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

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Date:	Mon, 3 Mar 2008 23:01:18 +0900
From:	FUJITA Tomonori <tomof@....org>
To:	htejun@...il.com
Cc:	fujita.tomonori@....ntt.co.jp
Subject: Re: [PATCH] block: fix residual byte count handling

On Mon, 03 Mar 2008 22:55:56 +0900
Tejun Heo <htejun@...il.com> wrote:

> FUJITA Tomonori wrote:
> >>>> FUJITA Tomonori wrote:
> >>>>>>> I can't see what changing the meaning of rq->data_len (and
> >>>>>>> investigating all the block drivers) gives us.
> >>>>>> No matter which way you go, you change the meaning of rq->data_len and
> >>>>>> you MUST inspect rq->data_len usage whichever way you go.
> >>>>> The patch doens't change that rq->data_len means the true data
> >>>>> length. But yeah, it breaks rq->data_len == sum(sg). So it might break
> >>>>> some drivers.
> >>>> Yeah, that's what I was saying.  You end up breaking one of the two
> >>>> assumptions.  As sglist is getting modified for any driver if it has DMA
> >>>> alignment set, whether rq->data_len is adjusted together or not, sglist
> >>>> and data_len usages have to be audited.
> >>> My patch (well, James' original approach) doesn't affect drivers that
> >>> don't use drain buffer. rq->data_len still means the true data length
> >>> and rq->data_len is equal to sum(sg) for them. So right now we need to
> >>> audit only libata.
> >> Your patch does change sglist for any driver which sets DMA alignment.
> > 
> > I overlook it. Where does it changes sglist?
> 
> At the end of blk_rq_map_user() together with data_len / extra_len
> mangling or were you talking about James' original patch?

With my patch, at the end of blk_rq_map_user, we have:

	if (len & queue_dma_alignment(q)) {
		unsigned int pad_len = (queue_dma_alignment(q) & ~len) + 1;

		rq->extra_len += pad_len;
	}


So no change as compared with 2.6.24?
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