Re: [Qemu-devel] [PATCH v4 18/24] qdev: hotplug: provide do_unplug handler

[David Gibson <david@gibson.dropbear.id.au>]

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On Wed, Sep 26, 2018 at 11:42:13AM +0200, David Hildenbrand wrote:
> The unplug and unplug_request handlers are special: They are not
> executed when unrealizing a device, but rather trigger the removal of a
> device from device_del() via object_unparent() - to effectively
> unrealize a device.
> 
> If such a device has a child bus and another device attached to
> that bus (e.g. how virtio devices are created with their proxy device),
> we will not get a call to the unplug handler. As we want to support
> hotplug handlers (and especially also some unplug logic to undo resource
> assignment) for such devices, we cannot simply call the unplug handler
> when unrealizing - it has a different semantic ("trigger removal").
> 
> To handle this scenario, we need a do_unplug handler, that will be
> executed for all devices with a hotplug handler.
> 
> While at it, introduce hotplug_fn_nofail and fix a spelling mistake in
> a comment.
> 
> Signed-off-by: David Hildenbrand <david@redhat.com>
> ---
>  hw/core/hotplug.c    | 10 ++++++++++
>  hw/core/qdev.c       |  6 ++++++
>  include/hw/hotplug.h | 26 ++++++++++++++++++++++++--
>  3 files changed, 40 insertions(+), 2 deletions(-)
> 
> diff --git a/hw/core/hotplug.c b/hw/core/hotplug.c
> index 2253072d0e..e7a68d5160 100644
> --- a/hw/core/hotplug.c
> +++ b/hw/core/hotplug.c
> @@ -45,6 +45,16 @@ void hotplug_handler_post_plug(HotplugHandler *plug_handler,
>      }
>  }
>  
> +void hotplug_handler_do_unplug(HotplugHandler *plug_handler,
> +                                 DeviceState *plugged_dev)

Hrm.  I really dislike things named "do_X".  The "do" rarely adds any
useful meaning.  And when there's also something called just plain
"X", it's *always* unclear how they relate to each other.

That's doubly true when it's a general interface like this, rather
than just some local functions.

-- 
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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