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Date:   Fri, 7 Jun 2019 18:45:32 +0200
From:   Christoph Hellwig <hch@lst.de>
To:     Hannes Reinecke <hare@suse.de>
Cc:     Christoph Hellwig <hch@lst.de>, axboe@fb.com,
        Matias Bjorling <mb@lightnvm.io>, linux-block@vger.kernel.org
Subject: Re: [PATCH 3/6] block: remove the bi_phys_segments field in struct
 bio
Message-ID: <20190607164532.GD7307@lst.de>
References: <20190606102904.4024-1-hch@lst.de> <20190606102904.4024-4-hch@lst.de> <481003ba-aa95-0d0e-ba1f-ce48f2c61105@suse.de>
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On Fri, Jun 07, 2019 at 08:02:55AM +0200, Hannes Reinecke wrote:
> > +void blk_queue_split(struct request_queue *q, struct bio **bio)
> > +{
> > +	unsigned int nr_segs;
> > +
> > +	__blk_queue_split(q, bio, &nr_segs);
> > +}
> >  EXPORT_SYMBOL(blk_queue_split);
> >  
> That looks a bit weird, and I guess some or other compiler might
> complain here about nr_segs being unused.
> Can't we modify __blk_queue_split() to accept a NULL argument here?

We could.  But that would bloat the fast path for absolutely no
reason.  Passing a by reference output argument that is then ignored
is a pretty common pattern.