Comment 5 for bug 1226351

Reviewed: https://review.openstack.org/59149
Committed: https://git.openstack.org/cgit/openstack/nova/commit/?id=c25c60f6a9ab1ccf12f72f76d400e7c9c0d090b3
Submitter: Jenkins
Branch: master

commit c25c60f6a9ab1ccf12f72f76d400e7c9c0d090b3
Author: Josh Durgin <email address hidden>
Date: Wed Jan 22 15:07:17 2014 -0800

    enable cloning for rbd-backed ephemeral disks

    Currently when using rbd as an image backend, nova downloads the
    glance image to local disk and then copies it again into rbd. This
    can be very slow for large images, and wastes bandwidth as well as
    disk space.

    When the glance image is stored in the same ceph cluster, the data is
    being pulled out and pushed back in unnecessarily. Instead, create a
    copy-on-write clone of the image. This is fast, and does not depend
    on the size of the image. Instead of taking minutes, booting takes
    seconds, and is not limited by the disk copy.

    Add some rbd utility functions from cinder to support cloning and
    let the rbd imagebackend rely on librbd instead of the rbd
    command line tool for checking image existence.

    Add an ImageHandler for rbd that does the cloning if an applicable
    image location is available. If no such location is available, or rbd
    is not configured for ephemeral disks, this handler does nothing, so
    enable it by default.

    blueprint rbd-clone-image-handler
    Closes-bug: 1226351
    Change-Id: I9b77a50206d0eda709df8356faaeeba35d232f22
    Signed-off-by: Josh Durgin <email address hidden>
    Signed-off-by: Zhi Yan Liu <email address hidden>