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

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Message-ID: <PH0PR12MB5481EC56E9951B99B98A6668DC6B9@PH0PR12MB5481.namprd12.prod.outlook.com>
Date:   Tue, 16 Aug 2022 02:07:42 +0000
From:   Parav Pandit <parav@...dia.com>
To:     "Zhu, Lingshan" <lingshan.zhu@...el.com>,
        Si-Wei Liu <si-wei.liu@...cle.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>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "xieyongji@...edance.com" <xieyongji@...edance.com>,
        "gautam.dawar@....com" <gautam.dawar@....com>
Subject: RE: [PATCH 1/2] vDPA: allow userspace to query features of a vDPA
 device


> From: Zhu, Lingshan <lingshan.zhu@...el.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@...el.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 
        */

> >>       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.