[libvirt-users] Pre-requisites to use Java bindings with QEMU

[Lior Vernia]

Hello Eric,

Thank you for your thorough answer. Of course if I don't have to run
libvirtd as a privileged user, then I don't have any problem with
interacting with QEMU through the standard mechanism.

So just to summarize, this is what I understand would suffice for my Java
program to be able to manage VMs through the bindings:
1. Install QEMU, libvirt daemon and libvirt QEMU driver (no worries about
the distribution-specific package names).
2. Run libvirtd (probably with the -d flag?).
3. Run Java program with same user that ran libvirtd, using the QEMU
session (as opposed to system) URI.

Please correct me if I got anything wrong or if I'm missing another
dependency.

Thanks again, Lior.


On Mon, May 13, 2013 at 6:40 PM, Eric Blake <eblake at redhat.com> wrote:

> On 05/11/2013 06:25 AM, Lior Vernia wrote:
> > Hello everyone,
> >
> > I've been reading through the articles on the website trying to
> understand
> > what's needed to use the libvirt Java bindings with a QEMU hypervisor,
> but
> > still have some uncertainties/questions:
> >
> > 1. It is my understanding that libvirtd has to be running on the machine
> > hosting the hypervisor. Correct?
>
> Yes.
>
> >
> > 2. For libvirtd to communicate with QEMU, QEMU has to be installed on the
> > machine hosting the hypervisor. Correct? I guess what I'm really asking
> is
> > whether the libvirt QEMU "driver" includes the QEMU source code, or
> rather
> > communicates with pre-installed executables.
>
> If you are running a guest under qemu-kvm, then QEMU _is_ the
> hypervisor, so yes, it has to be installed on the host machine.  In
> Fedora parlance, if you install the libvirt-daemon-driver-qemu package
> on your host machine, that will pull in all the dependencies your host
> machine needs to run a guest.  But note that the dependencies are
> satisfied by also pulling in the qemu-kvm package (that is, libvirtd
> includes a qemu driver, and then that package also pulls in the actual
> qemu package).
>
> >
> > 3. Assuming the answer to the two former questions is "yes", is there a
> way
> > to bypass libvirtd if the machine hosting the hypervisor is the same as
> the
> > one running the Java code? I'm asking because running libvirtd would
> > require privileged permissions, whereas QEMU itself can run with normal
> > user permissions. Is that a price I have to pay for the uniform interface
> > that libvirt presents?
>
> WHY would you want to interact with qemu directly?  Yes, you could write
> a program that does just that, but then your java program would be
> reinventing the work that libvirt already did for you.  You are correct
> that the price you pay for uniform access through libvirt is that you
> have to use libvirt's interfaces.  However, you are incorrect that you
> have to run privileged - it is possible to use the qemu:///session URI
> so that you can run an unprivileged libvirtd with no permissions beyond
> what the calling user has.
>
> --
> Eric Blake   eblake redhat com    +1-919-301-3266
> Libvirt virtualization library http://libvirt.org
>
>
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