Add metrics support

Signed-off-by: Humble Chirammal <hchiramm@redhat.com>

pkg/cephfs/nodeserver.go

@@ -263,6 +263,30 @@ func (ns *NodeServer) NodeUnstageVolume(ctx context.Context, req *csi.NodeUnstag
 	return &csi.NodeUnstageVolumeResponse{}, nil
 }
 
+func (ns *NodeServer) NodeGetVolumeStats(ctx context.Context, req *csi.NodeGetVolumeStatsRequest) (*csi.NodeGetVolumeStatsResponse, error) {
+
+	targetPath := req.GetVolumePath()
+	volId := req.GetVolumeId()
+
+	// Check if the volume is already mounted
+
+	isMnt, err := isMountPoint(targetPath)
+
+	if err != nil {
+		klog.Errorf("stat failed: %v", err)
+		return nil, status.Error(codes.Internal, err.Error())
+	}
+
+	if isMnt {
+		klog.Infof("cephfs: volume %s is already bind-mounted to %s", volId, targetPath)
+		return &csi.NodeGetVolumeStatsResponse{}, nil
+	}
+
+	klog.Infof("cephfs: successfully got stats for volume %s to %s", volId, targetPath)
+
+	return &csi.NodeGetVolumeStatsResponse{}, nil
+}
+
 // NodeGetCapabilities returns the supported capabilities of the node server
 func (ns *NodeServer) NodeGetCapabilities(ctx context.Context, req *csi.NodeGetCapabilitiesRequest) (*csi.NodeGetCapabilitiesResponse, error) {
 	return &csi.NodeGetCapabilitiesResponse{
@@ -274,6 +298,13 @@ func (ns *NodeServer) NodeGetCapabilities(ctx context.Context, req *csi.NodeGetC
 					},
 				},
 			},
+			{
+				Type: &csi.NodeServiceCapability_Rpc{
+					Rpc: &csi.NodeServiceCapability_RPC{
+						Type: csi.NodeServiceCapability_RPC_GET_VOLUME_STATS,
+					},
+				},
+			},
 		},
 	}, nil
 }