linux-kernel - Re: [PATCH 5/6] zsmalloc: remove unnecessary type casting

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Date:	Wed, 25 Apr 2012 09:35:25 -0400
From:	Nitin Gupta <ngupta@...are.org>
To:	Minchan Kim <minchan@...nel.org>
CC:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Seth Jennings <sjenning@...ux.vnet.ibm.com>,
	Dan Magenheimer <dan.magenheimer@...cle.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH 5/6] zsmalloc: remove unnecessary type casting

On 04/25/2012 02:23 AM, Minchan Kim wrote:

> Let's remove unnecessary type casting of (void *).
> 
> Signed-off-by: Minchan Kim <minchan@...nel.org>
> ---
>  drivers/staging/zsmalloc/zsmalloc-main.c |    3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)
> 
> diff --git a/drivers/staging/zsmalloc/zsmalloc-main.c b/drivers/staging/zsmalloc/zsmalloc-main.c
> index b7d31cc..ff089f8 100644
> --- a/drivers/staging/zsmalloc/zsmalloc-main.c
> +++ b/drivers/staging/zsmalloc/zsmalloc-main.c
> @@ -644,8 +644,7 @@ void zs_free(struct zs_pool *pool, void *obj)
>  	spin_lock(&class->lock);
>  
>  	/* Insert this object in containing zspage's freelist */
> -	link = (struct link_free *)((unsigned char *)kmap_atomic(f_page)
> -							+ f_offset);
> +	link = (struct link_free *)(kmap_atomic(f_page)	+ f_offset);
>  	link->next = first_page->freelist;
>  	kunmap_atomic(link);
>  	first_page->freelist = obj;



Incrementing a void pointer looks weired and should not be allowed by C
compilers though gcc and clang seem to allow this without any warnings.
(fortunately C++ forbids incrementing void pointers)

So, we should keep this cast to unsigned char pointer to avoid relying
on a non-standard, compiler specific behavior.

Thanks,
Nitin

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