Re: [PATCH v7 04/15] s390/vfio-ap: implement in-use callback for vfio_ap driver

[Pierre Morel]

On 2020-04-16 16:45, Tony Krowiak wrote:
> On 4/16/20 7:18 AM, Cornelia Huck wrote:
> > On Tue, 7 Apr 2020 15:20:04 -0400
> > Tony Krowiak <akrowiak@xxxxxxxxxxxxx> wrote:
> >
> > > Let's implement the callback to indicate when an APQN
> > > is in use by the vfio_ap device driver. The callback is
> > > invoked whenever a change to the apmask or aqmask would
> > > result in one or more queue devices being removed from the driver. The
> > > vfio_ap device driver will indicate a resource is in use
> > > if the APQN of any of the queue devices to be removed are assigned to
> > > any of the matrix mdevs under the driver's control.
> > >
> > > Signed-off-by: Tony Krowiak <akrowiak@xxxxxxxxxxxxx>
> > > ---
> > > Â drivers/s390/crypto/vfio_ap_drv.cÂÂÂÂ |Â 1 +
> > > Â drivers/s390/crypto/vfio_ap_ops.cÂÂÂÂ | 47 +++++++++++++++++----------
> > > Â drivers/s390/crypto/vfio_ap_private.h |Â 2 ++
> > > Â 3 files changed, 33 insertions(+), 17 deletions(-)
> > > @@ -1369,3 +1371,14 @@ void vfio_ap_mdev_remove_queue(struct ap_queue 
> > > *queue)
> > > ÂÂÂÂÂ kfree(q);
> > > ÂÂÂÂÂ mutex_unlock(&matrix_dev->lock);
> > > Â }
> > > +
> > > +bool vfio_ap_mdev_resource_in_use(unsigned long *apm, unsigned long 
> > > *aqm)
> > > +{
> > > +ÂÂÂ bool in_use;
> > > +
> > > +ÂÂÂ mutex_lock(&matrix_dev->lock);
> > > +ÂÂÂ in_use = vfio_ap_mdev_verify_no_sharing(NULL, apm, aqm) ? true : 
> > > false;
> > Maybe
> >
> > in_use = !!vfio_ap_mdev_verify_no_sharing(NULL, apm, aqm);
> >
> > ?
>
> To be honest, I find the !! expression very confusing. Every time I see 
> it, I have
> to spend time thinking about what the result of !! is going to be. I think
> the statement should be left as-is because it more clearly expresses
> the intent.



In other places you use
"
        ret = vfio_ap_mdev_verify_no_sharing(matrix_mdev);
        if (ret)
                goto share_err;
"
then why use a boolean here?

If you want to return a boolean and you do not want to use !! you can do:

 ...
  ret = vfio_ap_mdev_verify_no_sharing(NULL, apm, aqm);
...
  return (ret) ? false : true;

> > > +ÂÂÂ mutex_unlock(&matrix_dev->lock);
> > > +
> > > +ÂÂÂ return in_use;
> > > +}

--
Pierre Morel
IBM Lab Boeblingen