3 files changed, 45 insertions, 29 deletions
diff --git a/lib/btrfs/btrfstree/readnode.go b/lib/btrfs/btrfstree/readnode.go
index 7cc42f5..ac82c62 100644
--- a/lib/btrfs/btrfstree/readnode.go
+++ b/lib/btrfs/btrfstree/readnode.go
@@ -20,13 +20,13 @@ type NodeFile interface {
 	// ParentTree, given a tree ID, returns that tree's parent
 	// tree, if it has one.
 	//
-	//  - non-zero, true : the parent tree ID
+	//  - non-zero, ?, true : the parent tree ID
 	//
-	//  - 0, true : the tree does not have a parent
+	//  - 0, 0, true : the tree does not have a parent
 	//
-	//  - any, false : the tree's parent information could not be
+	//  - ?, ?, false : the tree's parent information could not be
 	//    looked up
-	ParentTree(btrfsprim.ObjID) (btrfsprim.ObjID, bool)
+	ParentTree(btrfsprim.ObjID) (btrfsprim.ObjID, btrfsprim.Generation, bool)
 }
 
 // FSReadNode is a utility function to help with implementing the
@@ -40,25 +40,33 @@ func FSReadNode(
 		return nil, fmt.Errorf("btrfs.FS.ReadNode: %w", err)
 	}
 
-	var treeParents []btrfsprim.ObjID
-	checkOwner := func(owner btrfsprim.ObjID, _ btrfsprim.Generation) error {
-		exp := path.Node(-1).FromTree
+	checkOwner := func(owner btrfsprim.ObjID, gen btrfsprim.Generation) error {
+		var treeParents []btrfsprim.ObjID
+
+		tree := path.Node(-1).FromTree
 		for {
-			if owner == exp {
+			if owner == tree {
+				// OK!
 				return nil
 			}
-			treeParents = append(treeParents, exp)
-			var ok bool
-			exp, ok = fs.ParentTree(exp)
-			if !ok {
+
+			treeParents = append(treeParents, tree)
+			parent, parentGen, parentOK := fs.ParentTree(tree)
+			if !parentOK {
 				// Failed look up parent info; fail open.
 				return nil
 			}
-			if exp == 0 {
+
+			if parent == 0 {
 				// End of the line.
 				return fmt.Errorf("expected owner in %v but claims to have owner=%v",
 					treeParents, owner)
 			}
+			if gen > parentGen {
+				return fmt.Errorf("claimed owner=%v might be acceptable in this tree (if generation<=%v) but not with claimed generation=%v",
+					owner, parentGen, gen)
+			}
+			tree = parent
 		}
 	}
 
diff --git a/lib/btrfs/io2_lv.go b/lib/btrfs/io2_lv.go
index 9f4e53f..03b2107 100644
--- a/lib/btrfs/io2_lv.go
+++ b/lib/btrfs/io2_lv.go
@@ -27,9 +27,8 @@ type FS struct {
 	cacheSuperblocks []*diskio.Ref[btrfsvol.PhysicalAddr, btrfstree.Superblock]
 	cacheSuperblock  *btrfstree.Superblock
 
-	cacheObjID2UUID map[btrfsprim.ObjID]btrfsprim.UUID
+	cacheObjID2All  map[btrfsprim.ObjID]treeInfo
 	cacheUUID2ObjID map[btrfsprim.UUID]btrfsprim.ObjID
-	cacheTreeParent map[btrfsprim.ObjID]btrfsprim.UUID
 }
 
 var _ diskio.File[btrfsvol.LogicalAddr] = (*FS)(nil)
diff --git a/lib/btrfs/io3_btree.go b/lib/btrfs/io3_btree.go
index 6df88f5..b60f54a 100644
--- a/lib/btrfs/io3_btree.go
+++ b/lib/btrfs/io3_btree.go
@@ -25,13 +25,18 @@ var _ btrfstree.NodeSource = (*FS)(nil)
 
 // btrfstree.NodeFile //////////////////////////////////////////////////////////
 
+type treeInfo struct {
+	UUID       btrfsprim.UUID
+	ParentUUID btrfsprim.UUID
+	ParentGen  btrfsprim.Generation
+}
+
 func (fs *FS) populateTreeUUIDs(ctx context.Context) {
-	if fs.cacheObjID2UUID != nil && fs.cacheUUID2ObjID != nil && fs.cacheTreeParent != nil {
+	if fs.cacheObjID2All != nil && fs.cacheUUID2ObjID != nil {
 		return
 	}
-	fs.cacheObjID2UUID = make(map[btrfsprim.ObjID]btrfsprim.UUID)
+	fs.cacheObjID2All = make(map[btrfsprim.ObjID]treeInfo)
 	fs.cacheUUID2ObjID = make(map[btrfsprim.UUID]btrfsprim.ObjID)
-	fs.cacheTreeParent = make(map[btrfsprim.ObjID]btrfsprim.UUID)
 	fs.TreeWalk(ctx, btrfsprim.ROOT_TREE_OBJECTID,
 		func(err *btrfstree.TreeError) {
 			// do nothing
@@ -42,8 +47,11 @@ func (fs *FS) populateTreeUUIDs(ctx context.Context) {
 				if !ok {
 					return
 				}
-				fs.cacheObjID2UUID[item.Key.ObjectID] = itemBody.UUID
-				fs.cacheTreeParent[item.Key.ObjectID] = itemBody.ParentUUID
+				fs.cacheObjID2All[item.Key.ObjectID] = treeInfo{
+					UUID:       itemBody.UUID,
+					ParentUUID: itemBody.ParentUUID,
+					ParentGen:  btrfsprim.Generation(item.Key.Offset),
+				}
 				fs.cacheUUID2ObjID[itemBody.UUID] = item.Key.ObjectID
 			},
 		},
@@ -51,27 +59,28 @@ func (fs *FS) populateTreeUUIDs(ctx context.Context) {
 }
 
 // ParentTree implements btrfstree.NodeFile.
-func (fs *FS) ParentTree(tree btrfsprim.ObjID) (btrfsprim.ObjID, bool) {
+func (fs *FS) ParentTree(tree btrfsprim.ObjID) (btrfsprim.ObjID, btrfsprim.Generation, bool) {
 	if tree < btrfsprim.FIRST_FREE_OBJECTID || tree > btrfsprim.LAST_FREE_OBJECTID {
 		// no parent
-		return 0, true
+		return 0, 0, true
 	}
 	fs.populateTreeUUIDs(context.TODO())
-	parentUUID, ok := fs.cacheTreeParent[tree]
+
+	all, ok := fs.cacheObjID2All[tree]
 	if !ok {
 		// could not look up parent info
-		return 0, false
+		return 0, 0, false
 	}
-	if parentUUID == (btrfsprim.UUID{}) {
+	if all.ParentUUID == (btrfsprim.UUID{}) {
 		// no parent
-		return 0, true
+		return 0, 0, true
 	}
-	parentObjID, ok := fs.cacheUUID2ObjID[parentUUID]
+	parentObjID, ok := fs.cacheUUID2ObjID[all.ParentUUID]
 	if !ok {
 		// could not look up parent info
-		return 0, false
+		return 0, 0, false
 	}
-	return parentObjID, true
+	return parentObjID, all.ParentGen, true
 }
 
 var _ btrfstree.NodeFile = (*FS)(nil)