Re: [PATCH v20 12/12] null_blk: add support for copy offload

Bart Van Assche
2024-05-22T17:52:26Z

On 5/21/24 07:46, Nitesh Shetty wrote:
> On 20/05/24 04:42PM, Bart Van Assche wrote:
>> On 5/20/24 03:20, Nitesh Shetty wrote:
>>> +    __rq_for_each_bio(bio, req) {
>>> +        if (seg == blk_rq_nr_phys_segments(req)) {
>>> +            sector_in = bio->bi_iter.bi_sector;
>>> +            if (rem != bio->bi_iter.bi_size)
>>> +                return status;
>>> +        } else {
>>> +            sector_out = bio->bi_iter.bi_sector;
>>> +            rem = bio->bi_iter.bi_size;
>>> +        }
>>> +        seg++;
>>> +    }
>>
>> _rq_for_each_bio() iterates over the bios in a request. Does a copy
>> offload request always have two bios - one copy destination bio and
>> one copy source bio? If so, is 'seg' a bio counter? Why is that bio
>> counter compared with the number of physical segments in the request?
>>
> Yes, your observation is right. We are treating first bio as dst and
> second as src. If not for that comparision, we might need to store the
> index in a temporary variable and parse based on index value.

I'm still wondering why 'seg' is compared with blk_rq_nr_phys_segments(req).

Thanks,

Bart.