On 21.12.2021 08:13, Greg Kroah-Hartman wrote:

On Tue, Dec 21, 2021 at 07:53:32AM +0100, Rafał Miłecki wrote:

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On 21.12.2021 07:45, Greg Kroah-Hartman wrote:

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On Tue, Dec 21, 2021 at 07:39:24AM +0100, Rafał Miłecki wrote:

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On 21.12.2021 07:33, Greg Kroah-Hartman wrote:

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On Mon, Dec 20, 2021 at 09:39:43PM +0100, Rafał Miłecki wrote:

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Hi Greg,

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

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

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     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.

Great.

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I don't understand addig-after-the-fact part. How is .is_bin_visible()
related to adding attributes for newly created cells?

You are adding a sysfs attribute to a device that is already registered
in the driver core, and so the creation of that attribute is never seen
by userspace.  The attribute needs to be attached to the device _BEFORE_
it is registered.

Also, huge hint, if a driver has to call as sysfs_*() call, something is
wrong.

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Do you mean I can
avoid calling sysfs_add_bin_file_to_group()?

Yes.

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Do you recall any existing example of such solution?

Loads.

Just add this attribute group to your driver as a default attribute
group and the driver core will create it for you if needed.

Or if you always need it, no need to mess sith is_bin_visible() at all,
I can't really understand what you are trying to do here at all.

Thanks a lot! In nvmem_register() first there is a call to the
device_register() and only later cells get added. I suppose I just have
to rework nvmem_register() order so that:
1. Cells are collected earlier. For each cell I allocate group attribute

No, add all of the attributes to the device at the beginning before you
register it, there's no need to allocate anything.

If you mean static structures I can't do that, because cells almost
never are static. They are not known in advance. nvmem allows cells to
be:
1. Specified in OF
2. Submitted as list while registering a NVMEM device

So every cells gets its own structure allocated dynamically. My plan is
to put bin_attribute in that struct and then create a group collecting
all those cells.

A device has a driver associated with it, and that driver has default
groups associated with it.  Use that, I am not saying to use static
structures, that is not how the driver model works at all.

I'm helpless on dealing with attributes.

I tried building a list of attributes dynamically but that of course
fails:

drivers/nvmem/core.c: In function ‘nvmem_register’:
drivers/nvmem/core.c:930:31: error: assignment of member ‘bin_attrs’ in read-only object
   930 |   nvmem_cells_group.bin_attrs = nvmem->cells_bin_attrs;
       |                               ^


What I'm trying to achieve is having
/sys/bus/nvmem/devices/*/cells/*
with each file being an attribute.


Please kindly point me to a single example of "struct attribute_group"
that has a variable list of attributes with each attribute having
runtime set name.

Almost all cases in kernel look like:
static const struct attribute_group foo_attr_group = {
	.attrs = foo_attrs,
};
with "foo_attrs" being a list of attributes with *predefined* names.

Every example of dynamic attributes (runtime created) I see in a kernel
(e.g. drivers/base/node.c) uses sysfs_*().