Solved the problem, basically libvirt pre-configures network tap devices and pre-opens /dev/vhost-net file and passes these to qemu as open, ready to use file descriptors. . It makes it very difficult to use any other file descriptor for a vhost kernel module. I had to just make sure that the vhost device file descriptor was the default directory i.e., /dev/vhost-net.

I also had to change the permissions for this default file descriptor and add it to "cgroup_device_acl".

On 24 July 2014 16:00, Asadullah Hussain <asadxflow@gmail.com> wrote:

Currently in the VM XML, I am passing the following command line argument as a passthrough argument:

-netdev type=tap,id=net1,script=no,downscript=no,ifname=port3,vhost=on

-device virtio-net-pci,netdev=net1,mac=00:00:00:00:00:01,csum=off,gso=off,guest_tso4=off,guest_tso6=off,guest_ecn=off

Is there another way to represent this in the XML file? maybe that may solve the problem.

On 24 July 2014 15:55, Asadullah Hussain <asadxflow@gmail.com> wrote:

On 24 July 2014 15:52, Daniel P. Berrange <berrange@redhat.com> wrote:

On Thu, Jul 24, 2014 at 03:48:06PM +0500, Asadullah Hussain wrote:
> Let me clarify my question, I am using unmodified stock qemu (1.4.0) and
> only the location of vhost file descriptor is different from default (I
> don't remove the default /dev/vhost-net directory)
>
> The VHOST file descriptor is present in "/dev/vhost-0" directory instead of
> the default "/dev/vhost-net". When I try to give vhostfd in the XML I get a
> different error:

Well I suggest you make your system use the expected device
name for /dev/vhost-net. Just as libvirt only targets mainline
QEMU, we only target mainline kernel / standard device layout

I was able to change my device name to /dev/vhost-net but still I get the error, the error itself isn't telling much about the problem:

2014-07-24 10:41:35.970+0000: 3183: error : qemuMonitorOpenUnix:293 : failed to connect to monitor socket: No such process

2014-07-24 10:41:35.970+0000: 3183: error : qemuProcessWaitForMonitor:1806 : internal error process exited while connecting to monitor: qemu-system-x86_64: -netdev type=tap,id=net1,script=no,downscript=no,ifname=port4,vhost=on: vhost-net requested but could not be initialized

qemu-system-x86_64: -netdev type=tap,id=net1,script=no,downscript=no,ifname=port4,vhost=on: Device 'tap' could not be initialized

Regards,
Daniel
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--
Cheers,

Asadullah Hussain

--
Cheers,

Asadullah Hussain

Cheers,

Asadullah Hussain