C API is not a complete solution as it does not define well enough how
will you integrate with QEMU without changing or adding to the source..
But combined with AVI's idea of some plug-in mechanism, which will use
this C API, it sounds like a complete and valid solution.
The monitor should be kept for backward compatibility, human interface
and be implemented on top of that API as well, so there will also be a
reference implementation of how to use the API and create a plug-in.
As of Daniel remarks regarding DBus:
- I actually have a newer version where commands are divided into
different DBus interfaces. So (hopefully) that solves the methods
naming problem.
- I had to pass the server name at the CLI, since I was executing
multiple instances of QEMU.. Having an external server, raises again
the question of how will that server communicate with each instance of
QEMU?
- It was easier for my project to configure QEMU after it started and
not through a file, that why there is a configuration method for each
option. of course there could also be a bulk method which receive them
all or even read them from a file (and actually with some extra work,
many of them could be made dynamics)
On Dec 11, 2007 5:00 PM, Daniel P. Berrange <address@hidden
<mailto:address@hidden>> wrote:
On Tue, Dec 11, 2007 at 08:51:32AM -0600, Anthony Liguori wrote:
> Dor Laor wrote:
> >Laurent Vivier wrote:
> >>Le mardi 11 décembre 2007 à 10:10 +0100, Fabrice Bellard a
écrit :
> >>
> >>>Hi,
> >>>
> >>
> >>Hi,
> >>
> >>
> >>>At this point I am not interested in integrating it into QEMU
as it is
> >>>one more API level to maintain in addition to the command
line monitor.
> >>>However, I can change my mind if several projects insists to
have a
> >>>similar interface.
> >>>
> >>
> >>perhaps the DBUS interface can replace the command line monitor ?
> >>We have just to move the command line interface to a client
speaking to
> >>qemu through the DBUS interface.
> >>
> >>
> >This is a valid option but the problem is that local user will
have to
> >use another tool (client) to
> >send commands. Another option is to have a common backend with
machine
> >& user interfaces.
> >For example, if we use dbus as the backend, monitor commands
will just
> >be translated into dbus.
> >The opposite option is also valid.
> >
> >Anyway, the motivation behind a new interface is that the monitor
> >interface is not good enough for automation:
> >There are not return status for commands, no option for async
> >notifications, no option for parallel actions in case
> >a command takes long time to complete (like snapshot).
>
> All of these are valid, and addressable. Return statuses can
just be
> added to the beginning of the output of each command (similar to how
> POP3 works). Async notification can be made to work by add
support to
> the monitor for a "select" command. Semantically, select would
block
> the monitor and then output events. For this to work really
well, you
> would have to support multiple simultaneous monitor sessions. The
> parallel options for long running commands is already address in KVM
> with the migration command. We just have to rework the
snapshotting to
> be properly asynchronous.
>
> >
> >So we either a new interface is added or the existing one will be
> >enhanced.
> >Since Qemu/KVM will be used in production its highly important
to have
> >a reliable channel to connects with mgmt daemons.
> >Dbus is a common practice for communication and used in Linux,
> >libvirt, etc. The question is whether to add a dbus server to
Qemu or
> >a client is sufficient.
>
> The main objection I have to dbus is that it's very heavy
weight. It
> implies a rather fat infrastructure and it not very suitable for
> embedding. QEMU has very few dependencies and that is a
strength ATM.
> People interested in embedding QEMU still want a good management
> interface so enhancing the monitor seems more preferable to me than
> adding a dbus dependency.
It is also not so easily portable to other OS like Windows & Mac
OS, who
will still be lacking a decent control API. As I mentioned in my other
thread, embedding a DBus in each individual QEMU process is not
the right
way to write DBus services either. If you want DBus (which is
questionable
in itself), then you want to have a single service which manages
all a QEMU
VMs. This mandates that the DBus service be outside the context of
the QEMU
process itself.
Dan.
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