Implement mounting via stage directory

Previously, multiple containers with the same mounted volume resulted in multiple
FUSE processes. This behaviour was breaking parallel modifications from different
containers, consumed extra resources, and after mounting via systemd was introduced,
led to the total inability to mount the same volume into multiple containers on
the same host.

Now only one FUSE process is started per volume, per host.

pkg/mounter/mounter.go

@@ -11,18 +11,18 @@ import (
 	"syscall"
 	"time"
 
-	"github.com/yandex-cloud/k8s-csi-s3/pkg/s3"
+	systemd "github.com/coreos/go-systemd/v22/dbus"
 	"github.com/golang/glog"
 	"github.com/mitchellh/go-ps"
 	"k8s.io/kubernetes/pkg/util/mount"
+
+	"github.com/yandex-cloud/k8s-csi-s3/pkg/s3"
 )
 
 // Mounter interface which can be implemented
 // by the different mounter types
 type Mounter interface {
-	Stage(stagePath string) error
-	Unstage(stagePath string) error
-	Mount(source, target, volumeID string) error
+	Mount(target, volumeID string) error
 }
 
 const (
@@ -70,12 +70,40 @@ func fuseMount(path string, command string, args []string) error {
 	return waitForMount(path, 10*time.Second)
 }
 
+func Unmount(path string) error {
+	if err := mount.New("").Unmount(path); err != nil {
+		return err
+	}
+	return nil
+}
+
+func SystemdUnmount(volumeID string) (bool, error) {
+	conn, err := systemd.New()
+	if err != nil {
+		glog.Errorf("Failed to connect to systemd dbus service: %v", err)
+		return false, err
+	}
+	defer conn.Close()
+	unitName := "geesefs-"+systemd.PathBusEscape(volumeID)+".service"
+	units, err := conn.ListUnitsByNames([]string{ unitName })
+	glog.Errorf("Got %v", units)
+	if err != nil {
+		glog.Errorf("Failed to list systemd unit by name %v: %v", unitName, err)
+		return false, err
+	}
+	if len(units) == 0 || units[0].ActiveState == "inactive" || units[0].ActiveState == "failed" {
+		return true, nil
+	}
+	_, err = conn.StopUnit(unitName, "replace", nil)
+	return true, err
+}
+
 func FuseUnmount(path string) error {
 	if err := mount.New("").Unmount(path); err != nil {
 		return err
 	}
 	// as fuse quits immediately, we will try to wait until the process is done
-	process, err := findFuseMountProcess(path)
+	process, err := FindFuseMountProcess(path)
 	if err != nil {
 		glog.Errorf("Error getting PID of fuse mount: %s", err)
 		return nil
@@ -107,7 +135,7 @@ func waitForMount(path string, timeout time.Duration) error {
 	}
 }
 
-func findFuseMountProcess(path string) (*os.Process, error) {
+func FindFuseMountProcess(path string) (*os.Process, error) {
 	processes, err := ps.Processes()
 	if err != nil {
 		return nil, err