[Libvir] Re: default hypervisor selection

[Anthony Liguori]

Daniel Veillard wrote:

>    - if /proc/xen doesn't exist (on linux, or /dev/xen on Solaris) well
>      we should not do that we are pretty sure we will get an error when
>      trying to connect
>    - if /proc/vz is present, well it's very likely that if the kernel
>      has been compiled with OpenVZ support, it's likely to be used as the
>      default virtualization
>    - if there is a kvm module loaded well we should probably use
>      qemu:///system if running as root or qemu:///session otherwise

While I definitely like the direction this thread is going in, I'd just 
warn that this sort of probing can be equally as harmful as the current 
behavior.

While Xen and KVM are mutually exclusive, the same is not true with 
OpenVZ/Linux Containers.  While it may be unlikely that both are 
actively being used, I find it very likely that in future distributions, 
both features will be present.

So you may probe that this is a Linux Containers capable host, but you 
may in fact be intending on using KVM for virtualization (and vice versa).

Regards,

Anthony Liguori


> I guess on Solaris an easy heuristic would allow to pick the right
> hypervisor by default too.
> At some point we may have multiple hypervisor support simultaneously
> on a linux system thanks to pv_ops, but right now it doesn't make too
> much sense to force a default Xen connection even when we know it won't
> work. 
> For a virsh specific solution there is the VIRSH_DEFAULT_CONNECT_URI
> environment variable, but it's not really user friendly and not very
> generic,
> 
>  What do people think ? I would be tempted to provide a patch to change
> do_open() behaviour on linux in the case name is NULL or "", and 
> then check what hypervisor might be present and running,
> 
> Daniel
>