netdev - Re: [PATCH] macvlan: verify MTU before lowerdev xmit

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Date:   Fri, 17 Nov 2017 23:18:25 +1100
From:   Daniel Axtens <dja@...ens.net>
To:     David Miller <davem@...emloft.net>
Cc:     netdev@...r.kernel.org, shannon.nelson@...cle.com
Subject: Re: [PATCH] macvlan: verify MTU before lowerdev xmit

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:

    <interface type='direct'>
      <mac address='52:54:00:e7:a2:ac'/>
      <source dev='enx0050b6655ff2' mode='private'/>
      <model type='rtl8139'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x07' function='0x0'/>
    </interface>
]

>
> Thank you.