On Fri, Aug 28, 2020 at 9:29 AM Nir Soffer <nsoffer@redhat.com> wrote:

On Thu, Aug 27, 2020, 16:38 Tal Nisan <tnisan@redhat.com> wrote:

On Fri, Aug 21, 2020 at 4:34 AM Germano Veit Michel <germano@redhat.com> wrote:

Hi,

Is there a reliable way to figure out if a snapshot is in preview only using information obtained from the storage domain metadata?

I'm trying to find a way to distinguish a problematic snapshot chain (double parent) from a snapshot in preview in order to improve dump-volume chains.

Currently dump-volume-chains throws an error (DuplicateParentError) if a snapshot is in preview for the image, as there is a 'Y' shape split in the chain

with 2 volumes (previous chain + preview) pointing to a common parent:

   image:    dff0a0c0-b731-4e5b-9f32-d97310ca40de

             Error: more than one volume pointing to the same parent volume e.g: (_BLANK_UUID<-a), (a<-b), (a<-c)

             Unordered volumes and children:

             - e6c7bec0-53c6-4729-a4a0-a9b3ef2b8c38 <- 5eb2b29d-82d6-4337-8511-3c86705d566e
               status: OK, voltype: LEAF, format: COW, legality: LEGAL, type: SPARSE, capacity: 1073741824, truesize: 1073741824

             - e0475853-4514-4464-99e7-b185cce9b67d <- deceff83-9d88-4f87-8304-d5bf74d119b1
               status: OK, voltype: LEAF, format: COW, legality: LEGAL, type: SPARSE, capacity: 1073741824, truesize: 1073741824

             - e6c7bec0-53c6-4729-a4a0-a9b3ef2b8c38 <- e0475853-4514-4464-99e7-b185cce9b67d
               status: OK, voltype: INTERNAL, format: COW, legality: LEGAL, type: SPARSE, capacity: 1073741824, truesize: 1073741824

             - 00000000-0000-0000-0000-000000000000 <- e6c7bec0-53c6-4729-a4a0-a9b3ef2b8c38
               status: OK, voltype: INTERNAL, format: RAW, legality: LEGAL, type: PREALLOCATED, capacity: 1073741824, truesize: 1073741824

From the engine side it's easy, but I'd need to solve this problem using only metadata from the storage.

The only thing I could think of is that one of the volumes pointing to the common parent has voltype LEAF. Any better ideas?

don't think that there is any, Engine is the orchestrator and due to that the info is only in the database

There is no good way, but you can look at the length of the chain, and the "ctime" value.

For example if this was the original chain:

a <- b <- c

if we preview a:

a <- b <- c

a <- d

You know that d is a preview volume.

If we preview b, we will have two chains of same length:

a <- b <- c

a <- b <- d

But the ctime value of d will be larger, since preview is created after

the leaf was created.

ctime is using time.time() so it is not affected by time zone changes

but it may be wrong due to host time changes, so it is not reliable.

Can you open a bug for this?

https://bugzilla.redhat.com/show_bug.cgi?id=1873382

I have a prototype working with some code I pasted in the bugzilla, but I don't think it's reliable and an overcomplication of what should be simple.