Re: Modifying RBD image changes it's snapshot

[Josh Durgin <josh.durgin@inktank.com>]

On 06/26/2013 05:40 AM, Karol Jurak wrote:
> Hi,
>
> I'm using ceph 0.56.6 and kernel 3.9.7 and it looks like modifying RBD image
> also changes it's snapshot. I can reproduce this as follows:
>
> # create and map an image
> rbd create --size 128 test-1
> rbd map test-1
>
> # write some data to the image
> dd if=/dev/zero of=/dev/rbd/rbd/test-1 bs=1M count=128
>
> # create and map a snapshot
> rbd snap create test-1@snap-1
> rbd map test-1@snap-1
>
> # verify that image and snapshot are identical
> md5sum /dev/rbd/rbd/test-1 /dev/rbd/rbd/test-1@snap-1
> fde9e0818281836e4fc0edfede2b8762  /dev/rbd/rbd/test-1
> fde9e0818281836e4fc0edfede2b8762  /dev/rbd/rbd/test-1@snap-1
>
> # modify the image
> dd if=/dev/urandom of=/dev/rbd/rbd/test-1 bs=512 count=1
>
> # compare checksums again
> md5sum /dev/rbd/rbd/test-1 /dev/rbd/rbd/test-1@snap-1
> 1d942c8a5bc7480cecb945ea0d020eed  /dev/rbd/rbd/test-1
> 1d942c8a5bc7480cecb945ea0d020eed  /dev/rbd/rbd/test-1@snap-1
>
> Checksums are identical although the snapshot isn't supposed to be modified.
>

Just reproduced on 3.10-rc7 as well. It seems the snapshot context
loading is broken for format 1 a t least, since unmapping and mapping
after the snapshot exists still has the same problem. I added
http://tracker.ceph.com/issues/5464 to track this.

Apparently the regression test for this hasn't been running, or we
would've caught this sooner.

Josh