Re: [virtio-dev] Add VIRTIO_NET_F_SPEED_DUPLEX (4) feature bit

[Jason Baron <jbaron@akamai.com>]

On 12/21/2017 06:37 AM, Yan Vugenfirer wrote:
> 
>> On 20 Dec 2017, at 17:00, Michael S. Tsirkin <mst@redhat.com> wrote:
>>
>> On Thu, Dec 14, 2017 at 03:31:54PM -0500, Jason Baron wrote:
>>> Hi,
>>>
>>> We have found it useful to have the virtio net device export a linkspeed
>>> and duplex setting, such that a guest linkspeed and duplex settings can
>>> be set automatically from the host side. We have some guest software
>>> that relies on this setting, and fails without a valid value provided.
>>
>> That software really should be fixed btw. You can't always reliably
>> figure out the speed, and it might change at any time.
>>
> Good point. Each time when there is a linked up indication from the host, we should expect that the settings can be different (for example backend changed).
> 

Indeed, I didn't implement the ability to dynamically update the
linkspeed via the host(say via a qemu monitor command), because I didn't
need it. But it could be added later if somebody wanted it...

Thanks,

-Jason

>>> Thus, I would like to propose adding a new feature bit:
>>>
>>> VIRTIO_NET_F_SPEED_DUPLEX (4) Device provides a linkspeed and duplex setting
>>
>>
>> I think a high feature bit would be better. Low bits can be
>> backported to legacy devices, so better used for things
>> like mtu, where communication just breaks otherwise,
>> and for net we are running out of these.
>>
>>
>>> I have provided sample qemu hypervisor and linux kernel guest code to
>>> implement this feature here:
>>>
>>> http://lkml.iu.edu/hypermail/linux/kernel/1712.1/05692.html
>>>
>>> Thanks,
>>>
>>> -Jason
>>
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>