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

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

On Thu, Dec 21, 2017 at 01:37:29PM +0200, 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).

Interesting.

So far the motivation was just to trick some proprietary software,
for that a static field might be enough.

If not - what is the motivation exactly? 


> >> 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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