From mboxrd@z Thu Jan 1 00:00:00 1970 From: Daniel Axtens Subject: Re: [PATCH] macvlan: verify MTU before lowerdev xmit Date: Fri, 17 Nov 2017 23:18:25 +1100 Message-ID: <87y3n5f69a.fsf@linkitivity.dja.id.au> References: <20171114103251.5495-1-dja@axtens.net> <20171117.145401.1277591015464586683.davem@davemloft.net> <871skxgv70.fsf@linkitivity.dja.id.au> <20171117.174131.854361434090179436.davem@davemloft.net> Mime-Version: 1.0 Content-Type: text/plain Cc: netdev@vger.kernel.org, shannon.nelson@oracle.com To: David Miller Return-path: Received: from mail-pf0-f176.google.com ([209.85.192.176]:44374 "EHLO mail-pf0-f176.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932122AbdKQMS3 (ORCPT ); Fri, 17 Nov 2017 07:18:29 -0500 Received: by mail-pf0-f176.google.com with SMTP id n89so1830640pfk.11 for ; Fri, 17 Nov 2017 04:18:29 -0800 (PST) In-Reply-To: <20171117.174131.854361434090179436.davem@davemloft.net> Sender: netdev-owner@vger.kernel.org List-ID: Hi Dave, > So how exactly do the oversized packets get to the macvlan device from > the VM in this scenerio? That detail seems to be missing from the > diagrams you provided earlier. The VM and the macvlan boxes are just > connected with a line. Inside the VM I'm using netperf talking on an interface which the guest believes to have a MTU of 1500. I'm setting up the VM using libvirt - my understanding is that libvirt creates a macvtap device in private mode, and qemu opens that tap device and writes data from the emulated network card (I see the same behaviour with a emulated rtl8139, e1000, and with virtio). I think I could replicate this with any userspace program - qemu is just the easiest for me at the moment. Hopefully that's what you had in mind? Let me know if you wanted different info. Regards, Daniel [The gory details, in case it matters: The VM has a network adaptor with the following XML:
] > > Thank you.