linux-kernel - Re: [PATCH 8/8] blk-map: reimplement blk_rq_map_user() using blk_rq_map_user

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Date:	Wed, 01 Apr 2009 22:28:02 +0900
From:	Tejun Heo <tj@...nel.org>
To:	FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>
CC:	axboe@...nel.dk, bharrosh@...asas.com,
	linux-kernel@...r.kernel.org, tj@...el.org
Subject: Re: [PATCH 8/8] blk-map: reimplement blk_rq_map_user() using blk_rq_map_user_iov()

FUJITA Tomonori wrote:
> Sounds a good idea. But I need to review that.
> 
> But 7/8 and 8/8 patches are not bug fixes at all (as I wrote, your
> descriptions about checking is untrue). It can't be for 2.6.30. So put
> them to the next patchset.

Yeah, it should.

>>>> reason blk_rq_map_user() had multiple bio chaining was to work around
>>>> BIO_MAX_SIZE.  blk_rq_map_user_iov() doesn't support multiple bio
>>>> chaining, so sans blk_rq_append_bio() or playing with rq/bio internals
>>>> directly, there's no way to use or even know about multiple bios.
>>> Yes, only non iovec interface of SG_IO supports large data
>>> transfer. Users have been lived with that.
>> This patch doesn't remove any feature.  You don't lose anything.  What
>> used to be done with multiple bios is now done with single bio.  The
>> implementation is simpler and shorter.  Using or not using multiple
>> bios doesn't (and shouldn't) make any difference to blk_map_*() users.
> 
> Hmm, with your change, blk_rq_map_user can't handle larger than
> BIO_MAX_SIZE, right?

Yes, it can.  The previous bio_kmalloc() thing was for this.

Thanks.

-- 
tejun
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