On 05/19/2010 01:49 AM, Huang, Zhiteng wrote:
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.
If you're using virtio networking, and vhost-net support is available on
your system, libvirt will automatically alter the qemu commandline
arguments to take advantage of it. libvirt checks for two things:
1) it runs "qemu-kvm --help" and looks for ",vhost=" in the output
(demonstrating that this build of qemu supports vhost)
2) it attempts to open "/dev/vhost-net" in rw mode (demonstrating that
the kernel support is there, either built into the kernel or loaded as a
You can verify libvirt has enabled vhost by looking at the generated
commandline in /var/log/libvirt/qemu/<domain>.log for
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 \
But the output clearly ignore the network.
<input type='mouse' bus='ps2'/>
<model type='cirrus' vram='9216' heads='1'/>
What's the problem here?
I haven't used domxml-from-native, so I can't help you there.
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
a vhost virtio NIC appears to the guest driver identically to a
user-space virtio NIC, so the same guest-side driver should work fine.
(Actually, the vhost NIC doesn't (yet) support shared buffers that the
user-space NIC does, but the guest's driver can deal with that)
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