linux-kernel - Re: [PATCH] printk: Use strlen/sizeof instead of hardcoded constants

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Date:   Wed, 31 Jul 2019 09:15:55 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Geert Uytterhoeven <geert+renesas@...der.be>
Cc:     Petr Mladek <pmladek@...e.com>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] printk: Use strlen/sizeof instead of hardcoded
 constants

On Wed, 31 Jul 2019 14:39:22 +0200
Geert Uytterhoeven <geert+renesas@...der.be> wrote:

> Replace hardcoded string length or size constants by proper strlen() or
> sizeof() constructs.  As the strings are constant, gcc will reduce the
> lengths or sizes to constants again.
> 
> Signed-off-by: Geert Uytterhoeven <geert+renesas@...der.be>
> ---
> Assembler output before/after compared: no change in generated code.
> ---
>  include/linux/printk.h |  3 +--
>  kernel/printk/printk.c | 12 ++++++------
>  2 files changed, 7 insertions(+), 8 deletions(-)
> 
> diff --git a/include/linux/printk.h b/include/linux/printk.h
> index cefd374c47b1f88e..9a85d2eb6ff63460 100644
> --- a/include/linux/printk.h
> +++ b/include/linux/printk.h
> @@ -77,8 +77,7 @@ static inline void console_verbose(void)
>  		console_loglevel = CONSOLE_LOGLEVEL_MOTORMOUTH;
>  }
>  
> -/* strlen("ratelimit") + 1 */
> -#define DEVKMSG_STR_MAX_SIZE 10
> +#define DEVKMSG_STR_MAX_SIZE sizeof("ratelimit")
>  extern char devkmsg_log_str[];
>  struct ctl_table;
>  
> diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
> index 1888f6a3b694cb88..e8f332f0ae3595e8 100644
> --- a/kernel/printk/printk.c
> +++ b/kernel/printk/printk.c
> @@ -121,15 +121,15 @@ static int __control_devkmsg(char *str)
>  	if (!str)
>  		return -EINVAL;
>  
> -	if (!strncmp(str, "on", 2)) {
> +	if (!strncmp(str, "on", strlen("on"))) {
>  		devkmsg_log = DEVKMSG_LOG_MASK_ON;
> -		return 2;
> -	} else if (!strncmp(str, "off", 3)) {
> +		return strlen("on");
> +	} else if (!strncmp(str, "off", strlen("off"))) {
>  		devkmsg_log = DEVKMSG_LOG_MASK_OFF;
> -		return 3;
> -	} else if (!strncmp(str, "ratelimit", 9)) {
> +		return strlen("off");
> +	} else if (!strncmp(str, "ratelimit", strlen("ratelimit"))) {

Perhaps replacing all these with str_has_prefix() may be a better idea.

-- Steve

>  		devkmsg_log = DEVKMSG_LOG_MASK_DEFAULT;
> -		return 9;
> +		return strlen("ratelimit");
>  	}
>  	return -EINVAL;
>  }