linux-kernel - Re: [PATCH v9 07/20] gpiolib: cdev: support GPIO_V2_GET_LINE_IOCTL and GPIO_V2_LINE_GET_VALUES

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Date:   Sun, 27 Sep 2020 12:00:04 +0300
From:   Andy Shevchenko <andy.shevchenko@...il.com>
To:     Kent Gibson <warthog618@...il.com>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "open list:GPIO SUBSYSTEM" <linux-gpio@...r.kernel.org>,
        Bartosz Golaszewski <bgolaszewski@...libre.com>,
        Linus Walleij <linus.walleij@...aro.org>,
        Arnd Bergmann <arnd@...db.de>
Subject: Re: [PATCH v9 07/20] gpiolib: cdev: support GPIO_V2_GET_LINE_IOCTL
 and GPIO_V2_LINE_GET_VALUES_IOCTL

On Sat, Sep 26, 2020 at 12:16 PM Kent Gibson <warthog618@...il.com> wrote:
> On Fri, Sep 25, 2020 at 01:06:02PM +0300, Andy Shevchenko wrote:

...

> Hmmm, there is more to it than I thought - gpiod_request_commit(),
> which this code eventually calls, interprets a null label (not an
> empty string) as indicating that the user has not set the label, in
> which case it will set the desc label to "?". So userspace cannot
> force the desc label to be empty.
>
> We need to keep that label as null in that case to maintain that
> behaviour.
>
> I will add a comment there though.
>
> Hmmm, having said that, does this form work for you:
>
>         if (ulr.consumer[0] != '\0') {
>                 /* label is only initialized if consumer is set */
>                 lr->label = kstrndup(ulr.consumer, sizeof(ulr.consumer) - 1, GFP_KERNEL);
>         ...
>
> It actually compiles slightly larger, I guess due to the extra parameter
> in the kstrndup() call, but may be slightly more readable??

I really don't want to delay this series, choose what you think is
better and we may amend it later.

-- 
With Best Regards,
Andy Shevchenko