Comment 2 for bug 1957073

Reviewed: https://review.opendev.org/c/openstack/cinder/+/824149
Committed: https://opendev.org/openstack/cinder/commit/3ddf7ca9ea9587318b8c903e2c43b1879846d1c2
Submitter: "Zuul (22348)"
Branch: master

commit 3ddf7ca9ea9587318b8c903e2c43b1879846d1c2
Author: Takashi Kajinami <email address hidden>
Date: Tue Jan 11 21:22:52 2022 +0900

    rbd: Fix snapshot delete when the source volume doesn't exist

    Currently snapshot delete requires access to the source volume and
    the operation fails if the source volume doesn't exist in the backend.
    This prevents some snapshots from being deleted when the source volume
    image is deleted from the backend for some reason (for example, after
    cluster format).

    This change makes the rbd driver to skip updating the source volume
    if it doesn't exist. A warning log is left so that operators can be
    aware of any skip event.

    Closes-Bug: #1957073
    Change-Id: Icd9dad9ad7b3ad71b3962b078e5b94670ac41c87