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

["Tan, Jianfeng" <jianfeng.tan@intel.com>]

On 3/29/2017 4:36 PM, Yuanhan Liu wrote:
> On Wed, Mar 29, 2017 at 04:33:20PM +0800, Tan, Jianfeng wrote:
>>
>> 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().
> 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