disk: set the BIOS boot and ESP partition type correctly for dos

Define two new const strings: DosBIOSBootID and DosESPID, which are used
for the BIOS boot and the EFI system partitions respectively on dos/mbr
partition tables.

In the new helper functions, use the partition table type to determine
which ID to use.  This means that the functions will return an error
when the partition table type is not set (or is set to an unknown
value).

pkg/disk/disk.go

@@ -63,6 +63,12 @@ const (
 
 	// Partition type ID for any native Linux filesystem on dos
 	DosLinuxTypeID = "83"
+
+	// Partition type ID for BIOS boot partition on dos
+	DosBIOSBootID = "ef02"
+
+	// Partition type ID for ESP on dos
+	DosESPID = "ef00"
 )
 
 // FSType is the filesystem type enum.

pkg/disk/partition_table.go

@@ -1068,16 +1068,31 @@ func AddPartitionsForBootMode(pt *PartitionTable, bootMode platform.BootMode) er
 	switch bootMode {
 	case platform.BOOT_LEGACY:
 		// add BIOS boot partition
-		pt.Partitions = append(pt.Partitions, mkBIOSBoot())
+		part, err := mkBIOSBoot(pt.Type)
+		if err != nil {
+			return err
+		}
+		pt.Partitions = append(pt.Partitions, part)
 		return nil
 	case platform.BOOT_UEFI:
 		// add ESP
-		pt.Partitions = append(pt.Partitions, mkESP(200*datasizes.MiB))
+		part, err := mkESP(200*datasizes.MiB, pt.Type)
+		if err != nil {
+			return err
+		}
+		pt.Partitions = append(pt.Partitions, part)
 		return nil
 	case platform.BOOT_HYBRID:
 		// add both
-		pt.Partitions = append(pt.Partitions, mkBIOSBoot())
-		pt.Partitions = append(pt.Partitions, mkESP(200*datasizes.MiB))
+		bios, err := mkBIOSBoot(pt.Type)
+		if err != nil {
+			return err
+		}
+		esp, err := mkESP(200*datasizes.MiB, pt.Type)
+		if err != nil {
+			return err
+		}
+		pt.Partitions = append(pt.Partitions, bios, esp)
 		return nil
 	case platform.BOOT_NONE:
 		return nil
@@ -1086,19 +1101,37 @@ func AddPartitionsForBootMode(pt *PartitionTable, bootMode platform.BootMode) er
 	}
 }
 
-func mkBIOSBoot() Partition {
+func mkBIOSBoot(ptType string) (Partition, error) {
+	var partType string
+	switch ptType {
+	case "dos":
+		partType = DosBIOSBootID
+	case "gpt":
+		partType = BIOSBootPartitionGUID
+	default:
+		return Partition{}, fmt.Errorf("error creating BIOS boot partition: unknown or unsupported partition table type: %s", ptType)
+	}
 	return Partition{
 		Size:     1 * datasizes.MiB,
 		Bootable: true,
-		Type:     BIOSBootPartitionGUID,
+		Type:     partType,
 		UUID:     BIOSBootPartitionUUID,
-	}
+	}, nil
 }
 
-func mkESP(size uint64) Partition {
+func mkESP(size uint64, ptType string) (Partition, error) {
+	var partType string
+	switch ptType {
+	case "dos":
+		partType = DosESPID
+	case "gpt":
+		partType = EFISystemPartitionGUID
+	default:
+		return Partition{}, fmt.Errorf("error creating EFI system partition: unknown or unsupported partition table type: %s", ptType)
+	}
 	return Partition{
 		Size: size,
-		Type: EFISystemPartitionGUID,
+		Type: partType,
 		UUID: EFISystemPartitionUUID,
 		Payload: &Filesystem{
 			Type:         "vfat",
@@ -1109,5 +1142,5 @@ func mkESP(size uint64) Partition {
 			FSTabFreq:    0,
 			FSTabPassNo:  2,
 		},
-	}
+	}, nil
 }