linux-kernel - Re: [PATCH] leds: Avoid needless strlen() for attributes

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Date:	Fri, 1 Aug 2008 13:36:22 -0700
From:	"Ray Lee" <ray-lk@...rabbit.org>
To:	"Sven Wegener" <sven.wegener@...aler.net>
Cc:	"Richard Purdie" <rpurdie@...ys.net>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] leds: Avoid needless strlen() for attributes

On Fri, Aug 1, 2008 at 1:30 PM, Sven Wegener <sven.wegener@...aler.net> wrote:
> There's no need for the additional call to strlen(), we can directly return the
> value returned by sprintf(). We now return a length value that doesn't include
> the final '\0', but user space shouldn't bother about it anyway.

Why not just add 1 to the return value of sprintf, and guarantee that
userspace sees the same thing before and after? It's simple enough to
do, and avoids guessing about what userspace may or may not be doing.

> Signed-off-by: Sven Wegener <sven.wegener@...aler.net>
> ---
>  drivers/leds/led-class.c     |    5 +----
>  drivers/leds/ledtrig-timer.c |    8 ++------
>  2 files changed, 3 insertions(+), 10 deletions(-)
>
> Patch is based on your current (024e8ac) leds git tree head.
>
> diff --git a/drivers/leds/led-class.c b/drivers/leds/led-class.c
> index 559a408..1aa24d3 100644
> --- a/drivers/leds/led-class.c
> +++ b/drivers/leds/led-class.c
> @@ -34,14 +34,11 @@ static ssize_t led_brightness_show(struct device *dev,
>                struct device_attribute *attr, char *buf)
>  {
>        struct led_classdev *led_cdev = dev_get_drvdata(dev);
> -       ssize_t ret = 0;
>
>        /* no lock needed for this */
>        led_update_brightness(led_cdev);
> -       sprintf(buf, "%u\n", led_cdev->brightness);
> -       ret = strlen(buf) + 1;
>
> -       return ret;
> +       return sprintf(buf, "%u\n", led_cdev->brightness);
>  }
>
>  static ssize_t led_brightness_store(struct device *dev,
> diff --git a/drivers/leds/ledtrig-timer.c b/drivers/leds/ledtrig-timer.c
> index 5c99f4f..db68196 100644
> --- a/drivers/leds/ledtrig-timer.c
> +++ b/drivers/leds/ledtrig-timer.c
> @@ -70,9 +70,7 @@ static ssize_t led_delay_on_show(struct device *dev,
>        struct led_classdev *led_cdev = dev_get_drvdata(dev);
>        struct timer_trig_data *timer_data = led_cdev->trigger_data;
>
> -       sprintf(buf, "%lu\n", timer_data->delay_on);
> -
> -       return strlen(buf) + 1;
> +       return sprintf(buf, "%lu\n", timer_data->delay_on);
>  }
>
>  static ssize_t led_delay_on_store(struct device *dev,
> @@ -116,9 +114,7 @@ static ssize_t led_delay_off_show(struct device *dev,
>        struct led_classdev *led_cdev = dev_get_drvdata(dev);
>        struct timer_trig_data *timer_data = led_cdev->trigger_data;
>
> -       sprintf(buf, "%lu\n", timer_data->delay_off);
> -
> -       return strlen(buf) + 1;
> +       return sprintf(buf, "%lu\n", timer_data->delay_off);
>  }
>
>  static ssize_t led_delay_off_store(struct device *dev,
> --
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