netdev - Re: [PATCH V2 3/6] vDPA: allow userspace to query features of a vDPA device

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Message-ID: <9ed635bf-1c92-f3c6-f6c6-5715a5a5ac92@intel.com>
Date:   Tue, 14 Jun 2022 10:53:10 +0800
From:   "Zhu, Lingshan" <lingshan.zhu@...el.com>
To:     Parav Pandit <parav@...dia.com>,
        "jasowang@...hat.com" <jasowang@...hat.com>,
        "mst@...hat.com" <mst@...hat.com>
Cc:     "virtualization@...ts.linux-foundation.org" 
        <virtualization@...ts.linux-foundation.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "xieyongji@...edance.com" <xieyongji@...edance.com>,
        "gautam.dawar@....com" <gautam.dawar@....com>
Subject: Re: [PATCH V2 3/6] vDPA: allow userspace to query features of a vDPA
 device



On 6/14/2022 4:42 AM, Parav Pandit wrote:
>
>> From: Zhu Lingshan <lingshan.zhu@...el.com>
>> Sent: Monday, June 13, 2022 6:17 AM
>> device
>>
>> 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@...el.com>
>> ---
>>   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 */
> I see now what was done incorrectly with commit cd2629f6df1ca.
>
> Above was done with wrong name prefix that missed MGMTDEV_. :(
> Please don't add VDPA_ prefix due to one mistake.
> Please reuse this VDPA_ATTR_DEV_SUPPORTED_FEATURES for device attribute as well.
currently we can reuse VDPA_ATTR_DEV_SUPPORTED_FEATURES to report device 
features for sure,
however this could confuse the readers since every attr should has its 
own unique
purpose.

I think if we add a new attr is a better practice and can avoid some 
potential bugs.
So I suggest we add a new attr for the device features, maybe 
VDPA_ATTR_VDPA_DEV_SUPPORTED_FEATURES
is not a pretty name, any suggestions?

Thanks,
Zhu Lingshan
>
>> +	VDPA_ATTR_VDPA_DEV_SUPPORTED_FEATURES,	/* u64 */
>>
>>   	VDPA_ATTR_DEV_QUEUE_INDEX,              /* u32 */
>>   	VDPA_ATTR_DEV_VENDOR_ATTR_NAME,		/* string */
>> --
>> 2.31.1