Re: [Qemu-devel] [PATCH 1/2] QMP: Introduce commands doc

[Avi Kivity <avi@redhat.com>]

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.

-- 
Do not meddle in the internals of kernels, for they are subtle and quick to panic.