Comment 20 for bug 1931004

Reviewed: https://review.opendev.org/c/openstack/cinder/+/808475
Committed: https://opendev.org/openstack/cinder/commit/07ead73eec0ac6b962b533b07861d6a81226fa37
Submitter: "Zuul (22348)"
Branch: stable/victoria

commit 07ead73eec0ac6b962b533b07861d6a81226fa37
Author: Jon Bernard <email address hidden>
Date: Wed Apr 14 11:14:13 2021 -0400

    RBD: use correct stripe unit in clone operation

    The recent release of Ceph Pacific saw a change to the clone() logic
    where invalid values of stripe unit would cause an error to be returned
    where previous versions would correct the value at runtime. This
    becomes a problem when creating a volume from an image, where the source
    RBD image may have a larger stripe unit than cinder's RBD driver is
    configured for. When this happens, clone() is called with a stripe unit
    that is too small given that of the source image and the clone fails.

    The RBD driver in Cinder has a configuration parameter
    'rbd_store_chunk_size' that stores the preferred object size for cloned
    images. If clone() is called without a stripe_unit passed in, the
    stripe unit defaults to the object size, which is 4MB by default. The
    issue arises when creating a volume from a Glance image, where Glance is
    creating images with a default stripe unit of 8MB (distinctly larger
    than that of Cinder). If we do not consider the incoming stripe unit
    and select the larger of the two, Ceph cannot clone an RBD image with a
    smaller stripe unit and raises an error.

    This patch adds a function in our driver's clone logic to select the
    larger of the two stripe unit values so that the appropriate stripe unit
    is chosen.

    It should also be noted that we're determining the correct stripe unit,
    but using the 'order' argument to clone(). Ceph will set the stripe
    unit equal to the object size (order) by default and we rely on this
    behaviour for the following reason: passing stripe-unit alone or with
    an order argument causes an invalid argument exception to be raised in
    pre-pacific releases of Ceph, as it's argument parsing appears to have
    limitations.

    Closes-Bug: #1931004
    Change-Id: Iec111ab83e9ed8182c9679c911e3d90927d5a7c3
    (cherry picked from commit 49a2c85eda9fd3cddc75fd904fe62c87a6b50735)
    (cherry picked from commit 5db58159feec3d2d39d1abf3637310f5ac60a3cf)
    Conflicts:
            cinder/tests/unit/volume/drivers/test_rbd.py