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

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Date:   Fri, 24 Apr 2020 13:07:38 -0400
From:   Tony Krowiak <akrowiak@...ux.ibm.com>
To:     Halil Pasic <pasic@...ux.ibm.com>,
        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,
        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 4/23/20 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.

>
> But I do agree, having a way to report why "won't do" to the end user is
> important for usability.
>
> Regards,
> Halil
>
>>>>   
>>>>> +			rc = -EADDRINUSE;
>>>>> +
>>>>> +	module_put(drv->owner);
>>>>> +
>>>>> +	return rc;
>>>>> +}