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

[Damien Le Moal]

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@xxxxxxxxxxx>
> Signed-off-by: Selvakumar S <selvakuma.s1@xxxxxxxxxxx>
> Signed-off-by: Nitesh Shetty <nj.shetty@xxxxxxxxxxx>
> Signed-off-by: Javier Gonzalez <javier.gonz@xxxxxxxxxxx>
> ---
>  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