rbd: use dummy image to workaround rbd scheduling bug

currently we have a bug in rbd mirror scheduling module.
After doing failover and failback the scheduling is not
getting updated and the mirroring snapshots are not
getting created periodically as per the scheduling
interval. This PR workarounds this one by doing below
operations

* Create a dummy (unique) image per cluster and this image
should be easily identified.

* During Promote operation on any image enable the
mirroring on the dummy image. when we enable the mirroring
on the dummy image the pool will get updated and the
scheduling will be reconfigured.

* During Demote operation on any image disable the mirroring
on the dummy image. the disable need to be done to enable
the mirroring again when we get the promote request to make
the image as primary

* When the DR is no more needed, this image need to be
manually cleanup as for now as we dont want to add a check
in the existing DeleteVolume code path for delete dummy image
as it impact the performance of the DeleteVolume workflow.

Signed-off-by: Madhu Rajanna <madhupr007@gmail.com>

internal/rbd/replicationcontrollerserver.go

@@ -23,6 +23,7 @@ import (
 	"regexp"
 	"strconv"
 	"strings"
+	"sync"
 	"time"
 
 	"github.com/ceph/ceph-csi/internal/util"
@@ -63,6 +64,19 @@ const (
 	schedulingStartTimeKey = "schedulingStartTime"
 )
 
+type operation string
+
+var (
+	// pool+"/"+key to check dummy image is created.
+	dummyImageCreated operation = "dummyImageCreated"
+	// pool+"/"+key to check mirroring enabled on dummy image.
+	dummyImageMirroringEnabled operation = "dummyImageMirrorEnabled"
+	// pool+"/"+key to check mirroring disabled on dummy image.
+	dummyImageMirroringDisabled operation = "dummyImageMirrorDisabled"
+	// Read write lock to ensure that only one operation is happening at a time.
+	operationLock = sync.Map{}
+)
+
 // ReplicationServer struct of rbd CSI driver with supported methods of Replication
 // controller server spec.
 type ReplicationServer struct {
@@ -232,6 +246,11 @@ func (rs *ReplicationServer) EnableVolumeReplication(ctx context.Context,
 		return nil, status.Error(codes.Internal, err.Error())
 	}
 
+	err = createDummyImage(ctx, rbdVol)
+	if err != nil {
+		return nil, status.Errorf(codes.Internal, "failed to create dummy image %s", err.Error())
+	}
+
 	if mirroringInfo.State != librbd.MirrorImageEnabled {
 		err = rbdVol.enableImageMirroring(mirroringMode)
 		if err != nil {
@@ -244,6 +263,88 @@ func (rs *ReplicationServer) EnableVolumeReplication(ctx context.Context,
 	return &replication.EnableVolumeReplicationResponse{}, nil
 }
 
+// getdummyImageName returns the csi-vol-dummy+cluster FSID as the image name.
+// each cluster should have a unique dummy image created. choosing the cluster
+// FSID for the same reason.
+func getdummyImageName(conn *util.ClusterConnection) (string, error) {
+	id, err := conn.GetFSID()
+	if err != nil {
+		return "", err
+	}
+
+	return fmt.Sprintf("csi-vol-dummy-%s", id), nil
+}
+
+// getOperationName returns the operation name for the given operation type
+// combined with the pool name.
+func getOperationName(poolName string, optName operation) string {
+	return fmt.Sprintf("%s/%s", poolName, optName)
+}
+
+// createDummyImage creates a dummy image as a workaround for the rbd
+// scheduling problem.
+func createDummyImage(ctx context.Context, rbdVol *rbdVolume) error {
+	optName := getOperationName(rbdVol.Pool, dummyImageCreated)
+	if _, ok := operationLock.Load(optName); !ok {
+		// create a dummy image
+		imgName, err := getdummyImageName(rbdVol.conn)
+		if err != nil {
+			return err
+		}
+		dummyVol := rbdVol
+		dummyVol.RbdImageName = imgName
+		err = createImage(ctx, dummyVol, dummyVol.conn.Creds)
+		if err != nil && !strings.Contains(err.Error(), "File exists") {
+			return err
+		}
+		operationLock.Store(optName, true)
+	}
+
+	return nil
+}
+
+// enableImageMirroring enables the mirroring for the dummy image.
+func enableMirroringOnDummyImage(rbdVol *rbdVolume, mirroringMode librbd.ImageMirrorMode) error {
+	optName := getOperationName(rbdVol.Pool, dummyImageMirroringEnabled)
+	if _, ok := operationLock.Load(optName); !ok {
+		imgName, err := getdummyImageName(rbdVol.conn)
+		if err != nil {
+			return err
+		}
+		dummyVol := rbdVol
+		dummyVol.RbdImageName = imgName
+		// this is a idempotent call we dont need to worry multiple enable calls
+		err = dummyVol.enableImageMirroring(mirroringMode)
+		if err != nil {
+			return err
+		}
+		operationLock.Store(optName, true)
+	}
+
+	return nil
+}
+
+// disableImageMirroring disables the mirroring for the dummy image.
+func disableMirroringOnDummyImage(rbdVol *rbdVolume) error {
+	optName := getOperationName(rbdVol.Pool, dummyImageMirroringDisabled)
+	if _, ok := operationLock.Load(optName); !ok {
+		imgName, err := getdummyImageName(rbdVol.conn)
+		if err != nil {
+			return err
+		}
+		dummyVol := rbdVol
+		dummyVol.RbdImageName = imgName
+
+		err = dummyVol.disableImageMirroring(false)
+		if err != nil {
+			return err
+		}
+		operationLock.Store(optName, true)
+	}
+
+	return nil
+}
+
 // DisableVolumeReplication extracts the RBD volume information from the
 // volumeID, If the image is present and the mirroring is enabled on the RBD
 // image it will disable the mirroring.
@@ -428,6 +529,16 @@ func (rs *ReplicationServer) PromoteVolume(ctx context.Context,
 		}
 	}
 
+	var mode librbd.ImageMirrorMode
+	mode, err = getMirroringMode(ctx, req.GetParameters())
+	if err != nil {
+		return nil, status.Errorf(codes.Internal, "failed to get mirroring node %s", err.Error())
+	}
+	err = enableMirroringOnDummyImage(rbdVol, mode)
+	if err != nil {
+		return nil, status.Errorf(codes.Internal, "failed to enable mirroring on dummy image %s", err.Error())
+	}
+
 	interval, startTime := getSchedulingDetails(req.GetParameters())
 	if interval != admin.NoInterval {
 		err = rbdVol.addSnapshotScheduling(interval, startTime)
@@ -500,6 +611,10 @@ func (rs *ReplicationServer) DemoteVolume(ctx context.Context,
 
 	// demote image to secondary
 	if mirroringInfo.Primary {
+		err = disableMirroringOnDummyImage(rbdVol)
+		if err != nil {
+			return nil, status.Errorf(codes.Internal, "failed to disable mirroring on dummy image %s", err.Error())
+		}
 		err = rbdVol.demoteImage()
 		if err != nil {
 			log.ErrorLog(ctx, err.Error())