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Re: [libvirt] [PATCH] Add support for 'passthru' mode for direct network interfaces



On Wed, May 11, 2011 at 10:46:55AM -0400, Laine Stump wrote:
> On 05/11/2011 08:21 AM, Daniel P. Berrange wrote:
> >On Tue, May 10, 2011 at 04:21:29PM -0600, Eric Blake wrote:
> >>On 05/10/2011 05:59 AM, D. Herrendoerfer wrote:
> >>>Hi all,
> >>>
> >>>starting with kernel 2.6.38 macvtap supports a 'passthru' mode for
> >>>attaching virtual functions
> >>>of a SRIOV capable network card directly to a VM.
> >>>This patch adds the capability to configure such a device.
> >>>
> >>>Signed-off-by: Dirk Herrendoerfer<d.herrendoerfer at herrendoerfer.name>
> >>>
> >>>diff --git a/docs/schemas/domain.rng b/docs/schemas/domain.rng
> >>>index 7163c6e..e2a66ae 100644
> >>>--- a/docs/schemas/domain.rng
> >>>+++ b/docs/schemas/domain.rng
> >>>@@ -2351,7 +2351,7 @@
> >>>    </define>
> >>>    <define name="bridgeMode">
> >>>      <data type="string">
> >>>-<param name="pattern">(vepa|bridge|private)</param>
> >>>+<param name="pattern">(vepa|bridge|private|passthru)</param>
> >>>      </data>
> >>>    </define>
> >>>    <define name="addrMAC">
> >>Missing corresponding documentation in docs/formatdomain.html.in to
> >>describe the new mode.
> >>
> >>What happens if you try to use this mode but you have an older kernel?
> >>Do we need to add any sanity checking to give a saner error message than
> >>just blindly trying the string and reporting back whatever message gets
> >>returned about an unknown argument?
> >>
> >>The rest of this patch looks okay to me (with my disclaimer that I've
> >>never used an SRIOV card), but I'd rather wait for a v2 than push this
> >>without documentation.
> >The kernel GIT commit actually has some useful info
> >
> >
> >commit eb06acdc85585f28864261f28659157848762ee4
> >Author: Sridhar Samudrala<sri us ibm com>
> >Date:   Thu Oct 28 13:10:50 2010 +0000
> >
> >     macvlan: Introduce 'passthru' mode to takeover the underlying device
> >
> >     With the current default 'vepa' mode, a KVM guest using virtio with
> >     macvtap backend has the following limitations.
> >     - cannot change/add a mac address on the guest virtio-net
> >     - cannot create a vlan device on the guest virtio-net
> >     - cannot enable promiscuous mode on guest virtio-net
> 
> I had read that commit notice earlier, and didn't understand the
> first item - which MAC address needs to be changed? Doesn't the
> guest have its own MAC address, unrelated to the MAC address of the
> underlying device on the host?

It is about allowing a guest to run a bridge device. Currently
only traffic with the guest's declared MAC addr works. So if
the guest acts as a bridge, that bridge traffic won't pass.

Daniel
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