Re: [Qemu-devel] [PATCH 00/11 v3] Refactor PCI/SHPC/PCIE hotplug to use a more generic hotplug API

[Igor Mammedov <imammedo@redhat.com>]

On Mon, 16 Dec 2013 15:26:37 -0800
Anthony Liguori <anthony@codemonkey.ws> wrote:

> Igor Mammedov <imammedo@redhat.com> writes:
> 
> > changes since v2:
> > * s/hotplugable/hotpluggable/
> > * move hotplug check to an earlier patch:
> >   "qdev: add "hotpluggable" property to Device"
> > --
> > Refactor PCI specific hotplug API to a more generic/reusable one.
> > Model it after SCSI-BUS like hotplug API replacing single hotplug
> > callback with hotplug/hot_unplug pair of callbacks as suggested by
> > Paolo.
> > Difference between SCSI-BUS and this approach is that the former
> > is BUS centric while the latter is device centred. Which is evolved
> > from the fact that hotplug callbacks used by ACPI/SHPC/PCIE are
> > implemented by devices rather than by bus and bus serves only as
> > a proxy to forward event to hotplug device.
> > Memory hotplug also exposes tha same usage pattern hence an attempt
> > to generalize hotplug API.
> >
> > Refactoring also simplifies wiring of a hotplug device with a bus,
> > all it needs is to set "hotplug-device" link on bus, which
> > would potentially allow to do it from configuration file,
> > there is not need to setup hotplug device callbacks on bus
> > synce it can get them via HOTPLUG_DEVICE API of "hotplug-device"
> > target.
> >
> > In addition device centred hotplug API may be used by bus-less
> > hotplug implementations as well if it's decided to use
> > link<foo...> instead of bus.
> 
> I'm having a hard time parsing this description.
> 
> Sharing hot plug code is a good thing.  Making hotplug a qdev-level
> concept seems like a bad thing to me.
we could add TYPE_BUS_DEVICE as Peter suggests but let me explain why
I've chosen DEVICE for it.
All current hotplug code depends on hotpluggable bus but periodically
there were suggestions to use link<>s for hotplug instead of bus.
Making hotplug the bus device only concept will not allow to move in 
direction of hotplug with links which are/were supposed to replace
buses in future.
As side effect series lays ground work for link based hotplug, it's
not complete but a step towards it. It still doesn't allow link based
hotplug, since purpose was to have unified hotplug interface across
PCI/SCSI/virtio devices/buses. 

Maybe we need TYPE_HOTPLUGGABLE_DEVICE so it could be abstracted from
bus as well and eventually it could be used with bussless devices?

> 
> The series is a net add of code so I don't think we're winning anything
> by generalizing here.
it will allow to remove different implementations of hotplug
mechanism in SCSI/virtio and maybe USB buses in addition to converted
PCI hotplug.

> Is there a use-case this enables that isn't possible today?
It was prompted by memory hotplug, alternative was that it can
re-implement hotplug mechanism in its own way or duplicating code
from scsi or pci buses/devices. Neither alternatives look nice when
there is a common usage pattern.

> Regards,
> 
> Anthony Liguori
> 
> >
> > Patches 8-11 are should be merged as one and are split only for
> > simplifying review (they compile fine but PCI hotplug is broken
> > until the last patch is applyed).
> >
> > git tree for testing:
> > https://github.com/imammedo/qemu/commits/hotplug_dev_inf_v3
> >
> > tested only ACPI and PCIE hotplug.
> >
> > Hervé Poussineau (1):
> >   qom: detect bad reentrance during object_class_foreach
> >
> > Igor Mammedov (9):
> >   define hotplug interface
> >   qdev: add to BusState "hotplug-handler" link
> >   qdev: add "hotpluggable" property to Device
> >   hw/acpi: move typeinfo to the file end
> >   qdev:pci: refactor PCIDevice to use generic "hotpluggable" property
> >   acpi/piix4pm: convert ACPI PCI hotplug to use hotplug-handler API
> >   pci/shpc: convert SHPC hotplug to use hotplug-handler API
> >   pci/pcie: convert PCIE hotplug to use hotplug-handler API
> >   hw/pci: switch to a generic hotplug handling for PCIDevice
> >
> > Paolo Bonzini (1):
> >   qom: do not register interface "types" in the type table
> >
> >  hw/acpi/piix4.c                | 151 ++++++++++++++++++++++-------------------
> >  hw/core/Makefile.objs          |   1 +
> >  hw/core/hotplug.c              |  48 +++++++++++++
> >  hw/core/qdev.c                 |  50 ++++++++++++--
> >  hw/display/cirrus_vga.c        |   2 +-
> >  hw/display/qxl.c               |   2 +-
> >  hw/display/vga-pci.c           |   2 +-
> >  hw/display/vmware_vga.c        |   2 +-
> >  hw/i386/acpi-build.c           |   6 +-
> >  hw/ide/piix.c                  |   4 +-
> >  hw/isa/piix4.c                 |   2 +-
> >  hw/pci-bridge/pci_bridge_dev.c |   9 +++
> >  hw/pci-host/piix.c             |   6 +-
> >  hw/pci/pci.c                   |  40 +----------
> >  hw/pci/pcie.c                  |  73 +++++++++++++-------
> >  hw/pci/pcie_port.c             |   8 +++
> >  hw/pci/shpc.c                  | 133 +++++++++++++++++++++++-------------
> >  hw/usb/hcd-ehci-pci.c          |   2 +-
> >  hw/usb/hcd-ohci.c              |   2 +-
> >  hw/usb/hcd-uhci.c              |   2 +-
> >  hw/usb/hcd-xhci.c              |   2 +-
> >  include/hw/hotplug.h           |  75 ++++++++++++++++++++
> >  include/hw/pci/pci.h           |  13 ----
> >  include/hw/pci/pci_bus.h       |   2 -
> >  include/hw/pci/pcie.h          |   5 ++
> >  include/hw/pci/shpc.h          |   8 +++
> >  include/hw/qdev-core.h         |   8 +++
> >  qom/object.c                   |  17 ++++-
> >  28 files changed, 455 insertions(+), 220 deletions(-)
> >  create mode 100644 hw/core/hotplug.c
> >  create mode 100644 include/hw/hotplug.h
> >
> > -- 
> > 1.8.3.1