[libvirt] [PATCH v2 for 5.3.0] storage_backend_rbd: Ignore rbd_diff_iterate error() if needed

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 sets @diff to 1 and returns -1. The idea is to stop iterating as soon as possible (i.e. we're iterating over a snapshot with some deltas). Unfortunately, returning a negative value from the callback means that iterate() function fails and thus we report an 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 Therefore, report an error if and only if it doesn't originates in the callback. 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; --- diff to v1: - Ignore error as suggested by Jason as it allows us to exit iteration early. src/storage/storage_backend_rbd.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) diff --git a/src/storage/storage_backend_rbd.c b/src/storage/storage_backend_rbd.c index f8c968e682..69f4fa2117 100644 --- a/src/storage/storage_backend_rbd.c +++ b/src/storage/storage_backend_rbd.c @@ -1101,7 +1101,9 @@ virStorageBackendRBDSnapshotFindNoDiff(rbd_image_t image, virStorageBackendRBDIterateCb, (void *)&diff); #endif - if (r < 0) { + /* We care for errors only if the callback wasn't called at all. If it + * was, rbd_diff_iterate() returns an error which we have to ignore. */ + if (r < 0 && diff == 0) { virReportSystemError(-r, _("failed to iterate RBD snapshot %s@%s"), imgname, snaps[i].name); goto cleanup; -- 2.21.0