Re: [Qemu-devel] Transitioning from HMP to QMP for QEMU

[Anthony Liguori]

On 12/15/2011 07:57 AM, Luiz Capitulino wrote:
> On Thu, 15 Dec 2011 13:02:40 +0000
> Stefan Hajnoczi<address@hidden>  wrote:
>
> > What is the status of QEMU's transition from HMP to the QMP interface?
>
> Depends on what you consider the transition to be.
>
> For management tools the transition can be considered done already because we
> do not support HMP as a stable interface.
>
> > My current understanding is that QEMU provides new HMP commands for
> > humans, but HMP is being phased out as an API.
>
> It already did.
>
> >   Management tools
> > should rely only on QMP for new commands.  That would mean new HMP
> > commands are not guaranteed to produce backwards-compatible output
> > because tools are not supposed to parse the output.
>
> Exactly.
>
> > On the libvirt side, new QEMU features should only be supported via
> > the json monitor in the future (i.e. human monitor patches should not
> > be sent/merged)? Existing HMP commands will still need the human
> > monitor support in order to handle old QEMU versions gracefully, but
> > I'm thinking about new commands only.
>
> Maybe it's a matter of terminology, but I have the impression you're
> talking about two things here:
>
>   1. HMP will always exist, in the meaning that qemu will always provide
>      a human interface. If we move it to a python script or some kind of
>      external process, that's an implementation detail.
>
>      This means that, if you're adding new functionality to qemu and it
>      does make sense for humans to use it, then it should have a HMP
>      version.
>
>   2. If you do add the HMP interface, that's for humans to consume and
>      its output/semantics should make sense for humans, not for management 
> tools.

3. All HMP commands will be implemented in terms of QMP commands (and only in 
terms of QMP commands).

There are still a lot of HMP commands that don't have an QMP analog.  Luiz, it 
might make sense to setup a wiki page which instructions on how to convert an 
HMP command to a QMP command using QAPI.

If we did that, we could probably get more folks involved in the conversion 
process.

Regards,

Anthony Liguori

> > Does everyone agree on this?  I think this is an important discussion
> > if we want our management interface to get better and more consistent
> > in the future.
> >
> > Stefan