Clarify log and return empty from helper functions

Longhorn 2187

Signed-off-by: Eric Weber <eric.weber@suse.com>

pkg/controller/control.go

@@ -1382,7 +1382,8 @@ func tryFreeze(devicePath string, freezePoint string, mounter mount.Interface, e
 		mounted = true
 
 		// We must verify it is still safe to freeze the filesystem. If the source mount was unmounted by someone else
-		// before we bind mounted, the bind mount could refer to the root filesystem.
+		// before we bind mounted, the bind mount could refer to the root filesystem. It does not matter if the source
+		// mount is unmounted AFTER our bind mount, as the bind mount is not affected.
 		var device string
 		device, _, err = mount.GetDeviceNameFromMount(mounter, freezePoint)
 		if err != nil || device != devicePath {

pkg/frontend/tgt/frontend.go

@@ -78,7 +78,7 @@ func (t *Tgt) Shutdown() error {
 	// If the engine is shutting down during a snapshot (in the preparation phase, before the snapshot operation obtains
 	// a lock) we may have left a frozen filesystem. This is a good opportunity to unfreeze it.
 	if err := util.UnfreezeFilesystemForDevice(t.Endpoint()); err != nil {
-		logrus.WithError(err).Errorf("Failed to clean up frozen file system during shutdown")
+		logrus.WithError(err).Errorf("Failed to clean up frozen file system; will continue tgt shutdown")
 	}
 
 	if t.dev != nil {

pkg/util/fsfreeze.go

@@ -31,17 +31,26 @@ const (
 // GetFreezePointFromDevicePath returns the absolute path to the canonical location we will try to mount a filesystem to
 // before freezeing it.
 func GetFreezePointFromDevicePath(devicePath string) string {
+	if devicePath == "" {
+		return ""
+	}
 	return GetFreezePointFromVolumeName(filepath.Base(devicePath))
 }
 
 // GetFreezePointFromVolumeName returns the absolute path to the canonical location we will try to mount a filesystem to
 // before freezeing it.
 func GetFreezePointFromVolumeName(volumeName string) string {
+	if volumeName == "" {
+		return ""
+	}
 	return filepath.Join(freezePointDirectory, volumeName)
 }
 
 // GetDevicePathFromVolumeName mirrors longhorndev.getDev. It returns the device path that go-iscsi-helper will use.
 func GetDevicePathFromVolumeName(volumeName string) string {
+	if volumeName == "" {
+		return ""
+	}
 	return filepath.Join(longhorndev.DevPath, volumeName)
 }