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Re: [Qemu-devel] [RFC] QEMU Dbus support - a proposal management API

From: Fabrice Bellard
Subject: Re: [Qemu-devel] [RFC] QEMU Dbus support - a proposal management API
Date: Tue, 11 Dec 2007 10:10:27 +0100
User-agent: Thunderbird (X11/20070727)


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.



Yuval Kashtan wrote:
Some answers:
- If there is interest I can re-create the patch so it will work against the current head. I thought to receive some comments about it first.. - thanks for the styling and configuration remarks, I will certainly fix these. But before I invest more time in it, I would like to hear what ppl think in general of management API? How do you like DBus as the infrastructure for that? and what do you think of the proposed implementation? - Currently only commands are implemented (with very few getters), but of course this can be further extended to include values reading and statistics. - This is very useful when you want to manage and control QEMU, for instance developing a GUI to attach and detach usb devices or controlling more than one instance of QEMU from a single management point, receiving parameters externally and more.

On Dec 10, 2007 10:51 PM, Blue Swirl <address@hidden <mailto:address@hidden>> wrote:

    On 12/10/07, Yuval Kashtan < address@hidden
    <mailto:address@hidden>> wrote:
     > Hello All,
     > Attached is a proposed patch which adds DBus support to QEMU.
    DBus is a
     > standard message bus for linux
     > ( http://www.freedesktop.org/wiki/Software/dbus )
     > The idea behind this is to allow for external programs such as
     > GUI or HyperVisors to communicate and control QEMU, in a standard
     > Although it is possible to connect to the monitor, an API is more
     > theres no need to parse texts and error messages, no
     > problems and in general is a much better idea.
     > Implementation:
     > This is done by creating a DBus server from QEMU which raise
    signals and act
     > upon methods.
     > Methods mainly implement same logic as the current command line
    options and
     > monitor does.
     > How to use:
     > To enable DBus support you'll have to add --enable-dbus when you
     > configure script.
     > Then when you execute QEMU, you'll have to add -dbus-service
     > where service_name follows the DBus naming convention (
     > To support QEMU configuration through DBus,  you'll also have to add
     > -dbus_configuration which will cause QEMU to wait until
    ConfigDone is called
     > through the DBus interface. this allows external programs time to
    call DBus
     > methods starting with Config_ which changes configuration (just
    as the CLI
     > does) thus enabling invocation of QEMU without parameters (beside
    the DBus
     > ones).
     > With that, we have implemented a nice python script that reads VM's
     > configuration from INI file.
     > To compile this you will also have to compile the attached
    freedesktop.org <http://freedesktop.org>
     > dsrv library (it is also attach for those who can't handle GIT) from:
     > git://people.freedesktop.org/~shaharf/dsrv
     > Features:
     > Currently support was added to all important CLI configuration
    and some
     > online monitor functions (such as connecting and disconnecting
    usb devices).
     > configuration methods begins with Config_ prefix and monitor ones
     > Monitor_.
     > For a complete list you can just execute qemu and connect with
     > to see what is supported.
     > All the dbus handling routines can be found in dbus-monitor.c.
     > I have two different implementations of this:
     > 1) A single threaded version. which comply to the qemu standard
    of not
     > opening additional threads.
     > 2) A multi threaded version which open an additional, single,
    thread which
     > handles all the DBus load. I actually believe this version is
    better as it
     > allows QEMU to continue execution of guest operations even when
    there are
     > DBus methods/signals to handle, whereas in the first option, DBus is
     > integrated into QEMU mainloop. Also this makes it possible to
    monitor even
     > during long operations (like monitoring the progress of savevm)
     > Please comment both on the idea of management API and the proposed
     > implementation.
     > Attached are:
     > RFC-QEMU-Dbus.patch - patch file including all necessary changes
    to qemu.
     > was made against QEMU HEAD as of 23/9 morning.
     > RFC-QEMU-Dbus-Interface.xml - the xml description of the DBus
    interface that
     > I suggest.
     > dsrv.tar.gz.txt - the dbus server library.

    I have no idea if this is useful. I would have tried the patch, but it
    does not apply to current CVS. Other comments:

    When configure is invoked with --enable-dbus, it should check for DBUS
    libraries and abort if not found.

    The coding style in monitor-dbus.c is different from what is commonly
    used in Qemu. Some long lines could be shortened.

    Enabling of DEBUG_ACPI and other ACPI changes are probably not
    directly needed so they should be in separate patches.

    Only commands are included, how about reading values and statistics?

Yuval Kashtan

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