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Date:   Mon, 31 Jan 2022 10:17:25 -0800
From:   Roman Gushchin <guro@fb.com>
To:     Waiman Long <longman@redhat.com>
CC:     Johannes Weiner <hannes@cmpxchg.org>,
        Michal Hocko <mhocko@kernel.org>,
        Vladimir Davydov <vdavydov.dev@gmail.com>,
        Andrew Morton <akpm@linux-foundation.org>,
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        Steven Rostedt <rostedt@goodmis.org>,
        Sergey Senozhatsky <senozhatsky@chromium.org>,
        Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
        Rasmus Villemoes <linux@rasmusvillemoes.dk>,
        <linux-kernel@vger.kernel.org>, <cgroups@vger.kernel.org>,
        <linux-mm@kvack.org>, Ira Weiny <ira.weiny@intel.com>,
        Rafael Aquini <aquini@redhat.com>
Subject: Re: [PATCH v2 1/3] lib/vsprintf: Avoid redundant work with 0 size
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References: <20220129205315.478628-1-longman@redhat.com>
 <20220129205315.478628-2-longman@redhat.com>
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On Sat, Jan 29, 2022 at 03:53:13PM -0500, Waiman Long wrote:
> For *scnprintf(), vsnprintf() is always called even if the input size is
> 0. That is a waste of time, so just return 0 in this case.
> 
> Signed-off-by: Waiman Long <longman@redhat.com>
> ---
>  lib/vsprintf.c | 8 +++++---
>  1 file changed, 5 insertions(+), 3 deletions(-)
> 
> diff --git a/lib/vsprintf.c b/lib/vsprintf.c
> index 3b8129dd374c..a65df546fb06 100644
> --- a/lib/vsprintf.c
> +++ b/lib/vsprintf.c
> @@ -2895,13 +2895,15 @@ int vscnprintf(char *buf, size_t size, const char *fmt, va_list args)
>  {
>  	int i;
>  
> +	if (!size)
> +		return 0;
> +
>  	i = vsnprintf(buf, size, fmt, args);
>  
>  	if (likely(i < size))
>  		return i;
> -	if (size != 0)
> -		return size - 1;
> -	return 0;
> +
> +	return size - 1;
>  }
>  EXPORT_SYMBOL(vscnprintf);

Acked-by: Roman Gushchin <guro@fb.com>

Thanks!