Create share from snapshot extra spec
This spec defines the addition of a new optional extra spec, create_share_from_snapshot_support, which removes the overload from snapshot_support. This is needed prior to the addition of new snapshot semantics, such as revert-to-snapshot. APIImpact DocImpact Partially implements: blueprint add-create-share-from-snapshot-extra-spec Change-Id: I4d95fe3609b7728ea7d9ed8be6e96241307f0002
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Clinton Knight
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You can adapt this file completely to your liking, but it should at least
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contain the root `toctree` directive.
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Ocata approved specs
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====================
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.. toctree::
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:glob:
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:maxdepth: 1
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specs/ocata/*
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Newton approved specs
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=====================
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@ -0,0 +1,201 @@
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..
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This work is licensed under a Creative Commons Attribution 3.0 Unported
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License.
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http://creativecommons.org/licenses/by/3.0/legalcode
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=====================================
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Create share from snapshot extra spec
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=====================================
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https://blueprints.launchpad.net/manila/+spec/add-create-share-from-snapshot-extra-spec
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This spec describes why and how we must separate the overloaded meaning of
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'snapshot_support' into two independent standard extra specs. Furthermore, to
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prevent the proliferation of required extra specs as well as to make the
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creation of new share types as simple and flexible as possible, we can make
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snapshot_support and each of the new snapshot-related extra specs optional.
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Problem description
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===================
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For a long time, manila has had the 'snapshot_support' standard extra spec,
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which has been overloaded to mean *two* things:
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* a driver can take a snapshot of a share, and
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* a driver can create new shares from a snapshot
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With additional snapshot semantics being proposed, including share revert and
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mountable snapshots, we expect that some drivers may support the new
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semantics without being able to create new shares from snapshots. It is
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therefore necessary to break the overload of 'snapshot_support'.
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We can add a new standard extra spec, create_share_from_snapshot_support, to
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indicate whether a backend can create new shares from share snapshots.
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The snapshot_support extra spec is currently required, which means an admin
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cannot create a type where snapshot_support is a "don't care", such that
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shares of that type will not offer snapshot features even if they exist on
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storage controllers than can take snapshots. By making snapshot_support and
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the other new snapshot-related extra specs optional, we can support "don't
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care" semantics on share types.
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Use cases
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=========
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A driver that can take snapshots of shares, but not create new shares from
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snapshots, will benefit from this change. For example, such a driver could
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report snapshot_support=True, create_share_from_snapshot_support=False, and
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revert_to_snapshot_support=True.
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Proposed change
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===============
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To accomplish this change, we will do the following:
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* Define the new extra spec, create_share_from_snapshot_support, at the next
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available microversion.
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* Add a database migration to add create_share_from_snapshot_support to each
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share type that contains snapshot_support. Because snapshot_support was
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overloaded prior to this change, we can simply copy the value of
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snapshot_support for each type to the new create_share_from_snapshot_support
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extra spec.
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* Add a database migration to add the new create_share_from_snapshot_support
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capability to the share record, so that manila has a record of each share's
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relevant snapshot capability at the time the share was created.
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* Copy the value of create_share_from_snapshot_support to each share upon
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share creation. If create_share_from_snapshot_support is not present on the
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share type, set the corresponding value on the share to False.
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* Continue copying the value of snapshot_support to each share upon share
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creation. Because snapshot_support is now optional, if snapshot_support is
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not present on the share type, set the corresponding value on the share to
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False.
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* Ensure create_share_from_snapshot_support is True when creating shares from
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snapshots.
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* Ensure that previous microversions cannot delete the snapshot_support extra
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spec from share types.
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* Ensure that previous microversions continue setting a default value of True
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for snapshot_support as well as create_share_from_snapshot_support.
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Alternatives
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------------
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We could leave the overload in place, but this would lead to confusing and
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incorrect behavior for drivers that can create snapshots but not create new
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shares from them.
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We could continue requiring snapshot_support and all new snapshot-related
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extra specs to be present on each share type, but that would prevent admins
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from creating share types with "don't care" semantics.
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Data model impact
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-----------------
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* Add create_share_from_snapshot_support field to share table, and copy value
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of snapshot_support to the new create_share_from_snapshot_support field for
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each share.
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* Add create_share_from_snapshot_support rows to the share_type_extra_specs
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table for each type that has snapshot_support, with the value copied from
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snapshot_support.
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REST API impact
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---------------
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At the microversion for this change:
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* The snapshot_support extra spec becomes deletable, as are the new
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snapshot-related extra specs.
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* Default values for snapshot_support are no longer provided. If not specified
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on a share type, snapshot_support and create_share_from_snapshot_support are
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not returned from the share types API for admin contexts. However, users see
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both values with a nominal value of False so that they know how shares of
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that type will behave.
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* The value of create_share_from_snapshot_support is checked on a share prior
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to creating a share from a snapshot (else HTTPBadRequest is returned).
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Driver impact
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-------------
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The value of create_share_from_snapshot_support is inferred for each driver
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based on the methods it contains, much as is already done for snapshot_support.
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Security impact
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---------------
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None
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Notifications impact
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--------------------
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None
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Other end user impact
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---------------------
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Prior to this change, python-manilaclient provided default values for the
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required extra spec snapshot_support. As of the new microversion, it will not
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provide a default for snapshot_support because the extra spec is no longer
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required.
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Performance Impact
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------------------
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None
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Other deployer impact
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---------------------
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None
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Developer impact
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----------------
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None
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Implementation
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==============
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Assignee(s)
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-----------
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Primary assignee:
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* clintonk (manila & python-manilaclient)
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Other contributors:
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* gouthamr (tempest & db-related tests)
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Work Items
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----------
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Code is all in one patch and has already been made available.
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Dependencies
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============
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None
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Testing
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=======
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New unit and tempest test coverage will be added for all of the added or
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changed functionality.
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Documentation Impact
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====================
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* API Ref: Add content about the API.
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* User Guide: Add content about the share types.
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* Admin Guide: Add content regarding the common capabilities and the don't care
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behavior.
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* Developer Ref: Add create_share_from_snapshot_support to common capabilities
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and the infamous driver matrix.
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References
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==========
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None
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