netdev - Re: [PATCH] macvlan: Introduce 'passthru' mode to takeover the underlying device

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Date:	Sat, 30 Oct 2010 19:03:46 +0200
From:	"Michael S. Tsirkin" <mst@...hat.com>
To:	Arnd Bergmann <arnd@...db.de>
Cc:	Sridhar Samudrala <sri@...ibm.com>,
	Patrick McHardy <kaber@...sh.net>,
	Stephen Hemminger <shemminger@...tta.com>,
	netdev <netdev@...r.kernel.org>,
	"kvm@...r.kernel.org" <kvm@...r.kernel.org>
Subject: Re: [PATCH] macvlan: Introduce 'passthru' mode to takeover the
 underlying device

On Fri, Oct 29, 2010 at 03:45:17PM +0200, Arnd Bergmann wrote:
> On Friday 29 October 2010, Sridhar Samudrala wrote:
> > 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
> 
> I believe this could be changed if there is a neeed, but I actually
> consider it one of the design points of macvlan that the guest
> is not able to change the mac address.

It's a policy question that we should not set at the kernel level.

> With 802.1Qbg you rely on
> the switch being able to identify the guest by its MAC address,
> which the host kernel must ensure.

This is required to be able to get feature parity with
both tun and device assignment. At the moment, changing
the mac when using macvtap silently breaks guest networking.

-- 
MST
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