Virtualization - Jun 2022 - [PATCH V2 5/6] vDPA: answer num of queue pairs = 1 to userspace when VIRTIO_NET_F_MQ == 0

> From: Zhu Lingshan <lingshan.zhu at intel.com>
> Sent: Monday, June 13, 2022 6:17 AM
> To: jasowang at redhat.com; mst at redhat.com
> Cc: virtualization at lists.linux-foundation.org; netdev at
vger.kernel.org; Parav
> Pandit <parav at nvidia.com>; xieyongji at bytedance.com;
> gautam.dawar at amd.com; Zhu Lingshan <lingshan.zhu at intel.com>
> Subject: [PATCH V2 5/6] vDPA: answer num of queue pairs = 1 to userspace
> when VIRTIO_NET_F_MQ == 0
> 
> 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
> 
Max_vq_pairs should not be printed when _MQ feature is not negotiated.
Existing code that returns 0 is correct following this line of the spec.

" The following driver-read-only field, max_virtqueue_pairs only exists if
VIRTIO_NET_F_MQ or VIRTIO_-
NET_F_RSS is set."
The field doesn't exist when _MQ is not there. Hence, it should not be
printed.
Is _RSS offered and is that why you see it?

If not a fix in the iproute2/vdpa should be done.

> After applying this commit, 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 1
> mtu 1500
> 
> Signed-off-by: Zhu Lingshan <lingshan.zhu at intel.com>
> ---
>  drivers/vdpa/vdpa.c | 7 ++++---
>  1 file changed, 4 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/vdpa/vdpa.c b/drivers/vdpa/vdpa.c index
> d76b22b2f7ae..846dd37f3549 100644
> --- a/drivers/vdpa/vdpa.c
> +++ b/drivers/vdpa/vdpa.c
> @@ -806,9 +806,10 @@ static int vdpa_dev_net_mq_config_fill(struct
> vdpa_device *vdev,
>  	u16 val_u16;
> 
>  	if ((features & BIT_ULL(VIRTIO_NET_F_MQ)) == 0)
> -		return 0;
> +		val_u16 = 1;
> +	else
> +		val_u16 = __virtio16_to_cpu(true, config-
> >max_virtqueue_pairs);
> 
> -	val_u16 = le16_to_cpu(config->max_virtqueue_pairs);
>  	return nla_put_u16(msg, VDPA_ATTR_DEV_NET_CFG_MAX_VQP,
> val_u16);  }
> 
> @@ -842,7 +843,7 @@ static int vdpa_dev_net_config_fill(struct
> vdpa_device *vdev, struct sk_buff *ms
>  			      VDPA_ATTR_PAD))
>  		return -EMSGSIZE;
> 
> -	return vdpa_dev_net_mq_config_fill(vdev, msg, features_driver,
> &config);
> +	return vdpa_dev_net_mq_config_fill(vdev, msg, features_device,
> +&config);
>  }
> 
>  static int
> --
> 2.31.1