Re: [Engine-devel] Adding atomic restore snapshot command at backend
----- Original Message -----
From: "Michael Pasternak" <mpastern(a)redhat.com>
To: "Livnat Peer" <lpeer(a)redhat.com>
Cc: "engine-devel" <engine-devel(a)ovirt.org>
Sent: Monday, May 28, 2012 2:37:10 PM
Subject: Re: [Engine-devel] Adding atomic restore snapshot command at backend
Hi Livnat,
On 05/28/2012 02:07 PM, Livnat Peer wrote:
> On 28/05/12 12:59, Michael Pasternak wrote:
>>
>> Currently 'restore snapshot' done in two steps on a client side:
>>
>> 1. TryBackToAllSnapshotsOfVm
>> 2. RestoreAllSnapshots
>>
>> This implementation creates race condition on 1 and therefore
>> unstable & bug prone,
IIRC, there is an easy way to fix this,
by polling on engine jobs and not vdsm tasks, no?
>> i suggested refactoring 2 to include 1 as single atomic
operation
>> at backend.
>>
>>
>
> Hi Michael,
>
> The two commands above are used for functionality that is needed
> regardless of the functionality you are looking for.
> We want to present the user the option to preview a snapshot
> without
> committing to it and without loosing the current snapshot.
> I think we need to model the the two options above in the REST, it
> is
> functionality that is used in the UI.
+1 for that.
this is out of scope of this RFE.
>
> What you are looking for is a functionality 'restore to snapshot',
> this
> functionality does not exist in the engine in a single step, and I
> think
> that because we assumed that the user can get it in two steps It
> wasn't
> prioritize so far.
the cons. of this approach is an async nature of the former command.
>
> Implementing the missing functionality with the two functions above
> is
> a compromise that was done in the API.
>
> To summarize I think the requirement you present is a missing
> functionality in the engine and solving it is not about refactoring
> the
> two existing verbs into one.
what i meant is not deprecating/refactoring old commands, but
introducing
new one that reusing them and expose as single (atomic) command
called
'RestoreAllSnapshots',
sorry if i wasn't clear.
another suggestion is to have a way to send to the engine list of commands that will be
performed.
>
> Thanks, Livnat
>
--
Michael Pasternak
RedHat, ENG-Virtualization R&D
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