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

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Date:   Thu, 21 Nov 2019 12:06:01 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     Jason Gunthorpe <jgg@...pe.ca>
Cc:     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>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Alex Williamson <alex.williamson@...hat.com>,
        Tiwei Bie <tiwei.bie@...el.com>
Subject: Re: [net-next v2 1/1] virtual-bus: Implementation of Virtual Bus


On 2019/11/20 下午9:41, Jason Gunthorpe wrote:
> On Wed, Nov 20, 2019 at 12:07:59PM +0800, Jason Wang wrote:
>
>> 1) create sub fucntion and do must to have pre configuration through devlink
>> 2) only after sub function is created one more available instance was added
>> and shown through sysfs
>> 3) user can choose to create and use that mdev instance as it did for other
>> type of device like vGPU
>> 4) devlink can still use to report other stuffs
> Why do we want the extra step #3? The user already indicated they want
> a mdev via #1


It's about the compatibility, but if you wish, I think we can develop 
devlink based lifecycle for mdev for sure.


>
> I have the same question for the PF and VF cases, why doesn't a mdev
> get created automatically when the VF is probed? Why does this need
> the guid stuff?


All you said here is possible, it's a design choice for the management 
interface.


>
> The guid stuff was intended for, essentially, multi-function devices
> that could be sliced up, I don't think it makes sense to use it for
> single-function VF devices like the ICF driver.


It doesn't harm, and indeed we have other choice, we can do it gradually 
on top.


>
> Overall the guid thing should be optional. Drivers providing mdev
> should be able to use another scheme, like devlink, to on demand
> create their mdevs.


Yes, that's for sure. I'm not against to devlink for mdev/subdev, I just 
say we should not make devlink the only choice for mdev/subdev.

Thanks


>
> Jason
>