On Thu, Jun 30, 2022 at 08:47:13AM +0800, Ming Lei wrote: > What is the difference between bio_set_pos and bio_rewind()? Both have > to restore bio->bi_iter(the sector part and the bvec part). > > Also how to update ->bi_done which 'counts bytes advanced'? You meant doing it in > very bio_advance()? then no, why do we have to pay the cost for very unusual > bio_rewind()? Yeah, we'll have to add a u32 to bvec_iter, and increment it in bio_advance(). This would us everything we want - you'll be able to restore a bio to an initial state and you just have to save 8 bytes, not a whole bvec_iter, and unlike bio_rewind it'll be safe to use after calling submit_bio(), _and_ it solves the problem that stashing a copy of bvec_iter doesn't save state in integrity or crypt context. > Or if I misunderstood your point, please cook a patch and I am happy to > take a close look, and posting one very raw idea with random data > structure looks not helpful much for this discussion technically. I can do that...
