Re: [Qemu-devel] Re: [libvirt] Supporting hypervisor specific APIs in libvirt

[Luiz Capitulino <lcapitulino@redhat.com>]

On Thu, 25 Mar 2010 08:55:42 -0500
Anthony Liguori <anthony@codemonkey.ws> wrote:

> On 03/25/2010 08:23 AM, Luiz Capitulino wrote:
> > On Wed, 24 Mar 2010 16:40:18 -0500
> > Anthony Liguori<anthony@codemonkey.ws>  wrote:
> >
> >    
> >>>> We need to have a common management interface for third party tools.
> >>>>
> >>>>          
> >>>    QMP? :-)
> >>>        
> >> Only if QMP is compatible with libvirt.  I don't want a user to have to
> >> choose between QMP and libvirt.
> >>      
> >   Why not? If all they want is a simple qemu session, they can use
> > QMP directly, on the other hand if what they want is more complex,
> > what's the problem of using a management API like libivrt?
> >    
> 
> My point is that libvirt should not be a separate management API but 
> effectively an add-on API that provides higher level features, better 
> integration with Linux host services, etc.

 Okay, I fully agree here.

> >>> If so, what C clients you expected beyond libvirt?
> >>>        
> >> Users want a C API.  I don't agree that libvirt is the only C interface
> >> consumer out there.
> >>      
> >   Actually, I do agree. Maybe, we don't have other C consumers because they
> > weren't crazy enough to parse the crap of the user Monitor (or they do,
> > but for simple things).
> >
> >   One possible future client is perf, for example.
> >
> >   Here is my solution (actually it's not mine, you have suggested
> > it some time ago): let's provide a convenient way for C clients to
> > use QMP. That is, let's have an overly simple library which takes
> > QDitcs, sends them to qemu through QMP and returns others QDicts.
> >
> >   Something like the _sketch_ below:
> >
> > // Open a connection
> > int qmp_open(..., QDict **greeting);
> >
> > // Register a callback for async messages, BUT note that the async message
> > // object is passed verbatim
> > void qmp_async_mes_handler(..., void (*async_mes_handler)(QDict *mes));
> >
> > // Send a QMP command
> > int qmp_send(..., const char *command, QDict *params, QDict **res);
> >    
> 
> Yes, this is the core API.  It's missing a mechanism to create a 
> QMPContext.  I'll also argue that we want a set of auto generated 
> wrappers like:

 Having the wrappers is one of the points we disagree, but as we have agreed
on starting with the core only, I don't see why keep arguing here.

 If, in the near feature, the need of having wrappers become evident
I'll be all for it (this statement is a bit dangerous though, as
this need can be subjective).

[...]

> > but the two main ideas are:
> >
> > 1. We don't do management
> >    
> 
> I really believe we need to stop thinking this way.  I'm not saying that 
> qemu-devel is the place where we design virt-manager, but we ought to 
> consider the whole stack as part of "we".

 Depends, if you mean that we should be involved with libvirt development,
than I completely agree.

 On the other hand, if you mean than qemu should provide its own management
API, than I tend to disagree. And I think this is a very important point of
the whole discussion, if you think this way I guess we should start a new
thread to collect feedback, listing pros and cons.

> >> I really think what we want is for a libvirt user to be able to call
> >> libqemu functions directly.  There shouldn't have to be libvirt specific
> >> functions for every operation we expose.
> >>      
> >   Not sure if this is too crazy but, considering this user wants to
> > use qemu features not implemented by libvirt yet, what about using both
> > libqmp (above) and libvirt at the same time?
> >    
> 
> Yes, that's *exactly* what I want.  Except I want to call it libqemu 
> because qmp is an implementation detail.

 libqemu is fine.