netdev - Re: virtio_net: can change MTU after installing program

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Message-ID: <bcd3721e-5938-d12d-d0e6-b53d337ff7ff@digitalocean.com>
Date:   Tue, 25 Feb 2020 21:31:21 -0700
From:   David Ahern <dahern@...italocean.com>
To:     Jason Wang <jasowang@...hat.com>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: virtio_net: can change MTU after installing program

On 2/25/20 9:02 PM, Jason Wang wrote:
>>
>> The simple solution causes a user visible change with 'ip -d li sh' by
>> showing a changing max mtu, but the ndo has a poor user experience in
>> that it just fails EINVAL (their is no extack) which is confusing since,
>> for example, 8192 is a totally legit MTU. Changing the max does return a
>> nice extack message.
> 
> 
> Or for simplicity, just forbid changing MTU when program is installed?

My preference is to show the reduced max MTU when a program is
installed. Allows the mtu to be increased to the max XDP allows for the
device.