On Fri, Dec 04, 2015 at 09:05:51AM +0100, Markus Armbruster wrote:
> David Gibson <da...@gibson.dropbear.id.au> 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)
> >> /p...@800000020000000.mmio[0] (qemu:memory-region)
> >> /p...@800000020000000.mmio-alias[0] (qemu:memory-region)
> >> /p...@800000020000000.io[0] (qemu:memory-region)
> >> /p...@800000020000000.io-alias[0] (qemu:memory-region)
> >> /pci.0 (PCI)
> >> /pci@800000020000000.iommu-root[0] (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.
Strictly speaking it's an incompatible change, yes. But I find it
hard to imagine anything would be relying on the {} behaviour. This
property is essentially a debugging interface to start with, and the
missing / empty case is examining it in a state that's unlikely to be
interesting.
--
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
signature.asc
Description: PGP signature
