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From: Markus Armbruster <armbru@redhat.com>
Subject: Re: [Qemu-devel] [PATCH 1/2] QMP: Introduce commands doc
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Date: Mon, 17 May 2010 13:19:49 +0200
In-Reply-To: <4BF107E1.2020600@redhat.com> (Avi Kivity's message of "Mon, 17
	May 2010 12:09:53 +0300")
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To: Avi Kivity <avi@redhat.com>
Cc: bazulay@redhat.com, juzhang@redhat.com, Gerd Hoffmann <kraxel@redhat.com>, qemu-devel@nongnu.org, Luiz Capitulino <lcapitulino@redhat.com>

Avi Kivity <avi@redhat.com> writes:

> On 05/17/2010 11:27 AM, Markus Armbruster wrote:
>>
>>    
>>>>> A slot is the hotpluggable entity.  Open your computer and you can
>>>>> actually see them.
>>>>>
>>>>>          
>>>> QEMU doesn't really know that.
>>>>
>>>>        
>>> How can that be?  Do we signal hotplug notifications to a function or
>>> to a slot?
>>>
>>> Can we hotplug a single function in an already occupied slot?
>>>      
>> What I meant to say: we have no concept of "slot" in the higher level
>> interfaces, we have only bus and device.
>>
>> If a PCI device has multiple functions, we have a separate qdev device
>> for each function.  You can't unplug a "slot" (concept doesn't exist in
>> qdev), only a qdev device.  Naturally, when you unplug a qdev device,
>> all functions in the same PCI slot need to go.  This happens deep down
>> in the bowels of ACPI, in piix4_device_hotplug().  qdev is not aware of
>> this magic relation between the qdev devices for functions in the same
>> slot.
>>    
>
> IMO, that's a serious bug.  A slot is a user visible entity, both in
> that devices can only be hotplugged only as slots, not functions, and
> to determine the maximum number of devices you can add.  If the user
> knows about it, qemu should too.
>
> We can easily represent a slot/device as a qbus with each of the
> functions as devices attached to it.

Dunno.  Gerd, what do you think?