On Wed, Jun 13, 2018 at 03:59:15PM +0200, Christoph Hellwig wrote: > On Wed, Jun 13, 2018 at 04:54:41AM -0400, Kent Overstreet wrote: > > 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. > > For bi_size, agreed this needs fixing. bi_sector is always restored > already by the callers, and the remaining fields are zeroed by bio_reset, > which does the right thing. This still shouldn't be a new helper. If the caller is restoring bi_sector they can restore bi_size as well, and restoring only part of bi_iter should not be encouraged as it's not safe in general - it is a quite reasonable thing to want to restore a bio to the state it was pre submission (e.g. for bouncing) and what you're doing is definitely _not_ safe in general.
