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From: Christoph Hellwig <hch@lst.de>
Subject: Re: [PATCH 3/3] target: use vfs_bvec_read/write
Date: Sun, 25 Jan 2015 14:43:04 +0100
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Cc: Christoph Hellwig <hch@lst.de>, Al Viro <viro@zeniv.linux.org.uk>,
	Jens Axboe <axboe@fb.com>,
	Nicholas Bellinger <nab@linux-iscsi.org>,
	linux-fsdevel@vger.kernel.org, target-devel@vger.kernel.org
To: Ming Lei <ming.lei@canonical.com>
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On Fri, Jan 23, 2015 at 10:08:01PM +0800, Ming Lei wrote:
> >
> >  	for_each_sg(sgl, sg, sgl_nents, i) {
> > -		iov[i].iov_len = sg->length;
> > -		iov[i].iov_base = kmap(sg_page(sg)) + sg->offset;
> > -	}
> > +		bvec[i].bv_page = sg_page(sg);
> > +		bvec[i].bv_len = sg->length;
> > +		bvec[i].bv_offset = sg->offset;
> 
> Sorry, I have one question: I understand one bvec should only cover
> one page, but
> one sg may cover lots of pages, so could ITER_BVEC handle that correctly?

Each scatterlist entry only contains a single page, which is returned
by sg_page(sg).  The existing code already relies on it because it
kmaps that page.