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

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 name="bridgeMode">
      <data type="string">
-<param name="pattern">(vepa|bridge|private)</param>
+<param name="pattern">(vepa|bridge|private|passthru)</param>
    <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?

     To address these limitations, this patch introduces a new mode called
     'passthru' when creating a macvlan device which allows takeover of the
     underlying device and passing it to a guest using virtio with macvtap

     Only one macvlan device is allowed in passthru mode and it inherits
     the mac address from the underlying device and sets it in promiscuous
     mode to receive and forward all the packets.


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