linux-kernel - Re: [PATCH] pm / wakeup: simplify the output logic of pm_show

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Date:   Fri, 14 Jan 2022 10:10:02 +0000
From:   Lee Jones <lee.jones@...aro.org>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     linux-kernel@...r.kernel.org,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Pavel Machek <pavel@....cz>, Len Brown <len.brown@...el.com>,
        linux-pm@...r.kernel.org
Subject: Re: [PATCH] pm / wakeup: simplify the output logic of
 pm_show_wakelocks()

On Thu, 13 Jan 2022, Greg Kroah-Hartman wrote:

> The buffer handling in pm_show_wakelocks() is tricky, and hopefully
> correct.  Ensure it really is correct by using sysfs_emit_at() which
> handles all of the tricky string handling logic in a PAGE_SIZE buffer
> for us automatically as this is a sysfs file being read from.
> 
> Cc: "Rafael J. Wysocki" <rafael@...nel.org>
> Cc: Pavel Machek <pavel@....cz>
> Cc: Len Brown <len.brown@...el.com>
> Cc: linux-pm@...r.kernel.org
> Cc: Lee Jones <lee.jones@...aro.org>
> Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> ---
>  kernel/power/wakelock.c | 11 ++++-------
>  1 file changed, 4 insertions(+), 7 deletions(-)

Reviewed-by: Lee Jones <lee.jones@...aro.org>

> diff --git a/kernel/power/wakelock.c b/kernel/power/wakelock.c
> index 105df4dfc783..52571dcad768 100644
> --- a/kernel/power/wakelock.c
> +++ b/kernel/power/wakelock.c
> @@ -39,23 +39,20 @@ ssize_t pm_show_wakelocks(char *buf, bool show_active)
>  {
>  	struct rb_node *node;
>  	struct wakelock *wl;
> -	char *str = buf;
> -	char *end = buf + PAGE_SIZE;
> +	int len = 0;
>  
>  	mutex_lock(&wakelocks_lock);
>  
>  	for (node = rb_first(&wakelocks_tree); node; node = rb_next(node)) {
>  		wl = rb_entry(node, struct wakelock, node);
>  		if (wl->ws->active == show_active)
> -			str += scnprintf(str, end - str, "%s ", wl->name);
> +			len += sysfs_emit_at(buf, len, "%s ", wl->name);
>  	}
> -	if (str > buf)
> -		str--;
>  
> -	str += scnprintf(str, end - str, "\n");
> +	len += sysfs_emit_at(buf, len, "\n");
>  
>  	mutex_unlock(&wakelocks_lock);
> -	return (str - buf);
> +	return len;
>  }
>  
>  #if CONFIG_PM_WAKELOCKS_LIMIT > 0

-- 
Lee Jones [李琼斯]
Principal Technical Lead - Developer Services
Linaro.org │ Open source software for Arm SoCs
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