On Wed, Jun 13, 2018 at 09:32:04AM +0200, Christoph Hellwig wrote: > On Tue, Jun 12, 2018 at 02:16:30AM -0400, Kent Overstreet wrote: > > On Mon, Jun 11, 2018 at 09:48:01PM +0200, Christoph Hellwig wrote: > > > This abstracts out a way to reuse a bio without destroying the > > > data pointers. > > > > What is the point of this? What "data pointers" does it not destroy? > > It keeps bi_vcnt and bi_size intact in addition to bi_max_vecs/bi_io_vec > already kept by the existing bio_reset. > > The befit is that you don't need to rebuild bi_vcnt, bio_io_vec and > bi_size when reusing the bio.
bi_size is not immutable though, it will usually be modified by drivers when you submit a bio. I see what you're trying to do, but your approach is busted given the way the block layer works today. You'd have to save bio->bi_iter before submitting the bio and restore it afterwards for it to work.
