linux-kernel - Re: [PATCH] drivers: target: target_core_mod: use div64_u64

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Date:	Thu, 09 Jan 2014 21:47:51 -0800
From:	"Nicholas A. Bellinger" <nab@...ux-iscsi.org>
To:	Hannes Reinecke <hare@...e.de>
Cc:	Chen Gang <gang.chen.5i5j@...il.com>,
	James Hogan <james.hogan@...tec.com>,
	linux-scsi@...r.kernel.org, target-devel@...r.kernel.org,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Fengguang Wu <fengguang.wu@...el.com>
Subject: Re: [PATCH] drivers: target: target_core_mod: use div64_u64_rem()
 instead of operator '%' for u64

On Thu, 2014-01-09 at 11:17 +0100, Hannes Reinecke wrote:
> On 01/09/2014 12:18 AM, Nicholas A. Bellinger wrote:
> > On Wed, 2014-01-08 at 08:32 +0100, Hannes Reinecke wrote:

<SNIP>

> >> Other than that the sector_div() patch is correct.
> >>
> >
> > <nod> Thanks for confirming that sector_div() is correct here vs. the
> > original code using modulo that Chen had pointed out.
> >
> Ah, _that_ was the issue.
> I was wondering why you kept on poking me ...
> 
> Well.
> No, that's actually _not_ correct.
> The correct fix would be
> 
> diff --git a/drivers/target/target_core_alua.c 
> b/drivers/target/target_core_alua.c
> index 54b1e52..12da9b3 100644
> --- a/drivers/target/target_core_alua.c
> +++ b/drivers/target/target_core_alua.c
> @@ -500,8 +500,7 @@ static inline int core_alua_state_lba_dependent(
> 
>                          if (segment_mult) {
>                                  u64 tmp = lba;
> -                               sector_div(tmp, segment_size * segment_mult);
> -                               start_lba = tmp;
> +                               start_lba = sector_div(tmp, segment_size * segment_mult);
> 
>                                  last_lba = first_lba + segment_size - 1;
>                                  if (start_lba >= first_lba &&
> (beware of line breaks ...)
> Thing is, we need to calculate the offset into the segment to figure out 
> which map entry to use.
> The actual number of the segment (as had been calculated with the 
> original fix) is immaterial here.
> 
> Sorry for this. The email thread just flew past me during Xmas
> with me not paying real attention.
> 

Applied + squashed.  Apologies for the initial pre-holiday BUG..

Thanks Hannes!

--nab

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