[ovirt-devel] Re: [storage] how to find if a snapshot is in preview based on storage domain metadata only?

On Fri, Aug 28, 2020 at 9:29 AM Nir Soffer <nsoffer(a)redhat.com&gt; wrote: > On Thu, Aug 27, 2020, 16:38 Tal Nisan <tnisan(a)redhat.com&gt; wrote: > >> >> >> On Fri, Aug 21, 2020 at 4:34 AM Germano Veit Michel <germano(a)redhat.com&gt; >> 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.