get_magic_at() {
	local file="$1"
	local pos="$2"
	get_image "$file" | dd bs=1 count=2 skip="$pos" 2>/dev/null | hexdump -v -n 2 -e '1/1 "%02x"'
}

platform_check_image_sdcard() {
	local file="$1"
	local magic diskdev partdev diff

	magic=$(get_magic_at "$file" 510)
	[ "$magic" != "55aa" ] && {
		echo "Failed to verify MBR boot signature."
		return 1
	}

	export_bootdevice && export_partdevice diskdev 0 || {
		echo "Unable to determine upgrade device"
	return 1
	}

	get_partitions "/dev/$diskdev" bootdisk

	#extract the boot sector from the image
	get_image "$@" | dd of=/tmp/image.bs count=1 bs=512b 2>/dev/null

	get_partitions /tmp/image.bs image

	#compare tables
	diff="$(grep -F -x -v -f /tmp/partmap.bootdisk /tmp/partmap.image)"

	rm -f /tmp/image.bs /tmp/partmap.bootdisk /tmp/partmap.image

	if [ -n "$diff" ]; then
		echo "Partition layout has changed. Full image will be written."
		ask_bool 0 "Abort" && exit 1
		return 0
	fi
}

platform_do_upgrade_sdcard() {
	local board=$(board_name)
	local diskdev partdev diff

	export_bootdevice && export_partdevice diskdev 0 || {
		echo "Unable to determine upgrade device"
	return 1
	}

	sync

	if [ "$UPGRADE_OPT_SAVE_PARTITIONS" = "1" ]; then
		get_partitions "/dev/$diskdev" bootdisk

		#extract the boot sector from the image
		get_image "$@" | dd of=/tmp/image.bs count=1 bs=512b

		get_partitions /tmp/image.bs image

		#compare tables
		diff="$(grep -F -x -v -f /tmp/partmap.bootdisk /tmp/partmap.image)"
	else
		diff=1
	fi

	if [ -n "$diff" ]; then
		get_image "$@" | dd of="/dev/$diskdev" bs=4096 conv=fsync

		# Separate removal and addtion is necessary; otherwise, partition 1
		# will be missing if it overlaps with the old partition 2
		partx -d - "/dev/$diskdev"
		partx -a - "/dev/$diskdev"
	else
		#write uboot image
		get_image "$@" | dd of="$diskdev" bs=512 skip=1 seek=1 count=2048 conv=fsync
		#iterate over each partition from the image and write it to the boot disk
		while read part start size; do
			if export_partdevice partdev $part; then
				echo "Writing image to /dev/$partdev..."
				get_image "$@" | dd of="/dev/$partdev" ibs="512" obs=1M skip="$start" count="$size" conv=fsync
			else
				echo "Unable to find partition $part device, skipped."
			fi
		done < /tmp/partmap.image

		#copy partition uuid
		echo "Writing new UUID to /dev/$diskdev..."
		get_image "$@" | dd of="/dev/$diskdev" bs=1 skip=440 count=4 seek=440 conv=fsync
	fi

	sleep 1
}

platform_copy_config_sdcard() {
	local partdev

	if export_partdevice partdev 1; then
		mkdir -p /boot
		[ -f /boot/kernel.img ] || mount -o rw,noatime /dev/$partdev /boot
		cp -af "$UPGRADE_BACKUP" "/boot/$BACKUP_FILE"
		sync
		umount /boot
	fi
}