Am 15.07.2013 17:37, schrieb Paolo Bonzini: > Il 15/07/2013 17:06, Andreas Färber ha scritto: >> Am 15.07.2013 16:43, schrieb Paolo Bonzini: >>> Il 15/07/2013 15:40, Andreas Färber ha scritto: >>>> Originally Paolo and me had implemented QOM realize at Object level. >>>> Paolo's goal was to set realized = true on /machine and it propagating from >>>> there on. This series now implements {realize,unrealize}_children at >>>> DeviceState level instead and propagates realized changes along busses >>>> rather >>>> than child<> properties. >>> >>> You are right that realize must be done after the bus is realized (and >>> unrealize must be done before the bus). But I'm afraid this opens a can >>> of worms. >>> >>>> On machine creation done, a depth-first search is done >>>> for devices from /machine, which are then expected to further propagate the >>>> property change. >>> >>> How do you ensure that devices are realized before their bus's parent >>> _and_ before their parent? With two constraints for each device, we >>> have a graph, not anymore a tree. Example: >>> >>> >>> (1) this is the composition tree >>> >>> /machine >>> ,------' | '------. >>> /pci-host /isa /superio >>> ,----' '----. >>> /i8254 /i8259 >>> >>> >>> (2) this is the bus tree >>> >>> PCI (/pci-host) >>> | >>> ISA (/isa) >>> ,-----------' '------. >>> /superio/i8254 /superio/i8259 >>> >>> >>> The constraints are: >>> >>> - pci-host before isa >>> - superio before superio/i8254 >>> - superio before superio/i8259 >>> - isa before superio/i8254 >>> - isa before superio/i8259 >>> >>> So the two valid orders are >>> >>> - /machine, pci-host, superio, isa, superio/i8254, superio/8259 >>> - /machine, pci-host, isa, superio, superio/i8254, superio/8259 >>> >>> You cannot say whether superio or isa are encountered first, so you >>> cannot say whether it is superio or isa that should "hold off" the visit >>> of their children (in either the QOM tree or the bus tree). What avoids >>> us having to do a full topological ordering of the graph? >> >> I would say your example is wrong. :) There should be no /machine/isa >> node. > > Why not? And anyway, just replace /superio with /pcnet-isa and > /superio/i8254 with /pcnet-isa/pcnet, and you get the same scenario. > > Perhaps you could say my example is wrong, because one of the two > constraints should not be there. If you have a good argument for that, > I can buy it. :) > >> Is this hypothetical or do we need to fix qemu.git? > > It is hypothetical, PC is not QOMified yet. > >> There will be a /machine/sysbus node though, which may lead to similar >> ordering uncertainties. However SysBusDevices don't usually have a >> hosting device today, so I don't think it's a problem at the moment. And >> not for busses either since they are no devices. If we have a >> /machine/superio that would be a SysBusDevice (in PReP it would be a >> PCIDevice and thus not directly on /machine), we would need to walk its >> children to their bus and its parent device and assure it is realized >> before - I think there's still sufficient time until 1.6 to get >> something minimal sorted out. > > I don't think this is 1.6 material, and there is no need to start with > something minimal. Let's focus on getting things right. > > Perhaps "right" means that only one of the two trees need to be visited. > That's what I did in my old prototype, but I'm fairly convinced it was > wrong. > >> Do you have a concrete example where we need such strict constraints? > > Does there need to be a concrete example?
My interest is this: Take a look at my tegra branch or PReP PCI or other composited SysBusDevices. Today I need to realize child devices in DeviceClass::realize, when I know that they should be realized through realize_children instead, outside of realize. So I don't want to convert all SysBusDevices to hand-code recursive realization (or at least the current version of it) and then go through and remove all that again in favor of realize_children. And since we are converting some devices for 1.6 I would like to have the work-saving solution for 1.6 as well. So it is not about /machine (2/3 is unused) but about the realize_children infrastructure (1/3). Andreas -- SUSE LINUX Products GmbH, Maxfeldstr. 5, 90409 Nürnberg, Germany GF: Jeff Hawn, Jennifer Guild, Felix Imendörffer; HRB 16746 AG Nürnberg