Re: [virtio-dev] [PATCH 4/4] virtio-net: add linkspeed and duplex settings to virtio-net

[Jason Baron <jbaron@akamai.com>]

On 03/04/2018 08:05 AM, Yan Vugenfirer wrote:
> 
> 
>> On 2 Mar 2018, at 22:19, Michael S. Tsirkin <mst@redhat.com
>> <mailto:mst@redhat.com>> wrote:
>>
>> On Fri, Mar 02, 2018 at 03:14:01PM +0800, Jason Wang wrote:
>>>
>>>
>>> On 2018年03月02日 11:46, Jason Baron wrote:
>>>> Although linkspeed and duplex can be set in a linux guest via
>>>> 'ethtool -s',
>>>> this requires custom ethtool commands for virtio-net by default.
>>>>
>>>> Introduce a new feature flag, VIRTIO_NET_F_SPEED_DUPLEX, which allows
>>>> the hypervisor to export a linkspeed and duplex setting. The user can
>>>> subsequently overwrite it later if desired via: 'ethtool -s'.
>>>>
>>>> Linkspeed and duplex settings can be set as:
>>>> '-device virtio-net,speed=10000,duplex=full'
>>>
>>> I was thinking whether or not it's better to decide the duplex by the
>>> type
>>> of backends.
>>>
>>> E.g userspace and vhost-kernel implement a in fact half duplex. But dpdk
>>> implement a full duplex.
>>>
>>> Thanks
>>
>> OTOH it's a priority for some people to be able to support migration
>> between different backend types. Breaking that won't be nice.
> 
> I think that in this case we need a way to update the settings of link
> speed and link duplex (maybe add QMP command). Migration between
> different backend types should cause link down\link up events. And this
> is a time for a driver to re-read the settings and update the OS.
> 
> Best regards,
> Yan.
> 

So the virtio_net driver in linux will re-read these settings on link up
events. So I could add a qmp command to set these (in addition to the
command-line) interface, if desired. Is there a consensus that we need
to add a qmp command here? Or can that be treated as a future item, if
somebody wants it?

Thanks,

-Jason