linux-kernel - Re: [PATCH v2] s390/vfio-ap: Driver feature advertisement

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Message-ID: <cffbae68-0439-470f-979b-efe83f54697c@linux.ibm.com>
Date: Thu, 12 Sep 2024 14:36:22 +0200
From: Boris Fiuczynski <fiuczy@...ux.ibm.com>
To: "Jason J. Herne" <jjherne@...ux.ibm.com>,
        Heiko Carstens <hca@...ux.ibm.com>
Cc: linux-s390@...r.kernel.org, linux-kernel@...r.kernel.org,
        akrowiak@...ux.ibm.com, borntraeger@...ibm.com, agordeev@...ux.ibm.com,
        gor@...ux.ibm.com
Subject: Re: [PATCH v2] s390/vfio-ap: Driver feature advertisement

On 9/12/24 2:24 PM, Jason J. Herne wrote:
> On 9/11/24 2:57 AM, Heiko Carstens wrote:
>> On Tue, Sep 10, 2024 at 07:34:40AM -0400, Jason J. Herne wrote:
>>> Advertise features of the driver for the benefit of automated tooling
>>> like Libvirt and mdevctl.
>>>
>>> Signed-off-by: Jason J. Herne <jjherne@...ux.ibm.com>
>>> Reviewed-by: Anthony Krowiak <akrowiak@...ux.ibm.com>
>>> Reviewed-by: Boris Fiuczynski <fiuczy@...ux.ibm.com>
>>> ---
>>>   Documentation/arch/s390/vfio-ap.rst | 34 +++++++++++++++++++++++++++++
>>>   drivers/s390/crypto/vfio_ap_drv.c   | 13 +++++++++++
>>>   2 files changed, 47 insertions(+)
>>
>> ...
>>
>>> +Driver Features
>>> +===============
>>> +The vfio_ap driver exposes a sysfs file containing supported features.
>>> +This exists so third party tools (like Libvirt and mdevctl) can 
>>> query the
>>> +availability of specific features.
>>> +
>>> +The features list can be found here: 
>>> /sys/bus/matrix/devices/matrix/features
>>> +
>>> +Entries are \n delimited. Each entry contains a key value pair. The 
>>> key is made
>>> +up of a combination of alphanumeric and underscore characters. The 
>>> separator
>>> +consists of a space, a colon and then another space. The value 
>>> consists of
>>> +alphanumeric, space, and underscore characters.
>>> +
>>> +Example:
>>> +cat /sys/bus/matrix/devices/matrix/features
>>> +flags : guest_matrix dyn ap_config
>>> +
>>> +Presently only a single field named flags is defined. It is meant to 
>>> advertise a
>>> +list of features the driver provides. The flags fields advertises 
>>> the following
>>> +features:
>>
>> I stumbled across this only now: sysfs files are not supposed to have
>> several key value pairs. Actually the file(name) itself is supposed to
>> be the key and its contents are the value. So I would expect:
>>
>> cat /sys/bus/matrix/devices/matrix/flags
>> guest_matrix dyn ap_config
>>
>> Which is also easier to parse. Is there a good reason why this does
>> not follow the general approach for sysfs files?
> 
> 
> We talked about a few designs for this feature. This patch represents 
> where we landed. I'm happy to make the change to the way you suggest but 
> I'll give some time for Boris or Tony to speak up if they disagree.

Heiko's expectation is fine by me.

-- 
Mit freundlichen Grüßen/Kind regards
    Boris Fiuczynski

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