linux-kernel - Re: [PATCH] block: fix residual byte count handling

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Message-ID: <47CDDC31.4070806@gmail.com>
Date:	Wed, 05 Mar 2008 08:33:05 +0900
From:	Tejun Heo <htejun@...il.com>
To:	FUJITA Tomonori <tomof@....org>
CC:	efault@....de, jens.axboe@...cle.com,
	fujita.tomonori@....ntt.co.jp,
	James.Bottomley@...senPartnership.com, akpm@...ux-foundation.org,
	linux-kernel@...r.kernel.org, linux-ide@...r.kernel.org,
	linux-scsi@...r.kernel.org, jgarzik@...ox.com, bzolnier@...il.com
Subject: Re: [PATCH] block: fix residual byte count handling

FUJITA Tomonori wrote:
> Hmm, does SCSI mid-layer need to care about how many bytes the block
> layer allocates? I don't think that extra_len is NOT good_bytes.
> 
> I think that the block layer had better take care about it (fix
> __end_that_request_first?).

Yeah, probably calling completion functions w/o bytes count is the right
thing to do but what I was talking about was what could break when the
semantics of rq->data_len changed.  If we keep rq->data_len() ==
sum(sg), we keep it business as usual for all the rest except for the
device application layer if we don't we do the reverse and SCSI midlayer
completion was a good example, I think.

Things going the other way is fine with me but I at least want to hear a
valid rationale.  Till now all I got is "because that's the true size"
which doesn't really make much sense to me.

Thanks.

-- 
tejun
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