Re: vDPA bus driver selection

From: Jason Wang <jasowang@redhat.com>
To: Parav Pandit <parav@nvidia.com>
Cc: Eli Cohen <elic@nvidia.com>, Michael Tsirkin <mst@redhat.com>,
	Linux Virtualization <virtualization@lists.linux-foundation.org>
Subject: Re: vDPA bus driver selection
Date: Fri, 29 Oct 2021 10:34:00 +0800	[thread overview]
Message-ID: <CACGkMEt+iwKc=O552rsMUWdmT1MGVpUJrKsjdjv7mv=4uX1uOQ@mail.gmail.com> (raw)
In-Reply-To: <PH0PR12MB54813F6CFDF8A1E1F7AE68B8DC869@PH0PR12MB5481.namprd12.prod.outlook.com>

On Thu, Oct 28, 2021 at 5:48 PM Parav Pandit <parav@nvidia.com> wrote:
>
>
>
> > From: Stefano Garzarella <sgarzare@redhat.com>
> > Sent: Thursday, October 28, 2021 3:08 PM
>
> > >> >$ vdpa/vdpa dev add mgmtdev vdpasim_net name vdpa0 mac
> > >> >00:11:22:33:44:55 $ echo 0 > /sys/bus/vdpa/drivers_autoprobe
> > >> >
> > >> >And after vdpa device creation, it manually binds to the desired
> > >> >driver such as,
> > >> >
> > >> >$ echo vdpa0 > /sys/bus/vdpa/drivers/virtio_vdpa/bind
> > >> >Or
> > >> >$ echo vdpa0 > /sys/bus/vdpa/drivers/vhost_vdpa/bind
> > >>
> > >> Cool, I didn't know that. This is very useful, but do you think it
> > >> might be better to integrate it with the netlink API and specify at
> > >> creation which bus driver to use?
> > >I think it is useful; for vduse case we need the ability to say "none"
> > >as well and when nothing specified it should be default driver.
> >
> > Yep, the default can be the actual behaviour.
> >
> > >
> > >More than netlink, I think we need the ability in the core kernel to
> > >make this choice.
> >
> > Okay, but I think we can include that in the vdpa tool.
> If functionality and interface exists in other part of the it is hard to wrap that in vdpa tool that does the duplicate work.
>
> >
> > >I haven't explored what is already available to make that happen.
> >
> > Me too, I only saw the .match() callback of "struct bus_type" that could be used
> > for this purpose.
> >
> > >If/once its available, I am sure it has more users than just vdpa.
> >
> > Make sense. I'll spend some time next week.
>
> Ok. yeah, may be a desired driver can be stored in the vdpa_device that match() routine can use.
> And if that driver is not available,  it returns EPROBE_DEFER; so whenever such driver is loaded it can be bind.
>
> But I think before wrapping something in vdpa, need to find a reason why the current interface doesn't solve the problem and also to figure out plumbing.

I agree. If it's something that can easily be addressed by the
management code (just a matter of the extra steps for manual setup).
It's probably not worth bothering.

Thanks

>

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