Re: [PATCH 2/7] dm: Simplify dm_table_determine_type()

[Mike Snitzer <snitzer@redhat.com>]

On Tue, Nov 15 2016 at  6:33pm -0500,
Bart Van Assche <bart.vanassche@sandisk.com> wrote:

> Use a single loop instead of two loops to determine whether or not
> all_blk_mq has to be set.
> 
> Signed-off-by: Bart Van Assche <bart.vanassche@sandisk.com>
> ---
>  drivers/md/dm-table.c | 25 ++++++++++++-------------
>  1 file changed, 12 insertions(+), 13 deletions(-)
> 
> diff --git a/drivers/md/dm-table.c b/drivers/md/dm-table.c
> index 49893fdc..fff4979 100644
> --- a/drivers/md/dm-table.c
> +++ b/drivers/md/dm-table.c
> @@ -871,7 +871,7 @@ static int dm_table_determine_type(struct dm_table *t)
>  {
>  	unsigned i;
>  	unsigned bio_based = 0, request_based = 0, hybrid = 0;
> -	bool verify_blk_mq = false;
> +	unsigned sq_count = 0, mq_count = 0;
>  	struct dm_target *tgt;
>  	struct dm_dev_internal *dd;
>  	struct list_head *devices = dm_table_get_devices(t);
> @@ -959,20 +959,15 @@ static int dm_table_determine_type(struct dm_table *t)
>  		}
>  
>  		if (q->mq_ops)
> -			verify_blk_mq = true;
> +			mq_count++;
> +		else
> +			sq_count++;
>  	}
> -
> -	if (verify_blk_mq) {
> -		/* verify _all_ devices in the table are blk-mq devices */
> -		list_for_each_entry(dd, devices, list)
> -			if (!bdev_get_queue(dd->dm_dev->bdev)->mq_ops) {
> -				DMERR("table load rejected: not all devices"
> -				      " are blk-mq request-stackable");
> -				return -EINVAL;
> -			}
> -
> -		t->all_blk_mq = true;
> +	if (sq_count && mq_count) {
> +		DMERR("table load rejected: not all devices are blk-mq request-stackable");
> +		return -EINVAL;
>  	}
> +	t->all_blk_mq = mq_count > 0;
>  
>  	return 0;
>  }
> @@ -1021,6 +1016,10 @@ bool dm_table_request_based(struct dm_table *t)
>  	return __table_type_request_based(dm_table_get_type(t));
>  }
>  
> +/*
> + * Returns true if all paths are blk-mq devices. Returns false if all paths
> + * are single queue block devices or if there are no paths.
> + */

This code isn't specific to multipath.  So "paths" is misplaced.
"devices" is more appropriate.  Not seeing the need for the comment to
be honest.  The function name is pretty descriptive.

>  bool dm_table_all_blk_mq_devices(struct dm_table *t)
>  {
>  	return t->all_blk_mq;
> -- 
> 2.10.1
>