Re: [PATCH] block: don't use for-inside-for in bio_for_each_segment_all

[Ming Lei <tom.leiming@gmail.com>]

On Sun, Apr 7, 2019 at 3:37 PM Ming Lei <tom.leiming@gmail.com> wrote:
>
> On Sun, Apr 7, 2019 at 2:53 PM Christoph Hellwig <hch@lst.de> wrote:
> >
> > The change itself looks fine to be, but a few comments on semingly
> > unrelated changes:
> >
> > > +#define bio_for_each_segment_all(bvl, bio, i, iter_all)                      \
> > > +     for (i = 0, bvl = bvec_init_iter_all(&iter_all);                \
> > > +             iter_all.idx < (bio)->bi_vcnt &&                        \
> > > +             (mp_bvec_advance(&((bio)->bi_io_vec[iter_all.idx]),     \
> > > +                              &iter_all), 1); i++)
> >
> > Instead of the complicated expression inside the for loop test
> > expression can't we move the index check into mp_bvec_advance and let
> > it return a bool?
>
> OK, will move index check into mp_bvec_advance.

oops, I recall the above line, because:

1) the index check expression is quite straight-forward

2) it has been in my todo list to re-use bvec_advance() to re-write
iterate_bvec()
given bvec_advance() is much light-weight than for_each_bvec(). If we
move the index check into bvec_advance(), the helper has to be moved
to bio.h, then we can't use that for iterate_bvec().

thanks,
Ming Lei