1 files changed, 84 insertions, 0 deletions
diff --git a/lib/btrfs/btree_util.go b/lib/btrfs/btree_util.go
new file mode 100644
index 0000000..2076114
--- /dev/null
+++ b/lib/btrfs/btree_util.go
@@ -0,0 +1,84 @@
+// Copyright (C) 2022  Luke Shumaker <lukeshu@lukeshu.com>
+//
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+package btrfs
+
+import (
+	"fmt"
+
+	"git.lukeshu.com/btrfs-progs-ng/lib/btrfs/btrfsitem"
+	"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     ObjID
+	RootNode   btrfsvol.LogicalAddr
+	Level      uint8
+	Generation Generation
+}
+
+// LookupTreeRoot is a utility function to help with implementing the 'Trees'
+// interface.
+func LookupTreeRoot(fs Trees, treeID ObjID) (*TreeRoot, error) {
+	sb, err := fs.Superblock()
+	if err != nil {
+		return nil, err
+	}
+	switch treeID {
+	case ROOT_TREE_OBJECTID:
+		return &TreeRoot{
+			TreeID:     treeID,
+			RootNode:   sb.RootTree,
+			Level:      sb.RootLevel,
+			Generation: sb.Generation, // XXX: same generation as LOG_TREE?
+		}, nil
+	case CHUNK_TREE_OBJECTID:
+		return &TreeRoot{
+			TreeID:     treeID,
+			RootNode:   sb.ChunkTree,
+			Level:      sb.ChunkLevel,
+			Generation: sb.ChunkRootGeneration,
+		}, nil
+	case TREE_LOG_OBJECTID:
+		return &TreeRoot{
+			TreeID:     treeID,
+			RootNode:   sb.LogTree,
+			Level:      sb.LogLevel,
+			Generation: sb.Generation, // XXX: same generation as ROOT_TREE?
+		}, nil
+	case BLOCK_GROUP_TREE_OBJECTID:
+		return &TreeRoot{
+			TreeID:     treeID,
+			RootNode:   sb.BlockGroupRoot,
+			Level:      sb.BlockGroupRootLevel,
+			Generation: sb.BlockGroupRootGeneration,
+		}, nil
+	default:
+		rootItem, err := fs.TreeSearch(ROOT_TREE_OBJECTID, func(key Key, _ uint32) int {
+			if key.ObjectID == treeID && key.ItemType == btrfsitem.ROOT_ITEM_KEY {
+				return 0
+			}
+			return Key{
+				ObjectID: treeID,
+				ItemType: btrfsitem.ROOT_ITEM_KEY,
+				Offset:   0,
+			}.Cmp(key)
+		})
+		if err != nil {
+			return nil, err
+		}
+		rootItemBody, ok := rootItem.Body.(btrfsitem.Root)
+		if !ok {
+			return nil, fmt.Errorf("malformed ROOT_ITEM for tree %v", treeID)
+		}
+		return &TreeRoot{
+			TreeID:     treeID,
+			RootNode:   rootItemBody.ByteNr,
+			Level:      rootItemBody.Level,
+			Generation: rootItemBody.Generation,
+		}, nil
+	}
+}