rbd: add MakeVolumeGroupID() utility function

The Manager.MakeVolumeGroupID() function can be used to build a CSI
VolumeGroupID from the backend (pool and name of the RBD-group). This
will be used when checking if an RBD-image belongs to a group already.
It is also possible to resolve the VolumeGroup by passing the
VolumeGroupID to the existing Manager.GetVolumeGroupByID() function.

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

internal/journal/volumegroupjournal.go

@@ -20,6 +20,7 @@ import (
 	"context"
 	"errors"
 	"fmt"
+	"strings"
 	"time"
 
 	"github.com/ceph/ceph-csi/internal/util"
@@ -166,6 +167,28 @@ func generateVolumeGroupName(namePrefix, groupUUID string) string {
 	return namePrefix + groupUUID
 }
 
+// MakeVolumeGroupID is a utility function that takes details of a VolumeGroup
+// and creates the CSI VolumeGroupId out of those.
+func MakeVolumeGroupID(clusterID string, poolID int64, name, prefix string) (string, error) {
+	namePrefix := prefix
+	if prefix == "" {
+		namePrefix = defaultVolumeGroupNamingPrefix
+	}
+
+	id, found := strings.CutPrefix(name, namePrefix)
+	if !found {
+		return "", fmt.Errorf("volume group name %q does not start with %q", name, namePrefix)
+	}
+
+	handle := util.CSIIdentifier{
+		ClusterID:  clusterID,
+		LocationID: poolID,
+		ObjectUUID: id,
+	}
+
+	return handle.ComposeCSIID()
+}
+
 /*
 CheckReservation checks if given request name contains a valid reservation
   - If there is a valid reservation, then the corresponding VolumeGroupData for