linux-kernel - Re: [PATCH v2 1/1] s390: vfio_ap: link the vfio_ap devices to the vfio

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Message-Id: <fd574b7b-7c2f-eeea-1d53-caadcd2fed48@linux.ibm.com>
Date:   Thu, 21 Feb 2019 13:10:10 +0100
From:   Pierre Morel <pmorel@...ux.ibm.com>
To:     Halil Pasic <pasic@...ux.ibm.com>,
        Cornelia Huck <cohuck@...hat.com>
Cc:     Tony Krowiak <akrowiak@...ux.ibm.com>, borntraeger@...ibm.com,
        linux-kernel@...r.kernel.org, linux-s390@...r.kernel.org,
        frankja@...ux.ibm.com, david@...hat.com, schwidefsky@...ibm.com,
        heiko.carstens@...ibm.com, freude@...ux.ibm.com
Subject: Re: [PATCH v2 1/1] s390: vfio_ap: link the vfio_ap devices to the
 vfio_ap bus subsystem

On 20/02/2019 13:51, Halil Pasic wrote:
> On Wed, 20 Feb 2019 10:27:31 +0100
> Cornelia Huck <cohuck@...hat.com> wrote:
> 
>> On Tue, 19 Feb 2019 22:31:17 +0100
>> Pierre Morel <pmorel@...ux.ibm.com> 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

...snip...

>>>>> +
>>>>> +static struct device_driver matrix_driver = {
>>>>> +    .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
>>>> two.
>>>
>>> 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.
>>
> 
> Nod.

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

> 
>>>
>>>
>>>>    
>>>>> +    .bus = &matrix_bus,
>>>>> +    .probe = matrix_probe,
>>>>
>>>> I would add:
>>>>       .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.
> 
> Regards,
> Halil
> 

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

Regards,
Pierre

-- 
Pierre Morel
Linux/KVM/QEMU in Böblingen - Germany