rbd: implement CSI-Addons ControllerGetVolumeGroup operation

With the ControllerGetVolumeGroup operation the caller can verify that a
VolumeGroup exists, and validate the volumes that are part of it.

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

internal/csi-addons/rbd/identity.go

@@ -120,6 +120,12 @@ func (is *IdentityServer) GetCapabilities(
 						Type: identity.Capability_VolumeGroup_MODIFY_VOLUME_GROUP,
 					},
 				},
+			}, &identity.Capability{
+				Type: &identity.Capability_VolumeGroup_{
+					VolumeGroup: &identity.Capability_VolumeGroup{
+						Type: identity.Capability_VolumeGroup_GET_VOLUME_GROUP,
+					},
+				},
 			})
 	}
 

internal/csi-addons/rbd/volumegroup.go

@@ -363,3 +363,41 @@ func (vs *VolumeGroupServer) ModifyVolumeGroupMembership(
 		VolumeGroup: csiVG,
 	}, nil
 }
+
+// ControllerGetVolumeGroup RPC call to get a volume group.
+//
+// From the spec:
+// ControllerGetVolumeGroupResponse should contain current information of a
+// volume group if it exists. If the volume group does not exist any more,
+// ControllerGetVolumeGroup should return gRPC error code NOT_FOUND.
+func (vs *VolumeGroupServer) ControllerGetVolumeGroup(
+	ctx context.Context,
+	req *volumegroup.ControllerGetVolumeGroupRequest,
+) (*volumegroup.ControllerGetVolumeGroupResponse, error) {
+	mgr := rbd.NewManager(vs.csiID, nil, req.GetSecrets())
+	defer mgr.Destroy(ctx)
+
+	// resolve the volume group
+	vg, err := mgr.GetVolumeGroupByID(ctx, req.GetVolumeGroupId())
+	if err != nil {
+		return nil, status.Errorf(
+			codes.NotFound,
+			"could not find volume group %q: %s",
+			req.GetVolumeGroupId(),
+			err.Error())
+	}
+	defer vg.Destroy(ctx)
+
+	csiVG, err := vg.ToCSI(ctx)
+	if err != nil {
+		return nil, status.Errorf(
+			codes.Internal,
+			"failed to convert volume group %q to CSI format: %v",
+			vg,
+			err)
+	}
+
+	return &volumegroup.ControllerGetVolumeGroupResponse{
+		VolumeGroup: csiVG,
+	}, nil
+}