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

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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>
---
  drivers/s390/crypto/vfio_ap_drv.c     |  1 +
  drivers/s390/crypto/vfio_ap_ops.c     | 47 +++++++++++++++++----------
  drivers/s390/crypto/vfio_ap_private.h |  2 ++
  3 files changed, 33 insertions(+), 17 deletions(-)
@@ -1369,3 +1371,14 @@ void vfio_ap_mdev_remove_queue(struct ap_queue *queue)
      kfree(q);
      mutex_unlock(&matrix_dev->lock);
  }
+
+bool vfio_ap_mdev_resource_in_use(unsigned long *apm, unsigned long *aqm)
+{
+    bool in_use;
+
+    mutex_lock(&matrix_dev->lock);
+    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;



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


--
Pierre Morel
IBM Lab Boeblingen




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