GitLab

Commit 7759eb23 ("block: remove bio_rewind_iter()") removed
a similar API for the following reasons:
    ```
    It is pointed that bio_rewind_iter() is one very bad API[1]:

    1) bio size may not be restored after rewinding

    2) it causes some bogus change, such as 5151842b (block: reset
    bi_iter.bi_done after splitting bio)

    3) rewinding really makes things complicated wrt. bio splitting

    4) unnecessary updating of .bi_done in fast path

    [1] https://marc.info/?t=153549924200005&r=1&w=2

    So this patch takes Kent's suggestion to restore one bio into its original
    state via saving bio iterator(struct bvec_iter) in bio_integrity_prep(),
    given now bio_rewind_iter() is only used by bio integrity code.
    ```
However, saving off a copy of the 32 bytes bio->bi_iter in case rewind
needed isn't efficient because it bloats per-bio-data for what is an
unlikely case. That suggestion also ignores the need to restore
crypto and integrity ...