.

wcfs/internal/zdata/δftail.go

@@ -99,8 +99,10 @@ type _ΔFileTail struct {
 // _ΔFileEpoch represent change to ZBigFile object.
 type _ΔFileEpoch struct {
 	Rev        zodb.Tid
-	newRoot    zodb.Oid // .blktab was changed to point to newRoot  ; VDEL if ZBigFile deleted
+	oldRoot    zodb.Oid // .blktab was pointing to oldRoot before   ; VDEL if ZBigFile deleted
+	newRoot    zodb.Oid // .blktab was changed to point to newRoot  ; ----//----
 	newBlkSize int64    // .blksize was changed to newBlkSize       ; -1   if ZBigFile deleted
+	// XXX +oldBlkSize ?
 }
 
 // zblkTrack keeps information in which root/blocks ZBlk is present as of @head.
@@ -310,6 +312,7 @@ func (δFtail *ΔFtail) Update(δZ *zodb.EventCommit) (_ ΔF, err error) {
 				δzfile[oid] = δ
 				δftail.vδE = append(δftail.vδE, _ΔFileEpoch{
 					Rev:        δZ.Tid,
+					oldRoot:    δ.blktabOld,
 					newRoot:    δ.blktabNew,
 					newBlkSize: δ.blksizeNew,
 				})