Re: [PATCH] block: allow for_each_bvec to support zero len bvec

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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?

It would seem better to me to put the bv_len test in bvec_iter_advance()
instead of making the macro more complicated.



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