[PATCH] rbd: ignore zero-overlap parent

[Alex Elder <elder@inktank.com>]

An rbd clone image that has an overlap with its parent of 0 is
effectively not a layered image at all.  Detect this case and treat
such an image as non-layered.  Issue a warning to be sure the user
knows what's going on.

This resolves:
    http://tracker.ceph.com/issues/5028

Signed-off-by: Alex Elder <elder@inktank.com>
---
 drivers/block/rbd.c |   10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/drivers/block/rbd.c b/drivers/block/rbd.c
index b9221a0..3a8135f 100644
--- a/drivers/block/rbd.c
+++ b/drivers/block/rbd.c
@@ -3655,9 +3655,13 @@ static int rbd_dev_v2_parent_info(struct
rbd_device *rbd_dev)
 	ceph_decode_64_safe(&p, end, parent_spec->snap_id, out_err);
 	ceph_decode_64_safe(&p, end, overlap, out_err);

-	rbd_dev->parent_overlap = overlap;
-	rbd_dev->parent_spec = parent_spec;
-	parent_spec = NULL;	/* rbd_dev now owns this */
+	if (overlap) {
+		rbd_dev->parent_spec = parent_spec;
+		parent_spec = NULL;	/* rbd_dev now owns this */
+		rbd_dev->parent_overlap = overlap;
+	} else {
+		rbd_warn(rbd_dev, "ignoring parent of clone with overlap 0\n");
+	}
 out:
 	ret = 0;
 out_err:
-- 
1.7.9.5