disk: define PartitionTableType enum for partition table types

Add a new enum, PartitionTableType, for referring to the two partition
table types, "dos" and "gpt".
This is currently not used but will be part of the new custom partition
table generator.

pkg/disk/disk.go

@@ -110,6 +110,41 @@ func NewFSType(s string) (FSType, error) {
 	}
 }
 
+// PartitionTableType is the partition table type enum.
+type PartitionTableType uint64
+
+const (
+	PT_NONE PartitionTableType = iota
+	PT_DOS
+	PT_GPT
+)
+
+func (t PartitionTableType) String() string {
+	switch t {
+	case PT_NONE:
+		return ""
+	case PT_DOS:
+		return "dos"
+	case PT_GPT:
+		return "gpt"
+	default:
+		panic(fmt.Sprintf("unknown or unsupported partition table type with enum value %d", t))
+	}
+}
+
+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)
+	}
+}
+
 // Entity is the base interface for all disk-related entities.
 type Entity interface {
 	// Clone returns a deep copy of the entity.