zfs: ability to specify sources for zfsGet

fix use for Placeholder, leave rest as previous behavior

zfs/zfs_test.go

@@ -30,3 +30,41 @@ func TestDatasetPathTrimNPrefixComps(t *testing.T) {
 	p.TrimNPrefixComps((1))
 	assert.True(t, p.Empty(), "empty trimming shouldn't do harm")
 }
+
+func TestZFSPropertySource(t *testing.T) {
+
+	tcs := []struct{
+		in zfsPropertySource
+		exp []string
+	}{
+		{
+			in: sourceAny,
+			exp: []string{"local", "default", "inherited", "-", "temporary"},
+		},
+		{
+			in: sourceTemporary,
+			exp: []string{"temporary"},
+		},
+		{
+			in: sourceLocal|sourceInherited,
+			exp: []string{"local", "inherited"},
+		},
+	}
+
+	toSet := func(in []string) map[string]struct{} {
+		m := make(map[string]struct{}, len(in))
+		for _, s := range in {
+			m[s] = struct{}{}
+		}
+		return m
+	}
+
+	for _, tc := range tcs {
+
+		res := tc.in.zfsGetSourceFieldPrefixes()
+		resSet := toSet(res)
+		expSet := toSet(tc.exp)
+		assert.Equal(t, expSet, resSet)
+	}
+
+}