Merge branch 'lukeshu/misc'

5 files changed, 142 insertions, 123 deletions

diff --git a/lib/btrfs/btrfstree/btree_forrest.go b/lib/btrfs/btrfstree/btree_forrest.go
index ace2b49..0bab610 100644
--- a/lib/btrfs/btrfstree/btree_forrest.go
+++ b/lib/btrfs/btrfstree/btree_forrest.go
@@ -34,8 +34,8 @@ func RootItemSearchFn(treeID btrfsprim.ObjID) func(btrfsprim.Key, uint32) int {
 	}
 }
 
-// LookupTreeRoot is a utility function to help with implementing the 'Trees'
-// interface.
+// LookupTreeRoot is a utility function to help with implementing the
+// 'TreeOperator' interface.
 func LookupTreeRoot(fs TreeOperator, sb Superblock, treeID btrfsprim.ObjID) (*TreeRoot, error) {
 	switch treeID {
 	case btrfsprim.ROOT_TREE_OBJECTID:
diff --git a/lib/btrfs/btrfstree/btree_tree.go b/lib/btrfs/btrfstree/btree_tree.go
index b01312f..e75eb0b 100644
--- a/lib/btrfs/btrfstree/btree_tree.go
+++ b/lib/btrfs/btrfstree/btree_tree.go
@@ -37,7 +37,7 @@ type TreeOperator interface {
 	//     002 (read node)
 	//     003 .Node() (or .BadNode())
 	//         for item in node.items:
-	//           if btrfsprim:
+	//           if interior:
 	//     004     .PreKeyPointer()
 	//     005     (recurse)
 	//     006     .PostKeyPointer()
@@ -68,7 +68,7 @@ type TreeWalkHandler struct {
 	Node     func(TreePath, *diskio.Ref[btrfsvol.LogicalAddr, Node]) error
 	BadNode  func(TreePath, *diskio.Ref[btrfsvol.LogicalAddr, Node], error) error
 	PostNode func(TreePath, *diskio.Ref[btrfsvol.LogicalAddr, Node]) error
-	// Callbacks for items on btrfsprim nodes
+	// Callbacks for items on interior nodes
 	PreKeyPointer  func(TreePath, KeyPointer) error
 	PostKeyPointer func(TreePath, KeyPointer) error
 	// Callbacks for items on leaf nodes
@@ -96,7 +96,7 @@ type TreeOperatorImpl struct {
 	NodeSource
 }
 
-// TreeWalk implements the 'Trees' interface.
+// TreeWalk implements the 'TreeOperator' interface.
 func (fs TreeOperatorImpl) TreeWalk(ctx context.Context, treeID btrfsprim.ObjID, errHandle func(*TreeError), cbs TreeWalkHandler) {
 	sb, err := fs.Superblock()
 	if err != nil {
@@ -110,12 +110,12 @@ func (fs TreeOperatorImpl) TreeWalk(ctx context.Context, treeID btrfsprim.ObjID,
 	fs.RawTreeWalk(ctx, *rootInfo, errHandle, cbs)
 }
 
-// TreeWalk is a utility method to help with implementing the 'Trees'.
-// interface.
+// RawTreeWalk is a utility method to help with implementing the
+// 'TreeOperator' interface.
 func (fs TreeOperatorImpl) RawTreeWalk(ctx context.Context, rootInfo TreeRoot, errHandle func(*TreeError), cbs TreeWalkHandler) {
 	path := TreePath{{
 		FromTree:         rootInfo.TreeID,
-		FromItemIdx:      -1,
+		FromItemSlot:     -1,
 		ToNodeAddr:       rootInfo.RootNode,
 		ToNodeGeneration: rootInfo.Generation,
 		ToNodeLevel:      rootInfo.Level,
@@ -169,14 +169,14 @@ func (fs TreeOperatorImpl) treeWalk(ctx context.Context, path TreePath, errHandl
 		return
 	}
 	if node != nil {
-		for i, item := range node.Data.BodyInternal {
+		for i, item := range node.Data.BodyInterior {
 			toMaxKey := path.Node(-1).ToMaxKey
-			if i+1 < len(node.Data.BodyInternal) {
-				toMaxKey = node.Data.BodyInternal[i+1].Key.Mm()
+			if i+1 < len(node.Data.BodyInterior) {
+				toMaxKey = node.Data.BodyInterior[i+1].Key.Mm()
 			}
 			itemPath := append(path, TreePathElem{
 				FromTree:         node.Data.Head.Owner,
-				FromItemIdx:      i,
+				FromItemSlot:     i,
 				ToNodeAddr:       item.BlockPtr,
 				ToNodeGeneration: item.Generation,
 				ToNodeLevel:      node.Data.Head.Level - 1,
@@ -203,10 +203,10 @@ func (fs TreeOperatorImpl) treeWalk(ctx context.Context, path TreePath, errHandl
 		}
 		for i, item := range node.Data.BodyLeaf {
 			itemPath := append(path, TreePathElem{
-				FromTree:    node.Data.Head.Owner,
-				FromItemIdx: i,
-				ToKey:       item.Key,
-				ToMaxKey:    item.Key,
+				FromTree:     node.Data.Head.Owner,
+				FromItemSlot: i,
+				ToKey:        item.Key,
+				ToMaxKey:     item.Key,
 			})
 			if errBody, isErr := item.Body.(*btrfsitem.Error); isErr {
 				if cbs.BadItem == nil {
@@ -244,7 +244,7 @@ func (fs TreeOperatorImpl) treeWalk(ctx context.Context, path TreePath, errHandl
 func (fs TreeOperatorImpl) treeSearch(treeRoot TreeRoot, fn func(btrfsprim.Key, uint32) int) (TreePath, *diskio.Ref[btrfsvol.LogicalAddr, Node], error) {
 	path := TreePath{{
 		FromTree:         treeRoot.TreeID,
-		FromItemIdx:      -1,
+		FromItemSlot:     -1,
 		ToNodeAddr:       treeRoot.RootNode,
 		ToNodeGeneration: treeRoot.Generation,
 		ToNodeLevel:      treeRoot.Level,
@@ -261,9 +261,9 @@ func (fs TreeOperatorImpl) treeSearch(treeRoot TreeRoot, fn func(btrfsprim.Key,
 		}
 
 		if node.Data.Head.Level > 0 {
-			// btrfsprim node
+			// interior node
 
-			// Search for the right-most node.Data.BodyInternal item for which
+			// Search for the right-most node.Data.BodyInterior item for which
 			// `fn(item.Key) >= 0`.
 			//
 			//    + + + + 0 - - - -
@@ -271,7 +271,7 @@ func (fs TreeOperatorImpl) treeSearch(treeRoot TreeRoot, fn func(btrfsprim.Key,
 			// There may or may not be a value that returns '0'.
 			//
 			// i.e. find the highest value that isn't too high.
-			lastGood, ok := slices.SearchHighest(node.Data.BodyInternal, func(kp KeyPointer) int {
+			lastGood, ok := slices.SearchHighest(node.Data.BodyInterior, func(kp KeyPointer) int {
 				return slices.Min(fn(kp.Key, math.MaxUint32), 0) // don't return >0; a key can't be "too low"
 			})
 			if !ok {
@@ -279,16 +279,16 @@ func (fs TreeOperatorImpl) treeSearch(treeRoot TreeRoot, fn func(btrfsprim.Key,
 				return nil, nil, iofs.ErrNotExist
 			}
 			toMaxKey := path.Node(-1).ToMaxKey
-			if lastGood+1 < len(node.Data.BodyInternal) {
-				toMaxKey = node.Data.BodyInternal[lastGood+1].Key.Mm()
+			if lastGood+1 < len(node.Data.BodyInterior) {
+				toMaxKey = node.Data.BodyInterior[lastGood+1].Key.Mm()
 			}
 			path = append(path, TreePathElem{
 				FromTree:         node.Data.Head.Owner,
-				FromItemIdx:      lastGood,
-				ToNodeAddr:       node.Data.BodyInternal[lastGood].BlockPtr,
-				ToNodeGeneration: node.Data.BodyInternal[lastGood].Generation,
+				FromItemSlot:     lastGood,
+				ToNodeAddr:       node.Data.BodyInterior[lastGood].BlockPtr,
+				ToNodeGeneration: node.Data.BodyInterior[lastGood].Generation,
 				ToNodeLevel:      node.Data.Head.Level - 1,
-				ToKey:            node.Data.BodyInternal[lastGood].Key,
+				ToKey:            node.Data.BodyInterior[lastGood].Key,
 				ToMaxKey:         toMaxKey,
 			})
 			FreeNodeRef(node)
@@ -305,7 +305,7 @@ func (fs TreeOperatorImpl) treeSearch(treeRoot TreeRoot, fn func(btrfsprim.Key,
 			// is returned.
 			//
 			// Implement this search as a binary search.
-			idx, ok := slices.Search(node.Data.BodyLeaf, func(item Item) int {
+			slot, ok := slices.Search(node.Data.BodyLeaf, func(item Item) int {
 				return fn(item.Key, item.BodySize)
 			})
 			if !ok {
@@ -313,10 +313,10 @@ func (fs TreeOperatorImpl) treeSearch(treeRoot TreeRoot, fn func(btrfsprim.Key,
 				return nil, nil, iofs.ErrNotExist
 			}
 			path = append(path, TreePathElem{
-				FromTree:    node.Data.Head.Owner,
-				FromItemIdx: idx,
-				ToKey:       node.Data.BodyLeaf[idx].Key,
-				ToMaxKey:    node.Data.BodyLeaf[idx].Key,
+				FromTree:     node.Data.Head.Owner,
+				FromItemSlot: slot,
+				ToKey:        node.Data.BodyLeaf[slot].Key,
+				ToMaxKey:     node.Data.BodyLeaf[slot].Key,
 			})
 			return path, node, nil
 		}
@@ -328,14 +328,14 @@ func (fs TreeOperatorImpl) prev(path TreePath, node *diskio.Ref[btrfsvol.Logical
 	path = path.DeepCopy()
 
 	// go up
-	for path.Node(-1).FromItemIdx < 1 {
+	for path.Node(-1).FromItemSlot < 1 {
 		path = path.Parent()
 		if len(path) == 0 {
 			return nil, nil, nil
 		}
 	}
 	// go left
-	path.Node(-1).FromItemIdx--
+	path.Node(-1).FromItemSlot--
 	if path.Node(-1).ToNodeAddr != 0 {
 		if node.Addr != path.Node(-2).ToNodeAddr {
 			FreeNodeRef(node)
@@ -344,7 +344,7 @@ func (fs TreeOperatorImpl) prev(path TreePath, node *diskio.Ref[btrfsvol.Logical
 				FreeNodeRef(node)
 				return nil, nil, err
 			}
-			path.Node(-1).ToNodeAddr = node.Data.BodyInternal[path.Node(-1).FromItemIdx].BlockPtr
+			path.Node(-1).ToNodeAddr = node.Data.BodyInterior[path.Node(-1).FromItemSlot].BlockPtr
 		}
 	}
 	// go down
@@ -360,19 +360,19 @@ func (fs TreeOperatorImpl) prev(path TreePath, node *diskio.Ref[btrfsvol.Logical
 		if node.Data.Head.Level > 0 {
 			path = append(path, TreePathElem{
 				FromTree:         node.Data.Head.Owner,
-				FromItemIdx:      len(node.Data.BodyInternal) - 1,
-				ToNodeAddr:       node.Data.BodyInternal[len(node.Data.BodyInternal)-1].BlockPtr,
-				ToNodeGeneration: node.Data.BodyInternal[len(node.Data.BodyInternal)-1].Generation,
+				FromItemSlot:     len(node.Data.BodyInterior) - 1,
+				ToNodeAddr:       node.Data.BodyInterior[len(node.Data.BodyInterior)-1].BlockPtr,
+				ToNodeGeneration: node.Data.BodyInterior[len(node.Data.BodyInterior)-1].Generation,
 				ToNodeLevel:      node.Data.Head.Level - 1,
-				ToKey:            node.Data.BodyInternal[len(node.Data.BodyInternal)-1].Key,
+				ToKey:            node.Data.BodyInterior[len(node.Data.BodyInterior)-1].Key,
 				ToMaxKey:         path.Node(-1).ToMaxKey,
 			})
 		} else {
 			path = append(path, TreePathElem{
-				FromTree:    node.Data.Head.Owner,
-				FromItemIdx: len(node.Data.BodyLeaf) - 1,
-				ToKey:       node.Data.BodyLeaf[len(node.Data.BodyLeaf)-1].Key,
-				ToMaxKey:    node.Data.BodyLeaf[len(node.Data.BodyLeaf)-1].Key,
+				FromTree:     node.Data.Head.Owner,
+				FromItemSlot: len(node.Data.BodyLeaf) - 1,
+				ToKey:        node.Data.BodyLeaf[len(node.Data.BodyLeaf)-1].Key,
+				ToMaxKey:     node.Data.BodyLeaf[len(node.Data.BodyLeaf)-1].Key,
 			})
 		}
 	}
@@ -402,7 +402,7 @@ func (fs TreeOperatorImpl) next(path TreePath, node *diskio.Ref[btrfsvol.Logical
 		}
 		path.Node(-2).ToNodeLevel = node.Data.Head.Level
 	}
-	for path.Node(-1).FromItemIdx+1 >= int(node.Data.Head.NumItems) {
+	for path.Node(-1).FromItemSlot+1 >= int(node.Data.Head.NumItems) {
 		path = path.Parent()
 		if len(path) == 1 {
 			return nil, nil, nil
@@ -418,7 +418,7 @@ func (fs TreeOperatorImpl) next(path TreePath, node *diskio.Ref[btrfsvol.Logical
 		}
 	}
 	// go right
-	path.Node(-1).FromItemIdx++
+	path.Node(-1).FromItemSlot++
 	if path.Node(-1).ToNodeAddr != 0 {
 		if node.Addr != path.Node(-2).ToNodeAddr {
 			FreeNodeRef(node)
@@ -427,7 +427,7 @@ func (fs TreeOperatorImpl) next(path TreePath, node *diskio.Ref[btrfsvol.Logical
 				FreeNodeRef(node)
 				return nil, nil, err
 			}
-			path.Node(-1).ToNodeAddr = node.Data.BodyInternal[path.Node(-1).FromItemIdx].BlockPtr
+			path.Node(-1).ToNodeAddr = node.Data.BodyInterior[path.Node(-1).FromItemSlot].BlockPtr
 		}
 	}
 	// go down
@@ -443,24 +443,24 @@ func (fs TreeOperatorImpl) next(path TreePath, node *diskio.Ref[btrfsvol.Logical
 		}
 		if node.Data.Head.Level > 0 {
 			toMaxKey := path.Node(-1).ToMaxKey
-			if len(node.Data.BodyInternal) > 1 {
-				toMaxKey = node.Data.BodyInternal[1].Key.Mm()
+			if len(node.Data.BodyInterior) > 1 {
+				toMaxKey = node.Data.BodyInterior[1].Key.Mm()
 			}
 			path = append(path, TreePathElem{
 				FromTree:         node.Data.Head.Owner,
-				FromItemIdx:      0,
-				ToNodeAddr:       node.Data.BodyInternal[0].BlockPtr,
-				ToNodeGeneration: node.Data.BodyInternal[0].Generation,
+				FromItemSlot:     0,
+				ToNodeAddr:       node.Data.BodyInterior[0].BlockPtr,
+				ToNodeGeneration: node.Data.BodyInterior[0].Generation,
 				ToNodeLevel:      node.Data.Head.Level - 1,
-				ToKey:            node.Data.BodyInternal[0].Key,
+				ToKey:            node.Data.BodyInterior[0].Key,
 				ToMaxKey:         toMaxKey,
 			})
 		} else {
 			path = append(path, TreePathElem{
-				FromTree:    node.Data.Head.Owner,
-				FromItemIdx: 0,
-				ToKey:       node.Data.BodyInternal[0].Key,
-				ToMaxKey:    node.Data.BodyInternal[0].Key,
+				FromTree:     node.Data.Head.Owner,
+				FromItemSlot: 0,
+				ToKey:        node.Data.BodyInterior[0].Key,
+				ToMaxKey:     node.Data.BodyInterior[0].Key,
 			})
 		}
 	}
@@ -476,7 +476,7 @@ func (fs TreeOperatorImpl) next(path TreePath, node *diskio.Ref[btrfsvol.Logical
 	return path, node, nil
 }
 
-// TreeSearch implements the 'Trees' interface.
+// TreeSearch implements the 'TreeOperator' interface.
 func (fs TreeOperatorImpl) TreeSearch(treeID btrfsprim.ObjID, fn func(btrfsprim.Key, uint32) int) (Item, error) {
 	sb, err := fs.Superblock()
 	if err != nil {
@@ -490,7 +490,7 @@ func (fs TreeOperatorImpl) TreeSearch(treeID btrfsprim.ObjID, fn func(btrfsprim.
 	if err != nil {
 		return Item{}, err
 	}
-	item := node.Data.BodyLeaf[path.Node(-1).FromItemIdx]
+	item := node.Data.BodyLeaf[path.Node(-1).FromItemSlot]
 	item.Body = item.Body.CloneItem()
 	FreeNodeRef(node)
 	return item, nil
@@ -503,7 +503,7 @@ func KeySearch(fn func(btrfsprim.Key) int) func(btrfsprim.Key, uint32) int {
 	}
 }
 
-// TreeLookup implements the 'Trees' interface.
+// TreeLookup implements the 'TreeOperator' interface.
 func (fs TreeOperatorImpl) TreeLookup(treeID btrfsprim.ObjID, key btrfsprim.Key) (Item, error) {
 	item, err := fs.TreeSearch(treeID, KeySearch(key.Compare))
 	if err != nil {
@@ -512,7 +512,7 @@ func (fs TreeOperatorImpl) TreeLookup(treeID btrfsprim.ObjID, key btrfsprim.Key)
 	return item, err
 }
 
-// TreeSearchAll implements the 'Trees' interface.
+// TreeSearchAll implements the 'TreeOperator' interface.
 func (fs TreeOperatorImpl) TreeSearchAll(treeID btrfsprim.ObjID, fn func(btrfsprim.Key, uint32) int) ([]Item, error) {
 	sb, err := fs.Superblock()
 	if err != nil {
@@ -526,7 +526,7 @@ func (fs TreeOperatorImpl) TreeSearchAll(treeID btrfsprim.ObjID, fn func(btrfspr
 	if err != nil {
 		return nil, err
 	}
-	middleItem := middleNode.Data.BodyLeaf[middlePath.Node(-1).FromItemIdx]
+	middleItem := middleNode.Data.BodyLeaf[middlePath.Node(-1).FromItemSlot]
 
 	ret := []Item{middleItem}
 	var errs derror.MultiError
@@ -540,7 +540,7 @@ func (fs TreeOperatorImpl) TreeSearchAll(treeID btrfsprim.ObjID, fn func(btrfspr
 		if len(prevPath) == 0 {
 			break
 		}
-		prevItem := prevNode.Data.BodyLeaf[prevPath.Node(-1).FromItemIdx]
+		prevItem := prevNode.Data.BodyLeaf[prevPath.Node(-1).FromItemSlot]
 		if fn(prevItem.Key, prevItem.BodySize) != 0 {
 			break
 		}
@@ -567,7 +567,7 @@ func (fs TreeOperatorImpl) TreeSearchAll(treeID btrfsprim.ObjID, fn func(btrfspr
 		if len(nextPath) == 0 {
 			break
 		}
-		nextItem := nextNode.Data.BodyLeaf[nextPath.Node(-1).FromItemIdx]
+		nextItem := nextNode.Data.BodyLeaf[nextPath.Node(-1).FromItemSlot]
 		if fn(nextItem.Key, nextItem.BodySize) != 0 {
 			break
 		}
diff --git a/lib/btrfs/btrfstree/path.go b/lib/btrfs/btrfstree/path.go
index dd2cb74..9b1a5c7 100644
--- a/lib/btrfs/btrfstree/path.go
+++ b/lib/btrfs/btrfstree/path.go
@@ -1,4 +1,4 @@
-// Copyright (C) 2022  Luke Shumaker <lukeshu@lukeshu.com>
+// Copyright (C) 2022-2023  Luke Shumaker <lukeshu@lukeshu.com>
 //
 // SPDX-License-Identifier: GPL-2.0-or-later
 
@@ -17,7 +17,7 @@ import (
 // system) to the a node or item within one of the btrees in the
 // system.
 //
-//   - The first element will always have an ItemIdx of -1.
+//   - The first element will always have an ItemSlot of -1.
 //
 //   - For .Item() callbacks, the last element will always have a
 //     NodeAddr of 0.
@@ -26,7 +26,7 @@ import (
 //
 //	[superblock: tree=B, lvl=3, gen=6]
 //	     |
-//	     | <------------------------------------------ pathElem={from_tree:B, from_idx=-1,
+//	     | <------------------------------------------ pathElem={from_tree:B, from_slot=-1,
 //	     |                                                       to_addr:0x01, to_gen=6, to_lvl=3}
 //	  +[0x01]-------------+
 //	  | lvl=3 gen=6 own=B |
@@ -34,7 +34,7 @@ import (
 //	  |0|1|2|3|4|5|6|7|8|9|
 //	  +-+-+-+-+-+-+-+-+-+-+
 //	                 |
-//	                 | <------------------------------ pathElem:{from_tree:B, from_idx:7,
+//	                 | <------------------------------ pathElem:{from_tree:B, from_slot:7,
 //	                 |                                           to_addr:0x02, to_gen:5, to_lvl:2}
 //	              +[0x02]--------------+
 //	              | lvl=2 gen=5 own=B  |
@@ -42,7 +42,7 @@ import (
 //	              |0|1|2|3|4|5|6|7|8|9|
 //	              +-+-+-+-+-+-+-+-+-+-+
 //	                           |
-//	                           | <-------------------- pathElem={from_tree:B, from_idx:6,
+//	                           | <-------------------- pathElem={from_tree:B, from_slot:6,
 //	                           |                                 to_addr:0x03, to_gen:5, to_lvl:1}
 //	                        +[0x03]-------------+
 //	                        | lvl=1 gen=5 own=A |
@@ -50,7 +50,7 @@ import (
 //	                        |0|1|2|3|4|5|6|7|8|9|
 //	                        +-+-+-+-+-+-+-+-+-+-+
 //	                               |
-//	                               | <---------------- pathElem={from_tree:A, from_idx:3,
+//	                               | <---------------- pathElem={from_tree:A, from_slot:3,
 //	                               |                             to_addr:0x04, to_gen:2, lvl:0}
 //	                             +[0x04]-------------+
 //	                             | lvl=0 gen=2 own=A |
@@ -58,7 +58,7 @@ import (
 //	                             |0|1|2|3|4|5|6|7|8|9|
 //	                             +-+-+-+-+-+-+-+-+-+-+
 //	                                |
-//	                                | <--------------- pathElem={from_tree:A, from_idx:1,
+//	                                | <--------------- pathElem={from_tree:A, from_slot:1,
 //	                                |                            to_addr:0, to_gen: 0, to_lvl:0}
 //	                              [item]
 type TreePath []TreePathElem
@@ -68,9 +68,9 @@ type TreePathElem struct {
 	// FromTree is the owning tree ID of the parent node; or the
 	// well-known tree ID if this is the root.
 	FromTree btrfsprim.ObjID
-	// FromItemIdx is the index of this KeyPointer in the parent
+	// FromItemSlot is the index of this KeyPointer in the parent
 	// Node; or -1 if this is the root and there is no KeyPointer.
-	FromItemIdx int
+	FromItemSlot int
 
 	// ToNodeAddr is the address of the node that the KeyPointer
 	// points at, or 0 if this is a leaf item and nothing is being
@@ -104,13 +104,13 @@ func (path TreePath) String() string {
 	} else {
 		var ret strings.Builder
 		fmt.Fprintf(&ret, "%s->", path[0].FromTree.Format(btrfsprim.ROOT_TREE_OBJECTID))
-		if len(path) == 1 && path[0] == (TreePathElem{FromTree: path[0].FromTree, FromItemIdx: -1}) {
+		if len(path) == 1 && path[0] == (TreePathElem{FromTree: path[0].FromTree, FromItemSlot: -1}) {
 			ret.WriteString("(empty-path)")
 		} else {
 			path[0].writeNodeTo(&ret)
 		}
 		for _, elem := range path[1:] {
-			fmt.Fprintf(&ret, "[%v]", elem.FromItemIdx)
+			fmt.Fprintf(&ret, "[%v]", elem.FromItemSlot)
 			if elem.ToNodeAddr != 0 {
 				ret.WriteString("->")
 				elem.writeNodeTo(&ret)
diff --git a/lib/btrfs/btrfstree/types_node.go b/lib/btrfs/btrfstree/types_node.go
index 0a89e05..150539d 100644
--- a/lib/btrfs/btrfstree/types_node.go
+++ b/lib/btrfs/btrfstree/types_node.go
@@ -89,7 +89,7 @@ type Node struct {
 
 	// The node's body (which one of these is present depends on
 	// the node's type, as specified in the header)
-	BodyInternal []KeyPointer // for btrfsprim nodes
+	BodyInterior []KeyPointer // for interior nodes
 	BodyLeaf     []Item       // for leave nodes
 
 	Padding []byte
@@ -105,7 +105,7 @@ type NodeHeader struct {
 	Generation    btrfsprim.Generation `bin:"off=0x50, siz=0x8"`
 	Owner         btrfsprim.ObjID      `bin:"off=0x58, siz=0x8"` // The ID of the tree that contains this node
 	NumItems      uint32               `bin:"off=0x60, siz=0x4"` // [ignored-when-writing]
-	Level         uint8                `bin:"off=0x64, siz=0x1"` // 0 for leaf nodes, >=1 for btrfsprim nodes
+	Level         uint8                `bin:"off=0x64, siz=0x1"` // 0 for leaf nodes, >=1 for interior nodes
 	binstruct.End `bin:"off=0x65"`
 }
 
@@ -122,10 +122,10 @@ func (node Node) MaxItems() uint32 {
 
 func (node Node) MinItem() (btrfsprim.Key, bool) {
 	if node.Head.Level > 0 {
-		if len(node.BodyInternal) == 0 {
+		if len(node.BodyInterior) == 0 {
 			return btrfsprim.Key{}, false
 		}
-		return node.BodyInternal[0].Key, true
+		return node.BodyInterior[0].Key, true
 	} else {
 		if len(node.BodyLeaf) == 0 {
 			return btrfsprim.Key{}, false
@@ -136,10 +136,10 @@ func (node Node) MinItem() (btrfsprim.Key, bool) {
 
 func (node Node) MaxItem() (btrfsprim.Key, bool) {
 	if node.Head.Level > 0 {
-		if len(node.BodyInternal) == 0 {
+		if len(node.BodyInterior) == 0 {
 			return btrfsprim.Key{}, false
 		}
-		return node.BodyInternal[len(node.BodyInternal)-1].Key, true
+		return node.BodyInterior[len(node.BodyInterior)-1].Key, true
 	} else {
 		if len(node.BodyLeaf) == 0 {
 			return btrfsprim.Key{}, false
@@ -186,7 +186,7 @@ func (node *Node) UnmarshalBinary(nodeBuf []byte) (int, error) {
 			n, nodeHeaderSize)
 	}
 	if node.Head.Level > 0 {
-		_n, err := node.unmarshalInternal(nodeBuf[n:])
+		_n, err := node.unmarshalInterior(nodeBuf[n:])
 		n += _n
 		if err != nil {
 			return n, fmt.Errorf("btrfsprim: %w", err)
@@ -214,7 +214,7 @@ func (node Node) MarshalBinary() ([]byte, error) {
 			nodeHeaderSize, node.Size)
 	}
 	if node.Head.Level > 0 {
-		node.Head.NumItems = uint32(len(node.BodyInternal))
+		node.Head.NumItems = uint32(len(node.BodyInterior))
 	} else {
 		node.Head.NumItems = uint32(len(node.BodyLeaf))
 	}
@@ -232,7 +232,7 @@ func (node Node) MarshalBinary() ([]byte, error) {
 	}
 
 	if node.Head.Level > 0 {
-		if err := node.marshalInternalTo(buf[nodeHeaderSize:]); err != nil {
+		if err := node.marshalInteriorTo(buf[nodeHeaderSize:]); err != nil {
 			return buf, err
 		}
 	} else {
@@ -244,7 +244,7 @@ func (node Node) MarshalBinary() ([]byte, error) {
 	return buf, nil
 }
 
-// Node: "internal" ////////////////////////////////////////////////////////////////////////////////
+// Node: "interior" ////////////////////////////////////////////////////////////////////////////////
 
 type KeyPointer struct {
 	Key           btrfsprim.Key        `bin:"off=0x0, siz=0x11"`
@@ -253,11 +253,11 @@ type KeyPointer struct {
 	binstruct.End `bin:"off=0x21"`
 }
 
-func (node *Node) unmarshalInternal(bodyBuf []byte) (int, error) {
+func (node *Node) unmarshalInterior(bodyBuf []byte) (int, error) {
 	n := 0
-	node.BodyInternal = make([]KeyPointer, node.Head.NumItems)
-	for i := range node.BodyInternal {
-		_n, err := binstruct.Unmarshal(bodyBuf[n:], &node.BodyInternal[i])
+	node.BodyInterior = make([]KeyPointer, node.Head.NumItems)
+	for i := range node.BodyInterior {
+		_n, err := binstruct.Unmarshal(bodyBuf[n:], &node.BodyInterior[i])
 		n += _n
 		if err != nil {
 			return n, fmt.Errorf("item %v: %w", i, err)
@@ -267,9 +267,9 @@ func (node *Node) unmarshalInternal(bodyBuf []byte) (int, error) {
 	return len(bodyBuf), nil
 }
 
-func (node *Node) marshalInternalTo(bodyBuf []byte) error {
+func (node *Node) marshalInteriorTo(bodyBuf []byte) error {
 	n := 0
-	for i, item := range node.BodyInternal {
+	for i, item := range node.BodyInterior {
 		bs, err := binstruct.Marshal(item)
 		if err != nil {
 			return fmt.Errorf("item %v: %w", i, err)
diff --git a/lib/btrfs/io3_btree.go b/lib/btrfs/io3_btree.go
index 18df98e..db4e42c 100644
--- a/lib/btrfs/io3_btree.go
+++ b/lib/btrfs/io3_btree.go
@@ -14,49 +14,46 @@ import (
 	"git.lukeshu.com/btrfs-progs-ng/lib/diskio"
 )
 
-func (fs *FS) TreeWalk(ctx context.Context, treeID btrfsprim.ObjID, errHandle func(*btrfstree.TreeError), cbs btrfstree.TreeWalkHandler) {
-	btrfstree.TreeOperatorImpl{NodeSource: fs}.TreeWalk(ctx, treeID, errHandle, cbs)
-}
+// This file is ordered from low-level to high-level.
 
-func (fs *FS) TreeLookup(treeID btrfsprim.ObjID, key btrfsprim.Key) (btrfstree.Item, error) {
-	return btrfstree.TreeOperatorImpl{NodeSource: fs}.TreeLookup(treeID, key)
-}
+// btrfstree.NodeSource ////////////////////////////////////////////////////////
 
-func (fs *FS) TreeSearch(treeID btrfsprim.ObjID, fn func(key btrfsprim.Key, size uint32) int) (btrfstree.Item, error) {
-	return btrfstree.TreeOperatorImpl{NodeSource: fs}.TreeSearch(treeID, fn)
+// ReadNode implements btrfstree.NodeSource.
+func (fs *FS) ReadNode(path btrfstree.TreePath) (*diskio.Ref[btrfsvol.LogicalAddr, btrfstree.Node], error) {
+	return btrfstree.FSReadNode(fs, path)
 }
 
-func (fs *FS) TreeSearchAll(treeID btrfsprim.ObjID, fn func(key btrfsprim.Key, size uint32) int) ([]btrfstree.Item, error) {
-	return btrfstree.TreeOperatorImpl{NodeSource: fs}.TreeSearchAll(treeID, fn)
-}
+var _ btrfstree.NodeSource = (*FS)(nil)
 
-var _ btrfstree.TreeOperator = (*FS)(nil)
+// btrfstree.NodeFile //////////////////////////////////////////////////////////
 
 func (fs *FS) populateTreeUUIDs(ctx context.Context) {
-	if fs.cacheObjID2UUID == nil || fs.cacheUUID2ObjID == nil || fs.cacheTreeParent == nil {
-		fs.cacheObjID2UUID = make(map[btrfsprim.ObjID]btrfsprim.UUID)
-		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
-			},
-			btrfstree.TreeWalkHandler{
-				Item: func(_ btrfstree.TreePath, item btrfstree.Item) error {
-					itemBody, ok := item.Body.(*btrfsitem.Root)
-					if !ok {
-						return nil
-					}
-					fs.cacheObjID2UUID[item.Key.ObjectID] = itemBody.UUID
-					fs.cacheTreeParent[item.Key.ObjectID] = itemBody.ParentUUID
-					fs.cacheUUID2ObjID[itemBody.UUID] = item.Key.ObjectID
+	if fs.cacheObjID2UUID != nil && fs.cacheUUID2ObjID != nil && fs.cacheTreeParent != nil {
+		return
+	}
+	fs.cacheObjID2UUID = make(map[btrfsprim.ObjID]btrfsprim.UUID)
+	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
+		},
+		btrfstree.TreeWalkHandler{
+			Item: func(_ btrfstree.TreePath, item btrfstree.Item) error {
+				itemBody, ok := item.Body.(*btrfsitem.Root)
+				if !ok {
 					return nil
-				},
+				}
+				fs.cacheObjID2UUID[item.Key.ObjectID] = itemBody.UUID
+				fs.cacheTreeParent[item.Key.ObjectID] = itemBody.ParentUUID
+				fs.cacheUUID2ObjID[itemBody.UUID] = item.Key.ObjectID
+				return nil
 			},
-		)
-	}
+		},
+	)
 }
 
+// ParentTree implements btrfstree.NodeFile.
 func (fs *FS) ParentTree(tree btrfsprim.ObjID) (btrfsprim.ObjID, bool) {
 	if tree < btrfsprim.FIRST_FREE_OBJECTID || tree > btrfsprim.LAST_FREE_OBJECTID {
 		// no parent
@@ -80,6 +77,28 @@ func (fs *FS) ParentTree(tree btrfsprim.ObjID) (btrfsprim.ObjID, bool) {
 	return parentObjID, true
 }
 
-func (fs *FS) ReadNode(path btrfstree.TreePath) (*diskio.Ref[btrfsvol.LogicalAddr, btrfstree.Node], error) {
-	return btrfstree.FSReadNode(fs, path)
+var _ btrfstree.NodeFile = (*FS)(nil)
+
+// btrfstree.TreeOperator //////////////////////////////////////////////////////
+
+// TreeWalk implements btrfstree.TreeOperator.
+func (fs *FS) TreeWalk(ctx context.Context, treeID btrfsprim.ObjID, errHandle func(*btrfstree.TreeError), cbs btrfstree.TreeWalkHandler) {
+	btrfstree.TreeOperatorImpl{NodeSource: fs}.TreeWalk(ctx, treeID, errHandle, cbs)
+}
+
+// TreeLookup implements btrfstree.TreeOperator.
+func (fs *FS) TreeLookup(treeID btrfsprim.ObjID, key btrfsprim.Key) (btrfstree.Item, error) {
+	return btrfstree.TreeOperatorImpl{NodeSource: fs}.TreeLookup(treeID, key)
+}
+
+// TreeSearch implements btrfstree.TreeOperator.
+func (fs *FS) TreeSearch(treeID btrfsprim.ObjID, fn func(key btrfsprim.Key, size uint32) int) (btrfstree.Item, error) {
+	return btrfstree.TreeOperatorImpl{NodeSource: fs}.TreeSearch(treeID, fn)
 }
+
+// TreeSearchAll implements btrfstree.TreeOperator.
+func (fs *FS) TreeSearchAll(treeID btrfsprim.ObjID, fn func(key btrfsprim.Key, size uint32) int) ([]btrfstree.Item, error) {
+	return btrfstree.TreeOperatorImpl{NodeSource: fs}.TreeSearchAll(treeID, fn)
+}
+
+var _ btrfstree.TreeOperator = (*FS)(nil)