linux-kernel - Re: [PATCH 14/17] scsi: replace custom rq mapping with blk_rq_map_kern

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Date:	Wed, 15 Apr 2009 13:25:04 +0900
From:	Tejun Heo <tj@...nel.org>
To:	FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>
CC:	petkovbb@...il.com, bharrosh@...asas.com,
	James.Bottomley@...senpartnership.com, linux-scsi@...r.kernel.org,
	axboe@...nel.dk, bzolnier@...il.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 14/17] scsi: replace custom rq mapping with	blk_rq_map_kern_sgl()

Hello,

Sorry about the delay.

FUJITA Tomonori wrote:
>> Basically, I opted for preallocating a sense request in the ->do_request
>> routine and do that only on demand, i.e. I reinitialize it only if it
>> got used in the irq handler. So in case you want to shove a rq sense in
>> front of the queue, you simply use the already prepared one. Then in the
>> irq handler it is being finished the usual ways (blk_end_request). Next
>> time around you ->do_request, you reallocate it again since it got eaten
>> in the last round.
> 
> Sounds a workable solution.

Haven't actually looked at the code but sweeeeeet.

>> The good thing is that now I don't need all those static block layer
>> structs in the driver (bio, bio_vec, etc) and do the preferred dynamic
>> allocation instead.
> 
> That's surely good.
> 
> Well, if you could remove the usage of request structure that are not
> came from blk_get_request, it will be super. But it's a different
> topic and Tejun can go forward without such change.
> 
>> The patch is ontop of Tejun's series at
>> http://git.kernel.org/?p=linux/kernel/git/tj/misc.git;a=shortlog;h=ide-phase1
>> with some small modifications in commit 15783b1443f810ae72cb5ccb3a3a3ccc3aeb8729
>> wrt proper sense buffer length.
> 
> I think that Tejun will drop some of the patchset. At least, we don't
> need blk_rq_map_kern_prealloc stuff. I think that Tejun doesn't need
> to play with the mapping API. Well, we need to play with the mapping
> API for OSD but it's not directly related with the block layer
> cleanups necessary for the libata SCSI separation.

Yeah, the blk_rq_map_kern_prealloc() was basically shifting rq map
from ide to blk/bio so that at least codes are all in one place.  If
it's not necessary, super.  :-)

I'll drop stuff from this and the other patchset and repost them with
Borislav's patch in a few hours.  Thanks guys.

-- 
tejun
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