linux-kernel - Re: [PATCH v3 1/2] dm-unstripe: unstripe RAID 0/dm-striped device

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Message-ID: <20171215152710.djma3jau7dbdrnjr@sbauer-Z170X-UD5>
Date:   Fri, 15 Dec 2017 08:27:11 -0700
From:   Scott Bauer <scott.bauer@...el.com>
To:     Randy Dunlap <rdunlap@...radead.org>
Cc:     dm-devel@...hat.com, snitzer@...hat.com, agk@...hat.com,
        linux-kernel@...r.kernel.org, keith.busch@...el.com,
        jonathan.derrick@...el.com
Subject: Re: [PATCH v3 1/2] dm-unstripe: unstripe RAID 0/dm-striped device

[snip]
On Wed, Dec 13, 2017 at 04:11:44PM -0800, Randy Dunlap wrote:
> 
> 	                                  >=
>

Thanks, good catch.

> > +	tot_sec = i_size_read(bbdev->bd_inode) >> SECTOR_SHIFT;
> > +	mod = tot_sec % target->chunk_sectors;
> 
> Did you build this on 32-bit also?  Is that '%' OK on 32-bit?

I've looked at this a bit and still can't figure out why this
modulo operation would operate differently on a 32 versus a 64
bit platform? I know sector_t is config dependent but the
sector_t should be promoted to 64 bit width during the modulo
operation.

Are you wondering whether sector_t is the right type for any of
the math in this file? Perhaps we should be safe and only use
u64s?