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

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Date:	Sun, 05 Jul 2009 11:11:56 +0800
From:	"Figo.zhang" <figo1802@...il.com>
To:	Ingo Molnar <mingo@...e.hu>
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

On Sun, 2009-07-05 at 05:01 +0200, Ingo Molnar wrote:
> * 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.
> 

thanks.


void *mempool_kmalloc(gfp_t gfp_mask, void *pool_data)
{
	size_t size = (size_t)(long)pool_data;
	return kmalloc(size, gfp_mask);
}

void *mempool_kzalloc(gfp_t gfp_mask, void *pool_data)
{
	size_t size = (size_t) pool_data;
	return kzalloc(size, gfp_mask);
}

at this point, is it no need for type-casting twice ? because size_t is
typedef "unsigned int" in x86_32, "unsigned long " in x86_64.

Best,
Figo.zhang

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