1 files changed, 54 insertions, 0 deletions
diff --git a/lib/btrfs/btrfstree/readnode.go b/lib/btrfs/btrfstree/readnode.go
new file mode 100644
index 0000000..bb80d20
--- /dev/null
+++ b/lib/btrfs/btrfstree/readnode.go
@@ -0,0 +1,54 @@
+// Copyright (C) 2022  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/btrfsprim"
+	"git.lukeshu.com/btrfs-progs-ng/lib/btrfs/btrfsvol"
+	"git.lukeshu.com/btrfs-progs-ng/lib/containers"
+	"git.lukeshu.com/btrfs-progs-ng/lib/diskio"
+)
+
+// FSReadNode is a utility function to help with implementing the
+// 'NodeSource' interface.
+func FSReadNode(
+	fs interface {
+		diskio.File[btrfsvol.LogicalAddr]
+		Superblock() (*Superblock, error)
+		ParentTree(btrfsprim.ObjID) (btrfsprim.ObjID, bool)
+	},
+	path TreePath,
+) (*diskio.Ref[btrfsvol.LogicalAddr, Node], error) {
+	sb, err := fs.Superblock()
+	if err != nil {
+		return nil, fmt.Errorf("btrfs.FS.ReadNode: %w", err)
+	}
+
+	var treeParents []btrfsprim.ObjID
+	checkOwner := func(owner btrfsprim.ObjID) error {
+		exp := path.Node(-1).FromTree
+		for {
+			if owner == exp {
+				return nil
+			}
+			treeParents = append(treeParents, exp)
+			var ok bool
+			exp, ok = fs.ParentTree(exp)
+			if !ok {
+				return fmt.Errorf("expected owner in %v but claims to have owner=%v",
+					treeParents, owner)
+			}
+		}
+	}
+
+	return ReadNode[btrfsvol.LogicalAddr](fs, *sb, path.Node(-1).ToNodeAddr, NodeExpectations{
+		LAddr:         containers.Optional[btrfsvol.LogicalAddr]{OK: true, Val: path.Node(-1).ToNodeAddr},
+		Level:         containers.Optional[uint8]{OK: true, Val: path.Node(-1).ToNodeLevel},
+		MaxGeneration: containers.Optional[btrfsprim.Generation]{OK: true, Val: path.Node(-1).FromGeneration},
+		Owner:         checkOwner,
+	})
+}