From 4d9b67cddd9b9bc320473a334cc8023a4186092f Mon Sep 17 00:00:00 2001 From: Ilya Dryomov Date: Thu, 24 Jul 2014 10:42:13 +0400 Subject: [PATCH] rbd: take snap_id into account when reading in parent info If we are mapping a snapshot, we must read in the parent_overlap value of that snapshot instead of that of the base image. Not doing so may in particular result in us returning zeros instead of user data: # cat overlap-snap.sh #!/bin/bash rbd create --size 10 --image-format 2 foo FOO_DEV=$(rbd map foo) dd if=/dev/urandom of=$FOO_DEV bs=1M &>/dev/null echo "Base image" dd if=$FOO_DEV bs=1 count=16 skip=$(((4 << 20) - 8)) 2>/dev/null | xxd rbd snap create foo@snap rbd snap protect foo@snap rbd clone foo@snap bar rbd snap create bar@snap BAR_DEV=$(rbd map bar@snap) echo "Snapshot" dd if=$BAR_DEV bs=1 count=16 skip=$(((4 << 20) - 8)) 2>/dev/null | xxd rbd resize --allow-shrink --size 4 bar echo "Snapshot after base image resize" dd if=$BAR_DEV bs=1 count=16 skip=$(((4 << 20) - 8)) 2>/dev/null | xxd # ./overlap-snap.sh Base image 0000000: e781 e33b d34b 2225 6034 2845 a2e3 36ed ...;.K"%`4(E..6. Snapshot 0000000: e781 e33b d34b 2225 6034 2845 a2e3 36ed ...;.K"%`4(E..6. Resizing image: 100% complete...done. Snapshot after base image resize 0000000: e781 e33b d34b 2225 0000 0000 0000 0000 ...;.K"%........ Even though bar@snap is taken with the old bar parent_overlap (8M), reads from bar@snap beyond the new bar parent_overlap (4M) return zeroes. Fix it. Signed-off-by: Ilya Dryomov Reviewed-by: Alex Elder --- drivers/block/rbd.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/drivers/block/rbd.c b/drivers/block/rbd.c index c460698..cbc89fa 100644 --- a/drivers/block/rbd.c +++ b/drivers/block/rbd.c @@ -4020,7 +4020,7 @@ static int rbd_dev_v2_parent_info(struct rbd_device *rbd_dev) goto out_err; } - snapid = cpu_to_le64(CEPH_NOSNAP); + snapid = cpu_to_le64(rbd_dev->spec->snap_id); ret = rbd_obj_method_sync(rbd_dev, rbd_dev->header_name, "rbd", "get_parent", &snapid, sizeof (snapid), -- 2.7.4