Re: [PATCH 2/2] block: enable zone-append for iov_iter of bvec type

Damien Le Moal
2020-07-03T05:33:01Z

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