You can specify the snapshot at image open as well. There is no need to refresh.
On Wed, Jan 11, 2017 at 7:14 PM, Victor Denisov <vdenisov@xxxxxxxxxxxx> wrote:
> Can I open an image and then redirect it to one of its snapshots?
>
> I see that there is a snap_set method.
> Do I understand correctly that I need to:
> open the image
> invoke snap_set method
> invoke refresh method
>
> Thanks in advance.
> V.
>
> On Wed, Jan 4, 2017 at 10:39 AM, Victor Denisov <vdenisov@xxxxxxxxxxxx> wrote:
>> I understood. Thanks!
>>
>> On Wed, Jan 4, 2017 at 10:34 AM, Jason Dillaman <jdillama@xxxxxxxxxx> wrote:
>>> The loop isn't that big of a deal -- but you could eliminate it
>>> entirely if you just index the in-memory snapshot table via the
>>> SnapshotNamespace variant instead of just indexing snapshots by name
>>> (e.g. ImageCtx::snap_ids key switches from a string to a namespace).
>>> This would be required anyway since you might otherwise have duplicate
>>> names between namespaces.
>>>
>>> On Wed, Jan 4, 2017 at 1:29 PM, Victor Denisov <vdenisov@xxxxxxxxxxxx> wrote:
>>>> It looks like next CDM is only next month. Let's try to figure it out in email.
>>>>
>>>>> Since you know which images are linked to the group and you know which
>>>>> snapshots are in the group and which group snapshots are in the image,
>>>>> you can reconcile any issues using the details in the
>>>>> GroupSnapshotNamespace -- there shouldn't be any need to depend on the
>>>>> actual snapshot name (it could technically just be a randomly assigned
>>>>> UUID).
>>>>
>>>> Let's say I have a consistency group and a snapshot of this group: CG
>>>> and CGSNAP.
>>>> Images in this snapshot I'll define as:
>>>> CG.images[0] - image1
>>>> CG.images[1] - image2
>>>> CG.images[2] - image3
>>>>
>>>> Image snapshots in cg snapshot will be:
>>>> CG.CGSNAP.snaps[0] - reference to snapshot of image 1
>>>> CG.CGSNAP.snaps[1] - reference to snapshot of image 2
>>>>
>>>> Imagine that this snapshot was created, but wasn't finalized.
>>>> CG.CGSNAP.state == PENDING.
>>>> CG.CGSNAP.snaps.length == 0;
>>>> I'll be writing in pseudo code.
>>>>
>>>> Now, let's say we want to remove this pending CGSNAP. This is the code
>>>> how it's currently implemented:
>>>>
>>>> for (image: CG.images) {
>>>> snap_name = image.id + "_" + CG.CGSNAP.id + "_" + CG.id // This name
>>>> is unique because of uniqueness of the tuple (image.id, CG.CGSNAP.id,
>>>> CG.id)
>>>> remove_image_snapshot(snap_name);
>>>> }
>>>> remove_cg_snap(CGSNAP);
>>>>
>>>> However, if we don't rely on the name then this is how I envision the code:
>>>>
>>>> for (image: CG.images) {
>>>> for (snap: image.snaps) {
>>>> if (snap.namespace.cg_id == CG.id && snap.namespace.cg_snap_id ==
>>>> CG.CGSNAP.id) { // this is our snapshot
>>>> remove_image_snapshot(snap.name);
>>>> }
>>>> }
>>>> }
>>>> remove_cg_snap(CGSNAP);
>>>>
>>>> In this solution I don't like the internal loop.
>>>> What do you think?
>>>>
>>>> Thanks,
>>>> Victor.
>>>>
>>>>
>>>> On Tue, Jan 3, 2017 at 6:56 PM, Jason Dillaman <jdillama@xxxxxxxxxx> wrote:
>>>>> After starting the process of creating a group snapshot, you will
>>>>> already have all the necessary data for the group snapshot namespace
>>>>> [1] (group pool, group id, and group snapshot id) and the group
>>>>> snapshot should be persistently recorded to disk as
>>>>> GROUP_SNAPSHOT_STATE_PENDING.
>>>>>
>>>>> Looking at the snapshot create state machine [2], I don't see any
>>>>> place that a crash (or similar failure) would matter before the actual
>>>>> image snapshot record is created atomically. You would pass the fully
>>>>> populated GroupSnapshotNamespace to snap_create, and if the snapshot
>>>>> is created, it's linked to the group via that namespace and any
>>>>> failures afterwards don't matter since they are linked -- if the
>>>>> snapshot fails to be created, it isn't linked to the group but the
>>>>> snapshot doesn't exist either so there isn't anything to clean up.
>>>>>
>>>>> Since you know which images are linked to the group and you know which
>>>>> snapshots are in the group and which group snapshots are in the image,
>>>>> you can reconcile any issues using the details in the
>>>>> GroupSnapshotNamespace -- there shouldn't be any need to depend on the
>>>>> actual snapshot name (it could technically just be a randomly assigned
>>>>> UUID).
>>>>>
>>>>> Perhaps we could talk about this at a future RBD standup meeting that
>>>>> you are able to join (or the next CDM).
>>>>>
>>>>> [1] https://github.com/ceph/ceph/blob/master/src/cls/rbd/cls_rbd_types.h#L249
>>>>> [2] https://github.com/ceph/ceph/blob/master/src/librbd/operation/SnapshotCreateRequest.h#L28
>>>>>
>>>>> On Tue, Jan 3, 2017 at 7:40 PM, Victor Denisov <vdenisov@xxxxxxxxxxxx> wrote:
>>>>>> Let's say we start creating a group snapshot.
>>>>>> We invoke async snap_create method in Operations class.
>>>>>> When we invoke this method we provide it with the snapshot name.
>>>>>>
>>>>>> While we are wating for the response we can be aborted.
>>>>>> As a result we will be able to find the exact image snapshot using only its name
>>>>>> as this was the only information we had at the time of running
>>>>>> snap_create method.
>>>>>>
>>>>>> If snap_create was successful we will be able to find the snapshot
>>>>>> otherwise we will not.
>>>>>> However if we allow renaming snapshots from GroupSnapshotNamespace
>>>>>> then we may not find the snapshot even if it
>>>>>> was created successfully.
>>>>>>
>>>>>> On Fri, Dec 16, 2016 at 6:53 AM, Jason Dillaman <jdillama@xxxxxxxxxx> wrote:
>>>>>>> Can you give a little background on this specific inconsistent case
>>>>>>> you are referring to?
>>>>>>>
>>>>>>> On Thu, Dec 15, 2016 at 7:05 PM, Victor Denisov <vdenisov@xxxxxxxxxxxx> wrote:
>>>>>>>> Yes, but if image's snapshot is renamed then I'm not able to find this
>>>>>>>> snapshot having only group's snapshot in an inconsistent state for
>>>>>>>> example.
>>>>>>>>
>>>>>>>> V.
>>>>>>>>
>>>>>>>> On Thu, Dec 15, 2016 at 7:10 AM, Jason Dillaman <jdillama@xxxxxxxxxx> wrote:
>>>>>>>>> I think I might be confused. When creating a group snapshot, we have
>>>>>>>>> the ConsistencyGroupSnapshot that allows you to store the necessary
>>>>>>>>> linkage between the image's snapshot and its associated group snapshot
>>>>>>>>> [1]. Why not just name the image's snapshots to the same name as the
>>>>>>>>> parent group snapshot name and search the snapshot's metadata to get
>>>>>>>>> the linkage?
>>>>>>>>>
>>>>>>>>> [1] https://github.com/ceph/ceph/blob/master/src/cls/rbd/cls_rbd_types.h#L255
>>>>>>>>>
>>>>>>>>> On Tue, Dec 13, 2016 at 8:03 PM, Victor Denisov <vdenisov@xxxxxxxxxxxx> wrote:
>>>>>>>>>> Jason,
>>>>>>>>>>
>>>>>>>>>> My current implementation of consistency group snapshot feature names
>>>>>>>>>> image snapshots like: <group_pool>_<group_id>_<group_snap_id>
>>>>>>>>>> I rely on this fact when I need to remove a consistency group. It's
>>>>>>>>>> necessary because if some of image snapshots were created, but the
>>>>>>>>>> whole group snapshot operation failed,
>>>>>>>>>> then the only way to find those dangling image snapshots is by this name.
>>>>>>>>>>
>>>>>>>>>> It means that we should forbid renaming snapshots from
>>>>>>>>>> ConsistencyGroupSnapshot namespace.
>>>>>>>>>>
>>>>>>>>>> Another option is to allocate image snapshot ids during the creation
>>>>>>>>>> of group snapshot, but this requires a major rewrite of the whole
>>>>>>>>>> process of snapshot creation for images.
>>>>>>>>>>
>>>>>>>>>> What is your opinion on this?
>>>>>>>>>>
>>>>>>>>>> Thanks,
>>>>>>>>>> V.
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>> On Tue, Nov 1, 2016 at 8:01 AM, Jason Dillaman <jdillama@xxxxxxxxxx> wrote:
>>>>>>>>>>> I chatted with Xing on IRC this morning re: Cinder generic groups. It
>>>>>>>>>>> sounds like RBD will need to support preserving the image's
>>>>>>>>>>> consistency group snapshots even if the image is removed from the
>>>>>>>>>>> group. In the OpenStack case, you won't have to worry about the image
>>>>>>>>>>> being deleted while it still has associated group snapshots.
>>>>>>>>>>>
>>>>>>>>>>> We will also want to support being able to clone child images from a
>>>>>>>>>>> group snapshot to ensure that we can thin provision new groups volumes
>>>>>>>>>>> when creating a new group from a group snapshot. This means that the
>>>>>>>>>>> group snapshots should be able to be protected/unprotected just like
>>>>>>>>>>> standard user snapshots.
>>>>>>>>>>>
>>>>>>>>>>> On Mon, Oct 31, 2016 at 9:07 AM, Jason Dillaman <jdillama@xxxxxxxxxx> wrote:
>>>>>>>>>>>> Looking at the Cinder codebase, I don't see any such restriction that
>>>>>>>>>>>> would prevent you from removing a volume from a consistency group that
>>>>>>>>>>>> has associated snapshots. I would double-check on the OpenStack
>>>>>>>>>>>> development mailing list if this is correct and is the intent. Worst
>>>>>>>>>>>> case, the RBD driver could raise an exception if there are still
>>>>>>>>>>>> consistency group snapshots associated to the image.
>>>>>>>>>>>>
>>>>>>>>>>>>
>>>>>>>>>>>> On Fri, Oct 28, 2016 at 6:41 PM, Victor Denisov <vdenisov@xxxxxxxxxxxx> wrote:
>>>>>>>>>>>>> Another thing that bothers me. When we remove an image from a consistency group.
>>>>>>>>>>>>> Should we remove all snapshots of this image that were created as part
>>>>>>>>>>>>> of a consistency group snapshot?
>>>>>>>>>>>>>
>>>>>>>>>>>>> The easiest solution would be to remove all snapshots that are in
>>>>>>>>>>>>> GroupSnapshotNamespace and reference this consistency group.
>>>>>>>>>>>>> I looked into cinder docs for this feature:
>>>>>>>>>>>>> http://docs.openstack.org/admin-guide/blockstorage-consistency-groups.html
>>>>>>>>>>>>>
>>>>>>>>>>>>> But it's not clear to me which behavior cinder expects.
>>>>>>>>>>>>>
>>>>>>>>>>>>> Thanks,
>>>>>>>>>>>>> V.
>>>>>>>>>>>>>
>>>>>>>>>>>>> On Wed, Oct 26, 2016 at 6:16 AM, Jason Dillaman <jdillama@xxxxxxxxxx> wrote:
>>>>>>>>>>>>>> In a perfect world, it would be nice to add a new optional to "rbd
>>>>>>>>>>>>>> snap ls" to show all snapshots (with a new column to indicate the
>>>>>>>>>>>>>> associated namespace).
>>>>>>>>>>>>>>
>>>>>>>>>>>>>> On Tue, Oct 25, 2016 at 11:07 PM, Victor Denisov <vdenisov@xxxxxxxxxxxx> wrote:
>>>>>>>>>>>>>>> Question. When we print out snapshots of an image, should the group
>>>>>>>>>>>>>>> snapshots be listed, or should they be marked as special snapshots?
>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>> Thanks,
>>>>>>>>>>>>>>> V.
>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>> On Mon, Oct 10, 2016 at 3:14 PM, Victor Denisov <vdenisov@xxxxxxxxxxxx> wrote:
>>>>>>>>>>>>>>>> Ok. I didn't have any intention to throw exceptions.
>>>>>>>>>>>>>>>> I was more concerned about whether it's ok to allocate and delete
>>>>>>>>>>>>>>>> objects or I should use smart pointers.
>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>> On Mon, Oct 10, 2016 at 7:18 AM, Jason Dillaman <jdillama@xxxxxxxxxx> wrote:
>>>>>>>>>>>>>>>>> The only place exceptions are routinely used is within the "::decode"
>>>>>>>>>>>>>>>>> functions. I would prefer to see the code not throwing new exceptions
>>>>>>>>>>>>>>>>> on purpose.
>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>> On Fri, Oct 7, 2016 at 2:26 PM, Victor Denisov <vdenisov@xxxxxxxxxxxx> wrote:
>>>>>>>>>>>>>>>>>> Are any exceptions used in librbd code? Should the code be exception safe?
>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>> Thanks,
>>>>>>>>>>>>>>>>>> V.
>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>> On Fri, Sep 16, 2016 at 10:37 AM, Jason Dillaman <jdillama@xxxxxxxxxx> wrote:
>>>>>>>>>>>>>>>>>>> On Thu, Sep 15, 2016 at 7:17 PM, Victor Denisov <vdenisov@xxxxxxxxxxxx> wrote:
>>>>>>>>>>>>>>>>>>>> if (struct_v >= 5) {
>>>>>>>>>>>>>>>>>>>> ::decode(snapshot_namespace, p);
>>>>>>>>>>>>>>>>>>>> } else {
>>>>>>>>>>>>>>>>>>>> snapshot_namespace = cls::rbd::UserSnapshotNamespace();
>>>>>>>>>>>>>>>>>>>> }
>>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>> then code for ::encode function of cls_rbd_snap would change accordingly:
>>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>> instead of
>>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>> boost::apply_visitor(cls::rbd::EncodeSnapshotTypeVisitor(bl),
>>>>>>>>>>>>>>>>>>>> snapshot_namespace);
>>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>> I would do:
>>>>>>>>>>>>>>>>>>>> ::encode(snapshot_namespace, bl);
>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>> +1 -- looks good to me
>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>> --
>>>>>>>>>>>>>>>>>>> Jason
>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>> --
>>>>>>>>>>>>>>>>> Jason
>>>>>>>>>>>>>>
>>>>>>>>>>>>>>
>>>>>>>>>>>>>>
>>>>>>>>>>>>>> --
>>>>>>>>>>>>>> Jason
>>>>>>>>>>>>
>>>>>>>>>>>>
>>>>>>>>>>>>
>>>>>>>>>>>> --
>>>>>>>>>>>> Jason
>>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>> --
>>>>>>>>>>> Jason
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>> --
>>>>>>>>> Jason
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>> --
>>>>>>> Jason
>>>>>
>>>>>
>>>>>
>>>>> --
>>>>> Jason
>>>
>>>
>>>
>>> --
>>> Jason
--
Jason
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