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

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Message-Id: <20090401221102O.fujita.tomonori@lab.ntt.co.jp>
Date:	Wed, 1 Apr 2009 22:10:53 +0900
From:	FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>
To:	tj@...nel.org
Cc:	fujita.tomonori@....ntt.co.jp, 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()

On Wed, 01 Apr 2009 22:03:39 +0900
Tejun Heo <tj@...nel.org> wrote:

> FUJITA Tomonori wrote:
> > No, we are not talking about blk_rq_append_bio().
> > 
> > We are talking about the multiple bio handling in blk_rq_map_user,
> > which is the feature that Mike added long time ago. The feature is
> > surely necessary for some users. So you can't remote it.
> 
> How would someone use that without blk_rq_append_bio()?  The only

Hmm, I'm not sure what you are talking about.

Why do we need to live without blk_rq_append_bio()?

You want to remove blk_rq_append_bio()? Please make your goal clear.


> 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.
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