On Tue, Jul 26, 2022 at 03:54:06PM +0000, Parav Pandit wrote:

quoted

From: Michael S. Tsirkin <mst@redhat.com>
Sent: Wednesday, July 13, 2022 1:27 AM

On Fri, Jul 01, 2022 at 10:07:59PM +0000, Parav Pandit wrote:

quoted

quoted

From: Zhu Lingshan <redacted>
Sent: Friday, July 1, 2022 9:28 AM
If VIRTIO_NET_F_MQ == 0, the virtio device should have one queue
pair, so when userspace querying queue pair numbers, it should
return mq=1 than zero.

Function vdpa_dev_net_config_fill() fills the attributions of the
vDPA devices, so that it should call vdpa_dev_net_mq_config_fill()
so the parameter in vdpa_dev_net_mq_config_fill() should be
feature_device than feature_driver for the vDPA devices themselves

Before this change, when MQ = 0, iproute2 output:
$vdpa dev config show vdpa0
vdpa0: mac 00:e8:ca:11:be:05 link up link_announce false
max_vq_pairs 0 mtu 1500

The fix belongs to user space.
When a feature bit _MQ is not negotiated, vdpa kernel space will not add

attribute VDPA_ATTR_DEV_NET_CFG_MAX_VQP.

quoted

When such attribute is not returned by kernel, max_vq_pairs should not be

shown by the iproute2.

quoted

We have many config space fields that depend on the feature bits and

some of them do not have any defaults.

quoted

To keep consistency of existence of config space fields among all, we don't

want to show default like below.

quoted

Please fix the iproute2 to not print max_vq_pairs when it is not returned by

the kernel.

Parav I read the discussion and don't get your argument. From driver's POV
_MQ with 1 VQ pair and !_MQ are exactly functionally equivalent.

But we are talking from user POV here.

From spec POV there's just driver and device, user would be part of
driver here.

quoted

It's true that iproute probably needs to be fixed too, to handle old kernels.
But iproute is not the only userspace, why not make it's life easier by fixing
the kernel?

Because it cannot be fixed for other config space fields which are control by feature bits those do not have any defaults.
So better to treat all in same way from user POV.

Consistency is good for sure. What are these other fields though?
Can you give examples so I understand please?

-- 
MST