[PATCH] printk: Use strlen/sizeof instead of hardcoded constants

[PATCH] printk: Use strlen/sizeof instead of hardcoded constants

[Geert Uytterhoeven]

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@glider.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"))) {
 		devkmsg_log = DEVKMSG_LOG_MASK_DEFAULT;
-		return 9;
+		return strlen("ratelimit");
 	}
 	return -EINVAL;
 }
-- 
2.17.1

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

[Steven Rostedt]

On Wed, 31 Jul 2019 14:39:22 +0200
Geert Uytterhoeven <geert+renesas@glider.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@glider.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;
>  }