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

[David Gibson]

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).

> 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
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.

-- 
David Gibson                    | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au  | minimalist, thank you.  NOT _the_ _other_
                                | _way_ _around_!
http://www.ozlabs.org/~dgibson

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