PATCH: Don't clobber VIF 'type' field when starting a HVM guest

["Daniel P. Berrange" <berrange@redhat.com>]

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In the Xen 3.1.0 series releases the 'VIF' config has a 'type' field which is
used to determine if using QEMU's emulated NIC vs netfront/back.

 - type=ioemu  -> Setup QEMU with an rtl8139 nic
 - type=netfront -> Setup netback, assuming HVM pv drivers
 - type is None  -> Setup QEMU with rtl8139 nic & netback


In Fedora (and libvirt) we default to leaving 'type' as None, so that users
do not have to change the Dom0 guest config simply to install PV drivers in
an HVM guest.

There is one unfortunate bug though - when you start a managed VM, XenD will
re-save its configuration out to disk under /var/lib/xend/domains/[UUID]
and in doing so, it converts type=None into type=netfront. This isn't an
immediate problem because the config in memory is never changed & still
has correct settings. But some days/months later when the machine is rebooted
or XenD is restarted, it reads the config from disk & thus the rtl8139 nic
disappears from all your HVM guests :-(

The attached patch fixes server/netif.py so that it respects type=None as
the rest of the XenD code does. The patch is against xen-3.1-testing.hg
but also needs to be applied to xen-unstable.hg

  Signed-off-by: Daniel P. Berrange <berrange@redhat.com>

Regards,
Dan.
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diff -r 912a5cb75c80 tools/python/xen/xend/server/netif.py
--- a/tools/python/xen/xend/server/netif.py	Wed Sep 19 15:49:56 2007 +0100
+++ b/tools/python/xen/xend/server/netif.py	Thu Sep 27 12:22:19 2007 -0400
@@ -108,17 +108,15 @@ class NetifController(DevController):
         ipaddr  = config.get('ip')
         model   = config.get('model')
 
-        if not typ:
-            typ = xoptions.netback_type
-
         if not mac:
             raise VmError("MAC address not specified or generated.")
 
         devid = self.allocateDeviceID()
 
         back = { 'script' : script,
-                 'mac'    : mac,
-                 'type'   : typ }
+                 'mac'    : mac }
+        if typ:
+            back['type'] = typ
         if ipaddr:
             back['ip'] = ipaddr
         if bridge:

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