Re: [Qemu-devel] Re: [PATCH 08/11] QMP: Port balloon command

[Avi Kivity]

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.