On 4/29/19 3:13 PM, Jason Dillaman wrote:
On Mon, Apr 29, 2019 at 8:57 AM Michal Privoznik <mprivozn@xxxxxxxxxx> 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@xxxxxxxxxx>
---
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.
Good catch. Let me post a v2.
Michal
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