On 4/4/22 17:26, Fabian Grünbichler wrote:
On April 1, 2022 5:24 pm, Aaron Lauterer wrote:
In rare situations, it could happen that the source and target path is
the same. For example, if the disk image is to be copied from one RBD
storage to another one on different Ceph clusters but the pools have the
same name.
In this situation, the clone operation will clone it to the same image and
one will end up with an empty destination volume.
This patch does not solve the underlying issue, but is a first step to
avoid potential data loss, for example when the 'delete source' option
is enabled as well.
We also need to delete the newly created image right away because the
regular cleanup gets confused and tries to remove the source image. This
will fail and we have an orphaned image which cannot be removed easily
because the same underlying root cause (same path) will falsely trigger
the "Drive::is_volume_in_use" check.
isn't this technically - just like for the container case - a problem in
general, not just for cloning a disk? I haven't tested this in practice,
but since you already have the reproducing setup ;)
e.g., given the following:
- storage A, krbd, cluster A, pool foo
- storage B, krbd, cluster B, pool foo
- VM 123, with scsi0: A:vm-123-disk-0 and no volumes on B
- qm set 123 -scsi1: B:1
next free slot on B is 'vm-123-disk-0', which will be allocated. mapping
will skip the map part, since the RBD path already exists (provided
scsi0's volume is already activated). the returned path will point to
the mapped blockdev corresponding to A:vm-123-disk-0, not B:..
guest writes to scsi1, likely corrupting whatever is on scsi0, since
most things that tend to get put on guest disks are not
multi-writer-safe (or something along the way notices it?)
if the above is the case, it might actually be prudent to just put the
check from your other patch into RBDPlugin.pm 's alloc method (and
clone and rename?) since we'd want to block any allocations on affected
systems?
Tested it and yep... unfortunately the wrong disk is attached. I am going to
implement the check in the RBDPlugin.pm.
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