On 23 Nov 2016, at 14:53, Arik Hadas <ahadas(a)redhat.com>
----- Original Message -----
> On Wed, Nov 23, 2016 at 2:59 PM, Arik Hadas <ahadas(a)redhat.com> wrote:
>> Hi All,
>> We are working on something that is expected to have a big impact, hence
>> this heads-up.
>> First, we want you to be aware of this change and provide your feedback to
>> make it as good as possible.
>> Second, until the proposed mechanism is fully merged there will be a chase
>> to cover all features unless new features are also implemented with the
>> new mechanism. So please, if you are working on something that
>> adds/changes something in the Libvirt's domain xml, do it with this new
>> mechanism as well (first version would be merged soon).
>> * Goal
>> Creating Libvirt XML in the engine rather than in VDSM.
>> ** Today's flow
>> Engine: VM business entity -> VM properties map
>> VDSM: VM properties map -> Libvirt XML
>> ** Desired flow
>> Engine: VM business entity -> Libvirt XML
>> * Potential Benefits
>> 1. Reduce the number of conversions from 2 to 1, reducing chances for
>> mistakes in the process.
>> 2. Reduce the amount of code in VDSM.
>> 3. Make VM related changes easier - today many of these changes need to be
>> reviewed in 2 projects, this will eliminate the one that tends to take
>> 4. Prevent shortcuts in the form of VDSM-only changes that should be better
>> reflected in the engine.
>> 5. Not to re-generate the XML on each rerun attempt of VM run/migration.
>> 6. Future - not to re-generate the XML on each attempt to auto-start HA VM
>> when using vm-leases (need to make sure we're using the up-to-date VM
>> configuration though).
>> 7. We already found improvements and cleanups that could be made while
>> touching this area (e.g., remove the boot order from devices in the
>> * Challenges
>> 1. Not to move host-specific information to the engine. For example, path
>> to storage domain or sockets of channels.
>> The solution is to use place-holders that will be replaced by VDSM.
>> 2. Backward compatibility.
>> 3. The more challenging part is the other direction - that will be the next
>> * Status
>> As a first step, we began with producing the Libvirt XML in the engine by
>> converting the VM properties map to XML in the engine 
>> And using the XML that is received as an input in VDSM 
> Thanks for the heads up!
> How does this, if at all, affect:
> 1. vdsm hooks
VDSM hooks will remain unaffected - they will get the same XML.
The only difference is that this XML will be one that was produced by the engine after
the replacement of its place-holders rather than one that is produced by VDSM from the
> 2. The interaction of engine, hosted-engine HA agent, engine vm
> configuration saved in shared storage, etc.? Will this require a
> change in ha-agent and the saved configuration?
In the foreseeable future VDSM should support creating the VM from VM properties map as
well - so legacy code will keep working, including the creation of the hosted-engine.
However, at some point the creation of the hosted-engine would also need to change I
it would be a bit more straightforward than today, instead of the fragile code creating
vdsm internal API properties you would be able to use a regular domain xml definition
which is easier to define and maintain than internal representation of features/parameters
The rest, other than the creation flow, will also remain unaffected.
>>  https://gerrit.ovirt.org/#/c/64473/
>>  https://gerrit.ovirt.org/#/c/65182/
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