linux-kernel - Re: [PATCH 1/2] kernel.h: Add DIV_ROUND_UP

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Message-Id: <1311667641.17766.249.camel@haakon2.linux-iscsi.org>
Date:	Tue, 26 Jul 2011 01:07:21 -0700
From:	"Nicholas A. Bellinger" <nab@...ux-iscsi.org>
To:	Joe Perches <joe@...ches.com>
Cc:	target-devel <target-devel@...r.kernel.org>,
	linux-scsi <linux-scsi@...r.kernel.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Christoph Hellwig <hch@....de>,
	Andy Grover <agrover@...hat.com>,
	Hannes Reinecke <hare@...e.de>,
	Roland Dreier <roland@...estorage.com>,
	James Bottomley <James.Bottomley@...senPartnership.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH 1/2] kernel.h: Add DIV_ROUND_UP_ULL usage

On Tue, 2011-07-26 at 00:53 -0700, Joe Perches wrote:
> On Tue, 2011-07-26 at 07:10 +0000, Nicholas A. Bellinger wrote:
> > Add new DIV_ROUND_UP_ULL macro usage for 32-bit architectures requiring
> > unsigned long long division of sectors * dev_max_sectors.
> []
> > diff --git a/include/linux/kernel.h b/include/linux/kernel.h
> []
> > +#define DIV_ROUND_UP_ULL(ll,d) \
> > +	({ unsigned long long _tmp = (ll)+(d)-1; do_div(_tmp, d); _tmp; })
> 
> Maybe use uint64_t and a temporary for d?
> 
> #define DIV_ROUND_UP_ULL(ll, d)				\
> ({							\
> 	typeof(d) _d = d;				\
> 	uint64_t _tmp = (uint64_t)(ll) + _d - 1;	\
> 	do_div(_tmp, _d);				\
> 	_tmp;						\
> })
> 
> 

Hi Joe,

Not sure on this one myself..  Would this case ever be strictly required
for proper 32-bit operation with unsigned long long division with
sector_t..?

--nab


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