pkg: add support for systemd >= 240 and native btrfs parititions

Systemd prior to version 240 was creating /var/lib/machines.raw as btrfs
volume for storing machined disks. However, this functionality is now
remove and now it stores it as regular files. More details here:
https://github.com/systemd/systemd/blob/401faa3533280b05fee972e0c64885caf4b31e4c/units/var-lib-machines.mount#L10

Additionally, it someone already have /var/lib/machines baked by btrfs,
machined won't create machines.raw, which will also cause setting up
cluster to fail.

This patch adds check, if machineImage exists and it not, it fallbacks
to just checking disk space available for /var/lib/machines.

Closes kinvolk#339 kinvolk#293

Signed-off-by: Mateusz Gozdek <mateusz@kinvolk.io>

pkg/bootstrap/node.go

@@ -62,19 +62,30 @@ func GetPoolSize(baseImageName string, nodes int) (int64, error) {
 	var extraSizeRatio float64 = 0.5
 	var err error
 
-	baseImageAbspath := path.Join(machinesDir, baseImageName+".raw")
-
-	if poolSize, err = getAllocatedFileSize(machinesImage); err != nil {
+	// Select correct path to check disk space. On older systemd versions
+	// machinesImage is used.
+	p := machinesDir
+	poolExists, err := CheckPoolExists()
+	if err != nil {
 		return 0, err
+	} else if poolExists {
+		p = machinesImage
+
+		if poolSize, err = getAllocatedFileSize(machinesImage); err != nil {
+			return 0, err
+		}
+
+		extraSize = int64(float64(poolSize) * extraSizeRatio)
 	}
-	extraSize = int64(float64(poolSize) * extraSizeRatio)
+
+	baseImageAbspath := path.Join(machinesDir, baseImageName+".raw")
 
 	if biSize, err = getAllocatedFileSize(baseImageAbspath); err != nil {
 		return 0, err
 	}
 	extraSize += int64(float64(biSize)*extraSizeRatio) * int64(nodes)
 
-	varDir, _ := path.Split(machinesImage)
+	varDir, _ := path.Split(p)
 	freeVolSpace, err := getVolFreeSpace(varDir)
 	if err != nil {
 		return 0, err
@@ -95,6 +106,17 @@ func GetPoolSize(baseImageName string, nodes int) (int64, error) {
 	return poolSize, nil
 }
 
+func CheckPoolExists() (bool, error) {
+	if _, err := os.Stat(machinesImage); err != nil {
+		if os.IsNotExist(err) {
+			return false, nil
+		} else {
+			return false, err
+		}
+	}
+	return true, nil
+}
+
 func setPoolLimit(poolSize int64) error {
 	var cmdPath string
 	var err error

pkg/cluster/cluster.go

@@ -368,15 +368,29 @@ func (c *Cluster) Start(numberNodes int, cniPluginDir, cniPlugin, flatcarChannel
 		return err
 	}
 
-	poolSize, err := bootstrap.GetPoolSize(bootstrap.BaseImageName, numberNodes)
+	poolExists, err := bootstrap.CheckPoolExists()
 	if err != nil {
 		return err
 	}
-	log.Printf("new poolSize to be : %d\n", poolSize)
-	if err := bootstrap.EnlargeStoragePool(poolSize); err != nil {
+
+	// TODO This shouldn't be hardcoded, but I don't know where to put it yet
+	imageName := "flatcar"
+	if poolExists {
+		imageName = bootstrap.BaseImageName
+	}
+
+	poolSize, err := bootstrap.GetPoolSize(imageName, numberNodes)
+	if err != nil {
 		return err
 	}
 
+	if poolExists {
+		log.Printf("new poolSize to be : %d\n", poolSize)
+		if err := bootstrap.EnlargeStoragePool(poolSize); err != nil {
+			return err
+		}
+	}
+
 	ctx, cancel := context.WithCancel(context.Background())
 	defer cancel()