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Re: [Libvir] default hypervisor selection



On Thu, Feb 21, 2008 at 02:36:10PM +0000, Daniel P. Berrange wrote:
>   - Else probe each registered driver in order until one succeeds
> 
> For the latter I think we could add a 'probe' method to the internal driver
> API table. Then we can just call 'probe' on each driver in turn until we 
> find one which is  available on the system. 
> 
> At the same time it could be worth having a public API to 'detect drivers'
> which will call probe for each driver and return a list of all drivers
> which are available. This allows an app to easily ask libvirt what it
> supports

  I actually started to look at that and while it sounds good 'on paper'
it's a bit messy in practice, for example:
   - test driver: if compiled in, you would think the probe should return
     true, but as a result if trying an operation whyle no hypervisor
     is available you would end up doing it on the test driver instead of
     returning a failure, annoying
   - qemu driver: well QEmu is actually a driver for a potentially large
     set, KVM, QEmu for the current architecture, QEmu for emulated
     architectures. Would the probe return true if it finds 
     /usr/bin/qemu-mips ? Or the KVM package may be present but would not be
     usable because the current kernel doesn't have a kvm module
 
  Trying to be a bit systematic purely based on the driver model proves harder
than expected, still worth trying but I prefer early feedback :-)

Daniel

-- 
Red Hat Virtualization group http://redhat.com/virtualization/
Daniel Veillard      | virtualization library  http://libvirt.org/
veillard redhat com  | libxml GNOME XML XSLT toolkit  http://xmlsoft.org/
http://veillard.com/ | Rpmfind RPM search engine  http://rpmfind.net/


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