On Thu, Jul 19, 2018 at 5:39 PM, Martin Wilck <mwilck@xxxxxxxx> wrote:
> If the last page of the bio is not "full", the length of the last
> vector slot needs to be corrected. This slot has the index
> (bio->bi_vcnt - 1), but only in bio->bi_io_vec. In the "bv" helper
> array, which is shifted by the value of bio->bi_vcnt at function
> invocation, the correct index is (nr_pages - 1).
>
> V2: improved readability following suggestions from Ming Lei.
>
> Fixes: 2cefe4dbaadf ("block: add bio_iov_iter_get_pages()")
> Signed-off-by: Martin Wilck <mwilck@xxxxxxxx>
> ---
> block/bio.c | 18 ++++++++----------
> 1 file changed, 8 insertions(+), 10 deletions(-)
>
> diff --git a/block/bio.c b/block/bio.c
> index 67eff5e..0964328 100644
> --- a/block/bio.c
> +++ b/block/bio.c
> @@ -912,16 +912,16 @@ EXPORT_SYMBOL(bio_add_page);
> */
> int bio_iov_iter_get_pages(struct bio *bio, struct iov_iter *iter)
> {
> - unsigned short nr_pages = bio->bi_max_vecs - bio->bi_vcnt;
> + unsigned short idx, nr_pages = bio->bi_max_vecs - bio->bi_vcnt;
> struct bio_vec *bv = bio->bi_io_vec + bio->bi_vcnt;
> struct page **pages = (struct page **)bv;
> - size_t offset, diff;
> + size_t offset;
> ssize_t size;
>
> size = iov_iter_get_pages(iter, pages, LONG_MAX, nr_pages, &offset);
> if (unlikely(size <= 0))
> return size ? size : -EFAULT;
> - nr_pages = (size + offset + PAGE_SIZE - 1) / PAGE_SIZE;
> + idx = nr_pages = (size + offset + PAGE_SIZE - 1) / PAGE_SIZE;
>
> /*
> * Deep magic below: We need to walk the pinned pages backwards
> @@ -934,17 +934,15 @@ int bio_iov_iter_get_pages(struct bio *bio, struct iov_iter *iter)
> bio->bi_iter.bi_size += size;
> bio->bi_vcnt += nr_pages;
>
> - diff = (nr_pages * PAGE_SIZE - offset) - size;
> - while (nr_pages--) {
> - bv[nr_pages].bv_page = pages[nr_pages];
> - bv[nr_pages].bv_len = PAGE_SIZE;
> - bv[nr_pages].bv_offset = 0;
> + while (idx--) {
> + bv[idx].bv_page = pages[idx];
> + bv[idx].bv_len = PAGE_SIZE;
> + bv[idx].bv_offset = 0;
> }
>
> bv[0].bv_offset += offset;
> bv[0].bv_len -= offset;
> - if (diff)
> - bv[bio->bi_vcnt - 1].bv_len -= diff;
> + bv[nr_pages - 1].bv_len -= nr_pages * PAGE_SIZE - offset - size;
>
> iov_iter_advance(iter, size);
> return 0;
> --
> 2.17.1
>
Reviewed-by: Ming Lei <ming.lei@xxxxxxxxxx>
BTW, we can make it for mainline too, then rebase Christoph's new patch
against this one.
Thanks,
Ming Lei
