[dm-devel] [PATCH 1/4] block: introduce submit_bio_noacct_add_head

[John Stoffel]

>>>>> "dannyshih" == dannyshih  <dannyshih at synology.com> writes:

dannyshih> From: Danny Shih <dannyshih at synology.com>
dannyshih> Porvide a way for stacking block device to re-submit the bio
dannyshih> which sholud be handled firstly.

You're spelling needs to be fixed in these messages.  

dannyshih> Signed-off-by: Danny Shih <dannyshih at synology.com>
dannyshih> Reviewed-by: Allen Peng <allenpeng at synology.com>
dannyshih> Reviewed-by: Alex Wu <alexwu at synology.com>
dannyshih> ---
dannyshih>  block/blk-core.c       | 44 +++++++++++++++++++++++++++++++++-----------
dannyshih>  include/linux/blkdev.h |  1 +
dannyshih>  2 files changed, 34 insertions(+), 11 deletions(-)

dannyshih> diff --git a/block/blk-core.c b/block/blk-core.c
dannyshih> index 96e5fcd..693dc83 100644
dannyshih> --- a/block/blk-core.c
dannyshih> +++ b/block/blk-core.c
dannyshih> @@ -1031,16 +1031,7 @@ static blk_qc_t __submit_bio_noacct_mq(struct bio *bio)
dannyshih>  	return ret;
dannyshih>  }
 
dannyshih> -/**
dannyshih> - * submit_bio_noacct - re-submit a bio to the block device layer for I/O
dannyshih> - * @bio:  The bio describing the location in memory and on the device.
dannyshih> - *
dannyshih> - * This is a version of submit_bio() that shall only be used for I/O that is
dannyshih> - * resubmitted to lower level drivers by stacking block drivers.  All file
dannyshih> - * systems and other upper level users of the block layer should use
dannyshih> - * submit_bio() instead.
dannyshih> - */
dannyshih> -blk_qc_t submit_bio_noacct(struct bio *bio)
dannyshih> +static blk_qc_t do_submit_bio_noacct(struct bio *bio, bool add_head)
dannyshih>  {
dannyshih>  	if (!submit_bio_checks(bio))
dannyshih>  		return BLK_QC_T_NONE;
dannyshih> @@ -1052,7 +1043,10 @@ blk_qc_t submit_bio_noacct(struct bio *bio)
dannyshih>  	 * it is active, and then process them after it returned.
dannyshih>  	 */
dannyshih>  	if (current->bio_list) {
dannyshih> -		bio_list_add(&current->bio_list[0], bio);
dannyshih> +		if (add_head)
dannyshih> +			bio_list_add_head(&current->bio_list[0], bio);
dannyshih> +		else
dannyshih> +			bio_list_add(&current->bio_list[0], bio);
dannyshih>  		return BLK_QC_T_NONE;
dannyshih>  	}
 
dannyshih> @@ -1060,9 +1054,37 @@ blk_qc_t submit_bio_noacct(struct bio *bio)
dannyshih>  		return __submit_bio_noacct_mq(bio);
dannyshih>  	return __submit_bio_noacct(bio);
dannyshih>  }
dannyshih> +
dannyshih> +/**
dannyshih> + * submit_bio_noacct - re-submit a bio to the block device layer for I/O
dannyshih> + * @bio:  The bio describing the location in memory and on the device.
dannyshih> + *
dannyshih> + * This is a version of submit_bio() that shall only be used for I/O that is
dannyshih> + * resubmitted to lower level drivers by stacking block drivers.  All file
dannyshih> + * systems and other upper level users of the block layer should use
dannyshih> + * submit_bio() instead.
dannyshih> + */
dannyshih> +blk_qc_t submit_bio_noacct(struct bio *bio)
dannyshih> +{
dannyshih> +	return do_submit_bio_noacct(bio, false);
dannyshih> +}
dannyshih>  EXPORT_SYMBOL(submit_bio_noacct);

So why is it named "submit_bio_noacct" when it's supposed to be only
used by layers submitting to lower level drivers.  How can this be
figured out by drivers automatically, so the writed doesn't have to
know about this?  
 
dannyshih>  /**
dannyshih> + * submit_bio_noacct - re-submit a bio, which needs to be handle firstly,
dannyshih> + *                     to the block device layer for I/O
dannyshih> + * @bio:  The bio describing the location in memory and on the device.
dannyshih> + *
dannyshih> + * alternative submit_bio_noacct() which add bio to the head of
dannyshih> + * current->bio_list.
dannyshih> + */

Firstly isn't proper english.  Maybe something like:

submit_bio_noacct - re-submit a bio which needs to be handled first
because <reasons> to the block device layer for I/O

But the name still sucks, and the *reason* the bio needs to be handled
differently isn't well explained. 

dannyshih> +blk_qc_t submit_bio_noacct_add_head(struct bio *bio)
dannyshih> +{
dannyshih> +	return do_submit_bio_noacct(bio, true);
dannyshih> +}
dannyshih> +EXPORT_SYMBOL(submit_bio_noacct_add_head);
dannyshih> +
dannyshih> +/**
dannyshih>   * submit_bio - submit a bio to the block device layer for I/O
dannyshih>   * @bio: The &struct bio which describes the I/O
dannyshih>   *
dannyshih> diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
dannyshih> index 070de09..b0080d0 100644
dannyshih> --- a/include/linux/blkdev.h
dannyshih> +++ b/include/linux/blkdev.h
dannyshih> @@ -905,6 +905,7 @@ static inline void rq_flush_dcache_pages(struct request *rq)
dannyshih>  extern int blk_register_queue(struct gendisk *disk);
dannyshih>  extern void blk_unregister_queue(struct gendisk *disk);
dannyshih>  blk_qc_t submit_bio_noacct(struct bio *bio);
dannyshih> +blk_qc_t submit_bio_noacct_add_head(struct bio *bio);
dannyshih>  extern void blk_rq_init(struct request_queue *q, struct request *rq);
dannyshih>  extern void blk_put_request(struct request *);
dannyshih>  extern struct request *blk_get_request(struct request_queue *, unsigned int op,
dannyshih> -- 
dannyshih> 2.7.4