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

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Date:   Thu, 16 Apr 2020 10:45:20 -0400
From:   Tony Krowiak <akrowiak@...ux.ibm.com>
To:     Cornelia Huck <cohuck@...hat.com>
Cc:     linux-s390@...r.kernel.org, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org, freude@...ux.ibm.com, borntraeger@...ibm.com,
        mjrosato@...ux.ibm.com, pmorel@...ux.ibm.com, pasic@...ux.ibm.com,
        alex.williamson@...hat.com, kwankhede@...dia.com,
        jjherne@...ux.ibm.com, fiuczy@...ux.ibm.com
Subject: Re: [PATCH v7 04/15] s390/vfio-ap: implement in-use callback for
 vfio_ap driver



On 4/16/20 7:18 AM, Cornelia Huck wrote:
> On Tue,  7 Apr 2020 15:20:04 -0400
> Tony Krowiak <akrowiak@...ux.ibm.com> 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@...ux.ibm.com>
>> ---
>>   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.

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