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Re: [Xen-devel] libvirt, libxl and QDISKs

On Wed, 2013-04-24 at 15:22 +0100, David Scott wrote:
> Hi,
> Now that libxl + qemu's built-in disk backend for ceph/rbd is working 
> nicely, I'm trying to get it all working through libvirt.
> When libvirt's libxl driver creates a libxl_device_disk, it applies a 
> few simple rules[1] covering specific file format types (qcow, qcow2, 
> vhd). If none of these rules apply then it defers to libxl's best guess:
>              * If driverName is not specified, default to raw as per
>              * xl-disk-configuration.txt in the xen documentation and let
>              * libxl pick a suitable backend.

Can you specify driverName in your config somehow? I confess I don't
know if this is ~= format or backend...

> Anyone got any thoughts? (Or perhaps I've missed something obvious! :-)

This is not the first time that the issue of hardcoded defaults in libxl
has come up recently (in fact I think you mentioned one of the others to

It seems to me that there is a need arising for a system wide libxl
configuration file which sets these sorts of defaults for all users of
libxl on that system and which can be modified according to admin
preference. As well as the disk backend selection (which is actually
probably pretty complex to express in a simple configuration file) this
has come up in the context of stubdomain usage and autoballooning.


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