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SubjectRe: [PATCH 4.19 01/16] block: introduce multi-page bvec helpers
On Thu, Nov 11, 2021 at 05:47:54PM +0100, Pavel Machek wrote:
> Hi!
>
> > From: Ming Lei <ming.lei@redhat.com>
> >
> > commit 3d75ca0adef4280650c6690a0c4702a74a6f3c95 upstream.
> >
> > This patch introduces helpers of 'mp_bvec_iter_*' for multi-page bvec
> > support.
> >
> > The introduced helpers treate one bvec as real multi-page segment,
> > which may include more than one pages.
> >
> > The existed helpers of bvec_iter_* are interfaces for supporting current
> > bvec iterator which is thought as single-page by drivers, fs, dm and
> > etc. These introduced helpers will build single-page bvec in flight, so
> > this way won't break current bio/bvec users, which needn't any
> > change.
>
> I don't understand why we have this in 4.19-stable. I don't see
> followup patches needing it, and it does not claim to fix a bug.


There is some more context on this at:
https://lore.kernel.org/linux-block/YXweJ00CVsDLCI7b@google.com/T/#u
and
https://lore.kernel.org/stable/YYVZBuDaWBKT3vOS@google.com/T/#u

Thanks,
- Zubin

>
> > +#define mp_bvec_iter_bvec(bvec, iter) \
> > +((struct bio_vec) { \
> > + .bv_page = mp_bvec_iter_page((bvec), (iter)), \
> > + .bv_len = mp_bvec_iter_len((bvec), (iter)), \
> > + .bv_offset = mp_bvec_iter_offset((bvec), (iter)), \
> > +})
> > +
> > +/* For building single-page bvec in flight */
> > + #define bvec_iter_offset(bvec, iter) \
> > + (mp_bvec_iter_offset((bvec), (iter)) % PAGE_SIZE)
> > +
>
> Plus this one is strange. IIRC preprocessor directives have to put #
> in column zero?
>
> Best regards,
> Pavel
> --
> http://www.livejournal.com/~pavelmachek


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