Implement config parser.

zfs/mapping.go

@@ -64,6 +64,11 @@ type DirectMapping struct {
 }
 
 func (m DirectMapping) Map(source DatasetPath) (target DatasetPath, err error) {
+
+	if m.Source == nil {
+		return m.Target, nil
+	}
+
 	if len(m.Source) != len(source) {
 		return nil, NoMatchError
 	}

zfs/zfs.go

@@ -35,6 +35,11 @@ func (p DatasetPath) ToString() string {
 	return strings.Join(p, "/")
 }
 
+func NewDatasetPath(s string) (p DatasetPath, err error) {
+	// TODO validation
+	return toDatasetPath(s), nil
+}
+
 func toDatasetPath(s string) DatasetPath {
 	return strings.Split(s, "/")
 }