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

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Message-ID: <e9a74fbb-4367-4595-9af7-47e3786b2cb1@linux.ibm.com>
Date: Fri, 13 Sep 2024 12:24:24 -0400
From: Anthony Krowiak <akrowiak@...ux.ibm.com>
To: Heiko Carstens <hca@...ux.ibm.com>,
        "Jason J. Herne"
 <jjherne@...ux.ibm.com>
Cc: linux-s390@...r.kernel.org, linux-kernel@...r.kernel.org,
        fiuczy@...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 9/11/24 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?

I am okay with this, but I would keep the sysfs filename  'features'.

cat /sys/bus/matrix/devices/matrix/features
guest_matrix dyn ap_config