disk: make PartitionTableType a string for otk-*

This commit switches the `PartitionTableType` from an enum to a
string. The reason is that the `otk` utils serialize this type
as a JSON. While the json is strictly internal and we make no
gurantees about it is still nicer to keep the strings because
otherwise the diff in the json looks something like:
```json
@@ -147,7 +147,7 @@ func TestUnmarshalOutput(t *testing.T) {
       "partition-table": {
         "Size": 911,
         "UUID": "",
-        "Type": "gpt",
+        "Type": 2,
         "Partitions": [
           {
             "Start": 0,
```
a perversing slightly easier dumability seems worth it (plus less
test code in cmd/otk/* needs to change).

cmd/otk/osbuild-gen-partition-table/main_test.go

@@ -147,7 +147,7 @@ func TestUnmarshalOutput(t *testing.T) {
       "partition-table": {
         "Size": 911,
         "UUID": "",
-        "Type": 0,
+        "Type": "",
         "Partitions": [
           {
             "Start": 0,
@@ -227,7 +227,7 @@ var expectedSimplePartOutput = `{
         "partition-table": {
           "Size": 11821645824,
           "UUID": "dbd21911-1c4e-4107-8a9f-14fe6e751358",
-          "Type": 2,
+          "Type": "gpt",
           "Partitions": [
             {
               "Start": 9048576,

pkg/disk/disk.go

@@ -119,39 +119,33 @@ func NewFSType(s string) (FSType, error) {
 	}
 }
 
-// PartitionTableType is the partition table type enum.
-type PartitionTableType uint64
+// PartitionTableType is the partition table type
+type PartitionTableType string
 
 const (
-	PT_NONE PartitionTableType = iota
-	PT_DOS
-	PT_GPT
+	PT_NONE PartitionTableType = ""
+	PT_DOS  PartitionTableType = "dos"
+	PT_GPT  PartitionTableType = "gpt"
 )
 
-func (t PartitionTableType) String() string {
-	switch t {
+func NewPartitionTableType(s string) (PartitionTableType, error) {
+	switch PartitionTableType(s) {
 	case PT_NONE:
-		return ""
+		return PT_NONE, nil
 	case PT_DOS:
-		return "dos"
+		return PT_DOS, nil
 	case PT_GPT:
-		return "gpt"
+		return PT_GPT, nil
 	default:
-		panic(fmt.Sprintf("unknown or unsupported partition table type with enum value %d", t))
+		return PT_NONE, fmt.Errorf("unknown or unsupported partition table type name: %s", s)
 	}
 }
 
-func NewPartitionTableType(s string) (PartitionTableType, error) {
-	switch s {
-	case "":
-		return PT_NONE, nil
-	case "dos":
-		return PT_DOS, nil
-	case "gpt":
-		return PT_GPT, nil
-	default:
-		return PT_NONE, fmt.Errorf("unknown or unsupported partition table type name: %s", s)
+func (t PartitionTableType) String() string {
+	if _, err := NewPartitionTableType(string(t)); err != nil {
+		panic(fmt.Sprintf("unknown or unsupported partition table type with value: %v", string(t)))
 	}
+	return string(t)
 }
 
 // Entity is the base interface for all disk-related entities.

pkg/disk/enums_test.go

@@ -26,8 +26,8 @@ func TestEnumPartitionTableType(t *testing.T) {
 	}
 
 	// error test: bad value
-	badPtt := disk.PartitionTableType(3)
-	assert.PanicsWithValue("unknown or unsupported partition table type with enum value 3", func() { _ = badPtt.String() })
+	badPtt := disk.PartitionTableType("bad")
+	assert.PanicsWithValue("unknown or unsupported partition table type with value: bad", func() { _ = badPtt.String() })
 
 	// error test: bad name
 	_, err := disk.NewPartitionTableType("not-a-type")

pkg/disk/partition_table.go

@@ -1109,7 +1109,7 @@ func mkBIOSBoot(ptType PartitionTableType) (Partition, error) {
 	case PT_GPT:
 		partType = BIOSBootPartitionGUID
 	default:
-		return Partition{}, fmt.Errorf("error creating BIOS boot partition: unknown or unsupported partition table enum: %d", ptType)
+		return Partition{}, fmt.Errorf("error creating BIOS boot partition: unknown or unsupported partition table type: %q", string(ptType))
 	}
 	return Partition{
 		Size:     1 * datasizes.MiB,
@@ -1127,7 +1127,7 @@ func mkESP(size uint64, ptType PartitionTableType) (Partition, error) {
 	case PT_GPT:
 		partType = EFISystemPartitionGUID
 	default:
-		return Partition{}, fmt.Errorf("error creating EFI system partition: unknown or unsupported partition table enum: %d", ptType)
+		return Partition{}, fmt.Errorf("error creating EFI system partition: unknown or unsupported partition table type: %q", string(ptType))
 	}
 	return Partition{
 		Size: size,

pkg/disk/partition_table_test.go

@@ -1185,19 +1185,19 @@ func TestAddPartitionsForBootMode(t *testing.T) {
 			},
 		},
 		"bad-pttype-bios": {
-			pt:       disk.PartitionTable{Type: disk.PartitionTableType(911)},
+			pt:       disk.PartitionTable{Type: disk.PartitionTableType("bad")},
 			bootMode: platform.BOOT_LEGACY,
-			errmsg:   "error creating BIOS boot partition: unknown or unsupported partition table enum: 911",
+			errmsg:   `error creating BIOS boot partition: unknown or unsupported partition table type: "bad"`,
 		},
 		"bad-pttype-uefi": {
-			pt:       disk.PartitionTable{Type: disk.PartitionTableType(911)},
+			pt:       disk.PartitionTable{Type: disk.PartitionTableType("bad")},
 			bootMode: platform.BOOT_UEFI,
-			errmsg:   "error creating EFI system partition: unknown or unsupported partition table enum: 911",
+			errmsg:   `error creating EFI system partition: unknown or unsupported partition table type: "bad"`,
 		},
 		"bad-pttype-hybrid": {
-			pt:       disk.PartitionTable{Type: disk.PartitionTableType(911)},
+			pt:       disk.PartitionTable{Type: disk.PartitionTableType("bad")},
 			bootMode: platform.BOOT_HYBRID,
-			errmsg:   "error creating BIOS boot partition: unknown or unsupported partition table enum: 911",
+			errmsg:   `error creating BIOS boot partition: unknown or unsupported partition table type: "bad"`,
 		},
 		"bad-bootmode": {
 			pt:       disk.PartitionTable{Type: disk.PT_GPT},