Re: [PATCH v8 9/9] null_blk: add support for copy offload

Damien Le Moal
2023-03-29T09:05:47Z

On 3/27/23 17:40, Anuj Gupta wrote:
> From: Nitesh Shetty <nj.shetty@samsung.com>
>
> Implementaion is based on existing read and write infrastructure.
>
> Suggested-by: Damien Le Moal <damien.lemoal@opensource.wdc.com>
> Signed-off-by: Anuj Gupta <anuj20.g@samsung.com>
> Signed-off-by: Nitesh Shetty <nj.shetty@samsung.com>
> Signed-off-by: Vincent Fu <vincent.fu@samsung.com>
> ---
> drivers/block/null_blk/main.c | 94 +++++++++++++++++++++++++++++++
> drivers/block/null_blk/null_blk.h | 7 +++
> 2 files changed, 101 insertions(+)
>
> diff --git a/drivers/block/null_blk/main.c b/drivers/block/null_blk/main.c
> index 9e6b032c8ecc..84c5fbcd67a5 100644
> --- a/drivers/block/null_blk/main.c
> +++ b/drivers/block/null_blk/main.c
> @@ -1257,6 +1257,81 @@ static int null_transfer(struct nullb *nullb, struct page *page,
> return err;
> }
>
> +static inline int nullb_setup_copy_read(struct nullb *nullb,
> + struct bio *bio)
> +{
> + struct nullb_copy_token *token = bvec_kmap_local(&bio->bi_io_vec[0]);
> +
> + memcpy(token->subsys, "nullb", 5);
> + token->sector_in = bio->bi_iter.bi_sector;
> + token->nullb = nullb;
> + token->sectors = bio->bi_iter.bi_size >> SECTOR_SHIFT;
> +
> + return 0;
> +}
> +
> +static inline int nullb_setup_copy_write(struct nullb *nullb,
> + struct bio *bio, bool is_fua)
> +{
> + struct nullb_copy_token *token = bvec_kmap_local(&bio->bi_io_vec[0]);
> + sector_t sector_in, sector_out;
> + void *in, *out;
> + size_t rem, temp;
> + unsigned long offset_in, offset_out;
> + struct nullb_page *t_page_in, *t_page_out;
> + int ret = -EIO;
> +
> + if (unlikely(memcmp(token->subsys, "nullb", 5)))
> + return -EOPNOTSUPP;
> + if (unlikely(token->nullb != nullb))
> + return -EOPNOTSUPP;
> + if (WARN_ON(token->sectors != bio->bi_iter.bi_size >> SECTOR_SHIFT))
> + return -EOPNOTSUPP;

EOPNOTSUPP is strange. These are EINVAL, no ?.

> +
> + sector_in = token->sector_in;
> + sector_out = bio->bi_iter.bi_sector;
> + rem = token->sectors << SECTOR_SHIFT;
> +
> + spin_lock_irq(&nullb->lock);
> + while (rem > 0) {
> + temp = min_t(size_t, nullb->dev->blocksize, rem);
> + offset_in = (sector_in & SECTOR_MASK) << SECTOR_SHIFT;
> + offset_out = (sector_out & SECTOR_MASK) << SECTOR_SHIFT;
> +
> + if (null_cache_active(nullb) && !is_fua)
> + null_make_cache_space(nullb, PAGE_SIZE);
> +
> + t_page_in = null_lookup_page(nullb, sector_in, false,
> + !null_cache_active(nullb));
> + if (!t_page_in)
> + goto err;
> + t_page_out = null_insert_page(nullb, sector_out,
> + !null_cache_active(nullb) || is_fua);
> + if (!t_page_out)
> + goto err;
> +
> + in = kmap_local_page(t_page_in->page);
> + out = kmap_local_page(t_page_out->page);
> +
> + memcpy(out + offset_out, in + offset_in, temp);
> + kunmap_local(out);
> + kunmap_local(in);
> + __set_bit(sector_out & SECTOR_MASK, t_page_out->bitmap);
> +
> + if (is_fua)
> + null_free_sector(nullb, sector_out, true);
> +
> + rem -= temp;
> + sector_in += temp >> SECTOR_SHIFT;
> + sector_out += temp >> SECTOR_SHIFT;
> + }
> +
> + ret = 0;
> +err:
> + spin_unlock_irq(&nullb->lock);
> + return ret;
> +}
> +
> static int null_handle_rq(struct nullb_cmd *cmd)
> {
> struct request *rq = cmd->rq;
> @@ -1267,6 +1342,14 @@ static int null_handle_rq(struct nullb_cmd *cmd)
> struct req_iterator iter;
> struct bio_vec bvec;
>
> + if (rq->cmd_flags & REQ_COPY) {
> + if (op_is_write(req_op(rq)))
> + return nullb_setup_copy_write(nullb, rq->bio,
> + rq->cmd_flags & REQ_FUA);
> + else

No need for this else.

> + return nullb_setup_copy_read(nullb, rq->bio);
> + }
> +
> spin_lock_irq(&nullb->lock);
> rq_for_each_segment(bvec, rq, iter) {
> len = bvec.bv_len;
> @@ -1294,6 +1377,14 @@ static int null_handle_bio(struct nullb_cmd *cmd)
> struct bio_vec bvec;
> struct bvec_iter iter;
>
> + if (bio->bi_opf & REQ_COPY) {
> + if (op_is_write(bio_op(bio)))
> + return nullb_setup_copy_write(nullb, bio,
> + bio->bi_opf & REQ_FUA);
> + else

No need for this else.

> + return nullb_setup_copy_read(nullb, bio);
> + }
> +
> spin_lock_irq(&nullb->lock);
> bio_for_each_segment(bvec, bio, iter) {
> len = bvec.bv_len;
> @@ -2146,6 +2237,9 @@ static int null_add_dev(struct nullb_device *dev)
> list_add_tail(&nullb->list, &nullb_list);
> mutex_unlock(&lock);
>
> + blk_queue_max_copy_sectors_hw(nullb->disk->queue, 1024);
> + blk_queue_flag_set(QUEUE_FLAG_COPY, nullb->disk->queue);

This should NOT be unconditionally enabled with a magic value of 1K sectors. The
max copy sectors needs to be set with a configfs attribute so that we can
enable/disable the copy offload support, to be able to exercise both block layer
emulation and native device support.

> +
> pr_info("disk %s created\n", nullb->disk_name);
>
> return 0;
> diff --git a/drivers/block/null_blk/null_blk.h b/drivers/block/null_blk/null_blk.h
> index eb5972c50be8..94e524e7306a 100644
> --- a/drivers/block/null_blk/null_blk.h
> +++ b/drivers/block/null_blk/null_blk.h
> @@ -67,6 +67,13 @@ enum {
> NULL_Q_MQ = 2,
> };
>
> +struct nullb_copy_token {
> + char subsys[5];
> + struct nullb *nullb;
> + u64 sector_in;
> + u64 sectors;
> +};
> +
> struct nullb_device {
> struct nullb *nullb;
> struct config_item item;

--
Damien Le Moal
Western Digital Research