config/fcos: warn if partition number for root isn't correct

Fixes coreos#243

This change warns if the partition number for the root label is not
specified or wrongly mentioned.

config/common/errors.go

@@ -47,6 +47,9 @@ var (
 	ErrUnknownBootDeviceLayout = errors.New("layout must be one of: aarch64, ppc64le, x86_64")
 	ErrTooFewMirrorDevices     = errors.New("mirroring requires at least two devices")
 
+	// partition
+	ErrWrongPartitionNumberForRoot = errors.New("new partition using reserved label \"root\"")
+
 	// MachineConfigs
 	ErrFieldElided            = errors.New("field ignored in raw mode")
 	ErrNameRequired           = errors.New("metadata.name is required")

config/fcos/v1_3/translate.go

@@ -64,6 +64,13 @@ func (c Config) ToIgn3_2Unvalidated(options common.TranslateOptions) (types.Conf
 		return types.Config{}, translate.TranslationSet{}, r
 	}
 	r.Merge(c.processBootDevice(&ret, &ts, options))
+	for _, disk := range ret.Storage.Disks {
+		for _, partition := range disk.Partitions {
+			if *partition.Label == "root" && partition.Number != 4 {
+				r.AddOnWarn(path.New("yaml", "fcos", "partition"), common.ErrWrongPartitionNumberForRoot)
+			}
+		}
+	}
 	return ret, ts, r
 }
 

config/fcos/v1_4/translate.go

@@ -64,6 +64,13 @@ func (c Config) ToIgn3_3Unvalidated(options common.TranslateOptions) (types.Conf
 		return types.Config{}, translate.TranslationSet{}, r
 	}
 	r.Merge(c.processBootDevice(&ret, &ts, options))
+	for _, disk := range ret.Storage.Disks {
+		for _, partition := range disk.Partitions {
+			if *partition.Label == "root" && partition.Number != 4 {
+				r.AddOnWarn(path.New("yaml", "fcos", "partition"), common.ErrWrongPartitionNumberForRoot)
+			}
+		}
+	}
 	return ret, ts, r
 }
 

config/fcos/v1_5_exp/translate.go

@@ -64,6 +64,13 @@ func (c Config) ToIgn3_4Unvalidated(options common.TranslateOptions) (types.Conf
 		return types.Config{}, translate.TranslationSet{}, r
 	}
 	r.Merge(c.processBootDevice(&ret, &ts, options))
+	for _, disk := range ret.Storage.Disks {
+		for _, partition := range disk.Partitions {
+			if *partition.Label == "root" && partition.Number != 4 {
+				r.AddOnWarn(path.New("yaml", "fcos", "partition"), common.ErrWrongPartitionNumberForRoot)
+			}
+		}
+	}
 	return ret, ts, r
 }