refact(image-factory): Detect boot and root partition by filesystem type

The debug shell derived the partition numbers from TARGET, which meant
it had to be told the layout it was about to inspect. blkid reports the
filesystem, so vfat is the boot partition and btrfs the root one for
every layout.

Signed-off-by: Simon Walz <contact@simonwalz.de>

Author: simonwalz

image-factory/mount_image.sh

@@ -38,17 +38,33 @@ partprobe "${LOOPDEV}"
 kpartx -av "${LOOPDEV}"
 sleep 1
 
-if [[ "${TARGET}" == "rpi" ]]; then
-  TARGET_BOOT_PARTITION_NUM=1
-  TARGET_ROOT_PARTITION_NUM=2
-else
-  TARGET_BOOT_PARTITION_NUM=2
-  TARGET_ROOT_PARTITION_NUM=3
-fi
+# Find the boot and root partitions by filesystem type. The partition numbers
+# differ per layout: MBR + FAT boot (1/2), GPT + bios_grub + ESP (2/3).
+LOOP_NAME="$(basename "${LOOPDEV}")"
+TARGET_BOOT_PARTITION=""
+TARGET_ROOT_PARTITION=""
+
+for part in "/dev/mapper/${LOOP_NAME}p"*; do
+	[[ -b "${part}" ]] || continue
+	case "$(blkid -s TYPE -o value "${part}" 2>/dev/null)" in
+		vfat)
+			[[ -n "${TARGET_BOOT_PARTITION}" ]] || TARGET_BOOT_PARTITION="${part}"
+			;;
+		btrfs)
+			[[ -n "${TARGET_ROOT_PARTITION}" ]] || TARGET_ROOT_PARTITION="${part}"
+			;;
+	esac
+done
+
+[[ -n "${TARGET_BOOT_PARTITION}" ]] \
+	|| raise "No FAT boot partition found in ${IMAGE}. Was the image built?"
+[[ -n "${TARGET_ROOT_PARTITION}" ]] \
+	|| raise "No BTRFS root partition found in ${IMAGE}. Was the image built?"
+
+echo "Boot partition: ${TARGET_BOOT_PARTITION} (vfat)"
+echo "Root partition: ${TARGET_ROOT_PARTITION} (btrfs)"
 
-TARGET_BOOT_PARTITION="/dev/mapper/$(basename "${LOOPDEV}")p${TARGET_BOOT_PARTITION_NUM}"
 export TARGET_BOOT_PARTITION
-TARGET_ROOT_PARTITION="/dev/mapper/$(basename "${LOOPDEV}")p${TARGET_ROOT_PARTITION_NUM}"
 export TARGET_ROOT_PARTITION
 TARGET_BOOT="${TARGET_BOOT:-"/mnt/boot"}"
 TARGET_ROOT="${TARGET_ROOT:-"/mnt/os"}"