From mboxrd@z Thu Jan  1 00:00:00 1970
From: Stephen Hemminger <stephen@networkplumber.org>
Subject: Re: [PATCH v1] add mtu set in virtio
Date: Sat, 27 Aug 2016 17:15:41 -0700
Message-ID: <20160827171541.5f6b17c2@xeon-e3>
References: <20160827005428.16556-1-sodey@sonusnet.com>
Mime-Version: 1.0
Content-Type: text/plain; charset=US-ASCII
Content-Transfer-Encoding: 7bit
Cc: <huawei.xie@intel.com>, <yuanhan.liu@linux.intel.com>, <dev@dpdk.org>
To: souvikdey33 <sodey@sonusnet.com>
Return-path: <dev-bounces@dpdk.org>
Received: from mail-pf0-f179.google.com (mail-pf0-f179.google.com
 [209.85.192.179]) by dpdk.org (Postfix) with ESMTP id 591F32142
 for <dev@dpdk.org>; Sun, 28 Aug 2016 02:15:29 +0200 (CEST)
Received: by mail-pf0-f179.google.com with SMTP id h186so39819830pfg.3
 for <dev@dpdk.org>; Sat, 27 Aug 2016 17:15:29 -0700 (PDT)
In-Reply-To: <20160827005428.16556-1-sodey@sonusnet.com>
List-Id: patches and discussions about DPDK <dev.dpdk.org>
List-Unsubscribe: <http://dpdk.org/ml/options/dev>,
 <mailto:dev-request@dpdk.org?subject=unsubscribe>
List-Archive: <http://dpdk.org/ml/archives/dev/>
List-Post: <mailto:dev@dpdk.org>
List-Help: <mailto:dev-request@dpdk.org?subject=help>
List-Subscribe: <http://dpdk.org/ml/listinfo/dev>,
 <mailto:dev-request@dpdk.org?subject=subscribe>
Errors-To: dev-bounces@dpdk.org
Sender: "dev" <dev-bounces@dpdk.org>

On Fri, 26 Aug 2016 20:54:28 -0400
souvikdey33 <sodey@sonusnet.com> wrote:

> This functionality is required mostly in the cloud infrastructure.
> For example, if we use gre or vxlan network between compute and
> controller, then we should not use 1500 mtu in the guest as with
> encapsulation the sixe of the packet will be more and will get 
> dropped in the infrastructure. So, in that case we should honor
> the mtu size sent by the dhcp server and configure the same on 
> the virtual interfaces in the guest. This will also keep a 
> consistent mtu through out the infrastructure.
> 
> souvikdey33 (1):
>   Signed-off-by: Souvik Dey <sodey@sonusnet.com>
> 
>  drivers/net/virtio/virtio_ethdev.c | 12 ++++++++++++
>  1 file changed, 12 insertions(+)
> 

Thanks for the patch, it is a good step forward but it looks
like more code is needed to do this safely. At a minimum,
need to check that MTU is not greater than VIRTIO_MAX_RX_PKTLEN.
And error return should be negative errno not -1.

Something like:
   if (mtu < VIRTIO_MIN_MTU || mtu > VIRTIO_MAX_RX_PKTLEN)
	return -EINVAL;

Looking at Linux driver, it allows MTU of up to 64K, yet DPDK
only allows 9728.  That should probably be fixed.