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Date: Fri, 26 Jun 2009 14:15:00 +0300
From: Avi Kivity <avi@redhat.com>
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Subject: Re: [Qemu-devel] Re: [PATCH 08/11] QMP: Port balloon command
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To: "Daniel P. Berrange" <berrange@redhat.com>
Cc: Anthony Liguori <aliguori@us.ibm.com>, ehabkost@redhat.com, jan.kiszka@siemens.com, dlaor@redhat.com, qemu-devel@nongnu.org, Luiz Capitulino <lcapitulino@redhat.com>

On 06/26/2009 12:42 PM, Daniel P. Berrange wrote:
> On Fri, Jun 26, 2009 at 12:21:01PM +0300, Avi Kivity wrote:
>    
>> On 06/25/2009 10:11 PM, Luiz Capitulino wrote:
>>      
>>>   Yes, having a library was suggested by Amit some months ago. The
>>> problem is that it has various issues wrt maintainability.
>>>
>>>   For example, libvirt is able to run two instances of different
>>> versions of qemu at the same time. How to handle this if you
>>> update libmonitor.so?
>>>
>>>        
>
> The sane way is to *NOT* break ABI of libmonitor.so, and not change
> the wire protocol in a non backwards compatible way. This is entirely
> doable, it just the maintainer of libmonitor/qemu to decide that  ABI
> stability is important. So if you find an existing API  / command
> needs to gain an extra argument, you don't change the existing API,
> you add a new one. Or ideally design the API upfront so that it
> can be extended without breaking back compatability.
>
>    

Yeah.

>> You could use dlopen().  The problem with a library is that it assumes
>> everyone is still trapped in C, which is not the case.
>>      
>
> dlopen() of a different libmonitor.so for every version of QEMU is just
> crazy, whether C or not. Maintain ABI&  protocol back compatability
> with new releases and avoid the issue in the first place.
>    

Right, I just like dlopen().

-- 
I have a truly marvellous patch that fixes the bug which this
signature is too narrow to contain.