rbd: cleanup NodeServer.createTargetMountPath()

The inverse checking and returning of is-a-mounted-path makes it
difficult to understand the function. It is easier to follow the code
when the function just returns what it says it does, hence added the
comment for the function too.

Some errors were returned directly, others were converted to gRPC
errors. This has been corrected now too, and the caller converts the
plain error to a gRPC error now.

Signed-off-by: Niels de Vos <ndevos@ibm.com>

Author: nixpanic

internal/rbd/nodeserver.go

@@ -721,12 +721,12 @@ func (ns *NodeServer) NodePublishVolume(
 	defer ns.VolumeLocks.Release(targetPath)
 
 	// Check if that target path exists properly
-	notMnt, err := ns.createTargetMountPath(ctx, targetPath, isBlock)
+	isMnt, err := ns.createTargetMountPath(ctx, targetPath, isBlock)
 	if err != nil {
-		return nil, err
+		return nil, status.Error(codes.Internal, err.Error())
 	}
 
-	if !notMnt {
+	if isMnt {
 		return &csi.NodePublishVolumeResponse{}, nil
 	}
 
@@ -878,37 +878,45 @@ func (ns *NodeServer) mountVolume(ctx context.Context, stagingPath string, req *
 	return nil
 }
 
+// createTargetMountPath check if the mountPath already has something mounted
+// on it. If not, the directory (for a filesystem volume) will be created.
+//
+// This function returns 'true' in case there is something mounted on the given
+// path already, 'false' when the path exists, but nothing is mounted there.
 func (ns *NodeServer) createTargetMountPath(ctx context.Context, mountPath string, isBlock bool) (bool, error) {
-	// Check if that mount path exists properly
 	isMnt, err := ns.Mounter.IsMountPoint(mountPath)
 	if err == nil {
-		return !isMnt, nil
+		return isMnt, nil
 	}
 	if !os.IsNotExist(err) {
-		return false, status.Error(codes.Internal, err.Error())
+		return false, fmt.Errorf("path %q exists, but detecting it as mount point failed: %w", mountPath, err)
 	}
-	if isBlock {
-		// #nosec
-		pathFile, e := os.OpenFile(mountPath, os.O_CREATE|os.O_RDWR, 0o750)
-		if e != nil {
-			log.DebugLog(ctx, "Failed to create mountPath:%s with error: %v", mountPath, err)
 
-			return !isMnt, status.Error(codes.Internal, e.Error())
-		}
-		if err = pathFile.Close(); err != nil {
-			log.DebugLog(ctx, "Failed to close mountPath:%s with error: %v", mountPath, err)
-
-			return !isMnt, status.Error(codes.Internal, err.Error())
-		}
-	} else {
+	// filesystem volume needs a directory
+	if !isBlock {
 		// Create a mountpath directory
 		if err = util.CreateMountPoint(mountPath); err != nil {
-			return !isMnt, status.Error(codes.Internal, err.Error())
+			return false, fmt.Errorf("failed to create mount path %q: %w", mountPath, err)
 		}
+
+		return false, nil
+	}
+
+	// block volume checks
+	// #nosec
+	pathFile, err := os.OpenFile(mountPath, os.O_CREATE|os.O_RDWR, 0o750)
+	if err != nil {
+		log.DebugLog(ctx, "Failed to create mountPath:%s with error: %v", mountPath, err)
+
+		return false, fmt.Errorf("failed to create mount file %q: %w", mountPath, err)
+	}
+	if err = pathFile.Close(); err != nil {
+		log.DebugLog(ctx, "Failed to close mountPath:%s with error: %v", mountPath, err)
+
+		return false, fmt.Errorf("failed to close mount file %q: %w", mountPath, err)
 	}
-	isMnt = false
 
-	return !isMnt, err
+	return false, nil
 }
 
 // NodeUnpublishVolume unmounts the volume from the target path.