Virtualization - Aug 2022 - [PATCH V4 3/6] vDPA: allow userspace to query features of a vDPA device

On Fri, Jul 22, 2022 at 07:53:06PM +0800, Zhu Lingshan
wrote:
> This commit adds a new vDPA netlink attribution
> VDPA_ATTR_VDPA_DEV_SUPPORTED_FEATURES. Userspace can query
> features of vDPA devices through this new attr.
> 
> Signed-off-by: Zhu Lingshan <lingshan.zhu at intel.com>

I think at least some discussion and documentation
of this attribute versus VDPA_ATTR_DEV_SUPPORTED_FEATURES
is called for.

Otherwise how do people know which one to use?

We can't send everyone to go read the lkml thread.
> ---
>  drivers/vdpa/vdpa.c       | 13 +++++++++----
>  include/uapi/linux/vdpa.h |  1 +
>  2 files changed, 10 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/vdpa/vdpa.c b/drivers/vdpa/vdpa.c
> index ebf2f363fbe7..9b0e39b2f022 100644
> --- a/drivers/vdpa/vdpa.c
> +++ b/drivers/vdpa/vdpa.c
> @@ -815,7 +815,7 @@ static int vdpa_dev_net_mq_config_fill(struct
vdpa_device *vdev,
>  static int vdpa_dev_net_config_fill(struct vdpa_device *vdev, struct
sk_buff *msg)
>  {
>  	struct virtio_net_config config = {};
> -	u64 features;
> +	u64 features_device, features_driver;
>  	u16 val_u16;
>  
>  	vdpa_get_config_unlocked(vdev, 0, &config, sizeof(config));
> @@ -832,12 +832,17 @@ static int vdpa_dev_net_config_fill(struct
vdpa_device *vdev, struct sk_buff *ms
>  	if (nla_put_u16(msg, VDPA_ATTR_DEV_NET_CFG_MTU, val_u16))
>  		return -EMSGSIZE;
>  
> -	features = vdev->config->get_driver_features(vdev);
> -	if (nla_put_u64_64bit(msg, VDPA_ATTR_DEV_NEGOTIATED_FEATURES, features,
> +	features_driver = vdev->config->get_driver_features(vdev);
> +	if (nla_put_u64_64bit(msg, VDPA_ATTR_DEV_NEGOTIATED_FEATURES,
features_driver,
> +			      VDPA_ATTR_PAD))
> +		return -EMSGSIZE;
> +
> +	features_device = vdev->config->get_device_features(vdev);
> +	if (nla_put_u64_64bit(msg, VDPA_ATTR_VDPA_DEV_SUPPORTED_FEATURES,
features_device,
>  			      VDPA_ATTR_PAD))
>  		return -EMSGSIZE;
>  
> -	return vdpa_dev_net_mq_config_fill(vdev, msg, features, &config);
> +	return vdpa_dev_net_mq_config_fill(vdev, msg, features_driver,
&config);
>  }
>  
>  static int
> diff --git a/include/uapi/linux/vdpa.h b/include/uapi/linux/vdpa.h
> index 25c55cab3d7c..39f1c3d7c112 100644
> --- a/include/uapi/linux/vdpa.h
> +++ b/include/uapi/linux/vdpa.h
> @@ -47,6 +47,7 @@ enum vdpa_attr {
>  	VDPA_ATTR_DEV_NEGOTIATED_FEATURES,	/* u64 */
>  	VDPA_ATTR_DEV_MGMTDEV_MAX_VQS,		/* u32 */
>  	VDPA_ATTR_DEV_SUPPORTED_FEATURES,	/* u64 */
> +	VDPA_ATTR_VDPA_DEV_SUPPORTED_FEATURES,	/* u64 */
>  
>  	VDPA_ATTR_DEV_QUEUE_INDEX,              /* u32 */
>  	VDPA_ATTR_DEV_VENDOR_ATTR_NAME,		/* string */
> -- 
> 2.31.1

> From: Michael S. Tsirkin <mst at redhat.com>
> Sent: Tuesday, August 9, 2022 3:24 PM
> 
> On Fri, Jul 22, 2022 at 07:53:06PM +0800, Zhu Lingshan wrote:
> > This commit adds a new vDPA netlink attribution
> > VDPA_ATTR_VDPA_DEV_SUPPORTED_FEATURES. Userspace can query
> features of
> > vDPA devices through this new attr.
> >
> > Signed-off-by: Zhu Lingshan <lingshan.zhu at intel.com>
> 
> 
> I think at least some discussion and documentation of this attribute versus
> VDPA_ATTR_DEV_SUPPORTED_FEATURES is called for.
> 
> Otherwise how do people know which one to use?
> 
> We can't send everyone to go read the lkml thread.
There is no race here. Commit log is missing example anyway.
I explained multiple times that this patch and/or its previous version cannot
proceed in same state.