Move files around [ci-skip]

6 files changed, 1284 insertions, 0 deletions

diff --git a/cmd/btrfs-rec/inspect/rebuildtrees/rebuild.go b/cmd/btrfs-rec/inspect/rebuildtrees/rebuild.go
new file mode 100644
index 0000000..cf334a0
--- /dev/null
+++ b/cmd/btrfs-rec/inspect/rebuildtrees/rebuild.go
@@ -0,0 +1,583 @@
+// Copyright (C) 2022-2023  Luke Shumaker <lukeshu@lukeshu.com>
+//
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+package rebuildnodes
+
+import (
+	"context"
+	"fmt"
+	"runtime"
+	"sort"
+	"time"
+
+	"github.com/datawire/dlib/dgroup"
+	"github.com/datawire/dlib/dlog"
+
+	"git.lukeshu.com/btrfs-progs-ng/lib/btrfs"
+	"git.lukeshu.com/btrfs-progs-ng/lib/btrfs/btrfsitem"
+	"git.lukeshu.com/btrfs-progs-ng/lib/btrfs/btrfsprim"
+	"git.lukeshu.com/btrfs-progs-ng/lib/btrfs/btrfstree"
+	"git.lukeshu.com/btrfs-progs-ng/lib/btrfs/btrfsvol"
+	"git.lukeshu.com/btrfs-progs-ng/lib/btrfsprogs/btrfsinspect"
+	"git.lukeshu.com/btrfs-progs-ng/lib/btrfsprogs/btrfsinspect/rebuildnodes/btrees"
+	"git.lukeshu.com/btrfs-progs-ng/lib/btrfsprogs/btrfsinspect/rebuildnodes/graph"
+	"git.lukeshu.com/btrfs-progs-ng/lib/btrfsprogs/btrfsinspect/rebuildnodes/keyio"
+	"git.lukeshu.com/btrfs-progs-ng/lib/containers"
+	"git.lukeshu.com/btrfs-progs-ng/lib/maps"
+	"git.lukeshu.com/btrfs-progs-ng/lib/textui"
+)
+
+type keyAndTree struct {
+	btrfsprim.Key
+	TreeID btrfsprim.ObjID
+}
+
+func (a keyAndTree) Compare(b keyAndTree) int {
+	if d := containers.NativeCompare(a.TreeID, b.TreeID); d != 0 {
+		return d
+	}
+	return a.Key.Compare(b.Key)
+}
+
+func (o keyAndTree) String() string {
+	return fmt.Sprintf("tree=%v key=%v", o.TreeID, o.Key)
+}
+
+type rebuilder struct {
+	sb    btrfstree.Superblock
+	graph graph.Graph
+	keyIO *keyio.Handle
+
+	rebuilt *btrees.RebuiltForrest
+
+	curKey struct {
+		TreeID btrfsprim.ObjID
+		Key    containers.Optional[btrfsprim.Key]
+	}
+	treeQueue          containers.Set[btrfsprim.ObjID]
+	retryItemQueue     map[btrfsprim.ObjID]containers.Set[keyAndTree]
+	addedItemQueue     containers.Set[keyAndTree]
+	settledItemQueue   containers.Set[keyAndTree]
+	augmentQueue       map[btrfsprim.ObjID]*treeAugmentQueue
+	numAugments        int
+	numAugmentFailures int
+}
+
+type treeAugmentQueue struct {
+	zero   map[Want]struct{}
+	single map[Want]btrfsvol.LogicalAddr
+	multi  map[Want]containers.Set[btrfsvol.LogicalAddr]
+}
+
+type Rebuilder interface {
+	Rebuild(context.Context) error
+	ListRoots(context.Context) map[btrfsprim.ObjID]containers.Set[btrfsvol.LogicalAddr]
+}
+
+func NewRebuilder(ctx context.Context, fs *btrfs.FS, nodeScanResults btrfsinspect.ScanDevicesResult) (Rebuilder, error) {
+	ctx = dlog.WithField(ctx, "btrfsinspect.rebuild-nodes.step", "read-fs-data")
+	sb, nodeGraph, keyIO, err := ScanDevices(ctx, fs, nodeScanResults) // ScanDevices does its own logging
+	if err != nil {
+		return nil, err
+	}
+
+	o := &rebuilder{
+		sb:    sb,
+		graph: nodeGraph,
+		keyIO: keyIO,
+	}
+	o.rebuilt = btrees.NewRebuiltForrest(sb, nodeGraph, keyIO, o)
+	return o, nil
+}
+
+func (o *rebuilder) ListRoots(ctx context.Context) map[btrfsprim.ObjID]containers.Set[btrfsvol.LogicalAddr] {
+	return o.rebuilt.ListRoots(ctx)
+}
+
+func (o *rebuilder) Rebuild(ctx context.Context) error {
+	ctx = dlog.WithField(ctx, "btrfsinspect.rebuild-nodes.step", "rebuild")
+
+	// Initialize
+	o.retryItemQueue = make(map[btrfsprim.ObjID]containers.Set[keyAndTree])
+	o.addedItemQueue = make(containers.Set[keyAndTree])
+	o.settledItemQueue = make(containers.Set[keyAndTree])
+	o.augmentQueue = make(map[btrfsprim.ObjID]*treeAugmentQueue)
+
+	// Seed the queue
+	o.treeQueue = containers.NewSet[btrfsprim.ObjID](
+		btrfsprim.ROOT_TREE_OBJECTID,
+		btrfsprim.CHUNK_TREE_OBJECTID,
+		// btrfsprim.TREE_LOG_OBJECTID, // TODO(lukeshu): Special LOG_TREE handling
+		btrfsprim.BLOCK_GROUP_TREE_OBJECTID,
+	)
+
+	// Run
+	for passNum := 0; len(o.treeQueue) > 0 || len(o.addedItemQueue) > 0 || len(o.settledItemQueue) > 0 || len(o.augmentQueue) > 0; passNum++ {
+		ctx := dlog.WithField(ctx, "btrfsinspect.rebuild-nodes.rebuild.pass", passNum)
+
+		// Crawl trees (Drain o.treeQueue, fill o.addedItemQueue).
+		if err := o.processTreeQueue(ctx); err != nil {
+			return err
+		}
+		runtime.GC()
+
+		if len(o.addedItemQueue) > 0 {
+			// Settle items (drain o.addedItemQueue, fill o.augmentQueue and o.settledItemQueue).
+			if err := o.processAddedItemQueue(ctx); err != nil {
+				return err
+			}
+		} else {
+			// Process items (drain o.settledItemQueue, fill o.augmentQueue and o.treeQueue).
+			if err := o.processSettledItemQueue(ctx); err != nil {
+				return err
+			}
+		}
+		runtime.GC()
+
+		// Apply augments (drain o.augmentQueue (and maybe o.retryItemQueue), fill o.addedItemQueue).
+		if err := o.processAugmentQueue(ctx); err != nil {
+			return err
+		}
+		runtime.GC()
+	}
+
+	return nil
+}
+
+// processTreeQueue drains o.treeQueue, filling o.addedItemQueue.
+func (o *rebuilder) processTreeQueue(ctx context.Context) error {
+	ctx = dlog.WithField(ctx, "btrfsinspect.rebuild-nodes.rebuild.substep", "collect-items")
+
+	queue := maps.SortedKeys(o.treeQueue)
+	o.treeQueue = make(containers.Set[btrfsprim.ObjID])
+
+	// Because trees can be wildly different sizes, it's impossible to have a meaningful
+	// progress percentage here.
+	o.curKey.Key.OK = false
+	for _, o.curKey.TreeID = range queue {
+		if err := ctx.Err(); err != nil {
+			return err
+		}
+		// This will call o.AddedItem as nescessary, which
+		// inserts to o.addedItemQueue.
+		_ = o.rebuilt.Tree(ctx, o.curKey.TreeID)
+	}
+
+	return nil
+}
+
+type settleItemStats struct {
+	textui.Portion[int]
+	NumAugments     int
+	NumAugmentTrees int
+}
+
+func (s settleItemStats) String() string {
+	// return textui.Sprintf("%v (queued %v augments across %v trees)",
+	return textui.Sprintf("%v (aug:%v trees:%v)",
+		s.Portion, s.NumAugments, s.NumAugmentTrees)
+}
+
+// processAddedItemQueue drains o.addedItemQueue, filling o.augmentQueue and o.settledItemQueue.
+func (o *rebuilder) processAddedItemQueue(ctx context.Context) error {
+	ctx = dlog.WithField(ctx, "btrfsinspect.rebuild-nodes.rebuild.substep", "settle-items")
+
+	queue := maps.Keys(o.addedItemQueue)
+	o.addedItemQueue = make(containers.Set[keyAndTree])
+	sort.Slice(queue, func(i, j int) bool {
+		return queue[i].Compare(queue[j]) < 0
+	})
+
+	var progress settleItemStats
+	progress.D = len(queue)
+	progressWriter := textui.NewProgress[settleItemStats](ctx, dlog.LogLevelInfo, textui.Tunable(1*time.Second))
+	ctx = dlog.WithField(ctx, "btrfsinspect.rebuild-nodes.rebuild.substep.progress", &progress)
+
+	for i, key := range queue {
+		progress.N = i
+		progressWriter.Set(progress)
+
+		ctx := dlog.WithField(ctx, "btrfsinspect.rebuild-nodes.rebuild.settle.item", key)
+		tree := o.rebuilt.Tree(ctx, key.TreeID)
+		incPtr, ok := tree.Items(ctx).Load(key.Key)
+		if !ok {
+			panic(fmt.Errorf("should not happen: failed to load already-added item: %v", key))
+		}
+		excPtr, ok := tree.PotentialItems(ctx).Load(key.Key)
+		if ok && tree.ShouldReplace(incPtr.Node, excPtr.Node) {
+			wantKey := WantWithTree{
+				TreeID: key.TreeID,
+				Key:    wantFromKey(key.Key),
+			}
+			o.wantAugment(ctx, wantKey, tree.LeafToRoots(ctx, excPtr.Node))
+			progress.NumAugments = o.numAugments
+			progress.NumAugmentTrees = len(o.augmentQueue)
+			progressWriter.Set(progress)
+		} else if !handleWouldBeNoOp(key.ItemType) {
+			o.settledItemQueue.Insert(key)
+		}
+	}
+
+	progress.N = len(queue)
+	progressWriter.Set(progress)
+	progressWriter.Done()
+	return nil
+}
+
+type processItemStats struct {
+	textui.Portion[int]
+	NumAugments     int
+	NumFailures     int
+	NumAugmentTrees int
+}
+
+func (s processItemStats) String() string {
+	// return textui.Sprintf("%v (queued %v augments and %v failures across %v trees)",
+	return textui.Sprintf("%v (aug:%v fail:%v trees:%v)",
+		s.Portion, s.NumAugments, s.NumFailures, s.NumAugmentTrees)
+}
+
+// processSettledItemQueue drains o.settledItemQueue, filling o.augmentQueue and o.treeQueue.
+func (o *rebuilder) processSettledItemQueue(ctx context.Context) error {
+	ctx = dlog.WithField(ctx, "btrfsinspect.rebuild-nodes.rebuild.substep", "process-items")
+
+	queue := maps.Keys(o.settledItemQueue)
+	o.settledItemQueue = make(containers.Set[keyAndTree])
+	sort.Slice(queue, func(i, j int) bool {
+		return queue[i].Compare(queue[j]) < 0
+	})
+
+	var progress processItemStats
+	progress.D = len(queue)
+	progressWriter := textui.NewProgress[processItemStats](ctx, dlog.LogLevelInfo, textui.Tunable(1*time.Second))
+	ctx = dlog.WithField(ctx, "btrfsinspect.rebuild-nodes.rebuild.substep.progress", &progress)
+
+	type keyAndBody struct {
+		keyAndTree
+		Body btrfsitem.Item
+	}
+	itemChan := make(chan keyAndBody, textui.Tunable(300)) // average items-per-node≈100; let's have a buffer of ~3 nodes
+	grp := dgroup.NewGroup(ctx, dgroup.GroupConfig{})
+	grp.Go("io", func(ctx context.Context) error {
+		defer close(itemChan)
+		for _, key := range queue {
+			if err := ctx.Err(); err != nil {
+				return err
+			}
+			ctx := dlog.WithField(ctx, "btrfsinspect.rebuild-nodes.rebuild.process.item", key)
+			item := keyAndBody{
+				keyAndTree: key,
+				Body:       o.rebuilt.Tree(ctx, key.TreeID).ReadItem(ctx, key.Key),
+			}
+			select {
+			case itemChan <- item:
+			case <-ctx.Done():
+			}
+		}
+		return nil
+	})
+	grp.Go("cpu", func(ctx context.Context) error {
+		defer progressWriter.Done()
+		o.curKey.Key.OK = true
+		for item := range itemChan {
+			ctx := dlog.WithField(ctx, "btrfsinspect.rebuild-nodes.rebuild.process.item", item.keyAndTree)
+			o.curKey.TreeID = item.TreeID
+			o.curKey.Key.Val = item.Key
+			handleItem(o, ctx, item.TreeID, btrfstree.Item{
+				Key:  item.Key,
+				Body: item.Body,
+			})
+			item.Body.Free()
+			if item.ItemType == btrfsitem.ROOT_ITEM_KEY {
+				o.treeQueue.Insert(item.ObjectID)
+			}
+			progress.N++
+			progress.NumAugments = o.numAugments
+			progress.NumFailures = o.numAugmentFailures
+			progress.NumAugmentTrees = len(o.augmentQueue)
+			progressWriter.Set(progress)
+		}
+		return nil
+	})
+	return grp.Wait()
+}
+
+// processAugmentQueue drains o.augmentQueue (and maybe o.retryItemQueue), filling o.addedItemQueue.
+func (o *rebuilder) processAugmentQueue(ctx context.Context) error {
+	ctx = dlog.WithField(ctx, "btrfsinspect.rebuild-nodes.rebuild.substep", "apply-augments")
+
+	resolvedAugments := make(map[btrfsprim.ObjID]containers.Set[btrfsvol.LogicalAddr], len(o.augmentQueue))
+	var progress textui.Portion[int]
+	for _, treeID := range maps.SortedKeys(o.augmentQueue) {
+		if err := ctx.Err(); err != nil {
+			return err
+		}
+		ctx := dlog.WithField(ctx, "btrfsinspect.rebuild-nodes.rebuild.augment.tree", treeID)
+		resolvedAugments[treeID] = o.resolveTreeAugments(ctx, treeID)
+		progress.D += len(resolvedAugments[treeID])
+	}
+	o.augmentQueue = make(map[btrfsprim.ObjID]*treeAugmentQueue)
+	o.numAugments = 0
+	o.numAugmentFailures = 0
+	runtime.GC()
+
+	progressWriter := textui.NewProgress[textui.Portion[int]](ctx, dlog.LogLevelInfo, textui.Tunable(1*time.Second))
+	ctx = dlog.WithField(ctx, "btrfsinspect.rebuild-nodes.rebuild.substep.progress", &progress)
+	for _, treeID := range maps.SortedKeys(resolvedAugments) {
+		ctx := dlog.WithField(ctx, "btrfsinspect.rebuild-nodes.rebuild.augment.tree", treeID)
+		for _, nodeAddr := range maps.SortedKeys(resolvedAugments[treeID]) {
+			if err := ctx.Err(); err != nil {
+				progressWriter.Set(progress)
+				progressWriter.Done()
+				return err
+			}
+			progressWriter.Set(progress)
+			// This will call o.AddedItem as nescessary, which
+			// inserts to o.addedItemQueue.
+			o.rebuilt.Tree(ctx, treeID).AddRoot(ctx, nodeAddr)
+			progress.N++
+		}
+	}
+	progressWriter.Set(progress)
+	progressWriter.Done()
+
+	return nil
+}
+
+func (o *rebuilder) enqueueRetry(ifTreeID btrfsprim.ObjID) {
+	if o.curKey.Key.OK {
+		if o.retryItemQueue[ifTreeID] == nil {
+			o.retryItemQueue[ifTreeID] = make(containers.Set[keyAndTree])
+		}
+		o.retryItemQueue[ifTreeID].Insert(keyAndTree{
+			TreeID: o.curKey.TreeID,
+			Key:    o.curKey.Key.Val,
+		})
+	} else {
+		o.treeQueue.Insert(o.curKey.TreeID)
+	}
+}
+
+func (o *rebuilder) resolveTreeAugments(ctx context.Context, treeID btrfsprim.ObjID) containers.Set[btrfsvol.LogicalAddr] {
+	// Define an algorithm that takes several lists of items, and returns a
+	// set of those items such that each input list contains zero or one of
+	// the items from your return set.  The same item may appear in multiple
+	// of the input lists.
+
+	type ChoiceInfo struct {
+		Count      int
+		Distance   int
+		Generation btrfsprim.Generation
+	}
+	choices := make(map[btrfsvol.LogicalAddr]ChoiceInfo)
+	// o.augmentQueue[treeID].zero is optimized storage for lists
+	// with zero items.  Go ahead and free that memory up.
+	o.augmentQueue[treeID].zero = nil
+	// o.augmentQueue[treeID].single is optimized storage for
+	// lists with exactly 1 item.
+	for _, choice := range o.augmentQueue[treeID].single {
+		if old, ok := choices[choice]; ok {
+			old.Count++
+			choices[choice] = old
+		} else {
+			choices[choice] = ChoiceInfo{
+				Count:      1,
+				Distance:   discardOK(o.rebuilt.Tree(ctx, treeID).COWDistance(o.graph.Nodes[choice].Owner)),
+				Generation: o.graph.Nodes[choice].Generation,
+			}
+		}
+	}
+	// o.augmentQueue[treeID].multi is the main list storage.
+	for _, list := range o.augmentQueue[treeID].multi {
+		for choice := range list {
+			if old, ok := choices[choice]; ok {
+				old.Count++
+				choices[choice] = old
+			} else {
+				choices[choice] = ChoiceInfo{
+					Count:      1,
+					Distance:   discardOK(o.rebuilt.Tree(ctx, treeID).COWDistance(o.graph.Nodes[choice].Owner)),
+					Generation: o.graph.Nodes[choice].Generation,
+				}
+			}
+		}
+	}
+
+	// > Example 1: Given the input lists
+	// >
+	// >     0: [A, B]
+	// >     2: [A, C]
+	// >
+	// > legal solutions would be `[]`, `[A]`, `[B]`, `[C]`, or `[B, C]`.  It
+	// > would not be legal to return `[A, B]` or `[A, C]`.
+	//
+	// > Example 2: Given the input lists
+	// >
+	// >     1: [A, B]
+	// >     2: [A]
+	// >     3: [B]
+	// >
+	// > legal solution would be `[]`, `[A]` or `[B]`.  It would not be legal
+	// > to return `[A, B]`.
+	//
+	// The algorithm should optimize for the following goals:
+	//
+	//  - We prefer that each input list have an item in the return set.
+	//
+	//    > In Example 1, while `[]`, `[B]`, and `[C]` are permissible
+	//    > solutions, they are not optimal, because one or both of the input
+	//    > lists are not represented.
+	//    >
+	//    > It may be the case that it is not possible to represent all lists
+	//    > in the result; in Example 2, either list 2 or list 3 must be
+	//    > unrepresented.
+	//
+	//  - Each item has a non-negative scalar "distance" score, we prefer
+	//    lower distances.  Distance scores are comparable; 0 is preferred,
+	//    and a distance of 4 is twice as bad as a distance of 2.
+	//
+	//  - Each item has a "generation" score, we prefer higher generations.
+	//    Generation scores should not be treated as a linear scale; the
+	//    magnitude of deltas is meaningless; only the sign of a delta is
+	//    meaningful.
+	//
+	//    > So it would be wrong to say something like
+	//    >
+	//    >     desirability = (-a*distance) + (b*generation)       // for some constants `a` and `b`
+	//    >
+	//    > because `generation` can't be used that way
+	//
+	//  - We prefer items that appear in more lists over items that appear in
+	//    fewer lists.
+	//
+	// The relative priority of these 4 goals is undefined; preferably the
+	// algorithm should be defined in a way that makes it easy to adjust the
+	// relative priorities.
+
+	ret := make(containers.Set[btrfsvol.LogicalAddr])
+	illegal := make(containers.Set[btrfsvol.LogicalAddr]) // cannot-be-accepted and already-accepted
+	accept := func(item btrfsvol.LogicalAddr) {
+		ret.Insert(item)
+		for _, list := range o.augmentQueue[treeID].multi {
+			if list.Has(item) {
+				illegal.InsertFrom(list)
+			}
+		}
+	}
+
+	sortedItems := maps.Keys(choices)
+	sort.Slice(sortedItems, func(i, j int) bool {
+		iItem, jItem := sortedItems[i], sortedItems[j]
+		if choices[iItem].Count != choices[jItem].Count {
+			return choices[iItem].Count > choices[jItem].Count // reverse this check; higher counts should sort lower
+		}
+		if choices[iItem].Distance != choices[jItem].Distance {
+			return choices[iItem].Distance < choices[jItem].Distance
+		}
+		if choices[iItem].Generation != choices[jItem].Generation {
+			return choices[iItem].Generation > choices[jItem].Generation // reverse this check; higher generations should sort lower
+		}
+		return iItem < jItem // laddr is as good a tiebreaker as anything
+	})
+	for _, item := range sortedItems {
+		if !illegal.Has(item) {
+			accept(item)
+		}
+	}
+
+	// Log our result
+	wantKeys := append(
+		maps.Keys(o.augmentQueue[treeID].single),
+		maps.Keys(o.augmentQueue[treeID].multi)...)
+	sort.Slice(wantKeys, func(i, j int) bool {
+		return wantKeys[i].Compare(wantKeys[j]) < 0
+	})
+	for _, wantKey := range wantKeys {
+		list, ok := o.augmentQueue[treeID].multi[wantKey]
+		if !ok {
+			list = containers.NewSet[btrfsvol.LogicalAddr](o.augmentQueue[treeID].single[wantKey])
+		}
+		chose := list.Intersection(ret)
+		switch {
+		case len(chose) == 0:
+			dlog.Infof(ctx, "lists[%q]: chose (none) from %v", wantKey, maps.SortedKeys(list))
+		case len(list) > 1:
+			dlog.Infof(ctx, "lists[%q]: chose %v from %v", wantKey, chose.TakeOne(), maps.SortedKeys(list))
+		default:
+			dlog.Debugf(ctx, "lists[%q]: chose %v from %v", wantKey, chose.TakeOne(), maps.SortedKeys(list))
+		}
+	}
+
+	// Free some memory
+	o.augmentQueue[treeID].single = nil
+	o.augmentQueue[treeID].multi = nil
+
+	return ret
+}
+
+////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
+
+func (queue *treeAugmentQueue) has(wantKey Want) bool {
+	if queue != nil {
+		if queue.zero != nil {
+			if _, ok := queue.zero[wantKey]; ok {
+				return true
+			}
+		}
+		if queue.single != nil {
+			if _, ok := queue.single[wantKey]; ok {
+				return true
+			}
+		}
+		if queue.multi != nil {
+			if _, ok := queue.multi[wantKey]; ok {
+				return true
+			}
+		}
+	}
+	return false
+}
+
+func (queue *treeAugmentQueue) store(wantKey Want, choices containers.Set[btrfsvol.LogicalAddr]) {
+	if len(choices) == 0 && wantKey.OffsetType > offsetExact {
+		// This wantKey is unlikely to come up again, so it's
+		// not worth the RAM of storing a negative result.
+		return
+	}
+	switch len(choices) {
+	case 0:
+		if queue.zero == nil {
+			queue.zero = make(map[Want]struct{})
+		}
+		queue.zero[wantKey] = struct{}{}
+	case 1:
+		if queue.single == nil {
+			queue.single = make(map[Want]btrfsvol.LogicalAddr)
+		}
+		queue.single[wantKey] = choices.TakeOne()
+	default:
+		if queue.multi == nil {
+			queue.multi = make(map[Want]containers.Set[btrfsvol.LogicalAddr])
+		}
+		queue.multi[wantKey] = choices
+	}
+}
+
+func (o *rebuilder) hasAugment(wantKey WantWithTree) bool {
+	return o.augmentQueue[wantKey.TreeID].has(wantKey.Key)
+}
+
+func (o *rebuilder) wantAugment(ctx context.Context, wantKey WantWithTree, choices containers.Set[btrfsvol.LogicalAddr]) {
+	if o.augmentQueue[wantKey.TreeID] == nil {
+		o.augmentQueue[wantKey.TreeID] = new(treeAugmentQueue)
+	}
+	o.augmentQueue[wantKey.TreeID].store(wantKey.Key, choices)
+	if len(choices) == 0 {
+		o.numAugmentFailures++
+		dlog.Debug(ctx, "ERR: could not find wanted item")
+	} else {
+		o.numAugments++
+		dlog.Debugf(ctx, "choices=%v", maps.SortedKeys(choices))
+	}
+}
diff --git a/cmd/btrfs-rec/inspect/rebuildtrees/rebuild_treecb.go b/cmd/btrfs-rec/inspect/rebuildtrees/rebuild_treecb.go
new file mode 100644
index 0000000..492436b
--- /dev/null
+++ b/cmd/btrfs-rec/inspect/rebuildtrees/rebuild_treecb.go
@@ -0,0 +1,86 @@
+// Copyright (C) 2022-2023  Luke Shumaker <lukeshu@lukeshu.com>
+//
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+package rebuildnodes
+
+import (
+	"context"
+	"fmt"
+
+	"git.lukeshu.com/btrfs-progs-ng/lib/btrfs/btrfsitem"
+	"git.lukeshu.com/btrfs-progs-ng/lib/btrfs/btrfsprim"
+	"git.lukeshu.com/btrfs-progs-ng/lib/btrfs/btrfsvol"
+)
+
+// AddedItem implements btrees.Callbacks.
+func (o *rebuilder) AddedItem(ctx context.Context, tree btrfsprim.ObjID, key btrfsprim.Key) {
+	o.addedItemQueue.Insert(keyAndTree{
+		TreeID: tree,
+		Key:    key,
+	})
+}
+
+// AddedRoot implements btrees.Callbacks.
+func (o *rebuilder) AddedRoot(ctx context.Context, tree btrfsprim.ObjID, root btrfsvol.LogicalAddr) {
+	if retries := o.retryItemQueue[tree]; retries != nil {
+		o.addedItemQueue.InsertFrom(retries)
+	}
+}
+
+// LookupRoot implements btrees.Callbacks.
+func (o *rebuilder) LookupRoot(ctx context.Context, tree btrfsprim.ObjID) (offset btrfsprim.Generation, item btrfsitem.Root, ok bool) {
+	wantKey := WantWithTree{
+		TreeID: btrfsprim.ROOT_TREE_OBJECTID,
+		Key: Want{
+			ObjectID:   tree,
+			ItemType:   btrfsitem.ROOT_ITEM_KEY,
+			OffsetType: offsetAny,
+		},
+	}
+	ctx = withWant(ctx, logFieldTreeWant, "tree Root", wantKey)
+	foundKey, ok := o._want(ctx, wantKey)
+	if !ok {
+		o.enqueueRetry(btrfsprim.ROOT_TREE_OBJECTID)
+		return 0, btrfsitem.Root{}, false
+	}
+	itemBody := o.rebuilt.Tree(ctx, wantKey.TreeID).ReadItem(ctx, foundKey)
+	defer itemBody.Free()
+	switch itemBody := itemBody.(type) {
+	case *btrfsitem.Root:
+		return btrfsprim.Generation(foundKey.Offset), *itemBody, true
+	case *btrfsitem.Error:
+		o.fsErr(ctx, fmt.Errorf("error decoding item: %v: %w", foundKey, itemBody.Err))
+		return 0, btrfsitem.Root{}, false
+	default:
+		// This is a panic because the item decoder should not emit ROOT_ITEM items as anything but
+		// btrfsitem.Root or btrfsitem.Error without this code also being updated.
+		panic(fmt.Errorf("should not happen: ROOT_ITEM item has unexpected type: %T", itemBody))
+	}
+}
+
+// LookupUUID implements btrees.Callbacks.
+func (o *rebuilder) LookupUUID(ctx context.Context, uuid btrfsprim.UUID) (id btrfsprim.ObjID, ok bool) {
+	wantKey := WantWithTree{
+		TreeID: btrfsprim.UUID_TREE_OBJECTID,
+		Key:    wantFromKey(btrfsitem.UUIDToKey(uuid)),
+	}
+	ctx = withWant(ctx, logFieldTreeWant, "resolve parent UUID", wantKey)
+	if !o._wantOff(ctx, wantKey) {
+		o.enqueueRetry(btrfsprim.UUID_TREE_OBJECTID)
+		return 0, false
+	}
+	itemBody := o.rebuilt.Tree(ctx, wantKey.TreeID).ReadItem(ctx, wantKey.Key.Key())
+	defer itemBody.Free()
+	switch itemBody := itemBody.(type) {
+	case *btrfsitem.UUIDMap:
+		return itemBody.ObjID, true
+	case *btrfsitem.Error:
+		o.fsErr(ctx, fmt.Errorf("error decoding item: %v: %w", wantKey, itemBody.Err))
+		return 0, false
+	default:
+		// This is a panic because the item decoder should not emit UUID_SUBVOL items as anything but
+		// btrfsitem.UUIDMap or btrfsitem.Error without this code also being updated.
+		panic(fmt.Errorf("should not happen: UUID_SUBVOL item has unexpected type: %T", itemBody))
+	}
+}
diff --git a/cmd/btrfs-rec/inspect/rebuildtrees/rebuild_wantcb.go b/cmd/btrfs-rec/inspect/rebuildtrees/rebuild_wantcb.go
new file mode 100644
index 0000000..adf3cff
--- /dev/null
+++ b/cmd/btrfs-rec/inspect/rebuildtrees/rebuild_wantcb.go
@@ -0,0 +1,400 @@
+// Copyright (C) 2022-2023  Luke Shumaker <lukeshu@lukeshu.com>
+//
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+package rebuildnodes
+
+import (
+	"bytes"
+	"context"
+	"fmt"
+
+	"github.com/datawire/dlib/dlog"
+
+	"git.lukeshu.com/btrfs-progs-ng/lib/btrfs/btrfsitem"
+	"git.lukeshu.com/btrfs-progs-ng/lib/btrfs/btrfsprim"
+	"git.lukeshu.com/btrfs-progs-ng/lib/btrfs/btrfssum"
+	"git.lukeshu.com/btrfs-progs-ng/lib/btrfs/btrfsvol"
+	"git.lukeshu.com/btrfs-progs-ng/lib/btrfsprogs/btrfsinspect/rebuildnodes/keyio"
+	"git.lukeshu.com/btrfs-progs-ng/lib/containers"
+)
+
+// fsErr implements rebuildCallbacks.
+func (o *rebuilder) fsErr(ctx context.Context, e error) {
+	dlog.Errorf(ctx, "filesystem error: %v", e)
+}
+
+// want implements rebuildCallbacks.
+func (o *rebuilder) want(ctx context.Context, reason string, treeID btrfsprim.ObjID, objID btrfsprim.ObjID, typ btrfsprim.ItemType) {
+	wantKey := WantWithTree{
+		TreeID: treeID,
+		Key: Want{
+			ObjectID:   objID,
+			ItemType:   typ,
+			OffsetType: offsetAny,
+		},
+	}
+	ctx = withWant(ctx, logFieldItemWant, reason, wantKey)
+	o._want(ctx, wantKey)
+}
+
+func (o *rebuilder) _want(ctx context.Context, wantKey WantWithTree) (key btrfsprim.Key, ok bool) {
+	if o.rebuilt.Tree(ctx, wantKey.TreeID) == nil {
+		o.enqueueRetry(wantKey.TreeID)
+		return btrfsprim.Key{}, false
+	}
+
+	// check if we already have it
+
+	tgt := wantKey.Key.Key()
+	if key, _, ok := o.rebuilt.Tree(ctx, wantKey.TreeID).Items(ctx).Search(func(key btrfsprim.Key, _ keyio.ItemPtr) int {
+		key.Offset = 0
+		return tgt.Compare(key)
+	}); ok {
+		return key, true
+	}
+
+	// OK, we need to insert it
+
+	if o.hasAugment(wantKey) {
+		return btrfsprim.Key{}, false
+	}
+	wants := make(containers.Set[btrfsvol.LogicalAddr])
+	o.rebuilt.Tree(ctx, wantKey.TreeID).PotentialItems(ctx).Subrange(
+		func(k btrfsprim.Key, _ keyio.ItemPtr) int {
+			k.Offset = 0
+			return tgt.Compare(k)
+		},
+		func(_ btrfsprim.Key, v keyio.ItemPtr) bool {
+			wants.InsertFrom(o.rebuilt.Tree(ctx, wantKey.TreeID).LeafToRoots(ctx, v.Node))
+			return true
+		})
+	o.wantAugment(ctx, wantKey, wants)
+	return btrfsprim.Key{}, false
+}
+
+// wantOff implements rebuildCallbacks.
+func (o *rebuilder) wantOff(ctx context.Context, reason string, treeID btrfsprim.ObjID, objID btrfsprim.ObjID, typ btrfsprim.ItemType, off uint64) {
+	wantKey := WantWithTree{
+		TreeID: treeID,
+		Key: Want{
+			ObjectID:   objID,
+			ItemType:   typ,
+			OffsetType: offsetExact,
+			OffsetLow:  off,
+		},
+	}
+	ctx = withWant(ctx, logFieldItemWant, reason, wantKey)
+	o._wantOff(ctx, wantKey)
+}
+
+func (o *rebuilder) _wantOff(ctx context.Context, wantKey WantWithTree) (ok bool) {
+	if o.rebuilt.Tree(ctx, wantKey.TreeID) == nil {
+		o.enqueueRetry(wantKey.TreeID)
+		return false
+	}
+
+	// check if we already have it
+
+	tgt := wantKey.Key.Key()
+	if _, ok := o.rebuilt.Tree(ctx, wantKey.TreeID).Items(ctx).Load(tgt); ok {
+		return true
+	}
+
+	// OK, we need to insert it
+
+	if o.hasAugment(wantKey) {
+		return false
+	}
+	wants := make(containers.Set[btrfsvol.LogicalAddr])
+	o.rebuilt.Tree(ctx, wantKey.TreeID).PotentialItems(ctx).Subrange(
+		func(k btrfsprim.Key, _ keyio.ItemPtr) int { return tgt.Compare(k) },
+		func(_ btrfsprim.Key, v keyio.ItemPtr) bool {
+			wants.InsertFrom(o.rebuilt.Tree(ctx, wantKey.TreeID).LeafToRoots(ctx, v.Node))
+			return true
+		})
+	o.wantAugment(ctx, wantKey, wants)
+	return false
+}
+
+// wantDirIndex implements rebuildCallbacks.
+func (o *rebuilder) wantDirIndex(ctx context.Context, reason string, treeID btrfsprim.ObjID, objID btrfsprim.ObjID, name []byte) {
+	wantKey := WantWithTree{
+		TreeID: treeID,
+		Key: Want{
+			ObjectID:   objID,
+			ItemType:   btrfsitem.DIR_INDEX_KEY,
+			OffsetType: offsetName,
+			OffsetName: string(name),
+		},
+	}
+	ctx = withWant(ctx, logFieldItemWant, reason, wantKey)
+
+	if o.rebuilt.Tree(ctx, treeID) == nil {
+		o.enqueueRetry(treeID)
+		return
+	}
+
+	// check if we already have it
+
+	tgt := wantKey.Key.Key()
+	found := false
+	o.rebuilt.Tree(ctx, treeID).Items(ctx).Subrange(
+		func(key btrfsprim.Key, _ keyio.ItemPtr) int {
+			key.Offset = 0
+			return tgt.Compare(key)
+		},
+		func(_ btrfsprim.Key, ptr keyio.ItemPtr) bool {
+			if itemName, ok := o.keyIO.Names[ptr]; ok && bytes.Equal(itemName, name) {
+				found = true
+			}
+			return !found
+		})
+	if found {
+		return
+	}
+
+	// OK, we need to insert it
+
+	if o.hasAugment(wantKey) {
+		return
+	}
+	wants := make(containers.Set[btrfsvol.LogicalAddr])
+	o.rebuilt.Tree(ctx, treeID).PotentialItems(ctx).Subrange(
+		func(key btrfsprim.Key, _ keyio.ItemPtr) int {
+			key.Offset = 0
+			return tgt.Compare(key)
+		},
+		func(_ btrfsprim.Key, ptr keyio.ItemPtr) bool {
+			if itemName, ok := o.keyIO.Names[ptr]; ok && bytes.Equal(itemName, name) {
+				wants.InsertFrom(o.rebuilt.Tree(ctx, treeID).LeafToRoots(ctx, ptr.Node))
+			}
+			return true
+		})
+	o.wantAugment(ctx, wantKey, wants)
+}
+
+func (o *rebuilder) _walkRange(
+	ctx context.Context,
+	items *containers.SortedMap[btrfsprim.Key, keyio.ItemPtr],
+	treeID, objID btrfsprim.ObjID, typ btrfsprim.ItemType,
+	beg, end uint64,
+	fn func(key btrfsprim.Key, ptr keyio.ItemPtr, beg, end uint64),
+) {
+	min := btrfsprim.Key{
+		ObjectID: objID,
+		ItemType: typ,
+		Offset:   0, // *NOT* `beg`
+	}
+	max := btrfsprim.Key{
+		ObjectID: objID,
+		ItemType: typ,
+		Offset:   end - 1,
+	}
+	items.Subrange(
+		func(runKey btrfsprim.Key, _ keyio.ItemPtr) int {
+			switch {
+			case min.Compare(runKey) < 0:
+				return 1
+			case max.Compare(runKey) > 0:
+				return -1
+			default:
+				return 0
+			}
+		},
+		func(runKey btrfsprim.Key, runPtr keyio.ItemPtr) bool {
+			runSizeAndErr, ok := o.keyIO.Sizes[runPtr]
+			if !ok {
+				panic(fmt.Errorf("should not happen: %v (%v) did not have a size recorded",
+					runPtr, keyAndTree{TreeID: treeID, Key: runKey}))
+			}
+			if runSizeAndErr.Err != nil {
+				o.fsErr(ctx, fmt.Errorf("get size: %v (%v): %w",
+					runPtr, keyAndTree{TreeID: treeID, Key: runKey},
+					runSizeAndErr.Err))
+				return true
+			}
+			runSize := runSizeAndErr.Size
+			if runSize == 0 {
+				return true
+			}
+			runBeg := runKey.Offset
+			runEnd := runBeg + runSize
+			if runEnd <= beg {
+				return true
+			}
+
+			fn(runKey, runPtr, runBeg, runEnd)
+			return true
+		})
+}
+
+type gap struct {
+	// range is [Beg,End)
+	Beg, End uint64
+}
+
+// Compare implements containers.Ordered.
+func (a gap) Compare(b gap) int {
+	return containers.NativeCompare(a.Beg, b.Beg)
+}
+
+func (o *rebuilder) _wantRange(
+	ctx context.Context, reason string,
+	treeID btrfsprim.ObjID, objID btrfsprim.ObjID, typ btrfsprim.ItemType,
+	beg, end uint64,
+) {
+	wantKey := WantWithTree{
+		TreeID: treeID,
+		Key: Want{
+			ObjectID:   objID,
+			ItemType:   typ,
+			OffsetType: offsetAny,
+		},
+	}
+	ctx = withWant(ctx, logFieldItemWant, reason, wantKey)
+	wantKey.Key.OffsetType = offsetRange
+
+	if o.rebuilt.Tree(ctx, treeID) == nil {
+		o.enqueueRetry(treeID)
+		return
+	}
+
+	// Step 1: Build a listing of the gaps.
+	//
+	// Start with a gap of the whole range, then subtract each run
+	// from it.
+	gaps := new(containers.RBTree[gap])
+	gaps.Insert(gap{
+		Beg: beg,
+		End: end,
+	})
+	o._walkRange(
+		ctx,
+		o.rebuilt.Tree(ctx, treeID).Items(ctx),
+		treeID, objID, typ, beg, end,
+		func(runKey btrfsprim.Key, _ keyio.ItemPtr, runBeg, runEnd uint64) {
+			var overlappingGaps []*containers.RBNode[gap]
+			gaps.Subrange(
+				func(gap gap) int {
+					switch {
+					case gap.End <= runBeg:
+						return 1
+					case runEnd <= gap.Beg:
+						return -1
+					default:
+						return 0
+					}
+				},
+				func(node *containers.RBNode[gap]) bool {
+					overlappingGaps = append(overlappingGaps, node)
+					return true
+				})
+			if len(overlappingGaps) == 0 {
+				return
+			}
+			gapsBeg := overlappingGaps[0].Value.Beg
+			gapsEnd := overlappingGaps[len(overlappingGaps)-1].Value.End
+			for _, gap := range overlappingGaps {
+				gaps.Delete(gap)
+			}
+			if gapsBeg < runBeg {
+				gaps.Insert(gap{
+					Beg: gapsBeg,
+					End: runBeg,
+				})
+			}
+			if gapsEnd > runEnd {
+				gaps.Insert(gap{
+					Beg: runEnd,
+					End: gapsEnd,
+				})
+			}
+		})
+
+	// Step 2: Fill each gap.
+	if gaps.Len() == 0 {
+		return
+	}
+	potentialItems := o.rebuilt.Tree(ctx, treeID).PotentialItems(ctx)
+	gaps.Range(func(rbNode *containers.RBNode[gap]) bool {
+		gap := rbNode.Value
+		last := gap.Beg
+		o._walkRange(
+			ctx,
+			potentialItems,
+			treeID, objID, typ, gap.Beg, gap.End,
+			func(k btrfsprim.Key, v keyio.ItemPtr, runBeg, runEnd uint64) {
+				// TODO: This is dumb and greedy.
+				if last < runBeg {
+					// log an error
+					wantKey.Key.OffsetLow = last
+					wantKey.Key.OffsetHigh = runBeg
+					wantCtx := withWant(ctx, logFieldItemWant, reason, wantKey)
+					o.wantAugment(wantCtx, wantKey, nil)
+				}
+				wantKey.Key.OffsetLow = gap.Beg
+				wantKey.Key.OffsetHigh = gap.End
+				wantCtx := withWant(ctx, logFieldItemWant, reason, wantKey)
+				o.wantAugment(wantCtx, wantKey, o.rebuilt.Tree(wantCtx, treeID).LeafToRoots(wantCtx, v.Node))
+				last = runEnd
+			})
+		if last < gap.End {
+			// log an error
+			wantKey.Key.OffsetLow = last
+			wantKey.Key.OffsetHigh = gap.End
+			wantCtx := withWant(ctx, logFieldItemWant, reason, wantKey)
+			o.wantAugment(wantCtx, wantKey, nil)
+		}
+		return true
+	})
+}
+
+// func implements rebuildCallbacks.
+//
+// interval is [beg, end)
+func (o *rebuilder) wantCSum(ctx context.Context, reason string, inodeTree, inode btrfsprim.ObjID, beg, end btrfsvol.LogicalAddr) {
+	inodeWant := WantWithTree{
+		TreeID: inodeTree,
+		Key: Want{
+			ObjectID:   inode,
+			ItemType:   btrfsitem.INODE_ITEM_KEY,
+			OffsetType: offsetExact,
+			OffsetLow:  0,
+		},
+	}
+	inodeCtx := withWant(ctx, logFieldItemWant, reason, inodeWant)
+	if !o._wantOff(inodeCtx, inodeWant) {
+		o.enqueueRetry(inodeTree)
+		return
+	}
+	inodePtr, ok := o.rebuilt.Tree(inodeCtx, inodeTree).Items(inodeCtx).Load(inodeWant.Key.Key())
+	if !ok {
+		panic(fmt.Errorf("should not happen: could not load key: %v", inodeWant))
+	}
+	inodeFlags, ok := o.keyIO.Flags[inodePtr]
+	if !ok {
+		panic(fmt.Errorf("should not happen: INODE_ITEM did not have flags recorded"))
+	}
+	if inodeFlags.Err != nil {
+		o.fsErr(inodeCtx, inodeFlags.Err)
+		return
+	}
+
+	if inodeFlags.NoDataSum {
+		return
+	}
+
+	o._wantRange(
+		ctx, reason,
+		btrfsprim.CSUM_TREE_OBJECTID, btrfsprim.EXTENT_CSUM_OBJECTID, btrfsprim.EXTENT_CSUM_KEY,
+		uint64(roundDown(beg, btrfssum.BlockSize)), uint64(roundUp(end, btrfssum.BlockSize)))
+}
+
+// wantFileExt implements rebuildCallbacks.
+func (o *rebuilder) wantFileExt(ctx context.Context, reason string, treeID btrfsprim.ObjID, ino btrfsprim.ObjID, size int64) {
+	o._wantRange(
+		ctx, reason,
+		treeID, ino, btrfsprim.EXTENT_DATA_KEY,
+		0, uint64(size))
+}
diff --git a/cmd/btrfs-rec/inspect/rebuildtrees/rebuild_wanttyp.go b/cmd/btrfs-rec/inspect/rebuildtrees/rebuild_wanttyp.go
new file mode 100644
index 0000000..2b471fe
--- /dev/null
+++ b/cmd/btrfs-rec/inspect/rebuildtrees/rebuild_wanttyp.go
@@ -0,0 +1,107 @@
+// Copyright (C) 2022-2023  Luke Shumaker <lukeshu@lukeshu.com>
+//
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+package rebuildnodes
+
+import (
+	"context"
+	"fmt"
+
+	"github.com/datawire/dlib/dlog"
+
+	"git.lukeshu.com/btrfs-progs-ng/lib/btrfs/btrfsprim"
+	"git.lukeshu.com/btrfs-progs-ng/lib/containers"
+)
+
+type wantOffsetType int8
+
+const (
+	offsetAny = wantOffsetType(iota)
+	offsetExact
+	offsetRange
+	offsetName
+)
+
+type Want struct {
+	ObjectID   btrfsprim.ObjID
+	ItemType   btrfsprim.ItemType
+	OffsetType wantOffsetType
+	OffsetLow  uint64
+	OffsetHigh uint64
+	OffsetName string
+}
+
+func (a Want) Compare(b Want) int {
+	if d := containers.NativeCompare(a.ObjectID, b.ObjectID); d != 0 {
+		return d
+	}
+	if d := containers.NativeCompare(a.ItemType, b.ItemType); d != 0 {
+		return d
+	}
+	if d := containers.NativeCompare(a.OffsetType, b.OffsetType); d != 0 {
+		return d
+	}
+	if d := containers.NativeCompare(a.OffsetLow, b.OffsetLow); d != 0 {
+		return d
+	}
+	if d := containers.NativeCompare(a.OffsetHigh, b.OffsetHigh); d != 0 {
+		return d
+	}
+	if d := containers.NativeCompare(a.OffsetName, b.OffsetName); d != 0 {
+		return d
+	}
+	return 0
+}
+
+func (o Want) Key() btrfsprim.Key {
+	return btrfsprim.Key{
+		ObjectID: o.ObjectID,
+		ItemType: o.ItemType,
+		Offset:   o.OffsetLow,
+	}
+}
+
+func wantFromKey(k btrfsprim.Key) Want {
+	return Want{
+		ObjectID:   k.ObjectID,
+		ItemType:   k.ItemType,
+		OffsetType: offsetExact,
+		OffsetLow:  k.Offset,
+	}
+}
+
+func (o Want) String() string {
+	switch o.OffsetType {
+	case offsetAny:
+		return fmt.Sprintf("{%v %v ?}", o.ObjectID, o.ItemType)
+	case offsetExact:
+		return fmt.Sprintf("{%v %v %v}", o.ObjectID, o.ItemType, o.OffsetLow)
+	case offsetRange:
+		return fmt.Sprintf("{%v %v %v-%v}", o.ObjectID, o.ItemType, o.OffsetLow, o.OffsetHigh)
+	case offsetName:
+		return fmt.Sprintf("{%v %v name=%q}", o.ObjectID, o.ItemType, o.OffsetName)
+	default:
+		panic(fmt.Errorf("should not happen: OffsetType=%#v", o.OffsetType))
+	}
+}
+
+type WantWithTree struct {
+	TreeID btrfsprim.ObjID
+	Key    Want
+}
+
+func (o WantWithTree) String() string {
+	return fmt.Sprintf("tree=%v key=%v", o.TreeID, o.Key)
+}
+
+const (
+	logFieldItemWant = "btrfsinspect.rebuild-nodes.rebuild.want"
+	logFieldTreeWant = "btrfsinspect.rebuild-nodes.rebuild.add-tree.want"
+)
+
+func withWant(ctx context.Context, logField, reason string, wantKey WantWithTree) context.Context {
+	ctx = dlog.WithField(ctx, logField+".reason", reason)
+	ctx = dlog.WithField(ctx, logField+".key", wantKey)
+	return ctx
+}
diff --git a/cmd/btrfs-rec/inspect/rebuildtrees/scan.go b/cmd/btrfs-rec/inspect/rebuildtrees/scan.go
new file mode 100644
index 0000000..17949ab
--- /dev/null
+++ b/cmd/btrfs-rec/inspect/rebuildtrees/scan.go
@@ -0,0 +1,77 @@
+// Copyright (C) 2022-2023  Luke Shumaker <lukeshu@lukeshu.com>
+//
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+package rebuildnodes
+
+import (
+	"context"
+	"time"
+
+	"github.com/datawire/dlib/dlog"
+
+	"git.lukeshu.com/btrfs-progs-ng/lib/btrfs"
+	"git.lukeshu.com/btrfs-progs-ng/lib/btrfs/btrfstree"
+	"git.lukeshu.com/btrfs-progs-ng/lib/btrfs/btrfsvol"
+	"git.lukeshu.com/btrfs-progs-ng/lib/btrfsprogs/btrfsinspect"
+	"git.lukeshu.com/btrfs-progs-ng/lib/btrfsprogs/btrfsinspect/rebuildnodes/graph"
+	"git.lukeshu.com/btrfs-progs-ng/lib/btrfsprogs/btrfsinspect/rebuildnodes/keyio"
+	"git.lukeshu.com/btrfs-progs-ng/lib/containers"
+	"git.lukeshu.com/btrfs-progs-ng/lib/maps"
+	"git.lukeshu.com/btrfs-progs-ng/lib/textui"
+)
+
+func ScanDevices(ctx context.Context, fs *btrfs.FS, scanResults btrfsinspect.ScanDevicesResult) (btrfstree.Superblock, graph.Graph, *keyio.Handle, error) {
+	dlog.Info(ctx, "Reading superblock...")
+	sb, err := fs.Superblock()
+	if err != nil {
+		return btrfstree.Superblock{}, graph.Graph{}, nil, err
+	}
+
+	dlog.Infof(ctx, "Reading node data from FS...")
+
+	var stats textui.Portion[int]
+	stats.D = countNodes(scanResults)
+	progressWriter := textui.NewProgress[textui.Portion[int]](
+		dlog.WithField(ctx, "btrfsinspect.rebuild-nodes.read.substep", "read-nodes"),
+		dlog.LogLevelInfo, textui.Tunable(1*time.Second))
+
+	nodeGraph := graph.New(*sb)
+	keyIO := keyio.NewHandle(fs, *sb)
+
+	progressWriter.Set(stats)
+	for _, devResults := range scanResults {
+		for _, laddr := range maps.SortedKeys(devResults.FoundNodes) {
+			if err := ctx.Err(); err != nil {
+				return btrfstree.Superblock{}, graph.Graph{}, nil, err
+			}
+			nodeRef, err := btrfstree.ReadNode[btrfsvol.LogicalAddr](fs, *sb, laddr, btrfstree.NodeExpectations{
+				LAddr: containers.Optional[btrfsvol.LogicalAddr]{OK: true, Val: laddr},
+			})
+			if err != nil {
+				btrfstree.FreeNodeRef(nodeRef)
+				return btrfstree.Superblock{}, graph.Graph{}, nil, err
+			}
+
+			nodeGraph.InsertNode(nodeRef)
+			keyIO.InsertNode(nodeRef)
+
+			btrfstree.FreeNodeRef(nodeRef)
+
+			stats.N++
+			progressWriter.Set(stats)
+		}
+	}
+	if stats.N != stats.D {
+		panic("should not happen")
+	}
+	progressWriter.Done()
+	dlog.Info(ctx, "... done reading node data")
+
+	if err := nodeGraph.FinalCheck(ctx, fs, *sb); err != nil {
+		return btrfstree.Superblock{}, graph.Graph{}, nil, err
+	}
+	keyIO.SetGraph(*nodeGraph)
+
+	return *sb, *nodeGraph, keyIO, nil
+}
diff --git a/cmd/btrfs-rec/inspect/rebuildtrees/util.go b/cmd/btrfs-rec/inspect/rebuildtrees/util.go
new file mode 100644
index 0000000..9d91f23
--- /dev/null
+++ b/cmd/btrfs-rec/inspect/rebuildtrees/util.go
@@ -0,0 +1,31 @@
+// Copyright (C) 2022  Luke Shumaker <lukeshu@lukeshu.com>
+//
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+package rebuildnodes
+
+import (
+	"golang.org/x/exp/constraints"
+
+	"git.lukeshu.com/btrfs-progs-ng/lib/btrfsprogs/btrfsinspect"
+)
+
+func countNodes(nodeScanResults btrfsinspect.ScanDevicesResult) int {
+	var cnt int
+	for _, devResults := range nodeScanResults {
+		cnt += len(devResults.FoundNodes)
+	}
+	return cnt
+}
+
+func roundDown[T constraints.Integer](n, d T) T {
+	return (n / d) * d
+}
+
+func roundUp[T constraints.Integer](n, d T) T {
+	return ((n + d - 1) / d) * d
+}
+
+func discardOK[T any](val T, _ bool) T {
+	return val
+}