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

[Boris Fiuczynski]

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@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?
>
>
> 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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