[dpdk-dev] [PATCH 3/5] net/virtio-user: support to report net status

[Tan, Jianfeng]

On 3/29/2017 4:00 PM, Yuanhan Liu wrote:
> On Wed, Mar 29, 2017 at 03:48:04PM +0800, Tan, Jianfeng wrote:
>>
>> On 3/29/2017 3:14 PM, Yuanhan Liu wrote:
>>> On Wed, Mar 29, 2017 at 03:07:28PM +0800, Tan, Jianfeng wrote:
>>>> On 3/29/2017 2:33 PM, Yuanhan Liu wrote:
>>>>> On Mon, Mar 27, 2017 at 07:46:32AM +0000, Tan, Jianfeng wrote:
>>>>>>>> diff --git a/drivers/net/virtio/virtio_user/virtio_user_dev.c
>>>>>>> b/drivers/net/virtio/virtio_user/virtio_user_dev.c
>>>>>>>> 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)
>>>>>>>>   	features &= ~(1ull << VIRTIO_NET_F_MAC);
>>>>>>>>   	/* Strip VIRTIO_NET_F_CTRL_VQ, as devices do not really need to
>>>>>>> know */
>>>>>>>>   	features &= ~(1ull << VIRTIO_NET_F_CTRL_VQ);
>>>>>>>> +	features &= ~(1ull << VIRTIO_NET_F_STATUS);
>>>>>>>>   	ret = dev->ops->send_request(dev, VHOST_USER_SET_FEATURES,
>>>>>>> &features);
>>>>>>>>   	if (ret < 0)
>>>>>>>>   		goto error;
>>>>>>>> diff --git a/drivers/net/virtio/virtio_user_ethdev.c
>>>>>>> b/drivers/net/virtio/virtio_user_ethdev.c
>>>>>>>> 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;
>>>>>>>> +	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.
>
>> 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().

Thanks,
Jianfeng

>
> 	--yliu
>
>> For vhost-user,
>> except explicitly cutting down the unix connection, I don't see a message of
>> vhost-user protocol to report that.
>>
>>>> But for backend driver, we need hide this feature, it
>>>> happens when we set_features to the backend driver.
>>> The feature negotion of virtio-user seems broken to me.
>>>
>>>
>> Why?
>> vhost does not claim to support this feature, VHOST_SUPPORTED_FEATURES.
>>
>> Thanks,
>> Jianfeng