Re: vDPA bus driver selection

Hi Parav,

On Wed, Oct 27, 2021 at 03:21:15PM +0000, Parav Pandit wrote:

Hi Stefano,

quoted

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. A use case could be for example a single host
handling VMs and bare-metal containers, so we would have both virtio-vdpa
and vhost-vdpa loaded and we want to attach some devices to VMs through
vhost-vdpa and others to containers through virtio-vdpa.

What do you think?

One option is, user keeps the drivers_autoprobe disabled for the vdpa bus using,

$ 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?

In an case of VDUSE, it makes more sense to bind to the one of the 
above driver after user space has connected the use space backend to 
the kernel device.

Yep, make sense.

Thanks,
Stefano

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