On Sun, Aug 10, 2025 at 04:07:47PM +0200, Christoph Hellwig wrote:
> On Fri, Aug 08, 2025 at 08:58:20AM -0700, Keith Busch wrote:
> > +static struct blk_map_iter blk_rq_map_iter(struct request *rq)
> > +{
> > + struct bio *bio = rq->bio;
> > +
> > + if (rq->rq_flags & RQF_SPECIAL_PAYLOAD) {
> > + return (struct blk_map_iter) {
> > + .bvec = &rq->special_vec,
> > + .iter = {
> > + .bi_size = rq->special_vec.bv_len,
> > + }
> > + };
>
> These large struct returns generate really horrible code if they aren't
> inlined (although that might happen here). I also find them not very
> nice to read. Any reason to just pass a pointer and initialize the
> needed fields?
I initially set out to make a macro, inpsired by other block iterator
setups like "bvec_iter_bvec", but I thought the extra cases to handle
was better implemented as an inline function. I am definitely counting
on this being inlined to produce good code, so I should have annotated
that. No problem with switching to take a pointer, but I doubt the
resulting assembly is better either way.
