Re: [PATCH net-next v3 1/3] virtio_net: propagate linkspeed/duplex settings from the hypervisor

On Thu, Jan 04, 2018 at 08:22:08PM +0200, Michael S. Tsirkin wrote:

On Thu, Jan 04, 2018 at 01:12:30PM -0500, Jason Baron wrote:

quoted

On 01/04/2018 12:05 PM, Michael S. Tsirkin wrote:

quoted

On Thu, Jan 04, 2018 at 12:16:44AM -0500, Jason Baron wrote:

quoted

The ability to set speed and duplex for virtio_net is 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'.

Note that VIRTIO_NET_F_SPEED_DUPLEX is defined as bit 63, the intention
is that device feature bits are to grow down from bit 63, since the
transports are starting from bit 24 and growing up.

Signed-off-by: Jason Baron <jbaron@akamai.com>
Cc: "Michael S. Tsirkin" <mst@redhat.com>
Cc: Jason Wang <redacted>
Cc: virtio-dev@lists.oasis-open.org
---
 drivers/net/virtio_net.c        | 19 ++++++++++++++++++-
 include/uapi/linux/virtio_net.h | 13 +++++++++++++
 2 files changed, 31 insertions(+), 1 deletion(-)

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index 6fb7b65..0b2d314 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c

@@ -2146,6 +2146,22 @@ static void virtnet_config_changed_work(struct work_struct *work)
 
 	vi->status = v;
 
+	if (virtio_has_feature(vi->vdev, VIRTIO_NET_F_SPEED_DUPLEX)) {

BTW we can avoid this read for when link goes down.
Not a big deal but still.

So you are saying that we can just set vi->speed and vi->duplex to
'unknown' when the link goes down and not check for the presence of
VIRTIO_NET_F_SPEED_DUPLEX?

If so, that could over-write what the user may have configured in the
guest via 'ethtool -s' when the link goes down, so that would be a
change in behavior, but perhaps that is ok?

No - what I am saying is that your patch overwrites the values
set by user when link goes down.

I suggest limiting this call to when

if (vi->status & VIRTIO_NET_S_LINK_UP)

and then the values are overwritten when link goes up
which seems closer to what a user might expect.

quoted

I think I would prefer to have the link down event still check for
VIRTIO_NET_F_SPEED_DUPLEX before changing speed/duplex. That way we
still have 2 modes for updating the fields:

1) completely guest controlled. Same as we have now and host does not
change any values and does not set VIRTIO_NET_F_SPEED_DUPLEX flag (hence
don't remove above check).

2) if speed or duplex or speed is set in the qemu command line, then set
the VIRTIO_NET_F_SPEED_DUPLEX and have host control the settings of
speed/duplex (with ability of guest to over-write if it wanted to).

I agree - I don't see a reason to touch the speed/duplex values when
VIRTIO_NET_F_SPEED_DUPLEX has not been negotiated.

quoted

quoted

quoted

+		u32 speed;
+		u8 duplex;
+
+		speed = virtio_cread32(vi->vdev,
+				       offsetof(struct virtio_net_config,
+						speed));
+		if (ethtool_validate_speed(speed))
+			vi->speed = speed;
+		duplex = virtio_cread8(vi->vdev,
+				       offsetof(struct virtio_net_config,
+						duplex));
+		if (ethtool_validate_duplex(duplex))
+			vi->duplex = duplex;
+	}
+
 	if (vi->status & VIRTIO_NET_S_LINK_UP) {
 		netif_carrier_on(vi->dev);
 		netif_tx_wake_all_queues(vi->dev);

OK so this handles the case when VIRTIO_NET_F_STATUS is set,
but when it's clear we need to call this from virtnet_probe.

I propose moving this chunk to a function and calling from two places.

good point. will update.

Thanks,

-Jason

quoted

quoted

@@ -2796,7 +2812,8 @@ static struct virtio_device_id id_table[] = {
 	VIRTIO_NET_F_CTRL_RX, VIRTIO_NET_F_CTRL_VLAN, \
 	VIRTIO_NET_F_GUEST_ANNOUNCE, VIRTIO_NET_F_MQ, \
 	VIRTIO_NET_F_CTRL_MAC_ADDR, \
-	VIRTIO_NET_F_MTU, VIRTIO_NET_F_CTRL_GUEST_OFFLOADS
+	VIRTIO_NET_F_MTU, VIRTIO_NET_F_CTRL_GUEST_OFFLOADS, \
+	VIRTIO_NET_F_SPEED_DUPLEX
 
 static unsigned int features[] = {
 	VIRTNET_FEATURES,

diff --git a/include/uapi/linux/virtio_net.h b/include/uapi/linux/virtio_net.h
index fc353b5..5de6ed3 100644
--- a/include/uapi/linux/virtio_net.h
+++ b/include/uapi/linux/virtio_net.h

@@ -57,6 +57,8 @@
 					 * Steering */
 #define VIRTIO_NET_F_CTRL_MAC_ADDR 23	/* Set MAC address */
 
+#define VIRTIO_NET_F_SPEED_DUPLEX 63	/* Device set linkspeed and duplex */
+
 #ifndef VIRTIO_NET_NO_LEGACY
 #define VIRTIO_NET_F_GSO	6	/* Host handles pkts w/ any GSO type */
 #endif /* VIRTIO_NET_NO_LEGACY */

@@ -76,6 +78,17 @@ struct virtio_net_config {
 	__u16 max_virtqueue_pairs;
 	/* Default maximum transmit unit advice */
 	__u16 mtu;
+	/*
+	 * speed, in units of 1Mb. All values 0 to INT_MAX are legal.
+	 * Any other value stands for unknown.
+	 */
+	__u32 speed;
+	/*
+	 * 0x00 - half duplex
+	 * 0x01 - full duplex
+	 * Any other value stands for unknown.
+	 */
+	__u8 duplex;
 } __attribute__((packed));
 
 /*

-- 
2.6.1