linux-kernel - Re: [PATCH v2] leds: Introduce userspace leds driver

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Date:   Fri, 16 Sep 2016 09:07:21 +0200
From:   Jacek Anaszewski <j.anaszewski@...sung.com>
To:     David Lechner <david@...hnology.com>, Pavel Machek <pavel@....cz>
Cc:     Richard Purdie <rpurdie@...ys.net>, linux-kernel@...r.kernel.org,
        linux-leds@...r.kernel.org, Marcel Holtmann <marcel@...tmann.org>
Subject: Re: [PATCH v2] leds: Introduce userspace leds driver

Hi David,

On 09/15/2016 05:25 PM, David Lechner wrote:
> On 09/15/2016 09:54 AM, Jacek Anaszewski wrote:
>> Hi Pavel,
>>
>> On 09/15/2016 03:01 PM, Pavel Machek wrote:
>>> Hi!
>>>
>>>>> @@ -0,0 +1,23 @@
>>>>> +/*
>>>>> + * Userspace driver support for leds subsystem
>>>>> + *
>>>>> + * This program is free software; you can redistribute it and/or
>>>>> modify
>>>>> + * it under the terms of the GNU General Public License as
>>>>> published by
>>>>> + * the Free Software Foundation; either version 2 of the License, or
>>>>> + * (at your option) any later version.
>>>>> + *
>>>>> + * This program is distributed in the hope that it will be useful,
>>>>> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
>>>>> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
>>>>> + * GNU General Public License for more details.
>>>>> + */
>>>>> +#ifndef _UAPI__ULEDS_H_
>>>>> +#define _UAPI__ULEDS_H_
>>>>> +
>>>>> +#define ULEDS_MAX_NAME_SIZE    80
>>>>> +
>>>>> +struct uleds_user_dev {
>>>>> +    char name[ULEDS_MAX_NAME_SIZE];
>>>>> +};
>>>
>>> We already have path component length limit somewhere, right? Just use
>>> it?
>>>
>>> (And is struct with char array good idea at all? Perphaps it can just
>>> use write() length up to something reasonable, and not bother with new
>>> header file for userspace?)
>>
>> In fact in this case the addition of another public header can be
>> avoided.
>>
>
> The main reason I did it this way is in case someone wants to extend
> this to also, for example, set the max_brightness value. If we use an
> arbitrary size string, we could never add max_brightness without
> breaking userspace.
>
> If we are sure we will never want to pass any other parameters other
> than name, then we can do away with the struct.

This is sound argument. Let's limit the name size to 64, as in case
of name variable in led_classdev_register(). This patch could also
add include directive "#include <uapi/leds/uleds.h>" to
drivers/leds/led-class.c and replace 64 with a new LED_MAX_NAME_LEN 
macro defined in the uleds.h header.

-- 
Best regards,
Jacek Anaszewski