netdev - Re: user space virtio-net exits with "truncating packet" error

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Message-Id: <200905142128.58111.rusty@rustcorp.com.au>
Date:	Thu, 14 May 2009 21:28:57 +0930
From:	Rusty Russell <rusty@...tcorp.com.au>
To:	Or Gerlitz <ogerlitz@...taire.com>
Cc:	Avi Kivity <avi@...hat.com>, netdev@...r.kernel.org,
	Gregory Haskins <ghaskins@...ell.com>,
	Anthony Liguori <anthony@...emonkey.ws>
Subject: Re: user space virtio-net exits with "truncating packet" error

On Thu, 14 May 2009 07:37:42 pm Or Gerlitz wrote:
> Hi,
>
> When running with jumbo frames (i.e set tap0 and guest nic mtu to 9k)
> and using 8k sized packets with iperf, the qemu process exits with
> "virtio-net truncating packet" which I see in the code of
> qemu/hw/virtio-net.c
>
> :: virtio_net_receive(). This happens only when the VM is receiving, if I
>
> send 8K packets from the VM things go fine.
>
> I use virtio based NIC in the VM and Linux 2.6.29.1 in both the VM and the
> host. Qemu is the one provided by kvm release 84 - whose sources don't
> point me to a specific git tree nor a maintainer, so I hope you can help
> me...

Maintainer Cc'd.  The answer is that virtio_net by default only supports 1500 
MTU; I've not tried larger MTUs.

Rusty.
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