7:07 p.m.
----- Original Message -----
From: "Alon Bar-Lev" <alonbl(a)redhat.com>
To: "Vojtech Szocs" <vszocs(a)redhat.com>
Cc: devel(a)ovirt.org, "Mark Proctor" <mdproctor(a)gmail.com>
Sent: Wednesday, November 5, 2014 4:32:31 PM
Subject: Re: [ovirt-devel] Thoughts on modularization
----- Original Message -----
> From: "Vojtech Szocs" <vszocs(a)redhat.com>
> To: "Alon Bar-Lev" <alonbl(a)redhat.com>
> Cc: devel(a)ovirt.org, "Mark Proctor" <mdproctor(a)gmail.com>
> Sent: Wednesday, November 5, 2014 5:24:14 PM
> Subject: Re: [ovirt-devel] Thoughts on modularization
>
>
>
> ----- Original Message -----
> > From: "Alon Bar-Lev" <alonbl(a)redhat.com>
> > To: "Vojtech Szocs" <vszocs(a)redhat.com>
> > Cc: devel(a)ovirt.org, "Mark Proctor" <mdproctor(a)gmail.com>
> > Sent: Wednesday, November 5, 2014 4:12:06 PM
> > Subject: Re: [ovirt-devel] Thoughts on modularization
> >
> >
> >
> > ----- Original Message -----
> > > From: "Vojtech Szocs" <vszocs(a)redhat.com>
> > > To: devel(a)ovirt.org
> > > Cc: "Mark Proctor" <mdproctor(a)gmail.com>
> > > Sent: Wednesday, November 5, 2014 5:04:24 PM
> > > Subject: [ovirt-devel] Thoughts on modularization
> > >
> > > Hi guys,
> > >
> > > I've discussed this recently with Yair and Mark, I just wanted to
share
> > > some more thoughts on this topic -- in particular, how modularization
> > > problem can be approached (regardless of implementation details).
> > >
> > > I see two approaches here. The typical one is to define APIs for
> > > modules
> > > to consume. For example, oVirt Engine extension API has API for auth
> > > stuff; oVirt UI plugin API has API for showing tabs and dialogs, etc.
> > > The advantage is strict consistency, disadvantage is burden of having
> > > to maintain the whole API. With this approach, you tell modules:
"This
> > > is the API to work with system, defining how you can plug into it."
> > >
> > > Now turn 180 degrees. The other approach, which is really interesting,
> > > is to let modules themselves export API. This naturally leads to module
> > > hierarchies. Ultimately, this leads to micro-kernel-style development,
> > > where all logic resides in modules. Now you might ask: "What if we
want
> > > to employ some consistent work flow across multiple modules? For
> > > example,
> > > have some pluggable *auth* infra?" -- this can be done via some
> > > "higher"
> > > level module, that exports API and "lower" level modules consume
that
> > > API.
> > >
> > > If you have any ideas, please share!
> >
> > Both solutions can be applied using existing extension api, an extension
> > can
> > locate other extension and interact with it the same way the core
> > interacts
> > with extensions.
>
> But how does core interact with extensions? I assume via well-defined
> API, i.e. in accordance with first approach mentioned above.
presentation:
http://www.ovirt.org/File:Ovirt_3.5_-_aaa.pdf
Thanks for sharing!
package org.ovirt.engine.api.extensions;
/**
* Interface of an extension.
*/
public interface Extension {
/**
* Invoke operation.
* @param input input parameters.
* @param output output parameters.
*
* <p>
* Interaction is done via the parameters.
* Exceptions are not allowed.
* </p>
* <p>
* Basic mappings available at {@link Base}.
* </p>
*
* @see Base
*/
void invoke(ExtMap input, ExtMap output);
}
OK, so it was my lack of knowledge of AAA implementation :)
Since Extension interface is invoke-based, I assume that Engine
core (backend) invokes extensions on specific occasions, right?
> With second approach mentioned above, core would not interact with
> extensions at all (or in a very limited way), instead - extensions
> would interact with each other. In other words, extension would not
> need to implement core-specific API (there would be none), instead
> it would inject its dependencies (other modules/extensions) and
> consume their APIs. This is the difference I wanted to point out :)
The extension interface is primitive to enable exactly that, provided java
people will open their minds :)
Simple interface means great flexibility, now I understand the
rationale behind typed maps in extension API.
What I had in mind was something like this (maybe crazy):
* imagine for a moment that the backend is fully modular
(logic lives in modules, no logic outside modules)
* @DependsOn("SomeOtherModule") // modules can form hierarchies
public class MyModule implements Module {
public void loaded() {} // executed just once per module
}
* API for fetching modules, i.e. getModuleByName('xxx')
API for exporting module API, i.e. exportApiObject(foo)
This way, you'd have one "core" module, providing most general
functionality/abstractions. Then you'd have more specific modules,
plugged into "core" module's API etc. In other words, hierarchy of
modules. This is essentially modularization taken to extreme :)
(BTW, above is just an idea.)
Regards,
Alon