On Tue, Dec 02, 2008 at 09:24:24PM +0000, Gihan Munasinghe wrote:
  

The "type" attribute is used to specify how the network card is connected
to the host networking. You're after something that changes what is 
exposed tto the guest.  The XML format for network interfaces already has 
support for a model element which accomplishes this. eg, for KVM we can
select VirtIO network card with:

    <interface type='bridge'>
        <model type="virtio"/>
        <source bridge='br0'/>
        <mac address='00:16:3e:00:a5:57'/>
    </interface>

  

This 'model' is not currently used in the Xen driver for libvirt, so
we should implement it. A value of 'none' doesn't really make sense.
For Xen >= 3.1.0, libvirt will no longer append type=ioemu by default.
This lets XenD configure by rtl8139 nic, and PV driver back/front.

So I think we just need to allow an explicit choice to override this

A couple of choices, either follow XenD's naming

   <model type="ioemu"/>
   <model type="netback"/>
Or take into account we might want to allow for full range of QEMU
nic choices, even if XenD doesn't (yet) expose it

   <model type="rtl8139"/>
   <model type="e1000"/>
   <model type="ne2k_pci"/>
   <model type="netback"/>

I think i tend towards the latter, since its more consistent with naming
in QEMU driver.

Daniel
  

if (def->ifname != NULL &&
        !STRPREFIX(def->ifname, "vif"))
        virBufferVSprintf(buf, "(vifname '%s')", def->ifname);

    if (def->model != NULL)
        virBufferVSprintf(buf, "(model '%s')", def->model);


So the model tag is already send to xend, and used in xend as well 
check the following xend code 

for devuuid in vmConfig['vif_refs']:
            devinfo = vmConfig['devices'][devuuid][1]
            dtype = devinfo.get('type', 'ioemu')
            if dtype != 'ioemu':
                continue
            nics += 1
            mac = devinfo.get('mac')
            if mac is None:
                raise VmError("MAC address not specified or generated.")
            bridge = devinfo.get('bridge', 'xenbr0')
            model = devinfo.get('model', 'rtl8139')
            ret.append("-net")
            ret.append("nic,vlan=%d,macaddr=%s,model=%s" %
                       (nics, mac, model))
            ret.append("-net")
            ret.append("tap,vlan=%d,ifname=tap%d.%d,bridge=%s" %
                       (nics, self.vm.getDomid(), nics-1, bridge))

        if nics == 0:
            ret.append("-net")
            ret.append("none")

Therefore only way I can achieve -net none switch, is by sending a (type != ioemu ) tag. sending in a ( model ) tag will not give me what I want. So simply I just want to update my xenstore configuration but I am going to ask qemu not to load any network at all.. So as far as 
qemu is concerned the domain does not have any network.. -net none. That's what I thought of using something like <interface type="none">. Am I missing something here.. 

Just to let you know, This is what I changed on the level of xend_internal.c 

 if ((hvm) && (xendConfigVersion < 4) && (def->type!=VIR_DOMAIN_NET_TYPE_NONE))
        virBufferAddLit(buf, "(type ioemu)");
    else{
                //Only send type none if the <interface type="none" vm formats>
                virBufferAddLit(buf, "(type none)");
        }

I need to send a explicit (type none) or any ( type !ioemu) to get the desired outcome. Thought none would make sense as I don't want any network configured  

Thanks 
Gihan