libvirt users - Jul 2014 - Re: vhost-net requested but could not be initialized

Thanks Wangkai but libvirt infact pre-configures network tap devices and
pre-opens /dev/vhost-net file and passes these to qemu as open, ready to
use file descriptors.

My issue is that my qemu requires that /dev/vhost-net directory is removed
and it's kernel module be unloaded. Then it creates a vhost -net device
using its own configuration.


On 24 July 2014 07:35, Wangkai (Kevin,C) <wangkai86@huawei.com> wrote:
>  For qemu, the default vhost drive file is “/dev/vhost-net”, when you
> configured vhost on.
>
> Give the command “modprobe vhost-net” to add host kernel support for vhost.
>
> This is cannot controlled by libvirt I think.
>
>
>
> Wangkai
>
>
>
> *From:* libvirt-users-bounces@redhat.com [mailto:
> libvirt-users-bounces@redhat.com] *On Behalf Of *Asadullah Hussain
> *Sent:* Thursday, July 24, 2014 12:43 AM
> *To:* libvirt-users@redhat.com
> *Subject:* [libvirt-users] vhost-net requested but could not be
> initialized
>
>
>
> I am using a custom qemu to launch a vhost enabled VM. The qemu doesn't
> use the default "/dev/vhost-net" directory as character device.
Due to this
> I am getting the error:
>
>
>
> qemu-system-x86_64: -netdev
> type=tap,id=net1,script=no,downscript=no,ifname=port3,vhost=on: vhost-net
> requested but could not be initialized
>
>
>
> ​Is there a way to tell libvirt to ​avoid using the default
> /dev/vhost-net file?
>
>
>
> I have tried using the pass-through arguments but libvirt still processes
> the command and throws the error.
>
>
>
> PS: I can successfully create a vhost VM using qemu command-line, so this
> is a libvirt issue.
>
>
>
> --
>
> Cheers,
>
>
>
> Asadullah Hussain
>


-- 
Cheers,

Asadullah Hussain

On Thu, Jul 24, 2014 at 08:42:47AM +0500, Asadullah Hussain
wrote:
> Thanks Wangkai but libvirt infact pre-configures network tap devices and
> pre-opens /dev/vhost-net file and passes these to qemu as open, ready to
> use file descriptors.
> 
> My issue is that my qemu requires that /dev/vhost-net directory is removed
> and it's kernel module be unloaded. Then it creates a vhost -net device
> using its own configuration.
Libvirt is only written to work against official upstream QEMU. If you
have modified your QEMU to work in a different way wrt net devices then
you'll have to modify your libvirt to cope or workaround the problems.

Regards,
Daniel
-- 
|: http://berrange.com      -o-    http://www.flickr.com/photos/dberrange/ :|
|: http://libvirt.org              -o-             http://virt-manager.org :|
|: http://autobuild.org       -o-         http://search.cpan.org/~danberr/ :|
|: http://entangle-photo.org       -o-       http://live.gnome.org/gtk-vnc :|

​The qemu that I am using isn't modified at all. It's the VHOST drivers
that are mounted elsewhere i.e., not on default /dev/vhost-net.

Here is the command that I use to launch my qemu VM:
qemu-system-x86_64 -cpu host -boot order=c -hda /root/Disks/ubuntu1.qcow2
-m 1024M -smp 2 --enable-kvm -name 'client 1' -nographic -vnc :2 -net
none
-no-reboot -mem-path /dev/hugepages -mem-prealloc -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
-netdev type=tap,id=net2,script=no,downscript=no,ifname=port4,vhost=on
-device
virtio-net-pci,netdev=net2,mac=00:00:00:00:00:02,csum=off,gso=off,guest_tso4=off,guest_tso6=off,guest_ecn=off
​
As you can see I have created tap interfaces port3 & port4 and I just want
to connect the VM to these VMs.


On 24 July 2014 13:31, Daniel P. Berrange <berrange@redhat.com> wrote:
> On Thu, Jul 24, 2014 at 08:42:47AM +0500, Asadullah Hussain wrote:
> > Thanks Wangkai but libvirt infact pre-configures network tap devices
and
> > pre-opens /dev/vhost-net file and passes these to qemu as open, ready
to
> > use file descriptors.
> >
> > My issue is that my qemu requires that /dev/vhost-net directory is
> removed
> > and it's kernel module be unloaded. Then it creates a vhost -net
device
> > using its own configuration.
>
> Libvirt is only written to work against official upstream QEMU. If you
> have modified your QEMU to work in a different way wrt net devices then
> you'll have to modify your libvirt to cope or workaround the problems.
>
> Regards,
> Daniel
> --
> |: http://berrange.com      -o-    http://www.flickr.com/photos/dberrange/
> :|
> |: http://libvirt.org              -o-             http://virt-manager.org
> :|
> |: http://autobuild.org       -o-         http://search.cpan.org/~danberr/
> :|
> |: http://entangle-photo.org       -o-       http://live.gnome.org/gtk-vnc
> :|
>


-- 
Cheers,

Asadullah Hussain