Re: vDPA bus driver selection

[Stefano Garzarella <sgarzare@redhat.com>]

On Thu, Oct 28, 2021 at 10:24:47AM +0800, Jason Wang wrote:
>On Thu, Oct 28, 2021 at 4:16 AM Michael S. Tsirkin <mst@redhat.com> wrote:
>>
>> On Wed, Oct 27, 2021 at 03:21:15PM +0000, Parav Pandit wrote:
>> > Hi Stefano,
>> >
>> > > From: Stefano Garzarella <sgarzare@redhat.com>
>> > > Sent: Wednesday, October 27, 2021 8:04 PM
>> > >
>> > > Hi folks,
>> > > I was trying to understand if we have a way to specify which vDPA bus driver
>> > > (e.g. vhost-vdpa, virtio-vdpa) a device should use.
>> > > IIUC we don't have it, and the first registered driver is used when a new device
>> > > is registered.
>> > >
>> > > I was thinking if it makes sense to extend the management API to specify which
>> > > bus driver to use for a device.
>
>Actually, we want to support this in the first version of vDPA bus.
>But for some reason it was dropped. The idea is to specify the device
>type 'virtio' or 'vhost'. But a concern is that, it may encourage
>vendor to implement e.g virtio specific device (without DMA
>isolation).

Yep, I see the issue about device type, so I think make sense to require 
the support of both, how it is now basically.

So instead of defining the type of the device, we could provide the 
possibility to choose which bus to connect it to, in this way we 
continue to require that both are supported.

As Michael suggested, instead of specify it at the creation time as was 
in my original idea, we can provide an API to attach/detach a device to 
a specific vDPA bus.

Of course, providing a default behaviour like now, which connects to the 
first registered.

Thanks,
Stefano

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