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

[Yan Vugenfirer <yvugenfi@redhat.com>]

> 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).

>> 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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