Re: [PATCH V10 05/19] block: introduce bvec_last_segment()

Ming Lei
2018-11-19T07:57:47Z

On Thu, Nov 15, 2018 at 03:23:56PM -0800, Omar Sandoval wrote:
> On Thu, Nov 15, 2018 at 04:52:52PM +0800, Ming Lei wrote:
> > BTRFS and guard_bio_eod() need to get the last singlepage segment
> > from one multipage bvec, so introduce this helper to make them happy.
> >
> > Cc: Dave Chinner <dchinner@redhat.com>
> > Cc: Kent Overstreet <kent.overstreet@gmail.com>
> > Cc: Mike Snitzer <snitzer@redhat.com>
> > Cc: dm-devel@redhat.com
> > Cc: Alexander Viro <viro@zeniv.linux.org.uk>
> > Cc: linux-fsdevel@vger.kernel.org
> > Cc: Shaohua Li <shli@kernel.org>
> > Cc: linux-raid@vger.kernel.org
> > Cc: linux-erofs@lists.ozlabs.org
> > Cc: David Sterba <dsterba@suse.com>
> > Cc: linux-btrfs@vger.kernel.org
> > Cc: Darrick J. Wong <darrick.wong@oracle.com>
> > Cc: linux-xfs@vger.kernel.org
> > Cc: Gao Xiang <gaoxiang25@huawei.com>
> > Cc: Christoph Hellwig <hch@lst.de>
> > Cc: Theodore Ts'o <tytso@mit.edu>
> > Cc: linux-ext4@vger.kernel.org
> > Cc: Coly Li <colyli@suse.de>
> > Cc: linux-bcache@vger.kernel.org
> > Cc: Boaz Harrosh <ooo@electrozaur.com>
> > Cc: Bob Peterson <rpeterso@redhat.com>
> > Cc: cluster-devel@redhat.com
>
> Reviewed-by: Omar Sandoval <osandov@fb.com>
>
> Minor comments below.
>
> > Signed-off-by: Ming Lei <ming.lei@redhat.com>
> > ---
> > include/linux/bvec.h | 25 +++++++++++++++++++++++++
> > 1 file changed, 25 insertions(+)
> >
> > diff --git a/include/linux/bvec.h b/include/linux/bvec.h
> > index 3d61352cd8cf..01616a0b6220 100644
> > --- a/include/linux/bvec.h
> > +++ b/include/linux/bvec.h
> > @@ -216,4 +216,29 @@ static inline bool mp_bvec_iter_advance(const struct bio_vec *bv,
> > .bi_bvec_done = 0, \
> > }
> >
> > +/*
> > + * Get the last singlepage segment from the multipage bvec and store it
> > + * in @seg
> > + */
> > +static inline void bvec_last_segment(const struct bio_vec *bvec,
> > + struct bio_vec *seg)
>
> Indentation is all messed up here.

Will fix it.

>
> > +{
> > + unsigned total = bvec->bv_offset + bvec->bv_len;
> > + unsigned last_page = total / PAGE_SIZE;
> > +
> > + if (last_page * PAGE_SIZE == total)
> > + last_page--;
>
> I think this could just be
>
> unsigned int last_page = (total - 1) / PAGE_SIZE;

This way is really elegant.

Thanks,
Ming