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

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Date:	Sat, 30 Oct 2010 18:57:50 +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. With 802.1Qbg you rely on
> the switch being able to identify the guest by its MAC address,
> which the host kernel must ensure.
> 
> > - cannot create a vlan device on the guest virtio-net
> 
> Why not? If this doesn't work, it's probably a bug!
> Why does the passthru mode enable it if it doesn't work
> already?
> 
> > - cannot enable promiscuous mode on guest virtio-net
> 
> Could you elaborate why such a setup would be useful?
> 
> 	Arnd

E.g. to support bridging in the guest.

-- 
MST
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