[libvirt] inability to open local read-only connection

[Tavares, John]

I initially used libvirt directly, but when I started running into the lack of a 32-bit library on 64-bit issue and the inconsistent effective root user behavior issue, I needed to abandon the use of it and turned to virsh as it had no such issues and pay the performance penalty for stability.  Maybe for our next release I will go back to it, but it is a little late in the game now for me to go back now.

It also looks like the default version that comes with each revision of RHEL is a bit dated.

-----Original Message-----
From: Daniel P. Berrange [mailto:berrange at redhat.com] 
Sent: Friday, August 20, 2010 9:58 AM
To: Tavares, John
Cc: Justin Clift; libvir-list at redhat.com
Subject: Re: [libvirt] inability to open local read-only connection

On Fri, Aug 20, 2010 at 08:49:50AM -0500, Tavares, John wrote:
> It is available via xm, so my point was if it can, why can't libvirt??

No particular reason why not, other than nobody has requested
it before. 

NB, 'xm uptime' is giving the uptime of the virtual domain,
not the guest OS running inside it.  ie if you reboot the guest
OS, the 'uptime' doesn't get reset because the virtual domain
itself (usually[1]) never stops.

> In the end, I had to switch to calling virsh until I can get
> all of problem resolved.
> 
> Ideally, virsh to would be able to provide most of the same 
> data as going thru libvirt directly.  It might also be nice 
> if it provided that data in a more machine parseable format.

We do plan to make it available in machine readable formats
in the future, but in most cases you'd be better off using
one of the APIs directly instead of virsh. There's a choice
of C, python, perl, java, ocaml, ruby. It would be significantly
more efficient to use the API becasue you would be avoiding the
overhead of opening & closing a connection for every single
data item collected.

Daniel

[1] For paravirt guests IIRC Xen may actually destroy & recreate
the virtual domain during a reboot, but fullvirt should be
transparent.
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