Re: [Qemu-ppc] [Qemu-devel] Posible regressions around spapr-dr-connector property drc-connector[]

[Markus Armbruster]

David Gibson <address@hidden> writes:

> On Thu, Dec 03, 2015 at 04:30:31PM +0100, Markus Armbruster wrote:
>> 1. Before commit 94649d4 "spapr: Don't use QOM [*] syntax for DR
>>    connectors", the indexes were small integers:
>> 
>>        (qemu) info qom-tree
>>        /machine (pseries-2.4-machine)
>>          /unattached (container)
>>            [...]
>>            /device[5] (spapr-pci-host-bridge)
>>              /address@hidden (qemu:memory-region)
>>              /address@hidden (qemu:memory-region)
>>              /address@hidden (qemu:memory-region)
>>              /address@hidden (qemu:memory-region)
>>              /pci.0 (PCI)
>>              /address@hidden (qemu:memory-region)
>>              /dr-connector[0] (spapr-dr-connector)
>>              /dr-connector[1] (spapr-dr-connector)
>>              /dr-connector[2] (spapr-dr-connector)
>>              [...]
>> 
>>    Since then, they're big ones:
>> 
>>              /dr-connector[1073741824] (spapr-dr-connector)
>>              /dr-connector[1073741825] (spapr-dr-connector)
>>              /dr-connector[1073741826] (spapr-dr-connector)
>> 
>>    The commit message doesn't quite spell out this change, and I'm
>>    therefore double-checkint it's intentional.  Is it?
>
> Yes, it's intentional.  The small integers were arbitrarily allocated
> by the QOM magic [*] code, whereas the big integers are actually
> meaningful values (essentially the DRC's global ID for the dynamic
> reconfiguration hypervisor interfaces).

Good.

>> 2. Before commit 6c2f9a1 "qapi: Make output visitor return qnull()
>>    instead of NULL", qom-get returned {}:
>> 
>>    Since then, it returns null:
>> 
>>        QMP> { "execute": "qom-get", "arguments": { "path": 
>> "/machine/unattached/device[5]/dr-connector[1073741950]", "property": "fdt" 
>> } }
>>        {"return": null}
>> 
>>    Does anyone care?
>
> Hm, I'm guessing this is a case where fdt is NULL internally.  Which I

Yes.

> think will happen before a device gets hotplugged into the DRC.  In
> that case null seems more correct to me than {}, since {} would also
> be what's shown for a present-but-empty device tree.

It was {} in 2.4.  Changing it to null so we can distingish "nothing"
from "empty" is an incompatible change.  May make sense anyway, but I
can't judge it.

Thanks!