netdev - RE: [PATCH linux-next v3 6/6] vdpa_sim_net: Add support for user supported devices

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Message-ID: <BY5PR12MB4322EC8D0AD648063C607E17DCAF0@BY5PR12MB4322.namprd12.prod.outlook.com>
Date:   Thu, 7 Jan 2021 03:48:18 +0000
From:   Parav Pandit <parav@...dia.com>
To:     "Michael S. Tsirkin" <mst@...hat.com>
CC:     "virtualization@...ts.linux-foundation.org" 
        <virtualization@...ts.linux-foundation.org>,
        "jasowang@...hat.com" <jasowang@...hat.com>,
        Eli Cohen <elic@...dia.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: RE: [PATCH linux-next v3 6/6] vdpa_sim_net: Add support for user
 supported devices



> From: Michael S. Tsirkin <mst@...hat.com>
> Sent: Tuesday, January 5, 2021 6:53 PM
> 
> On Tue, Jan 05, 2021 at 12:30:15PM +0000, Parav Pandit wrote:
> >
> >
> > > From: Michael S. Tsirkin <mst@...hat.com>
> > > Sent: Tuesday, January 5, 2021 5:45 PM
> > >
> > > On Tue, Jan 05, 2021 at 12:02:33PM +0000, Parav Pandit wrote:
> > > >
> > > >
> > > > > From: Michael S. Tsirkin <mst@...hat.com>
> > > > > Sent: Tuesday, January 5, 2021 5:19 PM
> > > > >
> > > > > On Tue, Jan 05, 2021 at 12:32:03PM +0200, Parav Pandit wrote:
> > > > > > Enable user to create vdpasim net simulate devices.
> > > > > >
> > > > > >
> > > >
> > > > > > $ vdpa dev add mgmtdev vdpasim_net name foo2
> > > > > >
> > > > > > Show the newly created vdpa device by its name:
> > > > > > $ vdpa dev show foo2
> > > > > > foo2: type network mgmtdev vdpasim_net vendor_id 0 max_vqs 2
> > > > > > max_vq_size 256
> > > > > >
> > > > > > $ vdpa dev show foo2 -jp
> > > > > > {
> > > > > >     "dev": {
> > > > > >         "foo2": {
> > > > > >             "type": "network",
> > > > > >             "mgmtdev": "vdpasim_net",
> > > > > >             "vendor_id": 0,
> > > > > >             "max_vqs": 2,
> > > > > >             "max_vq_size": 256
> > > > > >         }
> > > > > >     }
> > > > > > }
> > > > >
> > > > >
> > > > > I'd like an example of how do device specific (e.g. net
> > > > > specific) interfaces tie in to this.
> > > > Not sure I follow your question.
> > > > Do you mean how to set mac address or mtu of this vdpa device of
> > > > type
> > > net?
> > > > If so, dev add command will be extended shortly in subsequent
> > > > series to
> > > set this net specific attributes.
> > > > (I did mention in the next steps in cover letter).
> > > >
> > > > > > +static int __init vdpasim_net_init(void) {
> > > > > > +	int ret;
> > > > > > +
> > > > > > +	if (macaddr) {
> > > > > > +		mac_pton(macaddr, macaddr_buf);
> > > > > > +		if (!is_valid_ether_addr(macaddr_buf))
> > > > > > +			return -EADDRNOTAVAIL;
> > > > > > +	} else {
> > > > > > +		eth_random_addr(macaddr_buf);
> > > > > >  	}
> > > > >
> > > > > Hmm so all devices start out with the same MAC until changed?
> > > > > And how is the change effected?
> > > > Post this patchset and post we have iproute2 vdpa in the tree,
> > > > will add the
> > > mac address as the input attribute during "vdpa dev add" command.
> > > > So that each different vdpa device can have user specified
> > > > (different) mac
> > > address.
> > >
> > > For now maybe just avoid VIRTIO_NET_F_MAC then for new devices
> then?
> >
> > That would require book keeping existing net vdpa_sim devices created to
> avoid setting VIRTIO_NET_F_MAC.
> > Such book keeping code will be short lived anyway.
> > Not sure if its worth it.
> > Until now only one device was created. So not sure two vdpa devices with
> same mac address will be a real issue.
> >
> > When we add mac address attribute in add command, at that point also
> remove the module parameter macaddr.
> 
> Will that be mandatory? I'm not to happy with a UAPI we intend to break
> straight away ...
No. Specifying mac address shouldn't be mandatory. UAPI wont' be broken.