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

[Bart Van Assche]

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.