Re: About sbitmap_bitmap_show() and cleared bits (was Re: [PATCH RFC v7 07/12] blk-mq: Add support in hctx_tags_bitmap_show() for a shared sbitmap)

Bart Van Assche
2020-06-30T14:55:54Z

On 2020-06-29 08:32, John Garry wrote:
> I noticed that sbitmap_bitmap_show() only shows set bits and does not
> consider cleared bits. Is that the proper thing to do?
>
> I ask, as from trying to support sbitmap_bitmap_show() for hostwide
> shared tags feature, we currently use blk_mq_queue_tag_busy_iter() to
> find active requests (and associated tags/bits) for a particular hctx.
> So, AFAICT, would give a change in behavior for sbitmap_bitmap_show(),
> in that it would effectively show set and not cleared bits.
>
> Any thoughts on this?

Probably this is something that got overlooked when the cleared bits
were introduced? See e.g. 8c2def893afc ("sbitmap: fix
sbitmap_for_each_set()").

Bart.