Re: [PATCH v2 1/1] s390: vfio_ap: link the vfio_ap devices to the vfio_ap bus subsystem

From: Pierre Morel
Date: Thu Feb 21 2019 - 07:51:36 EST

On 21/02/2019 13:35, Christian Borntraeger wrote:

On 21.02.2019 13:10, Pierre Morel wrote:
On 20/02/2019 13:51, Halil Pasic wrote:
On Wed, 20 Feb 2019 10:27:31 +0100
Cornelia Huck <cohuck@xxxxxxxxxx> wrote:

On Tue, 19 Feb 2019 22:31:17 +0100
Pierre Morel <pmorel@xxxxxxxxxxxxx> wrote:

On 19/02/2019 19:52, Tony Krowiak wrote:
On 2/18/19 1:08 PM, Pierre Morel wrote:
Libudev relies on having a subsystem link for non-root devices. To


+static struct device_driver matrix_driver = {
+ÂÂÂ .name = "vfio_ap",

This is the same name used for the original device driver. I think
this driver ought to have a different name to avoid confusion.
How about vfio_ap_matrix or some other name to differentiate the

I would like too, but changing this will change the path to the mediated
device supported type.

Yes, we don't want to change that.


However if I cannot change the driver name, I can change the bus name to matrix.
At least one less "vfio_ap" name

+ÂÂÂ .bus = &matrix_bus,
+ÂÂÂ .probe = matrix_probe,

I would add:
 ÂÂÂÂ.suppress_bind_attrs = true;

This will remove the sysfs bind/unbind interfaces. Since there is only
one matrix device and it's lifecycle is controlled herein, there is no
sense in allowing a root user to bind/unbind it.

OTOH bind/unbind has no impact.
If no one else ask for this I will not change what has already been
reviewed by Conny and Christian.

As we only have one driver, it does not really make sense anyway.

I see this as a reason to suppress_bind_attrs. It is much easier than to
think about what should happen when one unbinds the matrix device from
the vfio_ap driver on the vfio_ap bus. With the code as is it seems to
just keep working as if nothing happened.
And /sys/devices/vfio_ap/matrix/mdev_supported_types/ referencing the
name of the driver that is already gone sounds a bit weird.


If there is no objection I will do this,
It seems more logical to me too.

Go ahead and send this as v3?

CC stable ?

Pierre Morel
Linux/KVM/QEMU in BÃblingen - Germany