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Re: [Fedora-xen] What's the Pre-requisites for virt-manager

On Fri, Nov 24, 2006 at 10:52:13AM +0800, Henry Zhang wrote:
> Thanks Dan, please see comments below.. :)
> Daniel P. Berrange ??????:
> >On Thu, Nov 23, 2006 at 07:54:24PM +0800, Henry Zhang wrote:
> >  
> >>hi Daniel,
> >>
> >>From the webpage, I can see that dbus and gnome-python-desktop are 
> >>optional, but when our release engineer try to build, seems they are 
> >>not, so could you confirm me if we can build/run virt-manager correctly 
> >>without Dbus?
> >>    
> >
> >Ah, I should perhaps clarify that a little. The DBus python libraries
> >are required to be present, but you don't have to have DBus running.
> So can I say: Dbus is necessary one for building virt-manager, while not 
> when running it?

The DBus python libraries *are* needed at runtime. If the DBus daemon isn't
present though, we catch the connection failure and disable that piece of
the virtmanager functionality on the fly.

> > If it fails to connect to the DBus daemon, the app will log a warning and
> >continue.  The GNome Python Desktop stuff is competely optional - if you
> >don't have the python bindings installed it will simply disable the VNC
> >password saving altogether.
> >
> >  
> >>I carefully read the content in "Dbus Services", My understanding is 
> >>that Dbus in virt-manager is used to make other external application 
> >>call some core function, so that they can get display the window/dialog .
> >>When Dbus is used?
> >>
> >>"The remote control module provides the DBus service 
> >><http://virt-manager.et.redhat.com/dbusservice.html> allowing various UI 
> >>functions to be controlled remotely.": My understanding for "remotely" 
> >>is to run virt-manager remotely, is it correct? so will dbus only used 
> >>when remotely? if some application in local machine, it may also use 
> >>Dbus to run some function?
> >>    
> >
> >Not quite - the intent with the DBus stuff is that if you run two copies
> >of virt-manager on the same machine, 
> For "two copies of virt-manager": my understanding is:
> Case 1: when I login, and run %/usr/binvirt-manager, then when I run 
> %/usr/bin/virt-manager in the same machine again,
> the second one is the copy of first one, and just use DBus/RPC to call.

Yes, the first copy you run of 'virt-manager' pops up the window directly.
The second concurrent copy will send a DBus message to the first, asking
it to popup a particular window, and then the second copy exits - since the
first copy is dealing with it now.

> Case2: When I login machine A, run %/usr/binvirt-manager, then remotely 
> access machine A through machine B,
> and run %/usr/bin/virt-manager again, so in this case, the second one is 
> the copy of the first one, and use Dbus/RPC.

In most cases the DBus daemon is only available if you are logged into
a local X / GNOME desktop session. If you are ssh'ing into a machine
remotely it typically won't have  DBus session available. So, when DBus
isn't available, many copies of virt-manager will be launched and have
no way to detect that another copy is already running.

When the DBus folks get the DBus connection automatically forwarding
over SSH, in the same way that X11 is forwarded, then the remote case
will work in same way as local case. I've no idea when that'll be
made to work though.

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