Hi all, we have had a problem for a while where the number of segments that the bvec iterators will iterate over don't match the value in req->nr_phys_segments, causing problems for anyone looking at nr_phys_segments and iterating over bvec directly instead of using blk_rq_map_sg. The first patch in this series fixes this by making sure nr_phys_segments matches the actual number of segments. Drivers using blk_rq_map_sg will still get the lower number returned from function eventually, but the fact that we don't reduce the value earlier will not allow some merges that we might otherwise allow. With that in place I also noticed that we do not properly account segements sizes on devices with a virt_boundary, but it turns out that segment sizes fundamentally don't make sense for such devices, as their "segment" is a fixed size "device page", and not a variable sized scatter/gather elements as in the block layer, so we make that fact formal. Once all that is sorted out it is pretty clear that there is no good reason to have the front/back segement accounting to start with. Changes since v1: - update a commit log - add fixes tags - drop the follow on patches not suitable for 5.2
