qcow2 merge_cow() question

[Vladimir Sementsov-Ogievskiy]

Hi!

I'm sorry, I feel I already asked about it, but can't now find the answer.
What are these ifs for?

          /* The data (middle) region must be immediately after the
           * start region */
          if (l2meta_cow_start(m) + m->cow_start.nb_bytes != offset) {
              continue;
          }
                                                                                                          
          /* The end region must be immediately after the data (middle)
           * region */
          if (m->offset + m->cow_end.offset != offset + bytes) {
              continue;
          }

How is it possible that data doesn't immediately follow start cow region or
end cow region doesn't immediately follow data region?


--
Best regards,
Vladimir