libvirt users - Aug 2013 - Re: Bridging Wireless Cards for KVM

Hi,

I hope this is the right place to ask this question. I was wondering if
there is a way to set up a KVM VM using an XML document as input into Virsh
that uses bridged networking over a wireless card.

I understand that wireless cards to not natively support, but I was able to
find a working solution here:
http://blog.ericwhite.ca/articles/2011/04/creating-a-wireless-bridge/.

The issue is, I can use this bridge by calling KVM directly. However, I
cannot figure out how to get this same configuration on an XML file that I
input into Virsh for the creation of a VM.

My understanding is that libvirt calls KVM/QEMU at some point, but I may be
mistaken.

Thanks,
Joshua

On Thu, Aug 08, 2013 at 08:55:27PM -0600, Joshua McKee
wrote:
> Hi,
> 
> I hope this is the right place to ask this question. I was wondering if
> there is a way to set up a KVM VM using an XML document as input into Virsh
> that uses bridged networking over a wireless card.
> 
> I understand that wireless cards to not natively support, but I was able to
> find a working solution here:
> http://blog.ericwhite.ca/articles/2011/04/creating-a-wireless-bridge/.
Ok, that's slightly different. The traditional integration with Linux
bridge devices is doing ethernet layer bridging - so all protocols
like IPv4, IPv6, etc, etc will "just work".

What that blog describes is protocol layer bridging, which with those
instructions only works for IPv4.

Libvirt doesn't have any explicit support for the latter. Though we have
thought about implementing it in the virtual network APIs, we've never
got around to it.
> The issue is, I can use this bridge by calling KVM directly. However, I
> cannot figure out how to get this same configuration on an XML file that I
> input into Virsh for the creation of a VM.
> 
> My understanding is that libvirt calls KVM/QEMU at some point, but I may be
> mistaken.
You might be able to get it working using the generic ethernet config

   http://libvirt.org/formatdomain.html#elementsNICSEthernet

That setup you specify a pre-created TAP device for the VM to use.
Of course it is upto you todo the manal config steps described in
that blog, so is more tedious from an admin pov.


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 :|

Thanks! Unfortunately, I am running into the following issue when
attempting to use the generic ethernet configuration:

$ virsh -c qemu:///system create /tmp/generic.xml
error: Failed to create domain from /tmp/generic.xml
error: internal error process exited while connecting to monitor: kvm:
-netdev tap,id=hostnet0: could not configure /dev/net/tun: Operation not
permitted
kvm: -netdev tap,id=hostnet0: Device 'tap' could not be initialized

This is the network part of my xml file:

<devices>
   <interface type="ethernet"/>


 ...
  <devices>
    <interface type='ethernet'/>
    ...
    <interface type='ethernet'>
      <target dev='vnet7'/>
      <script path='/etc/qemu-ifup-mynet'/>
    </interface>
  </devices>
  ...



In my /etc/libvirt/qemu.conf file I have the following set:

user = "root"
group ="root"
dynamic ownership = 0
clear_emulator_capabilities = 0
cgroup_device_acl = [
    "/dev/null", "/dev/full", "/dev/zero",
    "/dev/random", "/dev/urandom",
    "/dev/ptmx", "/dev/kvm", "/dev/kqemu",
    "/dev/rtc", "/dev/hpet",
    "/dev/net/tun",
]

I am running Ubuntu 12, which does not use SELinux.


On Fri, Aug 9, 2013 at 8:01 AM, Daniel P. Berrange
<berrange@redhat.com>wrote:
> On Thu, Aug 08, 2013 at 08:55:27PM -0600, Joshua McKee wrote:
> > Hi,
> >
> > I hope this is the right place to ask this question. I was wondering
if
> > there is a way to set up a KVM VM using an XML document as input into
> Virsh
> > that uses bridged networking over a wireless card.
> >
> > I understand that wireless cards to not natively support, but I was
able
> to
> > find a working solution here:
> > http://blog.ericwhite.ca/articles/2011/04/creating-a-wireless-bridge/.
>
> Ok, that's slightly different. The traditional integration with Linux
> bridge devices is doing ethernet layer bridging - so all protocols
> like IPv4, IPv6, etc, etc will "just work".
>
> What that blog describes is protocol layer bridging, which with those
> instructions only works for IPv4.
>
> Libvirt doesn't have any explicit support for the latter. Though we
have
> thought about implementing it in the virtual network APIs, we've never
> got around to it.
>
> > The issue is, I can use this bridge by calling KVM directly. However,
I
> > cannot figure out how to get this same configuration on an XML file
that
> I
> > input into Virsh for the creation of a VM.
> >
> > My understanding is that libvirt calls KVM/QEMU at some point, but I
may
> be
> > mistaken.
>
> You might be able to get it working using the generic ethernet config
>
>    http://libvirt.org/formatdomain.html#elementsNICSEthernet
>
> That setup you specify a pre-created TAP device for the VM to use.
> Of course it is upto you todo the manal config steps described in
> that blog, so is more tedious from an admin pov.
>
>
> 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:|
>