linux-kernel - Re: [PATCH 019 of 35] Convert bio_for_each_segment to fill in a fresh bio

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Date:	Thu, 2 Aug 2007 01:21:45 +0900
From:	Tejun Heo <htejun@...il.com>
To:	NeilBrown <neilb@...e.de>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 019 of 35] Convert bio_for_each_segment to fill in a fresh bio_vec

Hi,

On Tue, Jul 31, 2007 at 12:17:27PM +1000, NeilBrown wrote:
> i.e. instread of providing a pointer to each bio_vec, it provides
> a copy of each bio_vec.
> 
> This allows a future patch to cause bio_for_each_segment to
> provide bio_vecs that are not in the bi_io_vec list, thus allowing
> for offsets and length restrictions.
> 
> We consequently remove the only call for bio_kmap_atomic,
> and so remove that function as well.
> Also remove bio_kmap_irq.  No-one uses it, and bvec_kmap_irq
> is a much more usable interface.

I think this patch can be split into two but it's no big deal.

> +struct bio_iterator {
> +	int i;
> +};
>  #define bio_for_each_segment(bvl, bio, i)				\
> -	for (bvl = bio_iovec_idx((bio), 0), i = 0;			\
> -	     i < (bio)->bi_vcnt;					\
> -	     bvl++, i++)
> +	for (i.i = 0, bvl = *bio_iovec_idx((bio), i.i);			\
> +	     i.i < (bio)->bi_vcnt;					\
> +	     i.i++, bvl = *bio_iovec_idx((bio), i.i))

How about something like...

struct bio_iterator {
	int i;
	struct bio_vec tmp_bvec;
	/* might put bio here too? */
};

#define bio_for_each_segment(bvl, bio, i)				\
	for (bvl = bio_iter_init(&i, bio); i.i < (bio)->bi_vcnt;	\
	     bvl = bio_iter_next(&i, bio))

[static inline] struct bio_vec *bio_iter_init(struct bio_iterator *i,
					      struct bio *bio)
{
	i->i = 0;

	if (no further restrictions)
		return bio_iovec_idx(bio, 0);
	else {
		i->tmp_bvec = *bio_iovec_idx(bio, 0);
		apply restriction;
		return &i->tmp_bvec;
	}
}

[static inline] struct bio_vec *bio_iter_next(struct bio_iterator *i,
					      struct bio *bio)
{
	i->i++;

	if (no further restriction)
		return bio_iovec_idx(bio, i->i);
	else {
		i->tmp_bvec = *bio_iovec_idx(bio, i->i);
		apply restriction;
		return &i->tmp_bvec;
	}
}

-- 
tejun
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