[dm-devel] [PATCH V5 08/12] block: use per-task poll context to implement bio based io polling

[Christoph Hellwig]

On Mon, Apr 12, 2021 at 06:20:55PM +0800, Ming Lei wrote:
> > > +static inline void *bio_grp_data(struct bio *bio)
> > > +{
> > > +	return bio->bi_poll;
> > > +}
> > 
> > What is the purpose of this helper?  And why does it have to lose the
> > type information?
> 
> This patch stores bio->bi_end_io(shared with ->bi_poll) into one per-task
> data structure, and links all bios sharing same .bi_end_io into one list
> via ->bi_end_io. And their ->bi_end_io is recovered before calling
> bio_endio().
> 
> The helper is used for checking if one bio can be added to bio group,
> and storing the data. The helper just serves for document purpose.
> 
> And the type info doesn't matter.

So why is bi_poll typed to start with then just to need a accessor
to remove the typer information?