linux-kernel - Re: [PATCH v7 03/15] s390/zcrypt: driver callback to indicate resource in use

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Date:   Mon, 27 Apr 2020 17:36:28 -0400
From:   Tony Krowiak <akrowiak@...ux.ibm.com>
To:     Halil Pasic <pasic@...ux.ibm.com>
Cc:     Cornelia Huck <cohuck@...hat.com>, 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,
        alex.williamson@...hat.com, kwankhede@...dia.com,
        jjherne@...ux.ibm.com, fiuczy@...ux.ibm.com
Subject: Re: [PATCH v7 03/15] s390/zcrypt: driver callback to indicate
 resource in use



On 4/24/20 2:23 PM, Halil Pasic wrote:
> On Fri, 24 Apr 2020 13:07:38 -0400
> Tony Krowiak <akrowiak@...ux.ibm.com> wrote:
>
>>
>> On 4/23/20 11:33 PM, Halil Pasic wrote:
>>> On Thu, 16 Apr 2020 11:37:21 +0200
>>> Cornelia Huck <cohuck@...hat.com> wrote:
>>>
>>>> On Wed, 15 Apr 2020 13:10:10 -0400
>>>> Tony Krowiak <akrowiak@...ux.ibm.com> wrote:
>>>>
>>>>> On 4/14/20 8:58 AM, Cornelia Huck wrote:
>>>>>> On Tue,  7 Apr 2020 15:20:03 -0400
>>>>>> Tony Krowiak <akrowiak@...ux.ibm.com> wrote:
>>>>>>> +
>>>>>>> +	if (ap_drv->in_use)
>>>>>>> +		if (ap_drv->in_use(newapm, ap_perms.aqm))
>>>>>> Can we log the offending apm somewhere, preferably with additional info
>>>>>> that allows the admin to figure out why an error was returned?
>>>>> One of the things on my TODO list is to add logging to the vfio_ap
>>>>> module which will track all significant activity within the device
>>>>> driver. I plan to do that with a patch or set of patches specifically
>>>>> put together for that purpose. Having said that, the best place to
>>>>> log this would be in the in_use callback in the vfio_ap device driver
>>>>> (see next patch) where the APQNs that are in use can be identified.
>>>>> For now, I will log a message to the dmesg log indicating which
>>>>> APQNs are in use by the matrix mdev.
>>>> Sounds reasonable. My main issue was what an admin was supposed to do
>>>> until logging was in place :)
>>> Logging may not be the right answer here. Imagine somebody wants to build
>>> a nice web-tool for managing this stuff at scale -- e.g. something HMC. I
>>> don't think the solution is to let this tool parse the kernel messages
>>> and try to relate that to its own transactions.
>> I don't believe there is no right or wrong answer here; I simply don't
>> see the relevance of discussing a tool in this context. We are talking
>> about a sysfs attribute interface here, so - correct me if I'm
>> mistaken - our options for notifying the user that a queue is in use are
>> limited to the return code from the sysfs interface and logging. I would
>> expect that a tool would have to do something similar to the callback
>> implemented in the vfio_ap device driver and check the APQNs
>> removed against the APQNs assigned to the mdevs to determine which
>> is in use.
>>
> We are talking interface design. The relevance of discussing a tool is
> that any userspace tool must come by with whatever interface we come up
> now. IMHO thinking about the usage (and the client code) is very helpful
> in avoiding broken interface designs. AFAIK this is one of the basic
> ideas behind test driven development.

What can a sysfs interface, such as apmask/aqmask, do other than reply with
a return code given sysfs attributes that store data can only return a 
count?
I'm sorry, but I still don't see the relevance.

>
> Regards,
> Halil