vfs: Update parent directory modtimes on vfs actions

This isn't written back to the storage so might change on remount but
makes the VFS just a little more POSIX compatible.

vfs/dir.go

@@ -923,6 +923,10 @@ func (d *Dir) Create(name string, flags int) (*File, error) {
 	if d.vfs.Opt.ReadOnly {
 		return nil, EROFS
 	}
+	if err = d.SetModTime(time.Now()); err != nil {
+		fs.Errorf(d, "Dir.Create failed to set modtime on parent dir: %v", err)
+		return nil, err
+	}
 	// This gets added to the directory when the file is opened for write
 	return newFile(d, d.Path(), nil, name), nil
 }
@@ -957,6 +961,10 @@ func (d *Dir) Mkdir(name string) (*Dir, error) {
 	fsDir := fs.NewDir(path, time.Now())
 	dir := newDir(d.vfs, d.f, d, fsDir)
 	d.addObject(dir)
+	if err = d.SetModTime(time.Now()); err != nil {
+		fs.Errorf(d, "Dir.Mkdir failed to set modtime on parent dir: %v", err)
+		return nil, err
+	}
 	// fs.Debugf(path, "Dir.Mkdir OK")
 	return dir, nil
 }
@@ -1028,6 +1036,10 @@ func (d *Dir) RemoveName(name string) error {
 		fs.Errorf(d, "Dir.Remove error: %v", err)
 		return err
 	}
+	if err = d.SetModTime(time.Now()); err != nil {
+		fs.Errorf(d, "Dir.Remove failed to set modtime on parent dir: %v", err)
+		return err
+	}
 	return node.Remove()
 }
 
@@ -1098,6 +1110,10 @@ func (d *Dir) Rename(oldName, newName string, destDir *Dir) error {
 	// Show moved - delete from old dir and add to new
 	d.delObject(oldName)
 	destDir.addObject(oldNode)
+	if err = d.SetModTime(time.Now()); err != nil {
+		fs.Errorf(d, "Dir.Rename failed to set modtime on parent dir: %v", err)
+		return err
+	}
 
 	// fs.Debugf(newPath, "Dir.Rename renamed from %q", oldPath)
 	// fs.Debugf(d, "AFTER\n%s", d.dump())

vfs/dir_test.go

@@ -343,9 +343,12 @@ func TestDirOpen(t *testing.T) {
 func TestDirCreate(t *testing.T) {
 	_, vfs, dir, _ := dirCreate(t)
 
+	origModTime := dir.ModTime()
+	time.Sleep(100 * time.Millisecond) // for low rez Windows timers
 	file, err := dir.Create("potato", os.O_WRONLY|os.O_CREATE)
 	require.NoError(t, err)
 	assert.Equal(t, int64(0), file.Size())
+	assert.True(t, dir.ModTime().After(origModTime))
 
 	fd, err := file.Open(os.O_WRONLY | os.O_CREATE)
 	require.NoError(t, err)
@@ -385,8 +388,11 @@ func TestDirMkdir(t *testing.T) {
 	_, err := dir.Mkdir("file1")
 	assert.Error(t, err)
 
+	origModTime := dir.ModTime()
+	time.Sleep(100 * time.Millisecond) // for low rez Windows timers
 	sub, err := dir.Mkdir("sub")
 	assert.NoError(t, err)
+	assert.True(t, dir.ModTime().After(origModTime))
 
 	// check the vfs
 	checkListing(t, dir, []string{"file1,14,false", "sub,0,true"})
@@ -488,8 +494,11 @@ func TestDirRemoveAll(t *testing.T) {
 func TestDirRemoveName(t *testing.T) {
 	r, vfs, dir, _ := dirCreate(t)
 
+	origModTime := dir.ModTime()
+	time.Sleep(100 * time.Millisecond) // for low rez Windows timers
 	err := dir.RemoveName("file1")
 	require.NoError(t, err)
+	assert.True(t, dir.ModTime().After(origModTime))
 	checkListing(t, dir, []string(nil))
 	root, err := vfs.Root()
 	require.NoError(t, err)
@@ -538,8 +547,11 @@ func TestDirRename(t *testing.T) {
 	dir = node.(*Dir)
 
 	// Rename a file
+	origModTime := dir.ModTime()
+	time.Sleep(100 * time.Millisecond) // for low rez Windows timers
 	err = dir.Rename("file1", "file2", root)
 	assert.NoError(t, err)
+	assert.True(t, dir.ModTime().After(origModTime))
 	checkListing(t, root, []string{"dir2,0,true", "file2,14,false"})
 	checkListing(t, dir, []string{"file3,15,false"})