1 files changed, 88 insertions, 0 deletions
diff --git a/lib/btrfs/btrfstree/btree_forrest.go b/lib/btrfs/btrfstree/btree_forrest.go
new file mode 100644
index 0000000..ace2b49
--- /dev/null
+++ b/lib/btrfs/btrfstree/btree_forrest.go
@@ -0,0 +1,88 @@
+// Copyright (C) 2022-2023  Luke Shumaker <lukeshu@lukeshu.com>
+//
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+package btrfstree
+
+import (
+	"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"
+)
+
+// A TreeRoot is more-or-less a btrfsitem.Root, but simpler; returned by
+// LookupTreeRoot.
+type TreeRoot struct {
+	TreeID     btrfsprim.ObjID
+	RootNode   btrfsvol.LogicalAddr
+	Level      uint8
+	Generation btrfsprim.Generation
+}
+
+func RootItemSearchFn(treeID btrfsprim.ObjID) func(btrfsprim.Key, uint32) int {
+	return func(key btrfsprim.Key, _ uint32) int {
+		if key.ObjectID == treeID && key.ItemType == btrfsitem.ROOT_ITEM_KEY {
+			return 0
+		}
+		return btrfsprim.Key{
+			ObjectID: treeID,
+			ItemType: btrfsitem.ROOT_ITEM_KEY,
+			Offset:   0,
+		}.Compare(key)
+	}
+}
+
+// LookupTreeRoot is a utility function to help with implementing the 'Trees'
+// interface.
+func LookupTreeRoot(fs TreeOperator, sb Superblock, treeID btrfsprim.ObjID) (*TreeRoot, error) {
+	switch treeID {
+	case btrfsprim.ROOT_TREE_OBJECTID:
+		return &TreeRoot{
+			TreeID:     treeID,
+			RootNode:   sb.RootTree,
+			Level:      sb.RootLevel,
+			Generation: sb.Generation, // XXX: same generation as LOG_TREE?
+		}, nil
+	case btrfsprim.CHUNK_TREE_OBJECTID:
+		return &TreeRoot{
+			TreeID:     treeID,
+			RootNode:   sb.ChunkTree,
+			Level:      sb.ChunkLevel,
+			Generation: sb.ChunkRootGeneration,
+		}, nil
+	case btrfsprim.TREE_LOG_OBJECTID:
+		return &TreeRoot{
+			TreeID:     treeID,
+			RootNode:   sb.LogTree,
+			Level:      sb.LogLevel,
+			Generation: sb.Generation, // XXX: same generation as ROOT_TREE?
+		}, nil
+	case btrfsprim.BLOCK_GROUP_TREE_OBJECTID:
+		return &TreeRoot{
+			TreeID:     treeID,
+			RootNode:   sb.BlockGroupRoot,
+			Level:      sb.BlockGroupRootLevel,
+			Generation: sb.BlockGroupRootGeneration,
+		}, nil
+	default:
+		rootItem, err := fs.TreeSearch(btrfsprim.ROOT_TREE_OBJECTID, RootItemSearchFn(treeID))
+		if err != nil {
+			return nil, err
+		}
+		switch rootItemBody := rootItem.Body.(type) {
+		case *btrfsitem.Root:
+			return &TreeRoot{
+				TreeID:     treeID,
+				RootNode:   rootItemBody.ByteNr,
+				Level:      rootItemBody.Level,
+				Generation: rootItemBody.Generation,
+			}, nil
+		case *btrfsitem.Error:
+			return nil, fmt.Errorf("malformed ROOT_ITEM for tree %v: %w", treeID, rootItemBody.Err)
+		default:
+			panic(fmt.Errorf("should not happen: ROOT_ITEM has unexpected item type: %T", rootItemBody))
+		}
+	}
+}