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Re: [libvirt] Using Xen config files



On Wed, Aug 20, 2008 at 08:35:46AM -0400, Matthew Donovan wrote:
> I am trying to programmatically start Xen guest VMs (HVM) with libvirt (on
> Fedora Core 8) and I'm having some trouble with it. I've included my code
> below.  Essentially, the domain seems to get created correctly but it
> doesn't seem to run.
>
> I don't receive any error messages from the libvirt
> functions but the VM does not get any CPU time (as shown with "xm list").  
> 
> [root grape ~]$ xm list
> Name                                        ID   Mem VCPUs      State
> Time(s)
> Domain-0                                     0  1462     2     r-----
> 1313.5
> fc8.conf                                     7   128     1     ------
> 0.0
> 
> Can someone explain what I'm doing wrong here?  I've tried to get this
> working with linux and windows guests with the same results.

That's really strange.  Your program looks correct to me (but see my
comment about error handling below).  One thing you can do is to run
your program after first setting the environment variable
LIBVIRT_DEBUG=1 which will cause all calls to libvirt to be printed
out.  Just to make sure you are actually calling the functions that
you think you are calling.

> I've seen references on this mailing list to libvirt's ability to handle Xen
> configuration files but I haven't seen anything in the API documentation or
> public header files that refer to it.  Is there a public interface to
> specifying a configuration file?

No there isn't.  This ability refers to old versions of Xen which used
/etc/xen.  We have a driver that can parse files from here and present
those as inactive ("defined" but not running) domains, eg.  when you
do "virsh list".

For all other uses, use the libvirt XML configuration format.  The
advantage is that it will keep working with other types of
virtualization.

>     domain = virDomainDefineXML (con, fedora);
>     if (!domain) {
>         virErrorPtr err = virGetLastError ();
>         printf ("virDomainDefineXML failed: %s\n",
>                 err->message);

By the way, this error reporting is wrong.  Confusingly there are two
levels of errors stored by virterror, a global error and a
per-connection error.  The global error is only used where you don't
have a virConnectPtr object (almost the only time is just after
virConnectOpen fails, when conn == NULL).  The rest of the time you
should use virConnGetLastError:

  http://libvirt.org/html/libvirt-virterror.html#virConnGetLastError

Rich.

-- 
Richard Jones, Emerging Technologies, Red Hat  http://et.redhat.com/~rjones
virt-top is 'top' for virtual machines.  Tiny program with many
powerful monitoring features, net stats, disk stats, logging, etc.
http://et.redhat.com/~rjones/virt-top


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