On Wed, Jun 27, 2018 at 04:59:41PM -0700, Bart Van Assche wrote: > On 06/27/18 16:50, Ming Lei wrote: > > On Wed, Jun 27, 2018 at 01:12:31PM -0700, Bart Van Assche wrote: > > > Although __bio_clone_fast() copies bi_io_vec, it does not copy bi_vcnt, > > > the number of elements in bi_io_vec[] that contains data. Copy bi_vcnt > > > such that code that needs this member behaves identically for original > > > and for cloned requests. > > > > > > Signed-off-by: Bart Van Assche <[email protected]> > > > Cc: Christoph Hellwig <[email protected]> > > > Cc: Mike Snitzer <[email protected]> > > > Cc: Ming Lei <[email protected]> > > > Cc: Hannes Reinecke <[email protected]> > > > Cc: Johannes Thumshirn <[email protected]> > > > --- > > > block/bio.c | 1 + > > > 1 file changed, 1 insertion(+) > > > > > > diff --git a/block/bio.c b/block/bio.c > > > index f7e3d88bd0b6..55f8e0dedd69 100644 > > > --- a/block/bio.c > > > +++ b/block/bio.c > > > @@ -605,6 +605,7 @@ void __bio_clone_fast(struct bio *bio, struct bio > > > *bio_src) > > > bio->bi_opf = bio_src->bi_opf; > > > bio->bi_write_hint = bio_src->bi_write_hint; > > > bio->bi_iter = bio_src->bi_iter; > > > + bio->bi_vcnt = bio_src->bi_vcnt; > > > bio->bi_io_vec = bio_src->bi_io_vec; > > > > No, don't do that. > > Why not? I think it's a huge booby trap that cloned bio's have a bi_io_vec > but zero bi_vcnt.
One core idea of immutable bvec is to use bio->bi_iter and the original bvec table to iterate over anywhere in the bio. That is why .bi_io_vec needs to copy, but not see any reason why .bi_vcnt needs to do. Do you have use cases on .bi_vcnt for cloned bio? Thanks, Ming
