On Mon, Apr 29, 2019 at 8:57 AM Michal Privoznik <mprivozn(a)redhat.com&gt; wrote: > > When cloning an RBD volume we try to find a snapshot which is > not different to the image we're trying to clone. This boils down > to calling rbd_diff_iterate() or rbd_diff_iterate2() on systems > with newer ceph. These two are passed a callback - > virStorageBackendRBDIterateCb() which mistakenly states that if > a negative value is returned from the callback, the iteration is > stopped but no error is reported. Well, that is not the case. > I've looked into librbd sources and found that a negative value > does mean stop of iteration but it also means an error. That's > why any attempt to clone an RBD image results in the following > error: > > virsh # vol-clone --pool rbd_image_root coreos_2023 coreos00.disk > error: Failed to clone vol from coreos_2023 > error: failed to iterate RBD snapshot coreos_2023@base: Operation not > permitted > > Reported on libvirt-users list: > > https://www.redhat.com/archives/libvirt-users/2019-April/msg00060.html > > Signed-off-by: Michal Privoznik <mprivozn(a)redhat.com&gt; > --- > src/storage/storage_backend_rbd.c | 7 +------ > 1 file changed, 1 insertion(+), 6 deletions(-) > > diff --git a/src/storage/storage_backend_rbd.c b/src/storage/storage_backend_rbd.c > index f8c968e682..3fe188551c 100644 > --- a/src/storage/storage_backend_rbd.c > +++ b/src/storage/storage_backend_rbd.c > @@ -1031,14 +1031,9 @@ virStorageBackendRBDIterateCb(uint64_t offset ATTRIBUTE_UNUSED, > { > /* > * Just set that there is a diff for this snapshot, we do not care where > - * > - * When it returns a negative number the rbd_diff_iterate() function will stop > - * > - * That's why we return -1, meaning that there is a difference and we can stop > - * searching any further. > */ > *(int*) arg = 1; > - return -1; > + return 0; > } You could also tweak "virStorageBackendRBDSnapshotFindNoDiff" to ignore the error if "diff > 0". That would still allow it to fail-fast once a delta is found.