Re: [PATCH 1/2] vDPA: allow userspace to query features of a vDPA device

["Zhu, Lingshan" <lingshan.zhu@intel.com>]

On 8/16/2022 10:07 AM, Parav Pandit wrote:
>> From: Zhu, Lingshan <lingshan.zhu@intel.com>
>> Sent: Monday, August 15, 2022 9:49 PM
>>
>> On 8/16/2022 2:15 AM, Si-Wei Liu wrote:
>>>
>>> On 8/15/2022 2:26 AM, 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@intel.com>
>>>> ---
>>>>    drivers/vdpa/vdpa.c       | 17 +++++++++++++----
>>>>    include/uapi/linux/vdpa.h |  3 +++
>>>>    2 files changed, 16 insertions(+), 4 deletions(-)
>>>>
>>>> diff --git a/drivers/vdpa/vdpa.c b/drivers/vdpa/vdpa.c index
>>>> c06c02704461..efb55a06e961 100644
>>>> --- a/drivers/vdpa/vdpa.c
>>>> +++ b/drivers/vdpa/vdpa.c
>>>> @@ -491,6 +491,8 @@ static int vdpa_mgmtdev_fill(const struct
>>>> vdpa_mgmt_dev *mdev, struct sk_buff *m
>>>>            err = -EMSGSIZE;
>>>>            goto msg_err;
>>>>        }
>>>> +
>>>> +    /* report features of a vDPA management device through
>>>> VDPA_ATTR_DEV_SUPPORTED_FEATURES */
>>>>        if (nla_put_u64_64bit(msg, VDPA_ATTR_DEV_SUPPORTED_FEATURES,
>>>>                      mdev->supported_features, VDPA_ATTR_PAD)) {
>>>>            err = -EMSGSIZE;
>>>> @@ -815,7 +817,7 @@ 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 +834,19 @@ 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);
>>>> +
>>>> +    /* report features of a vDPA device through
>>>> VDPA_ATTR_VDPA_DEV_SUPPORTED_FEATURES */
>>>> +    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..d171b92ef522 100644
>>>> --- a/include/uapi/linux/vdpa.h
>>>> +++ b/include/uapi/linux/vdpa.h
>>>> @@ -46,7 +46,10 @@ enum vdpa_attr {
>>>>          VDPA_ATTR_DEV_NEGOTIATED_FEATURES,    /* u64 */
>>>>        VDPA_ATTR_DEV_MGMTDEV_MAX_VQS,        /* u32 */
>>>> +    /* features of a vDPA management device */
> Say comment as.
>        /* Features of the vDPA management device matching the virtio feature bits 0 to 63 when queried on the mgmt. device.
>          *  When returned on the vdpa device, it indicates virtio feature bits 0 to 63 of the vdpa device
>          */
This still suggests to re-use the attr VDPA_ATTR_DEV_SUPPORTED_FEATURES, 
I think a new attr should be better and easier
for others.
>
>>>>        VDPA_ATTR_DEV_SUPPORTED_FEATURES,    /* u64 */
>>>> +    /* features of a vDPA device, e.g., /dev/vhost-vdpa0 */
>>>> +    VDPA_ATTR_VDPA_DEV_SUPPORTED_FEATURES,    /* u64 */
>>> Append to the end, please. Otherwise it breaks userspace ABI.
>> OK, will fix it in V2
> I have read Se-Wei comment in the v4.
> However I disagree, we don’t need to continue the past mistake done with the naming.
>
> Please add a comment that VDPA_ATTR_DEV_SUPPORTED_FEATURES like above about the exception.
> We established that there is no race condition either.
> So no need to add new UAPI for some past history.
Yes, no race conditions, the thing is, it is not a good practice to 
re-use a netlink attr,
every attr should has its own purpose, no need to confuse others, I 
think we had this discussion before.

Thanks