From: Tejun Heo <htejun@gmail.com>
To: FUJITA Tomonori <tomof@acm.org>
Cc: jens.axboe@oracle.com, fujita.tomonori@lab.ntt.co.jp,
James.Bottomley@HansenPartnership.com, efault@gmx.de,
akpm@linux-foundation.org, linux-kernel@vger.kernel.org,
linux-ide@vger.kernel.org, linux-scsi@vger.kernel.org,
jgarzik@pobox.com, Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>
Subject: Re: [PATCH] block: fix residual byte count handling
Date: Tue, 04 Mar 2008 11:32:56 +0900 [thread overview]
Message-ID: <47CCB4D8.8090600@gmail.com> (raw)
In-Reply-To: <20080304111056X.tomof@acm.org>
FUJITA Tomonori wrote:
>> Yeah, libata did its own padding and needed to add draining. Private
>> implementation was complex as hell and James suggested moving them to
>> block layer. Are you suggesting moving them back to drivers?
>
> No, I'm not. I've been working on the IOMMUs to remove such
> workarounds in LLDs.
>
> What drivers need to do on this is just adding a padding length, that
> is, drivers don't need to change the structure of the sg list (like
> splitting a sg entry), right? And it doesn't break the SAS drivers
> that support SATAPI, does it?
>
> But I agree that drivers want to get a complete sglist so I'm fine
> with adjusting sglist entries in the block layer with your secode
> patch (separate out padding from alignment). As we discussed, I'm fine
> with breaking sum(sg) == rq->data_len as long as rq->data_len means
> the true data length.
As long as the second patch is in, what value rq->data_len indicates
doesn't matter to drivers which don't use explicit padding or draining,
so the situation is much more controlled. I don't care which value
rq->data_len would indicate. I'd prefer it equal sum(sg) as that value
is what IDE and libata which will be the major users of padding and/or
draining expect in rq->data_len but fixing up that shouldn't be too
difficult. I guess this can be determined by Jens. If Jens likes
rq->data_len to contain requested transfer size, I'll post updated patches.
>>>> buffer after it, it ends up with unaligned sg entry in the middle and
>>>> rq->data_len + rq->extra_len will overrun the sg entry after the drain
>>>> page which is really dangerous.
>>> The drivers know that they use drain buffer. They can take care about
>>> themselves on this too. If we want to do explicitly, we could have
>>> rq->pad_len and rq->drain_len instead of rq->extra_len, though I think
>>> that we are fine without these values because these drivers already
>>> tell the block layer what they want and know that the block layer
>>> gives it.
>> So, if a driver has requested aligning and draining, the driver should
>> extend the sg entry before the last one by the alignment if draining was
>> used for the request and extent the last sg if the draining wasn't used.
>> I'd rather just implement them in the drivers.
>
> The block layer extends the sg entry? The drivers just adjust
> sg->length?
Still, do you really wanna force such things into low level drivers?
That will be one extremely fragile API and will be really difficult to
tell when things go wrong.
--
tejun
next prev parent reply other threads:[~2008-03-04 2:33 UTC|newest]
Thread overview: 109+ messages / expand[flat|nested] mbox.gz Atom feed top
2008-02-21 8:42 regression: CD burning (k3b) went broke Mike Galbraith
2008-02-22 7:32 ` Jens Axboe
2008-02-23 7:42 ` Mike Galbraith
2008-02-24 7:54 ` Mike Galbraith
2008-02-26 9:48 ` Mike Galbraith
2008-02-26 13:36 ` Mike Galbraith
2008-02-26 23:08 ` Andrew Morton
2008-02-27 0:46 ` Jeff Garzik
2008-02-27 2:58 ` Mike Galbraith
2008-02-27 2:24 ` Mike Galbraith
2008-02-27 6:00 ` Mike Galbraith
2008-02-27 7:07 ` Mike Galbraith
2008-02-28 7:43 ` Tejun Heo
2008-02-28 8:20 ` Mike Galbraith
2008-02-28 8:50 ` [PATCH] block: fix residual byte count handling Tejun Heo
2008-02-28 15:35 ` Jens Axboe
2008-02-28 15:46 ` Tejun Heo
2008-02-29 16:47 ` James Bottomley
2008-02-29 20:11 ` Jens Axboe
2008-03-01 6:17 ` Tejun Heo
2008-03-01 15:19 ` James Bottomley
2008-03-02 14:52 ` FUJITA Tomonori
2008-03-02 18:46 ` Mike Christie
2008-03-03 3:27 ` Mike Galbraith
2008-03-03 2:40 ` Tejun Heo
2008-03-03 3:59 ` FUJITA Tomonori
2008-03-03 4:09 ` Tejun Heo
2008-03-03 6:08 ` [PATCH 1/2] " Tejun Heo
2008-03-03 6:10 ` [PATCH] block: separate out padding from alignment Tejun Heo
2008-03-03 18:27 ` James Bottomley
2008-03-03 8:26 ` [PATCH] block: fix residual byte count handling FUJITA Tomonori
2008-03-03 9:21 ` Tejun Heo
2008-03-03 12:17 ` FUJITA Tomonori
2008-03-03 13:38 ` Tejun Heo
2008-03-03 13:50 ` FUJITA Tomonori
2008-03-03 13:55 ` Tejun Heo
2008-03-03 14:01 ` FUJITA Tomonori
2008-03-03 14:22 ` Tejun Heo
2008-03-03 14:52 ` FUJITA Tomonori
2008-03-03 22:44 ` Tejun Heo
2008-03-04 2:11 ` FUJITA Tomonori
2008-03-04 2:32 ` Tejun Heo [this message]
2008-03-04 8:53 ` FUJITA Tomonori
2008-03-04 8:59 ` Jens Axboe
2008-03-04 9:06 ` FUJITA Tomonori
2008-03-04 9:22 ` FUJITA Tomonori
2008-03-04 9:30 ` Tejun Heo
2008-03-04 9:35 ` Jens Axboe
2008-03-04 9:40 ` Tejun Heo
2008-03-04 9:46 ` Jens Axboe
2008-03-04 12:37 ` Mike Galbraith
2008-03-04 12:39 ` Jens Axboe
2008-03-04 12:43 ` Mike Galbraith
2008-03-04 12:58 ` Mike Galbraith
2008-03-04 13:03 ` Jens Axboe
2008-03-04 14:25 ` Mike Galbraith
2008-03-04 18:17 ` Jens Axboe
2008-03-04 18:29 ` Jens Axboe
2008-03-04 18:35 ` Mike Galbraith
2008-03-04 18:45 ` Jens Axboe
2008-03-04 18:49 ` Mike Galbraith
2008-03-04 18:54 ` Jens Axboe
2008-03-04 19:26 ` Mike Galbraith
2008-03-04 19:28 ` Jens Axboe
2008-03-04 16:04 ` James Bottomley
2008-03-04 18:46 ` Jens Axboe
2008-03-04 17:34 ` walt
2008-03-04 17:59 ` Tejun Heo
2008-03-04 19:42 ` Kiyoshi Ueda
2008-03-04 12:40 ` Tejun Heo
2008-03-04 12:45 ` Mike Galbraith
2008-03-04 13:30 ` FUJITA Tomonori
2008-03-04 13:50 ` Tejun Heo
2008-03-04 16:17 ` Tejun Heo
2008-03-04 16:42 ` Tejun Heo
2008-03-04 18:26 ` Boaz Harrosh
2008-03-04 18:35 ` Tejun Heo
2008-03-04 18:27 ` James Bottomley
2008-03-04 18:33 ` Tejun Heo
2008-03-04 18:45 ` Mike Galbraith
2008-03-04 19:25 ` Jens Axboe
2008-03-04 19:33 ` Mike Galbraith
2008-03-04 19:34 ` Jens Axboe
2008-03-04 19:19 ` FUJITA Tomonori
2008-03-04 23:33 ` Tejun Heo
2008-03-04 23:54 ` Tejun Heo
2008-03-05 0:26 ` FUJITA Tomonori
2008-03-05 0:44 ` Tejun Heo
2008-03-06 4:56 ` FUJITA Tomonori
2008-03-06 5:02 ` Tejun Heo
2008-03-05 10:16 ` [PATCH] blk: missing add of padded bytes to io completion byte count Boaz Harrosh
2008-03-05 12:28 ` Mike Galbraith
2008-03-05 12:33 ` Jens Axboe
2008-03-05 12:46 ` Boaz Harrosh
2008-03-05 12:48 ` Jens Axboe
2008-03-05 13:45 ` Tejun Heo
2008-03-05 13:51 ` Jens Axboe
2008-03-05 14:08 ` Tejun Heo
2008-03-05 15:21 ` James Bottomley
2008-03-06 4:41 ` FUJITA Tomonori
2008-03-06 13:41 ` Jens Axboe
2008-03-07 0:07 ` Tejun Heo
2008-03-07 15:07 ` FUJITA Tomonori
2008-03-08 1:06 ` Tejun Heo
2008-03-20 12:54 ` FUJITA Tomonori
2008-03-05 14:46 ` Boaz Harrosh
2008-03-05 15:11 ` Tejun Heo
2008-03-06 5:02 ` FUJITA Tomonori
2008-03-04 9:29 ` [PATCH] block: fix residual byte count handling Tejun Heo
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