libvirt users - Nov 2014 - How to convert "device_model_version = "qemu-xen-traditiona"" into libvirt xml file How to convert "device_model_version = "qemu-xen-traditiona"" into libvirt xml file

I am using Xen-4.4.0, libvirt-1.2.9

My ubuntu.cfg is:

ubuntu10.cfg

bootloader = "/usr/local/lib/xen/boot/hvmloader"
builder="hvm"
memory = 512
name = "ubuntu"
vif = [ "type=ioemu,bridge=ovsbr0",
"type=ioemu,bridge=ovsbr0","type=ioemu,bridge=ovsbr0","type=ioemu,bridge=ovsbr0",,"type=ioemu,bridge=ovsbr0"]
device_model_version = "qemu-xen-traditional"


If I didnot add " device_model_version = "qemu-xen-traditional"
"  to ubuntu.cfg,  I only can add four NICs to VM.
If I  add five or more,,  I got these errors:

libxl: error: libxl_dm.c:1371:device_model_spawn_outcome: domain 12 device
model: spawn failed (rc=-3)
libxl: error: libxl_create.c:1186:domcreate_devmodel_started: device model did
not start: -3
libxl: error: libxl_dm.c:1475:kill_device_model: Device Model already exited


If I add " device_model_version = "qemu-xen-traditional" " 
to ubuntu.cfg, I can apply 8 NICs to VM.

But, I want to create domU by virsh(libvirt),  so How convert  "
device_model_version = "qemu-xen-traditional"" to xml file used
by virsh?
and How many NIC can a VM have? what leads to this limit？


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Best Regards,
yandong