fuse: cache fs.Node instances

A particular node should always be represented by a single instance.
This is necessary to allow the fuse library to assign a stable nodeId to
a node. macOS Sonoma trips over the previous, unstable behavior when
using fuse-t.

internal/fuse/dir.go

@@ -29,6 +29,7 @@ type dir struct {
 	parentInode uint64
 	node        *restic.Node
 	m           sync.Mutex
+	cache       treeCache
 }
 
 func cleanupNodeName(name string) string {
@@ -43,6 +44,7 @@ func newDir(root *Root, inode, parentInode uint64, node *restic.Node) (*dir, err
 		node:        node,
 		inode:       inode,
 		parentInode: parentInode,
+		cache:       *newTreeCache(),
 	}, nil
 }
 
@@ -87,6 +89,7 @@ func newDirFromSnapshot(root *Root, inode uint64, snapshot *restic.Snapshot) (*d
 			Subtree:    snapshot.Tree,
 		},
 		inode: inode,
+		cache: *newTreeCache(),
 	}, nil
 }
 
@@ -208,6 +211,7 @@ func (d *dir) Lookup(ctx context.Context, name string) (fs.Node, error) {
 		return nil, err
 	}
 
+	return d.cache.lookupOrCreate(name, func() (fs.Node, error) {
 		node, ok := d.items[name]
 		if !ok {
 			debug.Log("  Lookup(%v) -> not found", name)
@@ -227,6 +231,7 @@ func (d *dir) Lookup(ctx context.Context, name string) (fs.Node, error) {
 			debug.Log("  node %v has unknown type %v", name, node.Type)
 			return nil, syscall.ENOENT
 		}
+	})
 }
 
 func (d *dir) Listxattr(_ context.Context, req *fuse.ListxattrRequest, resp *fuse.ListxattrResponse) error {

internal/fuse/snapshots_dir.go

@@ -23,6 +23,7 @@ type SnapshotsDir struct {
 	parentInode uint64
 	dirStruct   *SnapshotsDirStructure
 	prefix      string
+	cache       treeCache
 }
 
 // ensure that *SnapshotsDir implements these interfaces
@@ -38,6 +39,7 @@ func NewSnapshotsDir(root *Root, inode, parentInode uint64, dirStruct *Snapshots
 		parentInode: parentInode,
 		dirStruct:   dirStruct,
 		prefix:      prefix,
+		cache:       *newTreeCache(),
 	}
 }
 
@@ -107,8 +109,12 @@ func (d *SnapshotsDir) Lookup(ctx context.Context, name string) (fs.Node, error)
 		return nil, syscall.ENOENT
 	}
 
+	return d.cache.lookupOrCreate(name, func() (fs.Node, error) {
 		entry := meta.names[name]
-	if entry != nil {
+		if entry == nil {
+			return nil, syscall.ENOENT
+		}
+
 		inode := inodeFromName(d.inode, name)
 		if entry.linkTarget != "" {
 			return newSnapshotLink(d.root, inode, entry.linkTarget, entry.snapshot)
@@ -116,9 +122,7 @@ func (d *SnapshotsDir) Lookup(ctx context.Context, name string) (fs.Node, error)
 			return newDirFromSnapshot(d.root, inode, entry.snapshot)
 		}
 		return NewSnapshotsDir(d.root, inode, d.inode, d.dirStruct, d.prefix+"/"+name), nil
-	}
-
-	return nil, syscall.ENOENT
+	})
 }
 
 // SnapshotLink

internal/fuse/tree_cache.go

@@ -0,0 +1,38 @@
+//go:build darwin || freebsd || linux
+// +build darwin freebsd linux
+
+package fuse
+
+import (
+	"sync"
+
+	"github.com/anacrolix/fuse/fs"
+)
+
+type treeCache struct {
+	nodes map[string]fs.Node
+	m     sync.Mutex
+}
+
+func newTreeCache() *treeCache {
+	return &treeCache{
+		nodes: map[string]fs.Node{},
+	}
+}
+
+func (t *treeCache) lookupOrCreate(name string, create func() (fs.Node, error)) (fs.Node, error) {
+	t.m.Lock()
+	defer t.m.Unlock()
+
+	if node, ok := t.nodes[name]; ok {
+		return node, nil
+	}
+
+	node, err := create()
+	if err != nil {
+		return nil, err
+	}
+
+	t.nodes[name] = node
+	return node, nil
+}