linux-kernel - Re: [GIT PULL] iscsi-target merge for v3.1-rc1

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Message-ID: <CA+55aFyNBaf2+=XJDLKNF1S5zMtpx38+Zd8uNd9k4ap4YpZmvw@mail.gmail.com>
Date:	Tue, 26 Jul 2011 00:09:40 -0700
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	"Nicholas A. Bellinger" <nab@...ux-iscsi.org>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	target-devel <target-devel@...r.kernel.org>,
	linux-scsi <linux-scsi@...r.kernel.org>,
	LKML <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>,
	Boaz Harrosh <openosd@...il.com>,
	Mike Christie <michaelc@...wisc.edu>
Subject: Re: [GIT PULL] iscsi-target merge for v3.1-rc1

On Mon, Jul 25, 2011 at 11:51 PM, Nicholas A. Bellinger
<nab@...ux-iscsi.org> wrote:
>
> How about the following to add a new DIV_ROUND_UP_ULL macro

Hmm.

>  #define DIV_ROUND_UP(n,d) (((n) + (d) - 1) / (d))
> +#define DIV_ROUND_UP_ULL(n,d) (                                \
> +{                                                      \
> +       unsigned long long _tmp = n, _off;              \
> +       int _res;                                       \
> +       /* Round up using asm/div64.h:do_div */         \
> +       _off = do_div(_tmp, d);                         \
> +       if (_off != 0)                                  \
> +               _tmp++;                                 \
> +       _res = _tmp;                                    \
> +}                                                      \
> +)

That looks buggy. Why the "_res = _tmp" there? All that does is to
truncate the result to "int", which looks bogus.

And it just looks unnecessarily complicated. Just a simple

#define DIV_ROUND_UP_ULL(ll,d) \
  ({ unsigned long long _tmp = (ll)+(d)-1; do_div(_tmp, d); _tmp; })

looks like it would work and be simpler. Avoid the conditional, do the
same "add 'd-1' thing as the regular ROUND_UP().

Untested. And not much thinking involved.

                     Linus
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