[virt-tools-list] [RFC] enable direct interface selection

Gerhard Stenzel gstenzel at linux.vnet.ibm.com
Tue Apr 5 12:37:00 UTC 2011

On Fri, 2011-04-01 at 12:21 -0400, Cole Robinson wrote:
> On 03/25/2011 11:33 AM, Gerhard Stenzel wrote:
> Thanks for the patches, though they are line wrapped, probably from just
> pasting into your mail client. Since we are using git now, it's probably worth
> configuring git send-email and sending patches directly to the list that way.
> Please also send 2 separate patches, specifying either virtinst: or
> virt-manager: in the subject

Thanks for the feedback. will try to follow the suggestions

> We should use source_dev instead of bridge here.

ok .. patch will follow

> We probably only want to enable this option for qemu connection and a
> sufficiently new libvirt. You can enable this by adding a check in
> virtinst/support.py, just follow the example for
> SUPPORT_CONN_HV_CHAR_SPICEVMC, but set the qemu version to 0 instead of 14000.
ok .. patch will follow

> Just to make sure I understand this correctly, a 'direct' interface in this
> context uses macvtap/macvlan to fake a single nic into having multiple MAC
> addresses, with the kernel multiplexing the network traffic as necc. Guests
> will get IP addresses from the host network, similar to using a shared bridge.
> Does this work with all hardware? Are there any downsides or caveats? Right
> now you hardcode vepa mode, what is the functional difference between bridge
> and vepa mode?

The difference between vepa and bridge is documented here:

see Direct attachment to physical interface

        All VMs' packets are sent to the external bridge. Packets whose
        destination is a VM on the same host as where the packet
        originates from are sent back to the host by the VEPA capable
        bridge (today's bridges are typically not VEPA capable).
        Packets whose destination is on the same host as where they
        originate from are directly delivered to the target macvtap
        device. Both origin and destination devices need to be in bridge
        mode for direct delivery. If either one of them is in vepa mode,
        a VEPA capable bridge is required.

I plan to make the mode value also selectable via drop down, but wanted
to see the initial reaction to the approach first.

> Thanks,
> Cole

Best regards, 

Gerhard Stenzel, 
IBM Deutschland Research & Development GmbH
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