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    SubjectRe: [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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