Re: [PATCH net-next v2 1/3] virtio_net: propagate linkspeed/duplex settings from the hypervisor

On 12/27/2017 04:43 PM, David Miller wrote:

From: Jason Baron <jbaron@akamai.com>
Date: Fri, 22 Dec 2017 16:54:01 -0500

quoted

The ability to set speed and duplex for virtio_net in useful in various
scenarios as described here:

16032be virtio_net: add ethtool support for set and get of settings

However, it would be nice to be able to set this from the hypervisor,
such that virtio_net doesn't require custom guest ethtool commands.

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'.

Signed-off-by: Jason Baron <jbaron@akamai.com>
Cc: "Michael S. Tsirkin" <mst@redhat.com>
Cc: Jason Wang <redacted>

Looks mostly fine to me but need some virtio_net reviewers on this one.

quoted

@@ -57,6 +57,8 @@
 					 * Steering */
 #define VIRTIO_NET_F_CTRL_MAC_ADDR 23	/* Set MAC address */
 
+#define VIRTIO_NET_F_SPEED_DUPLEX 63	/* Host set linkspeed and duplex */
+

Why use a value so far away from the largest existing one?

Just curious.

So that came from a discussion with Michael about which bit to use for
this, and he suggested using 63:

"
Transports started from bit 24 and are growing up.
So I would say devices should start from bit 63 and grow down.
"

https://patchwork.ozlabs.org/patch/848814/#1826669

I will add a comment to explain it.

Thanks,

-Jason