Re: [PATCH linux-next v3 0/6] vdpa: enable user to set mac, mtu

["Michael S. Tsirkin" <mst@redhat.com>]

On Fri, Aug 06, 2021 at 08:55:56AM +0000, Parav Pandit wrote:
> 
> 
> > From: Michael S. Tsirkin <mst@redhat.com>
> > Sent: Friday, August 6, 2021 2:12 PM
> 
> 
> > >  enum vdpa_attr {
> > > @@ -33,6 +34,16 @@ enum vdpa_attr {
> > >  	VDPA_ATTR_DEV_MAX_VQS,			/* u32 */
> > >  	VDPA_ATTR_DEV_MAX_VQ_SIZE,		/* u16 */
> > > +	VDPA_ATTR_DEV_NET_CFG_MACADDR,		/* binary */
> > > +	VDPA_ATTR_DEV_NET_STATUS,		/* u8 */
> > > +	VDPA_ATTR_DEV_NET_CFG_MAX_VQP,		/* u16 */
> > > +	VDPA_ATTR_DEV_NET_CFG_MTU,		/* u16 */
> > > +	VDPA_ATTR_DEV_NET_CFG_SPEED,		/* u16 */
> > > +	VDPA_ATTR_DEV_NET_CFG_DUPLEX,		/* u16 */
> > > +	VDPA_ATTR_DEV_NET_CFG_RSS_MAX_KEY_LEN,	/* u8 */
> > > +	VDPA_ATTR_DEV_NET_CFG_RSS_MAX_IT_LEN,	/* u16 */
> > > +	VDPA_ATTR_DEV_NET_CFG_RSS_HASH_TYPES,	/* u32 */
> > > +
> > >  	/* new attributes must be added above here */
> > >  	VDPA_ATTR_MAX,
> > >  };
> > 
> > The point is to try and not reinvent a dedicated vpda interface where a
> > generic one exits.
> > E.g. for phy things such as mac speed etc, I think most people are using
> > ethtool things right?
> 
> As you know vdpa is the backend device for the front-end netdevice accessed by the ethtool.
> vdpa management tool here is composing the vdpa device.
> 
> For example creator (hypervisor) of the vdpa devices knows that a guest VM is given 4 vcpus,
> So hypervisor creates a vdpa devices with config space layout as,
> max_virtqueue_pairs = 4.
> And the MAC address chosen by hypervisor in mac[6].
> 
> Guest VM ethtool can still chose to use less number of channels.
> 
> Typically,
> ethtool is for guest VM.
> vdpa device is in hypevisor.
> 
> How can hypervisor compose a vdpa device without any tool?
> How can it tell ethtool, what is supported and what are the defaults?
> 
> I must be misunderstanding your comment about ethtool.
> Can you please explain?


I am basically saying that we probably want to be able to
change MAC of a VDPA device on the host without desroying and recreating the device
as long as it's not in use.

For a VF I can do this on the host:

ip link set eth0 vf 1 mac 00:11:22:33:44:55

ideally same thing would work for vdpa.

-- 
MST

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