[libvirt] [PATCH 5/5] rbd: Implement buildVolFrom using RBD cloning

[John Ferlan]

On 01/27/2016 05:20 AM, Wido den Hollander wrote:
> RBD supports cloning by creating a snapshot, protecting it and create
> a child image based on that snapshot afterwards.
> 
> The RBD storage driver will try to find a snapshot with zero deltas between
> the current state of the original volume and the snapshot.
> 
> If such a snapshot is found a clone/child image will be created using
> the rbd_clone2() function from librbd.
> 
> rbd_clone2() is available in librbd since Ceph version Dumpling (0.67) which
> dates back to August 2013.
> 
> It will use the same features, strip size and stripe count as the parent image.
> 
> This implementation will only create a single snapshot on the parent image if
> never changes. This reduces the amount of snapshots created for that RBD image
> which benefits the performance of the Ceph cluster.
> 
> During build the decision will be made to use either rbd_diff_iterate() or
> rbd_diff_iterate2().
> 
> The latter is faster, but only available on Ceph versions after 0.94 (Hammer).
> 
> Cloning is only supported if RBD format 2 is used. All images created by libvirt
> are already format 2.
> 
> If a RBD format 1 image is used as the original volume the backend will report
> a VIR_ERR_OPERATION_UNSUPPORTED error.
> 
> Signed-off-by: Wido den Hollander <wido at widodh.nl>
> ---
>  src/storage/storage_backend_rbd.c | 341 ++++++++++++++++++++++++++++++++++++++
>  1 file changed, 341 insertions(+)
> 

ACK - pushed

John