Message-ID: <c49f2d6d-7974-5bc7-9bc1-ac265a23c2c0@gmail.com>
Date:   Mon, 20 Dec 2021 21:39:43 +0100
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Subject: Re: [PATCH 2/2] nvmem: expose NVMEM cells in sysfs
To:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc:     Srinivas Kandagatla <srinivas.kandagatla@linaro.org>,
        "Rafael J . Wysocki" <rafael@kernel.org>,
        Jonathan Corbet <corbet@lwn.net>,
        Daniel Vetter <daniel.vetter@ffwll.ch>,
        Dan Williams <dan.j.williams@intel.com>,
        Bjorn Helgaas <bhelgaas@google.com>,
        =?UTF-8?Q?Krzysztof_Wilczy=c5=84ski?= <kw@linux.com>,
        Heiner Kallweit <hkallweit1@gmail.com>,
        linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org,
        =?UTF-8?B?UmFmYcWCIE1pxYJlY2tp?= <rafal@milecki.pl>
References: <20211220064730.28806-1-zajec5@gmail.com>
 <20211220064730.28806-2-zajec5@gmail.com> <YcA4ArALDTjUedrb@kroah.com>
From:   =?UTF-8?B?UmFmYcWCIE1pxYJlY2tp?= <zajec5@gmail.com>
In-Reply-To: <YcA4ArALDTjUedrb@kroah.com>
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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:
>>   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?