disk: extract getDevicesNoRename() and tweak getDevices()

We currently do a lot of:
```
lastDevice := stageDevices[lastName]
delete(stageDevices, lastName)
stageDevices["device"] = lastDevice
```
which this commit consolidates into the `getDevices()` helper.
The only place that needs the "old" behavior is
`GenMountsDevicesFromPT` and here we can use the new
`getDevicesNoRename()` helper.

Note that this is still pretty messy and needs further refactor.

pkg/osbuild/device.go

@@ -27,13 +27,7 @@ func GenDeviceCreationStages(pt *disk.PartitionTable, filename string) []*Stage
 		switch ent := e.(type) {
 		case *disk.LUKSContainer:
 			// do not include us when getting the devices
-			stageDevices, lastName := getDevices(path[:len(path)-1], filename, true)
-
-			// "org.osbuild.luks2.format" expects a "device" to create the VG on,
-			// thus rename the last device to "device"
-			lastDevice := stageDevices[lastName]
-			delete(stageDevices, lastName)
-			stageDevices["device"] = lastDevice
+			stageDevices := getDevices(path[:len(path)-1], filename, true)
 
 			stage := NewLUKS2CreateStage(
 				&LUKS2CreateStageOptions{
@@ -64,13 +58,7 @@ func GenDeviceCreationStages(pt *disk.PartitionTable, filename string) []*Stage
 
 		case *disk.LVMVolumeGroup:
 			// do not include us when getting the devices
-			stageDevices, lastName := getDevices(path[:len(path)-1], filename, true)
-
-			// "org.osbuild.lvm2.create" expects a "device" to create the VG on,
-			// thus rename the last device to "device"
-			lastDevice := stageDevices[lastName]
-			delete(stageDevices, lastName)
-			stageDevices["device"] = lastDevice
+			stageDevices := getDevices(path[:len(path)-1], filename, true)
 
 			volumes := make([]LogicalVolume, len(ent.LogicalVolumes))
 			for idx, lv := range ent.LogicalVolumes {
@@ -104,11 +92,7 @@ func GenDeviceFinishStages(pt *disk.PartitionTable, filename string) []*Stage {
 		switch ent := e.(type) {
 		case *disk.LUKSContainer:
 			// do not include us when getting the devices
-			stageDevices, lastName := getDevices(path[:len(path)-1], filename, true)
-
-			lastDevice := stageDevices[lastName]
-			delete(stageDevices, lastName)
-			stageDevices["device"] = lastDevice
+			stageDevices := getDevices(path[:len(path)-1], filename, true)
 
 			if ent.Clevis != nil {
 				if ent.Clevis.RemovePassphrase {
@@ -119,13 +103,7 @@ func GenDeviceFinishStages(pt *disk.PartitionTable, filename string) []*Stage {
 			}
 		case *disk.LVMVolumeGroup:
 			// do not include us when getting the devices
-			stageDevices, lastName := getDevices(path[:len(path)-1], filename, true)
-
-			// "org.osbuild.lvm2.metadata" expects a "device" to rename the VG,
-			// thus rename the last device to "device"
-			lastDevice := stageDevices[lastName]
-			delete(stageDevices, lastName)
-			stageDevices["device"] = lastDevice
+			stageDevices := getDevices(path[:len(path)-1], filename, true)
 
 			stage := NewLVM2MetadataStage(
 				&LVM2MetadataStageOptions{
@@ -180,7 +158,7 @@ func deviceName(p disk.Entity) string {
 // The first returned value is a map of devices for the given path.
 // The second returned value is the name of the last device in the path. This is the device that should be used as the
 // source for the mount.
-func getDevices(path []disk.Entity, filename string, lockLoopback bool) (map[string]Device, string) {
+func getDevicesNoRename(path []disk.Entity, filename string, lockLoopback bool) (map[string]Device, string) {
 	var pt *disk.PartitionTable
 
 	do := make(map[string]Device)
@@ -219,9 +197,22 @@ func getDevices(path []disk.Entity, filename string, lockLoopback bool) (map[str
 			parent = name
 		}
 	}
+
 	return do, parent
 }
 
+func getDevices(path []disk.Entity, filename string, lockLoopback bool) map[string]Device {
+	do, parent := getDevicesNoRename(path, filename, lockLoopback)
+
+	// The last device in the chain must be named "device", because that's the device that mkfs stages run on.
+	// See their schema for reference.
+	lastDevice := do[parent]
+	delete(do, parent)
+	do["device"] = lastDevice
+
+	return do
+}
+
 // pathEscape implements similar path escaping as used by systemd-escape
 // https://github.com/systemd/systemd/blob/c57ff6230e4e199d40f35a356e834ba99f3f8420/src/basic/unit-name.c#L389
 func pathEscape(path string) string {
@@ -281,8 +272,8 @@ func GenMountsDevicesFromPT(filename string, pt *disk.PartitionTable) (string, [
 	mounts := make([]Mount, 0, len(pt.Partitions))
 	var fsRootMntName string
 	genMounts := func(mnt disk.Mountable, path []disk.Entity) error {
-		stageDevices, leafDeviceName := getDevices(path, filename, false)
-		mount, err := genOsbuildMount(leafDeviceName, mnt)
+		stageDevices, leafDevice := getDevicesNoRename(path, filename, false)
+		mount, err := genOsbuildMount(leafDevice, mnt)
 		if err != nil {
 			return err
 		}

pkg/osbuild/mkfs_stage.go

@@ -18,15 +18,7 @@ func GenFsStages(pt *disk.PartitionTable, filename string) []*Stage {
 	genStage := func(ent disk.Entity, path []disk.Entity) error {
 		switch e := ent.(type) {
 		case *disk.Filesystem:
-			// TODO: extract last device renaming into helper
-			stageDevices, lastName := getDevices(path, filename, true)
-
-			// The last device in the chain must be named "device", because that's
-			// the device that mkfs stages run on. See the stage schemas for
-			// reference.
-			lastDevice := stageDevices[lastName]
-			delete(stageDevices, lastName)
-			stageDevices["device"] = lastDevice
+			stageDevices := getDevices(path, filename, true)
 
 			switch e.GetFSType() {
 			case "xfs":
@@ -50,14 +42,7 @@ func GenFsStages(pt *disk.PartitionTable, filename string) []*Stage {
 				panic(fmt.Sprintf("unknown fs type: %s", e.GetFSType()))
 			}
 		case *disk.Btrfs:
-			stageDevices, lastName := getDevices(path, filename, true)
-
-			// The last device in the chain must be named "device", because that's
-			// the device that mkfs stages run on. See the stage schemas for
-			// reference.
-			lastDevice := stageDevices[lastName]
-			delete(stageDevices, lastName)
-			stageDevices["device"] = lastDevice
+			stageDevices := getDevices(path, filename, true)
 
 			options := &MkfsBtrfsStageOptions{
 				UUID:  e.UUID,
@@ -78,14 +63,7 @@ func GenFsStages(pt *disk.PartitionTable, filename string) []*Stage {
 			stages = append(stages, NewBtrfsSubVol(&BtrfsSubVolOptions{subvolumes}, &stageDevices, &[]Mount{mount}))
 		case *disk.Swap:
 			// TODO: extract last device renaming into helper
-			stageDevices, lastName := getDevices(path, filename, true)
-
-			// The last device in the chain must be named "device", because that's
-			// the device that the mkswap stage runs on. See the stage schema
-			// for reference.
-			lastDevice := stageDevices[lastName]
-			delete(stageDevices, lastName)
-			stageDevices["device"] = lastDevice
+			stageDevices := getDevices(path, filename, true)
 
 			options := &MkswapStageOptions{
 				UUID:  e.UUID,