[v3,03/18] qdev: let machine hotplug handler to override bus hotplug handler

From: Igor Mammedov <imammedo@redhat.com>

it will allow to return another hotplug handler than the default
one for a specific bus based device type. Which is needed to handle
non trivial plug/unplug sequences that need the access to resources
configured outside of bus where device is attached.

That will allow for returned hotplug handler to orchestrate wiring
in arbitrary order, by chaining other hotplug handlers when
it's needed.

PS:
It could be used for hybrid virtio-mem and virtio-pmem devices
where it will return machine as hotplug handler which will do
necessary wiring at machine level and then pass control down
the chain to bus specific hotplug handler.

Example of top level hotplug handler override and custom plug sequence:

  some_machine_get_hotplug_handler(machine){
      if (object_dynamic_cast(OBJECT(dev), TYPE_SOME_BUS_DEVICE)) {
          return HOTPLUG_HANDLER(machine);
      }
      return NULL;
  }

  some_machine_device_plug(hotplug_dev, dev) {
      if (object_dynamic_cast(OBJECT(dev), TYPE_SOME_BUS_DEVICE)) {
          /* do machine specific initialization */
          some_machine_init_special_device(dev)

          /* pass control to bus specific handler */
          hotplug_handler_plug(dev->parent_bus->hotplug_handler, dev)
      }
  }

Signed-off-by: Igor Mammedov <imammedo@redhat.com>
Signed-off-by: David Hildenbrand <david@redhat.com>
---
 hw/core/qdev.c         |  6 ++----
 include/hw/qdev-core.h | 11 +++++++++++
 2 files changed, 13 insertions(+), 4 deletions(-)

On Mon, May 14, 2018 at 12:00:08PM +0200, David Hildenbrand wrote:
> From: Igor Mammedov <imammedo@redhat.com>
> 
> it will allow to return another hotplug handler than the default
> one for a specific bus based device type. Which is needed to handle
> non trivial plug/unplug sequences that need the access to resources
> configured outside of bus where device is attached.
> 
> That will allow for returned hotplug handler to orchestrate wiring
> in arbitrary order, by chaining other hotplug handlers when
> it's needed.
> 
> PS:
> It could be used for hybrid virtio-mem and virtio-pmem devices
> where it will return machine as hotplug handler which will do
> necessary wiring at machine level and then pass control down
> the chain to bus specific hotplug handler.
> 
> Example of top level hotplug handler override and custom plug sequence:
> 
>   some_machine_get_hotplug_handler(machine){
>       if (object_dynamic_cast(OBJECT(dev), TYPE_SOME_BUS_DEVICE)) {
>           return HOTPLUG_HANDLER(machine);
>       }
>       return NULL;
>   }
> 
>   some_machine_device_plug(hotplug_dev, dev) {
>       if (object_dynamic_cast(OBJECT(dev), TYPE_SOME_BUS_DEVICE)) {
>           /* do machine specific initialization */
>           some_machine_init_special_device(dev)
> 
>           /* pass control to bus specific handler */
>           hotplug_handler_plug(dev->parent_bus->hotplug_handler, dev)
>       }
>   }

Hi, David.

I might be misreading, but isn't it more like the following?

    some_machine_device_plug(hotplug_dev, dev) {
        if (object_dynamic_cast(OBJECT(dev), TYPE_SOME_BUS_DEVICE)) {
            /* do machine specific initialization */
            some_machine_init_special_device(dev)
        } else {
            /* pass control to bus specific handler */
            hotplug_handler_plug(dev->parent_bus->hotplug_handler, dev)
        }
    }

> Signed-off-by: Igor Mammedov <imammedo@redhat.com>
> Signed-off-by: David Hildenbrand <david@redhat.com>
> ---
>  hw/core/qdev.c         |  6 ++----
>  include/hw/qdev-core.h | 11 +++++++++++
>  2 files changed, 13 insertions(+), 4 deletions(-)
> 
> diff --git a/hw/core/qdev.c b/hw/core/qdev.c
> index f6f92473b8..885286f579 100644
> --- a/hw/core/qdev.c
> +++ b/hw/core/qdev.c
> @@ -261,12 +261,10 @@ HotplugHandler *qdev_get_machine_hotplug_handler(DeviceState *dev)
>  
>  HotplugHandler *qdev_get_hotplug_handler(DeviceState *dev)
>  {
> -    HotplugHandler *hotplug_ctrl;
> +    HotplugHandler *hotplug_ctrl = qdev_get_machine_hotplug_handler(dev);
>  
> -    if (dev->parent_bus && dev->parent_bus->hotplug_handler) {
> +    if (hotplug_ctrl == NULL && dev->parent_bus) {
>          hotplug_ctrl = dev->parent_bus->hotplug_handler;
> -    } else {
> -        hotplug_ctrl = qdev_get_machine_hotplug_handler(dev);
>      }
>      return hotplug_ctrl;
>  }
> diff --git a/include/hw/qdev-core.h b/include/hw/qdev-core.h
> index 9453588160..e6a8eca558 100644
> --- a/include/hw/qdev-core.h
> +++ b/include/hw/qdev-core.h
> @@ -286,6 +286,17 @@ void qdev_init_nofail(DeviceState *dev);
>  void qdev_set_legacy_instance_id(DeviceState *dev, int alias_id,
>                                   int required_for_version);
>  HotplugHandler *qdev_get_machine_hotplug_handler(DeviceState *dev);
> +/**
> + * qdev_get_hotplug_handler: Get handler responsible for device wiring
> + *
> + * Find HOTPLUG_HANDLER for @dev that provides [pre|un]plug callbacks for it.
> + *
> + * Note: in case @dev has a parent bus, it will be returned as handler unless
> + * machine handler overrides it.
> + *
> + * Returns: pointer to object that implements TYPE_HOTPLUG_HANDLER interface
> + *          or NULL if there aren't any.
> + */
>  HotplugHandler *qdev_get_hotplug_handler(DeviceState *dev);
>  void qdev_unplug(DeviceState *dev, Error **errp);
>  void qdev_simple_device_unplug_cb(HotplugHandler *hotplug_dev,
> -- 
> 2.14.3
> 
>

On 15.05.2018 02:00, Murilo Opsfelder Araujo wrote:
> On Mon, May 14, 2018 at 12:00:08PM +0200, David Hildenbrand wrote:
>> From: Igor Mammedov <imammedo@redhat.com>
>>
>> it will allow to return another hotplug handler than the default
>> one for a specific bus based device type. Which is needed to handle
>> non trivial plug/unplug sequences that need the access to resources
>> configured outside of bus where device is attached.
>>
>> That will allow for returned hotplug handler to orchestrate wiring
>> in arbitrary order, by chaining other hotplug handlers when
>> it's needed.
>>
>> PS:
>> It could be used for hybrid virtio-mem and virtio-pmem devices
>> where it will return machine as hotplug handler which will do
>> necessary wiring at machine level and then pass control down
>> the chain to bus specific hotplug handler.
>>
>> Example of top level hotplug handler override and custom plug sequence:
>>
>>   some_machine_get_hotplug_handler(machine){
>>       if (object_dynamic_cast(OBJECT(dev), TYPE_SOME_BUS_DEVICE)) {
>>           return HOTPLUG_HANDLER(machine);
>>       }
>>       return NULL;
>>   }
>>
>>   some_machine_device_plug(hotplug_dev, dev) {
>>       if (object_dynamic_cast(OBJECT(dev), TYPE_SOME_BUS_DEVICE)) {
>>           /* do machine specific initialization */
>>           some_machine_init_special_device(dev)
>>
>>           /* pass control to bus specific handler */
>>           hotplug_handler_plug(dev->parent_bus->hotplug_handler, dev)
>>       }
>>   }
> 
> Hi, David.
> 
> I might be misreading, but isn't it more like the following?
> 
>     some_machine_device_plug(hotplug_dev, dev) {
>         if (object_dynamic_cast(OBJECT(dev), TYPE_SOME_BUS_DEVICE)) {
>             /* do machine specific initialization */
>             some_machine_init_special_device(dev)
>         } else {
>             /* pass control to bus specific handler */
>             hotplug_handler_plug(dev->parent_bus->hotplug_handler, dev)
>         }
>     }

There are various ways how to implement it ,this example if from Igor
and most probably not complete (only showcases how things are passed on
to the next handler).

I decided to implement it slightly different, to make it more flexible.
Best you have a look at the following patches in this series.

Thanks!

> 
>> Signed-off-by: Igor Mammedov <imammedo@redhat.com>
>> Signed-off-by: David Hildenbrand <david@redhat.com>
>> ---
>>  hw/core/qdev.c         |  6 ++----
>>  include/hw/qdev-core.h | 11 +++++++++++
>>  2 files changed, 13 insertions(+), 4 deletions(-)
>>
>> diff --git a/hw/core/qdev.c b/hw/core/qdev.c
>> index f6f92473b8..885286f579 100644
>> --- a/hw/core/qdev.c
>> +++ b/hw/core/qdev.c
>> @@ -261,12 +261,10 @@ HotplugHandler *qdev_get_machine_hotplug_handler(DeviceState *dev)
>>  
>>  HotplugHandler *qdev_get_hotplug_handler(DeviceState *dev)
>>  {
>> -    HotplugHandler *hotplug_ctrl;
>> +    HotplugHandler *hotplug_ctrl = qdev_get_machine_hotplug_handler(dev);
>>  
>> -    if (dev->parent_bus && dev->parent_bus->hotplug_handler) {
>> +    if (hotplug_ctrl == NULL && dev->parent_bus) {
>>          hotplug_ctrl = dev->parent_bus->hotplug_handler;
>> -    } else {
>> -        hotplug_ctrl = qdev_get_machine_hotplug_handler(dev);
>>      }
>>      return hotplug_ctrl;
>>  }
>> diff --git a/include/hw/qdev-core.h b/include/hw/qdev-core.h
>> index 9453588160..e6a8eca558 100644
>> --- a/include/hw/qdev-core.h
>> +++ b/include/hw/qdev-core.h
>> @@ -286,6 +286,17 @@ void qdev_init_nofail(DeviceState *dev);
>>  void qdev_set_legacy_instance_id(DeviceState *dev, int alias_id,
>>                                   int required_for_version);
>>  HotplugHandler *qdev_get_machine_hotplug_handler(DeviceState *dev);
>> +/**
>> + * qdev_get_hotplug_handler: Get handler responsible for device wiring
>> + *
>> + * Find HOTPLUG_HANDLER for @dev that provides [pre|un]plug callbacks for it.
>> + *
>> + * Note: in case @dev has a parent bus, it will be returned as handler unless
>> + * machine handler overrides it.
>> + *
>> + * Returns: pointer to object that implements TYPE_HOTPLUG_HANDLER interface
>> + *          or NULL if there aren't any.
>> + */
>>  HotplugHandler *qdev_get_hotplug_handler(DeviceState *dev);
>>  void qdev_unplug(DeviceState *dev, Error **errp);
>>  void qdev_simple_device_unplug_cb(HotplugHandler *hotplug_dev,
>> -- 
>> 2.14.3
>>
>>
>