Re: Add VIRTIO_NET_F_SPEED_DUPLEX (4) feature bit

["Michael S. Tsirkin" <mst@redhat.com>]

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.

> 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