From mboxrd@z Thu Jan  1 00:00:00 1970
From: Maxime Coquelin <maxime.coquelin@redhat.com>
Subject: Re: [PATCH v3 7/9] net/virtio: Add MTU feature support
Date: Wed, 5 Apr 2017 09:11:08 +0200
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To: "Tan, Jianfeng" <jianfeng.tan@intel.com>, aconole@redhat.com,
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Hi Jianfeng,

On 04/05/2017 06:52 AM, Tan, Jianfeng wrote:
> Hi Maxime,
>
> Have some confusion about this feature. Please help confirm.
>
> (1) With this feature, we only support to advertise MTU value which is
> defined by QEMU to frontend and backend driver separately. (2) But it
> does not allow frontend driver to set a different MTU to QEMU and then
> to vhost backend.
>
> Correct?
> If it's correct, why not MTU works like (2)?

Because idea is that the hosts advertises the maximum MTU value it
supports. The frontend driver is free to use a smaller value. The goal
of this change is to make possible to set a uniform MTU value across
the infrastructure, the management tools giving a hint to the guests on
the MTU value it should use.

Having the frontend setting the backend MTU dynamically would require 
some negotiation at runtime, and is out of the scope of this change.
Do you have some use cases for this?

Regards,
Maxime
> Thanks,
> Jianfeng