Re: [libvirt] [Qemu-devel] Re: Supporting hypervisor specific APIs in libvirt
On Thu, 25 Mar 2010 08:55:42 -0500
Anthony Liguori <anthony(a)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(a)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.