Re: [PATCH] block: Make __bio_clone_fast() copy bi_vcnt

Ming Lei
2018-06-28T23:10:47Z

On Thu, Jun 28, 2018 at 11:21 PM, Bart Van Assche
<bart.vanassche@wdc.com> wrote:
> On 06/27/18 17:30, Ming Lei wrote:
>>
>> One core idea of immutable bvec is to use bio->bi_iter and the original
>> bvec table to iterate over anywhere in the bio. That is why .bi_io_vec
>> needs to copy, but not see any reason why .bi_vcnt needs to do.
>>
>> Do you have use cases on .bi_vcnt for cloned bio?
>
>
> So far this is only a theoretical concern. There are many functions in the
> block layer that use .bi_vcnt, and it is a lot of work to figure out all the
> callers of all these functions.

No, any functions using .bi_vcnt on a cloned-bio may be a bug, and we should
take a close look.

Thanks,
Ming Lei