[libvirt] [PATCH 1/6] Add new API virDomainStreamDisk[Info] to header and drivers

[Stefan Hajnoczi]

On Fri, Apr 8, 2011 at 2:31 PM, Daniel P. Berrange <berrange at redhat.com> wrote:

I have CCed Anthony and Kevin.  Anthony drove the QED image streaming
and Kevin will probably be interested in the idea of allocating raw
images as a background activity while QEMU runs.

>    /*
>     * @path: fully qualified filename of the virtual disk
>     * @nregions: filled in the number of @region structs
>     * @regions: filled with a list of allocated regions
>     *
>     * Query the extents of allocated regions within the
>     * virtual disk file. The offsets in the list of regions
>     * are not guarenteed to be sorted in any explicit order.
>     */
>    int virDomainBlockGetAllocationMap(virDomainPtr dom,
>                                       const char *path,
>                                       unsigned int *nregions,
>                                       virDomainBlockRegionPtr *regions);

QEMU can provide this with its existing .bdrv_is_allocated() function.
 Kevin, do you have any thoughts on whether this API will work well?

> This takes care of things for running guests. It would be
> desirable to have the same functionality available when a
> guest is not running, via the virStorageVol APIs. Indeed,
> this would allow access to the allocation functionality
> for disks not explicitly associated with any VM yet.

Today QEMU doesn't really cover the offline case although in the
future it may be possible to have a qemu-img command that preallocates
images and can be aborted.

Stefan