From: Ming Lei <ming.lei@redhat.com>
To: Matthew Wilcox <willy@infradead.org>
Cc: Jens Axboe <axboe@kernel.dk>,
linux-block@vger.kernel.org,
Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>,
Al Viro <viro@zeniv.linux.org.uk>,
stable@vger.kernel.org
Subject: Re: [PATCH] block: allow for_each_bvec to support zero len bvec
Date: Mon, 10 Aug 2020 12:02:52 +0800 [thread overview]
Message-ID: <20200810040252.GC2202641@T590> (raw)
In-Reply-To: <20200810033309.GK17456@casper.infradead.org>
On Mon, Aug 10, 2020 at 04:33:09AM +0100, Matthew Wilcox wrote:
> On Mon, Aug 10, 2020 at 11:19:15AM +0800, Ming Lei wrote:
> > +++ b/include/linux/bvec.h
> > @@ -117,11 +117,18 @@ static inline bool bvec_iter_advance(const struct bio_vec *bv,
> > return true;
> > }
> >
> > +static inline void bvec_iter_skip_zero_bvec(struct bvec_iter *iter)
> > +{
> > + iter->bi_bvec_done = 0;
> > + iter->bi_idx++;
> > +}
> > +
> > #define for_each_bvec(bvl, bio_vec, iter, start) \
> > for (iter = (start); \
> > (iter).bi_size && \
> > ((bvl = bvec_iter_bvec((bio_vec), (iter))), 1); \
> > - bvec_iter_advance((bio_vec), &(iter), (bvl).bv_len))
> > + (bvl).bv_len ? bvec_iter_advance((bio_vec), &(iter), \
> > + (bvl).bv_len) : bvec_iter_skip_zero_bvec(&(iter)))
> >
>
> What if you have two zero-length bvecs in a row? Won't this just skip
> the first one?
The 2nd one will be skipped too when it is observed in next loop.
>
> It would seem better to me to put the bv_len test in bvec_iter_advance()
> instead of making the macro more complicated.
The reason is that block layer won't support zero length bvec, and I'd
not bother bvec_iter_advance() for adding this check.
Thanks,
Ming
next prev parent reply other threads:[~2020-08-10 4:03 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-08-10 3:19 [PATCH] block: allow for_each_bvec to support zero len bvec Ming Lei
2020-08-10 3:33 ` Matthew Wilcox
2020-08-10 4:02 ` Ming Lei [this message]
2020-08-10 7:52 ` Tetsuo Handa
2020-08-10 16:23 ` Ming Lei
2020-08-12 9:00 ` Ming Lei
2020-08-12 10:03 ` Tetsuo Handa
2020-08-12 12:47 ` Ming Lei
2020-08-12 12:51 ` Matthew Wilcox
2020-08-13 1:13 ` Tetsuo Handa
2020-08-27 13:27 ` Tetsuo Handa
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