		elif [ "${FSTYPE%[234]}" = "ext" ]; then
-			umount ${datamnt}
-			local_resize_ext4 ${DATA}
-
-			mount -w ${FSTYPE:+-t ${FSTYPE} }${ROOTFLAGS} ${DATA} ${datamnt}
-			mountoverlay_status="$?"
-
-			if [ "$resizepart_status" -eq 0 ]; then
-				:> ${RESIZE_STAT} && sync
-			fi
-		fi
-	fi
-
 	[ "$mountoverlay_status" != 0 ] && return
 
 	# Prepare & mount overlayfs
@@ -300,25 +254,9 @@
 	mount ${roflag} ${FSTYPE:+-t ${FSTYPE} }${ROOTFLAGS} ${ROOT} ${rootmnt}
 	mountroot_status="$?"
 
-	# Resize root filesystem
 	if [ -n "${remountopts}" ]; then
-		RESIZE_STAT=${rootmnt}/etc/fs.resized
-
-		if [ -f ${RESIZE_STAT} ]; then
-			mount ${remountopts} ${rootmnt}
-			mountroot_status="$?"
-
-		elif [ "${FSTYPE%[234]}" = "ext" ]; then
-			umount ${rootmnt}
-			local_resize_ext4 ${ROOT}
-
-			mount -w ${FSTYPE:+-t ${FSTYPE} }${ROOTFLAGS} ${ROOT} ${rootmnt}
-			mountroot_status="$?"
-
-			if [ "$resizepart_status" -eq 0 ]; then
-				:> ${RESIZE_STAT} && sync
-			fi
-		fi
+		mount ${remountopts} ${rootmnt}
+		mountroot_status="$?"
 	fi
 
 	if [ "$LOOP" ]; then