On Tue, Jun 26, 2012 at 11:11:51PM +0800, Shu Ming wrote:
> On 2012-6-26 20:45, Adam Litke wrote:
> >On Tue, Jun 26, 2012 at 09:53:10AM +0800, Xu He Jie wrote:
> >>On 06/26/2012 05:19 AM, Adam Litke wrote:
> >>>On Mon, Jun 25, 2012 at 05:53:31PM +0300, Dan Kenigsberg wrote:
> >>>>On Mon, Jun 25, 2012 at 08:28:29AM -0500, Adam Litke wrote:
> >>>>>On Fri, Jun 22, 2012 at 06:45:43PM -0400, Andrew Cathrow wrote:
> >>>>>>----- Original Message -----
> >>>>>>>From: "Ryan Harper" <ry...@us.ibm.com>
> >>>>>>>To: "Adam Litke" <a...@us.ibm.com>
> >>>>>>>Cc: "Anthony Liguori" <aligu...@redhat.com>, "VDSM Project 
> >>>>>>>Development" <vdsm-devel@lists.fedorahosted.org>
> >>>>>>>Sent: Friday, June 22, 2012 12:45:42 PM
> >>>>>>>Subject: Re: [vdsm] [virt-node] VDSM as a general purpose virt host 
> >>>>>>>manager
> >>>>>>>
> >>>>>>>* Adam Litke <a...@us.ibm.com> [2012-06-22 11:35]:
> >>>>>>>>On Thu, Jun 21, 2012 at 12:17:19PM +0300, Dor Laor wrote:
> >>>>>>>>>On 06/19/2012 08:12 PM, Saggi Mizrahi wrote:
> >>>>>>>>>>----- Original Message -----
> >>>>>>>>>>>From: "Deepak C Shetty" <deepa...@linux.vnet.ibm.com>
> >>>>>>>>>>>To: "Ryan Harper" <ry...@us.ibm.com>
> >>>>>>>>>>>Cc: "Saggi Mizrahi" <smizr...@redhat.com>, "Anthony Liguori"
> >>>>>>>>>>><aligu...@redhat.com>, "VDSM Project Development"
> >>>>>>>>>>><vdsm-devel@lists.fedorahosted.org>
> >>>>>>>>>>>Sent: Tuesday, June 19, 2012 10:58:47 AM
> >>>>>>>>>>>Subject: Re: [vdsm] [virt-node] VDSM as a general purpose virt
> >>>>>>>>>>>host manager
> >>>>>>>>>>>
> >>>>>>>>>>>On 06/19/2012 01:13 AM, Ryan Harper wrote:
> >>>>>>>>>>>>* Saggi Mizrahi<smizr...@redhat.com>  [2012-06-18 10:05]:
> >>>>>>>>>>>>>I would like to put on to the table for descussion the
> >>>>>>>>>>>>>growing
> >>>>>>>>>>>>>need for a way
> >>>>>>>>>>>>>to more easily reuse of the functionality of VDSM in order to
> >>>>>>>>>>>>>service projects
> >>>>>>>>>>>>>other than Ovirt-Engine.
> >>>>>>>>>>>>>
> >>>>>>>>>>>>>Originally VDSM was created as a proprietary agent for the
> >>>>>>>>>>>>>sole
> >>>>>>>>>>>>>purpose of
> >>>>>>>>>>>>>serving the then proprietary version of what is known as
> >>>>>>>>>>>>>ovirt-engine. Red Hat,
> >>>>>>>>>>>>>after acquiring the technology, pressed on with it's
> >>>>>>>>>>>>>commitment to
> >>>>>>>>>>>>>open source
> >>>>>>>>>>>>>ideals and released the code. But just releasing code into
> >>>>>>>>>>>>>the
> >>>>>>>>>>>>>wild doesn't
> >>>>>>>>>>>>>build a community or makes a project successful. Further more
> >>>>>>>>>>>>>when
> >>>>>>>>>>>>>building
> >>>>>>>>>>>>>open source software you should aspire to build reusable
> >>>>>>>>>>>>>components instead of
> >>>>>>>>>>>>>monolithic stacks.
> >>>>>>>>>>>>>
> >>>>>>>>>>>>Saggi,
> >>>>>>>>>>>>
> >>>>>>>>>>>>Thanks for sending this out.  I've been trying to pull
> >>>>>>>>>>>>together
> >>>>>>>>>>>>some
> >>>>>>>>>>>>thoughts on what else is needed for vdsm as a community.  I
> >>>>>>>>>>>>know
> >>>>>>>>>>>>that
> >>>>>>>>>>>>for some time downstream has been the driving force for all of
> >>>>>>>>>>>>the
> >>>>>>>>>>>>work
> >>>>>>>>>>>>and now with a community there are challenges in finding our
> >>>>>>>>>>>>own
> >>>>>>>>>>>>way.
> >>>>>>>>>>>>
> >>>>>>>>>>>>While we certainly don't want to make downstream efforts
> >>>>>>>>>>>>harder, I
> >>>>>>>>>>>>think
> >>>>>>>>>>>>we need to develop and support our own vision for what vdsm
> >>>>>>>>>>>>can be
> >>>>>>>>>>>>come,
> >>>>>>>>>>>>some what independent of downstream and other exploiters.
> >>>>>>>>>>>>
> >>>>>>>>>>>>Revisiting the API is definitely a much needed endeavor and I
> >>>>>>>>>>>>think
> >>>>>>>>>>>>adding some use-cases or sample applications would be useful
> >>>>>>>>>>>>in
> >>>>>>>>>>>>demonstrating whether or not we're evolving the API into
> >>>>>>>>>>>>something
> >>>>>>>>>>>>easier to use for applications beyond engine.
> >>>>>>>>>>>>
> >>>>>>>>>>>>>We would like to expose a stable, documented, well supported
> >>>>>>>>>>>>>API.
> >>>>>>>>>>>>>This gives
> >>>>>>>>>>>>>us a chance to rethink the VDSM API from the ground up. There
> >>>>>>>>>>>>>is
> >>>>>>>>>>>>>already work
> >>>>>>>>>>>>>in progress of making the internal logic of VDSM separate
> >>>>>>>>>>>>>enough
> >>>>>>>>>>>>>from the API
> >>>>>>>>>>>>>layer so we could continue feature development and bug fixing
> >>>>>>>>>>>>>while designing
> >>>>>>>>>>>>>the API of the future.
> >>>>>>>>>>>>>
> >>>>>>>>>>>>>In order to achieve this though we need to do several things:
> >>>>>>>>>>>>>     1. Declare API supportability guidelines
> >>>>>>>>>>>>>     2. Decide on an API transport (e.g. REST, ZMQ, AMQP)
> >>>>>>>>>>>>>     3. Make the API easily consumable (e.g. proper docs,
> >>>>>>>>>>>>>     example
> >>>>>>>>>>>>>     code, extending
> >>>>>>>>>>>>>        the API, etc)
> >>>>>>>>>>>>>     4. Implement the API itself
> >>>>>>In the earlier we'd discussed working to have similarities in the 
> >>>>>>modeling between the oVirt API and VDSM but that seems to have dropped 
> >>>>>>off the radar.
> >>>>>Yes, the current REST API has attempted to be compatible with the current
> >>>>>ovirt-engine API.  Going forward, I am not sure how easy this will be to
> >>>>>maintain given than engine is built on Java and vdsm is built on Python.
> >>>>Could you elaborate why the language difference is an issue? Isn't this
> >>>>what APIs are supposed to solve?
> >>>The main language issue is that ovirt-engine has built their API using a 
> >>>set of
> >>>Java-specific frameworks (JAXB and its dependents).  It's true, if you 
> >>>google
> >>>for 'python jaxb' you will find some sourceforge projects that attempt to 
> >>>bring
> >>>the jaxb interface to python but I don't think that's the right approach.  
> >>>If
> >>>you're writing a java project, do things the java way.  If you're writing a
> >>>python project, do them the python way.  Right now I am focused on 
> >>>defining the
> >>>current API (API.py/xmlrpc) mechanically (creating a schema and API
> >>>documentation).  XSD is not the correct language for that task (which is 
> >>>why I
> >>>forsee a divergence at least at first).  I want to take a stab at defining 
> >>>the
> >>>API in a beneficial, long-term manner.
> 
> Adam,
> 
> Can you explain why you think XSD is not the correct language?  Is
> it because of the lacking of full python language code generator? Is
> it possible to modify the existing code generator to address that
> issue?  What is the benefit to introduce a new schema/code generator
> to oVirt instead of changing the existing code generator?

XSD is designed to specify a schema for XML documents.  The vdsm API doesn't use
XML documents.  It is currently basic python types over RPC and we want to add
language bindings for C and Java too.  The QAPI schema language already exists
in the qemu project and there is existing generator code that we can reuse.  I
think it will be easier and better in the long run to use the proper schema for
the job rather than trying to contort the xsd schema stuff to fit our needs.

> 
> >>>
> >>>1) Completely define the current XMLRPC API including all functions, 
> >>>parameters,
> >>>and return values.  Complex data structures can be broken down into their 
> >>>basic
> >>>types.  These are: int, str, bool, list, dict, typed-dict, enum.  I have 
> >>>already
> >>>started this process and am using Qemu's QAPI schema language.  You can 
> >>>see that
> >>>here [1].  For an example of what that looks like describing the vdsm API 
> >>>see
> >>>this snippet [2].
> >>>
> >>>2) Import the parser/generator code from qemu for the above schema.  Vdsm 
> >>>will
> >>>require a few extensions such as typed-dictionaries, tuples, and type 
> >>>aliases.
> >>>Adapt the generator so that it can produce a libvdsm which provides API 
> >>>language
> >>>bindings for python, c, and java.
> >>>
> >>>3) Implement a vdsm shell in terms of libvdsm.  In fact, this can be 
> >>>largely
> >>>auto-generated from the schema and accompanying documentation.  This can 
> >>>serve
> >>>to model how new transports can be written.  For example, an AMQP 
> >>>implementation
> >>>can be implemented entirely outside of the vdsm project if we wished.  It 
> >>>only
> >>>needs to talk to vdsm via libvdsm.
> >>Maybe API layer can load API interface definition from this schema.
> >>Then we only define the api interface at one place. :)
> >>I am not sure now. still thinking.
> >I think the code for vdsm-shell can be auto-generated from the schema at 
> >build
> >time.  I prefer this over dynamic discovery because it is much simpler.`
> >
> >>>Easy as 1,2,3 :)
> >>>
> >>>[1] 
> >>>http://git.qemu.org/?p=qemu.git;a=blob;f=qapi-schema.json;h=3b6e3468b440b4b681f321c9525a3d83bea2137a;hb=HEAD
> >>>[2] http://fpaste.org/rt96/
> >>>
> >>>Probably more than you bargained for when asking for more info... :)
> >>>
> >>
> 
> 
> -- 
> Shu Ming <shum...@linux.vnet.ibm.com>
> IBM China Systems and Technology Laboratory
> 
> 

-- 
Adam Litke <a...@us.ibm.com>
IBM Linux Technology Center

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