istoreos: fallback overlay partition when disks id conflict

package/base-files/files/lib/functions/istoreos-boot.sh

@@ -1,17 +1,62 @@
 
+get_overlay_partition_fallback()
+{
+	local cmdline rootpart overlay_dev class
+	local MAJOR MINOR
+	if read cmdline < /proc/cmdline; then
+		case "$cmdline" in
+			*root=*)
+				rootpart="${cmdline##*root=}"
+				rootpart="${rootpart%% *}"
+			;;
+		esac
+		case "$rootpart" in
+			PARTUUID=[a-f0-9][a-f0-9][a-f0-9][a-f0-9][a-f0-9][a-f0-9][a-f0-9][a-f0-9]-02)
+				overlay_dev=`blkid -l -o device -t "${rootpart%-02}-03"`
+			;;
+			PARTUUID=????????-????-????-????-??????????02)
+				overlay_dev=`blkid -l -o device -t "${rootpart%02}03"`
+			;;
+			/dev/*)
+				overlay_dev="${rootpart%2}3"
+			;;
+			0x[a-f0-9][a-f0-9][a-f0-9] | 0x[a-f0-9][a-f0-9][a-f0-9][a-f0-9] | \
+			[a-f0-9][a-f0-9][a-f0-9] | [a-f0-9][a-f0-9][a-f0-9][a-f0-9])
+				rootpart=0x${rootpart#0x}
+				for class in /sys/class/block/*; do
+					while read line; do
+						export -n "$line"
+					done < "$class/uevent"
+					if [ $((rootpart/256)) = $MAJOR -a $(((rootpart%256) + 1)) = $MINOR ]; then
+						overlay_dev="/dev/${class#/sys/class/block/}"
+						break
+					fi
+				done
+			;;
+		esac
+		[ -z "$overlay_dev" ] && return 1
+		OVERLAY_DEV="$overlay_dev"
+		return 0
+	fi
+	return 1
+}
+
 . /lib/upgrade/common.sh
 
-get_overlay_partition()
+get_overlay_partition_default()
 {
 	local overlay_dev
-	export_bootdevice && export_partdevice overlay_dev 3 || {
+	export_bootdevice && export_partdevice overlay_dev 3 || return 1
+	[ -z "$overlay_dev" ] && return 1
+	OVERLAY_DEV="/dev/$overlay_dev"
+	return 0
+}
+
+get_overlay_partition()
+{
+	get_overlay_partition_default || get_overlay_partition_fallback || {
 		log "Unable to determine overlay partition"
 		return 1
 	}
-	if [ -z "$overlay_dev" ]; then
-		log "Unable to determine overlay partition"
-		return 1
-	fi
-	OVERLAY_DEV="/dev/$overlay_dev"
-
+	return 0
 }