Re: [PATCH] block: Simplify the bio cloning implementation

[Ming Lei <ming.lei@redhat.com>]

On Tue, Jun 26, 2018 at 03:26:24PM -0700, Bart Van Assche wrote:
> There is no good reason to use different code paths for different
> request operations. Hence remove the switch/case statement from
> bio_clone_bioset().
> 
> Signed-off-by: Bart Van Assche <bart.vanassche@wdc.com>
> Cc: Christoph Hellwig <hch@lst.de>
> Cc: Ming Lei <ming.lei@redhat.com>
> ---
>  block/bio.c | 15 ++-------------
>  1 file changed, 2 insertions(+), 13 deletions(-)
> 
> diff --git a/block/bio.c b/block/bio.c
> index f7e3d88bd0b6..4c27cc9ea55e 100644
> --- a/block/bio.c
> +++ b/block/bio.c
> @@ -691,19 +691,8 @@ struct bio *bio_clone_bioset(struct bio *bio_src, gfp_t gfp_mask,
>  	bio->bi_iter.bi_sector	= bio_src->bi_iter.bi_sector;
>  	bio->bi_iter.bi_size	= bio_src->bi_iter.bi_size;
>  
> -	switch (bio_op(bio)) {
> -	case REQ_OP_DISCARD:
> -	case REQ_OP_SECURE_ERASE:
> -	case REQ_OP_WRITE_ZEROES:
> -		break;
> -	case REQ_OP_WRITE_SAME:
> -		bio->bi_io_vec[bio->bi_vcnt++] = bio_src->bi_io_vec[0];
> -		break;
> -	default:
> -		bio_for_each_segment(bv, bio_src, iter)
> -			bio->bi_io_vec[bio->bi_vcnt++] = bv;
> -		break;
> -	}
> +	bio_for_each_segment(bv, bio_src, iter)
> +		bio->bi_io_vec[bio->bi_vcnt++] = bv;

The above change may not be correct for WRITE_SAME, since
bio_src->bi_iter.bi_size should be the actual bytes to write by drive.

Also Christoph has killed bio_clone_bioset() already, and I think that is
correct thing to do, see:

	https://marc.info/?l=linux-block&m=152938432207215&w=2

Thanks,
Ming