Re: [RFC 05/19] s390/zcrypt: base implementation of AP matrix device driver

[Tony Krowiak]

On 11/14/2017 12:00 PM, Cornelia Huck wrote:
> On Tue, 14 Nov 2017 11:37:05 -0500
> Tony Krowiak <akrowiak@xxxxxxxxxxxxxxxxxx> wrote:
>
> > On 11/14/2017 07:40 AM, Cornelia Huck wrote:
> > > On Fri, 13 Oct 2017 13:38:50 -0400
> > > Tony Krowiak <akrowiak@xxxxxxxxxxxxxxxxxx> wrote:
> > > > diff --git a/drivers/s390/crypto/ap_matrix_bus.c b/drivers/s390/crypto/ap_matrix_bus.c
> > > > index 4eb1e3c..66bfa54 100644
> > > > --- a/drivers/s390/crypto/ap_matrix_bus.c
> > > > +++ b/drivers/s390/crypto/ap_matrix_bus.c
> > > > @@ -75,10 +75,18 @@ static int ap_matrix_dev_create(void)
> > > >    	return 0;
> > > >    }
> > > >    
> > > > +struct ap_matrix *ap_matrix_get_device(void)
> > > > +{
> > > > +	return matrix;
> > > See the comments I had for the previous patch. In particular, I think
> > > it is better to retrieve a pointer to the matrix device via driver core
> > > methods.
> > I got some objections to creating a new bus and since there will only ever
> > be a single AP matrix device, I decided there really wasn't a need for an
> > AP matrix bus and got rid of it. I opted instead to create the matrix
> > device
> > in the init function of the vfio_ap_matrix driver. Rather than passing
> > around a
> > pointer, I put the following in vfio_ap_matrix_private.h:
> >
> >       struct ap_matrix {
> >           struct device device;
> >           spinlock_t qlock;
> >           struct list_head queues;
> >       };
> >
> >       extern struct ap_matrix ap_matrix;
> >
> > ... and declared the ap_matrix in  the driver (vfio_ap_matrix_drv.c)
> > file as:
> >
> >       struct ap_matrix ap_matrix;
> >
> > Does this seem like a reasonable approach?
> Getting rid of the bus as overhead is not unreasonable.
>
> I'm feeling a bit queasy about the extern, however. I'd prefer a getter
> function (that also makes sure refcounting rules are followed).
I now think I can avoid having to reference the ap_matrix device from
multiple places. The reason the device is referenced in vfio_ap_matrix_ops.c
is because there is a need for information about the AP queues that have 
been
bound to the vfio_ap_matrix device driver. If interfaces are provided by 
the
vfio_ap_matrix device driver to access the needed information, it
won't be necessary to reference the ap_matrix device directly in
vfio_ap_matrix_ops. I think this would be a better solution, don't you?
> We can't get around referencing this device from multiple files, can we?
The only way would be to roll up vfio_ap_matrix_ops.c into 
vfio_ap_matrix_drv.c. I followed the pattern established
by the vfio_ccw
>