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    SubjectRe: [PATCH 2/2] block: enable zone-append for iov_iter of bvec type
    Date
    On 2020/07/03 0:42, Kanchan Joshi wrote:
    > zone-append with bvec iov_iter gives WARN_ON, and returns -EINVAL.
    > Add new helper to process such iov_iter and add pages in bio honoring
    > zone-append specific constraints.
    >
    > Signed-off-by: Kanchan Joshi <joshi.k@samsung.com>
    > Signed-off-by: Selvakumar S <selvakuma.s1@samsung.com>
    > Signed-off-by: Nitesh Shetty <nj.shetty@samsung.com>
    > Signed-off-by: Javier Gonzalez <javier.gonz@samsung.com>
    > ---
    > block/bio.c | 31 ++++++++++++++++++++++++++++---
    > 1 file changed, 28 insertions(+), 3 deletions(-)
    >
    > diff --git a/block/bio.c b/block/bio.c
    > index 0cecdbc..ade9da7 100644
    > --- a/block/bio.c
    > +++ b/block/bio.c
    > @@ -975,6 +975,30 @@ static int __bio_iov_bvec_add_pages(struct bio *bio, struct iov_iter *iter)
    > iov_iter_advance(iter, size);
    > return 0;
    > }
    > +static int __bio_iov_bvec_append_add_pages(struct bio *bio, struct iov_iter *iter)
    > +{
    > + const struct bio_vec *bv = iter->bvec;
    > + unsigned int len;
    > + size_t size;
    > + struct request_queue *q = bio->bi_disk->queue;
    > + unsigned int max_append_sectors = queue_max_zone_append_sectors(q);
    > + bool same_page = false;
    > +
    > + if (WARN_ON_ONCE(!max_append_sectors))
    > + return -EINVAL;
    > +
    > + if (WARN_ON_ONCE(iter->iov_offset > bv->bv_len))
    > + return -EINVAL;
    > +
    > + len = min_t(size_t, bv->bv_len - iter->iov_offset, iter->count);
    > + size = bio_add_hw_page(q, bio, bv->bv_page, len,
    > + bv->bv_offset + iter->iov_offset,
    > + max_append_sectors, &same_page);
    > + if (unlikely(size != len))
    > + return -EINVAL;
    > + iov_iter_advance(iter, size);
    > + return 0;
    > +}
    >
    > #define PAGE_PTRS_PER_BVEC (sizeof(struct bio_vec) / sizeof(struct page *))
    >
    > @@ -1105,9 +1129,10 @@ int bio_iov_iter_get_pages(struct bio *bio, struct iov_iter *iter)
    >
    > do {
    > if (bio_op(bio) == REQ_OP_ZONE_APPEND) {
    > - if (WARN_ON_ONCE(is_bvec))
    > - return -EINVAL;
    > - ret = __bio_iov_append_get_pages(bio, iter);
    > + if (is_bvec)
    > + ret = __bio_iov_bvec_append_add_pages(bio, iter);
    > + else
    > + ret = __bio_iov_append_get_pages(bio, iter);
    > } else {
    > if (is_bvec)
    > ret = __bio_iov_bvec_add_pages(bio, iter);
    >

    The only user of this function that issues zone append requests is zonefs. The
    issued requests are not using bvec iter but a user direct IO buffer iter. So
    this change would have no user at all as far as I can see. Am I missing
    something ? What IO path makes this change necessary ?


    --
    Damien Le Moal
    Western Digital Research

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