[libvirt] [RFC Incomplete Patch] Libvirt + Openvswitch

[Dan Wendlandt]

Hello all,

I know of many people who want to spin up VMs using libvirt + kvm/qemu and
attach those VMs to an openvswitch bridge (see: http://www.openvswitch.org).
  However, the only way I know of to get this working is a kludge that uses
to tap devices along with <interface type="ethernet"> while running
ovs-vsctl outside of libvirt.  Even worse, doing this on RHEL/Fedora seems
to require privilege tweaks (e.g., running qemu as root, not dropping
capabilities), which may not be acceptable for production deployments
(see:
http://fedoraproject.org/wiki/How_to_debug_Virtualization_problems#Errors_using_.3Cinterface_type.3D.27ethernet.27.2F.3E).

So I would like to start taking steps toward better libvirt/openvswitch
integration.  My initial step has the fairly limit goal of enabling
kvm/qemu VM NICs to attach to an openvswitch bridge in much the same way VM
NIC can already attached to the linux bridge.  For example, specifying:

<interface type="openvswitch">
<source bridge="br0"/>
<mac address="ca:fe:de;ad:be:ef"/>
</interface>

I also wanted to add a new child element of <interface> that can be used to
specify some OVS specific configuration.  To start, I just want to expose a
single 'interfaceid' value (this parameter is specific to openvswitch).
Extending the previous example:

<interface type="openvswitch">
<source bridge="br0"/>
<mac address="ca:fe:de;ad:be:ef"/>
<openvswitchport interfaceid="interface-xyz"/>
</interface>

For this first step (see attached patch), I am only targeting the model
where the OVS bridge has been created externally ahead of time.  I am not
tackling any of the "network" logic that actually creates/destroys bridges,
as it is not needed for my target use case.

A couple notes about the attached patch:
- I haven't actually run this code.  I was just poking around the libvirt
code to learn about it and figured that a diff was the most concrete way to
propose what I was thinking of doing.  I would be curious for pointers
about big chunks of work that I may have missed (for example, I haven't
added any tests yet).
- the code was modeled on the network interface "bandwidth" code, that
calls out to 'tc' to configure bandwidth rates.  Ideally we would be able
to make direct C calls to OVS (and we plan to make that possible in the
future), but calling an external utility right now is the only viable
path.
- no attention was paid to style guidelines.  Will do that before any real
submission.
- I wasn't very clear on the notion of an "actual" net def, as opposed to a
normal net def.  What's the best place to look for documentation on this?

Anyway, I'm primarily looking for feedback about whether I'm barking up the
right tree before I spend time debugging or polishing the patch, so I would
appreciate thoughts, advice, etc.  Thanks,

Dan


-- 
~~~~~~~~~~~~~~~~~~~~~~~~~~~
Dan Wendlandt
Nicira Networks: www.nicira.com
twitter: danwendlandt
~~~~~~~~~~~~~~~~~~~~~~~~~~~
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