Ceph » rbd

scribble()-based DiffIterate tests are too weak: at least two regressions that should been caught by DiffIterate.DiffIterate or DiffIterate.DiffIterateStress were missed:

https://tracker.ceph.com/issues/50787
https://tracker.ceph.com/issues/63654

Aside from the randomness which can be both a good and a bad thing, asserts

https://github.com/ceph/ceph/blob/b27938f5f17898fc3da3d5af821957d6aee33501/src/test/librbd/test_librbd.cc#L7475
https://github.com/ceph/ceph/blob/b27938f5f17898fc3da3d5af821957d6aee33501/src/test/librbd/test_librbd.cc#L7648
https://github.com/ceph/ceph/blob/b27938f5f17898fc3da3d5af821957d6aee33501/src/test/librbd/test_librbd.cc#L7821
https://github.com/ceph/ceph/blob/b27938f5f17898fc3da3d5af821957d6aee33501/src/test/librbd/test_librbd.cc#L7902

ensure only that returned diff covers all changes that were made. If returned diff is too excessive or otherwise bogus, this isn't detected -- an implementation that always returns the entire range passed to rbd_diff_iterate2() as "new data" would pass all of these!