linux-kernel - Re: [PATCH 5/7] kernel/cpu: Convert snprintf() to scnprintf()

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Date:   Wed, 28 Sep 2022 10:35:44 +0100
From:   Steven Price <steven.price@....com>
To:     Jules Irenge <jbi.octave@...il.com>, tglx@...utronix.de
Cc:     sathyanarayanan.kuppuswamy@...ux.intel.com,
        linux-kernel@...r.kernel.org, dave.hansen@...ux.intel.com,
        ak@...ux.intel.com, Jason@...c4.com
Subject: Re: [PATCH 5/7] kernel/cpu: Convert snprintf() to scnprintf()

On 26/09/2022 19:52, Jules Irenge wrote:
> Coccinnelle reports a warning
> Warning: Use scnprintf or sprintf
> Adding to that, there has been a slow migration from snprintf to scnprintf.
> This LWN article explains the rationale for this change
> https: //lwn.net/Articles/69419/
> Ie. snprintf() returns what *would* be the resulting length,
> while scnprintf() returns the actual length.
> 
> Signed-off-by: Jules Irenge <jbi.octave@...il.com>

Using sysfs_emit() would be even better in this case, although it's
slightly different because it outputs a maximum of PAGE_SIZE rather than
PAGE_SIZE - 2 bytes. But I can't see any reason for that "- 2" - it
appears to have been added when the sysfs entry was added by Thomas
Gleixner in commit 05736e4ac13c ("cpu/hotplug: Provide knobs to control
SMT") but I don't see any justification for it.

Steve

> ---
>  kernel/cpu.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/kernel/cpu.c b/kernel/cpu.c
> index bbad5e375d3b..f358d89c9580 100644
> --- a/kernel/cpu.c
> +++ b/kernel/cpu.c
> @@ -2512,7 +2512,7 @@ static ssize_t control_show(struct device *dev,
>  {
>  	const char *state = smt_states[cpu_smt_control];
>  
> -	return snprintf(buf, PAGE_SIZE - 2, "%s\n", state);
> +	return scnprintf(buf, PAGE_SIZE - 2, "%s\n", state);
>  }
>  
>  static ssize_t control_store(struct device *dev, struct device_attribute *attr,
> @@ -2525,7 +2525,7 @@ static DEVICE_ATTR_RW(control);
>  static ssize_t active_show(struct device *dev,
>  			   struct device_attribute *attr, char *buf)
>  {
> -	return snprintf(buf, PAGE_SIZE - 2, "%d\n", sched_smt_active());
> +	return scnprintf(buf, PAGE_SIZE - 2, "%d\n", sched_smt_active());
>  }
>  static DEVICE_ATTR_RO(active);
>