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

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Date:   Thu, 21 Feb 2019 13:51:24 +0100
From:   Pierre Morel <pmorel@...ux.ibm.com>
To:     Christian Borntraeger <borntraeger@...ibm.com>,
        Halil Pasic <pasic@...ux.ibm.com>,
        Cornelia Huck <cohuck@...hat.com>
Cc:     Tony Krowiak <akrowiak@...ux.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 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@...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.
> 
> Go ahead and send this as v3?
> 

OK
CC stable ?


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