linux-kernel - Re: [PATCH 08/12] printk: Replace strncmp with str_has

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Date:   Mon, 29 Jul 2019 17:16:35 -0700
From:   Joe Perches <joe@...ches.com>
To:     Chuhong Yuan <hslester96@...il.com>
Cc:     Petr Mladek <pmladek@...e.com>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 08/12] printk: Replace strncmp with str_has_prefix

On Mon, 2019-07-29 at 23:15 +0800, Chuhong Yuan wrote:
> strncmp(str, const, len) is error-prone.
> We had better use newly introduced
> str_has_prefix() instead of it.
[]
> diff --git a/kernel/printk/braille.c b/kernel/printk/braille.c
[]
> @@ -11,10 +11,10 @@
>  
>  int _braille_console_setup(char **str, char **brl_options)
>  {
> -	if (!strncmp(*str, "brl,", 4)) {
> +	if (str_has_prefix(*str, "brl,")) {
>  		*brl_options = "";
>  		*str += 4;
> -	} else if (!strncmp(*str, "brl=", 4)) {
> +	} else if (str_has_prefix(*str, "brl=")) {
>  		*brl_options = *str + 4;

Better to get rid of the += 4 uses too by storing the result
of str_has_prefix and using that as the addend.

Perhaps
	size_t len;

	if ((len = str_has_prefix(*str, "brl,"))) {
		*brl_options = "";
		*str += len;
	} else if ((len = str_has_prefix(*str, "brl="))) {
		etc...

>  		*str = strchr(*brl_options, ',');
>  		if (!*str) {
> diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
[]
> @@ -121,13 +121,13 @@ static int __control_devkmsg(char *str)
>  	if (!str)
>  		return -EINVAL;
>  
> -	if (!strncmp(str, "on", 2)) {
> +	if (str_has_prefix(str, "on")) {
>  		devkmsg_log = DEVKMSG_LOG_MASK_ON;
>  		return 2;
> -	} else if (!strncmp(str, "off", 3)) {
> +	} else if (str_has_prefix(str, "off")) {
>  		devkmsg_log = DEVKMSG_LOG_MASK_OFF;
>  		return 3;
> -	} else if (!strncmp(str, "ratelimit", 9)) {
> +	} else if (str_has_prefix(str, "ratelimit")) {
>  		devkmsg_log = DEVKMSG_LOG_MASK_DEFAULT;
>  		return 9;
>  	}

here too.