Re: [PATCH] block: Make __bio_clone_fast() copy bi_vcnt

Ming Lei
2018-06-27T23:50:06Z

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 <bart.vanassche@wdc.com>
> Cc: Christoph Hellwig <hch@lst.de>
> Cc: Mike Snitzer <snitzer@redhat.com>
> Cc: Ming Lei <ming.lei@redhat.com>
> Cc: Hannes Reinecke <hare@suse.com>
> Cc: Johannes Thumshirn <jthumshirn@suse.de>
> ---
> 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.

For a cloned bio, both .bi_vcnt and .bi_io_vec can't be used directly,
and we have done huge such cleanup for supporting multipage bvec, that is
the great idea of immutable bvecs invented by Kent.

Thanks,
Ming