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Re: [Qemu-devel] [PATCH 00/11 v3] Refactor PCI/SHPC/PCIE hotplug to use
From: |
Igor Mammedov |
Subject: |
Re: [Qemu-devel] [PATCH 00/11 v3] Refactor PCI/SHPC/PCIE hotplug to use a more generic hotplug API |
Date: |
Wed, 18 Dec 2013 16:48:09 +0100 |
On Wed, 18 Dec 2013 11:36:52 +0100
Paolo Bonzini <address@hidden> wrote:
> Il 17/12/2013 20:38, Anthony Liguori ha scritto:
> > On Tue, Dec 17, 2013 at 4:38 AM, Paolo Bonzini <address@hidden> wrote:
> >> Il 17/12/2013 00:26, Anthony Liguori ha scritto:
> >>> Sharing hot plug code is a good thing. Making hotplug a qdev-level
> >>> concept seems like a bad thing to me.
> >>
> >> Can you explain what you mean?
> >
> > The question is whether "hotpluggable" as a property applies to all
> > devices or not.
I think Andreas asked me to provide "hotpluggable" property to
distinguish hotpluggable vs not hotpluggable DimmDevice via qom interface.
> >
> > But hotplug is strictly a bus level concept. It's a sequence of
> > events that correspond to what happens when you add a new device to a
> > bus after power on.
>
> Hotplugging a device is a special case of plugging a device. If a bus
> or device only supports cold-plug, that can be done using
> "bc->allow_hotplug = false" or "dc->hotpluggable = false".
Do we need per instance ability to set "hotpluggable" property?
For example board might want to mark some CPUs as not hotpluggable.
>
> Igor's interface applies just as well to the case of plugging a device
> at startup; I think separating the two makes little sense. And once you
> have cold-plug and hot-plug in qdev core, it makes sense to add unplug
> as well. Also because we already have surprise removal in qdev core
> (that's unparent) and we have some kind of unplug request support
> (device_del/dc->unplug).
>
> One possibility that remains is to put cold/hot-plug in a "BusDevice"
> class rather than in the core qdev:
>
> Device
> BusDevice <-- can be cold/hot-plugged
>
> but this adds more complication. For example, the same CPU can be
> hotpluggable or not depending on the board model, should the superclass
> be Device or BusDevice. And if we ever have multi-CPU targets, with the
> "core" CPU not hotpluggable and additional hotpluggable ones (e.g. for
> GPUs) what would be the superclass of the common CPU superclass?
>
> > The question is whether there can be code sharing without touching the
> > base class. You could certainly have a HotpluggableBusState and then
> > a HotpluggableDeviceState.
> >
> > Interfaces would be another option too.
>
> Interfaces are fine, but the question is who finds them and calls them.
> In this case, the discovery mechanism is a link property, and the
> calling mechanism is an explicit hook in the "realized" property.
If we don't need per instance "hotpluggable" state and we can call
interfaces from generic qdev/device code, then we would need at first
only TYPE_HOTPLUGGABLE_BUS_DEVICE_IF and later for link<> based hotplug
we could add just TYPE_HOTPLUGGABLE_DEVICE_IF. Difference would be in
the way they get access to hotplug device link, former one will use bus
for it and second some other way.
>
> If we had aspect-oriented programming, we would be marking join points
> instead of writing "if (dev->foo) bar(dev->foo)" conditionals. But the
> idea is the same.
>
> > The general concern is about polluting widely used base classes. It's
> > better if we can avoid adding things to DeviceState and Object
> > whenever possible.
>
> I agree. At the same time we should make base classes as small as
> possible, but not smaller than that.
>
> Paolo
>
- Re: [Qemu-devel] [PATCH 05/11] qdev: add "hotpluggable" property to Device, (continued)
- [Qemu-devel] [PATCH 09/11] pci/shpc: convert SHPC hotplug to use hotplug-handler API, Igor Mammedov, 2013/12/13
- [Qemu-devel] [PATCH 10/11] pci/pcie: convert PCIE hotplug to use hotplug-handler API, Igor Mammedov, 2013/12/13
- [Qemu-devel] [PATCH 11/11] hw/pci: switch to a generic hotplug handling for PCIDevice, Igor Mammedov, 2013/12/13
- Re: [Qemu-devel] [PATCH 00/11 v3] Refactor PCI/SHPC/PCIE hotplug to use a more generic hotplug API, Anthony Liguori, 2013/12/16
- Re: [Qemu-devel] [PATCH 00/11 v3] Refactor PCI/SHPC/PCIE hotplug to use a more generic hotplug API, Peter Crosthwaite, 2013/12/16
- Re: [Qemu-devel] [PATCH 00/11 v3] Refactor PCI/SHPC/PCIE hotplug to use a more generic hotplug API, Igor Mammedov, 2013/12/17
- Re: [Qemu-devel] [PATCH 00/11 v3] Refactor PCI/SHPC/PCIE hotplug to use a more generic hotplug API, Paolo Bonzini, 2013/12/17
- Re: [Qemu-devel] [PATCH 00/11 v3] Refactor PCI/SHPC/PCIE hotplug to use a more generic hotplug API, Michael S. Tsirkin, 2013/12/18
- Re: [Qemu-devel] [PATCH 00/11 v3] Refactor PCI/SHPC/PCIE hotplug to use a more generic hotplug API, Igor Mammedov, 2013/12/18