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Message-ID: <47CD03DE.3010703@suse.de>
Date: Tue, 04 Mar 2008 09:10:06 +0100
From: Hannes Reinecke <hare@...e.de>
To: Kiyoshi Ueda <k-ueda@...jp.nec.com>
Cc: jens.axboe@...cle.com, linux-kernel@...r.kernel.org,
linux-scsi@...r.kernel.org, dm-devel@...hat.com,
j-nomura@...jp.nec.com, michaelc@...wisc.edu
Subject: Re: [RFC PATCH 1/3] block: add rq->complete_io hook for request stacking
Hi Kiyoshi,
Kiyoshi Ueda wrote:
> Hi Hannes,
>
> On Mon, 03 Mar 2008 17:24:50 +0100, Hannes Reinecke wrote:
>> Hi Kiyoshi,
>>
>> Kiyoshi Ueda wrote:
>>> This patch adds ->complete_io() hook for request stacking.
>>> Request stacking drivers (such as request-based dm) can set
>>> a callback for completion.
>>> (The hook is not called in blk_end_io(), since request-based dm uses
>>> it for clone completion in the following appendix patches.)
>>>
>> [ .. ]
>> I would rather have rq->complete_io() to be pointing to blk_end_io in the
>> default case, this way rq->complete_io() would always be valid and we
>> would be saving us the if() clause.
>
> Thank you for the comment.
>
> I'm thinking about an idea come from Mike and Jens after the session
> at LSF'08:
> o stacking driver clones both bio and request and uses
> bio->bi_end_io and rq->end_io
> o stacking driver uses blk_complete_request() in rq->end_io
> so that stacking driver can work without queue lock
> With this idea, we don't need to add the new hook to request,
> and we can use request stacking on drivers using __blk_end_request().
>
Huh? I can't really imagine how this should work. If you start using
bio->bi_end_io() for stacking usage you'll end up with doing weird thing
with the bios ... Can you elaborate a bit more here?
> Currently, I'm trying to convert request-based dm to use the idea above.
> I'll post the new version as a RFC in the near future.
>
Oh, cool. Looking forward to it.
Cheers,
Hannes
--
Dr. Hannes Reinecke zSeries & Storage
hare@...e.de +49 911 74053 688
SUSE LINUX Products GmbH, Maxfeldstr. 5, 90409 Nürnberg
GF: Markus Rex, HRB 16746 (AG Nürnberg)
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