Implement NodeGetVolumeStats RPC

Exposing node capacity statistics facilitates features like alerting on
high disk usage.

driver/driver_test.go

@@ -73,8 +73,10 @@ func TestDriverSuite(t *testing.T) {
 		nodeId:   strconv.Itoa(nodeID),
 		doTag:    doTag,
 		region:   "nyc3",
-		mounter:  &fakeMounter{},
-		log:      logrus.New().WithField("test_enabed", true),
+		mounter: &fakeMounter{
+			mounted: map[string]string{},
+		},
+		log: logrus.New().WithField("test_enabed", true),
 
 		storage: &fakeStorageDriver{
 			volumes:   volumes,
@@ -360,25 +362,42 @@ func (f *fakeSnapshotsDriver) Delete(context.Context, string) (*godo.Response, e
 	panic("not implemented")
 }
 
-type fakeMounter struct{}
+type fakeMounter struct {
+	mounted map[string]string
+}
 
 func (f *fakeMounter) Format(source string, fsType string) error {
 	return nil
 }
 
 func (f *fakeMounter) Mount(source string, target string, fsType string, options ...string) error {
+	f.mounted[target] = source
 	return nil
 }
 
 func (f *fakeMounter) Unmount(target string) error {
+	delete(f.mounted, target)
 	return nil
 }
 
 func (f *fakeMounter) IsFormatted(source string) (bool, error) {
 	return true, nil
 }
 func (f *fakeMounter) IsMounted(target string) (bool, error) {
-	return true, nil
+	_, ok := f.mounted[target]
+	return ok, nil
+}
+
+func (f *fakeMounter) GetStatistics(volumePath string) (volumeStatistics, error) {
+	return volumeStatistics{
+		availableBytes: 3 * giB,
+		totalBytes:     10 * giB,
+		usedBytes:      7 * giB,
+
+		availableInodes: 3000,
+		totalInodes:     10000,
+		usedInodes:      7000,
+	}, nil
 }
 
 func godoResponse() *godo.Response {

driver/mounter.go

@@ -25,6 +25,7 @@ import (
 	"strings"
 
 	"github.com/sirupsen/logrus"
+	"golang.org/x/sys/unix"
 )
 
 type findmntResponse struct {
@@ -38,7 +39,14 @@ type fileSystem struct {
 	Options     string `json:"options"`
 }
 
+type volumeStatistics struct {
+	availableBytes, totalBytes, usedBytes    int64
+	availableInodes, totalInodes, usedInodes int64
+}
+
 // Mounter is responsible for formatting and mounting volumes
+// TODO(timoreimann): find a more suitable name since the interface encompasses
+// more than just mounting functionality by now.
 type Mounter interface {
 	// Format formats the source with the given filesystem type
 	Format(source, fsType string) error
@@ -57,6 +65,10 @@ type Mounter interface {
 	// propagated). It returns true if it's mounted. An error is returned in
 	// case of system errors or if it's mounted incorrectly.
 	IsMounted(target string) (bool, error)
+
+	// GetStatistics returns capacity-related volume statistics for the given
+	// volume path.
+	GetStatistics(volumePath string) (volumeStatistics, error)
 }
 
 // TODO(arslan): this is Linux only for now. Refactor this into a package with
@@ -272,3 +284,24 @@ func (m *mounter) IsMounted(target string) (bool, error) {
 
 	return targetFound, nil
 }
+
+func (m *mounter) GetStatistics(volumePath string) (volumeStatistics, error) {
+	var statfs unix.Statfs_t
+	// See http://man7.org/linux/man-pages/man2/statfs.2.html for details.
+	err := unix.Statfs(volumePath, &statfs)
+	if err != nil {
+		return volumeStatistics{}, err
+	}
+
+	volStats := volumeStatistics{
+		availableBytes: int64(statfs.Bavail) * int64(statfs.Bsize),
+		totalBytes:     int64(statfs.Blocks) * int64(statfs.Bsize),
+		usedBytes:      (int64(statfs.Blocks) - int64(statfs.Bfree)) * int64(statfs.Bsize),
+
+		availableInodes: int64(statfs.Ffree),
+		totalInodes:     int64(statfs.Files),
+		usedInodes:      int64(statfs.Files) - int64(statfs.Ffree),
+	}
+
+	return volStats, nil
+}

go.mod

@@ -33,7 +33,7 @@ require (
 	golang.org/x/net v0.0.0-20180406214816-61147c48b25b // indirect
 	golang.org/x/oauth2 v0.0.0-20180402223937-921ae394b943
 	golang.org/x/sync v0.0.0-20180314180146-1d60e4601c6f // indirect
-	golang.org/x/sys v0.0.0-20180406135729-3b87a42e500a // indirect
+	golang.org/x/sys v0.0.0-20180406135729-3b87a42e500a
 	golang.org/x/text v0.3.0 // indirect
 	golang.org/x/time v0.0.0-20180412165947-fbb02b2291d2 // indirect
 	google.golang.org/appengine v1.0.0 // indirect