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[libvirt] How to enable vhost for virtIO NIC?



Hi gurus on the list,

I'm trying to bring up a Linux with virtio vhost backend.  My system is running on kernel 2.6.34-rc7, libvirt 0.8.0.

Two questions regarding to vhost:

1) XML format for vhost
I didn't find any documents on libvirt.org description the XML or QMU argument format for vhost.  
According to http://www.linux-kvm.org/page/VhostNet#vhost-net_driver_projects, I tried *domxml-from-native* to convert following qemu argument to XML

qemu-system-x86_64 -m 1G disk-c.qcow2 \
-net nic,model=virtio,netdev=foo \
-netdev tap,id=foo,ifname=msttap0,script=/home/mst/ifup,downscript=no,vhost=on

But the output clearly ignore the network.
<domain type='qemu'>
  <name>unnamed</name>
  <uuid>9cc877c1-7ac2-463d-3d3f-fa8f8918fe23</uuid>
  <memory>1048576</memory>
  <currentMemory>1048576</currentMemory>
  <vcpu>1</vcpu>
  <os>
    <type arch='x86_64'>hvm</type>
  </os>
  <features>
    <acpi/>
  </features>
  <clock offset='utc'/>
  <on_poweroff>destroy</on_poweroff>
  <on_reboot>restart</on_reboot>
  <on_crash>destroy</on_crash>
  <devices>
    <emulator>qemu-system-x86_64</emulator>
    <input type='mouse' bus='ps2'/>
    <graphics type='sdl'/>
    <video>
      <model type='cirrus' vram='9216' heads='1'/>
    </video>
  </devices>
</domain>

What's the problem here?

2) Virtio driver.
It's said that vhost require guest kernel version > 2.6.31 because vhost requires MSI-X.  How about frontend of virtio driver?  Say I'm running a Windows 2008 (with MSI-X support) + virtio NIC, is it necessary to upgrade frontend driver too?

Regards,

HUANG, Zhiteng



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