Re: [Qemu-devel] [PATCH v4 1/1] s390 pci infrastructure modelling

[zyimin <zyimin@linux.vnet.ibm.com>]

On 7/9/2015 5:57 PM, Michael S. Tsirkin wrote:
> On Thu, Jul 09, 2015 at 05:30:08PM +0800, zyimin wrote:
>>
>> On 7/9/2015 3:48 PM, Michael S. Tsirkin wrote:
>>> On Wed, Jul 08, 2015 at 01:44:55PM +0800, Yi Min Zhao wrote:
>>>> @@ -588,9 +606,172 @@ static const TypeInfo s390_pcihost_info = {
>>>>       }
>>>>   };
>>>> +static void s390_pci_device_hot_plug(HotplugHandler *hotplug_dev,
>>>> +                                     DeviceState *dev, Error **errp)
>>>> +{
>>>> +    S390PCIBusDevice *zpci = S390_PCI_DEVICE(dev);
>>>> +    S390PCIBusDevice *tmp;
>>>> +    S390PCIFacility *f = S390_PCI_FACILITY(
>>>> +        object_resolve_path(TYPE_S390_PCI_FACILITY, NULL));
>>>> +
>>>> +    QTAILQ_FOREACH(tmp, &f->zpci_list, next) {
>>>> +        /* for now, we use fid to sort the list, need to use uid instead
>>>> +         * when uid is ready.
>>> What does ready mean in this context?
>> uid is a new feature on s390 arch for pci card management.
>> But support of uid on OS level has not been ready.
> Does this matter here? I thought it's an arbitrary order -
> just making it stable is enough?
I think there i sno matter here. Because uid is just for zpci management 
of firmware
and both of fid and uid are unique for all zpci devices attached to one 
guest. FID maybe
change after s390 machine restart. If machine reboot, host will scan PCI 
devices again
and will obtain new FID of every zPCI devices. For guest, it is isolated.
>
>>>> +         */
>>>> +        if (tmp->fid > zpci->fid) {
>>>> +            break;
>>>> +        }
>>>> +    }
>>>> +
>>>> +    if (tmp) {
>>>> +        QTAILQ_INSERT_BEFORE(tmp, zpci, next);
>>>> +    } else {
>>>> +        QTAILQ_INSERT_TAIL(&f->zpci_list, zpci, next);
>>>> +    }
>>>> +    f->token_valid = false;
>>>> +}
>>> This still means hotplug will change the index.
>>> How about just using an explicit property to set the index?
>>> Harder to use but keeps code simple.
>>>
>> These code were written by Hong Bo. I think he wants to use zpci->fid to
>> sort pci cards.
>> "index" what you talked is the order of hotplug? right? If it is, I think
>> this code actually
>> can change the index.
> I don't really understand what you are saying. id is how guest looks
> up the device, right? it shouldn't change really.
For guest, it will use a special instruction to get pci info of all 
attached pci devices.
For example, there are two pci devices which already are attached to the 
guest.
PCI1: fid=1, uid=1
PCI2: fid=3, uid=3
Then, you hotplug a new pci device to the guest:
PCI3: fid=2, uid=2
Although PCI2 is at the 3rd position of zpci_list, it will not effect 
guest looks up the device.
Because guest uses fid and fh to get zpci info and do pci operations. I 
think fid and uid is just
the explicit property what you said.