void blk_rq_next_segment (struct request * rq);
Points to the next segment in the request if the current segment is complete. Leaves things unchanged if this segment is not over or if no more segments are left in this request.
Meant to be used for bio traversal during I/O submission Does not affect any I/O completions or update completion state in the request, and does not modify any bio fields.
Decrementing rq->nr_sectors, rq->current_nr_sectors and rq->nr_cbio_sectors as data is transferred is the caller's responsibility and should be done before calling this routine.