netdev - Re: [net-next v2 1/1] virtual-bus: Implementation of Virtual Bus

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Date:   Wed, 20 Nov 2019 21:38:17 -0400
From:   Jason Gunthorpe <jgg@...pe.ca>
To:     "Michael S. Tsirkin" <mst@...hat.com>
Cc:     Jason Wang <jasowang@...hat.com>,
        Parav Pandit <parav@...lanox.com>,
        Jeff Kirsher <jeffrey.t.kirsher@...el.com>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        Dave Ertman <david.m.ertman@...el.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-rdma@...r.kernel.org" <linux-rdma@...r.kernel.org>,
        "nhorman@...hat.com" <nhorman@...hat.com>,
        "sassmann@...hat.com" <sassmann@...hat.com>,
        Kiran Patil <kiran.patil@...el.com>,
        Alex Williamson <alex.williamson@...hat.com>,
        "Bie, Tiwei" <tiwei.bie@...el.com>
Subject: Re: [net-next v2 1/1] virtual-bus: Implementation of Virtual Bus

On Wed, Nov 20, 2019 at 05:05:00PM -0500, Michael S. Tsirkin wrote:
> On Wed, Nov 20, 2019 at 12:45:25PM -0400, Jason Gunthorpe wrote:
> > > > For instance, this VFIO based approach might be very suitable to the
> > > > intel VF based ICF driver, but we don't yet have an example of non-VF
> > > > HW that might not be well suited to VFIO.
> > >
> > > I don't think we should keep moving the goalposts like this.
> > 
> > It is ABI, it should be done as best we can as we have to live with it
> > for a long time. Right now HW is just starting to come to market with
> > VDPA and it feels rushed to design a whole subsystem style ABI around
> > one, quite simplistic, driver example.
> 
> Well one has to enable hardware in some way. It's not really reasonable
> to ask for multiple devices to be available just so there's a driver and
> people can use them.

Er, this has actually been a fairly standard ask for new subsystems.

I think virtio is well grounded here compared to other things I've
seen, but it should still be done with a lot more NIC community involvement.

> At this rate no one will want to be the first to ship new devices ;)

Why?
 
> > > If people write drivers and find some infrastruture useful,
> > > and it looks more or less generic on the outset, then I don't
> > > see why it's a bad idea to merge it.
> > 
> > Because it is userspace ABI, caution is always justified when defining
> > new ABI.
> 
> Reasonable caution, sure. Asking Alex to block Intel's driver until
> someone else catches up and ships competing hardware isn't reasonable
> though. If that's your proposal I guess we'll have to agree to disagree.

Vendors may be willing to participate, as Mellanox is doing,
pre-product.

Jason