cephfs: add snap reserve/unreserve and snap exist functionalities

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

internal/cephfs/fsjournal.go

@@ -246,3 +246,132 @@ func reserveVol(ctx context.Context, volOptions *volumeOptions, secret map[strin
 
 	return &vid, nil
 }
+
+// reserveSnap is a helper routine to request a UUID reservation for the CSI SnapName and,
+// to generate the snapshot identifier for the reserved UUID.
+func reserveSnap(ctx context.Context, volOptions *volumeOptions, parentSubVolName string, snap *cephfsSnapshot, cr *util.Credentials) (*snapshotIdentifier, error) {
+	var (
+		vid       snapshotIdentifier
+		imageUUID string
+		err       error
+	)
+
+	j, err := snapJournal.Connect(volOptions.Monitors, cr)
+	if err != nil {
+		return nil, err
+	}
+	defer j.Destroy()
+
+	imageUUID, vid.FsSnapshotName, err = j.ReserveName(
+		ctx, volOptions.MetadataPool, util.InvalidPoolID,
+		volOptions.MetadataPool, util.InvalidPoolID, snap.RequestName,
+		snap.NamePrefix, parentSubVolName, "")
+	if err != nil {
+		return nil, err
+	}
+
+	// generate the snapshot ID to return to the CO system
+	vid.SnapshotID, err = util.GenerateVolID(ctx, volOptions.Monitors, cr, volOptions.FscID,
+		"", volOptions.ClusterID, imageUUID, volIDVersion)
+	if err != nil {
+		return nil, err
+	}
+
+	util.DebugLog(ctx, "Generated Snapshot ID (%s) for request name (%s)",
+		vid.SnapshotID, snap.RequestName)
+
+	return &vid, nil
+}
+
+// undoSnapReservation is a helper routine to undo a name reservation for a CSI SnapshotName.
+func undoSnapReservation(ctx context.Context, volOptions *volumeOptions, vid snapshotIdentifier, snapName string, cr *util.Credentials) error {
+	j, err := snapJournal.Connect(volOptions.Monitors, cr)
+	if err != nil {
+		return err
+	}
+	defer j.Destroy()
+
+	err = j.UndoReservation(ctx, volOptions.MetadataPool,
+		volOptions.MetadataPool, vid.FsSnapshotName, snapName)
+	return err
+}
+
+/*
+checkSnapExists checks to determine if passed in RequestName in volOptions exists on the backend.
+
+**NOTE:** These functions manipulate the rados omaps that hold information regarding
+volume names as requested by the CSI drivers. Hence, these need to be invoked only when the
+respective CSI driver generated volume name based locks are held, as otherwise racy
+access to these omaps may end up leaving them in an inconsistent state.
+
+These functions also cleanup omap reservations that are stale. I.e when omap entries exist and
+backing subvolumes are missing, or one of the omaps exist and the next is missing. This is
+because, the order of omap creation and deletion are inverse of each other, and protected by the
+request name lock, and hence any stale omaps are leftovers from incomplete transactions and are
+hence safe to garbage collect.
+*/
+func checkSnapExists(
+	ctx context.Context,
+	volOptions *volumeOptions,
+	parentSubVolName string,
+	snap *cephfsSnapshot,
+	cr *util.Credentials) (*snapshotIdentifier, *snapshotInfo, error) {
+	j, err := snapJournal.Connect(volOptions.Monitors, cr)
+	if err != nil {
+		return nil, nil, err
+	}
+	defer j.Destroy()
+
+	snapData, err := j.CheckReservation(
+		ctx, volOptions.MetadataPool, snap.RequestName, snap.NamePrefix, parentSubVolName, "")
+	if err != nil {
+		return nil, nil, err
+	}
+	if snapData == nil {
+		return nil, nil, nil
+	}
+	sid := &snapshotIdentifier{}
+	snapUUID := snapData.ImageUUID
+	snapID := snapData.ImageAttributes.ImageName
+	sid.FsSnapshotName = snapData.ImageAttributes.ImageName
+	snapInfo, err := getSnapshotInfo(ctx, volOptions, cr, volumeID(snapID), volumeID(parentSubVolName))
+	if err != nil {
+		if errors.Is(err, ErrSnapNotFound) {
+			err = j.UndoReservation(ctx, volOptions.MetadataPool,
+				volOptions.MetadataPool, snapID, snap.RequestName)
+			return nil, nil, err
+		}
+		return nil, nil, err
+	}
+
+	defer func() {
+		if err != nil {
+			err = deleteSnapshot(ctx, volOptions, cr, volumeID(snapID), volumeID(parentSubVolName))
+			if err != nil {
+				klog.Errorf(util.Log(ctx, "failed to delete snapshot %s: %v"), snapID, err)
+				return
+			}
+			err = j.UndoReservation(ctx, volOptions.MetadataPool,
+				volOptions.MetadataPool, snapID, snap.RequestName)
+			if err != nil {
+				klog.Errorf(util.Log(ctx, "removing reservation failed for snapshot %s: %v"), snapID, err)
+			}
+		}
+	}()
+	tm, err := parseTime(ctx, snapInfo.CreatedAt)
+	if err != nil {
+		return nil, nil, err
+	}
+
+	sid.CreationTime = tm
+	// found a snapshot already available, process and return it!
+	sid.SnapshotID, err = util.GenerateVolID(ctx, volOptions.Monitors, cr, volOptions.FscID,
+		"", volOptions.ClusterID, snapUUID, volIDVersion)
+	if err != nil {
+		return nil, nil, err
+	}
+	util.DebugLog(ctx, "Found existing snapshot (%s) with subvolume name (%s) for request (%s)",
+		snapData.ImageAttributes.RequestName, parentSubVolName, sid.FsSnapshotName)
+
+	return sid, &snapInfo, nil
+}