On 3/29/2017 4:36 PM, Yuanhan Liu wrote:

On Wed, Mar 29, 2017 at 04:33:20PM +0800, Tan, Jianfeng wrote:

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On 3/29/2017 4:00 PM, Yuanhan Liu wrote:

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On Wed, Mar 29, 2017 at 03:48:04PM +0800, Tan, Jianfeng wrote:

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On 3/29/2017 3:14 PM, Yuanhan Liu wrote:

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On Wed, Mar 29, 2017 at 03:07:28PM +0800, Tan, Jianfeng wrote:

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On 3/29/2017 2:33 PM, Yuanhan Liu wrote:

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On Mon, Mar 27, 2017 at 07:46:32AM +0000, Tan, Jianfeng wrote:

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diff --git a/drivers/net/virtio/virtio_user/virtio_user_dev.c

b/drivers/net/virtio/virtio_user/virtio_user_dev.c

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index 9777d6b..cc6f557 100644

--- a/drivers/net/virtio/virtio_user/virtio_user_dev.c
+++ b/drivers/net/virtio/virtio_user/virtio_user_dev.c

@@ -176,6 +176,7 @@ virtio_user_start_device(struct virtio_user_dev

*dev, uint8_t portid)

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  	features &= ~(1ull << VIRTIO_NET_F_MAC);
  	/* Strip VIRTIO_NET_F_CTRL_VQ, as devices do not really need to

know */

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  	features &= ~(1ull << VIRTIO_NET_F_CTRL_VQ);
+	features &= ~(1ull << VIRTIO_NET_F_STATUS);
  	ret = dev->ops->send_request(dev, VHOST_USER_SET_FEATURES,

&features);

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  	if (ret < 0)
  		goto error;

diff --git a/drivers/net/virtio/virtio_user_ethdev.c

b/drivers/net/virtio/virtio_user_ethdev.c

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index fa79419..fbdd0a8 100644

--- a/drivers/net/virtio/virtio_user_ethdev.c
+++ b/drivers/net/virtio/virtio_user_ethdev.c

@@ -121,7 +121,8 @@ virtio_user_get_features(struct virtio_hw *hw)
  	struct virtio_user_dev *dev = virtio_user_get_dev(hw);

  	/* unmask feature bits defined in vhost user protocol */
-	return dev->device_features &

VIRTIO_PMD_SUPPORTED_GUEST_FEATURES;

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+	return (dev->device_features | (1 << VIRTIO_NET_F_STATUS))
+		& VIRTIO_PMD_SUPPORTED_GUEST_FEATURES;

Why not handle the features at virtio_user_dev_init()?

You mean add VIRTIO_NET_F_STATUS when get_features from device? Yes, we could do that there. But we originally add device_features to only record features supported by device.

Aren't you adding the F_STATUS features to this device?

For virtio driver, yes, we are adding F_STATUS feature so the it sees a
device supporting LSC.

That means you are adding a device feature (F_STATUS) and reporting it to
the driver that this feature is always on, no matter whether the device
actually supports it or not? This looks wrong to me.

Why?

Because you were doing hack to make virtio-user work, while there is no
such hack in the QEMU virtio-pci implementation.

quoted

IMO, device is not necessary to know this feature.

F_STATUS is a device feature. If such feature is not claimed to be
supported by the device, the driver should ignore it. But you are
unconditionally letting the driver handle it, even though  the
virito-user device does not claim to support it.

Note that F_STATUS is set in the QEMU virtio-net PCI device.

In QEMU virtio-net PCI device, the device includes QEMU device emulation +
vhost backend driver. This feature only shows at QEMU device emulation,
instead of vhost backend driver. This is why we did not see this feature at
any vhost backends.
And the embedded virtio-user actually substitutes QEMU device emulation
part, so this feature should end at this layer.

Let's look this in this way, if we let this feature go through to vhost
user, it will be treated as an error in vhost_user_set_features().

Again, why can't we (virtio-user) follow QEMU?

Through F2F discussion, I got to know that you treat 
virtio_user_ethdev.c as front driver part. That makes sense. I'll move 
this change into vhost-user directory.

Thanks,
Jianfeng