Re: [PATCH v3 1/4] lib/vsprintf: Avoid redundant work with 0 size

[Mike Rapoport <rppt@kernel.org>]

On Mon, Jan 31, 2022 at 02:23:05PM -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.
> 
> Note that vsnprintf() will never return -1 to indicate an error. So
> skipping the call to vsnprintf() when size is 0 will have no functional
> impact at all.
> 
> Signed-off-by: Waiman Long <longman@redhat.com>
> Acked-by: David Rientjes <rientjes@google.com>
> Reviewed-by: Sergey Senozhatsky <senozhatsky@chromium.org>
> Acked-by: Roman Gushchin <guro@fb.com>

Acked-by: Mike Rapoport <rppt@linux.ibm.com>

> ---
>  lib/vsprintf.c | 8 +++++---
>  1 file changed, 5 insertions(+), 3 deletions(-)
> 
> diff --git a/lib/vsprintf.c b/lib/vsprintf.c
> index 3b8129dd374c..d419154b47bb 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 (unlikely(!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);
>  
> -- 
> 2.27.0
> 

-- 
Sincerely yours,
Mike.