linux-kernel - Re: [PATCH 1/5] block: add bio_map

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Date:	Thu, 6 Oct 2011 09:40:21 -0400
From:	Christoph Hellwig <hch@...radead.org>
To:	Boaz Harrosh <bharrosh@...asas.com>
Cc:	Christoph Hellwig <hch@...radead.org>,
	Rusty Russell <rusty@...tcorp.com.au>,
	Chris Wright <chrisw@...s-sol.org>,
	Jens Axboe <axboe@...nel.dk>,
	Stefan Hajnoczi <stefanha@...ux.vnet.ibm.com>,
	kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/5] block: add bio_map_sg

On Thu, Oct 06, 2011 at 12:51:39AM +0200, Boaz Harrosh wrote:
> I have some questions.
> 
> - Could we later use this bio_map_sg() to implement blk_rq_map_sg() and
>   remove some duplicated code?

I didn't even think about that, but it actually looks very possible
to factor the "meat" in the for each bvec loop into a common helper
used by both.

> - Don't you need to support a chained bio (bio->next != NULL)? Because
>   I did not see any looping in the last patch 
> 	[PATCH 5/5] virtio-blk: implement ->make_request
>   Or is it that ->make_request() is a single bio at a time?
>   If so could we benefit from both bio-chaining and sg-chaning to
>   make bigger IOs?

At this point ->make_request is a single bio interface.  I have some
WIP patches to do the onstack plugging per bio, at which point it would
change to take a list.  For this to work we'd need major changes to
all ->make_request drivers.

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