vfs: Add SetSys() methods to Node to allow caching stuff on a node

vfs/dir.go

@@ -32,6 +32,7 @@ type Dir struct {
 	entry   fs.Directory
 	read    time.Time       // time directory entry last read
 	items   map[string]Node // directory entries - can be empty but not nil
+	sys     interface{}     // user defined info to be attached here
 }
 
 func newDir(vfs *VFS, f fs.Fs, parent *Dir, fsDir fs.Directory) *Dir {
@@ -92,7 +93,16 @@ func (d *Dir) Path() (name string) {
 
 // Sys returns underlying data source (can be nil) - satisfies Node interface
 func (d *Dir) Sys() interface{} {
-	return nil
+	d.mu.RLock()
+	defer d.mu.RUnlock()
+	return d.sys
+}
+
+// SetSys sets the underlying data source (can be nil) - satisfies Node interface
+func (d *Dir) SetSys(x interface{}) {
+	d.mu.Lock()
+	d.sys = x
+	d.mu.Unlock()
 }
 
 // Inode returns the inode number - satisfies Node interface

vfs/dir_test.go

@@ -54,6 +54,10 @@ func TestDirMethods(t *testing.T) {
 	// Sys
 	assert.Equal(t, nil, dir.Sys())
 
+	// SetSys
+	dir.SetSys(42)
+	assert.Equal(t, 42, dir.Sys())
+
 	// Inode
 	assert.NotEqual(t, uint64(0), dir.Inode())
 

vfs/file.go

@@ -52,6 +52,7 @@ type File struct {
 	pendingModTime    time.Time                       // will be applied once o becomes available, i.e. after file was written
 	pendingRenameFun  func(ctx context.Context) error // will be run/renamed after all writers close
 	appendMode        bool                            // file was opened with O_APPEND
+	sys               interface{}                     // user defined info to be attached here
 
 	muRW sync.Mutex // synchonize RWFileHandle.openPending(), RWFileHandle.close() and File.Remove
 }
@@ -130,7 +131,16 @@ func (f *File) osPath() string {
 
 // Sys returns underlying data source (can be nil) - satisfies Node interface
 func (f *File) Sys() interface{} {
-	return nil
+	f.mu.RLock()
+	defer f.mu.RUnlock()
+	return f.sys
+}
+
+// SetSys sets the underlying data source (can be nil) - satisfies Node interface
+func (f *File) SetSys(x interface{}) {
+	f.mu.Lock()
+	f.sys = x
+	f.mu.Unlock()
 }
 
 // Inode returns the inode number - satisfies Node interface

vfs/file_test.go

@@ -58,6 +58,10 @@ func TestFileMethods(t *testing.T) {
 	// Sys
 	assert.Equal(t, nil, file.Sys())
 
+	// SetSys
+	file.SetSys(42)
+	assert.Equal(t, 42, file.Sys())
+
 	// Inode
 	assert.NotEqual(t, uint64(0), file.Inode())
 

vfs/vfs.go

@@ -54,6 +54,7 @@ type Node interface {
 	Open(flags int) (Handle, error)
 	Truncate(size int64) error
 	Path() string
+	SetSys(interface{})
 }
 
 // Check interfaces