Thanks Matthias for the explanation, I was working on the project which required libvirt to control/set networking on a given ESX host. I may need  
 
> Date: Sun, 5 Aug 2012 22:45:26 +0200
> Subject: Re: [libvirt] [PATCH v5] ESX: Add routines to interface driver
> From: matthias.bolte@googlemail.com
> To: ata.husain@hotmail.com
> CC: libvir-list@redhat.com
>
> 2012/8/5 Matthias Bolte <matthias.bolte@googlemail.com>:
> > 2012/8/2 Ata E Husain Bohra <ata.husain@hotmail.com>:
> >> Add following routines to esx_interface_driver:
> >> esxNumOfInterfaces,
> >> esxNumOfDefinedInterfaces,
> >> esxListInterfaces,
> >> esxListDefinedInterfaces,
> >> esxInterfaceLookupByMACString,
> >> esxInterfaceGetXMLDesc,
> >> esxInterfaceUndefine,
> >> esxInterfaceCreate,
> >> esxInterfaceDestroy
> >>
> >> Signed-off-by: Ata E Husain Bohra <ata.husain@hotmail.com>
> >
> > Okay, I finally had time to take a detailed look at the interface
> > driver and the related network driver and your proposed implementation
> > for the interface driver.
> >
> > I think listing HostVirtualNics in the interface driver is not the
> > correct mapping between vSphere API and libvirt. Also listing
> > HostVirtualNics as bridges is not correct because a HostVirtualNic is
> > not a bridge. A HostVirtualSwitch can be seen as a kind of bridge, but
> > a HostVirtualSwitch is more like a virtual network in libvirt terms.
> >
> > In terms of libvirt the interface driver is about physical NICs that
> > can be used to connect a libvirt virtual network to the physical
> > network. Therefore, the interface driver should just list the
> > PhysicalNics, but not the HostVirtualNics. I think there is currently
> > no place in the libvirt API to map the HostVirtualNics to. Also I
> > don't think that it is important to make the HostVirtualNics available
> > via libvirt API. I might be wrong here, but mapping them via libvirt
> > interface driver is still wrong in my opinion.
> >
> > Regarding the network driver, I think a libvirt virtual network is
> > best represented by a HostVirtualSwitch and the HostPortGroups are
> > mapped to the portgroups of a libvirt virtual switch.
> >
> > I'm sorry that I let you wait for quite a while now until I came to
> > this understanding that is contrary to your proposed interface driver.
>
> I missed to mention that I proposed an implementation for the
> interface and network drivers according to the described mapping:
>
> https://www.redhat.com/archives/libvir-list/2012-August/msg00307.html
> https://www.redhat.com/archives/libvir-list/2012-August/msg00308.html
>
> --
> Matthias Bolte
> http://photron.blogspot.com