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Date:   Mon, 19 Nov 2018 16:21:25 +0800
From:   Ming Lei <ming.lei@...hat.com>
To:     Christoph Hellwig <hch@....de>
Cc:     Jens Axboe <axboe@...nel.dk>, linux-block@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        Dave Chinner <dchinner@...hat.com>,
        Kent Overstreet <kent.overstreet@...il.com>,
        Mike Snitzer <snitzer@...hat.com>, dm-devel@...hat.com,
        Alexander Viro <viro@...iv.linux.org.uk>,
        linux-fsdevel@...r.kernel.org, Shaohua Li <shli@...nel.org>,
        linux-raid@...r.kernel.org, linux-erofs@...ts.ozlabs.org,
        David Sterba <dsterba@...e.com>, linux-btrfs@...r.kernel.org,
        "Darrick J . Wong" <darrick.wong@...cle.com>,
        linux-xfs@...r.kernel.org, Gao Xiang <gaoxiang25@...wei.com>,
        Theodore Ts'o <tytso@....edu>, linux-ext4@...r.kernel.org,
        Coly Li <colyli@...e.de>, linux-bcache@...r.kernel.org,
        Boaz Harrosh <ooo@...ctrozaur.com>,
        Bob Peterson <rpeterso@...hat.com>, cluster-devel@...hat.com
Subject: Re: [PATCH V10 09/19] block: introduce bio_bvecs()

On Fri, Nov 16, 2018 at 02:45:41PM +0100, Christoph Hellwig wrote:
> On Thu, Nov 15, 2018 at 04:52:56PM +0800, Ming Lei wrote:
> > There are still cases in which we need to use bio_bvecs() for get the
> > number of multi-page segment, so introduce it.
> 
> The only user in your final tree seems to be the loop driver, and
> even that one only uses the helper for read/write bios.
> 
> I think something like this would be much simpler in the end:
> 
> diff --git a/drivers/block/loop.c b/drivers/block/loop.c
> index d509902a8046..712511815ac6 100644
> --- a/drivers/block/loop.c
> +++ b/drivers/block/loop.c
> @@ -514,16 +514,18 @@ static int lo_rw_aio(struct loop_device *lo, struct loop_cmd *cmd,
>  	struct request *rq = blk_mq_rq_from_pdu(cmd);
>  	struct bio *bio = rq->bio;
>  	struct file *file = lo->lo_backing_file;
> +	struct bvec_iter bvec_iter;
> +	struct bio_vec tmp;
>  	unsigned int offset;
>  	int nr_bvec = 0;
>  	int ret;
>  
> +	__rq_for_each_bio(bio, rq)
> +		bio_for_each_bvec(tmp, bio, bvec_iter)
> +			nr_bvec++;
> +
>  	if (rq->bio != rq->biotail) {
> -		struct bvec_iter iter;
> -		struct bio_vec tmp;
>  
> -		__rq_for_each_bio(bio, rq)
> -			nr_bvec += bio_bvecs(bio);
>  		bvec = kmalloc_array(nr_bvec, sizeof(struct bio_vec),
>  				     GFP_NOIO);
>  		if (!bvec)
> @@ -537,7 +539,7 @@ static int lo_rw_aio(struct loop_device *lo, struct loop_cmd *cmd,
>  		 * API will take care of all details for us.
>  		 */
>  		__rq_for_each_bio(bio, rq)
> -			bio_for_each_bvec(tmp, bio, iter) {
> +			bio_for_each_bvec(tmp, bio, bvec_iter) {
>  				*bvec = tmp;
>  				bvec++;
>  			}
> @@ -551,7 +553,6 @@ static int lo_rw_aio(struct loop_device *lo, struct loop_cmd *cmd,
>  		 */
>  		offset = bio->bi_iter.bi_bvec_done;
>  		bvec = __bvec_iter_bvec(bio->bi_io_vec, bio->bi_iter);
> -		nr_bvec = bio_bvecs(bio);
>  	}
>  	atomic_set(&cmd->ref, 2);
>  
> diff --git a/include/linux/bio.h b/include/linux/bio.h
> index dcad0b69f57a..379440d1ced0 100644
> --- a/include/linux/bio.h
> +++ b/include/linux/bio.h
> @@ -200,30 +200,6 @@ static inline unsigned bio_segments(struct bio *bio)
>  	}
>  }
>  
> -static inline unsigned bio_bvecs(struct bio *bio)
> -{
> -	unsigned bvecs = 0;
> -	struct bio_vec bv;
> -	struct bvec_iter iter;
> -
> -	/*
> -	 * We special case discard/write same/write zeroes, because they
> -	 * interpret bi_size differently:
> -	 */
> -	switch (bio_op(bio)) {
> -	case REQ_OP_DISCARD:
> -	case REQ_OP_SECURE_ERASE:
> -	case REQ_OP_WRITE_ZEROES:
> -		return 0;
> -	case REQ_OP_WRITE_SAME:
> -		return 1;
> -	default:
> -		bio_for_each_bvec(bv, bio, iter)
> -			bvecs++;
> -		return bvecs;
> -	}
> -}
> -
>  /*
>   * get a reference to a bio, so it won't disappear. the intended use is
>   * something like:

OK, will do it in next version.

Thanks,
Ming

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