[libvirt] [PATCHv2 4/4] qemu: Implement shared memory device hot-unplug

[lhuang]

On 12/17/2015 08:26 PM, John Ferlan wrote:
>
> On 12/16/2015 09:43 PM, lhuang wrote:
>>
>> On 12/15/2015 08:39 PM, John Ferlan wrote:
>>> [...]
>>>
>>>>>> +    if (rc < 0)
>>>>>> +        return -1;
>>>>>> +
>>>>> I know this is a copy of the RemoveRNGDevice; however, this code
>>>>> doesn't
>>>>> remove an 'obj'. In fact, if !shmem->server.enabled, then we don't
>>>>> enter
>>>>> the monitor at all.
>>>>>
>>>>> Thus the following event probably won't happen...
>>>> I am not sure what your mean is ... i guess your mean the device remove
>>>> event we get from qmp monitor won't happen ? we will get that event if
>>>> qemu remove shmem device success, it should always happen if qemu really
>>>> remove it and there is no bugs on qemu :)
>>>>
>>> While reviewing I got lazy and didn't check the non hotplug case to how
>>> shmem is added to the vm, but the point I was trying to make is that "if
>>> (shmem->server.enabled)" fails (e.g. is false), then there is no "rc =
>>> qemuMonitorDelObject(priv->mon, objAlias);" call in this API (similar to
>>> RNG code), thus how does the following event get triggered?  Even if the
>>> condition was true, does detaching the char dev cause the event to be
>>> triggered?
>>> I thought the event was related to the DelObject code, but I didn't go
>>> follow that code
>> Oh, i see, event is not related to the object delete, i guess you have
>> checked the code and know how it works now ;-)
> Maybe you misunderstood - maybe I misunderstood your response... I
> didn't go searching through the code, but something just didn't seem
> right when looking so I wanted to note it.

Looks like i misunderstood :)

> Since I figured your model was RNG my thought process was how does RNG
> do it and what is different...
>
> AttachRNG has 3 steps AttachCharDev, AddObject, and AddDevice
> DetachRNG has 1 step DelDevice
> RemoveRNG has 2 steps DelObject and DetachCharDev
>
>
> AttachShmem has 2 steps AttachCharDev and AddDevice
> DetachShmem has 1 step DelDevice
> RemoveShmem has 1 step DetachCharDev
>
> I think my concern was more related to the difference where an RNG has
> an Object that gets removed, but Shmem doesn't.

ivshmem device doesn't have a QOM object, so no need to add/del a QOM 
object.

and you can check this doc:

http://wiki.qemu.org/TexiDemo

and see "Inter-VM Shared Memory device" part

> After closer inspection now it seems that this event generation needs to
> stay. The RemoveShmem code is generating the event not waiting on it
> which perhaps is where my thoughts were when I first went through the
> changes.

yes, virDomainEventDeviceRemovedNewFromObj() is generating a event and 
it can trigger the callback functions which registered in qemu driver.

Thanks for your help and reply

Luayo

> John
>
>> Thanks for your quick reply !
>>
>> Luyao
>>
>>> John
>>>
>>> [...]
>>>