linux-kernel - Re: [dm-devel] [PATCH 1/3] block: Add blk_queue_copy

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Date:	Tue, 22 Sep 2009 01:33:38 +0900
From:	"Jun'ichi Nomura" <j-nomura@...jp.nec.com>
To:	Jens Axboe <jens.axboe@...cle.com>,
	"Martin K. Petersen" <martin.petersen@...cle.com>
CC:	device-mapper development <dm-devel@...hat.com>,
	Alasdair G Kergon <agk@...hat.com>,
	Mike Snitzer <snitzer@...hat.com>, linux-kernel@...r.kernel.org
Subject: Re: [dm-devel] [PATCH 1/3] block: Add blk_queue_copy_limits()

Martin K. Petersen wrote:
>>>>>> "Jun'ichi" == Jun'ichi Nomura <j-nomura@...jp.nec.com> writes:
> 
> Jun'ichi> Umm, with this, BLK_DEF_MAX_SECTORS becomes upper bound of
> Jun'ichi> max_hw_sectors and the values of underlying devices are not
> Jun'ichi> propagated to the stacking devices.  
> 
> Well, max_sectors is already bounded by this.  max_hw_sectors only
> really matters for PC commands, so I'm not sure it's a big deal for
> DM. But I guess we could set the default max_hw_sectors to -1.
> 
> I'm just trying to avoid these scattered if-0-set-it-to-something-else
> cases.  I'd much rather have the defaults do the right thing.

I agree with that.
I had to do the if-0-set-it-to-something-else to avoid putting unnecessary
cap on max_hw_sectors.

If we aren't sure, shouldn't we set its default to -1 or putting comments
in blk_set_default_limits() at least to avoid possible confusion in future?

Thanks,
--
Jun'ichi Nomura, NEC Corporation 
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