linux-kernel - Re: [PATCH] staging/hv/osd: don't reimplement ALIGN macro

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Date:	Wed, 19 Jan 2011 13:43:57 +0100
From:	Jiri Slaby <jirislaby@...il.com>
To:	Uwe Kleine-König 
	<u.kleine-koenig@...gutronix.de>
CC:	Greg KH <gregkh@...e.de>, devel@...verdev.osuosl.org,
	Haiyang Zhang <haiyangz@...rosoft.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] staging/hv/osd: don't reimplement ALIGN macro

On 01/19/2011 09:54 AM, Uwe Kleine-König wrote:
> On Tue, Jan 18, 2011 at 09:37:15PM -0800, Greg KH wrote:
>> On Tue, Jan 18, 2011 at 04:39:11PM +0100, Uwe Kleine-König wrote:
>>> Signed-off-by: Uwe Kleine-König <u.kleine-koenig@...gutronix.de>
>>> ---
>>>  drivers/staging/hv/osd.h |    5 ++---
>>>  1 files changed, 2 insertions(+), 3 deletions(-)
>>>
>>> diff --git a/drivers/staging/hv/osd.h b/drivers/staging/hv/osd.h
>>> index ce064e8..61ae54c 100644
>>> --- a/drivers/staging/hv/osd.h
>>> +++ b/drivers/staging/hv/osd.h
>>> @@ -28,10 +28,9 @@
>>>  #include <linux/workqueue.h>
>>>  
>>>  /* Defines */
>>> -#define ALIGN_UP(value, align)	(((value) & (align-1)) ?		\
>>> -				 (((value) + (align-1)) & ~(align-1)) :	\
>>> -				 (value))
>>> +#define ALIGN_UP(value, align)		ALIGN((value), (align))
>>
>> How about dropping ALIGN_UP entirely and just using the built-in ALIGN()
>> macro instead?
> Can do.
> 
>>>  #define ALIGN_DOWN(value, align)	((value) & ~(align-1))
>>
>> Any chance to get rid of this as well with the ALIGN() macro, or is that
>> really not possible?
> it would be
> 
> 	#define ALIGN_DOWN(value, align) ALIGN((value) - (align) + 1, (align))
> 
> I think, but as it's only used once it might be easier to just use ALIGN
> there, too.
> 
> BTW, it's used as follows:
> 
> 	#define NUM_PAGES_SPANNED(addr, len)    ((ALIGN(addr+len, PAGE_SIZE) - \
> 						 ALIGN_DOWN(addr, PAGE_SIZE)) >>  \
> 						 PAGE_SHIFT)

(DIV_ROUND_UP(addr+len, PAGE_SIZE) - ((addr) >> PAGE_SHIFT)))

or maybe better

(PAGE_ALIGN(addr+len) >> PAGE_SHIFT - ((addr) >> PAGE_SHIFT))

> I wonder if there is already a function yielding this value?
> Wouldn't
> 
> 	((addr + len) >> PAGE_SHIFT) - (addr >> PAGE_SHIFT) + 1

No, this won't work (it's not equivalent).

regards,
-- 
js
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