Hi Greg,

On 20.12.2021 09:00, Greg Kroah-Hartman wrote:

On Mon, Dec 20, 2021 at 07:47:30AM +0100, Rafał Miłecki wrote:

quoted

  static void nvmem_cell_entry_add(struct nvmem_cell_entry *cell)
  {
+	struct device *dev = &cell->nvmem->dev;
+	int err;
+
  	mutex_lock(&nvmem_mutex);
  	list_add_tail(&cell->node, &cell->nvmem->cells);
  	mutex_unlock(&nvmem_mutex);
+
+	sysfs_attr_init(&cell->battr.attr);
+	cell->battr.attr.name = cell->name;
+	cell->battr.attr.mode = 0400;
+	cell->battr.read = nvmem_cell_attr_read;
+	err = sysfs_add_bin_file_to_group(&dev->kobj, &cell->battr,
+					  nvmem_cells_group.name);

Why not just use the is_bin_visible attribute instead to determine if
the attribute should be shown or not instead of having to add it
after-the-fact which will race with userspace and loose?

I'm sorry I really don't see how you suggest to get it done.

I can use .is_bin_visible() callback indeed to respect nvmem->root_only.
I don't understand addig-after-the-fact part. How is .is_bin_visible()
related to adding attributes for newly created cells? Do you mean I can
avoid calling sysfs_add_bin_file_to_group()? Do you recall any existing
example of such solution?