linux-kernel - Re: [PATCH]mempool.c : clean up type-casting twice

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Date:	Sun, 5 Jul 2009 05:01:00 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	"Figo.zhang" <figo1802@...il.com>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...l.org>,
	lkml <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH]mempool.c : clean up type-casting twice


* Figo.zhang <figo1802@...il.com> wrote:

> clean up type-casting twice
> 
> Signed-off-by: Figo.zhang <figo1802@...il.com>
> ---   
> mm/mempool.c |    6 +++---
>  1 files changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/mm/mempool.c b/mm/mempool.c
> index a46eb1b..0aec628 100644
> --- a/mm/mempool.c
> +++ b/mm/mempool.c
> @@ -303,7 +303,7 @@ EXPORT_SYMBOL(mempool_free_slab);
>   */
>  void *mempool_kmalloc(gfp_t gfp_mask, void *pool_data)
>  {
> -	size_t size = (size_t)(long)pool_data;
> +	size_t size = (size_t)pool_data;
>  	return kmalloc(size, gfp_mask);
>  }
>  EXPORT_SYMBOL(mempool_kmalloc);
> @@ -327,14 +327,14 @@ EXPORT_SYMBOL(mempool_kfree);
>   */
>  void *mempool_alloc_pages(gfp_t gfp_mask, void *pool_data)
>  {
> -	int order = (int)(long)pool_data;
> +	int order = (int)pool_data;
>  	return alloc_pages(gfp_mask, order);
>  }
>  EXPORT_SYMBOL(mempool_alloc_pages);
>  
>  void mempool_free_pages(void *element, void *pool_data)
>  {
> -	int order = (int)(long)pool_data;
> +	int order = (int)pool_data;
>  	__free_pages(element, order);

What's the motivation?

On 64-bit platforms, casting from a pointer (64-bit) straight to int 
(32-bit) can lose information and is thus a potential source of 
bugs, so certain compilers will warn about it with:

   warning: cast from pointer to integer of different size

The double cast is a "I know what I'm doing" signal.

	Ingo
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