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

[Anthony Krowiak]

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@xxxxxxxxxxxxx>
> > Reviewed-by: Anthony Krowiak <akrowiak@xxxxxxxxxxxxx>
> > Reviewed-by: Boris Fiuczynski <fiuczy@xxxxxxxxxxxxx>
> > ---
> >   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