Re: [dm-devel] [PATCH 05/26] block: add blk_alloc_disk and blk_cleanup_disk APIs

[Luis Chamberlain <mcgrof@kernel.org>]

On Fri, May 21, 2021 at 07:50:55AM +0200, Christoph Hellwig wrote:
> Add two new APIs to allocate and free a gendisk including the
> request_queue for use with BIO based drivers.  This is to avoid
> boilerplate code in drivers.
> 
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> ---
>  block/genhd.c         | 35 +++++++++++++++++++++++++++++++++++
>  include/linux/genhd.h | 22 ++++++++++++++++++++++
>  2 files changed, 57 insertions(+)
> 
> diff --git a/block/genhd.c b/block/genhd.c
> index e4974af3d729..6d4ce962866d 100644
> --- a/block/genhd.c
> +++ b/block/genhd.c
> @@ -1302,6 +1302,25 @@ struct gendisk *__alloc_disk_node(int minors, int node_id)
>  }
>  EXPORT_SYMBOL(__alloc_disk_node);
>  
> +struct gendisk *__blk_alloc_disk(int node)
> +{
> +	struct request_queue *q;
> +	struct gendisk *disk;
> +
> +	q = blk_alloc_queue(node);
> +	if (!q)
> +		return NULL;
> +
> +	disk = __alloc_disk_node(0, node);
> +	if (!disk) {
> +		blk_cleanup_queue(q);
> +		return NULL;
> +	}
> +	disk->queue = q;
> +	return disk;
> +}
> +EXPORT_SYMBOL(__blk_alloc_disk);

Its not obvious to me why using this new API requires you then to
set minors explicitly to 1, and yet here underneath we see the minors
argument passed is 0.

Nor is it clear from the documentation.

  Luis