Re: [Qemu-devel] [PATCH v1 0/8] MemoryDevice: introduce and use ResourceHandler

[David Hildenbrand <david@redhat.com>]

On 10.05.2018 15:02, Igor Mammedov wrote:
> On Wed, 9 May 2018 16:13:14 +0200
> David Hildenbrand <david@redhat.com> wrote:
> 
>> On 03.05.2018 17:49, David Hildenbrand wrote:
>>> Hotplug handlers usually have the following tasks:
>>> 1. Allocate some resources for a new device
>>> 2. Make the new device visible for the guest
>>> 3. Notify the guest about the new device
>>>
>>> Hotplug handlers have right now one limitation: They handle their own
>>> context and only care about resources they manage.
>>>
>>> We can have devices that need certain other resources that are e.g.
>>> system resources managed by the machine. We need a clean way to assign
>>> these resources (without violating layers as brought up by Igor).
>>>
>>> One example is virtio-mem/virtio-pmem. Both device types need to be
>>> assigned some region in guest physical address space. This device memory
>>> belongs to the machine and is managed by it. However, virito devices are
>>> hotplugged using the hotplug handler their proxy device implements. So we
>>> could trigger e.g. a PCI hotplug handler for virtio-pci or a CSS/CCW
>>> hotplug handler for virtio-ccw. But definetly not the machine.
>>>
>>> So let's generalize the task of "assigning" resources and use it directly
>>> for memory devices. We now have a clean way to support any kind of memory
>>> device - independent of the underlying device type. Right now, only one
>>> resource handler per device can be supported (in addition to the existing
>>> hotplug handler).
>>>
>>> You can find more details in patch nr 2.
>>>
>>> This work is based on the already queued patch series
>>>     "[PATCH v4 00/11] pc-dimm: factor out MemoryDevice"
>>>
>>> David Hildenbrand (8):
>>>   memory-device: always compile support for memory devices for SOFTMMU
>>>   qdev: introduce ResourceHandler as a first-stage hotplug handler
>>>   machine: provide default resource handler
>>>   memory-device: new functions to handle resource assignment
>>>   pc-dimm: implement new memory device functions
>>>   machine: introduce enforce_memory_device_align() and add it for pc
>>>   memory-device: factor out pre-assign into default resource handler
>>>   memory-device: factor out (un)assign into default resource handler
>>>
>>>  hw/Makefile.objs               |   2 +-
>>>  hw/core/Makefile.objs          |   1 +
>>>  hw/core/machine.c              |  70 +++++++++++++++++++++++
>>>  hw/core/qdev.c                 |  41 +++++++++++++-
>>>  hw/core/resource-handler.c     |  57 +++++++++++++++++++
>>>  hw/i386/pc.c                   |  31 ++++++-----
>>>  hw/mem/Makefile.objs           |   2 +-
>>>  hw/mem/memory-device.c         | 122 +++++++++++++++++++++++++----------------
>>>  hw/mem/pc-dimm.c               |  53 ++++++++----------
>>>  hw/mem/trace-events            |   4 +-
>>>  hw/ppc/spapr.c                 |   5 +-
>>>  include/hw/boards.h            |  17 ++++++
>>>  include/hw/mem/memory-device.h |  17 ++++--
>>>  include/hw/mem/pc-dimm.h       |   3 +-
>>>  include/hw/resource-handler.h  |  46 ++++++++++++++++
>>>  stubs/Makefile.objs            |   1 -
>>>  stubs/qmp_memory_device.c      |  13 -----
>>>  17 files changed, 364 insertions(+), 121 deletions(-)
>>>  create mode 100644 hw/core/resource-handler.c
>>>  create mode 100644 include/hw/resource-handler.h
>>>  delete mode 100644 stubs/qmp_memory_device.c
>>>   
>>
>> If there are no further comments, I'll send a v2 by the end of this
>> week. Thanks!
> I couldn't convince myself that ResourceHandler is really necessary.
> My main gripe with it, is that it imposes specific ordering wrt hotplug
> handler that resources will be touched. Other issue is that it looks
> a bit over-engineered with a lot of code fragmentation. Hence,
> 
> I'd suggest use simple hotplug handler chaining instead,
> which should take care of wiring up virtio-mem/virtio-pmem,
> keeping code compact at the same time.

I'll have a look tomorrow or next friday if that could work - not sure
yet about unplug vs. unplug requests. Unplug requests might be tricky.
Would be nice if it would work. Thanks!

> 
> Could you try something along these lines (I'll post a patch to
> override default hotplug handler as reply here for you to pick up,
> that should make following work):
> 
> diff --git a/hw/s390x/s390-virtio-ccw.c b/hw/s390x/s390-virtio-ccw.c
> index 100dfdc..c400c0c 100644
> --- a/hw/s390x/s390-virtio-ccw.c
> +++ b/hw/s390x/s390-virtio-ccw.c
> @@ -393,12 +393,30 @@ static void s390_machine_reset(void)
>      s390_ipl_prepare_cpu(ipl_cpu);
>      s390_cpu_set_state(S390_CPU_STATE_OPERATING, ipl_cpu);
>  }
> +static void s390_machine_device_pre_plug(HotplugHandler *hotplug_dev,
> +                                         DeviceState *dev, Error **errp)
> +{
> +    if (object_dynamic_cast(OBJECT(dev), TYPE_VIRTIO_MEM_CCW)) {
> +        /* do checks && set default values if it weren't set by user */
> +        /* possibly pass to device's bus pre_plug handler if need */
> +    }
> +}
>  
>  static void s390_machine_device_plug(HotplugHandler *hotplug_dev,
>                                       DeviceState *dev, Error **errp)
>  {
>      if (object_dynamic_cast(OBJECT(dev), TYPE_CPU)) {
>          s390_cpu_plug(hotplug_dev, dev, errp);
> +    } if (object_dynamic_cast(OBJECT(dev), TYPE_VIRTIO_MEM_CCW)) {
> +        HotplugHandler *hotplug_ctrl = dev->parent_bus->hotplug_handler;
> +
> +        /* do machine specific wiring, i.e.
> +         * assign resources specified by user or by foo_pre_plug(),
> +         * like map region into machine address space at specified address */
> +        if (OK) {
> +            /* pass control down to bus specific hotplug chain */
> +            hotplug_handler_plug(hotplug_ctrl, dev, errp);
> +        }
>      }
>  }
>  
> @@ -449,6 +467,8 @@ static HotplugHandler *s390_get_hotplug_handler(MachineState *machine,
>  {
>      if (object_dynamic_cast(OBJECT(dev), TYPE_CPU)) {
>          return HOTPLUG_HANDLER(machine);
> +    } (object_dynamic_cast(OBJECT(dev), TYPE_VIRTIO_MEM)) {
> +        return HOTPLUG_HANDLER(machine);
>      }
>      return NULL;
>  }
> 


-- 

Thanks,

David / dhildenb