Re: [Qemu-devel] [PATCH v4 03/14] qdev: let machine hotplug handler to override bus hotplug handler

[David Gibson]

On Thu, May 17, 2018 at 10:15:16AM +0200, David Hildenbrand wrote:
> From: Igor Mammedov 
> 
> 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 
> Signed-off-by: David Hildenbrand 

Reviewed-by: David Gibson 

I've been considering a similar change for a while; we'll also need
something like this in order to do hoplug for PCI devices under p2p
bridges on pseries (there's a PAPR specific hotplug model that we need
to use instead of SHP).

> ---
>  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,

-- 
David Gibson| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au  | minimalist, thank you.  NOT _the_ _other_
| _way_ _around_!
http://www.ozlabs.org/~dgibson


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[Qemu-devel] [PATCH v4 03/14] qdev: let machine hotplug handler to override bus hotplug handler

[David Hildenbrand]

From: Igor Mammedov 

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 
Signed-off-by: David Hildenbrand 
---
 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,
-- 
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