Re: [PATCH v6 21/21] s390: doc: detailed specifications for AP virtualization

Halil Pasic
2018-07-09T15:50:00Z

On 07/09/2018 05:21 AM, Pierre Morel wrote:
> On 03/07/2018 01:10, Halil Pasic wrote:
>>
>>
>> On 06/29/2018 11:11 PM, Tony Krowiak wrote:
>>> This patch provides documentation describing the AP architecture and
>>> design concepts behind the virtualization of AP devices. It also
>>> includes an example of how to configure AP devices for exclusive
>>> use of KVM guests.
>>>
>>> Signed-off-by: Tony Krowiak <akrowiak@linux.ibm.com>
>>
>> I don't like the design of external interfaces except for:
>> * cpu model features, and
>> * reset handling.
>>
>> In particular:
>>
>>
> ...snip...
>
>> 4) If I were to act out the role of the administrator, I would prefer to think of
>> specifying or changing the access controls of a guest in respect to AP (that is
>> setting the AP matrix) as a single atomic operation -- which either succeeds or fails.
>>
>> The operation should succeed for any valid configuration, and fail for any invalid
>> on.
>>
>> The current piecemeal approach seems even less fitting if we consider changing the
>> access controls of a running guest. AFAIK changing access controls for a running
>> guest is possible, and I don't see a reason why should we artificially prohibit this.
>>
>> I think the current sysfs interface for manipulating the matrix is good for
>> manual playing around, but I would prefer having an interface that is better
>> suited for programs (e.g. ioctl).
>
> I disagree with using ioctl.

Why? What speaks against ioctl?

> I agree that the current implementation is not right.
> The configuration of APM and AQM should always be guarantied as coherent
> within the host but it can be done doing the right checks when using the sysfs.
>

I'm glad we agree on this one at least.

Regards,
Halil